Polyunsaturated Lipid Oxidation Products And

POLYUNSATURATED LIPID OXIDATION PRODUCTS AND

THEIR BIOLOGICAL ACTIVITIES: SYNTHESIS, GENERATION,

EFFECTS AND PROTECTION

by YU-SHIUAN CHENG

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Thesis Advisors: Dr. Robert G. Salomon

Department of Chemistry

CASE WESTERN RESERVE UNIVERSITY May, 2019

CASE WESTERN RESERVE UNIVERSITY

SCHOOL OF GRADUATE STUDIES

We hereby approve the thesis/dissertation of

Yu-Shiuan Cheng

candidate for the degree of Doctor of Philosophy *.

Committee Chair

Dr. Michael G. Zagorski

Committee Member

Dr. Blanton S. Tolbert

Committee Member

Dr. Fu-Sen Liang

Committee Member

Dr. Masaru Miyagi

Date of Defense

March 25th, 2019

*We also certify that written approval has been obtained

for any proprietary material contained therein.

This thesis is dedicated to my parents and my sister.

iii

TABLE OF CONTENTS Table of Contents iv List of Schemes vii List of Tables x List of Figures xi Acknowledgements xvi List of Abbreviations and Acronyms xviii Abstract xxiv

Polyunsaturated Lipid Oxidation Products and Their Biological

Activities: Synthesis, Generation, Effects and Protection

1. Introduction 1

1.1 Reactive oxygen species and oxidative stress 2

1.2 Free radical-induced lipid peroxidation 4

1.3 Protein adducts of oxidatively truncated lipids 7

1.4 Levuglandins and their protein adducts 9

1.5 Light-induced damage in the retina 12

1.6 Age-related macular degeneration (AMD) 16

1.7 References 22

2. Total Synthesis Confirms the Molecular Structure Proposed for

Oxidized Levuglandin D2 30

2.1 Background 31

2.2 Results and Discussion 33

2.3 Conclusions 56

2.4 Experimental Procedures 57

2.5 References 74

3. Light-induced Generation and Toxicity of Docosahexaenoate-derived

Oxidation Products in Retinal Pigmented Epithelial Cells 80

3.1 Background 81

3.2 Results 86

3.3 Discussion 107

3.4 Conclusions 120

3.5 Experimental Procedures 123

3.5 References 138

4. 4-Hydroxy-7-oxo-5-heptenoic Acid (HOHA) Lactone-Induced

Oxidative Stress and Mitochondrial Dysfunction in Retinal Pigmented

Epithelial Cells: Protection by a Carnosine Analogue, L-Histidyl

Hydrazide 161

4.1 Background 162

4.2 Results 169

4.3 Discussion 186

4.4 Conclusions and Future Prospects 195

4.5 Experimental Procedures 197

4.6 References 211

Appendix 222

Bibliography 259

LIST OF SCHEMES

Chapter 1

Scheme 1.1. Oxidative fragmentation of PUFA phospholipids produces γ-hydroxy-α,β-unsaturated aldehydes. 7

Scheme 1.2. The cyclooxygenase (COX) and radical-induced cyclooxygenation of arachidonate produces isoLGs. 10

Scheme 1.3. Metabolism of LGs: generation of protein adducts, crosslinks and oxidized metabolites 12

Scheme 1.4. Type I and Type II photosensitized oxidation reactions 14

Scheme 1.5. Class I and Class II photochemical damage 16

Chapter 2

Scheme 2.1. Generation and proposed structure of ox-LGD2 31

Scheme 2.2. Synthetic design for ox-LGD2 33

Scheme 2.3. Synthesis of the upper side chain precursor 34

Scheme 2.4. Concise total synthesis of ox-LGD2 36

Scheme 2.5. Model study for selective removal of tert-butyl groups 39

Scheme 2.6. γ-Isomer model study 42

Scheme 2.7. Rearrangment of ox-LGE2 51

Chapter 3

Scheme 3.1. The work-flow for an ARPE-19 cell light damage model 91

vii

Chapter 4

Scheme 4.1. L-Histidyl hydrazide as an inhibitor of lipid peroxidation products formation. 193

viii

LIST OF TABLES

Chapter 2

Table 2.1. One-pot three-component coupling of alkyne 2.6 with cuprates and allylic halides 35

Table 2.2. One-pot three-component coupling of alkyne 2.6 with various vinyl cuprates to generate maleate 2.14 37

Table 2.3. Comparison of organocopper reagents for synthesis of 2.4 37

Table 2.4. Model study for the mono methylation of a maleic anhydride 40

Table 2.5. Generation of 2.1 and 2.2 by desilylation of 2.1p and 2.2p 43

Chapter 3

Table 3.1. Optimized mass spectrometer parameters, selected ions and collision energies for quantitation of the MitoClick product in ARPE-19 mitochondria-enriched cell lysate 129

Table 3.2. Workflow for Strata X-C spin column 1st SPE enrichment of HOHA/DHHA lactone-GSH derivatives from bovine retina extracts 133

Table 3.3. Workflow for Hypercarb 2nd SPE enrichment of HOHA/DHHA lactone-GSH derivatives from bovine retina extracts 133

Table 3.4. HPLC gradient for the determination of HOHA/DHHA lactone-GSH derivatives in light exposed bovine retina extract 134

Table 3.5. Optimized mass spectrometer parameters, MRM transitions and collision energies for quantitation of HOHA/DHHA lactone-GSH derivatives in bovine retina extract 135

Table 3.6. Workflow for Strata X-33u spin column SPE enrichment of HOHA/DHHA lactone-GSH derivatives from ARPE-19 extracellular medium 135

Table 3.7. HPLC gradient for the determination of HOHA/DHHA lactone-GSH derivatives in extracellular medium from light exposed ARPE-19 cells 136

Table 3.8. Optimized mass spectrometer parameters, selected ions and collision energies for quantitation of HOHA/DHHA lactone-GSH derivatives in ARPE-19 extracellular medium 136

LIST OF FIGURES

Chapter 1

Figure 1.1. Main sources of ROS production in cells 3

Figure 1.2. Lipid peroxidation pathways 5

Figure 1.3. Transmission of light in the human eye 13

Figure 1.4. Outer retina (photoreceptor and RPE) is susceptible to photooxidative damage. 15

Figure 1.5. Classification of AMD 17

Figure 1.6. The alternative complement pathway 20

Chapter 2

Figure 2.1. HPLC separation of three-component coupling products 2.4 and 2.4’ 38

Figure 2.2. HMBC (red) and NOESY (blue) correlations distinguishing the structures of 2.1p and 2.2p 42

1 Figure 2.3. Comparison of H NMR spectra of ox-LGD2 chemical shifts with CHD2CN resonance set at 1.90 ppm (A) at 500 MHz from total synthesis and (B) at 600 MHz from extraction of Gracilaria edulis 44

Figure 2.4. HMBC (red) and NOSEY (blue) correlations distinguishing the structures of 2.1, 2.2 and 2.2d 46

1 Figure 2.5. H NMR spectrum of the ox-LGD2 and ox-LGE2 mixture generated from the HF desilylation reaction 46

Figure 2.6. Evolution of ox-LGs in CD3CN: (Left) HPLC chromatograph; (Right) 1H NMR spectrum 48

1 6 Figure 2.7. H NMR spectrum of Δ -ox-LGE2 (2.2d) 49

Figure 2.8. HPLC chromatogram of ox-LGD2, two diastereomers of 6 ox-LGE2, and Δ -ox-LGE2 52

Figure 2.9. 1H NMR spectrum of peak 1 (Figure 2.8 HPLC chromatograph) collected at 44 min 53

Figure 2.10. HPLC chromatogram of ox-LGD2, minor diastereomer (b) of ox-LGE2 53

Chapter 3

Figure 3.1. Oxidative cleavage of DHA-PC delivers HOHA-PC. HOHA lactone is then released from bilayer phospholipid membranes by spontaneous intramolecular transesterification. Covalent adduction of HOHA-PC and HOHA lactone to primary amino groups of protein lysyl residues and phosphatidyl ethanolamines (PE) produces CEP derivatives. 83

Figure 3.2. Time-course for the formation of HOHA lactone GSH derivatives 87

Figure 3.3. Photogeneration of HOHA-PC from DHA-PC is followed by release of HOHA lactone. HOHA lactone-GSH adduct is generated by glutathionylation of HOHA lactone. NADPH-dependent reduction of the HOHA lactone-GSH adduct delivers the reduced GSH adduct, DHHA lactone- GSH, that is also produced by RPE cells exposed to HOHA lactone, e.g., that may be released by oxidatively damaged photoreceptor cells. 88

Figure 3.5. Internalization of A2E: representative images showing green A2E autofluorescence in ARPE-19 cells preloaded for 24 h with A2E 91

xii

for 48 h followed by 10 μM A2E for 24 h with 24 h recovery in basal medium 93

Figure 3.7. Quantitation of GSH levels remaining in DHA/A2E-laden ARPE-19 cells 10 min (Panel A) or 24 h (Panel B) after irradiation for various times from 0 to 60 min 94

Figure 3.8. Generation of CEP in ARPE-19 cells after 20 min exposure to blue light 96

Figure 3.9. Measurement of mitochondrial membrane potential in light exposed DHA-rich A2E-laden ARPE-19 cells 98

Figure 3.10. Measurement of cell viability by MTT assay 24 h after exposure of A2E-laden ARPE-19 cells to blue light (430 nm) for 0 to 60 min 99

Figure 3.11. Measurement of mitochondrial membrane potential changes in ARPE-19 cells upon exposure to HOHA lactone 100

Figure 3.12. Measurement of the cell viability of ARPE-19 cells after exposure to 0 to 40 μM HOHA lactone for 24 h assessed by MTT assay (Panel A) and by Alamar Blue assay (Panel B) 101

Figure 3.13. Senescence of ARPE-19 cells exposed to HOHA lactone 103

Figure 3.14. Lysosomal membrane perturbation in ARPE-19 cells after incubation with HOHA lactone 105

Figure 3.15. Generation of CEP in ARPE-19 cells upon exposure to HOHA lactone 106

Figure 3.16. Postulated synergistic contributions of A2E and a family of α,β-unsaturated aldehyde products of lipid oxidative cleavage to light-induced apoptosis of RPE cells 118

Chapter 4

Figure 4.1. Oxidative cleavage of DHA-PC delivers HOHA-PC. HOHA lactone is released from bilayer phospholipid membranes by spontaneous deacylation. Covalent adduction of HOHA-PC and HOHA lactone to primary amino groups of protein lysyl residues and phosphatidyl ethanolamines (PE) produces CEP derivatives. 165

xiii

Figure 4.2. Decline in the activities of mitochondrial OXPHOS complexes induced by HOHA lactone in ARPE-19 cells. Isolated mitochondria were incubated with HOHA lactone at the indicated concentrations for 0.5 h, and then the specific enzymatic activities of complexes (A) I, (B) II, (C) III and (D) IV were assayed spectrophotometrically (E) by monitoring NADH, 2,6-dicHOHA lactoneorophenolindophenol (DCPIP) or cytochrome c (Cyt c). 170

Figure 4.3. HOHA lactone induces the generation of mitochondrial ROS in ARPE-19 cells. (A) Time-course for the generation of total cellular ROS measured with the CM-H2DCFDA assay. (B) The mitochondrial ROS level was quantified by MitoSOX staining. (C) Representative MitoSOX staining images acquired using a Leica DMI 6000 B inverted fluorescent microscope. 172

Figure 4.4. HOHA lactone induces depletion of ATP, and mitochondrial membrane potential in ARPE-19 cells. (A) The ATP level was quantified by a luciferin-luciferase based assay, and the ATP level was measured. (B) The mitochondrial membrane potential (Δψm) was quantified with the JC-10 probe. 173

Figure 4.5. HOHA lactone induces depletion of GSH and loss of cell viability in ARPE-19 cells. (A) The intracellular GSH level was quantified by the DTNB method. The GSH level in the cell lysate was quantified by colorimetric assay; (B) Cell viability was quantified by an MTT assay. 174

Figure 4.6. HOHA lactone produced in photoreceptor disks dissociates into RPE cells where formation of covalent adducts with GSH, proteins and ethanolamine phospholipids cause mitochondrial dysfunction. A competing covalent adduction with HH may protect RPE cells against HOHA lactone-induced GSH depletion and cytotoxic covalent modification. 175

Figure 4.7. HH is a scavenger of HOHA lactone in RPE cells in culture. (A) The levels of HL after incubation for 1 h with various scavengers (1 mM) with HL (0.5 mM), i.e., scavenger/aldehyde ratio = 2:1) at 37 °C. (B) Reaction rate constants (Kobs) of scavengers (from panel A using Kobs sigmoidal curve fitting, %At = A0 × e ). (C) Comparison

xiv

of HL consumption after 1h incubation with scavengers (1 mM), i.e, scavenger/aldehyde ratio = 2:1; 10 mM, scavenger/aldehyde ratio = 20:1). 176

Figure 4.8. HH is a scavenger of HL in RPE cells in culture. (A) Mass spectra of HH covalent adducts with HL and (B) HL-GSH adduct. 177

Figure 4.9. HH is a scavenger of HL in RPE cells in culture. (A) Uptake of HH by ARPE-19 cells. HH in the cells was quantified by LC-MS/MS using a standard curve after 24 h incubation in a cell culture medium containing 50 ~ 800 µM HH. (B) HH is not cytotoxic toward ARPE-19 cells. ARPE-19 cells were exposed for 24 h to the indicated concentrations of HH and cell viability was measured by MTT assay. 178

Figure 4.10. Protection of ARPE-19 cells by HH against HOHA lactone-induced cell dysfunction. (A) Cell viability was measured using an MTT assay. (B) Mitochondrial membrane potential (Δψm) was measured using a JC-10 assay. (C) The GSH level in the cell lysate was quantified by a DTNB assay. 179

Figure 4.11. Protection of ARPE-19 cells by HH against HOHA lactone-induced cell dysfunction. (A) Mitochondrial ROS levels were quantified by MitoSOX staining. (B) The ATP level was quantified by a luciferin-luciferase based assay. 180

Figure 4.12. HH prevents adduction of HOHA lactone to proteins and ethanolamine phospholipids to form CEP derivatives in ARPE-19 cells. (A) Images were acquired using a Leica DMI 6000 B inverted fluorescent microscope. (B) Red fluorescence intensity was quantified as the CEP level. 181

Figure 4.13. Synthesis of αN-acyl HH derivatives. (A) Synthetic approach used for preparation of HH analogues. (B) Chemical structures of the HH analogues prepared. 182

Figure 4.14. Protection of RPE cell viability by HH analogues. ARPE- 19 cell viability (measured using an MTT assay). 183

Figure 4.15. Efficacy of HH and its αN-acyl derivatives for protecting the activities of mitochondrial complexes I, II and IV against HL toxicity. Isolated mitochondria were incubated with HH or its αN-acyl derivatives for 10 min followed by

HOHA lactone for 30 min and the specific enzymatic activities of complexes (A), complex II (B) and complex IV (C) were measured spectrophotometrically. 185

Figure 4.16. HOHA lactone depletes the endogenous antioxidant GSH, impairs the mitochondrial respiratory chain complexes and induces consequent ROS production, ATP depletion and mitochondrial membrane potential dissipation, leading to mitochondrial damage and cell death. 188

Appendix

Figure A2.1. 1H NMR spectrum of a methylation product mixture 2.1p and 2.2p 223

Figure A2.2. COSY spectrum of a methylation product mixture 2.1p and 2.2p 223

Figure A2.3. HSQC spectrum of a methylation product mixture 2.1p and 2.2p 224

Figure A2.4. HMBC spectrum of a methylation product mixture 2.1p and 2.2p 224

Figure A2.5. 2D NOESY spectrum of a methylation product mixture 2.1p and 2.2p 225

Figure A2.6. COSY spectrum of ox-LGD2 and ox-LGE2 (major) mixture from HF-treated reaction 225

Figure A2.7. HSQC spectrum of ox-LGD2 and ox-LGE2 (major) mixture from HF-treated reaction 226

Figure A2.8. HMBC spectrum of of ox-LGD2 and ox-LGE2 (major) mixture from HF-treated reaction 226

6 Figure A2.9. COSY spectrum of Δ -ox-LGE2 (2.2d) 227

6 Figure A2.10. HSQC spectrum of Δ -ox-LGE2 (2.2d) 227

6 Figure A2.11. HMBC spectrum of Δ -ox-LGE2 (2.2d) 228

6 Figure A2.12. 2D NOESY spectrum of Δ -ox-LGE2 (2.2d) 228

xvi

Figure A2.13. COSY spectrum of ox-LGD2 (2.1) 229

Figure A2.14. 2D NOESY spectrum of ox-LGD2 (2.1) 229

1 Figure A2.15. The H NMR (500 MHz, CDCl3) of 2.9 230

13 Figure A2.16. The C NMR (125 MHz, CDCl3) of 2.9 230

1 Figure A2.17. The H NMR (500 MHz, CDCl3) of 2.10 231

13 Figure A2.18. The C NMR (125 MHz, CDCl3) of 2.10 231

1 Figure A2.19. The H NMR (500 MHz, CDCl3) of 2.11 232

13 Figure A2.20. The C NMR (125 MHz, CDCl3) of 2.11 232

1 Figure A2.21. The H NMR (500 MHz, CDCl3) of 2.12 233

13 Figure A2.22. The C NMR (125 MHz, CDCl3) of 2.13 234

1 Figure A2.23. The H NMR (500 MHz, CDCl3) of 2.13 234

1 Figure A2.24. The H NMR (500 MHz, CDCl3) of 2.7 235

13 Figure A2.25. The C NMR (125 MHz, CDCl3) of 2.7 235

1 Figure A2.26. The H NMR (500 MHz, CDCl3) of 2.14 236

13 Figure A2.27. The C NMR (125 MHz, CDCl3) of 2.14 236

1 Figure A2.28. The H NMR (500 MHz, CDCl3) of 2.4 237

13 Figure A2.29. The C NMR (125 MHz, CDCl3) of 2.4 237

1 Figure A2.30. The H NMR (500 MHz, CDCl3) of 2.4’ 238

13 Figure A2.31. The C NMR (125 MHz, CDCl3) of 2.4’ 238

1 Figure A2.32. The H NMR (500 MHz, CDCl3) of 2.3 239

13 Figure A2.33. The C NMR (125 MHz, CDCl3) of 2.3 239

1 Figure A2.34. The H NMR (500 MHz, CDCl3) of 2.3’ 240

13 Figure A2.35. The C NMR (125 MHz, CDCl3) of 2.3’ 240

xvii

1 Figure A2.36. The H NMR (500 MHz, CDCl3) of 2.1p and 2.2p 241

13 Figure A2.37. The C NMR (125 MHz, CDCl3) of 2.1p and 2.2p 241

1 Figure A2.38. The H NMR (500 MHz, CDCl3) of 2.1p’ and 2.2p’ 242

1 Figure A2.39. The H NMR (500 MHz, CDCl3) of 2.1’ and 2.2’ 242

1 Figure A2.40. The H NMR (500 MHz, CDCl3) of ox-LGD2 (2.1), ox- LGE2 (2.2) 243

1 Figure A2.41. The H NMR (500 MHz, CDCl3) of ox-LGD2 (2.1) 243

13 Figure A2.42. The C NMR (125 MHz, CDCl3) of ox-LGE2 (2.2) with 6 minor ox-LGD2 (2.1) and Δ -ox-LGE2 (2.2d) 244

1 6 Figure A2.43. The H NMR (500 MHz, CDCl3) of Δ -ox-LGE2 (2.2d) 245

13 6 Figure A2.44. The C NMR (125 MHz, CDCl3) of Δ -ox-LGE2 (2.2d) 245

1 Figure A4.1. The H NMR (500 MHz, CDCl3) of Ac-His-OMe-Ac 246

13 Figure A4.2. The C NMR (125 MHz, CDCl3) of Ac-His-OMe-Ac 246

1 Figure A4.3. The H NMR (500 MHz, CDCl3) of t-Bu-His-OMe 247

13 Figure A4.4. The C NMR (125 MHz, CDCl3) of t-Bu-His-OMe 247

1 Figure A4.5. The H NMR (500 MHz, CDCl3) of c-P-His-OMe 248

13 Figure A4.6. The C NMR (125 MHz, CDCl3) of c-P-His-OMe 248

1 Figure A4.7. The H NMR (500 MHz, CDCl3) of c-H-His-OMe 249

13 Figure A4.8. The C NMR (125 MHz, CDCl3) of c-H-His-OMe 249

1 Figure A4.9. The H NMR (500 MHz, CDCl3) of nonanoyl-His-OMe 250

13 Figure A4.10. The C NMR (500 MHz, CDCl3) of nonanoyl-His-OMe 250

1 Figure A4.11. The H NMR (500 MHz, CDCl3) of decanoyl-His-OMe 251

13 Figure A4.12. The C NMR (125 MHz, CDCl3) of decanoyl-His-OMe 251

1 Figure A4.13. The H NMR (500 MHz, CDCl3) of undecanoyl-His-OMe 252

xviii

13 Figure A4.14. The C NMR (125 MHz, CDCl3) of undecanoyl-His-OMe 252

1 Figure A4.15. The H NMR (500 MHz, CDCl3) of dodecanoyl-His-OMe 253

13 Figure A4.16. The C NMR (125 MHz, CDCl3) of dodecanoyl-His-OMe 253

1 Figure A4.17. The H NMR (500 MHz, CDCl3) of His-hyd (3.1) 254

13 Figure A4.18. The C NMR (125 MHz, CDCl3) of His-hyd (3.1) 254

1 Figure A4.19. The H NMR (500 MHz, CDCl3) of Ac-His-hyd (3.2) 255

1 Figure A4.20. The H NMR (500 MHz, CDCl3) of t-Bu-His-hyd (3.3) 255

1 Figure A4.21. The H NMR (500 MHz, CDCl3) of c-P-His-hyd (3.5) 256

1 Figure A4.22. The H NMR (500 MHz, CDCl3) of c-H-His-hyd (3.6) 256

1 Figure A4.23. The H NMR (500 MHz, CDCl3) of nonanoyl-His-hyd (3.7) 257

1 Figure A4.24. The H NMR (500 MHz, CDCl3) of decanoyl-His-hyd (3.8) 257

1 Figure A4.25. The H NMR (500 MHz, CDCl3) of undecanoyl-His-hyd (3.9) 258

1 Figure A4.26. The H NMR (500 MHz, CDCl3) of dodecanoyl-His-hyd (3.10) 258

xix

ACKNOWLEDGEMENTS

I wish to express my deepest sense of gratitude and respect to my research advisor Dr.

Robert G. Salomon for his expert guidance, constant encouragement, and the amount of time he spent to shape me into a professional researcher over the years. He provided me with the best possible facilities, collaborations, opportunities and challenging tasks, which enable me to enhance my research aptitude and build a concrete foundation for my future goals.

I would like to thank my committee members, Dr. Michael G. Zagorski, Dr. Blanton S.

Tolbert, Dr. Fu-Sen Liang, Dr. Masaru Miyagi for their valuable time, efforts and suggestions on my candidate qualification and thesis. Thank Dr. Rajesh Viswanathan for his efforts on my candidate qualification.

It is my pleasure to acknowledge Dr. John Crabb, Cole Eye Institute, Cleveland Clinic

Foundation, for giving me the opportunity to work in his lab as well as his invaluable guidance on our collaboration. I also want to express my appreciation to lab members in

Dr. Crabb group, Dr. Geeng-Fu Jang, and Jack Crabb, for their help and friendship.

Special thanks to Dr. Geeng-Fu Jang for sharing his knowledge and for providing an expert training in UPLC-MS and Maldi-TOF.

I would like to thank Dr. Salomon’s group, former and current members: Dr. Mikhail

D. Linetsky, Dr. Wenyuan Yu, Dr. Yu Zhang, Dr. Hua Wang, Dr. Yalun Cui, Dr.

Wenzhao Bi, Dr. Junhong Guo, Dr. Nicholas D. Tomko, Emeka Udeigwe, Guangyin

Wang Xilin Gu, Haoting Li, Kevin Xiong for their thoughtful discussions and their friendship. Special thanks to Dr. Mikhail D. Linetsky and Dr. Wenyuan Yu for their invaluable consideration and help in my research.

I would like to thank Dr. Jim Faulk for his help on mass spectrometry and Dr.

Prashansa Agrawal for her assistance on NMR and other staff members in Chemistry

Department in Case Western Reserve University for their help in numerous occasions.

Also, I would like to thank Anthony Gardella at the Visual Sciences Research Center

(VSRC) imaging core for his assistance with fluorescence microscopy and Ms. Dawn

Smith for her help in maintaining cells.

Special thanks to Dr. Masaru Miyagi in Department of Pharmacology for his help, instruction and friendship. He taught me a lot about mass spectrometry, proteomics, bioinformatics and microbiology and was an invaluable resource for my questions and ideas.

Finally, I would like to express my deepest gratitude to my parents, and my sister for their endless love and encouragement.

xxi

LIST OF ABBREVIATIONS AND ACRONYMS

Abbreviations and Acronyms Equivalent

A2E N-retinyl-N-retinylidene ethanolamine

AA arachidonic acid

AB alamar blue

Aβ amyloid beta

Ac acetyl

ACN acetonitrile

AD Alzheimer’s disease

ADH alcohol dehydrogenase

AGE advanced glycation end products

ALDH aldehyde dehydrogenase

ALE advanced lipoxidation end products

AMD age-related macular degeneration

AO acridine orange

Ar argon

ARPE-19 a human retina pigmented epithelium cell line

ATP adenosine triphosphate

BSA bovine serum albumin

CAP carboxyalkylpyrrole

CAT catalase

CEP 2-(ω-carboxyethyl)pyrrole

xxii

CHP 2-(ω-carboxyheptyl)pyrrole

CID collision-induced dissociation

CL cell lysate

CM chloromethyl

CNV choroidal neovascularization

COSY correlation spectroscopy

COX cyclooxygenase

CPP 2-(ω-carboxypropyl)pyrrole

DAPI 4',6-diamidino-2-phenylindole

DBU 1,8-diazabicyclo-[5.4.0]undec-7-ene

DHA docosahexaenoic acid

DHHA 1,4-dihydroxyhept-5-enoic acid

DHN 1,4-dihydroxy-2-nonene

DMEM Dulbecco’s modified Eagle’s medium

DNA deoxyribonucleic acid

DPBS Dulbecco’s phosphate buffered saline

DTBMS di-tert-butylmethylsilyl

DTBMSH di-tert-butylmethylsilylsilane

EA ethyl acetate

ECM extracellular medium

EDTA ethylenediaminetetraacetic acid

ELISA enyzeme-linked immunosorbant assay

ER endoplasmic reticulum

xxiii

ESI electrospray ionization

ETC electron transport chain

FA formic acid

FADH flavin adenine dinucleotide

FBS fetal bovine serum

FMNH flavin mononucleotide

GA geographic atrophy

GC gas chromatography

Gly glycine

GPx glutathione peroxidase

GS glycosphingolipid

GSH reduced L-glutathione

GST glutathione S-transferase

HBSS Hank’s balanced salt solution

H2DCFDA 2',7'-dichlorodihydrofluorescein diacetate

HHE 4-hydroxy-2-hexenal

HMBC heteronuclear multiple-quantum correlation

HMPA hexamethylphosphorictriamide

HNA 4-hydroxy-2-nonenoic acid

HNE 4-hydroxy-2-nonenal

HODA-PC 9-hydroxy-12-oxododec-10-enoic acid ester of 2-lyso-phosphatidylcholine

HOHA 4-hydroxy-7-oxohept-5-enoic acid

HOHA-PC 2-(4-hydroxy-7-oxohept-5-enoyl)

xxiv

phosphatidylcholine

HOOA-PC 5-hydroxy-8-oxo-6-octenoic acid ester of 2- lyso-phosphatidylcholine

HPLC high performance liquid chromatography

HRP horseradish peroxidase

HSA human serum albumin

HSQC Heteronuclear single quantum coherence spectroscopy

HUVEC human umbilical vein endothelial cell

Hz Hertz

IgG immunoglobin G

ILM inner limiting membrane

INL inner nuclear layer

IPL inner plexiform layer

IS internal standard

J hyperfine coupling constant

JC-10 a 5,5’,6,6’-tetrachloro-1,1’,3,3’- tetraethylbenzimidazoylcarbocyanine iodide derivative

KLH keyhole limpet hemocyanine

LA linoleic acid

LC liquid chromatography

LD50 median lethal dose

LDH lactate dehydrogenase

LDL low-density lipoprotein

xxv

LGD2 levuglandin D2

LGE2 levuglandin E2

LO· lipid alkoxy radical

LOO· lipid perxoyl radical

LOOH lipid hydroperoxide

Lys lysine

Lyso-PC lysophosphatidylcholine

MDA malonaldehyde

MeOH methanol

MES 2-[morpholino]ethanesulfonic acid

MPO myeloperoxidase

MPTPs mitochondrial permeability transition pores

MRM multiple reaction monitoring

MS/MS tandem mass spectroscopy

MSA mouse serum albumin

MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl- 2H-tetrazolium bromide m/z mass-to-charge ratio

NaBH4 sodium borohydride

NADH nicotinamide adenine dinucleotide

NADPH nicotinamide adenine dinucleotide- phosphate

NF-κB nuclear factor kappa-B

NMR nuclear magnetic resonance

xxvi

NOESY nuclear Overhauser effect spectroscopy

OMe methoxy

OD optical density

ODS octadecylsiliyl

ONE 4-oxo-2-nonenal

Ox-LGD2 oxidized levuglandin D2

Ox-LGE2 oxidized levuglandin E2

OXPHOS oxidative phosphorylation system oxPL oxidatively truncated phospholipids

PA phosphatidic acid

PAGE polyacrylamide gel electrophoresis

PBS phosphate buffered saline

PBST Phosphate buffered saline with Tween-20

PC phosphatidylcholine

Pd(PPh3)4 tetrakis(triphenylphosphine)palladium (0)

PE phosphatidylethanolamine

PI phosphatidylinositol

PGH2 prostaglandin H2

PL phospholipid

PS phosphatidylserine

PLA2 phospholipase A2

PLD phospholipase D ppm parts per million

PUFA polyunsaturated fatty acid xxvii

PVDF polyvinylidene fluoride

ROS reactive oxygen species

RCS reactive carbonyl species

Rf retention factor

RPE retinal pigmented epithelium

SA β-gal senescence-associated β-galactosidase

SDS sodium dodecyl sulfate

SIM selected ion monitoring

SOD superoxide dismutase

SPE solid phase extraction

TAG triacylglycerol

TBDMS tert-butyldimethylsilyl

TBDMSOTf tert-butyldimethylsilyl triflate

TEA triethylamine

TFA trifluoroacetic acid

THF tetrahydrofuran

TLC thin layer chromatography

TLR toll-like receptor

TMS trimethylsilyl

TNB 5’-thio-2-nitrobenzoic acid

TPP triphenylphosphonium

TsOH p-toluenesulfonic acid monohydrate

UV ultraviolet

xxviii

VEGF vascular endothelial growth factor

xxix

Polyunsaturated Lipid Oxidation Products and Their Biological

Activities: Synthesis, Generation, Effect and Protection

Abstract

YU-SHIUAN CHENG

Oxidized lipids are generated from polyunsaturated fatty acid-containing phospholipids under conditions of oxidative stress, and are increasingly believed to be associated with age-related diseases. Oxidation of arachidonic acid (AA)-containing phospholipids generates levuglandins that possess reactive γ-ketoaldehyde functional arrays that avidly react with the primary amino groups in biomolecules, which are then transformed into pyrrole derivatives. These protein modifications can interfere with their functions. Recently, an oxidized form of levuglandin (LG)D2 (ox-LGD2) was isolated from the red alga Gracilaria edulis. It is presumably a detoxification metabolite of levuglandins. In order to confirm its structure, a concise total synthesis, implementing an efficient three-component coupling to assemble the main body, was developed in this study. Other than ox-LGD2, its regioisomer ox-LGE2 and unexpected rearranged isomer

6 Δ -ox-LGD2 were also successfully synthesized and well characterized.

Oxidation of phospholipids containing docosahexaenoic acid (DHA) generates truncation products, 4-hydroxy-7-oxo-hept-5-enoic acid (HOHA) phospholipids (PLs), which undergo spontaneous deacylation forming a biologically active compound,

HOHA-lactone. HOHA-lactone is a precursor of ω-carboxyethylpyrrole (CEP) that has significant pathological and physiological relevance to age-related macular degeneration

xxx

(AMD). It can also be metabolized by RPE cells through conjugation with glutathione

GSH, forming a Michael adduct HOHA-lactone GSH that is reduced to an alcohol 4,7- dihydroxyhept-5-enoic acid (DHHA)-lactone GSH and transported out of the cells.

DHHA-lactone GSH is considered as a relatively stable metabolite of HOHA-lactone. It can be used for monitoring the generation of HOHA-lactone. Two in vitro models were utilized to study light damage in retina. First, in a bovine retina tissue model, elevated levels of HOHA-lactone GSH and DHHA-lactone GSH were found in the bovine retina extract exposed to UVA or white light. Second, in a RPE cell model, elevated levels of

DHHA-lactone GSH were generated in DHA-rich cells upon light exposure of and even higher levels were generated in DHA-rich/A2E-laden cells. The increasing levels of

DHHA-lactone GSH in RPE cells, which indicates the increase of HOHA-lactone, were strongly correlated with a decrease of cell viability, cellular GSH levels, mitochondrial membrane potential, lysosome integrity, the increase of CEP levels and cellular senescence.

HOHA-lactone that had previously found to induce angiogenesis, apoptosis and activate the complement pathway, was now also found to cause mitochondrial dysfunction by impairing mitochondrial respiratory chain complexes – also called the oxidative phosphorylation system (OXPHOS) or the electron transport chain (ETC) – in this study. Damage of mitochondrial respiratory chain complexes leads to generation of mitochondrial reactive oxygen species (mtROS) and depletion of cell energy current and

ATP and then induce oxidative stress and eventually cell death.

The utility of L-histidyl hydrazide as a drug to scavenge HOHA-lactone to rescue cells from HOHA-lactone induced damage was tested to protect cells from oxidative

xxxi stress, prevent mitochondrial damage, alleviate the metabolic burden and, most importantly, protect the cells from death. Furthermore, a family of L-histidyl hydrazide derivatives was developed as potential drug candidates for future screening studies.

xxxii

CHAPTER 1

Introduction

1.1 Reactive oxygen species and oxidative stress

Oxygen is indispensable for metabolism and energy production in almost all biologic systems. However, reactive oxygen species (ROS) generated from life processes can cause damage to cells, tissues, and organs. ROS are a variety of highly reactive

− molecules including oxygen-related free radicals superoxide anion (O2 •), hydroxyl radical (HO•), hydroperoxyl radical (HO2•), nitric monoxide (NO•) and other non-radical

1 species such as singlet oxygen ( O2), hydrogen peroxide (H2O2), nitric oxide (NO), hypochlorous acid (HOCl), and peroxynitrite (ONOO−). These various ROS can either be generated exogenously or produced endogenously from several different sources (Fig.

1.1). While exogenous stimuli can induce the production of ROS, e.g., ultraviolet light, ionizing radiation, chemotherapeutics, inflammatory cytokines and environmental toxins,

ROS are also produced intracellularly through multiple mechanisms depending on the cell and tissue type. The major endogenous sources include NADPH oxidase (NOX) complexes and lipoxygenase in cell membranes, the electron transport chain in mitochondria, xanthine oxidases in the cytosol, cytochrome P450 on the endoplasmic reticulum and peroxisomes.1-4

Figure 1.1. Main sources of ROS production in cells

To maintain physiological homeostasis, cells utilize an intricate antioxidant defense system that includes the enzymatic scavengers superoxide dismutase (SOD), which rapidly converts O2• to H2O2, catalase (CAT) and glutathione peroxidase (GPx), which

1,5-7 convert H2O2 to H2O. A variety of other non-enzymatic antioxidants are important for scavenging ROS. These include ascorbic acid (vitamin C), tocopherol (vitamin E), retinoic acid (vitamin A), carotenoids, thiol antioxidants (glutathione, thioredoxin and lipoic acid), pyruvate, flavonoids and other small molecular weight compounds.5

The antioxidant defense system can be overwhelmed by various pathological or environmental factors that may result in dramatic increase of overall ROS levels. A disturbance in the balance between the production of ROS and antioxidant defenses is defined as “oxidative stress”.

Consequences of this stress include oxidative damage to cellular proteins, lipids and

DNA, which are detrimental and would lead to cell death or to acceleration of ageing and

3 age-related diseases. Oxidative stress is believed to contribute to the pathogenesis of many chronic diseases such as cancer, atherosclerosis, arthritis, diabetes, cardiovascular diseases and stroke. Also, various age-related diseases have been linked to oxidative stress, including Alzheimer’s disease, Parkinson’s disease, macular degeneration, glaucoma, presbycusis.

1.2 Free radical-induced lipid peroxidation

Lipids are essential components of cell membranes that maintain the structure and control the function of cells. Among the lipids, polyunsaturated fatty acids (PUFAs) are extremely susceptible to oxidation. They are primary targets of the attack by ROS, and their oxidation is associated with various pathological states.6 The primary reactions of lipid peroxidation (Fig. 1.2) include initiation: hydrogen-atom (LH) abstraction by peroxyl or alkoxyl radicals (L•); propagation: oxygen addition to carbon radicals (LOO•), peroxyl radical fragmentation or rearrangement, hydrogen atom transfer (LOOH), peroxyl radical addition to carbon-carbon doubles bonds or cyclization; and termination: peroxyl-peroxyl termination.7

Figure 1.2. Lipid peroxidation pathways (This work is a derivative of "Free Radical Toxicity " by Dan Cojocari, used under CC-BY-SA-4.0).

Lipid hydroperoxides (LOOH) are unstable. Depending on conditions, they undergo numerous secondary and tertiary reactions, which will proceed by free-radical mechanisms involving lipid peroxyl (LOO•) and lipid alkoxyl (LO•) radicals. The resulting peroxidation products can be divided into three categories:6

1. Chain-cleavage producing truncated oxidation products. Most of these products

are generated from β-cleavage of either of two C-C bonds adjacent to the

hydroperoxyl group. This cleavage gives two types of fragments. One derived

from the methyl terminus of the alkyl chain and one where the acyl fragment is

still bound through an ester linkage to the parent lipid molecule. 4-Hydroxynon-2-

enal (4-HNE) and 4-hydroxyhex-2-enal (4-HHE) are methyl-terminus fragments

resulting from oxidative cleavage of ω-6 and ω-3 PUFAs respectively while 9-

hydroxy-12-oxododec-10-enoic acid (HODA)-phospholipid (PL), 5-hydroxy-8-

oxooct-6-enoic acid (HOOA)-PL and 4-hydroxy-7-oxhept-5-enoic acid (HOHA)-

PL are acyl-containing aldehydes generated from peroxidation of linoleate (LA)-

PL, arachidonate (AA)-PL and docosahexaenoate (DHA)-PL esters of 2-lysoPLs,

respectively (Scheme 1.1).8, 9

2. Rearrangement oxidation products. These products are formed by rearrangement

of mono hydroperoxides or rearrangement and consecutive oxidation including

five-membered monocyclic peroxides, hydroperoxy-epidioxides, dihydroperoxides,

bicyclic-endoperoxides, etc. Prostaglandins and levuglandins are especially well-

known in this category.

3. Higher-molecular-weight oxidation products. The products result from dimerize-

tion or polymerization of peroxidized lipid molecules.

Scheme 1.1. Oxidative fragmentation of PUFA phospholipids produces γ-α,β- unsaturated hydroxyalkenals

1.3 Protein adducts of oxidatively truncated lipids

Among the truncated lipid oxidation products, the reactive carbonyl species (RCS) include α,β-unsaturated carbonyls that not only are carbonyl electrophiles, but also are electrophilic at the γ-carbon of the conjugated α,β-unsaturated bond. They form Schiff- base or Michael adducts with nucleophilic targets such as thiol and amino groups of lysine, histidine and cysteine in bio-molecules such as proteins, peptides (especially glutathione), DNA, and ethanolamine phospholipids. The modification of proteins or other bio-molecules can alter cellular functions and affect signal transduction or gene expression.10, 11 The resulting carbonylated proteins are a type of “advanced lipoxidation end-products (ALE)” which are considered a major hallmark of oxidative stress-related disorders.12

4-HNE, 4-HHE, and malonaldehyde (MDA) are some of the most extensively studied aldehydes. 4-HNE mediates a wide variety of biological processes from DNA damage

7 and mutagenesis, inflammatory response, cell growth, to apoptosis. 4-HNE is also involved in multiple signaling events including age-related NF-κB, AKT/PKB, Nrf2, mTOR signaling13, antioxidant response (Keap1/Nrf2 pathways), and DNA damage response signaling.14 Also, 4-HHE is a mediator of mitochondrial permeability transition15 and MDA disturbs amino phospholipid organization in membrane bilayers.16

In addition to the electrophiles such as 4-HNE, which dissociate from membranes or lipoprotein particles, the truncated oxidation products that are still bound to phospholipids have attracted increasing interest. γ-Hydroxyalkenal phospholipids such as

HODA-PL, HOOA-PL and HOHA-PL are found in oxidized low-density lipoprotein

(LDL) and their more oxidized derivatives are also ligands for the scavenger receptor

CD36 that trigger endocytosis of oxidized LDL by macrophage cells17 and promote the

CD36 mediated phagocytosis of oxidatively damaged rod photoreceptor cell tips by retinal pigmented epithelial (RPE) cells.18 Covalent adduction of γ-hydroxyalkenal phospholipids with proteins generates the corresponding 2-(ω-carboxyalkyl)pyrrole (CAP) modifications of proteins: 2-(ω-carboxyheptyl)pyrrole (CHP) from HODA-PL, 2-(ω- carboxypropyl)pyrrole (CPP) from HOOA-PL, and 2-(ω-carboxyethyl)pyrrole (CEP) from HOHA-PL. CHP immunoreactivity is detected in human plasma, and levels are significantly elevated in blood from renal failure and atherosclerosis patients.19 Plasma levels of CPP from sickle cell disease (SCD) clinic patients are significantly higher than those of individuals with no SCD or SCD patients hospitalized to treat a sickle cell crisis, who are routinely given transfusions and drugs that ameliorate the crisis, and presumably lower blood levels of CPP.20

A unique mechanism of CEP generation was discovered recently. Under physiological conditions (37 °C, pH 7.4), HOHA-PL spontaneously deacylates and forms a stable 5- membered lactone, HOHA-lactone. Although HOHA-PL can form an adduct that is subsequently released from the PL by phospholipolysis, the major precursor of CEP is

HOHA-lactone. In the retina, CEP localizes in photoreceptor rod outer segments and retinal pigment epithelium, and more intense CEP immunoreactivity is found in retina from human donors with age-related macular degeneration (AMD) compared with that in healthy human retina.21

CEP activates CEP-specific T-cells that promote the global retinal atrophy found in

“dry AMD” and toll-like receptor 2 (TLR2)-dependent expression and activation of the

NLRP3 inflammasome.22 CEP also induces choroidal neovascularization that characterizes “wet AMD” and promotes wound healing and tumor growth in a TLR2- dependent manner.23

1.4 Levuglandins and their protein adducts

Levuglandins are rearrangement peroxidation products of arachidonic acid (AA), a polyunsaturated fatty acid 20:4(ω-6). There are two pathways that the oxidation of AA-

PL can follow: cyclooxygenase (COX) enzymatic pathway and free-radical induced non- enzymatic pathway (Scheme 1.2).

For the enzymatic pathway, phospholipase A2 (PLA2) cleaves and releases free AA from phospholipid membranes. This is followed by transformation to prostaglandin H2

(PGH2) catalyzed by cyclooxygenase (COX) and hydroperoxidase. Prostaglandin

24 endoperoxide PGH2 is unstable (t1/2 = 5 min at 37 °C in aqueous solution) and undergoes rearrangements to provide physiologically active molecules25, including the

9 highly reactive levulinaldehyde derivatives, levuglandins (LG)D2 and LGE2. On the other hand, the non-enzymatic pathway is initiated by free radical-induced autooxidation of AA-PL and produces a series of stereoisomers and regioisomers of PGH2 (H2- isoprostanes). These H2-isoprostanes undergo nonenzymatic rearrangement to both stereoisomers and regioisomers of levuglandins, referred to collectively as isolevuglandins (isoLGs).26 Levuglandins are an enantiomerically pure structurally homogeneous subclass of isolevuglandins. An analogous series of free radical-induced oxidation reactions of docosahexaenoate (DHA)-PL delivers a series of 22-carbon isolevugladins.

Scheme 1.2. The cyclooxygenase (COX) and radical-induced cyclooxygenation of arachidonate produce isoLGs.

Owing to their reactive γ-ketoaldehyde functional arrays, LGs/isoLGs avidly react with the primary amino groups of protein lysyl residues,27 DNA, 28 and ethanolamine phospholipids29 producing pyrrole derivatives of protein lysyl residues (Scheme 1.3).

These highly alkylated pyrroles are further oxidized to lactams and hydroxylactams in the presence of oxygen30 or undergo oxidative pyrrole-pyrrole coupling to produce protein- protein crosslinks.31 Aminal crosslinks involving a single molecule of LG/isoLG are also formed (Scheme 1.3). Besides causing protein-protein cross-linking, LGs/isoLGs also produce DNA-protein cross-links (DPCs) by consecutively reacting with two primary amino group nucleophiles. LGs/isoLG-protein is associated with pathological processes including inhibition of tubulin polymerization to form microtubules, disruption of histone nucleosomal complexation with DNA,32 impairment of mitochondrial function through modification of cytochrome c,33 promotion of Alzheimer’s disease through COX-

34 associated isoLG-induced oligomerization of Aβ1-42 accumulation of cholesterol that contributes to AMD owing to modification of an oxidase, CYP27A1.35

Recently, an oxidized form of LGD2 (ox-LGD2) was isolated from the red alga

Gracilaria edulis and was also detected in mouse tissues and in the lysate of phorbol-12-

36 myristate-13-acetate-treated THP-1 cells incubated with arachidonic acid. Ox-LGD2 is a γ-hydroxybutenolide with prostanoid side chains. It lacks the reactive γ-ketoaldehyde functional array possessed by LGD2 and consequently is expected to be less prone than

LGD2 toward formation of covalent adducts with biomolecules. Therefore, ox-LGs might be considered detoxification metabolites of LGs, and their formation may prevent the pathological consequences associated with LGs.

Scheme 1.3. Metabolism of LGs: generation of protein adducts, crosslinks and oxidized metabolites.

1.5 Light-induced damage in the retina

The retina is a light-sensitive layer of tissue lining the inner surface of the back of the eyeball. The outer monolayer is known as the retinal pigment epithelium (RPE) while inside and adjacent to the RPE is the neurosensory retina, which is composed of photoreceptor cells, ganglion cells, bipolar cells, horizontal cells, amacrine cells and other non-neuronal cells. Exposure of the retina to excessive fluxes of visible light results in damage to the retina. Although the eye is exposed to daily fluxes of solar radiation and artificial light sources, not all spectral components of light can reach and be absorbed in the retina. The cornea absorbs wavelengths below 295 nm while the lens in

12 the adult human eye strongly absorbs high energy shorter-wavelength UVB (295-315 nm), and the full range of UVA (315-390 nm). The lenses of children transmit some

UVB and UVA in the spectral range of 300-340 nm and around 8% transmittance centered at 320 nm can reach the retina. The vitreous absorbs light above 1400 nm.

Therefore, the light reaching retina (Fig. 1.3) is mostly the visible component (390-

760nm) and some of the near infrared (760-1400nm).37

Figure 1.3. Transmission of light in the human eye

“Photochemical damage” is the most common form of retinal damage induced by light.

A photon is absorbed by a molecular chromophore and converts that molecule to an excited state that subsequently participates in chemical reactions.38 In “photosensitized damage”, one kind of photochemical damage, the excited singlet state chromophore undergoes intersystem crossing and forms an excited triplet state which will further interact with other molecules through two types of photosensitized oxidation reactions.

Type I: generation of free radicals via electron transfer and further reaction with oxygen or other molecules; Type II: generation of singlet oxygen via transfer of excitation energy from a chromophore (photosensitizer) in the triplet state to molecular oxygen.39 Both

13 types of photosensitize oxidation reactions can trigger a lipid peroxidation cascade

(Scheme 1.4).

Scheme 1.4. Type I and Type II photosensitized oxidation reactions.

The retina contains numerous endogenous photosensitizers such as vitamin A derivatives, lipofuscin, melanin, flavins and porphyrins, which accumulating with age. At the same time, the outer retina, photoreceptors and retinal pigment epithelium (RPE), is immediately adjacent to the choroidal circulation which continuously supplies oxygen to the retina.40 These conditions make the retina extremely susceptible to photooxidative damage (Fig. 1.4).

Figure 1.4. The outer retina (photoreceptor and RPE) is susceptible to photooxidative damage.

There are at least two different mechanisms responsible for photochemical damage of the retina.41, 42 Class I damage has an action spectrum coinciding with the absorption spectrum of the visual pigment, and it appears after exposures for rather long periods to relatively low irradiances (< 1 mW/cm2, white light). The initial damage is mainly restricted to the photoreceptors. Class I damage has also been further classified to two subgroups: the first is “rhodopsin” mediated damage as mainly found in rats,43 which has the action spectrum corresponding to the absorption spectrum of rhodopsin peaking at

500 nm; the second is damage mediated by “cone pigment”, as found in monkeys,44, 45 which can be induced selectively to blue, green or red cones by a series of exposures to narrow-band light centered at 463 nm and 520 nm and broad-band light in the range of

630-720 nm, respectively. While the damage to the green or red cones is temporary, the damage to blue cones is permanent.

Class II damage has an action spectrum that peaks at short wavelength. This type of damage is found with high irradiances (>10 mW/cm2, white light). The induced damage

15 increases continuously with decreasing wavelength and appears to be oxygen-dependent.

The initial damage is generally confined to the retinal pigment epithelium (RPE), which is believed to be due to high concentrations of photosensitizers and oxygen in the RPE.

However, while the damage owing to high irradiances is mainly in the RPE for wavelengths higher than 350 nm, and for lower wavelengths, the damage is mainly found in photoreceptors (Scheme 1.5).46, 47

Scheme 1.5. Class I and Class II photochemical damage.

1.6 Age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a progressive loss of central vision resulting from damage to the retinal pigmented epithelium (RPE) and neural retina that affects approximately 30-50 million people worldwide. Its prevalence increases with age.

There are three stages of AMD, defined by the Age-Related Eye Disease Study48 as

“early AMD”, “intermediate AMD” and “late AMD” (Fig. 1.5).

A B C D

Figure 1.5. Classification of AMD. Column A shows medium-size drusen (arrows) in early AMD, and Column B shows a large druse (arrows) in intermediate AMD. In Column C, a photograph of the fundus shows geographic atrophy (white arrow), and a histopathological photograph shows geographic atrophy with loss of Bruch’s membrane (black arrow). In Column D, the photograph of the fundus with neovascular age-related macular degeneration shows subretinal hemorrhage (blue arrow) and choroidal neovascularization (white arrow), and the histopathological photograph shows choroidal neovascularization (black arrow). Reproduced with permission from The New England Journal of Medicine (2008) Rama D Jager et al., Age-Related Macular Degeneration 358:24, 2606-2617, Copyright Massachusetts Medical Society.

Early AMD is characterized by the presence of a few (<20) medium-size drusen which are asymptomatic, insoluble extracellular aggregates or retinal pigmentary abnormalities.

People with early AMD typically do not have vision loss. Intermediate AMD is characterized by at least one large druse, numerous medium size drusen, or geographic atrophy that does not extend to the center of the macula, which may cause some vision loss but could be easily ignored by most people. Late or advanced AMD consists of two types: (1) geographic atrophy (dry AMD), in which there is a gradual breakdown of RPE cells and the overlying light-sensing retinal photoreceptors in the macula; (2) neovascular

AMD (wet AMD), is characterized by choroidal neovascularization (CNV) wherein newly immature blood vessels grow towards the outer retina from the underlying choroid.

These vessels leak fluid below or within the retina, which may lead to swelling and damage of the macula. Patients wet AMD can have sudden, profound visual loss within days to weeks.49, 50

A complex interplay of genetic and environmental factors contributes to the pathogenesis of AMD.51 Multiple genes and/or single nucleotide polymorphisms (SNPs) have been found associated with AMD, including various genes involved in the complement pathway, lipid metabolism and extracellular matrix remodeling.

Furthermore, RPE senescence,52 oxidative stress53 and immune dysfunction are also involved. Among these factors, oxidative stress and inflammation play an especially important role in the development of AMD.

Oxidative stress

The outer retina, composed by RPE and photoreceptors, is the main source of ROS owing to light exposure and a high oxygen concentration environment. Photoreceptor disks and RPE cells that are rich in polyunsaturated fatty acids, especially DHA, are sensitive to autooxidation and prone to oxidative stress. Furthermore, in RPE cells, daily ingestion of phagocytes containing oxidized membranes of shed disks, which incorporate oxidative degradation products, leads to the accumulation in RPE cells of lipofuscin, fine yellow-brown pigment granules composed of lipid-containing residues of lysosomal digestion. Lipofuscin is photoreactive and thus increases the susceptibility of the RPE to light damage with aging.

Inflammation

That the complement system plays a central role in the etiology of AMD is supported by several lines of evidence including (1) the presence of complement components in the choriocapillaris and the retina, especially in drusen; (2) increased membrane attack complex (MAC) in the choriocapillaris of AMD patients; and (3) the genetic association of complement factors CFH, C2/CFB, C3, CFI, and C9 with AMD. The complement system is a part of the innate immune system, that can respond to antigen-antibody complexes (classical pathway) or bacterial mannose groups (lectin pathway) and can also be active in a low-level continuous state (alternative pathway).

In the alternative pathway (Fig. 1.6), C3 is cleaved by convertases/plasma proteases to generate C3b. Factor B (FB) binds to C3b and the complex is cleaved by the plasma protease factor D (FD) forming the essential C3 convertase (C3bBb). The C3bBb complex is stabilized by binding oligomers of factor P (properdin), leading to an amplification loop that cleaves and assembles C3 to C3b to C3bBb continuously. The accumulation of C3b leads to C3b binding to C3bBb, thereby creating a new enzyme, the

C5 convertase (C3bBbC3b) that cleaves C5 to C5a and C5b. C5b then recruits and assembles C6, C7, C8 and 10-16 molecules of C9 to form the MAC, resulting in cell lysis.

Figure 1.6. The alternative complement pathway

Factor H (CFH) is the major negative regulator of the alternative pathway, which can bind to C3b and act as a cofactor for factor I (FI) mediated cleavage of C3b producing inactive proteins (iC3b) as well as accelerating decay of the C3bBb convertase. Factor H has multiple binding sites for C3b, heparin, C-reactive protein (CRP) and binding sites for cellular and biological surfaces. A genetic variant that results in the substitution of histidine 402 for tyrosine (Y402H) in the SCR7 domain of CFH is associated with the

20 highest risk of AMD.54 The protective variants of Factor H, carrying Y402, bind more strongly to heparin and CRP while the risk variants with H402 bind with lower affinity to their ligands, which reduces the ability of CFH to degrade C3 and regulate the alternative pathway. A 2-4 fold increase of AMD risks is observed in heterozygote carriers (only one allele of chromosome has risk variant) and a 3-7 fold increase is found in homozygote carriers (both alleles carries risk variant).55, 56 Variations in the factor B and

C2 genes are also associated with AMD.57 The L9H variant of factor B and the E318D variant of C2 (H10), as well as a variant in intron 10 of C2 and the R32Q variant of factor

B (H7), confer a significantly reduced risk of AMD.

1.7 References

(1) Finkel, T., and Holbrook, N. J. (2000) Oxidants, oxidative stress and the biology

of ageing. Nature 408, 239-247.

(2) Han, D., Williams, E., and Cadenas, E. (2001) Mitochondrial respiratory chain-

dependent generation of superoxide anion and its release into the intermembrane

space. Biochem. J 353, 411-416.

(3) Muller, F. (2000) The nature and mechanism of superoxide production by the

electron transport chain: Its relevance to aging. J Am Aging Assoc 23, 227-253.

(4) Rahman, T., Hosen, I., Islam, M. M. T., and Shekhar, H. U. (2012) Oxidative

stress and human health. Advances in Bioscience and Biotechnology 03, 997-1019.

(5) Valko, M., Rhodes, C. J., Moncol, J., Izakovic, M., and Mazur, M. (2006) Free

radicals, metals and antioxidants in oxidative stress-induced cancer. Chem. Biol.

Interact. 160, 1-40.

(6) Esterbauer, H. (1993) Cytotoxicity and genotoxicity of lipid-oxidation products.

Am. J. Clin. Nutr. 57, 779S-785S; discussion 785S-786S.

(7) Yin, H., Xu, L., and Porter, N. A. (2011) Free radical lipid peroxidation:

mechanisms and analysis. Chem. Rev. 111, 5944-5972.

(8) Gu, X., Sun, M., Gugiu, B., Hazen, S., Crabb, J. W., and Salomon, R. G. (2003)

Oxidatively truncated docosahexaenoate phospholipids: total synthesis,

generation, and Peptide adduction chemistry. J. Org. Chem. 68, 3749-3761.

(9) Salomon, R. G., and Gu, X. (2011) Critical insights into cardiovascular disease

from basic research on the oxidation of phospholipids: the gamma-

hydroxyalkenal phospholipid hypothesis. Chem. Res. Toxicol. 24, 1791-1802.

(10) Uchida, K. (2003) 4-Hydroxy-2-nonenal: a product and mediator of oxidative

stress. Prog. Lipid Res. 42, 318-343.

(11) Catala, A. (2006) An overview of lipid peroxidation with emphasis in outer

segments of photoreceptors and the chemiluminescence assay. Int. J. Biochem.

Cell Biol. 38, 1482-1495.

(12) Fedorova, M., Bollineni, R. C., and Hoffmann, R. (2014) Protein carbonylation as

a major hallmark of oxidative damage: update of analytical strategies. Mass

Spectrom. Rev. 33, 79-97.

(13) Zhang, H., and Forman, H. J. (2017) 4-hydroxynonenal-mediated signaling and

aging. Free Radic. Biol. Med. 111, 219-225.

(14) West, J. D., and Marnett, L. J. (2006) Endogenous reactive intermediates as

modulators of cell signaling and cell death. Chem. Res. Toxicol. 19, 173-194.

(15) Kristal, B. S., Park, B. K., and Yu, B. P. (1996) 4-Hydroxyhexenal is a potent

inducer of the mitochondrial permeability transition. J. Biol. Chem. 271, 6033-

6038.

(16) Jain, S. K. (1984) The accumulation of malonyldialdehyde, a product of fatty acid

peroxidation, can disturb aminophospholipid organization in the membrane

bilayer of human erythrocytes. J. Biol. Chem. 259, 3391-3394.

(17) Podrez, E. A., Poliakov, E., Shen, Z., Zhang, R., Deng, Y., Sun, M., Finton, P. J.,

Shan, L., Febbraio, M., Hajjar, D. P., Silverstein, R. L., Hoff, H. F., Salomon, R.

G., and Hazen, S. L. (2002) A novel family of atherogenic oxidized phospholipids

promotes macrophage foam cell formation via the scavenger receptor CD36 and

is enriched in atherosclerotic lesions. J. Biol. Chem. 277, 38517-38523.

(18) Sun, M., Finnemann, S. C., Febbraio, M., Shan, L., Annangudi, S. P., Podrez, E.

A., Hoppe, G., Darrow, R., Organisciak, D. T., Salomon, R. G., Silverstein, R. L.,

and Hazen, S. L. (2006) Light-induced oxidation of photoreceptor outer segment

phospholipids generates ligands for CD36-mediated phagocytosis by retinal

pigment epithelium: a potential mechanism for modulating outer segment

phagocytosis under oxidant stress conditions. J. Biol. Chem. 281, 4222-4230.

(19) Kaur, K., Salomon, R. G., O'Neil, J., and Hoff, H. F. (1997)

(Carboxyalkyl)pyrroles in human plasma and oxidized low-density lipoproteins.

Chem. Res. Toxicol. 10, 1387-1396.

(20) Guo, J., Wang, H., Hrinczenko, B., and Salomon, R. G. (2016) Efficient

Quantitative Analysis of Carboxyalkylpyrrole Ethanolamine Phospholipids:

Elevated Levels in Sickle Cell Disease Blood. Chem. Res. Toxicol. 29, 1187-1197.

(21) Gu, X., Meer, S. G., Miyagi, M., Rayborn, M. E., Hollyfield, J. G., Crabb, J. W.,

and Salomon, R. G. (2003) Carboxyethylpyrrole protein adducts and

autoantibodies, biomarkers for age-related macular degeneration. J. Biol. Chem.

278, 42027-42035.

(22) Cruz-Guilloty, F., Saeed, A. M., Duffort, S., Cano, M., Ebrahimi, K. B., Ballmick,

A., Tan, Y., Wang, H., Laird, J. M., Salomon, R. G., Handa, J. T., and Perez, V. L.

(2014) T cells and macrophages responding to oxidative damage cooperate in

pathogenesis of a mouse model of age-related macular degeneration. PLoS One 9,

e88201.

(23) Ebrahem, Q., Renganathan, K., Sears, J., Vasanji, A., Gu, X., Lu, L., Salomon, R.

G., Crabb, J. W., and Anand-Apte, B. (2006) Carboxyethylpyrrole oxidative

protein modifications stimulate neovascularization: Implications for age-related

macular degeneration. Proc. Natl. Acad. Sci. U. S. A. 103, 13480-13484.

(24) Salomon, R. G., Miller, D. B., Zagorski, M. G., and Coughlin, D. J. (1984)

Prostaglandin endoperoxides. 14. Solvent-induced fragmentation of prostaglandin

endoperoxides. New aldehyde products from PGH2 and a novel intramolecular

1,2-hydride shift during endoperoxide fragmentation in aqueous solution. J. Am.

Chem. Soc. 106, 6049-6060.

(25) Hamberg, M., and Samuelsson, B. (1973) Detection and isolation of an

endoperoxide intermediate in prostaglandin biosynthesis. Proc. Natl. Acad. Sci. U.

S. A. 70, 899-903.

(26) Salomon, R. G. (1985) Prostaglandin endoperoxide reaction mechanisms and the

discovery of levuglandins. Acc. Chem. Res. 18, 294-301.

(27) Salomon, R. G., Jirousek, M. R., Ghosh, S., and Sharma, R. B. (1987)

Prostaglandin endoperoxides 21. Covalent binding of levuglandin E2 with

proteins. Prostaglandins 34, 643-656.

(28) Murthi, K. K., Friedman, L. R., Oleinick, N. L., and Salomon, R. G. (1993)

Formation of DNA-protein cross-links in mammalian cells by levuglandin E2.

Biochemistry 32, 4090-4097.

(29) Bernoud-Hubac, N., Fay, L. B., Armarnath, V., Guichardant, M., Bacot, S.,

Davies, S. S., Roberts, L. J., 2nd, and Lagarde, M. (2004) Covalent binding of

isoketals to ethanolamine phospholipids. Free Radic. Biol. Med. 37, 1604-1611.

(30) Roberts, L. J., 2nd, Salomon, R. G., Morrow, J. D., and Brame, C. J. (1999) New

developments in the isoprostane pathway: identification of novel highly reactive

gamma-ketoaldehydes (isolevuglandins) and characterization of their protein

adducts. FASEB J. 13, 1157-1168.

(31) Bi, W., Jang, G.-F., Zhang, L., Crabb, J. W., Laird, J., Linetsky, M., and Salomon,

R. G. (2016) Molecular Structures of Isolevuglandin-Protein Cross-Links. Chem.

Res. Toxicol. 29, 1628-1640.

(32) Carrier, E. J., Zagol-Ikapitte, I., Amarnath, V., Boutaud, O., and Oates, J. A.

(2014) Levuglandin Forms Adducts with Histone H4 in a Cyclooxygenase-2-

Dependent Manner, Altering Its Interaction with DNA. Biochemistry 53, 2436-

2441.

(33) Stavrovskaya, I. G., Baranov, S. V., Guo, X., Davies, S. S., Roberts, L. J., 2nd,

and Kristal, B. S. (2010) Reactive gamma-ketoaldehydes formed via the

isoprostane pathway disrupt mitochondrial respiration and calcium homeostasis.

Free Radic. Biol. Med. 49, 567-579.

(34) Zagol-Ikapitte, I., Masterson, T. S., Amarnath, V., Montine, T. J., Andreasson, K.

I., Boutaud, O., and Oates, J. A. (2005) Prostaglandin H(2)-derived adducts of

proteins correlate with Alzheimer's disease severity. J. Neurochem. 94, 1140-1145.

(35) Charvet, C., Liao, W. L., Heo, G. Y., Laird, J., Salomon, R. G., Turko, I. V., and

Pikuleva, I. A. (2011) Isolevuglandins and mitochondrial enzymes in the retina:

mass spectrometry detection of post-translational modification of sterol-

metabolizing CYP27A1. J. Biol. Chem. 286, 20413-20422.

(36) Kanai, Y., Hiroki, S., Koshino, H., Konoki, K., Cho, Y., Cayme, M., Fukuyo, Y.,

and Yotsu-Yamashita, M. (2011) Identification of novel oxidized levuglandin D2

in marine red alga and mouse tissue. J. Lipid Res. 52, 2245-2254.

(37) Boettner, E. A., and Wolter, J. R. (1962) Transmission of the Ocular Media.

Invest. Ophthalmol. Vis. Sci. 1, 776-783.

(38) Jacques, S. L. (1992) Laser-tissue interactions. Photochemical, photothermal, and

photomechanical. Surg. Clin. North Am. 72, 531-558.

(39) Baptista, M. S., Cadet, J., Di Mascio, P., Ghogare, A. A., Greer, A., Hamblin, M.

R., Lorente, C., Nunez, S. C., Ribeiro, M. S., Thomas, A. H., Vignoni, M., and

Yoshimura, T. M. (2017) Type I and Type II Photosensitized Oxidation Reactions:

Guidelines and Mechanistic Pathways. Photochem. Photobiol. 93, 912-919.

(40) Eshaq, R. S., Wright, W. S., and Harris, N. R. (2014) Oxygen delivery,

consumption, and conversion to reactive oxygen species in experimental models

of diabetic retinopathy. Redox Biol 2, 661-666.

(41) Rozanowska, M., and Sarna, T. (2005) Light-induced damage to the retina: role of

rhodopsin chromophore revisited. Photochem. Photobiol. 81, 1305-1330.

(42) Wu, J., Seregard, S., and Algvere, P. V. (2006) Photochemical damage of the

retina. Surv. Ophthalmol. 51, 461-481.

(43) Williams, T. P., and Howell, W. L. (1983) Action spectrum of retinal light-

damage in albino rats. Invest. Ophthalmol. Vis. Sci. 24, 285-287.

(44) Sperling, H. G., Johnson, C., and Harwerth, R. S. (1980) Differential spectral

photic damage to primate cones. Vision Res. 20, 1117-1125.

(45) Harwerth, R. S., and Sperling, H. G. (1975) Effects of intense visible radiation on

the increment-threshold spectral sensitivity of the rhesus monkey eye. Vision Res.

15, 1193-1204.

(46) Ham, W. T., Jr., Mueller, H. A., Ruffolo, J. J., Jr., Guerry, D., 3rd, and Guerry, R.

K. (1982) Action spectrum for retinal injury from near-ultraviolet radiation in the

aphakic monkey. Am. J. Ophthalmol. 93, 299-306.

(47) Gorgels, T. G., and van Norren, D. (1995) Ultraviolet and green light cause

different types of damage in rat retina. Invest. Ophthalmol. Vis. Sci. 36, 851-863.

(48) Age-Related Eye Disease Study Research, G. (2000) Risk factors associated with

age-related macular degeneration. A case-control study in the age-related eye

disease study: Age-Related Eye Disease Study Report Number 3. Ophthalmology

107, 2224-2232.

(49) Ambati, J., and Fowler, B. J. (2012) Mechanisms of age-related macular

degeneration. Neuron 75, 26-39.

(50) Jager, R. D., Mieler, W. F., and Miller, J. W. (2008) Age-related macular

degeneration. N. Engl. J. Med. 358, 2606-2617.

(51) Shaw, P. X., Stiles, T., Douglas, C., Ho, D., Fan, W., Du, H., and Xiao, X. (2016)

Oxidative stress, innate immunity, and age-related macular degeneration. AIMS

Mol Sci 3, 196-221.

(52) Kozlowski, M. R. (2012) RPE cell senescence: a key contributor to age-related

macular degeneration. Med. Hypotheses 78, 505-510.

(53) Jarrett, S. G., and Boulton, M. E. (2012) Consequences of oxidative stress in age-

related macular degeneration. Mol. Aspects Med. 33, 399-417.

(54) Fritsche, L. G., Fariss, R. N., Stambolian, D., Abecasis, G. R., Curcio, C. A., and

Swaroop, A. (2014) Age-related macular degeneration: genetics and biology

coming together. Annu Rev Genomics Hum Genet 15, 151-171.

(55) Wegscheider, B. J., Weger, M., Renner, W., Steinbrugger, I., Marz, W.,

Mossbock, G., Temmel, W., El-Shabrawi, Y., Schmut, O., Jahrbacher, R., and

Haas, A. (2007) Association of complement factor H Y402H gene polymorphism

with different subtypes of exudative age-related macular degeneration.

Ophthalmology 114, 738-742.

(56) Klein, R. J., Zeiss, C., Chew, E. Y., Tsai, J. Y., Sackler, R. S., Haynes, C.,

Henning, A. K., SanGiovanni, J. P., Mane, S. M., Mayne, S. T., Bracken, M. B.,

Ferris, F. L., Ott, J., Barnstable, C., and Hoh, J. (2005) Complement factor H

polymorphism in age-related macular degeneration. Science 308, 385-389.

(57) Gold, B., Merriam, J. E., Zernant, J., Hancox, L. S., Taiber, A. J., Gehrs, K.,

Cramer, K., Neel, J., Bergeron, J., Barile, G. R., Smith, R. T., Group, A. M. D. G.

C. S., Hageman, G. S., Dean, M., and Allikmets, R. (2006) Variation in factor B

(BF) and complement component 2 (C2) genes is associated with age-related

macular degeneration. Nat. Genet. 38, 458-462.

CHAPTER 2

Total Synthesis Confirms the Molecular Structure Proposed for

Oxidized Levuglandin D2

2.1 Background

Levuglandins (LGs) are secoprostaglandin, levulinaldehyde derivatives with prostanoid side chains, that are generated through cyclooxygenase (COX)-induced oxidation of arachidonic acid followed by spontaneous non-enzymatic rearrangement, involving a novel intramolecular 1,2-hydride shift, of an endoperoxide intermediate

Scheme 2.1. Generation and proposed structure of ox-LGD2

1 PGH2 (Scheme 2.1). Hydride (highlighted in red in Scheme 2.1) migration from C-11 to an incipient ketone methyl group produces LGD2 while migration from C-9 produces

LGE2. LGs can also be generated through free radical-induced cyclooxygenation of arachidonate esterified to lyso phospholipids.2 Owing to their reactive γ-ketoaldehyde functional arrays, LGs avidly bind with the primary amino groups of protein lysyl residues,3 DNA4 and ethanolamine phospholipids.5 Within 1 minute of their generation during the production of PGH2 by cyclooxygenation of arachidonic acid, LGs are sequestered by covalent adduction to proteins.6 This covalent adduction as well as LG-

31 induced cross-linking of proteins7 and DNA4 interferes with protein function8 and contributes to pathological processes, including brain tissue damage,9 tubulin malfunc- tion,10 interference with the control of expression,11 Alzheimer’s disease (AD),12-15 age- related macular degeneration,16-18 atherosclerosis,19-22 end-stage renal disease,23 hyperoxia,5 myocardial infarction24 and sepsis.25

Recently, a natural product, presumed to be ox-LGD2 (2.1, Scheme 2.1), was isolated from the red alga Gracilaria edulis and was also detected in mouse tissues and in the lysate of phorbol-12-myristate-13-acetate treated THP-1 cells incubated with arachidonic

26 acid. Ox-LGD2 is a γ-hydroxy-butenolide with prostanoid side chains that is presumably generated through oxidation of LGs (Scheme 2.1). In view of the exceptionally high proclivity for LGs to form covalent adducts with primary amino groups in biomolecules, a competing alternative fate, i.e., oxidation to ox-LGs in vivo was unexpected. Thus, within 1 min of incubation with bovine serum albumin, 10

3 equivalents of LGE2 bind to the protein. Incubation of arachidonic acid with PGH- synthase-2 results in binding of 12 equivalents within 1 min.6 Furthermore the presumed conversion of LGs to ox-LGs involves an unusual dehydrogenation that introduces the butenolide C=C bond. Because ox-LGD2 lacks a reactive γ-ketoaldehyde functional array it is expected to be less prone than LGD2 toward formation of covalent adducts with biomolecules. Consequently, the conversion of LGs into ox-LGs might serve as a biological detoxification process that can prevent the pathological consequences associated with the generation of LGs and their covalent adduction with biomolecules. To confirm its molecular structure, and as a prelude to investigating its biological functions and biosynthesis, we developed a concise unambiguous total synthesis of ox-LGD2.

2.2 Results and Discussion

Retrosynthetic Analysis. Because the nonenzymatic rearrangement of PGH2 to LGD2 is accompanied by the formation of LGE2 that should lead to the production of ox-LGE2

(Scheme 2.1), our synthetic strategy (Scheme 2.2) was designed to also deliver this structural isomer. Although our synthesis did produce a mixture of regioisomeric ox-LGs, owing to a proclivity toward rearrangement of the 5,6-C=C bond, only the rearrangement

6 product Δ -ox-LGE2 is likely to be isolated from biological sources. The synthetic ox-

LGD2 proved identical to the compound isolated from biological sources.

Scheme 2.2. Synthetic design for ox-LGD2

A three component coupling strategy for preparing tri and tetrasubstituted olefins27 was adopted as a key step for the total synthesis of ox-LGs (Scheme 2.2). Thus, conjugate addition of a nucleophilic lower side chain fragment, a higher-order cyanocuprate derived from a vinylstannane 2.5, to di-tert-butyl acetylene dicarboxylate (2.6) and trapping of

33 the resulting vinyl nucleophile product with an electrophilic upper side chain fragment, an allylic bromide 2.7, was expected to deliver an anhydride 2.3 to which addition of a one-carbon nucleophile would deliver both ox-LGD2 (2.1) and ox-LGE2 (2.2). The mild conditions required to convert an intermediate di-tert-butyl ester 4 into a cyclic anhydride

2.3 were expected to be compatible with a sensitive allylic silyl ether functionality. A di- tert-butyl(methyl)silyl (DTBMS) ester in 2.3 was expected to be resistant to the reaction with methyllithium that is required for introduction of the final skeletal carbon.

Synthesis of the Carboxylic Acid Upper Side Chain. The upper side chain synthon, di-tert-butyl(methyl)silyl-(Z)-7-bromohept-5-enoate (2.7), was prepared from tetrahydrofuran and propargyl alcohol (Scheme 2.3). This new synthetic strategy for preparing 2.7 is an improvement over a previous synthesis involving alkylation of propargyl THP ether with 1-bromo-3-chloropropane, conversion of the bromide to a nitrile with cyanide in hot

Scheme 2.3. Synthesis of the upper side chain precursor

DMSO, hydrolysis of the nitrile, silylation, removal of the THP protecting group, catalytic partial hydrogenation and bromodehydroxylation.28 The use of P-2 nickel boride catalyst29 to selectively reduce the triple bond in 2.9 (Scheme 2.3) provided better selectivity than Lindlar’s catalyst used in a previous synthesis of 2.7.28 The lower side chain vinyl nucleophile precursor 2.5 is readily available from 1-octyn-3-ol.30 The use of a DTBMS ester was expected to prevent addition of MeLi to the terminal carboxyl during selective addition to the anhydride carbonyl in 2.3 and selective removal of tert-butyl protecting groups in 2.4, and yet allow removal of the silyl protecting groups in the final step of the synthesis.

Three-component Coupling. Stereocontrolled syn-addition of organocopper reagents

RCu(Me2S)MgBr2 to acetylene dicarboxylates had been employed to prepare various tri and tetra-substituted maleates and their corresponding maleic anhydrides.31, 32 In contrast with n-butylcuprate, yields were poor for the vinyl organocopper reagent generated from the lower side chain precursor 2.5 (Scheme 2.4, Table 2.1). Three-component coupling of

Table 2.1. One-pot Three-component Coupling of Alkyne 2.6 with Cuprates and Allylic Halides.

R1 R2 %Yield 75% 10%

35 the vinyltin 2.5 with acetylene 2.6 and the upper side chain precursor 2.7 delivered only a

5% of the yield of the desired product 2.4.

Scheme 2.4. Concise total synthesis of ox-LGD2

A model study with a series of lower- and higher-order vinyl cuprates (n = 1 or 2, m =

1 or 2), anionic ligands and reaction conditions revealed that several cycanocuprate reagents (Table 2.2) provided a nearly five-fold improvement in the yield of 2.14 compared to that with the organocopper reagent RCu(Me2S)MgBr2 employed previously.

A comparison of reagents (Table 2.3) identified a divinyl cyanocuprate intermediate 2.15

(n = 2, X = CN) as the reagent of choice for the production of 2.4 by conjunction with the upper side chain allylic bromide 2.7. The corresponding vinyl cyanocuprate 2.15 (n = 1,

X = CN) gave a substantially lower yield of three-component coupling (14% versus 53%)

Table 2.2. One-pot Three-component Coupling of Alkyne 2.6 with Various Vinyl Cuprates to Generate Maleate 2.14.

Entry X Y n Temperature Time 2.6 = m HMPA Additive %Yield (oC) (hr) (equiv.) (equiv.) 1 Br --- 1 -78 1.0 1.0 2.0 --- 10 % 2 CN Me 1 -78 1.0 1.0 2.0 --- 19 % 3 CN Me 1 -78, 40min 1.0 2.0 --- 16 % then -45, 40min 4 CN Thienyl 1 -78 1.5 1.0 2.0 --- 21 % 5 CN --- 1 -78 1.5 1.0 2.0 --- 43 %

6 CN --- 1 -78 1.5 1.0 2.0 BF3.OEt2 27 % 7 CN --- 1 -78 1.5 1.0 9.0 --- 46 % 8 CN --- 2 -78 1.5 1.0 2.0 --- 24 % 9 CN --- 2 -78 1.5 2.0 9.0 --- 46 %

Table 2.3. Comparison of Organocopper Reagents for Synthesis of 2.4.

Yield 2.4 : 2.4’ Reagent (%, isolated) Ratio (NMR) n = 2, X = CN 53% 54.5 : 45.5 n = 1, X = CN 14% 45.5 : 54.5 n = 1, X = Br 5% 50.0 : 50.0

and the corresponding vinyl bromocuprate 2.15 (n = 1, X = Br) was even worse (5%).

However, for all of the cuprates, there was no preference for the desired SN2 product 2.4 versus the unwanted SN2’ product 2.4’ (Scheme 2.4). Fortunately, these products of α and

γ substitution were readily separable by semi-preparative HPLC (Figure 2.1), using

CH3CN and iso-propanol as eluent.

Column: Luna C18 5m 10*250mm Flow rate :1mL/min Eluent: ACN/2-propanol (gradient) Detector: UV 254nm

Figure 2.1. HPLC separation of three-component coupling products 2.4 and 2.4’

Generation of the ox-LG Hydroxybutenolide. Our strategy to complete the carbon skeleton of ox-LGs envisioned selective addition of a methyl nucleophile to one of the ester carbonyls in 2.4. Conversion of the cis bis tert-butoxycarbonyl array in 2.4 into an anhydride 2.3 was envisioned as a strategy to selectively enhance the reactivity of the maleate carbonyls. However, this key manipulation would require selective dealkylation of the tert-butyl esters without desilylation. The development of methodology to accom- plish these goals and a concise total synthesis of ox-LGs (see Scheme 2.4 above) was enabled by two model studies. One model study (Scheme 2.5) confirmed the challenge of

Scheme 2.5. Model study for selective removal of tert-butyl groups. achieving the requisite selectivity. Treatment of di-tert-butyl ester 2.14 with formic acid simultaneously removed the tert-butyl groups and promoted cyclization to an anhydride, but also cleaved the TBDMS group to deliver anhydride 2.16. Treatment of 2.14 with

ZnBr2 promoted transesterification to deliver lactone 2.17. Ultimately, a mild deprotection method (silica gel/toluene/100 °C) selectively cleaved the tert-butyl esters in 2.14 without removing the silyl ether, delivering anhydride 2.18.33 Similar treatment of di-tert-

39 butyl ester 2.4 (see Scheme 2.4 above) selectively cleaved the tert-butyl esters and provided the desired cyclic anhydride intermediate 2.3 without removal of the silyl ether or silyl ester protecting groups.

As a model system for the selective mono methylation of the anhydride 2.3 (see

Scheme 2.4 above), dimethylmaleic anhydride (2.19), was treated with various methyl ogranometallics in the presence of the DTBMS ester 2.22 (Table 2.4). As planned, under

Table 2.4. Model Study for the Mono Methylation of a Maleic Anhydride.

Temp Time Products (NMR Yield, %) Reagent Equiv Solvent (oC) (min) 2.20 2.21 1.0 THF -78 90 64.5 35.5 1.0 THF -45 90 53.8 46.2 1.0 THF 0 90 46.0 52.9 1.0 THF 0 to 90 50.0 50.0

MeMgBr 1.0 Et2O -RT78 90 55.6 33.3 1.0 Et2O -45 90 63.0 34.2

1.0 Et2O 0 90 57.0 38.5 2.0 THF -78 90 59.7 40.3 2.0 THF 0 90 6.8 91.6 1.0 THF -78 90 82.8 17.2 1.0 THF -94 90 91.5 2.0 MeLi 1.0 THF -94 30 91.2 2.9 2.0 THF -78 90 66.9 33.1

MeCeCl2 1.0 THF -78 90 35.2 59.8

Me2CuLi 1.0 THF/Et2O -78 90 Extremely Low

Me2Cu(CN)Li2 1.0 THF/Et2O -78 90 Extremely Low

MeCu(CN)Li 2.0 THF/Et2O -78 90 Extremely Low

Me2Zn 2LiBr 1.0 THF/Et2O -78 90 Extremely Low

40 all conditions examined, the DTBMS ester exhibited no reactivity. MeMgBr, MeLi and

MeCeCl2 all generated the desired monomethylation product 2.20 and an undesired geminal dimethylation product 2.21. MeLi was the most selective at -78 °C. Nearly complete selectivity and excellent yield of the desired mono addition product 2.20 were achieved at -94 °C. Based on the integrated 1H NMR peak areas for resonances centered at δH 6.50 and 6.32 (Appendix Figure A2.1), corresponding to H-13 in 2.1p and 2.2p respectively (see Scheme 2.4 above), reaction of anhydride 2.3 with MeLi under these optimized reaction conditions delivered a 1:6 mixture of the silyl protected ox-LG derivatives 2.1p and 2.2p respectively. This unfortunate selectivity disfavoring the carbon skeleton required for ox-LGD2, the primary target of our total synthesis, was counter balanced by the serendipitous instability of ox-LGE2 that facilitated isolation of ox-LGD2 from the mixture (vide infra).

The structures assigned to the minor and major products 2.1p and 2.2p were indicated by their 2-D NMR spectra. A COSY spectrum (Appendix Figure A2.2) and an HSQC spectrum (Appendix Figure A2.3) confirmed assignments of the proton resonances in these isomers. In the HMBC spectrum of the mixture of isomers (Appendix Figure A2.4), strong long-range C-8–H-13 and C-9–H-13 correlations (Figure 2.2) indicate that the H-

13 peak belongs to isomer 2.2p (precursor of ox-LGE2). A C-11’–H-13’ correlation indicates that the H-13’ peak corresponds to the precursor 2.1p of ox-LGD2. The same conclusion is also supported by a NOESY spectrum of these isomers (Appendix Figure

A2.5) that exhibits a strong correlation (Figure 2.2) between the H3-10 and H2-7 resonances assigned to 2.2p whereas the resonances assigned to compound 2.1p show H-

10’–H-13’ correlation.

Figure 2.2. HMBC (red) and NOESY (blue) correlations distinguishing the structures of 2.1p and 2.2p.

Generation of Ox-LGD2 by Removal of the Silyl Ether and Silyl Ester Protecting

Groups. The γ-isomers 2.1p’ and 2.2p’ were generated from 2.4’ (Scheme 2.6) by the same chemistry employed to generate 2.1p and 2.2p from 2.4 (see Scheme 2.4 above).

Two reagents, Bu4NF in THF or 40% HF in CH3CN, both provided high isolated yields of 2.1’ and 2.2’ (81% or 100%) from a mixture of 2.1p’ and 2.2p’.

Scheme 2.6. γ-Isomer model study.

However, these two reagents gave very different results when applied to a mixture of the silyl protected isomers 2.1p and 2.2p. Treatment of the mixture of silylated isomers 42 with Bu4NF gave only18% yield of desilylated product (Table 2.5). Notably, isomerically pure ox-LGD2 was the only product isolated. Apparently, ox-LGE2 was selectively

1 destroyed under these reaction conditions. The H NMR spectrum of the ox-LGD2 generated by our total synthesis agreed with that reported previously for the ox-LGD2 extracted from Gracilaria edulis algae (Figure 2.3).

Table 2.5. Generation of 2.1 and 2.2 by Desilylation of 2.1p and 2.2p.

Reagent Products Products (NMR Yield, %) Total ox-LGD2 ox-LGE2

Bu4NF 18 100 0 HF Isolated70 14 86

Yield (%)

A B

C Position ox-LGD2 Synthetic From G. edulis δH δH 1 - - 2 2.17 2.25 3 1.58 1.60 4 2.12 2.14 5 5.40 5.40 6 5.39 5.39 7 3.00 3.04, 2.95 8 - - 9 - - 10 1.58 1.58 11 - - 12 - - 13 6.47 6.46 14 6.40 6.39 15 4.18 4.19 16 1.48 1.48 17 1.36 1.36 18 1.27 1.27 19 1.27 1.27 20 0.85 0.85

1 Figure 2.3. Comparison of H NMR spectra of ox-LGD2 chemical shift of CHD2CN was set at 1.90 ppm (A) at 500 MHz from total synthesis and (B) at 600 MHz extracted from Gracilaria edulis, from Kanai, Y., Hiroki, S., Koshino, H., Konoki, K., Cho, Y., Cayme, M., Fukuyo, Y., and Yotsu-Yamashita, M. J Lipid Res 2011 52, 2245-2254. © the American Society for Biochemistry and Molecular Biology. (C) comparison of chemical shifts.

Generation and Rearrangement of Ox-LGE2. Treatment of the mixture of silylated isomers with HF gave a much better total yield (70%) of desilylated products that consisted of a 1:6 mixture of ox-LGD2 (from 2.1p) and two diastereomers of ox-LGE2

1 (from 2.2p), the major isomer showing a doublet in the H NMR spectrum at ~δH 6.32

(ox-LGE2 (2.2a)) and a minor diastereomer evidenced by small shoulders on the major doublet (ox-LGE2 (2.2b)). The presence of the minor diastereomer was confirmed after

HPLC isolation (vide infra). The doublet, assigned to the major ox-LGE2 diastereomer, showed a first-order AMX (Δ/J = 15) spin system in contrast to the peaks assigned to ox-

LGD2 that exhibit a second-order ABX spin system (Δ/J ≈2) between H-13, H-14 and H-

15 (Figure 2.5). Two-dimensional NMR experiments, including HMBC, COSY and

HSQC (Appendix Figures A2.6-A2.8), further confirmed the structure of the major ox-

1 LGE2 diastereomer. The COSY spectrum (Appendix Figure A2.6) and the H NMR spectrum showed that the major ox-LGE2 isomer has a structure with connectivity nearly identical with ox-LGD2. This conclusion was bolstered by the HSQC spectrum

(Appendix Figure A2.7) that enabled an accurate assignment of the 13C NMR resonances.

However, an HMBC experiment (Appendix Figure A2.7) established that the position of

C-10 methyl group in the major product corresponded to that of ox-LGE2, the regioisomer of ox-LGD2. Similar to observations made in the structural characterization of the precursor 2.2p, a strong HMBC correlation (Figure 2.4, Appendix Figure A2.8) between the C-9 carbonyl and the C-13 vinyl carbon of the lower side chain as well as C-

8–H-13 and C-8–H-14 correlations indicated that the structure of the major product corresponds to ox-LGE2, which has a methyl group adjacent to the carboxyl side chain rather than adjacent to the vinyl side chain as in ox-LGD2.

Figure 2.4. HMBC (red) and NOSEY (blue) correlations distinguishing the structures of 2.1, 2.2 and 2.2d.

1 Figure 2.5. H NMR spectrum of ox-LGD2 and ox-LGE2 mixture from HF-treated reaction.

Upon standing in CD3CN solution at room temperature, the ox-LGE2 diastereomers in the mixture of ox-LGs, which was generated through desilylation with HF, decomposed.

The disappearance of the ox-LGE2 diastereomers from the mixture of ox-LGD2 and ox-

LGE2 diastereomers was accompanied by the appearance of a new product. The cis 5-6

6 C=C bond of the ox-LGE2 diastereomers migrated into conjugation to give Δ -ox-LGE2 while ox-LGD2 in the mixture remained unchanged.

6 1 1 The evolution of Δ -ox-LGE2 was monitored by RP-HPLC and H-NMR. In the H-

NMR spectrum, the disappearance of the vinyl hydrogen resonances corresponding to the cis C=C bond (H-5, 5.43 ppm; H-6, 5.51 ppm) and the appearance of vinyl hydrogen resonances corresponding to the trans double bond (H-6, H-7, 6.48~6.56 ppm), which appear as a second-order ABX2 spin system (Δ/J ≈1) coupled with the allylic hydrogens

(H-5), support the structural conclusions. In the HPLC chromatogram, the peak for the major ox-LGE2 diastereomer (tr = 49 min) diminished gradually while another peak (tr =

1 6 53 min) grew (Figure 2.6). The H NMR spectrum of pure Δ -ox-LGE2 isolated by HPLC

(Figure 2.7) confirmed the structure assigned.

1 Figure 2.6. Evolution of ox-LGs in CD3CN: (Left) HPLC chromatograph; (Right) H NMR spectrum; A: spectrum taken immediately after purification, B: after standing in

CD3CN for 24 h, C: 48 h, D: 7 days, E: 14 days.

1 6 Figure 2.7. H NMR spectrum of Δ -ox-LGE2 (2.2d).

6 Further confirmation of the Δ -ox-LGE2 structure assigned to the rearrangement product from the ox-LGE2 diastereomers was provided by 2D NMR spectra (Appendix

Figures A2.9-A2.12). Thus, two-dimensional NMR experiments, including HMBC,

COSY, HSQC and NOESY, confirmed the allylically rearranged structure assigned to the diastereomeric products generated by decomposition of the ox-LGE2 diastereomers.

COSY (Appendix Figure A2.9) H-H and HSQC (Appendix Figure A2.10) C-H one-bond

6 1 correlation supported the structure of Δ -ox-LGE2 deduced from H NMR, and allowed accurate assignment of 1H NMR and 13C NMR resonances even with the interference of a large solvent peak from CD3CN. A HMBC experiment (Appendix Figure A2.11) supported similar connectivity to that of ox-LGE2, i.e., strong correlation (Figure 2.4)

49 between the C-9 carbonyl and the C-13 vinyl carbon of the lower side chain as well as C-

8–H-13 and C-8–H-14 correlations indicating that the newly generated compound also has a methyl group adjacent to the carboxyl side chain. As expected, the atoms on the new trans double bond (atoms 6 and 7) showed strong correlation with nearby atoms as indicated in Appendix Figure A2.11. The strongest evidence supporting the proposed Δ6- ox-LGE2 structure was provided by a NOESY experiment. In the NOESY (Appendix

Figure A2.12), the H-10 methyl hydrogens only correlate (Figure 2.4) with the closest proton, which is H-7. Confirmation for the assignment of the resonances at 6.48~6.56 ppm to H-7 was indicated by the fact that the strongest peaks associated with H-10 are only found at 1.66 ppm and 6.54 ppm in contrast with the NOESY ox-LGD2 (Appendix

Figure A2.14) that only shows strong correlation (Figure 2.4) between H-10’ and H-13’.

The COSY of ox-LGD2 (Appendix Figure A2.13) further confirmed the structure of ox-

LGD2.

The facility with which the ox-LGE2 diastereomers rearrange, in contrast with the stability of ox-LGD2, is presumably associated with the acidity of the C-7 methylene hydrogens in ox-LGE2 but not ox-LGD2. Proton abstraction from C-7 by fluoride followed by protonation at C-5 provides a base catalyzed pathway for the isomerization

6 of ox-LGE2 to the more thermodynamically stable conjugated isomer Δ -ox-LGE2 that accompanies desilylation of 2p with Bu4NF (Scheme 2.7).

Scheme 2.7. Rearrangment of ox-LGE2.

Partial separation of ox-LGD2, two ox-LGE2 diastereomers and the product of ox-

6 LGE2 rearrangement, Δ -ox-LGE2 (2.2d), could be accomplished by reversed-phase

HPLC. Using CH3CN: H2O: acetic acid 35:65:0.1 (v/v) as eluent, ox-LGD2 and the minor diastereomer of ox-LGE2 (2.2b) eluted as a single peak at 44 min, then the major

6 diastereomer of ox-LGE2 (2.2a) eluted at 49 min, and finally rearranged ox-LGE2, Δ -ox-

1 LGE2 (2.2d), eluted at 53 min (Figure 2.8). The H NMR spectrum (Figure 2.9) of the first peak from Figure 2.8 showed that it contains ox-LGD2 (2.1) and the minor diastereomer 2.2b of ox-LGE2. This mixture was further resolved by HPLC eluting with

MeOH: H2O: acetic acid = 50:50:0.1 (Figure 2.10) into two symmetrical peaks, the first being the minor diastereomer 2.2b of ox-LGE2 and the second being the same ox-LGD2 diastereomer obtained from the desilylation with Bu4NF. Presumably, the absolute configuration at C-15 produced enzymatically is S. The configuration at C-11 remains unknown. Apparently one diastereomer of ox-LGD2 is favored both in the total synthesis and in its production in vivo. Thus, the fluoride catalyzed selective destruction of ox-

LGE2 was a fortunate discovery that readily allowed the isolation of pure ox-LGD2. It seems likely that oxidation of LGE2 that is cogenerated with LGD2 in the nonenzymatic

51 rearrangement of PGH2 would produce ox-LGE2 and also that this metabolite would

6 6 readily rearrange to Δ -ox-LGE2. The availability of a pure sample of Δ -ox-LGE2 from our total synthesis should enable the development of analytical protocols for its detection in biological samples. On the other hand, if the production of LGD2 is enzyme-catalyzed

6 in vivo, it may be selectively generated from PGH2, and neither ox-LGE2 nor Δ -oxLGE2 will be found because an enzyme-mediated rearrangement may not coproduce LGE2.

6 Figure 2.8. HPLC chromatogram of ox-LGD2, two diastereomers of ox-LGE2, and Δ -

ox-LGE2.

Figure 2.9. 1H NMR spectrum of peak 1 (Figure 2.8. HPLC chromatograph) collection at 44 min

Column: Luna C18 5m 4.6*250mm Flow rate: 0.6mL/min Eluent: MeOH: H2O: AcOH= 50:50:0.1 Detector: UV 254nm

Figure 2.10. HPLC chromatogram of ox-LGD2, and minor diastereomer 2b of ox-LGE2

A Physiological Role for the In Vivo Oxidation of Levuglandins. Whereas amyloid

Aβ1-42 incubated for 24 h with LGE2 is toxic to primary cultures of cerebral neurons of mice, exposure of the neurons to Aβ1-42 itself after 24 h incubation in the absence of

13 LGE2 has little or no effect. Brain levels of LG-protein lysyl adducts correlate with

Alzheimer’s disease (AD) severity.14 LG-lysyl adducts in proteins extracted from the hippocampus of brains from seven patients with clinical and pathological evidence of AD averaged 12.2-fold higher than in five age-matched controls. The levels of LG–lysyl adducts demonstrate a highly significant positive relationship (r = 0.92, p < 0.0001, n =

12) with the neurofibrilary tangle score according to the Braak and Braak method (Braak stage).34 LG–lysyl adduct levels also are positively correlated (r = 0.72, p < 0.01, n = 12) with CERAD neuritic plaque score.35

The oxidative conversion of LGs into ox-LGs in vivo provides a detoxification mechanism because ox-LGs lack the reactive γ-ketoaldehyde functional array of that accounts for their rapid formation of covalent adducts with biomolecules. Oxidative catabolism of LGs converts them into less reactive ox-LG end products. To be effective in protecting against the pathological consequences of LG-protein adduction, oxidative catabolism must be highly efficient. Even low levels of LGs promote the formation of the type of amyloid Aβ1-42 oligomers that have been associated with neurotoxicity and are a pathologic hallmark of AD. Thus, oligomerization of Aβ by LGE2 occurs with ratios of

13 LGE2:Aβ of only 1:10. This suggests that intermolecular crosslinking cannot be the sole mechanism for oligomerization, and raises the possibility that the formation of LG adducts of Aβ serves as a seed to accelerate oligomerization. AD pathology is associated with a deficiency in the ability to detoxify endogenous aldehydes. Mitochondrial

54 aldehyde dehydrogenase 2 (ALDH2) metabolizes aldehydes. In the Japanese population,

ALDH2 deficiency is caused by a mutant allele of the ALDH2 gene (ALDH2*2). In a large clinical study, the odds ratio for late onset AD in carriers of the ALDH2*2 allele was almost twice that in noncarriers.36 The discovery, now confirmed by total synthesis, that interception of LGs by oxidative catabolism to ox-LGs can compete with their adduction to proteins suggests that individuals with ALDH2 deficiency will exhibit elevated levels of LG-protein adducts compared to noncarriers of the ALDH2*2 allele.

2.3 Conclusions

Total synthesis played a pivotal role in the identification of levuglandins as products of the spontaneous rapid rearrangement of the prostaglandin endoperoxide PGH2 and in our discovery of a free radical oxidative pathway that also produces levuglandins as well as a large family of non-prostanoid structural isomers referred to collectively as isolevuglandins (isoLGs).2, 37-40 Pure samples of LGs and isoLGs available through total syntheses also enabled studies of their biological chemistry that had been presumed to be dominated by their rapid covalent adduction with primary amino groups in biomolecules.

In view of the exceptionally high proclivity for LGs to form covalent adducts with biomolecules, a competing alternative fate, i.e., oxidation to ox-LGs in vivo, was unexpected. The recent discovery, now confirmed by unambiguous total synthesis, that oxidative metabolism of LGD2 to ox-LGD2 (2.1) competes in vivo with this covalent adduction chemistry provides presumptive evidence for the proposition that pathology associated with LGs and isoLGs, e.g., AD, may not solely be a consequence of their generation and adduction with biomolecules, but also deficiencies in their detoxification by oxidative metabolism, e.g, by ALDH, that converts them into less reactive ox-LG end products. ALDH deficiency correlates with an almost 2-fold increase in odds ratio for late onset AD. Although the cogeneration of ox-LGE2 with ox-LGD2 in vivo is expected, our observation that ox-LGE2 readily undergoes allylic C=C bond migration, suggests that isolation of this metabolite of LGE2 from biological samples may be elusive. Detection

6 and isolation of the more thermodynamically stable rearrangement product, Δ -ox-LGE2

(2.2d), is now anticipated and will be facilitated by the availability of an authentic sample through the total synthesis reported herein.

2.4 Experimental Procedures

Materials. All reagents were obtained commercially unless otherwise noted.

Reactions were performed using glassware that was oven-dried at 120 °C. Air- and moisture-sensitive liquids and solutions were transferred via syringe or stainless steel cannula. Except for tetrahydrofuran (THF), toluene and CH2Cl2 were distilled under a nitrogen atmosphere prior to use, all other solvent were purchased from commercial suppliers and used as received. (E)-tert-butyldimethyl((1-(tributylstannyl)oct-1-en-3- yl)oxy)silane (2.5) was prepared as described previously.41

General Methods. Nuclear magnetic resonance (NMR) spectra were acquired on either a Varian Inova AS400 operating at 400 and 100 MHz, 500 MHz Bruker Ascend

Avance III HDTM equipped with ProdigyTM ultra-high sensitivity Multinuclear

Broadband CryoProbe operating at 500 and 125 MHz for 1H and 13C, respectively, and are referenced internally according to residual solvent signals. All ESI mass spectra were obtained from Thermo Finnigan LCQ Deca XP and all high-resolution mass spectra were recorded on a Kratos AEI MS25 RFA high-resolution mass spectrometer at 20 eV. High performance liquid chromatography (HPLC) was performed on Shimadzu UFLC system equipped with a 5 µm Phenomenex Luna C-18 column. Flash column chromatography was performed on 230-400 mesh silica gel supplied by E. Merck with ACS grade solvent.

Rf values are quoted for plates of thickness 0.25 mm. The plates were visualized with iodine, UV and phosphomolybdic acid reagents. All reactions were carried out under an argon atmosphere. Proton and carbon spectra of all new compounds are provided in

Appendix Figures A2.15-A2.44.

tert-Butyl(4-iodobutoxy)dimethylsilane (2.8). To a solution of tert-butyldimethylsilyl chloride (12.5 g, 0.083 mol) in CH3CN (40 mL) was added NaI (18.7 g, 0.125 mol) and dry THF (50 mL). The mixture was stirred overnight at room temperature (rt) in the dark. After the reaction has completed, the solution was then filtered through a sintered- glass funnel and the solid was washed with 25% EtOAc in hexanes. The filtered clear wine red solution was then rinsed with 50% saturated Na2S2O3 (3 x 15 mL) in a separatory funnel , the aqueous and organic layers were separated and sequentially extracted with 20% EtOAc in hexanes (2 × 50 mL). The combined organic layer was washed with brine, dried with Na2SO4. Solvent was then removed by rotary evaporation and the crude product was purified by chromatography on a silica gel column eluting with 100% of hexanes (Rf = 0.25) to give 2.8 (24.3 g, yield = 93%) as a clear oil. 2.8: Rf =

1 0.25 (hexanes); H NMR (400 MHz, CDCl3): δ 3.60 (t, 2H), 3.21 (t, 2H), 1.82 (m, 2H),

1.60 (m, 2H), 0.82 (s, 9H), 0.02 (s, 6H); 13C NMR: Spectra corresponding to literature;

+ HREIMS m/z 313.0487 [M] (calcd for C10H22IOSi, 313.0485).

(Z)-7-((tert-Butyldimethylsilyl)oxy)hept-2-yne-1-ol (2.9). Propargyl alcohol (1.79 g,

31.9 mmol), HMPA (22.8 g, 127 mmol, 4 equiv.) in 40 mL of dry THF was cooled to -40

°C in an CH3CN/dry ice bath. Butyl lithium (2.5 M, 26.0 mL, 2.0 equiv.) was added dropwise and the mixture was stirred at -40 °C for about 1 h. 2.8 (10.0 g, 31.9 mmol) in

THF (10 mL) at -40 °C was added via cannula to the mixture. The mixture was slowly

58 warmed to rt. After 4 h, the mixture was quenched with saturated aqueous NH4Cl solution (20 mL), extracted with diethyl ether, washed with H2O, then brine, then dried over anhydrous Na2SO4 and concentrated by rotary evaporation to afford clear yellow oil.

This crude product was purified by flash chromatography using 10% EtOAc in hexanes

(Rf = 0.20) to deliver a clear light yellow oil 2.9 5.2 g (yield = 67.3%) as a light yellow

1 oil. 2.9: Rf = 0.20 (9:1 hexanes/EtOAc); H NMR (500 MHz, CDCl3): δ 4.24 (d, 2H),

3.62(t, 2H), 2.24 (m, 2H), 1.55~1.59 (m, 4H), 0.89 (s, 9H), 0.05 (s, 6H); 13C NMR (125

MHz, CDCl3): δ 86.57, 78.61, 62.78, 51.58, 32.06, 26.10, 25.17, 18.70, 18.49, -5.15;

+ ESIMS m/z 243.07 [M + H] (calcd for C13H27O2Si, 243.17).

(Z)-7-((tert-Butyldimethylsilyl)oxy)hept-2-en-1-ol (2.10). Nickel acetate tetrahy- drate (7.14 g, 29 mmol) in 95% of EtOH (200 mL) was placed under a balloon of H2.

Sodium borohydride (1.09 g, 29 mmol) in EtOH (8 mL) was added at rt. After 20 min, ethylenediamine (7.0 g, 116 mmol) was added, followed by adding alkyne 2.9 (7.0 g, 29 mmol) in EtOH (10.0 mL). The reaction was monitored by TLC. After about 3 h, the reaction was filter through a pad of silica gel. The filtrate EtOH solution was concentrated by rotary evaporation. The residue was extracted with diethyl ether, washed with H2O, then brine, then dried over anhydrous Na2SO4 and concentrated by rotary evaporation to afford a clear oil. This crude product was purified by flash chromatography (hexanes/EtOAc = 4:1, Rf = 0.25) gave alkene 2.10 (6.14 g, 87%) as a clear oil. 2.10:

1 Rf = 0.25 (4:1 hexanes/EtOAc); H NMR (500 MHz, CDCl3): δ 5.59 (m, 1H), 5.34 (m,

1H), 4.18 (d, 2H), 3.60 (t, 2H), 2.10 (m, 2H), 1.52 (m, 2H), 1.40 (m, 2H), 0.89 (s, 9H),

13 0.04 (s, 6H); C NMR (125 MHz, CDCl3): δ 132.94, 128.59, 63.00, 58.58, 32.32, 27.18,

+ 25.98, 25.88, 18.37, -5.27; HREIMS m/z 243.1779 [M - H] (calcd for C13H27O2Si,

243.1780).

(Z)-7-((tert-Butyldimethylsilyl)oxy)hept-2-en-1-yl acetate (2.11). A solution of alcohol 2.10 (5.8 g, 23.7 mmol) in pyridine (25.5 mL) was cooled to 0 °C and then acetic anhydride (7.0 mL, 3 equiv.) was slowly added. The mixture was stirred for 40 min at that temperature under argon, and then allowed to warm to rt. After 2 h the mixture (clear light yellow) was quenched by addition of EtOH (10 mL) and concentrated by rotary- evaporation to afford clear yellow oil. The residue was washed with 1 M HCl and

1 concentrated to give 2.11 (6.46. g, 95%) as a clear oil: Rf = 0.20 (10:1 hexanes/Et2O); H

NMR (400 MHz, CDCl3): δ 5.63 (dt, 1H), 5.55 (dt, 1H), 4.61 (d, 2H), 3.60 (t, 2H), 2.12

(m, 2H), 2.06 (s, 3H), 1.51 (m, 2H), 1.43 (m, 2H), 0.89 (s, 9H), 0.04 (s, 6H); 13C NMR

(125 MHz, CDCl3): δ 171.16, 135.43, 123.57, 63.09, 60.53, 32.48, 27.44, 26.11, 25.86,

21.16, 18.50, -5.13; HREIMS m/z 227.1832 [M - C2H3O2] (calcd for C13H27OSi,

227.1831). This product was used without further purification for the preparation of the hydroxy acid 2.12.

(Z)-7-Hydroxyhept-5-enoic acid (2.12). To a solution of 2.11 (7.86 g, 27.0 mmol) in acetone (33 mL) at 0 °C was added Jones reagent dropwise until the orange color persisted for 20 min. The reaction was then quenched by addition of isopropyl alcohol

(20 mL), and then filtered through Celite to afford 7-acetoxyhept-5-ynoic acid after

60 removal of solvents by rotary evaporation. The crude (Z)-7-acetoxyhept-5-enoic acid was dissolved in EtOAc (36 mL) and extracted into 10% NaOH (5 x 25 mL). The aqueous layers were collected and acidified with 6 M HCl to pH = 1, followed by extraction with

EtOAc (5 x 50 mL). The organic layers were combined and washed with H2O, then brine, then dried over anhydrous magnesium sulfate, filtered and concentrated by rotary evaporation to afford a clear oil 2.12 (2.63 g) that exhibited a single spot Rf = 0.3 by TLC

1 with EtOAc. The yield is 68 % for the three steps. 2.12: Rf = 0.30 (EtOAc); H NMR (400

MHz, CDCl3): δ 5.63 (dt, 1H), 5.55 (dt, 1H), 4.20 (d, 2H), 2.32 (t, 2H), 2.15 (t, 2H), 1.68

+ (m, 2H); HREIMS m/z 126.0681 [M - H2O] (calcd for C7H10O2, 126.0681).

Di-tert-butyl(methyl)silyl (Z)-7-hydroxyhept-5-enoate (2.13). Acid 2.12 (1.00 g,

6.94 mmol) in anhydrous THF (10 mL) under argon was treated with dry triethylamine

(4.0 eq, 2.81 g, 27.3 mmol) at rt. And then di-tert-butylmethyl trifluoromethanesulfonate

(2.23 g, 7.28 mmol) was added dropwise. After about 30 min, the solution was concentrated in vacuo and the residue was purified by flash chromatography with

EtOAc/hexanes (1:4, Rf = 0.3) to give 2.13 (1.38 g, yield 67 %) as a clear oil. 2.13: Rf =

1 0.30 (4:1 hexanes/EtOAc); H NMR (400 MHz, CDCl3): δ 5.60 (m, 1H), 5.44 (m, 1H),

4.10 (d, 2H), 2.28 (t, 2H), 2.08 (q, 2H), 1.66 (m, 2H), 0.95 (s, 18H), 0.25 (s, 2H); 13C

NMR (125 MHz, CDCl3): δ 173.31, 131.62, 129.65, 58.33, 35.49, 27.51, 26.58, 24.84,

+ 20.28, -7.51; HREIMS m/z 283.2089 [M - OH] (calcd for C16H31O2Si, 283.2093).

Di-tert-butyl(methyl)silyl (Z)-7-bromohept-5-enoate (2.7). Methanesulfonyl chloride (343 mg, 3.0 mmol) was added dropwise to a chilled solution of 2.13 (500 mg, 0.166 mmol), triethylamine (337 mg, 3.33 mmol) in CH2Cl2 (6.0 mL) at -50 °C. The resulting white suspension was stirred for 45 min and then treated with a solution of lithium bromide (577 mg, 6.64 mmol) in THF (2.0 mL). The colorless mixture was then warmed slowly to -20 °C and stirred for 1 h. Then the reaction mixture was poured over H2O and extracted with pentane. The pentane extracts were washed with H2O, then brine, then dried and concentrated by rotary evaporation to deliver crude allylic bromide. The crude product was purified by flash chromatography with EtOAc /hexanes (1 : 25, Rf = 0.2) to

1 give pure 2.7 (503 mg, 83.3 %) as a clear oil. 2.7: Rf = 0.20 (25:1 hexanes/EtOAc); H

NMR (400 MHz, CDCl3): δ 5.76 (m, 1H), 5.59 (dt, 1H), 3.99 (d, 2H), 2.37 (t, 2H), 2.20

13 (q, 2H,), 1.74 (m, 2H), 1.02 (s, 18H), 0.32 (s, 3H); C NMR (100 MHz, CDCl3): δ

173.08, 134.80, 126.47, 35.72, 27.73, 27.15, 26.49, 24.71, 20.49, -7.28; HREIMS m/z

+ 305.0575, 307.0553 [M - C4H9] (calcd for C12H22BrO2Si, 305.0572, 307.0552).

Di-tert-Butyl 2-allyl-3-((E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)maleate

(2.14).

Method A (Lower-order cyanocuprate pathway):

A solution of vinyltin reagent (lower side chain precursor, 249 mg, 0.468 mmol) in dry

THF (3.0 mL) at -78 °C was treated with n-BuLi (1.6 M, 0.187 mL, 0.468 mmol). After

40 min, the light yellow solution was transferred dropwise via a cannula to a solution of copper cyanide (38 mg, 0.425 mmol) in anhydrous THF (2.0 mL) at -78 °C. The resulting clear solution was stirred at -78 °C for 2 hours. Then a solution of di-tert-butyl

62 acetylenedicarboxylate (96 mg, 0.425 mmol) in anhydrous THF (1.0 mL) was slowly added via cannula to the cuprate at -78 °C. The mixture was stirred at -78 °C for 50 min.

Freshly distilled HMPA (685 mg, 3.8 mmol) in THF was then added. After 15 min,

Pd(PPh3)4 (16 mg, 0.014 mmol) in THF (1.0 mL) was added by cannula, followed by the addition of allyl bromide (67 mg, 0.55 mmol) in THF (1.0 mL). Stirring was continued overnight at -78 °C and the mixture was then warmed to -45 °C and stirred for one more hour. Then the reaction mixture was quenched by addition of aqueous saturated

NH4Cl/NH4OH (pH 9, 5mL), and slowly warned to 0 °C. Diethyl ether was used to extract the mixture. The crude product was purified by flash chromatography with hexanes/Et2O (40:1 to 20:1) to give 2.14 (98.7 mg, yield = 45.7%). Rf = 0.25 (diethyl ether: hexanes = 1:20).

Method B (Higher-order cyanocuprate pathway):

A solution of vinyltin reagent 2.5 (lower side chain precursor, 249 mg, 0.468 mmol) in dry THF (3.0 mL) at -78 °C was treated with n-BuLi (1.6 M, 0.187 mL, 0.468 mmol).

After 40 min, the light yellow solution was transferred dropwise via a cannula to a solution of copper cyanide (20 mg, 0.223 mmol) in anhydrous THF (1.0 mL) at -78 °C.

The resulting clear solution was stirred at -78 °C for 2 hours. Then a solution of di-tert- butyl acetylenedicarboxylate (101 mg, 0.446 mmol) in anhydrous THF (1.0 mL) was slowly added via cannula to the cuprate at -78 °C. The mixture was stirred at -78 °C for

50 min. Freshly distilled HMPA (716 mg, 4.0 mmol) in THF was then added. After 15 min, Pd(PPh3)4 (16 mg, 0.014 mmol) in THF (1.0 mL) was added by cannula, followed by the addition of allyl bromide (57 mg, 0.47 mmol) in THF (1.0 mL). Stirring was continued overnight at -78 °C and the mixture was then warmed to -45 °C and stirred for

63 one more hour. Then the reaction mixture was quenched by addition of aqueous saturated NH4Cl/NH4OH (pH 9, 5mL), and slowly warned to 0 °C. Diethyl ether was used to extract the mixture. The crude product was purified by flash chromatography with hexanes/Et2O (40:1 to 20:1) to give 2.14 (103.6 mg, yield = 45.7%) as a clear oil. 2.14:

1 Rf = 0.25 (20:1 hexanes/Et2O); H NMR (400 MHz, CDCl3): δ 6.41 (d, 2H), 6.01 (q, 1H),

5.77 (m, 1H), 5.04 (q, 2H), 4.23 (m, 1H), 3.12 (d, 2H), 1.53 (s, 9H), 1.47 (s, 9H),

13 1.38~1.20 (8H), 0.89 (s, 9H), 0.87 (t, 3H), 0.03 (6H); C NMR (100 MHz, CDCl3): δ

167.78, 166.29, 142.15, 140.92, 134.59, 129.11, 122.09, 116.38, 81.84, 81.26, 72.98,

38.16, 32.40, 32.04, 28.26, 28.23, 26.07, 24.87, 22.82, 18.42, 14.15, -4.19, -4.60; HRMS

+ (EI): m/z calcd for C28H49O5Si (M -CH3), 493.3349, found 493.3350; calcd for

+ C25H43O5Si (M -C4H9), 451.2880, found 451.2889.

Three-component coupling product 2.4 and its regioisomer 2.4’. A solution of (E)- tert-butyldimethyl((1-(tributylstannyl)oct-1-en-3-yl)oxy)silane (2.5) (160 mg, 0.3 mmol) in dry THF (1.0 mL) at -78 °C was treated with n-BuLi (1.6 M, 0.12 mL, 0.3 mmol).

After 40 min, the light yellow solution was transferred dropwise via a cannula to a solution of copper cyanide (14 mg, 0.15 mmol) in anhydrous THF (2.0 mL) at -78 °C.

The resulting clear solution was stirred at -78 °C for 2 h. Then a solution of di-tert-butyl acetylenedicarboxylate (68 mg, 0.3 mmol) in anhydrous THF (1.0 mL) was slowly added via cannula to the cuprate at -78 °C. The mixture was stirred at -78 °C for 50 min.

Freshly distilled HMPA (480 mg, 2.7 mmol) in THF was then added. After 15 min,

Pd(PPh3)4 (12 mg, 0.01 mmol) in THF (1.0 mL) was added by cannula, followed by the

64 addition of 2.6 ( 55 mg, 0.15 mmol) in THF (1.0 mL). Stirring was continued overnight at

-78 °C and the mixture was then warmed to -45 °C and stirred for one more hour. Then the reaction mixture was quenched by addition of aqueous saturated NH4Cl/NH4OH (pH

9, 5 mL), and slowly warned to 0 °C. Diethyl ether was used to extract the mixture. The crude product was purified by flash chromatography with hexanes/Et2O (40:1 to 20:1) to give 2.4 and 2.4d (60 mg, yield = 54%) as clear oil. Rf = 0.25 (20:1 hexanes/Et2O).

Product 2.4 and 2.4d were then separated by HPLC (Luna C18 5 μm, 10 x 250 mm, gradient elution with CH3CN/2-propanol).

(4Z,7Z,9E)-7,8-Di-tert-butyl 1-(di-tert-butyl(methyl)silyl)-11-((tert-butyldimethylsilyl)oxy)hexadeca-4,7,9-triene-1,7,8-tricarboxylate (2.4): 1H NMR (500 MHz,

CDCl3): δ 6.41 (d, 1H, J = 15.8 Hz), 5.99 (dd, 1H, J = 15.8 Hz, J = 5.2 Hz), 5.40 (m, 1H),

5.31 (m, 1H), 4.22 (q, 1H, J = 5.2 Hz), 3.11 (d, 2H), 2.35 (t, 2H), 2.15 (m, 2H), 1.72 (m,

2H), 1.49 (m, 20H), 1.31~1.26 (m, 6H), 1.01 (s, 18H) 0.89 (m, 12H), 0.31 (s, 3H), 0.03 (d,

13 6H); C NMR (125 MHz, CDCl3): δ 173.18, 167.65, 166.41, 141.92, 139.75, 130.56,

130.27, 126.92, 122.01, 81.77, 81.29, 73.08, 38.15, 35.84, 31.95, 28.22, 28.15, 27.66,

27.05, 26.54, 25.99, 25.13, 24.81, 22.74, 20.41, 18.34, 14.17, -4.23, -4.66, -7.36;

+ HREIMS m/z 694.4463 [M - C4H8] (calcd for C38H70O7Si2, 694.4460).

(5Z,7E)-5,6-Di-tert-butyl 1-(di-tert-butyl(methyl)silyl) 9-((tert-butyldimethylsilyl)oxy)-4-vinyl¬tetradeca-5,7-diene-1,5,6-tricarboxylate (2.4’): 1H NMR (500 MHz,

CDCl3): δ 6.39 (d, 1H, J = 15.8 Hz), 5.95 (d, 1H, J = 17.0 Hz), 5.89 (1H, ddd, J = 9.9, 6.2,

2.6 Hz), 5.04 (d, 2H, J = 11.8 Hz), 4.21 (s, 1H), 3.27 (q, 1H, J = 7.5 Hz), 2.46~2.17 (m,

2H), 1.77~1.58 (m, 2H), 1.53 (m, 2H), 1.50 (s, 9H), 1.48(s, 9H), 1.37~1.18 (m, 6H), 1.01

(s, 18H) 0.90 (s, 9H), 0.87(t, 3H), 0.31 (s, 3H), 0.04 (d, J = 12.4 Hz ,6H); 13C NMR (125

MHz, CDCl3): δ 173.00, 167.40, 166.96, 141.25, 138.60, 137.09, 136.07, 121.16, 116.19,

81.77, 81.71, 73.07, 43.68, 38.19, 36.22, 32.68, 31.98, 28.25, 28.15, 27.66, 26.02, 24.84,

24.78, 23.49, 22.76, 20.39, 18.35, 14.18, -4.20, -4.66, -7.37; ESIMS m/z 773.20 [M +

+ Na] (calcd for C42H78O7Si2Na, 773.52).

(E)-di-tert-butyl(methyl)silyl 5-(4-(3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-

2,5-dioxo-2,5-dihydrofuran-3-yl)hept-6-enoate (2.3’). To a solution of 2.4’ (42 mg,

0.056 mmol) in toluene (5.0 mL) was added SiO2 (360 mg). The solution was boiled under reflux under argon for about 6 h, then cooled to rt, then diluted with 10 mL CH2Cl2, and filtered through a pad of Celite. The solution was concentrated under vacuum. The crude product 2.3' was used for the next step without further purification (33.0 mg, yield

1 = 95%). 2.3’: clear oil; Rf = 0.80 (10:1 hexanes/EtOAc); H NMR (500 MHz, CDCl3): δ

7.28 (ddd, 1H, J = 4 Hz, J = 5 Hz), 6.57 (ddd, 1H, J = 16 Hz, J = 7 Hz, J = 2Hz), 5.96 (m,

1H), 5.13 (m, 2H), 4.37 (t,1H), 3.43 (q, 1H), 2.34 (m, 2H), 1.82 (m, 2H), 1.66 (m, 1H)

1.55 (m, 3H), 1.37~1.25 (m, 6H), 1.00 (s, 18H), 0.93 (d, 9H), 0.89 (t, 3H) 0.31 (d, 3H),

13 0.09 (s, 3H), 0.04(s, 3H); C NMR (125 MHz, CDCl3): δ 172.49, 164.75, 164.26, 149.94,

140.31, 136.53, 135.86, 117.85, 114.31, 72.28, 41.18, 37.49, 35.63, 31.95, 31.82, 27.49,

25.85, 24.64, 23.25, 22.55, 20.25, 18.25, 14.02, -4.64, -4.76, -7.52; ESIMS m/z 643.20

+ [M + Na] (calcd for C34H60O6Si2Na, 643.38).

(Z)-Di-tert-butyl(methyl)silyl 7-(4-((E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1- yl)-2,5-dioxo-2,5-dihydrofuran-3-yl)hept-5-enoate (2.3). To a solution of 2.4 (21 mg,

0.028 mmol) in toluene (2.5 mL) was added SiO2 (200 mg). The solution was boiled under reflux under argon for about 6 h, then cooled to rt, then diluted with 5 mL CH2Cl2, and filtered through a pad of Celite. The solution was concentrated under vacuum. The crude product 2.3 was used for the next step without further purification (16.0 mg, yield=

1 91%). 2.3: clear oil; Rf = 0.80(10:1 hexanes/EtOAc); H NMR (500 MHz, CDCl3): δ 7.22

(dd, 1H, J = 16 Hz, J = 4.0 Hz), 6.54 (dt, 1H, J = 16 Hz), 5.56 (dt, 1H), 5.38 (dt, 1H), 4.37

(dd,1H, J = 4.0 Hz), 3.26 (d, 2H), 2.36 (t, 2H), 2.21 (m, 2H), 1.72 (tt, 2H) 1.56 (m, 2H),

1.37~1.25 (m, 6H), 1.02 (s, 18H), 0.93 (s, 9H), 0.88 (t, 3H) 0.32 (s, 3H), 0.06 (s, 6H); 13C

NMR (125 MHz, CDCl3): δ 173.05, 165.81, 164.67, 149.75, 138.12, 136.68, 133.33,

122.62, 114.64, 72.48, 37.66, 35.69, 31.96, 27.65, 26.92, 25.98, 24.79, 24.71, 22.70,

+ 22.48, 20.41, 18.38, 14.18, -4.45, -4.64, -7.36; HREIMS m/z 563.3226 [M - C4H9]

(calcd for C30H51O6Si2, 563.3224).

(E)-Di-tert-butyl(methyl)silyl 5-(4-(3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-

5-hydroxy-5-methyl-2-oxo-2,5-dihydrofuran-3-yl)hept-6-enoate (2.1p’) and (E)-di- tert-butyl(methyl)silyl 5-(4-(3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-2- hydroxy-2-methyl-5-oxo-2,5-dihydrofuran-3-yl)hept-6-enoate (2.2p'). Methyl lithium

(57.5 μL, 1.6 M in diethyl ether, 3.0 equiv.) was added to 2.3’ (19 mg) in dry THF (3.5 mL) at -94 , 3.0 equiv.) was added to l)oxy)oct-1-en-1-yl)-5-hydroxy-5-methyl-2-oxo-

2,5-dihydrofuran-3-ys NH4Cl. Diethyl ether was used to extract the mixture. The crude

67 product was purified by flash chromatography with hexanes/EtOAc (5 : 1, Rf = 0.3) to give a mixture of hydroxylactones 2.1p’ and 2.2p’ (8.2 mg, yield = 52% based on unrecovered starting material) as a clear oil. 1H NMR data showed there are sets of two peaks, which indicates that the product is a mixture of two hydroxylactones (1:1) 2.1p’

1 and 2.2p’: Rf = 0.30 (5:1 hexanes/EtOAc); H NMR (500 MHz, CDCl3): δ 7.02 (m, 0.5H, isomer 1), 6.54 (m, 1H, isomer 2), 6.34 (dd, 0.5H, isomer 1), 6.06 (m, 1H, isomer 1), 5.91

(dddt, 1H, isomer 2), 5.08 (m, 2H), 4.31 (m,1H), 3.26 (m, 1H), 2.33 (m, 2H), 1.79 (q, 2H),

1.63~1.72 (m, 3H), 1.49~1.62 (m, 4H), 1.23~1.39 (m, 6H), 1.00 (m, 18H), 0.93 (m, 9H),

0.88 (m, 3H) 0.30 (m, 3H), 0.05 (m, 6H); ESIMS m/z 659.27 [M + Na]+ (calcd for

C35H64O6Si2Na, 659.41).

(Z)-Di-tert-butyl(methyl)silyl 7-(4-((E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1- yl)-5-hydroxy-5-methyl-2-oxo-2,5-dihydrofuran-3-yl)hept-5-enoate (1p) and (Z)-di- tert-butyl(methyl)silyl 7-(4-((E)-3-((tert-butyldimethylsilyl)oxy)oct-1-en-1-yl)-2- hydroxy-2-methyl-5-oxo-2,5-dihydrofuran-3-yl)hept-5-enoate (2.2p). Methyl lithium

(18 μL, 1.6 M in diethyl ether, 1.2 equiv.) was added to 2.3 (15 mg) in dry THF (5 mL) at

-94 °C. The reaction was kept at -94 °C for 15 min. The reaction mixture was quenched with aqueous NH4Cl. Diethyl ether was used to extract the mixture. The crude product was purified by flash chromatography with hexanes/EtOAc (5 : 1, Rf = 0.3) to give a 1:6 mixture of hydroxylactones 2.1p and 2.2p based on the integrated 1H NMR peak areas for resonances centered at δ 6.50 and 6.32 (Appendix Figure A2), corresponding to H-13 in 2.1p and 2.2p respectively (4 mg, yield = 57% based on unrecovered starting material)

68 as a clear oil. 1H NMR data showed there are sets of two peaks, which indicates that the product is a mixture of two hydroxy lactones. Major regioisomer 2p: Rf = 0.30 (5:1

1 hexanes/EtOAc); H NMR (500 MHz, CDCl3): δ 6.96 (dt, 1H), 6.30 (d, 1H), 5.53 (m,

1H), 5.44 (m, 1H), 4.27 (m,1H), 3.21 (m, 2H), 2.36 (t, 2H), 2.20 (m, 2H), 1.72 (m, 2H),

1.65 (S, 3H), 1.51 (m, 2H), 1.34~1.23 (m, 6H), 1.02 (s, 18H), 0.92 (s, 9H), 0.93~0.86 (m,

13 3H) 0.32 (s, 3H), 0.05 (d, 6H); C NMR (125 MHz, CDCl3): δ 173.56, 169.38, 158.13,

141.89, 132.18, 124.45, 123.98, 115.10, 104.51, 72.81, 38.10, 35.67, 32.02, 29.85, 27.64,

26.04, 24.81, 24.71, 24.34, 24.00, 22.74, 20.41, 18.41, 14.20, -4.31, -4.64, -7.35; 2D-

NMR, COSY, NOESY, HMBC, HSQC (Figures S3-S6); HREIMS m/z 636.4103 [M]+

+ (calcd for C35H64O6Si2, 636.4241); m/z 579.3536 [M - C4H9] (calcd for C31H54O6Si2,

+ 579.3539); m/z 618.4133 [M - H2O] (calcd for C35H62O5Si2, 618.4136).

(E)-5-(5-Hydroxy-4-(3-hydroxyoct-1-en-1-yl)-5-methyl-2-oxo-2,5-dihydrofuran-3- yl)hept-6-enoic acid (1’) and (E)-5-(2-hydroxy-4-(3-hydroxyoct-1-en-1-yl)-2-methyl-

5-oxo-2,5-dihydrofuran-3-yl)hept-6-enoic acid (2.2’).

Method A: A solution of 2.1p’ and 2.2p’ (9 mg, 0.014 mmol) in THF (300 μL) was cooled to 0 °C and then tetra-n-butylammonium fluoride (Bu4NF, 1.0 M in THF with 5%

H2O, 148 μL) was added. After stirring at 0 °C for 15 min, the cold bath was removed and the clear tan solution was stirred at rt overnight. The progress of the reaction was monitored by TLC developing with 60% EtOAc in hexanes containing 1% acetic acid.

The reaction mixture was distributed between saturated aqueous sodium bicarbonate (9 mL) and n-pentane (9 mL). The organic layer was extracted with saturated aqueous

69 sodium bicarbonate, and then discarded. The combine aqueous extracts were carefully acidified to pH 3 by dropwise addition of 1.0 M HCl, and then extracted with diethyl ether (5 x 9 mL). The organic extracts were combined, dried over Na2SO4 and concentrated in vacuo. The crude product was purified by flash chromatography with

60% EtOAc in hexanes containing 1% acetic acid (Rf = 0.3) to give mixture 2.1’ and 2.2’.

(4.2 mg, yield = 81%) as a clear oil.

Method B: A mixture of 2.1p’ and 2.2p’ (3.0 mg, 0.0047 mmol) was treated with concentrated aqueous hydrofluoric acid (49% w/v) in CH3CN (10% v/v, 525 μL) in a polyethylene vial. The progress of the reaction was monitored by TLC developing with

60% EtOAc in hexanes containing 1% acetic acid. After 1.5 h, when the deprotection was complete by TLC, the solution was poured H2O (6 mL) and extracted with CH2Cl2 (6 mL) in a polyethylene container. The organic layer was separated and extracted with brine (6 mL). The aqueous layers were then back extracted with CH2Cl2 (3 x 6 mL). The organic extracts were combined, dried over Na2SO4 and concentrated in vacuo. The crude product was purified by flash chromatography with 60% EtOAc in hexanes containing 1% acetic acid (Rf = 0.3) to give a mixture of 2.1’ and 2.2’ (1.7 mg, yield = 99.6%) as a clear oil.

1 Two regioisomers 2.1’ and 2.2’: Rf = 0.30 (4:6 hexanes/EtOAc with 1% AcOH); H

NMR (500 MHz, CDCl3): δ 6.51 (d, 2H), 6.06 & 5.95 (m, 1H), 5.06 (m, 2H), 4.36 & 4.32

(m, 1H), 3.35 & 3.25 (m, 1H), 2.33 (m, 2H), 1.84 & 1.77 (m, 2H), 1.69~1.72 (m, 3H),

1.48~1.65 (m, 4H), 1.19~1.45(6H), 0.89 (m, 3H); ESIMS m/z 365.2 [M - H]- (calcd for

C20H29O6, 365.2).

(Z)-7-(5-Hydroxy-4-((E)-3-hydroxyoct-1-en-1-yl)-5-methyl-2-oxo-2,5-dihydrofuran-3-yl)hept-5-enoic acid (ox-LGD2, 2.1), (Z)-7-(2-hydroxy-4-((E)-3-hydroxyoct-

1-en-1-yl)-2-methyl-5-oxo-2,5-dihydro¬furan-3-yl)hept-5-enoic acid (ox-LGE2, 2.2) and (E)-7-(2-hydroxy-4-((E)-3-hydroxyoct-1-en-1-yl)-2-methyl-5-oxo-2,5-dihydro-

6 furan-3-yl)hept-6-enoic acid (Δ -ox-LGE2, 2.2d).

Method A: A mixture of 2.1p and 2.2p (9 mg, 0.0014 mmol) in THF (300 μL) was

o cooled to 0 C and then Bu4NF (1.0 M in THF with 5% H2O, 148 μL) was added. After stirring at 0 oC for 15 min, the cold bath was removed and the clear tan solution was stirred at rt overnight. The progress of the reaction was monitored by TLC developing with 60% EtOAc in hexanes containing 1% acetic acid. The reaction mixture was distributed between saturated aqueous sodium bicarbonate (9 mL) and n-pentane (9 mL).

The organic layer was extracted with saturated aqueous sodium bicarbonate, and then discarded. The combine aqueous extracts were carefully acidified to pH 3 by dropwise addition of 1.0 M HCl, and then extracted with diethyl ether (5 x 9 mL). The organic extracts were combined, dried over Na2SO4 and concentrated in vacuo. The crude product was purified by flash chromatography with 60% EtOAc in hexanes containing 1% acetic

1 acid (Rf = 0.3) to give ox-LGD2 (2.1, 1.0 mg, yield = 18%) as a clear oil: H NMR (500

MHz, CD3CN, 1.90 ppm): δ 6.47 (d, 1H), 6.40 (dd, 1H), 5.40 (m, 1H), 5.39 (m, 1H), 4.18

(brt, 1H), 3.00 (brt, 2H), 2.25 (m, 2H) 2.14 (m, 2H), 1.60 (m, 2H), 1.58 (s, 3H), 1.48 (m,

2H), 1.36 (m, 1H), 1.22~1.33(5H), 0.85 (t, 3H); 2D-NMR: COSY, NOESY (Appendix

Figures A13 and A14); MS (ESI): m/z calcd for C20H29O6 (M-H), 365.2, found 365.2;

+ HREIMS m/z 348.1936 [M - H2O] (calcd for C20H28O5, 348.1937).

Method B: A mixture of 2.1p and 2.2p (3.0 mg, 0.0047 mmol) was treated with concentrated aqueous hydrofluoric acid (49% w/v) in CH3CN (10% v/v, 525 μL) in a polyethylene vial. The progress of the reaction was monitored by TLC developing with

60% EtOAc in hexanes containing 1% acetic acid. After 1.5 h, when the deprotection was complete by TLC, the solution was poured into H2O (6 mL) and extracted with CH2Cl2 (6 mL) in a polyethylene container. The organic layer was separated and extracted with brine (6 mL). The aqueous layers were then back extracted with CH2Cl2 (3 x 6 mL). The organic extracts were combined, dried over Na2SO4 and concentrated in vacuo. The crude product was purified by flash chromatography with 60% EtOAc in hexanes containing

1% acetic acid (Rf = 0.3) to give a mixture of ox-LGD2 and ox-LGE2 (1.2 mg, yield =

70%) as a clear oil. TLC: Rf = 0.30 (4:6 hexanes/EtOAc with 1% AcOH); ox-LGE2 (2.2,

1 major diastereomer): H NMR (500 MHz, CD3CN, 1.94 ppm): δ 6.79 (dd, 1H), 6.32 (d,

1H), 5.51 (m, 1H), 5.43 (m, 1H), 4.14 (m, 1H), 3.21 (m, 2H), 2.29 (m, 2H) 2.18 (m, 2H),

1.66 (m, 2H), 1.56 (s, 3H), 1.48 (m, 2H), 1.30 (m, 1H), 1.25~1.35(5H), 0.88 (t, 3H); 13C

NMR (125 MHz, CD3CN): δ 174.51, 170.37, 160.65, 141.55, 132.34, 125.47, 124.14,

117.05, 105.72, 72.54, 37.97, 33.77, 32.44, 27.28, 25.86, 25.27, 24.48, 24.13, 23.29,

14.29; 2D-NMR: COSY, HMBC, HSQC (Figures S7-S9); ESIMS m/z 365.2 [M - H]-

(calcd for C20H29O6, 365.2);

6 1 Δ -ox-LGE2 (2.2d): H NMR (500 MHz, CD3CN, 1.94 ppm): δ 6.86 (dd, 1H), 6.51 (m,

2H), 6.43 (d, 1H), 4.14 (m, 1H), 2.29 (m, 4H), 1.64 (s, 3H), 1.59 (m, 2H), 1.41 (m, 1H),

13 1.51 (m, 2H), 1.26~1.36(5H), 0.88 (t, 3H); C NMR (125 MHz, CD3CN): δ 174.78,

169.78, 154.50, 144.21, 141.61, 121.41, 119.53, 117.90, 116.71, 104.48, 100.57, 72.30,

37.65, 33.83, 33.73, 32.09, 28.32, 25.63, 25.50, 24.70, 22.93, 13.93; 2D-NMR : COSY,

NOESY, HMBC, HSQC (Figures S12-S15); ESIMS m/z 365.2 [M - H]- (calcd for

+ C20H29O6, 365.2); HREIMS m/z 348.1933 [M - H2O] (calcd for C20H28O5, 348.1937)

2.5 References

(1) Salomon, R. G., Miller, D. B., Zagorski, M. G., and Coughlin, D. J. (1984)

Prostaglandin endoperoxides. 14. Solvent-induced fragmentation of prostaglandin

endoperoxides. New aldehyde products from PGH2 and a novel intramolecular

1,2-hydride shift during endoperoxide fragmentation in aqueous solution. J. Am.

Chem. Soc. 106, 6049-6060.

(2) Salomon, R. G., Subbanagounder, G., Singh, U., O'Neil, J., and Hoff, H. F. (1997)

Oxidation of low-density lipoproteins produces levuglandin-protein adducts.

Chem. Res. Toxicol. 10, 750-759.

(3) Salomon, R. G., Jirousek, M. R., Ghosh, S., and Sharma, R. B. (1987)

Prostaglandin endoperoxides 21. Covalent binding of levuglandin E2 with proteins.

Prostaglandins 34, 643-656.

(4) Murthi, K. K., Friedman, L. R., Oleinick, N. L., and Salomon, R. G. (1993)

Formation of DNA-protein cross-links in mammalian cells by levuglandin E2.

Biochemistry 32, 4090-4097.

(5) Bernoud-Hubac, N., Fay, L. B., Armarnath, V., Guichardant, M., Bacot, S.,

Davies, S. S., Roberts, L. J., 2nd, and Lagarde, M. (2004) Covalent binding of

isoketals to ethanolamine phospholipids. Free Radic. Biol. Med. 37, 1604-1611.

(6) Boutaud, O., Brame, C. J., Chaurand, P., Li, J., Rowlinson, S. W., Crews, B. C., Ji,

C., Marnett, L. J., Caprioli, R. M., Roberts, L. J., 2nd, and Oates, J. A. (2001)

Characterization of the lysyl adducts of prostaglandin H-synthases that are

derived from oxygenation of arachidonic acid. Biochemistry 40, 6948-6955.

(7) Iyer, R. S., Ghosh, S., and Salomon, R. G. (1989) Levuglandin E2 crosslinks

proteins. Prostaglandins 37, 471-480.

(8) Brame, C. J., Boutaud, O., Davies, S. S., Yang, T., Oates, J. A., Roden, D., and

Roberts, L. J., 2nd. (2004) Modification of proteins by isoketal-containing

oxidized phospholipids. J. Biol. Chem. 279, 13447-13451.

(9) Schmidley, J. W., Dadson, J., Iyer, R. S., and Salomon, R. G. (1992) Brain tissue

injury and blood-brain barrier opening induced by injection of LGE2 or PGE2.

Prostaglandins, Leukotrienes Essent. Fatty Acids 47, 105-110.

(10) Murthi, K. K., Salomon, R. G., and Sternlicht, H. (1990) Levuglandin E2 inhibits

mitosis and microtubule assembly. Prostaglandins 39, 611-622.

(11) Carrier, E. J., Zagol-Ikapitte, I., Amarnath, V., Boutaud, O., and Oates, J. A.

(2014) Levuglandin forms adducts with histone h4 in a cyclooxygenase-2-

dependent manner, altering its interaction with DNA. Biochemistry 53, 2436-2441.

(12) Boutaud, O., Andreasson, K. I., Zagol-Ikapitte, I., and Oates, J. A. (2005)

Cyclooxygenase-dependent lipid-modification of brain proteins. Brain Pathol. 15,

139-142.

(13) Boutaud, O., Montine, T. J., Chang, L., Klein, W. L., and Oates, J. A. (2006)

PGH2-derived levuglandin adducts increase the neurotoxicity of amyloid beta1-42.

J. Neurochem. 96, 917-923.

(14) Zagol-Ikapitte, I., Masterson, T. S., Amarnath, V., Montine, T. J., Andreasson, K.

I., Boutaud, O., and Oates, J. A. (2005) Prostaglandin H2-derived adducts of

proteins correlate with Alzheimer's disease severity. J. Neurochem. 94, 1140-1145.

(15) Sidorova, T. N., Yermalitskaya, L. V., Mace, L. C., Wells, K. S., Boutaud, O.,

Prinsen, J. K., Davies, S. S., Roberts, L. J., 2nd, Dikalov, S. I., Glabe, C. G.,

Amarnath, V., Barnett, J. V., and Murray, K. T. (2015) Reactive gamma-

ketoaldehydes promote protein misfolding and preamyloid oligomer formation in

rapidly-activated atrial cells. J Mol Cell Cardiol 79, 295-302.

(16) Charvet, C., Liao, W. L., Heo, G. Y., Laird, J., Salomon, R. G., Turko, I. V., and

Pikuleva, I. A. (2011) Isolevuglandins and mitochondrial enzymes in the retina:

mass spectrometry detection of post-translational modification of sterol-

metabolizing CYP27A1. J. Biol. Chem. 286, 20413-20422.

(17) Charvet, C. D., Saadane, A., Wang, M., Salomon, R. G., Brunengraber, H., Turko,

I. V., and Pikuleva, I. A. (2013) Pretreatment with pyridoxamine mitigates

isolevuglandin-associated retinal effects in mice exposed to bright light. J. Biol.

Chem. 288, 29267-29280.

(18) Charvet, C. D., Laird, J., Xu, Y., Salomon, R. G., and Pikuleva, I. A. (2013)

Posttranslational modification by an isolevuglandin diminishes activity of the

mitochondrial cytochrome P450 27A1. J. Lipid Res. 54, 1421-1429.

(19) Salomon, R. G. (2005) Levuglandins and isolevuglandins: stealthy toxins of

oxidative injury. Antioxid. Redox. Signal 7, 185-201.

(20) Salomon, R. G. (2005) Distinguishing levuglandins produced through the

cyclooxygenase and isoprostane pathways. Chem. Phys. Lipids 134, 1-20.

(21) Salomon, R. G. (2005) Isolevuglandins, oxidatively truncated phospholipids, and

atherosclerosis. Ann. N. Y. Acad. Sci. 1043, 327-342.

(22) Boutaud, O., Li, J., Zagol, I., Shipp, E. A., Davies, S. S., Roberts, L. J., 2nd, and

Oates, J. A. (2003) Levuglandinyl adducts of proteins are formed via a

prostaglandin H2 synthase-dependent pathway after platelet activation. J. Biol.

Chem. 278, 16926-16928.

(23) Podrez, E. A., O'Neil, J., Salomon, R. G., Schreiber, M. J., and Hoff, H. F. (1998)

Measurement of oxidation in plasma Lp(a) in CAPD patients using a novel

ELISA. Kidney Int 54, 637-645.

(24) Fukuda, K., Davies, S. S., Nakajima, T., Ong, B. H., Kupershmidt, S., Fessel, J.,

Amarnath, V., Anderson, M. E., Boyden, P. A., Viswanathan, P. C., Roberts, L. J.,

2nd, and Balser, J. R. (2005) Oxidative mediated lipid peroxidation recapitulates

proarrhythmic effects on cardiac sodium channels. Circ Res 97, 1262-1269.

(25) Poliakov, E., Brennan, M. L., Macpherson, J., Zhang, R., Sha, W., Narine, L.,

Salomon, R. G., and Hazen, S. L. (2003) Isolevuglandins, a novel class of

isoprostenoid derivatives, function as integrated sensors of oxidant stress and are

generated by myeloperoxidase in vivo. FASEB J. 17, 2209-2220.

(26) Kanai, Y., Hiroki, S., Koshino, H., Konoki, K., Cho, Y., Cayme, M., Fukuyo, Y.,

and Yotsu-Yamashita, M. (2011) Identification of novel oxidized levuglandin D2

in marine red alga and mouse tissue. J. Lipid Res. 52, 2245-2254.

(27) Mongrain, C., and Gaudreault, R. (1990) Synthesis of Mono and Disubstituted

Maleic Anhydrides from Di-tert-Butyl Acetylene Dicarboxylate. Synth. Commun.

20, 2491-2500.

(28) Bhide, R. S., Levison, B. S., Sharma, R. B., Ghosh, S., and Salomon, R. G. (1986)

Di-tert-butylmethylsilyl (DTBMS) trifluoromethanesulfonate. Preparation and

synthetic applications of DTBMS esters and enol ethers. Tetrahedron Lett. 27,

671-674.

(29) Brown, H. C., and Brown, C. A. (1963) The Reaction of Sodium Borohydride

with Nickel Acetate in Ethanol Solution--A Highly Selective Nickel

Hydrogenation Catalyst. J. Am. Chem. Soc. 85, 1005-1006.

(30) Corey, E. J., Niimura, K., Konishi, Y., Hashimoto, S., and Hamada, Y. (1986) A

new synthetic route to prostaglandins. Tetrahedron Lett. 27, 2199-2202.

(31) Nishiyama, H., Sasaki, M., and Itoh, K. (1981) Stereoselective Addition of

Readily Available Organocopper Reagents to Dimethyl Acetylenedicarboxylate.

Chem. Lett. 10, 905-908.

(32) Scholte, A. A., Eubanks, L. M., Poulter, C. D., and Vederas, J. C. (2004)

Synthesis and biological activity of isopentenyl diphosphate analogues. Bioorg.

Med. Chem. 12, 763-770.

(33) Jackson, R. W. (2001) A mild and selective method for the cleavage of tert-butyl

esters. Tetrahedron Lett. 42, 5163-5165.

(34) Braak, H., and Braak, E. (1995) Staging of Alzheimer's disease-related

neurofibrillary changes. Neurobiol. Aging 16, 271-278; discussion 278-284.

(35) Mirra, S. S., Heyman, A., McKeel, D., Sumi, S. M., Crain, B. J., Brownlee, L. M.,

Vogel, F. S., Hughes, J. P., van Belle, G., and Berg, L. (1991) The Consortium to

Establish a Registry for Alzheimer's Disease (CERAD). Part II. Standardization

of the neuropathologic assessment of Alzheimer's disease. Neurology 41, 479-486.

(36) Kamino, K., Nagasaka, K., Imagawa, M., Yamamoto, H., Yoneda, H., Ueki, A.,

Kitamura, S., Namekata, K., Miki, T., and Ohta, S. (2000) Deficiency in

mitochondrial aldehyde dehydrogenase increases the risk for late-onset

Alzheimer's disease in the Japanese population. Biochem. Biophys. Res. Commun.

273, 192-196.

(37) Salomon, R. G., Subbanagounder, G., O'Neil, J., Kaur, K., Smith, M. A., Hoff, H.

F., Perry, G., and Monnier, V. M. (1997) Levuglandin E2-protein adducts in

human plasma and vasculature. Chem. Res. Toxicol. 10, 536-545.

(38) Roy, S. C., Nagarajan, L., and Salomon, R. G. (1999) Total synthesis of

iso[7]levuglandin D-2. J. Org. Chem. 64, 1218-1224.

(39) Salomon, R. G., Batyreva, E., Kaur, K., Sprecher, D. L., Schreiber, M. J., Crabb, J.

W., Penn, M. S., DiCorletoe, A. M., Hazen, S. L., and Podrez, E. A. (2000)

Isolevuglandin-protein adducts in humans: products of free radical-induced lipid

oxidation through the isoprostane pathway. Biochim. Biophys. Acta. 1485, 225-

235.

(40) Poliakov, E., Meer, S. G., Roy, S. C., Mesaros, C., and Salomon, R. G. (2004)

Iso[7]LGD2-protein adducts are abundant in vivo and free radical-induced

oxidation of an arachidonyl phospholipid generates this D series isolevuglandin in

vitro. Chem. Res. Toxicol. 17, 613-622.

(41) Darwish, A., Lang, A., Kim, T., and Chong, J. M. (2008) The Use of Phosphine

Ligands to Control the Regiochemistry of Pd-Catalyzed Hydrostannations of 1-

Alkynes: Synthesis of (E)-1-Tributylstannyl-1-alkenes. Org. Lett. 10, 861-864.

CHAPTER 3

Light-induced Generation and Toxicity of Docosahexaenoate-derived Oxidation Products in Retinal Pigmented Epithelial Cells

3.1 Background

3.1.1 Photo-induced retinal damage contributes to RPE dysfunction and the pathogenesis AMD.

Age-related macular degeneration (AMD), a chronic, degenerative disorder in the maculae of the retina, is the leading cause of irreversible blindness among the elderly.1-4

Although the pathogenesis of AMD is complex and remains poorly understood, the retinal pigment epithelium (RPE) is considered to be a primary site of AMD pathology.2, 5

The RPE, a monolayer of cells interposed between the photoreceptors and the Bruch’s membrane-choroid complex, is critical for the maintenance and survival of the photoreceptors. RPE cell dysfunction and death play a vital role in the pathogenesis of

AMD.2, 5, 6 RPE cells accumulate aging pigments that aggregate as RPE lipofuscin that is associated with the progression of AMD.7-9 Lipofuscin consists of a poorly characterized highly complex mixture of lipids, lipid-modified proteins, chromophores and fluorophores. Multiple studies reported progressive accumulation of lipofuscin in aging human retina10, 11, AMD12-14 and Stargardt disease15-17 with lipofuscin occupying as much as 19% of cell volume in macular RPE cells from octogenerian donors.17, 18 Nevertheless, clinical studies suggest that this accumulation is more likely a result, and not a cause of

RPE cell death.19, 20 Two mechanisms postulated for photochemical retinal damage are class I photooxidation, the Noell photodamage mechanism, which has an action spectrum resembling rhodopsin photolysis21-24 and class II photodamage (“blue light”), and the

Ham mechanism25-27 with the majority of photolysis occurring in RPE cells that may be related to lipofuscin photochemical changes.

3.1.2 Docosahexaenoyl phospholipids are targets of photooxidative damage in the retina.

In the outer retina, the photoreceptor is enriched in DHA-containing phospholipids.

Retina contains high levels of lipids that are highly susceptible to oxidation, with docosahexaenoate (DHA) accounting for more than 80% of polyunsaturated fatty acyls

(PUFAs), mainly esterified into phospholipids in photoreceptor disk membranes.1, 3, 28, 29

The retina is especially prone to the generation of reactive oxygen species (ROS) because it experiences high levels of oxygen consumption, cumulative irradiation within the visible sector of sunlight and contains an abundance of photosensitizers. DHA-containing phospholipids are highly susceptible to light-induced peroxidation. Active phagocytosis of photoreceptor outer segments by the RPE cells removes oxidatively damaged photoreceptor discs that accumulate in rod outer segment tips. Under physiological conditions, ROS are neutralized by enzymatic and non-enzymatic defence mechanisms.

However, excess ROS production results in an imbalance between pro- and anti-oxidant processes, leading to oxidative stress.3, 30 We previously identified a family of truncated phospholipids that are generated by myeloperoxidase- or copper ion-promoted free radical-induced oxidative cleavage of DHA-phosphatidylcholine (PC) in liposomes.31

Primary products are a phospholipid aldehyde, the 4-hydroxy-7-oxohept-5-enoic acid

(HOHA) ester of 2-lyso-phosphatidylcholine (HOHA-PC) and 4-hydroxyhex-2-enal

(HHE). See Fig 3.1 for product structures and acronyms.

Figure 3.1. Oxidative cleavage of DHA-PC delivers HOHA-PC. HOHA lactone is released from bilayer phospholipid membranes by spontaneous intramolecular transesterification. Covalent adduction of HOHA-PC and HOHA lactone to primary amino groups of protein lysyl residues and phosphatidyl ethanolamines (PE) produces CEP derivatives.

HOHA-PC undergoes spontaneous deacylation to HOHA lactone (Fig. 3.1).32 HOHA lactone is of special interest because it is a reactive membrane-penetrant molecule that can diffuse from photoreceptor disc membranes into RPE cells or into the vasculature.

Covalent adduction of HOHA with primary amino groups of protein lysyl residues31 or

33 ethanolamine phospholipids generates 2-(ω-carboxyethyl)pyrrole (CEP) derivatives

(Fig. 3.1). Elevated CEP and anti-CEP autoantibody levels are present in blood from

AMD patients.34-36 HOHA is generated and CEP accumulates mainly in two thin regions of the retina where DHA is concentrated, in photoreceptor disc membranes of photoreceptor outer segments and in RPE cells that endocytose the oxidatively damaged tips of those photoreceptor cells.34 In vivo, exposure of rats to bright (~1200 lux; 200 microwatts/cm2) green light generates oxidatively-truncated DHA-derived phospholipids

83 in their retinas with the level of HOHA-PC reaching 1.5 times that of residual DHA-PC after 1 h.37

3.1.3 Generation of HOHA esters, their GSH adducts and CEP derivatives in cell free and RPE cell models.

Previously, we discovered that HOHA lactone, e.g., generated in oxidatively damaged photoreceptor discs, can diffuse through cell membranes into RPE cells where it is metabolized by conjugation with glutathione (GSH) producing HOHA lactone-GSH adducts.38 The present study, for the first time, demonstrated light-induced generation of

HOHA lactone-GSH adducts in cell-free bovine retina extracts and then established two in vitro RPE cell models that exhibit light-induced generation of HOHA lactone-GSH adducts and CEP derivatives. Thus, upon photo-oxidative insult of RPE cells CEP formation competes with interception of HOHA intermediates by glutathionylation. In the retina, RPE cells can accumulate DHA from shed rod photoreceptor outer segments through phagocytosis and from plasma lipoproteins secreted by the liver through active uptake from the choriocapillaris.39 By replacing oleic (18:1) phospholipids, unesterified

DHA is gradually incorporated into RPE cell membranes through phospholipid turnover.40 As a simple model system, to recapitulate the DHA-rich environment in the retina, we examined photo-induced oxidative damage of ARPE-19 cells whose membrane phospholipids were enriched in DHA by preincubation with unesterified DHA.

We also examined the effect of doping the DHA-rich ARPE-19 cells with N-retinyl-N- retinylidene ethanolamine (A2E)41, the first component of lipofuscin that has been structurally characterized.17, 42-47 Although we found that the presence of A2E approximately doubles the level of oxidative DHA damage as quantified by HOHA

84 lactone-GSH adduct production, we also found that A2E is not required to photo-induce

DHA oxidative damage in RPE cells leading to RPE dysfunction. Finally, we demonstrated the deleterious effects of exposure to HOHA lactone on RPE cell lysosomal membrane integrity and mitochondrial membrane potential and found that HOHA lactone can cause senescence in RPE cells.

3.2 Results

3.2.1 HOHA/DHHA lactone-GSH adducts are generated in bovine retina extract exposed to UVA

As a cell-free model of light-induced oxidative retinal damage, we irradiated bovine retina extracts in phosphate buffer with light sources emitting black light (1 mW/cm2), warm white light (7 mW/cm2) and cool white light (5 mW/cm2), respectively for one hour at room temperature. Two derivatives of HOHA lactone were detected. The first product was HOHA lactone-GSH that was quantified by quadrupole LC-MS/MS

(448.1301.1 as quantifier, 448.1319.1 as qualifier) (Fig. 3.2A and 3.2A’). The second product was the reduced HOHA lactone-GSH adduct, DHHA lactone-GSH,

(450.1286.1 as quantifier, 450.1373.1 as qualifier) (Fig 3.2B and 3.2B’) using

13 15 isotope-labelled internal standard (glycine- C2, N)-GSH derivatives; MW increase = +3 au). There is an exponential increase in the formation of both HOHA lactone derivatives

(Fig. 3.2C) with respect to the duration of irradiation. After one hour of light exposure at room temperature (23 °C, black light, 365nm), the levels of HOHA lactone-GSH and

DHHA lactone-GSH reached a total 3057 ± 284 fmol/mg protein.

A B

A’ B’

D E

Figure 3.2. Time-course of the formation of HOHA lactone GSH derivatives: aldehyde (HOHA lactone-GSH, Panel A) and alcohol (DHHA lactone-GSH, Panel B) in bovine retina extracts as the result of black light (UV) exposure determined by LC-MS/MS. The MRM transition in the Panel A for the HOHA lactone-GSH is 448.1301.1 and the MRM transition in Panel B for the DHHA lactone-GSH is 450.1321.1. Fig. 3.2A’ and Fig. 3.2B’ show the levels of HOHA lactone-GSH and DHHA lactone-GSH in the Fig. 3.2A and Fig. 3.2B time-course experiments, respectively. Panel C shows the accumulation of HOHA lactone-GSH (blue) and DHHA lactone-GSH (red) in bovine retina extract as the result of light exposure. Panel D: irradiation time dependence of total GSH derivative (HOHA lactone-GSH plus DHHA lactone-GSH) production after UV treatment for various time periods at 0 °C followed by 1 h incubation at 23 °C; Panel E: post irradiation incubation time dependence of total GSH derivative (HOHA lactone- GSH plus DHHA lactone-GSH) production after irradiation at 0 °C for 1 h followed by various periods of incubation at 23 °C. The data are presented as mean ± SD, n = 3 (three independent experiments).

We expected that light-induced oxidative damage of DHA-rich retina phospholipids would produce HOHA-containing phospholipids (Fig. 3.3). Our previous findings that

HOHA-PC undergoes spontaneous deacylation to HOHA lactone32 and that HOHA lactone is metabolized by conjugation with GSH38, suggested that oxidative damage of

DHA-phospholipids in retina extracts would produce HOHA lactone-GSH derivatives.

We now find an irradiation time-dependent increase in the formation of HOHA lactone-

GSH derivatives when retina extracts are irradiated at 0 °C for 0 to 1 h followed by incubation for 1 h in the dark at 23 °C (Fig. 3.4, Panel A). We also observed a time- dependent increase in HOHA lactone-GSH derivative levels during incubation in the dark after irradiation at 0 °C for 1 h (Fig. 3.4, Panel B).

Figure 3.3. Photogeneration of HOHA-PC from DHA-PC is followed by release of HOHA lactone. HOHA lactone-GSH adduct is generated by glutathionylation of HOHA lactone. NADPH-dependent reduction of the HOHA lactone-GSH adduct delivers the reduced GSH adduct, DHHA lactone-GSH, that is also produced by RPE cells exposed to HOHA lactone, e.g., that may be released by oxidatively damaged photoreceptor cells.

UV light is especially effective in promoting oxidative damage of retinal lipids in bovine retina extracts (Fig. 3.4). We also found that even ambient light can induce oxidative damage of DHA-containing phospholipids in retina extracts resulting in the formation of HOHA lactone-GSH adducts. Exposure of bovine retina extracts to 400 ~

700 nm wavelength light sources (warm white and cool white light) present in ambient indoor lighting induced the formation of HOHA lactone-GSH derivatives even at low light fluencies (total GSH derivatives: 1354 ± 159 fmol /mg protein for warm white light;

1854 ± 58 fmol/mg protein for cool white light; 623 ± 12 fmol/mg protein for dark control (Fig. 3.4). Although visible light caused less oxidative damage than UV light, chronic exposure to ambient indoor lighting can damage retinal lipids. Addition of

NADPH cofactor to retina extracts after irradiation caused the ratio of the reduced to unreduced HOHA lactone-GSH adduct to increase approximately two-fold (data not shown), implicating the involvement of aldo-ketose reductase catalysis48, e.g., by aldose reductase49 or alcohol dehydrogenase, in the formation of the reduced adduct DHHA lactone-GSH.

Figure 3.4. Quantitative LC-MS/MS analysis of HOHA lactone GSH derivatives (HOHA lactone-GSH plus DHHA lactone-GSH) production induced in bovine retina extracts by light sources of various wavelengths. (The adduct MRM transition for the HOHA lactone-GSH is 448.1301.1 and the MRM transition for the DHHA lactone-GSH is 450.1 321.1). The data are presented as mean ± SD, n = 3. Student’s t-test: ***- P<0.001

3.2.2 Light induces the generation of DHHA lactone-GSH in ARPE-19 cells supplemented with DHA ± A2E.

Our previous demonstration that UV irradiation of DHA-PC liposomes results in the generation of HOHA-PC37 led us to anticipate that RPE cells enriched in DHA phospholipids would also yield HOHA phospholipids, HOHA lactone and its GSH derivatives. A2E is a pyridinium bisretinoid component of lipofuscin50 that accumulates with age in the RPE, absorbs light and serves as a light-responsive sensitizer.51

Previously, irradiation of ARPE-19 cells doped with physiological concentrations of A2E

- with blue light was shown to induce oxidative stress, i.e., production of H2O2, O2 and

1 52, 53 O2 , and caused downregulation of the ROS-detoxifying enzymes SOD2 and catalase concomitant with the increase in GSSG levels.53 Therefore, in a second cell model, to promote light-induced oxidative damage, after loading with DHA and prior to light exposure, we supplemented DHA-rich ARPE-19 cells with A2E. Loading of RPE cells with A2E (Fig. 3.5) by the procedure we employed results in accumulation of intracellular granules, detectable by fluorescence confocal imaging, that colocalize with lysosomes.54 The levels of A2E accumulating in cells incubated with 10 to 25 µM A2E are comparable to the amounts present in equal numbers of RPE cells harvested from human eyes. Because A2E can act as an amphiphilic detergent that perturbs membrane integrity and concentration-dependent membrane leakage54, after incubation for 24 h with

A2E, extracellular A2E was removed and the cells were extensively washed with warm basal DMEM/F12 cell culture medium. Previous studies demonstrated that incubation with 10 – 25µM A2E achieves cell-associated levels that approximate the A2E levels (34

– 134 ng/105 cell) measured in human RPE isolated from healthy donor eyes.54 The

DHA/A2E laden cells were finally given one day of quiescence before light exposure to allow recovery of the cell membrane in surviving cells and the attrition of any membrane- damaged cells (see Scheme 3.1).

Scheme 3.1. The work-flow of the ARPE-19 cell light damage model.

A2E (-) A2E (10 M)

Figure 3.5. Internalization of A2E: representative images showing green A2E autofluorescence in ARPE-19 cells preloaded 24 h with A2E.

To determine the wavelength dependence of light-induced oxidative damage in our

RPE cell models, we used three different light sources: black light (1 mW/cm2), blue light

(3 mW/cm2) and cool-white light (5 mW/cm2) to induce oxidative stress in ARPE-19 cells (Fig. 3.6). Both black light (365 nm) and blue light (430 nm) caused an irradiation time-dependent increase of DHHA lactone-GSH in ARPE-19 cells supplemented only

91 with DHA. Cells supplemented with both DHA and A2E underwent a significantly greater increase of DHHA lactone-GSH compared to DHA-rich cells that do not contain

A2E. A 10-fold increase of DHHA lactone-GSH after 1 h black light exposure and 7-fold increase after 1h blue light exposure in A2E-laden cells compared to dark control groups.

White light exposure also caused an increase of the DHHA lactone-GSH but to a somewhat lesser extent than black or blue light irradiation of A2E-laden RPE cells (2- fold increase after 1h irradiation) but not in cells not supplemented with A2E. Cells not supplemented with A2E exhibited a greater than 400% of dark control level of DHHA lactone-GSH with blue light but no increase over the dark control level with white light.

Thus, the blue light component of white light did not make a detectable contribution to

DHA oxidation. On the other hand, ARPE-19 cells supplemented with DHA respond to higher wavelength UVA or visible light with oxidative damage of DHA and the response is enhanced by the presence of A2E. Although ambient white light does not induce DHA oxidation in the absence of A2E, the presence of this sensitizer confers susceptibility to ambient white light-induced oxidative stress in RPE cells, e.g., containing lipofuscin.

Consequently, the light-induced generation of HOHA-PC and HOHA lactone from DHA phospholipids is expected in all individuals, i.e., not only those sensitive to UV but also those exposed to visible light. The age-related accumulation of A2E in lipofuscin granules in RPE cells is expected to exacerbate but not be essential for the production of

HOHA lactone and its GSH adducts and CEP derivatives.

A B C

Figure 3.6. Generation of DHHA lactone-GSH upon exposure to black light (Panel A), blue light (Panel B) or white light (Panel C) in ARPE-19 cells (A2E(-)) pre-incubated with 50 μg/mL DHA for 48 h or cells (A2E(+)) pre-incubated with DHA for 48 h followed by 10 μM A2E for 24 h with 24 h recovery in basal medium. Levels of GSH derivatives were determined by LC-MS/MS. The adduct MRM transition monitored for DHHA lactone-GSH was 450.1321.1. The data are presented as mean ± SD, n = 3. Student’s t-test: *-P<0.05, **-P<0.01, ***-P<0.001,  = significant difference from A2E(-)/dark control; # = significant difference from A2E(+)/dark control.

3.2.3 Light exposure decreases GSH levels in DHA-rich A2E-laden ARPE-19 cells.

The GSH level in DHA-rich A2E-laden ARPE-19 cells was assessed immediately after exposure to blue light. Irradiation for only 10 min caused a massive (80%) depletion of the GSH level, from 49 ± 2 nmol/mg protein to 10 ± 1 nmol/mg protein, and a 90% decrease to 7 ± 2 nmol/mg protein was detected after 20 min. The GSH level did not decrease further and recovered slightly to 11 nmol/mg protein and greatly after 40 min to

37 nmol/mg protein after 60 min (Fig. 3.7A). The decrease of GSH level inversely correlates with the generation of HOHA lactone-GSH adduct. Thus, GSH is consumed to detoxify electrophilic lipid oxidation products, e.g., HOHA lactone and probably other unsaturated aldehydic degradation products of ω-6 and ω-3 PUFAs55, 56 generated upon irradiation. We also found that the GSH level in DHA-rich cells not supplemented with

A2E showed a similar decrease after 10 min, but recovered much faster than the cells

93 containing A2E. Also for A2E-laden cells not supplemented with DHA, the decrease of

GSH level was slower and only a slight recovery occurred by 60 min.

Furthermore, GSH levels in cells 24 h after light exposure for 10 min contained 3 times the levels of GSH (107 ± 2 nmol/mg protein) present in dark controls (36 ± 1 nmol/mg protein), but cells exposed to longer irradiation showed no return of their GSH level to dark control values. Apparently, GSH biosynthesis is upregulated in response to massive depletion by light-induced oxidative injury leading to cell recovery after short term irradiation. But the damage accompanying catastrophic light-induced GSH depletion was more extensive and not recoverable (Fig. 3.7B). Interestingly, in the non-A2E containing cells, a dramatic increase of GSH level was observed (6 – 7-fold increase after

60 min) and DHA-enriched cells showed a slightly higher level. In contrast, in the A2E- laden cells without DHA treatment, the recovery was not significant. According to these

A B

Figure 3.7. Quantitation of GSH levels remaining in DHA/A2E-laden ARPE-19 cells 10 min (Panel A) or 24 h (Panel B) after irradiation for various times from 0 to 60 min. The data are presented as mean ± SD, n = 3. Student’s t-test: *=P<0.05, **=P<0.01, ***=P<0.001.

94 observations, it is possible that after exposure to light, oxidized DHA or DHA could upregulate detoxification pathways promoting the synthesis of more GSH, but irradiation in the presence of A2E exacerbated the light damage resulting in no recovery of the GSH level. Apparently, the level of oxidative damage in the presence of A2E overwhelms the cells capacity to protect itself by upregulating antioxidant defences.

3.2.4 Light exposure generates CEP in DHA-rich A2E-laden ARPE-19 cells

Previously, we found that HOHA lactone is a major precursor of CEP derivatives, which have significant pathological and physiological relevance to AMD, cancer and wound healing.57-59 After exposure of DHA-rich, A2E-laden ARPE-19 cells to blue light for 20 min, they were washed, fixed with cold acetone and immunostained using primary rabbit anti-CEP polyclonal antibodies and goat anti-rabbit Texas Red-X secondary antibodies to detect CEP-epitopes on these cells (Fig. 3.8A). These antibodies detect both

CEP-protein and CEP-ethanolamine derivatives in contrast with LC-MS/MS analyses that have independently confirmed the occurrence of CEP-ethanolamine derivatives in vivo.33, 60 We observed a 50% increase in the red fluorescence intensity owing to immunostaining with anti-CEP antibody (Fig. 3.8C, 820 ± 92 RFU versus 414 ± 27 RFU in the dark control) and 477%, 110%, 126% increase compared to DHA(-)/A2E(-),

DHA(+)/A2E(-), DHA(-)/A2E(+) groups corresponding to a significant increase in levels of CEP. Thus, although the precursor of CEP, i.e., HOHA lactone, is captured by covalent adduction of GSH and aldehyde reduction to produce the unreactive end product

DHHA-GSH, reaction with primary amino groups, e.g., of ethanolamine phospholipids and protein lysyl residue ε-amino groups, to form CEPs, competes with GSH adduction.

DAPI F-actin CEP Merge Control

DAPI F-actin CEP Merge

exposed -

Light B DHA(-)/A2E(-) DHA(+)/A2E(-) DHA(-)/A2E(+)

Merge Merge Merge Control

Merge Merge Merge

exposed -

Light C

Figure 3.8. Generation of CEP in ARPE-19 cells after 20 min exposure to blue light. Panel A: Images of the generation of CEP in DHA-rich A2E-laden ARPE-19 cells (Top panel: Control; Bottom panel: light-exposed). Panel B: Images of CEP immunostaining in ARPE-19 cells (Top panel: Control; Bottom panel: light-exposed; From Left to right: DHA(-)/A2E(-), DHA(+)/A2E(-), DHA(-)/A2E(+)). Panel C: Quantification CEP levels in ARPE-19 cells. A2E-laden ARPE-19 cells were exposed to blue light for 20 min followed by 24 h incubation and then immunostained with rabbit anti-CEP polyclonal antibody/goat anti-rabbit Texas Red-X antibodies (red), Flash Phalloidin™ Green 488 (green, F-actin) and DAPI (blue). The figure is representative of 4~6 independent experiments, which showed very similar results. Student’s t-test: ***- P<0.001.

3.2.5 Light exposure induces mitochondrial damage and death of DHA-rich A2E- laden ARPE-19 cells.

Mitochondrial dysfunction is associated with various pathological states.61, 62 Decrease of mitochondrial membrane potential (Δψm) is a point of no return in the classical apoptosis pathway.63 We utilized two different probes to examine the mitochondrial membrane potential of ARPE-19 cells affected by light-induced oxidative stress.

MitoClick is a highly specific and sensitive Δψm quantitative probe, which contains a triphenylphosphonium (TPP) lipophilic cation, in a “click chemistry” molecule that forms

64 and accumulates specifically in mitochondria in response to Δψm. It is formed when one component containing an azido moiety (MitoAzide) and the other component, a cyclooctyne (MitoOct), react in a concentration-dependent manner by “click” chemistry to form the product MitoClick. An increase in Δψm accelerates mitochondrial MitoClick formation relative to that in the cytosol and even a miniscule increase of Δψm leads to a compounded increase of MitoClick that results in its utility to assess even miniscule changes of Δψm in vitro and in vivo and give an exact quantitation of Δψm by LC-MS/MS with normalization with total protein concentration rather the relative ratio. After light exposure, the TPP probe showed a dramatic decrease in the amount of MitoClick product indicating a decrease of mitochondrial membrane potential in the DHA-rich A2E-laden

APRE-19 cells. Δψm dropped 84% and 87% respectively after 1h exposure to blue light

(Fig. 3.9A) and black light (Fig. 3.9B), respectively. In contrast, DHA-rich cells not laden with A2E preserved healthy mitochondria after exposure to blue or black light (Fig. 3.9).

A B C

Figure 3.9. Measurement of mitochondrial membrane potential in light exposed DHA- rich A2E-laden ARPE-19 cells. Panel A: to cells exposed to black light (365 nm) for 0 and 1 h, after 24 h recovery, were added TPP probes for 3 h and the amount of MitoClick was quantified by LC-MS/MS; Panel B: to DHA-rich A2E-laden ARPE-19 cells exposed to blue light (430 nm) for 0 and 1 h, after 24 h recovery, were added the TPP probes for 3 h and the amount of MitoClick produced was quantified by LC-MS/MS; Panel C: DHA- rich A2E-laden ARPE-19 cells were exposed to blue light (365 nm) for 0 to 40 min and, after 24 h recovery, the Δψm was measured by JC-10. The data are presented as mean ± SD of %control, n = 3. The cells without light exposure (-) served as control. Student’s t- test: *-P<0.05, **- P<0.01, ***- P<0.001.

We confirmed the decreased mitochondrial membrane potential detected with the new

MitoClick probe using another probe that is widely applicable to in vitro studies of cellular mitochondrial membrane potential changes. JC-10, a 5,5’,6,6’-tetrachloro-

1,1’,3,3’-tetraethylbenzimidazoylcarbocyanine iodide derivative, is a cationic dye that accumulates in energized mitochondria. In healthy cells, the dye aggregates yielding red to orange fluorescent emission while in apoptotic cells, the dye remains in the cytoplasm in its monomeric form showing green fluorescence.65 JC-10, showed an irradiation time- dependent decrease in the ratio of red aggregate to green monomer from 37% to 77% after exposure to blue light for 10 minutes to 40 minutes indicating a decrease of Δψm due to the light-induced damage (Fig. 3.9C). The dysregulation of mitochondrial potential was accompanied by a decrease in cell viability. Thus, A2E-laden DHA-rich ARPE-19

98 cells also exhibited irradiation time-dependent cell death resulting from exposure to blue light as assessed by MTT assay. Cell viability decreased to 60% after 5 min irradiation, while only 10% of cells remained viable after irradiation for 60 minutes (Fig. 3.10).

Figure 3.10. Measurement of the cell viability by MTT assay 24 h after A2E-laden ARPE-19 cells were exposed to blue light (430 nm) for 0 to 60 min. The data are presented as mean ± SD of % control, n = 3. Student’s t-test: **- P<0.01, ***- P<0.001. The cells without light exposure (-) served as control.

3.2.6 HOHA lactone can cause mitochondrial damage, cellular senescence and induce cell death.

The identification of HOHA lactone derivatives of GSH and proteins, i.e. CEPs, provided presumptive evidence that light-induced generation of HOHA lactone in DHA- rich ARPE-19 cells contributes to mitochondrial dysfunction and death. We treated

ARPE-19 cells with HOHA lactone to confirm these pathological effects. After exposure to 20 μM HOHA lactone for 3 h, we observed a 1.5-fold increase of MitoClick levels in mitochondria (Fig. 3.11A) that indicated slightly higher mitochondrial membrane potential. Such mitochondrial hyperpolarization is generally exhibited by early apoptotic cells.66, 67 In contrast, treatment with 5 to 20 μM HOHA lactone for 24 h, induced a dose- dependent mitochondrial depolarization as measured by TPP MitoClick (Fig. 3.11B) and 99

JC-10 (Fig. 3.11C) probes. The levels of MitoClick decreased by 40% with exposure to

20 μM HOHA lactone and JC-10 showed a 60% decline in the ratio of red aggregate to green monomer fluorescence. This demonstrated severe damage of mitochondria by

HOHA lactone that caused an irreversible loss of mitochondrial membrane potential characteristic of late apoptotic cells.

A B C D

Figure 3.11. Measurement of mitochondrial membrane potential changes in ARPE-19 cells upon exposure to HOHA lactone. Panel A: dose-dependent effect of 3 h exposure to HOHA lactone on ARPE-19 cell mitochondrial membrane potential measured with the TPP MitoClick probe; Panel B: dose-dependent effect of 24 h exposure to HOHA lactone on ARPE-19 cell mitochondrial membrane potential measured with the TPP MitoClick probe; Panel C: effect of 24 h exposure to HOHA lactone on ARPE-19 cell mitochondrial membrane potential measured with the JC-10 probe; Panel D: effects of a single treatment (1X) with 5 μM HOHA lactone incubated for 8 h or a triple treatment (3X) with 5 μM HOHA lactone every 8 h, total incubation time was 24 h, measured with the TPP MitoClick probe. The data are presented as mean ± SD of % control, n = 3 (MitoClick) or n = 6 (JC-10). Student’s t-test: *-P<0.05, **- P<0.01, ***- P<0.001.

Having found that photo-induced oxidative damage of DHA-rich ARPE-19 cells leads to the formation of HOHA lactone-GSH adducts (Fig. 3.5 and Fig. 3.6) and that both light exposure (Fig. 3.9) and HOHA lactone treatment of these cells leads to a significant decline in the cell’s mitochondrial membrane potential (Fig. 3.11), we used two metabolic indicators, MTT and Alamar Blue (AB) to gauge the extent to which the decrease in mitochondrial membrane potential in these cells affects overall cell viability.

100

MTT is reduced by mitochondrial reductases as well as by "reducing equivalents" such as

NADPH, FADH, FMNH, and NADH generated in viable cells by passing electrons to the tetrazolium salt to form insoluble intracellular formazan as the result of the cellular metabolism. However, MTT cannot be reduced by mitochondrial cytochromes and other cytosolic reducing enzymes. On the other hand, AB can be reduced by mitochondrial reductases and cytochromes, as well as enzymes located in the cytoplasm, e.g., dihydrolipoamide dehydrogenase,68 NAD(P)H-quinone oxidoreductase69 and flavin reductase.70 Hence, AB reduction can also reveal impairments of cellular metabolism besides the direct measure of interrupted electron transport and mitochondrial dysfunction revealed by MTT.71 The AB assay (Fig. 3.12) clearly shows that HOHA lactone-induced damage goes beyond impairment of the mitochondria. At 20 μM HOHA lactone, the MTT assay revealed a 25% decline in viability of ARPE-19 cells (Fig. 3.12A) while the AB assay indicated a 50% decline (Fig. 3.12B). On the other hand, impairment of mitochondrial function is significant after exposure to10 μM HOHA lactone.

A B

Figure 3.12. Measurement of the cell viability of ARPE-19 cells after exposure to 0 to 40 μM HOHA lactone for 24 h assessed by MTT assay (Panel A) and by Alamar Blue assay (Panel B). The data are presented as mean ± SD of % control, n = 8.

101

Since replicative senescence can be induced by oxidative stress,72 and since we previously showed that low concentrations (0.1 − 1.0 μM) of HOHA lactone can induce oxidative stress in ARPE-19 cells73, we tested the hypothesis that exposure to HOHA lactone can induce replicative senescence in ARPE-19 cells. Using senescence-associated

β-galactosidase (SA β-gal) staining74 that detects lysosomal β-galactosidase75, we determined that exposure to HOHA lactone induces senescence in ARPE-19 cells. After

12 h incubation of ARPE-19 cells with 5 μM HOHA lactone, SA β-gal staining was 3.5 times greater in the HOHA lactone treated than in the control ARPE-19 cells (1X in Fig.

3.13A). This indicates that a sub-lethal dose of HOHA lactone produces a prematurely senescent phenotype in ARPE-19 cells which results in a permanent loss of the ability to proliferate and a lower the resistance to apoptosis.76 However, repeated treatments did not cause an increase in positive SA β-gal staining (3X, Fig. 3.13B). As noted above, we found that repeated (3X) treatment of ARPE-19 cells with HOHA lactone caused a greater decrease in mitochondrial membrane potential than a single (1X) treatment (Fig.

3.11D). The decrease level was almost identical to 24 h treatment with 10 μM HOHA lactone and at 10 μM concentration, ARPE-19 cells showed a dramatic cell death. This phenomenon indicated the low dosage of HOHA lactone might lead to cellular senescence in RPE cells, but due to less resistance to apoptosis, chronic exposure of the same concentration of HOHA lactone could further induce cell death.

102

A Control HOHA-lac (5 M) 1X HOHA-lac (5 M) 2X HOHA-lac (5 M) 3X

10X B 20X

Figure 3.13. Senescence in ARPE-19 cells exposed to HOHA lactone. Panel A: SA-β- Gal activity in ARPE-19 cells treated with 5 μM HOHA lactone and then maintained in fresh medium (DMEM/F12 containing 1% FBS) for a total of 7 days. Micrographs were obtained with bright field/phase contrast combined mode microscopy; Panel B: Quantification of SA-β-Gal positive cells shown in panel A (1X) and in those treated again after 12 h (2X) and 24 h (3X) with 5 μM HOHA lactone. SA-β-Gal positive regions were scored in 3 fields in duplicate wells. Results are expressed as the percentage of stained area (mean ± SD).

3.2.7 HOHA lactone induces lysosomal membrane permeabilization.

Lysosomal membrane permeabilization and loss of lysosomal integrity has been observed during oxidative stress-induced apoptosis and during the progression of cellular senescence.77, 78 Perturbation of the lysosomal membrane leads to lysosome leakage and loss their acidity.79, 80 To determine the effect of HOHA lactone on RPE cell lysosomal integrity, we used Acridine Orange (AO), a weak base metachromatic dye capable of crossing plasma membranes. AO accumulates within lysosomes because it becomes protonated under lysosomal acidic conditions. At low concentrations AO can differentiate lysosomes (reddish-orange granules) from other cellular components (diffuse green).81, 82

Accumulation of AO in lysosomes leads to a shift in emission wavelength from λ = 530 103 nm (green) to λ = 620 nm (red).82, 83 If the integrity of the lysosomal membrane is compromised to the point that lysosomal pH rises, AO becomes deprotonated and its fluorescence emission shifts back from red to green.82, 84 AO-treated ARPE-19 cells showed both green fluorescence emitted from the cytosol and nucleus and red fluorescence associated with lysosomes (Fig. 3.14A, control). Addition of 1 μM HOHA lactone to ARPE-19 cells followed by 24 h incubation drastically diminished AO red fluorescence emission to 51.0 ± 2.0 % of the fluorescence level in untreated ARPE-19 cells. An even more profound decrease to 24.4 ± 1.2% of control was seen in the cells treated with 10 μM HOHA lactone (Fig. 3.14B). Thus, upon exposure to HOHA lactone, lysosomes in ARPE-19 cells apparently lose their acidity indicating that low micromolar concentrations of HOHA lactone can induce lysosomal membrane permeabilization and loss of lysosomal integrity.

104

Control 1 M 2.5 M 5 M 10 M

DNA/RNA DNA/RNA Lysosome

Lysosome

Figure 3.14. Lysosomal membrane perturbation in ARPE-19 cells after incubation with HOHA lactone. Panel A: Inverted fluorescence microscope images (10X) of Acridine Orange sequestered in ARPE-19 intact lysosomes (red) or bound to DNA, RNA and other cell constituents (green). Panel B: Relative fluorescence intensity of AO-stained lysosomes in the control and in the HOHA lactone treated ARPE-19 cells after 24 h of incubation under standard conditions. ARPE-19 cells were incubated with 0~10 μM HOHA lactone for 24 h incubation and then stained with Acridine Orange. Lysosomal fluorescence was quantified in the raw image after background subtraction using Metamorph software. The figure is representative of 4 independent experiments, which showed very similar results. Student’s t-test: *-P<0.05, **- P<0.01, ***- P<0.001.

105

3.2.8 HOHA lactone increases the level of CEP in ARPE-19 cells.

Previously, we reported that upon treatment of ARPE-19 cells with 10 μM HOHA lactone, less than 5% was incorporated into GSH adducts.38 Thus, most of the HOHA lactone was not trapped by GSH and instead can react with other nucleophiles such as primary amino groups in biomolecules to generate CEPs. After treating ARPE-19 cells with 10 μM HOHA lactone, we observed a 100% increase in their far-red fluorescence intensity owing to immunostaining with anti-CEP antibody (Fig. 3.15) corresponding to a significant increase in levels of CEP. Thus, GSH did not capture all of the HOHA lactone.

Some of it reacted with proteins and ethanolamine phospholipids to generate CEP derivatives. A Control HOHA-lac (10 M)

Figure 3.15. Generation of CEP in ARPE-19 cells upon exposure to HOHA lactone. Panel A: Images revealing the generation of CEP in ARPE-19 cells (Left: Control; Right: cells exposed to 10 μM HOHA lactone). Panel B: Quantification of the levels of CEP in ARPE-19 cells. ARPE-19 cells were exposed to 10 μM HOHA lactone for 24 h and then immunostained with rabbit anti-CEP polyclonal antibody/goat anti-rabbit Texas Red-X antibodies. The figure is representative of two independent experiments that showed very similar results. Student’s t-test: ***- P<0.001.

106

3.3 Discussion

Interventional clinical studies on age-related eye disease that used antioxidants (e.g. vitamins C and E)85 and zinc86 show association of oxidative damage with AMD progression. While the data on the connection between exposure of the human eye to blue light and long-term chronic sunlight exposure haven’t produced a clear link between the involvement of these factors and the progression of AMD, some studies support the hypothesis. There is a significant association of blue light exposure and neovascular

AMD in patients with low antioxidant levels according to the European Eye Study.87 The

Beaver Dam Study showed that sunlight exposure is significantly associated with early

AMD.88 There is a significant association between long-term visible or blue light exposure and geographic atrophy or disciform scarring according the Chesapeake Bay

Watermen Study.89

Although the human lens can absorb most of the UV light >295 nm passing through the cornea by UV-absorbing chromophores, these must first accumulate to protect the human retina against damage by UVA light to which it is highly susceptible.90 More than

75% of 300 to 400 nm UV radiation is transmitted through lenses of individuals under 10 years of age.91 The accumulation of UV absorbing chromophores as the lens ages provides a lenticular UV filter that protects the retina from potentially harmful continuous

UV radiation exposure. UV transmission through lenses of individuals 25 or more years old is very low, i.e., ~1%.91, 92 Nevertheless, long wavelength UV radiation may play a role in degenerative processes in older patients, e.g., macular degeneration and retinitis pigmentosa, owing to a substantial increase in UV radiation reaching the retina after removal of their cataractous crystallin lenses by cataract surgery.93 Therefore, not only

107 children but also some adults could be susceptible to light-induced damage of their retinas when exposed to UV light. Previous studies found a positive correlation between increased exposure to certain spectral ranges of light (UV or blue light) and increased susceptibility to AMD.94 In the present study, we explored oxidative damage of DHA phospholipids that are especially abundant in retina. We monitored oxidative cleavage of

DHA induced by light of various spectral ranges to produce HOHA lactone-GSH adducts with in vitro models based on bovine retina extract and ARPE-19 cells enriched with

DHA ± A2E.

3.3.1 Exposure to light induces the generation of HOHA lactone-GSH adducts in bovine retina extracts.

We previously discovered that spontaneous phospholipolysis of HOHA-PC releases

HOHA lactone by a non-enzymatic transesterification32 and that HOHA lactone readily diffuses through cell membranes (see Fig. 3.3). RPE cells metabolize HOHA lactone producing and reducing the aldehyde group in the HOHA lactone-GSH adduct producing and excreting DHHA lactone-GSH.38 In a simple in vitro model of photo-induced PUFA oxidation in the retina, we now exposed an extract from bovine retina to longer wavelength UV light and monitored the levels of HOHA lactone-GSH adducts. We developed an enrichment protocol including liquid-liquid extraction followed by two consecutive solid-phase extractions that eliminates interference by the complex tissue matrix and enables their detection by LC-MS/MS. A continuous increase in levels of the

GSH adducts of HOHA lactone and DHHA lactone with increasing light exposure time was observed.

108

3.3.2 Photo-oxidative damage and lipofuscin accumulation in AMD retina.

A few cell types in the human eye are especially susceptible to the photo-oxidative damage. They include rods and cones that are photosensitive owing to the presence of visual pigments, retinoids and mitochondrial chromophores.90, 95, 96 These cells use UV and visible light responsive pigments to absorb photons as the first step in visual object perception.97-100 RPE cells are also photosensitive owing to the presence of melanin, lipofuscin and intermediate products of the visual cycle. Components of lipofuscin granules are phototoxic, and upon exposure to short and mid-range wavelengths of visible light under aerobic conditions generate ROS including superoxide anion, hydrogen peroxide, lipid hydroperoxides and singlet oxygen.101, 102 Elucidation of the excited states of purified lipofuscin showed that extractable chromophores from lipofuscin, which, upon excitation with blue light, form a triplet excited state which can transfer energy to molecular oxygen, resulting in the generation of singlet oxygen.103-105

Apparently, the ability of lipofuscin to interact with molecular oxygen and photo- generate superoxide radical is significantly enhanced with advancing age.106 In a cell culture model in which human RPE cells were loaded with lipofuscin granules and exposed light, only cells exposed to 390-550 nm light showed significant morphological changes, loss of lysosomal integrity, enhanced peroxidation of lipids and decreased viability.17, 18, 54 Along with increased susceptibility of RPE to light-induced cell damage107, 108, lipofuscin accumulation adversely affects RPE cell homeostasis and function.109, 110 Accumulation of excessive levels of lipofuscin in RPE cell lysosomes, which often manifests in their apoptosis, subsequent death of photoreceptor cells111 and the formation of drusen in the region of Bruch's membrane, have been considered initial

109 steps in the pathogenesis of AMD, and may promote light-induced oxidative damage in the disease process.4, 112 It has been hypothesized that early steps in AMD pathogenesis begin when RPE cells can no longer handle the accumulated lipofuscin and begin to excrete post-translationally modified debris. This includes biomolecules modified by 4- hydroxynon-2-enal (HNE) or malondialdehyde and other oxidative posttranslational protein modifications, e.g., advanced glycation end products (AGE) or CEP derivatives which deposit with possible cross-linking4 to the inner collagenous layer of Bruch’s membrane and contribute to drusen accumulation.112

A2E, a pyridinium bisretinoid derivative of all-trans-retinal, accumulates in RPE cells.43 Besides serving as a photosensitizer of oxidative damage, A2E inhibits lysosomal enzyme activities113, 114 and the resulting incomplete lysosomal degradation of phago- cytosed photoreceptor tips leads to accumulation of a granular residue in RPE cells with age, forming lipofuscin.110, 114, 115 The A2E containing lipofuscin absorbs light and acts as a photosensitizer that induces additional oxidative stress upon light exposure leading to damage of RPE cells. A2E accumulation contributes to the role of lipofuscin as a light absorber and photosensitizer in RPE cells. A previous model demonstrated susceptibility of RPE cells to photooxidative damage with fluorophore-laden RPE cells that were generated by phagocytosis of A2E.41 Nevertheless, the importance of A2E in the etiology of AMD has been challenged by the finding that, although the human retina has significant RPE lipofuscin throughout the periphery, there is no correlation between the distribution of A2E and lipofuscin. Furthermore, the levels of A2E were highest in the far periphery and decreased toward the macula.116 The spatial relationship between autofluorescence patterns and geographic atrophy progression in patients with AMD

110 suggests that fundus accumulation of A2E is a consequence of retinal atrophy rather than an essential driver of RPE cell death.19 Nevertheless, A2E accumulation could contribute to apoptosis by promoting photo-induced generation of HOHA lactone and other toxic lipid oxidation products and by serving as one of the mitochondria damaging factors released from permeabilized lysosomes.

3.3.3 Photooxidative generation of HOHA in A2E-free RPE cells may be an early step in AMD etiology.

We postulated that before the accumulation of A2E and lipofuscin, photooxidative generation of toxic HOHA-PC, HOHA lactone and CEP from DHA phospholipids can foster the early stages of RPE cell dysfunction and AMD. In the present study to mimic the continuous uptake in vivo of DHA by RPE cells, we enriched ARPE-19 cells with

DHA. We found that DHA supplemented ARPE-19 cells undergo photo-induced oxidative damage by UV and blue light, but not white light, in the absence of lipofuscin or A2E (Fig. 3.6). This suggests that AMD pathology can be initiated by photo-induced oxidation of DHA before accumulation of lipofuscin. Incorporation of A2E into these

DHA-enriched ARPE-19 cells almost doubled their proclivity to light-induced lipid oxidation and expanded the spectral range of their photosensitivity to white light (Fig.

3.6). Therefore, the accumulation of A2E can accelerate the disease process. The observation that levels of A2E in the macula are relatively low does not preclude an important role for A2E-promoted generation of HOHA lactone because it readily diffuses from its site of generation. Although the amounts of oxidative damage induced by white light with sensitization by A2E are small relative to those induced by intense blue light, cumulative A2E-induced oxidative damage resulting from chronic exposure to ambient

111 white light might make a significant contribution to the progression of AMD pathology.

Upon the exposure to longer wavelength UVA, blue light or even white light, the DHA- enriched ARPE-19 cells with longer light exposure times produced increasing levels of

DHHA-GSH, the reduced adduct of HOHA lactone with GSH.

3.3.4 CEP is coproduced with GSH adducts of photooxidatively generated HOHA in

RPE cells.

The most abundant PUFA in photoreceptor disk membranes, DHA, is the unique source of HOHA that in turn is the precursor of CEP. In the retina HOHA is generated and CEP accumulates mainly in two thin regions of the retina where DHA is concentrated, in photoreceptor disc membranes of photoreceptor outer segments and in RPE cells that endocytose the oxidatively damaged tips of those photoreceptor cells. Glutathione is an important antioxidant for scavenging reactive oxygen species and detoxifying electrophiles, especially the α,β-unsaturated aldehydes that are produced when cells are subjected to oxidative stress. We previously found that exposure of ARPE-19 cells to sublethal concentrations of HOHA lactone delivers HOHA lactone-GSH adducts, but the yield of GSH adducts was less than 5%. Apparently, the capacity for cells to detoxify this electrophile can be overwhelmed. The present study showed that exposure of DHA-rich

A2E-laden ARPE-19 cells to blue light for only 10 min caused the production of HOHA lactone-GSH adducts (see Fig. 3.6) and a massive (60%) depletion of the GSH level (see

Fig. 3.7). Although GSH serves as a first line of defense against oxidative stress, depletion of GSH seemed likely to limit its ability to completely neutralize all the lipid peroxidation metabolites or reactive oxygen species generated as a consequence of light exposure.

112

In the present study, immunostaining with anti-CEP antibody revealed elevation of

CEP levels in A2E-laden ARPE-19 cells after exposure to blue light (see Fig. 3.8) as well as in HOHA lactone treated ARPE-19 cells (see Fig. 3.14). By modifying biomolecules, e.g., by reacting with primary amino groups to generate CEP derivatives, HOHA lactone that is not trapped by GSH can induce various adverse events in the cells. CEP activates

CEP-specific T-cells involved in “dry AMD” and TLR2-dependent expression and activation of the NLRP3 inflammasome and induction of angiogenesis that characterizes

“wet AMD”.58 CEP derivatives accumulate in the retinas and blood plasma of individuals with AMD and are a biomarker of AMD.33, 34, 117 Some animal models that show phenotypic similarities with AMD also show statistically significant elevated levels of

CEP in retina and exhibit significantly elevated CEP autoantibody titer.33, 34, 117-119 These models include superoxide dismutase 2 ribozyme knockdown mice118 and rodents exposed to intense green97, 120, 121 or blue light.119, 122 Animal model studies also demonstrated that CEP derivatives induce choroidal neovascularization and promote wound healing and tumor growth in a toll-like receptor 2 (TLR2)-dependent manner 33, 57,

123. Furthermore, immunization of mice with CEP-modified mouse serum albumin induces AMD-like lesions in their retinas.124 CEP immunized mice also exhibit monocyte and macrophage migration into the interphotoreceptor matrix and elevated complement deposition in Bruch’s membrane.124 CEP immunization causes interferon-gamma (IFN-γ) and interleukin-17 (IL-17) production by CEP-specific T cells that promote inflammatory

M1 polarization of macrophages indicating that T cells and M1 macrophages activated by oxidative damage to DHA cooperate in AMD pathogenesis.125 No similar biological activities have been observed for the analogous pentylpyrrole or ethylpyrrole derivatives

113 produced by adduction of other γ-hydroxy-α,β-unsaturated aldehyde lipid oxidation products HNE or 4-hydroxyhex-2-enal, respectively, to proteins or ethanolamine phospholipids.

3.3.5 HOHA lactone causes mitochondrial damage.

The mitochondrion is the main site of intracellular ROS production which could be photo-generated upon light exposure.126 It is also the target of reactive lipid peroxidation products, including acrolein, malondialdehyde and HNE.127 Reactive electrophilic lipid oxidative degradation products generated from cell plasma membrane or inner mitochondrial membrane128 could inhibit the activity of mitochondrial enzymes, impair the mitochondrial functions and trigger apoptosis of RPE cells. The mitochondrial membrane potential is a major determinant and indicator of cell fate. During apoptosis, the opening of permeability transition pores leads to swelling of the mitochondrial matrix, rupture of the outer membrane and eventually causes irreversible collapse of the

129 mitochondrial membrane potential (Δψm ). Therefore, the decrease of mitochondrial membrane potential is a point of no return in the classical apoptosis pathway. In this study, we utilized a novel sensitive triphenylphosphonium (TPP) probe to quantitatively measure the Δψm. Changes in Δψm are proportional to the accumulation of the click chemistry product “MitoClick”. We also confirmed the results of these experiments with another orthogonal widely-used probe, JC-10. We observed that the ARPE-19 cells showed a dose dependent decrease of mitochondrial membrane potential after 24 h treatment with HOHA lactone (see Fig. 3.11B). As expected, an MTT cell viability assay showed that mitochondrial dehydrogenase activity also decreased after treatment with

HOHA lactone (Fig. 3.12). On the other hand, at an earlier time point, 3h after treatment

114 of ARPE-19 cells with HOHA lactone, we detected hyperpolarization of mitochondria

(Fig. 3.11A). Such mitochondrial hyperpolarization is generally exhibited by early apoptotic cells.66, 67 These observations indicate that HOHA lactone can trigger apoptosis of RPE cells. It is tempting to speculate that this induction of apoptosis starts with inhibition of ATP synthase or dephosphorylation of cytochrome c oxidase causing elevation of Δψm that leads to uncoupling of oxidative phosphorylation that, in turn, dissipates Δψm, damages inner mitochondrial membrane integrity and could eventually result in the cell death.130 These observations in our in vitro model suggest that HOHA lactone, and presumably other α,β- unsaturated aldehyde electrophiles generated in vivo by chronic photo-induced oxidative cleavage of PUFAs, can contribute to RPE cell dysfunction. We also observed that upon exposure to intense light, DHA-rich A2E-laden

APRE-19 cells showed an irradiance dependent mitochondrial depolarization and a decrease in mitochondrial dehydrogenase activity (MTT cell viability) indicating light- induced mitochondrial damage. Oxidative damage of DHA and the consequent production of HOHA-PC and HOHA lactone can contribute to reduction of mitochondrial potential induced in DHA-rich RPE cells by light exposure. But the presence of A2E less than doubles the levels of HOHA-derived DHHA-GSH produced upon exposure of these cells to light (Fig. 3.8) and the effect of 5 μM HOHA lactone in the absence of A2E is modest (Fig. 3.11). Therefore, the massive (90%) light-induced decrease of mitochondrial membrane potential in the presence of A2E but not in DHA- rich RPE cells lacking A2E (Fig. 3.9) suggests that mechanisms besides the effects of

HOHA lactone are important. One putative mechanism is a light-induced conversion of

A2E into a more toxic derivative, e.g. by epoxidation.131, 132 Another possibility is a

115 synergistic mechanism where HOHA lactone facilitates the release of A2E from lysosomes into the cytosol and subsequent mitochondrial accumulation while A2E sensitizes lipid oxidation leading to the production of more toxic α,β-unsaturated aldehydes including 4-HHE and HOHA lactone.

3.3.6 HOHA lactone causes lysosomal leakage.

Probably due to its deleterious effects on the cell plasma membrane, feeding A2E to

ARPE-19 cells inhibits the lysosomal ATP-driven proton pump,110 increases intralysosomal pH133 and selectively inhibits phagolysosomal degradation of photoreceptor phospholipids.114 Lipofuscin/A2E is sequestered in lysosomes, and when exposed to blue light, causes lysosomal membrane permeabilization.107, 108, 134 Blue light/A2E-driven lysosomal membrane permeabilization in ARPE-19 cells leads to activation of the NLRP3 inflammasome by leaking lysosomal enzymes resulting in secretion of inflammatory cytokines IL-1β and IL-18.134 A2E is a photosensitizer and if excited with blue light in the presence of molecular oxygen it generates ROS.46, 101, 105

Therefore, it promotes light-dependent lipid peroxidation,135 that inactivates acid phosphatase and ROS detoxifying enzymes53, 135, and causes RPE cell death.53, 134

We now discovered that light-induced oxidative damage of DHA-enriched ARPE-19 cells does not require the presence of A2E to produce the GSH adducted and reduced derivative, DHHA lactone-GSH, of HOHA lactone (Fig. 3.6), and exposure to 1 µM

HOHA lactone causes massive (50%) lysosomal leakage in ARPE-19 cells (Fig. 3.14).

Consequently, oxidative fragmentation of DHA can promote lysosomal leakage in the early stages of AMD before lipofuscin or A2E accumulate. Nevertheless, the ability of

A2E, and potentially other components of lipofuscin to double the efficiency of photo-

116 induced production of HOHA lactone-GSH suggests that the accumulation of lipofuscin/A2E in lysosomes exacerbates HOHA lactone-induced lysosomal leakage, i.e., by photosensitizing the oxidative fragmentation of DHA phospholipids to produce more

HOHA lactone in the advanced stages of AMD.

Apoptosis may be initiated by escape of lysosomal enzymes, such as cathepsin B, D, or L, into the cytosol. Lysosomal proteases activate caspases136 and cleave the Bcl-2 family member, Bid to a form that causes cytochrome c release from mitochondria.137

Consequently, lysosomal leakage, even in the absence of A2E, may cause mitochondrial dysfunction leading to release of cytochrome c, activation of caspase-9, and induction of apoptosis.138-140 A recent study found that exposure of ARPE-19 cells to 5 µM HNE causes lysosomal permeabilization, cathepsin B release into the cytoplasm, and apoptotic death.141 Our finding that HOHA-lactone induces ARPE-19 cell lysosomal permeabilization indicates that this biological activity is dependent on the α,β- unsaturated aldehyde functionality common to HNE and HOHA lactone, and that the γ- hydroxyl functionality in HNE is not essential. HHE, an α,β-unsaturated aldehyde homologue of HNE that is coproduced with HOHA-PC during oxidative fragmentation of

DHA-PC (Fig. 3.1), is also likely to cause lysosomal permeabilization in analogy with the effects of HNE and HOHA lactone (Fig. 3.16).

3.3.7 HOHA lactone and A2E can synergistically induce apoptosis in RPE cells.

Exposure of RPE cells to A2E results in accumulation of more than 90% in the lysosomes,54 and any A2E released from the lysosome into the cytosol accumulates specifically in the mitochondria.142 The induction of lysosomal membrane permeability by HOHA lactone, HHE and HNE might promote release of A2E from the lysosome that

117 then specifically targets the outer mitochondrial membrane and initiates apoptosis (Fig.

3.16). Thus, we postulate that A2E and a family of α,β-unsaturated aldehyde products of lipid oxidative cleavage contribute synergistically to cause light-induced apoptosis of

RPE cells. We postulate that the α,β-unsaturated aldehydes are especially effective in disrupting lysosomal membranes while A2E is especially effective in disrupting mitochondrial membranes, presumably as a consequence of the favorable interaction of the negatively charged mitochondrial membrane and the positively charged A2E molecule. A2E photosensitization can produce reactive oxygen species (ROS) that promote the oxidative fragmentation of membrane phospholipids to generate α,β- unsaturated aldehydes.

Figure 3.16. Postulated synergistic contributions of A2E and a family of α,β-unsaturated aldehyde products of lipid oxidative cleavage to light-induced apoptosis of RPE cells.

3.3.8 HOHA lactone causes senescence of RPE cells.

Stress-induced premature cellular senescence143 is one mechanism through which oxidative stress is postulated to contribute to the pathogenesis of AMD.144-146 Exposure to a variety of stresses, such as oxidizing or DNA damaging agents can induce cellular

118 senescence that corresponds to a permanent loss of the ability to proliferate, resistance to apoptosis and an altered pattern of gene expression. Hydrogen peroxide, an endogenous inducer of oxidative stress, which is produced in the retina under photo-oxidation conditions, was previously shown to induce senescence in ARPE-19 cells.72 Furthermore, we previously showed that low concentrations ( 0.1 − 1.0 μM) of HOHA lactone induce oxidative stress in ARPE-19 cells.73 Therefore, we hypothesized that HOHA lactone- induced oxidative stress could elicit a senescence response in RPE cells. We now find that treatment of ARPE-19 cells with a sub-lethal concentration of HOHA lactone produced elevated levels of senescence associated-β-galactosidase (SA-β-Gal) activity.

Since oxidative stress promotes lipid oxidation that produces HOHA-PC and HOHA lactone, even small amounts of these endogenously photo-generated electrophiles can contribute to chronic generation of more HOHA leading to senescence in RPE cells and contributing to the pathogenesis of AMD.

119

3.4 Conclusions

Previously, we discovered CEP58, a biologically active posttranslational protein modification that is abundant in AMD retinas and contributes to the pathogenesis of

AMD. Light induces oxidative cleavage of DHA phospholipids to generate the HOHA precursor of CEP in vivo. The level of HOHA-PC reaches 1.5 times that of residual

DHA-PC after 1 h exposure of dark adapted albino rats to bright (~1200 lux; 200 microwatts/cm2) green light.37 CEP accumulates mainly in two thin regions of the retina where DHA is concentrated, the photoreceptor outer segments and RPE cells.34

Previously, we also found that GSH in RPE cells traps HOHA lactone leading to the production of an unreactive reduced HOHA lactone-GSH end product, DHHA-GSH.

In the present study, model systems were developed and used to demonstrate that

HOHA and CEP can be generated by light-induced oxidative cleavage of DHA in RPE cells, and to explore possible contributions of this biochemistry to pathology induced in the retina upon exposure to light. In a cell-free model of light-induced oxidative retinal damage, we irradiated bovine retina supernatants in phosphate buffer and observed the production of HOHA lactone-GSH adducts. The same products were photo-generated in

ARPE-19 cells that were supplemented with DHA. Additional doping with the lipofuscin fluorophore A2E expanded the spectral range of ARPE-19 cell photosensitivity to longer wavelengths and nearly doubled the levels of HOHA lactone-GSH adducts produced.

However, presumptive evidence is presented that the accumulation of lipofuscin fluorophores is not essential to promote photo-induced oxidation of DHA in RPE cells.

Such generation of lipid-derived reactive electrophilic photo-oxidation products, e.g.,

HOHA lactone, and their derivatives, e.g., CEP, may be especially important in the early

120 stages of AMD pathogenesis before the accumulation of lipofuscin that characterizes the advanced stages of the disease. This conclusion is consistent with the clinical observation that fundus autofluorescence, which is primarily ascribable to A2E, correlates with advanced RPE alteration in AMD retinas, but not early RPE changes, as seen by histologic examination.20 A clinical study that characterized geographic atrophy progression in patients with AMD concluded that fundus autofluorescence patterns may be a consequence of enlarging atrophy and that the role of lipofuscin in promoting geographic atrophy growth is modest at best.19 Rather than being an essential driver of

RPE death and geographic atrophy, fundus accumulation of A2E seems to be a consequence of retinal atrophy.

Although we found that HOHA alone can foster loss of mitochondrial membrane potential, an additional mechanism is needed to account for the massive A2E-dependent photo-induced loss of mitochondrial membrane potential that we observed in DHA-rich

ARPE-19 cells loaded with A2E versus those without A2E. A possible mechanism is based on our discovery that low micromolar concentrations of HOHA lactone disrupt lysosomal membrane integrity in ARPE cells. A2E enters RPE cells in lysosomes and targets mitochondria upon leakage from lysosomes. We postulate that by disrupting lysosomal membranes, HOHA lactone and possibly other α,β-unsaturated aldehyde products of lipid oxidation facilitate entry of A2E into the cytosol that is required for it to attack mitochondria. A2E is especially effective in disrupting mitochondrial membranes, presumably as a consequence of the favorable interaction of the negatively charged mitochondrial membrane and the positively charged A2E molecule (Fig. 3.16). Thus,

A2E and possibly other α,β-unsaturated aldehyde products of lipid oxidative cleavage

121 could contribute synergistically to cause light-induced apoptosis of RPE cells. A2E can modestly (~2x) increase the yield of photo-induced HOHA production, and HOHA lactone can facilitate the escape of A2E from lysosomes leading to mitochondrial damage and apoptosis. Finally, the discovery that HOHA lactone induces RPE cell senescence provides an additional potential contribution of oxidative DHA damage to the pathogenesis of AMD.

122

3.5 Experimental Procedures

Materials. Dulbecco’s modified Eagle’s cell culture medium and Ham’s F12 cell culture medium F-12 (1:1 mixture, DMEM/F12), Dulbecco’s phosphate-buffered saline

(DPBS), Hank’s balanced salt solution (HBSS), 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) were purchased from Fisher Scientific (Pittsburgh,

PA). Fetal bovine serum (FBS) was from Equitech-Bio, Inc. (Kerrville, TX). Texas Red-

X Goat anti-Rabbit IgG (H+L) cross-adsorbed secondary antibody (T-6391) was from

ThermoFisher Scientific (Waltham, MA). Flash Phalloidin™ Green 488 was from

Biolegend (San Diego, CA). β-NADPH and docosahexaenoic acid (DHA) were obtained from Cayman Chemical (Ann Arbor, MI). All other chemicals and reagents, including L- glutathione (reduced), glutathione reductase (250 units/mL), 5,5’-dithiobis(2-nitrobenzoic acid) (DTNB), and all-trans retinal were purchased from Sigma-Aldrich (St. Louis, MO).

4-Hydroxy-7-oxohept-5-enoic acid (HOHA) lactone,147 HOHA lactone-GSH, HOHA

13 15 lactone-(glycine- C2, N)GSH, 4,7-dihydroxyhept-5-enoic acid (DHHA)-GSH, i.e.,

13 15 reduced HOHA lactone-GSH, and DHHA lactone-(glycine- C2, N)GSH were

38 synthesized as described previously. MitoOct, MitoAzide, MitoClick, d30-MitoClick and Tet were synthesized as reported elsewhere.64 A polyclonal rabbit anti-CEP antibody was raised and characterized as described previously.34 Bovine retina was obtained from

InVision BioResources (Seattle, WA). The Pierce 660 nm assay was obtained from

ThermoFisher Scientific (Waltham, MA) and used to determine a protein concentration in the lysates in accordance to the manufacture’s manual.

General Methods. NMR spectra were acquired on a 500 MHz Bruker Ascend Avance

III HDTM equipped with a Prodigy ultra-high sensitivity multinuclear broadband

123

CryoProbe operating at 500 and 125 MHz for 1H and 13C, respectively. They were referenced internally according to residual solvent signals. All ESI mass spectra were obtained from a Thermo Finnigan LCQ Deca XP (ThermoFisher Scientific, Waltham,

MA). High-performance liquid chromatography (HPLC) was performed on a Shimadzu

UFLC system equipped with a 5 μm Phenomenex Luna C-18 column (Torrance, CA).

Flash column chromatography was performed on 230−400 mesh silica gel supplied by

Sigma-Aldrich (St. Louis, MO) with ACS grade solvent. Rf values are quoted for plates with thickness of 0.25 mm. The plates were visualized with iodine, UV, and phosphomolybdic acid reagents. All reactions were carried out under an argon atmosphere. All reagents were obtained commercially unless otherwise noted. Reactions were performed using glassware that was oven-dried at 120 °C. Air- and moisture sensitive liquids and solutions were transferred via syringe or stainless-steel cannula.

Cell culture. The cell line ARPE-19 (ATCC; CRL-2302) derived from spontaneously arising retinal pigment epithelia of a healthy person148 was obtained from the American

Type Culture Collection (Manassas, VA). The stock cells were grown on 100-mm dishes in a humidified CO2 incubator at 37 °C and 5% CO2 in Ham’s F12 medium and

Dulbecco’s modified Eagle’s medium (DMEM) (50:50 ratio), containing L-glutamine and 10% heat-inactivated FBS. Cells were trypsinized and passaged every 2-3 days. Cell passages 20−30 were used.

Microscopy. Images were collected on a Leica DMI 6000B inverted fluorescence microscope (Leica Microsystems, Wetzlar, Germany) using a Retiga EXI camera

(QImaging, Vancouver, British Columbia). Image analysis was performed using

MetaMorph Imaging Software (Molecular Devices, Downington, PA).

124

Synthesis. The synthesis of A2E was performed according to the previous report.44 In brief, A2E was synthesized by combining all-trans retinal (100 mg, 2 equiv) and ethanolamine (7 mg, 1 equiv) in ethanol (10 mL) solution with 9.3 μL of acetic acid (1 equiv). The reaction mixture was allowed to stir for 3 days at room temperature in the dark. At the end of the reaction, the mixture was concentrated on a rotary evaporator, the residue was purified by silica gel column chromatography running with methanol

(MeOH):dichloromethane (CH2Cl2) (5:95) as eluent, further elution with

MeOH:CH2Cl2:trifluoroacetic acid (TFA) (8:92:0.001) and then the fractions containing the bulk of the crude A2E were combined and further purified by HPLC (Luna C18, 4.6 x

150 mm, 85–96% H2O/MeOH + 0.1% TFA for 20 min, 1.0 ml/min flow, monitor wavelength: 430 nm).

Irradiation of bovine retina extract. Two bovine retinas were homogenized in 10 mM pH 7.4 sodium phosphate buffer (1 mL) on ice for 1 min and the resulting homogenate was centrifuged (14,000 g, 10 min, 4 °C). The supernatant was transferred to a 1.5 mL microcentrifuge tube and centrifuged again (14,000 g, 10 min, 4 °C). The last supernatant was used for irradiation after dilution to a protein concentration of 2 mg/mL.

3 mL this retina extract was transferred to a quartz cuvette resting on ice and irradiated 10 cm from the light sources in a UV Stratalinker 1800 equipped with a bank of either five black (1 mW/cm2; F8T5/BL, wavelength range 350~400 nm peak wavelength 365 nm), warm white (7 mW/cm2; F8T5/WW, 3000K, wavelength range 400~700 nm, peak wavelength 400, 430, 480, 530, 590, 680 nm) or cool white (5 mW/cm2; F8T5/CW,

4100K, wavelength range 400~700 nm, peak wavelength 400, 430, 480, 530, 590, 680

125 nm) light tubes. Aliquots (300 μL) of the reaction mixture were withdrawn at each time point and incubated in the dark at 23 °C for 1 h before snap-freezing on dry ice.

Irradiation of ARPE-19 cells. ARPE-19 cells (75,000 or 200,000 cells/dish) were seeded in a 35 mm or 60 mm dish in 2 or 3 mL of complete DMEM/F12 cell culture medium supplemented with 10% FBS, respectively, and allowed to attach to the cell culture plates in a humidified CO2 incubator at 37 °C and 5% CO2. After 3 days of incubation, the cells were incubated with 1.5 mL or 2 mL of complete DMEM/F12 cell culture medium supplemented with 10% FBS containing 50 μg/mL DHA for another 2 days followed by incubation with 10 μM A2E in basal DMEM/F12 cell culture medium for 24 h under dimmed light conditions. The cells were starved in fresh basal DMEM/F12 cell culture medium for another 24 h before being irradiated as described above for various times in 1 mL or 2 mL HBSS, respectively.

HOHA lactone treatment. As described previously147, ARPE-19 cells (10,000 cells/ per well) were seeded into a 96-well flat bottom plate in 200 μL of complete DMEM/F12 medium supplemented with 10% FBS and allowed to attach to culture plates in a humidified CO2 incubator at 37 °C and 5% CO2. After the cells reached ~80% confluence, they were starved in 200 μL of basal DMEM/F12 cell culture medium for 4−5 h. Then the cell culture medium was aspirated followed by the addition of DMEM/F12 (180 μL) and 10x solutions of HOHA lactone in DPBS (20 μL) were added to create 0 to 40 μM final concentrations of HOHA lactone, in 6 replicate wells for each concentration, followed by 24 h incubation in a humidified CO2 incubator at 37 °C and 5% CO2.

MTT cell viability assays. After treatment with HOHA lactone or irradiation, the cell culture medium was aspirated from each well and the cells were incubated for 2 h at 37

126

°C with 10x solution of filter-sterilized MTT solution (5 mg/mL in DPBS) into the medium. The medium was then aspirated from each well, dimethyl sulfoxide (DMSO) was added to each well (200 μL for a 96 well plate or 1.5 mL for a 35 mm dish) to dissolve water-insoluble intracellular formazan crystals by carefully pipetting the contents of the wells. The optical density (OD) of formazan solutions at λ = 540 nm were measured with a plate reader (Spectramax M2, Molecular Devices, San Jose, CA) with a reference wavelength set λ = 670 nm.

Resazurin (Alamar Blue) cell viability assay.149 ARPE-19 cells (10,000 cells/ per well) were seeded in a 96-well flat bottom plate in 200 μL of complete DMEM/F12 cell culture medium supplemented with 10% FBS and allowed to attach to culture plates in a humidified CO2 incubator at 37 °C and 5% CO2. Once the cells reached ~80% confluence, they were starved in 200 μL of basal DMEM/F12 cell culture medium for 4−5 h. The cell culture medium was then aspirated followed by the addition of 180 μL of DMEM/F12 and 20 μL of 10x stock solutions of HOHA lactone in DPBS to create 0 to 40 μM final concentrations of HOHA lactone (6 replicate wells for each concentration) followed by

24 h incubation in a humidified CO2 incubator at 37 °C and 5% CO2. The medium was aspirated from each well and the cells were incubated for 4 h at 37 °C with a mixture of

10 μL of filter-sterilized Resazurin stock solution (440 μM in DPBS) with 90 μL of

DMEM/F12 cell culture medium. Fluorescence was finally measured by a fluorescence microplate reader (Spectramax M2, Molecular Device) set at λ Ex/Em = 545/595 nm.

JC-10 assay.65, 150 The assay was performed by the method described previously 65 with slight modifications. Briefly, after HOHA lactone treatment or 24 h after the execution of the standard light exposure model protocol described above, to ARPE-19

127 cells in a 96-well flat bottom plate in 100 μL of basal DMEM/F12 cell culture medium was added 100 μL of 5 μg/mL stock solutions of JC-10 in DPBS to establish 2.5 μg/mL final concentrations of JC-10. After subsequent incubation in a humidified CO2 incubator for 30 min at 37 °C and 5% CO2, the fluorescence was immediately measured with a fluorescence microplate reader (Spectramax M2, Molecular Device) set at λEx/Em =

490/525 nm (cut off at 515 nm) for the green monomer and 540/590 nm (cut off at 570 nm) for the red aggregate. Changes in mitochondrial membrane potential were derived from the green/red fluorescence ratio.

MitoClick assay. The assay was performed using a previously described method64 with slight modifications. Briefly, after HOHA lactone treatment or 24 h after the execution of standard light exposure model protocol, to ARPE-19 cells in a 60 mm dish in 2 mL of basal DMEM/F12 cell culture medium was added MitoOct and MitoAzide both to 5 μM final concentration followed by 3 h incubation in a humidified CO2 incubator at 37 °C and 5% CO2. After a cell culture medium aspiration, 1 mL of 50 μM

3-phenyl-1,2,4,5-tetrazine (Tet) in DPBS was added to each dish followed by incubation for 5 min at 23 °C followed by washing with 1 mL DPBS. The cells were then scraped into a 1.5 mL microcentrifuge tube and pelleted by centrifugation (16,000 g, 3 min, 4 °C).

The supernatant was discarded and the pellet was snap-frozen on dry ice. For analysis, the pellet was resuspended in 250 μL of 100% acetonitrile (ACN) with 0.1% formic acid

(FA) and 50 μM Tet, spiked with 50 pmol of d30-MitoClick and the mixture was water- sonicated for 5 min. After the sample was carefully vortexed for 2 min and centrifuged

(16,000 g, 15 min, 4 °C), the resulting solution was filtered into a fresh tube and 200 μL of each sample was transferred to another fresh tube and dried by Speed Vac. The sample

128 was then resuspended in 200 μL of 20% ACN with 0.1% FA, sonicated for 5 min, vortexed for 1 min and centrifuged (16,000 g, 10 min, 4 °C). The supernatant was transferred to a fresh tube and diluted 10 times with 20% ACN with 0.1% FA before LC-

MS/MS analysis. The LC-MS/MS system for the analysis consisted of a Thermo

Finnigan LCQ Deca XP with a Surveyor LC system. Liquid chromatography was performed using a Luna 5 μ Phenyl-Hexyl column (1 x 50 mm, 5 μm) with a Phenyl-

Hexyl guard column (2 x 4 mm) (both from Phenomenex). The mobile phase consisted of

0.1% FA in water (buffer A) and 95% ACN/0.1% FA (buffer B) delivered as a linear gradient as follows: 0-2 min, 5% B; 2-3 min, 5-25% B; 3-5 min, 25-75% B; 5-7 min, 75-

100% B; 7-10 min 100% B; 10-12 min, 100-5% B; 12-20 min, 5% B. The flow rate was

50 μL/min and a 10 μL volume was injected. Electrospray ionization mass spectrometry in the positive ion mode was employed to measure MitoClick product. The instrument parameters were as follows: the heated capillary temperature was 300 °C, the source voltage 4.5 kV, and the capillary voltage 11.00 V. Nitrogen was used as sheath and auxiliary gas. All data were processed with the Qual browser in Xcalibur software.

MS/MS experiments were performed by selecting an ion with an isolation width of 2 m/z.

See Table 3.1 for detailed mass spectrometer parameters and collision energy for each ion.

The changes in mitochondrial membrane potential were calculated using a MitoClick calibration curve built from authentic and labelled standard and normalized by the total protein concentration of the precipitated protein obtained from acetonitrile extraction.

Table 3.1. Optimized mass spectrometer parameters as well as the selected ions and collision energies for quantitation of MitoClick product in ARPE-19 mitochondria- enriched cell lysate. Analytes Parent ion Scan range Product ion Collision energy % MitoClick, product 415.4 200.0~500.0 364.1 30 d30-MitoClick, product 430.5 200.0~500.0 379.2 30 129

Quantification of Total Intracellular GSH in ARPE-19 Cells.151 The assay was performed using the method described previously.151 Aliquots (20 μL) of ARPE cell lysates from light irradiation time-course studies were assayed to determine total intracellular GSH levels using a 96-well microplate format described earlier.151 In these experiments, all of the reagents were prepared in 0.1 M potassium phosphate buffer with

5 mM EDTA disodium salt, pH 7.5 (KPE buffer). Briefly, 20 μL of KPE buffer, GSH standards, or samples were added to the respective microplate wells, followed by the addition of 120 μL of a freshly prepared 1:1 mixture of DTNB (2 mg/3 mL) and glutathione reductase (10 U/3 mL). Then, 60 μL of NADPH (2 mg/3 mL) was added and the plate was mixed well. The absorbance was read immediately at λ = 412 nm in a microplate reader (Spectramax M2, Molecular Devices). Measurements were taken every

20 s for 5 min (15 readings in total from 0–300 s). The total GSH concentration in the samples was determined by linear regression to calculate the values obtained from a standard curve.

Measurement of cell senescence associated β-galactosidase activity assay. The assay was performed using the method described previously.152 ARPE-19 cells (4.5 x 104 cells/ per well) were plated on an 8-chamber well (Lab-Tek II Chamber Slide System,

Nunc, Rochester, NY) in DEME/F12 with 10% FBS and incubated at 37 °C and 5% CO2.

On the following day, the cells were starved in basal DMEM/F12 medium for 12−16 h and then were treated with 5 μM HOHA lactone every 12 h once, twice or 3 times. After

HOHA lactone treatments, the cells were incubated in the DEME/F12 with 1%FBS for 5 days (total treatment time: 7 days). After the chambers were aspirated and washed twice

130 with DPBS, the cells were fixed with 3% formaldehyde in DPBS for 5 min. After washing twice with DPBS, the cells were incubated at 37 °C without CO2 overnight in staining solution (40 mM citric acid/pH 6.0 sodium phosphate buffer, 1 mg/mL 5-bromo-

4-chloro-3-indolyl-β-D-galacto-pyranoside (X-gal), 5 mM potassium ferrocyanide, 5 mM ferricyanide, 150 mM sodium chloride, and 2 mM magnesium chloride). All images were acquired with a Leica DMI 6000 B inverted fluorescent microscope under bright field and phase contrast combined mode using a Retiga EXI camera. The images were taken at

10x and 20x magnification. Image analysis was performed using ImageJ software and

10x images were used for quantitation of staining area.

Acridine Orange staining of ARPE-19 cells. ARPE-19 cells (7,500 cells/ per well) were plated on an 8-chamber well (Lab-Tek II Chamber Slide System, Nunc, Rochester,

NY) in DEME/F12 with 10% FBS and then incubated at 37 °C in 5% CO2 for three days until they reach 70-75% confluence. They were then starved in basal DMEM/F12 medium for 12−16 h and the basal DMEM/F12 medium was then changed to Phenol

Red-free medium immediately prior to HOHA lactone treatment. After incubation with 0-

10 μM HOHA lactone for 24 h, the medium was replaced with 1 μg/mL acridine orange in DMEM/F12 basal medium. After incubation at 37 °C in 5% CO2 for 30 min, the chambers were aspirated and washed twice with DPBS. The cells were fixed with 3% formaldehyde in DPBS for 15 min. After washing twice with DPBS, slides were mounted in DAPI Fluoromount-G (Southern Biotech, Birmingham, AL). All images were acquired with a Leica DMI 6000 B inverted fluorescence microscope using a Retiga EXI camera.

An FITC filter set was used for green fluorescence and a TX-red filter set for red fluorescence. Images were taken at 10x magnification.

131

Detection of CEP in ARPE-19 cells. ARPE-19 cells (1 x 104 cells/ per well) were plated on an 8-chamber well (Lab-Tek II Chamber Slide System, Nunc, Rochester, NY) in the DEME/F12 with 10% FBS and incubated at 37 °C in 5% CO2 for three days. After

10 μM HOHA lactone treatment or 24 h after the execution of the standard light exposure model protocol, the chambers were aspirated and washed twice with DPBS. The cells were fixed with cold acetone (-20 °C) for 12 min at -25 °C. After washing with PBST 3 times, the slides were blocked with 3% BSA in PBST for 1 h at 23 °C. The cells were probed with rabbit anti-CEP polyclonal antibody (in 3% BSA in PBST, 18 ng/mL) overnight at 4 °C, and washed exhaustively with PBST the next day. The slides were treated with Texas Red-X goat anti-rabbit antibody (1:100 dilution in 3% BSA in PBST;

T-6391, ThermoFisher Scientific, Waltham, MA) overnight at 4 °C, washed exhaustively with PBST and then aspirated. The slides were further incubated with 1:20 diluted in PBS stock solution of Flash Phalloidin™ Green 488 (Biolegend, 0.2 U/μL) in the dark for 30 min at 23 °C protected from light. After washing with PBST, slides were mounted in

DAPI Fluoromount-G (Southern Biotech, Birmingham, AL). All images were acquired with a Leica DMI 6000 B inverted fluorescent microscope using a Retiga EXI camera.

Image analysis was performed using Metamorph imaging software (Molecular Devices,

Downington, PA). The images were taken at 20x magnification.

HOHA lactone GSH adduct extraction and quantitation by LC-MS/MS.

From bovine retina extract. To an aliquot (300 μL) of light exposed retina extract or an aliquot of retina extract kept in the dark, was added dichloromethane (225 μL), methanol (300 μL) spiked with 250 fmol of isotopically labelled HOHA lactone-GSH and labeled DHHA lactone-GSH. The mixture was vortexed vigorously for 1 min and

132 then centrifuged (9,000 g, 10 min, 4 °C). The upper aqueous layer of the resulting three layers (aqueous/protein/DCM) was collected in a 1.5 mL Eppindorff LoBind tube (Fisher

Scientific, Pittsburgh, PA), and to the remaining layers were then added 250 μL of 0.2%

FA/H2O. The mixture was vortexed and then centrifuged (9,000 g, 10 min, 4 °C). The new upper aqueous layer was combined with the first aqueous layer, and dried to ~50 μL by SpeedVac. The dried sample was resuspended in 600μL with 0.2%FA/H2O, sonicated

10 min, vortexed for 1 min and then loaded onto the first solid phase extraction (SPE) column: Strata X-C spin column, spin column (Nest group Inc., Southborough, MA) packed with 30 mg of Strata X-C material (Phenomenex, Torrance, CA). See Table 3.2 for SPE purification workflow.

Table 3.2. Strata X-C spin column 1st SPE purification workflow for HOHA/DHHA lactone-GSH derivatives from bovine retina extract.

1. Conditioning 2. Sample loading 3. Wash 4. Elution Centrifuge 2000 rpm, 1min 2000 rpm, 2min 2000 rpm, 2min 2000 rpm, 2min

100% MeOH, Sample in 0.2% FA H2O, 0.2% FA H2O, 20% ACN/H2O + 50mM KCl + 1 0.5 mL *2 0.6 mL 0.5 mL *2 10mM NH4OAc, 0.333mL*5

0.2% FA H2O, Recovered flow-through, 0.1% FA H2O, 2 0.5 mL *2 0.6 mL 0.5 mL *2 Incubation no 10 min no 5 min each time

The eluates from the Strata X-C spin column were combined and diluted 4 times with

0.2% FA/H2O before loading onto the second SPE column, a Hypercarb cartridge (50 mg/1 mL, ThermoFisher Scientific, Waltham, MA). See Table 3.3 for SPE purification workflow.

Table 3.3. Hypercarb 2nd SPE purification workflow for HOHA/DHHA lactone-GSH derivatives from bovine retina extract.

1. Conditioning 2. Sample loading 3. Wash 4. Elution

Strata X-C diluted eluent, 5% ACN/ 0.2% 30% ACN/ 0.2% FA H2O, 1 100% ACN, 1 mL *2 7 mL FA H2O, 1 mL *2 0.6 mL

2 0.2% FA H2O, 1 mL *2

133

The Hypercarb SPE eluate was dried to ~50 μL by SpeedVac and then reconstituted to

180 μL with 0.2%FA/H2O before LC-MS/MS injection. Chromatographic separation was achieved with a Waters Acquity UPLC system (Waters, Milford, MA) equipped with a

Hypercarb column (1.0 mm i.d. × 100 mm length, 3 μm, ThermoFisher Scientific,

Waltham, MA). Mobile phase A consisted of HPLC grade water containing 0.2% FA.

Mobile phase B was HPLC grade acetonitrile containing 0.2% FA. Injection volume was

75 μL (PLNO, partial loop with needle overfill). The total run time was 40 min, the flow rate was 40 μL/min during elution and the linear elution gradient was from 5% to 95% solvent B in 9 min (see Table 3.4 for details).

Table 3.4. HPLC gradient used for the determination of HOHA/DHHA lactone-GSH derivatives in light exposed bovine retina extract.

Time (min) Flow Rate (mL/min) %A %B Curve Divert Initial 95.0 5.0 Waste 6.00 95.0 5.0 6 0.040 6.10 95.0 5.0 6 Detector 15.00 5.0 95.0 6 15.10 5.0 95.0 6 Waste 19.00 5.0 95.0 6 19.10 95.0 5.0 6 23.00 0.120 5.0 95.0 6 27.00 5.0 95.0 6 27.10 95.0 5.0 6 35.00 95.0 5.0 6 35.10 95.0 5.0 6 0.040 40.00 95.0 5.0 6

The analytes were detected with an API 3000 triple quadrupole electrospray mass spectrometer (AB Sciex, Framingham, MA) operated in the positive ion mode in the multiple reaction monitoring (MRM) scan mode. The source temperature was maintained at 300 °C, the heating gas (N2) was maintained at 3.5 L/min, nebulizer gas was set at 10, curtain gas was set at 10 and CAD was set at 8. Optimized parameters for detecting each analyte were determined using authentic samples. MS scans time was set at 100 msec for

134 one cycle. The optimum collision energy and other parameters were determined for each individual analyte (see Table 3.5 for details).

Table 3.5. The optimized mass spectrometer parameters as well as the MRM transitions and collision energies for quantitation of HOHA/DHHA lactone-GSH derivatives in bovine retina extract. Analytes Q1 DP FP Q3 CE CXP 319.1 21.0 18.0 HOHA lactone-GSH 448.1 61.0 370.0 301.1 27.0 14.0 321.1 23.0 16.0 DHHA lactone-GSH 450.2 61.0 370.0 286.1 31.0 14.0

13 15 322.1 21.0 18.0 HOHA lactone-(glycine- C2, N)GSH 451.1 61.0 370.0 304.1 27.0 16.0

13 15 324.1 23.0 16.0 DHHA lactone-(glycine- C2, N)GSH 453.2 61.0 370.0 289.1 29.0 14.0

From ARPE-19 cells. After one hour of irradiation followed by one hour of incubation in a humidified CO2 incubator at 37 °C and 5% CO2, the cells were scraped into a 5 mL Eppendorf tube and centrifuged (1000 RPM, TX-400 rotor, 4 °C, 5 min), the supernatant (extracellular medium, 2 mL) was loaded onto a Strata X-33u SPE cartridge

(Phenomenex). See Table 3.6 for SPE purification workflow. The Strata X-33u SPE eluent was dried to ~10 μL on a Speedvac and was reconstituted to 200 μL with 0.2%

FA/H2O before LC-MS/MS injection.

Table 3.6. Strata X-33u spin column SPE purification workflow for HOHA/DHHA lactone-GSH derivatives from ARPE-19 extracellular medium.

1. Conditioning 2. Sample loading 3. Wash 4. Elution

100% MeOH, Extracellular medium, 0.1% FA H2O, 50% ACN/ 0.1% FA H2O, 1 1 mL 2 mL 1 mL 0.6 mL

0.1% FA H2O, 0.1% FA H2O, 2 1 mL 0.3 mL rinse

Chromatographic separation was carried out with a Surveyor LC system equipped with a Hypersil GOLD C18 column (2.0 mm i.d. × 150 mm length, 5 μm, ThermoFisher

Scientific, Waltham, MA). Mobile phase A consisted of HPLC grade water containing

135

0.1% FA. Mobile phase B was HPLC grade acetonitrile containing 0.1% FA. ESI mass spectrometry was performed with a Thermo Finnigan LCQ Deca XP instrument in the positive ion mode using nitrogen as the sheath and auxiliary gas. The heated capillary temperature was 300 °C, the source voltage was 5 kV, and the capillary voltage was

11.00 V. All data were processed with the Qual browser in Xcalibur software

(ThermoFisher Scientific, Waltham, MA). For analysis of HOHA lactone-GSH or DHHA lactone-GSH, the injection volume was 50 μL, the total run time was 29 min, the flow rate was 200 μL/min and linear gradient used for elution was from 5% to 95% solvent B in 9 min (see Table 3.7 for details). MS/MS experiments were performed by selecting an ion with an isolation width of 2 m/z. See Table 3.8 for detailed mass spectrometer parameters and collision energy for each ion.

Table 3.7. HPLC gradient used for the determination of HOHA/DHHA lactone-GSH derivatives in extracellular medium from light exposed in ARPE-19 cells.

Time %A %B Initial 95.0 5.0 6.00 95.0 5.0 6.10 70.0 30.0 15.00 5.0 95.0 20.00 5.0 95.0 21.00 95.0 5.0 29.00 95.0 5.0

Table 3.8. Optimized mass spectrometer parameters as well as the selected ions and collision energies for quantitation of HOHA/DHHA lactone-GSH derivatives in ARPE- 19 extracellular medium. Analytes Parent ion Scan range Product ion Collision energy % GSH-HOHA lactone-GSH 448.1 200~400 301.1 40.0 DHHA lactone-GSH 450.1 200~400 321.1 26.0 13 15 DHHA lactone-(glycine- C2, N) GSH 453.1 200~400 324.1 26.0

136

Statistical Analysis. Unless specified in the text or legends, comparisons were made using one-way ANOVA followed by Holm-Sidak’s post-hoc multiple comparison test. If the normality test failed (Fig. 3.6C and Fig. 3.15), the Dunn’s rank test was used.

Statistical significance is shown as follows: *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Data are presented as mean ± standard deviation (SD).

137

3.5 References

(1) Beatty, S., Koh, H.-H., Phil, M., Henson, D., and Boulton, M. (2000) The Role of

Oxidative Stress in the Pathogenesis of Age-Related Macular Degeneration. Surv.

Ophthalmol. 45, 115-134.

(2) Wang, Y., Shen, D., Wang, V. M., Yu, C. R., Wang, R. X., Tuo, J., and Chan, C.

C. (2012) Enhanced apoptosis in retinal pigment epithelium under inflammatory

stimuli and oxidative stress. Apoptosis 17, 1144-1155.

(3) Nowak, J. Z. (2013) Oxidative stress, polyunsaturated fatty acids-derived

oxidation products and bisretinoids as potential inducers of CNS diseases: focus

on age-related macular degeneration. Pharmacol. Rep. 65, 288-304.

(4) de Jong, P. T. (2006) Age-related macular degeneration. N. Engl. J. Med. 355,

1474-1485.

(5) Yang, D., Elner, S. G., Clark, A. J., Hughes, B. A., Petty, H. R., and Elner, V. M.

(2011) Activation of P2X receptors induces apoptosis in human retinal pigment

epithelium. Invest. Ophthalmol. Vis. Sci. 52, 1522-1530.

(6) Flores-Bellver, M., Bonet-Ponce, L., Barcia, J. M., Garcia-Verdugo, J. M.,

Martinez-Gil, N., Saez-Atienzar, S., Sancho-Pelluz, J., Jordan, J., Galindo, M. F.,

and Romero, F. J. (2014) Autophagy and mitochondrial alterations in human

retinal pigment epithelial cells induced by ethanol: implications of 4-hydroxy-

nonenal. Cell Death Dis. 5, e1328.

(7) Delori, F. C., Goger, D. G., and Dorey, C. K. (2001) Age-related accumulation

and spatial distribution of lipofuscin in RPE of normal subjects. Invest.

Ophthalmol. Vis. Sci. 42, 1855-1866.

138

(8) Holz, F. G., Bellmann, C., Margaritidis, M., Schutt, F., Otto, T. P., and Volcker,

H. E. (1999) Patterns of increased in vivo fundus autofluorescence in the

junctional zone of geographic atrophy of the retinal pigment epithelium associated

with age-related macular degeneration. Graefes Arch. Clin. Exp. Ophthalmol. 237,

145-152.

(9) von Ruckmann, A., Fitzke, F. W., and Bird, A. C. (1997) Fundus

autofluorescence in age-related macular disease imaged with a laser scanning

ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 38, 478-486.

(10) Wolf, G. (2003) Lipofuscin and macular degeneration. Nutr. Rev. 61, 342-346.

(11) Rodriguez-Muela, N., Koga, H., Garcia-Ledo, L., de la Villa, P., de la Rosa, E. J.,

Cuervo, A. M., and Boya, P. (2013) Balance between autophagic pathways

preserves retinal homeostasis. Aging Cell 12, 478-488.

(12) Kliffen, M., van der Schaft, T. L., Mooy, C. M., and de Jong, P. T. (1997)

Morphologic changes in age-related maculopathy. Microsc. Res. Tech. 36, 106-

122.

(13) Katz, M. L. (2002) Potential role of retinal pigment epithelial lipofuscin

accumulation in age-related macular degeneration. Arch. Gerontol. Geriatr. 34,

359-370.

(14) Gliem, M., Muller, P. L., Finger, R. P., McGuinness, M. B., Holz, F. G., and

Charbel Issa, P. (2016) Quantitative Fundus Autofluorescence in Early and

Intermediate Age-Related Macular Degeneration. JAMA Ophthalmol 134, 817-

824.

139

(15) Ciccone, L., Lee, W., Zernant, J., Tanaka, K., Schuerch, K., Tsang, S. H., and

Allikmets, R. (2017) Hyperreflective Deposition in the Background of Advanced

Stargardt Disease. Retina.

(16) Dysli, C., Wolf, S., Hatz, K., and Zinkernagel, M. S. (2016) Fluorescence

Lifetime Imaging in Stargardt Disease: Potential Marker for Disease Progression.

Invest. Ophthalmol. Vis. Sci. 57, 832-841.

(17) Rozanowska, M., and Sarna, T. (2005) Light-induced damage to the retina: role of

rhodopsin chromophore revisited. Photochem. Photobiol. 81, 1305-1330.

(18) Feeney-Burns, L., Hilderbrand, E. S., and Eldridge, S. (1984) Aging human RPE:

morphometric analysis of macular, equatorial, and peripheral cells. Invest.

Ophthalmol. Vis. Sci. 25, 195-200.

(19) Biarnes, M., Arias, L., Alonso, J., Garcia, M., Hijano, M., Rodriguez, A., Serrano,

A., Badal, J., Muhtaseb, H., Verdaguer, P., and Mones, J. (2015) Increased

Fundus Autofluorescence and Progression of Geographic Atrophy Secondary to

Age-Related Macular Degeneration: The GAIN Study. Am. J. Ophthalmol. 160,

345-353 e345.

(20) Rudolf, M., Vogt, S. D., Curcio, C. A., Huisingh, C., McGwin, G., Jr., Wagner,

A., Grisanti, S., and Read, R. W. (2013) Histologic basis of variations in retinal

pigment epithelium autofluorescence in eyes with geographic atrophy.

Ophthalmology 120, 821-828.

(21) Noell, W. K. (1980) Possible mechanisms of photoreceptor damage by light in

mammalian eyes. Vision Res. 20, 1163-1171.

140

(22) Noell, W. K., Walker, V. S., Kang, B. S., and Berman, S. (1966) Retinal damage

by light in rats. Invest. Ophthalmol. 5, 450-473.

(23) Harwerth, R. S., and Sperling, H. G. (1975) Effects of intense visible radiation on

the increment-threshold spectral sensitivity of the rhesus monkey eye. Vision Res.

15, 1193-1204.

(24) Reme, C. E. (2005) The dark side of light: rhodopsin and the silent death of vision

the proctor lecture. Invest. Ophthalmol. Vis. Sci. 46, 2671-2682.

(25) Ham, W. T., Jr., Ruffolo, J. J., Jr., Mueller, H. A., Clarke, A. M., and Moon, M. E.

(1978) Histologic analysis of photochemical lesions produced in rhesus retina by

short-wave-length light. Invest. Ophthalmol. Vis. Sci. 17, 1029-1035.

(26) Ham, W. T., Jr., Ruffolo, J. J., Jr., Mueller, H. A., and Guerry, D., 3rd. (1980) The

nature of retinal radiation damage: dependence on wavelength, power level and

exposure time. Vision Res. 20, 1105-1111.

(27) Ham, W. T., Jr., Mueller, H. A., Ruffolo, J. J., Jr., and Clarke, A. M. (1979)

Sensitivity of the retina to radiation damage as a function of wavelength.

Photochem. Photobiol. 29, 735-743.

(28) Liang, F. Q., and Godley, B. F. (2003) Oxidative stress-induced mitochondrial

DNA damage in human retinal pigment epithelial cells: a possible mechanism for

RPE aging and age-related macular degeneration. Exp. Eye Res. 76, 397-403.

(29) SanGiovanni, J. P., and Chew, E. Y. (2005) The role of omega-3 long-chain

polyunsaturated fatty acids in health and disease of the retina. Prog. Retin. Eye

Res. 24, 87-138.

141

(30) Hidalgo, F. J., Alaiz, M., and Zamora, R. (2001) Pyrrolization and antioxidant

function of proteins following oxidative stress. Chem. Res. Toxicol. 14, 582-588.

(31) Gu, X., Sun, M., Gugiu, B., Hazen, S., Crabb, J. W., and Salomon, R. G. (2003)

Oxidatively truncated docosahexaenoate phospholipids: total synthesis,

generation, and Peptide adduction chemistry. J. Org. Chem. 68, 3749-3761.

(32) Choi, J., Zhang, W., Gu, X., Chen, X., Hong, L., Laird, J. M., and Salomon, R. G.

(2011) Lysophosphatidylcholine is generated by spontaneous deacylation of

oxidized phospholipids. Chem. Res. Toxicol. 24, 111-118.

(33) Wang, H., Guo, J., West, X. Z., Bid, H. K., Lu, L., Hong, L., Jang, G. F., Zhang,

L., Crabb, J. W., Clinical, G., Proteomic, A. M. D. S. G., Linetsky, M., and

Salomon, R. G. (2014) Detection and biological activities of carboxyethylpyrrole

ethanolamine phospholipids (CEP-EPs). Chem. Res. Toxicol. 27, 2015-2022.

(34) Gu, X., Meer, S. G., Miyagi, M., Rayborn, M. E., Hollyfield, J. G., Crabb, J. W.,

and Salomon, R. G. (2003) Carboxyethylpyrrole protein adducts and

autoantibodies, biomarkers for age-related macular degeneration. J. Biol. Chem.

278, 42027-42035.

(35) Gu, J., Pauer, G. J., Yue, X., Narendra, U., Sturgill, G. M., Bena, J., Gu, X.,

Peachey, N. S., Salomon, R. G., Hagstrom, S. A., Crabb, J. W., Clinical, G., and

Proteomic, A. M. D. S. G. (2009) Assessing susceptibility to age-related macular

degeneration with proteomic and genomic biomarkers. Mol. Cell. Proteomics 8,

1338-1349.

(36) Gu, J., Pauer, G. J., Yue, X., Narendra, U., Sturgill, G. M., Bena, J., Gu, X.,

Peachey, N. S., Salomon, R. G., Hagstrom, S. A., Crabb, J. W., Clinical, G., and

142

Proteomic, A. M. D. S. G. (2010) Proteomic and genomic biomarkers for age-

related macular degeneration. Advances in experimental medicine and biology

664, 411-417.

(37) Sun, M., Finnemann, S. C., Febbraio, M., Shan, L., Annangudi, S. P., Podrez, E.

A., Hoppe, G., Darrow, R., Organisciak, D. T., Salomon, R. G., Silverstein, R. L.,

and Hazen, S. L. (2006) Light-induced oxidation of photoreceptor outer segment

phospholipids generates ligands for CD36-mediated phagocytosis by retinal

pigment epithelium: a potential mechanism for modulating outer segment

phagocytosis under oxidant stress conditions. J. Biol. Chem. 281, 4222-4230.

(38) Wang, H., Linetsky, M., Guo, J., Yu, A. O., and Salomon, R. G. (2016)

Metabolism of 4-Hydroxy-7-oxo-5-heptenoic Acid (HOHA) Lactone by Retinal

Pigmented Epithelial Cells. Chem. Res. Toxicol. 29, 1198-1210.

(39) Kato, S., Osborne, N. N., Tamai, M., International Symposium on "Retinal, D.,

and Regeneration. Retinal degeneration and regeneration : proceedings of an

international symposium, Kanazawa, Japan, July 8-9, 1995, Kugler Publications,

Amsterdam; New York.

(40) Rodriguez de Turco, E. B., Parkins, N., Ershov, A. V., and Bazan, N. G. (1999)

Selective retinal pigment epithelial cell lipid metabolism and remodeling

conserves photoreceptor docosahexaenoic acid following phagocytosis. J.

Neurosci. Res. 57, 479-486.

(41) Sparrow, J. R., Nakanishi, K., and Parish, C. A. (2000) The lipofuscin fluorophore

A2E mediates blue light-induced damage to retinal pigmented epithelial cells.

Invest. Ophthalmol. Vis. Sci. 41, 1981-1989.

143

(42) Eldred, G. E., and Katz, M. L. (1988) Fluorophores of the human retinal pigment

epithelium: separation and spectral characterization. Exp. Eye Res. 47, 71-86.

(43) Eldred, G. E., and Lasky, M. R. (1993) Retinal age pigments generated by self-

assembling lysosomotropic detergents. Nature 361, 724-726.

(44) Parish, C. A., Hashimoto, M., Nakanishi, K., Dillon, J., and Sparrow, J. (1998)

Isolation and one-step preparation of A2E and iso-A2E, fluorophores from human

retinal pigment epithelium. Proc. Natl. Acad. Sci. U. S. A. 95, 14609-14613.

(45) Liu, J., Itagaki, Y., Ben-Shabat, S., Nakanishi, K., and Sparrow, J. R. (2000) The

biosynthesis of A2E, a fluorophore of aging retina, involves the formation of the

precursor, A2-PE, in the photoreceptor outer segment membrane. J. Biol. Chem.

275, 29354-29360.

(46) Sparrow, J. R., Zhou, J., Ben-Shabat, S., Vollmer, H., Itagaki, Y., and Nakanishi,

K. (2002) Involvement of oxidative mechanisms in blue-light-induced damage to

A2E-laden RPE. Invest. Ophthalmol. Vis. Sci. 43, 1222-1227.

(47) Gaillard, E. R., Avalle, L. B., Keller, L. M., Wang, Z., Reszka, K. J., and Dillon, J.

P. (2004) A mechanistic study of the photooxidation of A2E, a component of

human retinal lipofuscin. Exp. Eye Res. 79, 313-319.

(48) Alary, J., Fernandez, Y., Debrauwer, L., Perdu, E., and Gueraud, F. (2003)

Identification of intermediate pathways of 4-hydroxynonenal metabolism in the

rat. Chem. Res. Toxicol. 16, 320-327.

(49) Dixit, B. L., Balendiran, G. K., Watowich, S. J., Srivastava, S., Ramana, K. V.,

Petrash, J. M., Bhatnagar, A., and Srivastava, S. K. (2000) Kinetic and structural

144

characterization of the glutathione-binding site of aldose reductase. J. Biol. Chem.

275, 21587-21595.

(50) Ben-Shabat, S., Parish, C. A., Vollmer, H. R., Itagaki, Y., Fishkin, N., Nakanishi,

K., and Sparrow, J. R. (2002) Biosynthetic studies of A2E, a major fluorophore of

retinal pigment epithelial lipofuscin. J. Biol. Chem. 277, 7183-7190.

(51) Winkler, B. S., Boulton, M. E., Gottsch, J. D., and Sternberg, P. (1999) Oxidative

damage and age-related macular degeneration. Mol. Vis. 5, 32.

(52) Sparrow, J. R., Wu, Y., Kim, C. Y., and Zhou, J. (2010) Phospholipid meets all-

trans-retinal: the making of RPE bisretinoids. J. Lipid Res. 51, 247-261.

(53) Marie, M., Bigot, K., Angebault, C., Barrau, C., Gondouin, P., Pagan, D., Fouquet,

S., Villette, T., Sahel, J. A., Lenaers, G., and Picaud, S. (2018) Light action

spectrum on oxidative stress and mitochondrial damage in A2E-loaded retinal

pigment epithelium cells. Cell Death Dis. 9, 287.

(54) Sparrow, J. R., Parish, C. A., Hashimoto, M., and Nakanishi, K. (1999) A2E, a

lipofuscin fluorophore, in human retinal pigmented epithelial cells in culture.

Invest. Ophthalmol. Vis. Sci. 40, 2988-2995.

(55) Sadhukhan, S., Han, Y., Jin, Z., Tochtrop, G. P., and Zhang, G. F. (2014)

Glutathionylated 4-hydroxy-2-(E)-alkenal enantiomers in rat organs and their

contributions toward the disposal of 4-hydroxy-2-(E)-nonenal in rat liver. Free

Radic. Biol. Med. 70, 78-85.

(56) Csallany, A. S., Kim, S. S., and Gallaher, D. D. (2000) Response of urinary

lipophilic aldehydes and related carbonyl compounds to factors that stimulate

lipid peroxidation in vivo. Lipids 35, 855-862.

145

(57) West, X. Z., Malinin, N. L., Merkulova, A. A., Tischenko, M., Kerr, B. A.,

Borden, E. C., Podrez, E. A., Salomon, R. G., and Byzova, T. V. (2010) Oxidative

stress induces angiogenesis by activating TLR2 with novel endogenous ligands.

Nature 467, 972-976.

(58) Salomon, R. G. (2017) Carboxyethylpyrroles: From Hypothesis to the Discovery

of Biologically Active Natural Products. Chem. Res. Toxicol. 30, 105-113.

(59) Salomon, R. G., and Gu, X. (2011) Critical insights into cardiovascular disease

from basic research on the oxidation of phospholipids: the gamma-

hydroxyalkenal phospholipid hypothesis. Chem. Res. Toxicol. 24, 1791-1802.

(60) Guo, J., Wang, H., Hrinczenko, B., and Salomon, R. G. (2016) Efficient

Quantitative Analysis of Carboxyalkylpyrrole Ethanolamine Phospholipids:

Elevated Levels in Sickle Cell Disease Blood. Chemical research in toxicology 29,

1187-1197.

(61) Green, D. R., and Reed, J. C. (1998) Mitochondria and apoptosis. Science 281,

1309-1312.

(62) Petit, P. X., Lecoeur, H., Zorn, E., Dauguet, C., Mignotte, B., and Gougeon, M. L.

(1995) Alterations in mitochondrial structure and function are early events of

dexamethasone-induced thymocyte apoptosis. J. Cell Biol. 130, 157-167.

(63) Susin, S. A., Zamzami, N., Castedo, M., Daugas, E., Wang, H. G., Geley, S.,

Fassy, F., Reed, J. C., and Kroemer, G. (1997) The central executioner of

apoptosis: multiple connections between protease activation and mitochondria in

Fas/APO-1/CD95- and ceramide-induced apoptosis. J. Exp. Med. 186, 25-37.

146

(64) Logan, A., Pell, V. R., Shaffer, K. J., Evans, C., Stanley, N. J., Robb, E. L., Prime,

T. A., Chouchani, E. T., Cocheme, H. M., Fearnley, I. M., Vidoni, S., James, A.

M., Porteous, C. M., Partridge, L., Krieg, T., Smith, R. A., and Murphy, M. P.

(2016) Assessing the Mitochondrial Membrane Potential in Cells and In Vivo

using Targeted Click Chemistry and Mass Spectrometry. Cell Metab 23, 379-385.

(65) Li, K. R., Yang, S. Q., Gong, Y. Q., Yang, H., Li, X. M., Zhao, Y. X., Yao, J.,

Jiang, Q., and Cao, C. (2016) 3H-1,2-dithiole-3-thione protects retinal pigment

epithelium cells against Ultra-violet radiation via activation of Akt-mTORC1-

dependent Nrf2-HO-1 signaling. Sci. Rep. 6, 25525.

(66) Giovannini, C., Matarrese, P., Scazzocchio, B., Sanchez, M., Masella, R., and

Malorni, W. (2002) Mitochondria hyperpolarization is an early event in oxidized

low-density lipoprotein-induced apoptosis in Caco-2 intestinal cells. FEBS Lett.

523, 200-206.

(67) Kadenbach, B. (2003) Intrinsic and extrinsic uncoupling of oxidative

phosphorylation. Biochim. Biophys. Acta 1604, 77-94.

(68) Matsumoto, K., Yamada, Y., Takahashi, M., Todoroki, T., Mizoguchi, K., Misaki,

H., and Yuki, H. (1990) Fluorometric determination of carnitine in serum with

immobilized carnitine dehydrogenase and diaphorase. Clin. Chem. 36, 2072-2076.

(69) Belinsky, M., and Jaiswal, A. K. (1993) NAD(P)H:quinone oxidoreductase1 (DT-

diaphorase) expression in normal and tumor tissues. Cancer Metastasis Rev. 12,

103-117.

147

(70) Chikuba, K., Yubisui, T., Shirabe, K., and Takeshita, M. (1994) Cloning and

nucleotide sequence of a cDNA of the human erythrocyte NADPH-flavin

reductase. Biochem. Biophys. Res. Commun. 198, 1170-1176.

(71) Rampersad, S. N. (2012) Multiple applications of Alamar Blue as an indicator of

metabolic function and cellular health in cell viability bioassays. Sensors (Basel)

12, 12347-12360.

(72) Marazita, M. C., Dugour, A., Marquioni-Ramella, M. D., Figueroa, J. M., and

Suburo, A. M. (2016) Oxidative stress-induced premature senescence

dysregulates VEGF and CFH expression in retinal pigment epithelial cells:

Implications for Age-related Macular Degeneration. Redox Biol 7, 78-87.

(73) Guo, J., Linetsky, M., Yu, A. O., Zhang, L., Howell, S. J., Folkwein, H. J., Wang,

H., and Salomon, R. G. (2016) 4-Hydroxy-7-oxo-5-heptenoic Acid Lactone

Induces Angiogenesis through Several Different Molecular Pathways. Chem. Res.

Toxicol. 29, 2125-2135.

(74) Dimri, G. P., Lee, X., Basile, G., Acosta, M., Scott, G., Roskelley, C., Medrano, E.

E., Linskens, M., Rubelj, I., Pereira-Smith, O., and et al. (1995) A biomarker that

identifies senescent human cells in culture and in aging skin in vivo. Proc. Natl.

Acad. Sci. U. S. A. 92, 9363-9367.

(75) Lee, B. Y., Han, J. A., Im, J. S., Morrone, A., Johung, K., Goodwin, E. C., Kleijer,

W. J., DiMaio, D., and Hwang, E. S. (2006) Senescence-associated beta-

galactosidase is lysosomal beta-galactosidase. Aging Cell 5, 187-195.

(76) Campisi, J., and d'Adda di Fagagna, F. (2007) Cellular senescence: when bad

things happen to good cells. Nat. Rev. Mol. Cell Biol. 8, 729-740.

148

(77) Law, C. Y., Siu, C. W., Fan, K., Lai, W. H., Au, K. W., Lau, Y. M., Wong, L. Y.,

Ho, J. C. Y., Lee, Y. K., Tse, H. F., and Ng, K. M. (2016) Lysosomal membrane

permeabilization is involved in oxidative stress-induced apoptotic cell death in

LAMP2-deficient iPSCs-derived cerebral cortical neurons. Biochem Biophys Rep

5, 335-345.

(78) Chen, Y., McMillan-Ward, E., Kong, J., Israels, S. J., and Gibson, S. B. (2008)

Oxidative stress induces autophagic cell death independent of apoptosis in

transformed and cancer cells. Cell Death Differ. 15, 171-182.

(79) Gomez-Sintes, R., Ledesma, M. D., and Boya, P. (2016) Lysosomal cell death

mechanisms in aging. Ageing Res Rev 32, 150-168.

(80) Serrano-Puebla, A., and Boya, P. (2016) Lysosomal membrane permeabilization

in cell death: new evidence and implications for health and disease. Ann. N. Y.

Acad. Sci. 1371, 30-44.

(81) Uchimoto, T., Nohara, H., Kamehara, R., Iwamura, M., Watanabe, N., and

Kobayashi, Y. (1999) Mechanism of apoptosis induced by a lysosomotropic agent,

L-Leucyl-L-Leucine methyl ester. Apoptosis 4, 357-362.

(82) Sohaebuddin, S. K., and Tang, L. (2013) A simple method to visualize and assess

the integrity of lysosomal membrane in mammalian cells using a fluorescent dye.

Methods Mol. Biol. 991, 25-31.

(83) Lovelace, M. D., and Cahill, D. M. (2007) A rapid cell counting method utilising

acridine orange as a novel discriminating marker for both cultured astrocytes and

microglia. J. Neurosci. Methods 165, 223-229.

149

(84) Zareba, M., Raciti, M. W., Henry, M. M., Sarna, T., and Burke, J. M. (2006)

Oxidative stress in ARPE-19 cultures: do melanosomes confer cytoprotection?

Free Radic. Biol. Med. 40, 87-100.

(85) Age-Related Eye Disease Study Research, G. (2001) A randomized, placebo-

controlled, clinical trial of high-dose supplementation with vitamins C and E, beta

carotene, and zinc for age-related macular degeneration and vision loss: AREDS

report no. 8. Arch. Ophthalmol. 119, 1417-1436.

(86) Newsome, D. A., Swartz, M., Leone, N. C., Elston, R. C., and Miller, E. (1988)

Oral zinc in macular degeneration. Arch. Ophthalmol. 106, 192-198.

(87) Fletcher, A. E., Bentham, G. C., Agnew, M., Young, I. S., Augood, C.,

Chakravarthy, U., de Jong, P. T., Rahu, M., Seland, J., Soubrane, G., Tomazzoli,

L., Topouzis, F., Vingerling, J. R., and Vioque, J. (2008) Sunlight exposure,

antioxidants, and age-related macular degeneration. Arch. Ophthalmol. 126, 1396-

1403.

(88) Tomany, S. C., Cruickshanks, K. J., Klein, R., Klein, B. E., and Knudtson, M. D.

(2004) Sunlight and the 10-year incidence of age-related maculopathy: the Beaver

Dam Eye Study. Arch. Ophthalmol. 122, 750-757.

(89) Taylor, H. R., West, S., Munoz, B., Rosenthal, F. S., Bressler, S. B., and Bressler,

N. M. (1992) The long-term effects of visible light on the eye. Arch. Ophthalmol.

110, 99-104.

(90) Rozanowska, M. B. (2012) Light-induced damage to the retina: current

understanding of the mechanisms and unresolved questions: a symposium-in-print.

Photochem. Photobiol. 88, 1303-1308.

150

(91) Lerman, S. (1987) Chemical and physical properties of the normal and aging lens:

spectroscopic (UV, fluorescence, phosphorescence, and NMR) analyses. Am. J.

Optom. Physiol. Opt. 64, 11-22.

(92) Artigas, J. M., Felipe, A., Navea, A., Fandino, A., and Artigas, C. (2012) Spectral

transmission of the human crystalline lens in adult and elderly persons: color and

total transmission of visible light. Invest. Ophthalmol. Vis. Sci. 53, 4076-4084.

(93) Mainster, M. A. (1986) The spectra, classification, and rationale of ultraviolet-

protective intraocular lenses. Am. J. Ophthalmol. 102, 727-732.

(94) Fletcher, A. E. (2010) Free radicals, antioxidants and eye diseases: evidence from

epidemiological studies on cataract and age-related macular degeneration.

Ophthalmic Res. 44, 191-198.

(95) Hunter, J. J., Morgan, J. I., Merigan, W. H., Sliney, D. H., Sparrow, J. R., and

Williams, D. R. (2012) The susceptibility of the retina to photochemical damage

from visible light. Prog. Retin. Eye Res. 31, 28-42.

(96) van Norren, D., and Gorgels, T. G. (2011) The action spectrum of photochemical

damage to the retina: a review of monochromatic threshold data. Photochem.

Photobiol. 87, 747-753.

(97) Organisciak, D. T., and Vaughan, D. K. (2010) Retinal light damage: mechanisms

and protection. Prog. Retin. Eye Res. 29, 113-134.

(98) Maeda, A., Maeda, T., Golczak, M., Chou, S., Desai, A., Hoppel, C. L.,

Matsuyama, S., and Palczewski, K. (2009) Involvement of all-trans-retinal in

acute light-induced retinopathy of mice. J. Biol. Chem. 284, 15173-15183.

151

(99) Maeda, A., Maeda, T., Golczak, M., and Palczewski, K. (2008) Retinopathy in

mice induced by disrupted all-trans-retinal clearance. J. Biol. Chem. 283, 26684-

26693.

(100) Maeda, T., Golczak, M., and Maeda, A. (2012) Retinal photodamage mediated by

all-trans-retinal. Photochem. Photobiol. 88, 1309-1319.

(101) Rozanowska, M., Jarvis-Evans, J., Korytowski, W., Boulton, M. E., Burke, J. M.,

and Sarna, T. (1995) Blue light-induced reactivity of retinal age pigment. In vitro

generation of oxygen-reactive species. J. Biol. Chem. 270, 18825-18830.

(102) Dontsov, A. E., Glickman, R. D., and Ostrovsky, M. A. (1999) Retinal pigment

epithelium pigment granules stimulate the photo-oxidation of unsaturated fatty

acids. Free Radic. Biol. Med. 26, 1436-1446.

(103) Reszka, K., Eldred, G. E., Wang, R. H., Chignell, C., and Dillon, J. (1995) The

photochemistry of human retinal lipofuscin as studied by EPR. Photochem.

Photobiol. 62, 1005-1008.

(104) Gaillard, E. R., Atherton, S. J., Eldred, G., and Dillon, J. (1995) Photophysical

studies on human retinal lipofuscin. Photochem. Photobiol. 61, 448-453.

(105) Rozanowska, M., Wessels, J., Boulton, M., Burke, J. M., Rodgers, M. A.,

Truscott, T. G., and Sarna, T. (1998) Blue light-induced singlet oxygen generation

by retinal lipofuscin in non-polar media. Free Radic. Biol. Med. 24, 1107-1112.

(106) Rozanowska, M., Pawlak, A., Rozanowski, B., Skumatz, C., Zareba, M., Boulton,

M. E., Burke, J. M., Sarna, T., and Simon, J. D. (2004) Age-related changes in the

photoreactivity of retinal lipofuscin granules: role of chloroform-insoluble

components. Invest. Ophthalmol. Vis. Sci. 45, 1052-1060.

152

(107) Davies, S., Elliott, M. H., Floor, E., Truscott, T. G., Zareba, M., Sarna, T., Shamsi,

F. A., and Boulton, M. E. (2001) Photocytotoxicity of lipofuscin in human retinal

pigment epithelial cells. Free Radic. Biol. Med. 31, 256-265.

(108) Schutt, F., Davies, S., Kopitz, J., Holz, F. G., and Boulton, M. E. (2000)

Photodamage to human RPE cells by A2-E, a retinoid component of lipofuscin.

Invest. Ophthalmol. Vis. Sci. 41, 2303-2308.

(109) Liu, J., Lu, W., Reigada, D., Nguyen, J., Laties, A. M., and Mitchell, C. H. (2008)

Restoration of lysosomal pH in RPE cells from cultured human and ABCA4(-/-)

mice: pharmacologic approaches and functional recovery. Invest. Ophthalmol. Vis.

Sci. 49, 772-780.

(110) Bergmann, M., Schutt, F., Holz, F. G., and Kopitz, J. (2004) Inhibition of the

ATP-driven proton pump in RPE lysosomes by the major lipofuscin fluorophore

A2-E may contribute to the pathogenesis of age-related macular degeneration.

FASEB J. 18, 562-564.

(111) Suter, M., Reme, C., Grimm, C., Wenzel, A., Jaattela, M., Esser, P., Kociok, N.,

Leist, M., and Richter, C. (2000) Age-related macular degeneration. The

lipofusion component N-retinyl-N-retinylidene ethanolamine detaches

proapoptotic proteins from mitochondria and induces apoptosis in mammalian

retinal pigment epithelial cells. J. Biol. Chem. 275, 39625-39630.

(112) Kersten, E., Paun, C. C., Schellevis, R. L., Hoyng, C. B., Delcourt, C., Lengyel, I.,

Peto, T., Ueffing, M., Klaver, C. C. W., Dammeier, S., den Hollander, A. I., and

de Jong, E. K. (2018) Systemic and ocular fluid compounds as potential

biomarkers in age-related macular degeneration. Surv. Ophthalmol. 63, 9-39.

153

(113) Poliakov, E., Strunnikova, N. V., Jiang, J. K., Martinez, B., Parikh, T., Lakkaraju,

A., Thomas, C., Brooks, B. P., and Redmond, T. M. (2014) Multiple A2E

treatments lead to melanization of rod outer segment-challenged ARPE-19 cells.

Mol. Vis. 20, 285-300.

(114) Finnemann, S. C., Leung, L. W., and Rodriguez-Boulan, E. (2002) The lipofuscin

component A2E selectively inhibits phagolysosomal degradation of photoreceptor

phospholipid by the retinal pigment epithelium. Proc. Natl. Acad. Sci. U. S. A. 99,

3842-3847.

(115) Vives-Bauza, C., Anand, M., Shiraz, A. K., Magrane, J., Gao, J., Vollmer-Snarr,

H. R., Manfredi, G., and Finnemann, S. C. (2008) The age lipid A2E and

mitochondrial dysfunction synergistically impair phagocytosis by retinal pigment

epithelial cells. J. Biol. Chem. 283, 24770-24780.

(116) Ablonczy, Z., Higbee, D., Anderson, D. M., Dahrouj , M., Grey, A. C., Gutierrez,

D., Koutalos, Y., L., S. K., Hanneken, A., and Crouch, R. K. (2013) Lack of

correlation between the spatial distribution of A2E and lipofuscin fluorescence in

the human retinal pigment epithelium. Invest Ophthalmol Vis Sci. 54, 5535–5542.

(117) Crabb, J. W., Miyagi, M., Gu, X., Shadrach, K., West, K. A., Sakaguchi, H.,

Kamei, M., Hasan, A., Yan, L., Rayborn, M. E., Salomon, R. G., and Hollyfield, J.

G. (2002) Drusen proteome analysis: an approach to the etiology of age-related

macular degeneration. Proc. Natl. Acad. Sci. U. S. A. 99, 14682-14687.

(118) Justilien, V., Pang, J. J., Renganathan, K., Zhan, X., Crabb, J. W., Kim, S. R.,

Sparrow, J. R., Hauswirth, W. W., and Lewin, A. S. (2007) SOD2 knockdown

mouse model of early AMD. Invest. Ophthalmol. Vis. Sci. 48, 4407-4420.

154

(119) Renganathan, K., Gu, J., Rayborn, M. E., Crabb, J. S., Salomon, R. G., Collier, R.

J., Kapin, M. A., Romano, C., Hollyfield, J. G., and Crabb, J. W. (2013) CEP

biomarkers as potential tools for monitoring therapeutics. PLoS One 8, e76325.

(120) Marc, R. E., Jones, B. W., Watt, C. B., Vazquez-Chona, F., Vaughan, D. K., and

Organisciak, D. T. (2008) Extreme retinal remodeling triggered by light damage:

implications for age related macular degeneration. Mol. Vis. 14, 782-806.

(121) Organisciak, D. T., Darrow, R. M., Rapp, C. M., Smuts, J. P., Armstrong, D. W.,

and Lang, J. C. (2013) Prevention of retinal light damage by zinc oxide combined

with rosemary extract. Mol. Vis. 19, 1433-1445.

(122) Collier, R. J., Patel, Y., Martin, E. A., Dembinska, O., Hellberg, M., Krueger, D.

S., Kapin, M. A., and Romano, C. (2011) Agonists at the serotonin receptor (5-

HT(1A)) protect the retina from severe photo-oxidative stress. Invest. Ophthalmol.

Vis. Sci. 52, 2118-2126.

(123) Ebrahem, Q., Renganathan, K., Sears, J., Vasanji, A., Gu, X., Lu, L., Salomon, R.

G., Crabb, J. W., and Anand-Apte, B. (2006) Carboxyethylpyrrole oxidative

protein modifications stimulate neovascularization: Implications for age-related

macular degeneration. Proc. Natl. Acad. Sci. U. S. A. 103, 13480-13484.

(124) Hollyfield, J. G., Bonilha, V. L., Rayborn, M. E., Yang, X., Shadrach, K. G., Lu,

L., Ufret, R. L., Salomon, R. G., and Perez, V. L. (2008) Oxidative damage-

induced inflammation initiates age-related macular degeneration. Nat. Med. 14,

194-198.

(125) Cruz-Guilloty, F., Saeed, A. M., Duffort, S., Cano, M., Ebrahimi, K. B., Ballmick,

A., Tan, Y., Wang, H., Laird, J. M., Salomon, R. G., Handa, J. T., and Perez, V. L.

155

(2014) T cells and macrophages responding to oxidative damage cooperate in

pathogenesis of a mouse model of age-related macular degeneration. PLoS One 9,

e88201.

(126) Dorey, C. K., Delori, F. C., and Akeo, K. (1990) Growth of cultured RPE and

endothelial cells is inhibited by blue light but not green or red light. Curr. Eye Res.

9, 549-559.

(127) Li, X., Liu, Z., Luo, C., Jia, H., Sun, L., Hou, B., Shen, W., Packer, L., Cotman, C.

W., and Liu, J. (2008) Lipoamide protects retinal pigment epithelial cells from

oxidative stress and mitochondrial dysfunction. Free Radic. Biol. Med. 44, 1465-

1474.

(128) Kirkinezos, I. G., Bacman, S. R., Hernandez, D., Oca-Cossio, J., Arias, L. J.,

Perez-Pinzon, M. A., Bradley, W. G., and Moraes, C. T. (2005) Cytochrome c

association with the inner mitochondrial membrane is impaired in the CNS of

G93A-SOD1 mice. J. Neurosci. 25, 164-172.

(129) Ly, J. D., Grubb, D. R., and Lawen, A. (2003) The mitochondrial membrane

potential (deltapsi(m)) in apoptosis; an update. Apoptosis 8, 115-128.

(130) Perl, A., Gergely, P., Jr., Nagy, G., Koncz, A., and Banki, K. (2004)

Mitochondrial hyperpolarization: a checkpoint of T-cell life, death and

autoimmunity. Trends Immunol. 25, 360-367.

(131) Radu, R. A., Mata, N. L., Bagla, A., and Travis, G. H. (2004) Light exposure

stimulates formation of A2E oxiranes in a mouse model of Stargardt's macular

degeneration. Proc. Natl. Acad. Sci. U. S. A. 101, 5928-5933.

156

(132) Sparrow, J. R., Vollmer-Snarr, H. R., Zhou, J., Jang, Y. P., Jockusch, S., Itagaki,

Y., and Nakanishi, K. (2003) A2E-epoxides damage DNA in retinal pigment

epithelial cells. Vitamin E and other antioxidants inhibit A2E-epoxide formation.

J. Biol. Chem. 278, 18207-18213.

(133) Holz, F. G., Schutt, F., Kopitz, J., Eldred, G. E., Kruse, F. E., Volcker, H. E., and

Cantz, M. (1999) Inhibition of lysosomal degradative functions in RPE cells by a

retinoid component of lipofuscin. Invest. Ophthalmol. Vis. Sci. 40, 737-743.

(134) Brandstetter, C., Mohr, L. K., Latz, E., Holz, F. G., and Krohne, T. U. (2015)

Light induces NLRP3 inflammasome activation in retinal pigment epithelial cells

via lipofuscin-mediated photooxidative damage. J. Mol. Med. (Berl.) 93, 905-916.

(135) Wassell, J., Davies, S., Bardsley, W., and Boulton, M. (1999) The photoreactivity

of the retinal age pigment lipofuscin. J. Biol. Chem. 274, 23828-23832.

(136) Isahara, K., Ohsawa, Y., Kanamori, S., Shibata, M., Waguri, S., Sato, N., Gotow,

T., Watanabe, T., Momoi, T., Urase, K., Kominami, E., and Uchiyama, Y. (1999)

Regulation of a novel pathway for cell death by lysosomal aspartic and cysteine

proteinases. Neuroscience 91, 233-249.

(137) Stoka, V., Turk, B., Schendel, S. L., Kim, T. H., Cirman, T., Snipas, S. J., Ellerby,

L. M., Bredesen, D., Freeze, H., Abrahamson, M., Bromme, D., Krajewski, S.,

Reed, J. C., Yin, X. M., Turk, V., and Salvesen, G. S. (2001) Lysosomal protease

pathways to apoptosis. Cleavage of bid, not pro-caspases, is the most likely route.

J. Biol. Chem. 276, 3149-3157.

(138) Krajewski, S., Krajewska, M., Ellerby, L. M., Welsh, K., Xie, Z., Deveraux, Q. L.,

Salvesen, G. S., Bredesen, D. E., Rosenthal, R. E., Fiskum, G., and Reed, J. C.

157

(1999) Release of caspase-9 from mitochondria during neuronal apoptosis and

cerebral ischemia. Proc. Natl. Acad. Sci. U. S. A. 96, 5752-5757.

(139) Xu, J., Chen, S., Ku, G., Ahmed, S. H., Xu, J., Chen, H., and Hsu, C. Y. (2001)

Amyloid beta peptide-induced cerebral endothelial cell death involves

mitochondrial dysfunction and caspase activation. J. Cereb. Blood Flow Metab.

21, 702-710.

(140) Rodrigues, C. M., Sola, S., Silva, R., and Brites, D. (2000) Bilirubin and amyloid-

beta peptide induce cytochrome c release through mitochondrial membrane

permeabilization. Mol. Med. 6, 936-946.

(141) Rajapakse, D., Curtis, T., Chen, M., and Xu, H. (2017) Zinc Protects Oxidative

Stress-Induced RPE Death by Reducing Mitochondrial Damage and Preventing

Lysosome Rupture. Oxid. Med. Cell. Longev. 2017, 6926485.

(142) Schutt, F., Bergmann, M., Holz, F. G., Dithmar, S., Volcker, H. E., and Kopitz, J.

(2007) Accumulation of A2-E in mitochondrial membranes of cultured RPE cells.

Graefes Arch. Clin. Exp. Ophthalmol. 245, 391-398.

(143) Campisi, J., and Robert, L. (2014) Cell senescence: role in aging and age-related

diseases. Interdiscip Top Gerontol 39, 45-61.

(144) Matsunaga, H., Handa, J. T., Aotaki-Keen, A., Sherwood, S. W., West, M. D.,

and Hjelmeland, L. M. (1999) Beta-galactosidase histochemistry and telomere

loss in senescent retinal pigment epithelial cells. Invest. Ophthalmol. Vis. Sci. 40,

197-202.

(145) Kozlowski, M. R. (2012) RPE cell senescence: a key contributor to age-related

macular degeneration. Med. Hypotheses 78, 505-510.

158

(146) Honda, S., Hjelmeland, L. M., and Handa, J. T. (2002) Senescence associated beta

galactosidase activity in human retinal pigment epithelial cells exposed to mild

hyperoxia in vitro. Br. J. Ophthalmol. 86, 159-162.

(147) Wang, H., Linetsky, M., Guo, J., Choi, J., Hong, L., Chamberlain, A. S., Howell,

S. J., Howes, A. M., and Salomon, R. G. (2015) 4-Hydroxy-7-oxo-5-heptenoic

Acid (HOHA) Lactone is a Biologically Active Precursor for the Generation of 2-

(omega-Carboxyethyl)pyrrole (CEP) Derivatives of Proteins and Ethanolamine

Phospholipids. Chem. Res. Toxicol. 28, 967-977.

(148) Naggar, H., Van Ells, T. K., Ganapathy, V., and Smith, S. B. (2005) Regulation of

reduced-folate transporter-1 in retinal pigment epithelial cells by folate. Curr. Eye

Res. 30, 35-44.

(149) Anoopkumar-Dukie, S., Carey, J. B., Conere, T., O'Sullivan, E., van Pelt, F. N.,

and Allshire, A. (2005) Resazurin assay of radiation response in cultured cells. Br.

J. Radiol. 78, 945-947.

(150) Pietila, M., Lehtonen, S., Tuovinen, E., Lahteenmaki, K., Laitinen, S., Leskela, H.

V., Natynki, A., Pesala, J., Nordstrom, K., and Lehenkari, P. (2012) CD200

positive human mesenchymal stem cells suppress TNF-alpha secretion from

CD200 receptor positive macrophage-like cells. PLoS One 7, e31671.

(151) Rahman, I., Kode, A., and Biswas, S. K. (2006) Assay for quantitative

determination of glutathione and glutathione disulfide levels using enzymatic

recycling method. Nat. Protoc. 1, 3159-3165.

159

(152) Debacq-Chainiaux, F., Erusalimsky, J. D., Campisi, J., and Toussaint, O. (2009)

Protocols to detect senescence-associated beta-galactosidase (SA-betagal) activity,

a biomarker of senescent cells in culture and in vivo. Nat. Protoc. 4, 1798-1806.

160

CHAPTER 4

4-Hydroxy-7-oxo-5-heptenoic Acid (HOHA) Lactone-Induced Oxidative Stress and Mitochondrial Dysfunction in Retinal Pigmented Epithelial Cells: Protection by a Carnosine Analogue, L-Histidyl Hydrazide

161

4.1 Background

Bruch’s membrane-choroid complex, is critical for the maintenance of retinal homeostasis.2 Impaired RPE cell functions cause the formation of extracellular deposits called drusen that accumulate between the RPE and Bruch's membrane (dry AMD).

Choroidal neovascularization leads to leakage of blood into the macula and detachment of the neural retina (wet AMD). Over time AMD-associated RPE cell dysfunction and death results in photoreceptor dysfunction and blindness.

4.1.1 Mitochondrial dysfunction and age-related macular degeneration (AMD)

Although the pathogenesis of AMD is a complex multifactorial process and remains poorly understood, converging evidence from multiple studies implicate the role of mitochondrial dysfunction in AMD pathogenesis.3 Decline in the number and structural integrity of mitochondria4 and decreased content of proteins in the electron transport chain were observed in RPE cells from human donors with AMD.5

Each mitochondrion contains an outer and an inner membrane composed of phospholipid bilayers and proteins, an intermembrane space, numerous cristae, and the matrix.

The most prominent roles of mitochondria are to produce energy for the cell in the form of ATP, through the citric acid cycle and oxidative phosphorylation (OXPHOS), and to regulate cellular metabolism and homeostasis, e.g., through membrane potential (ΔΨm), reactive oxygen species (ROS) generation and mitophagy.

162

Failure in the balance of these processes triggers mitochondrial dysfunction. The collapse of ΔΨm and excessive production of mitochondrial ROS are precursors of cellular death. Therefore, when not repaired, this accumulation of dysfunctional mitochondria may lead to apoptosis or necrosis, and eventually contribute to development and progression of several diseases.

A recent study showed that RPE cells from AMD donors produce significantly higher

ROS levels than normal RPE cells under oxidative stress.6 Also, the levels of ATP produced by mitochondria are significantly lower in AMD RPE cells. This indicates lower mitochondrial activity and parallels with the finding that the level of ATP synthase

α, β, and δ subunits are lower in RPE mitochondria isolated from AMD than from normal donor eyes.7 Furthermore, in the transmitochondrial ARPE-19 cybrid model – cybrids were prepared by fusion of mitochondrial DNA-deficient Rho0 APRE-19 cell line with platelets isolated from either AMD patients or age-matched normal subjects – the AMD

RPE cybrids showed drastically diminished protein levels of OXPHOS complex I subunit

(NADH-coenzyme Q oxidoreductase), complex II subunit (succinate-coenzyme Q oxidoreductase), complex III subunit (coenzyme Q-cytochrome c oxidoreductase), complex IV subunit (cytochrome c oxidase), and complex V subunit (ATP synthase), suggesting compromised mitochondrial bioenergetics in the AMD cybrids compared to normal cybrids.8

4.1.2 Oxidative stress, lipid peroxidation and retinal pigmented epithelium (RPE) damage

Reactive oxygen species such as oxygen free radicals induce the peroxidation of polyunsaturated fatty acids, including arachidonic, linoleic, docosahexaenoic, and

163 eicosapentaenoic acids, within cell and organelle membranes.9 Decomposition of fatty acids leads to the generation of a plethora of aldehydic breakdown products, which include acrolein, 4-HNE, 4-HHE and HOHA lactone (HL), that are associated with several pathological states.

These α,β-unsaturated aldehydes are highly reactive and can covalently bind to lysine, histidine and cysteine amino acyl residues of cellular or mitochondrial proteins through

Schiff-base formation or Michael addition.10 Previously, we showed that phospholipid esters of DHA, the most abundant and oxidizable fatty acid in the retina (especially in the disc membranes of photoreceptor cells and in RPE cells) and brain, are oxidatively cleaved to generate 4-hydroxy-7-oxo-5-heptenoate (HOHA) phospholipids. We discovered that the HOHA ester of 2-lysophosphatidylcholine (HOHA-PC), readily undergoes intramolecular transesterification to release HOHA lactone (Figure 4.1).11

Covalent adduction of HOHA lactone with protein lysyl ε-amino groups generates 2-(ω- carboxyethyl)pyrrole (CEP) derivatives.12 Mounting evidence indicates that CEP has significant pathological relevance to age-related macular degeneration (AMD).13-15

Furthermore, HOHA lactone itself induces angiogenesis16, activates the alternative complement pathway17 and causes RPE cell dysfunction including cellular senescence, lysosomal membrane permeabilization and dissipation of mitochondrial membrane potential.18

164

Previous studies identified 4-HNE and acrolein as reactive α,β-unsaturated aldehydes capable of impairing mitochondrial functions and contributing to accumulation of oxidative damage markers. Brain mitochondria exposed to 30 µM 4-HNE show 40~60% inhibition of the complex I or complex II–driven oxygen consumption rate (OCR), while exposure to 3 µM acrolein show 20~50% inhibition of complex I or complex II–driven respiration.9, 19 Also, in rat liver mitochondria, complex I activity started to decrease after exposure to 500 µM acrolein (30% reduction) and complex II activity was decreased upon exposure to 100 µM acrolein (20% reduction). Unlike complex I, complex II, activities of complex III and IV were unchanged even at the highest concentration of acrolein (1 mM).20 We hypothesized that the generation of HOHA lactone, a DHA- derived α,β-unsaturated aldehyde, similarly contributes to mitochondrial dysfunction in

RPE cells, and that this toxicity contributes to the progression of age-related macular degeneration.

165

4.1.3 Prevention of α,β-unsaturated aldehyde-induced death of RPE cells

A possible strategy to prevent RPE cell death is to prevent α,β-unsaturated aldehyde- induced mitochondrial damage. There are two major ways to protect mitochondria from oxidative stress-induced dysfunction: (1) prevent the production of free radicals and reactive oxygen species or inhibit the ensuing peroxidation cascade that generates α,β- unsaturated aldehydes; and (2) scavenge α,β-unsaturated aldehyde products of lipid oxidation, e.g., 4-HNE, acrolein and HOHA lactone. For the first strategy, free radical scavenger drugs such as α-tocopherol and ascorbic acid are used.21 For the second strategy, FDA approved electrophile-trapping hydrazine derivatives, hydralazine and phenelzine protect brain mitochondrial function in vitro and in vivo following stroke or traumatic brain injury by scavenging the 4-HNE and acrolein.9 For brain mitochondria exposed to 4-HNE or acrolein, significant protection against complex I and complex II– driven increase in OCR is observed with phenelzine that simultaneously prevents the generation of 4-HNE and acrolein protein adducts as detected by immunoblotting with the corresponding antibodies.9 Also, suppression of the respiratory control ratio (RCR) observed in mitochondria isolated from peri-contusional brain tissue of controlled cortical impact traumatic brain injury (CCI-TBI) rats is prevented by phenelzine administration.

Furthermore, the same phenelzine dose significantly improves cortical tissue sparing at

14 days after TBI. These results suggest that phenelzine’s neuroprotective effect is due to mitochondrial protection by scavenging aldehydic lipid peroxidation products.9, 19

Carnosine, a natural dipeptide consisting of histidine and alanine, apparently acts as an inhibitor of advanced lipoxidation end-product (ALE)-induced mitochondrial damage through several mechanisms.22 First, it inhibits lipid oxidation and oxidative cleavage that

166 generates reactive carbonyl species by scavenging ROS, such as hydroxyl radical,23-25 peroxyl radical,24, 26, 27 singlet oxygen28 and nitric oxide.29 Second, it scavenges reactive carbonyl species.30-32 Third, it reacts with and detoxifies carbonylated proteins.33-35 The imidazole ring provides antioxidant, metal ion chelating and buffering activity, while the amino group of β-alanine and the imidazole ring synergistically act in trapping and inhibiting pathological consequences of ALE formation.

Carnosine treatment at physiologically relevant concentrations not only prevents malondialdehyde (MDA)-induced protein cross-linking and cytotoxicity36 but also provides a protective effect against toxicity induced by zinc and copper in cultured neurons.37 The cell protective effect of carnosine against neurotoxin β-amyloid peptide

(Aβ) mediated toxicity was also confirmed in other cell models, including the protection

38 39 of rat brain vascular endothelial cells against Aβ25-35, rat cerebellar granule cells and

40 differentiated PC12 against Aβ1-42. The HNE-carnosine Michael adduct and related metabolites are detected in biological matrices, including the urine of Zucker obese rats41 and oxidized skeletal muscle.42 Furthermore, carnosine competitively inhibits HNE- induced protein cross-linking43 by quenching HNE in vivo.

In the present study, the efficacy of L-histidyl hydrazide (HH), a carnosine analogue, for trapping HOHA lactone was assessed. HH possesses an imidazole ring and the L stereochemistry of the carnosine histidyl residue but also incorporates a super nucleophilic "hydrazide" amino group that is more aldehyde-reactive than the carnosine

β-alanyl amino group toward lipid-derived aldehydes. Previously, cell viability assays suggested that HH is more effective than carnosine and other histidine analogues in protecting neurons against 4-HNE toxicity,44 and may have therapeutic potential for the

167 treatment of stroke and some neurodegenerative conditions.45 However, its potential utility for ameliorating damage of the RPE induced by reactive carbonyl species leading to age-related macular degeneration was unknown. We now studied the ability of HH to alleviate the toxicity of HOHA lactone that causes mitochondrial dysfunction and oxidative stress in RPE cells.

The present study also tested the hypothesis that the α-amino group in HH is not essential for its protective activity against α,β-unsaturated aldehydes such as HOHA lactone. We found that certain α-N-acyl HH derivatives retain full prophylactic α,β- unsaturated aldehyde scavenging activity that protects RPE cells against HOHA lactone toxicity that is now shown to include inactivation of mitochondrial OXPHOS complexes, especially I and II.

168

4.2 Results

4.2.1 HOHA lactone damages OXPHOS complexes in mitochondria

The mitochondrial respiratory chain is comprised of four enzymatic complexes

(complexes I–IV) embedded in the inner mitochondrial membrane. They catalyze the oxidation of reducing equivalents using the terminal electron acceptor oxygen (O2), with the ultimate production of a proton gradient across the inner mitochondrial membrane to drive the synthesis of ATP by ATP synthase. Decreased activity of the inner membrane complexes is an index of oxidative mitochondrial dysfunction and is a key factor in a variety of human disorders.

The effects of exposing mitochondria to HOHA lactone on enzymatic activities of respiratory chain complexes I–IV were assayed spectrophotometrically. Mitochondria

(0.2 mg/mL protein) isolated from cultured ARPE-19 cells were incubated for 30 min with various concentrations of HOHA lactone. Mitochondrial complex I total activity decreases 72% after treatment with 10 µM (50 nmol/mg protein), 49% after treatment with 50 µM HOHA lactone but remains constant at 47% even after treatment with 100

µM HOHA lactone (Figure 4.2A, next page). In contrast, rotenone-sensitive activity of the mitochondrial complex I – calculated by subtracting total complex I activity

(mitochondria without rotenone) and rotenone-resistant activity (mitochondria with rotenone) – decreases by 53% after exposure to 10 µM HOHA lactone, by 90% after exposure to 50 µM HOHA lactone and all of this activity is lost after exposure to 100 µM

HOHA lactone (Figure 4.2A). There is also a strong HOHA lactone dose-dependent decrease of mitochondrial complex II activity. After treatment with 20 µM HOHA

169 lactone, complex II activity decreases by 19% and by 78%% after 100 µM HOHA lactone (Figure 4.2B).

Figure 4.2. Decline in the activities of mitochondrial OXPHOS complexes induced by HOHA lactone in ARPE-19 cells. Isolated mitochondria were incubated with HOHA lactone at the indicated concentrations for 0.5 h, and then the specific enzymatic activities of complexes (A) I, (B) II, (C) III and (D) IV were assayed spectrophotometrically (E) by monitoring NADH, 2,6-dichlorophenolindophenol (DCPIP) or cytochrome (Cyt) c see materials and methods for details). The data are presented as mean ± SEM of % control, n = 3; **P<0.01, ***P<0.001 compared with the non-treated control.

170

Mitochondrial complex IV is less susceptible to HOHA lactone than complexes I or II.

After treatment with 100 µM HOHA lactone, the complex IV activity only decreases by

20% (Figure 4.2D). Unlike complex I, II and IV, the activity of mitochondrial complex

III is not significantly affected by HOHA lactone treatment even at 100 µM (Figure 4.2C).

4.2.2 HOHA lactone promotes mitochondrial ROS generation and cellular dysfunction

The main sources of mitochondrial ROS are complex I and complex III of the respiratory chain.46 Especially under pathological conditions, complex I becomes a major

ROS source.47 Because HOHA lactone inhibits mitochondrial complex I, we expected that the resulting electron leakage would lead to superoxide generation and its release in the mitochondria.

Monitoring the generation of total cellular ROS in RPE cells with the CM-H2DCFDA probe, we observed a time and concentration dependent elevation of ROS in ARPE-19 cells (Figure 4.3A). To specifically measure the level of mitochondrial ROS, which is the main source of cellular ROS, we used MitoSOX staining. Even at low micromolar

HOHA lactone concentrations we detected an increase of mitochondrial ROS level in

ARPE-19 cells which peaked at 20 µM (3-fold) after 1h HOHA lactone incubation followed by a precipitous decline at 40 µM HOHA lactone (Figure 4.3B, 4.3C).

171

Figure 4.3. HOHA lactone induces the generation of mitochondrial ROS in ARPE-19 cells. (A) Time-course for the generation of total cellular ROS measured with the CM-

H2DCFDA assay. Cells were preloaded with CM-H2DCFDA dye for 1 h and then exposed to various concentrations of HOHA lactone for the time indicated. (B) The mitochondrial ROS level was quantified by MitoSOX staining. Cells were exposed to HOHA lactone for 1 h and stained with MitoSOX before measurement (see Materials and methods for details). The data are presented as mean ± SEM of % control, n = 3~6; *P<0.05, ***P<0.001. (C) Representative MitoSOX staining images acquired using a Leica inverted fluorescent microscope. Cells were exposed to HOHA lactone and then stained with MitoSOX before fixation, mounting and staining with DAPI.

In mitochondria with impaired respiration or a leaky inner membrane, the F0F1-

ATPase reverses and consumes ATP to maintain the ΔΨm at a suboptimal level by

48 pumping protons out of the matrix. However, continuous operation of F0F1-ATPase in reverse consumes cellular ATP reserves driving the cell into an energy crises and eventually leading to cell demise.48 The lowered driving force (proton motive force, pmf)

172 across the inner mitochondrial membrane may also inhibit ATP synthesis. HOHA lactone is a potent inhibitor of ATP synthesis in ARPE cells. Incubation of ARPE-19 cells with

40 µM HOHA lactone for 24 h causes a 75% decrease in the cellular ATP content compared with that of control cells (Figure 4.4A). In contrast, incubation of ARPE-19 cells with oligomycin A only caused a 45% decrease of the ATP level (Figure 4.4A).

Oligomycin A is a well-known ATP synthase inhibitor, which blocks the proton channel of ATP synthase (Fo subunit) and prevents oxidative phosphorylation of ADP to ATP.49

It remains to be determined to what extent blocking of mitochondrial energy metabolism and depletion of ATP in ARPE-19 cells by HOHA lactone results from damaging the mitochondrial respiratory chain, ATP synthase, or the citric acid cycle.

Figure 4.4. HOHA lactone induces depletion of ATP, and mitochondrial membrane potential in ARPE-19 cells. Cells were exposed to various concentrations of HOHA lactone for 24 h (A) the ATP level was quantified by a luciferin-luciferase based assay, and the ATP level was measured; (B) mitochondrial membrane potential (Δψm) was quantified with the JC-10 probe. The data are presented as mean ± SEM of % control, n = 3~6; *P<0.05, ***P<0.001.

The decrease of mitochondrial membrane potential (Δψm) is a point of no return in the classical apoptosis pathway.50 Exposure to HOHA lactone led to a decrease of mitochondrial membrane potential in ARPE-19 cells since ATP synthase was not able to

173 maintain Δψm under our experimental conditions. We detected a 60% decrease of Δψm by

JC-10 assay after incubation with 20 µM HOHA lactone (Figure 4.4B). Exposure to

HOHA lactone caused a dramatic decrease of total GSH levels in ARPE-19 cells. At 1

µM HOHA lactone, the GSH level dropped from 31 nmol/mg protein to 19 nmol/mg protein (39% decrease) and at 10 µM, only 10 nmol/mg protein was retained (68% decrease) (Figure 4.5A). Glutathione (GSH) is an important endogenous antioxidant that plays an important protection role in the cells. Excessive generation of ROS due to mitochondrial dysfunction leads to the depletion of GSH levels in the cell and loss of the ability to defend itself against oxidative stress. Mitochondrial and cellular dysfunction will eventually lead to cell death. Incubation for 24 h with HOHA lactone caused an observable decrease of cell viability at 5 µM (85% viable). The cell viability dropped to

27% after 24 h exposure 20 µM HOHA lactone and dropped to 19% after exposure to 30

µM HOHA lactone (Figure 4.5B).

Figure 4.5. HOHA lactone induces depletion of GSH and cell viability in ARPE-19 cells. Cells were exposed to various concentrations of HOHA lactone and after 24 h (A) the intracellular GSH level was quantified by the DTNB method. Cells were harvested and the GSH level in the cell lysate was quantified by colorimetric assay; (B) cell viability was quantified by an MTT assay. The data are presented as mean ± SEM of % control, n = 3~6; *P<0.05, ***P<0.001.

174

4.2.3 Evaluation of HH as a scavenger of HOHA lactone in cell culture.

DHA is especially abundant in photoreceptor disk membranes. The light-induced oxidative fragmentation of DHA phospholipids in these membranes releases HOHA lactone that diffuses through cell membranes into RPE cells where GSH adducts are formed and secreted (Figure 4.6). Mitochondrial dysfunction might result from adduction of HOHA lactone to mitochondrial proteins or ethanolamine phospholipids.

Figure 4.6. HOHA lactone produced in photoreceptor disks dissociates into RPE cells where formation of covalent adducts with GSH, proteins and ethanolamine phospholipids causes mitochondrial dysfunction. A competing covalent adduction with HH may protect RPE cells against HOHA lactone-induced GSH depletion and cytotoxic covalent modification.

To block the depletion of glutathione in RPE cells by α,β-unsaturated aldehydes and the cytotoxic consequences of HOHA lactone on RPE cells, we evaluated the efficacy of various electrophile scavengers for preventing cell death, that is expected to be especially important under pathological conditions where GSH levels are depressed. First, we

175 examined the ability of some common aldehyde traps to scavenge the HOHA lactone using RP-HPLC. At high concentration (20 to 1, 10 mM scavenger to 0.5 mM HOHA lactone), HH (100 %), L-carnosine (95 %), methoxyamine (100 %) and glutathione (99 %) effectively scavenge HOHA lactone within an hour (Figure 4.7C). However, at lower concentrations (2 to 1, 1 mM scavengers to 0.5 mM HOHA lactone), the widely-studied

L-carnosine (20 %) did not scavenge HOHA lactone efficiently; instead, only HH (99 %) showed an appreciable ability to scavenge HOHA lactone as effectively as glutathione

(100 %) in one-hour incubation experiments (Figure 4.7A-C).

Figure 4.7. HH is a scavenger of HOHA lactone in RPE cells in culture. (A) The levels of HOHA lactone after incubation for 1 h with various scavengers (1 mM) with HOHA lactone (0.5 mM; scavenger/aldehyde ratio = 2:1) at 37 °C. (B) Reaction rate constants (Kobs) of scavengers (from panel A using sigmoidal curve fitting, %At = A0 × eKobs). (C) Comparison of HOHA lactone consumption after 1h incubation with scavengers (1 mM, scavenger/aldehyde ratio = 2:1; 10 mM, scavenger/aldehyde ratio = 20:1).

4.2.4 HH forms covalent adducts with HOHA lactone and HOHA lactone-GSH

L-Carnosine forms a cyclic adduct with 4-HNE. Since HH, like L-carnosine, has a histidyl functional group and a terminal NH2 group, we expected that a similar adduct would also form with HOHA lactone. After 24 hours incubation of an equimolar mixture of HOHA lactone and HH at 37 oC, two ions appeared in the positive mode of the mass

176

+ + spectrum, [M+ H] = 292 and [M+H2O+H] = 310 (Figure 4.8A) that correspond the expected adducts.

We previously reported that HOHA lactone is metabolized by RPE cells to form

HOHA lactone-GSH adducts by Michael addition of glutathione to HOHA lactone. It still possesses an aldehyde group that can react with primary amino groups. We found that

HH reacts with HOHA lactone-GSH to form a Schiff-base adduct after 24 h incubation at

37 oC. In the positive mode of the mass spectrum, [M+ H]+= 599 and [1/2M+ H]+= 300 were found (Figure 4.8B).

Figure 4.8. HH is a scavenger of HOHA lactone in RPE cells in culture. Mass spectra of the HH covalent adducts with (A) HOHA lactone and (B) HOHA lactone-GSH.

4.2.5 Cellular uptake and cytotoxicity of HH

To examine if HH is taken up by ARPE-19 cells, we used LC-MS/MS to quantify its amount in ARPE-19 cells. After incubation with 50 to 800 µM HH for 24 h, a dose- dependent increase of its cellular levels (1.2 pmol per mg protein at 50 µM to 10 pmol per mg protein at 800 µM) indicated RPE cells are able to acquire HH from exogenous sources (Figure 4.9A). To examine the intrinsic toxicity of HH to the cells, we used the

MTT assay to evaluate the cell viability. After exposure to HH concentrations up to 1 mM, ARPE-19 cells did not show any significant decrease in cell viability. Thus, within

177 this concentration range, HH does not exhibit any cytotoxicity toward RPE cells (Figure

4.9B).

Figure 4.9. HH is a scavenger of HOHA lactone in RPE cells in culture. (A) Uptake of HH by ARPE-19 cells. HH in the cells was quantified by LC-MS/MS using a standard curve after 24 h incubation in a cell culture medium containing 50 ~ 800 µM HH. The data are presented as mean ± SEM, n = 3. (B) HH lacks cytoxicity toward ARPE-19 cells. ARPE-19 cells were exposed for 24 h to the indicated concentrations of HH and cell viability was measured by MTT assay. The data are presented as a box plot, n = 6.

4.2.6 Protective effect of HH on GSH levels, cell viability and mitochondrial health

HOHA lactone is cytotoxic to ARPE-19 cells, as are other α,β-unsaturated aldehydes such as 4-HNE and acrolein. Incubation of ARPE-19 cells for 24 h with 20 µM HOHA lactone results in 80% loss of metabolic viability (Figure 4.10A). The efficacy of HH for preventing RPE cell death induced by HOHA lactone was assessed with an MTT assay.

Incubation of cells for 1 h with 50 µM HH followed by incubation for 24 h with 20 µM

HOHA lactone caused ~50% decrease in viable cells compared ~80% decrease in the absence of HH. With 600 µM HH pretreatment, most of the cells were completely protected against HOHA lactone toxicity. Pretreatment with HH also diminished the decrease of mitochondrial membrane potential induced by HH (Figure 4.10B). In addition, while the levels of GSH after treatment with 20 μM HOHA lactone for 2 h,

178 decreased from 25 nmol/mg protein to 9 nmol/mg protein (70% decrease), 1 h pretreatment with HH attenuated the decrease of GSH (Figure 4.10C). In the presence of

25 μM HH, the GSH levels in RPE cells only decreased to 12 nmol/mg protein (~50% of control) and in the presence of 500 μM HH, the cells retained >90% of their GSH (Figure

4.10C).

Figure 4.10. Protection of ARPE-19 cells by HH against HOHA lactone -induced cell dysfunction. (A) Cell viability was measured using an MTT assay. (B) Mitochondrial membrane potential (Δψm) was measured using a JC-10 assay. Cells were exposed to

HOHA lactone after HH pretreatment (1h), and cell viability or Δψm were measured after 24 h incubation. The data are presented as mean ± SEM of % control, n = 6. (C) Cells were exposed to HOHA lactone after HH pretreatment (1 h) and harvested after 24 h. The intracellular GSH level in the cell lysate was quantified by a DTNB assay. The data are presented as mean ± SEM, n = 3; **P<0.01, ***P<0.001 compared with the value for HOHA lactone treatment in the absence of HH.

The efficacy of HH for preventing HOHA lactone-induced mitochondrial damage in

RPE cells was assessed. Pretreatment with 200 µM HH prior to incubation for 24 h with

179

20 µM HOHA lactone, allowed 80% retention of Δψm (Figure 4.10B). Pretreatment with

HH, also caused a dose-dependent decrease of mitochondrial ROS production. The levels dropped to basal in the presence of 400 µM HOHA lactone (Figure 4.11A). Incubation of

ARPE-19 cells with 40 µM HOHA lactone for 24 h also reduced the cellular ATP content to 25% that of control cells, while pretreatment with HH effectively abolished the decrease of ATP level (Figure 4.11B). These observations demonstrate that HOHA lactone can impair mitochondrial energy metabolism, and HH is able to ameliorate the metabolic damage engendered by α,β-unsaturated aldehyde electrophiles.

Figure 4.11. Protection of ARPE-19 cells by HH against HOHA lactone-induced cell dysfunction. (A) Mitochondrial ROS levels quantified by MitoSOX staining. Cells were exposed to HOHA lactone for 1 h after HH pretreatment, and stained with MitoSOX before measuring oxidized reagent in a microplate reader. (B) ATP level was quantified by a luciferin-luciferase based assay. Cells were exposed to HOHA lactone after 1 h HH pretreatment, and the ATP level was measured after subsequent 24 h incubation with HOHA lactone. The data are presented as mean ± SEM of % control, n = 3 for A and n = 5 for B; *P<0.05, **P<0.01 compared with HOHA lactone treatment in the absence of HH.

4.2.7 HH reduces CEP generation in RPE cells

HOHA lactone reacts with primary amino groups in biomolecules to generate CEPs.

These DHA-derived modifications have significant pathological and physiological

180 significance to AMD, cancer and wound healing. Treatment of ARPE-19 cells with 10

μM HOHA lactone caused a significant increase in levels of CEP indicated by a 100% increase in red fluorescence intensity owing to immunostaining with anti-CEP antibody

(Figure 4.12A). Pretreatment with concentrations of HH higher than 100 μM caused a significant drop in red fluorescence and at 200 μM the red fluorescence decreased almost to the basal level (Figure 4.12B). Thus HH efficiently scavenges HOHA lactone preventing its reaction with proteins and/or ethanolamine phospholipids and the consequent generation of CEP derivatives.

Figure 4.12. HH prevents adduction of HOHA lactone to proteins and ethanolamine phospholipids to form CEP derivatives in ARPE-19 cells. Cells were exposed to 10 μM HOHA lactone for 24 h with or without HH pretreatment and then immunostained with primary rabbit anti-CEP polyclonal antibody/secondary goat anti-rabbit Texas Red-X antibody. (A) Images were acquired using a Leica inverted fluorescent microscope. (B) Red fluorescence intensity was quantified as the CEP level. The figure is representative of four independent experiments that showed very similar results. The data are presented

181 as mean ± SEM; ***P<0.001 compared with the value for HOHA lactone treatment in the absence of HH.

4.2.8 Efficacy of Nα-acyl HH derivatives as HOHA lactone traps to prevent HOHA lactone cytotoxicity

Because HH is able to rescue RPE cells by scavenging HOHA lactone and its metabolites, to maximize its protection effect, a series of Nα-acyl HH derivatives was prepared to test the effect of increasing their lipophilicity. An efficient synthesis of derivatives of the α-amino group with acyl groups, including straight chains (n = 0, 8~11), branched chains or rings was achieved by reacting L-histidine methyl ester with either acyl chlorides or anhydrides followed by nucleophilic substitution with hydrazine (Figure

4.13).

Figure 4.13. Synthesis of Nα-acyl HH derivatives. (A) Synthetic approach used for preparation of HH analogues. (B) Chemical structures of HH analogues prepared.

182

AcHH (C1), tBocHH (C4) and tBuHH (C4), like HH are water soluble and were dissolved in phosphate buffered saline. However, cPHH (C5), cHHH (C6), nHH (C8), dHH (C9), uHH (C10) and DdHH (C11) are water-insoluble and were added to the culture medium as solutions in DMSO. Derivatives with long aliphatic chains were only slightly soluble even in DMSO. Thus, to avoid exceeding the tolerable concentration of

DMSO in the culture medium for the RPE cells, for the compounds with aliphatic chains longer than 9 carbons, 50 µM in culture medium contained a ~1% final concentration of

DMSO.

Figure 4.14. RPE cell viability protection by HH analogues. ARPE-19 cell viability (measured using MTT assay). Cells were exposed to HOHA lactone (20 µM) after pretreatment with 50 µM of HH or its Nα-acyl derivatives (cell viability was measured after 24 h). The data are presented as mean ± SEM of % control, n = 6; *P<0.05, ***P<0.001 compared with the value for HOHA lactone alone.

To compare their abilities to prevent HOHA lactone induced cell death, RPE cells were incubated with 20 µM HOHA lactone and 50 µM HH or the Nα-acyl derivatives.

Derivatives with carbon chains shorter than 7 gave protection comparable to unmodified

HH (Figure 4.14). This confirms the conclusion implicit in the structure of the HH-HL adduct (Figure 4.8A) that the α-amino group in HH is not important for the protective

183 efficacy of HH or its Nα-acyl derivatives. While longer and more hydrophobic aliphatic side chains at the N-terminus of HH, which increased its lipophilicity, apparently also caused these derivatives to be more cytotoxic, perhaps owing to the damage they cause to cell membranes.

To examine the ability of HH and its derivatives to protect mitochondrial respiratory chain complexes against the toxicity of HOHA lactone, isolated ARPE-19 cell mitochondria were pretreated with HH, AcHH, tBuHH or cHHH for 10 minutes before incubation with HOHA lactone. HOHA lactone at 20 µM was chosen as an optimal concentration to reduce, but not completely inhibit the enzyme activity for complex I, while 50 µM was chosen for complex II and 100 µM was selected for complex IV.

Complex I specific activity of mitochondria exposed to 20 µM HOHA lactone was only protected by pretreatment with 400 µM (a 20x excess) of histidyl hydrazide derivatives except for cHHH that did not show significant protection at any concentration tested. At 400 µM, HH showed a 2.5-fold increase of complex I activity, AcHH showed a

1.5-fold and tBuHH showed a 2-fold increase, but cHHH did not provide any protection

(Figure 4.15A). Nα-acylation did not improve the prophylactic efficacy of any of the derivatives relative to HH itself.

For mitochondria exposed to 50 µM HOHA lactone, significant protection of complex II activity was observed even by pretreatment with relatively low concentrations of the histidyl hydrazide derivatives except for cHHH. Especially at 80

µM, HH, AcHH and tBuHH all demonstrated 90~100% protection of enzyme activity while cHHH did not provide any protection (Figure 4.15B). Presumably because HOHA lactone did not exert much inhibition of complex IV activity in mitochondria exposed to

184

100 µM HOHA lactone, all of the derivatives provided full or almost full protection against the toxicity of HOHA lactone against complex IV (Figure 4.15C). Unexpectedly, even 1 mole % of HH, AcHH or cHHH relative to HOHA lactone was effective.

Figure 4.15. Protective efficacy of HH and its Nα-acyl derivatives for the protective activities of mitochondrial complexes I, II and IV against HOHA lactone toxicity.

Isolated mitochondria were incubated with HH or its Nα-acyl derivatives for 10 min followed by HOHA lactone for 30 min and the specific enzymatic activities of complexes (A), complex II (B) and complex IV (C) were measured spectrophotometrically (see Materials and methods for details). The data are presented as mean ± SEM of % control, n = 3; *P<0.05, **P<0.01, ***P<0.001 compared with the HOHA lactone alone value.

185

4.3 Discussion

Exposing RPE cells to light promotes both the generation HOHA lactone glutathione

(GSH) adducts and a competing production of 2-(ω-carboxyethyl)pyrrole (CEP) derivatives of proteins and ethanolamine phospholipids through adduction of HOHA to primary amino groups.18 CEP derivatives are found in plasma from individuals with age- related macular degeneration (AMD) and in drusen from AMD donor eye tissues. CEP promotes vascular angiogenesis51 and platelet activation through Toll-like receptor-2 and

Toll-like receptor-9 dependent signaling pathways.52 HOHA lactone can also stimulate angiogenesis through induction of VEGF secretion by RPE cells16, and promote RPE cell apoptosis consequent to lysosomal membrane permeabilization, mitochondrial membrane potential dissipation, cellular senescence18 and complement system induction.17

4.3.1 Mechanisms of HOHA lactone -induced mitochondrial dysfunction and oxidative stress

The pathogenesis of AMD involves apoptosis of RPE cells followed by death of the underlying photoreceptors.53 Mitochondrial dysfunction is a factor in the development and progression of AMD. Evidence supporting this view includes loss in mitochondrial mass, disrupted cristae, ruptured membranes, decreased content of proteins in the electron transport chain and fragmented mitochondrial (mt)DNA in RPE cells from human donors with AMD.5 Mitochondria are responsible for aerobic respiration and ATP synthesis by oxidative phosphorylation. In addition to being crucial for energy production and metabolic pathways, they also play key roles in integrating cell death stimuli and executing the apoptotic program. Impaired function of the electron transport chain (ETC) in the oxidative phosphorylation (OXPHOS) system can result in increased formation of

186 reactive oxygen species and cause disturbances of energy metabolism.46, 47 Decreased

ATP production leads to impairment of ATP-dependent processes, where all cellular functions are involved.54-56 Decrease of mitochondrial membrane potential is followed by opening of mitochondrial permeability transition pores (MPTPs).57-59 Subsequent release of cytochrome c and other proapoptotic factors from the intermembrane space of mitochondria induces the formation of apoptosomes and consequently triggers activation of caspases and ultimately leads to apoptosis.56 The present study found that the cytotoxicity of HOHA lactone toward RPE cells includes the induction of mitochondrial dysfunction.

Previously, we showed that HOHA lactone reduces ARPE-19 cell viability by the

MTT, Alamar blue and LDH assays. The MTT assay measures mitochondrial succinate dehydrogenase (Complex II) activity. It corresponds to the ability of HOHA lactone to affect mitochondrial metabolic activity. To further understand the effect of HOHA lactone on mitochondria, we now studied the individual activities of OXPHOS complexes

I to IV, mitochondrial ROS, cellular ATP level and mitochondrial membrane potential.

The results of those studies provide mechanistic insights into HOHA lactone-induced damage of mitochondria that lead to apoptosis or necrosis of RPE cells (Figure 4.16). By inducing inhibition of complex I, HOHA lactone causes a decrease of electron flow through upstream sites that are prone to electron leakage. With electrons remaining at the site longer than normal, molecular oxygen can react via a one-electron reduction to produce superoxide that is released from the mitochondria. Increased mitochondrial ROS generation was confirmed by MitoSOX staining. HOHA lactone also induced inhibition

187 of complexes II and IV, contributing further to HOHA lactone-induced OXPHOS dysfunction and aberrant mitochondrial respiration.

Figure 4.16. HOHA lactone depletes endogenous antioxidant GSH, impairs mitochondrial respiratory chain complexes, induces consequent ROS production, ATP depletion and mitochondrial membrane potential dissipation, leading to mitochondrial damage and cell death.

In intact mitochondria, the electron flow through the respiratory chain generates a proton electrochemical gradient, whose major component is the membrane potential

60 (ΔΨm), inside (matrix) negative. The proton gradient drives the ATP hydrolyzing F0F1-

ATPase to function as an ATP synthase that promotes the phosphorylation of ADP to 188

ATP.61 Inhibition of the electron transport chain by HOHA lactone leads to an imbalance of the charge distribution between the matrix and intermembrane space causing ΔΨm to decrease. To prevent this, the F0F1-ATPase starts to function as a proton pump and hydrolyses ATP. The anticipated decrease of cellular ATP level induced by HOHA lactone was observed using the Celltiter-glo assay. When severe damage of OXPHOS by

HOHA lactone becomes irreversible, the ATPase can no longer maintain the mitochondrial membrane potential causing collapse of the ΔΨm that was detected by the

JC-10 probe (Figure 4.4B). The increase of mitochondrial ROS levels gradually spreads to other cellular compartments and leads to a global increase of oxidative stress as was detected by CM-H2DCFDA staining (Figure 4.3A). Dissipation of the mitochondrial membrane potential is believed to be followed by opening of mitochondrial permeability transition pores (MPTPs)57-59 and release proapoptotic factors which will then further trigger apoptosis and induce cell death, which could be intensified by the decrease of the endogenous cellular antioxidant GSH.56

Scavenging α,β-unsaturated aldehyde products of lipid oxidation as a strategy for ameliorating aldehyde-induced mitochondrial damage must recognize the multiple sources of these toxins. Three sources of HOHA lactone may contribute to RPE mitochondrial dysfunction, exogenous HOHA lactone derived from photoreceptor disk membranes and endogenous HOHA lactone derived from the RPE cell membrane or from the mitochondrial inner membrane. HH in the interphotoreceptor matrix and GSH in the RPE cytosol can intercept exogenous HOHA lactone. To intercept endogenously generated HOHA lactone, HH must accumulate within the RPE cell cytosol. The concentration of HOHA lactone that we applied to isolated mitochondria to inhibit

189

OXPHOS complex activities may be higher than what is needed to cause mitochondrial respiratory impairment. Some of this HOHA lactone may be consumed by adduction to components of the outer mitochondrial membrane. Ultimately, only a smaller portion will reach the inner mitochondrial membrane where it reacts with various proteins involved in oxidative phosphorylation.62-64 For mitochondria in RPE cells under oxidative stress,

HOHA lactone may be generated within the stressed mitochondria and is therefore able to impair respiratory function at a much lower concentration compared with what we added exogenously. Similarly, if a major fraction of the HOHA lactone in RPE cells that impacts the mitochondria in vivo is from photoreceptor disk membranes in photoreceptor cell outer segments or in phagosomes within the RPE cells, the mitochondria would only be exposed to a portion of the exogenous HOHA lactone applied to RPE cells because some would be intercepted by covalent adduction to GSH within the cells.

4.3.2 HH, a potential drug for RPE protection against lipid peroxidation products

To defend against toxic oxidative metabolites, especially reactive α,β-unsaturated aldehydes, such as HOHA lactone, 4-HNE, 4-HHE or acrolein, RPE cells detoxify them by Michael addition of endogenous GSH. However, the cellular level of GSH may be insufficient if large quantities of these aldehydes are generated or if there is an abnormally low level of GSH in the cells.

The protective mechanism of L-carnosine against 4-HNE in cells was shown to involve formation of a cyclic adduct with 4-HNE.30 In analogy with L-carnosine, because

HH has an imidazole functional group and a terminal prmary amino group, it forms a similar adduct with HOHA lactone by a two-step reaction: Schiff-base formation between the aldehyde and a hydrazide (primary amine) followed by intramolecular Michael

190 addition between the histidine nitrogen and the C=C double bond. In the present study, to trap and detoxify HOHA lactone, we utilized the HH analogue of carnosine, which combines the imidazole ring and the L stereochemistry of “histidine” with an aldehyde- reactive “hydrazide” moiety. After the aldehyde carbonyl group reacts with the hydrazide moiety, the imidazole nitrogen undergoes an intramolecular Michael addition cyclization reaction. This increases its scavenging efficiency for α,β-unsaturated aldehydes.44 Also, placing the histidine residue at the C-terminus instead of the N-terminus avoids recognition and catabolism by the specific enzyme carnosinase.44, 65 HH was previously reported to be significantly more effective than carnosine and other histidine analogues in protecting neurons against 4-HNE toxicity and in alleviating brain damage related to stroke and improving functional outcome in a mouse model of focal ischemic stroke. In the present study, HOHA lactone scavenging activity tests showed that HH has superior efficacy compared to other common scavenging compounds including carnosine even at low concentrations. This suggested its potential utility as a cytoprotective drug that targets lipid peroxidation products.

We previously reported that HOHA lactone is metabolized by RPE cells forming

HOHA lactone-GSH that is then reduced to an alcohol, DHHA-lactone GSH by aldose reductase.18 However, deficiency of aldose reductase or the NADPH cofactor might lead to incomplete metabolism and stop at HOHA lactone-GSH, which still possesses an aldehyde functional group and retains the potential to react with amino groups. Now we discovered that HH can also react with HOHA lactone-GSH and form a Schiff-base adduct and quench its reactivity.

191

4.3.3 HH protects RPE cells against HOHA lactone induced mitochondrial impairment

Retina contains an abundance of polyunsaturated fatty acyls, especially DHA phospholipids that are extremely susceptible to light-induced peroxidation that generates oxidation metabolites including HOHA lactone and 4-HHE. Therefore, it was reasonable to presume that HH might act as a protective agent against oxidative damage in RPE cells and could be a potential therapeutic agent for the prevention, and therapy of AMD and other retinal disorders associated with oxidative stress. In the present study, we showed that HH was able to protect RPE cells against HOHA lactone induced cell death and to prevent depletion of cytosolic GSH by HOHA lactone-induced decrease. HH also inhibited the formation in RPE cells of CEP adducts, by adduction of HOHA lactone with proteins or ethanolamine phospholipids. Pretreatment of mitochondria with HH prevents

HOHA lactone -induced: (1) impairment of the activities of the mitochondrial respiratory chain complexes I, II and IV, (2) decreases of ATP levels and loss of mitochondrial membrane potential and (3) increased mitochondrial ROS generation.

These observations are consistent with HH serving as an inhibitor of advanced lipoxidation end product (ALE) formation and its pathological consequences through: (1) inhibiting lipid oxidation and breakdown to reactive carbonyl species (RCS) by scavenging the reactive oxygen species (ROS), (2) detoxifying reactive carbonyl species, such as HOHA lactone, 4-HNE, acrolein; and possibly (3) reacting with carbonylated proteins, such as lysine adducts, histidine adducts and cysteine adducts (Scheme 4.1).

192

Scheme 4.1. HH as an inhibitor of lipid peroxidation product formation and pathological reactions. Nu represents protein nucleophilic sites undergoing adduction to RCS. HH can act as inhibitor by: 1) inhibiting lipid oxidation and breakdown to RCS; 2) detoxifying RCS; and possibly 3) reacting with carbonylated proteins.

We now showed that exogenous HH can enter ARPE-19 cells and its level is maintained for at least 24 h. Furthermore, at concentrations as high as 1 mM, HH did not show any intrinsic toxicity, which will allow an increased concentration range for treatment. However, HH is a highly hydrophilic compound. To protect RPE cells against exogenous HOHA lactone that diffuses into RPE cells or against HOHA lactone

193 generated endogenously inside RPE cells, it is necessary for HH to diffuse into the cells.

To be effective as an intracellular inhibitor it must penetrate the RPE cell membrane.

Furthermore, therapeutic HH derivatives that are more lipophilic than HH might be advantageous for eyedrop delivery by allowing intraocular bioavailability through transcorneal penetration. Therefore, the present study also tested the hypothesis that more lipophilic N-acylated derivatives of the histidyl amino group might retain protective activity against α,β -unsaturated aldehydes such as HOHA lactone. We found that certain

Nα-acyl HH derivatives retain full prophylactic α,β-unsaturated aldehyde scavenging activity that protects RPE cells against HOHA lactone toxicity. However, derivatives with acyl chains longer than 7 carbons are cytotoxic to the cells, while compounds with side chain shorter than 7 showed protection comparable to HH against HOHA lactone induced cell death. However, among the four derivatives we examined, only the compounds with side chain shorter than 4 showed significant protection of mitochondrial

OXPHOS complexes I, II and IV.

194

4.4 Conclusions and Future Prospects

The present study tested the hypothesis that the HOHA lactone -induced damage to

RPE cells may involve mitochondria. We now showed that HOHA lactone inhibits mitochondrial respiration and leads to (1) electron leakage resulting in increasing oxidative stress and (2) imbalance of the charge distribution resulting in collapse of the

ΔΨm and accelerating mitochondrial ATP consumption. The dissipation of ΔΨm triggers apoptosis and induces cell death, which is intensified by the decrease of cellular intrinsic antioxidant GSH levels. This toxicity may contribute to the progression of age-related macular degeneration.

A strategy to protect the RPE cells against lipid peroxidation product-induced damage was designed. The present study indicated that HH in the interphotoreceptor matrix can intercept exogenous HOHA lactone derived from photoreceptor disk membranes.

However, to intercept endogenously generated HOHA lactone, HH must accumulate within the RPE cell cytosol. Derivatizing HH to more lipophilic analogues was envisioned as a potential strategy to facilitate trans membrane diffusion of an HH therapeutic and, possibly, to allow transcorneal delivery in eye drops. Towards this end, the present study established that the α-amino group in HH is not essential for its protective activity against α,β-unsaturated aldehydes such as HOHA lactone. Ac-HH, boc-HH, tBu-HH and cH-HH, which are Nα-acyl derivatives of HH, are equally effective as HH in protecting ARPE-19 cells against HOHA lactone toxicity (Figure 4.14).

Apparently, these Nα-acyl HH derivatives retain full prophylactic α,β-unsaturated aldehyde scavenging activity that protects mitochondria against HOHA lactone toxicity.

This finding may be useful for the design of therapeutic HH derivatives that are more

195 lipophilic than HH, which might be advantageous for eyedrop delivery by allowing intraocular bioavailability through transcorneal penetration. While HH itself showed the best efficacy, the N-acyl derivatives may be converted by deacetylating enzymes to HH after transcorneal diffusion into the aqueous humor and into RPE cells.

Immunotherapeutic drugs such as Avastin (bevacizumab) and Lucentis (ranibizumab), which are anti-VEGF (vascular endothelial growth factor) drugs that block growth of abnormal blood vessels and leakage of fluid from the vessels, were recently designed as eyedrops by including an oligoarginine cell-penetrating peptide (CPP) as chaperone agent.66 Daily, topically delivery of anti-VEGF with CPP in eyedrops was shown to be as efficacious as a single intravitreal (ivit) injection of anti-VEGF in reducing areas of

CNV in rat eyes. Therefore, co-administration of HH derivatives with anti-VEGF drugs as eye drops may be effective therapies for preventing oxidative stress-induced or age- related RPE degeneration.

196

4.5 Experimental Procedures

Materials. Dulbecco’s modified Eagle’s cell culture medium and Ham’s F12 cell culture medium F-12 (1:1 mixture, DMEM/F12), Dulbecco’s phosphate-buffered saline

(DPBS), Hank’s balanced salt solution (HBSS), 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) were purchased from Fisher Scientific (Pittsburgh,

PA). Heat-inactivated fetal bovine serum (FBS) was from Equitech-Bio, Inc. (Kerrville,

TX). Texas Red-X Goat anti-Rabbit IgG (H+L) cross-adsorbed secondary antibody (T-

6391) was from ThermoFisher Scientific (Waltham, MA). Flash Phalloidin™ Green 488 was from Biolegend (San Diego, CA). β-NADPH was obtained from Cayman Chemical

(Ann Arbor, MI). All other chemicals and reagents, including L-glutathione (reduced), glutathione reductase (250 units/mL) and 5,5’-dithiobis(2-nitrobenzoic acid) (DTNB) were purchased from Sigma-Aldrich (St. Louis, MO). 4-Hydroxy-7-oxohept-5-enoic acid

(HOHA) lactone was synthesized as described previously.67 A polyclonal rabbit anti-CEP antibody was raised and characterized as described previously.15 The Pierce 660 nm assay kit, Pierce BCA Protein Assay Kit and MitoSOX red reagent were obtained from

ThermoFisher Scientific (Waltham, MA) and used to determine a protein concentration in the lysates in accordance to the manufacture’s manual.

General Methods. NMR spectra were acquired on a 500 MHz Bruker Ascend Avance

III HDTM (Bruker, Billerica, MA) equipped with a Prodigy ultra-high sensitivity multinuclear broadband CryoProbe operating at 500 and 125 MHz for 1H and 13C, respectively. They were referenced internally according to residual solvent signals. All

ESI mass spectra were obtained from a Thermo Finnigan LCQ Deca XP (ThermoFisher

Scientific, Waltham, MA). High-performance liquid chromatography (HPLC) was

197 performed on a Shimadzu UFLC system equipped with a 5 μm Phenomenex Luna C-18 column (Torrance, CA). Flash column chromatography was performed on 230−400 mesh silica gel supplied by Sigma-Aldrich (St. Louis, MO) with ACS grade solvent. Rf values are quoted for plates with thickness of 0.25 mm. The plates were visualized with iodine,

UV, and/or phosphomolybdic acid reagents. All reactions were carried out under an argon atmosphere. All reagents were obtained commercially unless otherwise noted.

Reactions were performed using glassware that was oven-dried at 120 °C. Air and moisture sensitive liquids and solutions were transferred via syringe or stainless-steel cannula. Proton and carbon NMR spectra of all new compounds are provided in

Appendix Figures A4.1-A4.26.

Syntheses.

HH (1). Into a solution of L-histidine methyl ester (1.21 g, 5 mmol) in 15 mL of

MeOH was dropped in 970 µL of 98% hydrazine hydrate (20 mmol). The mixture was stirred for 24 h. The resulting white precipitate was removed by filtration and the filtrate was concentrated under reduced pressure. The yellow oily residue was treated with

MeOH and triturated a few more times to remove the remaining N2H4•HCl. The crude

1 product was then crystallized from a MeOH/Et2O mixture to give pure hydrazide. H

13 NMR (500 MHz, D2O) δ 7.65 (s, 1H), 6.88 (s, 1H), 3.61 (t, 2H), 2.82−2.91 (m, 2H); C

NMR (126 MHz, D2O) δ 173.48, 135.93, 132.43, 117.01, 53.25, 31.05.

N,Nα-Acetyl L-histidyl methyl ester. To a suspension of L-histidine methyl ester dihydrochloride (1.206 g, 5 mmol) in DCM (200 ml), Et3N (1.4 mL, 10 mmol), Ac2O

(2.17 mL, 23 mmol) was added dropwise and then the mixture was stirred at room temperature for 20 h. The mixture was washed with saturated aqueous solution of

198

NaHCO3 (2 x 50 mL). The organic layer was collected and the solvent was evaporated under reduced pressure. The residue was dried under reduced pressure, giving of Ac-L-

His-OMe·AcOH as a white solid. 1H NMR (500 MHz, DMSO-d6) δ 8.32 (s, 1H), 8.24 (d,

1H), 7.42 (s, 1H), 4.50 (q, 1H), 3.60 (s, 3H), 2.90 (dd, 1H), 2.82 (dd, 1H) 2.58 (s, 3H),

1.81 (s, 3H)

General method for the preparation of Nα-acyl L-histidyl methyl esters. To a suspension of L-histidine methyl ester dihydrochloride (1.206 g, 5 mmol) in dry DCM

(25 mL), Et3N (3.485 mL, 25 mmol) was added. Then acid chloride (5.25 mmol) was added dropwise at 0 °C and the reaction mixture was allowed to warm to RT and stirred until no more starting material was observed by TLC. The reaction mixture was poured into saturated NaHCO3 and extracted three times with CH2Cl2. The combined organic phases were washed with brine, dried over Na2SO4 and concentrated under reduced pressure. Purification by column chromatography (CH2Cl2/MeOH 10:1) gave the title compounds as a white solids: Rf = 0.15 (CH2Cl2/MeOH =10:1)

1 Nα-Trimethylacetyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ 7.58 (s,

1H), 6.81 (s, 1H), 4.76 (dt, J = 7.4, 5.1 Hz, 1H), 3.70 (s, 3H), 3.11 (qd, J = 14.9, 5.2 Hz,

2H), 1.21 (s, 9H).

1 Nα-Cyclohexanecarbonyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ

7.58 (s, 1H), 6.98 (s, 1H), 6.81 (s, 1H), 4.81 (dt, J = 7.7, 5.1 Hz, 1H), 3.70 (s, 3H), 3.11

(qd, J = 14.9, 5.2 Hz, 2H), 2.15 (tt, J = 11.7, 3.5 Hz, 1H), 1.92 – 1.82 (m, 2H), 1.81 – 1.73

(m, 2H), 1.69 – 1.62 (m, 1H), 1.43 (qt, J = 12.1, 3.1 Hz, 2H), 1.32 – 1.18 (m, 3H).

199

1 Nα-Cyclopentanecarbonyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ

7.57 (s, 1H), 6.81 (s, 1H), 4.81 (dt, J = 7.9, 5.2 Hz, 1H), 3.70 (s, 3H), 3.20 – 3.04 (m, 2H),

2.61 (p, J = 7.9 Hz, 1H), 1.92 – 1.51 (m, 8H).

1 Nα-Nonanoyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ 7.58 (s, 1H),

6.82 (s, 1H), 4.83 (dt, J = 7.7, 4.9 Hz, 1H), 3.70 (s, 3H), 3.19 – 3.03 (m, 2H), 2.23 (t, J =

7.7 Hz, 2H), 1.62 (d, J = 7.8 Hz, 2H), 1.36 – 1.19 (m, 10H), 0.87 (t, J = 6.8 Hz, 3H).

1 Nα-Decanoyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ 7.56 (s, 1H),

7.00 (s, 1H), 6.81 (s, 1H), 4.82 (dt, J = 7.7, 5.2 Hz, 1H), 3.70 (s, 3H), 3.11 (qd, J = 14.9,

5.2 Hz, 2H), 2.23 (t, J = 7.7 Hz, 2H), 1.62 (d, J = 7.5 Hz, 2H), 1.33 – 1.23 (m, 12H), 0.87

(t, J = 6.8 Hz, 3H).

1 Nα -Undecanoyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ 7.57 (s, 1H),

6.82 (s, 1H), 4.83 (dt, J = 7.9, 5.2 Hz, 1H), 3.70 (s 3H), 3.11 (qd, J = 14.9, 5.2 Hz, 2H),

2.23 (dd, J = 8.3, 6.9 Hz, 2H), 1.63 (q, J = 7.5 Hz, 2H), 1.27 (m, 14H), 0.88 (t, J = 6.8 Hz,

3H).

1 Nα-Dodecanoyl L-histidyl methyl ester. H NMR (500 MHz, CDCl3) δ 7.59 (s, 1H),

6.95 (s, 1H), 6.84 (s, 1H), 4.84 (dt, J = 7.7, 5.2 Hz, 1H), 3.72 (s, 3H), 3.13 (qd, J = 15.0,

5.2 Hz, 2H), 2.32 – 2.18 (m, 2H), 1.70 – 1.61 (m, 2H), 1.29 (d, J = 15.8 Hz, 16H), 0.90 (t,

J = 6.9 Hz, 3H).

General method for the preparation of Nα-acyl HH (2). To a solution of Nα-acyl-L-

His-OMe (1 mmol) in 10 mL of MeOH was added 194 µL of 98% hydrazine hydrate (4 mmol) dropwise. The mixture was then stirred for 24 h at room temperature. During the reaction the a white precipitate of the product formed. The product was collected by filteration and then dried under reduced pressure.

200

1 Nα-Acetyl HH. H NMR (500 MHz, D2O) δ 7.69 (s, 1H), 6.96 (s, 1H), 4.49 (dd, J =

8.1, 6.5 Hz, 1H), 3.07 – 2.96 (m, 2H), 1.98 (s, 3H).

1 6 Nα-Trimethylacetyl HH. H NMR (500 MHz, DMSO-d ) δ 11.80 (s, 1H), 8.96 (s,

1H), 7.52 (m, 2H), 6.76 (s, 1H), 4.39 (q, J = 7.2 Hz, 2H), 4.16 (s, 2H), 2.84 (d, J = 7.0 Hz,

2H), 1.05 (s, 9H).

1 6 Nα-Cyclohexanecarbonyl HH. H NMR (500 MHz, DMSO-d ) δ 11.72 (s, 1H), 9.03

(s, 1H), 7.79 (d, J = 8.3 Hz, 1H), 7.50 (s, 1H), 6.86 – 6.65 (m, 1H), 4.40 (td, J = 8.4, 5.4

Hz, 1H), 4.18 (s, 2H), 2.73 (t, J = 11.4 Hz, 2H), 2.12 (td, J = 11.1, 3.6 Hz, 1H), 1.71 –

1.54 (m, 5H), 1.19 (dddd, J = 36.3, 33.6, 17.2, 7.4 Hz, 5H).

1 6 Nα-Cyclopentanecarbonyl HH. H NMR (500 MHz, DMSO-d ) δ 11.74 (s, 1H), 9.06

(s, 1H), 7.86 (d, J = 8.3 Hz, 1H), 7.51 (s, 1H), 6.78 (s, 1H), 4.42 (td, J = 8.2, 5.4 Hz, 1H),

4.18 (s, 2H), 2.84 (s, 1H), 2.73 (dd, J = 14.7, 8.7 Hz, 1H), 2.57 (q, J = 7.8 Hz, 1H), 1.81 –

1.36 (m, 8H).

1 6 Nα-Nonanoyl HH. H NMR (500 MHz, DMSO-d ) δ 11.73 (s, 0.7H), 11.65(s, 0.3H),

9.05 (s, 1H), 7.91 (t, J = 10.6 Hz, 1H), 7.49 (s, 0.7H), 7.44 (s, 0.3H), 6.78 (s, 0.7H), 6.60

(s, 0.3H), 4.42 (t, J = 7.8 Hz, 1H), 4.21 (s, 0.66H), 4.16 (s, J = 4.3 Hz, 1.32H), 2.97 – 2.65

(m, 2H), 2.06 (q, J = 6.9 Hz, 2H), 1.41 (p, J = 7.4 Hz, 2H), 1.24 (m, 10H), 0.85 (t, J = 6.9

Hz, 3H).

1 6 Nα-Decanoyl HH. H NMR (500 MHz, DMSO-d ) δ 11.73 (s, 0.7H), 11.67 (s, 0.3H),

9.06 (s, 1H), 7.90 (d, J = 9.1 Hz, 1H), 7.51 (d, J = 12.9 Hz, 1H), 6.78 (s, 0.7H), 6.60 (s,

0.3H), 4.43 (d, J = 8.2 Hz, 1H), 4.21 (s, 0.66H), 4.16 (s, 1.32H), 2.97 – 2.65 (m, 2H),

2.12 – 1.93 (m, 2H), 1.41 (p, J = 7.6 Hz, 2H), 1.28 – 1.14 (m, 12H), 0.85 (t, J = 6.8 Hz,

3H).

201

1 6 Nα-Undecanoyl HH. H NMR (500 MHz, DMSO-d ) δ 11.73 (s, 1H), 9.06 (s, 1H),

7.91 (d, J = 8.2 Hz, 1H), 7.50 (d, J = 15.9 Hz, 1H), 6.78 (s, 0.7H), 6.63 (s, 0.3H), 4.42 (td,

J = 8.3, 5.6 Hz, 1H), 4.18 (s, 2H), 2.83 (s, 1H), 2.71 (dd, J = 14.6, 8.6 Hz, 1H), 2.05 (t, J

= 7.5 Hz, 2H), 1.55 – 1.32 (m, 2H), 1.29 – 1.14 (m, 16H), 0.85 (t, J = 6.8 Hz, 3H).

1 6 Nα-Dodecanoyl L-histidyl methyl ester. H NMR (500 MHz, DMSO-d ) δ 11.73 (s,

1H), 9.06 (s, 1H), 7.90 (d, J = 9.0 Hz, 1H), 7.51 (d, J = 12.5 Hz, 1H), 6.78 (s, 0.7H), 6.61

(s, 0.3H), 4.43 (s, 1H), 4.16 (s, 2H), 2.92 – 2.67 (m, 2H), 2.05 (s, 2H), 1.52 – 1.36 (m,

2H), 1.22 (d, J = 11.0 Hz, 18H), 0.85 (t, J = 6.7 Hz, 3H).

Cell culture. The cell line ARPE-19 (ATCC; CRL-2302), derived from spontaneously arising retinal pigment epithelia of a healthy person68, was obtained from the American

Type Culture Collection (Manassas, VA). The stock cells were grown on 100-mm dishes in a humidified CO2 incubator at 37 °C under 5% CO2 in Ham’s F12 medium and

Dulbecco’s modified Eagle’s medium (DMEM) (50:50 ratio), containing L-glutamine and 10% heat-inactivated FBS. Cells were trypsinized and passaged every 2-3 days. Cell passages 21−30 were used.

Microscopy. Images were collected on a Leica DMI 6000B inverted fluorescence microscope (Leica Microsystems, Wetzlar, Germany) using a Retiga EXI camera

(QImaging, Vancouver, British Columbia). Image analysis was performed using

MetaMorph Imaging Software (Molecular Devices, Downington, PA).

MTT cell viability assays. As described previously69, ARPE-19 cells (10,000 cells/ per well) were seeded into a 96-well flat bottom plate in 200 μL of complete DMEM/F12 medium supplemented with 10% FBS and allowed to attach to culture plates in a

202 humidified CO2 incubator at 37 °C under 5% CO2. After the cells reached ~80% confluence, they were starved in 200 μL of basal DMEM/F12 cell culture medium for 5 h overnight. The cells were then preincubated with HH or its Nα-acyl derivatives for 1 h, 6 replicate wells for each concentration, followed by 24 h incubation in 20 μM HOHA lactone in a humidified CO2 incubator at 37 °C under 5% CO2. The cell culture medium was then aspirated from each well and the cells were incubated for 2 h at 37 °C with 20

μL of filter (0.2 μm PES syringe filter)-sterilized MTT solution (5 mg/mL in DPBS) plus

180 μL of DMEM/F12 medium. The medium was aspirated from each well. Then dimethyl sulfoxide (DMSO) was added to each well (200 μL) to dissolve water-insoluble intracellular formazan crystals by repeatedly pipetting up and down the solution. The optical density (OD) of the formazan solutions at λ = 540 nm were measured with a plate reader (Spectramax M2, Molecular Devices, San Jose, CA) with a reference wavelength set λ = 670 nm to account for well content scattering.

Mitochondrial membrane potential assay. The JC-10 assay was performed by the method described previously70 with slight modifications. Briefly, after HOHA lactone treatment described above, to ARPE-19 cells in a 96-well flat bottom plate in 100 μL of basal DMEM/F12 cell culture medium was added 100 μL of 5 μg/mL stock solutions of

JC-10 in DPBS to establish 2.5 μg/mL final concentrations of JC-10 in each well. After subsequent incubation in a humidified CO2 incubator for 30 min at 37 °C under 5% CO2, the fluorescence was immediately measured with a fluorescence microplate reader

(Spectramax M2, Molecular Device, San Jose, CA) set at λEx/Em = 490/525 nm (cut off at

λ = 515 nm) for the green monomer and λEx/Em = 540/590 nm (cut off at λ = 570 nm) for

203 the red aggregate. Changes in mitochondrial membrane potential were derived from the green/red fluorescence ratio.

Mitochondrial Reactive Oxygen Species Assay. The production of superoxide in mitochondria was visualized with MitoSOX Red (Life Technologies, Waltham, MA).

ARPE-19 cells (10,000 cells/ per well) were plated on an 8-chamber well (Lab-Tek II

Chamber Slide System, Nunc, Rochester, NY) in the DEME/F12 with 10% FBS and incubated at 37 °C in 5% CO2 for three days. After being starved overnight, the cells were treated with 0 ~ 10 μM HOHA lactone and incubated for an additional 1 h.

Following cell culture medium aspiration, the cells were incubated with 5 μM MitoSOX in HBSS for 15 minutes at 37 °C. Cells were washed in warm DMEM/F12, fixed with 3.7%

PFA for 10 minutes, washed with DPBS, and mounted with DAPI Fluoromount-G

(Southern Biotech, Birmingham, AL). All images were acquired with a Leica DMI 6000

B inverted fluorescent microscope using a Retiga EXI camera. Image analysis was performed using Metamorph imaging software (Molecular Devices, Downington, PA).

The images were acquired at 20x magnification.

For quantitation, the assay was performed in 96-well microplate (5,000 cells/ per well) format by the method described above. After MitoSOX staining, the cells were washed with HBSS and the fluorescence was immediately measured without medium using a fluorescence microplate reader (Spectramax M2, Molecular Device) set at λEx/Em =

510/580 nm (cut off at λ = 570 nm) and normalized by BCA assay71 for the total protein concentration in each well. The BCA assay was conducted in original wells by adding 50

μL of lysis buffer (GoldBio, GB-180) to each well, and then using Pierce BCA assay kit

204 following the manufacturer’s protocol. Normalization was conducted by dividing the microplate reading by the measured total protein concentration.

Total Cellular Reactive Oxygen Species Assay. ARPE-19 cells (5,000 cells/ per well) were seeded into a 96-flat bottom well plate for three days. After starving overnight, the cells were incubated with 2 μM CM-H2DCFDA in HBSS for 45 minutes at 37 °C. After washing with HBSS, cells were treated with 0 ~ 20 μM HOHA lactone and well fluorescence was measured at various times using a fluorescence microplate reader

(Spectramax M2, Molecular Device) set at λEx/Em = 485/535 nm (cut off at λ = 530 nm) and normalized by the total protein concentration by BCA assay of each well as described above.

Quantification of Total Intracellular GSH in ARPE-19 Cells. ARPE-19 cells

(75,000 cells/ per dish) were seeded into 35 mm dishes in DMEM/F12 for three days.

After cells became confluent, they were starved for 3 h. The cells were then preincubated in HH for 1 h followed by 24 h incubation in 20 μM HOHA lactone. Aliquots (20 μL) of

ARPE cell lysates were assayed to determine total intracellular GSH levels using a 96- well microplate format described earlier.72 In these experiments, all of the reagents were prepared in 0.1 M potassium phosphate buffer with 5 mM EDTA disodium salt, pH 7.5

(KPE buffer). Briefly, 20 μL of KPE buffer, GSH standards, or samples were added to the respective microplate wells, followed by the addition of 120 μL of a freshly prepared

1:1 mixture of DTNB (2 mg/3 mL) and glutathione reductase (10 U/3 mL). Then, 60 μL of NADPH (2 mg/3 mL) was added and the plate was mixed well. The absorbance was read immediately at λ = 412 nm in a microplate reader (Spectramax M2, Molecular

Devices). Measurements were taken every 20 s for 5 min (15 readings in total from 0-300

205 s). The total GSH concentration in the samples was determined by linear regression to calculate the values obtained from a standard curve.

Determination of cellular ATP in ARPE-19 Cells. To measure cellular ATP levels,

CellTiter-Glo (Promega, Madison, WI, USA) was used according to manufacturer’s directions. In brief, after equilibrating to room temperature, an equal volume of the

CellTiter-Glo reagent was added to the cell medium of HOHA lactone treated cells and mixed for 2 minutes on an orbital shaker. Then the plate was incubated for 10 minutes at room temperature to stabilize the luminescence, and then was immediately measured with a luminescence microplate reader (Spectramax M2, Molecular Devices)

Detection of CEP in ARPE-19 cells. ARPE-19 cells (10,000 cells/ per chamber) were plated on an 8-chamber slide (Lab-Tek II Chamber Slide System, Nunc, Rochester, NY) in DEME/F12 with 10% FBS and then incubated at 37 °C under 5% CO2 for three days.

After 10 μM HOHA lactone treatment or 24 h after the execution of the standard light exposure model protocol, the chambers were aspirated and washed twice with DPBS. The cells were fixed with cold acetone (-20 °C) for 12 min at -25 °C. After washing with

PBST three times, the slides were blocked with 3% BSA in PBST for 1 h at 23 °C. The cells were probed with rabbit anti-CEP polyclonal antibody (in 3% BSA in PBST, 18

μg/mL) overnight at 4 °C, and washed exhaustively with PBST the next day. The slides were treated with Texas Red-X goat anti-rabbit antibody (1:100 dilution in 3% BSA in

PBST; T-6391, ThermoFisher Scientific, Waltham, MA) overnight at 4 °C, washed exhaustively with PBST and then aspirated. The slides were further incubated with 1:20 diluted in PBS stock solution of Flash Phalloidin™ Green 488 (0.2 U/μL, Biolegend, San

Diego, CA) in the dark (protected from light) for 30 min at 23 °C. After washing with

206

PBST, slides were mounted with DAPI containing Fluoromount-G (Southern Biotech,

Birmingham, AL). All images were acquired with a Leica DMI 6000 B inverted fluorescent microscope using a Retiga EXI camera. Image analysis was performed using

Metamorph imaging software (Molecular Devices, Downington, PA). The images were acquired at 20x magnification.

Isolation of mitochondria from ARPE-19 cells. ARPE-19 cells were cultured in T-

150 flasks, and trypsinized once they reached confluency (10~15 ×106 cells). After washing twice with DPBS by centrifuging at 1,000g for 5 min at 4 °C, the pellet was flash-frozen in liquid nitrogen, then thawed and suspended in 1 mL of 10 mM ice-cold hypotonic Tris buffer (pH 7.6). After the suspension was homogenized carefully with a

Teflon tissue grinder on ice, 200 μL of 1.5 M sucrose solution was added, vortexed thoroughly and centrifuged at 600g for 10 min at 4 °C. The supernatant was collected and centrifuged at 14,000g for 10 min at 4 °C. The resulting mitochondrial pellet was resuspended in 0.5 mL of 10 mM ice-cold hypotonic Tris buffer (pH 7.6), then divided into aliquots and stored at -80 °C. The cell mitochondrial solution was thawed and subjected to three cycles of freeze-thawing in liquid nitrogen/37 °C water bath to disrupt the mitochondrial membranes just before use. The mitochondrial protein concentration was determined using the Pierce 660 nm Protein Assay kit.

Assays for mitochondrial enzyme activities. Mitochondrial respiratory chain enzymatic activities (complexes I-IV) were assessed as previously described73 and accommodated in a 96-well microplate format.

Complex I activity: Mitochondria (2 μg) were added to the assay medium containing potassium phosphate buffer (50 mM, pH 7.5), fatty acid-free BSA (3 mg/mL), KCN (300

207

μM), NADH (100 μM) and distilled water. After reading the baseline at 340 nm for 2 minutes, ubiquinone1 (60 μM) was added and the decrease in absorbance was recorded at

340 nm for 60 minutes. In parallel, the same quantity of reagents and samples but with the addition of rotenone solution (10 μM) was used.

Complex II activity: Mitochondria (1 μg) were added to the assay medium containing potassium phosphate buffer (25 mM, pH 7.5), fatty acid-free BSA (1 mg/mL), KCN (300

μM), succinate (20 mM), 2,6-dichlorophenolindophenol (DCPIP) sodium salt (80 μM) and distilled water. The mixture was incubated at 37 °C for 10 minutes, and then the baseline was recorded at 600 nm for 2 minutes. Then decylubiquinone (DUB, 50 μM) was applied and the decrease in absorbance at 600 nm was recorded for 60 minutes.

Complex III activity: Mitochondria (1 μg) were added to the assay medium containing potassium phosphate buffer (25 mM, pH 7.5), KCN (500 μM), EDTA (100

μM), oxidized cytochrome c (75 μM), Tween-20 (0.025% (vol/vol)) and distilled water.

After reading the baseline at 550 nm for 2 minutes, decylubiquinol (100 μM) was used and then the increase in absorbance at 550 nm was recorded for 15 minutes.

Complex IV activity: Mitochondria (1 μg) were added to the assay medium containing potassium phosphate buffer (25 mM, pH 7.0), KCN (300 μM), reduced cytochrome c (50 μM) and distilled water. The decrease in absorbance at 550 nm was recorded for 15 minutes.

HPLC analysis of HOHA lactone scavenging activity. 10 mM or 100 mM solutions of the compounds and 0.5 mM solution of HOHA lactone in DPBS were prepared. In a screw cap-equipped vial were mixed 10 μL of the compound solution and 100 μL of the

HOHA lactone solution (final molar ratio between compound and aldehyde = 1:2 or 1:20).

208

The resulting mixture was sealed and incubated at 37 °C. At time (T) = 0, 15, 30, 45 and

60 min a 20 μL of sample was withdrawn from the vial and injected into the HPLC system. Reverse-phase HPLC was conducted using a Shimadzu UFLC system equipped with a 5 μm 4.6 × 250 mm Phenomenex Luna C18 column (mobile phase (isocratic):

Water/methanol/formic acid 70:30:0.1, flow rate: 1 mL/min). Peak areas corresponding to the unreacted HOHA lactone were integrated and the residual concentration was calculated according to the formula: HOHA lactone residual concentration (%) = (A0 / At)

× 100 where A0 is the peak area at time 0 and At is the peak area at each sampling time.

The data were plotted on a graph reporting the residual % or consuming % concentration of compound vs. time (for each compound the analysis was run in duplicate; values are the mean ± SD).

Quantitation of HH uptake by LC-MS/MS. ARPE-19 cells (200,000 cells/dish) were seeded into a 60 mm dish and were grown to confluency. After being starved in basal DMEM/F12 cell culture medium overnight, the cells were treated with 0-800 μM

HH for 24 h. Before harvest, the cells were washed extensively with HBSS to remove any residual HH. The cell pellets were frozen in dry ice and resuspended in methanol.

The suspensions were then vortexed and sonicated to extract the cellular-associated HH.

The cells were then scraped and pelleted by centrifugation (1,000 g, 5 min, 4 °C). The supernatant was discarded and the pellet was snap-frozen on dry ice. For analysis, the pellet was resuspended in 500 μL of neat methanol (MeOH), then was bath-sonicated for

5 min. After the sample was carefully vortexed for 1 min and centrifuged (14,000 g, 15 min, 4 °C), 400 μL of supernatant was transferred to another fresh tube and dried under a stream of nitrogen. The sample was then resuspended in 200 μL of 0.1% FA, sonicated

209 for 5 min, vortexed for 1 min and the resulting solution was filtered (0.2 μm PVDF syringe filter) into a fresh tube before LC-MS/MS analysis. The LC-MS/MS system for the analysis consisted of a Thermo Finnigan LCQ Deca XP with a Surveyor LC system.

Liquid chromatography was performed using a Gemini-NX C18 column (2.1 × 150 mm,

5 μm) with a Gemini-NX C18 guard column (2 × 4 mm) (both from Phenomenex). An isocratic HPLC method with water/methanol/formic acid 95:5:0.1 was used and the total run time was 6 min. The flow rate was 200 μL/min and a 10 μL volume was injected.

Electrospray ionization mass spectrometry in the positive ion mode was employed. The instrument parameters were as follows: the heated capillary temperature was 200 °C, the source voltage 4.0 kV, and the capillary voltage 11.00 V. Nitrogen was used as sheath and auxiliary gas. All data were processed with the Qual browser in Xcalibur software.

MS/MS experiments were performed by selecting an ion with an isolation width of 2 m/z and collision energy at 26%. Selected ion recording at m/z 153.0 from CID fragmentation of m/z 170.1 in the positive ion mode was used to identify HH. The cellular amounts were calculated using a calibration curve built from the authentic standard and normalized by the total protein concentration of the precipitated protein obtained after methanol extraction. Normalization was conducted by dividing the amounts determined by LC-MS by the total protein concentration measured by a Pierce 660 nm assay.

Statistical Analysis. Unless specified in the text or legends, comparisons were made using one-way ANOVA followed by Holm-Sidak’s post-hoc multiple comparison test.

Statistical significance is shown as follows: *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Data are presented as mean ± standard error of mean (SEM).

210

4.5 References

(1) Klein, R., Chou, C. F., Klein, B. E., Zhang, X., Meuer, S. M., and Saaddine, J. B.

(2011) Prevalence of age-related macular degeneration in the US population. Arch.

Ophthalmol. 129, 75-80.

(2) Strauss, O. (2005) The retinal pigment epithelium in visual function. Physiol. Rev.

85, 845-881.

(3) Terluk, M. R., Kapphahn, R. J., Soukup, L. M., Gong, H., Gallardo, C.,

Montezuma, S. R., and Ferrington, D. A. (2015) Investigating mitochondria as a

target for treating age-related macular degeneration. J. Neurosci. 35, 7304-7311.

(4) Feher, J., Kovacs, I., Artico, M., Cavallotti, C., Papale, A., and Balacco Gabrieli,

C. (2006) Mitochondrial alterations of retinal pigment epithelium in age-related

macular degeneration. Neurobiol. Aging 27, 983-993.

(5) Nordgaard, C. L., Berg, K. M., Kapphahn, R. J., Reilly, C., Feng, X., Olsen, T. W.,

and Ferrington, D. A. (2006) Proteomics of the retinal pigment epithelium reveals

altered protein expression at progressive stages of age-related macular

degeneration. Invest. Ophthalmol. Vis. Sci. 47, 815-822.

(6) Golestaneh, N., Chu, Y., Xiao, Y. Y., Stoleru, G. L., and Theos, A. C. (2017)

Dysfunctional autophagy in RPE, a contributing factor in age-related macular

degeneration. Cell Death Dis. 8, e2537.

(7) Nordgaard, C. L., Karunadharma, P. P., Feng, X., Olsen, T. W., and Ferrington, D.

A. (2008) Mitochondrial proteomics of the retinal pigment epithelium at

progressive stages of age-related macular degeneration. Invest. Ophthalmol. Vis.

Sci. 49, 2848-2855.

211

(8) Nashine, S., Cohen, P., Nesburn, A. B., Kuppermann, B. D., and Kenney, M. C.

(2018) Characterizing the protective effects of SHLP2, a mitochondrial-derived

peptide, in macular degeneration. Sci. Rep. 8, 15175.

(9) Cebak, J. E., Singh, I. N., Hill, R. L., Wang, J. A., and Hall, E. D. (2017)

Phenelzine Protects Brain Mitochondrial Function In Vitro and In Vivo following

Traumatic Brain Injury by Scavenging the Reactive Carbonyls 4-Hydroxynonenal

and Acrolein Leading to Cortical Histological Neuroprotection. J. Neurotrauma

34, 1302-1317.

(10) Poon, H. F., Calabrese, V., Scapagnini, G., and Butterfield, D. A. (2004) Free

radicals: key to brain aging and heme oxygenase as a cellular response to

oxidative stress. J. Gerontol. A Biol. Sci. Med. Sci. 59, 478-493.

(11) Choi, J., Zhang, W., Gu, X., Chen, X., Hong, L., Laird, J. M., and Salomon, R. G.

(2011) Lysophosphatidylcholine is generated by spontaneous deacylation of

oxidized phospholipids. Chem. Res. Toxicol. 24, 111-118.

(12) Gu, X., Sun, M., Gugiu, B., Hazen, S., Crabb, J. W., and Salomon, R. G. (2003)

Oxidatively truncated docosahexaenoate phospholipids: total synthesis,

generation, and Peptide adduction chemistry. J. Org. Chem. 68, 3749-3761.

(13) Gu, J., Pauer, G. J., Yue, X., Narendra, U., Sturgill, G. M., Bena, J., Gu, X.,

Peachey, N. S., Salomon, R. G., Hagstrom, S. A., Crabb, J. W., Clinical, G., and

Proteomic, A. M. D. S. G. (2009) Assessing susceptibility to age-related macular

degeneration with proteomic and genomic biomarkers. Mol. Cell. Proteomics 8,

1338-1349.

212

(14) Gu, J., Pauer, G. J., Yue, X., Narendra, U., Sturgill, G. M., Bena, J., Gu, X.,

Peachey, N. S., Salomon, R. G., Hagstrom, S. A., Crabb, J. W., Clinical, G., and

Proteomic, A. M. D. S. G. (2010) Proteomic and genomic biomarkers for age-

related macular degeneration. Adv. Exp. Med. Biol. 664, 411-417.

(15) Gu, X., Meer, S. G., Miyagi, M., Rayborn, M. E., Hollyfield, J. G., Crabb, J. W.,

and Salomon, R. G. (2003) Carboxyethylpyrrole protein adducts and

autoantibodies, biomarkers for age-related macular degeneration. J. Biol. Chem.

278, 42027-42035.

(16) Guo, J., Linetsky, M., Yu, A. O., Zhang, L., Howell, S. J., Folkwein, H. J., Wang,

H., and Salomon, R. G. (2016) 4-Hydroxy-7-oxo-5-heptenoic Acid Lactone

Induces Angiogenesis through Several Different Molecular Pathways. Chem. Res.

Toxicol. 29, 2125-2135.

(17) Linetsky, M., Bondelid, K. S., Losovskiy, S., Gabyak, V., Rullo, M. J., Stiadle, T.

I., Munjapara, V., Saxena, P., Ma, D., Cheng, Y. S., Howes, A. M., Udeigwe, E.,

and Salomon, R. G. (2018) 4-Hydroxy-7-oxo-5-heptenoic Acid Lactone Is a

Potent Inducer of the Complement Pathway in Human Retinal Pigmented

Epithelial Cells. Chem. Res. Toxicol. 31, 666-679.

(18) Cheng, Y. S., Linetsky, M., Gu, X., Ayyash, N., Gardella, A., and Salomon, R. G.

(2018) Light-induced generation and toxicity of docosahexaenoate-derived

oxidation products in retinal pigmented epithelial cells. Exp. Eye Res.

(19) Singh, I. N., Gilmer, L. K., Miller, D. M., Cebak, J. E., Wang, J. A., and Hall, E.

D. (2013) Phenelzine mitochondrial functional preservation and neuroprotection

213

after traumatic brain injury related to scavenging of the lipid peroxidation-derived

aldehyde 4-hydroxy-2-nonenal. J. Cereb. Blood Flow Metab. 33, 593-599.

(20) Sun, L., Luo, C., Long, J., Wei, D., and Liu, J. (2006) Acrolein is a mitochondrial

toxin: effects on respiratory function and enzyme activities in isolated rat liver

mitochondria. Mitochondrion 6, 136-142.

(21) Sachdeva, M., Karan, M., Singh, T., and Dhingra, S. (2014) Oxidants and

Antioxidants in Complementary and Alternative Medicine: A Review. Spatula

DD - Peer Reviewed Journal on Complementary Medicine and Drug Discovery 4,

(22) Boldyrev, A. A., Aldini, G., and Derave, W. (2013) Physiology and

pathophysiology of carnosine. Physiol. Rev. 93, 1803-1845.

(23) Decker, E. A., Livisay, S. A., and Zhou, S. (2000) A re-evaluation of the

antioxidant activity of purified carnosine. Biochemistry (Mosc.) 65, 766-770.

(24) Kang, J. H., Kim, K. S., Choi, S. Y., Kwon, H. Y., Won, M. H., and Kang, T. C.

(2002) Protective effects of carnosine, homocarnosine and anserine against

peroxyl radical-mediated Cu,Zn-superoxide dismutase modification. Biochim.

Biophys. Acta 1570, 89-96.

(25) Kohen, R., Yamamoto, Y., Cundy, K. C., and Ames, B. N. (1988) Antioxidant

activity of carnosine, homocarnosine, and anserine present in muscle and brain.

Proc. Natl. Acad. Sci. U. S. A. 85, 3175-3179.

(26) Boldyrev, A. A., Kurella, E. G., Rubtsov, A. M., Tiulina, O. V., Shara, M., and

Shentiurts, M. (1992) [Direct measurement of the interaction of carnosine and its

analogs with free radicals]. Biokhimiia 57, 1360-1365.

214

(27) Choi, S. Y., Kwon, H. Y., Kwon, O. B., and Kang, J. H. (1999) Hydrogen

peroxide-mediated Cu,Zn-superoxide dismutase fragmentation: protection by

carnosine, homocarnosine and anserine. Biochim. Biophys. Acta 1472, 651-657.

(28) Dursun, N., Taskin, E., and Ozturk, F. (2011) Protection against adriamycin-

induced cardiomyopathy by carnosine in rats: role of endogenous antioxidants.

Biol. Trace Elem. Res. 143, 412-424.

(29) Nicoletti, V. G., Santoro, A. M., Grasso, G., Vagliasindi, L. I., Giuffrida, M. L.,

Cuppari, C., Purrello, V. S., Stella, A. M., and Rizzarelli, E. (2007) Carnosine

interaction with nitric oxide and astroglial cell protection. J. Neurosci. Res. 85,

2239-2245.

(30) Aldini, G., Carini, M., Beretta, G., Bradamante, S., and Facino, R. M. (2002)

Carnosine is a quencher of 4-hydroxy-nonenal: through what mechanism of

reaction? Biochem. Biophys. Res. Commun. 298, 699-706.

(31) Aldini, G., Granata, P., and Carini, M. (2002) Detoxification of cytotoxic

alpha,beta-unsaturated aldehydes by carnosine: characterization of conjugated

adducts by electrospray ionization tandem mass spectrometry and detection by

liquid chromatography/mass spectrometry in rat skeletal muscle. J. Mass

Spectrom. 37, 1219-1228.

(32) Zhou, S., and Decker, E. A. (1999) Ability of carnosine and other skeletal muscle

components to quench unsaturated aldehydic lipid oxidation products. J. Agric.

Food. Chem. 47, 51-55.

(33) Brownson, C., and Hipkiss, A. R. (2000) Carnosine reacts with a glycated protein.

Free Radic. Biol. Med. 28, 1564-1570.

215

(34) Hipkiss, A. R., and Brownson, C. (2000) Carnosine reacts with protein carbonyl

groups: another possible role for the anti-ageing peptide? Biogerontology 1, 217-

223.

(35) Hipkiss, A. R., Brownson, C., and Carrier, M. J. (2001) Carnosine, the anti-ageing,

anti-oxidant dipeptide, may react with protein carbonyl groups. Mech. Ageing Dev.

122, 1431-1445.

(36) Cheng, J., Wang, F., Yu, D. F., Wu, P. F., and Chen, J. G. (2011) The cytotoxic

mechanism of malondialdehyde and protective effect of carnosine via protein

cross-linking/mitochondrial dysfunction/reactive oxygen species/MAPK pathway

in neurons. Eur. J. Pharmacol. 650, 184-194.

(37) Horning, M. S., Blakemore, L. J., and Trombley, P. Q. (2000) Endogenous

mechanisms of neuroprotection: role of zinc, copper, and carnosine. Brain Res.

852, 56-61.

(38) Preston, J. E., Hipkiss, A. R., Himsworth, D. T., Romero, I. A., and Abbott, J. N.

(1998) Toxic effects of beta-amyloid(25-35) on immortalised rat brain endothelial

cell: protection by carnosine, homocarnosine and beta-alanine. Neurosci. Lett. 242,

105-108.

(39) Boldyrev, A., Koudinov, A., Berezov, T., and Carpenter, D. O. (2004) Amyloid-

beta induced cell death is independent of free radicals. J. Alzheimers Dis. 6, 633-

638; discussion 673-681.

(40) Fu, Q., Dai, H., Hu, W., Fan, Y., Shen, Y., Zhang, W., and Chen, Z. (2008)

Carnosine protects against Abeta42-induced neurotoxicity in differentiated rat

PC12 cells. Cell. Mol. Neurobiol. 28, 307-316.

216

(41) Orioli, M., Aldini, G., Benfatto, M. C., Facino, R. M., and Carini, M. (2007) HNE

Michael adducts to histidine and histidine-containing peptides as biomarkers of

lipid-derived carbonyl stress in urines: LC-MS/MS profiling in Zucker obese rats.

Anal. Chem. 79, 9174-9184.

(42) Orioli, M., Aldini, G., Beretta, G., Facino, R. M., and Carini, M. (2005) LC-ESI-

MS/MS determination of 4-hydroxy-trans-2-nonenal Michael adducts with

cysteine and histidine-containing peptides as early markers of oxidative stress in

excitable tissues. J. Chromatogr. B Analyt. Technol. Biomed. Life Sci. 827, 109-

118.

(43) Liu, Y., Xu, G., and Sayre, L. M. (2003) Carnosine inhibits (E)-4-hydroxy-2-

nonenal-induced protein cross-linking: structural characterization of carnosine-

HNE adducts. Chem. Res. Toxicol. 16, 1589-1597.

(44) Guiotto, A., Calderan, A., Ruzza, P., Osler, A., Rubini, C., Jo, D. G., Mattson, M.

P., and Borin, G. (2005) Synthesis and evaluation of neuroprotective alpha,beta-

unsaturated aldehyde scavenger histidyl-containing analogues of carnosine. J.

Med. Chem. 48, 6156-6161.

(45) Tang, S. C., Arumugam, T. V., Cutler, R. G., Jo, D. G., Magnus, T., Chan, S. L.,

Mughal, M. R., Telljohann, R. S., Nassar, M., Ouyang, X., Calderan, A., Ruzza,

P., Guiotto, A., and Mattson, M. P. (2007) Neuroprotective actions of a histidine

analogue in models of ischemic stroke. J. Neurochem. 101, 729-736.

(46) Murphy, M. P. (2009) How mitochondria produce reactive oxygen species.

Biochem. J 417, 1-13.

217

(47) Taddei, M. L., Giannoni, E., Raugei, G., Scacco, S., Sardanelli, A. M., Papa, S.,

and Chiarugi, P. (2012) Mitochondrial Oxidative Stress due to Complex I

Dysfunction Promotes Fibroblast Activation and Melanoma Cell Invasiveness. J

Signal Transduct 2012, 684592.

(48) Chinopoulos, C., and Adam-Vizi, V. (2010) Mitochondria as ATP consumers in

cellular pathology. Biochim. Biophys. Acta 1802, 221-227.

(49) Jastroch, M., Divakaruni, A. S., Mookerjee, S., Treberg, J. R., and Brand, M. D.

(2010) Mitochondrial proton and electron leaks. Essays Biochem. 47, 53-67.

(50) Green, D., and Kroemer, G. (1998) The central executioners of apoptosis:

caspases or mitochondria? Trends Cell Biol. 8, 267-271.

(51) West, X. Z., Malinin, N. L., Merkulova, A. A., Tischenko, M., Kerr, B. A.,

Borden, E. C., Podrez, E. A., Salomon, R. G., and Byzova, T. V. (2010) Oxidative

stress induces angiogenesis by activating TLR2 with novel endogenous ligands.

Nature 467, 972-976.

(52) Biswas, S., Xin, L., Panigrahi, S., Zimman, A., Wang, H., Yakubenko, V. P.,

Byzova, T. V., Salomon, R. G., and Podrez, E. A. (2016) Novel

phosphatidylethanolamine derivatives accumulate in circulation in hyperlipidemic

ApoE-/- mice and activate platelets via TLR2. Blood 127, 2618-2629.

(53) Giddabasappa, A., Bauler, M., Yepuru, M., Chaum, E., Dalton, J. T., and

Eswaraka, J. (2010) 17-beta estradiol protects ARPE-19 cells from oxidative

stress through estrogen receptor-beta. Invest. Ophthalmol. Vis. Sci. 51, 5278-5287.

(54) Jaiswal, M., Haelterman, N. A., Sandoval, H., Xiong, B., Donti, T., Kalsotra, A.,

Yamamoto, S., Cooper, T. A., Graham, B. H., and Bellen, H. J. (2015) Impaired

218

Mitochondrial Energy Production Causes Light-Induced Photoreceptor

Degeneration Independent of Oxidative Stress. PLoS Biol. 13, e1002197.

(55) Rhein, V., Baysang, G., Rao, S., Meier, F., Bonert, A., Muller-Spahn, F., and

Eckert, A. (2009) Amyloid-beta leads to impaired cellular respiration, energy

production and mitochondrial electron chain complex activities in human

neuroblastoma cells. Cell. Mol. Neurobiol. 29, 1063-1071.

(56) Hroudova, J., Singh, N., and Fisar, Z. (2014) Mitochondrial dysfunctions in

neurodegenerative diseases: relevance to Alzheimer's disease. Biomed Res Int

2014, 175062.

(57) Crompton, M. (1999) The mitochondrial permeability transition pore and its role

in cell death. Biochem. J 341 ( Pt 2), 233-249.

(58) Scorrano, L., Petronilli, V., and Bernardi, P. (1997) On the voltage dependence of

the mitochondrial permeability transition pore. A critical appraisal. J. Biol. Chem.

272, 12295-12299.

(59) Haworth, R. A., and Hunter, D. R. (1979) The Ca2+-induced membrane transition

in mitochondria. II. Nature of the Ca2+ trigger site. Arch. Biochem. Biophys. 195,

460-467.

(60) Vedel, F., Lalanne, É., Sabar, M., Chétrit, P., and De Paepe, R. (1999) The

mitochondrial respiratory chain and ATP synthase complexes: Composition,

structure and mutational studies. Plant Physiol. Biochem. 37, 629-643.

(61) Jonckheere, A. I., Smeitink, J. A., and Rodenburg, R. J. (2012) Mitochondrial

ATP synthase: architecture, function and pathology. J. Inherit. Metab. Dis. 35,

211-225.

219

(62) Wu, J., Luo, X., and Yan, L. J. (2015) Two dimensional blue native/SDS-PAGE

to identify mitochondrial complex I subunits modified by 4-hydroxynonenal

(HNE). Front. Physiol. 6, 98.

(63) Winger, A. M., Taylor, N. L., Heazlewood, J. L., Day, D. A., and Millar, A. H.

(2007) The Cytotoxic lipid peroxidation product 4-hydroxy-2-nonenal covalently

modifies a selective range of proteins linked to respiratory function in plant

mitochondria. J. Biol. Chem. 282, 37436-37447.

(64) Kaplan, P., Tatarkova, Z., Racay, P., Lehotsky, J., Pavlikova, M., and Dobrota, D.

(2007) Oxidative modifications of cardiac mitochondria and inhibition of

cytochrome c oxidase activity by 4-hydroxynonenal. Redox Rep 12, 211-218.

(65) Teufel, M., Saudek, V., Ledig, J. P., Bernhardt, A., Boularand, S., Carreau, A.,

Cairns, N. J., Carter, C., Cowley, D. J., Duverger, D., Ganzhorn, A. J., Guenet, C.,

Heintzelmann, B., Laucher, V., Sauvage, C., and Smirnova, T. (2003) Sequence

identification and characterization of human carnosinase and a closely related

non-specific dipeptidase. J. Biol. Chem. 278, 6521-6531.

(66) de Cogan, F., Hill, L. J., Lynch, A., Morgan-Warren, P. J., Lechner, J., Berwick,

M. R., Peacock, A. F. A., Chen, M., Scott, R. A. H., Xu, H., and Logan, A. (2017)

Topical Delivery of Anti-VEGF Drugs to the Ocular Posterior Segment Using

Cell-Penetrating Peptides. Invest. Ophthalmol. Vis. Sci. 58, 2578-2590.

(67) Wang, H., Linetsky, M., Guo, J., Yu, A. O., and Salomon, R. G. (2016)

Metabolism of 4-Hydroxy-7-oxo-5-heptenoic Acid (HOHA) Lactone by Retinal

Pigmented Epithelial Cells. Chem Res Toxicol 29, 1198-1210.

220

(68) Naggar, H., Van Ells, T. K., Ganapathy, V., and Smith, S. B. (2005) Regulation of

reduced-folate transporter-1 in retinal pigment epithelial cells by folate. Current

eye research 30, 35-44.

(69) Wang, H., Linetsky, M., Guo, J., Choi, J., Hong, L., Chamberlain, A. S., Howell,

S. J., Howes, A. M., and Salomon, R. G. (2015) 4-Hydroxy-7-oxo-5-heptenoic

Acid (HOHA) Lactone is a Biologically Active Precursor for the Generation of 2-

(omega-Carboxyethyl)pyrrole (CEP) Derivatives of Proteins and Ethanolamine

Phospholipids. Chem Res Toxicol 28, 967-977.

(70) Li, K. R., Yang, S. Q., Gong, Y. Q., Yang, H., Li, X. M., Zhao, Y. X., Yao, J.,

Jiang, Q., and Cao, C. (2016) 3H-1,2-dithiole-3-thione protects retinal pigment

epithelium cells against Ultra-violet radiation via activation of Akt-mTORC1-

dependent Nrf2-HO-1 signaling. Scientific reports 6, 25525.

(71) Smith, P. K., Krohn, R. I., Hermanson, G. T., Mallia, A. K., Gartner, F. H.,

Provenzano, M. D., Fujimoto, E. K., Goeke, N. M., Olson, B. J., and Klenk, D. C.

(1985) Measurement of protein using bicinchoninic acid. Anal. Biochem. 150, 76-

85.

(72) Rahman, I., Kode, A., and Biswas, S. K. (2006) Assay for quantitative

determination of glutathione and glutathione disulfide levels using enzymatic

recycling method. Nature protocols 1, 3159-3165.

(73) Spinazzi, M., Casarin, A., Pertegato, V., Salviati, L., and Angelini, C. (2012)

Assessment of mitochondrial respiratory chain enzymatic activities on tissues and

cultured cells. Nat. Protoc. 7, 1235-1246.

221

Appendix

222

Figure A2.1. 1H NMR spectrum of a methylation product mixture of 2.1p and 2.2p.

Figure A2.2. COSY spectrum of a methylation product mixture 2.1p and 2.2p.

223

Figure A2.3. HSQC spectrum of a methylation product mixture 2.1p and 2.2p.

Figure A2.4. HMBC spectrum of a methylation product mixture 2.1p and 2.2p.

224

Figure A2.5. 2D NOESY spectrum of a methylation product mixture 2.1p and 2.2p.

Figure A2.6. COSY spectrum of ox-LGD2 and ox-LGE2 (major) mixture from HF- treated reaction

225

Figure A2.7. HSQC spectrum of ox-LGD2 and ox-LGE2 (major) mixture from HF- treated reaction.

Figure A2.8. HMBC spectrum of of ox-LGD2 and ox-LGE2 (major) mixture from HF- treated reaction.

226

6 Figure A2.9. COSY spectrum of Δ -ox-LGE2 (2.2d).

6 Figure A2.10. HSQC spectrum of Δ -ox-LGE2 (2.2d).

227

6 Figure A2.11. HMBC spectrum of Δ -ox-LGE2 (2.2d).

6 Figure A2.12. 2D NOESY spectrum of Δ -ox-LGE2 (2.2d).

228

Figure A2.13. COSY spectrum of ox-LGD2 (2.1).

Figure A2.14. 2D NOESY spectrum of ox-LGD2 (2.1).

229

1 Figure A2.15. The H NMR (500 MHz, CDCl3) of 2.9

13 Figure A2.16. The C NMR (125 MHz, CDCl3) of 2.9

230

1 Figure A2.17. The H NMR (500 MHz, CDCl3) of 2.10

13 Figure A2.18. The C NMR (125 MHz, CDCl3) of 2.10

231

1 Figure A2.19. The H NMR (500 MHz, CDCl3) of 2.11

13 Figure A2.20. The C NMR (125 MHz, CDCl3) of 2.11

232

1 Figure A2.21. The H NMR (500 MHz, CDCl3) of 2.12

233

1 Figure A2.22. The H NMR (500 MHz, CDCl3) of 2.13

13 Figure A2.23. The C NMR (125 MHz, CDCl3) of 2.13

234

1 Figure A2.24. The H NMR (500 MHz, CDCl3) of 2.7

13 Figure A2.25. The C NMR (125 MHz, CDCl3) of 2.7

235

1 Figure A2.26. The H NMR (500 MHz, CDCl3) of 2.14

13 Figure A2.27. The C NMR (125 MHz, CDCl3) of 2.14

236

1 Figure A2.28. The H NMR (500 MHz, CDCl3) of 2.4

13 Figure A2.29. The C NMR (125 MHz, CDCl3) of 2.4

237

1 Figure A2.30. The H NMR (500 MHz, CDCl3) of 2.4’

13 Figure A2.31. The C NMR (125 MHz, CDCl3) of 2.4’

238

1 Figure A2.32. The H NMR (500 MHz, CDCl3) of 2.3

13 Figure A2.33. The C NMR (125 MHz, CDCl3) of 2.3

239

1 Figure A2.34. The H NMR (500 MHz, CDCl3) of 2.3’

13 Figure A2.35. The C NMR (125 MHz, CDCl3) of 2.3’

240

1 Figure A2.36. The H NMR (500 MHz, CDCl3) of 2.1p and 2.2p

13 Figure A2.37. The C NMR (125 MHz, CDCl3) of 2.1p and 2.2p

241

1 Figure A2.38. The H NMR (500 MHz, CDCl3) of 2.1p’ and 2.2p’

1 Figure A2.39. The H NMR (500 MHz, CDCl3) of 2.1’ and 2.2’

242

1 Figure A2.40. The H NMR (500 MHz, CDCl3) of ox-LGD2 (2.1), ox-LGE2 (2.2)

1 Figure A2.41. The H NMR (500 MHz, CDCl3) of ox-LGD2 (2.1)

243

13 Figure A2.42. The C NMR (125 MHz, CDCl3) of ox-LGE2 (2.2) with minor ox-LGD2 6 (2.1) and Δ -ox-LGE2 (2.2d)

1 6 Figure A2.43. The H NMR (500 MHz, CDCl3) of Δ -ox-LGE2 (2.2d)

244

13 6 Figure A2.44. The C NMR (125 MHz, CDCl3) of Δ -ox-LGE2 (2.2d)

245

1 Figure A4.1. The H NMR (500 MHz, CDCl3) of Ac-His-OMe-Ac

13 Figure A4.2. The C NMR (125 MHz, CDCl3) of Ac-His-OMe-Ac

246

1 Figure A4.3. The H NMR (500 MHz, CDCl3) of tBu-His-OMe

13 Figure A4.4. The C NMR (125 MHz, CDCl3) of tBu-His-OMe

247

1 Figure A4.5. The H NMR (500 MHz, CDCl3) of cP-His-OMe

13 Figure A4.6. The C NMR (125 MHz, CDCl3) of cP-His-OMe

248

1 Figure A4.7. The H NMR (500 MHz, CDCl3) of cH-His-OMe

13 Figure A4.8. The C NMR (125 MHz, CDCl3) of cH-His-OMe

249

1 Figure A4.9. The H NMR (500 MHz, CDCl3) of nonanoyl-His-OMe

13 Figure A4.10. The C NMR (125 MHz, CDCl3) of nonanoyl -His-OMe

250

1 Figure A4.11. The H NMR (500 MHz, CDCl3) of decanoyl-His-OMe

13 Figure A4.12. The C NMR (125 MHz, CDCl3) of decanoyl -His-OMe

251

1 Figure A4.13. The H NMR (500 MHz, CDCl3) of undecanoyl-His-OMe

13 Figure A4.14. The C NMR (125 MHz, CDCl3) of undecanoyl -His-OMe

252

1 Figure A4.15. The H NMR (500 MHz, CDCl3) of dodecanoyl-His-OMe

13 Figure A4.16. The C NMR (125 MHz, CDCl3) of dodecanoyl -His-OMe

253

1 Figure A4.17. The H NMR (500 MHz, CDCl3) of His-hyd

13 Figure A4.18. The C NMR (125 MHz, CDCl3) of His-hyd

254

1 Figure A4.19. The H NMR (500 MHz, CDCl3) of Ac-His-hyd

1 Figure A4.20. The H NMR (500 MHz, CDCl3) of tBu-His-hyd

255

1 Figure A4.21. The H NMR (500 MHz, CDCl3) of cP-His-hyd

1 Figure A4.22. The H NMR (500 MHz, CDCl3) of cH-His-hyd

256

1 Figure A4.23. The H NMR (500 MHz, CDCl3) of nonanoyl-His-hyd

1 Figure A4.24. The H NMR (500 MHz, CDCl3) of decanoyl-His-hyd

257

1 Figure A4.25. The H NMR (500 MHz, CDCl3) of undecanoyl-His-hyd

1 Figure A4.26. The H NMR (500 MHz, CDCl3) of dodecanoyl-His-hyd

258

Bibliography 1-250 251-293

259

(1) Ablonczy, Z., Higbee, D., Anderson, D. M., Dahrouj , M., Grey, A. C., Gutierrez,

D., Koutalos, Y., L., S. K., Hanneken, A., and Crouch, R. K. (2013) Lack of

correlation between the spatial distribution of A2E and lipofuscin fluorescence in

the human retinal pigment epithelium. Invest Ophthalmol Vis Sci. 54, 5535–5542.

(2) Age-Related Eye Disease Study Research, G. (2000) Risk factors associated with

age-related macular degeneration. A case-control study in the age-related eye

disease study: Age-Related Eye Disease Study Report Number 3. Ophthalmology

107, 2224-2232.

(3) Age-Related Eye Disease Study Research, G. (2001) A randomized, placebo-

controlled, clinical trial of high-dose supplementation with vitamins C and E, beta

carotene, and zinc for age-related macular degeneration and vision loss: AREDS

report no. 8. Arch. Ophthalmol. 119, 1417-1436.

(4) Alary, J., Fernandez, Y., Debrauwer, L., Perdu, E., and Gueraud, F. (2003)

Identification of intermediate pathways of 4-hydroxynonenal metabolism in the

rat. Chem. Res. Toxicol. 16, 320-327.

(5) Aldini, G., Carini, M., Beretta, G., Bradamante, S., and Facino, R. M. (2002)

Carnosine is a quencher of 4-hydroxy-nonenal: through what mechanism of

reaction? Biochem. Biophys. Res. Commun. 298, 699-706.

(6) Aldini, G., Granata, P., and Carini, M. (2002) Detoxification of cytotoxic

alpha,beta-unsaturated aldehydes by carnosine: characterization of conjugated

adducts by electrospray ionization tandem mass spectrometry and detection by

liquid chromatography/mass spectrometry in rat skeletal muscle. J. Mass

Spectrom. 37, 1219-1228.

260

(7) Ambati, J., and Fowler, B. J. (2012) Mechanisms of age-related macular

degeneration. Neuron 75, 26-39.

(8) Anoopkumar-Dukie, S., Carey, J. B., Conere, T., O'Sullivan, E., van Pelt, F. N.,

and Allshire, A. (2005) Resazurin assay of radiation response in cultured cells. Br.

J. Radiol. 78, 945-947.

(9) Artigas, J. M., Felipe, A., Navea, A., Fandino, A., and Artigas, C. (2012) Spectral

transmission of the human crystalline lens in adult and elderly persons: color and

total transmission of visible light. Invest. Ophthalmol. Vis. Sci. 53, 4076-4084.

(10) Baptista, M. S., Cadet, J., Di Mascio, P., Ghogare, A. A., Greer, A., Hamblin, M.

R., Lorente, C., Nunez, S. C., Ribeiro, M. S., Thomas, A. H., Vignoni, M., and

Yoshimura, T. M. (2017) Type I and Type II Photosensitized Oxidation Reactions:

Guidelines and Mechanistic Pathways. Photochem. Photobiol. 93, 912-919.

(11) Beatty, S., Koh, H.-H., Phil, M., Henson, D., and Boulton, M. (2000) The Role of

Oxidative Stress in the Pathogenesis of Age-Related Macular Degeneration. Surv.

Ophthalmol. 45, 115-134.

(12) Belinsky, M., and Jaiswal, A. K. (1993) NAD(P)H:quinone oxidoreductase1 (DT-

diaphorase) expression in normal and tumor tissues. Cancer Metastasis Rev. 12,

103-117.

(13) Ben-Shabat, S., Parish, C. A., Vollmer, H. R., Itagaki, Y., Fishkin, N., Nakanishi,

K., and Sparrow, J. R. (2002) Biosynthetic studies of A2E, a major fluorophore of

retinal pigment epithelial lipofuscin. J. Biol. Chem. 277, 7183-7190.

(14) Bergmann, M., Schutt, F., Holz, F. G., and Kopitz, J. (2004) Inhibition of the

ATP-driven proton pump in RPE lysosomes by the major lipofuscin fluorophore

261

A2-E may contribute to the pathogenesis of age-related macular degeneration.

FASEB J. 18, 562-564.

(15) Bernoud-Hubac, N., Fay, L. B., Armarnath, V., Guichardant, M., Bacot, S.,

Davies, S. S., Roberts, L. J., 2nd, and Lagarde, M. (2004) Covalent binding of

isoketals to ethanolamine phospholipids. Free Radic. Biol. Med. 37, 1604-1611.

(16) Bhide, R. S., Levison, B. S., Sharma, R. B., Ghosh, S., and Salomon, R. G. (1986)

Di-tert-butylmethylsilyl (DTBMS) trifluoromethanesulfonate. Preparation and

synthetic applications of DTBMS esters and enol ethers. Tetrahedron Lett. 27,

671-674.

(17) Bi, W., Jang, G.-F., Zhang, L., Crabb, J. W., Laird, J., Linetsky, M., and Salomon,

R. G. (2016) Molecular Structures of Isolevuglandin-Protein Cross-Links. Chem.

Res. Toxicol. 29, 1628-1640.

(18) Biarnes, M., Arias, L., Alonso, J., Garcia, M., Hijano, M., Rodriguez, A., Serrano,

A., Badal, J., Muhtaseb, H., Verdaguer, P., and Mones, J. (2015) Increased

Fundus Autofluorescence and Progression of Geographic Atrophy Secondary to

Age-Related Macular Degeneration: The GAIN Study. Am. J. Ophthalmol. 160,

345-353 e345.

(19) Biswas, S., Xin, L., Panigrahi, S., Zimman, A., Wang, H., Yakubenko, V. P.,

Byzova, T. V., Salomon, R. G., and Podrez, E. A. (2016) Novel

phosphatidylethanolamine derivatives accumulate in circulation in hyperlipidemic

ApoE-/- mice and activate platelets via TLR2. Blood 127, 2618-2629.

(20) Boettner, E. A., and Wolter, J. R. (1962) Transmission of the Ocular Media.

Invest. Ophthalmol. Vis. Sci. 1, 776-783.

262

(21) Boldyrev, A., Koudinov, A., Berezov, T., and Carpenter, D. O. (2004) Amyloid-

beta induced cell death is independent of free radicals. J. Alzheimers Dis. 6, 633-

638; discussion 673-681.

(22) Boldyrev, A. A., Aldini, G., and Derave, W. (2013) Physiology and

pathophysiology of carnosine. Physiol. Rev. 93, 1803-1845.

(23) Boldyrev, A. A., Kurella, E. G., Rubtsov, A. M., Tiulina, O. V., Shara, M., and

Shentiurts, M. (1992) [Direct measurement of the interaction of carnosine and its

analogs with free radicals]. Biokhimiia 57, 1360-1365.

(24) Boutaud, O., Andreasson, K. I., Zagol-Ikapitte, I., and Oates, J. A. (2005)

Cyclooxygenase-dependent lipid-modification of brain proteins. Brain Pathol. 15,

139-142.

(25) Boutaud, O., Brame, C. J., Chaurand, P., Li, J., Rowlinson, S. W., Crews, B. C., Ji,

C., Marnett, L. J., Caprioli, R. M., Roberts, L. J., 2nd, and Oates, J. A. (2001)

Characterization of the lysyl adducts of prostaglandin H-synthases that are

derived from oxygenation of arachidonic acid. Biochemistry 40, 6948-6955.

(26) Boutaud, O., Li, J., Zagol, I., Shipp, E. A., Davies, S. S., Roberts, L. J., 2nd, and

Oates, J. A. (2003) Levuglandinyl adducts of proteins are formed via a

prostaglandin H2 synthase-dependent pathway after platelet activation. J. Biol.

Chem. 278, 16926-16928.

(27) Boutaud, O., Montine, T. J., Chang, L., Klein, W. L., and Oates, J. A. (2006)

PGH2-derived levuglandin adducts increase the neurotoxicity of amyloid beta1-

42. J. Neurochem. 96, 917-923.

263

(28) Braak, H., and Braak, E. (1995) Staging of Alzheimer's disease-related

neurofibrillary changes. Neurobiol. Aging 16, 271-278; discussion 278-284.

(29) Brame, C. J., Boutaud, O., Davies, S. S., Yang, T., Oates, J. A., Roden, D., and

Roberts, L. J., 2nd. (2004) Modification of proteins by isoketal-containing

oxidized phospholipids. J. Biol. Chem. 279, 13447-13451.

(30) Brandstetter, C., Mohr, L. K., Latz, E., Holz, F. G., and Krohne, T. U. (2015)

Light induces NLRP3 inflammasome activation in retinal pigment epithelial cells

via lipofuscin-mediated photooxidative damage. J. Mol. Med. (Berl.) 93, 905-916.

(31) Brown, H. C., and Brown, C. A. (1963) The Reaction of Sodium Borohydride

with Nickel Acetate in Ethanol Solution--A Highly Selective Nickel

Hydrogenation Catalyst. J. Am. Chem. Soc. 85, 1005-1006.

(32) Brownson, C., and Hipkiss, A. R. (2000) Carnosine reacts with a glycated protein.

Free Radic. Biol. Med. 28, 1564-1570.

(33) Campisi, J., and d'Adda di Fagagna, F. (2007) Cellular senescence: when bad

things happen to good cells. Nat. Rev. Mol. Cell Biol. 8, 729-740.

(34) Campisi, J., and Robert, L. (2014) Cell senescence: role in aging and age-related

diseases. Interdiscip Top Gerontol 39, 45-61.

(35) Carrier, E. J., Zagol-Ikapitte, I., Amarnath, V., Boutaud, O., and Oates, J. A.

(2014) Levuglandin Forms Adducts with Histone H4 in a Cyclooxygenase-2-

Dependent Manner, Altering Its Interaction with DNA. Biochemistry 53, 2436-

2441.

264

(36) Catala, A. (2006) An overview of lipid peroxidation with emphasis in outer

segments of photoreceptors and the chemiluminescence assay. Int. J. Biochem.

Cell Biol. 38, 1482-1495.

(37) Cebak, J. E., Singh, I. N., Hill, R. L., Wang, J. A., and Hall, E. D. (2017)

Phenelzine Protects Brain Mitochondrial Function In Vitro and In Vivo following

Traumatic Brain Injury by Scavenging the Reactive Carbonyls 4-Hydroxynonenal

and Acrolein Leading to Cortical Histological Neuroprotection. J. Neurotrauma

34, 1302-1317.

(38) Charvet, C., Liao, W. L., Heo, G. Y., Laird, J., Salomon, R. G., Turko, I. V., and

Pikuleva, I. A. (2011) Isolevuglandins and mitochondrial enzymes in the retina:

mass spectrometry detection of post-translational modification of sterol-

metabolizing CYP27A1. J. Biol. Chem. 286, 20413-20422.

(39) Charvet, C. D., Laird, J., Xu, Y., Salomon, R. G., and Pikuleva, I. A. (2013)

Posttranslational modification by an isolevuglandin diminishes activity of the

mitochondrial cytochrome P450 27A1. J. Lipid Res. 54, 1421-1429.

(40) Charvet, C. D., Saadane, A., Wang, M., Salomon, R. G., Brunengraber, H., Turko,

I. V., and Pikuleva, I. A. (2013) Pretreatment with pyridoxamine mitigates

isolevuglandin-associated retinal effects in mice exposed to bright light. J. Biol.

Chem. 288, 29267-29280.

(41) Chen, Y., McMillan-Ward, E., Kong, J., Israels, S. J., and Gibson, S. B. (2008)

Oxidative stress induces autophagic cell death independent of apoptosis in

transformed and cancer cells. Cell Death Differ. 15, 171-182.

265

(42) Cheng, J., Wang, F., Yu, D. F., Wu, P. F., and Chen, J. G. (2011) The cytotoxic

mechanism of malondialdehyde and protective effect of carnosine via protein

cross-linking/mitochondrial dysfunction/reactive oxygen species/MAPK pathway

in neurons. Eur. J. Pharmacol. 650, 184-194.

(43) Cheng, Y. S., Linetsky, M., Gu, X., Ayyash, N., Gardella, A., and Salomon, R. G.

(2018) Light-induced generation and toxicity of docosahexaenoate-derived

oxidation products in retinal pigmented epithelial cells. Exp. Eye Res.

(44) Chikuba, K., Yubisui, T., Shirabe, K., and Takeshita, M. (1994) Cloning and

nucleotide sequence of a cDNA of the human erythrocyte NADPH-flavin

reductase. Biochem. Biophys. Res. Commun. 198, 1170-1176.

(45) Chinopoulos, C., and Adam-Vizi, V. (2010) Mitochondria as ATP consumers in

cellular pathology. Biochim. Biophys. Acta 1802, 221-227.

(46) Choi, J., Zhang, W., Gu, X., Chen, X., Hong, L., Laird, J. M., and Salomon, R. G.

(2011) Lysophosphatidylcholine is generated by spontaneous deacylation of

oxidized phospholipids. Chem. Res. Toxicol. 24, 111-118.

(47) Choi, S. Y., Kwon, H. Y., Kwon, O. B., and Kang, J. H. (1999) Hydrogen

peroxide-mediated Cu,Zn-superoxide dismutase fragmentation: protection by

carnosine, homocarnosine and anserine. Biochim. Biophys. Acta 1472, 651-657.

(48) Ciccone, L., Lee, W., Zernant, J., Tanaka, K., Schuerch, K., Tsang, S. H., and

Allikmets, R. (2017) Hyperreflective Deposition in the Background of Advanced

Stargardt Disease. Retina.

(49) Collier, R. J., Patel, Y., Martin, E. A., Dembinska, O., Hellberg, M., Krueger, D.

S., Kapin, M. A., and Romano, C. (2011) Agonists at the serotonin receptor (5-

266

HT(1A)) protect the retina from severe photo-oxidative stress. Invest. Ophthalmol.

Vis. Sci. 52, 2118-2126.

(50) Corey, E. J., Niimura, K., Konishi, Y., Hashimoto, S., and Hamada, Y. (1986) A

new synthetic route to prostaglandins. Tetrahedron Lett. 27, 2199-2202.

(51) Crabb, J. W., Miyagi, M., Gu, X., Shadrach, K., West, K. A., Sakaguchi, H.,

Kamei, M., Hasan, A., Yan, L., Rayborn, M. E., Salomon, R. G., and Hollyfield, J.

G. (2002) Drusen proteome analysis: an approach to the etiology of age-related

macular degeneration. Proc. Natl. Acad. Sci. U. S. A. 99, 14682-14687.

(52) Crompton, M. (1999) The mitochondrial permeability transition pore and its role

in cell death. Biochem. J 341 ( Pt 2), 233-249.

(53) Cruz-Guilloty, F., Saeed, A. M., Duffort, S., Cano, M., Ebrahimi, K. B., Ballmick,

A., Tan, Y., Wang, H., Laird, J. M., Salomon, R. G., Handa, J. T., and Perez, V. L.

(2014) T cells and macrophages responding to oxidative damage cooperate in

pathogenesis of a mouse model of age-related macular degeneration. PLoS One 9,

e88201.

(54) Csallany, A. S., Kim, S. S., and Gallaher, D. D. (2000) Response of urinary

lipophilic aldehydes and related carbonyl compounds to factors that stimulate

lipid peroxidation in vivo. Lipids 35, 855-862.

(55) Darwish, A., Lang, A., Kim, T., and Chong, J. M. (2008) The Use of Phosphine

Ligands to Control the Regiochemistry of Pd-Catalyzed Hydrostannations of 1-

Alkynes: Synthesis of (E)-1-Tributylstannyl-1-alkenes. Org. Lett. 10, 861-864.

267

(56) Davies, S., Elliott, M. H., Floor, E., Truscott, T. G., Zareba, M., Sarna, T., Shamsi,

F. A., and Boulton, M. E. (2001) Photocytotoxicity of lipofuscin in human retinal

pigment epithelial cells. Free Radic. Biol. Med. 31, 256-265.

(57) de Cogan, F., Hill, L. J., Lynch, A., Morgan-Warren, P. J., Lechner, J., Berwick,

M. R., Peacock, A. F. A., Chen, M., Scott, R. A. H., Xu, H., and Logan, A. (2017)

Topical Delivery of Anti-VEGF Drugs to the Ocular Posterior Segment Using

Cell-Penetrating Peptides. Invest. Ophthalmol. Vis. Sci. 58, 2578-2590.

(58) de Jong, P. T. (2006) Age-related macular degeneration. N. Engl. J. Med. 355,

1474-1485.

(59) Debacq-Chainiaux, F., Erusalimsky, J. D., Campisi, J., and Toussaint, O. (2009)

Protocols to detect senescence-associated beta-galactosidase (SA-betagal) activity,

a biomarker of senescent cells in culture and in vivo. Nat. Protoc. 4, 1798-1806.

(60) Decker, E. A., Livisay, S. A., and Zhou, S. (2000) A re-evaluation of the

antioxidant activity of purified carnosine. Biochemistry (Mosc.) 65, 766-770.

(61) Delori, F. C., Goger, D. G., and Dorey, C. K. (2001) Age-related accumulation

and spatial distribution of lipofuscin in RPE of normal subjects. Invest.

Ophthalmol. Vis. Sci. 42, 1855-1866.

(62) Dimri, G. P., Lee, X., Basile, G., Acosta, M., Scott, G., Roskelley, C., Medrano, E.

E., Linskens, M., Rubelj, I., Pereira-Smith, O., and et al. (1995) A biomarker that

identifies senescent human cells in culture and in aging skin in vivo. Proc. Natl.

Acad. Sci. U. S. A. 92, 9363-9367.

(63) Dixit, B. L., Balendiran, G. K., Watowich, S. J., Srivastava, S., Ramana, K. V.,

Petrash, J. M., Bhatnagar, A., and Srivastava, S. K. (2000) Kinetic and structural

268

characterization of the glutathione-binding site of aldose reductase. J. Biol. Chem.

275, 21587-21595.

(64) Dontsov, A. E., Glickman, R. D., and Ostrovsky, M. A. (1999) Retinal pigment

epithelium pigment granules stimulate the photo-oxidation of unsaturated fatty

acids. Free Radic. Biol. Med. 26, 1436-1446.

(65) Dorey, C. K., Delori, F. C., and Akeo, K. (1990) Growth of cultured RPE and

endothelial cells is inhibited by blue light but not green or red light. Curr. Eye Res.

9, 549-559.

(66) Dursun, N., Taskin, E., and Ozturk, F. (2011) Protection against adriamycin-

induced cardiomyopathy by carnosine in rats: role of endogenous antioxidants.

Biol. Trace Elem. Res. 143, 412-424.

(67) Dysli, C., Wolf, S., Hatz, K., and Zinkernagel, M. S. (2016) Fluorescence

Lifetime Imaging in Stargardt Disease: Potential Marker for Disease Progression.

Invest. Ophthalmol. Vis. Sci. 57, 832-841.

(68) Ebrahem, Q., Renganathan, K., Sears, J., Vasanji, A., Gu, X., Lu, L., Salomon, R.

G., Crabb, J. W., and Anand-Apte, B. (2006) Carboxyethylpyrrole oxidative

protein modifications stimulate neovascularization: Implications for age-related

macular degeneration. Proc. Natl. Acad. Sci. U. S. A. 103, 13480-13484.

(69) Eldred, G. E., and Katz, M. L. (1988) Fluorophores of the human retinal pigment

epithelium: separation and spectral characterization. Exp. Eye Res. 47, 71-86.

(70) Eldred, G. E., and Lasky, M. R. (1993) Retinal age pigments generated by self-

assembling lysosomotropic detergents. Nature 361, 724-726.

269

(71) Eshaq, R. S., Wright, W. S., and Harris, N. R. (2014) Oxygen delivery,

consumption, and conversion to reactive oxygen species in experimental models

of diabetic retinopathy. Redox Biol 2, 661-666.

(72) Esterbauer, H. (1993) Cytotoxicity and genotoxicity of lipid-oxidation products.

Am. J. Clin. Nutr. 57, 779S-785S; discussion 785S-786S.

(73) Fedorova, M., Bollineni, R. C., and Hoffmann, R. (2014) Protein carbonylation as

a major hallmark of oxidative damage: update of analytical strategies. Mass

Spectrom. Rev. 33, 79-97.

(74) Feeney-Burns, L., Hilderbrand, E. S., and Eldridge, S. (1984) Aging human RPE:

morphometric analysis of macular, equatorial, and peripheral cells. Invest.

Ophthalmol. Vis. Sci. 25, 195-200.

(75) Feher, J., Kovacs, I., Artico, M., Cavallotti, C., Papale, A., and Balacco Gabrieli,

C. (2006) Mitochondrial alterations of retinal pigment epithelium in age-related

macular degeneration. Neurobiol. Aging 27, 983-993.

(76) Finkel, T., and Holbrook, N. J. (2000) Oxidants, oxidative stress and the biology

of ageing. Nature 408, 239-247.

(77) Finnemann, S. C., Leung, L. W., and Rodriguez-Boulan, E. (2002) The lipofuscin

component A2E selectively inhibits phagolysosomal degradation of photoreceptor

phospholipid by the retinal pigment epithelium. Proc. Natl. Acad. Sci. U. S. A. 99,

3842-3847.

(78) Fletcher, A. E. (2010) Free radicals, antioxidants and eye diseases: evidence from

epidemiological studies on cataract and age-related macular degeneration.

Ophthalmic Res. 44, 191-198.

270

(79) Fletcher, A. E., Bentham, G. C., Agnew, M., Young, I. S., Augood, C.,

Chakravarthy, U., de Jong, P. T., Rahu, M., Seland, J., Soubrane, G., Tomazzoli,

L., Topouzis, F., Vingerling, J. R., and Vioque, J. (2008) Sunlight exposure,

antioxidants, and age-related macular degeneration. Arch. Ophthalmol. 126, 1396-

1403.

(80) Flores-Bellver, M., Bonet-Ponce, L., Barcia, J. M., Garcia-Verdugo, J. M.,

Martinez-Gil, N., Saez-Atienzar, S., Sancho-Pelluz, J., Jordan, J., Galindo, M. F.,

and Romero, F. J. (2014) Autophagy and mitochondrial alterations in human

retinal pigment epithelial cells induced by ethanol: implications of 4-hydroxy-

nonenal. Cell Death Dis. 5, e1328.

(81) Fritsche, L. G., Fariss, R. N., Stambolian, D., Abecasis, G. R., Curcio, C. A., and

Swaroop, A. (2014) Age-related macular degeneration: genetics and biology

coming together. Annu Rev Genomics Hum Genet 15, 151-171.

(82) Fu, Q., Dai, H., Hu, W., Fan, Y., Shen, Y., Zhang, W., and Chen, Z. (2008)

Carnosine protects against Abeta42-induced neurotoxicity in differentiated rat

PC12 cells. Cell. Mol. Neurobiol. 28, 307-316.

(83) Fukuda, K., Davies, S. S., Nakajima, T., Ong, B. H., Kupershmidt, S., Fessel, J.,

Amarnath, V., Anderson, M. E., Boyden, P. A., Viswanathan, P. C., Roberts, L. J.,

2nd, and Balser, J. R. (2005) Oxidative mediated lipid peroxidation recapitulates

proarrhythmic effects on cardiac sodium channels. Circ. Res. 97, 1262-1269.

(84) Gaillard, E. R., Atherton, S. J., Eldred, G., and Dillon, J. (1995) Photophysical

studies on human retinal lipofuscin. Photochem. Photobiol. 61, 448-453.

271

(85) Gaillard, E. R., Avalle, L. B., Keller, L. M., Wang, Z., Reszka, K. J., and Dillon, J.

P. (2004) A mechanistic study of the photooxidation of A2E, a component of

human retinal lipofuscin. Exp. Eye Res. 79, 313-319.

(86) Giddabasappa, A., Bauler, M., Yepuru, M., Chaum, E., Dalton, J. T., and

Eswaraka, J. (2010) 17-beta estradiol protects ARPE-19 cells from oxidative

stress through estrogen receptor-beta. Invest. Ophthalmol. Vis. Sci. 51, 5278-5287.

(87) Giovannini, C., Matarrese, P., Scazzocchio, B., Sanchez, M., Masella, R., and

Malorni, W. (2002) Mitochondria hyperpolarization is an early event in oxidized

low-density lipoprotein-induced apoptosis in Caco-2 intestinal cells. FEBS Lett.

523, 200-206.

(88) Gliem, M., Muller, P. L., Finger, R. P., McGuinness, M. B., Holz, F. G., and

Charbel Issa, P. (2016) Quantitative Fundus Autofluorescence in Early and

Intermediate Age-Related Macular Degeneration. JAMA Ophthalmol 134, 817-

824.

(89) Gold, B., Merriam, J. E., Zernant, J., Hancox, L. S., Taiber, A. J., Gehrs, K.,

Cramer, K., Neel, J., Bergeron, J., Barile, G. R., Smith, R. T., Group, A. M. D. G.

C. S., Hageman, G. S., Dean, M., and Allikmets, R. (2006) Variation in factor B

(BF) and complement component 2 (C2) genes is associated with age-related

macular degeneration. Nat. Genet. 38, 458-462.

(90) Golestaneh, N., Chu, Y., Xiao, Y. Y., Stoleru, G. L., and Theos, A. C. (2017)

Dysfunctional autophagy in RPE, a contributing factor in age-related macular

degeneration. Cell Death Dis. 8, e2537.

272

(91) Gomez-Sintes, R., Ledesma, M. D., and Boya, P. (2016) Lysosomal cell death

mechanisms in aging. Ageing Res Rev 32, 150-168.

(92) Gorgels, T. G., and van Norren, D. (1995) Ultraviolet and green light cause

different types of damage in rat retina. Invest. Ophthalmol. Vis. Sci. 36, 851-863.

(93) Green, D., and Kroemer, G. (1998) The central executioners of apoptosis:

caspases or mitochondria? Trends Cell Biol. 8, 267-271.

(94) Green, D. R., and Reed, J. C. (1998) Mitochondria and apoptosis. Science 281,

1309-1312.

(95) Gu, J., Pauer, G. J., Yue, X., Narendra, U., Sturgill, G. M., Bena, J., Gu, X.,

Peachey, N. S., Salomon, R. G., Hagstrom, S. A., Crabb, J. W., Clinical, G., and

Proteomic, A. M. D. S. G. (2009) Assessing susceptibility to age-related macular

degeneration with proteomic and genomic biomarkers. Mol. Cell. Proteomics 8,

1338-1349.

(96) Gu, J., Pauer, G. J., Yue, X., Narendra, U., Sturgill, G. M., Bena, J., Gu, X.,

Peachey, N. S., Salomon, R. G., Hagstrom, S. A., Crabb, J. W., Clinical, G., and

Proteomic, A. M. D. S. G. (2010) Proteomic and genomic biomarkers for age-

related macular degeneration. Adv. Exp. Med. Biol. 664, 411-417.

(97) Gu, X., Meer, S. G., Miyagi, M., Rayborn, M. E., Hollyfield, J. G., Crabb, J. W.,

and Salomon, R. G. (2003) Carboxyethylpyrrole protein adducts and

autoantibodies, biomarkers for age-related macular degeneration. J. Biol. Chem.

278, 42027-42035.

273

(98) Gu, X., Sun, M., Gugiu, B., Hazen, S., Crabb, J. W., and Salomon, R. G. (2003)

Oxidatively truncated docosahexaenoate phospholipids: total synthesis,

generation, and Peptide adduction chemistry. J. Org. Chem. 68, 3749-3761.

(99) Guiotto, A., Calderan, A., Ruzza, P., Osler, A., Rubini, C., Jo, D. G., Mattson, M.

P., and Borin, G. (2005) Synthesis and evaluation of neuroprotective alpha,beta-

unsaturated aldehyde scavenger histidyl-containing analogues of carnosine. J.

Med. Chem. 48, 6156-6161.

(100) Guo, J., Linetsky, M., Yu, A. O., Zhang, L., Howell, S. J., Folkwein, H. J., Wang,

H., and Salomon, R. G. (2016) 4-Hydroxy-7-oxo-5-heptenoic Acid Lactone

Induces Angiogenesis through Several Different Molecular Pathways. Chem. Res.

Toxicol. 29, 2125-2135.

(101) Guo, J., Wang, H., Hrinczenko, B., and Salomon, R. G. (2016) Efficient

Quantitative Analysis of Carboxyalkylpyrrole Ethanolamine Phospholipids:

Elevated Levels in Sickle Cell Disease Blood. Chem. Res. Toxicol. 29, 1187-1197.

(102) Ham, W. T., Jr., Mueller, H. A., Ruffolo, J. J., Jr., and Clarke, A. M. (1979)

Sensitivity of the retina to radiation damage as a function of wavelength.

Photochem. Photobiol. 29, 735-743.

(103) Ham, W. T., Jr., Mueller, H. A., Ruffolo, J. J., Jr., Guerry, D., 3rd, and Guerry, R.

K. (1982) Action spectrum for retinal injury from near-ultraviolet radiation in the

aphakic monkey. Am. J. Ophthalmol. 93, 299-306.

(104) Ham, W. T., Jr., Ruffolo, J. J., Jr., Mueller, H. A., Clarke, A. M., and Moon, M. E.

(1978) Histologic analysis of photochemical lesions produced in rhesus retina by

short-wave-length light. Invest. Ophthalmol. Vis. Sci. 17, 1029-1035.

274

(105) Ham, W. T., Jr., Ruffolo, J. J., Jr., Mueller, H. A., and Guerry, D., 3rd. (1980) The

nature of retinal radiation damage: dependence on wavelength, power level and

exposure time. Vision Res. 20, 1105-1111.

(106) Hamberg, M., and Samuelsson, B. (1973) Detection and isolation of an

endoperoxide intermediate in prostaglandin biosynthesis. Proc. Natl. Acad. Sci. U.

S. A. 70, 899-903.

(107) Han, D., Williams, E., and Cadenas, E. (2001) Mitochondrial respiratory chain-

dependent generation of superoxide anion and its release into the intermembrane

space. Biochem. J 353, 411-416.

(108) Harwerth, R. S., and Sperling, H. G. (1975) Effects of intense visible radiation on

the increment-threshold spectral sensitivity of the rhesus monkey eye. Vision Res.

15, 1193-1204.

(109) Haworth, R. A., and Hunter, D. R. (1979) The Ca2+-induced membrane transition

in mitochondria. II. Nature of the Ca2+ trigger site. Arch. Biochem. Biophys. 195,

460-467.

(110) Hidalgo, F. J., Alaiz, M., and Zamora, R. (2001) Pyrrolization and antioxidant

function of proteins following oxidative stress. Chem. Res. Toxicol. 14, 582-588.

(111) Hipkiss, A. R., and Brownson, C. (2000) Carnosine reacts with protein carbonyl

groups: another possible role for the anti-ageing peptide? Biogerontology 1, 217-

223.

(112) Hipkiss, A. R., Brownson, C., and Carrier, M. J. (2001) Carnosine, the anti-ageing,

anti-oxidant dipeptide, may react with protein carbonyl groups. Mech. Ageing Dev.

122, 1431-1445.

275

(113) Hollyfield, J. G., Bonilha, V. L., Rayborn, M. E., Yang, X., Shadrach, K. G., Lu,

L., Ufret, R. L., Salomon, R. G., and Perez, V. L. (2008) Oxidative damage-

induced inflammation initiates age-related macular degeneration. Nat. Med. 14,

194-198.

(114) Holz, F. G., Bellmann, C., Margaritidis, M., Schutt, F., Otto, T. P., and Volcker,

H. E. (1999) Patterns of increased in vivo fundus autofluorescence in the

junctional zone of geographic atrophy of the retinal pigment epithelium associated

with age-related macular degeneration. Graefes Arch. Clin. Exp. Ophthalmol. 237,

145-152.

(115) Holz, F. G., Schutt, F., Kopitz, J., Eldred, G. E., Kruse, F. E., Volcker, H. E., and

Cantz, M. (1999) Inhibition of lysosomal degradative functions in RPE cells by a

retinoid component of lipofuscin. Invest. Ophthalmol. Vis. Sci. 40, 737-743.

(116) Honda, S., Hjelmeland, L. M., and Handa, J. T. (2002) Senescence associated beta

galactosidase activity in human retinal pigment epithelial cells exposed to mild

hyperoxia in vitro. Br. J. Ophthalmol. 86, 159-162.

(117) Horning, M. S., Blakemore, L. J., and Trombley, P. Q. (2000) Endogenous

mechanisms of neuroprotection: role of zinc, copper, and carnosine. Brain Res.

852, 56-61.

(118) Hroudova, J., Singh, N., and Fisar, Z. (2014) Mitochondrial dysfunctions in

neurodegenerative diseases: relevance to Alzheimer's disease. Biomed Res Int

2014, 175062.

276

(119) Hunter, J. J., Morgan, J. I., Merigan, W. H., Sliney, D. H., Sparrow, J. R., and

Williams, D. R. (2012) The susceptibility of the retina to photochemical damage

from visible light. Prog. Retin. Eye Res. 31, 28-42.

(120) Isahara, K., Ohsawa, Y., Kanamori, S., Shibata, M., Waguri, S., Sato, N., Gotow,

T., Watanabe, T., Momoi, T., Urase, K., Kominami, E., and Uchiyama, Y. (1999)

Regulation of a novel pathway for cell death by lysosomal aspartic and cysteine

proteinases. Neuroscience 91, 233-249.

(121) Iyer, R. S., Ghosh, S., and Salomon, R. G. (1989) Levuglandin E2 crosslinks

proteins. Prostaglandins 37, 471-480.

(122) Jackson, R. W. (2001) A mild and selective method for the cleavage of tert-butyl

esters. Tetrahedron Lett. 42, 5163-5165.

(123) Jacques, S. L. (1992) Laser-tissue interactions. Photochemical, photothermal, and

photomechanical. Surg. Clin. North Am. 72, 531-558.

(124) Jager, R. D., Mieler, W. F., and Miller, J. W. (2008) Age-related macular

degeneration. N. Engl. J. Med. 358, 2606-2617.

(125) Jain, S. K. (1984) The accumulation of malonyldialdehyde, a product of fatty acid

peroxidation, can disturb aminophospholipid organization in the membrane

bilayer of human erythrocytes. J. Biol. Chem. 259, 3391-3394.

(126) Jaiswal, M., Haelterman, N. A., Sandoval, H., Xiong, B., Donti, T., Kalsotra, A.,

Yamamoto, S., Cooper, T. A., Graham, B. H., and Bellen, H. J. (2015) Impaired

Mitochondrial Energy Production Causes Light-Induced Photoreceptor

Degeneration Independent of Oxidative Stress. PLoS Biol. 13, e1002197.

277

(127) Jarrett, S. G., and Boulton, M. E. (2012) Consequences of oxidative stress in age-

related macular degeneration. Mol. Aspects Med. 33, 399-417.

(128) Jastroch, M., Divakaruni, A. S., Mookerjee, S., Treberg, J. R., and Brand, M. D.

(2010) Mitochondrial proton and electron leaks. Essays Biochem. 47, 53-67.

(129) Jonckheere, A. I., Smeitink, J. A., and Rodenburg, R. J. (2012) Mitochondrial

ATP synthase: architecture, function and pathology. J. Inherit. Metab. Dis. 35,

211-225.

(130) Justilien, V., Pang, J. J., Renganathan, K., Zhan, X., Crabb, J. W., Kim, S. R.,

Sparrow, J. R., Hauswirth, W. W., and Lewin, A. S. (2007) SOD2 knockdown

mouse model of early AMD. Invest. Ophthalmol. Vis. Sci. 48, 4407-4420.

(131) Kadenbach, B. (2003) Intrinsic and extrinsic uncoupling of oxidative

phosphorylation. Biochim. Biophys. Acta 1604, 77-94.

(132) Kamino, K., Nagasaka, K., Imagawa, M., Yamamoto, H., Yoneda, H., Ueki, A.,

Kitamura, S., Namekata, K., Miki, T., and Ohta, S. (2000) Deficiency in

mitochondrial aldehyde dehydrogenase increases the risk for late-onset

Alzheimer's disease in the Japanese population. Biochem. Biophys. Res. Commun.

273, 192-196.

(133) Kanai, Y., Hiroki, S., Koshino, H., Konoki, K., Cho, Y., Cayme, M., Fukuyo, Y.,

and Yotsu-Yamashita, M. (2011) Identification of novel oxidized levuglandin D2

in marine red alga and mouse tissue. J. Lipid Res. 52, 2245-2254.

(134) Kang, J. H., Kim, K. S., Choi, S. Y., Kwon, H. Y., Won, M. H., and Kang, T. C.

(2002) Protective effects of carnosine, homocarnosine and anserine against

278

peroxyl radical-mediated Cu,Zn-superoxide dismutase modification. Biochim.

Biophys. Acta 1570, 89-96.

(135) Kaplan, P., Tatarkova, Z., Racay, P., Lehotsky, J., Pavlikova, M., and Dobrota, D.

(2007) Oxidative modifications of cardiac mitochondria and inhibition of

cytochrome c oxidase activity by 4-hydroxynonenal. Redox Rep 12, 211-218.

(136) Kato, S., Osborne, N. N., Tamai, M., International Symposium on "Retinal, D.,

and Regeneration. Retinal degeneration and regeneration : proceedings of an

international symposium, Kanazawa, Japan, July 8-9, 1995, Kugler Publications,

Amsterdam; New York.

(137) Katz, M. L. (2002) Potential role of retinal pigment epithelial lipofuscin

accumulation in age-related macular degeneration. Arch. Gerontol. Geriatr. 34,

359-370.

(138) Kaur, K., Salomon, R. G., O'Neil, J., and Hoff, H. F. (1997)

(Carboxyalkyl)pyrroles in human plasma and oxidized low-density lipoproteins.

Chem. Res. Toxicol. 10, 1387-1396.

(139) Kersten, E., Paun, C. C., Schellevis, R. L., Hoyng, C. B., Delcourt, C., Lengyel, I.,

Peto, T., Ueffing, M., Klaver, C. C. W., Dammeier, S., den Hollander, A. I., and

de Jong, E. K. (2018) Systemic and ocular fluid compounds as potential

biomarkers in age-related macular degeneration. Surv. Ophthalmol. 63, 9-39.

(140) Kirkinezos, I. G., Bacman, S. R., Hernandez, D., Oca-Cossio, J., Arias, L. J.,

Perez-Pinzon, M. A., Bradley, W. G., and Moraes, C. T. (2005) Cytochrome c

association with the inner mitochondrial membrane is impaired in the CNS of

G93A-SOD1 mice. J. Neurosci. 25, 164-172.

279

(141) Klein, R., Chou, C. F., Klein, B. E., Zhang, X., Meuer, S. M., and Saaddine, J. B.

(2011) Prevalence of age-related macular degeneration in the US population. Arch.

Ophthalmol. 129, 75-80.

(142) Klein, R. J., Zeiss, C., Chew, E. Y., Tsai, J. Y., Sackler, R. S., Haynes, C.,

Henning, A. K., SanGiovanni, J. P., Mane, S. M., Mayne, S. T., Bracken, M. B.,

Ferris, F. L., Ott, J., Barnstable, C., and Hoh, J. (2005) Complement factor H

polymorphism in age-related macular degeneration. Science 308, 385-389.

(143) Kliffen, M., van der Schaft, T. L., Mooy, C. M., and de Jong, P. T. (1997)

Morphologic changes in age-related maculopathy. Microsc. Res. Tech. 36, 106-

122.

(144) Kohen, R., Yamamoto, Y., Cundy, K. C., and Ames, B. N. (1988) Antioxidant

activity of carnosine, homocarnosine, and anserine present in muscle and brain.

Proc. Natl. Acad. Sci. U. S. A. 85, 3175-3179.

(145) Kozlowski, M. R. (2012) RPE cell senescence: a key contributor to age-related

macular degeneration. Med. Hypotheses 78, 505-510.

(146) Krajewski, S., Krajewska, M., Ellerby, L. M., Welsh, K., Xie, Z., Deveraux, Q. L.,

Salvesen, G. S., Bredesen, D. E., Rosenthal, R. E., Fiskum, G., and Reed, J. C.

(1999) Release of caspase-9 from mitochondria during neuronal apoptosis and

cerebral ischemia. Proc. Natl. Acad. Sci. U. S. A. 96, 5752-5757.

(147) Kristal, B. S., Park, B. K., and Yu, B. P. (1996) 4-Hydroxyhexenal is a potent

inducer of the mitochondrial permeability transition. J. Biol. Chem. 271, 6033-

6038.

280

(148) Law, C. Y., Siu, C. W., Fan, K., Lai, W. H., Au, K. W., Lau, Y. M., Wong, L. Y.,

Ho, J. C. Y., Lee, Y. K., Tse, H. F., and Ng, K. M. (2016) Lysosomal membrane

permeabilization is involved in oxidative stress-induced apoptotic cell death in

LAMP2-deficient iPSCs-derived cerebral cortical neurons. Biochem Biophys Rep

5, 335-345.

(149) Lee, B. Y., Han, J. A., Im, J. S., Morrone, A., Johung, K., Goodwin, E. C., Kleijer,

W. J., DiMaio, D., and Hwang, E. S. (2006) Senescence-associated beta-

galactosidase is lysosomal beta-galactosidase. Aging Cell 5, 187-195.

(150) Lerman, S. (1987) Chemical and physical properties of the normal and aging lens:

spectroscopic (UV, fluorescence, phosphorescence, and NMR) analyses. Am. J.

Optom. Physiol. Opt. 64, 11-22.

(151) Li, K. R., Yang, S. Q., Gong, Y. Q., Yang, H., Li, X. M., Zhao, Y. X., Yao, J.,

Jiang, Q., and Cao, C. (2016) 3H-1,2-dithiole-3-thione protects retinal pigment

epithelium cells against Ultra-violet radiation via activation of Akt-mTORC1-

dependent Nrf2-HO-1 signaling. Sci. Rep. 6, 25525.

(152) Li, X., Liu, Z., Luo, C., Jia, H., Sun, L., Hou, B., Shen, W., Packer, L., Cotman, C.

W., and Liu, J. (2008) Lipoamide protects retinal pigment epithelial cells from

oxidative stress and mitochondrial dysfunction. Free Radic. Biol. Med. 44, 1465-

1474.

(153) Liang, F. Q., and Godley, B. F. (2003) Oxidative stress-induced mitochondrial

DNA damage in human retinal pigment epithelial cells: a possible mechanism for

RPE aging and age-related macular degeneration. Exp. Eye Res. 76, 397-403.

281

(154) Linetsky, M., Bondelid, K. S., Losovskiy, S., Gabyak, V., Rullo, M. J., Stiadle, T.

I., Munjapara, V., Saxena, P., Ma, D., Cheng, Y. S., Howes, A. M., Udeigwe, E.,

and Salomon, R. G. (2018) 4-Hydroxy-7-oxo-5-heptenoic Acid Lactone Is a

Potent Inducer of the Complement Pathway in Human Retinal Pigmented

Epithelial Cells. Chem. Res. Toxicol. 31, 666-679.

(155) Liu, J., Itagaki, Y., Ben-Shabat, S., Nakanishi, K., and Sparrow, J. R. (2000) The

biosynthesis of A2E, a fluorophore of aging retina, involves the formation of the

precursor, A2-PE, in the photoreceptor outer segment membrane. J. Biol. Chem.

275, 29354-29360.

(156) Liu, J., Lu, W., Reigada, D., Nguyen, J., Laties, A. M., and Mitchell, C. H. (2008)

Restoration of lysosomal pH in RPE cells from cultured human and ABCA4(-/-)

mice: pharmacologic approaches and functional recovery. Invest. Ophthalmol. Vis.

Sci. 49, 772-780.

(157) Liu, Y., Xu, G., and Sayre, L. M. (2003) Carnosine inhibits (E)-4-hydroxy-2-

nonenal-induced protein cross-linking: structural characterization of carnosine-

HNE adducts. Chem. Res. Toxicol. 16, 1589-1597.

(158) Logan, A., Pell, V. R., Shaffer, K. J., Evans, C., Stanley, N. J., Robb, E. L., Prime,

T. A., Chouchani, E. T., Cocheme, H. M., Fearnley, I. M., Vidoni, S., James, A.

M., Porteous, C. M., Partridge, L., Krieg, T., Smith, R. A., and Murphy, M. P.

(2016) Assessing the Mitochondrial Membrane Potential in Cells and In Vivo

using Targeted Click Chemistry and Mass Spectrometry. Cell Metab 23, 379-385.

282

(159) Lovelace, M. D., and Cahill, D. M. (2007) A rapid cell counting method utilising

acridine orange as a novel discriminating marker for both cultured astrocytes and

microglia. J. Neurosci. Methods 165, 223-229.

(160) Ly, J. D., Grubb, D. R., and Lawen, A. (2003) The mitochondrial membrane

potential (deltapsi(m)) in apoptosis; an update. Apoptosis 8, 115-128.

(161) Maeda, A., Maeda, T., Golczak, M., Chou, S., Desai, A., Hoppel, C. L.,

Matsuyama, S., and Palczewski, K. (2009) Involvement of all-trans-retinal in

acute light-induced retinopathy of mice. J. Biol. Chem. 284, 15173-15183.

(162) Maeda, A., Maeda, T., Golczak, M., and Palczewski, K. (2008) Retinopathy in

mice induced by disrupted all-trans-retinal clearance. J. Biol. Chem. 283, 26684-

26693.

(163) Maeda, T., Golczak, M., and Maeda, A. (2012) Retinal photodamage mediated by

all-trans-retinal. Photochem. Photobiol. 88, 1309-1319.

(164) Mainster, M. A. (1986) The spectra, classification, and rationale of ultraviolet-

protective intraocular lenses. Am. J. Ophthalmol. 102, 727-732.

(165) Marazita, M. C., Dugour, A., Marquioni-Ramella, M. D., Figueroa, J. M., and

Suburo, A. M. (2016) Oxidative stress-induced premature senescence

dysregulates VEGF and CFH expression in retinal pigment epithelial cells:

Implications for Age-related Macular Degeneration. Redox Biol 7, 78-87.

(166) Marc, R. E., Jones, B. W., Watt, C. B., Vazquez-Chona, F., Vaughan, D. K., and

Organisciak, D. T. (2008) Extreme retinal remodeling triggered by light damage:

implications for age related macular degeneration. Mol. Vis. 14, 782-806.

283

(167) Marie, M., Bigot, K., Angebault, C., Barrau, C., Gondouin, P., Pagan, D., Fouquet,

S., Villette, T., Sahel, J. A., Lenaers, G., and Picaud, S. (2018) Light action

spectrum on oxidative stress and mitochondrial damage in A2E-loaded retinal

pigment epithelium cells. Cell Death Dis. 9, 287.

(168) Matsumoto, K., Yamada, Y., Takahashi, M., Todoroki, T., Mizoguchi, K., Misaki,

H., and Yuki, H. (1990) Fluorometric determination of carnitine in serum with

immobilized carnitine dehydrogenase and diaphorase. Clin. Chem. 36, 2072-2076.

(169) Matsunaga, H., Handa, J. T., Aotaki-Keen, A., Sherwood, S. W., West, M. D.,

and Hjelmeland, L. M. (1999) Beta-galactosidase histochemistry and telomere

loss in senescent retinal pigment epithelial cells. Invest. Ophthalmol. Vis. Sci. 40,

197-202.

(170) Mirra, S. S., Heyman, A., McKeel, D., Sumi, S. M., Crain, B. J., Brownlee, L. M.,

Vogel, F. S., Hughes, J. P., van Belle, G., and Berg, L. (1991) The Consortium to

Establish a Registry for Alzheimer's Disease (CERAD). Part II. Standardization

of the neuropathologic assessment of Alzheimer's disease. Neurology 41, 479-486.

(171) Mongrain, C., and Gaudreault, R. (1990) Synthesis of Mono and Disubstituted

Maleic Anhydrides from Di-tert-Butyl Acetylene Dicarboxylate. Synth. Commun.

20, 2491-2500.

(172) Muller, F. (2000) The nature and mechanism of superoxide production by the

electron transport chain: Its relevance to aging. J Am Aging Assoc 23, 227-253.

(173) Murphy, M. P. (2009) How mitochondria produce reactive oxygen species.

Biochem. J 417, 1-13.

284

(174) Murthi, K. K., Friedman, L. R., Oleinick, N. L., and Salomon, R. G. (1993)

Formation of DNA-protein cross-links in mammalian cells by levuglandin E2.

Biochemistry 32, 4090-4097.

(175) Murthi, K. K., Salomon, R. G., and Sternlicht, H. (1990) Levuglandin E2 inhibits

mitosis and microtubule assembly. Prostaglandins 39, 611-622.

(176) Naggar, H., Van Ells, T. K., Ganapathy, V., and Smith, S. B. (2005) Regulation of

reduced-folate transporter-1 in retinal pigment epithelial cells by folate. Curr. Eye

Res. 30, 35-44.

(177) Nashine, S., Cohen, P., Nesburn, A. B., Kuppermann, B. D., and Kenney, M. C.

(2018) Characterizing the protective effects of SHLP2, a mitochondrial-derived

peptide, in macular degeneration. Sci. Rep. 8, 15175.

(178) Newsome, D. A., Swartz, M., Leone, N. C., Elston, R. C., and Miller, E. (1988)

Oral zinc in macular degeneration. Arch. Ophthalmol. 106, 192-198.

(179) Nicoletti, V. G., Santoro, A. M., Grasso, G., Vagliasindi, L. I., Giuffrida, M. L.,

Cuppari, C., Purrello, V. S., Stella, A. M., and Rizzarelli, E. (2007) Carnosine

interaction with nitric oxide and astroglial cell protection. J. Neurosci. Res. 85,

2239-2245.

(180) Nishiyama, H., Sasaki, M., and Itoh, K. (1981) Stereoselective Addition of

Readily Available Organocopper Reagents to Dimethyl Acetylenedicarboxylate.

Chem. Lett. 10, 905-908.

(181) Noell, W. K. (1980) Possible mechanisms of photoreceptor damage by light in

mammalian eyes. Vision Res. 20, 1163-1171.

285

(182) Noell, W. K., Walker, V. S., Kang, B. S., and Berman, S. (1966) Retinal damage

by light in rats. Invest. Ophthalmol. 5, 450-473.

(183) Nordgaard, C. L., Berg, K. M., Kapphahn, R. J., Reilly, C., Feng, X., Olsen, T. W.,

and Ferrington, D. A. (2006) Proteomics of the retinal pigment epithelium reveals

altered protein expression at progressive stages of age-related macular

degeneration. Invest. Ophthalmol. Vis. Sci. 47, 815-822.

(184) Nordgaard, C. L., Karunadharma, P. P., Feng, X., Olsen, T. W., and Ferrington, D.

A. (2008) Mitochondrial proteomics of the retinal pigment epithelium at

progressive stages of age-related macular degeneration. Invest. Ophthalmol. Vis.

Sci. 49, 2848-2855.

(185) Nowak, J. Z. (2013) Oxidative stress, polyunsaturated fatty acids-derived

oxidation products and bisretinoids as potential inducers of CNS diseases: focus

on age-related macular degeneration. Pharmacol. Rep. 65, 288-304.

(186) Organisciak, D. T., Darrow, R. M., Rapp, C. M., Smuts, J. P., Armstrong, D. W.,

and Lang, J. C. (2013) Prevention of retinal light damage by zinc oxide combined

with rosemary extract. Mol. Vis. 19, 1433-1445.

(187) Organisciak, D. T., and Vaughan, D. K. (2010) Retinal light damage: mechanisms

and protection. Prog. Retin. Eye Res. 29, 113-134.

(188) Orioli, M., Aldini, G., Benfatto, M. C., Facino, R. M., and Carini, M. (2007) HNE

Michael adducts to histidine and histidine-containing peptides as biomarkers of

lipid-derived carbonyl stress in urines: LC-MS/MS profiling in Zucker obese rats.

Anal. Chem. 79, 9174-9184.

286

(189) Orioli, M., Aldini, G., Beretta, G., Facino, R. M., and Carini, M. (2005) LC-ESI-

MS/MS determination of 4-hydroxy-trans-2-nonenal Michael adducts with

cysteine and histidine-containing peptides as early markers of oxidative stress in

excitable tissues. J. Chromatogr. B Analyt. Technol. Biomed. Life Sci. 827, 109-

118.

(190) Parish, C. A., Hashimoto, M., Nakanishi, K., Dillon, J., and Sparrow, J. (1998)

Isolation and one-step preparation of A2E and iso-A2E, fluorophores from human

retinal pigment epithelium. Proc. Natl. Acad. Sci. U. S. A. 95, 14609-14613.

(191) Perl, A., Gergely, P., Jr., Nagy, G., Koncz, A., and Banki, K. (2004)

Mitochondrial hyperpolarization: a checkpoint of T-cell life, death and

autoimmunity. Trends Immunol. 25, 360-367.

(192) Petit, P. X., Lecoeur, H., Zorn, E., Dauguet, C., Mignotte, B., and Gougeon, M. L.

(1995) Alterations in mitochondrial structure and function are early events of

dexamethasone-induced thymocyte apoptosis. J. Cell Biol. 130, 157-167.

(193) Pietila, M., Lehtonen, S., Tuovinen, E., Lahteenmaki, K., Laitinen, S., Leskela, H.

V., Natynki, A., Pesala, J., Nordstrom, K., and Lehenkari, P. (2012) CD200

positive human mesenchymal stem cells suppress TNF-alpha secretion from

CD200 receptor positive macrophage-like cells. PLoS One 7, e31671.

(194) Podrez, E. A., O'Neil, J., Salomon, R. G., Schreiber, M. J., and Hoff, H. F. (1998)

Measurement of oxidation in plasma Lp(a) in CAPD patients using a novel

ELISA. Kidney Int. 54, 637-645.

(195) Podrez, E. A., Poliakov, E., Shen, Z., Zhang, R., Deng, Y., Sun, M., Finton, P. J.,

Shan, L., Febbraio, M., Hajjar, D. P., Silverstein, R. L., Hoff, H. F., Salomon, R.

287

G., and Hazen, S. L. (2002) A novel family of atherogenic oxidized phospholipids

promotes macrophage foam cell formation via the scavenger receptor CD36 and

is enriched in atherosclerotic lesions. J. Biol. Chem. 277, 38517-38523.

(196) Poliakov, E., Brennan, M. L., Macpherson, J., Zhang, R., Sha, W., Narine, L.,

Salomon, R. G., and Hazen, S. L. (2003) Isolevuglandins, a novel class of

isoprostenoid derivatives, function as integrated sensors of oxidant stress and are

generated by myeloperoxidase in vivo. FASEB J. 17, 2209-2220.

(197) Poliakov, E., Meer, S. G., Roy, S. C., Mesaros, C., and Salomon, R. G. (2004)

Iso[7]LGD2-protein adducts are abundant in vivo and free radical-induced

oxidation of an arachidonyl phospholipid generates this D series isolevuglandin in

vitro. Chem. Res. Toxicol. 17, 613-622.

(198) Poliakov, E., Strunnikova, N. V., Jiang, J. K., Martinez, B., Parikh, T., Lakkaraju,

A., Thomas, C., Brooks, B. P., and Redmond, T. M. (2014) Multiple A2E

treatments lead to melanization of rod outer segment-challenged ARPE-19 cells.

Mol. Vis. 20, 285-300.

(199) Poon, H. F., Calabrese, V., Scapagnini, G., and Butterfield, D. A. (2004) Free

radicals: key to brain aging and heme oxygenase as a cellular response to

oxidative stress. J. Gerontol. A Biol. Sci. Med. Sci. 59, 478-493.

(200) Preston, J. E., Hipkiss, A. R., Himsworth, D. T., Romero, I. A., and Abbott, J. N.

(1998) Toxic effects of beta-amyloid(25-35) on immortalised rat brain endothelial

cell: protection by carnosine, homocarnosine and beta-alanine. Neurosci. Lett. 242,

105-108.

288

(201) Radu, R. A., Mata, N. L., Bagla, A., and Travis, G. H. (2004) Light exposure

stimulates formation of A2E oxiranes in a mouse model of Stargardt's macular

degeneration. Proc. Natl. Acad. Sci. U. S. A. 101, 5928-5933.

(202) Rahman, I., Kode, A., and Biswas, S. K. (2006) Assay for quantitative

determination of glutathione and glutathione disulfide levels using enzymatic

recycling method. Nat. Protoc. 1, 3159-3165.

(203) Rahman, T., Hosen, I., Islam, M. M. T., and Shekhar, H. U. (2012) Oxidative

stress and human health. Advances in Bioscience and Biotechnology 03, 997-1019.

(204) Rajapakse, D., Curtis, T., Chen, M., and Xu, H. (2017) Zinc Protects Oxidative

Stress-Induced RPE Death by Reducing Mitochondrial Damage and Preventing

Lysosome Rupture. Oxid. Med. Cell. Longev. 2017, 6926485.

(205) Rampersad, S. N. (2012) Multiple applications of Alamar Blue as an indicator of

metabolic function and cellular health in cell viability bioassays. Sensors (Basel)

12, 12347-12360.

(206) Reme, C. E. (2005) The dark side of light: rhodopsin and the silent death of vision

the proctor lecture. Invest. Ophthalmol. Vis. Sci. 46, 2671-2682.

(207) Renganathan, K., Gu, J., Rayborn, M. E., Crabb, J. S., Salomon, R. G., Collier, R.

J., Kapin, M. A., Romano, C., Hollyfield, J. G., and Crabb, J. W. (2013) CEP

biomarkers as potential tools for monitoring therapeutics. PLoS One 8, e76325.

(208) Reszka, K., Eldred, G. E., Wang, R. H., Chignell, C., and Dillon, J. (1995) The

photochemistry of human retinal lipofuscin as studied by EPR. Photochem.

Photobiol. 62, 1005-1008.

289

(209) Rhein, V., Baysang, G., Rao, S., Meier, F., Bonert, A., Muller-Spahn, F., and

Eckert, A. (2009) Amyloid-beta leads to impaired cellular respiration, energy

production and mitochondrial electron chain complex activities in human

neuroblastoma cells. Cell. Mol. Neurobiol. 29, 1063-1071.

(210) Roberts, L. J., 2nd, Salomon, R. G., Morrow, J. D., and Brame, C. J. (1999) New

developments in the isoprostane pathway: identification of novel highly reactive

gamma-ketoaldehydes (isolevuglandins) and characterization of their protein

adducts. FASEB J. 13, 1157-1168.

(211) Rodrigues, C. M., Sola, S., Silva, R., and Brites, D. (2000) Bilirubin and amyloid-

beta peptide induce cytochrome c release through mitochondrial membrane

permeabilization. Mol. Med. 6, 936-946.

(212) Rodriguez de Turco, E. B., Parkins, N., Ershov, A. V., and Bazan, N. G. (1999)

Selective retinal pigment epithelial cell lipid metabolism and remodeling

conserves photoreceptor docosahexaenoic acid following phagocytosis. J.

Neurosci. Res. 57, 479-486.

(213) Rodriguez-Muela, N., Koga, H., Garcia-Ledo, L., de la Villa, P., de la Rosa, E. J.,

Cuervo, A. M., and Boya, P. (2013) Balance between autophagic pathways

preserves retinal homeostasis. Aging Cell 12, 478-488.

(214) Roy, S. C., Nagarajan, L., and Salomon, R. G. (1999) Total synthesis of

iso[7]levuglandin D-2. J. Org. Chem. 64, 1218-1224.

(215) Rozanowska, M., Jarvis-Evans, J., Korytowski, W., Boulton, M. E., Burke, J. M.,

and Sarna, T. (1995) Blue light-induced reactivity of retinal age pigment. In vitro

generation of oxygen-reactive species. J. Biol. Chem. 270, 18825-18830.

290

(216) Rozanowska, M., Pawlak, A., Rozanowski, B., Skumatz, C., Zareba, M., Boulton,

M. E., Burke, J. M., Sarna, T., and Simon, J. D. (2004) Age-related changes in the

photoreactivity of retinal lipofuscin granules: role of chloroform-insoluble

components. Invest. Ophthalmol. Vis. Sci. 45, 1052-1060.

(217) Rozanowska, M., and Sarna, T. (2005) Light-induced damage to the retina: role of

rhodopsin chromophore revisited. Photochem. Photobiol. 81, 1305-1330.

(218) Rozanowska, M., Wessels, J., Boulton, M., Burke, J. M., Rodgers, M. A.,

Truscott, T. G., and Sarna, T. (1998) Blue light-induced singlet oxygen generation

by retinal lipofuscin in non-polar media. Free Radic. Biol. Med. 24, 1107-1112.

(219) Rozanowska, M. B. (2012) Light-induced damage to the retina: current

understanding of the mechanisms and unresolved questions: a symposium-in-print.

Photochem. Photobiol. 88, 1303-1308.

(220) Rudolf, M., Vogt, S. D., Curcio, C. A., Huisingh, C., McGwin, G., Jr., Wagner,

A., Grisanti, S., and Read, R. W. (2013) Histologic basis of variations in retinal

pigment epithelium autofluorescence in eyes with geographic atrophy.

Ophthalmology 120, 821-828.

(221) Sachdeva, M., Karan, M., Singh, T., and Dhingra, S. (2014) Oxidants and

Antioxidants in Complementary and Alternative Medicine: A Review. Spatula

DD - Peer Reviewed Journal on Complementary Medicine and Drug Discovery 4,

(222) Sadhukhan, S., Han, Y., Jin, Z., Tochtrop, G. P., and Zhang, G. F. (2014)

Glutathionylated 4-hydroxy-2-(E)-alkenal enantiomers in rat organs and their

291

contributions toward the disposal of 4-hydroxy-2-(E)-nonenal in rat liver. Free

Radic. Biol. Med. 70, 78-85.

(223) Salomon, R. G. (1985) Prostaglandin endoperoxide reaction mechanisms and the

discovery of levuglandins. Acc. Chem. Res. 18, 294-301.

(224) Salomon, R. G. (2005) Levuglandins and isolevuglandins: stealthy toxins of

oxidative injury. Antioxid. Redox. Signal 7, 185-201.

(225) Salomon, R. G. (2005) Distinguishing levuglandins produced through the

cyclooxygenase and isoprostane pathways. Chem. Phys. Lipids 134, 1-20.

(226) Salomon, R. G. (2005) Isolevuglandins, oxidatively truncated phospholipids, and

atherosclerosis. Ann. N. Y. Acad. Sci. 1043, 327-342.

(227) Salomon, R. G. (2017) Carboxyethylpyrroles: From Hypothesis to the Discovery

of Biologically Active Natural Products. Chem. Res. Toxicol. 30, 105-113.

(228) Salomon, R. G., Batyreva, E., Kaur, K., Sprecher, D. L., Schreiber, M. J., Crabb, J.

W., Penn, M. S., DiCorletoe, A. M., Hazen, S. L., and Podrez, E. A. (2000)

Isolevuglandin-protein adducts in humans: products of free radical-induced lipid

oxidation through the isoprostane pathway. Biochim. Biophys. Acta. 1485, 225-

235.

(229) Salomon, R. G., and Gu, X. (2011) Critical insights into cardiovascular disease

from basic research on the oxidation of phospholipids: the gamma-

hydroxyalkenal phospholipid hypothesis. Chem. Res. Toxicol. 24, 1791-1802.

(230) Salomon, R. G., Jirousek, M. R., Ghosh, S., and Sharma, R. B. (1987)

Prostaglandin endoperoxides 21. Covalent binding of levuglandin E2 with

proteins. Prostaglandins 34, 643-656.

292

(231) Salomon, R. G., Miller, D. B., Zagorski, M. G., and Coughlin, D. J. (1984)

Prostaglandin endoperoxides. 14. Solvent-induced fragmentation of prostaglandin

endoperoxides. New aldehyde products from PGH2 and a novel intramolecular

1,2-hydride shift during endoperoxide fragmentation in aqueous solution. J. Am.

Chem. Soc. 106, 6049-6060.

(232) Salomon, R. G., Subbanagounder, G., O'Neil, J., Kaur, K., Smith, M. A., Hoff, H.

F., Perry, G., and Monnier, V. M. (1997) Levuglandin E2-protein adducts in

human plasma and vasculature. Chem. Res. Toxicol. 10, 536-545.

(233) Salomon, R. G., Subbanagounder, G., Singh, U., O'Neil, J., and Hoff, H. F. (1997)

Oxidation of low-density lipoproteins produces levuglandin-protein adducts.

Chem. Res. Toxicol. 10, 750-759.

(234) SanGiovanni, J. P., and Chew, E. Y. (2005) The role of omega-3 long-chain

polyunsaturated fatty acids in health and disease of the retina. Prog. Retin. Eye

Res. 24, 87-138.

(235) Schmidley, J. W., Dadson, J., Iyer, R. S., and Salomon, R. G. (1992) Brain tissue

injury and blood-brain barrier opening induced by injection of LGE2 or PGE2.

Prostaglandins, Leukotrienes Essent. Fatty Acids 47, 105-110.

(236) Scholte, A. A., Eubanks, L. M., Poulter, C. D., and Vederas, J. C. (2004)

Synthesis and biological activity of isopentenyl diphosphate analogues. Bioorg.

Med. Chem. 12, 763-770.

(237) Schutt, F., Bergmann, M., Holz, F. G., Dithmar, S., Volcker, H. E., and Kopitz, J.

(2007) Accumulation of A2-E in mitochondrial membranes of cultured RPE cells.

Graefes Arch. Clin. Exp. Ophthalmol. 245, 391-398.

293

(238) Schutt, F., Davies, S., Kopitz, J., Holz, F. G., and Boulton, M. E. (2000)

Photodamage to human RPE cells by A2-E, a retinoid component of lipofuscin.

Invest. Ophthalmol. Vis. Sci. 41, 2303-2308.

(239) Scorrano, L., Petronilli, V., and Bernardi, P. (1997) On the voltage dependence of

the mitochondrial permeability transition pore. A critical appraisal. J. Biol. Chem.

272, 12295-12299.

(240) Serrano-Puebla, A., and Boya, P. (2016) Lysosomal membrane permeabilization

in cell death: new evidence and implications for health and disease. Ann. N. Y.

Acad. Sci. 1371, 30-44.

(241) Shaw, P. X., Stiles, T., Douglas, C., Ho, D., Fan, W., Du, H., and Xiao, X. (2016)

Oxidative stress, innate immunity, and age-related macular degeneration. AIMS

Mol Sci 3, 196-221.

(242) Sidorova, T. N., Yermalitskaya, L. V., Mace, L. C., Wells, K. S., Boutaud, O.,

Prinsen, J. K., Davies, S. S., Roberts, L. J., 2nd, Dikalov, S. I., Glabe, C. G.,

Amarnath, V., Barnett, J. V., and Murray, K. T. (2015) Reactive gamma-

ketoaldehydes promote protein misfolding and preamyloid oligomer formation in

rapidly-activated atrial cells. J. Mol. Cell. Cardiol. 79, 295-302.

(243) Singh, I. N., Gilmer, L. K., Miller, D. M., Cebak, J. E., Wang, J. A., and Hall, E.

D. (2013) Phenelzine mitochondrial functional preservation and neuroprotection

after traumatic brain injury related to scavenging of the lipid peroxidation-derived

aldehyde 4-hydroxy-2-nonenal. J. Cereb. Blood Flow Metab. 33, 593-599.

(244) Smith, P. K., Krohn, R. I., Hermanson, G. T., Mallia, A. K., Gartner, F. H.,

Provenzano, M. D., Fujimoto, E. K., Goeke, N. M., Olson, B. J., and Klenk, D. C.

294

(1985) Measurement of protein using bicinchoninic acid. Anal. Biochem. 150, 76-

85.

(245) Sohaebuddin, S. K., and Tang, L. (2013) A simple method to visualize and assess

the integrity of lysosomal membrane in mammalian cells using a fluorescent dye.

Methods Mol. Biol. 991, 25-31.

(246) Sparrow, J. R., Nakanishi, K., and Parish, C. A. (2000) The lipofuscin fluorophore

A2E mediates blue light-induced damage to retinal pigmented epithelial cells.

Invest. Ophthalmol. Vis. Sci. 41, 1981-1989.

(247) Sparrow, J. R., Parish, C. A., Hashimoto, M., and Nakanishi, K. (1999) A2E, a

lipofuscin fluorophore, in human retinal pigmented epithelial cells in culture.

Invest. Ophthalmol. Vis. Sci. 40, 2988-2995.

(248) Sparrow, J. R., Vollmer-Snarr, H. R., Zhou, J., Jang, Y. P., Jockusch, S., Itagaki,

Y., and Nakanishi, K. (2003) A2E-epoxides damage DNA in retinal pigment

epithelial cells. Vitamin E and other antioxidants inhibit A2E-epoxide formation.

J. Biol. Chem. 278, 18207-18213.

(249) Sparrow, J. R., Wu, Y., Kim, C. Y., and Zhou, J. (2010) Phospholipid meets all-

trans-retinal: the making of RPE bisretinoids. J. Lipid Res. 51, 247-261.

(250) Sparrow, J. R., Zhou, J., Ben-Shabat, S., Vollmer, H., Itagaki, Y., and Nakanishi,

K. (2002) Involvement of oxidative mechanisms in blue-light-induced damage to

A2E-laden RPE. Invest. Ophthalmol. Vis. Sci. 43, 1222-1227.

(251) Sperling, H. G., Johnson, C., and Harwerth, R. S. (1980) Differential spectral

photic damage to primate cones. Vision Res. 20, 1117-1125.

295

(252) Spinazzi, M., Casarin, A., Pertegato, V., Salviati, L., and Angelini, C. (2012)

Assessment of mitochondrial respiratory chain enzymatic activities on tissues and

cultured cells. Nat. Protoc. 7, 1235-1246.

(253) Stavrovskaya, I. G., Baranov, S. V., Guo, X., Davies, S. S., Roberts, L. J., 2nd,

and Kristal, B. S. (2010) Reactive gamma-ketoaldehydes formed via the

isoprostane pathway disrupt mitochondrial respiration and calcium homeostasis.

Free Radic. Biol. Med. 49, 567-579.

(254) Stoka, V., Turk, B., Schendel, S. L., Kim, T. H., Cirman, T., Snipas, S. J., Ellerby,

L. M., Bredesen, D., Freeze, H., Abrahamson, M., Bromme, D., Krajewski, S.,

Reed, J. C., Yin, X. M., Turk, V., and Salvesen, G. S. (2001) Lysosomal protease

pathways to apoptosis. Cleavage of bid, not pro-caspases, is the most likely route.

J. Biol. Chem. 276, 3149-3157.

(255) Strauss, O. (2005) The retinal pigment epithelium in visual function. Physiol. Rev.

85, 845-881.

(256) Sun, L., Luo, C., Long, J., Wei, D., and Liu, J. (2006) Acrolein is a mitochondrial

toxin: effects on respiratory function and enzyme activities in isolated rat liver

mitochondria. Mitochondrion 6, 136-142.

(257) Sun, M., Finnemann, S. C., Febbraio, M., Shan, L., Annangudi, S. P., Podrez, E.

A., Hoppe, G., Darrow, R., Organisciak, D. T., Salomon, R. G., Silverstein, R. L.,

and Hazen, S. L. (2006) Light-induced oxidation of photoreceptor outer segment

phospholipids generates ligands for CD36-mediated phagocytosis by retinal

pigment epithelium: a potential mechanism for modulating outer segment

phagocytosis under oxidant stress conditions. J. Biol. Chem. 281, 4222-4230.

296

(258) Susin, S. A., Zamzami, N., Castedo, M., Daugas, E., Wang, H. G., Geley, S.,

Fassy, F., Reed, J. C., and Kroemer, G. (1997) The central executioner of

apoptosis: multiple connections between protease activation and mitochondria in

Fas/APO-1/CD95- and ceramide-induced apoptosis. J. Exp. Med. 186, 25-37.

(259) Suter, M., Reme, C., Grimm, C., Wenzel, A., Jaattela, M., Esser, P., Kociok, N.,

Leist, M., and Richter, C. (2000) Age-related macular degeneration. The

lipofusion component N-retinyl-N-retinylidene ethanolamine detaches

proapoptotic proteins from mitochondria and induces apoptosis in mammalian

retinal pigment epithelial cells. J. Biol. Chem. 275, 39625-39630.

(260) Taddei, M. L., Giannoni, E., Raugei, G., Scacco, S., Sardanelli, A. M., Papa, S.,

and Chiarugi, P. (2012) Mitochondrial Oxidative Stress due to Complex I

Dysfunction Promotes Fibroblast Activation and Melanoma Cell Invasiveness. J

Signal Transduct 2012, 684592.

(261) Tang, S. C., Arumugam, T. V., Cutler, R. G., Jo, D. G., Magnus, T., Chan, S. L.,

Mughal, M. R., Telljohann, R. S., Nassar, M., Ouyang, X., Calderan, A., Ruzza,

P., Guiotto, A., and Mattson, M. P. (2007) Neuroprotective actions of a histidine

analogue in models of ischemic stroke. J. Neurochem. 101, 729-736.

(262) Taylor, H. R., West, S., Munoz, B., Rosenthal, F. S., Bressler, S. B., and Bressler,

N. M. (1992) The long-term effects of visible light on the eye. Arch. Ophthalmol.

110, 99-104.

(263) Terluk, M. R., Kapphahn, R. J., Soukup, L. M., Gong, H., Gallardo, C.,

Montezuma, S. R., and Ferrington, D. A. (2015) Investigating mitochondria as a

target for treating age-related macular degeneration. J. Neurosci. 35, 7304-7311.

297

(264) Teufel, M., Saudek, V., Ledig, J. P., Bernhardt, A., Boularand, S., Carreau, A.,

Cairns, N. J., Carter, C., Cowley, D. J., Duverger, D., Ganzhorn, A. J., Guenet, C.,

Heintzelmann, B., Laucher, V., Sauvage, C., and Smirnova, T. (2003) Sequence

identification and characterization of human carnosinase and a closely related

non-specific dipeptidase. J. Biol. Chem. 278, 6521-6531.

(265) Tomany, S. C., Cruickshanks, K. J., Klein, R., Klein, B. E., and Knudtson, M. D.

(2004) Sunlight and the 10-year incidence of age-related maculopathy: the Beaver

Dam Eye Study. Arch. Ophthalmol. 122, 750-757.

(266) Uchida, K. (2003) 4-Hydroxy-2-nonenal: a product and mediator of oxidative

stress. Prog. Lipid Res. 42, 318-343.

(267) Uchimoto, T., Nohara, H., Kamehara, R., Iwamura, M., Watanabe, N., and

Kobayashi, Y. (1999) Mechanism of apoptosis induced by a lysosomotropic agent,

L-Leucyl-L-Leucine methyl ester. Apoptosis 4, 357-362.

(268) Valko, M., Rhodes, C. J., Moncol, J., Izakovic, M., and Mazur, M. (2006) Free

radicals, metals and antioxidants in oxidative stress-induced cancer. Chem. Biol.

Interact. 160, 1-40.

(269) van Norren, D., and Gorgels, T. G. (2011) The action spectrum of photochemical

damage to the retina: a review of monochromatic threshold data. Photochem.

Photobiol. 87, 747-753.

(270) Vedel, F., Lalanne, É., Sabar, M., Chétrit, P., and De Paepe, R. (1999) The

mitochondrial respiratory chain and ATP synthase complexes: Composition,

structure and mutational studies. Plant Physiol. Biochem. 37, 629-643.

298

(271) Vives-Bauza, C., Anand, M., Shiraz, A. K., Magrane, J., Gao, J., Vollmer-Snarr,

H. R., Manfredi, G., and Finnemann, S. C. (2008) The age lipid A2E and

mitochondrial dysfunction synergistically impair phagocytosis by retinal pigment

epithelial cells. J. Biol. Chem. 283, 24770-24780.

(272) von Ruckmann, A., Fitzke, F. W., and Bird, A. C. (1997) Fundus

autofluorescence in age-related macular disease imaged with a laser scanning

ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 38, 478-486.

(273) Wang, H., Guo, J., West, X. Z., Bid, H. K., Lu, L., Hong, L., Jang, G. F., Zhang,

L., Crabb, J. W., Clinical, G., Proteomic, A. M. D. S. G., Linetsky, M., and

Salomon, R. G. (2014) Detection and biological activities of carboxyethylpyrrole

ethanolamine phospholipids (CEP-EPs). Chem. Res. Toxicol. 27, 2015-2022.

(274) Wang, H., Linetsky, M., Guo, J., Choi, J., Hong, L., Chamberlain, A. S., Howell,

S. J., Howes, A. M., and Salomon, R. G. (2015) 4-Hydroxy-7-oxo-5-heptenoic

Acid (HOHA) Lactone is a Biologically Active Precursor for the Generation of 2-

(omega-Carboxyethyl)pyrrole (CEP) Derivatives of Proteins and Ethanolamine

Phospholipids. Chem. Res. Toxicol. 28, 967-977.

(275) Wang, H., Linetsky, M., Guo, J., Yu, A. O., and Salomon, R. G. (2016)

Metabolism of 4-Hydroxy-7-oxo-5-heptenoic Acid (HOHA) Lactone by Retinal

Pigmented Epithelial Cells. Chem. Res. Toxicol. 29, 1198-1210.

(276) Wang, Y., Shen, D., Wang, V. M., Yu, C. R., Wang, R. X., Tuo, J., and Chan, C.

C. (2012) Enhanced apoptosis in retinal pigment epithelium under inflammatory

stimuli and oxidative stress. Apoptosis 17, 1144-1155.

299

(277) Wassell, J., Davies, S., Bardsley, W., and Boulton, M. (1999) The photoreactivity

of the retinal age pigment lipofuscin. J. Biol. Chem. 274, 23828-23832.

(278) Wegscheider, B. J., Weger, M., Renner, W., Steinbrugger, I., Marz, W.,

Mossbock, G., Temmel, W., El-Shabrawi, Y., Schmut, O., Jahrbacher, R., and

Haas, A. (2007) Association of complement factor H Y402H gene polymorphism

with different subtypes of exudative age-related macular degeneration.

Ophthalmology 114, 738-742.

(279) West, J. D., and Marnett, L. J. (2006) Endogenous reactive intermediates as

modulators of cell signaling and cell death. Chem. Res. Toxicol. 19, 173-194.

(280) West, X. Z., Malinin, N. L., Merkulova, A. A., Tischenko, M., Kerr, B. A.,

Borden, E. C., Podrez, E. A., Salomon, R. G., and Byzova, T. V. (2010) Oxidative

stress induces angiogenesis by activating TLR2 with novel endogenous ligands.

Nature 467, 972-976.

(281) Williams, T. P., and Howell, W. L. (1983) Action spectrum of retinal light-

damage in albino rats. Invest. Ophthalmol. Vis. Sci. 24, 285-287.

(282) Winger, A. M., Taylor, N. L., Heazlewood, J. L., Day, D. A., and Millar, A. H.

(2007) The Cytotoxic lipid peroxidation product 4-hydroxy-2-nonenal covalently

modifies a selective range of proteins linked to respiratory function in plant

mitochondria. J. Biol. Chem. 282, 37436-37447.

(283) Winkler, B. S., Boulton, M. E., Gottsch, J. D., and Sternberg, P. (1999) Oxidative

damage and age-related macular degeneration. Mol. Vis. 5, 32.

(284) Wolf, G. (2003) Lipofuscin and macular degeneration. Nutr. Rev. 61, 342-346.

300

(285) Wu, J., Luo, X., and Yan, L. J. (2015) Two dimensional blue native/SDS-PAGE

to identify mitochondrial complex I subunits modified by 4-hydroxynonenal

(HNE). Front. Physiol. 6, 98.

(286) Wu, J., Seregard, S., and Algvere, P. V. (2006) Photochemical damage of the

retina. Surv. Ophthalmol. 51, 461-481.

(287) Xu, J., Chen, S., Ku, G., Ahmed, S. H., Xu, J., Chen, H., and Hsu, C. Y. (2001)

Amyloid beta peptide-induced cerebral endothelial cell death involves

mitochondrial dysfunction and caspase activation. J. Cereb. Blood Flow Metab.

21, 702-710.

(288) Yang, D., Elner, S. G., Clark, A. J., Hughes, B. A., Petty, H. R., and Elner, V. M.

(2011) Activation of P2X receptors induces apoptosis in human retinal pigment

epithelium. Invest. Ophthalmol. Vis. Sci. 52, 1522-1530.

(289) Yin, H., Xu, L., and Porter, N. A. (2011) Free radical lipid peroxidation:

mechanisms and analysis. Chem. Rev. 111, 5944-5972.

(290) Zagol-Ikapitte, I., Masterson, T. S., Amarnath, V., Montine, T. J., Andreasson, K.

I., Boutaud, O., and Oates, J. A. (2005) Prostaglandin H(2)-derived adducts of

proteins correlate with Alzheimer's disease severity. J. Neurochem. 94, 1140-1145.

(291) Zareba, M., Raciti, M. W., Henry, M. M., Sarna, T., and Burke, J. M. (2006)

Oxidative stress in ARPE-19 cultures: do melanosomes confer cytoprotection?

Free Radic. Biol. Med. 40, 87-100.

(292) Zhang, H., and Forman, H. J. (2017) 4-hydroxynonenal-mediated signaling and

aging. Free Radic. Biol. Med. 111, 219-225.

301

(293) Zhou, S., and Decker, E. A. (1999) Ability of carnosine and other skeletal muscle

components to quench unsaturated aldehydic lipid oxidation products. J. Agric.

Food. Chem. 47, 51-55.

302