Mechanistic Studies of S-Nitrosothiol Reactions with Reference to Potential Physiological Activity
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Durham E-Theses Mechanistic studies of S-nitrosothiol reactions with reference to potential physiological activity McAninly, John How to cite: McAninly, John (1994) Mechanistic studies of S-nitrosothiol reactions with reference to potential physiological activity, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/5481/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk 2 The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. Mechanistic Studies of S-Nitrosothiol Reactions With Reference To Potential Physiological Activity by John McAninly B.Sc, M.I. Biol., M.R. Pharm. S. A thesis submitted for the degree of Doctor of Philosophy of the University of Durham December 1994 MAY 1995 MECHANISTIC STUDIES OF S-NITROSOTfflOL REACTIONS WITH REFERENCE TO POTENTIAL PHYSIOLOGICAL ACTIVITY by John McAninly A thesis submitted for the degree of Doctor of Philosophy in the Department of Chemistry, University of Durham, December 1994 ABSTRACT A study of the reactions of various S-nitrosothiols, particularly S-nitroso-N- acetylpenicillamine (SNAP), was undertaken. These compounds were known to produce nitric oxide (NO) when decomposing, which has important and diverse biological roles. An example of their use in physiological research was demonstrated. The Griess method was used to determine the stoichiometry of nitrite production from S-nitrosothiol decomposition in various buffer solutions. In all cases the production was found to be almost quantitative. The kinetic measurement of SNAP decomposition in a variety of buffers and pH was undertaken. The results were complex and often erratic, conforming to first order but also half order kinetics in many cases. There was some indication that decomposition products and light could affect the reaction. The presence of disulphide (dimer) as a major reaction product was confirmed in the case of SNAP. Free-radical traps were used to probe the decomposition mechanism, as were hemin and haemoglobin as NO detectors to determine decomposition kinetics. The true agent of S-nitrosothiol decomposition was found to be intrinsic copper in the water supply and buffer salts. S-nitrosothiols were found to be stoichiometrically decomposed by Hg2+ ions, but catalytically decomposed by Cu2+ ions. Kinetic measurement confirmed the complex nature of the catalysis. The importance of SNO and NH2, and SNO and COO" as binding sites was demonstrated. Some explanation was found for the differing structure/reactivity relationships observed. It was shown that transnitrosation of a thiol could occur, involving thiolate anion attack upon the S-nitrosothiol. However, the reaction appeared to be very slow at physiological pH. The nitrosation of N-methylaniline by S-nitrosothiols was found to occur only in the presence of oxygen - direct transfer of NO did not occur, nitrosation being mediated after SNAP decomposition. To my wife and family MEMORANDUM The work for this thesis has been undertaken in the Chemistry Department of the University of Durham between October 1990 and September 1993. It is the original work of the author unless otherwise stated otherwise. None of this work has been submitted for any other degree. COPYRIGHT The copyright of this thesis lies with the author. No quotation from it should be published without prior written consent and any data taken from it should be acknowledged. ACKNOWLEDGEMENTS I would like to thank my supervisor, Prof. D.L.H. Williams for his guidance, encouragement and his friendship throughout my time in Durham. I am also grateful for the friendship and support of my laboratory colleagues, past and present, including Alan, Simon, Javid, Tim, Rachel, Simon, Alex and Jonathan. I would like to thank all members of department staff for their help, but especially Mr C. Greenhalgh for his help with apparatus, software and wordprocessing. I must also thank Stuart Askew and Dr A.R. Butler, at the University of St Andrews, for their hospitality and advice during visits. Finally I wish to thank the Wellcome Trust for funding my appointment Contents Page Chapter One: The Biological Roles of Nitric Oxide 1.1 Historical Perspective 2 1.2 Discovery of the Physiological Role of Nitric Oxide 4 1.3 Formation and Mechanism of Action of Nitric Oxide 5 1.4 Multiple Roles of Nitric Oxide 9 4.1 Vasculature 4.2 Platelets 4.3 Nervous System 4.4 Immunological Reactions 1.5 Therapeutic Possibilities of Nitric Oxide 13 1.6 Conclusion 15 References 16 Chapter Two: Aspects of the Chemistry of Nitric Oxide and some of its Compounds 2.1 The Chemistry of Nitric Oxide 21 2.2 Nitrosating Reagents 25 2.3 C-nitrosation 26 2.4 N-nitrosation 29 2.5 O-nitrosation 31 2.6 S-nitrosation 33 References 42 Chapter Three: Aspects of S-nitrosothioI Decomposition In Aqueous Solution 3.1 Use of a Griess Reagent To Measure Nitrite Production 47 1.1 Introduction 1.2 Calibration and Initial Set-up 1.3 Decomposition of SNAP in distilled water 1.4 Nitrite production from SNAP in Different Buffers 3.2 Effects of Buffer/pH on SNAP Decomposition 53 (Measured by Griess Method) 3.3 Buffers As Catalysts of SNAP Decomposition ? 55 3.1 SNAP decomposition in Phosphate/NaOH Buffer at pH 7.4 3.2 SNAP decomposition in TRIS/HCl Buffer at pH 7.4 3.3 SNAP decomposition in TRIS/Maleic acid/NaOH Buffer at low pH 3.4 Decomposition of SNAP in DGA/NaOH Buffer 60 4.1 Varying pH 4.2 SNAP as a dry solid 4.3 Presence of oxygen 4.4 Parallel study 4.5 Presence of free thiol 4.6 Summary 3.5 Dissolution of SNAP in Buffer 64 3.6 Decomposition of SNAP in NaOH/Distilled water 66 6.1 Effect of Initial pH on SNAP Decomposition 6.2 Absorbance and pH decline with SNAP 6.3 Effect of nitrogen, oxygen and carbon dioxide 3.7 Anomalous decomposition of SNAC 77 3.8 Analysis of SNAP Decomposition Products 79 8.1 UV spectra 8.2 Thin-Layer Chromatography (TLC) 8.3 NMR 8.4 Titration of Decomposed SNAP solution 3.9 Use of Free-Radical Trapping Reagents 84 9.1 Introduction 9.2 SNAP Decomposition in DGA/NaOH Buffer 9.3 Phenol 9.4 Furan 9.5 Salicylic acid 9.6 Tetramethyl pyrroline N-oxide (M4P0) 3.10 Hemin and Haemoglobin as NO Detectors 99 10.1 Introduction 10.2 Hemin 10.3 Haemoglobin 3.11 Summary 108 References 110 Chapter Four: Decomposition of S-nitrosothiols By Metal Ions 4.1 Introduction 112 4.2 The Effects of Various Metal Ions 112 4.3 SNAP decomposition with varying Cu(II) ion concentration 118 4.4 pH/buffer dependence 121 4.1 SNAP 4.2 SNOG 4.3 SNAC 4.4 SCYS 4.5 SNOCAP 4.6 SMAA 4.7 STLA 4.5 N-acetylation as a stabilising structure 126 4.6 Esterification as a stabilising/destabilising structure 127 6.1 Work with phosphate buffer 6.2 Peculiar reaction of SMMA 4.7 SMAA decomposition examined 131 4.8 Stopped flow analysis of S-nitroso-cysteine decay 133 4.9 Summary 138 9.1 Introduction 9.2 Buffer solutions 9.3 Copper-induced decomposition 9.4 Structure and reactivity 4.10 Conclusion 147 References 150 Chapter Five: Transnitrosation 5.1 Thiolate Anion Attack on a S-nitrosothiol 152 1.1 Introduction 1.2 SNAP and MAA 1.3 Effect of additional thiol 1.4 Possible use of Abs^j^x differences to detect transnitrosation 5.2 Direct Nitrosation of a Substrate by a S-nitrosothiol? 159 2.1 Introduction 2.2 SNAP and N-methylaniline (NMA) 2.3 Effect of Varying SNAP and NMA 2.4 Use of other S-nitrosothiols 5.3 Investigation of MMA Reaction With SNAP 164 3.1 Introduction 3.2 Investigation 3.3 Summary References 168 Chapter Six: Experimental Details 6.1 Experimental Methods 170 1.1 U. V. / Visible Spectrophotometry 1.2 Stopped Flow Spectrophotometry 1.3 pH Measurement 1.4 Analysis 1.5 Kinetic Analysis 6.2 Chemical Methods 176 2.1 S-nitrosothiol synthesis 2.2 Attempts at thiol syntheses 6.3 Haemoglobin Preparation 181 3.1 Blood Preparation 3.2 Dialysis 3.3 Sterilisation 3.4 Calibration References 185 Appendix A: The Use of SNAP in Experimental Physiology A.l Introduction 187 A.2 Rat-tail Artery Vasodilation Study 187 A.3 Conclusion 190 References 191 Appendix B: Research Colloquia, Semmars, Lectures and Conferences B. 1 First Year Induction Course, October 1990 194 B.2 Research Colloquia, Seminars and Lectures 195 B.3 Conferences Attended 202 List of Abbreviations 203 Chapter 1 The Biological Roles Of Nitric Oxide 1.1 Historical Perspective The last decade has seen a remarkable increase in our understanding of the numerous biological roles of nitric oxide, this being the case even when measured against the general exponential trend in the growth of scientific information. Ironically, a wide range of pro-drugs, which are now known to generate nitric oxide in vivo, have been used therapeutically for the last 150 years, albeit without any real insight into their mode of action.