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Generation of Reactive Oxygen Species in the Anterior Eye Segment BBA Clinical 6 (2016) 49–68 Contents lists available at ScienceDirect BBA Clinical journal homepage: www.elsevier.com/locate/bbaclin Review article Generation of reactive oxygen species in the anterior eye segment. Synergistic codrugs of N-acetylcarnosine lubricant eye drops and mitochondria-targeted antioxidant act as a powerful therapeutic platform for the treatment of cataracts and primary open-angle glaucoma☆ Mark A. Babizhayev ⁎ Innovative Vision Products, Inc., 3511 Silverside Road, Suite 105, County of New Castle, DE 19810, USA article info abstract Article history: Senile cataract is a clouding of the lens in the aging eye leading to a decrease in vision. Symptoms may Received 13 January 2016 include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at Received in revised form 5 April 2016 night. This may result in trouble driving, reading, or recognizing faces. Cataracts are the cause of half of blindness Accepted 11 April 2016 and 33% of visual impairment worldwide. Cataracts result from the deposition of aggregated proteins in the Available online 19 April 2016 eye lens and lens fiber cells plasma membrane damage which causes clouding of the lens, light scattering, Keywords: and obstruction of vision. ROS induced damage in the lens cell may consist of oxidation of proteins, DNA Aging eye damage and/or lipid peroxidation, all of which have been implicated in cataractogenesis. The inner eye pressure Age-related cataracts (also called intraocular pressure or IOP) rises because the correct amount of fluid can't drain out of the eye. Eye lens and aqueous humor With primary open-angle glaucoma, the entrances to the drainage canals are clear and should be working cor- Membrane derangement rectly. The clogging problem occurs further inside the drainage canals, similar to a clogged pipe below the Mitochondria and lens epithelial cells drain in a sink. Reactive oxygen species The excessive oxidative damage is a major factor of the ocular diseases because the mitochondrial Lipid peroxidation and phospholipid hydroper- respiratory chain in mitochondria of the vital cells is a significant source of the damaging reactive oxygen oxides species superoxide and hydrogen peroxide. However, despite the clinical importance of mitochondrial oxidative Ophthalmic compositions of N-acetylcarnosine and mitochondria-targeted antioxidants damage, antioxidants have been of limited therapeutic success. This may be because the antioxidants are not se- lectively taken up by mitochondria, but instead are dispersed throughout the body, ocular tissues and fluids' moieties. This work is an attempt to integrate how mitochondrial reactive oxygen species (ROS) are altered in the aging eye, along with those protective and repair therapeutic systems believed to regulate ROS levels in ocular tissues and how damage to these systems contributes to age-onset eye disease and cataract formation. Mitochondria-targeted antioxidants might be used to effectively prevent ROS-induced oxidation of lipids and proteins in the inner mitochondrial membrane in vivo. The authors developed and patented the new ophthalmic compositions including N-acetylcarnosine acting as a prodrug of naturally targeted to mitochondria L-carnosine endowed with pluripotent antioxidant activities, combined with mitochondria-targeted rechargeable antioxi- dant (either MitoVit E, Mito Q or SkQs) as a potent medicine to treat ocular diseases. Such specificity is explained by the fact that developed compositions might be used to effectively prevent ROS-induced oxidation of lipids and proteins in the inner mitochondrial membrane in vivo and outside mitochondria in the cellular and tissue struc- tures of the lens and eye compartments. Mitochondrial targeting of compounds with universal types of antioxidant activity represents a promising ap- proach for treating a number of ROS-related ocular diseases of the aging eye and can be implicated in the man- agement of cataracts and primary open-angle glaucoma. © 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). ☆ The eyes are one of the most powerful tools a man can have. With one look, one can relay the most intimate message. After the connection is made, words ceasetoexist. ⁎ Corresponding author at: Innovative Vision Products, Inc., Moscow Division, Ivanovskaya 20, Suite 74, Moscow 127434, Russian Federation. E-mail addresses: [email protected], [email protected]. http://dx.doi.org/10.1016/j.bbacli.2016.04.004 2214-6474/© 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 50 M.A. Babizhayev / BBA Clinical 6 (2016) 49–68 Contents 1. Introductiontooxidativestress......................................................50 1.1. Oxidation-inducedhallmarkofmoleculardamagesinhumancataracts.................................51 2. Oxidativestress,mitochondriaandtheapoptoticpathway..........................................51 3. Therelationofmitochondriatoage-onseteyedisease............................................57 4. Theroleofmolecularchaperoneproteinsinoculartissuesandformitochondrialfunction............................58 5. Reactiveoxygenspeciesandthemitochondriaofvertebratelenses......................................59 6. Oxidativestress-induceddamagesinglaucoma...............................................60 7. Targetingmitochondriaduringtherapeutictreatmentofcataractsandcellularstructuresoftissuesinanterioreyechamber............60 8. Conclusion...............................................................64 Conflictofinterest..............................................................65 TransparencyDocument............................................................65 Acknowledgments..............................................................65 References..................................................................65 1. Introduction to oxidative stress to cellular macromolecules such as DNA, proteins, and lipids ensues. Such a state of “oxidative stress” is thought to contribute to the patho- Partially reduced metabolites of molecular oxygen (O2) are referred genesis of a number of age-related sight threatening eye diseases. to as “reactive oxygen species” (ROS) due to their higher reactivities rel- Oxidation of phospholipids and accumulation of their oxygenated inter- ative to molecular O2. ROS are generated intracellularly through a vari- mediates have long been considered as participants of two possibly in- ety of processes, for example, as by-products of normal aerobic terrelated processes: cell/tissue damage and danger signaling [1]. metabolism and as second messengers in various signal transduction However, direct experimental evidence supporting these views is pathways. ROS can also be derived from exogenous sources, either scarce, mostly due to technological difficulties in quantitative assess- being taken up directly by cells from the extracellular milieu, or pro- ments of peroxidized phospholipids. The traditional point of view is duced as a consequence of the cell's exposure to some environmental that oxidative stress causes – through yet to identified mechanisms – insult. Reactive oxygen species (ROS) are generated as by-products of random free radical peroxidation of phospholipids whereby the rule of cellular metabolism, primarily in the mitochondria. Although ROS are preferable oxidation of most polyunsaturated fatty acids dominates essential participants in cell signaling and regulation, when their cellu- over the types of phospholipids based on the specificity of their polar lar production overwhelms the intrinsic antioxidant capacity, damage head-groups. In contrast, peroxidation pathways catalyzed by specific Scheme 1. The production of reactive oxygen species (ROS) in mitochondria. M.A. Babizhayev / BBA Clinical 6 (2016) 49–68 51 catalysts – such as cytochrome c in apoptotic cells – should non- consist of oxidation of proteins, DNA damage and/or lipid peroxidation, randomly oxidize those classes of phospholipids that are localized in all of which have been implicated in cataractogenesis (reviewed in Ref. the immediate proximity to the catalytic sites. Among those of particu- [14]). Loss of protein sulfhydryl groups, and the oxidation of methionine lar interest in the context of peroxidation reactions are cardiolipins residues, are progressive and increase as the cataract worsens until (CLs), a critical phospholipid component of cellular membranes from N90% of cysteine and half the methionine residues are oxidized in the bacteria to mammals. The importance of CL peroxidation in mammals most advanced form. By contrast, there may be no significant oxidation is also emphasized by its critical role in the function of numerous mito- of proteins in the center of the lens with advancing age, even past age chondrial enzymes involved in electron transport chain function and 80. The key factor in preventing oxidation seems to be the concentration other proteins involved in energetic metabolism which include cyto- of nuclear glutathione (GSH). The phospholipid composition of adult chrome c (cyt c) oxidase [2], creatine kinase [3], ATP synthase [4] and human lens membranes differs dramatically from that of any other the mitochondrial ADP carrier [5] among others. (See Scheme 1.) mammalian membrane [15]. The relative and absolute amount of sphingolipids, including dihydrosphingomyelin and sphingomyelin,
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