OXIDATION-INDUCED MEMBRANE DAMAGE IN CATARACTOGENESIS

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Increase in cell membrane permeability to cations, is a common occurrence in cataracts, leading to intracellular ionic imbalance. Oxidation of protein occurs in human senile cataract, leading to crosslinking and the formation of high molecular weight crystallin aggregates. The peroxidation of membrane lipids may participate in both membrane permeability increases and protein oxidation. Lipids are more prone to oxidation than proteins, generating peroxide intermediates and free radicals that can initiate further oxidation of proteins. We hypothesize that oxygen-derived free radicals are the agents that trigger cataractogenesis by inducing peroxidation of membrane lipids, an early event in both membrane damage and protein oxidation. We will determine the sequence of appearance of relatively stable oxidants, hydrogen peroxide, lipid peroxide and the products of oxidation of cell membrane components in human donor normal lenses as a function of age, and in surgically extracted cataractous lenses by radioisotopic and enzyme-coupled spectrophotometric and spectrofluorometric techniques. Lipids and lipid peroxides will be identified by HPLC and their adducts by TLC. Adducts of lipid peroxidation products and proteins will be analysed by column chromatography and gel electrophoresis. Lipid repair mechanisms will be determined using radioactive probes. The formation of disulfide crosslinks in key plasma membrane proteins such as gap junction protein, MIP26 will be measured chromatographically and thiols spectrophotometrically. Na+, K+-activated and Ca2+-activated ATPases will be monitored biochemically for age-related loss in activity and oxidation. To test the hypothesis that oxidants will accelerate and antioxidants will retard the development of cataractous changes in the Emory mouse, a model of human senile cataract, we shall observe the effects of a low level of oxidative stress by feeding selenium in the diet, or an antioxidant, acetylsalicylate, in diet.