Age-related macular degeneration (ARMD) is the leading cause of vision loss in elderly Americans. The photoreceptor damage that results in blindness in ARMD is usually secondary to injured retinal pigment epithelial (RPE) cells. There is substantial circumstantial data to support the hypothesis that ARMD may be related to oxidative injury and that RPE cells exhibit early signs of the disease. We now have data directly showing glutathione (GSH) to be an important antioxidant capable of protecting cultured human RPE cells from oxidative injury. In addition, preliminary studies demonstrate that plasma levels of GSH decrease with age and that there may be lower plasma GSH levels in ARMD patients. In this application, we propose to further define the role of GSH in protection of the RPE from oxidative injury. Two groups of studies will be performed to evaluate the effects of aging and ARMD on GSH: l) blood levels of GSH will be measured in a cohort of patients without ARMD as well as those with well characterized ARMD, including a sub-population of patients not taking micronutrient antioxidant supplementation, and 2) GSH synthetic capacity will be determined in eyes of donors of varying ages, with and without ARMD by measuring the rate of GSH synthesis and activity of the enzyme catalyzing GSH synthesis, gamma-glutamycysteine synthetase (GCS), in cultured RPE cells, and by measurement of mRNA for GCS in fresh RPE from autopsy eyes. Further studies will be performed to determine whether GSH synthetic capacity can be manipulated therapeutically using different GSH precursors, hormonal inducers, or phenolic antioxidants that may induce GCS activity. Finally, mechanistic studies will establish l) whether improved maintenance of intracellular GSH leads to increased peroxide elimination and better maintenance of the intracellular antioxidants, ascorbate and alpha-tocopherol, and 2) whether exogenous GSH can protect by preventing damage to two critical plasma membrane transport systems, Na+,K+ATPase and Ca2+-ATPase. The results of these studies will provide critical data to help in our understanding of the pathogenesis of ARMD and could provide the platform for future therapies.
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