TRACE ELEMENT DYNAMICS IN THE VERTEBRATE EYE

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Cataract formation is a major health and economic problems. Although the exact mechanisms underlying cataractognesis are not known, there is compelling evidence that oxidative damage is a major component of this process. Iron catalyzes oxidative reactions and causes damage to lens proteins, DNA and membranes which is similar to the type to the type of damage found in cataractous lenses. The iron storage protein, ferritin, can protect cells from oxidative damage by safely sequestering large amounts of iron. The importance of ferritin to normal lens function is underscored by the recent finding that humans with a dominantly inherited abnormality in ferritin synthesis exhibit early bilateral cataracts. The PI found that the lens epithelial cells synthesize ferritin, that ascorbic acid and glutathione increase ferritin concentration and that the damaging oxidant, hydrogen peroxide decreases ferritin synthesis. Therefore, she hypothesizes that: In the lens, the iron-binding capability of ferritin is a critical component of lens antioxidant potential. Ascorbic acid increases de novo ferritin synthesis and iron incorporation into this protein, thereby protecting the lens from oxidative damage. Hydrogen peroxide, in addition to directly damaging lens cells, decreases lens antioxidant potential by decreasing ferritin synthesis. Based upon this hypothesis the specific aims are to determine the time and concentration dependent effects of ascorbic acid, glutathione, iron and hydrogen peroxide on ferritin synthesis, subunit composition, subcellular localization, and ability to incorporate iron. In addition, the ability of ferritin to protect lens epithelial cells against oxidative damage will be determined by increasing ferritin concentration in these cells prior to exposing them to damaging concentrations of peroxide. The results of these experiments will provide key information regarding the roles of ferritin and ascorbic acid in iron metabolism in the lens and may provide a specific protective biochemical mechanism supporting the use of ascorbic acid supplementation for prevention of cataract progression.