Analysis of cataractous and experimentally stressed lenses by 31P-NMR and other techniques shows significant changes in the concentrations of small, acid_soluble organic phosphate compounds (organic-P). Changes in lenticular organic-P may be diagnostic of early metabolic events in the formation of cataracts; however, the mechanisms of these changes are not understood. This laboratory has found that the stress-related decrease of lenticular P-choline, an intermediate in phospholipid (P-lipid) and membrane biosynthesis, results from four competing processes. Following osmotic or oxidative stress, P-choline leaks from the lens, its synthesis decreases, and both its hydrolysis and its utilization ( for P-lipid synthesis) increase. It is proposed to study P-choline as a model organic-P, to quantify its synthesis leakage, hydrolysis, and utilization to fully account for its decreased concentration in cataractous lenses and in lenses subjected to osmotic stress (diabetic rats or rat lenses cultured in 30 mM xylose or galactose) or to oxidative stress (culture with H202 or with photosensitizers and light). It is also proposed to compare the changes in P-choline with changes in other organic-P compounds to determine whether the mechanisms which affect P-choline may also affect structurally-similar, metabolically related compounds. HPLC and other very sensitive techniques will be used to quantify the changes in several organic-P compounds in oxidatively and osmotically-stressed lenses, with emphasis on compounds involved in membrane turnover. Radiotracer techniques will be used to measure changes in lens permeability toward organic-P compounds and to study changes in their metabolism. Incorporation of P- choline, P-ethanolamine, and other precursors into P-lipids will be quantified and compared to determine whether the observed increase in P-choline utilization is an isolated event or whether synthesis of several P-lipids change in parallel as might be expected membrane repair. Also, the ability of lenses to recover normal permeability of transport properties will be measured following damage by various amounts of exposure to transient osmotic and oxidative stress. The results of these studies will significantly increase our understanding of the response of lenses to cataractogenic stress and the effects of stress on a v vital class of biological compounds.
