Effect of tannin on oxidative damage of ocular lens.

The protective effect of geraniin (tannin from Geranium thunbergii) against oxidative damage was examined in the mouse ocular lens. Oxidative damage in the lens was induced by diamide, diazene dicarboxylic acid bis (N,N-dimethylamide); diamide oxidized the sulfhydryl groups in both the membrane and cytoplasm but did not increase lipid peroxide. Geraniin showed protective effects on the changes in the Na+/K+ ratio, GSH level, Na,K-ATPase activity, GSH reductase activity and the sulfhydryl level of the membranous protein in the diamide-treated lens, but such protective effects of geraniin were not observed in the cell-free system of the lens. In addition, geraniin itself was unable to reduce GSSG to GSH and also unable to inhibit the oxidative reaction of the sulfhydryl group to diamide. These results suggest that in the intact lens geraniin would act primarily on the lens cell membrane surface to inhibit an influx of diamide into the inner part of the plasma membrane and the cytoplasm, and consequently that geraniin may protect sulfhydryl groups in the cell membrane and cytoplasm from their oxidation by diamide and keep the redox system of the lens in a normal state.