Cholesterol may act as an antioxidant in lens membranes

Purpose. Oxidative damage has been considered as a major factor involved in cataract formation. We have recently shown that cholesterol oxides accumul ate in human cataractous lenses. The biological significance of accumulatio n of oxysterols in the lens is still poorly understood. However, it has bee n proposed that cholesterol may act as an antioxidant. This study was desig ned to establish whether cholesterol may act as an antioxidant in the lens. Methods: Bovine lens membranes (BLM) were oxidised by incubation with an at e-compound. Lipid hydroperoxides were measured by the FOX-assay, vitamin E was determined by HPLC, cholesterol and cholesterol oxides were isolated in a C-18 column and quantified by gas chromatography. Susceptibility of lipo somes and BLM to oxidation was determined by the fluorescence quenching of parinaric acid. Results: Oxidation of BLM results in the production of lipid hydroperoxides , consumption of endogenous vitamin E and formation of cholesterol oxides. Cholesterol presents some important characteristics generally ascribed to a n antioxidant molecule: its presence in liposomes increases the vesicle res istance to oxidation and its oxidised forms are stable as they are unable t o stimulate further propagation of peroxidation reactions. Moreover, the pr otective effect of cholesterol in liposomes is comparable to that of vitami n E, suggesting that cholesterol possibly acts by intercepting the peroxyl radicals formed during lipid peroxidation. Conclusions. Although cholesterol oxides may present a variety of noxious e ffects in the cells its presence in lens membrane is likely to be associate d with the expression of its antioxidant effect, contributing to maintain l ens transparency.