Lipid peroxidation in human stratum corneum lipid liposomes induced by artificially generated uv radiation and natural sunlight. Dependence on lipid composition

The human stratum corneum is exposed permanently to solar ultraviolet light . UV radiation is able to induce lipid peroxidation. In the presented study , liposomes prepared from human stratum corneum Lipids as well as from synt hetic lipid mixtures were exposed to UV radiation. The W-induced oxidation was followed by quantification of lipid oxidation products (malondialdehyde and lipid hydroperoxides) as well as by the oxygen consumption. As describ ed previously, high cholesterol concentrations in the vesicle membranes led to an increased formation of lipid hydroperoxides. In addition, the malond ialdehyde generation was decreased (Lasch, J., U. Schonfelder, S. Zellmer, M. Walke and D. Beckert (1997) Biochim. Biophys. Acta 1349 (2), 171-181). H owever, the total oxygen consumption during the UV irradiation was not infl uenced by the cholesterol concentration. A possible antioxidative effect of cholesterol is discussed. To clarify the mechanism of oxidation, cholester ol oxidation products were analyzed by high-performance thin-layer chromato graphy. The appearance of 7 alpha- and 7 beta-hydroxy-cholesterol indicated the type I oxidation mechanism, in which oxygen radicals appear as interme diates. Finally, liposomes were exposed to natural solar light. A similar r elationship between malondialdehyde and lipid hydroperoxide formation was o bserved. The oxidation mechanism was identified as type I, too.