Mechanism of skin surface lipid peroxidation

The correlation between the amount of lipid peroxide and squalene in skin surface lipid was observed by statistical analysis. To investigate the mechanism of skin surface lipid peroxidation, especially the role of active oxygen, squalene was irradiated by long wavelength ultraviolet light (UVA) with or without the photosensitizer, 8-methoxypsoralen (8MOP). Sodium azide (NaN3), a singlet oxygen quencher, or deuterium oxide, which elongates the life time of singlet oxygen, were also added in these experiments. The lipid peroxidation was detectable by observing malondialdehyde (MDA) formation. The MDA value in squalene solution was increased by UVA irradiation, and this effect was enhanced under the presence of 8MOP. These effects were repressed by the addition of NaN3 in the experimental system. These results may show that squalene peroxidation was mediated by singlet oxygen. Epidermal keratin could inhibit the increase of MDA values in human skin surface lipid in vitro. The inhibitory effect of epidermal protein on the deposition or the formation of lipid peroxide in skin surface was suggested.