Hydroxyl radical formation by UV-irradiated epidermal cells.

To elucidate the mechanism of sunlight-induced skin damage, guinea pigs were exposed to UV light (280-320 nm, UV B, 4 J/cm2) and a homogenate of the epidermis was examined by means of the thiobarbituric acid (TBA) test. Three hours after the exposure, TBA-malondialdehyde adducts had increased while glutathione reductase activity had decreased, indicating lipid peroxidation. To detect the initial species, spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was applied to a suspension of illuminated epidermal cells (0.5 J/cm2). An ESR signal obtained only with irradiation comprised a 1:2:2:1 quartet [a(N)= a(beta H) = 1.49 mT] attributable to a spin adduct of hydroxyl radicals. These results suggest that sunlight exposure of skin may lead to hydroxyl radical generation and simultaneous lipid peroxidation.