Hydrogen peroxide and catalase in UVA-induced lipid peroxidation in cultured fibroblasts.

UVA-induced lipid peroxidation in cultured human skin fibroblasts, as measured by the release in the supernatant of thiobarbituric acid-reactive substances, is found to be linear with increasing irradiation dose (up to about 250 kJ m(-2)). Concomitantly, within this dose range catalase is strongly inactivated by UVA radiation according to an exponential process (k≈0.01 kJ(-1) m(2)). This suggests that catalase is not involved in modulating the peroxidation process. Inactivation of catalase by 3-amino-1,2,4-triazole can be efficiently achieved prior to irradiation. This inactivation has no consequence on the extent of peroxidation triggered by subsequent exposure to UVA radiation. It may be therefore strongly suggested that catalase is not, via H2O2 removal, a key enzyme in the cellular defence equipment towards UV A-peroxidative stress. An alternative interpretation may be formulated which supports the view that H2O2 produced upon exposure to UVA has no or very little role in triggering the lipid peroxidation process.