Effect of peroxide radicals on UVB-induced DNA damage

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The induction of DNA damage caused by UV-B and UV-C was investigated by use of cultured L-132 cells. DNA strand breaks occurred dose-dependently, the extent of strand breaks inversely correlated well with the number of viable L-132 cells after 24 h incubation. About 10-fold dose of UV-B irradiation was required to induce the similar extent of strand breaks to those induced by UV-C.Similarly about 10-fold dose of UV-B was required to produce the similar amount of pyrimidine dimers determined by ELISA.Strand breaks induced by UV-B,however, were not fully repaired in viable cells remained after incubation of cells for longer period of time, although UV-C-induced strand breaks were repaired time-dependently. Furthermore, an experiment with a cell-free system, where the induction of strand breaks by repair enzymes was not taken place, indicated that UV-B caused direct DNA strand breaks significantly more than those caused by one-tenth dose of UV-C.The data shown here suggest that UV-B-induced DNA damage was mediated, at least in part, via a diffrent mechanism from UV-C induce one. We also investigated the effect of peroxide radicals on UV-induced DNA damage, by use of inhibitors for superoxide dismutase and catalase and of a radical scavenger. UV-C-induced DNA damage was affected by them, althougt no obvious difference was observed on UV-B-induced one, suggesting again that the damage caused by UV-B is differ from that caused by UV-C.