The biological activity of hydrogen peroxide VII. L-Histidine increases incorporation of H2O2 into cells and enhances formation of 8-oxodeoxyguanosine by UV-C plus H2O2 but not by H2O2 alone

L-Histidine (L-His) enhances the clastogenic effects of hydrogen peroxide ( H2O2) We previously suggested the involvement of active transport in the ef ficient influx of an L-HiS-H2O2 adduct into cells (Oya-Ohta et al. [1]). In this study, we detected intracellular H2O2 by monitoring formation of 2 ' ,7 ' -dichlorofluorescein (DCF) from its precursor. More fluoroproduct accu mulated dose-dependently in cells treated with a mixture of L-His and H2O2 (mixture) than with H2O2 alone. This observation supports our hypothesis th at active transport is involved in the enhanced incorporation of H2O2 into cells. Moreover, both mixture and the L-HiS-H2O2 adduct were less active in the generation of hydroxylradicals ((OH)-O-.) upon addition of FeCl2 than was H2O2 alone in a cell-free system. This result suggests that the Fenton reaction might occur more effectively around the nucleus in cells. An immun ohistochemical assay using 8-oxodG-specific monoclonal antibodies did not r eveal whether the accumulation of H2O2 generates 8-oxodeoxyguanosine (8-oxo dG). No 8-oxodG was evident in cells treated with mixture or with H2O2 alon e, or even in cells treated with H2O2 at high doses up to 20 mM and, in som e cases, pre-treated with catalase inhibitors. It appears, therefore, that (OH)-O-. and, specifically, (OH)-O-. derived from intracellular Fenton reac tions, might not play a role in the formation of 8-oxodG. However, exposure to UV-C of cells treated with H2O2 yielded more 8-oxodG in the presence of L-His than in the absence of L-His. Thus, the previously observed enhancin g effects of L-His were also noted during the induction of formation of 8-o xodG by W-C plus H2O2 The formation of 8-oxodG in response to W-C alone was very limited and, hence, H2O2 Seemed to be an effective source of (OH)-O-. only in the presence of W-C. It is suggested that the (OH)-O-. that induce s formation of 8-oxodG is not (OH)-O-. formed via intracellular Fenton reac tions but is (OH)-O-. formed via the dissociation of H2O2 under W-C. (C) 20 01 Published by Elsevier Science B.V.