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

摘要

L-Histidine (L-His) enhances the clastogenic effects of hydrogen peroxide (H2O2) We previously suggested the involvement of active transport in the efficient 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 accumulated dose-dependently in cells treated with a mixture of L-His and H2O2 (mixture) than with H2O2 alone. This observation supports our hypothesis that 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 immunohistochemical assay using 8-oxodG-specific monoclonal antibodies did not reveal whether the accumulation of H2O2 generates 8-oxodeoxyguanosine (8-oxodG). No 8-oxodG was evident in cells treated with mixture or with H2O2 alone, or even in cells treated with H2O2 at high doses up to 20 mM and, in some cases, pre-treated with catalase inhibitors. It appears, therefore, that (OH)-O-. and, specifically, (OH)-O-. derived from intracellular Fenton reactions, 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 enhancing effects of L-His were also noted during the induction of formation of 8-oxodG 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 induces formation of 8-oxodG is not (OH)-O-. formed via intracellular Fenton reactions but is (OH)-O-. formed via the dissociation of H2O2 under W-C. (C) 2001 Published by Elsevier Science B.V. [References: 31]