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The radiomimetic agent hydrogen peroxide is known to produce DNA strand breaks, chromosome damage and cell death. It has also been identified as one of the cytotoxic agents formed during certain drug metabolism and by phagocytic cells in the respiratory burst. Our laboratory recently identified the ultimate reactive species responsible for the DNA-damaging and cytotoxic effect of H2O2 as being hydroxyl radical. This was achieved by the use of the specific iron chelator o-phenanthroline, which prevents the occurrence of a Fenton reaction between H2O2 and chromatin bound ferrous ions. In this paper we show that H2O2 is able to induce mutation at the HGPRT locus in V79 cells and morphological transformation of C3H/10T1/2 cells. o-Phenanthroline abolishes both effects, indicating that hydroxyl radical is directly involved in mutation and carcinogenesis.

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Chinese hamster cells (V79) resistant to high concentrations of Cd2+ in the medium were obtained by using the procedure of Beach & Palmiter [(1981) Proc. Natl. Acad. Sci. U.S.A. 78, 2110-2114], which in mouse led to amplification of metallothionein (MT) genes and to an enrichment in cellular MT. The Cd-resistant V79 clones isolated were significantly more resistant than parental cells to oxidative stress by extracellular H2O2 or a mixture of H2O2 and superoxide anion (O2-) generated by xanthine oxidase plus acetaldehyde. On a per-cell basis, there was no difference between the two cells in their total H2O2-decomposing or O2-(-)dismutating activity. The most likely explanation is that an enrichment in MT content in the Cd-resistant cells was responsible for this effect, because of the antioxidant properties already described for this protein.