Induction of lung-specific DNA damage by metabolically methylated arsenics via the production of free radicals.

To clarify the genotoxicity of inorganic arsenics, we focused on the genotoxic effect of metabolically methylated arsenics in mammals. Oral administration to mice of dimethylarsinic acid (DMAA), a major metabolite of inorganic arsenics, induced lung-specific DNA damage, i.e., DNA single-strand breaks and the clumping of heterochromatin. The lung-specific strand breaks were not caused by DMAA itself, but by dimethylarsine, a further metabolite of DMAA. An in vitro experiment indicated that DNA single-strand breaks by dimethylarsine were suppressed by the presence of superoxide dismutase and catalase, suggesting that the strand breaks were induced via the production of free-radical species including active oxygens. Dimethylarsenic peroxyl radical [(CH3)2AsOO.] and superoxide anion radical produced from the reaction between molecular oxygen and dimethylarsine were detected by electron-spin resonance analysis using a spin-trapping agent and the cytochrome-c method, respectively. Of these two radicals, the dimethylarsenic peroxyl radical rather than the superoxide anion radical is assumed to play the dominant role in causing the DNA damage, at least for DNA single-strand breaks.