Induction of oxyradicals by arsenic: Implication for mechanism of genotoxicity

Although arsenic is a well-established human carcinogen, the mechanisms by which it induces cancer remain poorly understood. We previously showed arse nite to be a potent mutagen in human-hamster hybrid (A(L)) cells, and that it induces predominantly multilocus deletions. We show here by confocal sca nning microscopy with the fluorescent probe 5'.6'-chloromethyl-2'.7'-dichlo rodihydrofluorescein diacetate that arsenite induces, within 5 min after tr eatment, a dose-dependent increase of up to 3-fold in intracellular oxyradi cal production. Concurrent treatment of cells with arsenite and the radical scavenger DMSO reduced the fluorescent intensity to control levels. ESR sp ectroscopy with 4-hydroxy-2,2.6,6-tetramethyl-1-hydroxypiperidine (TEMPOL-H ) as a probe in conjunction with superoxide dismutase and catalase to quenc h superoxide anions and hydrogen peroxide, respectively, indicates that ars enite increases the levels of superoxide-driven hydroxyl radicals in these cells. Furthermore, reducing the intracellular levels of nonprotein sulfhyd ryls (mainly glutathione) in A(L) cells with buthionine S-R-sulfoximine inc reases the mutagenic potential of arsenite by more than 5-fold. The data ar e consistent with our previous results with the radical scavenger DMSO, whi ch reduced the mutagenicity of arsenic in these cells, and provide convinci ng evidence that reactive oxygen species, particularly hydroxyl radicals, p lay an important causal role in the genotoxicity of arsenical compounds in mammalian cells.