Molecular and Cellular Biochemistry 234/235: 301–308, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.

Although arsenic is a well-established human carcinogen, the underlying carcinogenic mechanism(s) is not known. Using the human-hamster hybrid (A L) cell mutagenic assay that is sensitive in detecting mutagens that induce predominately multilocus deletions, we showed previously that arsenite is indeed a potent gene and chromosomal mutagen and that oxyradicals may be involved in the mutagenic process. In the present study, the effects of free radical scavenging enzymes on the cytotoxic and mutagenic potential of arsenic were examined using the A L cells. Concurrent treatment of cells with either superoxide dis-mutase or catalase reduced both the cytotoxicity and mutagenicity of arsenite by an average of 2–3 fold, respectively. Using immunoperoxidase staining with a monoclonal antibody specific for 8-hydroxy-2′-deoxyguanosine (8-OHdG), we demonstrated that arsenic induced oxidative DNA damage in A L cells. This induction was significantly reduced in the presence of the anti-oxidant enzymes. Furthermore, reducing the intracellular levels of non-protein sulfhydryls (mainly glutathione) using buthionine S-R-Sulfoximine increased the total mutant yield by more than 3-fold as well as the proportion of mutants with multilocus deletions. Taken together, our data provide clear evidence that reactive oxygen species play an important causal role in the genotoxicity of arsenic in mammalian cells. (Mol Cell Biochem 234/235: 301–308, 2002) Key words: arsenic, mutagenicity, oxidative stress, antioxidant enzymes, 8-OHd