| Humans are considered the most sensitive species to arsenic exposure with increased risk to skin, lung and bladder cancer. Epidemiologic studies of workers simultaneously exposed to benzo[a]pyrene (BaP) and arsenite (As) report additive to multiplicative effects. These studies are supported by both in vitro and in animal studies demonstrating an increase in BaP DNA adduct levels when co-treated with BaP and arsenite than when treated with BaP alone. Glutathione, the major thiol compound responsible for maintaining redox homeostasis, may provide cellular protection against, arsenite's ability to increase the likelihood of DNA damage. We examined the effect of arsenite and glutathione on BaP DNA adduct levels in the absence of cellular processes, characterized the effect of modulating glutathione levels in Hepa-1 cells and in C57BL/6 mice through the use of buthionine sulfoximine (BSO) and glutathione ethyl ester (GSHEE) treatment, and examined the impact of arsenite and BaP coexposure on glutathione deficient knockout mice and mouse embryonic fibroblasts. In the absence of glutathione S-transferases, normal intracellular glutathione concentrations did not reduce BaP-DNA adduct levels and arsenite increased adduct levels (p=0.0028) via an unidentified mechanism. A 24 hour pretreatment of arsenite in Hepa-1 cells potentiated BaP DNA adduct formation (p=0.002), although lower than observed with a 30 minute pretreatment period. Glutathione modulation, through pharmacological methods or by examining glutathione deficient models, demonstrated no effect on DNA adduct levels after BaP treatment, or after arsenite BaP co-treatment. Experimentation with C57/BL6 mice showed that arsenic co-treatment increased average BaP adduct levels in both lung and skin; the increase was statistically significant in the lung (p=0.048). A reduction in glutathione level increased BaP adduct levels, although only significantly in the skin of mice treated with BSO (p=0.028). Treatment with GSHEE did not reduce adduct levels in any tissue measured. These results are consistent with previous in vitro and in vivo findings and suggest that glutathione plays a minor role in arsenic's ability to potentiate BaP DNA adduct formation. |
