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ORGANIC AND INORGANIC ARSENICALS SENSITIZE HUMAN BRONCHIAL EPITHELIAL CELLS TO HYDROGEN PEROXIDE-INDUCED DNA DAMAGE
Citation:
MOLINELLI, ALEXANDRO, M. STYBLO, J. NAKAMURA, J. SWENBERG, AND M. C. MADDEN. ORGANIC AND INORGANIC ARSENICALS SENSITIZE HUMAN BRONCHIAL EPITHELIAL CELLS TO HYDROGEN PEROXIDE-INDUCED DNA DAMAGE. Presented at American Association for Cancer Research Annual Meeting, Anaheim, CA, April 16 - 20, 2005.
Description:
The lungs are a target organ for arsenic carcinogenesis, however, its mechanism of action remains unclear. Furthermore, it has been suggested that inorganic arsenic (iAs) can potentiate DNA damage induced by other agents. Once inside the human body iAs generally undergoes two different metabolic changes. Pentavalent forms of the semimetal can be reduced to their trivalent forms; and the inorganic forms can undergo a sequence of methylation reactions. Recent studies suggest that methylated forms of trivalent arsenic can be more cytotoxic and genotoxic than the inorganic forms. To study the possible mechanistic link between arsenic and lung carcinogenesis we examined the induction of DNA breaks in human bronchial epithelial cells by organic and inorganic arsenicals. We also investigated whether these arsenicals could modify DNA damage caused by hydrogen peroxide, a potent oxidant. To assess DNA single-strand breaks (SSBs) we utilized the alkaline single cell gel electrophoresis technique (comet assay). The human bronchial epithelial cell line (BEAS-2B) was exposed to iAs (as sodium arsenite) or dimethylarsine iodide (DMAs), a dimethylated form of trivalent arsenic, at non-cytotoxic concentrations as determined by the neutral red assay. We did not find any statistically significant increases in SSBs between the control and iAs-treated cells (1 nM - 10 _M) after a 4h exposure. However, we found that DMAs increased DNA SSBs at 1- 10 _M after 4h. To test if arsenic compounds have any effect on hydrogen peroxideinduced DNA SSBs we pre-treated the BEAS-2B cells with iAs or DMAs for 4h. After pre-treatment the cells were rinsed and exposed to 20 _M hydrogen peroxide for 30 min. at 4oC. We found that hydrogen peroxide-exposed cells that were pre-treated with iAs (at 10 _M) and DMAs (at 1 and 10 _M) had a statistically significant increase (p < 0.05) in DNA SSBs when compared to control cells that were pre-treated with cell media alone. In summary, it appears that iAs by itself does not induce DNA SSBs in lung cells under the conditions tested. However, DMAs can cause DNA SSBs directly. We also found that iAs and DMAs sensitize the BEAS-2B cells to hydrogen peroxide-induced oxidative DNA damage. We hypothesize that this interaction could be caused by depletion of antioxidants, Fenton-like reactions between As and hydrogen peroxide, inhibition of SSB repair, or stimulation of DNA nicking by damage dependent enzymes. Further analyses into the possible contributions of the aforementioned factors are underway. [This abstract may not reflect official EPA policy. AM supported by EPA/UNC T829472].