DECREASED DNA REPAIR GENE EXPRESSION AMONG INDIVIDUALS EXPOSED TO ARSENIC IN US DRINKING WATER.
Angeline S. Andrew 1,2,3, Margaret R. Karagas 1,3, Joshua W. Hamilton 2,3
1 Department of Community and Family Medicine, and
2 Department of Pharmacology and Toxicology,
3 Center for Environmental Health Sciences at Dartmouth, Dartmouth Medical School, Hanover, NH 03755-3835.

Exposure to high levels of arsenic in drinking water is associated with the occurrence of several types of cancers including lung, bladder and skin, as well as vascular disease and diabetes. However, the mechanism by which arsenic acts as a human carcinogen is not known. At low levels, arsenic is not directly genotoxic, but likely acts as a co-mutagen. We hypothesize that arsenic may act as a carcinogen, at least in part, through inhibition of DNA repair mechanisms, leading indirectly to increased mutations from other DNA damaging agents. In cell culture, low concentrations of arsenic inhibited nucleotide excision repair (NER) after UV irradiation, and specifically decreased incision frequency. Nucleotide excision repair is a major DNA repair pathway that removes DNA lesions including certain DNA crosslinks, UV photolesions, and bulky chemical adducts. The nucleotide excision repair system requires the cooperative function of many gene products for damage recognition, incision, excision, elongation, and ligation to restore DNA structure. The molecular mechanism underlying inhibition of nucleotide excision repair by arsenic is unknown, but could be due to decreased expression of critical genes involved in nucleotide excision repair. To test this hypothesis, we isolated mRNA from cryopreserved lymphocytes taken from a subset of individuals enrolled in a population based case-control study of bladder cancer in New Hampshire. Nucleotide excision repair gene expression was assessed by RT-PCR of nine individual genes normalized to GAPDH. Arsenic levels were determined in toenail clippings using instrumental neutron activation analysis and drinking water samples using high resolution ICP-MS with hydride generation. In a linear regression analysis, toenail arsenic levels were inversely correlated with expression of critical members of the nucleotide excision repair incision complex, ERCC1 and XPF, as well as the TFIIH DNA helicase XPB. Expression of these genes was significantly decreased in subjects whose drinking water arsenic levels were >10 mg/L (p<0.05). In contrast, there was no correlation between arsenic exposure and expression of either XPG or XPA. These results indicate that intake of arsenic in drinking water at levels >10 mg/L may decrease nucleotide excision repair gene expression, and support the hypothesis of a mechanistic role for nucleotide excision repair inhibition in arsenic-induced carcinogenesis (supported by NIEHS ES07373, NCI CA57494).