Arsenic-induced nitrative DNA damage in human HaCaT keratinocytes

Arsenic is a most likely environmental carcinogenic species that poses a significant health risk in humans. Epidemiological evidence strongly implicates exposure to arsenic in the causation of human cancer of the skin, lung, and urinary bladder (IARC, 2004). Chronic exposure to arsenic leads to the development of lesions on the skin, including hyperkeratosis, hyperpigmentation and cancer. Dermatitis following the exposure to arsenic is a hallmark of the early stages of arsenic poisoning. In this study, we performed immunocytochemical method to examine the formation of 8-nitroguanine, a mutagenic DNA lesion formed during inflammation, in long term arsenic-treated spontaneously immortalized, non-tumorigenic human epidermal keratinocytes (HaCaT) cell line. When HaCaT cells were exposed chronically for 18 weeks to an environmentally relevant level of arsenic (0.05 ppm) in vitro, malignant transformation occurred as evidenced by the formation of highly aggressive squamous cell carcinoma after inoculation into nude mice. Arsenic induced 8-nitroguanine formation, inducible nitric oxide synthase (iNOS) and nuclear factor-kB (NF-kB) expression in the HaCaT keratinocytes and xenograft tumors. The staining intensity of 8-nitroguanine, iNOS, NF-kB and p53 in arsenic-treated cells was significantly greater than that in non-treated control at every twenty four days. These results suggest that arsenic can induce formation of 8-nitroguanine via iNOS expression, which may contribute to carcinogenesis. Therefore, the formation of nitrative DNA damage could be one of the mechanisms responsible for arsenic-induced carcinoma. 8-Nitroguanine could be a useful indicator of the risk of skin cancer development in response to chronic arsenic toxicosis.