Superfund Research Program

Genotoxic and Cell Signaling Pathways of Arsenic in Mammalian Cells

Project Leader: Tom K. Hei (Columbia University Mailman School of Public Health)
Grant Number: P42ES010349
Funding Period: 2000 - 2011

Project-Specific Links

Final Progress Reports

Year:   2010  2005 

The overall goals of this project focus on 1) the mechanisms of the DNA damaging effects of arsenic in mammalian cells, particularly the role of mitochondrial DNA mutations and the subsequent induction of reactive oxygen and reactive nitrogen species; and 2) the mechanism for arsenic-induced apoptosis (programmed cell death) in melanoma cells.  During the 2000-2005 funding period, Dr. Hei’s team found that treatment of human-hamster hybrid (A_L) cells with a 1.75 mg/ml dose of sodium arsenite for five days (survival level of ~ 22%) resulted in a consistent loss of mtDNA. The findings were based on southern blotting using random-primed ³²P-labelled mtDNA as probe. The observation is consistent with our recent observation that mitochondrial DNA deficient (rho zero) cells are significantly less responsive to the mutagenic effects of arsenic.

Dr. Graziano’s group recently reported evidence that exposure of children to arsenic in drinking water is associated with reduced intellectual function. This is consistent with Dr. Hei’s recent observation that the non-differentiated rat PC-12 cells, which are neuronal in nature, are extremely sensitive to sodium arsenite treatment, responding by the development of apoptosis and secondary necrosis 6 hours after treatment. Using poly-D-Lysine as coating matrix and neural growth factor beta (NGFb 100 ng/ml for 4 days), Dr. Hei’s team succeeded in establishing differentiated PC-12 cell culture.  Furthermore, similar to the non-differentiated cells, these differentiated PC-12 cells (in the absence of NGFb) showed a seven-fold increase in apoptosis following treatment with sodium arsenite (5 mM for 16 hr). Concurrent treatment of these arsenite-exposed cells with either LY294002 (a specific inhibitor of phosphatidylinositol 3-kinase) or NS398 (a specific inhibitor of cyclooxygenase-2) further enhanced the apoptotic incidence. Since the PC-12 cells, in the presence of NGFb exhibit many of the phenotypic characteristics of differentiated neurons, these findings provide evidence that the PC-12 model is an excellent model in evaluating the induction and mechanism of arsenite toxicity to neuronal cells.

Arsenic is an important environmental carcinogen that affects millions of people worldwide through contaminated water supplies. For decades, arsenic was considered a non-genotoxic carcinogen. Using the highly sensitive A_L mutation assay, Dr. Hei showed that arsenic is indeed a potent gene and chromosomal mutagen and mitochondria are a primary target in arsenic-induced genotoxic response. A better understanding of the mutagenic/carcinogenic mechanism of arsenic should provide a basis for better interventional approach in both treatment and prevention of arsenic induced cancer.  On the other hand, melanoma is often a deadly disease due to the lack of effective treatment options. Despite the dramatic increase in the incidence of malignant melanoma in the past decades, the molecular mechanisms of its progression and extreme resistance to treatment, which kill cells by induction of programmed cell death (apoptosis), remain largely unknown. Dr. Hei’s present study, however, indicates that arsenic can also be a double-edge sword and could, potentially, benefit thousands of melanoma patients each year who fail conventional therapeutic regimens.