Comparative Cytotoxicity of Inorganic Arsenite and Methylarsenite in Human Brain Cells

The overall goal of this study is to elucidate the potential effect(s) of arsenic on a variety of human brain cells. Arsenic is the most pervasive Group A human environmental carcinogen. Long-term exposure to arsenic is associated with human diseases including cancer, cardiovascular disease, and diabetes. More immediate are the health effects on neurological development and associated disorders in infants and children exposed to arsenic in utero. Arsenic is metabolized in various organs and tissues into more toxic methylated species, including methylarsenite (MAs(III)), so the question arises whether the methylate species are responsible for the neurological effects of arsenic. Arsenic enters the brain through the blood-brain barrier and produces toxicity in the brain microvascular endothelial cells, glia (astrocytes and microglia), and neurons. In this study, we first assessed the toxicity in different types of brain cells exposed to either inorganic trivalent As(III) or MAs(III) using both morphological and cytotoxicity cell-based analysis. Second, we determined the methylation of arsenicals and the expression levels of the methylation enzyme, As(III) S-adenosylmethionine (SAM) methyltransferase (AS3MT), in several types of brain cells. We showed that the toxicity to neurons of MAs(III) was significantly higher than that of As(III). Interestingly, the differences in cytotoxicity between cell types was not due to expression of AS3MT, as this was expressed in neurons and glia but not in endothelial cells. These results support our hypothesis that MAs(III) is the likely physiological neurotoxin rather than inorganic arsenic species.