Cobalamin and arsenic metabolism.

Chronic arsenic exposure through contaminated drinking water is a risk factor for cancers, cardiovascular disease, and neurologic impairment. Metabolic conversion of inorganic As (iAs) to dimethylarsinic acid (DMA) reduces toxicity and facilitates urinary As (uAs) elimination, but the intermediate metabolite monomethylarsonic (MMA) may have increased cytoxic and genotoxic effects. Adequate folate facilitates iAs methylation to DMA and MMA and appears to enhance urinary elimination, but the potential influence of cobalamin, which also facilitates methylation, is unclear. Hall et al. (p. 1724) conducted a cross-sectional study of uAs metabolites (%iAs, %MMA, and %DMA) among 778 Bangladeshi adults, many of whom were exposed to elevated As and were classified as cobalamin deficient. Cobalamin-deficient participants had increased %iAs and %MMA relative to cobalamin-sufficient participants, with stronger associations observed among those with adequate versus deficient folate levels. The authors conclude that cobalamin appeared to facilitate iAs methylation to potentially toxic MMA metabolites in participants with adequate folate.