Metabolism and disposition of arsenic species from controlled dosing with sodium arsenite in adult female CD-1 mice. III. Toxicokinetic studies following oral and intravenous administration.

Arsenic is a ubiquitous contaminant, with typical dietary intake below 1 μg/kg bw/d and drinking water exposures up to 50 μg/kg bw/d. Arsenic exposures are associated with human diseases and doses of toxicological concern are similar to typical dietary intake. Metabolism of arsenite to dimethylarsinate (DMA) by arsenite-3-methyltransferase (As3MT) promotes clearance, but also generates reactive trivalent intermediates that bind extensively to cellular thiols. This study measured pentavalent and trivalent arsenic species in blood and tissues after oral and intravenous administration of arsenite (50 μg/kg bw). After oral administration, the intestine and liver contained elevated levels of As and MMA, relative to erythrocytes, lung, and kidney, suggesting incomplete conversion to DMA during first-pass metabolism. However, blood concentrations of the predominant species, DMA, were similar for oral and intravenous dosing. While all tissues examined contained DMA, muscle, brain, and plasma had undetectable levels of MMA. Tissue levels of arsenic species were similar following intravenous vs. oral administration, except lower in the intestine. The results confirm the role of metabolism in producing fluxes of putatively toxic trivalent arsenic intermediates. Tissue dosimetry suggests that the intestine, liver, lung, and kidney could be more susceptible to effects of bound arsenic, relative to muscle and brain.