Arsenic speciation in bile and urine following oral and intravenous exposure to inorganic and organic arsenics in rats

Although inorganic arsenate (iAs(V)) and arsenite (iAs(III)) are metabolized in liver and excreted into bile and urine, the metabolites in the bile after the oral intake of iAs remain unclear. Male Sprague-Dawley rats were orally (po) or intravenously (iv) exposed to iAs and methylated arsenics, and the arsenic speciation in the urine and bile was analyzed by high performance liquid chromatography-inductively coupled argon plasma mass spectrometry. Arsenic caused induction of multidrug resistance-associated protein 2 (MRP2), and changes of glutathione (GSH) levels in the liver and bile were also determined. The metabolic speciation studies revealed that arsenic was excreted into bile in the methylarsenic-diglutathione (MADG) and/or dimethylarsenic acid (DMA(V)) forms in iAs(III)- or iAs(V)-po rats, but that MADG and arsenic-triglutathione (ATG) are the main forms excreted into bile both in iAs(III)- and iAs(V)-iv rats. In MADG-po rats, the MADG was excreted into bile in the MADG and DMA(V) forms. Monomethylarsonic acid (MMA(V))- and DMA(V)-iv rats did not excrete significant amounts of either MMA(V) or DMA(V) into bile and mostly excreted into urine in the unchanged chemical forms. Taken together, the DMA(V) detected in the bile is mostly supposed to be the dissociation of dimethylarsenic-glutathione (DMAG). Urinary arsenic speciation showed that arsenic metabolized to 43% methylated DMA(V), 47% unmethylated iAs(III), and 10% iAs(V) in iAs(III)-iv rats, whereas only 3% methylated DMA(V), 87% unmethylated iAs(V), and 10% iAs(III) were detected in iAs(V)-iv rats. Arsenic was accumulated dose dependently, and arsenic concentration was significantly higher in the iAs(III)-po rat liver than in the iAs(V)-po rat liver. GSH levels in the bile were decreased by relatively higher doses of iAs(V)-po, but significantly increased by iAs(III)- or iAs(V)-iv. iAs-exposure increased the expression of MRP2 in the liver. Pretreatment with buthionine sulfoximine predominantly inhibited arsenic excretion into bile in iAs-iv rats. In conclusion, our data demonstrated that biliary and urinary arsenic excretion and speciation are affected by the route, dose, and chemical forms of arsenical administration, and GSH plays a key role in arsenic metabolism. We are also first to show that DMA(V) that probably originated from DMAG is excreted into the bile in iAs-po rats.