Effects of endogenous hydrogen peroxide and glutathione on the stability of arsenic metabolites in rat bile

Trivalent arsenicals such as arsenite (iAsIII), monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII) are more toxic than analogous pentavalent compounds such as arsenate (iAsV), monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV). It has been reported that arsenic-glutathione (As-GSH) complexes such as arsenic triglutathione (ATG) and methylarsenic diglutathione (MADG) are major metabolites in rat bile following intravenous administration of iAsIII. Recently, we have shown that both ATG and MADG are unstable and easily hydrolyzed to iAsIII and MMAIII, respectively, and that MMAIII is oxidized to MMAV in bile. In the present study we report the effects of H2O2 and GSH on the stability of As-GSH complexes in rat bile. Male SD rats were injected intravenously with saline or iAsIII at a dose of 0.2 or 2.0 mg As/kg body weight, and bile fluid was collected on ice for 30 min. To estimate the stability of As-GSH complexes in bile, ATG or MADG was added to untreated, heat-treated, catalase-treated, or dialyzed bile, and then incubated at 37 °C for 10 min. Concentrations of biliary H2O2 and GSH in the higher dose group were 12.6- and 4.5-times higher than the control value, respectively. Exogenously added trivalent arsenicals were oxidized to pentavalent arsenicals in the bile depending on the biliary concentration of H2O2. Both catalase and dialysis prevented oxidation of trivalent arsenicals to the corresponding pentavalent compounds. Exogenously added GSH stabilized As-GSH complexes in bile. These results suggest that H2O2 converts trivalent arsenicals to less toxic pentavalent arsenicals, whereas GSH prevents hydrolysis of As-GSH complexes and the generation of unconjugated toxic trivalent arsenicals.