Arsenite and methylarsonite inhibit mitochondrial metabolism and glucose-stimulated insulin secretion in INS-1 832/13 beta cells

摘要

Growing evidence suggests that exposure to environmental contaminants contributes to the current diabetes epidemic. Inorganic arsenic (iAs), a drinking water and food contaminant, is one of the most widespread environmental diabetogens according to epidemiological studies. Several schemes have been proposed to explain the diabetogenic effects of iAs exposure; however, the exact mechanism remains unknown. We have shown that in vitro exposure to low concentrations of arsenite (iAs(III)) or its trivalent methylated metabolites, methylarsonite (MAsIII) and dimethylarsinite (DMAsIII), inhibits glucose-stimulated insulin secretion (GSIS) from isolated pancreatic islets, with little effect on insulin transcription or total insulin content. The goal of this study was to determine if exposure to trivalent arsenicals impairs mitochondrial metabolism, which plays a key role in the regulation of GSIS in beta cells. We used a Seahorse extracellular flux analyzer to measure oxygen consumption rate (OCR), a proxy for mitochondrial metabolism, in cultured INS-1 832/13 beta cells exposed to iAs(III), MAsIII, or DMAsIII and stimulated with either glucose or pyruvate, a final product of glycolysis and a substrate for the Krebs cycle. We found that 24-h exposure to 2 mu M iAs(III) or 0.375-0.5 mu M MAsIII inhibited OCR in both glucose- and pyruvate-stimulated beta cells in a manner that closely paralleled GSIS inhibition. In contrast, 24-h exposure to DMAsIII (up to 2 A mu M) had no effects on either OCR or GSIS. These results suggest that iAs(III) and MAsIII may impair GSIS in beta cells by inhibiting mitochondrial metabolism, and that at least one target of these arsenicals is pyruvate decarboxylation or downstream reactions.