Human red blood cell uptake and sequestration of arsenite and selenite: Evidence of seleno-bis(S-glutathionyl) arsinium ion formation in human cells.

ABSTRACT

Over 200 million people worldwide are exposed to the human carcinogen, arsenic, in contaminated drinking water. In laboratory animals, arsenic and the essential trace element, selenium, can undergo mutual detoxification through the formation of the seleno-bis(S-glutathionyl) arsinium ion [(GS)2AsSe]-, which undergoes biliary and fecal elimination. [(GS)2AsSe]-, formed in animal red blood cells (RBCs), sequesters arsenic and selenium, and slows the distribution of both compounds to peripheral tissues susceptible to toxic effects. In human RBCs, the influence of arsenic on selenium accumulation, and vice versa, is largely unknown. The study aims were to characterize arsenite (AsIII) and selenite (SeIV) uptake by human RBCs, to determine if SeIV and AsIII increase the respective accumulation of the other in human RBCs, and ultimately to determine if this occurs through the formation and sequestration of [(GS)2AsSe]-. 75SeIV accumulation was temperature and Cl--dependent, inhibited by 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid (H2DIDS) (IC50 1 ± 0.2 µM), and approached saturation at 30 µM, suggesting uptake is mediated by the erythrocyte anion-exchanger 1 (AE1 or Band 3, gene SLC4A1). HEK293 cells overexpressing AE1 showed concentration-dependent 75SeIV uptake. 73AsIII uptake by human RBCs was temperature-dependent, partly reduced by aquaglyceroporin 3 inhibitors, and not saturated. AsIII increased 75SeIV accumulation (in the presence of albumin) and SeIV increased 73AsIII accumulation in human RBCs. Near-edge X-ray absorption spectroscopy revealed the formation of [(GS)2AsSe]- in human RBCs exposed to both AsIII and SeIV. The sequestration of [(GS)2AsSe]- in human RBCs potentially slows arsenic distribution to susceptible tissues and could reduce arsenic-induced disease.