Stimulation of reactive oxygen, but not reactive nitrogen species, in vascular endothelial cells exposed to low levels of arsenite

Elevated levels of arsenite, the trivalent form of arsenic, in drinking wat er correlates with increased vascular disease and vessel remodeling. Previo us studies from this laboratory demonstrated that environmentally relevant concentrations of arsenite caused oxidant-dependent increases in nuclear tr anscription factor levels in cultured porcine vascular endothelial cells. T he current studies characterized the reactive species generated in these ce lls exposed to levels of arsenite that initiate cell signaling. These expos ures did not deplete 5'-triphosphate, nor did they affect basal or bradykin in-stimulated intracellular free Ca2+ levels, indicating that they were not lethal. Electron paramagnetic resonance (EPR) spectroscopy, including spin trapping with carboxy-PTIO (cPTIO), demonstrated that 5 mu M or less of ar senite did not increase (NO)-N-. levels over a 30-min period relative to (N O)-N-. release stimulated by bradykinin. However, these same levels of arse nite rapidly increased both oxygen consumption and superoxide formation, as measured by EPR oximetry and spin trapping with 5,5-dimethyl-1-pyrroline N -oxide (DMPO), respectively. Pretreatment of the cells with DPI, apocynin, or superoxide dismutase abolished arsenite-stimulated DMPO-OH adduct format ion. Finally arsenite increased extracellular accumulation of H2O2, measure d as oxidation of homovanillic acid, with the same time and dose dependence , as seen for superoxide formation. These data suggest that superoxide and H2O2 are the predominant reactive species produced by endothelial cells aft er arsenite exposures that stimulate cell signaling and activate transcript ion factors. (C) 1999 Elsevier Science Inc.