Superoxide limits cyclosporine-A-induced formation of peroxynitrite in endothelial cells

Peroxynitrite (ONOO-) is a potent oxidant formed by the nonenzymatic reaction between superoxide anion (O-2(.-)) and nitric oxide (NO.) in a one-to-one stoichiometry. Accumulated evidence suggests that endothelial dysfunction coincides with an enhanced NO. synthase expression and O-2(.-) production, facilitating ONOO- formation, In vivo, formation of ONOO- has been associated with atherosclerosis and vascular aging. The immunosuppressor Cyclosporine A (CsA) has been associated to human endothelial dysfunction and accelerated atherosclerosis. We have previously shown that CsA induced a transcriptionally mediated increase of the eNOS gene expression and that CsA induced the formation of nitric oxide, O-2(.-), and ONOO- in vascular endothelial cells. In this work, we evaluate the CsA-induced relative amounts of formation of O-2(.-) and NO., providing data consistent with a role of O-2(.-), and not NO., as the limiting factor in the CsA-dependent intracellular formation of ONOO- in vascular endothelial cells. Furthermore, when endothelial cells were treated with CsA in a situation of increased generation of superoxide such as that provided by high glucose levels, a further increase in the formation of peroxynitrite was detected. The temporal availability of O-2(,-) for peroxynitrite formation may thus become critical in the pathophysiological scenarios where reactive nitrogen intermediates are operative, (C) 2002 Elsevier Science Inc.