Acute inhibition of superoxide formation and Rac1 activation by nitric oxide and iloprost in human vascular smooth muscle cells in response to the thromboxane A2 analogue, U46619

BackgroundThe over-production of superoxide (O2−) derived from NADPH oxidase (NOX) plays a central role in cardiovascular diseases. By contrast, nitric oxide (NO) and prostacyclin (PGI2) are vasculoprotective. The effect of the NO donor, NONOate and iloprost on O2− formation, p47phox and Rac1 activation in human vascular smooth muscle cells (hVSMCs) was investigated.MethodshVSMCs were incubated with 10 nM thromboxane A2 analogue, U46619 for 16 h, and then with apocynin (a NOX inhibitor), NONOate or iloprost for 1 h and O2− measured spectrophometrically. The role of cyclic AMP and cyclic GMP was examined by co-incubation of drugs with protein kinase (PK) A and G inhibitors listed above. Rac1 was studied using pull-down assays.ResultsNONOate and iloprost inhibited O2− formation, acutely, effects blocked by inhibition of PKG and PKA, respectively. Rac1 and p47phox activation and translocation to the plasma membrane was completely inhibited by NONOate and iloprost, effects again reversed by co-incubation with PKG or PKA inhibitors.ConclusionsNO and PGI2 block the acute activity of NOX in hVSMCs via the cGMP–PKG axis (for NO) and by the cAMP–PKA axis (for iloprost) through inhibition of Rac1 and p47phox translocation. These findings have implications in the pathophysiology and treatment of CVD.