Activation of NAD(P)H Oxidases by Thromboxane A2 Receptor Uncouples Endothelial Nitric Oxide Synthase

Objective—The thromboxane receptor (TPr) and multiple TPr ligands, including thromboxane A2 (TxA2) and prostaglandin H2, are elevated during vascular and atherothrombotic diseases. How TPr stimulation causes vascular injury remains poorly defined. This study was conducted to investigate the mechanism by which TPr stimulation leads to vascular injury. Methods and Results—Exposure of bovine aortic endothelial cells to either [1S-(1α,2β(5Z),3α(1E,3R),4α]-7-[3-(3-hydroxy-4-(d′-iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1] heptan-2-yl]-5′-heptenoic acid (IBOP) or U46619, 2 structurally related TxA2 mimetics, for 24 hours markedly increased the release of superoxide anions (O2·−) and peroxynitrite (ONOO−) but reduced cyclic GMP, an index of nitric oxide bioactivity. IBOP also significantly suppressed activity of endothelial nitric oxide synthase (eNOS), increased enzyme-inactive eNOS monomers, and reduced levels of tetrahydrobiopterin, an essential eNOS cofactor. IBOP- and U46619-induced increases in O2·− were a...