Augmented oxidative stress and preserved vasoconstriction induced by hydrogen peroxide in coronary arteries in obesity: role of COX-2.

BACKGROUND AND
PURPOSE: Oxidative stress plays a key role in the vascular and metabolic abnormalities associated with obesity. Herein, we assessed whether obesity can increase coronary vasoconstriction induced by hydrogen peroxide (H2 O2 ) and the signalling pathways involving COX-2 and superoxide (O2.- ) generation. EXPERIMENTAL APPROACH: Contractile responses to H2 O2 and O2.- generation were measured in coronary arteries from genetically obese Zucker rats (OZR) and compared to lean Zucker rats (LZR). KEY
RESULTS: Both basal and H2 O2 -stimulated O2.- production were enhanced in coronary arteries from OZR, but H2 O2 -induced vasoconstriction was unchanged. The selective COX-2 inhibitor NS398 significantly reduced H2 O2 -induced contractions in endothelium-denuded arteries from LZR and OZR, but only in endothelium-intact arteries from LZR. PGI2 (IP) receptor antagonism modestly reduced the vasoconstrictor action of H2 O2 while antagonism of the PGE2 receptor 4 (EP4 ) enhanced H2 O2 contractions in arteries from OZR but not LZR. Basal release of COX-2-derived PGE2 was higher in coronary arteries from OZR where the selective agonist of EP4 receptors TCS 2519 evoked potent relaxations. COX-2 was up-regulated after acute exposure to H2 O2 in coronary endothelium and vascular smooth muscle (VSM) and inhibition of COX-2 markedly reduced H2 O2 -elicited O2.- generation in coronary arteries and myocardium. Expression of Nox subunits in VSM and NADPH-stimulated O2.- generation was enhanced and contributed to H2 O2 vasoconstriction in arteries from obese rats. CONCLUSION AND IMPLICATIONS: COX-2 contributes to cardiac oxidative stress and to the endothelium-independent O2.- -mediated coronary vasoconstriction induced by H2 O2 in obesity, which is offset by the release of COX-2-derived endothelial PGE2 acting on EP4 vasodilator receptors.