TNF-α contributes to endothelial dysfunction in ischemia/reperfusion injury

Background-Despite the importance of endothelial function for coronary regulation, there is little information and virtually no consensus about the causal mechanisms of endothelial dysfunction in myocardial ischemia/reperfusion (I/R) injury. Because tumor necrosis factor-alpha (TNF-alpha) is reportedly expressed during ischemia and can induce vascular inflammation leading to endothelial dysfunction, we hypothesized that this inflammatory cytokine may play a pivotal role in I/R injury-induced coronary endothelial dysfunction. Methods and Results-To test this hypothesis, we used a murine model of I/R ( 30 minutes/90 minutes) in conjunction with neutralizing antibodies to block the actions of TNF-alpha. TNF-alpha expression was increased > 4-fold after I/R. To determine whether TNF-alpha abrogates endothelial function after I/R, we assessed endothelial-dependent (ACh) and endothelial-independent ( SNP) vasodilation. In sham controls, ACh induced dose-dependent vasodilation that was blocked by the nitric oxide synthase ( NOS) inhibitor L-NMMA (10 mu mol/ L), suggesting a key role for NO. In the I/R group, dilation to ACh was blunted, but SNP-induced dilation was preserved. Subsequent incubation of vessels with the superoxide (O-2(.-)) scavenger (TEMPOL), or with the inhibitors of xanthine oxidase (allopurinol, oxypurinol), or previous administration of anti-TNF-alpha restored endothelium-dependent dilation in the I/R group and reduced I/R- stimulated O-2(.-) production in arteriolar endothelial cells. Activation of xanthine oxidase with I/R was prevented by allopurinol or anti-TNF-alpha. Conclusions - These results suggest that myocardial I/R initiates expression of TNF-alpha, which induces activation of xanthine oxidase and production of O-2(.-), leading to coronary endothelial dysfunction.