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-α (TNF-α) 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-α. TNF-α expression was increased >4-fold after I/R. To determine whether TNF-α 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 μmol/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-α 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-α. Conclusions— These results suggest that myocardial I/R initiates expression of TNF-α, which induces activation of xanthine oxidase and production of O 2 ·− , leading to coronary endothelial dysfunction.