Effect of the NADPH oxidase inhibitor apocynin on ischemia-reperfusion lung injury

Apocynin (4-hydroxy-3-methoxy-acetophenone) inhibits NADPH oxidase in activated polymorphonuclear (PMN) leukocytes, preventing the generation of reactive oxygen species. To determine if apocynin attenuates ischemia-reperfusion lung injury, we examined the effects of apocynin (0.03, 0.3, and 3 mM) in isolated in situ sheep lungs. In diluent-treated lungs, reperfusion with blood (180 min) after 30 min of ischemia (ventilation 28% O-2,5% CO2) caused leukocyte sequestration in the lung and increased vascular permeability [reflection coefficient for albumin (sigma(alb)) 0.47 +/- 0.10, filtration coefficient (K-f) 0.14 +/- 0.03 g . min(-1) . mmHg(-1) . 100 g(-1)] compared with nonreperfused lungs (sigma(alb) 0.77 +/- 0.03, K-f 0.03 +/- 0.01 g . min(-1) . mmHg(-1) . 100 g(-1); P< 0.05). Apocynin attenuated the increased protein permeability at 0.3 and 3 mM (sigma(alb) 0.69 +/- 0.05 and 0.91 +/- 0.03, respectively, P< 0.05); K-f was decreased by 3 mM apocynin (0.05 +/- 0.01 g . min(-1) . mmHg(-1) . 100 g(-1), P< 0.05). Diphenyleneiodonium (DPI, 5 mu M), a structurally unrelated inhibitor of NADPH oxidase, worsened injury (K-f 0.32 +/- 0.07 g . min(-1) . mmHg(-1) . 100 g(-1), P< 0.05). Neither apocynin nor DPI affected leukocyte sequestration. Apocynin and DPI inhibited whole blood chemiluminescence and isolated PMN leukocyte-induced resazurin reduction, confirming NADPH oxidase inhibition. Apocynin inhibited pulmonary artery hypertension and perfusate concentrations of cyclooxygenase metabolites, including thromboxane B-2. The cyclooxygenase inhibitor indomethacin had no effect on the increased vascular permeability, suggesting that cyclooxygenase inhibition was not the explanation for the apocynin results. Apocynin prevented ischemia-reperfusion lung injury, but the mechanism of protection remains unclear.