Endothelial nitric oxide synthase protects the post-ischemic liver: potential interactions with superoxide

Hepatic ischemia and reperfusion (I/R) continues to represent a significant cause of post-transplant liver failure. The roles that certain free radicals including nitric oxide (NO) and superoxide (O(2)(-)) play in this process are not well understood. The present study was designed to assess the role of endothelial cell nitric oxide synthase (eNOS) in I/R-induced liver injury in a murine model of hepatic I/R. Forty five minutes of partial (70%) hepatic ischemia followed by 3 and 6 h of reperfusion resulted in a significant increase in liver injury which occurred in the absence of neutrophil infiltration. eNOS-deficient mice displayed enhanced liver injury when compared to their wild type controls again in the absence of neutrophil infiltration. Interestingly, basal liver blood flow was significantly decreased in these mice when compared to controls though their blood flow during reperfusion was not significantly reduced from their wild type controls. Treatment of eNOS(-/-) mice with gadolinium chloride, a potent inhibitor of Kupffer cell function, but not superoxide dismutase, significantly reduced post-ischemic hepatocellular injury while either treatment protected the wild type mouse livers. Taken together, these data suggest that NO derived from eNOS may act to protect the post-ischemic liver possibly by suppression of Kupffer cell function and not by modulation of tissue perfusion. Further the data presented here would indicate that the protective effects conferred by SOD are related to its ability to increase the bioavailability of NO rather than by attenuating superoxide-dependent reactions. Data generated from these studies may prove useful in developing new drug therapies to treat the post-ischemic liver.