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Tumor necrosis factor–induced, superoxide‐mediated neutrophil accumulation in cold ischemic/reperfused rat liver

The mechanisms of hepatic ischemia/reperfusion injury are complicated and multifactorial. This study was designed to examine superoxide generation and neutrophil accumulation in cold ischemic‐reperfused rat livers after elimination of Kupffer cells and to determine the role of superoxide/tumor necrosis factor (TNF) interactions. Rat Kupffer cells were eliminated by liposome‐encapsulated dichloromethylene diphosphonate injected intravenously. Livers from control and treated rats were isolated and preserved in University of Wisconsin solution (4°C) for 0, 12, and 24 hours and then perfused for 60 minutes with oxygenated Krebs‐Henseleit bicarbonate buffer (37°C) by adding neutrophils into the perfusate. Superoxide generation was measured by using real‐time chemiluminescence (CL) during perfusion, and neutrophil accumulation was assessed by measuring myeloperoxidase activity in the liver tissue. In the control livers, CL intensity markedly increased on reoxygenation, and after neutrophil infusion it increased again with a lag period of 10 minutes. Total CL intensity and myeloperoxidase activity increased with the duration of cold preservation. TNF release into the effluent perfusate was detectable only after 24 hours of preservation, and lactate dehydrogenase release was high. Elimination of Kupffer cells attenuated CL intensity and TNF and lactate dehydrogenase release and resulted in reduced myeloperoxidase activity. Electron microscopy revealed amelioration of hepatocyte swelling and endothelial cell disruption when Kupffer cells were eliminated. After 24 hours of preservation, superoxide generation was inhibited in the control livers by anti‐TNF antiserum, whereas TNF release was not inhibited by superoxide dismutase. These results suggest that TNF induces superoxide generation by Kupffer cells, which mediates neutrophil accumulation and causes cellular injury in the initial phase of reperfusion.