Hepatic dysfunction often results in multi-organ injury, with the pulmonary and neuronal systems frequently affected. The exact mediators of this distant organ injury are poorly understood, and in many instances the initiators and propagators of the hepatic injury are ill-defined. While under certain conditions the extra-hepatic organs are injured due to failure of the liver to adequately clear toxic substances, it is also possible that the liver may be induced to synthesize mediators which actively participate in hepatic and distant organ damage. A likely candidate for a soluble mediator produced in the liver which will injure distant organs is tumor necrosis factor (TNF). This potent peptide mediator has been strongly implicated as the major cytokine causing the multi-organ damage observed in septic shock. We have developed a nonlethal rat model of partial hepatic ischemia/reperfusion (I/R) which induces systemic levels of TNF, associated with severe liver and lung damage. Pretreatment of the animals with a polyclonal anti-murine TNF antibody, which cross reacts with rat TNF, is able to completely block the pulmonary injury and significantly inhibit hepatic injury. We intend to vigorously pursue these initial observations by carefully documenting TNF gene expression within the ischemic liver by immunoprecipitation with Western blot analysis, Northern blot analysis, immunoperoxidase, electron microscopy with immunogold detection of TNF, and in situ hybridization for TNF mRNA. Organ injury in the liver, lungs, and brain will be carefully quantitated after hepatic I/R by several exacting, state-of-the-art methodologies, and the precise role of TNF in the ensuing pathophysiologic alterations will be determined by blocking these alterations with a specific anti-TNF antibody. Particular attention will be paid to relationship of TNF release, neutrophil activation and organ injury. Since TNF most likely initiates a cascade of events, clinically relevant therapeutic modalities will be employed to block the organ injury by inhibiting or deactivating oxygen free radicals. The above studies deal with the acute (<24 hours) events observed after hepatic I/R, but we have also observed severe hepatic fibrosis 2 weeks after the ischemic insult, and the deposition of collagen was significantly inhibited by our anti-TNF antibody. The chronic effects of hepatic I/R will be assessed by quantitating the fibrotic response in terms of collagen production, and identifying potential secondary mediators induced by the initial production of TNF. These studies will provide detailed assessment of th multi-organ damage observed after hepatic I/R, yield insight into the mechanisms of injury and allow reproducible model to study both the acute and chronic effects of hepatic ischemia/ reperfusion.
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