Mechanisms of Neutrophil-induced Liver Toxicity

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DESCRIPTION (provided by applicant): Ischemia-reperfusion (IRP) injury is an important clinical problem, which determines morbidity and mortality after liver transplantation, liver surgery and hemorrhagic or septic shock. IRP injury is an even bigger issue in steatotic livers. A self-perpetuating inflammatory response is a key component of the overall tissue injury during reperfusion. Resident macrophages (Kupffer cells) and recruited neutrophils are the main cell types directly responsible for parenchymal cell damage. Reactive oxygen species (ROS) generated by these inflammatory cells diffuse into hepatocytes and trigger an intracellular oxidant stress, which ultimately causes necrotic cell death. Sulfhydryl groups can provide the necessary electrons to reductively inactivate these ROS. Therefore, we hypothesize that strengthening the endogenous antioxidant capacity in target cells may be most effective in preventing cell injury by Kupffer cells and neutrophils and thereby attenuating the inflammatory response without compromising vital host-defense functions of these cells. Metallothioneins (MTs) are sulfhydryl-rich polypeptides, which contain 18-23 cysteine residues per molecule. MT-1 and MT-2 are highly inducible genes and have been shown to be effective scavengers of ROS in vitro. However, virtually nothing is known about the induction of MTs during hepatic IRP or ischemic preconditioning in both lean and steatotic livers. Therefore, the overall aims of this proposal are to provide a comprehensive analysis of the postischemic gene expression of metallothioneins and to study their pathophysiological role during hepatic IRP injury in lean livers and ethanol-induced steatotic livers as well as their potential to use MT gene expression as therapeutic target. Hence our specific experimental aims are: 1./2. Characterize postischemic induction of MTs and evaluate the potential protection against a Kupffer cell and neutrophil-induced oxidant stress and injury or its effects on micro-circulatory dysfunction during IRP injury in lean and steatotic livers. 3. Evaluate the induction of MTs during ischemic preconditioning and its overall impact on the protective effects of this procedure in lean and steatotic livers. 4. Study hepatoprotective mechanisms of MT induction in cultured mouse hepatocytes. The project will provide the preclinical basis for the development of a novel therapeutic strategy, which selectively targets the detrimental effects of an excessive inflammatory response during reperfusion without compromising the host defense function of neutrophils and Kupffer cells. Public Health Relevance: An inflammatory response with activation of Kupffer cells and neutrophils contribute to a wide variety of liver pathologies including hepatic ischemia-reperfusion injury (transplantation, tumor resections), alcoholic hepatitis, steatohepatitis and obstructive cholestasis. However, these leukocytes also fulfill a vital host defense function against invading microorganisms. Therefore, it is critical to identify and test novel therapeutic strategies, which selectively target the detrimental effects of an excessive inflammatory response without compromising the host defense function of neutrophils and Kupffer cells.