Liver transplantation surgery is an accepted therapy for children and adults with end-stage liver disease, providing good long-term survival and a return to normal activities. Lack of donor organs and primary graft nonfunction are major obstacles to more widespread and successful application of liver transplantation surgery. Livers from only about 60% of brain dead organ donors are actually utilized for human liver transplantation. The remainder are discarded as unacceptably marginal because of various donor criteria, including hypotension, shock and excessive vasopressors. During our previous period of support, we showed that critical changes leading to liver graft failure after cold storage involves a reperfusion injury that activates Kupffer cells and damages sinusoidal endothelial cells. These changes cause microcirculatory disturbances, leukocyte margination, and parenchymal cell death, leading ultimately to primary graft non-function and death. Warm hypoxia reoxygenation and endotoxin also cause Kupffer cell activation and endothelial cell changes. Our underlying hypothesis to be tested in the work proposed is that stresses prior to storage, such as ischemia, hypoxia and shock, produce a marginal class of marginal livers that is predisposed to reperfusion injury after storage. Our overall goal is understand the cellular and biochemical mechanisms underlying this injury and to develop effective, clinically relevant strategies to prevent, avoid or reverse this injury, thereby expanding the donor organ pool significantly. Our Specific Aims are 1) to understand cellular mechanisms of reperfusion injury in models using cultured endothelial cells and Kupffer cells, 2) to determine mechanisms underlying storage/reperfusion injury and graft failure of marginal livers, 3) to develop simple, clinically applicable cytochemical methods to discriminate between acceptable and unacceptable livers prior to surgery, 4) to evaluate new rinse protocols to minimize reperfusion injury to marginal livers, and 5) to develop treatments to prevent primary graft non-function. We will address specific mechanistic issues using cultured cell systems and perfused livers using a variety of techniques, many developed by us, from cell biology, pharmacology, biochemistry and molecular biology, but in all cases we will validate our findings in the clinically relevant model of orthotopic rat liver transplantation with arterialization. These studies will provide useful new information for understanding the pathogenesis of primary graft non- function, distinguishing viable from non-viable stored livers, and improving postoperative graft survival and function. The new information generated and methods developed will lead to more complete utilization of available organs and bring about more successful overall outcome of liver transplantation therapy.