Alcohol is a potent immunosuppressive agent and the alcohol-consuming patient is an immunocompromised host. As such, alcohol predisposes individuals to bacterial and viral infections, and increases morbidity and mortality. The liver contains the largest population of fixed macrophages (i.e. Kupffer cells) within the body which play an essential role in immune surveillance against bacteria or bacterial products, such as lipopolysaccharide (LPS). The liver is also the primary location for ethanol metabolism. Therefore, the long-term goal of this project is to elucidate the cellular mechanisms by which ethanol alters metabolic control and impairs immune function in the liver during infection, and clarify how these changes influence susceptibility to infection. Two working hypotheses will be considered: (1) ethanol alters LPS-induced changes in basal and hormone-mediated substrate utilization of both parenchymal and nonparenchymal cells; and (2) ethanol alters intercellular communication in the liver by influencing the release and/or action of paracrine mediators that are produced by Kupffer cells in response to LPS, thereby modulating substrate metabolism and function in both parenchymal and nonparenchymal cells. As a result of these metabolic changes, the functional capabilities of these cells will be limited and, therefore, host defense impaired. Hypothesis #1 will be addressed by specific aims directed at determining whether ethanol, LPS or ethanol plus LPS alter substrate utilization by isolated parenchymal and nonparenchymal (Kupffer and endothelial) cells. Experiments will be performed in which ethanol and LPS are administered in vivo and substrate utilization examined either in vivo (glucose utilization) or in vitro (glucose, glutamine and palmitate oxidation). Similar types of experiments will be performed following the in vitro addition of ethanol and LPS. Several indices of immune function will also be assessed in parenchymal and nonparenchymal cells, and correlated to the metabolic alterations.
The specific aims for hypothesis #2 will be directed at determining whether ethanol alters the intercellular communication among liver cell types. Metabolic and functional studies will be performed on parenchymal, Kupffer and endothelial cells that will have been incubated with conditioned medium from LPS-stimulated Kupffer cells or ethanol-treated parenchymal cells. Furthermore, specific paracrine mediators present in the LPS-stimulated media will be quantitated and immune modulators examined for their ability to alter liver cell metabolism and function. In any experiment where ethanol alters either basal or LPS-induced changes, additional experiments will be performed to determine whether this is a direct effect or a change mediated by the metabolism of ethanol. These studies will provide novel an important information on the mechanism of ethanol-induced changes in Kupffer and endothelial cell metabolism an function under basal conditions and during an infectious challenge, and will substantially aid our understanding of the factors which modulate host defense by the liver. The results will also broaden our understanding of other conditions in which immune deficiency is present.
