ETHANOL EFFECTS ON PROTEOLYTIC SYSTEMS IN THE LIVER

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The central hypothesis of the proposed investigation is that ethanol consumption inhibits hepatic proteolysis by affecting the lysosomal and extralysosomal proteolytic pathways in the liver. An ethanol-elicited inhibition of protein degradation is one of the principal factors responsible for ethanol-induced protein accumulation in the liver, a phenomenon which contributes to hepatomegaly resulting from chronic drinking. Our aim in these investigations is to examine two key hepatic proteolytic systems in rat liver and to determine to what degree they are affected by acute and,/or chronic ethanol administration. The systems to be analyzed are the hepatic autophagic/lysosomal system and the ubiquitin proteolytic pathway. These pathways are responsible for the complete degradation of most intracellular proteins. Disruption of their intracellular function(s) may lead to other disturbances in liver cell function. The specific objectives of this proposal are to examine the effects of acute and/or chronic ethanol consumption on 1) The formation and maturation of hepatic autophagic vacuoles, 2) endogenous proteolytic activities as well as HSP-70-mediated proteolytic activities of liver lysosomes 3) the content of hepatic ubiquitin as well as ubiquitin dependent conjugation and proteolytic activities in rat liver extracts, and 4) the activities of these proteolytic systems in different zones of the hepatic lobule. The latter objective will be important in determining whether any relationship exists between the ethanol-induced reduction in hepatic proteolysis and ethanol-elicited specific cell injury. Our investigation will utilize recently updated techniques for the enrichment and isolation of autophagic vacuoles from the livers of control and ethanol-fed rats. We will analyze these vacuoles morphologically and biochemically in order to determine whether ethanol ingestion affects the formation, maturation and proteolytic capacities of these organelles. We will then assess the effects of ethanol consumption, as well as that of ethanol's initial oxidation product acetaldehyde, on the formation and the degradation of ubiquitin-protein conjugates. Finally, we will analyze the protein content, the rates of protein catabolism, as well as the aforementioned proteolytic systems in isolated perivenous and periportal hepatocytes from control and ethanol-fed rats. Since the liver is responsible for the regulation of serum protein, amino acid, lipid and glucose levels, it is important to understand the effects of ethanol toxicity or hepatic protein metabolism.