INTERACTION OF ETHANOL WITH HEPATIC MICROSOMES

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After having established the microsomal ethanol oxidizing system (MEOS) as an entity distinct from alcohol dehydrogenase (ADH) and catalase, the applicant now wishes to address the question of the mechanism involved and the role of MEOS in ethanol metabolism in vitro and in vivo. Specifically, the ethanol-induced form of cytochrome P-450 will be purified from rats, deermice and baboons. We will characterize the purified protein(s) in terms of molecular weight, spectra, substrate specificity and peptide mapping. Despite known differences in the cytochrome P-450 of these species, we hope to find a common change that may shed some light on the nature of the ethanol-induced alteration and its specificity for ethanol as a substrate. We will also determine to what extent hydroxyl radicals are involved in ethanol oxidation mediated by the ethanol-induced form of cytochrome P-450. Furthermore, we will assess whether the changes in cytochrome P-450 result in altered metabolism of other substrates such as steroid hormones and retinoic acid (a form of vitamin A of significance for the nutritional status of the alcoholic), carcinogens (of possible importance for the enhanced incidence of cancers in the alcoholic) and in enhanced hepatotoxicity of industrial solvents and commonly used drugs, including promotion of lipid peroxidation (of relevance to the pathogenesis of alcoholic liver injury). To assess the relative importance of MEOS and to determine how much it contributes to the metabolic tolerance that develops after chronic ethanol consumption, we will compare the fate of (3H) xylitol and (H3) ethanol in hepatocytes isolated from ADH+ and ADH- deermice. In the same experimental model we will study the isotope effect of deuterium to differentiate MEOS from the other alcohol oxidizing systems, both in isolated hepatocytes and in vivo. The broad aim of our study is to contribute to our understanding of how alcoholics differ from non-alcoholics in biochemical terms; specifically we plan to determine to what extent changes produced in the microsomal cytochrome P-450 by alcohol consumption alters the response of the alcoholic to endogenous and exogenous compounds in a way that may affect alcohol induced liver pathology, its prevention and its treatment.