EFFECTS OF ALCOHOL ON HEPATIC DRUG METABOLISM

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The ultimate goal is to delineate the mechanisms by which long-term (chronic) exposure to alcoholic beverages alters drug metabolising functions in the liver. The experimental system consists of a primary culture of chicken embryo hepatocytes which allows the determination of direct effects of alcohols and other agents on the liver. We have found that chemicals as simple as ethanol and the major higher chain alcohols in commercial alcoholic beverages cause induction of cytochrome P450 (P450), UPD Glucuronyl Transferase (UDPGT), and 5-aminolevulinate (ALA) synthase in these cultured hepatocytes. The alcohols all induce a protein of 50K molecular weight that cross-reacts with antisera prepared against purified isozymes of P450 induced by phenobarbital-like inducers. The antigenic homology and the substrate specificities of induced UDPGT and P450 suggest that 2- to 5-carbon alcohols are causing a phenobarbital-like induction in these hepatocytes. We propose to purify ethanol-inducible isozyme(s) of P450 from chicken embryos and compare their characteristics with isozymes of P450 induced by phenobarbital or methylcholanthrene-like inducers, such as substrate specificity, peptide maps, antigenicity and separation of the P450 isozymes by HPLC. We have shown that induction of P450 by various alcohols and pyrazoles depends almost entirely on hydrophobicity of these compounds. We will also test phenobarbital-like inducers of P450 with different hydrophobic or electronic constituents to determine if the correlation with hydrophobicity for induction of P450 applies to these phenobarbital-like inducers or only applies to alcohols and pyrazoles. Considerable controversy exists over the extent of ethanol metabolism by P450 in the intact liver. We have measured ethanol metabolism by the intact cultured chick hepatocytes and found changes in ethanol metabolism corresponding to changes in alcohol dehydrogenase activities. We propose experiments to determine if changes in cytochrome P450 such as induction by ethanol or inhibition by piperonyl butoxide, has any effect on ethanol metabolism by the intact cells. If induction of P450 by ethanol increases ethanol metabolism in these cells, we will determine the specificity, if any, of various inducers of P450 to cause this increase.