Comparison of the Levels of Enzymes Involved in Drug Metabolism between Transgenic or Gene-knockout and the Parental Mice

Abstract

Drug-metabolizing enzymes are involved in the metabolic activation or detoxification of carcinogens. To evaluate animals developed as models for alternative carcinogenicity testing, we investigated whether or not a gene manipulation including the transgene of ras and the knocking out of a tumor suppressor gene such as p53 orXPA could alter the expression of representative drug-metabolizing enzymes directly or indirectly. Expression of several isoforms of cytochrome P450 (CYP) in the liver of rasH2, p53 ( +/- ), Tg.AC, and XPA (-/-) mice with or without treatment of prototype inducer, phenobarbital or 3-methylcholanthrene, was analyzed by Western immunoblotting in comparison with their parental strains of mice. In addition, the activities of 3 major phase II enzymes, UDP-glucronosyltransferase, sulfotransferase, and glutathione S-transferase, were compared between the gene-manipulated and the corresponding parental strains of mice. Results demonstrate that XPA gene knockout appeared to increase constitutive expression of CYP2B and CYP3A isoforms. Overexpression of human c-Ha-ras gene or p53 gene knockout appeared to increase constitutive UGT activity toward 4-nitrophenol. The content or activities of almost all other enzymes examined in the present study do not appear to be affected by the gene manipulation.

Keywords

Alternative models carcinogenicity testing cytochrome P450 isoform p53 ( +/- )phase II enzymes rasH2 Tg.AC XPA (-/-).

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