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[Functional analysis of drug metabolizing enzymes using gene knockout animals].

Several gene knockout mice have been widely used to analyze the role of drug-metabolizing enzymes in pharmacologic and physiologic responses. The metabolic shift of endogenous and exogenous compounds causes pharmacologic and physiologic alterations. Microsomal epoxide hydrolase (mEH)-null mice are less susceptible to the skin tumorigenesis, splenic immunotoxicity, and embryonic toxicity of 7,12-dimethylbenz[a] anthracene (DMBA). The production of DMBA-3,4-diol is detected in the target organs of wild-type mice, but not in those of mEH-null mice. Soluble epoxide hydrolase (sEH)-null mice exhibit markedly reduced rates of epoxyeicosatrienoic acid conversion to dihydroxyei-cosatrienoic acid in the liver and kidney. Furthermore, sEH-null male mice have a lower blood pressure phenotype compared with male wild-type mice, suggesting the importance of sEH in blood pressure regulation. Nuclear bile acid receptor, farnesoid X receptor (FXR)-null mice are distinguished from wild-type mice by elevated bile acid levels in the liver and serum. However, hepatic lithocholic acid (LCA) levels are lower in LCA-fed FXR-null female mice compared to those in wild-type female mice. Furthermore, FXR-null female mice are less susceptible to liver damage by LCA compared with female wild-type mice. Marked increases in hepattic LCA-sulfating activity and hepatic hydroxysteroid sulfotransferase and biliary sulfated bile acid levels are detected in FXR-null female mice, suggesting the protective role of hydroxysteroid sulfotransferase in LCA-induced liver damage. These and other studies indicate that mice null for drug-metabolizing enzymes and nuclear receptors are of great value in the study of the role of drug-metabolizing enzymes in pharmacologic and physiologic responses.