Glucocorticoid-Responsive Hepatic Cytochromes P-450 in the Rat: Multiplicity and Differential Regulation

The multiplicity of glucocorticoid-responsive hepatic cytochromes P-450 in the rat was investigated by developing a series of monoclonal antibody probes directed against purified steroid-inducible isozymes from the rat (P-450p) and man (HLp). Two antibodies, termed 1G8 and 13-7-10, showed unique specificity for purified cytochromes P-450 upon immunoblot analyses. These antibodies were further characterized in terms of their reactivity toward proteins in liver microsomes from untreated and xenobiotic-treated rats. Three P-450p-related proteins were identified using 1G8 and 13-7-10 to monitor the expression of P-450p family subtypes. In untreated rats, members of this family exhibited sex-specific expression. Treatment with various chemicals resulted in differential induction of the 1G8- and 13-7-10-reactive proteins, demonstrating distinct regulatory features of these immunochemically-related proteins. While searching for novel inducers of the P-450p family, the imidazole antifungal drug clot rimazole was found to significantly increase total cytochrome P-450. Detailed studies were undertaken to investigate the mechanism by which clotrimazole and other antifungal drugs induce hepatic cytochrome P-450. The effect of treatment of rats with the antifungal drugs clotrimazole, miconazole, or ketoconazole on the expression of three distinct P-450 gene families (glucocorticoid-responsive P-450p, phenobarbital-responsive P-450b/e , and ethanol-responsive P-450j) was determinded by measuring: 1) microsomal enzymatic activities with marker substrates, 2) the microsomal content of immunoreactive cytochromes P-450 with specific antibodies, and 3) the amounts of liver RNA hybridizing to cloned P-450 cDNAs. These studies establish that P-450p is the predominant P-450 isozyme induced by clotrimazole, miconazole, and ketoconazole. Two of these drugs, clotrimazole and miconazole also induced P-450b/e , whereas ketoconazole induced P-450j. Differential increases in specific P-450 mRNAs and proteins resulted from treatment of rats with these imidazol e antifungal drugs, suggesting that multiple cellular events are involved t heir mechanism of P-450 induction. In conclusion, expression of the P-450p family of cytochromes P-450 in rat liver is under complex regulatory control and is subject to modulation by clinically useful drugs