Gender differences in hepatic sex steroid and drug metabolism result from hormonal regulation of specific cytochrome P450 genes (CYP). In male rats, bile duct ligation (BDL) is associated with down-regulation of the male-specific genes, CYP2C11 and CYP3A2, together with a decrease in serum testosterone levels and a two-to threefold increase in serum estradiol concentrations. We anticipated that if estrogen is responsible for down-regulation of male-specific CYPs in BDL male rats, the female-specific CYP2C12, which is not normally present in adult male rat liver, should be up-regulated. We examined this proposal by determining the profile of hepatic cytochrome P450 enzymes in female rats subjected to BDL, and by seeking evidence for expression of CYP2C12 in male rats that do not normally express this gene. In female rats killed 5 days after BDL, total cytochrome P450 content and NADPH-cytochrome P450-reductase (P450-reductase) were decreased to 74% and 58% of control, respectively. Microsomal enzyme activities attributable to CYP2A1, CYP2C6, and CYP2E1 were 50% to 60% of control, but ethylmorphine Ndemethylase, which in female liver is catalyzed by CYP2C12 and to a lesser extent CYP2C6, was significantly less affected (81% of control). Likewise, levels of CYP2C6 and P450-reductase proteins were decreased in proportion to the corresponding enzyme activities (50% to 60%), while CYP2C12 protein (and mRNA levels) were not altered in BDL female rat liver. In sham-operated male rats, transcripts for CYP2C12 were rarely detected, but mRNA levels rose to appreciable levels within 24 hours of BDL, and CYP2C12 protein was expressed in hepatic microsomes of BDL male rats. Administration of estradiol to male rats produced a similar elevation of CYP2C12 mRNA, to values Ο·40% of female rats. It is concluded that CYP2C12 is up-regulated in male rats with cholestasis caused by BDL, while CYP2C12 protein is preserved in female rats when other microsomal proteins are decreased. These changes may be related to the increase in serum estradiol levels that result from altered hepatic steroid metabolism. The results demonstrate that activities of individual drug-metabolizing enzymes in liver disease can be determined by dysregulation of the constitutive expression of hepatic CYP genes. (HEPATOLOGY 1998;28:624-630.)
Hepatic cytochrome P450 (P450) proteins play an important role in the biotransformation of many foreign compounds and physiological substrates, including drugs, procarcinogens, bile acids, and steroid hormones. The broad range of substrate specificities is explained by the existence of multiple genes (CYPs) for the cytochromes P450, each of which encodes an individual protein that catalyzes a relatively specific range of enzyme reactions. In rat liver, for instance, the activities of several P450s are indicated by the regio-and stereo-specific hydroxylation of C19-steroid hormones, including testosterone and progesterone. [1][2][3][4][5][6] Rats exhibit striking sex differences in hepatic drug and steroid metabolism, and this is accounted for by sexually dimorphic expression of several CYPs. In male rat liver, CYP2C11 and CYP3A2 are the predominant forms of P450; both are absent in female rat liver microsomes. 7 Conversely, CYP2C12 is the major form in female rat liver, but is not expressed at the mRNA level in male rat liver. 7-10 CYP2C11 and CYP2C12 are regulated by different serum profiles of sex steroids and growth hormone. Thus, CYP2C11 is expressed developmentally because of hypothalamic imprinting by androgen during the neonatal period, 8-10 and hepatic levels are maintained in the adult male rat by circulating androgen through the highly pulsatile male pattern of pituitary growth hormone secretion. 10 Expression of CYP2C12 in female rats requires continuous secretion of growth hormone into the circulation, 10,11 a pattern that is stimulated by estrogens. 12 In patients with liver disease, drug and steroid oxidation may be impaired because of altered levels of hepatic microsomal P450. [13][14][15] In experimental cholestasis produced by bile duct ligation (BDL) in male rats, hepatic levels of total P450 are also reduced. [16][17][18] There have been conflicting explanations for the mechanism for this effect. Thus, Hutterer et al. 16 proposed that destruction of P450 caused by the detergent effects of bile acids was the major factor, but Mackinnon et al. 17 observed that synthesis of microsomal proteins was decreased in experimental cholestasis. In recent studies from this laboratory, 18 we noted a generalized lowering of all P450s, such as CYP2C6 and CYP2E1, but a disproportionate lowering of the male sex-specific proteins, CYP2C11 and CYP3A2, in livers of male rats with BDL; the reduction of the Abbreviations: CYP, cytochrome P450; BDL, bile duct ligation; P450-reductase, NADPH-cytochrome P450 reductase.