Hepatic catecholestrogen synthases: differential effect of sex, inducers of cytochromes P-450 and of antibody to the glucocorticoid inducible cytochrome P-450 on NADPH-dependent estrogen-2-hydroxylase and on organic hydroperoxide-dependent estrogen-2/4-hydroxylase activity of rat hepatic microsomes.
Formation of catecholestrogens (CE) by rat hepatic microsomes was re-examined because as recently shown; (1) CE formation can be catalyzed by an NADPH-dependent estrogen-4-hydroxylase (E-4-H(NADPH)) and by a peroxidatic, organic hydroperoxide-dependent estrogen-2/4-hydroxylase (E-2/4-H(OHP)), in addition to the established NADPH-dependent estrogen 2-hydroxylase (E-2-H(NADPH)); and (2) the indirect radiometric and the COMT-coupled radioenzymatic assays, used in many previous studies, may fail to provide an accurate measure, in particular, of 4-OH-CE. Using a direct product isolation assay, hepatic microsomes of both male and female rats were shown to express E-2/4-H(OHP) activity with properties similar to those of peroxidatic activity in other tissues. The activities of E-2/4-H(OHP) and E-2-H(NADPH) were affected differently by 5 out of 7 inducers of cytochromes P-450 administered in vivo. Phenobarbital and dexamethasone caused a 4- and 2-3-fold increase in E-2-H(NADPH) activity, respectively, but only a 38 and 20% increase in E-2/4-H(OHP) activity. Ketoconazol and beta-naphtoflavone caused a modest increase in E-2-H(NADPH) activity but a decrease in OHP-dependent activity. Clofibrate decreased peroxidatic activity by 50% and NADPH-dependent activity by approximately 20%. Both activities were increased by ethanol but decreased by isoniazide, an agent which induces the same form of cytochromes P-450 as ethanol. Polyclonal antibody against P-450p, a form of P-450 induced by glucocorticoids, inhibited E-2-H(NADPH) but not E-2/4-H(OHP) activity of untreated and of dexamethasone- and phenobarbital-treated rats. This study establishes that CE formation may occur in liver via the peroxidatic pathway and indicates that this pathway depends on forms of P-450 different from those mediating E-2-H(NADPH) activity. It also confirms and extends previous observations of the involvement of multiple, constitutive and induced forms of cytochrome P-450 in NADPH-dependent 2-hydroxylation in liver.
Bui
Q D
QD
Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Weisz
J
J
Wrighton
S A
SA
D000818:Animals; D000906:Antibodies; D001571:Benzoflavones / Q000494:pharmacology*; D002994:Clofibrate / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D003907:Dexamethasone / Q000494:pharmacology*; D004790:Enzyme Induction; D004958:Estradiol / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000378:metabolism; D002393:Estrogens, Catechol / Q000096:biosynthesis*; D005260:Female; D007538:Isoniazid / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009249:NADP / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012737:Sex Factors; D019324:beta-Naphthoflavone
D000906:Antibodies; D001571:Benzoflavones; D002393:Estrogens, Catechol; D004958:Estradiol; D009249:NADP; D019324:beta-Naphthoflavone; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; C001390:2-hydroxyestradiol; C014036:4-hydroxyestradiol; D002994:Clofibrate; D007538:Isoniazid; D010634:Phenobarbital