Regioselective progesterone hydroxylation catalyzed by eleven rat hepatic cytochrome P-450 isozymes

Abstract

Quantitative high-pressure liquid chromatographic assays were developed that separate progesterone and 17 authentic monohydroxylated derivatives. The assays were utilized to investigate the hydroxylation of progesterone by 11 purified rat hepatic cytochrome P-450 isozymes and 8 different rat hepatic microsomal preparations. In a reconstituted system, progesterone was most efficiently metabolized by cytochrome P-450h followed by P-450g and P-450b. Seven different monohydroxylated progesterone metabolites were identified. 16 alpha-Hydroxyprogesterone, formed by 8 of the 11 isozymes, was the only detectable metabolite formed by cytochromes P-450b and P-450e. 2 alpha-Hydroxyprogesterone was formed almost exclusively by cytochrome P-450h, and 6 alpha-hydroxyprogesterone and 7 alpha-hydroxyprogesterone were only formed by P-450a. 6 beta-hydroxylation of progesterone was catalyzed by four isozymes with cytochrome P-450g being the most efficient, and 15 alpha-hydroxyprogesterone was formed as a minor metabolite by cytochromes P-450g, P-450h, and P-450i. None of the isozymes catalyzed 17 alpha-hydroxylation of progesterone, and only cytochrome P-450k had detectable 21-hydroxylase activity. 16 alpha-Hydroxylation catalyzed by cytochrome P-450b was inhibited in the presence of dilauroylphosphatidylcholine (1.6-80 microM), while this phospholipid either stimulated (up to 3-fold) or had no effect on the metabolism of progesterone by the other purified isozymes. Results of microsomal metabolism in conjunction with antibody inhibition experiments indicated that cytochromes P-450a and P-450h were the sole 7 alpha- and 2 alpha-hydroxylases, respectively, and that P-450k or an immunochemically related isozyme contributed greater than 80% of the 21-hydroxylase activity observed in microsomes from phenobarbital-induced rats.

Gender-specific induction of cytochrome P450s in nonylphenol-treated FVB/NJ mice

“…2,3, Table 5). Steroid 6α-hydroxylase activity is attributed to CYP2A1 in rats (Swinney et al, 1987), but Cyp2a is only a putative 6α-hydroxylase in mice to our knowledge (Baldwin and LeBlanc, 1992).…”

Pharmacokinetics and Disposition of the Kavalactone Kawain: Interaction With Kava Extract and Kavalactones in Vivo and in Vitro

“…2␣-, 6␤-, and 16␤-Testosterone hydroxylase activities, markers of CYP2C11, 3A1/2, and 2B1 activities, respectively, were determined by the method of Wood et al (1983). Progesterone 21-hydroxylase activity, a marker for the activity of CYP2C6, was determined by the method of Swinney et al (1987). P-glycoprotein ATPase Assay.…”

Role of the aromatic hydrocarbon receptor in the suppression of cytochrome P-450 2C11 by polycyclic aromatic hydrocarbons

“…Levels of CYPZC11 are undetectable in female rats at any age but increase dramatically at maturation in male rats (Ryan and Levin, 1993). It is the predorninant constlutive hepatic microsomal CYP in untreated male rats catalyzing steroid 16a-and Pa-hydroxylation (Swinney et al, 1987). CYP2Cl1 appears to be important in the metabolism of endogenous steroid hormones and the bioactivation of procarcinogens (Waxman, 1988;Butler et al.…”