Publications

• Characterization of the oxidative metabolites of 17beta-estradiol and estrone formed by 15 selectively expressed human cytochrome p450 isoforms.

  Lee A.J., Cai M.X., Thomas P.E., Conney A.H., Zhu B.T.

  We systematically characterized the oxidative metabolites of 17beta-estradiol and estrone formed by 15 human cytochrome P450 (CYP) isoforms. CYP1A1 had high activity for 17beta-estradiol 2-hydroxylation, followed by 15alpha-, 6alpha-, 4-, and 7alpha-hydroxylation. However, when estrone was the sub ... >> More

  We systematically characterized the oxidative metabolites of 17beta-estradiol and estrone formed by 15 human cytochrome P450 (CYP) isoforms. CYP1A1 had high activity for 17beta-estradiol 2-hydroxylation, followed by 15alpha-, 6alpha-, 4-, and 7alpha-hydroxylation. However, when estrone was the substrate, CYP1A1 formed more 4-hydroxyestrone than 15alpha- or 6alpha-hydroxyestrone, with 2-hydroxyestrone as the major metabolite. CYP1A2 had the highest activity for the 2-hydroxylation of both 17beta-estradiol and estrone, although it also had considerable activity for their 4-hydroxylation (9-13% of 2-hydroxylation). CYP1B1 mainly catalyzed the formation of catechol estrogens, with 4-hydroxyestrogens predominant. CYP2A6, 2B6, 2C8, 2C9, 2C19, and 2D6 each showed a varying degree of low catalytic activity for estrogen 2-hydroxylation, whereas CYP2C18 and CYP2E1 did not show any detectable estrogen-hydroxylating activity. CYP3A4 had strong activity for the formation of 2-hydroxyestradiol, followed by 4-hydroxyestradiol and an unknown polar metabolite, and small amounts of 16alpha- and 16beta-hydroxyestrogens were also formed. The ratio of 4-to 2-hydroxylation of 17beta-estradiol or estrone with CYP3A4 was 0.22 or 0.51, respectively. CYP3A5 had similar catalytic activity for the formation of 2- and 4- hydroxyestrogens. Notably, CYP3A5 had an unusually high ratio of 4-to 2-hydroxylation of 17beta-estradiol or estrone (0.53 or 1.26, respectively). CYP3A4 and 3A5 also catalyzed the formation of nonpolar estrogen metabolite peaks (chromatographically less polar than estrone). CYP3A7 had a distinct catalytic activity for the 16alpha-hydroxylation of estrone, but not 17beta-estradiol. CYP4A11 had little catalytic activity for the metabolism of 17beta-estradiol and estrone. In conclusion, many human CYP isoforms are involved in the oxidative metabolism of 17beta-estradiol and estrone, with a varying degree of catalytic activity and distinct regioselectivity. << Less

  Endocrinology 144:3382-3398(2003) [PubMed] [EuropePMC]

  This publication is cited by 12 other entries.

• Human cytochrome P450 3A7 has a distinct high catalytic activity for the 16alpha-hydroxylation of estrone but not 17beta-estradiol.

  Lee A.J., Conney A.H., Zhu B.T.

  Like catechol estrogens, 16alpha-hydroxylated estrogens are hormonally active, chemically reactive, and potentially mutagenic. We report here our novel findings that human CYP3A7 has a distinct high catalytic activity for the NADPH-dependent 16alpha-hydroxylation of estrone (E(1); at 10 nM to 200 ... >> More

  Like catechol estrogens, 16alpha-hydroxylated estrogens are hormonally active, chemically reactive, and potentially mutagenic. We report here our novel findings that human CYP3A7 has a distinct high catalytic activity for the NADPH-dependent 16alpha-hydroxylation of estrone (E(1); at 10 nM to 200 microM substrate concentrations) but not for the 16alpha-hydroxylation of 17beta-estradiol (E(2)). At a physiologically relevant low substrate concentration (10 nM), CYP3A7 had a strong catalytic activity for the 16alpha-hydroxylation of E(1), and the ratio of its 16alpha-hydroxylation to 2-hydroxylation was 107%. In addition to 16alpha-hydroxylation, CYP3A7 also had catalytic activity for the 2-, 4-, 6beta-, and 16beta-hydroxylation of E(1). However, when E(2) was the substrate, CYP3A7 had only very weak catalytic activity for its 16alpha-hydroxylation (<6% of E(1) 16alpha-hydroxylation), and the ratio of its 16alpha-hydroxylation to 2-hydroxylation was 10-33%. Enzyme kinetic analysis showed that the maximal velocity and substrate-binding affinity (1/K(m)) for CYP3A7-mediated 16alpha-hydroxylation of E(1) were both approximately 10 times higher than those for E(2), thereby giving the maximal velocity:K(m) ratio of >100 times higher for the 16alpha-hydroxylation of E(1) than for E(2). Given the recent findings that human CYP3A7 is a polymorphic isoform also expressed in adult liver and certain extrahepatic tissues (in addition to fetal tissues), our data raise the possibility that CYP3A7 may be an important catalyst for the local and/or systemic formation of the procarcinogenic 16alpha-hydroxyestrone in women. << Less

  Cancer Res. 63:6532-6536(2003) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.

• 17 beta-estradiol hydroxylation catalyzed by human cytochrome P450 1B1.

  Hayes C.L., Spink D.C., Spink B.C., Cao J.Q., Walker N.J., Sutter T.R.

  The 4-hydroxy metabolite of 17 beta-estradiol (E2) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbon-receptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of E2. This activity was associated with human P450 1B1. To de ... >> More

  The 4-hydroxy metabolite of 17 beta-estradiol (E2) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbon-receptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of E2. This activity was associated with human P450 1B1. To determine the relationship of the human P450 1B1 gene product and E2 4-hydroxylation, the protein was expressed in Saccharomyces cerevisiae. Microsomes from the transformed yeast catalyzed the 4- and 2-hydroxylation of E2 with Km values of 0.71 and 0.78 microM and turnover numbers of 1.39 and 0.27 nmol product min-1.nmol P450-1, respectively. Treatment of MCF-7 human breast cancer cells with the aryl hydrocarbon-receptor ligand indolo[3,2-b]carbazole resulted in a concentration-dependent increase in P450 1B1 and P450 1A1 mRNA levels, and caused increased rates of 2-, 4-, 6 alpha-, and 15 alpha-hydroxylation of E2. At an E2 concentration of 10 nM, the increased rates of 2- and 4-hydroxylation were approximately equal, emphasizing the significance of the low Km P450 1B1-component of E2 metabolism. These studies demonstrate that human P450 1B1 is a catalytically efficient E2 4-hydroxylase that is likely to participate in endocrine regulation and the toxicity of estrogens. << Less

  Proc Natl Acad Sci U S A 93:9776-9781(1996) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Role of human cytochrome P450 1A1, 1A2, 1B1, and 3A4 in the 2-, 4-, and 16alpha-hydroxylation of 17beta-estradiol.

  Badawi A.F., Cavalieri E.L., Rogan E.G.

  The steady-state kinetics and specific activity of 2-, 4-, and 16alpha-hydroxylation of 17beta-estradiol (E(2)) were evaluated for human cytochrome P450 (CYP) 1A1, 1A2, 1B1, and 3A4 enzymes, using complementary DNA-expressed CYP isoforms. CYP1A2 showed the highest 2-hydroxylation activity, followe ... >> More

  The steady-state kinetics and specific activity of 2-, 4-, and 16alpha-hydroxylation of 17beta-estradiol (E(2)) were evaluated for human cytochrome P450 (CYP) 1A1, 1A2, 1B1, and 3A4 enzymes, using complementary DNA-expressed CYP isoforms. CYP1A2 showed the highest 2-hydroxylation activity, followed by CYP1A1, 1B1, and 3A4. CYP1B1 had the highest 4-hydroxylation activity, followed by CYP1A2, 1A1, and 3A4. The 16alpha-hydroxylation reaction was catalyzed mainly by CYP1A2 and, to a similar, slightly lower extent, CYP3A4 and 1A1, with a lesser contribution by CYP1B1. The E(2) 2-, 4-, and 16alpha-hydroxylation activities of human liver microsomes were 1.3 +/- 0.3, 0.5 +/- 0.06, and 0.3 +/-0.05 nmol metabolite/min/nmol P450, respectively. The contribution of CYP1A1 and 1B1 (mainly extrahepatic) to the E(2) hydroxylation reactions, relative to CYP1A2 and 3A4 (predominantly hepatic), may be relevant to understanding the process of hormonal carcinogenesis both in liver and in extrahepatic tissues. << Less

  Metabolism 50:1001-1003(2001) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.