In vitro model of mammary estrogen metabolism: structural and kinetic differences between catechol estrogens 2- and 4-hydroxyestradiol.

Dawling S, Hachey DL, Roodi N, Parl FF
Chem Res Toxicol. 2004 17 (9): 1258-64

PMID: 15377160 · DOI:10.1021/tx0498657

Estrogens and their oxidative metabolites, the catechol estrogens, have been implicated in the development of breast cancer; yet, relatively little is known about estrogen metabolism in the breast. To determine how the parent hormone, 17 beta-estradiol (E(2)), is metabolized, we used recombinant, purified phase I enzymes, cytochrome P450 (CYP) 1A1 and 1B1, with the phase II enzymes catechol-O-methyltransferase (COMT) and glutathione S-transferase P1 (GSTP1), all of which are expressed in breast tissue. We employed both gas and liquid chromatography with mass spectrometry to measure E(2), the catechol estrogens 2-hydroxyestradiol (2-OHE(2)) and 4-hydroxyestradiol (4-OHE(2)), as well as methoxyestrogens and estrogen-GSH conjugates. The oxidation of E(2) to 2-OHE(2) and 4-OHE(2) was exclusively regulated by CYP1A1 and 1B1, regardless of the presence or concentration of COMT and GSTP1. COMT generated two products, 2-methoxyestradiol and 2-hydroxy-3-methoxyestradiol, from 2-OHE(2) but only one product, 4-methoxyestradiol, from 4-OHE(2). Similarly, GSTP1 yielded two conjugates, 2-OHE(2)-1-SG and 2-OHE(2)-4-SG, from the corresponding quinone 2-hydroxyestradiol-quinone and one conjugate, 4-OHE(2)-2-SG, from 4-hydroxyestradiol-quinone. Using the experimental data, we developed a multicompartment kinetic model for the oxidative metabolism of the parent hormone E(2), which revealed significant differences in rate constants for its C-2 and C-4 metabolites. The results demonstrated a tightly regulated interaction of phase I and phase II enzymes, in which the latter decreased the concentration of catechol estrogens and estrogen quinones, thereby reducing the potential of these oxidative estrogen metabolites to induce DNA damage.

MeSH Terms (19)

Animals Aryl Hydrocarbon Hydroxylases Catechol O-Methyltransferase Cytochrome P-450 CYP1A1 Cytochrome P-450 CYP1B1 Estradiol Estrogens, Catechol Glutathione S-Transferase pi Glutathione Transferase Humans Isoenzymes Kinetics Mammary Glands, Animal Mammary Glands, Human Models, Chemical Models, Molecular Oxidation-Reduction Recombinant Proteins Structure-Activity Relationship

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