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Role of human hepatic cytochrome P450 1A2 and 3A4 in the metabolic activation of estrone. 1997

M Shou, and K R Korzekwa, and E N Brooks, and K W Krausz, and F J Gonzalez, and H V Gelboin
Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.

The metabolic activation of estrone (E1), a potent estrogen was investigated using recombinant human cytochrome P450 enzymes, 1A2, 2B6, 2C8, 2C9, 2C9R144C, 2E1, 3A4, 3A5 and liver microsomes from 14 human organ donors. At least five products of E1 were detected and quantitated by HPLC and gas chromatography-mass spectrometry (GC-MS). Among these metabolites, 16alpha-OH-E1, 2-OH-E1 and 4-OH-E1, which are believed to be associated with estrogen carcinogenesis in animals, were definitively identified. Of all P450s examined, 1A2 and 3A4 exhibited the highest activities with turnovers of 3.4 and 2.5 nmol/min/nmol P450 for the total metabolism of E1, respectively, while 3A5, 2C9 and 2C9R144C showed moderate activities. 2B6, 2E1 and 2C8 did not produce any significant amount of products. 1A2 formed almost exclusively the 2-OH-E1 at a rate of 3.3 nmol/min/nmol but 3A4 preferentially formed the metabolite X1 (an unknown hydroxylation product) and 16alpha-OH-E1. Kinetic characterization showed that the Km values of 1A2, 3A4 and 3A5 were 14, 95 and 64 microM and Vmax were 5.43, 0.68 and 0.35 min(-1), respectively. All human liver microsomes were capable of metabolizing estrone and a 4-fold variation was seen between individuals. The relative amount of metabolites formed was generally 2-OH-E1 > metabolite X1 > 4-OH-E1 > 16alpha-OH-E1 > metabolite X2. 3A4/5 enzyme complex was assessed by inhibitory monoclonal antibody specific for 3A4/5 to contribute 60-88% to the formation of individual metabolites in human liver except for 2-OH-E1 (3%). The formation of 2-OH-E1 and 16alpha-OH-E1 by 14 human liver microsomes was significantly correlated with caffeine 3-demethylation supported by 1A2 (r2 = 0.87) and with testosterone 6beta-hydroxylation by 3A4 (r2 = 0.66), respectively. Thus the metabolic patterns exhibited by human liver are likely due to the combined activities of the P450 1A2 and 3A4 enzymes.

UI MeSH Term Description Entries
D008297 Male Males
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D002851 Chromatography, High Pressure Liquid Liquid chromatographic techniques which feature high inlet pressures, high sensitivity, and high speed. Chromatography, High Performance Liquid,Chromatography, High Speed Liquid,Chromatography, Liquid, High Pressure,HPLC,High Performance Liquid Chromatography,High-Performance Liquid Chromatography,UPLC,Ultra Performance Liquid Chromatography,Chromatography, High-Performance Liquid,High-Performance Liquid Chromatographies,Liquid Chromatography, High-Performance
D003577 Cytochrome P-450 Enzyme System A superfamily of hundreds of closely related HEMEPROTEINS found throughout the phylogenetic spectrum, from animals, plants, fungi, to bacteria. They include numerous complex monooxygenases (MIXED FUNCTION OXYGENASES). In animals, these P-450 enzymes serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids; (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs (BIOTRANSFORMATION). They are classified, according to their sequence similarities rather than functions, into CYP gene families (>40% homology) and subfamilies (>59% homology). For example, enzymes from the CYP1, CYP2, and CYP3 gene families are responsible for most drug metabolism. Cytochrome P-450,Cytochrome P-450 Enzyme,Cytochrome P-450-Dependent Monooxygenase,P-450 Enzyme,P450 Enzyme,CYP450 Family,CYP450 Superfamily,Cytochrome P-450 Enzymes,Cytochrome P-450 Families,Cytochrome P-450 Monooxygenase,Cytochrome P-450 Oxygenase,Cytochrome P-450 Superfamily,Cytochrome P450,Cytochrome P450 Superfamily,Cytochrome p450 Families,P-450 Enzymes,P450 Enzymes,Cytochrome P 450,Cytochrome P 450 Dependent Monooxygenase,Cytochrome P 450 Enzyme,Cytochrome P 450 Enzyme System,Cytochrome P 450 Enzymes,Cytochrome P 450 Families,Cytochrome P 450 Monooxygenase,Cytochrome P 450 Oxygenase,Cytochrome P 450 Superfamily,Enzyme, Cytochrome P-450,Enzyme, P-450,Enzyme, P450,Enzymes, Cytochrome P-450,Enzymes, P-450,Enzymes, P450,Monooxygenase, Cytochrome P-450,Monooxygenase, Cytochrome P-450-Dependent,P 450 Enzyme,P 450 Enzymes,P-450 Enzyme, Cytochrome,P-450 Enzymes, Cytochrome,Superfamily, CYP450,Superfamily, Cytochrome P-450,Superfamily, Cytochrome P450
D004970 Estrone An aromatized C18 steroid with a 3-hydroxyl group and a 17-ketone, a major mammalian estrogen. It is converted from ANDROSTENEDIONE directly, or from TESTOSTERONE via ESTRADIOL. In humans, it is produced primarily by the cyclic ovaries, PLACENTA, and the ADIPOSE TISSUE of men and postmenopausal women. Folliculin (Hormone),Estrone, (+-)-Isomer,Estrone, (8 alpha)-Isomer,Estrone, (9 beta)-Isomer,Estrovarin,Kestrone,Unigen,Wehgen
D005260 Female Females
D005822 Genetic Vectors DNA molecules capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. Many are derived from PLASMIDS; BACTERIOPHAGES; or VIRUSES. They are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain GENETIC MARKERS to facilitate their selective recognition. Cloning Vectors,Shuttle Vectors,Vectors, Genetic,Cloning Vector,Genetic Vector,Shuttle Vector,Vector, Cloning,Vector, Genetic,Vector, Shuttle,Vectors, Cloning,Vectors, Shuttle
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D006899 Mixed Function Oxygenases Widely distributed enzymes that carry out oxidation-reduction reactions in which one atom of the oxygen molecule is incorporated into the organic substrate; the other oxygen atom is reduced and combined with hydrogen ions to form water. They are also known as monooxygenases or hydroxylases. These reactions require two substrates as reductants for each of the two oxygen atoms. There are different classes of monooxygenases depending on the type of hydrogen-providing cosubstrate (COENZYMES) required in the mixed-function oxidation. Hydroxylase,Hydroxylases,Mixed Function Oxidase,Mixed Function Oxygenase,Monooxygenase,Monooxygenases,Mixed Function Oxidases,Function Oxidase, Mixed,Function Oxygenase, Mixed,Oxidase, Mixed Function,Oxidases, Mixed Function,Oxygenase, Mixed Function,Oxygenases, Mixed Function
D000328 Adult A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available. Adults

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