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Human liver microsomal diazepam metabolism using cDNA-expressed cytochrome P450s: role of CYP2B6, 2C19 and the 3A subfamily. 1996

S Ono, and T Hatanaka, and S Miyazawa, and M Tsutsui, and T Aoyama, and F J Gonzalez, and T Satoh
Central Laboratory for Research and Development, Amersham K.K., Chiba, Japan.

1. We have examined the metabolism of diazepam by ten human cytochrome P450 forms (CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4 and 3A5) expressed in HepG2 cells using a recombinant vaccinia virus system. 2. Among the P450 forms tested, diazepam was significantly demethylated by CYP2B6, 2C9, 2C19, 3A4 and 3A5, with 2C19 exhibiting the highest rate at concentrations < 0.1 mM, and hydroxylated only by the latter three enzymes, with 3A5 being the most active. The N-demethylation activity of diazepam by 2C19 at a concentration of 20 microM was six times of that by 3A4. However, that by 2C9 was detected at only a trace level. 3. CYP2C19, 3A4 and 3A5 of the ten human P450s catalysed the 3-hydroxylation of nordiazepam, and 2B6, the 2C subfamily and the 3A subfamily catalysed the N-demethylation of temazepam. CYP3A4 exhibited the highest activity of nordiazepam 3-hydroxylation and temazepam N-demethylation. 4. Diazepam N-demethylation by human liver microsomes correlated with diazepam 3-hydroxylation, but not S-mephenytoin 4'-hydroxylation. 5. Our results suggest that in the human liver, the metabolism of diazepam to nordiazepam is mediated by CYP3A4, which has been reported as the most abundant P450 form in human liver as well as 2C19, which has been reported as a polymorphic enzyme.

UI MeSH Term Description Entries
D008862 Microsomes, Liver Closed vesicles of fragmented endoplasmic reticulum created when liver cells or tissue are disrupted by homogenization. They may be smooth or rough. Liver Microsomes,Liver Microsome,Microsome, Liver
D010089 Oxidoreductases, N-Demethylating N-Demethylase,N-Demethylases,Oxidoreductases, N Demethylating,Demethylating Oxidoreductases, N,N Demethylase,N Demethylases,N Demethylating Oxidoreductases,N-Demethylating Oxidoreductases
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
D003975 Diazepam A benzodiazepine with anticonvulsant, anxiolytic, sedative, muscle relaxant, and amnesic properties and a long duration of action. Its actions are mediated by enhancement of GAMMA-AMINOBUTYRIC ACID activity. 7-Chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one,Apaurin,Diazemuls,Faustan,Relanium,Seduxen,Sibazon,Stesolid,Valium
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
D001189 Aryl Hydrocarbon Hydroxylases A large group of cytochrome P-450 (heme-thiolate) monooxygenases that complex with NAD(P)H-FLAVIN OXIDOREDUCTASE in numerous mixed-function oxidations of aromatic compounds. They catalyze hydroxylation of a broad spectrum of substrates and are important in the metabolism of steroids, drugs, and toxins such as PHENOBARBITAL, carcinogens, and insecticides. Microsomal Monooxygenases,Xenobiotic Monooxygenases,Hydroxylases, Aryl Hydrocarbon,Monooxygenases, Microsomal,Monooxygenases, Xenobiotic
D014151 Anti-Anxiety Agents Agents that alleviate ANXIETY, tension, and ANXIETY DISORDERS, promote sedation, and have a calming effect without affecting clarity of consciousness or neurologic conditions. ADRENERGIC BETA-ANTAGONISTS are commonly used in the symptomatic treatment of anxiety but are not included here. Anti-Anxiety Agent,Anti-Anxiety Drug,Anxiolytic,Anxiolytic Agent,Anxiolytic Agents,Tranquilizing Agents, Minor,Anti-Anxiety Drugs,Anti-Anxiety Effect,Anti-Anxiety Effects,Antianxiety Effect,Antianxiety Effects,Anxiolytic Effect,Anxiolytic Effects,Anxiolytics,Tranquillizing Agents, Minor,Agent, Anti-Anxiety,Agent, Anxiolytic,Agents, Anti-Anxiety,Agents, Anxiolytic,Agents, Minor Tranquilizing,Agents, Minor Tranquillizing,Anti Anxiety Agent,Anti Anxiety Agents,Anti Anxiety Drug,Anti Anxiety Drugs,Anti Anxiety Effect,Anti Anxiety Effects,Drug, Anti-Anxiety,Drugs, Anti-Anxiety,Effect, Anti-Anxiety,Effect, Antianxiety,Effect, Anxiolytic,Effects, Anti-Anxiety,Effects, Antianxiety,Effects, Anxiolytic,Minor Tranquilizing Agents,Minor Tranquillizing Agents
D015153 Blotting, Western Identification of proteins or peptides that have been electrophoretically separated by blot transferring from the electrophoresis gel to strips of nitrocellulose paper, followed by labeling with antibody probes. Immunoblotting, Western,Western Blotting,Western Immunoblotting,Blot, Western,Immunoblot, Western,Western Blot,Western Immunoblot,Blots, Western,Blottings, Western,Immunoblots, Western,Immunoblottings, Western,Western Blots,Western Blottings,Western Immunoblots,Western Immunoblottings

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