Modulation of CYP2C9 activity and hydrogen peroxide production by cytochrome b5

Abstract Cytochromes P450 (CYP) play a major role in drug detoxification, and cytochrome b5 (cyt b5) stimulates the catalytic cycle of mono-oxygenation and detoxification reactions. Collateral reactions of this catalytic cycle can lead to a significant production of toxic reactive oxygen species (ROS). One of the most abundant CYP isoforms in the human liver is CYP2C9, which catalyzes the metabolic degradation of several drugs including nonsteroidal anti-inflammatory drugs. We studied modulation by microsomal membrane-bound and soluble cyt b5 of the hydroxylation of salicylic acid to gentisic acid and ROS release by CYP2C9 activity in human liver microsomes (HLMs) and by CYP2C9 baculosomes. CYP2C9 accounts for nearly 75% of salicylic acid hydroxylation in HLMs at concentrations reached after usual aspirin doses. The anti-cyt b5 antibody SC9513 largely inhibits the rate of salicylic acid hydroxylation by CYP2C9 in HLMs and CYP2C9 baculosomes, increasing the KM approximately threefold. Besides, soluble human recombinant cyt b5 stimulates the Vmax nearly twofold while it decreases nearly threefold the Km value in CYP2C9 baculosomes. Regarding NADPH-dependent ROS production, soluble recombinant cyt b5 is a potent inhibitor both in HLMs and in CYP2C9 baculosomes, with inhibition constants of 1.04 ± 0.25 and 0.53 ± 0.06 µM cyt b5, respectively. This study indicates that variability in cyt b5 might be a major factor underlying interindividual variability in the metabolism of CYP2C9 substrates.

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GLUCURONIDATION OF THE ASPIRIN METABOLITE SALICYLIC ACID BY EXPRESSED UDP-GLUCURONOSYLTRANSFERASES AND HUMAN LIVER MICROSOMES

Drug Metabolism and Disposition ◽

10.1124/dmd.105.005652 ◽

2005 ◽

Vol 34 (2) ◽

pp. 199-202 ◽

Cited By ~ 46

Author(s):

Gwendolyn E. Kuehl ◽

Jeannette Bigler ◽

John D. Potter ◽

Johanna W. Lampe

Keyword(s):

Salicylic Acid ◽

Human Liver ◽

Liver Microsomes ◽

Human Liver Microsomes

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Interindividual variation in the isomerization of 4- hydroxytamoxifen by human liver microsomes: involvement of cytochromes P450

Carcinogenesis ◽

10.1093/carcin/15.12.2733 ◽

1994 ◽

Vol 15 (12) ◽

pp. 2733-2738 ◽

Cited By ~ 29

Author(s):

M.L. Williams ◽

M. S. Lennard ◽

I. J. Martin ◽

G. T. Tucker

Keyword(s):

Human Liver ◽

Cytochromes P450 ◽

Liver Microsomes ◽

Human Liver Microsomes ◽

Interindividual Variation

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IN VITRO METABOLISM OF THE CALMODULIN ANTAGONIST DY-9760e (3-[2-[4-(3-CHLORO-2-METHYLPHENYL)-1-PIPERAZINYL]ETHYL]-5,6-DIMETHOXY-1-(4-IMIDAZOLYLMETHYL)-1H-INDAZOLE DIHYDROCHLORIDE 3.5 HYDRATE) BY HUMAN LIVER MICROSOMES: INVOLVEMENT OF CYTOCHROMES P450 IN ATYPICAL KINETICS AND POTENTIAL DRUG INTERACTIONS

Drug Metabolism and Disposition ◽

10.1124/dmd.105.004903 ◽

2005 ◽

Vol 33 (11) ◽

pp. 1628-1636 ◽

Cited By ~ 5

Author(s):

Shuko Tachibana ◽

Yuko Fujimaki ◽

Hiroyuki Yokoyama ◽

Osamu Okazaki ◽

Ken-ichi Sudo

Keyword(s):

Drug Interactions ◽

Human Liver ◽

Cytochromes P450 ◽

Liver Microsomes ◽

Human Liver Microsomes ◽

In Vitro Metabolism ◽

Potential Drug ◽

Calmodulin Antagonist

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Characterization of O-demethylations and Aromatic Hydroxylations Mediated by Cytochromes P450 in the Metabolism of Flavonoid Aglycons

Croatica Chemica Acta ◽

10.5562/cca3528 ◽

2019 ◽

Vol 92 (1) ◽

pp. 115-123 ◽

Cited By ~ 4

Author(s):

Goran Benković ◽

Hrvoje Rimac ◽

Željan Maleš ◽

Siniša Tomić ◽

Zoran Lončar ◽

...

Keyword(s):

Cytochrome P450 ◽

Human Liver ◽

Cytochromes P450 ◽

Liver Microsomes ◽

Cytochrome P450 Enzymes ◽

Uv Detector ◽

Aromatic Hydroxylation ◽

Metabolism Of Xenobiotics ◽

Kinetics Of

One of the most important groups of metabolic enzymes is cytochrome P450 superfamily. These enzymes are important in terms of the catalytic diversity and the large number of xenobiotics that are detoxified or activated by converting to reactive metabolites. Flavonoids are xenobiotics to which humans are exposed through diet. Data on their oxidative metabolism mediated by cytochromes P450 are limited. The aim of this study was to determine the enzymatic kinetics of O-demethylation and aromatic hydroxylation of flavonoid aglycons on recombinant cytochrome P450 enzymes and human liver microsomes systems. The study was performed on ten flavonoids, namely 3,7-dihydroxyflavone, 7-hydroxyflavone, acacetin, apigenin, flavone, galangin, kaempferol, naringenin, sakuranetin, and tangeretin using liquid chromatography coupled with mass spectrometry and UV detector. Most relevant enzyme involved in metabolism of flavonoid aglycons is CYP1A2, and its catalytic effectiveness ranges from 0.5 to 2.9 × 106 M–1 min–1. Having in mind high expression and involvement of CYP1A2 in metabolism of xenobiotics including drugs, and its intraindividual differences in expression and activity, potential of drug-flavonoid competitive interactions/inhibitions should be considered when consuming dietary supplement and foods rich in flavonoids.

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