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Human cytochrome P450 enzymes of importance for the bioactivation of methyleugenol to the proximate carcinogen 1′-hydroxymethyleugenol

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Author: Jeurissen, S.M.F. · Bogaards, J.J.P. · Boersma, M.G. · Horst, J.P.F. ter · Awad, H.M. · Fiamegos, Y.C. · Beek, T.A. van · Alink, G.M. · Sudhölter, E.J.R. · Cnubben, N.H.P. · Rietjens, I.M.C.M.
Type:article
Date:2006
Institution: TNO Kwaliteit van Leven
Source:Chemical Research in Toxicology, 1, 19, 111-116
Identifier: 239068
doi: doi:10.1021/tx050267h
Keywords: Biology · Biomedical Research · 1' hydroxymethyleugenol · barbituric acid derivative · carcinogen · cytochrome P450 · cytochrome P450 1A2 · cytochrome P450 2A6 · cytochrome P450 2C19 · cytochrome P450 2C9 · cytochrome P450 2D6 · methyleugenol · unclassified drug · article · carcinogenicity · concentration (parameters) · enzyme activation · enzyme kinetics · enzyme specificity · enzyme substrate · human · hydroxylation · incubation time · insect cell · lifestyle · liver microsome · nonhuman · sensitivity analysis · smoking · Aryl Hydrocarbon Hydroxylases · Benzoflavones · Biotransformation · Carcinogens · Cell Line · Cytochrome P-450 CYP1A2 · Cytochrome P-450 Enzyme System · Enzyme Inhibitors · Eugenol · Flavoring Agents · Humans · Kinetics · Microsomes, Liver · Mixed Function Oxygenases · Recombinant Proteins · Risk Assessment · Sulfaphenazole · Insecta

Abstract

In vitro studies were performed to elucidate the human cytochrome P450 enzymes involved in the bioactivation of methyleugenol to its proximate carcinogen 1′-hydroxymethyleugenol. Incubations with Supersomes, expressing individual P450 enzymes to a high level, revealed that P450 1A2, 2A6, 2C9, 2C19, and 2D6 are intrinsically able to 1′-hydroxylate methyleugenol. An additional experiment with Gentest microsomes, expressing the same individual enzymes to roughly average liver levels, indicated that P450 1A2, 2C9, 2C19, and 2D6 contribute to methyleugenol 1′-hydroxylation in the human liver. A study, in which correlations between methyleugenol 1′-hydroxylation in human liver microsomes from 15 individuals and the conversion of enzyme specific substrates by the same microsomes were investigated, showed that P450 1A2 and P450 2C9 are important enzymes in the bioactivation of methyleugenol. This was confirmed in an inhibition study in which pooled human liver microsomes were incubated with methyleugenol in the presence and absence of enzyme specific inhibitors. Kinetic studies revealed that at physiologically relevant concentrations of methyleugenol P450 1A2 is the most important enzyme for bioactivation of methyleugenol in the human liver showing an enzyme efficiency (kcat/Km) that is ∼30, 50, and >50 times higher than the enzyme efficiencies of, respectively, P450 2C9, 2C19, and 2D6. Only when relatively higher methyleugenol concentrations are present P450 2C9 and P450 2C19 might contribute as well to the bioactivation of methyleugenol in the human liver. A 5-fold difference in activities was found between the 15 human liver microsomes of the correlation study (range, 0.89-4.30 nmol min-1 nmol P450-1). Therefore, interindividual differences might cause variation in sensitivity toward methyleugenol. Especially lifestyle factors such as smoking (induces P450 1A) and the use of barbiturates (induces P450 2C) can increase the susceptibility for adverse effects of methyleugenol. © 2006 American Chemical Society.