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Updated: Jul 24, 2026

Methods to Evaluate Cytotoxicity and Immunosuppression of Combustible Tobacco Product Preparations
Published on: January 11, 2015
Isoflavones inhibit nicotine C-oxidation catalyzed by human CYP2A6
Miki Nakajima1, Masahiro Itoh, Hiroyuki Yamanaka
1Drug Metabolism and Toxicology, Division of Pharmaceutical Sciences, Graduate School of Medical Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. nmiki@kenroku.kanazawa-u.ac.jp
Abstract:
The inhibitory effects of isoflavones (daidzein, genistein, and glycitein) on human cytochrome P450 (CYP) 2A6 activities were investigated. Daidzein, genistein, and glycitein uncompetitively inhibited nicotine C-oxidation catalyzed by recombinant CYP2A6 expressed in baculovirus-infected insect cells with Ki values of 1.3 +/- 0.3 microM, 0.7 +/- 0.2 microM, and 5.2 +/- 0.8 microM, respectively, but not coumarin 7-hydroxylation. Effects of the intake of soy isoflavones on in vivo nicotine metabolism were investigated with 7 healthy Japanese homozygotes of CYP2A6*1. The cotinine/nicotine ratio of the plasma concentrations 2 hours after chewing 1 piece of nicotine gum under the basal condition (after abstaining from soy foods for 1 week) was 8.8 +/- 2.6 (4.4-11.4). The ratio was significantly (P < .05) reduced to 6.7 +/- 1.6 (4.0-8.2) after consumption of a soy isoflavone supplement (60 mg of total isoflavones/d) for 5 days. The authors found that isoflavone contained in soy products significantly decreased nicotine metabolism.
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