title: Benzydamine N-oxygenation as an index for flavin-containing monooxygenase activity and benzydamine N-demethylation by cytochrome P450 enzymes in liver microsomes from rats, dogs, monkeys, and humans.
abstract: Benzydamine is an anti-inflammatory drug that undergoes flavin-containing monooxygenase (FMO)-dependent metabolism to benzydamine N-oxide; however, benzydamine N-demethylation is also catalyzed by liver microsomes. In this study, benzydamine N-oxygenation and N-demethylation mediated by liver microsomes from rats, dogs, monkeys, and humans were characterized comprehensively. Values of the maximum velocity/Michaelis constant ratio for benzydamine N-oxygenation by liver microsomes from dogs and rats were higher than those from monkeys and humans, despite roughly similar rates of N-demethylation in the four species. Benzydamine N-oxygenation by liver microsomes was extensively suppressed by preheating liver microsomes at 45 °C for 5 min or at 37 °C for 5-10 min without NADPH, and benzydamine N-demethylation was strongly inhibited by 1-aminbobenztriazole. Liver microsomal benzydamine N-oxygenation was inhibited by dimethyl sulfoxide and methimazole, whereas N-demethylation was inhibited by quinidine. High benzydamine N-oxygenation activities of recombinant human FMO1 and FMO3 and human kidney microsomes were observed at pH 8.4, whereas N-demethylation by cytochrome P450 2D6 was faster at pH 7.4. These results suggest that benzydamine N-oxygenation and N-demethylation are mediated by FMO1/3 and P450s, respectively, and that the contribution of FMO to metabolic eliminations of new drug candidates might be underestimated under certain experimental conditions suitable for P450 enzymes.
authors.affiliation: DMPK Research Laboratories, Research Division, Mitsubishi Tanabe Pharma Corporation, Toda, Saitama, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Taniguchi-Takizawa
authors.affiliation: Laboratory of DMPK, Showa Pharmaceutical University, 3-3165 Higashi-tamagawa Gakuen, Machida, Tokyo 194-8543, Japan.
authors.forename: Makiko
authors.initials: M
authors.lastname: Shimizu
authors.affiliation: DMPK Research Laboratories, Research Division, Mitsubishi Tanabe Pharma Corporation, Toda, Saitama, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kume
authors.affiliation: Laboratory of DMPK, Showa Pharmaceutical University, 3-3165 Higashi-tamagawa Gakuen, Machida, Tokyo 194-8543, Japan. Electronic address: hyamazak@ac.shoyaku.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamazaki
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000378:metabolism*; D001591:Benzydamine / Q000031:analogs & derivatives* / Q000378:metabolism; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004285:Dogs; D006801:Humans; D066298:In Vitro Techniques; D008252:Macaca fascicularis; D008297:Male; D008745:Methylation; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins; D013045:Species Specificity
chemical_list: D000893:Anti-Inflammatory Agents; D011994:Recombinant Proteins; C048872:benzydamine N-oxide; D001591:Benzydamine; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming)
keywords: CYP2D6; FMO1; FMO3; NADPH; Preheating of liver microsomes