title: Cytochrome P450 2C8 and flavin-containing monooxygenases are involved in the metabolism of tazarotenic acid in humans.
abstract: Upon oral administration, tazarotene is rapidly converted to tazarotenic acid by esterases. The main circulating agent, tazarotenic acid is subsequently oxidized to the inactive sulfoxide metabolite. Therefore, alterations in the metabolic clearance of tazarotenic acid may have significant effects on its systemic exposure. The objective of this study was to identify the human liver microsomal enzymes responsible for the in vitro metabolism of tazarotenic acid. Tazarotenic acid was incubated with 1 mg/ml pooled human liver microsomes, in 100 mM potassium phosphate buffer (pH 7.4), at 37 degrees C, over a period of 30 min. The microsomal enzymes that may be involved in tazarotenic acid metabolism were identified through incubation with microsomes containing cDNA-expressed human microsomal isozymes. Chemical inhibition studies were then conducted to confirm the identity of the enzymes potentially involved in tazarotenic acid metabolism. Reversed-phase high performance liquid chromatography was used to quantify the sulfoxide metabolite, the major metabolite of tazarotenic acid. Upon incubation of tazarotenic acid with microsomes expressing CYP2C8, flavin-containing monooxygenase 1 (FMO1), or FMO3, marked formation of the sulfoxide metabolite was observed. The involvement of these isozymes in tazarotenic acid metabolism was further confirmed by inhibition of metabolite formation in pooled human liver microsomes by specific inhibitors of CYP2C8 or FMO. In conclusion, the in vitro metabolism of tazarotenic acid to its sulfoxide metabolite in human liver microsomes is mediated by CYP2C8 and FMO.
authors.affiliation: Allergan Inc., Department of Pharmacokinetics and Drug Metabolism, 2525 DuPont Drive, Irvine, CA 92612, USA. Attar_Mayssa@Allergan.com
authors.forename: Mayssa
authors.initials: M
authors.lastname: Attar
authors.forename: Dahai
authors.initials: D
authors.lastname: Dong
authors.forename: Kah-Hiing John
authors.initials: KH
authors.lastname: Ling
authors.forename: Diane D-S
authors.initials: DD
authors.lastname: Tang-Liu
mesh_terms: D020533:Angiogenesis Inhibitors / Q000378:metabolism; D013956:Antithyroid Agents / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation / Q000379:methods; D065727:Cytochrome P-450 CYP2C8; D004305:Dose-Response Relationship, Drug; D006801:Humans; D066298:In Vitro Techniques; D020128:Inhibitory Concentration 50; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods; D008713:Methimazole / Q000378:metabolism; D008862:Microsomes, Liver; D009539:Nicotinic Acids / Q000737:chemistry / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism*; D017239:Paclitaxel / Q000378:metabolism; D012451:Safrole / Q000031:analogs & derivatives* / Q000378:metabolism; D013723:Teratogens / Q000737:chemistry / Q000378:metabolism*; D012176:Retinoids
chemical_list: D020533:Angiogenesis Inhibitors; D013956:Antithyroid Agents; D001189:Aryl Hydrocarbon Hydroxylases; D065727:Cytochrome P-450 CYP2C8; D008713:Methimazole; D009539:Nicotinic Acids; D010105:Oxygenases; D017239:Paclitaxel; D012451:Safrole; D013723:Teratogens; C086827:tazarotene; D012176:Retinoids; C020066:dimethylaniline monooxygenase (N-oxide forming); C450259:CYP2C8 protein, human; C005746:sulfoxide