title: Mechanism-based inactivation of cytochrome P450 2B6 by isoimperatorin.
abstract: Isoimperatorin (IIMP), a 6,7-furanocoumarin derivative, occurs in many common medicinal herbs. Human exposure to IIMP mainly results from intake of fruits, foods and medicinal herbs. We examined the irreversible inhibitory effect of IIMP on cytochrome P450 2B6. IIMP was found to cause time-dependent inhibition of CYP2B6. In addition, the loss of CYP2B6 activity occurred in a NAPDH- and concentration-dependent manner. About 60% of activity of CYP2B6 was suppressed after its incubation with IIMP at 25 μM for 9 min. Enzyme kinetic studies were performed, kinact for IIMP was found to be 0.071 min(-1), and KI was 17.1 μM, respectively. Glutathione and catalase/superoxide dismutase showed little protective effects on CYP2B6 against the inactivation by IIMP. S-Mephenytoin, a substrate of CYP2B6, mildly prevented the enzyme from the inactivation induced by IIMP. The estimated partition ratio of the inactivation was approximately 211. Additionally, a γ-ketoenal intermediate was identified in microsomal incubations with IIMP. CYPs 2B6, 2D6, and 1A2 were the major enzymes responsible for the metabolic activation of IIMP. In conclusion, IIMP is a mechanism-based inactivator of CYP2B6. The formation of γ-ketoenal intermediate may be responsible for the enzyme inactivation.
authors.affiliation: School of Pharmacy, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, PR China.
authors.forename: Jiaojiao
authors.initials: J
authors.lastname: Cao
authors.affiliation: School of Pharmacy, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, PR China.
authors.forename: Liwei
authors.initials: L
authors.lastname: Zheng
authors.affiliation: School of Pharmacy, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, PR China.
authors.forename: Lin
authors.initials: L
authors.lastname: Ji
authors.affiliation: School of Pharmacy, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, PR China.
authors.forename: Dan
authors.initials: D
authors.lastname: Lu
authors.affiliation: School of Pharmacy, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, PR China. Electronic address: yingpeng1999@163.com.
authors.forename: Ying
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Key Laboratory of Structure-Based Drug Design & Discovery of Ministry of Education, Shenyang Pharmaceutical University, Shenyang, Liaoning 110016, PR China; Center for Developmental Therapeutics, Seattle Children's Research Institute, Division of Gastroenterology and Hepatology, Department of Pediatrics, University of Washington School of Medicine, Seattle, WA 98101, United States. Electronic address: jiang.zheng@seattlechildrens.org.
authors.forename: Jiang
authors.initials: J
authors.lastname: Zheng
mesh_terms: D002374:Catalase / Q000378:metabolism; D065702:Cytochrome P-450 CYP2B6 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D011564:Furocoumarins / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology; D006801:Humans; D009249:NADP / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013997:Time Factors
chemical_list: D011564:Furocoumarins; C055542:isoimperatorin; D009249:NADP; D002374:Catalase; D065702:Cytochrome P-450 CYP2B6; D013482:Superoxide Dismutase; D005978:Glutathione
keywords: Cytochrome P450 2B6; Isoimperatorin; Mechanism-based inactivator; Reactive metabolite