title: Potent inhibition of cytochrome P450 2B6 by sibutramine in human liver microsomes.
abstract: The present study was performed to evaluate the potency and specificity of sibutramine as an inhibitor of the activities of nine human CYP isoforms in liver microsomes. Using a cocktail assay, the effects of sibutramine on specific marker reactions of the nine CYP isoforms were measured in human liver microsomes. Sibutramine showed potent inhibition of CYP2B6-mediated bupropion 6-hydroxylation with an IC50 value of 1.61μM and Ki value of 0.466μM in a competitive manner at microsomal protein concentrations of 0.25mg/ml; this was 3.49-fold more potent than the typical CYP2B6 inhibitor thio-TEPA (Ki=1.59μM). In addition, sibutramine slightly inhibited CYP2C19 activity (Ki=16.6μM, noncompetitive inhibition) and CYP2D6 activity (Ki=15.7μM, noncompetitive inhibition). These observations indicated 35.6- and 33.7-fold decreases in inhibition potency, respectively, compared with that of CYP2B6 by sibutramine. However, no inhibition of CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6, or CYP2E1 activities was observed. In addition, the CYP2B6 inhibitory potential of sibutramine was enhanced at a lower microsomal protein concentration of 0.05mg/ml. After 30min preincubation of human liver microsomes with sibutramine in the presence of NADPH, no shift in IC50 was observed in terms of inhibition of the activities of the nine CYPs, suggesting that sibutramine is not a time-dependent inactivator. These observations suggest that sibutramine is a selective and potent inhibitor of CYP2B6 in vitro, whereas inhibition of other CYPs is substantially lower. These in vitro data support the use of sibutramine as a well-known inhibitor of CYP2B6 for routine screening of P450 reversible inhibition when human liver microsomes are used as the enzyme source.
authors.affiliation: College of Pharmacy, The Catholic University of Korea, Bucheon 420-743, Republic of Korea.
authors.forename: Soo Hyeon
authors.initials: SH
authors.lastname: Bae
authors.forename: Min Jo
authors.initials: MJ
authors.lastname: Kwon
authors.forename: Eu Jin
authors.initials: EJ
authors.lastname: Choi
authors.forename: Yu Fen
authors.initials: YF
authors.lastname: Zheng
authors.forename: Kee Dong
authors.initials: KD
authors.lastname: Yoon
authors.forename: Kwang-Hyeon
authors.initials: KH
authors.lastname: Liu
authors.forename: Soo Kyung
authors.initials: SK
authors.lastname: Bae
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors*; D003503:Cyclobutanes / Q000493:pharmacokinetics / Q000494:pharmacology*; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004353:Drug Evaluation, Preclinical; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors*; D013852:Thiotepa / Q000494:pharmacology
chemical_list: D003503:Cyclobutanes; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D013852:Thiotepa; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C045793:CYP2C19 protein, human; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D010089:Oxidoreductases, N-Demethylating; C058254:sibutramine
keywords: CYP; CYP2B6; Cocktail assay; Human liver microsomes; IC(50); K(i); LC–MS/MS; Potent inhibitor; Sibutramine; cytochrome P450; inhibition constant; liquid chromatography–tandem mass spectrometry; the 50% inhibitory concentration