Journal of Clinical Toxicology
Open Access
ISSN: 2161-0495
+44 1478 350008
ISSN: 2161-0495
+44 1478 350008
Yu Fen Zheng, Doyun Kim and Soo Kyung Bae
Catholic University of Korea, Bucheon, Republic of Korea
Posters & Accepted Abstracts: J Clin Toxicol
Objective: The aim of this study was to investigate the enantioselective differences of sibutramine enantiomers in the inhibition of human CYP enzymes in vitro Methods: Using a cocktail assay, the effects of sibutramine enantiomers (R/S- form) and 4-(4-chlorobenzyl) pyridine (CBP) on the 9 CYP isoform specific marker reactions were screened in human liver microsomes. According to USFDA guidelines, phenacetin (50 �¼M), coumarin (5 �¼M), bupropion (50 �¼M), rosiglitazone (1 �¼M), tolbutamide (100 �¼M), omeprazole (20 �¼M), dextrophan (5 �¼M), chlorzoxazone (50 �¼M) and midazolam (5 �¼M) were chosen as substrates of CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A, respectively. Cocktails, test compounds and NADPH regenerating system were incubated 15 min after 5 pre-incubation with human liver microsomes (HLMs) in vitro for competitive screening. The respective metabolites of the nine substrates and internal standard chlorpropamide (200 ng/mL) were measured by LC-MS/MS system. Results: CBP showed more potent inhibitory effect on CYP2B6 with IC50 values of 0.014 �¼M than sibutramine enantiomers (7.07 �¼M for R-form and 2.43 �¼M for S-form) based on bupropion-dependent inhibition. However, CBP also potently inhibited other CYPs except CYP3A4. In addition, R-sibutramine less slightly inhibited dextromethorphan-mediated CYP2D6 activities relative to S-sibutramine, and the IC50 value was more than 50 �¼M for R-sibutramine and 24.21 �¼M for S-sibutramine, respectively. Conclusion: Based on these data, R-sibutramine was selective and potent inhibitor for CYP2B6 in vitro and S-sibutramine potently inhibited CYP2B6 and slight inhibited CYP2D6 when human liver microsomes were used as the enzyme source. Thus, the present findings signified that R-isomer of sibutramine is a potent stereoselective inhibitor of CYP2B6, whereas, inhibition for other CYPs was substantially negligible.
Yu Fen Zheng is a graduate student with major in Pharmacology/Pharmacokinetics of The Catholic University of Korea.