Original Research
Copyright ©The Author(s) 2001. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Dec 15, 2001; 7(6): 830-835
Published online Dec 15, 2001. doi: 10.3748/wjg.v7.i6.830
Chiral metabolism of propafenone in rat hepatic microsomes treated with two inducers
Quan Zhou, Tong-Wei Yao, Su Zeng
Quan Zhou, Tong-Wei Yao, Su Zeng, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310031, Zhejiang Province, China
Quan Zhou, Second Hospital of Medical School, Zhejiang University, Hangzhou 310031, Zhejiang Province, China
Author contributions: All authors contributed equally to the work.
Supported by the National Natural Science Foundation of China (NO.39370805, NO.39770868) and Zhejiang Natural Science Foundation (№ RC97016)of Zhejiang Province
Correspondence to: Prof. Su Zeng, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310031, China. zengsu@zjuem.zju.edu.cn
Telephone: +86-571-87217060, Fax: +86-571-87217086.
Received: June 2, 2001
Revised: July 19, 2001
Accepted: August 5, 2001
Published online: December 15, 2001
Abstract

AIM: To study the influence of inducers of drug metabolism enzyme, β-naphthoflavone (BNF) and dexamethasone (DEX), on the stereoselective metabolism of propafenone in the rat hepatic microsomes.

METHODS: Phase I metabolism of propafenone was studied using the microsomes induced by BNF and DEX and the non-induced microsome was used as the control. The enzymatic kinetics parameters of propafenone enantiomers were calculated by regress analysis of Eadie-Hofstee Plots. Propafenone enantiomer concentrations were assayed by a chiral HPLC.

RESULTS: The metabolite of propafenone, N-desalkylpropafenone, was found after incubation of propafenone with the rat hepatic microsomes induced by BNF and DEX. In these two groups, the stereoselectivity favoring R (-) isomer was observed in metabolism at low substrate concentrations of racemic propafenone, but lost the stereoselectivity at high substrate concentrations. However, in control group, no stereoselectivity was observed. The enzyme kinetic parameters were: ① Km. Control group: R (-) 83 ± 6, S (+) 94 ± 7; BNF group: R (-) 105 ± 6, S (+) 128 ± 14; DEX group: R (-) 86 ± 11, S (+) 118 ± 16; ② υmax. Control group: R (-) 0.75 ± 0.16, S (+) 0.72 ± 0.07; BNF group: R (-)1.04 ± 0.15, S (+)1.0 7 ± 14; DEX group: R (-) 0.93 ± 0.06, S (+) 1.04 ± 0.09; ③ Clint. Control group: R (-) 8.9 ± 1.1, S (+) 7.6 ± 0.7; BNF group: R (-)9.9 ± 0.9, S (+)8.3 ± 0.7; DEX group: R (-) 10.9 ± 0.8, S (+) 8.9 ± 0.9. The enantiomeric differences in Km and Clint were both significant, but not in υmax, in BNF and DEX group. Whereas enantiomeric differences in three parameters were all insignificant in control group. Furthermore, Km and υ max were both significantly less than those in BNF or DEX group. In the rat liver microsome in duced by DEX, nimodipine (NDP) decreased the stereoselectivity in propafenone metabolism at low substrate concentration. The inhibition of NDP on the metabolism of propafenone was stereo selective with R (-)-isomer being impaired more than S (+)-isomer. The inhibition constant (Ki) of S (+)- and R (-)-propafenone, calculated from Dixon plots, was 15.4 and 8.6 mg•L¯¹, respectively.

CONCLUSION: CYP1A subfamily (induced by BNF) and CYP3A4 (induced by DEX) have pronounced contribution to propafenone N-desalkylation which exhibited stereose lectivity depending on substrate concentration. The molecular base for this phenomenon is the stereo selectivity in affinity of substrate to the enzyme activity centers instead of at the catalyzing sites.

Keywords: propafenone/metabolism; mitochondria; liver; rat; optical rotation