Original Articles
Copyright ©The Author(s) 2000. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Feb 15, 2000; 6(1): 74-78
Published online Feb 15, 2000. doi: 10.3748/wjg.v6.i1.74
Stereoselective propranolol metabolism in two drug induced rat hepatic microsomes
Xin Li, Su Zeng
Xin Li, Su Zeng, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310031, China
Xin Li, male, born on 1966-06-27 in Zhejiang, College of Pharmacy, China Pharmaceutical University, BS in 1987; College of Pharmaceutical Sciences, Zhejiang University, MS in 1998; now associate professor, majoring in drug metabolism, having 11 papers published.
Author contributions: All authors contributed equally to the work.
Supported by the National Natural Science Foundation of China, No. 39370 805.
Correspondence to: Prof. Su Zeng, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310031, China
Telephone: +86-571-7217203
Received: July 21, 1999
Revised: September 2, 1999
Accepted: September 18, 1999
Published online: February 15, 2000

AIM: To study the influence of inducers BNF and PB on the stere oselective metabolism of propranolol in rat hepatic microsomes.

METHODS: Phase I metabolism of propranolol was studied by using the microsomes induced by BNF and PB and the non-induced microsome as the control. The enzymatic kinetic parameters of propranolol enantiomers were calculated by regression analysis of Lineweaver-Burk plots. Propranolol concentrations we re assayed by HPLC.

RESULTS: A RP-HPLC method was developed to determine propranol ol concentration in rat hepatic microsomes. The linearity equations for R (+)pr opranolol and S (-)propranolol were A = 705.7C + 311.2C (R = 0.9987) and A = 697.2C+311.4C (R = 0.9970) respectively. Recoveries of each enant iomer were 98.9%, 99.5%, 101.0% at 60 μmol/L, 120 μmol/L, 240 μmol/L respectively. At the concentration level of 120 μmol/L, propranolol enantiomers were metabolized at different rates in different microsomes. The concentration ratio R (+)/S (-) of control and PB induced microsomes increased with time, whereas that of microsome induced by BNF decreased. The assayed enzyme parameters were: 1. Km. Control group: R (+)30 ± 8, S (-) 18 ± 5; BNF group: R (+) 34 ± 3, S (-)39 ± 7; PB group: R (+)38 ± 17, S (-) 36 ± 10. 2. Vmax. Control group: R (+)1.5 ± 0.2, S (-)2.9 ± 0.3; BNF group: R (+)3.8 ± 0.3, S (-)3. 3 ± 0.5 ; PB group: R (+)0.07 ± 0.03, S (-)1.94 ± 0. 07. 3. Clint. Control group: R (+)60 ± 3, S (-) 170 ± 30; BNF group: R (+)111.0 ± 1, S (-) 84 ± 5; PB group: R (+)2.0 ± 2, S (-)56.0 ± 1. The enzyme parameters compared with unpaired t tests showed that no stereoselectivity was observed in enzymatic affinity of three microsomes to enantiomers and their catalytic abilities were quite different and had stereoselectivities. Compared with the control, microsome induced by BNF enhanced enzyme activity to propranolol R (+)enantiomer, and microsome induced by PB showed less enzyme activity to propranolol S (-)-enan tiomer which remains the same stereoselectivities as that of the control.

CONCLUSION: Enzyme activity centers of the microsome were changed in composition and regioselectivity after the induction of BNF and PB, and the stereoselectivities of propranolol cytochrome P450 metabolism in rat hepatic microsomes were likely due to the stereoselectivities of the catalyzing function in enzyme. CYP-1A subfamily induced by BNF exhibited pronounced contribution to propranolol metabolism with stereoselectivity to R (+)-enantiomer. CYP-2B subfamily induced by PB exhibited moderate contribution to propranolol metabolism, but still had the stereoselectivity of S (-)-enantiomer.

Keywords: propranolol, enantiomers, rat hepatic micro some, phenobarbital, β-naphthoflavone