Enzyme kinetics of clausenamide enantiomers in rat liver microsomes.
- Author:
Chuan-jiang ZHU
1
;
Jun-tian ZHANG
Author Information
- Publication Type:Journal Article
- MeSH: Animals; Drugs, Chinese Herbal; isolation & purification; metabolism; Female; Hydroxylation; Kinetics; Lactams; chemistry; isolation & purification; metabolism; Lignans; chemistry; isolation & purification; metabolism; Microsomes, Liver; metabolism; NADP; metabolism; Plants, Medicinal; chemistry; Rats; Rats, Wistar; Rutaceae; chemistry; Stereoisomerism
- From: Acta Pharmaceutica Sinica 2003;38(9):654-657
- CountryChina
- Language:Chinese
-
Abstract:
AIMTo investigate the enzyme kinetics of (-)3S,4R,5R,6S-clausenamide[(-)-Clau] and (+)-3R,4S,5S,6R-clausenamide[(+)-Clau] catalyzed by rat liver microsomes and compare their stereoselective differences.
METHODSAn in vitro metabolic system was built by using rat liver microsomes and NADPH-generating system. Clau and its metabolites were determined simultaneously by a reversed-phase high performance liquid chromatography. The kinetic parameters, K(m), Vmax, and metabolic rate, Vmax/K(m), were calculated by Eadie-Hofstee plot.
RESULTSIn the metabolic system, (-)-Clau was found to be mainly metabolized to 7-hydroxy-, 5-hydoxy- and 4-hydroxy-Clau, and 7-hydroxylation was a preferential pathway which exhibited higher Vmax/K(m) value (0.135 microL.min-1.mg-1) than those of 5- and 4-hydroxylation (0.063 and 0.068 microL.min-1.mg-1, respectively). For (+)-Clau, it was mainly metabolized to 4-hydroxy-Clau, whereas 7-hydroxy- and 4-hydroxy-Clau were so small that they could not be detected systematically. 4-Hydroxylation of (+)-Clau showed highest Vmam/K(m) value (0.547 microL.min-1.mg-1) among all the metabolites tested, which was 8.0 times higher than that of 4-hydroxylation of its antipode.
CONCLUSIONThe data indicated that there were obvious substrate stereoselective differences in the hydroxylation metabolism of (+)- and (-)-Clau, which provided an explanation of the difference of pharmacokinetic characteristics of Clau enantiomers in rats.