[Enzyme kinetics of clausenamide enantiomers in rat liver microsomes].
OBJECTIVE
To 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.


METHODS
An 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.


RESULTS
In 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.


CONCLUSIONS
The 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.
Zhu
Chuan-jiang
CJ
Department of Pharmacology, Institute of Materia Medica, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100050, China.
Zhang
Jun-tian
JT
D000818:Animals; D004365:Drugs, Chinese Herbal / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D006900:Hydroxylation; D007700:Kinetics; D007769:Lactams / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D017705:Lignans / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010946:Plants, Medicinal / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D027821:Rutaceae / Q000737:chemistry; D013237:Stereoisomerism
D004365:Drugs, Chinese Herbal; D007769:Lactams; D017705:Lignans; C053048:clausenamide; D009249:NADP