Affiliation:
1. Drug Metabolism and Analytical Chemistry Research Laboratory, New Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd, Tokyo, Japan
Abstract
Abstract
An in-vitro study was conducted to investigate the metabolism of nefiracetam in human liver microsomes and to identify the enzymes responsible for the metabolism. Nefiracetam was hydroxylated by human liver microsomes to 5-hydroxynefiracetam (5-OHN). Eadie-Hofstee plots for the formation of 5-OHN suggested substrate activation. The kinetic parameters, apparent Km, Vmax, and Hill coefficient, for the formation of 5-OHN by pooled human liver microsomes were 4012 μM, 2.66 nmol min−1 (mg protein)−1, and 1.65, respectively. The formation of 5-OHN was significantly correlated with cytochrome P450 (CYP) 3A4-mediated testosterone 6β-hydroxylase activity and dextromethorphan N-demethylase activity. The 5-OHN formation was inhibited (94%) by antibody to human CYP3A4/5. The 5-OHN formation was also inhibited by the CYP3A4 inhibitors ketoconazole and troleandomycin, but not significantly inhibited by several other P450 inhibitors. The microsomes containing cDNA-expressed CYP3A4 formed 5-OHN with sigmoidal kinetics. CYP3A5-containing microsomes did not form 5-OHN. These results indicated that CYP3A, most likely CYP3A4, was the major isozyme responsible for the formation of 5-OHN in human liver microsomes. CYP1A2 and CYP2C19 microsomes were also capable of forming 5-OHN. However, the contribution of CYP1A2 was considered to be relatively minor compared with that of CYP3A4, and the contribution of CYP2C19 was assumed to be negligible, based on the result of the immunoinhibition study and taking into account both the turnover rate by each isozyme and the relative abundance of each isozyme in human liver. We conclude that on average the formation of 5-OHN, the major metabolite of nefiracetam, is principally mediated by CYP3A4 with a relatively minor contribution by CYP1A2.
Publisher
Oxford University Press (OUP)
Subject
Pharmaceutical Science,Pharmacology
Reference36 articles.
1. Activation and inhibition of benzo-(a)pyrene and aflatoxin B1 metabolism in human liver microsomes by naturally occurring flavonoids;Buening;Cancer Res.,1981
2. Bio-transformation of anew pyrrolidinone congnition-enhancing agent: isolation and identification of metabolites in human urine;Fujimaki;Xenobiotica,1990
3. Single- and multiple-dose pharmacokinetics of nefiracetam, a new nootropic agent, in healthy volunteers;Fujimaki;J. Pharm. Pharmacol.,1992
4. Pharmacokinetics of nefiracetam and three metabolites in humans and stereoselective hydroxylation of its pyrrolidine ring;Fujimaki;Xenobiotica,1993
5. In vitro metabolism of nefiracetam by liver microsomes from rats, dogs, and monkeys;Fujimaki;Arzneim. Forsch.,1995
Cited by
5 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献