Received for publication June 25, 2004.
Revised October 17, 2004.
Accepted for publication October 22, 2004.

CYP2D6 CATALYZES 5-HYDROXYLATION OF 1 (2-PYRIMIDINYL)- PIPERAZINE (1-PP), AN ACTIVE METABOLITE OF SEVERAL PSYCHOACTIVE DRUGS, IN HUMAN LIVER MICROSOMES

Abstract

1-(2-Pyrimidinyl)-piperazine (1-PP) is an active metabolite of several psychoactive drugs including buspirone. 1-PP is also the major metabolite in the human circulation and rat brains following oral administration of buspirone. This study was conducted to identify the enzyme responsible for the metabolic conversion of 1-PP to 5-hydroxy-1-(2-pyrimidinyl)- piperazine (HO-1-PP) in human liver microsomes (HLM). The product HO-1-PP was quantified by a validated LC/MS/MS method. In the presence of NADPH, 1-PP (100 & [micro]M) was incubated separately with human cDNA- expressed CYP isozymes (including CYP2D6, 3A4, 1A2, 2A6, 2C9, 2C19, 2E1 and 2B6) at 37°C. CYP2D6 catalyzed the formation of HO-1-PP from 1-PP. This catalytic activity was >95% inhibited by quinidine, a CYP2D6 inhibitor. HO-1-PP formation rates correlated well with the bufuralol 1-hydroxylase (CYP2D6) activities of individual HLMs. The formation of HO-1-PP followed a Michaelis Menten kinetics with a Km of 171 µM and Vmax of 313 pmole/min.mg protein in HLM. Collectively, these results indicate that polymorphic CYP2D6 is responsible for the conversion of 1-PP to HO-1-PP.

Key words: CYP2D, cytochrome P450 catalyzed oxidations, liver microsomes