Cyp2d6 Catalyzes 5-hydroxylation of 1-(2-pyrimidinyl)- Piperazine (1-pp), an Active Metabolite of Several Psychoactive Drugs, in Human Liver Microsomes

1 Abbreviations used: HLM, human liver microsomes; HO-1-PP, 5-hydroxy-1-(2-pyrimidinyl)-piperazine; LC/MS, liquid chromatography/mass spectrometry; NADPH, β-nicotinamide adenine dinucleotide phosphate sodium (reduced form); 1-PP, 1-(2-pyrimidinyl)-piperazine 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 µM) was incubated separately with human cDNA-expressed cytochrome P450 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. This article has not been copyedited and formatted. The final version may differ from this version.