Identification of cytochrome P450 enzymes involved in the metabolism of 4'-methoxy-alpha-pyrrolidinopropiophenone (MOPPP), a designer drug, in human liver microsomes.

1. The metabolism of 4'-methoxy-alpha-pyrrolidinopropiophenone (MOPPP), a novel designer drug, to its demethylated major metabolite 4'-hydroxy-pyrrolidinopropio-phenone (HO-PPP) was studied in pooled human liver microsomes (HLM) and in cDNA-expressed human hepatic cytochrome P450 (CYP) enzymes. 2. CYP2C19 catalysed the demethylation with apparent Km and Vmax values of 373.4 +/- 45.1 microM and 6.0 +/- 0.3 pmol min(-1) pmol(-1) CYP, respectively (mean +/- SD). Both CYP2D6 and HLM exhibited clear biphasic profiles with apparent K(m,1) values of 1.3 +/- 0.4 and 22.0 +/- 6.5 microM, respectively, and V(max,1) values of 1.1 +/- 0.1 pmol min(-1) pmol(-1) CYP and 169.1 +/- 20.5 pmol min(-1) mg(-1) protein, respectively. 3. Percentages of intrinsic clearances of MOPPP by particular CYPs were calculated using the relative activity factor (RAF) approach with (S)-mephenytoin-4'-hydroxylation or bufuralol-1'-hydroxylation as index reactions for CYP2C19 or CYP2D6, respectively. 4. MOPPP, HO-PPP and the standard 3',4'-methylenedioxy-pyrrolidinopropio-phenone (MDPPP) were separated and analysed by liquid chromatography-mass spectrometry in the selected-ion monitoring (SIM) mode. 5. The CYP2D6 specific chemical inhibitor quinidine (3 microM) significantly (p<0.0001) inhibited HO-PPP formation by 91.8 +/- 0.5% (mean +/- SEM) in incubation mixtures with HLM and 2 microM MOPPP. 6. It can be concluded from the data obtained from kinetic and inhibition studies that polymorphically expressed CYP2D6 is the enzyme mainly responsible for MOPPP demethylation.