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

Abstract

1. The metabolism of 4′-methoxy-α-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 μM and 6.0 ± 0.3 pmol min−1 pmol−1 CYP, respectively (mean ± SD). Both CYP2D6 and HLM exhibited clear biphasic profiles with apparent Km,1 values of 1.3 ± 0.4 and 22.0 ± 6.5 μM, respectively, and Vmax,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 μM) significantly ( p<0.0001) inhibited HO-PPP formation by 91.8 ± 0.5% (mean ± SEM) in incubation mixtures with HLM and 2 μM 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.