TY - JOUR T1 - IDENTIFICATION OF CYTOCHROME P450 ENZYMES INVOLVED IN THE METABOLISM OF 4′-METHYL-α-PYRROLIDINOPROPIOPHENONE, A NOVEL SCHEDULED DESIGNER DRUG, IN HUMAN LIVER MICROSOMES JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 979 LP - 982 DO - 10.1124/dmd.31.8.979 VL - 31 IS - 8 AU - Dietmar Springer AU - Liane D. Paul AU - Roland F. Staack AU - Thomas Kraemer AU - Hans H. Maurer Y1 - 2003/08/01 UR - http://dmd.aspetjournals.org/content/31/8/979.abstract N2 - 4′-Methyl-α-pyrrolidinopropiophenone (MPPP) is a new drug of abuse. It is believed to have an abuse potential similar to that of amphetamines. Previous studies with Wistar rats had shown that MPPP was metabolized mainly by hydroxylation in position 4′ followed by dehydrogenation to the corresponding carboxylic acid. The aim of the study presented here was to identify the human hepatic cytochrome P450 (P450) enzymes involved in the biotransformation of MPPP to 4′-hydroxymethyl-pyrrolidinopropiophenone. Baculovirus-infected insect cell microsomes and human liver microsomes were used for this purpose. Only CYP2C19 and CYP2D6 catalyzed this hydroxylation. The apparent Km and Vmax values for the latter were 9.8 ± 2.5 μM and 13.6 ± 0.7 pmol/min/pmol P450, respectively. CYP2C19 was not saturable over the tested substrate range (2–1000 μM) and interestingly showed a biphasic kinetic profile with apparent Km,1 and Vmax,1 values of 47.2 ± 12.5 μM and 8.1 ± 1.4 pmol/min/pmol P450, respectively. Experiments with pooled human liver microsomes also revealed biphasic nonsaturable kinetics with apparent Km,1 and Vmax,1 values of 57.0 ± 20.9 μM and 199.7 ± 59.7 pmol/min/mg of protein for the high affinity enzyme, respectively. Incubation of 2 μM MPPP with 3 μM of the CYP2D6-specific inhibitor quinidine resulted in significant (p < 0.01) turnover inhibition (11.8 ± 1.6% of control). Based on kinetic data corrected for the relative activity factors, CYP2D6 is the enzyme mainly responsible for MPPP hydroxylation, confirmed by CYP2D6 inhibition studies. The American Society for Pharmacology and Experimental Therapeutics ER -