Metabolism of N,N-dialkylated amphetamines, including deprenyl, by CYP2D6 expressed in a human cell line.

1. Five N,N-dialkylated amphetamines, N-methyl-N-propargylamphetamine (deprenyl; DEP), N-benzyl-N-methylamphetamine (benzphetamine; BPA), N-allyl-N-methylamphetamine (AMA), N,N-diallylamphetamine (DAA) and N-methyl-N-propylamphetamine (MPA), were metabolized in vitro with a microsomal preparation from cells expressing human CYP2D6 to determine what influence the N,N-dialkyl substituents had on the extent of N-dealkylation and/or aromatic ring oxidation. 2. The results obtained from experiments with the first two substrates, DEP and BPA, were surprisingly different. Whereas DEP was N-demethylated and N-depropargylated by the CYP2D6 enzyme system, no metabolites were formed from BPA. Subsequently, it was determined that AMA, DAA and MPA also underwent CYP2D6-catalysed N-dealkylation. Both N-methyl- and N-allylamphetamine were identified as products of AMA metabolism; similarly, metabolism of MPA produced both N-methyl- and N-propargylamphetamine, and N-allylamphetamine was the sole metabolite of DAA. 3. No N,N-didealkylated product (i.e. amphetamine) was isolated from incubates of any of the five substrates, and none of the N,N-dialkylated substrates was metabolized to a ring-hydroxylated product. 4. Rates of these CYP2D6-catalysed reactions were dependent on the nature and degree of unsaturation of the N-substituents.

Involvement of CYP2D6 in the in vitro metabolism of amphetamine, two N-alkylamphetamines and their 4-methoxylated derivatives.

1. Amphetamine (AM) and five amphetamine derivatives, N-ethylamphetamine (NEA), N-butylamphetamine (NBA), 4-methoxyamphetamine (M-AM), 4-methoxy-N-ethylamphetamine (M-NEA) and 4-methoxy-N-butylamphetamine (M-NBA) were incubated with microsomal preparations from cells expressing human CYP2D6 to determine whether the enzyme was capable of catalyzing the direct ring oxidation of all substrates; the N-dealkylation of NEA, NBA, M-NEA and M-NBA; and the O-demethylation of M-AM, M-NEA and M-NBA. 2. None of the six compounds examined was N-dealkylated to any extent. 3. The only metabolites produced from AM, NEA and NBA were the corresponding ring 4-hydroxylated compounds, and the rates of formation were low. 4. All ring 4-methoxylated substrates were efficiently O-demethylated by CYP2D6 to their corresponding phenols. The size of the N-alkyl group influenced the rates of formation of these phenolamines. In contrast to reported findings with 2- and 3-methoxyamphetamines, none of the 4-methoxyamphetamines was ring-oxidized in the CYP2D6 enzyme system to 2- or 3-hydroxy-4-methoxyamphetamines or to dihydroxyamphetamines.

Metabolism of amitriptyline with CYP2D6 expressed in a human cell line.

1. Expressed human cytochrome P450 enzyme CPY2D6 was used to metabolize amitriptyline (AMI). It was established that CYP2D6 not only catalyzed ring 10-hydroxylation of AMI, but also mediated its N-demethylation to nortriptyline (NT), as well as the formation of 10-hydroxy-NT from NT. When the metabolism of AMI by CYP2D6 was repeated in the presence of quinidine, none of the metabolites, 10-hydroxy-AMI, NT and 10-hydroxy-NT, was formed. 2. Biochemical parameters of NT formation from AMI were determined, yielding Km = 47.48 +/- 1.32 microM; Vmax = 3.95 +/- 0.11 nmol/h/mg protein. The same parameters were calculated for the formation of 10-hydroxy-AMI (E + Z-isomers) from AMI, yielding Km = 10.70 +/- 0.20 microM; Vmax = 8.99 +/- 0.47 nmol/h/mg protein. 3. The formation of 10-hydroxy-NT from AMI proceeded primarily via NT and to a much lesser extent via 10-hydroxy-AMI. 4. Quantitative analyses of AMI and its metabolites were difficult to reproduce when the metabolites were analysed underivatized. Two derivatization procedures, acetylation and trifluoroacetylation, were employed to improve assay reproducibility.