Vol. 29, Issue 8, 1156-1161, August 2001

Inhibition of Rat Liver Microsomal CYP1A2 and CYP2B1 Activity by N-(2-Heptyl)-N-methyl-propargylamine and by N-(2-Heptyl)-propargylamine

L. E. Dyck and B. A. Davis¹

Neuropsychiatry Research Unit, Department of Psychiatry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

(R)-N-(2-Heptyl)-N-methyl-propargylamine (R-2HMP) and (R)-N-(2-heptyl)-propargylamine (R-2HPA) are analogs of R-deprenyl. R-Deprenyl, a selective monoamine oxidase B inhibitor, is a mechanism-based inactivator of purified CYP2B1. The aim of the present study was to determine whether R-2HMP and R-2HPA behaved like deprenyl with respect to inhibiting cytochrome P450 (CYP450) enzyme activity. The activities of CYP1A2 and CYP1A1 were assessed by measuring the deethylation of 7-ethoxyresorufin by liver microsomes obtained from control and -naphthoflavone-treated female Wistar rats, respectively. CYP2B1 activity was assessed by measuring depentylation of 7-pentoxyresorufin by liver microsomes obtained from phenobarbital-treated rats. The activity of CYP1A1 was unaffected by 100 µM concentrations of R-deprenyl, R-2HMP, or R-2HPA. In contrast, the activities of CYP1A2 and CYP2B1 were significantly decreased. In general, the percentage of CYP1A2 activity remaining in the presence of 100 µM of one of these propargylamines ranged from 45 to 56%, whereas 10% or less of CYP2B1 activity remained. No marked differences between the various propargylamines were observed. The IC₅₀ values for the inhibition of CYP2B1 activity by R-deprenyl, R-2HMP, and R-2HPA were found to be 2.6, 8.5, and 3.6 µM, respectively. The S-enantiomers of deprenyl, 2HMP, and 2HPA also inhibited the activity of microsomal CYP2B1. R-2HMP, R-2HPA, and S-2HPA were found to be mechanism-based inactivators of CYP2B1 activity. The inactivation constants k_inact and K_I were found to be as follows: R-deprenyl, 1.3 µM and 0.32 min¹; R-2HMP, 0.8 µM and 0.08 min¹; R-2HPA, 0.5 µM and 0.36 min¹; and S-2HPA, 0.24 µM and 0.18 min¹.