Effect of 24 cytochrome P450 2D6 variants found in the Chinese population on the N-demethylation of amitriptyline in vitro.

Context: Amitriptyline (AT), one of the tricyclic antidepressants, is still widely used for the treatment of the depression and control of anxiety states and panic disorders in the developing countries.Objective: This study evaluates the catalytic activities of CYP2D6*1, CYP2D6*2, CYP2D6*10 and 22 novel alleles in Han Chinese population and their effects on the N-demethylation of AT in vitro.Materials and methods: CYP2D6*1 and 24 CYP2D6 allelic variants were highly expressed in insect cells, and all variants were characterized using AT as a substrate. Reactions were performed at 37 degrees C with 10-1000M substrate for 30min. We established a HPLC method to quantify the levels of nortriptyline (NT). The kinetic parameters K-m, V-max and intrinsic clearance (V-max/K-m) of NT were calculated.Results: Among the 24 CYP2D6 variants, all variants exhibited decreased intrinsic clearance values compared with wild-type CYP2D6.1. Kinetic parameters of two CYP2D6 variants (CYP2D6*92, *96) could not be determined because of absent enzyme activities.Conclusions: The comprehensive in vitro assessment of CYP2D6 variants provides significant insight into allele-specific activity towards AT in vivo.