-PURPOSE: The inhibitory effects of antidepressants, such as imipramine, desipramine, and fluvoxamine, on dopamine formation from p-tyramine catalyzed by cytochrome P450 (CYP) 2D6.2 (Arg296Cys, Ser486Thr) and CYP2D6.10 (Pro34Ser, Ser486Thr), were compared with those on dopamine formation catalyzed by CYP2D6.1 (wild type), to investigate the effect of a CYP2D6 polymorphism on neuroactive amine metabolism in the brain. METHODS: Inhibition constants (Ki) of the antidepressants toward dopamine formation catalyzed by CYP2D6.1, CYP2D6.2, and CYP2D6.10, which were expressed in recombinant Escherichia coli, were compared. RESULTS: Imipramine and desipramine competitively or noncompetitively inhibited dopamine formation mediated by CYP2D6.1, CYP2D6.2, and CYP2D6.10 with Ki values of 3.9-4.9, 5.9-9.6, and 26.7-37.5 µM, respectively. The maximal velocity (Vmax) values for dopamine formation by all CYP2D6 variants gradually increased with increasing fluvoxamine concentrations up to 40-100 µM, indicating that fluvoxamine stimulated dopamine formation. CONCLUSIONS: These results suggest that the inhibition/stimulation of CYP2D6-mediated dopamine formation by these antidepressants would be affected by CYP2D6 polymorphism in the brain.

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CYP2D catalyze dopamine formation from pand m-tyramine in the brain, and human CYP2D6 is polymorphic Imipramine, a tricyclic antidepressant, and fluvoxamine, an SSRI, are CYP2D6 inhibitors. Dopamine formation from p-tyramine mediated by CYP2D6 variants, CYP2D6.2 and CYP2D6.10 was compared, and the effect of genetic polymorphism on the inhibitory effects of antidepressants was investigated.[Methods] CYP2D6.1, CYP2D6.2, and CYP2D6.10 expressed in recombinant Escherichia coli were used. Dopamine formation from p-tyramine in the presence of antidepressants such as imipramine, desipramine, fluvoxamine, fluoxetine, and paroxetine was determined by HPLC.[Results] CYP2D6.10 had higher Michaelis constants of dopamine formation than CYP2D6.1 and CYP2D6.2. Inhibition constant of imipramine and desipramine against CYP2D6.10 were higher than that against CYP2D6.1. Fluoxetine and paroxetine inhibited CYP2D6.1-mediated dopamine formation. The maximal velocity for all CYP2D6 variants gradually increased with increasing fluvoxamine concentrations.[Conclusions] CYP2D6 polymorphism might affect the inhibitory effect of antidepressants on dopamine formation in the brain.

Background] Dopamine is formed from pand m-tyramine through ring-hydroxylation by polymorphic human CYP2D6 and rat CYP2D4 in the brain. The inhibitory effects of steroid hormones, and related compounds including typical CYP2D inhibitors and antidepressants on dopamine formation from p-tyramine, catalyzed by CYP2D6.2 (Arg296Cys,