PURPOSE: The effects of selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine and paroxetine on dopamine formation from p-tyramine, mediated by cytochrome P450 (CYP) 2D6.2 (Arg296Cys, Ser486Thr) and CYP2D6.10 (Pro34Ser, Ser486Thr), were compared with their effects on CYP2D6.1 (wild type)-mediated dopamine formation, to investigate the influence of a CYP2D6 polymorphism on neuroactive amine metabolism in the brain. METHODS: The Michaelis constants (Km) and maximal velocity (Vmax) values of dopamine formation mediated by CYP2D6.1, CYP2D6.2, and CYP2D6.10 (expressed in recombinant Escherichia coli), and inhibition constants (Ki) of the SSRIs toward dopamine formation catalyzed by the CYP2D6 variants were estimated. RESULTS: The Km values for CYP2D6.2 and CYP2D6.10 decreased at lower fluoxetine concentrations, while the Vmax values for all CYP2D6 variants increased, indicating that fluoxetine stimulated dopamine formation. Conversely, paroxetine competitively inhibited dopamine formation mediated by CYP2D6.1, CYP2D6.2, and CYP2D6.10 with Ki values of 0.47, 1.33, and 31.3 µM, respectively. CONCLUSIONS: These results suggest that the inhibition/stimulation of CYP2D6
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.
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