Effect of psychotropic drugs on the 21-hydroxylation of neurosteroids, progesterone and allopregnanolone, catalyzed by rat CYP2D4 and human CYP2D6 in the brain

We determined the effects of psychotropic drugs on the cytochrome P450 2D (CYP2D)-mediated 21-hydroxylation of progesterone (PROG) and allopregnanolone (ALLO) with the goal of clarifying whether neurosteroid levels are affected by psychotropic drugs in the brain. PROG or ALLO was incubated with rat CYP2D4 or human CYP2D6 in the presence of typical psychotropic drugs, fluoxetine, imipramine, desipramine, mazindol, and GBR12909, and the 21-hydroxylated metabolites of PROG and ALLO were determined by high performance liquid chromatography and liquid chromatography-tandem mass spectrometry, respectively. Fluoxetine competitively inhibited CYP2D4-mediated PROG 21-hydroxylation and increased both K_m and V_max values of CYP2D6-mediated PROG 21-hydroxylation. In addition, fluoxetine competitively inhibited ALLO 21-hydroxylation mediated by CYP2D4 and CYP2D6. Imipramine, desipramine, mazindol, and GBR12909 competitively inhibited PROG 21-hydroxylation mediated by CYP2D4 and/or CYP2D6, and all psychotropic drugs inhibited ALLO 21-hydroxylation mediated by CYP2D4 and/or CYP2D6. The inhibition constants (K_i values) of imipramine, desipramine, and mazindol against the 21-hydroxylation of PROG and ALLO by CYP2D6 were lower than those by CYP2D4. These results indicate that psychotropic drugs including fluoxetine affected the metabolism of neurosteroids, such as PROG and ALLO in the brain, suggesting that the regulation of the neurosteroid levels is modified by central nervous system-active drugs that inhibit brain CYP2D isoforms.