Molecular Mechanisms of the Regulation of Liver Cytochrome P450 by Brain NMDA Receptors and via the Neuroendocrine Pathway-A Significance for New Psychotropic Therapies

Abstract

Recent investigations have highlighted the potential utility of the selective antagonist of the NMDA receptor GluN2B subunit for addressing major depressive disorders. Our previous study showed that the systemic administration of the antagonist of the GluN2B subunit of the NMDA receptor, the compound CP-101,606, affected liver cytochrome P450 expression and activity. To discern between the central and peripheral mechanisms of enzyme regulation, our current study aimed to explore whether the intracerebral administration of CP-101,606 could impact cytochrome P450. The injection of CP-101,606 to brain lateral ventricles (6, 15, or 30 µg/brain) exerted dose-dependent effects on liver cytochrome P450 enzymes and hypothalamic or pituitary hormones. The lowest dose led to an increase in the activity, protein, and mRNA level of CYP2C11 compared to the control. The activities of CYP2A, CYP2B, CYP2C11, CYP2C6, CYP2D, and protein levels of CYP2B, CYP2C11 were enhanced compared to the highest dose. Moreover, CP-101,606 increased the CYP1A protein level coupled with elevated CYP1A1 and CYP1A2 mRNA levels, but not activity. The antagonist decreased the pituitary somatostatin level and increased the serum growth hormone concentration after the lowest dose, while independently decreasing the serum corticosterone concentration of the dose. The findings presented here unveil a novel physiological regulatory mechanism whereby the brain glutamatergic system, via the NMDA receptor, influences liver cytochrome P450. This regulatory process appears to involve the endocrine system. These results may have practical applications in predicting alterations in cytochrome P450 activity and endogenous metabolism, and potential metabolic drug-drug interactions elicited by drugs that cross the blood-brain barrier and affect NMDA receptors.

Keywords: CP-101,606; NMDA receptor; activity/expression; cytochrome P450; liver; neuroendocrine regulation.

Figure 1

The impact of a 5-day intracerebral administration of CP-101,606, a selective antagonist targeting the GluN2B subunit of the NMDA receptor, at three different doses (6, 15, or 30 µg/brain) on cytochrome P450 enzyme activity. The activity of various CYP enzymes was assessed as follows: CYP1A, measured by the rates of caffeine 8-hydroxylation and 3-N-demethylation (A); CYP2A, measured by the rates of testosterone 7α-hydroxylation (B); CYP2B, measured by the rates of testosterone 16β-hydroxylation (C); CYP2C11, measured by the rates of testosterone 2α- and 16α-hydroxylation (D); CYP3A, measured by the rates of testosterone 2β- and 6β-hydroxylation (E); CYP2C6, measured by the rates of warfarin 7-hydroxylation (F); and CYP2D, measured by the rates of bufuralol 1′-hydroxylation (G). The values are presented as the mean ± S.E.M. (n = 9–10 rats). Statistical analysis was performed using one-way ANOVA followed by Tukey’s post hoc test. Statistical significance was indicated as follows: * p < 0.05; ** p < 0.01; *** p < 0.001.

Figure 2

The influence of a 5-day intracerebral administration of CP-101,606, a selective antagonist targeting the GluN2B subunit of the NMDA receptor, at two selected doses (6 or 30 µg/brain) on the protein levels of cytochrome P450 enzymes. The following CYP enzymes were analyzed: CYP1A (A), CYP2A (B), CYP2B (C), CYP2C11 (D), CYP3A (E), CYP2C6 (F), and CYP2D (G). The values are expressed as the mean ± S.E.M. (n = 8 rats). One-way ANOVA followed by Tukey’s post hoc test was utilized for statistical analysis. Statistical significance was represented as follows: * p < 0.05; ** p < 0.01.

Figure 3

The impact of a 5-day treatment with two selected doses (6 or 30 µg/brain) of CP-101,606 on the intensity of cytochrome P450 protein bands (CYP1A, CYP2A, CYP2B, CYP2C11, CYP3A, CYP2C6, and CYP2D) in liver microsomes. Rat cDNA-expressed CYP enzymes were utilized as standards in the analysis. The figure shows the Western immunoblot analysis of representative CYP protein bands. The mean values ± S.E.M. (n = 8 rats) of the respective CYP protein levels are presented in Figure 2A–G. STD—standard.

Figure 4

The influence of a 5-day intracerebral administration of CP-101,606, a selective antagonist targeting the GluN2B subunit of the NMDA receptor, at two selected doses (6 or 30 µg/brain) on the mRNA levels of the cytochrome P450 enzymes: CYP1A1 (A), CYP1A2 (B), CYP2C11 (C), CYP2B1 (D), and CYP2B2 (E). The data are presented as the mean ± S.E.M. (n = 9–10 rats). One-way ANOVA followed by Tukey’s post hoc test was employed for statistical analysis. Statistical significance was indicated as follows: *** p < 0.001; **** p < 0.0001; ns—non-significant.

Figure 5

The influence of a 5-day intracerebral administration of CP-101,606, a selective antagonist targeting the GluN2B subunit of the NMDA receptor, at two selected doses (6 or 30 µg/brain) on the serum hormones: triiodothyronine (T₃) (A), thyroxine (T₄) (B), corticosterone (C), growth hormone (GH) (D), and pituitary gland hormones: somatostatin (E) and growth hormone-releasing hormone (GHRH) (F). The data represent the mean ± S.E.M. (8–10 rats). One-way ANOVA followed by Tukey’s post hoc test was used for statistical analysis. Statistical significance was denoted as follows: * p < 0.05; ** p < 0.01; *** p < 0.001.