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

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.

The Effect of the Selective N-methyl-D-aspartate (NMDA) Receptor GluN2B Subunit Antagonist CP-101,606 on Cytochrome P450 2D (CYP2D) Expression and Activity in the Rat Liver and Brain.

The CYP2D enzymes of the cytochrome P450 superfamily play an important role in psychopharmacology, since they are engaged in the metabolism of psychotropic drugs and endogenous neuroactive substrates, which mediate brain neurotransmission and the therapeutic action of those drugs. The aim of this work was to study the effect of short- and long-term treatment with the selective antagonist of the GluN2B subunit of the NMDA receptor, the compound CP-101,606, which possesses antidepressant properties, on CYP2D expression and activity in the liver and brain of male rats. The presented work shows time-, organ- and brain-structure-dependent effects of 5-day and 3-week treatment with CP-101,606 on CYP2D. Five-day treatment with CP-101,606 increased the activity and protein level of CYP2D in the hippocampus. That effect was maintained after the 3-week treatment and was accompanied by enhancement in the CYP2D activity/protein level in the cortex and cerebellum. In contrast, a 3-week treatment with CP-101,606 diminished the CYP2D activity/protein level in the hypothalamus and striatum. In the liver, CP-101,606 decreased CYP2D activity, but not the protein or mRNA level, after 5-day or 3-week treatment. When added in vitro to liver microsomes, CP-101,606 diminished the CYP2D activity during prolonged incubation. While in the brain, the observed decrease in the CYP2D activity after short- and long-term treatment with CP-101,606 seems to be a consequence of the drug effect on enzyme regulation. In the liver, the direct inhibitory effect of reactive metabolites formed from CP-101,606 on the CYP2D activity may be considered. Since CYP2Ds are engaged in the metabolism of endogenous neuroactive substances, it can be assumed that apart from antagonizing the NMDA receptor, CP-101,606 may modify its own pharmacological effect by affecting brain cytochrome P450. On the other hand, an inhibition of the activity of liver CYP2D may slow down the metabolism of co-administered substrates and lead to pharmacokinetic drug-drug interactions.

Serotonin Receptors of 5-HT2 Type in the Hypothalamic Arcuate Nuclei Positively Regulate Liver Cytochrome P450 via Stimulation of the Growth Hormone-Releasing Hormone/Growth Hormone Hormonal Pathway.

Our recent study carried out after local injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine into the arcuate nucleus (ARC) of the hypothalamus suggested a positive influence of the serotonergic innervation of the ARC on growth hormone (GH) secretion and GH-dependent expression of cytochrome P450. The aim of our present study was to determine the effect of the activation of the serotonin (5-HT)-type receptors, 5-HT1 or 5-HT2, in the ARC on the expression and activity of cytochrome P450 in the liver of male rats. The serotonergic agonist 5-carboxyamidotryptamine [(5-CT), a 5-HT1-type receptor agonist] or 2,5-dimethoxy-4-iodoamphetamine [(DOI), a 5-HT2-type receptor agonist] was injected into the ARC for 5 days. The activity and expression of cytochrome P450 isoenzymes and the levels of serum and pituitary hormones were estimated. DOI significantly increased the activity and expression (both mRNA and protein levels) of CYP2C11, CYP3A1/23, and CYP3A2, which positively correlated with an increase in the pituitary growth hormone-releasing hormone (GHRH) and serum GH level. The injection of 5-CT into the ARC did not affect the activity of liver P450 enzymes or hormone levels. The obtained results indicate that 5-HT2, but not the 5-HT1-type receptors in the ARC, are engaged in the positive neuroendocrine regulation of cytochrome P450, possibly by the stimulation of hypothalamic GHRH release and pituitary GH secretion, and an increase in the serum GH concentration. Further studies are going to identify which of the 5-HT2 receptor subtypes (5-HT2A, 5-HT2B, or 5-HT2C) is responsible for the observed neuroendocrine regulation of cytochrome P450.

The engagement of brain cytochrome P450 in the metabolism of endogenous neuroactive substrates: a possible role in mental disorders.

The current state of knowledge indicates that the cerebral cytochrome P450 (CYP) plays an important role in the endogenous metabolism in the brain. Different CYP isoenzymes mediate metabolism of many endogenous substrates such as monoaminergic neurotransmitters, neurosteroids, cholesterol, vitamins and arachidonic acid. Therefore, these enzymes may affect brain development, susceptibility to mental and neurodegenerative diseases and may contribute to their pathophysiology. In addition, they can modify the therapeutic effects of psychoactive drugs at the place of their target action in the brain, where the drugs can act by affecting the metabolism of endogenous substrates. The article focuses on the role of cerebral CYP isoforms in the metabolism of neurotransmitters, neurosteroids, and cholesterol, and their possible involvement in animal behavior, as well as in stress, depression, schizophrenia, cognitive processes, learning, and memory. CYP-mediated alternative pathways of dopamine and serotonin synthesis may have a significant role in the local production of these neurotransmitters in the brain regions where the disturbances of these neurotransmitter systems are observed in depression and schizophrenia. The local alternative synthesis of neurotransmitters may be of great importance in the brain, since dopamine and serotonin do not pass the blood-brain barrier and cannot be supplied from the periphery. In vitro studies indicate that human CYP2D6 catalyzing dopamine and serotonin synthesis is more efficient in these reactions than the rat CYP2D isoforms. It suggests that these alternative pathways may have much greater significance in the human brain but confirmation of these assumptions requires further studies.

Activation of 5-HT1A Receptors in the Hypothalamic Paraventricular Nuclei Negatively Regulates Cytochrome P450 Expression and Activity in Rat Liver.

Our recent work suggested a negative effect for the serotonergic innervation of the paraventricular nuclei (PVN) of the hypothalamus on growth hormone secretion and growth hormone-dependent expression of CYP2C11. The aim of our present research was to determine the effect of the activation of the 5-hydroxytryptamine [(5-HT) serotonin] 5-HT1 or 5-HT2 receptors in the PVN on the expression and activity of cytochrome P450 in male rat liver. The serotonergic agonists 5-carboxyamidotryptamine [(5-CT), a 5-HT1 receptor-type agonist], 8-hydroxy-2-(di-n-propyloamino)-tetralin [(8-OH-DPAT), a 5-HT1A receptor agonist], sumatriptan (a 5-HT1B/D receptor agonist), and 2,5-dimethoxy-4-iodoamphetamine [(DOI), a 5-HT2A/C receptor agonist] were individually injected into the PVN. The liver cytochrome P450 activity and expression and the levels of serum and pituitary and hypothalamic hormones were measured. 5-CT and 8-OH-DPAT significantly decreased the activity and expression of CYP2C11 at both the mRNA and protein levels, which was accompanied by an increase in pituitary and hypothalamic somatostatin levels and a decrease in the serum growth hormone concentration. The expression of CYP3A1/23 also decreased. The serum corticosterone concentration declined after the injection of 8-OH-DPAT. The obtained results indicated that 5-HT1A but not the 5-HT1B/D or 5-HT2 receptors in the PVN are engaged in the negative neuroendocrine regulation of cytochrome P450 via the stimulation of hypothalamic somatostatin secretion and in the decreases in the serum growth hormone and corticosterone concentrations. Since the affected enzymes metabolize steroids and drugs and 5-HT1A receptors are engaged in the action of psychotropic drugs, the results obtained may be of both physiologic and pharmacological meaning.

The Effect of Chronic Treatment with Lurasidone on Rat Liver Cytochrome P450 Expression and Activity in the Chronic Mild Stress Model of Depression.

Recent studies indicated an important role of the monoaminergic nervous systems (dopaminergic, noradrenergic, and serotonergic systems) and stress in the regulation of cytochrome P450 (CYP) expression and activity in the liver. The aim of our present research was to determine the effect of the novel atypical neuroleptic drug with antidepressant properties lurasidone, on the expression (mRNA and protein level) and activity of liver CYP isoforms involved in the metabolism of drugs and endogenous steroids, in the chronic mild stress (CMS) model of depression. Male Wistar rats were subjected to CMS for 7 weeks. Lurasidone (3 mg/kg per os per day) was administered to nonstressed or stressed animals for 5 weeks (weeks 3-7 of CMS). It has been found that 1) CMS moderately affects CYP (CYP2B, CYP2C11, and CYP3A), and its effects are different from those observed after other kinds of psychologic stress, such as repeated restraint stress or early-life maternal deprivation; 2) chronic lurasidone influences the expression and/or activity of CYP2B, CYP2C11, and CYP3A isoforms; and 3) CMS modifies the action of lurasidone on CYP expression and function, leading to different effects of the neuroleptic in nonstressed and stressed rats. Based on the obtained results, it can be suggested that the metabolism of endogenous substrates (e.g., steroids) and drugs, catalyzed by the isoforms CYP2B, CYP2C11, or CYP3A, may proceed at a different rate in the two groups of animals (nonstressed and stressed) in the rat CMS model.

Melatonin Supports CYP2D-Mediated Serotonin Synthesis in the Brain.

Melatonin is used in the therapy of sleep and mood disorders and as a neuroprotective agent. The aim of our study was to demonstrate that melatonin supported (via its deacetylation to 5-methoxytryptamine) CYP2D-mediated synthesis of serotonin from 5-methoxytryptamine. We measured serotonin tissue content in some brain regions (the cortex, hippocampus, nucleus accumbens, striatum, thalamus, hypothalamus, brain stem, medulla oblongata, and cerebellum) (model A), as well as its extracellular concentration in the striatum using an in vivo microdialysis (model B) after melatonin injection (100 mg/kg i.p.) to male Wistar rats. Melatonin increased the tissue concentration of serotonin in the brain structures studied of naïve, sham-operated, or serotonergic neurotoxin (5,7-dihydroxytryptamine)-lesioned rats (model A). Intracerebroventricular quinine (a CYP2D inhibitor) prevented the melatonin-induced increase in serotonin concentration. In the presence of pargyline (a monoaminoxidase inhibitor), the effect of melatonin was not visible in the majority of the brain structures studied but could be seen in all of them in 5,7-dihydroxytryptamine-lesioned animals when serotonin storage and synthesis via a classic tryptophan pathway was diminished. Melatonin alone did not significantly increase extracellular serotonin concentration in the striatum of naïve rats but raised its content in pargyline-pretreated animals (model B). The CYP2D inhibitor propafenone given intrastructurally prevented the melatonin-induced increase in striatal serotonin in those animals. The obtained results indicate that melatonin supports CYP2D-catalyzed serotonin synthesis from 5-methoxytryptamine in the brain in vivo, which closes the serotonin-melatonin-serotonin biochemical cycle. The metabolism of exogenous melatonin to the neurotransmitter serotonin may be regarded as a newly recognized additional component of its pharmacological action.

The cytochrome P450 2D-mediated formation of serotonin from 5-methoxytryptamine in the brain in vivo: a microdialysis study.

The cytochrome P450 2D (CYP2D) mediates synthesis of serotonin from 5-methoxytryptamine (5-MT), shown in vitro for cDNA-expressed CYP2D-isoforms and liver and brain microsomes. We aimed to demonstrate this synthesis in the brain in vivo. We measured serotonin tissue content in brain regions after 5-MT injection into the raphe nuclei (Model-A), and its extracellular concentration in rat frontal cortex and striatum using an in vivo microdialysis (Model-B) in male Wistar rats. Naïve rats served as control animals. 5-MT injection into the raphe nuclei of PCPA-(tryptophan hydroxylase inhibitor)-pretreated rats increased the tissue concentration of serotonin (from 40 to 90% of the control value, respectively, in the striatum), while the CYP2D inhibitor quinine diminished serotonin level in some brain structures of those animals (Model-A). 5-MT given locally through a microdialysis probe markedly increased extracellular serotonin concentration in the frontal cortex and striatum (to 800 and 1000% of the basal level, respectively) and changed dopamine concentration (Model-B). Quinine alone had no effect on serotonin concentration; however, given jointly with 5-MT, it prevented the 5-MT-induced increase in cortical serotonin in naïve rats and in striatal serotonin in PCPA-treated animals. These results indicate that the CYP2D-catalyzed alternative pathway of serotonin synthesis from 5-MT is relevant in the brain in vivo, and set a new target for the action of psychotropics.

Damage to the Brain Serotonergic System Increases the Expression of Liver Cytochrome P450.

Genes coding for cytochrome P450 are regulated by endogenous hormones such as the growth hormone, corticosteroids, thyroid, and sex hormones. Secretion of these hormones is regulated by the respective hypothalamus-pituitary-secretory organ axes. Since the brain sends its serotonergic projections from the raphe nuclei to the hypothalamus, we have assumed that damage to these nuclei may affect the neuroendocrine regulation of cytochrome P450 expression in the liver. Thereby, 5,7-dihydroxytryptamine (5,7-DHT), a serotonergic neurotoxin, was injected into the dorsal and median raphe nuclei of male Wistar rats. Ten days after the neurotoxin injections, the brain concentrations of neurotransmitters, serum hormone, and cytokine levels, as well as the expression of cytochrome P450 in the liver were measured. Injection of 5,7-DHT decreased serotonin concentration in the brain followed by a significant rise in the levels of the growth hormone, corticosterone, and testosterone, and a drop in triiodothyronine concentration in the serum. No changes in interleukin (IL) levels (IL-2 and IL-6) were observed. Simultaneously, the activity and protein level of liver CYP1A, CYP3A1, and CYP2C11 rose (the activity of CYP2A/2B/2C6/2D was not significantly changed). Similarly, the mRNA levels of CYP1A1, CYP1A2, CYP2C11, and CYP3A1 were elevated. This is the first report demonstrating the effect of intracerebral administration of serotonergic neurotoxin on liver cytochrome P450. The obtained results indicate involvement of the brain serotonergic system in the neuroendocrine regulation of liver cytochrome P450 expression. The physiologic and pharmacological significance of the findings is discussed.

The catalytic competence of cytochrome P450 in the synthesis of serotonin from 5-methoxytryptamine in the brain: an in vitro study.

Brain serotonin has been implicated in the pathophysiology of a wide spectrum of psychiatric disorders, as well as in the mechanism of action of psychotropic drugs. The aim of present study was to identify rat cytochrome P450 (CYP) isoforms which can catalyze the O-demethylation of 5-methoxytryptamine to serotonin, and to find out whether that alternative pathway of serotonin synthesis may take place in the brain. The study was conducted on cDNA-expressed CYPs (rat CYP1A1/2, 2A1/2, 2B1, 2C6/11/13, 2D1/2/4/18, 2E1, 3A2 and human CYP2D6), on rat brain and liver microsomes and on human liver microsomes (the wild-type CYP2D6 or the allelic variant 2D6*4*4). Of the rat CYP isoforms studied, CYP2D isoforms were the most efficient in catalyzing the O-demethylation of 5-methoxytryptamine to serotonin, but they were less effective than the human isoform CYP2D6. Microsomes from different brain regions were capable of metabolizing 5-methoxytryptamine to serotonin. The reaction was inhibited by the specific CYP2D inhibitors quinine and fluoxetine. Human liver microsomes of the wild-type CYP2D6 metabolized 5-methoxytryptamine to serotonin more effectively than did the defective CYP2D6*4*4 ones. The obtained results indicate that rat brain CYP2D isoforms catalyze the formation of serotonin from 5-methoxytryptamine, and that the deficit or genetic defect of CYP2D may affect serotonin metabolism in the brain. The results are discussed in the context of their possible physiological and pharmacological significance in vivo.

The Engagement of Cytochrome P450 Enzymes in Tryptophan Metabolism.

Tryptophan is metabolized along three main metabolic pathways, namely the kynurenine, serotonin and indole pathways. The majority of tryptophan is transformed via the kynurenine pathway, catalyzed by tryptophan-2,3-dioxygenase or indoleamine-2,3-dioxygenase, leading to neuroprotective kynurenic acid or neurotoxic quinolinic acid. Serotonin synthesized by tryptophan hydroxylase, and aromatic L-amino acid decarboxylase enters the metabolic cycle: serotonin → N-acetylserotonin → melatonin → 5-methoxytryptamine→serotonin. Recent studies indicate that serotonin can also be synthesized by cytochrome P450 (CYP), via the CYP2D6-mediated 5-methoxytryptamine O-demethylation, while melatonin is catabolized by CYP1A2, CYP1A1 and CYP1B1 via aromatic 6-hydroxylation and by CYP2C19 and CYP1A2 via O-demethylation. In gut microbes, tryptophan is metabolized to indole and indole derivatives. Some of those metabolites act as activators or inhibitors of the aryl hydrocarbon receptor, thus regulating the expression of CYP1 family enzymes, xenobiotic metabolism and tumorigenesis. The indole formed in this way is further oxidized to indoxyl and indigoid pigments by CYP2A6, CYP2C19 and CYP2E1. The products of gut-microbial tryptophan metabolism can also inhibit the steroid-hormone-synthesizing CYP11A1. In plants, CYP79B2 and CYP79B3 were found to catalyze N-hydroxylation of tryptophan to form indole-3-acetaldoxime while CYP83B1 was reported to form indole-3-acetaldoxime N-oxide in the biosynthetic pathway of indole glucosinolates, considered to be defense compounds and intermediates in the biosynthesis of phytohormones. Thus, cytochrome P450 is engaged in the metabolism of tryptophan and its indole derivatives in humans, animals, plants and microbes, producing biologically active metabolites which exert positive or negative actions on living organisms. Some tryptophan-derived metabolites may influence cytochrome P450 expression, affecting cellular homeostasis and xenobiotic metabolism.

The effect of brain serotonin deficit (TPH2-KO) on the expression and activity of liver cytochrome P450 enzymes in aging male Dark Agouti rats.

BACKGROUND: Liver cytochrome P450 (CYP) greatly contributes to the metabolism of endogenous substances and drugs. Recent studies have demonstrated that CYP expression in the liver is controlled by the central nervous system via hormonal pathways. In particular, the expression of hepatic CYPs is negatively regulated by the brain serotoninergic system. The present study aimed to investigate changes in the function of the main liver drug-metabolizing CYP enzymes as a result of serotonin depletion in the brain of aging rats, caused by knockout of brain tryptophan hydroxylase gene (TPH2-KO). METHODS: The hepatic CYP mRNA (qRT-PCR), protein level (Western blotting) and activity (HPLC), and serum hormone levels (ELISA) were measured in Dark Agouti wild-type (WT) male rats (mature 3.5-month-old and senescent 21-month-old) and in TPH2-KO senescent animals. RESULTS: The expression/activity of the studied CYPs decreased with age in the liver of wild-type rats. The deprivation of serotonin in the brain of aging males decreased the mRNA level of most of the studied CYPs (CYP1A/2A/2B/3A), and lowered the protein level of CYP2C11 and CYP3A. In contrast, the activities of CYP2C11, CYP3A and CYP2C6 were increased. The expression of cytochrome b5 decreased in aging rats, but increased in TPH2-deficient senescent animals. The serum concentration of growth hormone declined in the aged and further dropped down in TPH2-deficient senescent rats. CONCLUSIONS: Rat liver cytochrome P450 functions deteriorate with age, which may impair drug metabolism. The TPH2 knockout, which deprives brain serotonin, affects cytochrome P450 expression and activity differently in mature and senescent male rats.

The mechanisms of interactions of psychotropic drugs with liver and brain cytochrome P450 and their significance for drug effect and drug-drug interactions.

Cytochrome P450 (CYP) plays an important role in psychopharmacology. While liver CYP enzymes are responsible for the biotransformation of psychotropic drugs, brain CYP enzymes are involved in the local metabolism of these drugs and endogenous neuroactive substances, such as neurosteroids, and in alternative pathways of neurotransmitter biosynthesis including dopamine and serotonin. Recent studies have revealed a relation between the brain nervous system and cytochrome P450, indicating that CYP enzymes metabolize endogenous neuroactive substances in the brain, while the brain nervous system is engaged in the central neuroendocrine and neuroimmune regulation of cytochrome P450 in the liver. Therefore, the effect of neuroactive drugs on cytochrome P450 should be investigated not only in vitro, but also at in vivo conditions, since only in vivo all mechanisms of drug-enzyme interaction can be observed, including neuroendocrine and neuroimmune modulation. Psychotropic drugs can potentially affect cytochrome P450 via a number of mechanisms operating at the level of the nervous, hormonal and immune systems, and the liver. Their effect on cytochrome P450 in the brain is often different than in the liver and region-dependent. Since psychotropic drugs can affect cytochrome P450 both in the liver and brain, they can modify their own pharmacological effect at both pharmacokinetic and pharmacodynamic level. The article describes the mechanisms by which psychotropic drugs can change the expression/activity of cytochrome P450 in the liver and brain, and discusses the significance of those mechanisms for drug action and drug-drug interactions. Moreover, the brain CYP2D6 is considered as a potential target for psychotropics.

Cytochrome P450 2D (CYP2D) enzyme dysfunction associated with aging and serotonin deficiency in the brain and liver of female Dark Agouti rats.

Among the enzymes that support brain metabolism, cytochrome P450 (CYP) enzymes occupy an important place. These enzymes catalyze the biotransformation pathways of neuroactive endogenous substrates (neurosteroids, neurotransmitters) and are necessary for the detoxification processes. The aim of the present study was to assess changes in the CYP2D activity and protein level during the aging process and as a result of serotonin deficiency in the female brain. The CYP2D activity was measured in brain and liver microsomes of Dark Agouti wild type (WT) female rats (mature 15-week-old and senescent 18-month-old rats) and in tryptophan hydroxylase 2 (TPH2)-deficient senescent female rats. The CYP2D activity in mature WT Dark Agouti females was independent of the changing phases of the estrous cycle. In senescent WT females rats, the CYP2D activity and protein level were decreased in the cerebral cortex, hippocampus, cerebellum and liver, but increased in the brain stem. In the other examined structures (frontal cortex, hypothalamus, thalamus, striatum), the enzyme activity did not change. In aging TPH2-deficient females, the CYP2D activity and protein levels were decreased in the frontal cortex, hypothalamus and brain stem (activity only), remaining unchanged in other brain structures and liver, relative to senescent WT females. In summary, the aging process and TPH2 deficit affect the CYP2D activity and protein level in female rats, which may have a negative impact on the compensatory capacity of CYP2D in the synthesis of serotonin and dopamine in cerebral structures involved in cognitive and emotional functions. In the liver, the CYP2D-catalyzed drug metabolism may be diminished in elderly females. The results in female rats are compared with those obtained previously in males. It is concluded that aging and serotonin deficiency exert sex-dependent effects on brain CYP2D, which seem to be less favorable in females concerning CYP2D-mediated neurotransmitter synthesis, but beneficial regarding slower neurosteroid metabolism.

Cytochrome P450 mediates dopamine formation in the brain in vivo.

The cytochrome P450-mediated synthesis of dopamine from tyramine has been shown in vitro. The aim of the present study was to demonstrate the ability of rat cytochrome P450 (CYP) 2D to synthesize dopamine from tyramine in the brain in vivo. We employed two experimental models using reserpinized rats with a blockade of the classical pathway of dopamine synthesis from tyrosine. Model A estimated dopamine production from endogenous tyramine in brain structures in vivo (ex vivo measurement of a tissue dopamine level), while Model B measured extracellular dopamine produced from exogenous tyramine (an in vivo microdialysis). In Model A, quinine (a CYP2D inhibitor) given intraperitoneally caused a significant decrease in dopamine level in the striatum and nucleus accumbens and tended to fall in the substantia nigra and frontal cortex. In Model B, an increase in extracellular dopamine level was observed after tyramine given intrastructurally (the striatum). After joint administration of tyramine and quinine, the amount of the dopamine formed was significantly lower compared to the group receiving tyramine only. The results of the two complementary experimental models indicate that the hydroxylation of tyramine to dopamine may take place in rat brain in vivo, and that CYP2D catalyzes this reaction.

Chronic treatment with asenapine affects cytochrome P450 2D (CYP2D) in rat brain and liver. Pharmacological aspects.

Neuroleptics have to be used for a long time to produce a therapeutic effect. Cytochrome P450 2D (CYP2D) enzymes mediate alternative pathways of neurotransmitter synthesis (i.e. tyramine hydroxylation to dopamine and 5-methoxytryptamine O-demethylation to serotonin), and metabolism of neurosteroids. The aim of our present study was to examine the influence of chronic treatment with the new atypical neuroleptic asenapine on CYP2D in rat brain. In parallel, liver CYP2D was investigated for comparison. Asenapine added in vitro to microsomes of control rats competitively, but weakly inhibited the activity of CYP2D (brain: Ki = 385 µM; liver: Ki = 36 µM). However, prolonged administration of asenapine (0.3 mg/kg sc. for 2 weeks) significantly diminished the activity and protein level of CYP2D in the frontal cortex, nucleus accumbens, hippocampus and cerebellum, but did not affect the enzyme in the hypothalamus, brain stem, substantia nigra and the remainder of the brain. In contrast, asenapine enhanced the enzyme activity and protein level in the striatum. In the liver, chronically administered asenapine reduced the activity and protein level of CYP2D, and the CYP2D1 mRNA level. In conclusion, prolonged administration of asenapine alters the CYP2D expression in the brain structures and in the liver. Through affecting the CYP2D activity in the brain, asenapine may modify its pharmacological effect. By increasing the CYP2D expression/activity in the striatum, asenapine may accelerate the synthesis of dopamine (via tyramine hydroxylation) and serotonin (via 5-methoxytryptamine O-demethylation), and thus alleviate extrapyramidal symptoms. By reducing the CYP2D expression/activity in other brain structures asenapine may diminish the 21-hydroxylation of neurosteroids and thus have a beneficial influence on the symptoms of schizophrenia. In the liver, by reducing the CYP2D activity, asenapine may slow the biotransformation of concomitantly administered CYP2D substrates (drugs) during continuous treatment of schizophrenia or bipolar disorders.

The Selective NMDA Receptor GluN2B Subunit Antagonist CP-101,606 with Antidepressant Properties Modulates Cytochrome P450 Expression in the Liver.

Recent research indicates that selective NMDA receptor GluN2B subunit antagonists may become useful for the treatment of major depressive disorders. We aimed to examine in parallel the effect of the selective NMDA receptor GluN2B subunit antagonist CP-101,606 on the pituitary/serum hormone levels and on the regulation of cytochrome P450 in rat liver. CP-101,606 (20 mg/kg ip. for 5 days) decreased the activity of CYP1A, CYP2A, CYP2B, CYP2C11 and CYP3A, but not that of CYP2C6. The alterations in enzymatic activity were accompanied by changes in the CYP protein and mRNA levels. In parallel, a decrease in the pituitary growth hormone-releasing hormone, and in serum growth hormone and corticosterone (but not T3 and T4) concentration was observed. After a 3-week administration period of CP-101,606 less changes were found. A decrease in the CYP3A enzyme activity and protein level was still maintained, though no change in the mRNA level was found. A slight decrease in the serum concentration of corticosterone was also maintained, while GH level returned to the control value. The obtained results imply engagement of the glutamatergic system in the neuroendocrine regulation of cytochrome P450 and potential involvement of drugs acting on NMDA receptors in metabolic drug-drug interactions.

The effects of agomelatine and imipramine on liver cytochrome P450 during chronic mild stress (CMS) in the rat.

BACKGROUND: The aim of our research was to determine the effects of chronic treatment with the atypical antidepressant agomelatine on the expression and activity of liver cytochrome P450 (CYP) in the chronic mild stress (CMS) model of depression, and to compare the results with those obtained for the first-generation antidepressant imipramine. METHODS: Male Wistar rats were subjected to CMS for 7 weeks. Imipramine (10 mg/kg ip/day) or agomelatine (40 mg/kg ip/day) was administered to nonstressed or stressed animals for 5 weeks (weeks 3-7 of CMS). The levels of cytochrome P450 mRNA, protein and activity were measured in the liver. RESULTS: Agomelatine and imipramine produced different broad-spectrum effects on cytochrome P450. Like imipramine, agomelatine increased the expression/activity of CYP2B and CYP2C6, and decreased the CYP2D activity. Unlike imipramine, agomelatine raised the expression/activity of CYP1A, CYP2A and reduced that of CYP2C11 and CYP3A. CMS modified the effects of antidepressants at transcriptional/posttranscriptional level; however, the enzyme activity in stressed rats remained similar to that in nonstressed animals. CMS alone decreased the CYP2B1 mRNA level and increased that of CYP2C11. CONCLUSION: We conclude the following: (1) the effects of agomelatine and imipramine on cytochrome P450 are different and involve both central and peripheral regulatory mechanisms, which implicates the possibility of drug-drug interactions; (2) CMS influences the effects of antidepressants on cytochrome P450 expression, but does not change appreciably their effects on the enzyme activity. This suggests that the rate of antidepressant drug metabolism under CMS is similar to that under normal conditions.

The effect of ageing and cerebral serotonin deficit on the activity of cytochrome P450 2D (CYP2D) in the brain and liver of male rats.

Brain cytochrome P450 (CYP) contributes to the local metabolism of endogenous substrates and drugs. The aim of present study was to ascertain whether the cytochrome P450 2D (CYP2D) activity changes with ageing and in cerebral serotonin deficit. Kinetics of 5-methoxytryptamine O-demethylation to serotonin was studied and the CYP2D activity was measured in brain and liver microsomes of Dark Agouti wild type (WT) rats (mature 3.5-month-old and senescent 21-month-old rats) and in tryptophan hydroxylase 2 (TPH2)-deficient senescent rats. The CYP2D activity and protein level decreased in the frontal cortex of senescent WT rats, but increased in senescent TPH2-deficient rats (compared to senescent WT). In contrast, in the hippocampus, hypothalamus and striatum the CYP2D activity/protein level increased with ageing, but did not change in senescent TPH2-deficient animals (compared to senescent WT). The activity and protein level of liver CYP2D was lower in senescent WT rats than in the mature animals and further decreased in senescent TPH2-deficient rats. In conclusion, ageing and TPH2-deficit affect the CYP2D activity and protein level, which may have a positive impact on neurotransmitter synthesis in brain structures involved in cognitive, emotional or motor functions, but a negative effect on drug metabolism in the liver.

Stimulation of 5-HT2C serotonin receptor subtype in the hypothalamic arcuate nuclei (ARC) increases the cytochrome P450 activity in the liver.

BACKGROUND: Our previous study has demonstrated that activation of the 5-HT2, but not 5-HT1 serotonin receptor type in the hypothalamic arcuate nucleus (ARC) is responsible for the neuroendocrine regulation of liver cytochrome P450. The goal of these studies was to determine whether 5-HT2C serotonin receptor subtype in the ARC is engaged in the regulation of liver cytochrome P450. METHODS: The 5-HT2C serotonin receptor agonist CP-809,101 was injected into the ARC for 5 days. The liver cytochrome P450 activity and protein level were measured. RESULTS: In rats receiving an injection of the 5-HT2C serotonin receptor agonist CP-809,101 into the ARC (1 µg/side) for five days, the activities of CYP2B, CYP2C11 and CYP3A significantly increased corresponding with the elevated enzyme protein level. CONCLUSIONS: The obtained results suggest that the 5-HT2C serotonin receptor subtype in the ARC is involved in the positive neuroendocrine regulation of cytochrome P450. Further studies are in progress to explain the physiological mechanism which is responsible for the observed regulation of cytochrome P450 by 5-HT2C receptor present in the ARC.