Cytochrome P450 mediates dopamine formation in the brain in vivo

Assessment of the relationship between the dopaminergic pathway and severe acute respiratory syndrome coronavirus 2 infection, with related neuropathological features, and potential therapeutic approaches in COVID-19 infection

Dopamine is a known catecholamine neurotransmitter involved in several physiological processes, including motor control, motivation, reward, cognition, and immune function. Dopamine receptors are widely distributed throughout the nervous system and in immune cells. Several viruses, including human immunodeficiency virus and Japanese encephalitis virus, can use dopaminergic receptors to replicate in the nervous system and are involved in viral neuropathogenesis. In addition, studies suggest that dopaminergic receptors may play a role in the progression and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. When SARS-CoV-2 binds to angiotensin-converting enzyme 2 receptors on the surface of neuronal cells, the spike protein of the virus can bind to dopaminergic receptors on neighbouring cells to accelerate its life cycle and exacerbate neurological symptoms. In addition, recent research has shown that dopamine is an important regulator of the immune-neuroendocrine system. Most immune cells express dopamine receptors and other dopamine-related proteins, indicating the importance of dopaminergic immune regulation. The increase in dopamine concentration during SARS-CoV2 infection may reduce immunity (innate and adaptive) that promotes viral spread, which could lead to neuronal damage. In addition, dopaminergic signalling in the nervous system may be affected by SARS-CoV-2 infection. COVID -19 can cause various neurological symptoms as it interacts with the immune system. One possible treatment strategy for COVID -19 patients could be the use of dopamine antagonists. To fully understand how to protect the neurological system and immune cells from the virus, we need to study the pathophysiology of the dopamine system in SARS-CoV-2 infection.

High-throughput assessment of metabolism-mediated neurotoxicity by combining 3D-cultured neural stem cells and liver cell spheroids

Despite the fact that biotransformation in the liver plays an important role in the augmented toxicity and detoxification of chemicals, relatively little efforts have been made to incorporate biotransformation into in vitro neurotoxicity testing. Conventional in vitro systems for neurotoxicity tests lack the capability of investigating the qualitative and quantitative differences between parent chemicals and their metabolites in the human body. Therefore, there is a need for an in vitro toxicity screening system that can incorporate hepatic biotransformation of chemicals and predict the susceptibility of their metabolites to induce neurotoxicity. To address this need, we adopted 3D cultures of metabolically competent HepaRG cell line with ReNcell VM and established a high-throughput, metabolism-mediated neurotoxicity testing system. Briefly, spheroids of HepaRG cells were generated in an ultralow attachment (ULA) 384-well plate while 3D-cultured ReNcell VM was established on a 384-pillar plate with sidewalls and slits (384PillarPlate). Metabolically sensitive test compounds were added in the ULA 384-well plate with HepaRG spheroids and coupled with 3D-cultured ReNcell VM on the 384PillarPlate, which allowed us to generate metabolites in situ by HepaRG cells and test them against neural stem cells. We envision that this approach could be potentially adopted in pharmaceutical and chemical industries when high-throughput screening (HTS) is necessary to assess neurotoxicity of compounds and their metabolites.

Metabolome subtyping reveals multi-omics characteristics and biological heterogeneity in major psychiatric disorders

Growing evidence suggests that major psychiatric disorders (MPDs) share common etiologies and pathological processes. However, the diagnosis is currently based on descriptive symptoms, which ignores the underlying pathogenesis and hinders the development of clinical treatments. This highlights the urgency of characterizing molecular biomarkers and establishing objective diagnoses of MPDs. Here, we collected untargeted metabolomics, proteomics and DNA methylation data of 327 patients with MPDs, 131 individuals with genetic high risk and 146 healthy controls to explore the multi-omics characteristics of MPDs. First, differential metabolites (DMs) were identified and we classified MPD patients into 3 subtypes based on DMs. The subtypes showed distinct metabolomics, proteomics and DNA methylation signatures. Specifically, one subtype showed dysregulation of complement and coagulation proteins, while the DNA methylation showed abnormalities in chemical synapses and autophagy. Integrative analysis in metabolic pathways identified the important roles of the citrate cycle, sphingolipid metabolism and amino acid metabolism. Finally, we constructed prediction models based on the metabolites and proteomics that successfully captured the risks of MPD patients. Our study established molecular subtypes of MPDs and elucidated their biological heterogeneity through a multi-omics investigation. These results facilitate the understanding of pathological mechanisms and promote the diagnosis and prevention of MPDs.

Molecular Toxicology and Pathophysiology of Comorbid Alcohol Use Disorder and Post-Traumatic Stress Disorder Associated with Traumatic Brain Injury

The increasing comorbidity of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) associated with traumatic brain injury (TBI) is a serious medical, economic, and social issue. However, the molecular toxicology and pathophysiological mechanisms of comorbid AUD and PTSD are not well understood and the identification of the comorbidity state markers is significantly challenging. This review summarizes the main characteristics of comorbidity between AUD and PTSD (AUD/PTSD) and highlights the significance of a comprehensive understanding of the molecular toxicology and pathophysiological mechanisms of AUD/PTSD, particularly following TBI, with a focus on the role of metabolomics, inflammation, neuroendocrine, signal transduction pathways, and genetic regulation. Instead of a separate disease state, a comprehensive examination of comorbid AUD and PTSD is emphasized by considering additive and synergistic interactions between the two diseases. Finally, we propose several hypotheses of molecular mechanisms for AUD/PTSD and discuss potential future research directions that may provide new insights and translational application opportunities.

Biotransformation of Efavirenz and Proteomic Analysis of Cytochrome P450s and UDP-Glucuronosyltransferases in Mouse, Macaque, and Human Brain-Derived In Vitro Systems

Antiretroviral drugs such as efavirenz (EFV) are essential to combat human immunodeficiency virus (HIV) infection in the brain, but little is known about how these drugs are metabolized locally. In this study, the cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT)-dependent metabolism of EFV was probed in brain microsomes from mice, cynomolgus macaques, and humans as well as primary neural cells from C57BL/6N mice. Utilizing ultra high performance liquid chromatography high-resolution mass spectrometry (uHPLC-HRMS), the formation of 8-hydroxyefavirenz (8-OHEFV) from EFV and the glucuronidation of P450-dependent metabolites 8-OHEFV and 8,14-dihydroxyefavirenz (8,14-diOHEFV) were observed in brain microsomes from all three species. The direct glucuronidation of EFV, however, was only detected in cynomolgus macaque brain microsomes. In primary neural cells treated with EFV, microglia were the only cell type to exhibit metabolism, forming 8-OHEFV only. In cells treated with the P450-dependent metabolites of EFV, glucuronidation was detected only in cortical neurons and astrocytes, revealing that certain aspects of EFV metabolism are cell type specific. Untargeted and targeted proteomics experiments were used to identify the P450s and UGTs present in brain microsomes. Eleven P450s and 11 UGTs were detected in human brain microsomes, whereas seven P450s and 14 UGTs were identified in mouse brain microsomes and 15 P450s and four UGTs, respectively, were observed in macaque brain microsomes. This was the first time many of these enzymes have been noted in brain microsomes at the protein level. This study indicates the potential for brain metabolism to contribute to pharmacological and toxicological outcomes of EFV in the brain. SIGNIFICANCE STATEMENT: Metabolism in the brain is understudied, and the persistence of human immunodeficiency virus (HIV) infection in the brain warrants the evaluation of how antiretroviral drugs such as efavirenz are metabolized in the brain. Using brain microsomes, the metabolism of efavirenz by both cytochrome P450s (P450s) and UDP-glucuronosyltransferases (UGTs) is established. Additionally, proteomics of brain microsomes characterizes P450s and UGTs in the brain, many of which have not yet been noted in the literature at the protein level.

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.

The Atypical Antipsychotic Lurasidone Affects Brain but Not Liver Cytochrome P450 2D (CYP2D) Activity. A Comparison with Other Novel Neuroleptics and Significance for Drug Treatment of Schizophrenia

The aim of this work was to study the effect of prolonged lurasidone administration on the cytochrome 2D (CYP2D) expression and activity in the rat liver and selected brain structures involved in the therapeutic or side effects of this neuroleptic. Male Wistar rats received lurasidone (1 mg/kg ip.) for two weeks. The activity of CYP2D was measured in brain and liver microsomes as the rate of bufuralol 1′-hydroxylation. The CYP2D protein level was determined in microsomes by Western blot analysis. The CYP2D gene expression was estimated in liver tissue by a qRT-PCR method. Lurasidone decreased the activity and protein level of CYP2D in the frontal cortex but increased them in the striatum, nucleus accumbens, brain stem, substantia nigra, and the remainder of the brain. The neuroleptic did not affect CYP2D in the hippocampus, hypothalamus, and cerebellum. In the liver, lurasidone did not affect the CYP2D activity and protein level, though it enhanced the mRNA of CYP2D1 without affecting that of CYP2D2, CYP2D3, CYP2D4, and CYP2D5. In conclusion, lurasidone regulates brain (but not liver) CYP2D activity/protein level in a region-dependent manner, which is similar to that of other atypical neuroleptics (iloperidone and asenapine) as concerns the frontal cortex (down-regulation) and nigrostriatal pathway (up-regulation) and may be of pharmacological significance. However, further molecular studies with selective receptor agonists are necessary to find out which individual monoaminergic receptors/signaling pathways are involved in the regulation of the rat CYP2D4 and human CYP2D6 enzyme in particular brain structures.

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.

CYP450 2D6 and 2C19 genotypes in ADHD: not related with treatment resistance but with over-representation of 2C19 ultra-metabolizers

OBJECTIVES

Cytochrome P450 (CYP450) is a major enzyme system involved in drug metabolism as well as regulation of brain function. Although individual variability in CYP enzymes have been studied in terms of personality traits and treatment effects, no study up to now evaluated CYP polymorphisms in children with attention deficit/hyperactivity disorder (ADHD). We aimed to define the genetic profiles of CYP2D6 and CYP2C19 relevant alleles in children with ADHD according to treatment status and compare the frequencies according to past results.

METHODS

Three hundred and seventeen patients with ADHD-Combined Presentation were enrolled; symptom severity was evaluated by parents and clinicians while adverse effects of previous treatments were evaluated with parent and child reports. Reverse blotting on strip assays was used for genotyping and descriptive and bivariate analyses were conducted. A p-value was set at 0.05 (two-tailed).

RESULTS

Children were divided into treatment-naïve (n=194, 61.2%) and treatment-resistant (n=123, 38.8%) groups. Within the whole sample PM, EM and UM status according to 2D6 were 3.8% (n=12), 94.3% (n=299) and 21.9% (n=6); respectively. PM, IM, EM and UM status according to 2C19 were 2.5% (n=8), 19.8% (n=63), 48.6% (n=154) and 29.0% (n=92), respectively. No relationship with treatment resistance, comorbidity or gender could be found. Importantly, CYP2C19 UMs were significantly more frequent in ADHD patients compared to previous studies in the general population.

CONCLUSIONS

CYPs may be a rewarding avenue of research to elucidate the etiology and treatment of patients with ADHD.

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.

Long-Term Treatment with Atypical Antipsychotic Iloperidone Modulates Cytochrome P450 2D (CYP2D) Expression and Activity in the Liver and Brain via Different Mechanisms

CYP2D enzymes engage in the synthesis of endogenous neuroactive substances (dopamine, serotonin) and in the metabolism of neurosteroids. The present work investigates the effect of iloperidone on CYP2D enzyme expression and activity in rat brains and livers. Iloperidone exerted a weak direct inhibitory effect on CYP2D activity in vitro in the liver and brain microsomes (K_i = 11.5 μM and K_i = 462 μM, respectively). However, a two-week treatment with iloperidone (1 mg/kg ip.) produced a significant decrease in the activity of liver CYP2D, which correlated positively with the reduced CYP2D1, CYP2D2 and CYP2D4 protein and mRNA levels. Like in the liver, iloperidone reduced CYP2D activity and protein levels in the frontal cortex and cerebellum but enhanced these levels in the nucleus accumbens, striatum and substantia nigra. Chronic iloperidone did not change the brain CYP2D4 mRNA levels, except in the striatum, where they were significantly increased. In conclusion, by affecting CYP2D activity in the brain, iloperidone may modify its pharmacological effect, via influencing the rate of dopamine and serotonin synthesis or the metabolism of neurosteroids. By elevating the CYP2D expression/activity in the substantia nigra and striatum (i.e., in the dopaminergic nigrostriatal pathway), iloperidone may attenuate extrapyramidal symptoms, while by decreasing the CYP2D activity and metabolism of neurosteroiods in the frontal cortex and cerebellum, iloperidone can have beneficial effects in the treatment of schizophrenia. In the liver, pharmacokinetic interactions involving chronic iloperidone and CYP2D substrates are likely to occur.

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.

HIV-Associated Apathy/Depression and Neurocognitive Impairments Reflect Persistent Dopamine Deficits

Individuals living with human immunodeficiency virus type 1 (HIV-1) are often plagued by debilitating neurocognitive impairments and affective alterations;the pathophysiology underlying these deficits likely includes dopaminergic system dysfunction. The present review utilized four interrelated aims to critically examine the evidence for dopaminergic alterations following HIV-1 viral protein exposure. First, basal dopamine (DA) values are dependent upon both brain region andexperimental approach (i.e., high-performance liquid chromatography, microdialysis or fast-scan cyclic voltammetry). Second, neurochemical measurements overwhelmingly support decreased DA concentrations following chronic HIV-1 viral protein exposure. Neurocognitive impairments, including alterations in pre-attentive processes and attention, as well as apathetic behaviors, provide an additional line of evidence for dopaminergic deficits in HIV-1. Third, to date, there is no compelling evidence that combination antiretroviral therapy (cART), the primary treatment regimen for HIV-1 seropositive individuals, has any direct pharmacological action on the dopaminergic system. Fourth, the infection of microglia by HIV-1 viral proteins may mechanistically underlie the dopamine deficit observed following chronic HIV-1 viral protein exposure. An inclusive and critical evaluation of the literature, therefore, supports the fundamental conclusion that long-term HIV-1 viral protein exposure leads to a decreased dopaminergic state, which continues to persist despite the advent of cART. Thus, effective treatment of HIV-1-associated apathy/depression and neurocognitive impairments must focus on strategies for rectifying decreases in dopamine function.

Alterations of Cytochrome P450s and UDP-Glucuronosyltransferases in Brain Under Diseases and Their Clinical Significances

Cytochrome P450s (CYPs) and UDP-glucuronosyltransferases (UGTs) are both greatly important metabolic enzymes in various tissues, including brain. Although expressions of brain CYPs and UGTs and their contributions to drug disposition are much less than liver, both CYPs and UGTs also mediate metabolism of endogenous substances including dopamine and serotonin as well as some drugs such as morphine in brain, demonstrating their important roles in maintenance of brain homeostasis or pharmacological activity of drugs. Some diseases such as epilepsy, Parkinson's disease and Alzheimer's disease are often associated with the alterations of CYPs and UGTs in brain, which may be involved in processes of these diseases via disturbing metabolism of endogenous substances or resisting drugs. This article reviewed the alterations of CYPs and UGTs in brain, the effects on endogenous substances and drugs and their clinical significances. Understanding the roles of CYPs and UGTs in brain provides some new strategies for the treatment of central nervous system diseases.

Cytochrome P450 expression and regulation in the brain

The regulation of brain cytochrome P450 enzymes (CYPs) is different compared with respective hepatic enzymes. This may result from anatomical bases and physiological functions of the two organs. The brain is composed of a variety of functional structures built of different interconnected cell types endowed with specific receptors that receive various neuronal signals from other brain regions. Those signals activate transcription factors or alter functioning of enzyme proteins. Moreover, the blood-brain barrier (BBB) does not allow free penetration of all substances from the periphery into the brain. Differences in neurotransmitter signaling, availability to endogenous and exogenous active substances, and levels of transcription factors between neuronal and hepatic cells lead to differentiated expression and susceptibility to the regulation of CYP genes in the brain and liver. Herein, we briefly describe the CYP enzymes of CYP1-3 families, their distribution in the brain, and discuss brain-specific regulation of CYP genes. In parallel, a comparison to liver CYP regulation is presented. CYP enzymes play an essential role in maintaining the levels of bioactive molecules within normal ranges. These enzymes modulate the metabolism of endogenous neurochemicals, such as neurosteroids, dopamine, serotonin, melatonin, anandamide, and exogenous substances, including psychotropics, drugs of abuse, neurotoxins, and carcinogens. The role of these enzymes is not restricted to xenobiotic-induced neurotoxicity, but they are also involved in brain physiology. Therefore, it is crucial to recognize the function and regulation of CYP enzymes in the brain to build a foundation for future medicine and neuroprotection and for personalized treatment of brain diseases.

Integrating biokinetics and in vitro studies to evaluate developmental neurotoxicity induced by chlorpyrifos in human iPSC-derived neural stem cells undergoing differentiation towards neuronal and glial cells

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Human iPSC-derived NSCs undergoing differentiation possess some metabolic competence.

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CPF entered the cells and was biotrasformed into its two main metabolites (CPFO and TCP).

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After repeated exposure, very limited bioaccumulation of CPF was observed.

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Treatment with CPF decreased neurite outgrowth, synapse number and electrical activity.

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Treatment with CPF increased BDNF levels and the percentage of astrocytes.

For some complex toxicological endpoints, chemical safety assessment has conventionally relied on animal testing. Apart from the ethical issues, also scientific considerations have been raised concerning the traditional approach, highlighting the importance for considering real life exposure scenario. Implementation of flexible testing strategies, integrating multiple sources of information, including in vitro reliable test methods and in vitro biokinetics, would enhance the relevance of the obtained results. Such an approach could be pivotal in the evaluation of developmental neurotoxicity (DNT), especially when applied to human cell-based models, mimicking key neurodevelopmental processes, relevant to human brain development.

Here, we integrated the kinetic behaviour with the toxicodynamic alterations of chlorpyrifos (CPF), such as in vitro endpoints specific for DNT evaluation, after repeated exposure during differentiation of human neural stem cells into a mixed culture of neurons and astrocytes. The upregulation of some cytochrome P450 and glutathione S-transferase genes during neuronal differentiation and the formation of the two major CPF metabolites (due to bioactivation and detoxification) supported the metabolic competence of the used in vitro model. The alterations in the number of synapses, neurite outgrowth, brain derived neurotrophic factor, the proportion of neurons and astrocytes, as well as spontaneous electrical activity correlated well with the CPF ability to enter the cells and be bioactivated to CPF-oxon. Overall, our results confirm that combining in vitro biokinetics and assays to evaluate effects on neurodevelopmental endpoints in human cells should be regarded as a key strategy for a quantitative characterization of DNT effects.

Human CYP2D6 in the Brain Is Protective Against Harmine-Induced Neurotoxicity: Evidence from Humanized CYP2D6 Transgenic Mice

CYP2D6 metabolically inactivates several neurotoxins, including beta-carbolines, which are implicated in neurodegenerative diseases. Variation in CYP2D6 within the brain may alter local inactivation of neurotoxic beta-carbolines, thereby influencing neurotoxicity. The beta-carboline harmine, which induces hypothermia and tremor, is metabolized by CYP2D6 to the non-hypothermic/non-tremorgenic harmol. Transgenic mice (TG), expressing human CYP2D6 in addition to their endogenous mouse CYP2D, experience less harmine-induced hypothermia and tremor compared with wild-type mice (WT). We first sought to elucidate the role of CYP2D in general within the brain in harmine-induced hypothermia and tremor severity. A 4-h intracerebroventricular (ICV) pretreatment with the CYP2D inhibitor propranolol increased harmine-induced hypothermia and tremor in TG and increased harmine-induced hypothermia in WT. We next sought to specifically demonstrate that human CYP2D6 expressed in TG brain altered harmine response severity. A 24-h ICV propranolol pretreatment, which selectively and irreversibly inhibits human CYP2D6 in TG brain, increased harmine-induced hypothermia. This 24-h pretreatment had no impact on harmine response in WT, as propranolol is not an irreversible inhibitor of mouse CYP2D in the brain, thus confirming no off-target effects of ICV propranolol pretreatment. Human CYP2D6 activity in TG brain was sufficient in vivo to mitigate harmine-induced neurotoxicity. These findings suggest that human CYP2D6 in the brain is protective against beta-carboline-induced neurotoxicity and that the extensive interindividual variability in CYP2D6 expression in human brain may contribute to variation in susceptibility to certain neurotoxin-associated neurodegenerative disorders.

Highly Variable Pharmacokinetics of Tyramine in Humans and Polymorphisms in OCT1, CYP2D6, and MAO-A

Tyramine, formed by the decarboxylation of tyrosine, is a natural constituent of numerous food products. As an indirect sympathomimetic, it can have potentially dangerous hypertensive effects. In vitro data indicated that the pharmacokinetics of tyramine possibly depend on the organic cation transporter OCT1 genotype and on the CYP2D6 genotype. Since tyramine is a prototypic substrate of monoamine oxidase A (MAO-A), genetic polymorphisms in MAO-A may also be relevant. The aims of this study were to identify to what extent the interindividual variation in pharmacokinetics and pharmacodynamics of tyramine is determined by genetic polymorphisms in OCT1, CYP2D6, and MAO-A. Beyond that, we wanted to evaluate tyramine as probe drug for the in vivo activity of MAO-A and OCT1. Therefore, the pharmacokinetics, pharmacodynamics, and pharmacogenetics of tyramine were studied in 88 healthy volunteers after oral administration of a 400 mg dose. We observed a strong interindividual variation in systemic tyramine exposure, with a mean AUC of 3.74 min*µg/ml and a high mean CL/F ratio of 107 l/min. On average, as much as 76.8% of the dose was recovered in urine in form of the MAO-catalysed metabolite 4-hydroxyphenylacetic acid (4-HPAA), confirming that oxidative deamination by MAO-A is the quantitatively most relevant metabolic pathway. Systemic exposure of 4-HPAA varied only up to 3-fold, indicating no strong heritable variation in peripheral MAO-A activity. Systolic blood pressure increased by more than 10 mmHg in 71% of the volunteers and correlated strongly with systemic tyramine concentration. In less than 10% of participants, individually variable blood pressure peaks by >40 mmHg above baseline were observed at tyramine concentrations of >60 µg/l. Unexpectedly, the functionally relevant polymorphisms in OCT1 and CYP2D6, including the CYP2D6 poor and ultra-rapid metaboliser genotypes, did not significantly affect tyramine pharmacokinetics or pharmacodynamics. Also, the MOA-A genotypes, which had been associated in several earlier studies with neuropsychiatric phenotypes, had no significant effects on tyramine pharmacokinetics or its metabolism to 4-HPAA. Thus, variation in tyramine pharmacokinetics and pharmacodynamics is not explained by obvious genomic variation, and human tyramine metabolism did not indicate the existence of ultra-low or -high MAO-A activity.

Effect of copper nanoparticles on brain cytochrome P450 enzymes in rats

The aim of the present study was to evaluate the long‑term effect of copper nanoparticles (CuNPs) on cytochrome P450 (CYP450) enzymes in the rat brain. Rats were repeatedly gavaged with different forms of copper sources for 28 days, and the levels of oxidative stress and CYP450 mRNA and protein expression in the rat brain were subsequently analyzed. The results demonstrated that a high dose of CuNPs (200 mg/kg) induced severe oxidative stress in the rat brain along with a decrease in the levels of total superoxide dismutase and glutathione, and an increase in hydroxyl radicals and malondialdehyde. A medium dose of CuNPs reduced CYP450 2C11 and CYP450 3A1 protein expression in the rat brain, whereas high doses of CuNPs resulted in decreased expression of most CYP450 enzyme proteins, and inhibition of pregnane X receptor and constitutive androstane receptor expression. The results suggested that CuNPs may inhibit CYP450 enzyme expression by increasing the levels of oxidative stress and decreasing the expression of nuclear receptors in the rat brain, which affects the metabolism of drugs and endogenous hormones in the brain.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Dopamine, Oxidative Stress and Protein-Quinone Modifications in Parkinson's and Other Neurodegenerative Diseases

Dopamine (DA) is the most important catecholamine in the brain, as it is the most abundant and the precursor of other neurotransmitters. Degeneration of nigrostriatal neurons of substantia nigra pars compacta in Parkinson's disease represents the best-studied link between DA neurotransmission and neuropathology. Catecholamines are reactive molecules that are handled through complex control and transport systems. Under normal conditions, small amounts of cytosolic DA are converted to neuromelanin in a stepwise process involving melanization of peptides and proteins. However, excessive cytosolic or extraneuronal DA can give rise to nonselective protein modifications. These reactions involve DA oxidation to quinone species and depend on the presence of redox-active transition metal ions such as iron and copper. Other oxidized DA metabolites likely participate in post-translational protein modification. Thus, protein-quinone modification is a heterogeneous process involving multiple DA-derived residues that produce structural and conformational changes of proteins and can lead to aggregation and inactivation of the modified proteins.

CYP2D6 Pharmacogenetics Testing and Post-Cesarean Section Pain Scores-a Preliminary Study

OBJECTIVE

Prospective observational study to analyze CYP2D6 pharmacogenetics in 55 Portuguese adult parturients undergoing elective cesarean section and to investigate the association between CYP2D6 alleles and pain score.

METHODS

DNA was extracted from peripheral blood by standard methods. Genetic analysis included allelic discrimination (CYP2D6*1, *2, *3, *4, *5, *6, *10, *17, and *41) and copy number determination with TaqMan probes by real-time polymerase chain reaction (PCR). Allele duplications were confirmed (long PCR and PCR-restriction fragment length polymorphism). Theoretical metabolic profiles prediction was based on genetic data and activity scores. Association was investigated between genotypes and predicted phenotypes with pain scores. Statistical analysis was performed by using a χ2 test, and significance was set at P < 0.05.

RESULTS

The percentage of poor, intermediate, extensive, and ultrarapid metabolizers found were 9%, 38%, 46%, and 7%, respectively. The results reveal a positive association between alleles *4, *10, and pain.

CONCLUSIONS

A positive association was found between predicted reduced or null activity of CYP2D6 and increased pain. It can be hypothesized that if CYP2D6 activity is reduced, tyramine metabolism will decrease, resulting in reduced formation of endogenous dopamine. Consequently, activation of the signal transduction pathways that controls pain and analgesic effect may be reduced, leading to an increase in pain. Therefore, we would recommend CYP2D6 genotyping to anticipate the needs for analgesia, which will help to adjust opioid dose and maximize clinical efficacy while reducing side effects.

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.

Dopamine: Functions, Signaling, and Association with Neurological Diseases

The dopaminergic system plays important roles in neuromodulation, such as motor control, motivation, reward, cognitive function, maternal, and reproductive behaviors. Dopamine is a neurotransmitter, synthesized in both central nervous system and the periphery, that exerts its actions upon binding to G protein-coupled receptors. Dopamine receptors are widely expressed in the body and function in both the peripheral and the central nervous systems. Dopaminergic signaling pathways are crucial to the maintenance of physiological processes and an unbalanced activity may lead to dysfunctions that are related to neurodegenerative diseases. Unveiling the neurobiology and the molecular mechanisms that underlie these illnesses may contribute to the development of new therapies that could promote a better quality of life for patients worldwide. In this review, we summarize the aspects of dopamine as a catecholaminergic neurotransmitter and discuss dopamine signaling pathways elicited through dopamine receptor activation in normal brain function. Furthermore, we describe the potential involvement of these signaling pathways in evoking the onset and progression of some diseases in the nervous system, such as Parkinson's, Schizophrenia, Huntington's, Attention Deficit and Hyperactivity Disorder, and Addiction. A brief description of new dopaminergic drugs recently approved and under development treatments for these ailments is also provided.

The activity of brain and liver cytochrome P450 2D (CYP2D) is differently affected by antidepressants in the chronic mild stress (CMS) model of depression in the rat

The effect of two second-generation antidepressants escitalopram and venlafaxine on the activity of brain and liver cytochrome P450 2D (CYP2D) involved in the metabolism of psychotropics and neurotransmitters was determined in the chronic mild stress (CMS) model of depression. Escitalopram or venlafaxine (10 mg/kg ip/day each) were administered to control and CMS rats for 5 weeks. The activity of CYP2D was studied by measurement of the rate of bufuralol 1'-hydroxylation in microsomes derived from the liver or different brain structures. The obtained results indicate that CMS and the studied antidepressants had different effects on the CYP2D activity depending on the location of the enzyme. In the brain, CMS produced an increase in the CYP2D activity in the hippocampus. Chronic escitalopram or venlafaxine had no effect on the CYP2D activity in the brain of nonstressed rats, however, the antidepressants increased the enzyme activity in the frontal cortex, hypothalamus and cerebellum of stressed animals. In the liver, CMS did not affect the CYP2D activity, while chronic escitalopram or venlafaxine significantly decreased the CYP2D activity and protein level in nonstressed and stressed rats. We conclude that: 1) CMS stimulates the CYP2D activity in the hippocampus and triggers the stimulatory effect of antidepressants on CYP2D in other brain structures; 2) the local brain metabolism of CYP2D substrates (neurosteroids, neurotransmitters, psychotropics) may be enhanced by CMS and/or antidepressants; 3) in contrast to the brain, the liver metabolism of CYP2D substrates may be slower during long-term treatment with escitalopram or venlafaxine.

A Systems Model of Parkinson's Disease Using Biochemical Systems Theory

Parkinson's disease (PD), a neurodegenerative disorder, affects millions of people and has gained attention because of its clinical roles affecting behaviors related to motor and nonmotor symptoms. Although studies on PD from various aspects are becoming popular, few rely on predictive systems modeling approaches. Using Biochemical Systems Theory (BST), this article attempts to model and characterize dopaminergic cell death and understand pathophysiology of progression of PD. PD pathways were modeled using stochastic differential equations incorporating law of mass action, and initial concentrations for the modeled proteins were obtained from literature. Simulations suggest that dopamine levels were reduced significantly due to an increase in dopaminergic quinones and 3,4-dihydroxyphenylacetaldehyde (DOPAL) relating to imbalances compared to control during PD progression. Associating to clinically observed PD-related cell death, simulations show abnormal parkin and reactive oxygen species levels with an increase in neurofibrillary tangles. While relating molecular mechanistic roles, the BST modeling helps predicting dopaminergic cell death processes involved in the progression of PD and provides a predictive understanding of neuronal dysfunction for translational neuroscience.

The Involvement of PPARs in the Selective Regulation of Brain CYP2D by Growth Hormone

Brain CYP2D is responsible for the synthesis of endogenous neurotransmitters such as dopamine and serotonin. This study is to investigate the effects of cerebral CYP2D on mouse behavior and the mechanism whereby growth hormone regulates brain CYP2D. The inhibition of cerebellar CYP2D significantly affected the spatial learning and exploratory behavior of mice. CYP2D expression was lower in the brain in GHR-/- mice than that in WT mice; however, hepatic CYP2D levels were similar. Brain PPARα expression in male GHR-/- mice were markedly higher than those in WT mice, while brain PPARγ levels were decreased or unchanged in different regions. However, both hepatic PPARα and PPARγ in male GHR-/- mice were markedly higher than those in WT mice. Pulsatile GH decreased the PPARα mRNA level and increased the mRNA levels of CYP2D6 and PPARγ in SH-SY5Y cells. A luciferase assay showed that PPARγ activated the CYP2D6 gene promoter while PPARα inhibited its function. Pulsatile GH decreased the binding of PPARα to the CYP2D6 promoter by 40% and promoted the binding of PPARγ to the CYP2D6 promoter by approximately 60%. The male GH secretory pattern altered PPAR expression and the binding of PPARs to the CYP2D promoter, leading to the elevation of brain CYP2D in a tissue-specific manner. Growth hormone may alter the learning and memory functions in patients receiving GH replacement therapy via brain CYP2D.

Relationship between the hippocampal expression of selected cytochrome P450 isoforms and the animal performance in the hippocampus-dependent learning task

Despite very extensive studies on the molecular mechanisms of memory formation, relatively little is known about the molecular correlates of individual variation in the learning skills within a random population of young normal subjects. The role of cytochrome P450 (CYP) enzymes in the brain also remains poorly understood. On the other hand, these enzymes are known to be related to the metabolism of substances important for neural functions including steroids, fatty acids, and retinoic acid. In the present study, we examined the potential correlation between the animals' performance in a place learning task and the levels of selected CYP isoforms (CYP2E1, CYP2D1 and CYP7A1) in the rat hippocampus. According to their performance, rats were classified as "good" learners (percent error/number of trials to criterion ≤ group mean - 3SEM) or "poor" learners (percent error/number of trials to criterion ≥ group mean + 3SEM). The CYP enzyme levels were determined by Western Blot at the early, intermediary and advanced stages of the task acquisition (day 4, day 8 and after reaching a performance criterion of 83% correct responses). In this study, as expected, CYP2E1 and CYP2D1 isoforms have been found in the rat hippocampus. However, a putative CYP7A1 isoform was also visualized. Hippocampal expression of these enzymes was shown to be dependent on the stage of learning and animals' cognitive status. In "good" learners compared to "poor" learners, significantly higher levels of CYP2E1 were found at the early stage of training, significantly higher levels of CYP2D1 were found at the intermediate stage of training, and significantly higher levels of CYP7A1-like protein were found after reaching the acquisition criterion. These findings suggest that the differential expression of some CYP isoforms in the hippocampus may have impact on individual learning skills and that different CYP isoforms may play different roles during the learning process.

Emerging role of dopamine in neovascularization of pheochromocytoma and paraganglioma

Dopamine is a catecholamine that acts both as a neurotransmitter and as a hormone, exerting its functions via dopamine (DA) receptors that are present in a broad variety of organs and cells throughout the body. In the circulation, DA is primarily stored in and transported by blood platelets. Recently, the important contribution of DA in the regulation of angiogenesis has been recognized. In vitro and in vivo studies have shown that DA inhibits angiogenesis through activation of the DA receptor type 2. Overproduction of catecholamines is the biochemical hallmark of pheochromocytoma (PCC) and paraganglioma (PGL). The increased production of DA has been shown to be an independent predictor of malignancy in these tumors. The precise relationship underlying the association between DA production and PCC and PGL behavior needs further clarification. Herein, we review the biochemical and physiologic aspects of DA with a focus on its relations with VEGF and hypoxia inducible factor related angiogenesis pathways, with special emphasis on DA producing PCC and PGL.-Osinga, T. E., Links, T. P., Dullaart, R. P. F., Pacak, K., van der Horst-Schrivers, A. N. A., Kerstens, M. N., Kema, I. P. Emerging role of dopamine in neovascularization of pheochromocytoma and paraganglioma.

Immunomodulatory Effects Mediated by Dopamine

Dopamine (DA), a neurotransmitter in the central nervous system (CNS), has modulatory functions at the systemic level. The peripheral and central nervous systems have independent dopaminergic system (DAS) that share mechanisms and molecular machinery. In the past century, experimental evidence has accumulated on the proteins knowledge that is involved in the synthesis, reuptake, and transportation of DA in leukocytes and the differential expression of the D1-like (D1R and D5R) and D2-like receptors (D2R, D3R, and D4R). The expression of these components depends on the state of cellular activation and the concentration and time of exposure to DA. Receptors that are expressed in leukocytes are linked to signaling pathways that are mediated by changes in cAMP concentration, which in turn triggers changes in phenotype and cellular function. According to the leukocyte lineage, the effects of DA are associated with such processes as respiratory burst, cytokine and antibody secretion, chemotaxis, apoptosis, and cytotoxicity. In clinical conditions such as schizophrenia, Parkinson disease, Tourette syndrome, and multiple sclerosis (MS), there are evident alterations during immune responses in leukocytes, in which changes in DA receptor density have been observed. Several groups have proposed that these findings are useful in establishing clinical status and clinical markers.

In situ hybridization study of CYP2D mRNA in the common marmoset brain

The common marmoset is a non-human primate that has increasingly employed in the biomedical research including the fields of neuroscience and behavioral studies. Cytochrome P450 (CYP) 2D has been speculated to be involved in psycho-neurologic actions in the human brain. In the present study, to clarify the role of CYP2D in the marmoset brain, we investigated the expression patterns of CYP2D mRNA in the brain using in situ hybridization (ISH). In addition, to identify the gene location of CYP2D19, a well-studied CYP2D isoform in the common marmoset, a fluorescence in situ hybridization (FISH) study was performed. Consistent with findings for the human brain, CYP2D mRNA was localized in the neuronal cells of different brain regions; e.g., the cerebral cortex, hippocampus, substantia nigra, and cerebellum. FISH analysis showed that the CYP2D19 gene was located on chromosome 1q, which is homologous to human chromosome 22 on which the CYP2D6 gene exists. These results suggest that CYP2D in the marmoset brain may play the same role as human CYP2D6 in terms of brain actions, and that the CYP2D19 gene is conserved in a syntenic manner. Taken together, these findings suggest that the common marmoset is a useful model for studying psychiatric disorders related to CYP2D dysfunction in the brain.

Pathophysiological implications of neurovascular P450 in brain disorders

Over the past decades, the significance of cytochrome P450 (CYP) enzymes has expanded beyond their role as peripheral drug metabolizers in the liver and gut. CYP enzymes are also functionally active at the neurovascular interface. CYP expression is modulated by disease states, impacting cellular functions, detoxification, and reactivity to toxic stimuli and brain drug biotransformation. Unveiling the physiological and molecular complexity of brain P450 enzymes will improve our understanding of the mechanisms underlying brain drug availability, pharmacological efficacy, and neurotoxic adverse effects from pharmacotherapy targeting brain disorders.

Sex hormones regulate cerebral drug metabolism via brain miRNAs: down-regulation of brain CYP2D by androgens reduces the analgesic effects of tramadol

BACKGROUND AND PURPOSE

Brain cytochrome P450 2D (CYP2D) metabolises exogenous neurotoxins, endogenous substances and neurotransmitters. Brain CYP2D can be regulated in an organ-specific manner, but the possible regulatory mechanisms are poorly understood. We investigated the involvement of miRNAs in the selective regulation of brain CYP2D by testosterone and the corresponding alteration of the pharmacological profiles of tramadol by testosterone.

EXPERIMENTAL APPROACH

The regulation of CYP2D and brain-enriched miRNAs by testosterone was investigated using SH-SY5Y cells, U251 cells, and HepG2 cells as well as orchiectomized growth hormone receptor knockout (GHR-KO) mice and rats. Concentration-time curves of tramadol in rat brain were determined using a microdialysis technique. The analgesic action of tramadol was assessed by the tail-flick test in rats.

KEY RESULTS

miR-101 and miR-128-2 bound the 3'-untranslated region of the CYP2D6 mRNA and decreased its level. Testosterone decreased CYP2D6 catalytic function via the up-regulation of miR-101 and miR-128-2 in SH-SY5Y and U251 cells, but not in HepG2 cells. Orchiectomy decreased the levels of miR-101 and miR-128-2 in the hippocampus of male GHR-KO mice, indicating that androgens regulate miRNAs directly, not via the alteration of growth hormone secretion patterns. Changes in the pharmacokinetic and pharmacodynamic profiles of tramadol by orchiectomy was attenuated by either testosterone supplementation or a specific brain CYP2D inhibitor.

CONCLUSIONS AND IMPLICATIONS

The selective regulation of brain CYP2D via brain-enriched miRNAs, following changes in androgen levels, such as in testosterone therapy, androgen deprivation therapy and/or ageing may alter the response to centrally active substances.

Polymorphism in CYP2D6 and CYP2C19, members of the cytochrome P450 mixed-function oxidase system, in the metabolism of psychotropic drugs

Numerous studies in the field of psychopharmacological treatment have investigated the possible contribution of genetic variability between individuals to differences in drug efficacy and safety, motivated by the wide individual variation in treatment response. Genomewide analyses have been conducted in several large-scale studies on antidepressant drug response. However, no consistent findings have emerged from these studies. In a recent meta-analysis of genomewide data from the three studies capturing common variation for association with symptomatic improvement and remission revealed the absence of any strong genetic association and failed to replicate results of individual studies in the pooled data. However, there are good reasons to consider the possible importance of pharmacogenetic variants separately. These variants explain a large portion of the manifold variability in individual drug metabolism. More than 20 psychotropic drugs have now been relabelled by the FDA adding information on polymorphic drug metabolism and therapeutic recommendations. Furthermore, dose recommendations for polymorphisms in drug metabolizing enzymes, first and foremost CYP2D6 and CYP2C19, have been issued with the advice to reduce the dosage in poor metabolizers to 50% or less (in eight cases), or to choose an alternative treatment. Beside the well-described role in hepatic drug metabolism, these enzymes are also expressed in the brain and play a role in biotransformation of endogenous substrates. These polymorphisms may therefore modulate brain metabolism and affect the function of the neural substrates of cognition and emotion.

Systems genomics evaluation of the SH-SY5Y neuroblastoma cell line as a model for Parkinson's disease

Background

The human neuroblastoma cell line, SH-SY5Y, is a commonly used cell line in studies related to neurotoxicity, oxidative stress, and neurodegenerative diseases. Although this cell line is often used as a cellular model for Parkinson’s disease, the relevance of this cellular model in the context of Parkinson’s disease (PD) and other neurodegenerative diseases has not yet been systematically evaluated.

Results

We have used a systems genomics approach to characterize the SH-SY5Y cell line using whole-genome sequencing to determine the genetic content of the cell line and used transcriptomics and proteomics data to determine molecular correlations. Further, we integrated genomic variants using a network analysis approach to evaluate the suitability of the SH-SY5Y cell line for perturbation experiments in the context of neurodegenerative diseases, including PD.

Conclusions

The systems genomics approach showed consistency across different biological levels (DNA, RNA and protein concentrations). Most of the genes belonging to the major Parkinson’s disease pathways and modules were intact in the SH-SY5Y genome. Specifically, each analysed gene related to PD has at least one intact copy in SH-SY5Y. The disease-specific network analysis approach ranked the genetic integrity of SH-SY5Y as higher for PD than for Alzheimer’s disease but lower than for Huntington’s disease and Amyotrophic Lateral Sclerosis for loss of function perturbation experiments.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1154) contains supplementary material, which is available to authorized users.

Role of brain cytochrome P450 (CYP2D) in the metabolism of monoaminergic neurotransmitters

This article focuses on recent research on the cytochrome P450 2D (CYP2D) catalyzed synthesis of the monoaminergic neurotransmitters dopamine and serotonin in the brain and on the influence of psychotropic drugs on the activity of brain CYP2D. Recent in vitro and in vivo studies performed in rodents indicate that dopamine and serotonin may be formed in the brain via alternative CYP2D-mediated pathways, i.e., tyramine hydroxylation and 5-methoxytryptamine O-demethylation, respectively. The contribution of these alternative pathways to the total synthesis of brain neurotransmitters may be higher in humans and may be significantly increased under specific conditions, such as tyrosine hydroxylase and amino acid decarboxylase or tryptophan hydroxylase deficiency. These alternative pathways of neurotransmitter synthesis may also become more efficient when the CYP2D enzyme is mutated or activated by inducers (e.g., alcohol, nicotine, psychotropics), which may be of importance in some neurodegenerative or psychiatric diseases. In addition to the previously observed influence of antidepressants and neuroleptics on CYP2D in the liver, the investigated drugs also produce an effect on CYP2D in the brain. However, their effect on brain CYP2D is different than that in the liver and is structure-dependent. The observed psychotropic drug-brain CYP2D interactions may be important for the metabolism of endogenous neuroactive substrates (e.g., monoaminergic neurotransmitters, neurosteroids) and for the local biotransformation of drugs. The results are discussed with regard to the contribution of CYP2D to the total synthesis of neurotransmitters in the brain in vivo as well as the possible significance of these alternative pathways in specific physiological and pathological conditions and in the pharmacological actions of psychotropic drugs.

Ethanol self-administration and nicotine treatment increase brain levels of CYP2D in African green monkeys

BACKGROUND AND PURPOSE

CYP2D6 metabolizes many centrally acting drugs, neurotoxins and endogenous neurochemicals, and differences in brain levels of CYP2D have been associated with brain function and drug response. Alcohol consumers and smokers have higher levels of CYP2D6 in brain, but not liver, suggesting ethanol and/or nicotine may induce human brain CYP2D6. We investigated the independent and combined effects of chronic ethanol self-administration and nicotine treatment on CYP2D expression in African green monkeys.

EXPERIMENTAL APPROACH

Forty monkeys were randomized into control, ethanol-only, nicotine-only and ethanol + nicotine groups. Two groups voluntarily self-administered 10% ethanol in sucrose solution for 4 h·day(-1) , whereas two groups consumed sucrose solution on the same schedule. Two groups received daily s.c. injections of 0.5 mg·kg(-1) nicotine in saline bid, whereas two groups were injected with saline on the same schedule.

KEY RESULTS

Both nicotine and ethanol dose-dependently increased CYP2D in brain; brain mRNA was unaffected, and neither drug altered hepatic CYP2D protein or mRNA. The combination of ethanol and nicotine increased brain CYP2D protein levels to a greater extent than either drug alone (1.2-2.2-fold, P < 0.05 among the eight brain regions assessed). Immunohistochemistry revealed the induction of brain CYP2D protein within specific cell types and regions in the treatment groups.

CONCLUSIONS AND IMPLICATIONS

Ethanol and nicotine increase brain CYP2D protein levels in monkeys, in a region and treatment-specific manner, suggesting that CNS drug responses, neurodegeneration and personality may be affected among people who consume alcohol and/or nicotine.

The endogenous substrates of brain CYP2D

CYP2D6, one of the major cytochrome P450 isoforms present in the human brain, is associated with the incidence and prevalence of central nervous system (CNS) diseases. Human CYP2D6 and rat CYP2D are involved in the metabolism of various neurotransmitters and neurosteroids. Brain CYP2D can be regulated by endogenous steroids, including sex hormones. The alteration of CYP2D-mediated metabolism induced by endogenous steroids may cause changes in sensitivity to environmental and industrial toxins and carcinogens as well as physiological and pathophysiological processes controlled by biologically active compounds. This review summarizes the current knowledge regarding the distribution, endogenous substrates, and regulation of brain CYP2D.

HIV gp120- and methamphetamine-mediated oxidative stress induces astrocyte apoptosis via cytochrome P450 2E1

HIV-1 glycoprotein 120 (gp120) is known to cause neurotoxicity via several mechanisms including production of proinflammatory cytokines/chemokines and oxidative stress. Likewise, drug abuse is thought to have a direct impact on the pathology of HIV-associated neuroinflammation through the induction of proinflammatory cytokines/chemokines and oxidative stress. In the present study, we demonstrate that gp120 and methamphetamine (MA) causes apoptotic cell death by inducing oxidative stress through the cytochrome P450 (CYP) and NADPH oxidase (NOX) pathways. The results showed that both MA and gp120 induced reactive oxygen species (ROS) production in concentration- and time-dependent manners. The combination of gp120 and MA also induced CYP2E1 expression at both mRNA (1.7±0.2- and 2.8±0.3-fold in SVGA and primary astrocytes, respectively) and protein (1.3±0.1-fold in SVGA and 1.4±0.03-fold in primary astrocytes) levels, suggesting the involvement of CYP2E1 in ROS production. This was further confirmed by using a selective inhibitor of CYP2E1, diallylsulfide (DAS), and CYP2E1 knockdown using siRNA, which significantly reduced ROS production (30–60%). As the CYP pathway is known to be coupled with the NOX pathway, including Fenton–Weiss–Haber (FWH) reaction, we examined whether the NOX pathway is also involved in ROS production induced by either gp120 or MA. Our results showed that selective inhibitors of NOX, diphenyleneiodonium (DPI), and FWH reaction, deferoxamine (DFO), also significantly reduced ROS production. These findings were further confirmed using specific siRNAs against NOX2 and NOX4 (NADPH oxidase family). We then showed that gp120 and MA both induced apoptosis (caspase-3 activity and DNA lesion using TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling) assay) and cell death. Furthermore, we showed that DAS, DPI, and DFO completely abolished apoptosis and cell death, suggesting the involvement of CYP and NOX pathways in ROS-mediated apoptotic cell death. In conclusion, this is the first report on the involvement of CYP and NOX pathways in gp120/MA-induced oxidative stress and apoptotic cell death in astrocytes, which has clinical implications in neurodegenerative diseases, including neuroAIDS.

Complexity of dopamine metabolism

: Parkinson's disease (PD) coincides with a dramatic loss of dopaminergic neurons within the substantia nigra. A key player in the loss of dopaminergic neurons is oxidative stress. Dopamine (DA) metabolism itself is strongly linked to oxidative stress as its degradation generates reactive oxygen species (ROS) and DA oxidation can lead to endogenous neurotoxins whereas some DA derivatives show antioxidative effects. Therefore, DA metabolism is of special importance for neuronal redox-homeostasis and viability.In this review we highlight different aspects of dopamine metabolism in the context of PD and neurodegeneration. Since most reviews focus only on single aspects of the DA system, we will give a broader overview by looking at DA biosynthesis, sequestration, degradation and oxidation chemistry at the metabolic level, as well as at the transcriptional, translational and posttranslational regulation of all enzymes involved. This is followed by a short overview of cellular models currently used in PD research. Finally, we will address the topic from a medical point of view which directly aims to encounter PD.