Cytochrome P450-mediated drug metabolism in the brain

Brain Cytochrome P450: Navigating Neurological Health and Metabolic Regulation

Human cytochrome P450 (CYP) enzymes in the brain represent a crucial frontier in neuroscience, with far-reaching implications for drug detoxification, cellular metabolism, and the progression of neurodegenerative diseases. The brain's complex architecture, composed of interconnected cell types and receptors, drives unique neuronal signaling pathways, modulates enzyme functions, and leads to distinct CYP gene expression and regulation patterns compared to the liver. Despite their relatively low levels of expression, brain CYPs exert significant influence on drug responses, neurotoxin susceptibility, behavior, and neurological disease risk. These enzymes are essential for maintaining brain homeostasis, mediating cholesterol turnover, and synthesizing and metabolizing neurochemicals, neurosteroids, and neurotransmitters. Moreover, they are key participants in oxidative stress responses, neuroprotection, and the regulation of inflammation. In addition to their roles in metabolizing psychotropic drugs, substances of abuse, and endogenous compounds, brain CYPs impact drug efficacy, safety, and resistance, underscoring their importance beyond traditional drug metabolism. Their involvement in critical physiological processes also links them to neuroprotection, with significant implications for the onset and progression of neurodegenerative diseases. Understanding the roles of cerebral CYP enzymes is vital for advancing neuroprotective strategies, personalizing treatments for brain disorders, and developing CNS-targeting therapeutics. This review explores the emerging roles of CYP enzymes, particularly those within the CYP1-3 and CYP46 families, highlighting their functional diversity and the pathological consequences of their dysregulation on neurological health. It also examines the potential of cerebral CYP-based biomarkers to improve the diagnosis and treatment of neurodegenerative disorders, offering new avenues for therapeutic innovation.

Exploring Kp,uu,BBB values smaller than unity in remoxipride: A physiologically-based CNS model approach highlighting brain metabolism in drugs with passive blood-brain barrier transport

(AIM)

Kp,uu,BBB values are crucial indicators of drug distribution into the brain, representing the steady-state relationship between unbound concentrations in plasma and in brain extracellular fluid (brainECF). Kp,uu,BBB values < 1 are often interpreted as indicators of dominant active efflux transport processes at the blood-brain barrier (BBB). However, the potential impact of brain metabolism on this value is typically not addressed. In this study, we investigated the brain distribution of remoxipride, as a paradigm compound for passive BBB transport with yet unexplained brain elimination that was hypothesized to represent brain metabolism.

(METHODS)

The physiologically-based LeiCNS pharmacokinetic predictor (LeiCNS-PK model) was used to compare brain distribution of remoxipride with and without Michaelis-Menten kinetics at the BBB and/or brain cell organelle levels. To that end, multiple in-house (IV 0.7, 3.5, 4, 5.2, 7, 8, 14 and 16 mg kg-1) and external (IV 4 and 8 mg kg-1) rat microdialysis studies plasma and brainECF data were analysed.

(RESULTS)

The incorporation of active elimination through presumed brain metabolism of remoxipride in the LeiCNS-PK model significantly improved the prediction accuracy of experimentally observed brainECF profiles of this drug. The model integrated with brain metabolism in both barriers and organelles levels is named LeiCNS-PK3.5.

(CONCLUSION)

For drugs with Kp,uu,BBB values < 1, not only the current interpretation of dominant BBB efflux transport, but also potential brain metabolism needs to be considered, especially because these may be concentration dependent. This will improve the mechanistic understanding of the processes that determine brain PK profiles.

A multi-ancestry cerebral cortex transcriptome-wide association study identifies genes associated with smoking behaviors

Transcriptome-wide association studies (TWAS) have provided valuable insight in identifying genes that may impact cigarette smoking. Most of previous studies, however, mainly focused on European ancestry. Limited TWAS studies have been conducted across multiple ancestries to explore genes that may impact smoking behaviors. In this study, we used cis-eQTL data of cerebral cortex from multiple ancestries in MetaBrain, including European, East Asian, and African samples, as reference panels to perform multi-ancestry TWAS analyses on ancestry-matched GWASs of four smoking behaviors including smoking initiation, smoking cessation, age of smoking initiation, and number of cigarettes per day in GWAS & Sequencing Consortium of Alcohol and Nicotine use (GSCAN). Multiple-ancestry fine-mapping approach was conducted to identify credible gene sets associated with these four traits. Enrichment and module network analyses were further performed to explore the potential roles of these identified gene sets. A total of 719 unique genes were identified to be associated with at least one of the four smoking traits across ancestries. Among those, 249 genes were further prioritized as putative causal genes in multiple ancestry-based fine-mapping approach. Several well-known smoking-related genes, including PSMA4, IREB2, and CHRNA3, showed high confidence across ancestries. Some novel genes, e.g., TSPAN3 and ANK2, were also identified in the credible sets. The enrichment analysis identified a series of critical pathways related to smoking such as synaptic transmission and glutamate receptor activity. Leveraging the power of the latest multi-ancestry GWAS and eQTL data sources, this study revealed hundreds of genes and relevant biological processes related to smoking behaviors. These findings provide new insights for future functional studies on smoking behaviors.

CYP1B1-RMDN2 Alzheimer's disease endophenotype locus identified for cerebral tau PET

Determining the genetic architecture of Alzheimer's disease pathologies can enhance mechanistic understanding and inform precision medicine strategies. Here, we perform a genome-wide association study of cortical tau quantified by positron emission tomography in 3046 participants from 12 independent studies. The CYP1B1-RMDN2 locus is associated with tau deposition. The most significant signal is at rs2113389, explaining 4.3% of the variation in cortical tau, while APOE4 rs429358 accounts for 3.6%. rs2113389 is associated with higher tau and faster cognitive decline. Additive effects, but no interactions, are observed between rs2113389 and diagnosis, APOE4, and amyloid beta positivity. CYP1B1 expression is upregulated in AD. rs2113389 is associated with higher CYP1B1 expression and methylation levels. Mouse model studies provide additional functional evidence for a relationship between CYP1B1 and tau deposition but not amyloid beta. These results provide insight into the genetic basis of cerebral tau deposition and support novel pathways for therapeutic development in AD.

Exploring the Regulation of Cytochrome P450 in SH-SY5Y Cells: Implications for the Onset of Neurodegenerative Diseases

Human individual differences in brain cytochrome P450 (CYP) metabolism, including induction, inhibition, and genetic variation, may influence brain sensitivity to neurotoxins and thus participate in the onset of neurodegenerative diseases. The aim of this study was to explore the modulation of CYPs in neuronal cells. The experimental approach was focused on differentiating human neuroblastoma SH-SY5Y cells into a phenotype resembling mature dopamine neurons and investigating the effects of specific CYP isoform induction. The results demonstrated that the differentiation protocols using retinoic acid followed by phorbol esters or brain-derived neurotrophic factor successfully generated SH-SY5Y cells with morphological neuronal characteristics and increased neuronal markers (NeuN, synaptophysin, β-tubulin III, and MAO-B). qRT-PCR and Western blot analysis showed that expression of the CYP 1A1, 3A4, 2D6, and 2E1 isoforms was detectable in undifferentiated cells, with subsequent increases in CYP 2E1, 2D6, and 1A1 following differentiation. Further increases in the 1A1, 2D6, and 2E1 isoforms following β-naphthoflavone treatment and 1A1 and 2D6 isoforms following ethanol treatment were evident. These results demonstrate that CYP isoforms can be modulated in SH-SY5Y cells and suggest their potential as an experimental model to investigate the role of CYPs in neuronal processes involved in the development of neurodegenerative diseases.

More than a number: Incorporating the aged phenotype to improve in vitro and in vivo modeling of neurodegenerative disease

Age is the number one risk factor for developing a neurodegenerative disease (ND), such as Alzheimer's disease (AD) or Parkinson's disease (PD). With our rapidly ageing world population, there will be an increased burden of ND and need for disease-modifying treatments. Currently, however, translation of research from bench to bedside in NDs is poor. This may be due, at least in part, to the failure to account for the potential effect of ageing in preclinical modelling of NDs. While ageing can impact upon physiological response in multiple ways, only a limited number of preclinical studies of ND have incorporated ageing as a factor of interest. Here, we evaluate the aged phenotype and highlight the critical, but unmet, need to incorporate aspects of this phenotype into both the in vitro and in vivo models used in ND research. Given technological advances in the field over the past several years, we discuss how these could be harnessed to create novel models of ND that more readily incorporate aspects of the aged phenotype. This includes a recently described in vitro panel of ageing markers, which could help lead to more standardised models and improve reproducibility across studies. Importantly, we cannot assume that young cells or animals yield the same responses as seen in the context of ageing; thus, an improved understanding of the biology of ageing, and how to appropriately incorporate this into the modelling of ND, will ensure the best chance for successful translation of new therapies to the aged patient.

The potential impact of CYP and UGT drug-metabolizing enzymes on brain target site drug exposure

Drug metabolism is one of the critical determinants of drug disposition throughout the body. While traditionally associated with the liver, recent research has unveiled the presence and functional significance of drug-metabolizing enzymes (DMEs) within the brain. Specifically, cytochrome P-450 enzymes (CYPs) and UDP-glucuronosyltransferases (UGTs) enzymes have emerged as key players in drug biotransformation within the central nervous system (CNS). This comprehensive review explores the cellular and subcellular distribution of CYPs and UGTs within the CNS, emphasizing regional expression and contrasting profiles between the liver and brain, humans and rats. Moreover, we discuss the impact of species and sex differences on CYPs and UGTs within the CNS. This review also provides an overview of methodologies for identifying and quantifying enzyme activities in the brain. Additionally, we present factors influencing CYPs and UGTs activities in the brain, including genetic polymorphisms, physiological variables, pathophysiological conditions, and environmental factors. Examples of CYP- and UGT-mediated drug metabolism within the brain are presented at the end, illustrating the pivotal role of these enzymes in drug therapy and potential toxicity. In conclusion, this review enhances our understanding of drug metabolism's significance in the brain, with a specific focus on CYPs and UGTs. Insights into the expression, activity, and influential factors of these enzymes within the CNS have crucial implications for drug development, the design of safe drug treatment strategies, and the comprehension of drug actions within the CNS. To that end, CNS pharmacokinetic (PK) models can be improved to further advance drug development and personalized therapy.

Effects of unburned tobacco smoke on inflammatory and oxidative mediators in the rat prefrontal cortex

Although the Food and Drug Administration has authorized the marketing of "heat-not-burn" (HnB) electronic cigarettes as a modified risk tobacco product (MRTP), toxicological effects of HnB smoke exposure on the brain are still unexplored. Here, paramagnetic resonance of the prefrontal cortex (PFC) of HnB-exposed rats shows a dramatic increase in reactive radical species (RRS) yield coupled with an inflammatory response mediated by NF-κB-target genes including TNF-α, IL-1β, and IL-6 and the downregulation of peroxisome proliferator-activated receptor (PPAR) alpha and gamma expression. The PFC shows higher levels of 8-hydroxyguanosine, a marker of DNA oxidative damage, along with the activation of antioxidant machinery and DNA repair systems, including xeroderma pigmentosum group C (XPC) protein complex and 8-oxoguanine DNA glycosylase 1. HnB also induces the expression of drug-metabolizing enzymes such as CYP1A1, CYP2A6, CYP2B6, and CYP2E, particularly involved in the biotransformation of nicotine and several carcinogenic agents such as aldehydes and polycyclic aromatic hydrocarbons here recorded in the HnB stick smoke. Taken together, these effects, from disruption of redox homeostasis, inflammation, PPAR manipulation along with enhanced bioactivation of neurotoxicants, and upregulation of cMYC protooncogene to impairment of primary cellular defense mechanisms, suggest a possible increased risk of brain cancer. Although the HnB device reduces the emission of tobacco toxicants, our findings indicate that its consumption may carry a risk of potential adverse health effects, especially in non-smokers so far. Further studies are needed to fully understand the long-term effects of these devices.

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.

Extracellular vesicles: Critical bilateral communicators in periphery-brain crosstalk in central nervous system disorders

Growing evidence shows that there is a comorbid mechanism between the central nervous system (CNS) and the peripheral organs. The bilateral transmission of signal molecules in periphery-brain crosstalk plays an important role in the underlying mechanism, which result from complex networks of neurohumoral circuits. Secreted by almost all cells and considered innovative information transport systems, extracellular vesicles (EVs) encapsulate and deliver nucleic acids, proteins, lipids, and various other bioactive regulators. Moreover, EVs can cross the blood-brain barrier (BBB), they are also identified primarily as essential communicators between the periphery and the CNS. In addition to transporting molecules under physiological or pathological conditions, EVs also show novel potential in targeted drug delivery. In this review, we discuss the mechanisms implicated in the transport of EVs in crosstalk between the peripheral and the central immune systems as well as in crosstalk between the peripheral organs and the brain in CNS disorders, especially in neurodegenerative diseases, stroke, and trauma. This work will help in elucidating the contributions of EVs to brain health and disorders, and promote the development of new strategies for minimally invasive treatment.

Novel CYP1B1-RMDN2 Alzheimer's disease locus identified by genome-wide association analysis of cerebral tau deposition on PET

Determining the genetic architecture of Alzheimer's disease (AD) pathologies can enhance mechanistic understanding and inform precision medicine strategies. Here, we performed a genome-wide association study of cortical tau quantified by positron emission tomography in 3,136 participants from 12 independent studies. The CYP1B1-RMDN2 locus was associated with tau deposition. The most significant signal was at rs2113389, which explained 4.3% of the variation in cortical tau, while APOE4 rs429358 accounted for 3.6%. rs2113389 was associated with higher tau and faster cognitive decline. Additive effects, but no interactions, were observed between rs2113389 and diagnosis, APOE4 , and Aβ positivity. CYP1B1 expression was upregulated in AD. rs2113389 was associated with higher CYP1B1 expression and methylation levels. Mouse model studies provided additional functional evidence for a relationship between CYP1B1 and tau deposition but not Aβ. These results may provide insight into the genetic basis of cerebral tau and novel pathways for therapeutic development in AD.

Intranasal (R, S)-ketamine delivery induces sustained antidepressant effects associated with changes in cortical balance of excitatory/inhibitory synaptic activity

In 2019, an intranasal (IN) spray of esketamine SPRAVATO® was approved as a fast-acting antidepressant by drug Agencies US FDA and European EMA. At sub-anesthetic doses, (±)-ketamine, a non-competitive glutamate N-methyl-d-aspartate (NMDA) receptor antagonist, increases the overall excitability of the medial prefrontal cortex (mPFC), an effect being essential for its rapid antidepressant activity. We wondered if this effect of ketamine could come from changes in the balance between neuronal excitation and inhibition (E/I balance) in the mPFC. Here, we performed a preclinical approach to study neurochemical and behavioral responses to a single IN ketamine dose in BALB/cJ mice, a strain more sensitive to stress. By using in vivo microdialysis, we measured cortical E/I balance as the ratio between glutamate to GABA extracellular levels 24 h post-ketamine. We found, for the first time, that E/I balance was shifted in favor of excitation rather than inhibition in the mPFC but more robustly with IN KET than with a single intraperitoneal (IP) dose. Increases in plasma and brain ketamine, norketamine and HNKs levels suggest different metabolic profiles of IP and IN ketamine 30 min post-dose. A significantly larger proportion of ketamine and HNKs in the brain are derived from the IN route 30 min post-dose. It may be linked to the greater magnitude in E/I ratio following IN delivery relative to IP at t24 h. This study suggests that both IP and IN are effective brain delivery methods inducing similar sustained antidepressant efficacy of KET, but the way they induced neurotransmitter changes is slightly different.

Letrozole treatment alters hippocampal gene expression in common marmosets (Callithrix jacchus)

Aromatase inhibitors (AIs) are a class of drugs commonly given to patients with estrogen receptor (ER)-dependent breast cancers to reduce estrogenic stimulation. However, AIs like Letrozole are associated with negative side effects such as cognitive deficits, sleep disturbances and hot flashes. We have previously shown that these negative effects can be recapitulated in common marmosets (Callithrix jacchus) treated with Letrozole (20 μg daily) for 4 weeks and that marmosets treated with Letrozole show increased levels of estradiol in the hippocampus (Gervais et al., 2019). In order to better understand the mechanisms through which AIs affect cognitive function and increase steroid levels in the hippocampus, we used bulk, paired-end RNA-sequencing to examine differentially expressed genes among Letrozole-treated (LET; n = 8) and vehicle-treated (VEH; n = 8) male and female animals. Gene ontology results show significant reduction across hundreds of categories, some of the most significant being inflammatory response, stress response, MHC Class II protein complex binding, T-cell activation, carbohydrate binding and signaling receptor binding in LET animals. GSEA results indicate that LET females, but not LET males, show enrichment for hormonal gene sets. Based on the transcriptional changes observed, we conclude that AIs may differentially affect the sexes in part due to processes mediated by the CYP-450 superfamily. Ongoing studies will further investigate the longitudinal effects of AIs on behavior and whether AIs increase the risk of stress-induced neurodegeneration.

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.

Cytochrome P450 enzymes and metabolism of drugs and neurotoxins within the mammalian brain

Cytochrome P450 enzymes (CYPs) that metabolize xenobiotics are expressed and active in the brain. These CYPs contribute to the metabolism of many centrally acting compounds, including clinically used drugs, drugs of abuse, and neurotoxins. Although CYP levels are lower in the brain than in the liver, they may influence central substrate and metabolite concentrations, which could alter resulting centrally-mediated responses to these compounds. Additionally, xenobiotic metabolizing CYPs are highly variable due to genetic polymorphisms and regulation by endogenous and xenobiotic molecules. In the brain, these CYPs are sensitive to xenobiotic induction. As a result, CYPs in the brain vary widely, including among humans, and this CYP variation may influence central metabolism and resulting response to centrally acting compounds. It has been demonstrated, using experimental manipulation of CYP activity in vivo selectively within the brain, that CYP metabolism in the brain alters central substrate and metabolite concentrations, as well as drug response and neurotoxic effects. This suggests that variability in xenobiotic metabolizing CYPs in the human brain may meaningfully contribute to individual differences in response to, and effects of, centrally acting drugs and neurotoxins. This chapter will provide an overview of CYP expression in the brain, endogenous- and xenobiotic-mediated CYP regulation, and the functional impact of CYP-mediated metabolism of drugs and neurotoxins in the brain, with a focus on experimental approaches in mice, rats, and non-human primates, and a discussion regarding the potential role of xenobiotic metabolizing CYPs in the human brain.

Association of the Val66Met polymorphism of the BDNF gene and the deletional mutation of CYP2D6 gene with the prevalence and severity of depressive disorder in an Eastern Indian population

BACKGROUND

The Val66Met single nucleotide polymorphism (SNP) of the brain-derived growth factor (BDNF) and deletional mutation of the cytochrome P4502D6 (CYP2D6) have been reported to be linked to the etiology and severity of depressive disorders (DD) in a variable manner among different ethnicities and populations.

AIMS

The present study was aimed to find the relationship of mutational variations of these two neurotrophins with the severity of DD and their serum cortisol levels as a marker of the stress factor.

METHODS

In 104 drug-naïve newly diagnosed cases of DD and 106 control subjects, the severity of depression was assessed using the HAM-D score. Val66Met SNP of the BDNF was analyzed in them using restriction digestion of its polymerase chain reaction (PCR) product. CYP2D6 deletional variants were detected by the absence of their PCR products. Serum cortisol levels were measured by the enzyme-linked immunosorbent assay (ELISA) technique.

RESULTS

The Chi-square test (Χ² = 1.42, P = 0.49) did not show any higher prevalence of Val66Met SNP of the BDNF gene in the case group. A correlation coefficient (R) of -0.14 for HAM-D score with a P value of 0.29 signified no direct link of the severity of DD with this SNP. However, a Χ² of 12.68 with P < 0.001 indicated a significantly higher prevalence of the CYP2D6 deletional mutants in DD cases, whereas an R-value of 0.39 for HAM-D score with P < 0.001 suggested a significantly higher severity of DD having with them. Serum cortisol level showed a significant positive correlation with the deletional variants of CYP2D6 (R = 0.198, P = 0.04) and the HAM-D score (R = 0.22, P = 0.025).

CONCLUSION

We conclude that CYP2D6 deletion significantly contributes to the severity and stress factor in the DD patients in our study population. Early identification of these mutations may provide important molecular and cellular predisposition for the disease and may lay the ground for possible more effective measures of intervention.

Diagnosis of Parkinson's disease by investigating the inhibitory effect of serum components on P450 inhibition assay

Parkinson's disease (PD) is the second most common neurodegenerative disease, and diagnostic methods and biomarkers for patients without subjective motor symptoms have not yet been established. Previously, we developed a cytochrome P450 inhibition assay that detects alterations in metabolite levels associated with P450s caused by inflammation and exposure to endogenous or exogenous substances. However, it is unknown whether the P450 inhibition assay can be applied in PD diagnosis. Here, we determined whether the P450 inhibition assay can discriminate sera between patients with PD and healthy individuals. The results of the assay revealed that the P450 inhibition assay can discriminate PD with an area under the receiver operating characteristic curve (AUC) value of 0.814-0.914 in rats and an AUC value of 0.910 in humans. These findings demonstrate that the P450 inhibition assay can aid in the future development of liquid biopsy-based diagnostic methods for PD.

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.

Radiosynthesis and in Vivo and ex Vivo Evaluation of Isomeric [11C]methoxy Analogs of Nimesulide as Brain Cyclooxygenase-2-Targeted Imaging Agents

Our previous studies identified that nimesulide analogs which bear a methoxy substituent at the para-position of the phenyl ring could be potential radiotracer candidates for detecting disorders related to cyclooxygenase-2 (COX-2) expression and activity in vivo using positron emission tomography (PET) in the brain. The present study was conducted to evaluate the in vivo characteristics of ¹¹C-labeled para-methoxy nimesulide ([¹¹C]1d) as a brain COX-2-targeted imaging agent compared to other isomeric methoxy analogs of nimesulide ([¹¹C]1b and [¹¹C]1c). [¹¹C]1b-d were synthesized with reasonable yield and purity by the methylation of the O-desmethyl precursor with [¹¹C]methyl triflate in the presence of NaOH at room temperature. We performed in vivo biodistribution analysis, brain PET imaging, ex vivo autoradiography, and metabolite analysis in mice. The uptake of [¹¹C]1b-d was lower in the brain than in other tissues, including in the blood, and both [¹¹C]1c and [¹¹C]1d were rapidly metabolized. However, [¹¹C]1d showed a small, but significant, specific signal and heterogeneous distribution in the brain. In vivo evaluation suggested that [¹¹C]1d might correlate with COX-2 expression in the brain. Given its instability in vivo, [¹¹C]1d seems unsuitable as a brain-COX-2 radioimaging agent. Further structural refinement of these radiotracers is necessary to enhance their uptake in the brain and to achieve sufficient metabolic stability.

Induced pluripotent stem cell-based organ-on-a-chip as personalized drug screening tools: A focus on neurodegenerative disorders

The Organ-on-a-Chip (OoC) technology shows great potential to revolutionize the drugs development pipeline by mimicking the physiological environment and functions of human organs. The translational value of OoC is further enhanced when combined with patient-specific induced pluripotent stem cells (iPSCs) to develop more realistic disease models, paving the way for the development of a new generation of patient-on-a-chip devices. iPSCs differentiation capacity leads to invaluable improvements in personalized medicine. Moreover, the connection of single-OoC into multi-OoC or body-on-a-chip allows to investigate drug pharmacodynamic and pharmacokinetics through the study of multi-organs cross-talks. The need of a breakthrough thanks to this technology is particularly relevant within the field of neurodegenerative diseases, where the number of patients is increasing and the successful rate in drug discovery is worryingly low. In this review we discuss current iPSC-based OoC as drug screening models and their implication in development of new therapies for neurodegenerative disorders.

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.

CYP 450 enzymes influence (R,S)-ketamine brain delivery and its antidepressant activity

Esketamine, the S-stereoisomer of (R,S)-ketamine was recently approved by drug agencies (FDA, EMA), as an antidepressant drug with a new mechanism of action. (R,S)-ketamine is a N-methyl-d-aspartate receptor (NMDA-R) antagonist putatively acting on GABAergic inhibitory synapses to increase excitatory synaptic glutamatergic neurotransmission. Unlike monoamine-based antidepressants, (R,S)-ketamine exhibits rapid and persistent antidepressant activity at subanesthetic doses in preclinical rodent models and in treatment-resistant depressed patients. Its major brain metabolite, (2R,6R)-hydroxynorketamine (HNK) is formed following (R,S)-ketamine metabolism by various cytochrome P450 enzymes (CYP) mainly activated in the liver depending on routes of administration [e.g., intravenous (largely used for a better bioavailability), intranasal spray, intracerebral, subcutaneous, intramuscular or oral]. Experimental or clinical studies suggest that (2R,6R)-HNK could be an antidepressant drug candidate. However, questions still remain regarding its molecular and cellular targets in the brain and its role in (R,S)-ketamine's fast-acting antidepressant effects. The purpose of the present review is: 1) to review (R,S)-ketamine pharmacokinetic properties in humans and rodents and its metabolism by CYP enzymes to form norketamine and HNK metabolites; 2) to provide a summary of preclinical strategies challenging the role of these metabolites by modifying (R,S)-ketamine metabolism, e.g., by administering a pre-treatment CYP inducers or inhibitors; 3) to analyze the influence of sex and age on CYP expression and (R,S)-ketamine metabolism. Importantly, this review describes (R,S)-ketamine pharmacodynamics and pharmacokinetics to alert clinicians about possible drug-drug interactions during a concomitant administration of (R,S)-ketamine and CYP inducers/inhibitors that could enhance or blunt, respectively, (R,S)-ketamine's therapeutic antidepressant efficacy in patients.

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 (Ki = 11.5 μM and Ki = 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.

Cytochrome P450 Enzymes and Drug Metabolism in Humans

Human cytochrome P450 (CYP) enzymes, as membrane-bound hemoproteins, play important roles in the detoxification of drugs, cellular metabolism, and homeostasis. In humans, almost 80% of oxidative metabolism and approximately 50% of the overall elimination of common clinical drugs can be attributed to one or more of the various CYPs, from the CYP families 1–3. In addition to the basic metabolic effects for elimination, CYPs are also capable of affecting drug responses by influencing drug action, safety, bioavailability, and drug resistance through metabolism, in both metabolic organs and local sites of action. Structures of CYPs have recently provided new insights into both understanding the mechanisms of drug metabolism and exploiting CYPs as drug targets. Genetic polymorphisms and epigenetic changes in CYP genes and environmental factors may be responsible for interethnic and interindividual variations in the therapeutic efficacy of drugs. In this review, we summarize and highlight the structural knowledge about CYPs and the major CYPs in drug metabolism. Additionally, genetic and epigenetic factors, as well as several intrinsic and extrinsic factors that contribute to interindividual variation in drug response are also reviewed, to reveal the multifarious and important roles of CYP-mediated metabolism and elimination in drug therapy.

A Comparison of Calcium Aggregation and Ultracentrifugation Methods for the Preparation of Rat Brain Microsomes for Drug Metabolism Studies

Preparation of brain microsomes by the calcium chloride aggregation method has been suggested as an alternative to the ultracentrifugation method. However, the effects of the calcium chloride concentration on the quality of the microsomal fractions are not known. Brain microsomes were prepared from the adult rat brains using the high-speed ultracentrifugation and low-speed calcium chloride (10-100 mM) aggregation methods (n = 5-6 per group). The microsomal protein yield (spectrometry), the cytochrome P450 reductase (CPR) activity (spectrometry), and the monooxygenase activities (UPLC-MS/MS) of CYP2D and CYP2E1 were determined in the obtained fractions. Increasing the concentrations of calcium chloride progressively increased the protein yield of the low-speed microsomal fractions. However, the increased yield was associated with a significant decrease in the activities of CPR, CYP2D, and CYP2E1. Additionally, the CYP2D and CYP2E1 activities were significantly correlated with the CPR activities of the fractions. In conclusion, when an ultracentrifuge is available, preparation of brain microsomes by the ultracentrifugation method might be preferable. However, the calcium aggregation method at a calcium chloride concentration of 10 mM is an acceptable alternative to the ultracentrifuge method.

Many Drugs of Abuse May Be Acutely Transformed to Dopamine, Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.

A Review of Oxidative Stress Products and Related Genes in Early Alzheimer's Disease

Oxidative stress is associated with the progression of Alzheimer’s disease (AD). Reactive oxygen species can modify lipids, DNA, RNA, and proteins in the brain. The products of their peroxidation and oxidation are readily detectable at incipient stages of disease. Based on these oxidation products, various biomarker-based strategies have been developed to identify oxidative stress levels in AD. Known oxidative stress-related biomarkers include lipid peroxidation products F2-isoprostanes, as well as malondialdehyde and 4-hydroxynonenal which both conjugate to specific amino acids to modify proteins, and DNA or RNA oxidation products 8-hydroxy-2’-deoxyguanosine (8-OHdG) and 8-hydroxyguanosine (8-OHG), respectively. The inducible enzyme heme oxygenase type 1 (HO-1) is found to be upregulated in response to oxidative stress-related events in the AD brain. While these global biomarkers for oxidative stress are associated with early-stage AD, they generally poorly differentiate from other neurodegenerative disorders that also coincide with oxidative stress. Redox proteomics approaches provided specificity of oxidative stress-associated biomarkers to AD pathology by the identification of oxidatively damaged pathology-specific proteins. In this review, we discuss the potential combined diagnostic value of these reported biomarkers in the context of AD and discuss eight oxidative stress-related mRNA biomarkers in AD that we newly identified using a transcriptomics approach. We review these genes in the context of their reported involvement in oxidative stress regulation and specificity for AD. Further research is warranted to establish the protein levels and their functionalities as well as the molecular mechanisms by which these potential biomarkers are involved in regulation of oxidative stress levels and their potential for determination of oxidative stress and disease status of AD patients.

Xenobiotic transport and metabolism in the human brain

Organisms have metabolic pathways responsible for eliminating endogenous and exogenous toxicants. Generally, we associate the liver par excellence as the organ in charge of detoxifying the body; however, this process occurs in all tissues, including the brain. Due to the presence of the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB), the Central Nervous System (CNS) is considered a partially isolated organ, but similar to other organs, the CNS possess xenobiotic transporters and metabolic pathways associated with the elimination of xenobiotic agents. In this review, we describe the different systems related to the detoxification of xenobiotics in the CNS, providing examples in which their association with neurodegenerative processes is suspected. The CNS detoxifying systems include carrier-mediated, active efflux and receptor-mediated transport, and detoxifying systems that include phase I and phase II enzymes, as well as those enzymes in charge of neutralizing compounds such as electrophilic agents, reactive oxygen species (ROS), and free radicals, which are products of the bioactivation of xenobiotics. Moreover, we discuss the differential expression of these systems in different regions of the CNS, showing the different detoxifying needs and the composition of each region in terms of the cell type, neurotransmitter content, and the accumulation of xenobiotics and/or reactive compounds.

MAM-2201, One of the Most Potent-Naphthoyl Indole Derivative-Synthetic Cannabinoids, Exerts Toxic Effects on Human Cell-Based Models of Neurons and Astrocytes

Considering the consequences on human health, in general population and workplace, associated with the use of new psychoactive substances and their continuous placing on the market, novel in vitro models for neurotoxicology research, applying human-derived CNS cells, may provide a means to understand the mechanistic basis of molecular and cellular alterations in brain. Cytotoxic effects of MAM-2201, a potent-naphthoyl indole derivative-synthetic cannabinoid, have been evaluated applying a panel of human cell-based models of neurons and astrocytes, testing different concentrations (1-30 µM) and exposure times (3-24-48 h). MAM-2201 induced toxicity in primary neuron-like cells (hNLCs), obtained from transdifferentiation of mesenchymal stem cells derived from human umbilical cord. Effects occurred in a concentration- and time-dependent manner. The lowest concentration affecting cell viability, metabolic function, apoptosis, morphology, and neuronal markers (MAP-2, NSE) was 5 μM, and even 1 μM induced apoptosis. Effects appeared early (3 h) and persisted after 24 and 48 h. Similar behavior was evidenced for human D384-astrocytes treated with MAM-2201. Differently, human SH-SY5Y-neurons, both differentiated and undifferentiated, were not sensitive to MAM-2201. On D384, the different altered endpoints were reversed, attenuated, or not antagonized by AM251 indicating that CB1 receptors may partially mediate MAM-2201-induced cytotoxicity. While in hNLCs, all toxic effects caused by MAM-2201 were apparently unrelated to CB-receptors since they were not evidenced by immunofluorescence. The present in vitro findings demonstrate the cytotoxicity of MAM-2201 on human primary neurons (hNLCs) and astrocytes cell line (D384), and support the use of these cellular models as species-specific in vitro tools suitable to clarify the neurotoxicity mechanisms of synthetic cannabinoids.

Drug-Metabolizing Cytochrome P450 Enzymes Have Multifarious Influences on Treatment Outcomes

Drug metabolism is a critical process for the removal of unwanted substances from the body. In humans, approximately 80% of oxidative metabolism and almost 50% of the overall elimination of commonly used drugs can be attributed to one or more of various cytochrome P450 (CYP) enzymes from CYP families 1-3. In addition to the basic metabolic effects for elimination, CYP enzymes in vivo are capable of affecting the treatment outcomes in many cases. Drug-metabolizing CYP enzymes are mainly expressed in the liver and intestine, the two principal drug oxidation and elimination organs, where they can significantly influence the drug action, safety, and bioavailability by mediating phase I metabolism and first-pass metabolism. Furthermore, CYP-mediated local drug metabolism in the sites of action may also have the potential to impact drug response, according to the literature in recent years. This article underlines the ability of CYP enzymes to influence treatment outcomes by discussing CYP-mediated diversified drug metabolism in primary metabolic sites (liver and intestine) and typical action sites (brain and tumors) according to their expression levels and metabolic activity. Moreover, intrinsic and extrinsic factors of personal differential CYP phenotypes that contribute to interindividual variation of treatment outcomes are also reviewed to introduce the multifarious pivotal role of CYP-mediated metabolism and clearance in drug therapy.

Cytochrome P450 CYP2E1 Suppression Ameliorates Cerebral Ischemia Reperfusion Injury

Despite existing strong evidence on oxidative markers overproduction following ischemia/reperfusion (I/R), the mechanism by which oxidative enzyme Cytochrome P450-2E1 (CYP2E1) contributes to I/R outcomes is not clear. In this study, we sought to evaluate the functional significance of CYP2E1 in I/R. CYP2E1 KO mice and controls were subjected to middle cerebral artery occlusion (MCAo-90 min) followed by 24 h of reperfusion to induce focal I/R injury as an acute stage model. Then, histological and chemical analyses were conducted to investigate the role of CYP2E1 in lesion volume, oxidative stress, and inflammation exacerbation. Furthermore, the role of CYP2E1 on the blood-brain barrier (BBB) integrity was investigated by measuring 20-hydroxyecosatetraenoic acid (20-HETE) activity, as well as, in vivo BBB transfer rate. Following I/R, the CYP2E1 KO mice exhibited a significantly lower lesion volume, and neurological deficits compared to controls (p < 0.005). Moreover, reactive oxygen species (ROS) production, apoptosis, and neurodegeneration were significantly lower in the CYP2E1(−/−) I/R group (p < 0.001). The BBB damage was significantly lower in CYP2E1(−/−) mice compared to wild-type (WT) (p < 0.001), while 20-HETE production was increased by 41%. Besides, inflammatory cytokines expression and the number of activated microglia were significantly lower in CYP2E1(−/−) mice following I/R. CYP2E1 suppression ameliorates I/R injury and protects BBB integrity by reducing both oxidative stress and inflammation.

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.

Cytochrome P450 Metabolism of Polyunsaturated Fatty Acids and Neurodegeneration

Due to the aging population in the world, neurodegenerative diseases have become a serious public health issue that greatly impacts patients' quality of life and adds a huge economic burden. Even after decades of research, there is no effective curative treatment for neurodegenerative diseases. Polyunsaturated fatty acids (PUFAs) have become an emerging dietary medical intervention for health maintenance and treatment of diseases, including neurodegenerative diseases. Recent research demonstrated that the oxidized metabolites, particularly the cytochrome P450 (CYP) metabolites, of PUFAs are beneficial to several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease; however, their mechanism(s) remains unclear. The endogenous levels of CYP metabolites are greatly affected by our diet, endogenous synthesis, and the downstream metabolism. While the activity of omega-3 (ω-3) CYP PUFA metabolites and omega-6 (ω-6) CYP PUFA metabolites largely overlap, the ω-3 CYP PUFA metabolites are more active in general. In this review, we will briefly summarize recent findings regarding the biosynthesis and metabolism of CYP PUFA metabolites. We will also discuss the potential mechanism(s) of CYP PUFA metabolites in neurodegeneration, which will ultimately improve our understanding of how PUFAs affect neurodegeneration and may identify potential drug targets for neurodegenerative diseases.

Biotransformation in the fish Prochilodus lineatus: An organ-specific approach to cyp1a gene expression and biochemical activity

The biotransformation ability of the organism is the result of organ-specific responses. This paper presents a molecular and biochemical approach to elucidate the biotransformation mechanisms in different organs of Prochilodus lineatus induced at 6, 24, and 96 h after a benzo[a]pyrene (B[a]P) injection. The induction in cyp1a transcription showed an organ-specific intensity at every tested time time. The EROD (ethoxyresorufin-O-deethylase) activity increased rapidly (6 h) in the liver and the kidney; the gills and the brain showed an increase at 24 h; and the gills demonstrated the highest activity among all the organs tested. There was no increase in glutathione S-transferase (GST) activity or lipoperoxidation. The decreased hepatic glutathione content (GSH) may be due to its role as an antioxidant. B[a]P was detected in the bile, confirming the xenobiotic efflux from the metabolizing organs. The gills, liver, brain, and kidney of P. lineatus presented an integrated mechanism to deal with the xenobiotic biotransformation.

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.

Pharmacokinetic Principles and Their Application to Central Nervous System Tumors

Despite increasing knowledge of the biologic drivers of central nervous system tumors, most targeted agents trialed to date have not shown activity against these tumors in clinical trials. To effectively treat central nervous system tumors, an active drug must achieve and maintain an effective exposure at the tumor site for a long enough period of time to exert its intended effect. However, this is difficult to assess and achieve due to the constraints of drug delivery to the central nervous system. To address this complex problem, an understanding of pharmacokinetic principles is necessary. Pharmacokinetics is classically described as the quantitative study of drug absorption, distribution, metabolism, and elimination. The innate chemical properties of a drug, its administration (dose, route and schedule), and host factors all influence these four key pharmacokinetic phases. The central nervous system adds a level of complexity to standard plasma pharmacokinetics as it is a coupled drug compartment. This review will discuss special considerations of pharmacokinetics in the context of therapeutic development for central nervous system tumors.

Human CYP2D6 Is Functional in Brain In Vivo: Evidence from Humanized CYP2D6 Transgenic Mice

CYP2D metabolizes many drugs that act within the brain, and variable expression of CYP2D in the brain may alter local drug and metabolite levels sufficiently to affect behavioral responses. Transgenic mice that express human CYP2D6 (TG) were compared to wild type mice (WT). Following selective inhibition of human CYP2D6 in TG brain, we demonstrated in vivo that human CYP2D6 in the brain was sufficient to alter a drug-induced behavioral response. After a 4-h pre-treatment with intracerebroventricular (i.c.v.) propranolol, CYP2D activity in vivo and in vitro was reduced in TG brain, whereas CYP2D activity in vivo, but not in vitro, was reduced in WT brain. After a 24-h pre-treatment with i.c.v. propranolol, CYP2D activity in vivo and in vitro was reduced in TG brain, whereas CYP2D activity in vivo and in vitro was not changed in WT brain. These results indicate that i.c.v. propranolol irreversibly inhibited human CYP2D6 in TG brain but not mouse CYP2D in TG and WT brain. Pre-treatments with propranolol did not change liver CYP2D activity in vivo or in vitro. Furthermore, 24-h pre-treatment with i.c.v. propranolol resulted in a significant decrease of the haloperidol-induced catalepsy response in TG, but not in WT, without changing serum haloperidol levels in either mouse line. These studies reveal a new tool to selectively and irreversibly inhibit human CYP2D6 in TG brain and indicate that human CYP2D6 has a functional role within the brain sufficient to impact the central nervous system response from peripherally administered drugs.

Functional cytochrome P450 1A enzymes are induced in mouse and human islets following pollutant exposure

AIMS/HYPOTHESIS

Exposure to environmental pollution has been consistently linked to diabetes incidence in humans, but the potential causative mechanisms remain unclear. Given the critical role of regulated insulin secretion in maintaining glucose homeostasis, environmental chemicals that reach the endocrine pancreas and cause beta cell injury are of particular concern. We propose that cytochrome P450 (CYP) enzymes, which are involved in metabolising xenobiotics, could serve as a useful biomarker for direct exposure of islets to pollutants. Moreover, functional CYP enzymes in islets could also impact beta cell physiology. The aim of this study was to determine whether CYP1A enzymes are activated in islets following direct or systemic exposure to environmental pollutants.

METHODS

Immortalised liver (HepG2) and rodent pancreatic endocrine cell lines (MIN6, βTC-6, INS1, α-TC1, α-TC3), as well as human islets, were treated in vitro with known CYP1A inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene (3-MC). In addition, mice were injected with either a single high dose of TCDD or multiple low doses of TCDD in vivo, and islets were isolated 1, 7 or 14 days later.

RESULTS

CYP1A enzymes were not activated in any of the immortalised beta or alpha cell lines tested. However, both 3-MC and TCDD potently induced CYP1A1 gene expression and modestly increased CYP1A1 enzyme activity in human islets after 48 h. The induction of CYP1A1 in human islets by TCDD was prevented by cotreatment with a cytokine mixture. After a systemic single high-dose TCDD injection, CYP1A1 enzyme activity was induced in mouse islets ~2-fold, ~40-fold and ~80-fold compared with controls after 1, 7 and 14 days, respectively, in vivo. Multiple low-dose TCDD exposure in vivo also caused significant upregulation of Cyp1a1 in mouse islets. Direct TCDD exposure to human and mouse islets in vitro resulted in suppressed glucose-induced insulin secretion. A single high-dose TCDD injection resulted in lower plasma insulin levels, as well as a pronounced increase in beta cell death.

CONCLUSIONS/INTERPRETATION

Transient exposure to TCDD results in long-term upregulation of CYP1A1 enzyme activity in islets. This provides evidence for direct exposure of islets to lipophilic pollutants in vivo and may have implications for islet physiology.

mRNA levels of drug-metabolizing enzymes in 11 brain regions of cynomolgus macaques

The cynomolgus macaque is an important nonhuman primate species in drug metabolism studies, in part because of its evolutionary closeness to humans. Cytochromes P450 (P450s) have been investigated in the major drug-metabolizing organs, i.e., the liver and small intestine, but have not been fully investigated in the brain. However, recent investigations have indicated possible important roles for P450s in the brain. In this study, by using the quantitative polymerase chain reaction, we measured the mRNA levels of 38 cynomolgus drug-metabolizing enzymes, including 19 P450s, 10 UDP-glycosyltransferases, and 9 other enzymes, in 11 brain regions. Among these drug-metabolizing enzymes, expression of 32 enzyme mRNAs were detected in one or more brain regions, indicating their possible roles in the brain. Further investigation of metabolic activities would facilitate better understanding of the importance of these enzymes in the brain.

Circulating Extracellular Vesicles Containing Xenobiotic Metabolizing CYP Enzymes and Their Potential Roles in Extrahepatic Cells Via Cell-Cell Interactions

The cytochrome P450 (CYP) family of enzymes is known to metabolize the majority of xenobiotics. Hepatocytes, powerhouses of CYP enzymes, are where most drugs are metabolized into non-toxic metabolites. Additional tissues/cells such as gut, kidneys, lungs, blood, and brain cells express selective CYP enzymes. Extrahepatic CYP enzymes, especially in kidneys, also metabolize drugs into excretable forms. However, extrahepatic cells express a much lower level of CYPs than hepatocytes. It is possible that the liver secretes CYP enzymes, which circulate via plasma and are eventually delivered to extrahepatic cells (e.g., brain cells). CYP circulation likely occurs via extracellular vesicles (EVs), which carry important biomolecules for delivery to distant cells. Recent studies have revealed an abundance of several CYPs in plasma EVs and other cell-derived EVs, and have demonstrated the role of CYP-containing EVs in xenobiotic-induced toxicity via cell–cell interactions. Thus, it is important to study the mechanism for packaging CYP into EVs, their circulation via plasma, and their role in extrahepatic cells. Future studies could help to find novel EV biomarkers and help to utilize EVs in novel interventions via CYP-containing EV drug delivery. This review mainly covers the abundance of CYPs in plasma EVs and EVs derived from CYP-expressing cells, as well as the potential role of EV CYPs in cell–cell communication and their application with respect to novel biomarkers and therapeutic interventions.

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.

Ciprofloxacin-induces free radical production in rat cerebral microsomes

In the presence of ciprofloxacin (CPFX), free radical adduct formation was demonstrated in rat cerebral microsomes using a spin trap α-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone by electron spin resonance spectroscopy. Active microsomes, dihydronicotinamide-adenine dinucleotide phosphate, and ciprofloxacin were necessary for the formation of a spin trap/radical adduct. Adduct formation increased dose-dependently at 0.5-1 mM CPFX concentration for 180 min, and 0.3-1 mM concentration level for 240 min. The addition of SKF 525A, ZnCl₂ or desferrioxamine to the incubation system caused complete inhibition of the radical formation. However, pretreatment of microsomal system with superoxide dismutase (SOD) did not induce any protective effect. Induction of lipid peroxidation, and depletion of thiol levels by CPFX were also shown in the system. These results strongly suggested that CPFX produces free radical(s) in the cerebral microsomes of rats.

Rat brain CYP2D activity alters in vivo central oxycodone metabolism, levels and resulting analgesia

Oxycodone is metabolized by CYP2D to oxymorphone. Despite oxymorphone being a more potent opioid-receptor agonist, its contribution to oxycodone analgesia may be minor because of low peripheral production, low blood-brain barrier permeability and central nervous system efflux. CYP2D metabolism within the brain may contribute to variation in central oxycodone and oxymorphone levels, thereby affecting analgesia. Brain CYP2D expression and activity are subject to exogenous regulation; nicotine induces rat brain, but not liver, CYP2D consistent with higher brain CYP2D in smokers. We assessed the role of rat brain CYP2D in orally administered oxycodone metabolism (in vivo brain microdialysis) and analgesia (tail-flick test) by inhibiting brain CYP2D selectively with intracerebroventricular propranolol (mechanism-based inhibitor) and inducing brain CYP2D with nicotine. Inhibiting brain CYP2D increased brain oxycodone levels (1.8-fold; P < 0.03) and analgesia (1.5-fold AUC0-60 ; P < 0.001) after oxycodone, while inducing brain CYP2D increased brain oxymorphone levels (4.6-fold; P < 0.001) and decreased analgesia (0.8-fold; P < 0.02). Inhibiting the induced brain CYP2D reversed the change in oxycodone levels (1.2-fold; P > 0.1) and analgesia (1.1-fold; P > 0.3). Brain, but not plasma, metabolic ratios were affected by pre-treatments. Peak analgesia was inversely correlated with ex vivo brain (P < 0.003), but not hepatic (P > 0.9), CYP2D activity. Altering brain CYP2D did not affect analgesia from oral oxymorphone (P > 0.9 for AUC0-60 across all groups), which is not a CYP2D substrate. Thus, brain CYP2D metabolism alters local oxycodone levels and response, suggesting that people with increased brain CYP2D activity may have reduced oxycodone response. Factors that alter individual oxycodone response may be useful for optimizing treatment and minimizing abuse liability.

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.

β-Naphtoflavone and Ethanol Induce Cytochrome P450 and Protect towards MPP⁺ Toxicity in Human Neuroblastoma SH-SY5Y Cells

Cytochrome P450 (CYP) isozymes vary their expression depending on the brain area, the cell type, and the presence of drugs. Some isoforms are involved in detoxification and/or toxic activation of xenobiotics in central nervous system. However, their role in brain metabolism and neurodegeneration is still a subject of debate. We have studied the inducibility of CYP isozymes in human neuroblastoma SH-SY5Y cells, treated with β-naphtoflavone (β-NF) or ethanol (EtOH) as inducers, by qRT-PCR, Western blot (WB), and metabolic activity assays. Immunohistochemistry was used to localize the isoforms in mitochondria and/or endoplasmic reticulum (ER). Tetrazolium (MTT) assay was performed to study the role of CYPs during methylphenyl pyridine (MPP⁺) exposure. EtOH increased mRNA and protein levels of CYP2D6 by 73% and 60% respectively. Both β-NF and EtOH increased CYP2E1 mRNA (4- and 1.4-fold, respectively) and protein levels (64% both). The 7-ethoxycoumarin O-deethylation and dextromethorphan O-demethylation was greater in treatment samples than in controls. Furthermore, both treatments increased by 22% and 18%, respectively, the cell viability in MPP⁺-treated cells. Finally, CYP2D6 localized at mitochondria and ER. These data indicate that CYP is inducible in SH-SY5Y cells and underline this in vitro system for studying the role of CYPs in neurodegeneration.

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.