The Unique Regulation of Brain Cytochrome P450 2 (CYP2) Family Enzymes by Drugs and Genetics

The Effect of Maternal High-Fat or High-Carbohydrate Diet during Pregnancy and Lactation on Cytochrome P450 2D (CYP2D) in the Liver and Brain of Rat Offspring

Cytochrome P450 2D (CYP2D) is important in psychopharmacology as it is engaged in the metabolism of drugs, neurosteroids and neurotransmitters. An unbalanced maternal diet during pregnancy and lactation can cause neurodevelopmental abnormalities and increases the offspring's predisposition to neuropsychiatric diseases. The aim of the present study was to evaluate the effect of maternal modified types of diet: a high-fat diet (HFD) and high-carbohydrate diet (HCD) during pregnancy and lactation on CYP2D in the liver and brain of male offspring at 28 (adolescent) or 63 postnatal days (young adult). The CYP2D activity and protein level were measured in the liver microsomes and the levels of mRNAs of CYP2D1, 2D2 and 2D4 were investigated both in the liver and brain. In the liver, both HFD and HCD increased the mRNA levels of all the three investigated CYP2D genes in adolescents, but an opposite effect was observed in young adults. The CYP2D protein level increased in adolescents but not in young adults. In contrast, young adults showed significantly decreased CYP2D activity. Similar effect of HFD on the CYP2D mRNAs was observed in the prefrontal cortex, while the effect of HCD was largely different than in the liver (the CYP2D2 expression was not affected, the CYP2D4 expression was decreased in young adults). In conclusion, modified maternal diets influence the expression of individual CYP2D1, CYP2D2 and CYP2D4 genes in the liver and brain of male offspring, which may affect the metabolism of CYP2D endogenous substrates and drugs and alter susceptibility to brain diseases and pharmacotherapy outcome.

Clozapine treatment and astrocyte activity in treatment resistant schizophrenia: A proton magnetic resonance spectroscopy study

Clozapine is the only antipsychotic approved for treating treatment-resistant schizophrenia (TRS), characterized by persistent positive symptoms despite adequate antipsychotic treatment. Unfortunately, clozapine demonstrates clinical efficacy in only ~30-60 % of patients with TRS (clozapine-responders; ClzR+), while the remaining ~40-70 % are left with no pharmacological recourse for improvement (clozapine-resistant; ClzR-). Mechanism(s) underlying clozapine's superior efficacy remain unclear. However, in vitro evidence suggests clozapine may mitigate glutamatergic dysregulations observed in TRS, by modulating astrocyte activity in ClzR+, but not ClzR-. A factor that if proven correct, may help the assessment of treatment response and development of more effective antipsychotics. To explore the presence of clozapine-astrocyte interaction and clinical improvement, we used 3 T proton-magnetic resonance spectroscopy to quantify levels of myo-Inositol, surrogate biomarker of astrocyte activity, in regions related to schizophrenia neurobiology: Dorsal-anterior-cingulate-cortex (dACC), left-dorsolateral-prefrontal-cortex (left-DLPFC), and left-striatum (left-striatum) of 157 participants (ClzR- = 30; ClzR+ = 37; responders = 38; controls = 52). Clozapine treatment was assessed using clozapine to norclozapine plasma levels, 11-12 h after last clozapine dose. Measures for symptom severity (i.e., Positive and Negative Symptoms Scale) and cognition (i.e., Mini-Mental State Examination) were also recorded. Higher levels of myo-Inositol were observed in TRS groups versus responders and controls (dACC (p < 0.001); left-striatum (p = 0.036); left-DLPFC (p = 0.023)). In ClzR+, but not ClzR-, clozapine to norclozapine ratios were positively associated with myo-Inositol levels (dACC (p = 0.004); left-DLPFC (p < 0.001)), and lower positive symptom severity (p < 0.001). Our results support growing in vitro evidence of clozapine-astrocyte interaction in clozapine-responders. Further research may determine the viability of clozapine-astrocyte interactions as an early marker of clozapine response.

Clearing the Smoke: What Protects Smokers from Parkinson's Disease?

The link between smoking and a lower risk of Parkinson's disease (PD) is one of the strongest environmental or lifestyle associations in neuroepidemiology. Growing evidence supports the hypothesis that the association is based on a neuroprotective effect of smoking on PD, despite the plausible alternative that smoking serves as a marker for a proximal protective influence without itself conferring benefit. But how smoking could protect against neurodegeneration in PD is not well understood. Of several candidate molecules and mechanisms that have been nominated, nicotine has received the most attention. However, randomized controlled clinical trials of nicotine in PD have failed to demonstrate benefit on motor endpoints, including the NIC-PD study in which recently diagnosed participants were randomly assigned to placebo or nicotine treatment for 1 year. Given these results, the time is right to evaluate the neuroprotective potential of other molecules and biochemical cascades triggered by smoking. Here, we review the evidence supporting smoking's possible protective effect on PD, compounds in tobacco and smoke that might mediate such benefit, and non-causal classes of explanation, including reverse causation and the prospect of shared genetic determinants of smoking and PD resistance. The therapeutic potential of non-nicotine components of smoke is suggested by studies supporting multiple alternative mechanisms ranging from monoamine oxidase inhibitors to gut microbiome disruption to antioxidant response induction by chronic exposure to low levels of carbon monoxide. Rigorous investigation is warranted to evaluate this molecule and others for disease-preventing and disease-modifying activity in PD models and, if warranted, in clinical trials. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Association of regular use of ibuprofen and paracetamol, genetic susceptibility, and new-onset dementia in the older population

OBJECTIVE

Although the possible efficacy and adverse effects of paracetamol and ibuprofen on dementia are of global clinical and public health importance, to date, the relationship of the use of paracetamol and ibuprofen with incident dementia remains uncertain. We aimed to assess the prospective association of regular use of ibuprofen and paracetamol with new-onset dementia in an older population.

METHODS

This study included 212,968 participants from the UK Biobank, aged ≥60 years, with available data of ibuprofen, paracetamol use and without dementia at baseline. The primary outcome was new-onset all-cause dementia. The secondary outcomes included new-onset Alzheimer's disease and new-onset vascular dementia.

RESULTS

During a median follow-up of 12.3 years, 6407 (3.0%) participants developed new-onset all-cause dementia. Participants who regularly used paracetamol had a significantly higher risk of new-onset all-cause dementia (adjusted HR, 1.18; 95%CI: 1.10-1.26), compared with non-users. However, there was no significant association between regular use of ibuprofen and new-onset all-cause dementia (users vs. non-users; adjusted HR, 1.06; 95%CI: 0.97-1.16). Furthermore, APOE ε4 dosage and genetic risk scores (GRS) of Alzheimer's disease calculated by 25 single nucleotide polymorphisms did not significantly modify the relationship of regular use of paracetamol and ibuprofen with new-onset all-cause dementia (Both P-interactions >0.05). Similar results were found in the propensity score analysis. Similar findings were also observed for new-onset Alzheimer's disease and new-onset vascular dementia.

CONCLUSIONS

Regular use of paracetamol, but not ibuprofen, was associated with a significantly higher risk of new-onset dementia in the old population, regardless of genetic risks of dementia.

Medroxyprogesterone acetate positively modulates specific GABAA-receptor subtypes - affecting memory and cognition

Medroxyprogesterone acetate (MPA) is a progestin widely used in humans as hormone replacement therapy and at other indications. Many progestin metabolites, as the progesterone metabolite allopregnanolone, have GABA_A-receptor modulatory effects and are known to affect memory, learning, appetite, and mood. In women, 4 years chronic treatment with MPA doubles the frequency of dementia and in rats, MPA causes cognitive impairment related to the GABAergic system. Activation of the membrane bound GABA_A receptor results in a chloride ion flux that can be studied by whole-cell patch-clamp electrophysiological recordings. The purpose of this study was to clarify the modulatory effects of MPA and specific MPA metabolites, with structures like known GABA_A-receptor modulators, on different GABA_A-receptor subtypes. An additional aim was to verify the results as steroid effects on GABA response in single cells taken from rat hypothalamus. HEK-293 cell-lines permanently expressing the recombinant human GABA_A-receptor subtype α1β2γ2L or α5β3γ2L or α2β3γ2S were created. The MPA metabolites 3α5α-MPA,3β5α-MPA and 3β5β-MPA were synthesised and purified for electrophysiological patch-clamp measurements with a Dynaflow system. The effects of MPA and tetrahydrodeoxycorticosterone were also studied. None of the studied MPA metabolites affected the responses mediated by α1β2γ2L or α5β3γ2L GABA_A receptors. Contrary, MPA clearly acted both as a positive modulator and as a direct activator of the α5β3γ2L and α2β3γ2S GABA_A receptors. However, in concentrations up to 10 μM, MPA was inactive at the α1β2γ2L GABA_A receptor. In the patch-clamp recordings from dissociated cells of the preoptic area in rats, MPA increased the amplitude of responses to GABA. In addition, MPA alone without added GABA, evoked a current response. In conclusion, MPA acts as a positive modulator of specific GABA_A receptor subtypes expressed in HEK cells and at native GABA receptors in single cells from the hypothalamic preoptic area.

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.

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.

Polymorphisms in genes related to oxidative stress and inflammation: Emerging links with the pathogenesis and severity of Cerebral Cavernous Malformation disease

Cerebral Cavernous Malformation (CCM) is a cerebrovascular disease of genetic origin affecting 0.5% of the population and characterized by abnormally enlarged and leaky capillaries that predispose to seizures, neurological deficits, and intracerebral hemorrhage (ICH). CCM occurs sporadically or is inherited as dominant condition with incomplete penetrance and highly variable expressivity. Three disease genes have been identified: KRIT1 (CCM1), CCM2 and CCM3. Previous results demonstrated that loss-of-function mutations of CCM genes cause pleiotropic effects, including defective autophagy, altered reactive oxygen species (ROS) homeostasis, and enhanced sensitivity to oxidative stress and inflammatory events, suggesting a novel unifying pathogenetic mechanism, and raising the possibility that CCM disease onset and severity are influenced by the presence of susceptibility and modifier genes. Consistently, genome-wide association studies (GWAS) in large and homogeneous cohorts of patients sharing the familial form of CCM disease and identical mutations in CCM genes have led to the discovery of distinct genetic modifiers of major disease severity phenotypes, such as development of numerous and large CCM lesions, and susceptibility to ICH. This review deals with the identification of genetic modifiers with a significant impact on inter-individual variability in CCM disease onset and severity, including highly polymorphic genes involved in oxidative stress, inflammatory and immune responses, such as cytochrome P450 monooxygenases (CYP), matrix metalloproteinases (MMP), and Toll-like receptors (TLR), pointing to their emerging prognostic value, and opening up new perspectives for risk stratification and personalized medicine strategies.

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.

Anatomical distribution and expression of CYP in humans: Neuropharmacological implications

The cytochrome P450 (CYP450) superfamily is responsible for the metabolism of most xenobiotics and pharmacological treatments generally used in clinical settings. Genetic factors as well as environmental determinants acting through fine epigenetic mechanisms modulate the expression of CYP over the lifespan (fetal vs. infancy vs. adult phases) and in diverse organs. In addition, pathological processes might alter the expression of CYP. In this selective review, we sought to summarize the evidence on the expression of CYP focusing on three specific aspects: (a) the anatomical distribution of the expression in body districts relevant in terms of drug pharmacokinetics (liver, gut, and kidney) and pharmacodynamics, focusing for the latter on the brain, since this is the target organ of psychopharmacological agents; (b) the patterns of expression during developmental phases; and (c) the expression of CYP450 enzymes during pathological processes such as cancer. We showed that CYP isoforms show distinct patterns of expression depending on the body district and the specific developmental phases. Of particular relevance for neuropsychopharmacology is the complex regulatory mechanisms that significantly modulate the complexity of the pharmacokinetic regulation, including the concentration of specific CYP isoforms in distinct areas of the brain, where they could greatly affect local substrate and metabolite concentrations of drugs.

The role of CYP2D in rat brain in methamphetamine-induced striatal dopamine and serotonin release and behavioral sensitization

RATIONALE

Cytochrome P450 2D (CYP2D) enzymes metabolize many addictive drugs, including methamphetamine. Variable CYP2D metabolism in the brain may alter CNS drug/metabolite concentrations, consequently affecting addiction liability and neuropsychiatric outcomes; components of these can be modeled by behavioral sensitization in rats.

METHODS

To investigate the role of CYP2D in the brain in methamphetamine-induced behavioral sensitization, rats were pretreated centrally with a CYP2D irreversible inhibitor (or vehicle) 20 h prior to each of 7 daily methamphetamine (0.5 mg/kg subcutaneous) injections. In vivo brain microdialysis was used to assess brain drug and metabolite concentrations, and neurotransmitter release.

RESULTS

CYP2D inhibitor (versus vehicle) pretreatment enhanced methamphetamine-induced stereotypy response sensitization. CYP2D inhibitor pretreatment increased brain methamphetamine concentrations and decreased the brain p-hydroxylation metabolic ratio. With microdialysis conducted on days 1 and 7, CYP2D inhibitor pretreatment exacerbated stereotypy sensitization and enhanced dopamine and serotonin release in the dorsal striatum. Day 1 brain methamphetamine and amphetamine concentrations correlated with dopamine and serotonin release, which in turn correlated with the stereotypy response slope across sessions (i.e., day 1 through day 7), used as a measure of sensitization.

CONCLUSIONS

CYP2D-mediated methamphetamine metabolism in the brain is sufficient to alter behavioral sensitization, brain drug concentrations, and striatal dopamine and serotonin release. Moreover, day 1 methamphetamine-induced neurotransmitter release may be an important predictor of subsequent behavioral sensitization. This suggests the novel contribution of CYP2D in the brain to methamphetamine-induced behavioral sensitization and suggests that the wide variation in human brain CYP2D6 may contribute to differential methamphetamine responses and chronic effects.

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.

Predation threats for a 24-h period activated the extension of axons in the brains of Xenopus tadpoles

The threat of predation is a driving force in the evolution of animals. We have previously reported that Xenopus laevis enhanced their tail muscles and increased their swimming speeds in the presence of Japanese larval salamander predators. Herein, we investigated the induced gene expression changes in the brains of tadpoles under the threat of predation using 3′-tag digital gene expression profiling. We found that many muscle genes were expressed after 24 h of exposure to predation. Ingenuity pathway analysis further showed that after 24 h of a predation threat, various signal transduction genes were stimulated, such as those affecting the actin cytoskeleton and CREB pathways, and that these might increase microtubule dynamics, axonogenesis, cognition, and memory. To verify the increase in microtubule dynamics, DiI was inserted through the tadpole nostrils. Extension of the axons was clearly observed from the nostril to the diencephalon and was significantly increased (P ≤ 0.0001) after 24 h of exposure to predation, compared with that of the control. The dynamic changes in the signal transductions appeared to bring about new connections in the neural networks, as suggested by the microtubule dynamics. These connections may result in improved memory and cognition abilities, and subsequently increase survivability.

Certain ortho-hydroxylated brominated ethers are promiscuous kinase inhibitors that impair neuronal signaling and neurodevelopmental processes

The developing nervous system is remarkably sensitive to environmental signals, including disruptive toxins, such as polybrominated diphenyl ethers (PBDEs). PBDEs are an environmentally pervasive class of brominated flame retardants whose neurodevelopmental toxicity mechanisms remain largely unclear. Using dissociated cortical neurons from embryonic Rattus norvegicus, we found here that chronic exposure to 6-OH-BDE-47, one of the most prevalent hydroxylated PBDE metabolites, suppresses both spontaneous and evoked neuronal electrical activity. On the basis of our previous work on mitogen-activated protein kinase (MAPK)/extracellular signal-related kinase (ERK) (MEK) biology and our observation that 6-OH-BDE-47 is structurally similar to kinase inhibitors, we hypothesized that certain hydroxylated PBDEs mediate neurotoxicity, at least in part, by impairing the MEK-ERK axis of MAPK signal transduction. We tested this hypothesis on three experimental platforms: 1) in silico, where modeling ligand-protein docking suggested that 6-OH-BDE-47 is a promiscuous ATP-competitive kinase inhibitor; 2) in vitro in dissociated neurons, where 6-OH-BDE-47 and another specific hydroxylated BDE metabolite similarly impaired phosphorylation of MEK/ERK1/2 and activity-induced transcription of a neuronal immediate early gene; and 3) in vivo in Drosophila melanogaster, where developmental exposures to 6-OH-BDE-47 and a MAPK inhibitor resulted in offspring displaying similarly increased frequency of mushroom-body β-lobe midline crossing, a metric of axonal guidance. Taken together, our results support that certain ortho-hydroxylated PBDE metabolites are promiscuous kinase inhibitors and can cause disruptions of critical neurodevelopmental processes, including neuronal electrical activity, pre-synaptic functions, MEK-ERK signaling, and axonal guidance.

CYP2B6 Polymorphisms Are Associated with Ischemic Stroke Risk in a Chinese Han Population

Genetic factors have been demonstrated to play an important role in the pathology of ischemic stroke (IS). This study was conducted to explore the association between CYP2B6 polymorphisms and IS risk in a Chinese Han population. Four single-nucleotide polymorphisms (SNPs) in CYP2B6 from 477 cases and 495 controls were genotyped using the Agena MassARRAY. The odds ratio (OR) and 95% confidence interval (CI) were calculated under genetic models and haplotype analysis to assess the association between SNPs and IS risk. We found that rs2099361 was associated with an increased IS risk (CC vs. AA: overall: OR = 1.85, 95% CI: 1.16-2.93, P = 0.010; age ≤ 60: OR = 1.94, 95% CI: 1.02-3.70, P = 0.045; male: OR = 2.17, 95% CI: 1.22-3.86, P = 0.009). The GT genotype of rs4803420 was associated with a reduced IS risk (OR = 0.74, 95% CI: 0.57-0.98, P = 0.036); the GG genotype was associated with an increased IS risk in women (OR = 2.31, 95% CI: 1.00-5.31, P = 0.049). The rs1038376 polymorphism was associated with reduced IS risk for age ≤ 60 years (AT vs. TT: OR = 0.63, 95% CI: 0.40-0.99, P = 0.046). Interestingly, there were significant differences in some clinical indicator levels between case and control groups, and genotypes of SNPs. Our results indicated that CYP2B6 polymorphisms (rs2099361, rs4803420, and rs1038376) were associated with the risk of IS. Further studies are still needed to validate our findings with larger sample sizes.

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.

Comparison of In Vitro Stereoselective Metabolism of Bupropion in Human, Monkey, Rat, and Mouse Liver Microsomes

BACKGROUND AND OBJECTIVES

Bupropion is an atypical antidepressant and smoking cessation aid associated with wide intersubject variability. This study compared the formation kinetics of three phase I metabolites (hydroxybupropion, threohydrobupropion, and erythrohydrobupropion) in human, marmoset, rat, and mouse liver microsomes. The objective was to establish suitability and limitations  for subsequent use of nonclinical species to model bupropion central nervous system (CNS) disposition in humans.

METHODS

Hepatic microsomal incubations were conducted separately for the R- and S-bupropion enantiomers, and the formation of enantiomer-specific metabolites was determined using LC-MS/MS. Intrinsic formation clearance (CL_int) of metabolites across the four species was determined from the formation rate versus substrate concentration relationship.

RESULTS

The total clearance of S-bupropion was higher than that of R-bupropion in monkey and human liver microsomes. The contribution of hydroxybupropion to the total racemic bupropion clearance was 38%, 62%, 17%, and 96% in human, monkey, rat, and mouse, respectively.  In the same species order, threohydrobupropion contributed 53%, 23%, 17%, and 3%, and erythrohydrobupropion contributed 9%, 14%, 66%, and 1.3%, respectively, to racemic bupropion clearance.

CONCLUSION

The results demonstrate that phase I metabolism in monkeys best approximates that observed in humans, and support the preferred use of this species to investigate possible pharmacokinetic factors that influence the CNS disposition of bupropion and contribute to its high intersubject variability.

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 AUC_0-60 ; 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 AUC_0-60 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 cellular basis of fetal endoplasmic reticulum stress and oxidative stress in drug-induced neurodevelopmental deficits

Prenatal substance exposure is a growing public health concern worldwide. Although the opioid crisis remains one of the most prevalent addiction problems in our society, abuse of cocaine, methamphetamines, and other illicit drugs, particularly amongst pregnant women, are nonetheless significant and widespread. Evidence demonstrates prenatal drug exposure can affect fetal brain development and thus can have long-lasting impact on neurobehavioral and cognitive performance later in life. In this review, we highlight research examining the most prevalent drugs of abuse and their effects on brain development with a focus on endoplasmic reticulum stress and oxidative stress signaling pathways. A thorough exploration of drug-induced cellular stress mechanisms during prenatal brain development may provide insight into therapeutic interventions to combat effects of prenatal drug exposure.

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.

Molecular mechanisms involved in the protective actions of Selective Estrogen Receptor Modulators in brain cells

Synthetic selective modulators of the estrogen receptors (SERMs) have shown to protect neurons and glial cells against toxic insults. Among the most relevant beneficial effects attributed to these compounds are the regulation of inflammation, attenuation of astrogliosis and microglial activation, prevention of excitotoxicity and as a consequence the reduction of neuronal cell death. Under pathological conditions, the mechanism of action of the SERMs involves the activation of estrogen receptors (ERs) and G protein-coupled receptor for estrogens (GRP30). These receptors trigger neuroprotective responses such as increasing the expression of antioxidants and the activation of kinase-mediated survival signaling pathways. Despite the advances in the knowledge of the pathways activated by the SERMs, their mechanism of action is still not entirely clear, and there are several controversies. In this review, we focused on the molecular pathways activated by SERMs in brain cells, mainly astrocytes, as a response to treatment with raloxifene and tamoxifen.

The dawn of precision medicine in HIV: state of the art of pharmacotherapy

INTRODUCTION

Combination antiretroviral therapy (ART) reduces viral load to under the limit of detection, successfully decreasing HIV-related morbidity and mortality. Due to viral mutations, complex drug combinations and different patient response, there is an increasing demand for individualized treatment options for patients.

AREAS COVERED

This review first summarizes the pharmacokinetic and pharmacodynamic profile of clinical first-line drugs, which serves as guidance for antiretroviral precision medicine. Factors which have influential effects on drug efficacy and thus precision medicine are discussed: patients' pharmacogenetic information, virus mutations, comorbidities, and immune recovery. Furthermore, strategies to improve the application of precision medicine are discussed.

EXPERT OPINION

Precision medicine for ART requires comprehensive information on the drug, virus, and clinical data from the patients. The clinically available genetic tests are a good starting point. To better apply precision medicine, deeper knowledge of drug concentrations, HIV reservoirs, and efficacy associated genes, such as polymorphisms of drug transporters and metabolizing enzymes, are required. With advanced computer-based prediction systems which integrate more comprehensive information on pharmacokinetics, pharmacodynamics, pharmacogenomics, and the clinically relevant information of the patients, precision medicine will lead to better treatment choices and improved disease outcomes.

Cytochrome P450 in Pharmacogenetics: An Update

Interindividual variability in drug disposition is a major cause of lack of efficacy and adverse effects of drug therapies. The majority of hepatically cleared drugs are metabolized by cytochrome P450 (CYP) enzymes, mainly in families CYP1, CYP2, and CYP3. Genes encoding these enzymes are highly variable with allele distribution showing considerable differences between populations. Genetic variability of especially CYP2C9, CYP2C19, CYP2D6, and CYP3A5 is known to have clear clinical impact on drugs that are metabolized by these enzymes. CYP1A2, CYP2A6, CYP2B6, CYP2C8, and CYP3A4 all show variability that affects pharmacokinetics of drugs as well, but so far the evidence regarding their clinical implications is not as conclusive. In this review, we provide an up-to-date summary of the pharmacogenetics of the major human drug-metabolizing CYP enzymes, focusing on clinically significant examples.

CYP2A6 Genetic Variation Alters Striatal-Cingulate Circuits, Network Hubs, and Executive Processing in Smokers

BACKGROUND

Variation in the CYP2A6 gene alters the rate of nicotine metabolic inactivation and is associated with smoking behaviors and cessation success rates. The underlying neurobiological mechanisms of this genetic influence are unknown.

METHODS

Intrinsic functional connectivity strength, a whole-brain, data-driven, graph theory-based method, was applied to resting-state functional magnetic resonance imaging data in 66 smokers and 92 nonsmokers. A subset of subjects (n = 23/20; smokers/nonsmokers) performed the monetary incentive delay task, probing reward anticipation, and a go/no-go task, probing response inhibition, on two occasions, in the presence and absence of a nicotine patch.

RESULTS

A significant CYP2A6 genotype × smoking effect was found in the dorsal anterior cingulate cortex and ventral striatum, such that the normal (vs. slow) genotype individuals showed greater functional connectivity strength among smokers but not nonsmokers. Functional connectivity strength was negatively associated with severity of nicotine dependence in slow metabolizers. Both hubs were biased by inputs from the insula identified from seed-based connectivity. Similar gene × environment interactions were seen in ventral striatum during smoking abstinence when subjects performed the monetary incentive delay task and in dorsal anterior cingulate cortex when they performed the go/no-go task; both reductions were "normalized" in smokers (and increased in nonsmokers) after acute nicotine administration.

CONCLUSIONS

Because the CYP2A6 effect was seen only in smokers, these data suggest that the rate of nicotine metabolism-and thus the concentration of nicotine presented to the brain over the course of nicotine addiction-shapes brain circuits that, among other functions, compute reward and impulsivity processes.

Efavirenz and Metabolites in Cerebrospinal Fluid: Relationship with CYP2B6 c.516G→T Genotype and Perturbed Blood-Brain Barrier Due to Tuberculous Meningitis

Efavirenz (EFZ) has been associated with neuropsychiatric side effects. Recently, the 8-hydroxy-EFZ (8OH-EFZ) metabolite has been shown to be a potent neurotoxin in vitro, inducing neuronal damage at concentrations of 3.3 ng/ml. EFZ induced similar neuronal damage at concentrations of 31.6 ng/ml. We investigated the effect of genotype and blood-brain barrier integrity on EFZ metabolite concentrations in cerebrospinal fluid (CSF). We measured CSF drug concentrations in subjects from two separate study populations: 47 subjects with tuberculous meningitis (TBM) coinfection in Vietnam receiving 800 mg EFZ with standard antituberculous treatment and 25 subjects from the PARTITION study in the United Kingdom without central nervous system infection receiving 600 mg EFZ. EFZ and metabolite concentrations in CSF and plasma were measured and compared with estimates of effectiveness and neurotoxicity from available published in vitro and in vivo data. The effect of the CYP2B6 c.516G→T genotype (GG genotype, fast EFV metabolizer status; GT genotype, intermediate EFV metabolizer status; TT genotype, slow EFV metabolizer status) was examined. The mean CSF concentrations of EFZ and 8OH-EFZ in the TBM group were 60.3 and 39.3 ng/ml, respectively, and those in the no-TBM group were 15.0 and 5.9 ng/ml, respectively. Plasma EFZ and 8OH-EFZ concentrations were similar between the two groups. CSF EFZ concentrations were above the in vitro toxic concentration in 76% of samples (GG genotype, 61%; GT genotype, 90%; TT genotype, 100%) in the TBM group and 13% of samples (GG genotype, 0%; GT genotype, 18%; TT genotype, 50%) in the no-TBM group. CSF 8OH-EFZ concentrations were above the in vitro toxic concentration in 98% of the TBM group and 87% of the no-TBM group; levels were independent of genotype but correlated with the CSF/plasma albumin ratio. Potentially neurotoxic concentrations of 8OH-EFZ are frequently observed in CSF independently of the CYP2B6 genotype, particularly in those with impaired blood-brain barrier integrity.

Genetic polymorphism of metabolic enzymes modifies the risk of chronic solvent-induced encephalopathy

In the present study, we investigate whether genetic polymorphism in enzymes involved in the metabolism of organic solvents influences susceptibility to chronic solvent encephalopathy (CSE), which is one of the major effects of long-term exposure to organic solvents. Polymorphisms in the genes encoding CYP1A1, CYP2E1, EPHX1, GSTM1, GSTT1 and GSTP1 enzymes were determined in a group of male CSE patients ( N = 97) and controls ( N = 214). The selection of the patients was based on a standard diagnostic protocol, including interviews, neuropsychological tests and questionnaires directed to somatic, cognitive and mood symptoms and exposure, in combination with well-defined decision rules. As controls, healthy workers of similar socio-economic background, without memory problems and with no known exposure to organic solvents, were included in the study. Comparing patients and controls, higher frequencies of the variant *5B allele of the CYP2E1 gene (OR: 5.8; 95% CI: 1.8-18.8) and of the variant GSTP1*C allele (OR: 0.40; 95% CI: 0.17-0.94) were found. Homozygous carriers of the exon 4 EPHX1 Arg139 variant allele had a lower risk (OR:0.25; 95% CI: 0.06-1.13).

The present study indicates that genetic polymorphism of CYP2E1, EPHX1 and GSTP1 modify the risk of developing CSE.

Temporal control of glucocorticoid neurodynamics and its relevance for brain homeostasis, neuropathology and glucocorticoid-based therapeutics

Glucocorticoids mediate plethora of actions throughout the human body. Within the brain, they modulate aspects of immune system and neuroinflammatory processes, interfere with cellular metabolism and viability, interact with systems of neurotransmission and regulate neural rhythms. The influence of glucocorticoids on memory and emotional behaviour is well known and there is increasing evidence for their involvement in many neuropsychiatric pathologies. These effects, which at times can be in opposing directions, depend not only on the concentration of glucocorticoids but also the duration of their presence, the temporal relationship between their fluctuations, the co-influence of other stimuli, and the overall state of brain activity. Moreover, they are region- and cell type-specific. The molecular basis of such diversity of effects lies on the orchestration of the spatiotemporal interplay between glucocorticoid- and mineralocorticoid receptors, and is achieved through complex dynamics, mainly mediated via the circadian and ultradian pattern of glucocorticoid secretion. More sophisticated methodologies are therefore required to better approach the study of these hormones and improve the effectiveness of glucocorticoid-based therapeutics.

Nicotine Increases Codeine Analgesia Through the Induction of Brain CYP2D and Central Activation of Codeine to Morphine

CYP2D metabolically activates codeine to morphine, which is required for codeine analgesia. Permeability across the blood-brain barrier, and active efflux, suggests that initial morphine in the brain after codeine is due to brain CYP2D metabolism. Human CYP2D is higher in the brains, but not in the livers, of smokers and 7-day nicotine treatment induces rat brain, but not hepatic, CYP2D. The role of nicotine-induced rat brain CYP2D in the central metabolic activation of peripherally administered codeine and resulting analgesia was investigated. Rats received 7-day nicotine (1 mg/kg subcutaneously) and/or a single propranolol (CYP2D mechanism-based inhibitor; 20 μg intracerebroventricularly) pretreatment, and then were tested for analgesia and drug levels following codeine (20 mg/kg intraperitoneally) or morphine (3.5 mg/kg intraperitoneally), matched for peak analgesia. Nicotine increased codeine analgesia (1.59X AUC(0-30 min) vs vehicle; p<0.001), while propranolol decreased analgesia (0.56X; p<0.05); co-pretreatment was similar to vehicle controls (1.23X; p>0.1). Nicotine increased, while propranolol decreased, brain, but not plasma, morphine levels, and analgesia correlated with brain (p<0.02), but not plasma (p>0.4), morphine levels after codeine. Pretreatments did not alter baseline or morphine analgesia. Here we show that brain CYP2D alters drug response despite the presence of substantial first-pass metabolism of codeine and further that nicotine induction of brain CYP2D increases codeine response in vivo. Thus variation in brain CYP2D activity, due to genetics or environment, may contribute to individual differences in response to centrally acting substrates. Exposure to nicotine may increase central drug metabolism, not detected peripherally, contributing to altered drug efficacy, onset time, and/or abuse liability.

Cell type-specific expression and localization of cytochrome P450 isoforms in tridimensional aggregating rat brain cell cultures

Within the Predict-IV FP7 project a strategy for measurement of in vitro biokinetics was developed, requiring the characterization of the cellular model used, especially regarding biotransformation, which frequently depends on cytochrome P450 (CYP) activity. The extrahepatic in situ CYP-mediated metabolism is especially relevant in target organ toxicity. In this study, the constitutive mRNA levels and protein localization of different CYP isoforms were investigated in 3D aggregating brain cell cultures. CYP1A1, CYP2B1/B2, CYP2D2/4, CYP2E1 and CYP3A were expressed; CYP1A1 and 2B1 represented almost 80% of the total mRNA content. Double-immunolabeling revealed their presence in astrocytes, in neurons, and to a minor extent in oligodendrocytes, confirming the cell-specific localization of CYPs in the brain. These results together with the recently reported formation of an amiodarone metabolite following repeated exposure suggest that this cell culture system possesses some metabolic potential, most likely contributing to its high performance in neurotoxicological studies and support the use of this model in studying brain neurotoxicity involving mechanisms of toxication/detoxication.

Primary role of cytochrome P450 2B6 in the oxidative metabolism of 2,2',4,4',6-pentabromodiphenyl ether (BDE-100) to hydroxylated BDEs

Human exposure to polybrominated diphenyl ethers (PBDEs) through various routes poses deleterious health effects. PBDEs are biotransformed into hydroxylated metabolites (OH-BDEs) via cytochrome P450s (P450s), which may add to their neurotoxic effects. This study characterizes the in vitro metabolism of 2,2',4,4',6-pentabromodiphenyl ether (BDE-100), one of the most abundant PBDE congeners found in humans, by recombinant human P450s and pooled human liver microsomes (HLMs). Ten recombinant P450s were individually incubated with BDE-100 to monitor P450-specific metabolism. P450 2B6 was found to be the predominant enzyme responsible for nearly all formation of six mono-OH-pentaBDE and two di-OH-pentaBDE metabolites. Four metabolites were identified as 3-hydroxy-2,2',4,4',6-pentabromodiphenyl ether (3-OH-BDE-100), 5'-hydroxy-2,2',4,4',6-pentabromodiphenyl ether (5'-OH-BDE-100), 6'-hydroxy-2,2',4,4',6-pentabromodiphenyl ether (6'-OH-BDE-100), and 4'-hydroxy-2,2',4,5',6-pentabromodiphenyl ether (4'-OH-BDE-103) through use of reference standards. The two remaining mono-OH-pentaBDE metabolites were hypothesized using mass spectral fragmentation characteristics of derivatized OH-BDEs, which allowed prediction of an ortho-OH-pentaBDE and a para-OH-pentaBDE positional isomer. Additional information based on theoretical boiling point calculations using COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) and experimental chromatographic retention times were used to identify the hypothesized metabolites as 2'-hydroxy-2,3',4,4',6-pentabromodiphenyl ether (2'-OH-BDE-119) and 4-hydroxy-2,2',4',5,6-pentabromodiphenyl ether (4-OH-BDE-91), respectively. Kinetic studies of BDE-100 metabolism using P450 2B6 and HLMs revealed Km values ranging from 4.9 to 7.0 μM and 6-10 μM, respectively, suggesting a high affinity toward the formation of OH-BDEs. Compared to the metabolism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) reported in previous studies, BDE-100 appears to be more slowly metabolized by P450s due to the presence of a third ortho-substituted bromine atom.

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.

Imperatorin is a mechanism-based inactivator of CYP2B6

Imperatorin (IMP) is the major active ingredient in many common medicinal herbs. We examined the irreversible inhibitory effect of IMP on CYP2B6. IMP produced a time- and concentration-dependent inactivation of CYP2B6. About 70% of activity of CYP2B6 was suppressed after its incubation with 1.5 μM IMP for 9 minutes. KI and kinact were found to be 0.498 μM and 0.079 min(-1), respectively. The loss of CYP2B6 activity required the presence of NADPH. Glutathione and catalase/superoxide dismutase showed little protection against the IMP-induced enzyme inactivation. Ticlopidine, a substrate of CYP2B6, showed protection of the enzyme against the inactivation induced by IMP. The estimated partition ratio of the inactivation was approximately 4. Additionally, a γ-ketoenal intermediate was identified in microsomal incubations with IMP. CYP1A2, CYP2A6, CYP2B6, CYP2D6, CYP2E1, CYP3A4, and CYP3A5 were found to be involved in bioactivation of IMP. In conclusion, IMP is a mechanism-based inactivator of CYP2B6. The formation of γ-ketoenal intermediate may account for the enzyme inactivation.

Identification of a functional antioxidant response element within the eighth intron of the human ABCC3 gene

The ATP-binding cassette (ABC) family of transporters, including ABCC3, is a large family of efflux pumps that plays a pivotal role in the elimination of xenobiotics from the body. ABCC3 has been reported to be induced during hepatic stress conditions and through the progression of some forms of cancer. Several lines of evidence have implicated the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in this induction. However, although rodent models have been investigated, a functional antioxidant response element (ARE) in the human ABCC3 gene has not been identified. The purpose of this study was to identify and characterize the ARE(s) responsible for mediating the Nrf2-dependent induction of the human ABCC3 gene. A high-throughput chromatin immunoprecipitation-sequencing analysis performed in A549 cells revealed a specific interaction between Nrf2 and the eighth intron of the human ABCC3 gene rather than the more prototypical flanking region of the gene. Subsequent in silico analysis of the intron identified two putative ARE elements that contained the core consensus ARE sequence commonly found in several Nrf2-responsive genes. Functional characterization of these two AREs using luciferase-reporter constructs with ARE mutant constructs revealed that one of these putative AREs is functionally active. Finally, DNA pull-down assays confirmed specific binding of these intronic AREs by Nrf2 in vitro. Our findings identify a functional Nrf2 response element within the eighth intron of the ABCC3 gene, which may provide mechanistic insight into the induction of ABCC3 during antioxidant response stimuli.

A mechanistic view of polybrominated diphenyl ether (PBDE) developmental neurotoxicity

Polybrominated diphenyl ethers (PBDEs), extensively used in the past few decades as flame retardants in a variety of consumer products, have become world-wide persistent environmental pollutants. Levels in North America are usually higher than those in Europe and Asia, and body burden is 3-to-9-fold higher in infants and toddlers than in adults. The latter has raised concern for potential developmental toxicity and neurotoxicity of PBDEs. Experimental studies in animals and epidemiological observations in humans suggest that PBDEs may be developmental neurotoxicants. Pre- and/or post-natal exposure to PBDEs may cause long-lasting behavioral abnormalities, particularly in the domains of motor activity and cognition. The mechanisms underlying the developmental neurotoxic effects of PBDEs are not known, though several hypotheses have been put forward. One general mode of action relates to the ability of PBDEs to impair thyroid hormone homeostasis, thus indirectly affecting the developing brain. An alternative or additional mode of action involves a direct effect of PBDEs on nervous system cells; PBDEs can cause oxidative stress-related damage (DNA damage, mitochondrial dysfunction, apoptosis), and interfere with signal transduction (particularly calcium signaling), and with neurotransmitter systems. Important issues such as bioavailability and metabolism of PBDEs, extrapolation of results to low level of exposures, and the potential effects of interactions among PBDE congeners and between PBDEs and other contaminants also need to be taken into account.

Predictors of blood trihalomethane concentrations in NHANES 1999-2006

BACKGROUND

Trihalomethanes (THMs) are water disinfection by-products that have been associated with bladder cancer and adverse birth outcomes. Four THMs (bromoform, chloroform, bromodichloromethane, dibromochloromethane) were measured in blood and tap water of U.S. adults in the National Health and Nutrition Examination Survey (NHANES) 1999-2006. THMs are metabolized to potentially toxic/mutagenic intermediates by cytochrome p450 (CYP) 2D6 and CYP2E1 enzymes.

OBJECTIVES

We conducted exploratory analyses of blood THMs, including factors affecting CYP2D6 and CYP2E1 activity.

METHODS

We used weighted multivariable regressions to evaluate associations between blood THMs and water concentrations, survey year, and other factors potentially affecting THM exposure or metabolism (e.g., prescription medications, cruciferous vegetables, diabetes, fasting, pregnancy, swimming).

RESULTS

From 1999 to 2006, geometric mean blood and water THM levels dropped in parallel, with decreases of 32%-76% in blood and 38%-52% in water, likely resulting, in part, from the lowering of the total THM drinking water standard in 2002-2004. The strongest predictors of blood THM levels were survey year and water concentration (n = 4,232 total THM; n = 4,080 bromoform; n = 4,582 chloroform; n = 4,374 bromodichloromethane; n = 4,464 dibromochloromethane). We detected statistically significant inverse associations with diabetes and eating cruciferous vegetables in all but the bromoform model. Medications did not consistently predict blood levels. Afternoon/evening blood samples had lower THM concentrations than morning samples. In a subsample (n = 230), air chloroform better predicted blood chloroform than water chloroform, suggesting showering/bathing was a more important source than drinking.

CONCLUSIONS

We identified several factors associated with blood THMs that may affect their metabolism. The potential health implications require further study.

Genetic variation in the CYP2B6 gene is related to circulating 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) concentrations: an observational population-based study

BACKGROUND

Since human CYP2B6 has been identified as the major CYP enzyme involved in the metabolism of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and that human 2B6 is a highly polymorphic CYP, with known functional variants, we evaluated if circulating concentrations of a major brominated flame retardant, BDE-47, were related to genetic variation in the CYP2B6 gene in a population sample.

METHODS

In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (men and women all aged 70), 25 single nucleotide polymorphisms (SNPs) in the CYP2B6 gene were genotyped. Circulating concentrations of BDE-47 were analyzed by high-resolution gas chromatography coupled to high-resolution mass spectrometry (HRGC/ HRMS).

RESULTS

Several SNPs in the CYP2B6 gene were associated with circulating concentrations of BDE-47 (P = 10-4 to 10-9). The investigated SNPs came primarily from two haplotypes, although the correlation between the haplotypes was rather high. Conditional analyses adjusting for the SNP with the strongest association with the exposure (rs2014141) did not provide evidence for independent signals.

CONCLUSION

Circulating concentrations of BDE-47 were related to genetic variation in the CYP2B6 gene in an elderly population.

Monocrotophos induces the expression and activity of xenobiotic metabolizing enzymes in pre-sensitized cultured human brain cells

The expression and metabolic profile of cytochrome P450s (CYPs) is largely missing in human brain due to non-availability of brain tissue. We attempted to address the issue by using human brain neuronal (SH-SY5Y) and glial (U373-MG) cells. The expression and activity of CYP1A1, 2B6 and 2E1 were carried out in the cells exposed to CYP inducers viz., 3-methylcholanthrene (3-MC), cyclophosphamide (CPA), ethanol and known neurotoxicant- monocrotophos (MCP), a widely used organophosphorous pesticide. Both the cells show significant induction in the expression and CYP-specific activity against classical inducers and MCP. The induction level of CYPs was comparatively lower in MCP exposed cells than cells exposed to classical inducers. Pre-exposure (12 h) of cells to classical inducers significantly added the MCP induced CYPs expression and activity. The findings were concurrent with protein ligand docking studies, which show a significant modulatory capacity of MCP by strong interaction with CYP regulators-CAR, PXR and AHR. Similarly, the known CYP inducers- 3-MC, CPA and ethanol have also shown significantly high docking scores with all the three studied CYP regulators. The expression of CYPs in neuronal and glial cells has suggested their possible association with the endogenous physiology of the brain. The findings also suggest the xenobiotic metabolizing capabilities of these cells against MCP, if received a pre-sensitization to trigger the xenobiotic metabolizing machinery. MCP induced CYP-specific activity in neuronal cells could help in explaining its effect on neurotransmission, as these CYPs are known to involve in the synthesis/transport of the neurotransmitters. The induction of CYPs in glial cells is also of significance as these cells are thought to be involved in protecting the neurons from environmental insults and safeguard them from toxicity. The data provide better understanding of the metabolizing capability of the human brain cells against xenobiotics.

The Alzheimer pandemic: is paracetamol to blame?

HISTORICAL BACKGROUND

The clinical recognition of a form of dementia closely resembling Alzheimer's disease dates from around 1800. The role of analgesics derived from coal-tar in the spread of the pandemic is traced in terms of the introduction of phenacetin (PN) in 1887; its nephrotoxicity; the observation of lesions characteristic of the disease by Fischer and Alzheimer; the discovery of paracetamol (PA) as the major metabolite of PN; the linking of kidney injury and dementia with high PN usage; and the failure of PN replacement by PA to halt and reverse the exponential, inexorable rise in the incidence of Alzheimer-type dementia. Fischer observed his first case before Alzheimer; it is proposed to rename the syndrome Fischer-Alzheimer disease (F-AD). Disease development: PA-metabolising enzymes are localised in the synaptic areas of the frontal cortex and hippocampus, where F-AD lesions arise. The initiating chemical lesions in liver poisoning comprise covalent binding of a highly reactive product of PA metabolism to proteins; similar events are believed to occur in brain, where alterations in the antigenic profiles of cerebral proteins activate the microglia. β-Amyloid forms, and, like PA itself, induces nitric oxide synthase. Peroxynitrite modifies cerebral proteins by nitrating tyrosine residues, further challenging the microglia and exacerbating the amyloid cascade. Spontaneous reinnervation, N-acetyl cysteine administration and tyrosine supplementation may attenuate the early stages of F-AD development.

CONCLUSION

F-AD is primarily a man-made condition with PA as its principal risk factor.

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.

Cytochrome P450-mediated drug metabolism in the brain

Cytochrome P450 enzymes (CYPs) metabolize many drugs that act on the central nervous system (CNS), such as antidepressants and antipsychotics; drugs of abuse; endogenous neurochemicals, such as serotonin and dopamine; neurotoxins; and carcinogens. This takes place primarily in the liver, but metabolism can also occur in extrahepatic organs, including the brain. This is important for CNS-acting drugs, as variation in brain CYP-mediated metabolism may be a contributing factor when plasma levels do not predict drug response. This review summarizes the characterization of CYPs in the brain, using examples from the CYP2 subfamily, and discusses sources of variation in brain CYP levels and metabolism. Some recent experiments are described that demonstrate how changes in brain CYP metabolism can influence drug response, toxicity and drug-induced behaviours. Advancing knowledge of brain CYP-mediated metabolism may help us understand why patients respond differently to drugs used in psychiatry and predict risk for psychiatric disorders, including neurodegenerative diseases and substance abuse.

CYP2E1 T7632A and 9-bp insertion polymorphisms and colorectal cancer risk: a meta-analysis based on 4,592 cases and 5,918 controls

Previous studies suggest that genetic factors play important roles in the development of colorectal cancer. CYP2E1 T7632A and 9-bp insertion polymorphisms may influence the risk of colorectal cancer, but published results are conflicting. We therefore conducted a meta-analysis comprising 9 case-control studies with 4,592 cases and 5,918 controls. Odds ratios (ORs) with 95 % confidence interval (95 % CI) were used to assess the strength of the associations of CYP2E1 T7632A and 9-bp insertion polymorphisms with colorectal cancer. For CYP2E1 T7632A polymorphism, meta-analysis showed that there was no significant association between the CYP2E1 T7632A polymorphism and colorectal cancer risk under all contrast models (A vs. T: OR = 1.06, 95 % CI 0.88-1.29, P = 0.528; AA vs. TT: OR = 0.85, 95 % CI 0.61-1.19, P = 0.351; AA/TA vs. TT: OR = 1.08, 95 % CI 0.87-1.34, P = 0.484; and AA vs.

TT/TA

OR = 0.87, 95 % CI 0.62-1.21, P = 0.395). For CYP2E1 96-bp insertion polymorphism, meta-analysis showed that there was a significant association between the CYP2E1 96-bp insertion polymorphism and colorectal cancer risk under the allele contrast model and the dominant contrast model (for the allele contrast model: OR = 1.20, 95 % CI 1.06-1.36, P = 0.005; for the dominant contrast model: OR = 1.25, 95 % CI 1.07-1.45, P = 0.005). Subgroup analysis by race suggested that there was an obvious association between the CYP2E1 96-bp insertion polymorphism and colorectal cancer risk in Asians under the codominant contrast model. In conclusion, our meta-analysis demonstrates that there is a significant association between the CYP2E1 96-bp insertion polymorphism and colorectal cancer risk, and CYP2E1 9-bp insertion polymorphism is a risk factor for developing colorectal cancer.