Metabolism, pharmacogenetics, and metabolic drug-drug interactions of antipsychotic drugs

Regulation of Ion Channel Function in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes by Cancer Cell Secretion Through DNA Methylation

Background

Cardiac dysfunction including arrhythmias appear frequently in patients with cancers, which are expected to be caused mainly by cardiotoxic effects of chemotherapy. Experimental studies investigating the effects of cancer cell secretion without chemotherapy on ion channel function in human cardiomyocytes are still lacking.

Methods

The human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) generated from three healthy donors were treated with gastrointestinal (GI) cancer (AGS and SW480 cells) medium for 48 h. The qPCR, patch-clamp, western blotting, immunostaining, dot blotting, bisulfite sequence, and overexpression of the ten-eleven translocation (TET) enzyme were performed for the study.

Results

After treated with cancer cell secretion, the maximum depolarization velocity and the action potential amplitude were reduced, the action potential duration prolonged, peak Na⁺ current, and the transient outward current were decreased, late Na⁺ and the slowly activating delayed rectifier K⁺ current were increased. Changes of mRNA and protein level of respective channels were detected along with altered DNA methylation level in CpG island in the promoter regions of ion channel genes and increased protein levels of DNA methyltransferases. Phosphoinositide 3-kinase (PI3K) inhibitor attenuated and transforming growth factor-β (TGF-β) mimicked the effects of cancer cell secretion.

Conclusions

GI cancer cell secretion could induce ion channel dysfunction, which may contribute to occurrence of arrhythmias in cancer patients. The ion channel dysfunction could result from DNA methylation of ion channel genes via activation of TGF-β/PI3K signaling. This study may provide new insights into pathogenesis of arrhythmia in cancer patients.

Attribute Supervised Probabilistic Dependent Matrix Tri-Factorization Model for the Prediction of Adverse Drug-Drug Interaction

Adverse drug-drug interaction (ADDI) becomes a significant threat to public health. Despite the detection of ADDIs is experimentally implemented in the early development phase of drug design, many potential ADDIs are still clinically explored by accidents, leading to a large number of morbidity and mortality. Several computational models are designed for ADDI prediction. However, they take no consideration of drug dependency, although many drugs usually produce synergistic effects and own highly mutual dependency in treatments, which contains underlying information about ADDIs and benefits ADDI prediction. In this paper, we design a dependent network to model the drug dependency and propose an attribute supervised learning model Probabilistic Dependent Matrix Tri-Factorization (PDMTF) for ADDI prediction. In particular, PDMTF incorporates two drug attributes, molecular structure and side effect, and their correlation to model the adverse interactions among drugs. The dependent network is represented by a dependent matrix, which is first formulated by the row precision matrix of the predicted attribute matrices and then regularized by the molecular structure similarities among drugs. Meanwhile, an efficient alternating algorithm is designed for solving the optimization problem of PDMTF. Experiments demonstrate the superior performance of the proposed model when compared with eight baselines and its two variants.

[Comorbidity of cardiovascular diseases and cancers: Problems in the diagnosis of cardiotoxic effects of chemo- and radiation therapy]

Cardiovascular diseases (CVD) and cancers are the leaders in their prevalence and the major causes of death in economically developed countries, determining their high sociomedical significance in society. Improvement of methods for the early diagnosis and treatment of cancers has contributed to increases in relapse-free survival and life expectancy in these patients. At the same time, the new problems have emerged particularly in the development of various cardiovascular events/diseases when treating cancer, which may predict worse prognosis in patients and be an independent cause of death. To search for new markers of cardiotoxicity at early stages and to develop effective methods for the prevention and personalized treatment of cancer and CVD are the problems that can be solved only by joint efforts of cardiologists and oncologists.

Genetics of tardive dyskinesia

Tardive dyskinesia (TD) is one of the most serious adverse side effects of antipsychotic drugs and is an important topic of pharmacogenetic studies. Since there is a genetic susceptibility for developing this adverse reaction, and given that it is hard to predict its development prior to or during the early period of medication, the genetic study of TD is a promising research topic that has a direct clinical application. Moreover, such studies would improve our understanding of the genetic mechanism(s) underlying abnormal dyskinetic movement. A substantial number of case-control association studies of TD have been performed, with numbers of studies focusing on the genes involved in antipsychotic drug metabolism, such as those for cytochrome P450 (CYP) and oxidative stress related genes as well as various neurotransmitter related genes. These studies have produced relatively consistent though controversial findings for certain polymorphisms such as CYP2D6*10, DRD2 Taq1A, DRD3 Ser9Gly, HTR2A T102C, and MnSOD Ala9Val. Moreover, the application of the genome-wide association study (GWAS) to the susceptibility of TD has revealed certain associated genes that previously were never considered to be associated with TD, such as the rs7669317 on 4q24, GLI2 gene, GABA pathway genes, and HSPG2 gene. Although a substantial number of genetic studies have investigated TD, many of the positive findings have not been replicated or are inconsistent, which could be due to differences in study design, sample size, and/or subject ethnicity. We expect that more refined research will be performed in the future to resolve these issues, which will then enable the genetic prediction of TD and clinical application thereof.

Cardio-oncology/onco-cardiology

An understanding of onco-cardiology or cardio-oncology is critical for the effective care of cancer patients. Virtually all antineoplastic agents are associated with cardiotoxicity, which can be divided into 5 categories: direct cytotoxic effects of chemotherapy and associated cardiac systolic dysfunction, cardiac ischemia, arrhythmias, pericarditis, and chemotherapy-induced repolarization abnormalities. Radiation therapy can also lead to coronary artery disease and fibrotic changes to the valves, pericardium, and myocardium. All patients being considered for chemotherapy, especially those who have prior cardiac history, should undergo detailed cardiovascular evaluation to optimize the treatment. Serial assessment of left ventricular systolic function and cardiac biomarkers might also be considered in selected patient populations. Cardiotoxic effects of chemotherapy might be decreased by the concurrent use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, or beta-blockers. Antiplatelet or anticoagulation therapy might be considered in patients with a potential hypercoagulable state associated with chemotherapy or cancer. Open dialogue between both cardiologists and oncologists will be required for optimal patient care.

MDR1 gene polymorphisms and response to acute risperidone treatment

Polymorphic multidrug resistant protein 1 (MDR1) transports drugs against a concentration gradient across the blood-brain barrier and reduces their accumulation in the brain. MDR1 may therefore influence antipsychotic brain availability contributing to inter-individual differences in treatment response and adverse effects, regardless of plasma concentrations. In the present study we investigated the influence of two common MDR1 polymorphisms on the improvement of psychopathological symptoms and occurrence of extrapyramidal side effects (EPS) in Slovenian schizophrenia patients acutely treated with risperidone. A total of 59 clinically well defined patients with first episode schizophrenia spectrum disorders or after tapering their maintenance treatment were genotyped for MDR1 C3435T and G2677T/A. Steady-state plasma concentrations of risperidone active moiety (sum of risperidone and the 9-hydroxyrisperidone) were determined. G2677T/A and C3435T genotypes were not associated to psychopathological symptoms, efficacy of treatment and risk for parkinsonism. Marginal associations with akathisia (p=0.039 and p=0.042, respectively) and dystonia (p=0.013 and p=0.034, respectively) were observed for both G2677T/A and C3435T genotypes. However, higher AIMS and BARS scores were observed only in heterozygous carriers of G2677T/A and C3435T polymorphisms and there was no tendency of gene-dose effect. The present study does not suggest a major influence of MDR1 G2677T/A and C3435T polymorphisms on treatment response during short-term risperidone therapy in patients with schizophrenia or schizoaffective disorder.

ABCB1 and cytochrome P450 polymorphisms: clinical pharmacogenetics of clozapine

To examine the genetic factors influencing clozapine kinetics in vivo, 75 patients treated with clozapine were genotyped for CYPs and ABCB1 polymorphisms and phenotyped for CYP1A2 and CYP3A activity. CYP1A2 activity and dose-corrected trough steady-state plasma concentrations of clozapine correlated significantly (r = -0.61; P = 1 x 10), with no influence of the CYP1A2*1F genotype (P = 0.38). CYP2C19 poor metabolizers (*2/*2 genotype) had 2.3-fold higher (P = 0.036) clozapine concentrations than the extensive metabolizers (non-*2/*2). In patients comedicated with fluvoxamine, a strong CYP1A2 inhibitor, clozapine and norclozapine concentrations correlate with CYP3A activity (r = 0.44, P = 0.075; r = 0.63, P = 0.007, respectively). Carriers of the ABCB1 3435TT genotype had a 1.6-fold higher clozapine plasma concentrations than noncarriers (P = 0.046). In conclusion, this study has shown for the first time a significant in vivo role of CYP2C19 and the P-gp transporter in the pharmacokinetics of clozapine. CYP1A2 is the main CYP isoform involved in clozapine metabolism, with CYP2C19 contributing moderately, and CYP3A4 contributing only in patients with reduced CYP1A2 activity. In addition, ABCB1, but not CYP2B6, CYP2C9, CYP2D6, CYP3A5, nor CYP3A7 polymorphisms, influence clozapine pharmacokinetics.

Pharmacogenetics and pharmacogenomics of schizophrenia: a review of last decade of research

The last decade of research into the pharmacogenetics of antipsychotics has seen the development of genetic tests to determine the patients' metabolic status and the first attempts at personalization of antipsychotic treatment. The most significant results are the association between drug metabolic polymorphisms, mainly in cytochrome P450 genes, with variations in drug metabolic rates and side effects. Patients with genetically determined CYP2D6 poor metabolizer (PMs) status may require lower doses of antipsychotic. Alternatively, CYP2D6 ultrarapid matabolizers (UMs) will need increased drug dosage to obtain therapeutic response. Additionally, polymorphisms in dopamine and serotonin receptor genes are repeatedly found associated with response phenotypes, probably reflecting the strong affinities that most antipsychotics display for these receptors. In particular, there is important evidence suggesting association between dopamine 2 receptor (D2) polymorphisms (Taq I and -141-C Ins/Del) and a dopamine 3 receptor (D3) polymorphism (Ser9Gly) with antipsychotic response and drug-induced tardive dyskinesia. Additionally, there is accumulating evidence indicating the influence of a 5-HT2C polymorphism (-759-T/C) in antipsychotic-induced weight gain. Application of this knowledge to clinical practice is slowly gathering pace, with pretreatment determination of individual's drug metabolic rates, via CYP genotyping, leading the field. Genetic determination of patients' metabolic status is expected to bring clinical benefits by helping to adjust therapeutic doses and reduce adverse reactions. Genetic tests for the pretreatment prediction of antipsychotic response, although still in its infancy, have obvious implications for the selection and improvement of antipsychotic treatment. These developments can be considered as successes, but the objectives of bringing pharmacogenetic and pharmacogenomic research in psychiatric clinical practice are far from being realized. Further development of genetic tests is required before the concept of tailored treatment can be applied to psychopharmatherapy. This review aims to summarize the key findings from the last decade of research in the field. Current knowledge on genetic prediction of drug metabolic status, general response and drug-induced side effects will be reviewed and future pharmacogenomic and epigenetic research will be discussed.

Intérêt des antidépresseurs chez le patient schizophrène présentant un syndrome dépressif

INTRODUCTION

Depression is common in people with schizophrenia and is associated with substantial morbidity explaining also the considerable attention and recognition of this entity as suggested by the inclusion of the post-psychotic depression in DSM IV and ICD 10. The prevalence of this disorder varies according to the type of approach used (range between 7% to 75%). Prescription of antidepressants plus antipsychotic treatment is frequent in clinical practice (11 to 43%).

BACKGROUND

Pharmacokinetic and metabolic interactions have been identified. The cytochrome P450 has been identified as being implicated in the metabolism of most psychotropics, mainly through the CYP1A2, CYP2C19, CYP2D6, CYP3A4 isoenzymes. Tricyclic antidepressants are likely to increase chlorpromazine plasma levels. Similarly, antipsychotics such as perphenazine, chlorpromazine or haloperidol can increase antidepressant plasma levels, through the inhibition of CYP 450 isoenzymes (CYP2D6). Most of the Specific Serotonin Recapture Inhibitors (SSRIs) are likely to inhibit one or several CYP450 isoenzymes. The inhibition is moderate to marked for CYP1A2 (fluvoxamine and fluoxetine), CYP2C19 (fluoxetine, fluvoxamine and sertraline), CYP2D6 (paroxetine, fluoxetine and sertraline), and CYP3A4 (fluvoxamine, fluoxetine and sertraline). In the US, one-fourth of psychiatrists report the use of depression-rating scales in schizophrenic patients. Non specific scales (Hamilton Depression Rating Scale or Beck Depression Inventory) are the most commonly used in spite of the fact that these scales do not allow the distinction of depressive from negative symptoms in schizophrenic patients.

LITERATURE FINDINGS

Due to these limitations, more specific assessment tools for depressive symptoms in schizophrenia are required. Two specific scales for assessing depressive symptoms in schizophrenic patients have been constructed and validated. The Calgary Depression Scale (CDS) is a nine item scale, each item scored from 0 to 3. This scale was derived from the HDRS and the Present State Examination. Factor analysis showed that the CDS is unidimensional, has high internal consistency, and significant strong correlation with scores on the HDRS, Beck and BPRS depression scales. The CDS has been validated in different languages (Brazilian, Danish, French...). It has been shown that there is no overlap between negative or extrapyramidal and depressive symptoms assessed by the PDS in schizophrenic patients. The Psychotic Depression Scale (PDS) is a 32 item scale derived from the HDRS, PANSS, CPRS and AMDP, each item being rated from 0 to 7. A principal component analysis of the PDS items using a Varimax rotation disclosed 8 orthogonal components that account for 71% of the variance. These components involved the following dimensions : depressive mood, inhibition, vegetative signs, paranoid signs, strangeness of thought, inverse vegetative signs, guilt feelings and cognitive signs. The analysis revealed that the 'depressive mood' factor of the PDS was correlated with the 'depressive' factor and was slightly correlated with the cognitive factor of the PANSS. This first factor was not correlated with either the "negative" factor of the PANSS, or the Positive or Excitement factor of the PANSS. Hence, this PDS, factor distinguished depressive signs from negative symptoms. Due to their metrologic properties, specific scales should be preferred. However, only one open trial (of an antipsychotic) and two double blind controlled trials (one comparison of 2 antipsychotics and one comparison of an cholinesterase inhibitor versus placebo) have been published using the CDS. Likewise, only one double blind controlled trial using the PDS (comparison of 2 antipsychotics) has been published. No study of the effect of antidepressants in depressed schizophrenic patients has been published, using either the CDS or the PDS assessment criteria.

DISCUSSION

These specific scales are rarely used in clinical practice. Only about 1% of the US psychiatrists reported the use of the Calgary Depression Scale. Several open clinical trials have assessed the efficacy of antidepressant agents added to antipsychotic in patients with schizophrenia. They have produced inconsistent results but have suffered from methodological limits (short duration of the studies, non homogeneous inclusion criteria, heterogeneous assessment methods...). Due to the lack of a reference drug, double blind placebo-controlled trial are necessary. A recent meta-analysis has been performed on results of trials that have investigated the clinical efficacy of antidepressant medication (either tricyclics, SSRIs or others) in the treatment of depression in schizophrenic patients. In a subset of 5 trials (209 patients), the proportion improved in the antidepressant group was 26% (95% CI 10 to 42) higher than in the placebo group. The estimated number needed to treat was 4. In a subgroup of 6 studies (267 patients), the standardized mean difference on the HDRS score was -0.27 (95% CI - 0.7 to -0.2). There was no evidence that antidepressant treatment induced a deterioration of psychotic symptoms in these trials.

CONCLUSION

The results provide weak evidence for the efficacy of antidepressants in patients with schizophrenia and depression. Today, the only SSRI tested in the treatment of depression in schizophrenic patients is sertraline. One study led to positive results. Since the meta-analysis, one additional study has been performed comparing sertraline to placebo. No difference between the 2 treatment groups was demonstrated but the power of the trial was rather low. Further research is required to determine the best approach towards treating depression in patients with schizophrenia, with clinical trials performed for longer periods, using appropriate assessment criteria such as depressive symptoms and quality of life.

The influence of long-term treatment with psychotropic drugs on cytochrome P450: the involvement of different mechanisms

This paper emphasises that besides the direct action of psychotropic drugs on cytochrome P450 (CYP) (i.e., the binding of the parent drug to the enzyme) indirect mechanisms of CYP-psychotropic interactions, namely the formation of CYP-reactive metabolite complexes and their influence on enzyme regulation, are also very important. The described interactions that are time-, drug- and CYP isoform-dependent may overlap during long-term treatment. The final result of the overlapping depends on the dosage and time interval after the last administration of a drug, which determines the concentration of the parent drug and its metabolites in the environment of the enzyme. These interactions may occur not only in the liver, but also in the brain, and may change the activity of CYP towards the metabolism of drugs, sex steroids, neurosteroids and amine neurotransmitters. The role of the CNS in the regulation of CYP by psychotropics and the significance of CYP-psychotropic interactions for pharmacological and clinical profiling of these drugs is discussed. In addition, different experimental approaches for studying CNS-acting drugs are compared.

Lack of cataleptogenic potentiation with non-imidazole H3 receptor antagonists reveals potential drug–drug interactions between imidazole-based H3 receptor antagonists and antipsychotic drugs

Since H3 receptor (H3R) antagonists/inverse agonists can improve cognitive function in animal models, they may have the potential to be used as add-on therapy in the treatment of schizophrenia, a disease with significant cognitive deficits. However, a recent study showed potentiation of haloperidol-induced catalepsy by ciproxifan, an imidazole-containing H3R antagonist/inverse agonist, suggesting there is a potential risk of exacerbating extrapyramidal symptoms (EPS) if H3R antagonists were used as adjunctive treatment [Pillot, C., Ortiz, J., Heron, A., Ridray, S., Schwartz, J.C. and Arrang, J.M., Ciproxifan, a histamine H3-receptor antagonist/inverse agonist, potentiates neurochemical and behavioral effects of haloperidol in the rat, J Neurosci, 22 (2002) 7272-80]. In order to clarify the basis of this finding, we replicated this result and extended the work with another imidazole and two non-imidazole H3R antagonists. The results indicate that ciproxifan significantly augmented the effects of haloperidol and risperidone on catalepsy. Another imidazole H3R antagonist, thioperamide, also potentiated the effect of risperidone on catalepsy. In contrast, no catalepsy-enhancing effects were observed when selective non-imidazole H3R antagonists, ABT-239 and A-431404, were coadministered with haloperidol and/or risperidone. As ciproxifan and thioperamide are inhibitors of cytochrome P450 enzymes, responsible for metabolizing risperidone and haloperidol, the possibility that the augmentation of antipsychotics by imidazoles resulted from drug-drug interactions was tested. A drug metabolism study revealed that an imidazole, but not a non-imidazole, potently inhibited the metabolism of haloperidol and risperidone. Furthermore, ketoconazole, an imidazole-based CYP 3A4 inhibitor, significantly augmented risperidone-induced catalepsy. Together, these data suggest the potentiation of antipsychotic-induced catalepsy may result from pharmacokinetic drug-drug interactions and support the potential utility of non-imidazole H3R antagonists in treatment of cognitive impairment in schizophrenia without increased risk of increased EPS in patients.

Inhibition of rat liver CYP2D in vitro and after 1-day and long-term exposure to neuroleptics in vivo-possible involvement of different mechanisms

The aim of the present study was to investigate the influence of classic and atypical neuroleptics on the activity of rat CYP2D measured as a rate of ethylmorphine O-deethylation. The reaction was studied in control liver microsomes in the presence of neuroleptics, as well as in microsomes of rats treated intraperitoneally (i.p.) for 1-day or 2-weeks (twice a day) with pharmacological doses of the drugs (promazine, levomepromazine, thioridazine, perazine 10 mg kg(-1); chlorpromazine 3 mg kg(-1); haloperidol 0.3 mg kg(-1); risperidone 0.1 mg kg(-1); sertindole 0.05 mg kg(-1)), in the absence of the neuroleptics in vitro. Neuroleptics added in vitro to control liver microsomes decreased the activity of the rat CYP2D by competitive or mixed inhibition of the enzyme. Thioridazine (Ki=15 microM) was the most potent inhibitor of the rat CYP2D among the drugs studied, whose effect was more pronounced than that of the other neuroleptics tested: phenothiazines (Ki=18-23 microM), haloperidol (Ki=32 microM), sertindole (Ki=51 microM) or risperidone (Ki=165 microM). The investigated neuroleptics-when given to rats in vivo-also seemed to exert an inhibitory effect on CYP2D via other mechanisms. One-day exposure of rats to the classic neuroleptics decreased the activity of CYP2D in rat liver microsomes. After chronic treatment with the investigated neuroleptics, the decreased CYP2D activity produced by the phenothiazines was still maintained, while that caused by haloperidol diminished. Moreover, risperidone decreased the activity of that enzyme. The obtained results indicate drug- and time-dependent interactions between the investigated neuroleptics and the CYP2D subfamily of rat cytochrome P-450, which may proceed via different mechanisms: (1) competitive or mixed inhibition of CYP2D shown in vitro, the inhibitory effects of phenothiazines being stronger than those of haloperidol or atypical neuroleptics, but weaker than the effects of the respective drugs on human CYP2D6; (2) in vivo inhibition of CYP2D, produced by both 1-day and chronic treatment with phenothiazines, which suggests inactivation of enzyme by intermediate metabolites; (3) in vivo inhibition of CYP2D by risperidone, produced only by chronic treatment with the drug, which suggests its influence on the enzyme regulation.

Pharmacokinetic Factors in the Adverse Cardiovascular Effects of Antipsychotic Drugs

Antipsychotics may cause serious adverse cardiovascular effects, including prolonged QT interval and sudden death. This review considers antipsychotic-induced cardiovascular events from three perspectives: high-risk drugs, high-risk individuals and high-risk drug interactions. Pharmacokinetic drug interactions involving the cytochrome P450 (CYP) enzymatic pathway and pharmacodynamic interactions leading to direct cardiotoxic effects are discussed. Original reports on antipsychotic-induced drug interactions are reviewed, with consideration of management guidelines. The literature was reviewed from 1 January 1966 to 1 February 2002. The literature search revealed only 12 original articles published on antipsychotic drug interactions leading to cardiovascular adverse events. Only 4 of the 12 reports were prospective studies; the remainder were either retrospective or anecdotal.Although poor study designs preclude a definitive statement, it appears that pharmacokinetic interactions primarily involved the CYP2D6 and CYP3A4 enzymatic pathways. Those involving the CYP2D6 isozyme included interactions with tricyclic antidepressants, selective serotonergic reuptake inhibitors and beta-blockers. Among these drug interactions, tricyclic antidepressants were most likely to reach clinical significance because of their limited therapeutic index. Drug interactions related to the CYP3A4 pathway were generally less severe, and involved high-potency antipsychotics coadministered with inhibitors such as clarithromycin. Strategies are discussed for the management of adverse cardiovascular events related to antipsychotic drug interactions, including the use of an algorithm. Large, randomised, placebo-controlled studies with strict inclusion criteria are needed to determine the role that antipsychotics play in QT prolongation and sudden death.

Disposition of 1,2,3,4,-tetrahydroisoquinoline in the brain of male Wistar and Dark Agouti rats

Direct evidence for accumulation of 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo- and exogenous substance suspected of producing Parkinsonism in humans, has not yet been shown. This study aimed to examine TIQ disposition in the whole rat brain and in the striatum and substantia nigra (SN). TIQ was administered to male Wistar and Dark Agouti rats (20, 40 and 100 mg/kg i.p.) alone or jointly with specific CYP2D inhibitor quinine (20, 40, 80 mg/kg i.p.), acutely or chronically. TIQ concentration in brain of both strains was several-fold higher than in plasma. The level of its metabolite, 4-OH-TIQ, was very low in the brain and plasma of TIQ-treated Wistar while in those receiving additionally quinine or in Dark Agouti rats, 4-OH-TIQ was absent or negligible. Inhibition of CYP2D catalyzing TIQ 4-hydroxylation in the liver had no influence on TIQ accumulation in the brain. Exogenous TIQ was actively transported from periphery into the brain by the organic cation transporter system, mainly OCT3, and quickly eliminated from it by P-glycoprotein. TIQ accumulation after chronic injection to Wistar rats was short-lasting and limited to SN. High concentration of TIQ in SN induces while in the liver inhibits the nigral and hepatic activity CYP2D, respectively.

Pharmacogenetics of schizophrenia

Patients display significant differences in response to therapeutic agents which may be caused by a variety of factors. Among them, genetic components presumably play a major role. Pharmacogenetics is the field of research that attempts to unravel the relationship between genetic variation affecting drug metabolism (pharmacokinetic level) or drug targets (pharmacodynamic level) and interindividual differences in pharmacoresponse. In schizophrenia, pharmacokinetic studies have shown the role of genetic variants of the cytochrome P450 enzymes CYP2D6, CYP2C19, and CYP2C9 in the metabolism of neuroleptic drugs. At the level of the drug target, variants of the dopamine D3 and D4, and 5-HT2A and 5-HT2C receptors have been examined. A general problem of pharmacogenetic studies in schizophrenia is the high number of controversial findings which may be related to the lack of standardized phenotype definition. Recently, guidelines for an exact and comparable phenotype characterization have been proposed and will aid in designing and evaluating pharmacogenetic studies in the future. The final goal of pharmacogenetic studies-making a prediction of drug response at the level of the individual patient-will require a simultaneous look at a large number of response-determining genetic variants by applying the tools of pharmacogenomics, e.g. large-scale Single Nucleotide Polymorphism (SNP) detection and genotyping.

Toxicological interactions involving psychiatric drugs and alcohol: an update

This review focuses on the toxicological interactions between alcohol (ethanol) and psychiatric drugs (antidepressants and antipsychotics), including those leading to fatal poisoning. Acute or chronic ingestion of alcohol when combined with psychiatric drugs may lead to several clinically significant toxicological interactions. The metabolism of these drugs is generally but not always delayed by acute alcohol ingestion. Drugs undergoing metabolism may also show increased metabolic clearance with chronic alcohol ingestion. Therefore, the net effect may be influenced by internal (e.g. disease, age, gender), external (e.g. environment, diet) and pharmacokinetic (e.g. dose, timing of ingestion, gastrointestinal absorption, distribution and elimination) factors. Cases of fatal poisoning involving coadministration of psychiatric drugs, alcohol and other drugs prompted this review.

Pharmacogenetics for the individualization of psychiatric treatment

Drug treatment of psychiatric disorders is troubled by severe adverse effects, low compliance and lack of efficacy in about 30% of patients. Pharmacogenetic research in psychiatry aims to elucidate the reasons for treatment failure and adverse reactions. Genetic variations in cytochrome P450 (CYP) enzymes have the potential to directly influence the efficacy and tolerability of commonly used antipsychotic and antidepressant drugs. The activity of psychiatric drugs can also be influenced by genetic alterations affecting the drug target molecule. These include the dopaminergic and serotonergic receptors, neurotransmitter transporters and other receptors and enzymes involved in psychiatric disorders. Association studies investigating the relation between genetic polymorphisms in metabolic enzymes and neurotransmitter receptors on psychiatric treatment outcome provide a step towards the individualization of psychiatric treatment through enabling the selection of the most beneficial drug according to the individual's genetic background.

In vitro interactions between a potential muscle relaxant E2101 and human cytochromes P450

E2101 or N-methyl-[1-[1-(2-fluorophenethyl)piperidine-4-yl]-1H-indol-6-yl] acetamide, an antagonist of 5-hydroxytryptamine receptor subtypes 1A and 2, is currently under development for the potential treatment of skeletal muscle associated spasticity. Here we characterized the in vitro metabolism of E2101 using human liver enzymes including human liver microsomal preparations, human liver S9 fractions, and individual forms of recombinant cytochromes P450 (P450s). Our results showed that E2101 was metabolized by P450s to form monohydroxylated (M1 and M2), dihydroxylated (M3), and N-dealkylated metabolites (M4). The structures of these major microsomal metabolites were proposed based on LC/MS/MS analyses. All four metabolites, M1-M4, were formed by CYP3A4. Metabolites, M1, M2, and M4, were also formed by CYP2C19 and M2 and M3 by CYP2D6. The potential P450 inhibition and induction of E2101 were also evaluated. E2101 was determined to be a competitive inhibitor of CYP2C19 and CYP2D6 with K(i) of 15 and 48 microM, respectively, as determined by both Dixon plots and simultaneously nonlinear regression analyses. Induction of major P450 expression was not detected immunochemically after 72-h exposure to 10 or 50 microM E2101 in primary hepatocyte cultures obtained from three subjects. Taken together, E2101 is expected to metabolically interact with major human P450 enzymes including CYP2C19, CYP2D6, and CYP3A4, and a low risk of drug-drug interaction would be anticipated in clinical studies.

Pharmacogenetics in affective disorders

Pharmacogenetics will be of substantial help in the field of affective disorders pharmacotherapy. The possible definition of a genetic liability profile for drug side-effects and efficacy will be of great help in treatments that need weeks to months to be effective. During the last few years, a number of groups have reported possible liability genes. The efficacy and time of onset of selective serotonin reuptake inhibitors have been associated with a polymorphism in the promoter region of the transporter (SERTPR) in many independent studies, while variants at the tryptophan hydroxylase gene, 5-HT2a receptor and G-protein beta3 have been associated with them in pilot studies. Lithium long-term prophylactic efficacy has been associated with SERTPR, TPH and inositol polyphosphate 1-phosphatase variants, though in unreplicated samples. A number of further candidate genes were not associated with these treatments. In conclusion, both acute and long-term treatments appear to be, at least to some extent, under genetic influence and preliminary data have identified possible liability genes.

CYP2D6 polymorphisms and atypical antipsychotic weight gain

Reports have linked atypical antipsychotics (AAPs) with weight gain. The polymorphic CYP2D6 involved in metabolism has been associated with medication morbidity. Eleven subjects receiving olanzapine were genotyped for CYP2D6 to examine the relationship between 2D6 and AAP weight gain. Using a linear regression, the dependent variable was percent change in body mass index (BMI). Genotype, dose and duration of treatment were independent. Genotype was significant (P<0.0097) for those with a *1/*3 or *4 genotype experiencing a larger percent BMI change than those with a *1/*1 genotype. This may be due to increased olanzapine concentrations leading to increased exposure, which may trigger AAP weight gain.

Cytochrome P450 polymorphisms and response to antipsychotic therapy

Antipsychotic drugs are used for the treatment of schizophrenia and other related psychotic disorders. The antipsychotics currently available include older or classical compounds and newer or atypical agents. Most antipsychotic drugs are highly lipophilic compounds and undergo extensive metabolism by cytochrome P450 (CYP) enzymes in order to be excreted. There is a wide interindividual variability in the biotransformation of antipsychotic drugs, resulting in pronounced differences in steady-state plasma concentrations and, possibly, in therapeutic and toxic effects, during treatment with fixed doses. Many classical and some newer antipsychotics are metabolized to a significant extent by the polymorphic CYP2D6, which shows large interindividual variation in activity. Other CYPs, especially CYP1A2 and CYP3A4, also contribute to the interindividual variability in the kinetics of antipsychotics and occurrence of drug interactions. No relationship between CYP2D6 genotype or activity and therapeutic effects of classical antipsychotic drugs has been found in the few studies performed. On the other hand, some investigations suggest that poor metabolizers (PMs) of CYP2D6 would be more prone to over-sedation and, possibly, Parkinsonism during treatment with classical antipsychotics, while other studies, mostly retrospective, have been negative or inconclusive. For the newer antipsychotics, such data are lacking. To date, CYP2D6 phenotyping and genotyping appear, therefore, to be clinically useful for dose predicting only in special cases and for a limited number of antipsychotics, while their usefulness in predicting clinical effects must be further explored.

Cytochrome P450 2B (CYP2B)-mediated activation of methyl-parathion in rat brain extracts

The role of cytochrome P450 (CYP) and the CYP isoform involved in the activation of the widely used pesticide methyl-parathion (MePA) were investigated in rat brain extracts by measuring the effect of different CYP inhibitors on acetylcholinesterase (AChE) inhibition by MePA. Brain extracts provide a useful tool to study the activation mechanisms of organophosphorus compounds (OP) since they contain both the activating enzyme(s) and the molecular target for OP toxicity. As expected, in incubations of rat brain extract supplemented with NADPH, AChE activity was non-competitively inhibited by the presence of MePA, indicating that MePA was activated to its reactive metabolite methyl-paraoxon (MePO). Indeed, Vmax(app) decreased from 13.4 to 8.7 micromol thionitrobenzoic acid (TNB)/min per mg protein. MePA activation by rat brain extracts, as measured by the AChE inhibition produced by the presence of the pesticide in the incubation, was fully prevented by previously bubbling the incubation mix with CO, by the presence of monoclonal anti-rat CYP2B1/2B2 antibodies and by the addition of phenobarbital (PB), a CYP2B substrate. Interestingly, MePA showed a greater affinity for CYP2B than PB. CYP1A1 antibodies showed no effect on MePA activation. The presence of cytochrome P450 2B (CYP2B) in the rat brain extracts was confirmed by immunoblotting. These results demonstrate indisputably the responsibility of CYP2B in MePA activation in the rat brain in vitro, suggesting that metabolic activation of OP compounds in situ might be crucial for their organ specific toxicity to the central nervous system also in vivo.

Psychopharmacogenetics--a challenge for pharmacotherapy in psychiatry

Differences in response to treatment or the incidence of adverse drug effects are quite common in clinical psychopharmacotherapy. Although several factors may account for these discrepancies, there is increasing knowledge that genetic factors play a major role. The aim of pharmacogenetics, a new and rapidly growing field in research, is to elucidate the variability in drug response and metabolism due to hereditary differences. According to the hypotheses on the mechanisms of drug action, several mutations in genes coding for neurotransmitter receptors, degrading enzymes, transport proteins or enzymes of the drug metabolizing system (P-450 isoenzymes) have been identified and investigated in psychiatric disorders over the last years. Although some controversy exists among the results, many studies are supportive of the hypothesis that psychopharmacogenetics will be helpful in predicting an individual patient's drug response while minimising the rate of side effects.

The pharmacology and toxicology of atypical antipsychotic agents

Recently, atypical antipsychotic agents have largely replaced traditional agents as first-line drugs for the treatment of schizophrenia. It is likely that atypical agents will soon account for the majority of poisonings from antipsychotic agents that present to health care facilities in the US. This article reviews the pharmacodynamics, pharmacokinetics, and toxicology of atypical antipsychotic drugs, chiefly clozapine, risperidone, olanzapine, and quetiapine. A descriptive summary of the human overdose experience with these agents is provided. Adverse effect and drug interaction data are reviewed. Based on the available pharmacodynamic, pharmacokinetic, and human overdose data, recommendations on management are provided.

Pharmacogenomics and schizophrenia

Although antipsychotic drugs are effective in alleviating schizophrenic symptoms, individual differences in patient response suggest that genetic components play a major role, and pharmacogenetic studies have indicated the possibility for a more individually based pharmacotherapy. The new field of pharmacogenomics, which focuses on genetic determinants of drug response at the level of the entire human genome, is important for development and prescription of safer and more effective individually tailored drugs. DNA microarray (DNA chip) analysis enables genome-wide scanning, using the high-density single nucleotide polymorphisms map. Pharmacogenomics will aid in understanding how genetics influence disease development and drug response, and contribute to discovery of new treatments. The rate of discovery of those polymorphisms will depend on the quality of the drug response phenotype. Prospective genotyping of schizophrenic patients for the many genes at the level of the drug target, drug metabolism, and disease pathways will contribute to individualized therapy matching the patient's unique genetic make-up with an optimally effective drug.

High-resolution quantification of specific mRNA levels in human brain autopsies and biopsies

Quantification of mRNA levels in human cortical brain biopsies and autopsies was performed using a fluorogenic 5' nuclease assay. The reproducibility of the assay using replica plates was 97%-99%. Relative quantities of mRNA from 16 different genes were evaluated using a statistical approach based on ANCOVA analysis. Comparison of the relative mRNA levels between two groups of samples with different time postmortem revealed unchanged relative expression levels for most genes. Only CYP26A1 mRNA levels showed a significant decrease with prolonged time postmortem (p = 0.00004). Also, there was a general decrease in measured mRNA levels for all genes in autopsies compared to biopsies; however, on comparing mRNA levels after adjusting with reference genes, no significant differences were found between mRNA levels in autopsies and biopsies. This observation indicates that studies of postmortem material can be performed to reveal the relative in vivo mRNA levels of genes. Power calculations were done to determine the number of individuals necessary to detect differences in mRNA levels of 1.5-fold to tenfold using the strategy described here. This analysis showed that samples from at least 50 individuals per group, patients and controls, are required for high-resolution ( approximately twofold changes) differential expression screenings in the human brain. Experiments done on ten individuals per group will result in a resolution of approximately fivefold changes in expression levels. In general, the sensitivity and resolution of any differential expression study will depend on the sample size used and the between-individual variability of the genes analyzed.

Biotransformation of post-clozapine antipsychotics: pharmacological implications

The need to develop new antipsychotics that have fewer motor adverse effects and offer better treatment of negative symptoms has led to a new generation of drugs. Most of these drugs undergo extensive first-pass metabolism and are cleared almost exclusively by metabolism, except for amisulpride whose clearance is largely due to urinary excretion. Risperidone has metabolic routes in common with ziprasidone but shows differences in regard to other main pathways: the benzisoxazole moiety of risperidone is oxidised by cytochrome P450 (CYP) 2D6 to the active 9-hydroxyrisperidone, whereas the benzisothiazole of ziprasidone is primarily oxidised by CYP3A4, yielding sulfoxide and sulfone derivatives with low affinity for target receptors in vitro. Olanzapine, quetiapine and zotepine also have some common metabolic features. However, for the thienobenzodiazepine olanzapine a main metabolic route is direct conjugation at the benzodiazepine nucleus, whereas for the dibenzothiazepine quetiapine and the dibenzothiepine zotepine it is CYP3A4-mediated oxidation, leading to sulfoxidation, hydroxylation and dealkylation for quetiapine, but N-demethylation to the active nor-derivative for zotepine. Although the promising benzisoxazole (iloperidone) and benzisothiazole (perospirone) antipsychotics share some metabolic routes with the structurally related available drugs, they too have pharmacologically relevant compound-specific pathways. For some of the new antipsychotics we know the isoenzymes involved in their main metabolic pathways and the endogenous and exogenous factors that, by affecting enzyme activity, can potentially modify steady-state concentrations of the parent drug or its metabolite(s), but we know very little about others (e.g. amisulpride isomers, nemonapride). For yet others, information is scarce about the activity of the main metabolites and whether and how these contribute to the effect of the parent drug. Aging reduces the clearance of most antipsychotics, except amisulpride (which requires further evaluation) and ziprasidone. Liver impairment has little or no effect on the pharmacokinetics of olanzapine, quetiapine, risperidone (and 9-hydroxy-risperidone) and ziprasidone, but information is lacking for amisulpride. Renal impairment significantly reduces the clearance and prolongs the elimination half-life of amisulpride and risperidone. Again, studies are still not available for some drugs (zotepine) and have focused on the parent drug for others (olanzapine, quetiapine, ziprasidone) despite the fact that renal impairment would be expected to lower the clearance of more polar metabolites. Addressing these issues may assist clinicians in the design of safe and effective regimens for this group of drugs, and in selecting the best agent for each specific population.