Impact of the ABCB1 gene polymorphism on plasma 9-hydroxyrisperidone and active moiety levels in Japanese patients with schizophrenia

Review: Influence of the CYP450 Genetic Variation on the Treatment of Psychotic Disorders

Second-generation antipsychotic metabolism is mainly carried out by the CYP450 superfamily, which is highly polymorphic. Therefore, knowing the influence of the different known CYP450 polymorphisms on antipsychotic plasmatic levels and, consequently, the biological effect could contribute to a deeper knowledge of interindividual antipsychotic treatment variability, prompting possible solutions. Considering this, this state of the art review aimed to summarize the current knowledge about the influence of the diverse characterized phenotypes on the metabolism of the most used second-generation antipsychotics. Forty studies describing different single nucleotide polymorphisms (SNPs) associated with the genes CYP1A2, CYP2D6, CYP3A4, CYP3A5, and ABCB1 and their influence on pharmacokinetics of olanzapine, clozapine, aripiprazole, risperidone, and quetiapine. Most of the authors concluded that although significant differences in the pharmacokinetic parameters between the different phenotypes could be observed, more thorough studies describing pharmacokinetic interactions and environmental conditions, among other variables, are needed to fully comprehend these pharmacogenetic interactions.

Effects of CYP2D6, CYP3A5, and ABCB1 gene polymorphisms on the pharmacokinetics of two risperidone long-acting injection microsphere formulations

BACKGROUND

LY03004, a novel investigational risperidone long-acting injection (LAI) microsphere formulation, can release risperidone more quickly after injection than Risperdal Consta®. This study aimed to investigate the effects of genetic polymorphisms on the pharmacokinetics of LY03004 compared with those on Risperdal Consta®.

METHODS

A total of 100 Chinese patients with stable schizophrenia were randomly assigned to the LY03004 or Risperdal Consta® treatment group. Each patient received five biweekly intramuscular injections of 25 mg risperidone long-acting injection microspheres. A total of 34 blood samples before and after injections from Day 1 to Day 113 were collected from each patient, and polymorphic alleles of cytochrome P450 enzymes CYP2D6 (*4, *10, *14), CYP3A5 (*3), and ABCB1 (C1236 > T, G2677T/A, and C3435T) were analyzed using Sanger sequencing and polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

The risperidone C_max,ss, C_min,ss, AUC_0-tau,ss, and the ratio of risperidone to 9-hydroxyrisperidone (9-OH-R) in CYP2D6 intermediate metabolizers (IMs) were significantly different compared with those in normal metabolizers (NMs) in both the LY03004 and Risperdal Consta® groups (P < 0.05). However, 9-OH-R was not significantly different between IMs and NMs (P > 0.05). The AUC_0-tau,ss of the active moiety (risperidone plus 9-OH-R) was 6.51 ± 3.34 in NMs and 7.00 ± 1.81 in IMs (P = 0.071) in the LY03004 group and 6.07 ± 2.31 and 7.95 ± 3.42 (P = 0.053) in NMs and IMs, respectively, in the Risperdal Consta® group. In the LY03004 group, the C_max,ss of risperidone in carriers of the ABCB1-C3435T TT variant was significantly lower than that in CC and CT carriers (TT 7.76 ± 4.23 ng/mL, CT 11.6 ± 8.27 ng/mL, CC 14.3 ± 7.66 ng/ml; P = 0.045), but no significant differences were found in the active moiety. In the Risperdal Consta® group, C3435T TT carriers had significantly lower C_min,ss of the active moiety (TT 5.09 ± 4.38 ng/mL, CT 11.4 ± 8.42 ng/mL, CC 14.3 ± 6.43 ng/mL; P = 0.007). Furthermore, C_min,ss of the active moiety was significantly different among all ABCB1-G2677T/A genotypes (P < 0.05).

CONCLUSION

The pharmacokinetics of risperidone and the ratio of risperidone to 9-OH-R were highly dependent on CYP2D6 activity. However, there was no significant effect in 9-OH-R. A future study involving a larger sample is required to verify whether CYP2D6 IMs have lower risperidone active moiety clearance than CYP2D6 NMs for LAI formulations. In addition, the risperidone active moiety was eliminated faster in ABCB1-G2677T/A and C3435T TT carriers receiving Risperdal Consta®.

ABCB1, ABCG2 and CYP2D6 polymorphism effects on disposition and response to long-acting risperidone

The relevance of the multidrug resistance (ABCB1) and breast cancer resistance (ABCG2) protein transporter polymorphisms for treatment with long-acting intramuscular (LAI) risperidone is largely unknown. We explored the relationship between these polymorphisms and cytochrome P450 (CYP) 2D6 genotype-predicted phenotype in their effects on drug disposition and clinical outcomes in adults with schizophrenia. In a 24-week observational study, patients initiated on LAI-risperidone (n=101) were genotyped [enzymes (CYP2D6 dupl,*3,*4,*5,*6,*41; CYP3A4*22, CYP3A5*3), transporters (ABCG2 421C>A; ABCB1 1236C>T, 2677G>T/A, 3435C>T)] and evaluated for steady-state (weeks 6-8) serum levels of dose-corrected risperidone, 9-OH-risperidone, risperidone+9-OH-risperidone (active moiety), and for response to treatment (PANSS, reduction vs. baseline ≥30% at week 12 and ≥45% at week 24). CYP2D6 normal/ultrarapid metabolizers (NM/UM) (vs. other) had lower risperidone (29%) and active moiety levels (24%) (9-OH-risperidone not affected). The effect on the three analytes was mild (0 to 23% reduction) in ABCG2 wild-type homozygotes and pronounced (44-55% reduction) in ABCG2 variant allele carriers. ABCG2 variant had no effect on disposition in CYP2D6 "other" phenotypes, while the effect was pronounced in CYP2D6 NM/UM subjects (31-37% reduction). ABCB1 polymorphisms had no effect on exposure to risperidone. CYP2D6 NM/UM phenotype tended to lower odds of PANSS response, ABCG2 variant was associated with 4-fold higher odds and ABCB1 (1236C>T, 2677G>T/A, 3435C>T) overall mainly wild-type genotype was associated with around 4--fold lower odds of response. In patients treated with LAI-risperidone, CYP2D6 phenotype effect on systemic exposure is conditional on the ABCG2 421C>A polymorphism. ABCG2 and ABCB1 polymorphisms affect clinical response independently of systemic risperidone disposition.

A Machine Learning Model to Predict Risperidone Active Moiety Concentration Based on Initial Therapeutic Drug Monitoring

Risperidone is an efficacious second-generation antipsychotic (SGA) to treat a wide spectrum of psychiatric diseases, whereas its active moiety (risperidone and 9-hydroxyrisperidone) concentration without a therapeutic reference range may increase the risk of adverse drug reactions. We aimed to establish a prediction model of risperidone active moiety concentration in the next therapeutic drug monitoring (TDM) based on the initial TDM information using machine learning methods. A total of 983 patients treated with risperidone between May 2017 and May 2018 in Beijing Anding Hospital were collected as the data set. Sixteen predictors (the initial TDM value, dosage, age, WBC, PLT, BUN, weight, BMI, prolactin, ALT, MECT, Cr, AST, Ccr, TDM interval, and RBC) were screened from 26 variables through univariate analysis (p < 0.05) and XGBoost (importance score >0). Ten algorithms (XGBoost, LightGBM, CatBoost, AdaBoost, Random Forest, support vector machine, lasso regression, ridge regression, linear regression, and k-nearest neighbor) compared the model performance, and ultimately, XGBoost was chosen to establish the prediction model. A cohort of 210 patients treated with risperidone between March 1, 2019, and May 31, 2019, in Beijing Anding Hospital was used to validate the model. Finally, the prediction model was evaluated, obtaining R ² (0.512 in test cohort; 0.374 in validation cohort), MAE (10.97 in test cohort; 12.07 in validation cohort), MSE (198.55 in test cohort; 324.15 in validation cohort), RMSE (14.09 in test cohort; 18.00 in validation cohort), and accuracy of the predicted TDM within ±30% of the actual TDM (54.82% in test cohort; 60.95% in validation cohort). The prediction model has promising performance to facilitate rational risperidone regimen on an individualized level and provide reference for other antipsychotic drugs' risk prediction.

The polymorphic variants DRD2 rs1800497 and ABCB1 3435C>T are associated with antipsychotic safety parameters in adolescents with an acute psychotic episode: the results of a pilot study

Children and adolescents are more likely than adults to experience adverse side effects when taking antipsychotics. Pharmacogenetic testing allows one to more accurately choose the initial dose of a drug. The genes of pharmacokinetic factors have been shown to be of high prognostic value for the safety of antipsychotics in adults.

Patients and methods. The study enrolled 36 adolescents (58.3% male) (mean age, 14.83±1.84 years). All the patients took an antipsychotic. The follow-up lasted 28 days. On 14 and 28 days of treatment, its efficiency and safety were evaluated using the Children's Global Assessment Scale (CGAS), the Positive and Negative Syndrome Scale (PANSS), the Udvalg for Kliniske Undersњgelser Side Effects Rating Scale (UKU-SERS), the Simpson-Angus Scale (SAS), and the Barnes Akathisia Rating Scale (BARS). The patients were genotyped for CYP3A4*22, CYP3A5*3, CYP2D6*4, *9, *10, ABCB1 1236C>T, 2677G>T/A, 3435C>T, DRD2 rs1800497, DRD4 rs1800955, and HTR2A rs6313.

Results and discussion. The decrease in the mean score of the PANSS subscale “Productive symptoms” was more pronounced in carriers of the DRD2 rs1800497 polymorphic variant (-6.5 [-10.25; -3.75] vs -3 [-6.5; -2 ] on 14 day (p=0.028) and (-11 [-13; -9.5] vs -5 [-9; -3.5] on 28 day (p=0.001) compared to baseline. The carriage of ABCB1 3435CT+TT was associated with worse tolerance to pharmacotherapy on 14 day (the total score of the UKU-SERS M, 8 [3; 11.75] vs M, 2 [1; 6]; p=0.034). The carriers of DRD2 rs1800497 reported a greater severity of antipsychotic-induced neurological disorders (UKU-SERS subscale score M, 1 [0; 2.25] vs M 0 [0; 1]; p=0.029).

Conclusion. The polymorphic variants DRD2 rs1800497 and ABCB1 3435C>T were established to be significantly associated with the efficacy and safety of antipsychotics in adolescents with an acute psychotic episode.

CYP2D6 Genetic Polymorphisms and Risperidone Pharmacokinetics: A Systematic Review and Meta-analysis

BACKGROUND

Risperidone is a second-generation antipsychotic drug metabolized to an active metabolite, 9-hydroxyrisperidone, primarily by cytochrome P450 (CYP) 2D6 and to a lesser extent by CYP3A4. The extent to which drug metabolism genetics impacts risperidone and 9-hydroxyrisperidone exposure has not been clarified.

OBJECTIVE

A systematic review and meta-analysis evaluated the impact of genetically defined CYP2D6 function on risperidone pharmacokinetics applying a standardized genotype-phenotype translation system.

METHODS

A comprehensive electronic database search identified studies reporting relationships between genetically determined CYP2D6 metabolism and risperidone pharmacokinetic properties. The exposure of risperidone or active moiety (risperidone + 9-hydroxyrisperidone) was measured by dose-adjusted steady-state serum or plasma concentration or area under the concentration-time curve as primary outcomes. Subjects were assigned to CYP2D6 poor metabolizer, intermediate metabolizer, normal metabolizer, or ultrarapid metabolizer groups using a standardized genotype-phenotype translation method. Effect sizes between groups were pooled and stratified by single or multiple dosing regimens.

RESULTS

A total of 15 studies involving 2125 adult subjects were included in the meta-analysis. Following multiple-dose oral administration, compared with CYP2D6 normal metabolizers, the risperidone dose-adjusted steady-state serum/plasma concentration was 2.35-fold higher in intermediate metabolizers (95% confidence interval [CI] 1.77-3.13, p<0.0001) and 6.20-fold higher in poor metabolizers (95% CI 5.05-7.62, p<0.0001); the active moiety dose-adjusted steady-state concentration was 1.18-fold higher in intermediate metabolizers (95% CI 1.11-1.25, p<0.0001) and 1.44-fold higher in poor metabolizers (95% CI 1.23-1.69, p<0.0001). Higher area under the concentration-time curve of risperidone and active moiety was also found in single-dose studies.

CONCLUSION

Genetically defined impaired CYP2D6 activity is associated with increased exposure of both risperidone and risperidone + 9-hydroxyrisperidone in adults receiving oral formulations. Additional studies are needed to quantify the clinical impact of these relationships.

Paliperidone, a relatively novel atypical antipsychotic drug, is a substrate for breast cancer resistance protein

Paliperidone (PAL) is a relatively novel atypical antipsychotic drug for schizophrenia that induces markedly varying responses. Breast cancer resistance protein (BCRP) is a recently discovered member of the ATP-binding cassette superfamily that has been used to control drug absorption, distribution and elimination, and especially to impede drug entry into the brain. To the best of our knowledge, the present study is the first to investigate the possibility of using PAL as a BCRP substrate. The intracellular accumulation and bidirectional transport were investigated using transfected 293 cell/BCRP and porcine renal endothelial cell (LLC-PK1)/BCRP cell monolayers and BCRP overexpression was confirmed by reverse transcription-quantitative polymerase chain reaction and western blot analysis. The in vitro affinity to BCRP was assessed in human BCRP (Arg482) membranes. The intracellular accumulation and bidirectional transport investigations demonstrated that BCRP can efflux PAL from cells and significantly decrease its cellular concentration over a concentration range of 0.1-50 µM. The in vitro affinity experiments indicated that PAL has a moderate affinity to BCRP at 0.1-100 µM. These results together suggest that PAL is a substrate for BCRP and that it can affect the blood-brain barrier penetration of PAL at therapeutic dosages.

Usefulness of Pharmacogenetic Analysis in Psychiatric Clinical Practice: A Case Report

There are many factors involved in the effectiveness and efficiency of psychiatric drug treatment. One of them is psychotropic drug metabolism, which takes place mostly in the liver through the P450 enzyme system. However, there are genotypic variants of this system’s enzymes that can directly affect both the efficacy and the onset of side effects of a given therapeutic regimen. These genotypic changes could partly explain the lack of efficacy of treatment in certain patients. We report the case of a patient diagnosed with bipolar type I disorder that presented multiple and frequent manic episodes in which the efficacy and tolerability of several pharmacological regimens with mood stabilizers and antipsychotics was scarce. The choice of medical treatment should be based on its efficacy and side effect profile. This decision can be made more accurately using the information provided by pharmacogenetic analysis. This case illustrates the importance of pharmacogenetic studies in clinical practice. The results of pharmacogenetic analysis helped to decide on a better treatment plan to achieve clinical improvement and reduce drug-induced adverse effects.

Effects of ABCB1 gene polymorphisms on autonomic nervous system activity during atypical antipsychotic treatment in schizophrenia

BACKGROUND

There are interindividual differences in the adverse effects of atypical antipsychotics, which include autonomic nervous system (ANS) dysfunction. Accordingly, to clarify the interindividual differences in the adverse effects of specific atypical antipsychotics in schizophrenia, we investigated the association between ANS dysfunction and ATP-binding cassette transport sub-family B member 1 (ABCB1) gene polymorphisms in patients with schizophrenia.

METHODS

In total, 233 Japanese patients with schizophrenia participated in this study. All of the participants received an atypical antipsychotic as monotherapy: 89 participants received risperidone, 69 olanzapine, 48 aripiprazole, and 27 quetiapine. ANS activity was assessed by means of a power spectral analysis of heart rate variability. Four single nucleotide polymorphisms (SNPs) in ABCB1 (rs1045642, rs1128503, rs2032582, and rs2235048) were genotyped using the TaqMan method.

RESULTS

For aripiprazole, sympathetic and total autonomic nervous activities were significantly lower in the rs1045642 T allele carrier-rs2235048 C allele carrier group than in the rs1045642 non-T allele carrier-rs2235048 non-C allele carrier group. In addition, in the aripiprazole group, the T-C-T-A haplotype (rs1045642-rs2235048-rs1128503-rs2032582) was associated with decreased ANS activity. However, there were no significant associations between ANS activity and ABCB1 gene polymorphisms in the risperidone, olanzapine, and quetiapine groups. Multiple regression analysis revealed that sympathetic and total nervous activities were significantly associated with the ABCB1 rs1045642-rs2235048 genotype and the T-C-T-A haplotype (rs1045642-rs2235048-rs1128503-rs2032582).

CONCLUSION

We suggest that ABCB1 genetic polymorphisms affect aripiprazole-related ANS dysfunction but do not affect risperidone-, olanzapine-, or quetiapine-related ANS dysfunction.

Serum Concentrations of Paliperidone After Administration of the Long-Acting Injectable Formulation

Background:

The pharmacokinetics of long-acting intramuscular paliperidone in a naturalistic setting is not well documented. The objective of this study was to investigate the relationship between dose and serum concentrations of paliperidone using data from a routine therapeutic drug monitoring service.

Methods:

Serum concentration measurements in 310 samples from 110 male and 75 female patients receiving depot injections of paliperidone were retrospectively retrieved from the therapeutic drug monitoring database.

Results:

The median dose was 100 mg every 28 days. The median concentration/dose (C/D) ratio of paliperidone was 16.1 (nmol/L)/(mg/d), with a 10–90 percentile range of 7.8–31.0 (nmol/L)/(mg/d). Dose-adjusted serum concentrations were 33% higher in patients 65 years or older and more than 50% lower in patients taking the p-glycoprotein inducer carbamazepine. There were no significant effects of sex or dose on the C/D ratio. The median serum concentrations of paliperidone at the end of the dose interval were 31 nmol/L at an intramuscular dose of 50 mg/28 d, 53 nmol/L after a dose of 75 mg/28 d, 59 nmol/L after a dose of 100 mg/28 d, and 93 nmol/L after a dose of 150 mg/28 d. Forty-five percent of the measurements were lower than the suggested therapeutic range of 20–60 ng/mL (47–140 nmol/L).

Conclusions:

The data show a 4-fold interindividual difference in dose-adjusted serum concentrations within the 10–90 percentile range and illustrate the significant effects of age and p-glycoprotein induction on the pharmacokinetics of paliperidone. The study also indicates that at least in some patients, it might take longer time than anticipated to reach steady state.

ABCB1 and CYP2D6 polymorphisms and treatment response of psychotic patients in a naturalistic setting

OBJECTIVES

The aim of our study was to examine the association between ABCB1 polymorphisms G2677T/A (rs2032582) and C3435T (rs1045642) and common CYP2D6 variants, with the response to antipsychotic treatment of psychotic patients, in a naturalistic setting, in Greece.

METHODS

One hundred patients suffering from schizophrenia and other psychotic disorders were included in the study. Dosages were normalized to chlorpromazine equivalents. Response following 1 month of treatment was assessed as either a continuous variable, using the distribution of the corrected Positive and Negative Syndrome Scale percent change, or as a dichotomous variable defined as the number of patients scoring ≥30% from the corrected baseline Positive and Negative Syndrome Scale score. Genotyping was achieved with established polymerase chain reaction-restriction fragment length polymorphism methods.

RESULTS

With response treated as a continuous variable, the homozygous recessive rs2032582 genotypes (TT) who were simultaneously carriers of a loss-of-function CYP2D6 allele (*4 or *5) responded significantly worse than the rest of the patients. Comparison of genotype frequencies revealed a statistically significant association of the above combination. No significant association between chlorpromazine equivalents and the tested genotypes was detected.

CONCLUSION

We have detected a possible interaction between ABCB1 and CYP2D6 in affecting response of psychotic patients to drug treatment, in a naturalistic setting.

Advancing psychiatric pharmacogenomics using drug development paradigms

Drugs used to treat psychiatric disorders, even when taken as directed, fail to provide adequate relief for a sizeable proportion of patients. Despite our advancements in understanding human genetics and development of high-throughput tools to probe variation, pharmacogenomics has yielded marginal ability to predict drug response for psychiatric disorders. Here, I review the current pharmacogenomics paradigm, identifying opportunities to incorporate drug development strategies designed to increase the probability of delivering a successful molecule to the clinic. This includes using in-depth pharmacokinetic profiles, clear measures of target engagement and target-specific pharmacodynamic responses orthogonal to clinical response. The complex pharmacological profiles psychiatric drugs require re-examination of simplified clinical response-oriented pharmacogenetic hypotheses, in favor of a more complete patient profile.

Genetic deletion of P-glycoprotein alters stress responsivity and increases depression-like behavior, social withdrawal and microglial activation in the hippocampus of female mice

P-glycoprotein (P-gp) is an ABC transporter expressed at the blood brain barrier and regulates the brain uptake of various xenobiotics and endogenous mediators including glucocorticoid hormones which are critically important to the stress response. Moreover, P-gp is expressed on microglia, the brain's immune cells, which are activated by stressors and have an emerging role in psychiatric disorders. We therefore hypothesised that germline P-gp deletion in mice might alter the behavioral and microglial response to stressors. Female P-gp knockout mice displayed an unusual, frantic anxiety response to intraperitoneal injection stress in the light-dark test. They also tended to display reduced conditioned fear responses compared to wild-type (WT) mice in a paradigm where a single electric foot-shock stressor was paired to a context. Foot-shock stress reduced social interaction and decreased microglia cell density in the amygdala which was not varied by P-gp genotype. Independently of stressor exposure, female P-gp deficient mice displayed increased depression-like behavior, idiosyncratic darting behavior, age-related social withdrawal and hyperactivity, facilitated sensorimotor gating and altered startle reactivity. In addition, P-gp deletion increased microglia cell density in the CA3 region of the hippocampus, and the microglial cells exhibited a reactive, hypo-ramified morphology. Further, female P-gp KO mice displayed increased glucocorticoid receptor (GR) expression in the hippocampus. In conclusion, this research shows that germline P-gp deletion affected various behaviors of relevance to psychiatric conditions, and that altered microglial cell activity and enhanced GR expression in the hippocampus may play a role in mediating these behaviors.

Pharmacogenomics and Efficacy of Risperidone Long-Term Treatment in Thai Autistic Children and Adolescents

The purpose of this study was to evaluate the association of pharmacogenomic factors and clinical outcome in autistic children and adolescents who were treated with risperidone for long periods. Eighty-two autistic subjects diagnosed with DSM-IV and who were treated with risperidone for more than 1 year were recruited. Pharmacogenomics and clinical outcome (CGI-I, aggressive, overactivity and repetitive score) were evaluated. Almost all patients showed stable symptoms on aggressive behaviour (89.02%), overactivity (71.95%), repetitive (70.89%) behaviour and all clinical symptoms (81.71%). Only 4.48% of patients showed minimally worse CGI-I score. Patients in the non-stable symptom group had DRD2 Taq1A non-wild-type (TT and CT) frequencies higher than the clinically stable group (p = 0.04), whereas other gene polymorphisms showed no significant association. Haplotype ACCTCAT (rs6311, rs1045642, rs1128503, rs1800497, rs4436578, rs1799978, rs6280) showed a significant association with non-stable clinical outcome (χ²  = 6.642, p = 0.010). Risperidone levels showed no association with any clinical outcome. On the other hand, risperidone dose, 9-OH risperidone levels and prolactin levels were significantly higher in the non-stable compared to the stable symptom group (p = 0.013, p = 0.044, p = 0.030). Increased appetite was the most common adverse drug reaction and associated with higher body-weight, whereas it was not significantly associated with genetic variations and non-genetic information. In conclusion, risperidone showed efficacy to control autism, especially aggressive symptoms in long-term treatment. However, Taq1A T - carrier of dopamine 2 receptor gene - is associated with non-stable response in risperidone-treated patients. This study supports pharmacogenomics testing for personalized therapy with risperidone in autistic children and adolescents.

Impact of CYP2D6 Polymorphism on Steady-State Plasma Levels of Risperidone and 9-Hydroxyrisperidone in Thai Children and Adolescents with Autism Spectrum Disorder

OBJECTIVE

The purpose of this study was to investigate the influence of CYP2D6 gene polymorphisms on plasma concentrations of risperidone and its metabolite in Thai children and adolescents with autism spectrum disorder (ASD).

METHODS

All 97 autism spectrum disorder patients included in this study had been receiving risperidone at least for 1 month. The CYP2D6 genotypes were determined by real-time polymerase chain reaction (PCR)-based allelic discrimination for CYP2D6*4, *10, and *41 alleles. Plasma concentrations of risperidone and 9-hydroxyrisperidone were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Among the 97 patients, the most important nonfunctional alleles (CYP2D6*4 and *5) were detected, whereas the most common allele was CYP2D6*10 (55.9%). CYP2D6 genotyping revealed 90 (92.78%) patients to be extensive metabolizers (EM) and 7 (7.22%) to be intermediate metabolizers (IM). Plasma levels of risperidone were significantly higher in individuals with CYP2D6*5/*10 (p = 0.02), CYP2D6*10/*10 (p = 0.04), and CYP2D6*10/*41 (p = 0.04). Additionally, the plasma concentration of risperidone/9-OH risperidone ratio in patients with a CYP2D6 activity score of 0.5 were significantly higher than those with a CYP2D6 activity score of 2 (p = 0.04). Conversely, no significant influence was found among CYP2D6 polymorphisms, plasma concentrations of 9-hydroxyrisperidone, and the total active moiety.

CONCLUSIONS

This is the first study to investigate the effects of CYP2D6 genetic polymorphisms on the plasma concentrations of risperidone in Thai children with ASD. The findings indicate that CYP2D6 polymorphisms affect the plasma concentrations of risperidone and the risperidone/9-hydroxyrisperidone ratio. Genetic screening for CYP2D6 polymorphisms could help to predict unexpected adverse events caused by the higher plasma concentration of risperidone.

Morphometric analysis of the cerebral expression of ATP-binding cassette transporter protein ABCB1 in chronic schizophrenia: Circumscribed deficits in the habenula

There is increasing evidence that microvascular abnormalities and malfunction of the blood-brain barrier (BBB) significantly contribute to schizophrenia pathophysiology. The ATP-binding cassette transporter ABCB1 is an important molecular component of the intact BBB, which has been implicated in a number of neurodegenerative and psychiatric disorders, including schizophrenia. However, the regional and cellular expression of ABCB1 in schizophrenia is yet unexplored. Therefore, we studied ABCB1 protein expression immunohistochemically in twelve human post-mortem brain regions known to play a role in schizophrenia, in 13 patients with schizophrenia and nine controls. In ten out of twelve brain regions under study, no significant differences were found with regard to the numerical density of ABCB1-expressing capillaries between all patients with schizophrenia and control cases. The left and right habenular complex, however, showed significantly reduced capillary densities in schizophrenia patients. In addition, we found a significantly reduced density of ABCB1-expressing neurons in the left habenula. Reduced ABCB1 expression in habenular capillaries might contribute to increased brain levels of proinflammatory cytokines in patients with schizophrenia, while decreased expression of this protein in a subpopulation of medial habenular neurons (which are probably purinergic) might be related to abnormalities of purines and their receptors found in this disease.

Pharmacogenetics of second-generation antipsychotics

This review considers pharmacogenetics of the so called 'second-generation' antipsychotics. Findings for polymorphisms replicating in more than one study are emphasized and compared and contrasted with larger-scale candidate gene studies and genome-wide association study analyses. Variants in three types of genes are discussed: pharmacokinetic genes associated with drug metabolism and disposition, pharmacodynamic genes encoding drug targets, and pharmacotypic genes impacting disease presentation and subtype. Among pharmacokinetic markers, CYP2D6 metabolizer phenotype has clear clinical significance, as it impacts dosing considerations for aripiprazole, iloperidone and risperidone, and variants of the ABCB1 gene hold promise as biomarkers for dosing for olanzapine and clozapine. Among pharmacodynamic variants, the TaqIA1 allele of the DRD2 gene, the DRD3 (Ser9Gly) polymorphism, and the HTR2C -759C/T polymorphism have emerged as potential biomarkers for response and/or side effects. However, large-scale candidate gene studies and genome-wide association studies indicate that pharmacotypic genes may ultimately prove to be the richest source of biomarkers for response and side effect profiles for second-generation antipsychotics.