MDR1 gene polymorphism: therapeutic response to paroxetine among patients with major depression

ABCB1 C1236T, G2677TA and C3435T Genetic Polymorphisms and Antidepressant Response Phenotypes: Results from a Portuguese Major Depressive Disorder Cohort

P-glycoprotein (P-GP) is a transporter molecule expressed on the apical surface of capillary endothelial cells of the Blood-Brain Barrier (BBB), whose activity heavily influences drug distribution, including antidepressants. This transporter is encoded by ABCB1 gene, and genetic variations within ABCB1 gene have been proposed to affect drug efflux and have been previously associated with depression. In this context, we aimed to evaluate the role of C1236T, G2677TA and C3435T ABCB1 genetic polymorphisms in antidepressant treatment phenotypes from a cohort of patients harboring Major Depressive Disorder. Patients enrolled in the study consisted of 80 individuals with Major Depressive Disorder, who took part in a 27-month follow-up study at HML, Portugal. To investigate the correlation between ABCB1 polymorphisms and antidepressant response phenotypes, DNA was extracted from peripheral blood, and C1236T, C3435T and G2677TA polymorphisms were genotyped with TaqMan® SNP Genotyping Assays. Despite the fact that the evaluated polymorphisms (C1236T, C3435T and G2677TA) were not associated with treatment resistant depression, or relapse, we observed that patients carrying TT genotype of the C3435T polymorphism remit earlier than the ones carrying CC or CT genotypes (10.2 weeks vs. 14.9 and 21.3, respectively, p = 0.028, Log-rank test). Since we found an association with C3435T and time to remission, and not to the absence of remission, we suggest that this polymorphism could have an impact on antidepressant drug distribution, and thus influence on the time to remission will occur, without influencing the risk of remission itself.

Candidate genetic variants and antidepressant-related fall risk in middle-aged and older adults

BACKGROUND

Antidepressant use has been associated with increased fall risk. Antidepressant-related adverse drug reactions (e.g. orthostatic hypotension) depend partly on genetic variation. We hypothesized that candidate genetic polymorphisms are associated with fall risk in older antidepressant users.

METHODS

The association between antidepressant use and falls was cross-sectionally investigated in a cohort of Dutch older adults by logistic regression analyses. In case of significant interaction product term of antidepressant use and candidate polymorphism, the association between the variant genotype and fall risk was assessed within antidepressant users and the association between antidepressant use and fall risk was investigated stratified per genotype. Secondly, a look-up of the candidate genes was performed in an existing genome-wide association study on drug-related falls in antidepressant users within the UK Biobank. In antidepressant users, genetic associations for our candidate polymorphisms for fall history were investigated.

RESULTS

In antidepressant users(n = 566), for rs28371725 (CYP2D6*41) fall risk was decreased in TC/variant allele carriers compared to CC/non-variant allele carriers (OR = 0.45, 95% CI 0.26-0.80). Concerning rs1057910 (CYP2C9*3), fall risk was increased in CA/variant allele carriers compared to AA/non-variant allele carriers (OR = 1.95, 95% CI 1.17-3.27). Regarding, rs1045642 (ABCB1), fall risk was increased in AG/variant allele carriers compared to GG/non-variant allele carriers (OR = 1.69, 95% CI 1.07-2.69). Concerning the ABCB1-haplotype (rs1045642/rs1128503), fall risk was increased in AA-AA/variant allele carriers compared to GG-GG/non-variant allele carriers (OR = 1.86, 95% CI 1.05-3.29). In the UK Biobank, in antidepressant users(n = 34,000) T/variant-allele of rs28371725 (CYP2D*41) was associated with increased fall risk (OR = 1.06, 95% CI 1.01-1.12). G/non-variant-allele of rs4244285 (CY2C19*2) was associated with decreased risk (OR = 0.96, 95% CI 0.92-1.00).

CONCLUSION

This is the first study showing that certain genetic variants modify antidepressant-related fall risk. The results were not always consistent across the studies and should be validated in a study with a prospective design. However, pharmacogenetics might have value in antidepressant (de)prescribing in falls prevention.

ABCB1 variants and sex affect serotonin transporter occupancy in the brain

Strategies to personalize psychopharmacological treatment promise to improve efficacy and tolerability. We measured serotonin transporter occupancy immediately after infusion of the widely prescribed P-glycoprotein substrate citalopram and assessed to what extent variants of the ABCB1 gene affect drug target engagement in the brain in vivo. A total of 79 participants (39 female) including 31 patients with major depression and 48 healthy volunteers underwent two PET/MRI scans with the tracer [¹¹C]DASB and placebo-controlled infusion of citalopram (8 mg) in a cross-over design. We tested the effect of six ABCB1 single nucleotide polymorphisms and found lower SERT occupancy in ABCB1 rs2235015 minor allele carriers (n = 26, MAF = 0.18) compared to major allele homozygotes (t₇₃ = 2.73, p_FWE < 0.05) as well as in men compared to women (t₇₃ = 3.33, p_FWE < 0.05). These effects were robust to correction for citalopram plasma concentration, age and diagnosis. From occupancy we derived the ratio of occupied to unoccupied SERT, because in theory this measure is equal to the product of drug affinity and concentration at target sites. A model combining genotype with basic clinical variables, predicted that, at the same dosage, occupied to unoccupied SERT ratio was -14.48 ± 5.38% lower in rs2235015 minor allele carriers, +19.10 ± 6.95% higher in women, -4.83 ± 2.70% lower per 10 kg bodyweight, and -2.68 ± 3.07% lower per 10 years of age. Our results support the exploration of clinical algorithms with adjustment of initial citalopram dosing and highlight the potential of imaging-genetics for precision pharmacotherapy in psychiatry.

ABCB1 Gene Is Associated With Clinical Response to SNRIs in a Local Chinese Han Population

Background: The relation between the ATP-binding cassette subfamily B member 1 (ABCB1) gene and major depressive disorder (MDD) has been studied in a local Chinese Han population. MDD is associated with the rs2032582 (G2677T) and rs1128503 (C1236T) single-nucleotide polymorphisms (SNPs) of ABCB1 but not with rs1045642, rs2032583, rs2235040, and rs2235015. This study aims to explore the potential correlations of therapeutic responses with selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) in a local Chinese Han population.

Methods: The study population included 292 patients with MDD. All patients were assessed at baseline and at first, second, fourth, and sixth weeks according to the 17-item Hamilton Rating Scale for Depression (HAM-D17) to determine their therapeutic responses to SSRIs and SNRIs.

Results: In the SSRI therapy group, the genotype or allele distribution of six SNPs was not significantly different between responders and nonresponders. In the SNRI therapy group, only rs2032583 was associated with a therapeutic response to SNRIs. The C allele of the ABCB1 rs2032583 polymorphism was negatively correlated with therapeutic responses according to logistic regression analysis.

Conclusion: The ABCB1 gene polymorphisms may not be associated with therapeutic responses to SSRIs but not with SNRIs. The TT genotype of rs2032583 could be a predictive factor of improved treatment responses to SNRIs in the Chinese population. These findings should be replicated in future studies with larger patient groups.

Genetic variants in major depressive disorder: From pathophysiology to therapy

In spite of promising preclinical results there is a decreasing number of new registered medications in major depression. The main reason behind this fact is the lack of confirmation in clinical studies for the assumed, and in animals confirmed, therapeutic results. This suggests low predictive value of animal studies for central nervous system disorders. One solution for identifying new possible targets is the application of genetics and genomics, which may pinpoint new targets based on the effect of genetic variants in humans. The present review summarizes such research focusing on depression and its therapy. The inconsistency between most genetic studies in depression suggests, first of all, a significant role of environmental stress. Furthermore, effect of individual genes and polymorphisms is weak, therefore gene x gene interactions or complete biochemical pathways should be analyzed. Even genes encoding target proteins of currently used antidepressants remain non-significant in genome-wide case control investigations suggesting no main effect in depression, but rather an interaction with stress. The few significant genes in GWASs are related to neurogenesis, neuronal synapse, cell contact and DNA transcription and as being nonspecific for depression are difficult to harvest pharmacologically. Most candidate genes in replicable gene x environment interactions, on the other hand, are connected to the regulation of stress and the HPA axis and thus could serve as drug targets for depression subgroups characterized by stress-sensitivity and anxiety while other risk polymorphisms such as those related to prominent cognitive symptoms in depression may help to identify additional subgroups and their distinct treatment. Until these new targets find their way into therapy, the optimization of current medications can be approached by pharmacogenomics, where metabolizing enzyme polymorphisms remain prominent determinants of therapeutic success.

Effect of ABCB1 C3435T Polymorphism on Pharmacokinetics of Antipsychotics and Antidepressants

P-glycoprotein, encoded by ABCB1, is an ATP-dependent drug efflux pump which exports substances outside the cell. Some studies described connections between C3435T polymorphism T allele and lower P-glycoprotein expression; therefore, homozygous T/T could show higher plasma levels. Our aim was to evaluate the effect of C3435T on pharmacokinetics of 4 antipsychotics (olanzapine, quetiapine, risperidone and aripiprazole) and 4 antidepressants (trazodone, sertraline, agomelatine and citalopram). The study included 473 healthy volunteers receiving a single oral dose of one of these drugs, genotyped by real-time PCR. Multivariate analysis was performed to adjust the effect of sex and genotype of the main cytochrome P450 enzymes. C3435T polymorphism had an effect on olanzapine pharmacokinetics, as T/T individuals showed lower clearance and volume of distribution. T/T individuals showed lower T_1/2 of 9-OH-risperidone, but this difference disappeared after multivariate correction. T/T homozygous individuals showed lower dehydro-aripiprazole and trazodone area under the concentration-time curve, along with lower half-life and higher clearance of trazodone. C/T genotype was associated to higher citalopram maximum concentration. C3435T had no effect on quetiapine, sertraline or agomelatine pharmacokinetics. C3435T can affect the elimination of some drugs in different ways. Regarding risperidone, trazodone and dehydro-aripiprazole, we observed enhanced elimination while it was reduced in olanzapine and citalopram. However, in quetiapine, aripiprazole, sertraline and agomelatine, no changes were detected. These results suggest that P-glycoprotein polymorphisms could affect CNS drugs disposition, but the genetic factor that alters its activity is still unknown. This fact leads to consider the analysis of ABCB1 haplotypes instead of individual variants.

Peripheral biomarkers of major depression and antidepressant treatment response: Current knowledge and future outlooks

BACKGROUND

In recent years, we have accomplished a deeper understanding about the pathophysiology of major depressive disorder (MDD). Nevertheless, this improved comprehension has not translated to improved treatment outcome, as identification of specific biologic markers of disease may still be crucial to facilitate a more rapid, successful treatment. Ongoing research explores the importance of screening biomarkers using neuroimaging, neurophysiology, genomics, proteomics, and metabolomics measures.

RESULTS

In the present review, we highlight the biomarkers that are differentially expressed in MDD and treatment response and place a particular emphasis on the most recent progress in advancing technology which will continue the search for blood-based biomarkers.

LIMITATIONS

Due to space constraints, we are unable to detail all biomarker platforms, such as neurophysiological and neuroimaging markers, although their contributions are certainly applicable to a biomarker review and valuable to the field.

CONCLUSIONS

Although the search for reliable biomarkers of depression and/or treatment outcome is ongoing, the rapidly-expanding field of research along with promising new technologies may provide the foundation for identifying key factors which will ultimately help direct patients toward a quicker and more effective treatment for MDD.

Does G2677T Polymorphism of the MDR1 Gene Make a Difference in the Therapeutic Response to Paroxetine in Depressed Patients in a Slovakian Population?

Background

The role of multidrug resistance 1 gene (MDR1 or ABCB1) polymorphism G2677T was studied in relation to paroxetine therapeutic efficacy and its side effects, as well as its association with selected demographic and clinical characteristics of patients with depressive disorder.

Material/Methods

To evaluate therapeutic efficacy, all patients (n=61) were rated at week 0, 2, 4, and 6 using the Hamilton Rating Scale for Depression (HAMD-21). They were labelled as “responders” (a decrease in HAMD ≥50%) and “nonresponders”. The frequency of the side effects of nausea and sexual dysfunction were assessed using the Utvalg for Kliniske Undersogelser rating scale. The PCR-restriction fragment length polymorphism method was used for genotyping.

Results

A significantly enhanced therapeutic efficacy of paroxetine was observed in patients carrying at least one T allele at week 4 (GG versus GT: 0.049; GG versus GT+TT: 0.035) and week 6 (GG versus TT: 0.001; GG versus GT+TT: 0.016; GG+GT versus TT: 0.003; G versus T: 0.001). On the other hand, carriers of the T allele showed only a nonsignificant increase in HAMD-21 score reduction. In the present study, no significant association between G2677T polymorphism and side effects was detected. However, we found a marginally significant difference between GG and GT genotypes regarding family history of depressive disorder (p=0.049).

Conclusions

Our study provided evidence for the potential effect of MDR1 G2677T polymorphism on paroxetine therapeutic efficacy, and eventually on depressive disorder family history. Larger multicenter studies and studies across other ethnic groups are needed to elucidate the contradictory implications of G2677T polymorphism with depressive disorder and its treatment.

Nanomedicine applications in women's health: state of the art

State-of-the-art applications of nanomedicine have the potential to revolutionize the diagnosis, prevention, and treatment of a range of conditions and diseases affecting women’s health. In this review, we provide a synopsis of potential applications of nanomedicine in some of the most dominant fields of women’s health: mental health, sexual health, reproductive medicine, oncology, menopause-related conditions and dementia. We explore published studies arising from in vitro and in vivo experiments, and clinical trials where available, to reveal novel and highly promising therapeutic applications of nanomedicine in these fields. For the first time, we summarize the growing body of evidence relating to the use of nanomaterials as experimental tools for the detection, prevention, and treatment of significant diseases and conditions across the life course of a cisgender woman, from puberty to menopause; revealing the far-reaching and desirable theoretical impact of nanomedicine across different medical disciplines. We also present an overview of potential concerns regarding the therapeutic applications of nanomedicine and the factors currently restricting the growth of applied nanomedicine.

Pharmacogenomics and Biomarkers of Depression

The standard of care for antidepressant treatment in major depressive disorder (MDD) is a trial-and-error approach. Patients often have to undergo multiple medication trials for weeks to months before finding an effective treatment. Clinical factors such as severity of baseline symptoms and the presence of specific individual (anhedonia or insomnia) or cluster (atypical, melancholic, or anxious) of symptoms are commonly used without any evidence of their utility in selecting among currently available antidepressants. Genomic and proteomic biomarker have gained recent attention for their potential in informing antidepressant medication selection. In this report, we have reviewed some of the major pharmacogenomics studies along with individual genetic and proteomic biomarker of antidepressant response. Additionally, we have reviewed the blood-based protein biomarkers that can inform selection of one antidepressant over another. Among all currently available biomarkers, C-reactive protein (CRP) appears to be the most promising and pragmatic choice. Low CRP (<1 mg/L) in patients with MDD predicts better response to escitalopram while higher levels are associated with better response to noradrenergic/dopaminergic antidepressants. Future studies are needed to demonstrate the superiority of a CRP-based treatment assignment over high-quality measurement-based care in real-world clinical practices.

Possibility of Predicting Serotonin Transporter Occupancy From the In Vitro Inhibition Constant for Serotonin Transporter, the Clinically Relevant Plasma Concentration of Unbound Drugs, and Their Profiles for Substrates of Transporters

Accurate prediction of target occupancy facilitates central nervous system drug development. In this review, we discuss the predictability of serotonin transporter (SERT) occupancy in human brain estimated from in vitro K_i values for human SERT and plasma concentrations of unbound drug (C_u,plasma), as well as the impact of drug transporters in the blood-brain barrier. First, the geometric means of in vitro K_i values were compared with the means of in vivo K_i values (K_i,u,plasma) which were calculated as C_u,plasma values at 50% occupancy of SERT obtained from previous clinical positron emission tomography/single photon emission computed tomography imaging studies for 6 selective serotonin transporter reuptake inhibitors and 3 serotonin norepinephrine reuptake inhibitors. The in vitro K_i values for 7 drugs were comparable to their in vivo K_i,u,plasma values within 3-fold difference. SERT occupancy was overestimated for 5 drugs (P-glycoprotein substrates) and underestimated for 2 drugs (presumably uptake transporter substrates, although no evidence exists as yet). In conclusion, prediction of human SERT occupancy from in vitro K_i values and C_u,plasma was successful for drugs that are not transporter substrates and will become possible in future even for transporter substrates, once the transporter activities will be accurately estimated from in vitro experiments.

Influence of ABCB1 polymorphisms and serum concentrations on venlafaxine response in patients with major depressive disorder

BACKGROUND

The pharmacokinetics and the pharmacodynamics of antidepressants show large inter-individual variations which result in unpredictable clinical responses.

AIM

The aim of the study was to examine the effect of ABCB1 polymorphisms and the serum concentrations on the efficacy and tolerability of venlafaxine in patients with major depressive disorder (MDD).

METHODS

Fifty-two outpatients who met the Diagnostic and Statistical Manual of Mental Disorders Fourth Edition (DSM-IV) criteria for MDD were recruited for the study. The severity of depression was assessed using the 17-item Hamilton Rating Scale for Depression scale (HDRS₁₇) and tolerability was assessed based on a query regarding side-effects for 6 weeks. The ABCB1 C3435T/A and G2677T/A polymorphisms were genotyped by PCR/RFLP and steady-state serum venlafaxine concentrations were measured by high-performance liquid chromatography.

RESULTS

Patients with the TT genotype for the C3435T and the TT/TA genotype for the G2677T/A polymorphism showed significantly higher frequencies in venlafaxine-induced akathisia. This relationship was not observed for efficacy. As regards serum venlafaxine concentrations, patient groups showed no significant differences in efficacy and tolerability.

CONCLUSION

The results suggest that individuals with the TT-TT/TA genotypes for the C3435T-G2677T/A polymorphisms of ABCB1 may be pre-disposed to a risk of akathisia.

ABCB1 genotyping in the treatment of depression

P-glycoprotein (P-gp), the gene product of ABCB1, is a drug transporter at the blood–brain barrier and could be a limiting factor for entrance of antidepressants into the brain, the target site of antidepressant action. Animal studies showed that brain concentrations of many antidepressants depend on P-gp. In humans, ABCB1 genotyping in the treatment of depression rests on the assumption that genetic variations in ABCB1 explain individual differences in antidepressant response via their effects on P-gp expression at the blood–brain barrier. High P-gp expression is hypothesized to lead to lower and often insufficient brain concentrations of P-gp substrate antidepressants. In this review, we summarize 32 studies investigating the question of whether ABCB1 polymorphisms predict clinical efficacy and/or tolerability of antidepressants in humans and evaluate the clinical application status of ABCB1 genotyping in depression treatment.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

Pharmacogenetics of major depressive disorder: top genes and pathways toward clinical applications

The pharmacogenetics of antidepressants has been not only a challenging but also frustrating research field since its birth in the 1990s. Indeed, great expectations followed the first evidence of familiar aggregation of antidepressant response. Despite the progress from candidate gene studies to genome-wide association studies (GWAS), results fell out the expectations and they were often inconsistent. Anyway, the cumulative evidence supports the involvement of some genes and molecular pathways in antidepressant efficacy. The best single genes are SLC6A4, HTR2A, BDNF, GNB3, FKBP5, ABCB1, and cytochrome P450 genes (CYP2D6 and CYP2C19). Molecular pathways involved in inflammation and neuroplasticity show the greatest support. The first studies evaluating benefits of genotype-guided antidepressant treatments provided encouraging results and confirmed the relevance of SLC6A4, HTR2A, ABCB1, and cytochrome P450 genes. Further progress in genotyping and data analysis would allow to move forward and complete the understanding of antidepressant pharmacogenetics and its translation into clinical applications.

ABCB1 gene variants and antidepressant treatment outcome: A meta-analysis

The efflux pump P-glycoprotein (P-gp), a gene product of the ABCB1 gene, plays a pivotal role in the transfer of various molecules across the blood-brain barrier. P-gp protects the brain by selectively extruding its substrates, including certain antidepressive drugs, thereby limiting their uptake into the brain. Uhr et al. [2008] first showed that ABCB1 variants predicted the remission to antidepressants with P-gp substrate properties in patients suffering from major depression (MD). Other studies investigating the influence of ABCB1 polymorphisms on antidepressant treatment response produced inconclusive results. In this meta-analysis, we systematically summarized 16 pharmacogenetic studies focused on the association of ABCB1 variants and antidepressant treatment outcome in patients with MD (overall n = 2695). We investigated the association of treatment outcome and six ABCB1 single nucleotide polymorphisms (SNPs): rs2032583, rs2235015, rs2235040, rs1045642, rs2032582, rs1128503. We stratified for admission status, ethnicity, and prescription of concomitant medication. SNP rs2032583 showed a nominally significant association across all studies (P = 0.035, SNP was studied in a total of 2,037 patients) and a significant Bonferroni-corrected association among inpatients (P = 1.5 × 10(-05) , n = 485). Also SNP rs2235015 was significantly associated with antidepressant treatment outcome withstanding Bonferroni correction (P = 3.0 × 10(-04) ) among inpatients in a smaller subsample (n = 195). There were no significant associations of the other SNPs tested with antidepressant treatment outcome. Future pharmacogenetic association studies should focus on the role of the ABCB1 SNP rs2032583 in antidepressant outcome prediction.

ABCB1 (MDR1) predicts remission on P-gp substrates in chronic depression

The hypothesis that allelic variation in the multidrug resistance-1 (MDR1 or ABCB1) gene encoding the P-glycoprotein (P-gp) blood-brain barrier efflux pump is associated with remission and side effects was tested in chronic major depression patients treated with P-gp substrates. In 83 patients from the REVAMP trial, frequency of and time to remission as well as side effects was tested among genotype groups at 6 ABCB1 single nucleotide polymorphisms (SNPs). These six SNPs are significantly associated with remission and time to remission, with minor allele carriers on rs2235040 and rs9282564 attaining statistical significance after controlling for the other ABCB1 SNPs. The six ABCB1 SNPs are also significantly associated with the average side effects. However, here common homozygotes on rs2235040 and rs9282564 demonstrated significantly higher side effects after controlling for the effects of the other ABCB1 SNPs. These findings confirm and extend previous observations that minor alleles of two ABCB1 SNPs predict remission to treatment with substrates and demonstrate that common homozygotes on these SNPs experience greater side effects. Results point to the potential importance of ABCB1 variation for personalized medicine approaches to treating depression.

Understanding the pharmacogenetics of selective serotonin reuptake inhibitors

INTRODUCTION

The genetic background of antidepressant response represents a unique opportunity to identify biological markers of treatment outcome. Encouraging results alternating with inconsistent findings made antidepressant pharmacogenetics a stimulating but often discouraging field that requires careful discussion about cumulative evidence and methodological issues.

AREAS COVERED

The present review discusses both known and less replicated genes that have been implicated in selective serotonin reuptake inhibitors (SSRIs) efficacy and side effects. Candidate genes studies and genome-wide association studies (GWAS) were collected through MEDLINE database search (articles published till January 2014). Further, GWAS signals localized in promising genetic regions according to candidate gene studies are reported in order to assess the general comparability of results obtained through these two types of pharmacogenetic studies. Finally, a pathway enrichment approach is applied to the top genes (those harboring SNPs with p < 0.0001) outlined by previous GWAS in order to identify possible molecular mechanisms involved in SSRI effect.

EXPERT OPINION

In order to improve the understanding of SSRI pharmacogenetics, the present review discusses the proposal of moving from the analysis of individual polymorphisms to genes and molecular pathways, and from the separation across different methodological approaches to their combination. Efforts in this direction are justified by the recent evidence of a favorable cost-utility of gene-guided antidepressant treatment.

The clinical application of ABCB1 genotyping in antidepressant treatment: a pilot study

BACKGROUND

The gene product of the ABCB1 gene, the P-glycoprotein, functions as a custodian molecule in the blood-brain barrier and regulates the access of most antidepressants into the brain. Previous studies showed that ABCB1 polymorphisms predicted the response to antidepressants that are substrates of the P-gp, while the response to nonsubstrates was not influenced by ABCB1 polymorphisms. The aim of the present study was to evaluate the clinical application of ABCB1 genotyping in antidepressant pharmacotherapy.

METHODS

Data came from 58 depressed inpatients participating in the Munich Antidepressant Response Signature (MARS) project, whose ABCB1 gene test results were implemented into the clinical decision making process. Hamilton Depression Rating Scale (HAM-D) scores, remission rates, and duration of hospital stay were documented with dose and kind of antidepressant treatment.

RESULTS

Patients who received ABCB1 genotyping had higher remission rates [χ2(1) = 6.596, p = 0.005, 1-sided] and lower Hamilton sores [t(111) = 2.091, p = 0.0195, 1-sided] at the time of discharge from hospital as compared to patients without ABCB1 testing. Among major allele homozygotes for ABCB1 single nucleotide polymorphisms (SNPs) rs2032583 and rs2235015 (TT/GG genotype), an increase in dose was associated with a shorter duration of hospital stay [rho(28) = -0.441, p = 0.009, 1-sided], whereas other treatment strategies (eg, switching to a nonsubstrate) showed no significant associations with better treatment outcome. Discussion The implementation of ABCB1 genotyping as a diagnostic tool influenced clinical decisions and led to an improvement of treatment outcome. Patients carrying the TT/GG genotype seemed to benefit from an increase in P-gp substrate dose.

CONCLUSION

Results suggest that antidepressant treatment of depression can be optimized by the clinical application of ABCB1 genotyping.

Are there meaningful biomarkers of treatment response for depression?

During the past decades, the prevalence of affective disorders has been on the rise globally, with only one out of three patients achieving remission in acute treatment with antidepressants. The identification of physiological markers that predict treatment course proves useful in increasing therapeutic success. On the basis of well-documented, recent findings in depression research, we highlight and discuss the most promising biomarkers for antidepressant therapy response. These include genetic variants and gene expression profiles, proteomic and metabolomic markers, neuroendocrine function tests, electrophysiology and imaging techniques. Ultimately, this review proposes an integrative use of biomarkers for antidepressant treatment outcome.

From pharmacogenetics to pharmacogenomics: the way toward the personalization of antidepressant treatment

OBJECTIVE

Major depressive disorder is the most common psychiatric disorder, worldwide, yet response and remission rates are still unsatisfactory. The identification of genetic predictors of antidepressant (AD) response could provide a promising opportunity to improve current AD efficacy through the personalization of treatment. The major steps and findings along this path are reviewed together with their clinical implications and limitations.

METHOD

We systematically reviewed the literature through MEDLINE and Embase database searches, using any word combination of "antidepressant," "gene," "polymorphism," "pharmacogenetics," "genome-wide association study," "GWAS," "response," and "adverse drug reactions." Experimental works and reviews published until March 2012 were collected and compared.

RESULTS

Numerous genes pertaining to several functional systems were associated with AD response. The more robust findings were found for the following genes: solute carrier family 6 (neurotransmitter transporter), member 4; serotonin receptor 1A and 2A; brain-derived neurotrophic factor; and catechol-O-methyltransferase. Genome-wide association studies (GWASs) provided many top markers, even if none of them reached genome-wide significance.

CONCLUSIONS

AD pharmacogenetics have not produced any knowledge applicable to routine clinical practice yet, as results were mainly inconsistent across studies. Despite this, the rising awareness about methodological deficits of past studies could allow for the identication of more suitable strategies, such as the integration of the GWAS approach with the candidate gene approach, and innovative methodologies, such as pathway analysis and study of depressive endophenotypes.

Mechanisms of antidepressant resistance

Depression is one of the most frequent and severe mental disorder. Since the discovery of antidepressant (AD) properties of the imipramine and then after of other tricyclic compounds, several classes of psychotropic drugs have shown be effective in treating major depressive disorder (MDD). However, there is a wide range of variability in response to ADs that might lead to non response or partial response or in increased rate of relapse or recurrence. The mechanisms of response to AD therapy are poorly understood, and few biomarkers are available than can predict response to pharmacotherapy. Here, we will first review markers that can be used to predict response to pharmacotherapy, such as markers of drug metabolism or blood-brain barrier (BBB) function, the activity of specific brain areas or neurotransmitter systems, hormonal dysregulations or plasticity, and related molecular targets. We will describe both clinical and preclinical studies and describe factors that might affect the expression of these markers, including environmental or genetic factors and comorbidities. This information will permit us to suggest practical recommendations and innovative treatment strategies to improve therapeutic outcomes.

The lack of association between components of metabolic syndrome and treatment resistance in depression

RATIONALE

Although a number of studies investigated the link between major depressive disorder (MDD) and metabolic syndrome (MetS), the association between MetS and treatment-resistant depression (TRD) is still not clear.

OBJECTIVES

The aim of the study was to investigate the relationship between TRD and MetS and/or components of MetS and cardiovascular risk factors. Given the high prevalence of both conditions, the hypothesis was that TRD would be significantly associated with MetS.

METHODS

This cross-sectional study included 203 inpatients with MDD, assessed for the treatment resistance, MetS and its components, and severity of MDD. Diagnoses and evaluations were made with SCID based on DSM-IV, National Cholesterol Education Program Adult Treatment Panel III criteria, and the Hamilton Depression Rating Scale.

RESULTS

TRD prior to study entry was found in 26.1 % of patients, while MetS was observed in 33.5 % of patients. The prevalence of MetS did not differ significantly between TRD and non-TRD patients. In addition, the frequency of the altered values of particular components of the MetS or cardiovascular risk factors was not associated with treatment resistance in depressed patients. Patients with TRD were older, had a higher number of lifetime episodes of depression and suicide attempts, and longer duration of MDD compared to non-TRD patients.

CONCLUSIONS

The occurrence of either MetS or the particular components of the MetS and other cardiovascular risk factors was similar between TRD and non-TRD patients. Although there is a bidirectional relationship between depression and MetS, neither MetS nor its components appear to influence treatment resistance to antidepressants.

Human P-glycoprotein differentially affects antidepressant drug transport: relevance to blood-brain barrier permeability

The pharmacological concept that inhibition of the drug efflux pump P-glycoprotein (P-gp) enhances brain distribution of the antidepressant imipramine in the rat has recently been demonstrated. To determine if these findings are relevant to humans, the present study investigated if imipramine is a transported substrate of human P-gp. Furthermore, additional experiments were carried out to determine if findings in relation to imipramine and human P-gp would apply to other antidepressants from a range of different classes. To this end, bidirectional transport experiments were carried out in the ABCB1-transfected MDCKII-MDR1 cell line. Transported substrates of human P-gp are subjected to net efflux in this system, exhibiting a transport ratio (TR) ≥ 1.5, and directional efflux is attenuated by co-incubation of a P-gp inhibitor. Imipramine was identified as a transported substrate of human P-gp (TR = 1.68, attenuated by P-gp inhibition). However, the antidepressants amitriptyline, duloxetine, fluoxetine and mirtazapine were not transported substrates of human P-gp (TR ≤ 1.16 in all cases). These results offer insight into the role of P-gp in the distribution of antidepressants, revealing that rodent findings pertaining to imipramine may translate to humans. Moreover, the present results highlight that other antidepressants may not be transported substrates of human P-gp.

Pharmacogenetics of antidepressant drugs: an update after almost 20 years of research

Major depressive disorder (MDD) is an emergent cause of personal and socio-economic burden, both for the high prevalence of the disorder and the unsatisfying response rate of the available antidepressant treatments. No reliable predictor of treatment efficacy and tolerance in the single patient is available, thus drug choice is based on a trial and error principle with poor clinical efficiency. Among modulators of treatment outcome, genetic polymorphisms are thought to explain a significant share of the inter-individual variability. The present review collected the main pharmacogenetic findings primarily about antidepressant response and secondly about antidepressant induced side effects, and discussed the main strengths and limits of both candidate and genome-wide association studies and the most promising methodological opportunities and challenges of the field. Despite clinical applications of antidepressant pharmacogenetics are not available yet, previous findings suggest that genotyping may be applied in the clinical practice. In order to reach this objective, further rigorous pharmacogenetic studies (adequate sample size, study of better defined clinical subtypes of MDD, adequate covering of the genetic variability), their combination with the results obtained through complementary methodologies (e.g., pathway analysis, epigenetics, transcriptomics, and proteomics), and finally cost-effectiveness trials are required.

Pharmacogenetics in major depression: a comprehensive meta-analysis

A number of candidate gene studies focused on major depression (MD) and antidepressant (AD) efficacy have been carried out, but results mainly remain inconclusive. We performed a comprehensive meta-analysis of published candidate gene studies focused on AD efficacy in MD to evaluate the cumulative evidence. A random-effect model was applied to study the polymorphisms with genotypic counts available from at least three independent studies. On the base of previous evidence, the analysis was stratified by ethnicity (Caucasian, Asian, and other/mixed), and AD class (SSRIs and mixed/other ADs). Genotypic data were available for 16 polymorphisms in 11 genes. After the exclusion of 5-HTTLPR in SLC6A4 included in another recent meta-analysis, 15 polymorphisms in 11 genes were included in the present meta-analysis (BDNF rs6265, SLC6A4 STin2, HTR1A rs6295, HTR2A rs6311, rs6313 and rs7997012, HTR6 rs1805054, TPH1 rs1800532, SLC6A2 rs5569, COMT rs4680, GNB3 rs5443, FKBP5 rs1360780 and rs3800373, and ABCB1 rs1045642 and rs2032582). Our results suggested that BDNF rs6265 (Val66Met) heterozygous genotype was associated with better SSRIs response compared to the homozygous genotypes, particularly in Asians (OR=1.53, 95%CI 1.12-2.07, p=0.007). SLC6A4 STin2, HTR2A rs6311 and rs7997012, GNB3 rs5443, FKBP5 rs1360780 and rs3800373, and ABCB1 rs2032582 showed associations with AD efficacy, but these results were highly dependent on one or two single studies. In conclusion, our findings suggested the BDNF Val66Met as the best single candidate involved in AD response, with a selective effect on SSRI treatment. Our overall results supported no major effect of any single gene variant on AD efficacy.

ABCB1 gene polymorphisms are associated with fatal intoxications involving venlafaxine but not citalopram

P-glycoprotein (P-gp), encoded by the ABCB1/MDR1 gene, is a drug transporter at the blood-brain barrier. Several polymorphisms in the ABCB1 gene are known to affect the activity and/or expression of P-gp, thereby influencing the treatment response and toxicity of P-gp substrates like citalopram and venlafaxine. In this study, we aimed to investigate the frequency of ABCB1 genotypes in forensic autopsy cases involving these two antidepressants. Further, the distribution of ABCB1 genotypes in deaths related to intoxication was compared to cases not associated to drug intoxication. The study included 228 forensic autopsy cases with different causes and manners of deaths. The ABCB1 single nucleotide polymorphisms (SNPs) G1199A, C1236T, C3435T and G2677T/A for these individuals were determined. The SNPs C1236T and C3435T in venlafaxine-positive cases were significantly different between the intoxication cases and non-intoxications. This was not seen for cases involving citalopram, indicating that the effect of genetic variants might be substrate specific. This novel finding should, however, be confirmed in future studies with larger number of cases.

MDR1 in paroxetine-induced sexual dysfunction

Paroxetine-induced sexual dysfunction represents a frequent treatment complication of otherwise efficient antidepressants. The genetic polymorphism of pharmacokinetic genes may contribute to the occurrence of such dysfunctions. This study presents the effect of MDR1 gene polymorphisms on sexual function in 18 women with bulimia nervosa, 18 women with anxiety disorders, and 19 healthy control subjects. It also deals with the relation between MDR1 gene polymorphisms and paroxetine-induced sexual dysfunction. The results demonstrated that MDR1 G2677T/A gene polymorphism allele carriers treated with paroxetine presented with difficulties with orgasm (p = .008) and lubrication (p < .001).

Epigenetic Modulation of Mood Disorders

BACKGROUND

Mood disorders are expressed in many heterogeneous forms, varying from anxiety to severe major clinical depression. The disorders are expressed in individual variety through manifestations governed by co-morbidities, symptom frequency, severity, and duration, and the effects of genes on phenotypes. The underlying etiologies of mood disorders consist of complex interactive operations of genetic and environmental factors. The notion of endophenotypes, which encompasses the markers of several underlying liabilities to the disorders, may facilitate efforts to detect and define, through staging, the genetic risks inherent to the extreme complexity of disease state.

AIMS

This review evaluates the role of genetic biomarkers in assisting clinical diagnosis, identification of risk factors, and treatment of mood disorders.

METHODS

Through a systematic assessment of studies investigating the epigenetic basis for mood disorders, the present review examines the interaction of genes and environment underlying the pathophysiology of these disorders.

RESULTS

The majority of research findings suggest that the notion of endophenotypes, which encompasses the markers of several underlying liabilities to the disorders, may facilitate efforts to detect and define, through staging, the genetic risks inherent to the extreme complexity of the disease states. Several strategies under development and refinement show the propensity for derivation of essential elements in the etiopathogenesis of the disorders affecting drug-efficacy, drug metabolism, and drug adverse effects, e.g., with regard to selective serotonin reuptake inhibitors. These include: transporter gene expression and genes encoding receptor systems, hypothalamic-pituitary-adrenal axis factors, neurotrophic factors, and inflammatory factors affecting neuroimmune function. Nevertheless, procedural considerations of pharmacogenetics presume the parallel investment of policies and regulations to withstand eventual attempts at misuse, thereby ensuring patient integrity.

CONCLUSIONS

Identification of genetic biomarkers facilitates choice of treatment, prediction of response, and prognosis of outcome over a wide spectrum of symptoms associated with affective states, thereby optimizing clinical practice procedures. Epigenetic regulation of primary brain signaling, e.g., serotonin and hypothalamic-pituitary-adrenal function, and factors governing their metabolism are necessary considerations. The participation of neurotrophic factors remains indispensable for neurogenesis, survival, and functional maintenance of brain systems.

Polymorphisms of the drug transporter gene ABCB1 predict side effects of treatment with cabergoline in patients with PRL adenomas

INTRODUCTION

Treatment with dopamine agonists in patients with prolactin (PRL) adenomas and Parkinson's disease is associated with central side effects. Central side effects may depend on a substance's ability to pass the blood-brain barrier, which can be actively controlled by transporter molecules such as the P-glycoprotein (P-gp) encoded by the ABCB1 gene.

MATERIALS AND METHODS

We aimed to determine whether cabergoline is transported by the P-gp and whether polymorphisms of its encoding ABCB1 gene predict central side effects of cabergoline therapy in patients with PRL adenomas. i) In an experimental mouse model lacking the homologues of the human ABCB1 gene (Abcb1ab double knockout mouse model), we examined whether cabergoline is a substrate of the P-gp using eight mutant and eight wild-type mice. ii) In a human case-control study including 79 patients with PRL adenomas treated with cabergoline at the Max Planck Institute of Psychiatry in Munich, we investigated the association of four selected ABCB1 gene single nucleotide polymorphisms (SNPs) (rs1045642, rs2032582, rs2032583 and rs2235015), with the occurrence of central side effects under cabergoline therapy.

RESULTS

i) In the experimental mouse model, we observed that brain concentrations of cabergoline were tenfold higher in the mutant mice compared with their wild-type littermates, implying that cabergoline is indeed a substrate of the transporter P-gp at the blood-brain barrier level. ii) In the human study, we observed significant negative associations under cabergoline for the C-carriers and heterozygous CT individuals of SNP rs1045642 with two central side effects (frequency of fatigue and sleep disorders) and for the G-carriers of SNP rs2032582 with the enhancement of dizziness. For the SNPs rs2235015 and rs2032583, no associations with central side effects under cabergoline were found.

DISCUSSION

This is the first study demonstrating that individual ABCB1 gene polymorphisms, reflecting a different expression and function of the P-gp, could predict the occurrence of central side effects under cabergoline. Our findings can be viewed as a step into personalised therapy in PRL adenoma patients.

Clinically significant psychotropic drug-drug interactions in the primary care setting

In recent years, the growing numbers of patients seeking care for a wide range of psychiatric illnesses in the primary care setting has resulted in an increase in the number of psychotropic medications prescribed. Along with the increased utilization of psychotropic medications, considerable variability is noted in the prescribing patterns of primary care providers and psychiatrists. Because psychiatric patients also suffer from a number of additional medical comorbidities, the increased utilization of psychotropic medications presents an elevated risk of clinically significant drug interactions in these patients. While life-threatening drug interactions are rare, clinically significant drug interactions impacting drug response or appearance of serious adverse drug reactions have been documented and can impact long-term outcomes. Additionally, the impact of genetic variability on the psychotropic drug's pharmacodynamics and/or pharmacokinetics may further complicate drug therapy. Increased awareness of clinically relevant psychotropic drug interactions can aid clinicians to achieve optimal therapeutic outcomes in patients in the primary care setting.

ABCB1 gene variants influence tolerance to selective serotonin reuptake inhibitors in a large sample of Dutch cases with major depressive disorder

P-glycoprotein (P-gp), an ATP-driven efflux pump in the blood-brain barrier, has a major impact on the delivery of antidepressant drugs in the brain. Genetic variants in the gene ABCB1 encoding for P-gp have inconsistently been associated with adverse effects. In order to resolve these inconsistencies, we conducted a study in a large cohort of patients with major depressive disorder with the aim to unravel the association of ABCB1 variants with adverse effects of antidepressants and in particular with selective serotonin reuptake inhibitors (SSRIs), which display affinity as substrate for P-gp. The Netherlands Study of Depression and Anxiety (NESDA) study was used as a clinical sample. For 424 patients data were available on drug use, side effects. We selected six ABCB1 gene variants (1236T>C, 2677G>T/A, 3435T>C, rs2032583, rs2235040 and rs2235015) and analyzed them for association with adverse drug effects using multinomial regression analysis for both single variants and haplotypes. We found a significant association between the number of SSRI-related adverse drug effects and rs2032583 (P=0.001), rs2235040 (P=0.002) and a haplotype (P=0.002). Moreover, serotonergic effects (sleeplessness, gastrointestinal complaints and sexual effects) were significantly predicted by these variants and haplotype (P=0.002/0.003). We conclude that adverse drug effects with SSRI treatment, in particular serotonergic effects, are predicted by two common polymorphisms of the ABCB1 gene.

Interactions between antidepressants and P-glycoprotein at the blood-brain barrier: clinical significance of in vitro and in vivo findings

The drug efflux pump P-glycoprotein (P-gp) plays an important role in the function of the blood-brain barrier by selectively extruding certain endogenous and exogenous molecules, thus limiting the ability of its substrates to reach the brain. Emerging evidence suggests that P-gp may restrict the uptake of several antidepressants into the brain, thus contributing to the poor success rate of current antidepressant therapies. Despite some inconsistency in the literature, clinical investigations of potential associations between functional single nucleotide polymorphisms in ABCB1, the gene which encodes P-gp, and antidepressant response have highlighted a potential link between P-gp function and treatment-resistant depression (TRD). Therefore, co-administration of P-gp inhibitors with antidepressants to patients who are refractory to antidepressant therapy may represent a novel therapeutic approach in the management of TRD. Furthermore, certain antidepressants inhibit P-gp in vitro, and it has been hypothesized that inhibition of P-gp by such antidepressant drugs may play a role in their therapeutic action. The present review summarizes the available in vitro, in vivo and clinical data pertaining to interactions between antidepressant drugs and P-gp, and discusses the potential relevance of these interactions in the treatment of depression.

Association between the functional polymorphism (C3435T) of the gene encoding P-glycoprotein (ABCB1) and major depressive disorder in the Japanese population

Human P-glycoprotein (P-gp), which is encoded by ABCB1 (ATP-binding cassette, sub-family B member 1), is expressed in the blood brain barrier and protects the brain from many kinds of drugs and toxins including glucocorticoids by acting as an efflux pump. We examined whether functional polymorphisms of ABCB1 give susceptibility to major depressive disorder (MDD). The five functional single nucleotide polymorphisms (SNPs), A-41G (rs2188524), T-129C (rs3213619), C1236T (Gly412Gly: rs1128503), G2677A/T (Ala893Ser/Thr: rs2032582), and C3435T (Ile1145Ile: rs1045642) were genotyped in 631 MDD patients and 1100 controls in the Japanese population. A tri-allelic SNP, G2677A/T, was genotyped by pyrosequencing and the remaining SNPs were genotyped by the TaqMan 5'-exonuclease allelic discrimination assay. The minor T3435 allele was significantly increased in MDD patients than in the controls (χ(2) = 4.5, df = 1, p = 0.034, odds ratio [OR] 1.16, 95% confidential interval [CI] 1.01-1.34). Homozygotes for the T3435 allele was significantly more common in patients than in the controls (χ(2) = 7.5, df = 1, p = 0.0062, OR 1.43, 95%CI 1.11-1.85). With respect to the other 4 SNPs, there was no significant difference in genotype or allele distribution. In the haplotype-based analysis, the proportion of individuals with the TT1236-TT3435 haploid genotype was significantly increased in patients than in controls (χ(2) = 8.5, df = 1, p = 0.0037, OR 1.50, 95%CI 1.14-1.98). Our results suggest that the T3435 allele or carrying two copies of this allele confers susceptibility to MDD in the Japanese population.

Pharmacogenetics of antidepressant drugs: current clinical practice and future directions

While antidepressants are widely used to treat mood and anxiety disorders, only half of the patients will respond to antidepressant treatment and only one-third of patients experience a full remission of symptoms. The identification of genetic biomarkers that predict antidepressant-treatment response can improve current clinical practice. This is an emerging field known as pharmacogenetics, which comprises of genetic studies on both the pharmacokinetics and pharmacodynamics of treatment response. Recent studies on antidepressant-treatment response have focused on both aspects of pharmacogenetics research, identifying new candidate genes that may predict better treatment response for patients. This paper reviews recent findings on the pharmacogenetics of antidepressant drugs and future clinical applications. Ultimately, these studies should lead to the use of genetic testing to guide the use of antidepressants in clinical practice.

Paroxetine for the treatment of depression: a critical update

INTRODUCTION

A growth in the market for antidepressants, paired with an ever-increasing population affected from depressive disorder, requires a critical re-evaluation of most prescribed antidepressants, in order to provide up-to-date practical prescribing information for clinicians. Paroxetine represents a widely prescribed and reliable antidepressant for the expert clinician, but the latest data do not rank it amongst the most effective and tolerable newer antidepressants.

AREAS COVERED

This paper reviews latest data on paroxetine and investigates its clinical efficacy and safety in different groups of patients.

EXPERT OPINION

In previous subanalysis and metaregression analysis, paroxetine failed to show clear differences in terms of efficacy across clinical subgroups. Thus, nowadays the pharmacokinetic and pharmacodynamic properties of the molecule are fundamental to guiding its prescription, both for efficacy and tolerability issues, for example, it can have a high impact on sexual function and weight should also be considered at the beginning of treatment. Since prescription is still based mainly on its side-effect profile, newer and more accurate directions for an individualized prescription are needed.

Functional significance of genetic polymorphisms in P-glycoprotein (MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2)

Recent pharmacogenomic/pharmacogenetic (PGx) studies have disclosed important roles for drug transporters in the human body. Changes in the functions of drug transporters due to drug/food interactions or genetic polymorphisms, for example, are associated with large changes in pharmacokinetic (PK) profiles of substrate drugs, leading to changes in drug response and side effects. This information is extremely useful not only for drug development but also for individualized treatment. Among drug transporters, the ATP-binding cassette (ABC) transporters are expressed in most tissues in humans, and play protective roles; reducing drug absorption from the gastrointestinal tract, enhancing drug elimination into bile and urine, and impeding the entry of drugs into the central nervous system and placenta. In addition to PK/pharmacodynamic (PD) issues, ABC transporters are reported as etiologic and prognostic factors (or biomarkers) for genetic disorders. Although a consensus has not yet been reached, clinical studies have demonstrated that the PGx of ABC transporters influences the overall outcome of pharmacotherapy and contributes to the pathogenesis and progression of certain disorders. This review explains the impact of PGx in ABC transporters in terms of PK/PD, focusing on P-glycoprotein and breast cancer resistance protein (BCRP).

In vitro transport profile of carbamazepine, oxcarbazepine, eslicarbazepine acetate, and their active metabolites by human P-glycoprotein

PURPOSE

Antiepileptic drugs (AEDs) are widely used not only in the treatment of epilepsy but also as treatments for psychiatric disorders. Pharmacoresistance of AEDs in the treatment of epilepsy and psychiatric disorders is a serious problem. Transport of antiepileptic drugs by P-glycoprotein (Pgp, ABCB1, or MDR1), which is overexpressed in the blood-brain barrier, may be a mechanism for resistance of AEDs. For most AEDs, conflicting evidence precludes consensus on whether they are substrates of Pgp. The objective of this study was to evaluate whether analogs and metabolites of the AED carbamazepine are substrates of human Pgp.

METHODS

Polarized cell lines MDCKII and LLC transfected with the human MDR1 gene were used in the bidirectional transport assay and concentration equilibrium transport assay. The expression of Pgp was detected by real-time polymerase chain reaction (PCR) and immunofluorescent staining. Rhodamine-123 uptake was also determined.

KEY FINDINGS

Pgp did not transport carbamazepine, but it did transport its active metabolite carbamazepine-10,11-epoxide. Pgp also pumped eslicarbazepine acetate and oxcarbazepine, as well as their active metabolite (S)-licarbazepine. Transport of the drugs was in the order of ESL>OXC>S-LC>CBZ-E in concentration equilibrium conditions. The transport of these drugs was blocked by Pgp inhibitors tariquidar and verapamil.

SIGNIFICANCE

All carbamazepine analogs or metabolites tested are Pgp substrates, except for carbamazepine. These data suggest that resistance to carbamazepine, oxcarbazepine, or eslicarbazepine acetate may be attributed to increased efflux function of Pgp because they or their active metabolites are Pgp substrates.

Pharmacogenetics of antidepressants

Up to 60% of depressed patients do not respond completely to antidepressants (ADs) and up to 30% do not respond at all. Genetic factors contribute for about 50% of the AD response. During the recent years the possible influence of a set of candidate genes as genetic predictors of AD response efficacy was investigated by us and others. They include the cytochrome P450 superfamily, the P-glycoprotein (ABCB1), the tryptophan hydroxylase, the catechol-O-methyltransferase, the monoamine oxidase A, the serotonin transporter (5-HTTLPR), the norepinephrine transporter, the dopamine transporter, variants in the 5-hydroxytryptamine receptors (5-HT1A, 5-HT2A, 5-HT3A, 5-HT3B, and 5-HT6), adrenoreceptor beta-1 and alpha-2, the dopamine receptors (D2), the G protein beta 3 subunit, the corticotropin releasing hormone receptors (CRHR1 and CRHR2), the glucocorticoid receptors, the c-AMP response-element binding, and the brain-derived neurotrophic factor. Marginal associations were reported for angiotensin I converting enzyme, circadian locomotor output cycles kaput protein, glutamatergic system, nitric oxide synthase, and interleukin 1-beta gene. In conclusion, gene variants seem to influence human behavior, liability to disorders and treatment response. Nonetheless, gene × environment interactions have been hypothesized to modulate several of these effects.

ABCB1 (MDR1) polymorphisms and antidepressant response in geriatric depression

OBJECTIVE

Variation in the ATP-binding cassette, subfamily B, member 1 transporter (ABCB1) (multidrug-resistance gene 1) gene has been investigated as a predictor of response to treatment with a variety of medications such as antiarrhythmics, chemotherapeutic agents, anti-HIV medications, and some psychotropics. The ABCB1 gene product, P-glycoprotein, affects the transport of drugs out of many cell types, including endothelial cells at the blood-brain barrier. We sought to determine if ABCB1 polymorphisms predict response to antidepressant treatment in geriatric patients.

METHODS

We compared the effects of ABCB1 genetic variation on the therapeutic response to paroxetine, a P-glycoprotein substrate, and to mirtazapine, which is not thought to be transported by ABCB1, in a sample of 246 elderly patients with major depression treated in a clinical trial setting. A total of 15 single nucleotide polymorphisms in the ABCB1 gene were assessed in each patient. Two of these ABCB1 single nucleotide polymorphisms were earlier reported to predict treatment response in patients prescribed with P-glycoprotein substrate antidepressants.

RESULTS

The two earlier identified ABCB1 markers for antidepressant response predicted time to remission in our paroxetine-treated patients, but not in the mirtazapine-treated patients. These results replicate the published findings of others. If a Bonferroni correction for type I error is made, our results do not reach the criteria for statistical significance. However, the Bonferroni correction may be too conservative given the strong linkage disequilibrium among some of the markers and our aim to replicate the earlier published findings.

CONCLUSION

Our study provides confirmation that certain ABCB1 polymorphisms predict response to substrate medications in geriatric patients.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

The promise and reality of pharmacogenetics in psychiatry

Existing psychotropic medications for the treatment of mental illnesses, including antidepressants, mood stabilizers, and antipsychotics, are clinically suboptimal. They are effective in only a subset of patients or produce partial responses, and they are often associated with debilitating side effects that discourage adherence. There is growing enthusiasm in the promise of pharmacogenetics to personalize the use of these treatments to maximize their efficacy and tolerability; however, there is still a long way to go before this promise becomes a reality. This article reviews the progress that has been made in research toward understanding how genetic factors influence psychotropic drug responses and the challenges that lie ahead in translating the research findings into clinical practices that yield tangible benefits for patients with mental illnesses.

Glucocorticoid dysregulations and their clinical correlates. From receptors to therapeutics

Clinicians have long known that a substantial proportion of patients treated with high-dose glucocorticoids experience a variety of serious side effects, including metabolic syndrome, bone loss, and mood shifts, such as depressive symptomatology, manic or hypomanic symptoms, and even suicide. The reason for individual variability in expression or severity of these side effects is not clear. However, recent emerging literature is beginning to shed light on possible mechanisms of these effects. As an introduction to this volume, this chapter will review the basic biology of glucocorticoid release and molecular mechanisms of glucocorticoid receptor function, and will discuss how dysregulation of glucocorticoid action at all levels could contribute to such side effects. At the molecular level, glucocorticoid receptor polymorphisms may be associated either with receptor hypofunction or hyperfunction and could thus contribute to differential individual sensitivity to the effects of glucocorticoid treatment. Numerous factors regulate hypothalamic-pituitary-adrenal (HPA) axis responsiveness, which could also contribute to individual differences in glucocorticoid side effects. One of these is sex hormone status and the influence of estrogen and progesterone on HPA axis function and mood. Another is immune system activity, in which immune molecules, such as interleukins and cytokines, activate the HPA axis and alter brain function, including memory, cognition, and mood. The effects of cytokines in inducing sickness behaviors, which overlap with depressive symptomatology, could also contribute to individual differences in such symptomatology. Taken together, this knowledge will have important relevance for identifying at-risk patients to avoid or minimize such side effects when they are treated with glucocorticoids. A framework for assessment of patients is proposed that incorporates functional, physiological, and molecular biomarkers to identify subgroups of patients at risk for depressive symptomatology associated with glucocorticoid treatment, and for prevention of side effects, which in many cases can be life-threatening.

Pharmacogenomics of antidepressant drugs

While antidepressant pharmacotherapy is an effective treatment of depression, it is still hampered by the slow onset of appreciable clinical improvement and a series of side effects. Moreover, a substantial group of patients does not achieve remission or fails to respond at all. One possible source accounting for these variations in treatment outcome are genetic differences. In recent years a number of pharmacogenetic studies on antidepressant drugs have been published. This manuscript summarizes findings related to the pharmacogenetics of genes involved in the pharmacokinetics as well as pharmacodynamics of antidepressants to date. Illustrated by examples from current candidate gene- and whole genome association studies, this manuscript critically discusses aspects of pharmacogenetic studies in antidepressant response related to study design and clinical relevance.