Candidate genes expression profile associated with antidepressants response in the GENDEP study: differentiating between baseline 'predictors' and longitudinal 'targets'

Cumulative meta-analysis of interleukins 6 and 1β, tumour necrosis factor α and C-reactive protein in patients with major depressive disorder

Cumulative meta-analyses are used to evaluate the extent to which further studies are needed to confirm or refute a hypothesis. We used this approach to assess observational evidence on systemic inflammation in individuals with major depressive disorder. We identified 58 studies of four common inflammatory markers in a literature search of PubMed, Embase and PsychInfo databases in May 2014. Pooled data from the earliest eight studies already showed an association between interleukin-6 concentrations and major depression; 23 more recent studies confirmed this finding (d=0.54, p<0.0001). A significant association between C-reactive protein levels and major depression was noted after 14 studies and this did not change after addition of six more studies (d=0.47, p<0.0001). For these two inflammatory markers, there was moderate heterogeneity in study-specific estimates, subgroup differences were small, and publication bias appeared to be an unlikely explanation for the findings. Sensitivity analyses including only high-quality studies and subjects free of antidepressant medication further verified the associations. While there was a link between tumour necrosis factor-α levels and major depression (d=0.40, p=0.002), the cumulative effect remained uncertain due to the extensive heterogeneity in study-specific estimates and inconsistencies between subgroups. No evidence was found for the association between interleukin-1β levels and major depression (d=-0.05, p=0.86). In conclusion, this cumulative meta-analysis confirmed higher mean levels of interleukin-6 and C-reactive protein in patients with major depression compared to non-depressed controls. No consistent association between tumour necrosis factor-α, interleukin-1β and major depression was observed. Future studies should clarify the specific immune mechanisms involved as well as continue testing anti-inflammatory therapies in patients suffering from major depression.

Serum cytokines and anxiety in adolescent depression patients: Gender effect

The present study compares the serum cytokine levels between adolescent depression patients and healthy controls and assesses correlation between depression, anxiety scores and serum levels of eight cytokines. Study also checked the variation in serum levels with medication status (medication free/naïve vs. patients on medication). Following clinical and psychometric assessment of 77 adolescent (aged 13-18 years) depression patients (49 males and 28 females; 56 medication free/naïve) and 54 healthy controls (25 males, 29 females), eight cytokines (IL-1β, IL-2, IL-6, IL-10, TNF-α, IFN-γ, TGF-β1 and IL-17A {denoted IL-17 throughout}) were measured in serum using ELISA. Depressed adolescents had significantly high levels of IL-2 (p<0.001) and IL-6 (p=0.03) as compared to controls. The female population skewed the result of one cytokine (IL-6) in patients. Anxiety scores showed positive correlation (only in female patients) with IL-1β, IL-10 and negative correlation with TGF-β1 and IL-17. The gender effect in relationship between anxiety and cytokines was not straightforward. On comparing study groups on the medication/naïve status, IL-2 and TGF-β1 showed significant difference between the groups (p<0.001, p=0.007 higher in medicated). Depression in adolescents was associated with elevation of proinflammatory serum cytokines with a gender bias for females. Anxiety scores correlated negatively with TGF-β1 and IL-17.

The links between chronic obstructive pulmonary disease and comorbid depressive symptoms: role of IL-2 and IFN-γ

Depression is highly prevalent in COPD patients, and both diseases are believed to be associated with inflammation. The aim of this study was to elucidate the role of the immune system alterations in pathogenesis of depression in COPD patients. Blood was collected from patients diagnosed with chronic obstructive pulmonary disease and comorbid depressive symptoms [COPD + DS, (N = 13)], from individuals with either COPD (N = 16) or recurrent depressive disorder (rDD) alone (N = 15), and from healthy controls (N = 19). Surface phenotype expression of T regulatory and T effector cells was analyzed with a flow cytometry, and IL-2, IL-6, IL-8, IFN-γ, IL-17, and neopterin were detected with ELISA. We demonstrated that COPD, depression, and COPD with comorbid depression are associated with increased IL-6 levels when compared with healthy controls 42.2 ± 1.87, 40.9 ± 2.12, 41.7 ± 1.31, and 33.2 ± 1.23 pg/ml, respectively (p < 0.05). A significant increase in neopterin levels was observed both in rDD and COPD patients when compared with controls (15.69 ± 0.095, 13.98 ± 0.887 vs. 9.22 ± 0.466 nmol/l, p < 0.001 and p < 0.05, respectively). Concentrations of IFN-γ were significantly increased in COPD + DS patients when compared with controls (24.3 ± 1.49 and 17.8 ± 0.70 pg/ml, respectively, p < 0.05). IL-2 levels were highest in COPD + DS (3.20 ± 0.389 pg/ml) and differed significantly when this group was compared with controls (2.20 ± 0.184 pg/ml), p ≤ 0.05). In this study, we demonstrated for the first time that depressive symptoms in COPD patients may be related to inflammatory state as confirmed by increased levels of IL-6 both in COPD and depression and also in COPD with comorbid depressive symptoms, despite the fact that the patients were treated with anti-inflammatory drugs and/or antidepressants. We also identified IFN-γ and IL-2 as putative inflammatory agents associated with depressive symptoms in COPD patients. Prospective studies will need to confirm whether measuring IL-2 and IFN-γ can identify COPD patients at risk of depression. These findings suggest that T helper cell 1-derived cellular immune activation may play significant role in developing depressive symptoms in COPD patients.

Behavioural and neurobiological consequences of macrophage migration inhibitory factor gene deletion in mice

Background

Evidence from clinical studies and animal models show that inflammation can lead to the development of depression. Macrophage migration inhibitory factor (MIF) is an important multifunctional cytokine that is synthesized by several cell types in the brain. MIF can increase production of other cytokines, activates cyclooxygenase (COX)-2 and can counter-regulate anti-inflammatory effects of glucocorticoids. Increased plasma levels of MIF are associated with hypothalamic–pituitary–adrenal (HPA) axis dysregulation and depressive symptoms in patients. In contrast, MIF knockout (KO) mice have been found to exhibit increased depressive-like behaviour. The exact role for MIF in depression is therefore still controversial. To further understand the role of MIF in depression, we studied depressive-like behaviour in congenic male and female MIF KO mice and wild-type (WT) littermates and the associated neurobiological mechanisms underlying the behavioural outcome.

Methods

MIF KO and WT mice were tested for spontaneous locomotor activity in the open-field test, anhedonia-like behaviour in the sucrose preference test (SPT), as well as behavioural despair in the forced swim test (FST) and tail suspension test (TST). Brain and serum levels of cytokines, the enzymes COX-2 and indoleamine-2,3-dioxygenase (IDO) and the glucocorticoid hormone corticosterone were measured by RT-qPCR and/or high-sensitivity electrochemiluminescence-based multiplex immunoassays. Monoamines and metabolites were examined using HPLC.

Results

We found that MIF KO mice of both sexes displayed decreased depressive-like behaviour as measured in the FST. In the TST, a similar, but non-significant, trend was also found. IFN-γ levels were decreased, and dopamine metabolism increased in MIF KO mice. Decreased brain IFN-γ levels predicted higher striatal dopamine levels, and high dopamine levels in turn were associated with reduced depressive-like behaviour. In the SPT, there was a sex-specific discrepancy, where male MIF KO mice showed reduced anhedonia-like behaviour whereas female KO mice displayed increased anhedonia-like behaviour. Our results suggest that this relates to the increased corticosterone levels detected in female, but not male, MIF KO mice.

Conclusions

Our findings support that MIF is involved in the generation of depressive-like symptoms, potentially by the effects of IFN-γ on dopamine metabolism. Our data further suggests a sex-specific regulation of the involved mechanisms.

Cortisol and Inflammatory Biomarkers Predict Poor Treatment Response in First Episode Psychosis

BACKGROUND

Cortisol and inflammatory markers have been increasingly reported as abnormal at psychosis onset. The main aim of our study was to investigate the ability of these biomarkers to predict treatment response at 12 weeks follow-up in first episode psychosis.

METHODS

In a longitudinal study, we collected saliva and blood samples in 68 first episode psychosis patients (and 57 controls) at baseline and assessed response to clinician-led antipsychotic treatment after 12 weeks. Moreover, we repeated biological measurements in 39 patients at the same time we assessed the response. Saliva samples were collected at multiple time points during the day to measure diurnal cortisol levels and cortisol awakening response (CAR); interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-8, IL-10, tumor necrosis factor-α, and interferon-γ (IFN-γ) levels were analyzed from serum samples. Patients were divided into Non-Responders (n = 38) and Responders (n = 30) according to the Remission symptom criteria of the Schizophrenia Working Group Consensus.

RESULTS

At first onset, Non-Responders had markedly lower CAR (d = 0.6, P = .03) and higher IL-6 and IFN-γ levels (respectively, d = 1.0, P = .003 and d = 0.9, P = .02) when compared with Responders. After 12 weeks, Non-Responders show persistent lower CAR (P = .01), and higher IL-6 (P = .04) and IFN-γ (P = .05) when compared with Responders. Comparison with controls show that these abnormalities are present in both patients groups, but are more evident in Non-Responders.

CONCLUSIONS

Cortisol and inflammatory biomarkers at the onset of psychosis should be considered as possible predictors of treatment response, as well as potential targets for the development of novel therapeutic agents.

Harm avoidance involved in mediating the association between nerve growth factor (NGF) gene polymorphisms and antidepressant efficacy in patients with major depressive disorder

BACKGROUND

Antidepressants have variable efficacies in subjects with major depressive disorder (MDD). Nerve growth factor (NGF) has been suggested to play an important role in the pathogenesis of depressive symptoms and the response to antidepressant therapy. The aim of this study was to examine whether NGF gene polymorphisms are associated with the antidepressant therapeutic efficacy in subjects with MDD.

METHODS

A naturalistic follow-up study was carried out on 557 subjects with MDD. Of the enrolled patients, 304 completed the 8-week open-label antidepressant treatment. Seven single-nucleotide polymorphisms (SNPs) of the NGF gene were genotyped. The 21-item Hamilton Depression Rating Scale was used to assess depressive severity from baseline to endpoint. Tridimensional Personality Questionnaire was used to assess baseline personality traits. Single marker and haplotype analyses were conducted. Binary logistic regression was used to calculate odds ratios of remission. Structural equation modeling was used to analyze the predicted mediation effect.

RESULTS

A significant difference in genotype frequencies between remitters and non-remitters was observed in three NGF SNPs (rs12760036, rs7523654, and rs17033692). The haplotype analysis revealed that the CCC haplotype (rs2254527-rs6678788-rs12760036) was associated with a higher remission rate, while the CCA haplotype was associated with a lower remission rate. The harm avoidance psychological factor partially mediated the effect of NGF variants on antidepressant efficacy.

LIMITATIONS

The selected SNPs may not cover whole NGF gene.

CONCLUSIONS

NGF variants are associated with remission rates after 8-week antidepressant treatment, and harm avoidance partially mediated the effect of NGF variants on treatment outcomes.

Neurotrophic factors in depression in response to treatment

BACKGROUND

Brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor A (VEGF) have been suggested to play a role in the pathophysiology of depression. The neurotrophic model of depression hypothesises that the serum level of e.g. BDNF is decreased during depression and increased in response to treatment. The aim of the present study was to investigate BDNF and VEGF as potential predictors of response to antidepressant treatment.

METHODS

We investigated the longitudinal associations between depression scores and serum levels of these neurotrophic factors during antidepressant treatment in 90 individuals with depression of at least moderate severity. Serum levels were measured at baseline and after 8 and 12 weeks of treatment with nortriptyline or escitalopram.

RESULTS

No baseline or longitudinal correlations between depression scores and serum levels of BDNF and VEGF were found, and the baseline serum levels did not predict the MADRS depression score after 12 weeks of treatment or the improvement in depression scores. Interestingly, we observed a significant baseline and longitudinal correlation between serum levels of BDNF and VEGF. The two classes of antidepressant treatment did not affect the results differently.

LIMITATIONS

Information on potential factors influencing the serum levels is missing.

CONCLUSION

Our results do not support the neurotrophic model of depression, since a significant decrease in serum BDNF and VEGF levels after 12 weeks of antidepressant treatment was observed. Our study encourages future studies with large sample sizes, more observations and a longer follow-up period.

Insufficient glucocorticoid signaling and elevated inflammation in coronary heart disease patients with comorbid depression

Coronary heart disease (CHD) and depression are very common and often co-existing disorders. In addition to psychological and social morbidity, depression exacerbates adverse cardiac outcomes in CHD patients. Inflammation has been proposed as one of the mechanisms involved in the association between these two debilitating diseases. Therefore, the present study aimed to evaluate inflammatory responses as well as to investigate the pathophysiological mechanisms underlying the putative inflammatory activation in CHD patients with and without depression, by assessing the function of two important biological factors regulating inflammation, the hypothalamus-pituitary-adrenal (HPA) axis and the glucocorticoid receptor (GR). Eighty-three CHD patients with (n=28) and without (n=55) comorbid depression were recruited from primary care services in South London. Depression status was assessed by means of Clinical Interview Schedule Revised for diagnosis of depression, and Beck Depression Inventory for the presence of depressive symptoms. Serum C-reactive protein (CRP), plasma vascular endothelial growth factor (VEGF), and plasma and salivary cortisol were measured using commercially available ELISA kits. Gene expression of GR and interleukin-6 (IL-6) were conducted via qPCR. GR sensitivity was evaluated in vitro in isolated peripheral blood mononuclear cells using the dexamethasone inhibition of lipopolysaccharide-stimulated IL-6 levels. Serum levels of kynurenine pathway metabolites were measured using high performance liquid chromatography. Our results show that CHD patients with depression had higher levels of CRP, IL-6 gene expression, and VEGF compared with CHD non-depressed, as well as lower plasma and saliva cortisol levels. The CHD depressed group also exhibited a reduction in GR expression and sensitivity. Finally, tryptophan levels were significantly lower in patients with depression, who also showed an increased kynurenine/tryptophan ratio. In conclusion, CHD patients with depression had elevated levels of inflammation in the context of HPA axis hypoactivity, GR resistance, and increased activation of the kynurenine pathway. Reduced cortisol bioavailability and attenuated glucocorticoid responsiveness due to decreased expression and sensitivity of GR may lead to insufficient glucocorticoid signaling and thus elevation of inflammation in these patients.

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.

Interleukin-6 as a predictor of symptom resolution in psychological distress: a cohort study

BACKGROUND

Elevated levels of interleukin-6 (IL-6) have been associated with the development of common mental disorders, such as depression, but its role in symptom resolution is unclear.

METHOD

We examined the association between IL-6 and symptom resolution in a non-clinical sample of participants with psychological distress.

RESULTS

Relative to high IL-6 levels, low levels at baseline were associated with symptom resolution at follow-up [age- and sex-adjusted risk ratio (RR) = 1.15, 95% confidence interval (CI) 1.06-1.25]. Further adjustment for covariates had little effect on the association. Symptomatic participants with repeated low IL-6 were more likely to be symptom-free at follow-up compared with those with repeated high IL-6 (RR = 1.21, 95% CI 1.03-1.41). Among the symptomatic participants with elevated IL-6 at baseline, IL-6 decreased along with symptom resolution.

CONCLUSIONS

IL-6 is potentially related to the mechanisms underlying recovery from symptoms of mental ill health. Further studies are needed to examine these mechanisms and to confirm the findings in relation to clinical depression.

Immune and neurotrophin stimulation by electroconvulsive therapy: is some inflammation needed after all?

A low-grade inflammatory response is commonly seen in the peripheral blood of major depressive disorder (MDD) patients, especially those with refractory and chronic disease courses. However, electroconvulsive therapy (ECT), the most drastic intervention reserved for these patients, is closely associated with an enhanced haematogenous as well as neuroinflammatory immune response, as evidenced by both human and animal studies. A related line of experimental evidence further shows that inflammatory stimulation reinforces neurotrophin expression and may even mediate dramatic neurogenic and antidepressant-like effects following exposure to chronic stress. The current review therefore attempts a synthesis of our knowledge on the neurotrophic and immunological aspects of ECT and other electrically based treatments in psychiatry. Perhaps contrary to contemporary views, we conclude that targeted potentiation, rather than suppression, of inflammatory responses may be of therapeutic relevance to chronically depressed patients or a subgroup thereof.

Depression during pregnancy: molecular regulations of mothers' and children's behaviour

Depression in pregnancy (also called 'antenatal depression') is being increasingly recognized as a clinically relevant condition that affects obstetric outcome, maternal behaviour and children's future mental health. The present review focuses on the molecular mechanisms operating in utero that underlie the potential effects of antenatal depression on mothers' and children's behaviour. In particular, I discuss evidence, coming largely from animal and cellular studies, that activation of the main hormonal stress-response system, the HPA (hypothalamic-pituitary-adrenal) axis, in mothers who are depressed during pregnancy may affect maternal care as well as offspring's behaviour and future psychopathology. The evidence summarized in the present review supports the notion that preventing or treating depression in pregnancy will alleviate not only the suffering of mothers, but also the suffering of the next generation.

Pathogenesis of depression: Insights from human and rodent studies

Major depressive disorder (MDD) will affect one out of every five people in their lifetime and is the leading cause of disability worldwide. Nevertheless, mechanisms associated with the pathogenesis of MDD have yet to be completely understood and current treatments remain ineffective in a large subset of patients. In this review, we summarize the most recent discoveries and insights for which parallel findings have been obtained in human depressed subjects and rodent models of mood disorders in order to examine the potential etiology of depression. These mechanisms range from synaptic plasticity mechanisms to epigenetics and the immune system where there is strong evidence to support a functional role in the development of specific depression symptomology. Ultimately we conclude by discussing how novel therapeutic strategies targeting central and peripheral processes might ultimately aid in the development of effective new treatments for MDD and related stress disorders.

CHL1, ITGB3 and SLC6A4 gene expression and antidepressant drug response: results from the Munich Antidepressant Response Signature (MARS) study

Aim: The identification of antidepressant drugs (ADs) response biomarkers in depression is of high clinical importance. We explored CHL1 and ITGB3 expression as tentative response biomarkers. Materials & methods: In vitro sensitivity to ADs, as well as gene expression and genetic variants of the candidate genes CHL1, ITGB3 and SLC6A4 were measured in lymphoblastoid cell lines (LCLs) of 58 depressed patients. Results: An association between the clinical remission of depression and the basal expression of CHL1 and ITGB3 was discovered. Individuals whose LCLs expressed higher levels of CHL1 or ITGB3 showed a significantly better remission upon AD treatment. In addition individuals with the CHL1 rs1516338 TT genotype showed a significantly better remission after 5 weeks AD treatment than those carrying a CC genotype. No association between the in vitro sensitivity of LCLs toward AD and the clinical remission could be detected. Conclusion: CHL1 expression in patient-derived LCLs correlated with the clinical outcome. Thus, it could be a valid biomarker to predict the success of an antidepressant therapy.

Original submitted 8 December 2014; Revision submitted 2 March 2015

Evidence-based guidelines for treating depressive disorders with antidepressants: A revision of the 2008 British Association for Psychopharmacology guidelines

A revision of the 2008 British Association for Psychopharmacology evidence-based guidelines for treating depressive disorders with antidepressants was undertaken in order to incorporate new evidence and to update the recommendations where appropriate. A consensus meeting involving experts in depressive disorders and their management was held in September 2012. Key areas in treating depression were reviewed and the strength of evidence and clinical implications were considered. The guidelines were then revised after extensive feedback from participants and interested parties. A literature review is provided which identifies the quality of evidence upon which the recommendations are made. These guidelines cover the nature and detection of depressive disorders, acute treatment with antidepressant drugs, choice of drug versus alternative treatment, practical issues in prescribing and management, next-step treatment, relapse prevention, treatment of relapse and stopping treatment. Significant changes since the last guidelines were published in 2008 include the availability of new antidepressant treatment options, improved evidence supporting certain augmentation strategies (drug and non-drug), management of potential long-term side effects, updated guidance for prescribing in elderly and adolescent populations and updated guidance for optimal prescribing. Suggestions for future research priorities are also made.

Inflammation and neuronal plasticity: a link between childhood trauma and depression pathogenesis

During the past two decades, there has been increasing interest in understanding and characterizing the role of inflammation in major depressive disorder (MDD). Indeed, several are the evidences linking alterations in the inflammatory system to Major Depression, including the presence of elevated levels of pro-inflammatory cytokines, together with other mediators of inflammation. However, it is still not clear whether inflammation represents a cause or whether other factors related to depression result in these immunological effects. Regardless, exposure to early life stressful events, which represent a vulnerability factor for the development of psychiatric disorders, act through the modulation of inflammatory responses, but also of neuroplastic mechanisms over the entire life span. Indeed, early life stressful events can cause, possibly through epigenetic changes that persist over time, up to adulthood. Such alterations may concur to increase the vulnerability to develop psychopathologies. In this review we will discuss the role of inflammation and neuronal plasticity as relevant processes underlying depression development. Moreover, we will discuss the role of epigenetics in inducing alterations in inflammation-immune systems as well as dysfunction in neuronal plasticity, thus contributing to the long-lasting negative effects of stressful life events early in life and the consequent enhanced risk for depression. Finally we will provide an overview on the potential role of inflammatory system to aid diagnosis, predict treatment response, enhance treatment matching, and prevent the onset or relapse of Major Depression.

RNA expression profiling in depressed patients suggests retinoid-related orphan receptor alpha as a biomarker for antidepressant response

Response to antidepressant treatment is highly variable with some patients responding within a few weeks, whereas others have to wait for months until the onset of clinical effects. Gene expression profiling may be a tool to identify markers of antidepressant treatment response and new potential drug targets. In a first step, we selected 12 male, age- and severity-matched pairs of remitters and nonresponders, and analyzed expression profiles in peripheral blood at admission and after 2 and 5 weeks of treatment using Illumina expression arrays. We identified 127 transcripts significantly associated with treatment response with a minimal P-value of 9.41 × 10(-)(4) (false discovery rate-corrected). Analysis of selected transcripts in an independent replication sample of 142 depressed inpatients confirmed that lower expression of retinoid-related orphan receptor alpha (RORa, P=6.23 × 10(-4)), germinal center expressed transcript 2 (GCET2, P=2.08 × 10(-2)) and chitinase 3-like protein 2 (CHI3L2, P=4.45 × 10(-2)) on admission were associated with beneficial treatment response. In addition, leukocyte-specific protein 1 (LSP1) significantly decreased after 5 weeks of treatment in responders (P=2.91 × 10(-2)). Additional genetic, in vivo stress responsitivity data and murine gene expression findings corroborate our finding of RORa as a transcriptional marker of antidepressant response. In summary, using a genome-wide transcriptomics approach and subsequent validation studies, we identified several transcripts including the circadian gene transcript RORa that may serve as biomarkers indicating antidepressant treatment response.

New insights into the neurobiological mechanisms of major depressive disorders

OBJECTIVE

To review the current evidence about the neurobiological mechanisms in major depressive disorders (MDD) and the key findings from studies using neuroimaging tools and animal models.

METHOD

This paper gives an overview of the role of genetic and environmental factors in the pathophysiology of MDD and describes the structural changes in brain structures of depressed individuals. A closer look is given at the molecular processes and neurotransmitters implicated in this mental disorder. Moreover, this paper discusses key findings from recent research using animal models and their relevance for clinical applications.

RESULTS

Although the exact cause of MDD is not known, there is enough evidence showing that genetic, psychological and environmental factors significantly increase the risk of developing this disease. Individuals affected by MDD exhibit a reduced volume of structures such as the amygdala, hippocampus and basal ganglia, as well as altered level of neurotransmitters in the brain.

CONCLUSION

The studies presented in this review show promising results that could shed light on the molecular mechanisms of MDD. However, more work needs to be done to better understand this psychiatric disorder and promote the development of new treatment strategies.

SLC6A2 variants may predict remission from major depression after venlafaxine treatment in Han Chinese population

OBJECTIVE

Venlafaxine, an antidepressant of the serotonin-norepinephrine reuptake inhibitor (SNRI) type, is used to treat patients with major depressive disorder (MDD). Much evidence suggests that genetic polymorphisms may modulate serotonergic and noradrenergic function, thereby affecting the treatment efficacy of venlafaxine. The aim of this study was to examine whether polymorphisms in the norepinephrine transporter gene (SLC6A2) associate with remission after venlafaxine treatment for MDD.

METHOD

An 8-week naturalistic treatment study with venlafaxine was carried out in 243 Han Chinese patients with MDD. The patients were screened for seven single-nucleotide polymorphisms of the SLC6A2 gene. Of the enrolled patients, 161 completed the 8-week treatment. The 21-item Hamilton Depression Rating Scale (HDRS) was used to assess the improvement of depressive symptoms in each subject from baseline to the endpoint. For better presentation of time-course change of remission status, a Cox regression analysis for remission incidence during the 8-week treatment was conducted.

RESULTS

Between remitters and non-remitters, significant differences in genotype frequencies were observed in five of the investigated SLC6A2 variants (rs28386840, rs1532701, rs40434, rs13333066, rs187714). GCG haplotype (rs40434 - rs13333066 - rs187714) in the SLC6A2 gene showed a association with non-remission. A Cox regression analysis for remission incidence during the 8-week treatment course significantly depends on SLC6A2 variants (rs28386840, rs40434, and rs187714).

CONCLUSION

Our results suggest that the variation of the SLC6A2 gene is associated with treatment remission after venlafaxine in patients with MDD.

The BDNF Val(66)Met polymorphism is associated with escitalopram response in depressed patients

BACKGROUND

The brain-derived neurotrophic factor (BDNF) gene is a candidate gene in therapeutic responses to antidepressants. The aim of the study was to determine the effects of BDNF allelic variability on responses to escitalopram treatment at 3 weeks after treatment initiation and at a 6-week endpoint.

METHODS

We included 187 Caucasian subjects with depression; 153 completed the 6-week study. Clinical evaluation was performed using the Montgomery and Asberg Depression Rating Scale (MADRS) before and after 3-6 weeks of treatment.

RESULTS

After 3 weeks of treatment, we saw significantly better treatment responses in the Met carriers and greater antidepressant resistance among the Val/Val homozygotes. Relative to Val/Val homozygous (59.78 %), a significantly greater proportion of subjects Met-carriers (77.94 %) responded to escitalopram treatment (χ (2) = 5.88, p = 0.015). After 6 weeks, we found the same pattern of results but this effect did not reach statistical significance (χ (2) = 2.07, p = 0.15).

CONCLUSION

These findings highlight a significant association between the BDNF valine to methionine substitution (Val(66)Met) polymorphism and the treatment response to escitalopram in a Caucasian population of severely depressed inpatients.

Testing the predictive value of peripheral gene expression for nonremission following citalopram treatment for major depression

Major depressive disorder (MDD) in general, and anxious-depression in particular, are characterized by poor rates of remission with first-line treatments, contributing to the chronic illness burden suffered by many patients. Prospective research is needed to identify the biomarkers predicting nonremission prior to treatment initiation. We collected blood samples from a discovery cohort of 34 adult MDD patients with co-occurring anxiety and 33 matched, nondepressed controls at baseline and after 12 weeks (of citalopram plus psychotherapy treatment for the depressed cohort). Samples were processed on gene arrays and group differences in gene expression were investigated. Exploratory analyses suggest that at pretreatment baseline, nonremitting patients differ from controls with gene function and transcription factor analyses potentially related to elevated inflammation and immune activation. In a second phase, we applied an unbiased machine learning prediction model and corrected for model-selection bias. Results show that baseline gene expression predicted nonremission with 79.4% corrected accuracy with a 13-gene model. The same gene-only model predicted nonremission after 8 weeks of citalopram treatment with 76% corrected accuracy in an independent validation cohort of 63 MDD patients treated with citalopram at another institution. Together, these results demonstrate the potential, but also the limitations, of baseline peripheral blood-based gene expression to predict nonremission after citalopram treatment. These results not only support their use in future prediction tools but also suggest that increased accuracy may be obtained with the inclusion of additional predictors (eg, genetics and clinical scales).

Astrocytic TNFα regulates the behavioral response to antidepressants

Recent studies have suggested that cytokines, and in particular tumor necrosis factor alpha (TNFα), have a role in modulating antidepressant efficacy. To directly test this idea, we compared the response of TNFα(-/-) mice and astrocyte-specific TNFα(-/-) mice to the antidepressants fluoxetine and desipramine. Using standard behavior models for measuring antidepressant efficacy, the forced swim test (FST) and tail suspension test (TST), we determined that TNFα(-/-) mice were essentially normal in basal behavior in the FST and TST. However, TNFα(-/-) mice showed no behavioral response to a standard dose of chronic antidepressant treatment, in sharp contrast to wildtype mice. Similar results were seen with acute antidepressant treatment, but TNFα(-/-) mice did respond to a very high-dose acute antidepressant treatment. We also assessed in vitro and in vivo effects of fluoxetine on TNFα expression. Glia responded to serotonin in vitro and fluoxetine in vivo by upregulating TNFα mRNA. Consistent with this source of TNFα, mice with an astrocyte-specific deletion of TNFα also did not respond to standard chronic antidepressant treatment. These data suggest that astrocytic TNFα is important to the sensitivity of the behavioral response to administration of antidepressants.

FKBP5 genotype-dependent DNA methylation and mRNA regulation after psychosocial stress in remitted depression and healthy controls

BACKGROUND

Polymorphisms in the FK506 binding protein 5 (FKBP5) gene have been shown to influence glucocorticoid receptor sensitivity, stress response regulation, and depression risk in traumatized subjects, with most consistent findings reported for the functional variant rs1360780. In the present study, we investigated whether the FKBP5 polymorphism rs1360780 and lifetime history of major depression are associated with DNA methylation and FKBP5 gene expression after psychosocial stress.

METHODS

A total of 116 individuals with a positive (n = 61) and negative (n = 55) lifetime history of major depression participated in the Trier Social Stress Test. We assessed plasma cortisol concentrations, FKBP5 mRNA expression, and CpG methylation of FKBP5 intron 7 in peripheral blood cells.

RESULTS

Genotype-dependent plasma cortisol response to psychosocial stress exposure was observed in healthy controls, with the highest and longest-lasting cortisol increase in subjects with the TT genotype of the FKBP5 polymorphism rs1360780, and healthy controls carrying the T risk allele responded with a blunted FKBP5 mRNA expression after psychosocial stress. No genotype effects could be found in remitted depression.

CONCLUSIONS

The FKBP5 rs1360780 polymorphism is associated with plasma cortisol and FKBP5 mRNA expression after psychosocial stress in healthy controls but not in remitted depression. Preliminary results of the DNA methylation analysis suggest that epigenetic modifications could be involved.

Plasma amino acid profiling in major depressive disorder treated with selective serotonin reuptake inhibitors

AIMS

Amino acids are important body metabolites and seem to be helpful for understanding pathogenesis and predicting therapeutic response in major depressive disorder (MDD). We performed amino acid profiling to discover potential biomarkers in major depressive patients treated with selective serotonin reuptake inhibitors (SSRIs).

METHODS

Amino acid profiling using aTRAQ™ kits for Amino Acid Analysis in Physiological Fluids on a liquid chromatography-tandem mass spectrometry (LC-MS/MS) system was performed on 158 specimens at baseline and at 6 weeks after the initiation of SSRI treatment for 68 patients with MDD and from 22 healthy controls.

RESULTS

Baseline alpha-aminobutyric acid (ABA) discriminated the patients according to the therapeutic response. Plasma glutamic acid concentration and glutamine/glutamic acid ratio were different between before and after SSRI treatment only in the response group. Comparing patients with MDD with healthy controls, alterations of ten amino acids, including alanine, beta-alanine, beta-aminoisobutyric acid, cystathionine, ethanolamine, glutamic acid, homocystine, methionine, O-phospho-L-serine, and sarcosine, were observed in MDD.

CONCLUSION

Metabolism of amino acids, including ABA and glutamic acid, has the potential to contribute to understandings of pathogenesis and predictions of therapeutic response in MDD.

New hypothesis and treatment targets of depression: an integrated view of key findings

Major depressive disorder (MDD) is a common and devastating psychiatric disorder characterized by persistent low mood, cognitive disorder, and impaired social function. Despite its complex mechanisms, increasing evidence has identified the involvement of neurotrophic factors, inflammatory cytokines, the hypothalamus-pituitary-adrenal axis, and glutamate receptors in the pathophysiology of this illness. The present review synthesizes recent research achievements to define the network between different hypotheses of MDD and to understand which part is most pivotal for its pathogenesis. By integrating MDD-related signal pathways, we highlight brain-derived neurotrophic factor (BDNF) dysfunction and increased apoptosis as the final common cascades, and new therapeutic strategies aiming to enhance BDNF function have been shown to exert a rapid and effective antidepressant action.

The Involvement of TNF-α in Cognitive Dysfunction Associated with Major Depressive Disorder: An Opportunity for Domain Specific Treatments

Major depressive disorder is a highly prevalent, chronic and recurring disorder, associated with substantial impairment in cognitive and interpersonal functions. Accumulating evidence suggests that inflammatory processes play an important role in the etio-pathogenesis, phenomenology, comorbidity and treatment of MDD. Suboptimal remission rates and the persistence of cognitive deficits contribute to functional impairment in MDD inviting the need for the development of mechanistically novel and domain specific treatment approaches. The MEDLINE/ Pubmed database was searched from inception to February, 9th, 2014 with combinations of the following search terms: 'TNF-alpha', 'depression', 'infliximab', 'etanercept', 'adalimumab', 'golimumab' and 'certolizumab'. Preclinical and clinical evidence linking TNF-α to MDD pathophysiology were reviewed as well as the current status of TNF-α modulators as novel agents for the treatment of MDD. Experimental models and clinical studies provide encouraging preliminary evidence for the efficacy of TNF- α antagonists in mitigating depressive symptoms and improving cognitive deficits. Further studies are warranted to confirm these data in larger randomized controlled trials in primary psychiatric populations. Translational research provides a promising perspective that may aid the development and/or repurposing of mechanism-based treatments for depressive symptoms and cognitive impairment in MDD.

Gene-environment interaction in major depression: focus on experience-dependent biological systems

Major depressive disorder (MDD) is a multifactorial and polygenic disorder, where multiple and partially overlapping sets of susceptibility genes interact each other and with the environment, predisposing individuals to the development of the illness. Thus, MDD results from a complex interplay of vulnerability genes and environmental factors that act cumulatively throughout individual's lifetime. Among these environmental factors, stressful life experiences, especially those occurring early in life, have been suggested to exert a crucial impact on brain development, leading to permanent functional changes that may contribute to lifelong risk for mental health outcomes. In this review, we will discuss how genetic variants (polymorphisms, SNPs) within genes operating in neurobiological systems that mediate stress response and synaptic plasticity, can impact, by themselves, the vulnerability risk for MDD; we will also consider how this MDD risk can be further modulated when gene × environment interaction is taken into account. Finally, we will discuss the role of epigenetic mechanisms, and in particular of DNA methylation and miRNAs expression changes, in mediating the effect of the stress on the vulnerability risk to develop MDD. Taken together, we aim to underlie the role of genetic and epigenetic processes involved in stress- and neuroplasticity-related biological systems on the development of MDD after exposure to early life stress, thereby building the basis for future research and clinical interventions.

Towards a personalized treatment in depression: endocannabinoids, inflammation and stress response

The complex nature of depression is mirrored by difficulties in tailoring its treatment. Key underlying mechanisms of this mental disorder include elevated inflammation and a dysregulated hypothalamic-pituitary-adrenal (HPA) axis. More recently, the endocannabinoid system has been proposed as another important component in the pathogenesis of depression, and strong evidence suggests that all three systems communicate with each other. A growing number of genetic studies have investigated polymorphisms in depression in each of these systems separately. However, no study to date has looked at these genes in conjunction. In this article we will review the crosstalk between the endocannabinoid system, immune system and HPA axis; and discuss the evidence of gene polymorphisms and their relation to the risk of depression and its treatment. We propose future directions where genes of these three systems are considered from a joint perspective to improve prediction of treatment response, taking into account potentially overlooked genetic variations.

Cytokine variations and mood disorders: influence of social stressors and social support

Stressful events have been implicated in the evolution of mood disorders. In addition to brain neurotransmitters and growth factors, the view has been offered that these disorders might be provoked by the activation of the inflammatory immune system as well as by de novo changes of inflammatory cytokines within the brain. The present review describes the impact of social stressors in animals and in humans on behavioral changes reminiscent of depressive states as well as on cytokine functioning. Social stressors increase pro-inflammatory cytokines in circulation as well as in brain regions that have been associated with depression, varying with the animal's social status and/or behavioral methods used to contend with social challenges. Likewise, in humans, social stressors that favor the development of depression are accompanied by elevated circulating cytokine levels and conversely, conditions that limit the cytokine elevations correlated with symptom attenuation or reversal. The implications of these findings are discussed in relation to the potentially powerful effects of social support, social identity, and connectedness in maintaining well-being and in diminishing symptoms of depression.

Accumulation of cytoplasmic glucocorticoid receptor is related to elevation of FKBP5 in lymphocytes of depressed patients

We have previously shown that patients with the major depressive disorder (MDD) exhibited elevated phosphorylation of the lymphocyte glucocorticoid receptor (GR) at serine 226 (S226). Here, we further analyse potential alterations of GR signalization in lymphocytes of MDD patients, i.e. the cytoplasmic/nuclear distribution of GR, levels of FK506-binding protein 5 (FKBP5) and glucocorticoid-induced leucine zipper (GILZ). The FKBP5 acts as an important regulator of GR activation, by decreasing ligand binding and impeding translocation of the receptor to the nucleus, while GILZ mediates glucocorticoid anti-inflammatory effects. Our result showed that the depressed patients had significantly higher GR levels in the cytoplasm compared to controls, which was accompanied by higher FKBP5 levels. Linear regression model demonstrated significantly higher correlation between FKBP5 and cytoplasmic GR than the presence of MDD itself or phosphorylation of nuclear GR at S226. There were no differences in the levels of GILZ isoforms. Therefore, the results suggest that accumulation of the GR in cytoplasm is related to the elevation of FKBP5, adding one more step in understanding altered GR signalling in lymphocytes, and potentially brain tissue, of MDD patients.

Omega-3 fatty acids in the prevention of interferon-alpha-induced depression: results from a randomized, controlled trial

BACKGROUND

Interferon (IFN)-α therapy for chronic hepatitis C virus infection is frequently associated with depression. The routine prophylaxis with antidepressants might expose patients to adverse effects, hence, the need for alternative preventive interventions. Omega-3 polyunsaturated fatty acids are safe and effective essential nutritional compounds used for the treatment of depression, putatively through an anti-inflammatory action. In addition, lower erythrocyte levels of omega-3 polyunsaturated fatty acids have been associated with an increased risk of IFN-induced depression.

METHODS

We conducted a 2-week, double-blind, placebo-controlled trial comparing eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and placebo for the prevention of IFN-α-induced depression. A total of 162 patients consented to participate and were randomized to the study. All of the patients completed the 2-week trial; 152 participants were followed throughout the 24 weeks of IFN-α treatment and were included in the analysis.

RESULTS

Compared with placebo, the incident rates of IFN-α-induced depression were significantly lower in EPA-treated but not in DHA-treated patients (10% and 28%, respectively, versus 30% for placebo, p = .037). Both EPA and DHA significantly delayed the onset of IFN-induced depression (week of onset: 12.0 and 11.7, respectively, versus 5.3 for placebo, p = .002). EPA and DHA were both well tolerated in this population. EPA treatment increased both EPA and DHA erythrocyte levels, but DHA only increased DHA erythrocyte levels.

CONCLUSIONS

EPA is effective in the prevention of depression in hepatitis C virus patients received IFN-α therapy. Our study confirms the notion that anti-inflammatory strategies are effective antidepressants in the context of depression associated with inflammation.

Brain-derived neurotrophic factor Val66Met polymorphism association with antidepressant efficacy: a systematic review and meta-analysis

INTRODUCTION

Previous studies of the association of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism with antidepressant efficacy are inconsistent. Thus, we conducted a systematic review and meta-analysis.

METHODS

We searched MEDLINE, PubMed, EMBASE, and Chinese Databases (Biomedical Literature Database, National Knowledge Infrastructure, Weipu, and WanFang) up to March 2013 for relevant studies (584 retrieved, 16 met inclusion criteria). We conducted six comparisons for both response and remission rates for three genotypes in Caucasians and Asians (4 weeks or ≥6 weeks; selective serotonin reuptake inhibitors [SSRIs], serotonin-noradrenaline reuptake inhibitors, or mixed antidepressants).

RESULTS

Met carriers had a better response rate than Val/Val. In Asians, the Met carrier was positively associated with response rate (odds ratio; 95% confidence interval: 1.48; 1.02-2.14) in the SSRI group (1.81; 1.10-2.97) and with treatments ≥6 weeks. Met/Val showed a positive association with the response rate versus homozygotes (1.60; 1.20-2.13) and for ≥6 weeks (mixed antidepressant, 1.36; 1.04-1.77; SSRI, 1.55; 1.11-2.17). There was a weak effect of Met/Val versus Val/Val in response to SSRIs (mixed time, 2.07; 1.48-2.89; ≥6 weeks, 2.25; 1.53-3.32). For remission, Met/Val was better than the homozygotes (1.71; 1.09-2.68, Asians, SSRIs only).

DISCUSSION

Our meta-analysis confirms the effects of the BDNF polymorphism on SSRI response in Asians. This effect may be dependent on ethnic origin because BDNF had a lesser influence on response in mixed race studies. Antidepressants were more effective in groups with a treatment duration ≥6 weeks. Thus, future investigators should carefully consider their outcome observation end point.

Cytokine gene variations associated with subsyndromal depressive symptoms in patients with breast cancer

PURPOSE

This study explored the relationships between variations in cytokines genes and depressive symptoms in a sample of patients who were assessed prior to and for six months following breast cancer surgery. Phenotypic differences between Resilient (n = 155) and Subsyndromal (n = 180) depressive symptom classes, as well as variations in cytokine genes were evaluated.

METHOD

Patients were recruited prior to surgery and followed for six months. Growth mixture modeling was used to identify distinct latent classes based on Center for Epidemiological Studies Depression (CES-D) Scale scores. Eighty-two single nucleotide polymorphisms and 35 haplotypes among 15 candidate cytokine genes were evaluated.

RESULTS

Patients in the Subsyndromal class were significantly younger, more likely to be married or partnered, and reported a significantly lower functional status. Variation in three cytokine genes (i.e., interferon gamma receptor 1 (IFNGR1 rs9376268), interleukin 6 (IL6 rs2069840), tumor necrosis factor alpha (TNFA rs1799964)), as well as age and functional status predicted membership in the Subsyndromal versus the Resilient class.

CONCLUSIONS

A variation in TNFA that was associated with Subsyndromal depressive symptoms in a sample of patients and their family caregivers was confirmed in this sample. Variations in cytokine genes may place these patients at higher risk for the development of Subsyndromal levels of depressive symptoms.

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.

Inflammatory and metabolic dysregulation and the 2-year course of depressive disorders in antidepressant users

Scarce evidence suggests that inflammatory and metabolic dysregulation predicts poor response to antidepressants, which could result in worse depression outcome. This study prospectively examined whether inflammatory and metabolic dysregulation predicted the 2-year course of depressive disorders among antidepressant users. Data were from the Netherlands Study of Depression and Anxiety, including 315 persons (18-65 years) with a current depressive disorder (major depressive disorder, dysthymia) at baseline according to the DSM-IV criteria and using antidepressants. Inflammatory (C-reactive protein, interleukin-6 (IL-6), tumor-necrosis factor-α) and metabolic (waist circumference, triglycerides, high-density lipoprotein (HDL) cholesterol, blood pressure, fasting glucose) factors were measured at baseline. Primary outcome for course of depression was indicated by whether or not a DSM-IV depressive disorder diagnosis was still/again present at 2-year follow-up, indicating chronicity of depression. Elevated IL-6, low HDL cholesterol, hypertriglyceridemia, and hyperglycemia were associated with chronicity of depression in antidepressant users. Persons showing ⩾ 4 inflammatory or metabolic dysregulations had a 1.90 increased odds of depression chronicity (95% CI = 1.12-3.23). Among persons who recently (ie, at most 3 months) started antidepressant medication (N = 103), having ⩾ 4 dysregulations was associated with a 6.85 increased odds of depression chronicity (95% CI = 1.95-24.06). In conclusion, inflammatory and metabolic dysregulations were found to predict a more chronic course of depressive disorders among patients using antidepressants. This could suggest that inflammatory and metabolic dysregulation worsens depression course owing to reduced antidepressant treatment response and that alternative intervention treatments may be needed for depressed persons with inflammatory and metabolic dysregulation.

Monitoring candidate gene expression variations before, during and after a first major depressive episode in a 51-year-old man

BACKGROUND

Although psychiatric disorders are frequently characterized by clinical heterogeneity, high recurrence, and unpredictable prognosis, studies of mRNA expression variations in blood cells from psychiatric patients constitute a promising avenue to establish clinical biomarkers. We report here, to our knowledge, the first genetic monitoring of a major depressive episode (MDE).

CASE PRESENTATION

The subject is a 51-year-old male, who was healthy at baseline and whose blood mRNA was monitored over 67 weeks for expression variations of 9 candidate genes. At week 20 the subject experienced a mild to moderate unexpected MDE, and oral antidepressant treatment was initiated at week 29. At week 36, the patient recovered from his MDE. After 6 months, antidepressant treatment was discontinued and the subject remained free of depressive symptoms. Genetic monitoring revealed that mRNA expression of SLC6A4/5HTT increased with the emergence of a depressive state, which later returned to basal levels after antidepressant treatment and during MDE recovery. PDLIM5, S100A10 and TNF mRNA showed also an interesting pattern of expression with regards to MDE evolution.

CONCLUSION

This case demonstrated the applicability of peripheral mRNA expression as a way to monitor the natural history of MDE.

Putative transcriptomic biomarkers in the inflammatory cytokine pathway differentiate major depressive disorder patients from control subjects and bipolar disorder patients

Mood disorders consist of two etiologically related, but distinctly treated illnesses, major depressive disorder (MDD) and bipolar disorder (BPD). These disorders share similarities in their clinical presentation, and thus show high rates of misdiagnosis. Recent research has revealed significant transcriptional differences within the inflammatory cytokine pathway between MDD patients and controls, and between BPD patients and controls, suggesting this pathway may possess important biomarker properties. This exploratory study attempts to identify disorder-specific transcriptional biomarkers within the inflammatory cytokine pathway, which can distinguish between control subjects, MDD patients and BPD patients. This is achieved using RNA extracted from subject blood and applying synthesized complementary DNA to quantitative PCR arrays containing primers for 87 inflammation-related genes. Initially, we use ANOVA to test for transcriptional differences in a 'discovery cohort' (total n = 90) and then we use t-tests to assess the reliability of any identified transcriptional differences in a 'validation cohort' (total n = 35). The two most robust and reliable biomarkers identified across both the discovery and validation cohort were Chemokine (C-C motif) ligand 24 (CCL24) which was consistently transcribed higher amongst MDD patients relative to controls and BPD patients, and C-C chemokine receptor type 6 (CCR6) which was consistently more lowly transcribed amongst MDD patients relative to controls. Results detailed here provide preliminary evidence that transcriptional measures within inflammation-related genes might be useful in aiding clinical diagnostic decision-making processes. Future research should aim to replicate findings detailed in this exploratory study in a larger medication-free sample and examine whether identified biomarkers could be used prospectively to aid clinical diagnosis.

Fresh approaches to antidepressant drug discovery

INTRODUCTION

The success of antidepressant research has long been challenged by a limited mechanistic understanding of depression pathogenesis and antidepressant treatment response. Progress in this field has thereby consistently been hindered by a lack of novel conceptual approaches and sophisticated experimental techniques to dissect the highly intricate neurobiology of depression. Using fresh approaches to investigate the cellular and molecular mechanisms underlying depression will thus be vital for discovery of novel antidepressant targets.

AREAS COVERED

This article provides an overview of some fundamental problems that depression research is currently facing and critically evaluates how these issues could be addressed by future research. It also discusses novel conceptual and technological advances in the field of neuroscience, particularly in regard to how they may help in providing unprecedented insight into the molecular mechanisms of depression pathogenesis.

EXPERT OPINION

Although progress in antidepressant drug discovery has been limited over recent years, modern innovations in neuroscience, molecular biology, genetics and bioinformatics are just beginning to revolutionize depression research and to reveal novel and promising treatment targets. Integrating findings from a range of relevant experimental models and using the most advanced technology will be vital for the future success of antidepressant drug discovery.

Targeting classical IL-6 signalling or IL-6 trans-signalling in depression?

INTRODUCTION

Increased IL-6 and soluble IL-6 receptor (sIL-6R) levels in depressed patients was first shown over 20 years ago. The pro-inflammatory effects of IL-6 are predominantly mediated by IL-6 trans-signalling via the sIL-6R, whereas IL-6R membrane signalling has anti-inflammatory effects.

AREAS COVERED

We review data on IL-6 and sIL-6R in inflammation, depression, animal models of depression and the effects of different classes of antidepressants. The biological context for IL-6 trans-signalling as a pathogenic factor in depression involves its role in the acute phase response, disorders in zinc and the erythron, hypothalamic-pituitary-adrenal axis activation, induction of the tryptophan catabolite pathway, oxidative stress, bacterial translocation, transition towards sensitisation, autoimmune processes and neuroprogression and the multicausal aetiology of depression, considering that psychosocial stressors and comorbid immune-inflammatory diseases are associated with the onset of depression.

EXPERT OPINION

The homeostatic functions of IL-6 imply that ubiquitous IL-6 inhibitors, for example, tocilizumab, may not be the optimal treatment target in depression. A more promising target may be to increase soluble glycoprotein 130 (sgp130) inhibition of IL-6 trans-signalling, while allowing the maintenance of IL-6R membrane signalling. Future research should delineate the effects of treatments with sgp130Fc in combination with antidepressants in various animal models of chronic depression.

The inflammatory cytokines: molecular biomarkers for major depressive disorder?

Cytokines are pleotropic cell signaling proteins that, in addition to their role as inflammatory mediators, also affect neurotransmitter systems, brain functionality and mood. Here we explore the potential utility of cytokine biomarkers for major depressive disorder. Specifically, we explore how genetic, transcriptomic and proteomic information relating to the cytokines might act as biomarkers, aiding clinical diagnosis and treatment selection processes. We advise future studies to investigate whether cytokine biomarkers might differentiate major depressive disorder patients from other patient groups with overlapping clinical characteristics. Furthermore, we invite future pharmacogenetic studies to investigate whether early antidepressant-induced changes to cytokine mRNA or protein levels precede behavioral changes and act as longer-term predictors of clinical antidepressant response.

Kynurenines in CNS disease: regulation by inflammatory cytokines

The kynurenine pathway (KP) metabolizes the essential amino acid tryptophan and generates a number of neuroactive metabolites collectively called the kynurenines. Segregated into at least two distinct branches, often termed the “neurotoxic” and “neuroprotective” arms of the KP, they are regulated by the two enzymes kynurenine 3-monooxygenase and kynurenine aminotransferase, respectively. Interestingly, several enzymes in the pathway are under tight control of inflammatory mediators. Recent years have seen a tremendous increase in our understanding of neuroinflammation in CNS disease. This review will focus on the regulation of the KP by inflammatory mediators as it pertains to neurodegenerative and psychiatric disorders.

Effort-related motivational effects of the pro-inflammatory cytokine interleukin 1-beta: studies with the concurrent fixed ratio 5/ chow feeding choice task

RATIONALE

Effort-related motivational symptoms such as anergia and fatigue are common in patients with depression and other disorders. Research implicates pro-inflammatory cytokines in depression, and administration of cytokines can induce effort-related motivational symptoms in humans.

OBJECTIVES

The present experiments focused on the effects of the pro-inflammatory cytokine interleukin 1-beta (IL-1β) on effort-related choice behavior.

METHODS

Rats were tested on a concurrent fixed ratio 5 lever pressing/chow feeding choice procedure, which assesses the tendency of rats to work for a preferred food (high carbohydrate pellets) in the presence of a concurrently available but less preferred substitute (laboratory chow).

RESULTS

IL-1β (1.0-4.0 μg/kg IP) shifted choice behavior, significantly decreasing lever pressing and increasing intake of the freely available chow. The second experiment assessed the ability of the adenosine A2A antagonist (E)-phosphoric acid mono-[3-[8-[2-(3-methoxyphenyl)vinyl]-7-methyl-2,6-dioxo-1-prop-2-ynyl-1,2,6,7-tetrahydropurin-3-yl] propyl] ester disodium salt (MSX-3) to reverse the behavioral effects of IL-1β. MSX-3 attenuated the effort-related impairments produced by IL-1β, increasing lever pressing and also decreasing chow intake. In the same dose range that shifted effort-related choice behavior, IL-1β did not alter food intake or preference in parallel free-feeding choice studies, indicating that these low doses were not generally suppressing appetite or altering preference for the high carbohydrate pellets. In addition, IL-1β did not affect core body temperature.

CONCLUSIONS

These results indicate that IL-1β can reduce the tendency to work for food, even at low doses that do not produce a general sickness, malaise, or loss of appetite. This research has implications for the involvement of cytokines in motivational symptoms such as anergia and fatigue.

Pharmacogenomic predictors of citalopram treatment outcome in major depressive disorder

OBJECTIVES

A significant proportion of patients with major depressive disorder (MDD) do not improve following treatment with first-line antidepressants and, currently, there are no objective indicators of predictors of antidepressant response. The aim of this study was to investigate pre-treatment peripheral gene expression differences between future remitters and non-responders to citalopram treatment and identify potential pharmacogenomic predictors of response.

METHODS

We conducted a gene expression study using Affymetrix HG-U133 Plus2 microarrays in peripheral blood samples from untreated individuals with MDD (N = 77), ascertained at a community outpatient clinic, prior to an 8-week treatment with citalopram. Gene expression differences were assessed between remitters and non-responders to treatment. Technical validation of significant probesets was carried out by qRT-PCR.

RESULTS

A total of 434 probesets displayed significant correlation to change in score and 33 probesests were differentially expressed between eventual remitters and non-responders. Probesets for SMAD 7 (SMA- and MAD-related protein 7) and SIGLECP3 (sialic acid-binding immunoglobulin-like lectin, pseudogene 3) were the most significant differentially expressed genes following FDR correction, and both were down-regulated in individuals who responded to treatment.

CONCLUSIONS

These findings point to SMAD7 and SIGLECP3 as candidate predictive biomarkers of antidepressant response.

Association between serum brain-derived neurotrophic factor and plasma interleukin-6 in major depressive disorder with melancholic features

Inflammatory processes as well as attenuation of brain-derived neurotrophic factor (BDNF) availability are involved in the pathophysiology of major depressive disorder (MDD). Although it is generally presumed that these two systems interact negatively in the brain, preclinical and human in vitro studies have shown synergistic rather than antagonistic interactions in the periphery. We therefore examined the association between serum levels of BDNF and plasma levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in patients with MDD (n=1070) and non-depressed controls (n=379) from the Netherlands Study of Depression and Anxiety. We used multiple regression analyses with serum BDNF as the dependent variable and we specifically tested the presence of BDNF-cytokine associations in DSM-IV-assigned melancholic MDD patients, identified by the Inventory of Depressive Symptomatology. After adjustment for sociodemographics, sampling variability, lifestyle indicators, somatic diseases and medication use, BDNF levels were predicted by the interaction between MDD diagnosis and IL-6 (p-interaction=.006). Stratified analyses showed that BDNF levels are indeed positively associated with IL-6 levels in MDD patients (β=.07, p=.02), but not in non-depressed controls (β=-.07, p=.23). When further stratified for melancholic and non-melancholic MDD (p-interaction=.005), IL-6 emerged as a robust positive predictor of BDNF only in the melancholic sample (β=.21, p=.01), wherein serum BDNF levels were accordingly enhanced. Post-hoc exploratory analyses verified an accentuated positive association of BDNF levels with leucocyte counts in melancholia. No significant associations emerged between BDNF and TNF-α. Overall, our cross-sectional approach may have disclosed an allostatic, BDNF-inducing component of peripheral immunity and/or an immunotrophic function of peripheral BDNF. Both scenarios may warrant further exploration, as they could inform new research concepts towards immune-based antidepressive treatment strategies.

MIF: mood improving/inhibiting factor?

Although major depressive disorder imposes a serious public health burden and affects nearly one in six individuals in developed countries over their lifetimes, there is still no consensus on its pathophysiology. Inflammation and cytokines have emerged as a promising new avenue in depression research, and, in particular, macrophage migration inhibitory factor (MIF) has been shown to be significant in depression physiology. In this review we summarize current research on MIF and depression. We highlight the arguments for MIF as a pro- and antidepressant species and discuss the potential implications for therapeutics.