Identification of IL6 as a susceptibility gene for major depressive disorder

Association of Single Nucleotide Polymorphisms of Cytokine Genes with Depression, Schizophrenia and Bipolar Disorder

Immune gene variants are known to be associated with the risk of psychiatric disorders, their clinical manifestations, and their response to therapy. This narrative review summarizes the current literature over the past decade on the association of polymorphic variants of cytokine genes with risk, severity, and response to treatment for severe mental disorders such as bipolar disorder, depression, and schizophrenia. A search of literature in databases was carried out using keywords related to depressive disorder, bipolar disorder, schizophrenia, inflammation, and cytokines. Gene lists were extracted from publications to identify common genes and pathways for these mental disorders. Associations between polymorphic variants of the IL1B, IL6, and TNFA genes were the most replicated and relevant in depression. Polymorphic variants of the IL1B, IL6, IL6R, IL10, IL17A, and TNFA genes have been associated with schizophrenia. Bipolar disorder has mainly been associated with polymorphic variants of the IL1B gene. Interestingly, the IL6R gene polymorphism (rs2228145) was associated with all three diseases. Some cytokine genes have also been associated with clinical presentation and response to pharmacotherapy. There is also evidence that some specific polymorphic variants may affect the expression of cytokine genes. Thus, the data from this review indicate a link between neuroinflammation and severe mental disorders.

A Systematic Review of Candidate Genes for Major Depression

Background and Objectives: The aim of this systematic review was to analyse which candidate genes were examined in genetic association studies and their association with major depressive disorder (MDD). Materials and Methods: We searched PUBMED for relevant studies published between 1 July 2012 and 31 March 2019, using combinations of keywords: “major depressive disorder” OR “major depression” AND “gene candidate”, “major depressive disorder” OR “major depression” AND “polymorphism”. Synthesis focused on assessing the likelihood of bias and investigating factors that may explain differences between the results of studies. For selected gene list after literature overview, functional enrichment analysis and gene ontology term enrichment analysis were conducted. Results: 141 studies were included in the qualitative review of gene association studies focusing on MDD. 86 studies declared significant results (p < 0.05) for 172 SNPs in 85 genes. The 13 SNPs associations were confirmed by at least two studies. The 18 genetic polymorphism associations were confirmed in both the previous and this systematic analysis by at least one study. The majority of the studies (68.79 %) did not use or describe power analysis, which may have had an impact over the significance of their results. Almost a third of studies (N = 54) were conducted in Chinese Han population. Conclusion: Unfortunately, there is still insufficient data on the links between genes and depression. Despite the reported genetic associations, most studies were lacking in statistical power analysis, research samples were small, and most gene polymorphisms have been confirmed in only one study. Further genetic research with larger research samples is needed to discern whether the relationship is random or causal. Summations: This systematic review had summarized all reported genetic associations and has highlighted the genetic associations that have been replicated. Limitations: Unfortunately, most gene polymorphisms have been confirmed only once, so further studies are warranted for replicating these genetic associations. In addition, most studies included a small number of MDD cases that could be indicative for false positive. Considering that polymorphism loci and associations with MDD is also vastly dependent on interpersonal variation, extensive studies of gene interaction pathways could provide more answers to the complexity of MDD.

Unravelling the broader complexity of IL-6 involvement in health and disease

The classification of interleukin-6 (IL-6) as a pro-inflammatory cytokine undervalues the biological impact of this cytokine in health and disease. With broad activities affecting the immune system, tissue homeostasis and metabolic processes, IL-6 displays complex biology. The significance of these involvements has become increasingly important in clinical settings where IL-6 is identified as a prominent target for therapy. Here, clinical experience with IL-6 antagonists emphasises the need to understand the context-dependent properties of IL-6 within an inflammatory environment and the anticipated or unexpected consequences of IL-6 blockade. In this review, we will describe the immunobiology of IL-6 and explore the gamut of IL-6 bioactivity affecting the clinical response to biological drugs targeting this cytokine pathway.

Levels of Interleukin 6 as a Predictor of Metabolic Syndrome in Schizophrenic Patients Receiving Combination Therapy of Typical and Atypical Antipsychotics

BACKGROUND: Schizophrenia is a severe psychiatric disorder that causes disability and is often accompanied by physical illness. Based on the American Heart Association criteria, metabolic syndrome is common in schizophrenic patients, with a prevalence of 43% in Clinical Antipsychotic Trials of Intervention Effectiveness. The metabolic syndrome in patients with schizophrenia results from the side effects of antipsychotics. The metabolic syndrome will also show high levels of IL-6. This situation can have biological implications, which can then affect the health of schizophrenic patients. AIM: This study aims to determine serum IL-6 levels as a predictor of metabolic syndrome in patients with metabolic syndrome due to side effects of using antipsychotic therapy. METHODS: This prospective cohort study was not randomized, with the number of subjects was 28 schizophrenic patients who were evenly divided into two groups, namely, the group receiving atypical and typical combination therapy. Therapy was given to both groups for 3 months, and measurements and checks of bodyweight, abdominal circumference, blood pressure, BMI, TG, GDP, and Il-6 levels were carried out at baseline and 3rd month. Comparative and correlation tests were carried out between groups. RESULTS: Some schizophrenic patients were categorized as metabolic syndrome and not a metabolic syndrome in both therapy groups (p < 0.020). However, atypical antipsychotic drug combinations are more likely to experience the metabolic syndrome. There was a change in the mean Il-6 levels at baseline and the 3rd month in both groups (p < 0.0001). There was a more excellent mean value of IL-6 levels at 3rd month with metabolic syndrome than those without metabolic syndrome. There was a greater mean value of IL-6 levels at third month with metabolic syndrome compared with those without metabolic syndrome in the haloperidol and chlorpromazine groups (p <0.005), the risperidone and clozapine groups (p <0.002). CONCLUSION: Metabolic syndrome is more common in schizophrenic patients receiving atypical than typical combination therapy. The body’s response to the metabolic syndrome results in an increase in IL-6 levels due to an inflammatory process in visceral fat which accumulates due to weight gain due to the administration of antipsychotics. In schizophrenic patients with metabolic syndrome, IL-6 levels are higher than those without metabolic syndrome, so that IL-6 levels can be used as a predictor of metabolic syndrome in schizophrenic patients receiving antipsychotic therapy.

Childhood maltreatment correlates with higher concentration of transforming growth factor beta (TGF-β) in adult patients with major depressive disorder

Transforming growth factor beta (TGF-β), which has a role as a regulatory cytokine, has not been widely investigated in patients with major depressive disorder (MDD) who experienced childhood trauma. The aim of our study was to investigate the differences in circulating TGF-β levels between the patients with major depressive disorder (MDD) with and without child maltreatment (CM) history, and to compare them to the corresponding control subjects' groups (with or without CM). Blood samples were obtained from 55 patients, fulfilling DSM-IV-R criteria for a current MDD episode without psychotic symptoms, and 45 healthy controls, matched for age and gender. Participants were administered the Childhood Trauma Questionnaire (CTQ). Serum TGF-β concentration was determined by enzyme-linked immunosorbent assay. The concentration of TGF-β was significantly higher in patients with MDD with CM history, compared to MDD patients with no CM, as well as both control groups. Furthermore, we have shown that the combined effect of CM history and MDD affected TGF-β levels in adulthood, which was not observed in the control group with CM. These results indicate that MDD patients with the experience of CM have altered immune-regulatory response, and they may constitute a specific subtype within this heterogenic disorder (ecophenotype).

Potential depression and antidepressant-response biomarkers in human lymphoblast cell lines from treatment-responsive and treatment-resistant subjects: roles of SSRIs and omega-3 polyunsaturated fatty acids

While several therapeutic strategies exist for depression, most antidepressant drugs require several weeks before reaching full biochemical efficacy and remission is not achieved in many patients. Therefore, biomarkers for depression and drug-response would help tailor treatment strategies. This study made use of banked human lymphoblast cell lines (LCLs) from normal and depressed subjects; the latter divided into remitters and non-remitters. Due to the fact that previous studies have shown effects on growth factors, cytokines, and elements of the cAMP-generating system as potential biomarkers for depression and antidepressant action, these were examined in LCLs. Initial gene and protein expression profiles for signaling cascades related to neuroendocrine and inflammatory functions differ among the three groups. Growth factor genes, including VEGFA and BDNF were significantly down-regulated in cells from depressed subjects. In addition, omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been reported to act as both antidepressants and anti-inflammatories, but the mechanisms for these effects are not established. Here we showed that n-3 PUFAs and escitalopram (selective serotonin reuptake inhibitors, SSRIs) treatment increased adenylyl cyclase (AC) and BDNF gene expression in LCLs. These data are consistent with clinical observations showing that n-3 PUFA and SSRI have antidepressant affects, which may be additive. Contrary to observations made in neuronal and glial cells, n-3 PUFA treatment attenuated cAMP accumulation in LCLs. However, while lymphoblasts show paradoxical responses to neurons and glia, patient-derived lymphoblasts appear to carry potential depression biomarkers making them an important tool for studying precision medicine in depressive patients. Furthermore, these data validate usefulness of n-3 PUFAs in treatment for depression.

Genome-wide association study of circulating interleukin 6 levels identifies novel loci

Interleukin 6 (IL-6) is a multifunctional cytokine with both pro- and anti-inflammatory properties with a heritability estimate of up to 61%. The circulating levels of IL-6 in blood have been associated with an increased risk of complex disease pathogenesis. We conducted a two-staged, discovery and replication meta genome-wide association study (GWAS) of circulating serum IL-6 levels comprising up to 67 428 (ndiscovery = 52 654 and nreplication = 14 774) individuals of European ancestry. The inverse variance fixed effects based discovery meta-analysis, followed by replication led to the identification of two independent loci, IL1F10/IL1RN rs6734238 on chromosome (Chr) 2q14, (Pcombined = 1.8 × 10-11), HLA-DRB1/DRB5 rs660895 on Chr6p21 (Pcombined = 1.5 × 10-10) in the combined meta-analyses of all samples. We also replicated the IL6R rs4537545 locus on Chr1q21 (Pcombined = 1.2 × 10-122). Our study identifies novel loci for circulating IL-6 levels uncovering new immunological and inflammatory pathways that may influence IL-6 pathobiology.

Inflammatory Genotype Moderates the Association Between Anxiety and Systemic Inflammation in Adults at Risk for Cardiovascular Disease

BACKGROUND

Cardiovascular disease is a significant health problem in the United States, attributed to more than 30% of all deaths annually. Anxiety has been associated with cardiovascular disease risk and is thought to be associated with cardiovascular disease risk through inflammatory pathways.

OBJECTIVE

The purposes of this study were to examine the relationship between anxiety and systemic inflammation in individuals at risk for cardiovascular disease and to determine if single-nucleotide polymorphisms (SNPs) associated with inflammation moderate this relationship.

METHODS

A secondary analysis was conducted using baseline data from a study investigating the impact of genetics on response to a cardiovascular disease risk reduction intervention. Anxiety was measured using the Brief Symptom Inventory. Protein levels for C-reactive protein and interleukin-6 (IL-6) were measured in serum, and genomic DNA was assayed for SNPs in the C-reactive protein, IL-6, and IL-6R genes. Multiple linear regressions were performed to examine if anxiety predicted inflammation and if SNPs moderated associations.

RESULTS

Participants (N = 398) were white, aged 51 ± 13 years, and 73% women. There was a significant interaction between rs4129267 genotype and anxiety (P = .010), with the association significant only for individuals with the CC genotype (b = 0.243, SE = 0.04, P < .001). No moderation effect existed for rs1205 or rs1800797.

CONCLUSION

Anxiety was positively associated with IL-6 protein levels, but moderation analysis indicated that this was significant only for individuals with the rs4129267 CC genotype. This suggests that genotypic differences may exist in anxiety response, placing certain individuals at higher risk for inflammation and, subsequently, cardiovascular disease.

A Comprehensive Analysis of the Effect of SIRT1 Variation on the Risk of Schizophrenia and Depressive Symptoms

Depressive symptoms could be considered a mutual manifestation of major depressive disorder and schizophrenia. Rs3758391 is a functional locus of Sirtuin (SIRT1) involving depression etiology. In this study, we hypothesized that the SIRT1 SNP rs3758391 might be a hazard for schizophrenia pathogenesis, especially related to the appearance of depressive symptoms. We recruited 723 healthy controls and 715 schizophrenia patients, the occurrence of psychotic and depressive symptoms was evaluated by Calgary Depression Scale (CDSS) and PANSS. Meanwhile, qt-PCR was used to detect the mRNA levels of SIRT1 in peripheral blood of 197 olanzapine monotherapy schizophrenia patients. 45.6% of schizophrenia patients had depressive symptoms. In the patient group, mRNA levels of patients with depressive symptoms were significantly lower than those without depressive symptoms (P < 0.01). CDSS scores of schizophrenia patients with different rs3758391 genotypes were significantly different (P < 0.01). Post hoc comparisons indicated that the CDSS scores of rs3758391 C/C and C/T carriers were higher than those of T/T carriers (Ps < 0.01). In the occipital cortex, our eQTL analysis showed that there was a clear correlation between rs3758391 and the SIRT1 mRNA levels. Our preliminary findings provide suggestive evidence that SIRT1 makes schizophrenia patients more prone to depressive symptoms. This SNP might be a biomarker of depression in schizophrenia.

Origin and Function of Stress-Induced IL-6 in Murine Models

Acute psychological stress has long been known to decrease host fitness to inflammation in a wide variety of diseases, but how this occurs is incompletely understood. Using mouse models, we show that interleukin-6 (IL-6) is the dominant cytokine inducible upon acute stress alone. Stress-inducible IL-6 is produced from brown adipocytes in a beta-3-adrenergic-receptor-dependent fashion. During stress, endocrine IL-6 is the required instructive signal for mediating hyperglycemia through hepatic gluconeogenesis, which is necessary for anticipating and fueling "fight or flight" responses. This adaptation comes at the cost of enhancing mortality to a subsequent inflammatory challenge. These findings provide a mechanistic understanding of the ontogeny and adaptive purpose of IL-6 as a bona fide stress hormone coordinating systemic immunometabolic reprogramming. This brain-brown fat-liver axis might provide new insights into brown adipose tissue as a stress-responsive endocrine organ and mechanistic insight into targeting this axis in the treatment of inflammatory and neuropsychiatric diseases.

Identification of a functional human-unique 351-bp Alu insertion polymorphism associated with major depressive disorder in the 1p31.1 GWAS risk loci

Genome-wide association studies (GWAS) have reported substantial single-nucleotide polymorphisms (SNPs) associated with major depressive disorder (MDD), but the underlying functional variations in the GWAS risk loci are unclear. Here we show that the European MDD genome-wide risk-associated allele of rs12129573 at 1p31.1 is associated with MDD in Han Chinese, and this SNP is in strong linkage disequilibrium (LD) with a human-unique Alu insertion polymorphism (rs70959274) in the 5' flanking region of a long non-coding RNA (lncRNA) LINC01360 (Long Intergenic Non-Protein Coding RNA 1360), which is preferably expressed in human testis in the currently available expression datasets. The risk allele at rs12129573 is almost completely linked with the absence of this Alu insertion. The Alu insertion polymorphism (rs70959274) is significantly associated with a lower RNA level of LINC01360 and acts as a transcription silencer likely through modulating the methylation of its internal CpG sites. Luciferase assays confirm that the presence of Alu insertion at rs70959274 suppresses transcriptional activities in human cells, and deletion of the Alu insertion through CRISPR/Cas9-directed genome editing increases RNA expression of LINC01360. Deletion of the Alu insertion in human cells also leads to dysregulation of gene expression, biological processes and pathways relevant to MDD, such as the alterations of mRNA levels of DRD2 and FLOT1, transcription of genes involved in synaptic transmission, neurogenesis, learning or memory, and the PI3K-Akt signaling pathway. In summary, we identify a human-unique DNA repetitive polymorphism in robust LD with the MDD risk-associated SNP at the prominent 1p31.1 GWAS loci, and offer insights into the molecular basis of the illness.

Role of Interleukin-6 in Depressive Disorder

Major depressive disorder (MDD), which is a leading psychiatric illness across the world, severely affects quality of life and causes an increased incidence of suicide. Evidence from animal as well as clinical studies have indicated that increased peripheral or central cytokine interleukin-6 (IL-6) levels play an important role in stress reaction and depressive disorder, especially physical disorders comorbid with depression. Increased release of IL-6 in MDD has been found to be a factor associated with MDD prognosis and therapeutic response, and may affect a wide range of depressive symptomatology. However, study results of the IL6 genetic effects in MDD are controversial. Increased IL-6 activity may cause depression through activation of hypothalamic-pituitary-adrenal axis or influence of the neurotransmitter metabolism. The important role of neuroinflammation in MDD pathogenesis has created a new perspective that the combining of blood IL-6 and other depression-related cytokine levels may help to classify MDD biological subtypes, which may allow physicians to identify the optimal treatment for MDD patients. To modulate the IL-6 activity by IL-6-related agents, current antidepressive agents, herb medication, pre-/probiotics or non-pharmacological interventions may hold great promise for the MDD patients with inflammatory features.

The Relationship between DNA Methylation and Antidepressant Medications: A Systematic Review

Major depressive disorder (MDD) is the leading cause of disability worldwide and is associated with high rates of suicide and medical comorbidities. Current antidepressant medications are suboptimal, as most MDD patients fail to achieve complete remission from symptoms. At present, clinicians are unable to predict which antidepressant is most effective for a particular patient, exposing patients to multiple medication trials and side effects. Since MDD’s etiology includes interactions between genes and environment, the epigenome is of interest for predictive utility and treatment monitoring. Epigenetic mechanisms of antidepressant medications are incompletely understood. Differences in epigenetic profiles may impact treatment response. A systematic literature search yielded 24 studies reporting the interaction between antidepressants and eight genes (BDNF, MAOA, SLC6A2, SLC6A4, HTR1A, HTR1B, IL6, IL11) and whole genome methylation. Methylation of certain sites within BDNF, SLC6A4, HTR1A, HTR1B, IL11, and the whole genome was predictive of antidepressant response. Comparing DNA methylation in patients during depressive episodes, during treatment, in remission, and after antidepressant cessation would help clarify the influence of antidepressant medications on DNA methylation. Individuals’ unique methylation profiles may be used clinically for personalization of antidepressant choice in the future.

Effect of the interleukin 10 polymorphisms on interleukin 10 production and visceral hypersensitivity in Chinese patients with diarrhea-predominant irritable bowel syndrome

Background:

Irritable bowel syndrome (IBS), a functional gastrointestinal disorder, is characterized by cytokine imbalance. Previously, decreased plasma interleukin 10 (IL-10) level was reported in patients with IBS, which may be due to genetic polymorphisms. However, there are no reports correlating the IL-10 polymorphisms with IL-10 production in patients with IBS. This study aimed to analyze the effect of IL-10 polymorphisms on IL-10 production and its correlation with the clinical symptoms in Chinese patients with diarrhea-predominant IBS (IBS-D).

Methods:

Two IL-10 single nucleotide polymorphisms (rs1800871 and rs1800896) were detected in 120 patients with IBS-D and 144 healthy controls (HC) using SNaPshot. IBS symptom severity score, Bristol scale, hospital anxiety, and depressive scale (HADS) were used to evaluate the clinical symptoms, as well as the psychological status and visceral sensitivity of the subjects. IL-10 levels in the plasma and peripheral blood mononuclear cell (PBMC) culture supernatant were measured using enzyme-linked immunosorbent assay, while those in ileal and colonic mucosal biopsies were measured using immunohistochemistry.

Results:

The frequency of rs1800896 C allele was significantly lower in the patients with IBS-D than that in the HC (odds ratio: 0.49, 95% confidence interval: 0.27–0.92, P = 0.0240). The IL-10 levels in the plasma (P = 0.0030) and PBMC culture supernatant (P = 0.0500) of the CT genotype subjects were significantly higher than those in the TT genotype subjects. The CT genotype subjects exhibited a higher pain threshold in the rectal distention test than the TT genotype subjects. Moreover, IL-10 rs1800871 GG genotype subjects showed an increase in the HADS score compared to other genotype subjects.

Conclusions:

IL-10 rs1800896 C allele is correlated with higher IL-10 levels in the plasma and the PBMC culture supernatant, which is associated with a higher pain threshold in the Chinese patients with IBS-D. This study provides an explicit relationship of IL-10 polymorphisms with IL-10 production, which might help in understanding the pathogenesis of IBS-D.

Genetic Advance in Depressive Disorder

Major depressive disorder (MDD) and bipolar disorder (BPD) are both chronic, severe mood disorder with high misdiagnosis rate, leading to substantial health and economic burdens to patients around the world. There is a high misdiagnosis rate of bipolar depression (BD) just based on symptomology in depressed patients whose previous manic or mixed episodes have not been well recognized. Therefore, it is important for psychiatrists to identify these two major psychiatric disorders. Recently, with the accumulation of clinical sample sizes and the advances of methodology and technology, certain progress in the genetics of major depression and bipolar disorder has been made. This article reviews the candidate genes for MDD and BD, genetic variation loci, chromosome structural variation, new technologies, and new methods.

Novel Treatment Targets Based on Insights in the Etiology of Depression: Role of IL-6 Trans-Signaling and Stress-Induced Elevation of Glutamate and ATP

Inflammation and psychological stress are risk factors for major depression and suicide. Both increase central glutamate levels and activate the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Both factors also affect the function of the chloride transporters, Na-K-Cl-cotransporter-1 (NKCC1) and K-Cl-cotransporter-2 (KCC2), and provoke interleukin-6 (IL-6) trans-signaling. This leads to measurable increases in circulating corticosteroids, catecholamines, anxiety, somatic and psychological symptoms, and a decline in cognitive functions. Recognition of the sequence of pathological events allows the prediction of novel targets for therapeutic intervention. Amongst others, these include blockade of the big-K potassium channel, blockade of the P2X4 channel, TYK2-kinase inhibition, noradrenaline α2B-receptor antagonism, nicotinic α7-receptor stimulation, and the Sgp130Fc antibody. A better understanding of downstream processes evoked by inflammation and stress also allows suggestions for tentatively better biomarkers (e.g., SERPINA3N, MARCKS, or ¹³C-tryptophan metabolism).

Genetics of IL6 polymorphisms: Case-control study of the risk of endometrial cancer

Background

Endometrial cancer is the most common gynaecological malignancy. Cytokines gene may be important in endometrial cancer development. This study sought to investigate whether the IL4, IL6 two gene genetic variants were associated with susceptibility to endometrial cancer (EC) in Hainan Chinese Han women by a hospital‐based study.

Methods

The genetic polymorphisms for IL4 and IL6 were analyzed by Agena MassARRAY method. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by unconditional logistic regression.

Results

We observed a significant increase in risk of endometrial cancer of rs1524107 (IL6) (T/C, OR = 1.61, 95% CI = 1.09–2.37, p = 1.55 × 10⁻²), rs2066992 (IL 6) (OR = 3.09, 95% CI = 2.11–4.53, p = 3.13 × 10⁻⁹). However, for IL4 gene, no associations emerged the SNP and EC risk.

Conclusion

This study demonstrated that IL6 gene polymorphisms are significantly associated with increased EC susceptibility in Hainan Chinese Han women.

High concentrations of serum interleukin-6 and interleukin-8 in patients with bipolar disorder

Immune system dysregulation plays a key role in the physiopathology of bipolar disorder (BD) and major depressive disorder (MDD). However, whether interleukins might be biomarkers to distinguish these 2 affective disorders is unclear. Here, we assessed the differences in serum levels of interleukin 6 (IL-6) and interleukin 8 (IL-8) as well as C-reactive protein (CRP) in patients with MDD and BD. In total, we enrolled 21 MDD patients, 26 BD patients, and 20 healthy controls. We collected a total of 35 samples from BD patients in 3 different phases, depression phase, manic phase, and remission stage, and 27 samples from MDD patients in acute and remission phases. Serum IL-6 and IL-8 levels were assessed with solid phase sandwich ELISA-based quantitative arrays, and CRP levels were determined with an automatic analyzer. Both serum IL-6 and IL-8 levels were elevated in BD patients but not MDD patients. Subgroup analysis indicated elevated serum IL-6 in both the depression and manic phases in BD patients. The serum CRP levels did not change in either BD or MDD patients. However, sex differences in CRP concentrations were observed in healthy controls. Furthermore, there were linear correlations between the CRP levels and Bech-Rafaelsen Mania Rating Scale (BRMS) scores in BD patients. IL-6 and IL-8 levels may serve as biomarkers to differentiate between MDD and BD patients, even when the clinical manifestations are atypical. IL-6 may be used for the differential diagnosis of MDD and depressive episodes in BD.

Association between IL-6 and metabolic syndrome in schizophrenia patients treated with second-generation antipsychotics

OBJECTIVE

Second-generation antipsychotics (SGAs) have a high risk of causing metabolic syndrome (MetS). There is accumulating evidence supporting the fact that the activation of inflammatory pathway contributes to the development of MetS and further aggravates cognitive impairment. This study aimed to investigate the relationship between interleukin-6 (IL-6), cognitive function, and MetS in schizophrenia patients treated with SGAs.

METHODS

One hundred and seventy-four patients with schizophrenia using SGAs were divided into MetS and non-MetS group, based on the criteria of the National Cholesterol Education Program's Adult Treatment Panel III. Cognitive function was measured using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). A total of 138 patients and 29 healthy controls were examined in the plasma IL-6 levels.

RESULTS

The prevalence of MetS in schizophrenia patients treated with SGAs was 33% in this study. There were no significant differences in cognitive functions (both RBANS total score and subscale score) between MetS and non-Mets patients (P>0.05). Patients with MetS had higher plasma levels of IL-6 compared to non-MetS patients (P=0.019). However, such difference was only found in male patients (male: P=0.012; female: P=0.513). The partial correlational analysis further showed that IL-6 levels were notably negative related to the HDL levels in male schizophrenia patients after age, years of education, body mass index (BMI), age of onset, total disease course, and equal dose of olanzapine were controlled (male: P=0.009; female: P=0.450). In addition, the multiple regression analysis (stepwise model) performed in the male patient subgroup showed that IL-6 (beta =-0.283, t=-2.492, P=0.015) was an independent contributor to the HDL levels. However, the IL-6 was not an independent contributor to the HDL levels in female patients.

CONCLUSION

Our findings provide evidence suggesting that the immune-inflammatory effect of IL-6 on SGAs-induced MetS may be in a gender manner.

Reduced immunity to measles in adults with major depressive disorder

BACKGROUND

Depression can impair the immunogenicity of vaccine administration in adults. Whereas many vaccinations are administered in childhood, it is not known whether adolescent or adult onset depression is associated with impairments in the maintenance of protection of childhood vaccines. This study tested the hypothesis that individuals with adolescent or adult onset mood disorders would display compromised immunity to measles, a target of childhood vaccination.

METHODS

IgG antibodies to measles were quantified using a solid phase immunoassay in volunteers with bipolar disorder (BD, n = 64, mean age of onset = 16.6 ± 5.6), currently depressed individuals with major depressive disorder (cMDD, n = 85, mean age of onset = 17.9 ± 7.0), remitted individuals with a history of MDD (rMDD, n = 82, mean age of onset = 19.2 ± 8.6), and non-depressed comparison controls (HC, n = 202), all born after the introduction of the measles vaccine in the USA in 1963.

RESULTS

Relative to HC, both the cMDD group (p = 0.021, adjusted odds ratios (OR) = 0.47, confidence interval (CI) = 0.24-0.90), and the rMDD group (p = 0.038, adjusted OR = 0.50, CI = 0.26-0.97) were less likely to test seropositive for measles. Compared with unmedicated MDD participants, currently medicated MDD participants had a longer lifetime duration of illness and were less likely to test seropositive for measles.

CONCLUSIONS

Individuals with adolescent or adult onset MDD are less likely to test seropositive for measles. Because lower IgG titers are associated with increased risk of measles infection, MDD may increase the risk and severity of infection possibly because of impaired maintenance of vaccine-related protection from measles.

Association between increased serum interleukin-6 levels and sustained attention deficits in patients with major depressive disorder

BACKGROUND

The pathophysiology of cognitive impairment in patients with the major depressive disorder (MDD) may involve neuroinflammation mediated by cytokines.

OBJECTIVE

The aim of this study was to examine the serum interleukin-6 (IL-6) levels, sustained attention, and their association in patients with MDD.

METHODS

Thirty patients with MDD and 30 healthy controls were enrolled in this case-control study. Sustained attention was measured using the Rapid Visual Information Processing (RVP) task in the Cambridge Neuropsychological Tests Automated Battery. The serum IL-6 levels of all subjects were assessed by sandwich enzyme-linked immunosorbent assays.

RESULTS

There were significant differences in the log10RVP total hits, log10RVP total misses, and log10RVP mean latency between patients with MDD and healthy controls (F = 6.04, p = 0.017; F = 19.77, p < 0.0001; F = 14.42, p < 0.0001, respectively). The serum levels of Log10IL-6 were significantly higher in patients with MDD than in healthy controls (F = 192.27, p < 0.0001). The log10IL-6 levels were also positively correlated with the log10RVP mean latency in patients with MDD (r = 0.45, p = 0.013). A further stepwise multivariate regression analysis indicated that the log10IL-6 levels were significantly associated with the log10RVP mean latency in patients with MDD (β = 0.31, t = 2.41, p = 0.025).

CONCLUSIONS

Our data suggested that increased IL-6 levels were associated with the psychopathology of MDD, and that abnormal IL-6 levels were implicated in the impairment of sustained attention in patients with MDD.

Different levels of pro- and anti-inflammatory cytokines in patients with unipolar and bipolar depression

BACKGROUND

Immune system dysregulation is critical in the physiopathology of major depressive disorder (MDD) and bipolar disorder (BD). However, it is unclear whether both diseases present the same inflammatory patterns during depressive episodes. We explored the differences in pro- and anti-inflammatory cytokines between unipolar and bipolar depression (BDD) and the trajectory of these cytokines after acute-phase treatment.

METHODS

Sixty-four MDD patients, 61 BDD patients, and 62 healthy controls (HCs) were enrolled. We assessed the clinical features and cytokines plasma levels at baseline and week 12. The pro-inflammatory cytokines (IL-6, TNF-α) and anti-inflammatory cytokines (IL-4, IL-13) of all subjects were assessed by multiplexed sandwich ELISA-based quantitative arrays.

RESULTS

Before acute-phase treatment, the initial levels of TNF-α and IL-13 were significantly lower in the BDD patients than in the MDD patients. The results demonstrated that there was no relationship between each cytokine level and clinical features of unipolar and bipolar depressions. After 12 weeks, TNF-α, IL-4, and IL-13 levels became lower in MDD patients than in the other two groups regardless of the patients' response to treatment while the levels of TNF-α and IL-4 increased only in the BDD responders.

LIMITATIONS

The effects of different drugs on inflammatory cytokines in MDD or BDD could not be explored further due to the relatively small sample size.

CONCLUSION

Even within the same depressive states, MDD and BDD patients present different inflammatory features, particularly in regard to pro-inflammatory TNF-α and anti-inflammatory IL-13. In addition, the fluctuations of cytokines induced by medication may provide a hint regarding the prediction of treatment response.

Higher concentration of interleukin 6 - A possible link between major depressive disorder and childhood abuse

Little is known about the correlation between IL-6 and childhood abuse and neglect which may be risk factors for the development of affective disorders in adulthood. The aim of this study was to analyze differences in serum concentrations of IL-6 between patients with major depressive disorder and healthy controls, and to investigate possible correlations with adverse childhood experiences. Peripheral venous blood samples were obtained from 64 patients who fulfilled DSM-IV-R criteria for a current major depressive episode without psychotic symptoms (MDD) and 53 healthy controls, matched for age and gender. Participants were assessed by the Beck Depression Inventory (BDI), Childhood Trauma Questionnaire (CTQ), Hamilton Depression Rating Scale (HDRS) and Hamilton Anxiety Rating Scale (HARS). The concentration of IL-6 was significantly higher in patients with major depressive disorder compared to healthy controls. The total score of childhood trauma questionnaire highly statistically significantly correlated with IL-6 levels in patient group. Persons who were physically abused, physically neglected and emotionally abused had higher levels of IL-6. Interleukin 6 as a pro-inflammatory immune marker could be an important developmental mediator linking physical and emotional abuse in early life with the development of depressive disorder in adulthood.

The Gene Encoding Protocadherin 9 (PCDH9), a Novel Risk Factor for Major Depressive Disorder

Genomic analyses have identified only a handful of robust risk loci for major depressive disorder (MDD). In addition to the published genome-wide significant genes, it is believed that there are undiscovered 'treasures' underlying the current MDD genome-wide association studies (GWASs) and gene expression data sets, and digging into these data will allow better understanding of the illness and development of new therapeutic approaches. For this purpose, we performed a meta-analytic study combining three MDD GWAS data sets (23andMe, CONVERGE, and PGC), and then conducted independent replications of significant loci in two additional samples. The genome-wide significant variants then underwent explorative analyses on MDD-related phenotypes, cognitive function alterations, and gene expression in brains. In the discovery meta-analysis, a previously unidentified single-nucleotide polymorphism (SNP) rs9540720 in the PCDH9 gene was genome-wide significantly associated with MDD (p=1.69 × 10^-8 in a total of 89 610 cases and 246 603 controls), and the association was further strengthened when additional replication samples were included (p=1.20 × 10^-8 in a total of 136 115 cases and 355 275 controls). The risk SNP was also associated with multiple MDD-related phenotypes and cognitive function impairment in diverse samples. Intriguingly, the risk allele of rs9540720 predicted lower PCDH9 expression, consistent with the diagnostic analysis results that PCDH9 mRNA expression levels in the brain and peripheral blood tissues were reduced in MDD patients compared with healthy controls. These convergent lines of evidence suggest that PCDH9 is likely a novel risk gene for MDD. Our study highlights the necessity and importance of excavating the public data sets to explore risk genes for MDD, and this approach is also applicable to other complex diseases.

The effects of interleukin-6 neutralizing antibodies on symptoms of depressed mood and anhedonia in patients with rheumatoid arthritis and multicentric Castleman's disease

Cytokines, including interleukin-6 (IL-6), modulate neuronal plasticity and stress coping. Depressive symptoms and major depressive disorder (MDD) have been associated with changes in cytokines and their signaling. The current study examined the effect of IL-6 monoclonal antibody administration on depressive symptoms in patients with rheumatoid arthritis (RA) or multicentric Castleman's disease (MCD). The data were obtained from two phase 2, double-blind, placebo-controlled trials designed to test the efficacy of sirukumab in RA (N=176) or of siltuximab in MCD (N=65), and were analyzed post hoc to investigate the effects of these IL-6 antibodies on depressive symptoms. The SF-36 questionnaire items on depressed-mood and anhedonia were combined as the measure for depressive symptoms. The study participants were grouped by the presence/absence of prevalent depressed mood and anhedonia (PDMA, meaning either depressed mood or anhedonia was present at least 'most of the time' and the other at least 'some of the time' for four weeks) at baseline; 26.1% of the RA sample and 15.4% of the MCD sample met criteria for PDMA at baseline. Compared with placebo, sirukumab and siltuximab produced significantly greater improvements on depressive symptoms. To account for an effect on mood due to changes in RA or MCD, the analysis was (1) adjusted for symptom severities using DAS28-CRP for RA and MCDOS for MCD alone or together with bodily pain and physical functioning, and (2) performed within RA and MCD non-responders. Improvement in depressive symptoms remained significant in the treated group for both drugs. The significance over placebo was also observed in the siltuximab study. The improvement in depressive symptoms by sirukumab correlated positively with the baseline soluble IL-6 receptor levels. The data together suggest that the IL-6 antibodies improve depressive symptoms in patients with RA and MCD. Further studies are needed to elucidate to what extents the IL-6 antibodies improve depressive symptoms through improving primary disease dependent and independent mechanisms, especially in RA patients, and the brain mechanisms underlying depressive symptom improvements.

Investigating the epigenetic profile of the inflammatory gene IL-6 in late-life depression

BACKGROUND

It is well established that there is a link between inflammation and depression, with several studies reporting increased circulating levels of the pro-inflammatory cytokine, interleukin-6 (IL6), in depressed individuals. Peripheral epigenetic marks, including DNA methylation, hold promise as biomarkers for a range of complex conditions, with potential to inform diagnosis and tailor interventions. The aim of this study was to determine whether individuals with depression display differential methylation of the IL6 gene promoter compared to individuals without depression.

METHODS

The ESPRIT study of later life neuropsychiatric disorders used a random sampling framework to select non-institutionalised participants aged ≥65 years and over living in the Montpellier region of France. Major depressive disorder (MDD) was assessed using the Mini International Neuropsychiatric Interview (MINI) according to DSM-IV criteria. High levels of depressive symptoms were defined as a score of ≥16 on the Centre for Epidemiologic Studies Depression Scale (CES-D). IL6 promoter DNA methylation was measured on a sub-sample of 380 participants who provided buccal samples.

RESULTS

Individuals with depression (current MDD or high depressive symptoms) had lower IL6 methylation levels at one of the four sites investigated, however the effect size was small (∆ 2.4%, SE 0.009, p = 0.006). Interestingly, antidepressant use was independently associated with higher IL-6 methylation at the same site (∆ 4.6%, SE 0.019, p = 0.015). In multivariate linear regression analyses adjusting for covariates, including sex and smoking status, these associations remained. There was no effect modification when considering IL6 genotype.

CONCLUSION

This study presents evidence that IL6 methylation may be a marker of depression status in older individuals, however further work is now needed to replicate these findings and to assess the association with inflammatory status of individuals.

The NCAN gene: schizophrenia susceptibility and cognitive dysfunction

BACKGROUND

Cognitive dysfunction has been recognized as a cardinal feature of schizophrenia. Elucidating the neurobiological substrates of cognitive dysfunction in schizophrenia would help identify the underlying mechanism of this disorder. The rs1064395 single nucleotide polymorphism, within the gene encoding neurocan (NCAN), is reported to be associated with schizophrenia in European populations and may influence brain structure in patients with schizophrenia.

METHODS

In this study, we aimed to explore whether NCAN rs1064395 confers some risk for schizophrenia and cognitive dysfunction in Han Chinese. We recruited 681 patients with schizophrenia and 699 healthy subjects. Two hundred and fifty-four patients were evaluated according to Repeatable Battery for the Assessment of Neuropsychological Status (RBANS).

RESULTS

There were no significant differences in genotype or allele distributions of the rs1064395 polymorphism between the schizophrenia and control groups. Patients showed significantly poorer performance than controls on immediate memory, visuospatial skill, language, attention, delayed memory, and total RBANS score. Patients with the A/A or A/G genotype of rs1064395 had lower scores of immediate memory, visuospatial skill, attention, and total RBANS score than those with the G/G genotype. We performed an expression quantitative trait loci analysis and observed a significant association between rs1064395 and NCAN expression in the frontal (P=0.0022, P=0.022 after Bonferroni correction) and cerebellar cortex (P=0.0032, P=0.032 after Bonferroni correction).

CONCLUSION

Our findings indicate that this single nucleotide polymorphism may be a risk factor for cognitive dysfunction in patients with schizophrenia. Further investigations are warranted for validation purposes and to identify the precise mechanism by which rs1064395 influences cognitive performance in patients with schizophrenia.