Promoter variants in IL18 are associated with onset of depression in patients previously exposed to stressful-life events

Cytokine gene polymorphisms and suicide risk in an Indian ancestral population: A case-control study

BACKGROUND

India currently accounts for a majority of global suicide deaths. Research in European ancestry has established that suicide mortality has a significant genetic component, and suggests that inflammation may play a crucial role in the pathophysiology of suicide. Inflammation is also highly relevant in regions of increased pollution exposure, such as the megacities of India. To address the existing gaps in genetic research on suicide and possible association with inflammatory biomarkers, we examined genetic polymorphism and clinical risk phenotypes in a population-based suicide-death cohort, India.

MATERIAL AND METHODS

Genotyping of IL-1β(rs16944) & (rs1143627), IL-4(rs2070874), IL-6(rs1800795) and IL-10(rs1800896) was done in 234 post-mortem suicide-death cases and 256 post-mortem controls (N = 490) using PCR RFLP method.

RESULTS

Our analyses identified three significant (p < 0.001) associations of cytokine variants with suicide death, including IL-1β(rs16944), OR = 0.627; IL-4(rs2070874), OR = 0.524; and IL-6(rs1800795), OR = 2.509. Cases were more likely female and were more likely to have a history of psychiatric illness, though rate of psychiatric illness was low in suicide cases(9%).

CONCLUSION

Our genetic results are generally consistent with previous research on risk for depression and suicidal behaviour, and both genetic and phenotypic results provide new insights into risk factors that may contribute to suicide in India.

Network pharmacology- and molecular docking-based investigation on the mechanism of action of Si-ni San in the treatment of depression combined with anxiety and experimental verification in adolescent rats

Background

The incidence rate of adolescent depression and anxiety has been increasing since the outbreak of COVID-19, which there are no effective therapeutic drugs available. Si-ni San is commonly used in traditional Chinese medicine for the treatment of depression-like as well as anxiety-like behavior, but its mechanism for treating depression combined with anxiety during adolescence is not yet clear.

Methods

Network pharmacology was used to explore potential drug molecules and related targets, molecular docking and molecular dynamics (MD) simulation were used to evaluate the interaction between the potential drug molecules and related targets, and a model of anxiety combined with depression in adolescent rats as well as the following behavioral tests and molecular biology tests were used to verify the results from network pharmacology and molecular docking.

Results

As a result, 256 active ingredients of Si-ni San and 1128 potential targets were screened out. Among them, quercetin, Luteolin, kaempferol, 7-Methoxy-2-methyl isoflavone, formononetin showed to be the most potential ingredients; while STAT3, IL6, TNF, AKT1, AKT1, TP53, IL1B, MAPK3, VEGFA, CASP3, MMP9 showed to be the most potential targets. AGE-RAGE signaling pathway in diabetic complications, IL-17 signaling pathway, HIF-1 signaling pathway, PI3K-Akt signaling pathway and TNF signaling pathway, which are involved in anti-inflammation processes, showed to be the most probable pathways regulated by Si-ni San. Molecular docking and MD simulation between the compounds to inflammation-associated targets revealed good binding abilities of quercetin, Luteolin, kaempferol, nobiletin and formononetin to PTGS2 and PPARγ. In the experiment with adolescent rats, Si-ni San markedly suppressed early maternal separation (MS) combined with adolescent chronic unpredictable mild stress (CUMS)-induced depression combined with anxiety. The qPCR results further indicated that Si-ni San regulated the oxidative stress and inflammatory response.

Conclusion

This study demonstrates that adolescent anxiety- and depression-like behavior induced by MS combined CUMS can be ameliorated by Si-ni San by improved inflammation in hippocampus via targeting TNF pathway and Nrf2 pathway, helping to reveal the mechanism of Si-ni San in treating adolescent depression combined with anxiety.

The relationship of peripheral blood cell inflammatory biomarkers and psychological stress in unmedicated major depressive disorder

BACKGROUND

Recent research has explored the linkage between major depressive disorder (MDD) and inflammation, especially via altered peripheral blood immune markers. However, the relationship between several novel leukocyte-derived ratios (LDR) and psychological stress in MDD remains uncertain. This study aimed to explore the relationship between LDR, clinical characteristics, recent life events, and childhood maltreatment in MDD patients.

METHODS

A cross-sectional case-control study was conducted involving 59 healthy controls (HC) and 50 unmedicated MDD patients. Subjects underwent psychological assessments and peripheral blood measurements. LDR assessed in this study included neutrophil-to-lymphocyte ratio (NLR), derived NLR (dNLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), white blood cell-to-mean platelet volume ratio (WMR), systemic immune inflammation index (SII), multiplication of neutrophil and monocyte counts (MNM), and systemic inflammation response index (SIRI).

RESULTS

MDD patients displayed significant alterations in WMR, PLR, and MNM compared to HC, as well as correlations between several LDR and various clinical features (duration of untreated psychosis and dNLR, the nine-item Patient Health Questionnaire and PLR, the 7-item Generalized Anxiety Disorder Questionnaire and SIRI (NLR and dNLR). There was a significant difference in the comparison of WMR in first-episode patients than in recurrent patients. Analyses further revealed an association between Life Event Scale total scores and NLR (dNLR). No correlation was found between Childhood Trauma Questionnaire total (or subscale) scores and LDR. Additionally, WMR and dNLR presented potential predictive value for distinguishing between MDD and HC.

CONCLUSION

The study concludes that MDD and some clinical features are associated with alterations in some peripheral blood LDR. These findings emphasize the potential role of peripheral blood LDR in the pathogenesis and clinical heterogeneity of MDD.

A Combined Effect of Polygenic Scores and Environmental Factors on Individual Differences in Depression Level

The risk of depression could be evaluated through its multifactorial nature using the polygenic score (PGS) approach. Assuming a "clinical continuum" hypothesis of mental diseases, a preliminary assessment of individuals with elevated risk for developing depression in a non-clinical group is of high relevance. In turn, epidemiological studies suggest including social/lifestyle factors together with PGS to address the "missing heritability" problem. We designed regression models, which included PGS using 27 SNPs and social/lifestyle factors to explain individual differences in depression levels in high-education students from the Volga-Ural region (VUR) of Eurasia. Since issues related to population stratification in PGS scores may lead to imprecise variant effect estimates, we aimed to examine a sensitivity of PGS calculated on summary statistics of depression and neuroticism GWAS from Western Europeans to assess individual proneness to depression levels in the examined sample of Eastern Europeans. A depression score was assessed using the revised version of the Beck Depression Inventory (BDI) in 1065 young adults (age 18-25 years, 79% women, Eastern European ancestry). The models based on weighted PGS demonstrated higher sensitivity to evaluate depression level in the full dataset, explaining up to 2.4% of the variance (p = 3.42 × 10^-7); the addition of social parameters enhanced the strength of the model (adjusted r² = 15%, p < 2.2 × 10^-16). A higher effect was observed in models based on weighted PGS in the women group, explaining up to 3.9% (p = 6.03 × 10^-9) of variance in depression level assuming a combined SNPs effect and 17% (p < 2.2 × 10^-16)-with the addition of social factors in the model. We failed to estimate BDI-measured depression based on summary statistics from Western Europeans GWAS of clinical depression. Although regression models based on PGS from neuroticism (depression-related trait) GWAS in Europeans were associated with a depression level in our sample (adjusted r² = 0.43%, p = 0.019-for unweighted model), the effect was mainly attributed to the inclusion of social/lifestyle factors as predictors in these models (adjusted r² = 15%, p < 2.2 × 10^-16-for unweighted model). In conclusion, constructed PGS models contribute to a proportion of interindividual variability in BDI-measured depression in high-education students, especially women, from the VUR of Eurasia. External factors, including the specificity of rearing in childhood, used as predictors, improve the predictive ability of these models. Implementation of ethnicity-specific effect estimates in such modeling is important for individual risk assessment.

The NLRP3 inflammasome in depression: Potential mechanisms and therapies

Increasing evidence suggests that the failure of clinical antidepressants may be related with neuroinflammation. The NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome is an intracellular multiprotein complex, and has been considered as a key contributor to the development of neuroinflammation. Inhibition of NLRP3 inflammasome is an effective method for depression treatment. In this review, we summarized current researches highlighting the role of NLRP3 inflammasome in the pathology of depression. Firstly, we discussed NLRP3 inflammasome activation in patients with depression and animal models. Secondly, we outlined the possible mechanisms driving the activation of NLRP3 inflammasome. Thirdly, we discussed the pathogenetic role of NLRP3 inflammasome in depression. Finally, we overviewed the current and potential antidepressants targeting the NLRP3 inflammasome. Overall, the inhibition of NLRP3 inflammasome activation may be a potential therapeutic strategy for inflammation-related depression.

Interleukin-18 in metabolism: From mice physiology to human diseases

Interleukin-18 (IL-18) is a classical member of the IL-1 superfamily of cytokines. As IL-1β, IL-18 precursor is processed by inflammasome/caspase-1 into a mature and biologically active form. IL-18 binds to its specific receptor composed of two chains (IL-18Rα and IL-18Rβ) to trigger a similar intracellular signaling pathway as IL-1, ultimately leading to activation of NF-κB and inflammatory processes. Independently of this IL-1-like signaling, IL-18 also specifically induces IFN-γ production, driving the Th1 immune response. In circulation, IL-18 binds to the IL-18 binding protein (IL-18BP) with high affinity, letting only a small fraction of free IL-18 able to trigger receptor-mediated signaling. In contrast to other IL-1 family members, IL-18 is produced constitutively by different cell types, suggesting implications in normal physiology. If the roles of IL-18 in inflammatory processes and infectious diseases are well described, recent experimental studies in mice have highlighted the action of IL-18 signaling in the control of energy homeostasis, pancreatic islet immunity and liver integrity during nutritional stress. At the same time, clinical observations implicate IL-18 in various metabolic diseases including obesity, type 1 and 2 diabetes and nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). In the present review, we summarize and discuss both the physiological actions of IL-18 in metabolism and its potential roles in pathophysiological mechanisms leading to the most common human metabolic disorders, such as obesity, diabetes and NAFLD/NASH.

Preliminary investigation of two promoter region polymorphisms of the TNFA gene in patients with recurrent depressive disorder

Immune system dysregulation plays a role in the pathogenesis of complex human diseases, including psychiatric disorders. In addition, elevated levels of pro-inflammatory cytokines, including tumor necrosis factor α (TNF-α) may be conditioned by the presence of specific polymorphic variants. The present case-controlled preliminary study evaluated the prevalence of TNFA gene single nucleotide polymorphisms (SNPs) G-308A (rs1800629) and T-1031C (rs1799964) in 83 Polish patients with depression by restriction fragment length polymorphism analysis. The results were compared with the frequencies of genotypes in a geographically- and ethnically-matched group of individuals without depression. No statistically significant difference in genotype/allele frequency was observed for either SNP between the two groups. No association was found between the particular genotypes and selected demographic/clinical features, including sex, age at diagnosis or severity of depressive symptoms before/after pharmacotherapy. Thus, there does not appear to be any connection between the studied SNPs and the development and progression of depression; however, further studies are required with larger cohorts to better understand this aspect of depression.

The effects of genotype on inflammatory response in hippocampal progenitor cells: A computational approach

Cell culture models are valuable tools to study biological mechanisms underlying health and disease in a controlled environment. Although their genotype influences their phenotype, subtle genetic variations in cell lines are rarely characterised and taken into account for in vitro studies. To investigate how the genetic makeup of a cell line might affect the cellular response to inflammation, we characterised the single nucleotide variants (SNPs) relevant to inflammation-related genes in an established hippocampal progenitor cell line (HPC0A07/03C) that is frequently used as an in vitro model for hippocampal neurogenesis (HN). SNPs were identified using a genotyping array, and genes associated with chronic inflammatory and neuroinflammatory response gene ontology terms were retrieved using the AmiGO application. SNPs associated with these genes were then extracted from the genotyping dataset, for which a literature search was conducted, yielding relevant research articles for a total of 17 SNPs. Of these variants, 10 were found to potentially affect hippocampal neurogenesis whereby a majority (n=7) is likely to reduce neurogenesis under inflammatory conditions. Taken together, the existing literature seems to suggest that all stages of hippocampal neurogenesis could be negatively affected due to the genetic makeup in HPC0A07/03C cells under inflammation. Additional experiments will be needed to validate these specific findings in a laboratory setting. However, this computational approach already confirms that in vitro studies in general should control for cell lines subtle genetic variations which could mask or exacerbate findings.

Depression: Biological markers and treatment

Nowadays depression is considered as a systemic illness with different biological mechanisms involved in its etiology, including inflammatory response, hypothalamic-pituitary-adrenal (HPA) axis dysregulation and neurotransmitter and neurotrophic systems imbalance. Novel "omics" approaches, such as metabolomics and glycomics provide information about altered metabolic pathways and metabolites, as well as disturbances in glycosylation processes affected by or causing the development of depression. The clinical diagnosis of depression continues to be established based on the presence of the specific symptoms, but due to its heterogeneous underlying biological background, that differs according to the disease stage, there is an unmet need for treatment response biomarkers which would facilitate the process of appropriate treatment selection. This paper provides an overview of the role of major stress response system, the HPA axis, and its dysregulation in depression, possible involvement of neurotrophins, especially brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor and insulin-like growth factor-1, in the development of depression. Article discusses how activated inflammation processes and increased cytokine levels, as well as disturbed neurotransmitter systems can contribute to different stages of depression and could specific metabolomic and glycomic species be considered as potential biomarkers of depression. The second part of the paper includes the most recent findings about available medical treatment of depression. The described biological factors impose an optimistic conclusion that they could represent easy obtainable biomarkers potentially predicting more personalized treatment and diagnostic options.

Inflammation-Associated Synaptic Alterations as Shared Threads in Depression and Multiple Sclerosis

In the past years, several theories have been advanced to explain the pathogenesis of Major Depressive Disorder (MDD), a neuropsychiatric disease that causes disability in general population. Several theories have been proposed to define the MDD pathophysiology such as the classic "monoamine-theory" or the "glutamate hypothesis." All these theories have been recently integrated by evidence highlighting inflammation as a pivotal player in developing depressive symptoms. Proinflammatory cytokines have been indeed claimed to contribute to stress-induced mood disturbances and to major depression, indicating a widespread role of classical mediators of inflammation in emotional control. Moreover, during systemic inflammatory diseases, peripherally released cytokines circulate in the blood, reach the brain and cause anxiety, anhedonia, social withdrawal, fatigue, and sleep disturbances. Accordingly, chronic inflammatory disorders, such as the inflammatory autoimmune disease multiple sclerosis (MS), have been associated to higher risk of MDD, in comparison with overall population. Importantly, in both MS patients and in its experimental mouse model, Experimental Autoimmune Encephalomyelitis (EAE), the notion that depressive symptoms are reactive epiphenomenon to the MS pathology has been recently challenged by the evidence of their early manifestation, even before the onset of the disease. Furthermore, in association to such mood disturbance, inflammatory-dependent synaptic dysfunctions in several areas of MS/EAE brain have been observed independently of brain lesions and demyelination. This evidence suggests that a fine interplay between the immune and nervous systems can have a huge impact on several neurological functions, including depressive symptoms, in different pathological conditions. The aim of the present review is to shed light on common traits between MDD and MS, by looking at inflammatory-dependent synaptic alterations associated with depression in both diseases.

The cytokine network in the pathogenesis of major depressive disorder. Close to translation?

Major depressive disorder (MDD) is a common condition that afflicts the general population across a broad spectrum of ages and social backgrounds. MDD has been identified by the World Health Organization as a leading cause of disability worldwide. Approximately 30% of patients are poor responsive to standard of care (SOC) treatment and novel therapeutic approaches are warranted. Since chronic inflammation, as it is often observed in certain cancers, type 2 diabetes, psoriasis and chronic arthritis, are accompanied by depression, it has been suggested that immunoinflammatory processes may be involved in the pathogenesis of MDD. Cytokines are a group of glycoproteins secreted from lymphoid and non-lymphoid cells that orchestrate immune responses. It has been suggested that a dysregulated production of cytokines may be implicated in the pathogenesis and maintenance of MDD. On the basis of their functions, cytokines can be subdivided in pro-inflammatory and anti-inflammatory cytokines. Since abnormal blood and cerebrospinal fluid of both pro and anti-inflammatory cytokines are altered in MDD, it has been suggested that abnormal cytokine homeostasis may be implicated in the pathogenesis of MDD and possibly to induction of therapeutic resistance. We review current data that indicate that cytokines may represent a useful tool to identify MDD patients that may benefit from tailored immunotherapeutic approaches and may represent a potential tailored therapeutic target.

Plasma levels of Interleukin 18 but not amyloid-β or Tau are elevated in female depressive patients

BACKGROUND

Depression is associated with inflammation and Alzheimer's disease (AD). However, detailed molecular mechanisms linking mood, neuroinflammation and AD remain unclear. Although changes in peripheral inflammatory factors such as Interleukin 18 (IL18), and AD-associated amyloid-β (Aβ) peptides have been linked to depression, a solid relationship between these factors in depressive disorder has yet to be established. This study aims to further determine whether plasma IL18, Aβ40, Aβ42, and the AD-associated tangle component Tau, as well as IL18 single nucleotide polymorphisms (SNPs) may be biomarkers for depression.

METHODS

We measured plasma IL18, Aβ40, Aβ42, and Tau in 64 depressive patients and 75 healthy controls, and characterized genotypes of three IL18 SNPs (rs187238, rs1946518 and rs1946519) in these subjects. Comparisons between depressive patients and controls were carried out in males, in females or in combination. Regression analyses were conducted to examine the correlation between these parameters.

RESULTS

We found that none of the plasma levels of IL18, Aβ40, Aβ42, and Tau, the ratio of Aβ42/Aβ40, and the genotypes of IL18 SNPs were significantly different between combined depressive patients and combined healthy controls, or between male depressive patients and male controls. However, IL18 levels were less in females than in males in healthy people and were significantly increased in female depressive patients compared to female controls. Moreover, IL18 and standardized IL18 were correlated with standardized Aβ42/Aβ40 ratio and standardized Tau in depressive patients.

CONCLUSIONS

Plasma IL18 may be a potential biomarker for depression in women.

Association study of polymorphisms within inflammatory genes and methylation status in treatment response in major depression

Background:

Although pharmacogenetics for major depressive disorder (MDD) is gaining momentum, the role of genetics in differences in response to antidepressant treatment is controversial, as they depend on multifactorial and polygenic phenotypes. Previous studies focused on the genes of the serotonergic system, leaving apart other pathological factors such as the inflammatory pathway. The main objective of the study was to assess whether treatment response might be associated with specific inflammation-related genetic variants or their methylation status.

Methods:

41 SNPs in 8 inflammatory genes: interleukin (IL) 1-β, IL2, IL6, IL6R, IL10, IL18, tumor necrosis factor (TNF)-α and interferon (IFN)-γ were genotyped in 153 patients with MDD, who were evaluated with the Mausdley Staging Method to determine treatment response profiles. Pyrosequencing reactions and methylation quantification were performed in a PyroMark Q24 in 5 selected CpG islands of IL1- β, IL6 and IL6R. Linear and logistic regression analyses were conducted, including age and gender as covariates using PLINK 1.07.

Results:

Allelic distribution of IL1- β rs1143643 was significantly associated with MSM scores (FDR corrected p = 0.04). Allelic distribution of IL6R rs57569414 showed a trend towards significance with MSM scores (p = 0.002; FDR corrected p = 0.07). Haplotype analyses showed associations between allelic combinations of IL1-β and IL10 with treatment response (FDR corrected p < 0.01). Methylation percentage of treatment responders was only higher in an IL6R CpG island (p < 0.05).

Conclusions:

These exploratory findings suggest that IL1-β and, marginally, IL6R polymorphisms may affect treatment response in major depression. If confirmed, these results may account for the heterogeneous phenotypes of major depression that underlie differences in treatment response.

The Innate Immune System and Inflammatory Priming: Potential Mechanistic Factors in Mood Disorders and Gulf War Illness

Gulf War Illness is a chronic multisystem disorder affecting approximately a third of the Veterans of the Gulf War, manifesting with physical and mental health symptoms such as cognitive impairment, neurological abnormalities, and dysregulation of mood. Among the leading theories into the etiology of this multisystem disorder is environmental exposure to the various neurotoxins encountered in the Gulf Theatre, including organophosphates, nerve agents, pyridostigmine bromide, smoke from oil well fires, and depleted uranium. The relationship of toxin exposure and the pathogenesis of Gulf War Illness converges on the innate immune system: a nonspecific form of immunity ubiquitous in nature that acts to respond to both exogenous and endogenous insults. Activation of the innate immune system results in inflammation mediated by the release of cytokines. Cytokine mediated neuroinflammation has been demonstrated in a number of psychiatric conditions and may help explain the larger than expected population of Gulf War Veterans afflicted with a mood disorder. Several of the environmental toxins encountered by soldiers during the first Gulf War have been shown to cause upregulation of inflammatory mediators after chronic exposure, even at low levels. This act of inflammatory priming, by which repeated exposure to chronic subthreshold insults elicits robust responses, even after an extended period of latency, is integral in the connection of Gulf War Illness and comorbid mood disorders. Further developing the understanding of the relationship between environmental toxin exposure, innate immune activation, and pathogenesis of disease in the Gulf War Veterans population, may yield novel therapeutic targets, and a greater understanding of disease pathology and subsequently prevention.

Neuroimmunomodulation in Major Depressive Disorder: Focus on Caspase 1, Inducible Nitric Oxide Synthase, and Interferon-Gamma

Major depressive disorder (MDD) is one of the leading causes of disability worldwide, and its incidence is expected to increase. Despite tremendous efforts to understand its underlying biological mechanisms, MDD pathophysiology remains elusive and pharmacotherapy outcomes are still far from ideal. Low-grade chronic inflammation seems to play a key role in mediating the interface between psychological stress, depressive symptomatology, altered intestinal microbiology, and MDD onset. We review the available pre-clinical and clinical evidence of an involvement of pro-inflammatory pathways in the pathogenesis, treatment, and remission of MDD. We focus on caspase 1, inducible nitric oxide synthase, and interferon gamma, three inflammatory systems dysregulated in MDD. Treatment strategies aiming at targeting such pathways alone or in combination with classical therapies could prove valuable in MDD. Further studies are needed to assess the safety and efficacy of immune modulation in MDD and other psychiatric disorders with neuroinflammatory components.

Principles of inflammasome priming and inhibition: Implications for psychiatric disorders

The production of inflammatory proteins by the innate immune system is a tightly orchestrated procedure that allows the body to efficiently respond to exogenous and endogenous threats. Recently, accumulating evidence has indicated that disturbances in the inflammatory response system not only provoke autoimmune disorders, but also can have deleterious effects on neuronal function and mental health. As inflammation in the brain is primarily mediated by microglia, there has been an expanding focus on the mechanisms through which these cells initiate and propagate neuroinflammation. Microglia can enter persistently active states upon their initial recognition of an environmental stressor and are thereafter prone to elicit amplified and persistent inflammatory responses following subsequent exposures to stressors. A recent focus on why primed microglia cells are susceptible to environmental insults has been the NLRP3 inflammasome. Its function within the innate immune system is regulated in such a manner that supports a role for the complex in gating neuroinflammatory responses. The activation of NLRP3 inflammasome in microglia results in the cleavage of zymogen inflammatory interleukins into functional forms that elicit a number of consequential effects in the local neuronal environment. There is evidence to support the principle that within primed neuroimmune systems a lowered threshold for NLRP3 activation can cause persistent neuroinflammation or the amplified production of inflammatory cytokines, such as IL-1β and IL-18. Over the course of an individual's lifetime, persistent neuroinflammation can subsequently lead to the pathophysiological signatures that define psychological disorders. Therefore, targeting the NLRP3 inflammasome complex may represent an innovative and consequential approach to limit neuroinflammatory states in psychiatric disorders, such as major depressive disorder.

NLRP3 inflammasome-driven pathways in depression: Clinical and preclinical findings

Over the past three decades, an intricate interaction between immune activation, release of pro-inflammatory cytokines and changes in brain circuits related to mood and behavior has been described. Despite extensive efforts, questions regarding when inflammation becomes detrimental or how we can target the immune system to develop new therapeutic strategies for the treatment of psychiatric disorders remain unresolved. In this context, novel aspects of the neuroinflammatory process activated in response to stressful challenges have recently been documented in major depressive disorder (MDD). The Nod-like receptor pyrin containing 3 inflammasome (NLRP3) is an intracellular multiprotein complex responsible for a number of innate immune processes associated with infection, inflammation and autoimmunity. Recent data have demonstrated that NLRP3 activation appears to bridge the gap between immune activation and metabolic danger signals or stress exposure, which are key factors in the pathogenesis of psychiatric disorders. In this review, we discuss both preclinical and clinical evidence that links the assembly of the NLRP3 complex and the subsequent proteolysis and release of the pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18) in chronic stress models and patients with MDD. Importantly, we also focus on the therapeutic potential of targeting the NLRP3 inflammasome complex to improve stress resilience and depressive symptoms.

Altered serum levels of TNF-α, IL-6, and IL-18 in depressive disorder patients

OBJECTIVE

Depressive disorder is associated with abnormal changes in cytokines levels. This study aimed to assess serum concentrations of tumor necrosis factor (TNF) α, interleukin (IL) 6, and IL-18 in depressive patients. The correlations between these three cytokine concentrations and the patients' clinical characteristics were also assessed.

METHODS

Serum TNF-α, IL-6, and IL-18 concentrations were assessed using enzyme-linked immunosorbent assay from 64 depressive patients and 80 healthy control subjects. Depressive symptoms of patients were assessed using Hamilton Depression Scale-17.

RESULTS

Depressive patients had increased serum TNF-α and IL-6 concentrations but decreased IL-18 concentrations than controls. TNF-α and IL-6 concentrations were significantly positively associated with Hamilton Depression Scale-17 scores in depressive patients.

CONCLUSION

These findings provided additional evidence that altered TNF-α, IL-6, and IL-18 activities may contribute to the pathophysiology of depressive disorder.

The Role of Interleukin-18, Oxidative Stress and Metabolic Syndrome in Alzheimer's Disease

The role of interleukins (ILs) and oxidative stress (OS) in precipitating neurodegenerative diseases including sporadic Alzheimer's disease (AD), requires further clarification. In addition to neuropathological hallmarks-extracellular neuritic amyloid-β (Aβ) plaques, neurofibrillary tangles (NFT) containing hyperphosphorylated tau and neuronal loss-chronic inflammation, as well as oxidative and excitotoxic damage, are present in the AD brain. The pathological sequelae and the interaction of these events during the course of AD need further investigation. The brain is particularly sensitive to OS, due to the richness of its peroxidation-sensitive fatty acids, coupled with its high oxygen demand. At the same time, the brain lack robust antioxidant systems. Among the multiple mechanisms and triggers by which OS can accumulate, inflammatory cytokines can sustain oxidative and nitrosative stress, leading eventually to cellular damage. Understanding the consequences of inflammation and OS may clarify the initial events underlying AD, including in interaction with genetic factors. Inflammatory cytokines are potential inducers of aberrant gene expression through transcription factors. Susceptibility disorders for AD, including obesity, type-2 diabetes, cardiovascular diseases and metabolic syndrome have been linked to increases in the proinflammatory cytokine, IL-18, which also regulates multiple AD related proteins. The association of IL-18 with AD and AD-linked medical conditions are reviewed in the article. Such data indicates that an active lifestyle, coupled to a healthy diet can ameliorate inflammation and reduce the risk of sporadic AD.

Consensus paper of the WFSBP Task Force on Genetics: Genetics, epigenetics and gene expression markers of major depressive disorder and antidepressant response

Major depressive disorder (MDD) is a heritable disease with a heavy personal and socio-economic burden. Antidepressants of different classes are prescribed to treat MDD, but reliable and reproducible markers of efficacy are not available for clinical use. Further complicating treatment, the diagnosis of MDD is not guided by objective criteria, resulting in the risk of under- or overtreatment. A number of markers of MDD and antidepressant response have been investigated at the genetic, epigenetic, gene expression and protein levels. Polymorphisms in genes involved in antidepressant metabolism (cytochrome P450 isoenzymes), antidepressant transport (ABCB1), glucocorticoid signalling (FKBP5) and serotonin neurotransmission (SLC6A4 and HTR2A) were among those included in the first pharmacogenetic assays that have been tested for clinical applicability. The results of these investigations were encouraging when examining patient-outcome improvement. Furthermore, a nine-serum biomarker panel (including BDNF, cortisol and soluble TNF-α receptor type II) showed good sensitivity and specificity in differentiating between MDD and healthy controls. These first diagnostic and response-predictive tests for MDD provided a source of optimism for future clinical applications. However, such findings should be considered very carefully because their benefit/cost ratio and clinical indications were not clearly demonstrated. Future tests may include combinations of different types of biomarkers and be specific for MDD subtypes or pathological dimensions.

A Functional Interleukin-18 Haplotype Predicts Depression and Anxiety through Increased Threat-Related Amygdala Reactivity in Women but Not Men

Common functional polymorphisms in the gene encoding interleukin-18 (IL18), a cytokine belonging to the IL-1 superfamily that can induce synthesis of several other cytokines, have been associated with major depressive episodes following the experience of stressful life events. The neural mechanisms underlying these associations remain unexamined. Here we use an imaging genetics strategy to examine the effects of risk-related IL18 haplotypes comprising rs187238 and rs1946518 on threat-related amygdala reactivity and, through an indirect effect, stress-related symptoms of depression and anxiety in 448 non-Hispanic Caucasian university students. Analyses indicated that women but not men possessing an IL18 haplotype comprising both risk-related alleles evidenced increased threat-related left centromedial amygdala reactivity relative to other haplotype groups. Moreover, in women only, increased threat-related left centromedial amygdala reactivity predicted increased symptoms of depression and anxiety in individuals also reporting higher levels of life stress. Path analyses revealed a significant indirect effect of IL18 risk haplotype on symptoms of depression and anxiety through increased threat-related amygdala reactivity. These results suggest that a common functional IL18 haplotype associated with heightened proinflammatory responses confers susceptibility to stress-related depression and anxiety through effects on threat-related amygdala function, a risk pathway specific to women. If replicated, these patterns can inform the search for personalized interventions targeting neurobiological pathways of risk associated with inflammation.

Genetic Contributions of Inflammation to Depression

This paper describes the effects of immune genes genetic variants and mRNA expression on depression's risk, severity, and response to antidepressant treatment, through a systematic review on all papers published between 2000 and 2016. Our results, based largely on case-control studies, suggest that common genetic variants and gene-expression pathways are involved in both immune activation and depression. The most replicated and relevant genetic variants include polymorphisms in the genes for interleukin (IL)-1β, IL-6, IL-10, monocyte chemoattractant protein-1, tumor necrosis factor-alpha, C-reactive protein, and phospholipase A2. Moreover, increased blood cytokines mRNA expression (especially of IL-1β) identifies patients that are less likely to respond to conventional antidepressants. However, even for the most replicated findings there are inconsistent results, not only between studies, but also between the immune effects of the genetic variants and the resulting effects on depression. We find evidence that these discrepant findings may be explained, at least in part, by the heterogeneity of the depression immunophenotype, by environmental influences and gene × environment interactions, and by the complex interfacing of genetic variants with gene expression. Indeed, some of the most robust findings have been obtained in patients developing depression in the context of treatment with interferon-alpha, a widely used model to mimic depression in the context of inflammation. Further 'omics' approaches, through GWAS and transcriptomics, will finally shed light on the interaction between immune genes, their expression, and the influence of the environment, in the pathogenesis of depression.

Association of TNF-alpha G-308A gene polymorphism with depression: a meta-analysis

BACKGROUND

Although many studies have investigated the association of a single nucleotide polymorphism in TNF-α G-308A gene with depression, their association is still controversial. To clarify this, we performed a meta-analysis.

METHOD

Studies related to TNF-α G-308A and depression were retrieved from PubMed, Medline, Embase, and Scopus (up to April 18, 2017). The odds ratios (ORs) and 95% confidence intervals (CIs) were estimated in the models of allele comparison (G vs A), homozygote comparison (GG vs AA), dominant (GG vs GA + AA), and recessive (GG + GA vs AA) to estimate the strength of the associations.

RESULTS

A total of 10 case-control studies were included in this meta-analysis. Overall, no significant association between TNF-α G-308A and depression was found (G vs A: OR [95% CI] =1.09 [0.92, 1.29]; GG vs AA: 1.24 [0.71, 2.15]; GG vs GA + AA: 1.01 [0.76, 1.35]; GG + GA vs AA: 1.22 [0.70, 2.13]). In subgroup analyses by ethnicity or age group, no statistically significant association between TNF-α G-308A polymorphisms and depression was shown.

CONCLUSION

This meta-analysis revealed that TNF-α G-308A polymorphism is not associated with susceptibility to depression.

The function of NOD-like receptors in central nervous system diseases

NOD-like receptors (NLRs) are critical cytoplasmic pattern-recognition receptors (PRRs) that play an important role in the host innate immune response and immunity homeostasis. There is a growing body of evidence that NLRs are involved in a wide range of inflammatory diseases, including cancer, metabolic diseases, and autoimmune disorders. Recent studies have indicated that the proteins of the NLR family are linked with the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), and psychological diseases. In this review, we mainly focus on the role of NLRs and the underlying signaling pathways in central nervous system (CNS) diseases. © 2016 Wiley Periodicals, Inc.

Pathogenetic and Therapeutic Applications of Tumor Necrosis Factor-α (TNF-α) in Major Depressive Disorder: A Systematic Review

Major depressive disorder (MDD) is characterized by mood, vegetative, cognitive, and even psychotic symptoms and signs that can cause substantial impairments in quality of life and functioning. Up to now, the exact pathogenesis of MDD remains poorly understood. Recent research has begun to reveal that the pro-inflammatory cytokines, particularly, tumor necrosis factor-α (TNF-α), play an integral role in the pathophysiology of depressive disorders and the mechanism of antidepressant treatment. On the base of several observations: it is found that subsets of MDD patients have enhanced plasma levels TNF-α; antidepressant treatments had linked with the decline of TNF-α; central administration of TNF-α gives rise to sickness behavior which shares features with depression; and a blockade of it can ameliorate depressive symptomatology in animal models and clinical trials. In this review article, we focus on recent evidence linking TNF-α and MDD looking at data from animal and clinical studies, illustrating the pathophysiological role, susceptibility and its therapeutic application in depression. We conclude by discussing future directions for research, in particular the opportunities for the development of novel therapeutics that target TNF-α. This will be very important for designing preventative strategies and for the identification of new drug targets and preventative strategies.

Interleukin 1B gene (IL1B) variation and internalizing symptoms in maltreated preschoolers

Evidence now implicates inflammatory proteins in the neurobiology of internalizing disorders. Genetic factors may influence individual responses to maltreatment; however, little work has examined inflammatory genetic variants in adults and none in children. The present study examined the role of an interleukin 1B gene (IL1B) variant in preschoolers exposed to maltreatment and other forms of adversity in internalizing symptom development. One hundred ninety-eight families were enrolled, with one child (age 3-5 years) from each family. Adversity measures included child protective service documentation of moderate-severe maltreatment in the last 6 months and interview-assessed contextual stressors. Internalizing symptoms were measured using the Child Behavior Checklist and the Diagnostic Infant and Preschool Assessment. Maltreated children had higher major depressive disorder (MDD) and posttraumatic stress disorder symptoms and marginally higher internalizing symptoms on the Child Behavior Checklist. Controlling for age, sex, and race, IL1B genotype was associated with MDD symptoms (p = .002). Contextual stressors were significantly associated with MDD and posttraumatic stress disorder and marginally with internalizing symptoms. The IL1B genotype interacted with contextual stress such that children homozygous for the minor allele had more MDD symptoms (p = .045). These results suggest that genetic variants of IL1B may modulate the development of internalizing symptoms in the face of childhood adversity.

Hippocampal volume and depressive symptoms are linked to serum IL-18 in schizophrenia

Objective:

Since schizophrenia (SCZ) is often accompanied by hippocampal abnormalities and dysregulation of cytokine production, this study aimed to investigate the impact of the cytokine interleukin (IL)-18, whose biological system appears to be perturbed in SCZ, on brain structure and clinical severity in patients with chronic SCZ.

Methods:

The serum levels of IL-18, including its free bioactive form (i.e., the cytokine fraction not bound to its specific endogenous inhibitor IL-18 binding protein), were evaluated in a case-control study involving 71 individuals with SCZ diagnosis and 29 healthy controls. All participants underwent brain MRI automatic evaluation for hippocampal volume estimation. The Positive and Negative Syndrome Scale (PANSS) was administered to measure severity of symptoms in patients with SCZ.

Results:

Lower amounts of free IL-18 were related to smaller hippocampal volume measures in patients with SCZ. Furthermore, in line with a possible neuroprotective effect of the cytokine, higher levels of free IL-18 corresponded to lower subscores of PANSS depression in patients with SCZ.

Conclusions:

These findings demonstrate that the levels of circulating bioactive IL-18 are related to both hippocampal volume and severity of psychopathologic symptoms in patients with SCZ, confirming the involvement of the cytokine in SCZ pathophysiology and suggesting hippocampal-dependent and neuroprotective functions of IL-18 in this clinical context.

Elevated levels of IL-6 and IL-18 in manic and hypomanic states in rapid cycling bipolar disorder patients

Inflammatory system dysregulation may be involved in the pathophysiology of bipolar disorder with peripheral cytokine levels varying between affective states; however, the evidence is based primarily on case-control studies and limited by methodological issues. The objectives of the present study were to assess alterations of peripheral cytokine levels between affective states in rapid cycling bipolar disorder patients and to compare these with levels in healthy control subjects. In a longitudinal design, repeated measurements of plasma levels of IL-6, IL-10, IL-18, IL-1β and TNF-α were obtained in affective states of varying polarity during 6-12 months in 37 rapid cycling bipolar disorder patients and compared with repeated measurements in 40 age- and gender matched healthy control subjects, using rigorous laboratory-, clinical- and statistical methodology. Adjusting for demographical, clinical- and lifestyle factors, levels of IL-6 (p<0.05) and IL-18 (p<0.005) were significantly elevated in rapid cycling bipolar disorder patients in a manic/hypomanic state, compared with a depressed and a euthymic state. Compared with healthy control subjects, unadjusted levels of IL-6 (p<0.05) and IL-18 (p<0.05) were elevated in manic/hypomanic bipolar disorder patients. Levels of IL-10 and IL-1β were undetectable in the majority of samples; high TNF-α assay variability was found. The results support a role for altered peripheral immune response signaling in rapid cycling bipolar disorder and suggest that IL-6 and IL-18 could be markers of manic episodes.

Interleukin-18 alters protein expressions of neurodegenerative diseases-linked proteins in human SH-SY5Y neuron-like cells

Chronic inflammation and oxidative stress (OS) are present in Alzheimer's disease (AD) brains in addition to neuronal loss, Amyloid-β (Aβ) plaques and hyperphosphorylated tau-protein neurofibrillary tangles (NFTs). Previously we showed that levels of the pro-inflammatory cytokine, interleukin-18 (IL-18), are elevated in post-mortem AD brains. IL-18 can modulate the tau kinases, Cdk5 and GSK3β, as well as Aβ-production. IL-18 levels are also increased in AD risk diseases, including type-2 diabetes and obesity. Here, we explored other IL-18 regulated proteins in neuron-like SH-SY5Y cells. Differentiated SH-SY5Y cells, incubated with IL-18 for 24, 48, or 72 h, were analyzed by two-dimensional gel electrophoresis (2D-DIGE). Specific altered protein spots were chosen and identified with mass spectrometry (MS) and verified by western immunoblotting (WIB). IL-18 had time-dependent effects on the SH-SY5Y proteome, modulating numerous protein levels/modifications. We concentrated on those related to OS (DDAH2, peroxiredoxins 2, 3, and 6, DJ-1, BLVRA), Aβ-degradation (MMP14, TIMP2), Aβ-aggregation (Septin-2), and modifications of axon growth and guidance associated, collapsin response mediator protein 2 (CRMP2). IL-18 significantly increased antioxidative enzymes, indicative of OS, and altered levels of glycolytic α- and γ-enolase and multifunctional 14-3-3γ and -ε, commonly affected in neurodegenerative diseases. MMP14, TIMP2, α-enolase and 14-3-3ε, indirectly involved in Aβ metabolism, as well as Septin-2 showed changes that increase Aβ levels. Increased 14-3-3γ may contribute to GSK3β driven tau hyperphosphorylation and CRMP2 Thr514 and Ser522 phosphorylation with the Thr555-site, a target for Rho kinase, showing time-dependent changes. IL-18 also increased caspase-1 levels and vacuolization of the cells. Although our SH-SY5Y cells were not aged, as neurons in AD, our work suggests that heightened or prolonged IL-18 levels can drive protein changes of known relevance to AD pathogenesis.

Interleukin 18 activates MAPKs and STAT3 but not NF-κB in hippocampal HT-22 cells

Interleukin (IL)-18 is a cytokine previously demonstrated to participate in neuroinflammatory processes. Since the components of the IL-18 receptor complex are expressed in neurons throughout the brain, IL-18 is also believed to directly influence neuronal function. Here we tested this hypothesis on mouse hippocampal neurons by measuring the effects of IL-18 on three pathways previously shown to be regulated by this cytokine in non-neuronal cells: the MAPK pathways, p38 and ERK1/2 MAPKs, STAT3 and NF-κB. Experiments were carried out in vitro using the immortalized hippocampal neuronal line HT-22 or in vivo following i.c.v. injection with recombinant mouse IL-18. We showed that IL-18 did not activate NF-κB in HT-22 cells whereas it induced a rapid (within 15min) activation of the MAPK pathways. Moreover, we demonstrated that IL-18 treatment enhanced P-STAT3 (Tyr705)/STAT3 ratio in the nucleus of HT-22 cells after 30-60min of exposure. A similar increase in P-STAT3 (Tyr705)/STAT3 ratio was observed in the whole hippocampus one hour after i.c.v. injection. These data demonstrate that IL-18 can act directly on neuronal cells affecting the STAT3 pathway; therefore, possibly regulating the expression of specific genes within the hippocampus. This effect may help to explain some of the IL-18-induced effects on synaptic plasticity and functionality within the hippocampal system.

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.

Targeting the inflammatory pathway as a therapeutic tool for major depression

In the last decades convergent findings from several lines of evidence has revealed a robust association between major depressive disorder (MDD) and inflammatory pathways. Despite this, the translation of these findings into new and better treatments for MDD has not occurred. The objective of this study is to comprehensively review what is already known with reasonable certainty on inflammatory pathways in MDD, to clarify some points that have been insufficiently studied and to discuss the implications of these findings for future studies targeting inflammatory pathways as a therapeutic tool for individuals with MDD.

TNF-alpha -308G>A polymorphism is associated with suicide attempts in major depressive disorder

BACKGROUND

Despite the substantial role of the cytokine network in depression and suicide, few studies have investigated the role of genetic polymorphisms of pro- and anti-inflammatory cytokines in suicide in major depressive disorder (MDD). The aim of this study was to investigate whether tumor necrosis factor-alpha (TNF-alpha) -308G>A, interferon-gamma (IFN-gamma) +874A>T, and interleukin-10 (IL-10) -1082A>G are associated with increased risk for suicide attempts in MDD.

METHODS

Among patients with MDD, 204 patients who had attempted suicide and 97 control patients who had not attempted suicide were recruited. A chi-square test was used to identify a possible risk genotype or allele type for suicide. A subsequent multivariate logistic regression analysis was conducted to investigate the influence of a risk genotype or allele type adjusted for other environmental factors. The lethality of the suicide attempt was also tested between genotype and allele types among suicidal patients with MDD.

RESULTS

The GG genotype of the TNF-alpha -308G>A polymorphism was found to significantly increase risk for suicide attempt (adjusted OR=2.630, 95% CI=1.206 to 5.734). IFN-gamma +874A>T and IL-10 -1082A>G were not associated with risk for suicide. Lethality of the suicide attempt was not associated with any of the three cytokine genotypes or allele types.

LIMITATIONS

Limitations include a relatively small sample size and a cross-sectional design.

CONCLUSIONS

TNF-alpha -308G>A polymorphism is an independent risk factor for suicide attempts in MDD. Future studies should clarify the neural mechanisms by which the GG genotype of TNF-alpha -308G>A influences suicide in MDD.

Gene environment interaction studies in depression and suicidal behavior: An update

Increasing evidence supports the involvement of both heritable and environmental risk factors in major depression (MD) and suicidal behavior (SB). Studies investigating gene-environment interaction (G × E) may be useful for elucidating the role of biological mechanisms in the risk for mental disorders. In the present paper, we review the literature regarding the interaction between genes modulating brain functions and stressful life events in the etiology of MD and SB and discuss their potential added benefit compared to genetic studies only. Within the context of G × E investigation, thus far, only a few reliable results have been obtained, although some genes have consistently shown interactive effects with environmental risk in MD and, to a lesser extent, in SB. Further investigation is required to disentangle the direct and mediated effects that are common or specific to MD and SB. Since traditional G × E studies overall suffer from important methodological limitations, further effort is required to develop novel methodological strategies with an interdisciplinary approach.

The role of immune genes in the association between depression and inflammation: a review of recent clinical studies

The role for dysregulation of the immune system in the pathogenesis of depressive disorder is well established, and emerging research suggests the role of an underlying genetic vulnerability. The purpose of this review is to summarize the existing literature on the genetic variants involved in neurobiological pathways associated with both immune activation and depression. Using PubMed, Scopus, The Cochrane Library, Embase, Ovid of Medline, PsycINFO and ISI web of Knowledge, we selected 52 papers which are relevant for this literature review. Findings across the literature suggest that functional allelic variants of genes for interleukin-1beta (IL)-1β, tumor necrosis factor-alpha (TNF-α) and C-reactive protein (CRP), as well as genetic variations affecting T-cell function, may increase the risk for depression. Moreover, single nucleotide polymorphisms (SNPs) in the IL-1β, IL-6 and IL-11 genes, and in those regulating T-cell function may be associated with reduced responsiveness to antidepressant therapy. There is also some evidence indicative of a role of genetic variants of the enzymes, Cyclo-oxygenase2 (COX-2) and Phospholipase2 (PLA2), in the aetiology of depression. Finally, SNPs in genes related to the serotonin pathway may play a fundamental role in the shared genetic liability to both immune activation and depressive symptoms. Our review confirms that genetic variants influence the biological mechanisms by which the innate immune system contributes to the development of depression. However, future studies are necessary to identify the molecular mechanisms underlying these associations.

Imipramine reverses alterations in cytokines and BDNF levels induced by maternal deprivation in adult rats

A growing body of evidence is pointing toward an association between immune molecules, as well brain-derived neurotrophic factor (BDNF) and the depression. The present study was aimed to evaluate the behavioral and molecular effects of the antidepressant imipramine in maternally deprived adult rats. To this aim, maternally deprived and non-deprived (control group) male rats were treated with imipramine (30mg/kg) once a day for 14 days during their adult phase. Their behavior was then assessed using the forced swimming test. In addition to this, IL-10, TNF-α and IL-1β cytokines were assessed in the serum and cerebrospinal fluid (CSF). In addition, BDNF protein levels were assessed in the prefrontal cortex, hippocampus and amygdala. In deprived rats treated with saline was observed an increase on immobility time, compared with non-deprived rats treated with imipramine (p<0.05). Deprived rats treated with saline presented a decrease on BDNF levels in the amygdala (p<0.05), compared with all other groups. The IL-10 levels were decreased in the serum (p<0.05). TNF-α and IL-1β levels were increased in the serum and CSF of deprived rats treated with saline (p<0.05). Interestingly, imipramine treatment reversed the effects of maternal deprivation on BDNF and cytokines levels (p<0.05). Finally, these findings further support a relationship between immune activation, neurotrophins and the depression, and considering the action of imipramine, it is suggested that classic antidepressants could exert their effects by modulating the immune system.