Single-Nucleotide Polymorphisms in Interleukin 6 (IL-6) Gene Are Associated with Suicide Behavior in an Iranian Population

Suicidality in civilian women with PTSD: Possible link to childhood maltreatment, proinflammatory molecules, and their genetic variations

Background

Posttraumatic stress disorder (PTSD) is a robust risk factor for suicide. Studies have suggested an association between suicide and elevated inflammatory markers, although such evidence in PTSD is scarce. Suicide risk, PTSD, and inflammatory molecules are all shown to be associated with childhood maltreatment and genetic factors.

Methods

We examined the association between suicidal ideation/risk and inflammatory markers in 83 civilian women with PTSD, and explored the possible influence of childhood maltreatment and inflammatory genes. Suicidal ideation and risk were assessed using the Beck Depression Inventory-II and the Mini-International Neuropsychiatric Interview. Childhood maltreatment history was assessed with the Childhood Trauma Questionnaire (CTQ). Blood levels of high-sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6) and high-sensitivity tumor necrosis factor-α were measured. Genetic polymorphisms of CRP rs2794520 and IL6 rs1800796 were genotyped.

Results

Suicidal ideation was significantly positively correlated with hsCRP (p = 0.002) and IL-6 (p = 0.015) levels. Suicide risk weighted score was significantly positively correlated with hsCRP (p = 0.016) levels. The risk alleles of CRP rs2794520 and IL6 rs1800796 leading to increased respective protein levels were dose-dependently associated with higher risk of suicide (p = 0.007 and p = 0.029, respectively). The CTQ total score was significantly correlated with suicidal ideation and risk, but not with inflammatory marker levels. Furthermore, a multivariate regression analysis controlling for PTSD severity and potential confounders revealed that rs2794520 and rs1800796, but not hsCRP or IL-6 levels, significantly predicted suicidal ideation (p < 0.001) and risk (p = 0.007), respectively.

Conclusion

Genetic variations within inflammatory genes might be useful in detecting PTSD patients at high risk of suicide.

High Serum Levels of IL-6 Are Associated with Suicide Attempt but Not with High Lethality Suicide Attempts: A Preliminary Case-Control Study

Suicide attempts are an emerging health problem around the world. Increased levels of IL-6 have been associated with suicidal behavior. Therefore, the aims of this study were to evaluate the serum levels of IL-6 in individuals with suicide attempts and a comparison group and to associate the IL-6 levels with the lethality of the suicide attempt. Additionally, we associated the rs2228145 polymorphism of the IL6R gene with suicide attempts or with the IL-6 serum levels. Suicide attempts and their lethality were evaluated using the Columbia Suicide Severity Rating Scale. The serum concentrations of IL-6 were measured by the ELISA technique in individuals with suicide attempts and then compared to a control group. The rs2228145 polymorphism of the IL6R gene was analyzed by real-time polymerase chain reaction. We found elevated serum levels of IL-6 in the suicide attempt group when compared to the control group (F = 10.37, p = 0.002). However, we found no differences of the IL-6 levels between high and low lethality. The IL6R gene polymorphism rs2479409 was not associated with suicide attempts. Our data suggest that IL-6 serum is increased in individuals with suicide attempts.

Genetic variations related to inflammation in suicidal ideation and behavior: A systematic review

BACKGROUND/OBJECTIVES

Immune-inflammatory changes have been found in all types of suicidal ideation and behavior (SIB), independently of associated mental disorders. Since several Single Nucleotide Polymorphisms (SNPs) affect the function of inflammation-related genes, we searched the literature for genetic variations potentially altering inflammatory processes in SIB.

METHODS

We included studies that looked for associations between SIB and SNPs in genes related to inflammatory processes. Case reports, literature reviews, and animal studies were excluded. Articles were retrieved from PubMed and PsycINFO databases, Google Scholar and GreySource Index until September 17th, 2022. Quality was assessed using Q-Genie.

RESULTS

We analyzed 32 studies. SIB has been associated with eighteen SNPs located in genes encoding for interleukin-8 (rs4073), C-reactive protein (rs1130864), tumor necrosis factor α (rs1800629, rs361525, and rs1099724), tumor necrosis factor receptor 2 (rs1061622), transforming growth factor β-1 (rs1982073), acid phosphatase 1 (rs7419262, rs300774), interleukin-10 (rs1800896), interferon γ (rs2430561), amino-carboxy muconate semialdehyde decarboxylase (rs2121337), interleukin 7 (rs10448044, rs10448042), macrophage migration inhibitory factor (rs755622), interleukin 1-α (rs1800587), and interleukin 1-β (rs1143634 and rs16944. A genome-wide association study reported one association at the threshold of significance with the rs300774 SNP, located in the 2p25 region containing ACP1 gene.

DISCUSSION

The studies included were methodologically and clinically diverse and of moderate quality. Their findings suggest that some inflammation-related SNPs could increase the likelihood of SIB but the evidence to date is insufficient. Further research using gene-gene (GxG) and gene-environment (GxE) approaches is warranted.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk], identifier [CRD42022296310].

The role of gene polymorphisms, and analysis of peripheral and central levels of interleukins in suicidal behavior: A systematic review

In terms of the physiological characteristics of suicidal behavior (SB) disorder, an increase inflammation response has been reported in these individuals. Therefore, the pro-inflammatory and anti-inflammatory activities of interleukins are adequate markers to research in order to understand the pathogenesis of SB. For that reason, the aim of this systematic review was to evaluate the role of interleukins in individuals with suicidal behavior disorder. A systematic search was performed in PubMed, Scopus and EBSCO databases up to July 2019. We used the words "interleukin" AND "suicide", "interleukin" AND "suicidal", and "IL-". Articles where interleukins concentrations were measured in individuals with SB and/or genetic studies addressing interleukins genes variants as possible markers to SB were included. A total of 54 articles were included. Articles that measured interleukin levels comprised 1111 cases and 1588 controls; whereas the genetic studies comprised 3082 cases and 5148 controls. These studies evaluated the concentrations of IL-1β, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-10, sIL-2R in serum, plasma. The pro-inflammatory interleukins concentrations were higher in cases than in controls; however, we observed heterogeneity in the measurements and sample sources. Whereas, 9 polymorphisms of IL-1α, IL-1β, IL-6, IL-1β-8 genes were analyzed in association with suicide behavior disorder, though no conclusive outcomes were attained. Our results suggest that individuals with suicide risk undergo continuous stress that could trigger the release and circulation of pro-inflammatory interleukins and therefore their concentration in plasma. However, more studies are necessary in order to reach conclusively outcomes.

Inflamed Mind: Multiple Genetic Variants of IL6 Influence Suicide Risk Phenotypes in Interaction With Early and Recent Adversities in a Linkage Disequilibrium-Based Clumping Analysis

Background: Understanding and predicting suicide remains a challenge, and a recent paradigm shift regarding the complex relationship between the immune system and the brain brought attention to the involvement of inflammation in neuropsychiatric conditions including suicide. Among cytokines, IL-6 has been most frequently implicated in suicide, yet only a few candidate gene studies and without considering the effect of stress investigated the role of IL6 in suicidal behaviour. Our study aimed to investigate the association of IL6 variation with a linkage disequilibrium-based clumping method in interaction with childhood adversities and recent stress on manifestations along the suicide spectrum. Methods: One thousand seven hundred and sixty-two participants provided information on previous suicide attempts, current suicidal ideation, thoughts of death, and hopelessness, and were genotyped for 186 variants in IL6. Early childhood adversities were recorded with an instrument adapted from the Childhood Trauma Questionnaire, recent life events were registered using the List of Threatening Life Events. Following a 3-step quality control, logistic and linear regression models were run to explore the effect of genotype and gene-environment interactions on suicide phenotypes. All regression models were followed by a clumping process based on empirical estimates of linkage disequilibrium between clumps of intercorrelated SNPs. Interaction effects of distinct types of recent life events were also analysed. Results: No clumps with significant main effects emerged, but we identified several clumps significantly interacting with childhood adversities on lifetime suicide attempts, current suicidal ideation, and current thoughts of death. We also identified clumps significantly interacting with recent negative life events on current suicidal ideation. We reported no clumps with significant effect on hopelessness either as a main effect or in interaction with childhood adversities or recent stress. Conclusion: We identified variant clumps in IL6 influencing suicidal behaviour, but only in interaction with childhood or recent adversities. Our results may bring us a step further in understanding the role of neuroinflammation and specifically of IL-6 in suicide, towards identifying novel biological markers of suicidal behaviour especially in those exposed to stressful experiences, and to fostering the adaptation of a new paradigm and identifying novel approaches and targets in the treatment of suicidal behaviour.

Increased circulatory IL-6 during 8-week fluoxetine treatment is a risk factor for suicidal behaviors in youth

OBJECTIVE

Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat anxiety and/or depression in pediatric populations. However, the response rates are low (approximately 50%). Moreover, SSRI use is frequently associated with adverse events (AE). Currently there are no available biomarkers for treatment response/AE. Identification of biomarkers predicting early response and/or AE could help maximize the benefit-risk ratio for the use of SSRIs, and accelerate matching of treatments to patients. Pro-inflammatory cytokines were proposed as potential biomarkers.

METHOD

Ninety-two patients (35 boys and 57 girls) with major depressive disorder and/or anxiety disorders, aged 13.90 ± 2.41 years, were treated with fluoxetine (FLX) for 8 weeks. Plasma concentrations of TNFα, IL-6, and IL-1β were measured by enzyme linked immunosorbent assays before and after FLX treatment. Clinical response and AE were measured using several clinical scales, including the Clinical Global Impression - improvement, Children's Depression Rating Scale-Revised, the Beck Depression Inventory, the Screen for Child Anxiety Related Emotional Disorders, the Columbia suicide severity rating scale, and the Suicide Ideation Questionnaire.

RESULTS

IL-6 levels increased after treatment only in the group of children who developed FLX-associated suicidality.

CONCLUSION

An increase in IL-6 levels during treatment may be a risk factor for the emergence of FLX-associated suicidality (OR = 1.70). Further studies are necessary to clarify the role and mechanism(s) of this cytokine in the pathogenesis of this life-threatening AE.

Assessment of Association between NINJ2 Polymorphisms and Suicide Attempts in an Iranian Population

Suicidal behavior as a psychological problem with high public health burden is associated with a number of genetically determined risk factors. In the current study, we investigated the association between two polymorphisms within the NINJ2 gene and risk of suicide in an Iranian population. The study included 295 individuals who attempted suicide with soft suicide methods, 234 suicide victims and 410 normal controls. The rs11833579 SNP was associated with death from suicide in a codominant model in that the AG genotype decreased the risk of death from suicide compared with the GG genotype (OR (95% CI) = 0.49 (0.34-0.71), adjusted P value = 4e-04). This SNP was also associated with death from suicide in dominant (AG + AA versus GG: OR (95% CI) = 0.63 (0.46-0.87), adjusted P value = 0.011) and overdominant (AG versus GG + AA: OR (95% CI) = 0.49 (0.35-0.69), adjusted P value < 0.0001) models. In addition, this SNP was associated with soft suicide attempts in a codominant model (AG versus AA + GG: OR (95% CI) = 0.7 (0.5-0.98), adjusted P value = 0.02). The rs3806263 SNP was associated with death from suicide in allelic (A versus G: OR (95% CI) = 1.48 (1.17-1.88), adjusted P value = 0.002), codominant (AA versus GG: OR (95% CI) = 3.14 (1.89-5.21), adjusted P value < 0.0001), recessive (AA versus GG + AG: OR (95% CI) = 3.47 (2.15-5.61), adjusted P value < 0.0001), overdominant (AG versus AA + GG: OR (95% CI) = 0.62 (0.45-0.87), adjusted P value = 0.0092) and log-additive models (OR (95% CI) = 1.45 (1.15-1.83), adjusted P value = 0.0034). When comparing allele/genotype frequencies of this SNP between suicide victims and soft suicide attempters, significant associations were found in allelic, codominant, recessive and log-additive models. The AG haplotype (rs11833579 and rs3806263, respectively) was significantly less prevalent among suicide victims compared with controls (OR (95% CI) = 0.37 (0.26-0.52), adjusted P value < 0.0001). This haplotype was also less prevalent among suicide victims vs. soft suicide attempters (OR (95% CI) = 0.43 (0.31-0.61), adjusted P value < 0.0001). The GA haplotype (rs11833579 and rs3806263, respectively) was less frequent among suicide victims compared with controls (OR (95% CI) = 0.63 (0.45-0.89), adjusted P value = 0.0156). Finally, the AA haplotype was more prevalent among suicide victims compared with both controls (OR (95% CI) = 2.37 (1.56-3.6), adjusted P value = 0.0002) and soft suicide attempters (OR (95% CI) = 1.92 (1.32-2.78), adjusted P value = 0.0012). Thus, these two SNPs might be regarded as genetic determinants of suicide risk in Iranian populations. Further studies in different populations are needed to verify these results.

Gene-level genome-wide association analysis of suicide attempt, a preliminary study in a psychiatric Mexican population

Background

Evidence suggests that liability for suicide behavior is heritable; additionally, suicide has been partly related to other psychiatric disorders. Nevertheless, most of the information reported so far address Caucasian and Asian individuals. Hence, our aim was to conduct a gene‐level association study in Mexican psychiatric individuals diagnosed with suicide attempt.

Methods

We recruited 192 individuals from two clinical centers in Mexico. All participants were born in Mexico and had Mexican parents and grandparents. Direct genotyping was performed using the commercial platform Infinium PsychArray BeadChip. A p‐value lower than 1e‐05 was considered as gene‐level significant and a p‐value lower than 1e‐04 was considered as gene‐level nominal significant.

Results

Our analyses showed that SCARA5 was associated to suicide intent at a gene‐level with statistical significance (p‐value = 1.12e‐6). Other genes were nominally associated with suicide attempt: GHSR (p‐value = 0.0004), RGS10 (p‐value = 5.13e‐5), and STK33 (p‐value = 3.62e‐5). Regarding gene variant analyses, the SNPs with a statistical association (p > .05) were rs561361616, rs1537577, rs11198999 for RGS10, and rs11041981, rs11041993, rs11041994, rs11041995, rs11041997, rs10840083, rs10769918 for STK33. For these genes, previous studies have associated SCARA5 with depression, GHSR with alcohol dependence and depression, and RGS10 with schizophrenia and depression. To date, STK33 has not been associated with any psychiatric disorder.

Conclusion

Our outcomes revealed that SCARA5, GHSR, RGS10 and STK33 could be considered as risk biomarkers for suicide attempt behavior in our Mexican psychiatric sample. We recommend to perform larger scale analyses to have conclusive results.