The neurobiology of suicide - A Review of post-mortem studies

Chronic social defeat stress induces anxiety-like behaviors via downregulation of serotonin transporter in the prefrontal serotonergic system in mice

The serotonergic (5-HTergic) system is closely involved in the pathophysiology of mood and anxiety disorders and the responsibility of this system may differ for each symptom. In this study, we examined the relationship between the dysfunction of the 5-HTergic system and abnormal behaviors in the social defeat stress model, an animal model of mood and anxiety disorders and in mice with knockdown of Slc6a4, the gene encoding SERT. Monoamine content, serotonin (5-HT) release, 5-HT uptake, 5-HT transporter (SERT) protein levels, and behaviors were investigated in mice subjected to chronic social defeat stress and in mice with knockdown of Slc6a4, in 5-HTergic neurons projecting to the prefrontal cortex (PFC). Furthermore, DNA methylation of Slc6a4 was examined in mice subjected to chronic social defeat stress. Increased turnover, increased extracellular basal levels, decreased release and decreased uptake of 5-HT, and decreased SERT protein levels were observed in the PFC of the stressed mice. The decreased 5-HT uptake correlated with anxiety-like behavior characterized by decreased time spent in the open arms of the elevated plus maze. DNA methylation was increased in the CpG island of Slc6a4 in 5-HTergic neurons projecting to the PFC of the stressed mice. Similar to the stressed mice, mice with Slc6a4 knockdown in 5-HTergic neurons projecting to the PFC also showed decreased release and uptake of 5-HT in the PFC and increased anxiety-like behavior. Chronic stress may induce anxiety due to dysfunction in the prefrontal 5-HTergic system via decreased SERT expression in the PFC.

Whole-brain structural and functional neuroimaging of individuals who attempted suicide and people who did not: A systematic review and exploratory coordinate-based meta-analysis

Suicide is the cause of death of approximately 800,000 people a year. Despite the relevance of this behaviour, risk assessment tools rely on clinician experience and subjective ratings. Given that previous suicide attempts are the single strongest predictors of future attempts, we designed a systematic review and coordinate-based meta-analysis to demonstrate whether neuroimaging features can help distinguish individuals who attempted suicide from subjects who did not. Out of 5,659 publications from PubMed, Scopus, and Web of Science, we summarised 102 experiments and meta-analysed 23 of them. A cluster in the right superior temporal gyrus, a region implicated in emotional processing, might be functionally hyperactive in individuals who attempted suicide. No statistically significant differences in brain morphometry were evidenced. Furthermore, we used JuSpace to show that this cluster is enriched in 5-HT1A heteroreceptors in the general population. This exploratory meta-analysis provides a putative neural substrate linked to previous suicide attempts. Heterogeneity in the analytical techniques and weak or absent power analysis of the studies included in this review currently limit the applicability of the findings, the replication of which should be prioritised.

Electroretinography and suicidal behaviors: a systematic review

BACKGROUND

Electroretinogram (ERG) is one of the tools used to investigate the electrophysiological underpinnings of mental health illnesses and major clinical phenomena (e.g., suicide) to improve their diagnosis and care. While multiple studies have reported specific ERG changes among individuals with suicidal behaviors, we know of no review that has been done to characterize their findings to inform future research.

METHODS

This review included available literature concerning ERG and suicidal behaviors. The paper's first section briefly overviews the theoretical basis of ERG and neurotransmitters involved in suicidal behaviors. The second section describes the findings of a review of studies reporting ERG findings among individuals with suicidal behaviors.

RESULTS

Most reviewed studies reported normal amplitude and implicit time of the a-waves, but the latency in individuals with suicidal behaviors was lower than normal. Additionally, the b-waves amplitude was reduced, but the implicit time and latency were increased. The b-a amplitude ratio and oscillatory potential were decreased.

CONCLUSION

Despite identifying certain ERG correlates with suicidal behaviors in the existing studies, there is a need for adequately powered and methodologically robust studies to advance clinical translation.

Gene Expression Analysis in Postmortem Brains from Individuals Who Died by Suicide: A Systematic Review

Around the world, more the 700,000 individuals die by suicide every year. It is necessary to understand the mechanisms associated with suicidal behavior. Recently, an increase in gene expression studies has been in development. Through a systematic review, we aimed to find a candidate gene in gene expression studies on postmortem brains of suicide completers. Databases were systematically searched for published studies. We performed an online search using PubMed, Scopus and Web of Science databases to search studies up until May 2023. The terms included were "gene expression", "expressed genes", "microarray", "qRT-PCR", "brain samples" and "suicide". Our systematic review included 59 studies covering the analysis of 1450 brain tissues from individuals who died by suicide. The majority of gene expression profiles were obtained of the prefrontal cortex, anterior cingulate cortex, dorsolateral prefrontal cortex, ventral prefrontal cortex and orbital frontal cortex area. The most studied mRNAs came of genes in glutamate, γ-amino-butyric acid and polyamine systems. mRNAs of genes in the brain-derived neurotrophic factor, tropomyosin-related kinase B (TrkB), HPA axis and chemokine family were also studied. On the other hand, psychiatric comorbidities indicate that suicide by violent death can alter the profile of mRNA expression.

Implementing Evidence-Based Suicide Prevention Strategies for Greatest Impact

Suicide remains a leading cause of death in the United States and globally. In this review, epidemiological trends in mortality and suicide risk are presented, with consideration given to the impact of the COVID-19 pandemic. A public health model of suicide prevention with a community and clinical framework, along with advances in scientific discovery, offer new solutions that await widespread implementation. Actionable interventions with evidence for reducing risk for suicidal behavior are presented, including universal and targeted strategies at community, public policy, and clinical levels. Clinical interventions include screening and risk assessment; brief interventions (e.g., safety planning, education, and lethal means counseling) that can be done in primary care, emergency, and behavioral health settings; psychotherapies (cognitive-behavioral, dialectical behavior, mentalization therapy); pharmacotherapy; and systemwide procedures for health care organizations (training, policies, workflow, surveillance of suicide indicators, use of health records for screening, care steps). Suicide prevention strategies must be prioritized and implemented at scale for greatest impact.

Identification of novel targets and pathways to distinguish suicide dependent or independent on depression diagnosis

In recent years, postmortem brain studies have revealed that some molecular, cellular, and circuit changes associated with suicide, have an independent or additive effect on depression. The aim of the present study is to identify potential phenotypic, tissue, and sex-specific novel targets and pathways to distinguish depression or suicide from major depressive disorder (MDD) comorbid with suicide. The mRNA expression profiling datasets from two previous independent postmortem brain studies of suicide and depression (GSE102556 and GSE101521) were retrieved from the GEO database. Machine learning analysis was used to differentiate three regrouped gene expression profiles, i.e., MDD with suicide, MDD without suicide, and suicide without depression. Weighted correlation network analysis (WGCNA) was further conducted to identify the key modules and hub genes significantly associated with each of these three sub-phenotypes. TissueEnrich approaches were used to find the essential brain tissues and the difference of tissue enriched genes between depression with or without suicide. Dysregulated gene expression cross two variables, including phenotypes and tissues, were determined by global analysis with Vegan. RRHO analysis was applied to examine the difference in global expression pattern between male and female groups. Using the optimized machine learning model, several ncRNAs and mRNAs with higher AUC and MeanDecreaseGini, including GCNT1P1 and AC092745.1, etc., were identified as potential molecular targets to distinguish suicide with, or without MDD and depression without suicide. WGCNA analysis identified some key modules significantly associated with these three phenotypes, and the gene biological functions of the key modules mainly relate to ncRNA and miRNA processing, as well as oxidoreductase and dehydrogenase activity. Hub genes such as RP11-349A22.5, C20orf196, MAPK8IP3 and RP11-697N18.2 were found in these key modules. TissueEnrich analysis showed that nucleus accumbens and subiculum were significantly changed among the 6 brain regions studied. Global analysis with Vegan and RRHO identified PRS26, ARNT and SYN3 as the most significantly differentially expressed genes across phenotype and tissues, and there was little overlap between the male and female groups. In this study, we have identified novel gene targets, as well as annotated functions of co-expression patterns and hub genes that are significantly distinctive between depression with suicide, depression without suicide, and suicide without depression. Moreover, global analysis across three phenotypes and tissues confirmed the evidence of sex difference in mood disorders.

The Role of the Microbiome-Brain-Gut Axis in the Pathogenesis of Depressive Disorder

The role of gut microbiota and its association with the central nervous system via the microbiome-brain-gut axis has been widely discussed in the literature. The aim of this review is to investigate the impact of gut microbiota on the development of depression and underlying molecular mechanisms. There are two possible pathways in which this interaction might occur. The first one suggests that depressive disorder could lead to dysbiosis and one of the causes may be the influence on the hypothalamic-pituitary-adrenal (HPA) axis. The second one considers if changes in the composition of gut microbiota might cause depressive disorder. The mechanisms that could be responsible for this interaction include the secretion of neurotransmitters, gut peptides and the activation of the immune system. However, current knowledge on this topic does not allow for us to state an unambiguous conclusion, and future studies that take into consideration more precise stress-measurement methods are needed to further explore direct mechanisms of the interaction between gut microbiota and mental health.

A Comprehensive Review of the Literature on Sleep Difficulties and Suicidality in Youth to Inform an Integrative Developmental Model and Future Directions

Purpose of Review

Suicide is currently the second leading cause of death among youth. Identification of modifiable near-term risk factors can inform suicide prevention strategies. One promising, readily assessed factor is sleep. We critically review the literature on sleep and suicidal thoughts and behaviors among youth.

Recent Findings

Most studies examining the youth sleep-suicidality relationship are from epidemiological samples in which both sleep problems and suicidality were assessed over variable timeframes using limited items from scales not designed to measure these constructs. Nonetheless, these data overwhelmingly support an association between suicidality and a range of sleep difficulties (e.g., insomnia, short/long sleep, weekend oversleep), above and beyond depressive symptoms. Limited studies include clinical samples or prospective designs. We review potential mechanisms and present a developmentally-informed integrative model.

Summary

Literature supports a clear association between sleep difficulties and youth suicidality. Future directions include prospective longitudinal studies and targeted prevention efforts.

A pharmacovigilance approach for assessing the occurrence of suicide-related events induced by antiepileptic drugs using the Japanese adverse drug event report database

Increased suicidality after antiepileptic drug (AED) treatment remains controversial. This study aimed to investigate the occurrence of suicide-related events (SREs) in Japan. SREs signals with AEDs used orally were evaluated by calculating reporting odds ratios (RORs) and information components (ICs) using the Japanese Adverse Drug Event Report (JADER) database from April 2004 to December 2021. Additionally, factors affecting the occurrence of SREs and time-to-onset from the initial AED treatment were analyzed. Of 22 AEDs, 12 (perampanel hydrate, nitrazepam, levetiracetam, clonazepam, clobazam, sodium valproate, phenobarbital, lamotrigine, lacosamide, gabapentin, zonisamide, and carbamazepine) showed signals of SREs. Patients in their 20 and 30 s, female sex, and concomitant use of multiple AEDs affected the occurrence of SREs. In six AEDs, the median time-to-onset of SREs in patients taking all AEDs was <100 days. The pharmacovigilance approach revealed that several AEDs displayed suicidality signals. Female patients, those in their 20 and 30 s, undergoing combination therapy with ≥2 AEDs, and patients early (<100 days from the initial treatment) in the course of AED therapy should be cautioned about SREs.

Effects of vitamin D-related gene polymorphisms on attempted suicide

OBJECTIVE

Emerging evidence suggests that vitamin D might protect from attempted suicide. The study aimed to investigate the associations between single-nucleotide polymorphisms (SNPs) related to vitamin D levels identified in a large genome-wide association study and attempted suicide in rural China.

METHODS

This 1:1 matched case-control study included altogether 510 suicide attempters and 510 community controls. Genotypes of four target SNPs (DHCR7-rs12785878, CYP2R1-rs10741657, GC-rs2282679, and CYP24A1-rs6013897) were determined, and a genetic risk score (GRS) was constructed to evaluate the combined effect of them. Demographic and psychological information was acquired through face-to-face interviews.

RESULTS

The A allele of CYP24A1-rs6013897 was significantly associated with attempted suicide (OR = 1.27, 95% CI, 1.03-1.58, P = 0.029), even after adjusting for demographic and psychological confounders (adjusted OR = 1.53, 95% CI, 1.01-2.30, P = 0.043). The GRS analyses revealed a significantly higher risk of attempted suicide with a greater number of low vitamin D alleles (adjusted OR = 1.33, 95% CI, 1.13-1.58, P < 0.001). Subgroup analyses stratified by sex indicated that the genetic associations were only significant among males with adjusted ORs of 3.77 (95% CI, 1.56-9.10) for the A allele of rs6013897 and 2.04 (95% CI, 1.32-3.17) for GRS.

CONCLUSIONS

Our findings identity CYP24A1-rs6013897 as a potential biomarker for attempted suicide and indicate that a genetic predisposition to lower vitamin D levels may contribute to attempted suicide. It suggests the possibility that vitamin D may have the preventive potential for attempted suicide.

A candidate biological network formed by genes from genomic and hypothesis-free scans of suicide

Information about genes and the biology of suicidal behavior (SB) is noisy due to heterogenous outcomes (suicide attempts or deaths), as well as many different genes and overlapping biological processes implicated. One approach to test the unbiased biological coherence of disease genes, is to use genes from hypothesis-free genetic scans and to investigate if they aggregate close to each other in cellular gene and protein interaction networks ("interactomes"). Therefore, we used network methods to study the biological coherence among genes (n = 229) from genome-wide association studies (GWAS) and whole exome sequencing (WES) of suicide outcome. Results showed that the suicide GWAS+WES genes has significant aggregation in three major interactome database assemblies, a hallmark of biological similarity and increased likelihood of being involved in the same outcome (suicide). This pinpointed e.g. genes on chromosome 19, which are also associated with lipid metabolism, schizophrenia and bipolar disorder. We identified a subset of GWAS+WES "core" genes (n = 54) which are the most proximal to each other in the context of three interactome assemblies, and present a candidate network module of suicide which is specific for nervous system tissues. The n = 54 most proximal "core" genes showed overrepresentation of synaptic and nervous system development genes, as well as network paths to other SB genes having increased evidence diversity. Overall, results suggested the existence of a coherent biology in suicide outcome and provide unbiased biological support concerning links to other SB genes, as well as e.g. bipolar disorder, excitatory/inhibitory function and ketamine treatment in SB.

Epigenetic marks in suicide: a review

Suicide is a complex phenomenon and a global public health problem that involves several biological factors that could contribute to the pathophysiology of suicide. There is evidence that epigenetic factors influence some psychiatric disorders, suggesting a predisposition to suicide or suicidal behavior. Here, we review studies of molecular mechanisms of suicide in an epigenetic perspective in the postmortem brain of suicide completers and peripheral blood cells of suicide attempters. Besides, we include studies of gene-specific DNA methylation, epigenome-wide association, histone modification, and interfering RNAs as epigenetic factors. This review provides an overview of the epigenetic mechanisms described in different biological systems related to suicide, contributing to an understanding of the genetic regulation in suicide. We conclude that epigenetic marks are potential biomarkers in suicide, and they could become attractive therapeutic targets due to their reversibility and importance in regulating gene expression.

Sex differences in brain gene expression among suicide completers

BACKGROUND

Suicide rates vary substantially by sex. Suicides committed by males significantly outnumber female suicides. Disparities in community and social factors provide a partial explanation for this phenomenon. Thus, the evaluation of sex differences at a biological level might contribute to the elucidation of the factors involved in this imbalance. The aim of the present study was to evaluate sex-specific gene expression patterns in the suicidal brain.

METHODS

postmortem samples from the dorsolateral prefrontal cortex (DLPFC) of 75 Latino individuals were analyzed. We considered the following groups: i) male suicides (n = 38), ii) female suicides (n = 10), iii) male controls (n = 20), and iv) female controls (n = 7). Gene expression profiles were evaluated by microarrays. Differentially expressed genes among the groups were identified with a linear model. Similarities and differences in the gene sets between the sexes were identified.

RESULTS

Differentially expressed genes were identified between suicides and controls of each sex: 1,729 genes in females and 1,997 genes in males. Female-exclusive suicide genes were related to cell proliferation and immune response. Meanwhile, male-exclusive suicide genes were associated to DNA binding and ribonucleic protein complex. Sex-independent suicide genes showed enrichment in mitochondrial and vesicular functions.

LIMITATIONS

Relatively small sample size. Our diagnosis approach was limited to information found on coroner's records. The analysis was limited to a single brain area (DLPFC) and we used microarrays.

CONCLUSION

Previously unexplored sex differences in the brain gene expression of suicide completers were identified, providing valuable foundation for the evaluation of sex-specific factors in suicide.

Suicide in DSM-5: Current Evidence for the Proposed Suicide Behavior Disorder and Other Possible Improvements

Suicide continues to be one of the greatest challenges faced by mental health clinicians and researchers, an issue made worse by increasing trends in the global suicide rate. Suicide behavior disorder (SBD) was introduced in DSM-5 as a disorder for further consideration and potential acceptance into the diagnostic system. There are numerous positive developments that would arise from the addition of a suicide-related diagnosis. Utilizing the 2009 guidelines established by Kendler and colleagues, the present review examines the evidence for SBD's validity and discusses the diagnosis' potential clinical benefits and limitations. Altogether, growing evidence indicates that SBD has preliminary validity and benefit. SBD presents with several significant limitations, however, and possible alternative additions to future DSMs are highlighted.

Biomarkers of suicidal behaviors: A comprehensive critical review

Suicide is a relevant worldwide public health problem. Many studies have shown that different demographic and clinical factors are potentially associated with suicidal behavior. Other studies have reported data about the role of biomarkers in the onset of suicidal behaviors. Specifically, researchers have found that suicidal risk may be increased by abnormalities in serotonergic system, hypothalamic-pituitary-adrenal axis, lipid metabolism, immune system and neuronal plasticity. The identification of specific biological parameters associated with self-harm may be helpful to implement prevention strategies and also to detect new therapeutic strategies. In this review, we summarize and analyze the results of main studies about neurobiological mechanisms related to suicidal behavior, also exploring the possible interconnection between the different biological systems.

Sleep difficulties and suicidality in youth: current research and future directions

Studies have established a clear relationship between subjective sleep problems and the continuum of suicidality in adolescents. These studies are primarily cross-sectional in nature and conducted with epidemiological and depressed clinical samples. More recent studies focus on prospective data. Herein, we provide an update on current studies on the sleep-suicide association among youth. To further the critical mission of youth suicide prevention, future directions include more nuanced study of sleep employing a sleep health framework, longitudinal studies employing both objective and subjective sleep measures, fine-grained temporal associations between these constructs and their fluctuations over time, as well as enhanced understanding of the mechanisms underlying these associations.

Correlations Among the HLA-DQB1 Alleles and Suicidal Behavior

Suicide is a worldwide health problem with multiple causes, including genetic factors. The major histocompatibility complex (MHC) is represented by an assembly of gene encoding the human leukocyte antigen (HLA). The purpose of our study was to determine associations between the HLA profiles and predisposition for suicidal behavior. We harvested blood samples from persons with history of suicidal attempts (case group) and persons never exhibiting such behavior (control group). The DNA was extracted and amplified via polymerase chain reaction (PCR) to determine the HLA-DQB1 profiles. Statistical data processing was performed with the Epi Info program. We found that the presence of the HLA-DQB1*02 allele increases the risk of suicidal behavior, while HLA-DQB1*05 alleviates such risk. The genotype that presented the most increased risk for suicidal behavior was found to be HLA-DQB1*02/HLA-DQB1*03. Our study has demonstrated the presence of several associations between HLA profiles and suicidal behavior.

Historical trends in suicide risk for the residents of mainland China: APC modeling of the archived national suicide mortality rates during 1987-2012

PURPOSE

Distinctive and dramatic changes in the history of China with a rapid suicide decline in recent years present an opportunity to investigate the risk of suicide. In this study, we investigated suicide risk with a historical perspective with archived data to inform suicide research and prevention policies and strategies.

METHOD

Documented age-specific suicide mortality rates in 1987-2012 were decomposed into age, period, and cohort effect using APC-modeling method and intrinsic estimator (IE) technique. The estimated effects were further analyzed by numerical differentiation.

RESULTS

The data satisfactorily fit the constructed APC models. Cohort effect indicated that suicide risk in China fluctuated at very high levels during 1903-1967, followed by a sharp decline during 1968-1977, and reached the lowest level in 1983-1987 before increased again. Period effect confirmed the declining trend since 1987. Three sunny cohorts with reduced suicide risk and four cloudy cohorts with increased risk were, respectively, associated with significant cultural, social, political, and economic events in China since the 1900s.

CONCLUSIONS

The mega trends in the suicide risk at the population level are closely related to significant historical events in China. Suicide is anticipated to increase because of the growing risk for the young cohorts (particularly young females) as the country further develops. Study findings suggest the significance of national strategies for suicide prevention and control, including maintenance of social harmony and stability, provision of more opportunities for development, enhancement of social integration, and restriction of suicide facilitating factors.

Serotonin receptors and suicide, major depression, alcohol use disorder and reported early life adversity

Serotonin neurotransmitter deficits are reported in suicide, major depressive disorder (MDD) and alcohol use disorder (AUD). To compare pathophysiology in these disorders, we mapped brain serotonin transporter (SERT), 5-HT1A, and 5-HT2A receptor binding throughout prefrontal cortex and in anterior cingulate cortex postmortem. Cases and controls died suddenly minimizing agonal effects and had a postmortem interval ≤24 h to avoid compromised brain integrity. Neuropathology and toxicology confirmed absence of neuropathology and psychotropic medications. For most subjects (167 of 232), a DSM-IV Axis I diagnosis was made by psychological autopsy. Autoradiography was performed in right hemisphere coronal sections at a pre-genual level. Linear model analyses included sex and age with group and Brodmann area as interaction terms. SERT binding was lower in suicides (p = 0.004) independent of sex (females < males, p < 0.0001), however, the lower SERT binding was dependent on MDD diagnosis (p = 0.014). Higher SERT binding was associated with diagnosis of alcoholism (p = 0.012). 5-HT1A binding was greater in suicides (p < 0.001), independent of MDD (p = 0.168). Alcoholism was associated with higher 5-HT1A binding (p < 0.001) but only in suicides (p < 0.001). 5-HT2A binding was greater in suicides (p < 0.001) only when including MDD (p = 0.117) and alcoholism (p = 0.148) in the model. Reported childhood adversity was associated with higher SERT and 5-HT1A binding (p = 0.004) in nonsuicides and higher 5-HT2A binding (p < 0.001). Low SERT and more 5-HT1A and 5-HT2A binding in the neocortex in depressed suicides is dependent on Axis I diagnosis and reported childhood adversity. Findings in alcoholism differed from those in depression and suicide indicating a distinct serotonin system pathophysiology.

Alterations in Gene and Protein Expression of Cannabinoid CB2 and GPR55 Receptors in the Dorsolateral Prefrontal Cortex of Suicide Victims

Recent studies point to the cannabinoid CB2 receptors (CB2r) and the non-cannabinoid receptor GPR55 as potential key targets involved in the response to stress, anxiety, and depression. Considering the close relationship between neuropsychiatric disorders and suicide, the purpose of this study was to evaluate the potential alterations of CB2r and GPR55 in suicide victims. We analyzed gene and protein expression of both receptors by real-time PCR and western blot, respectively, in the dorsolateral prefrontal cortex (DLPFC) of 18 suicide victims with no clinical psychiatric history or treatment with anxiolytics or antidepressants, and 15 corresponding controls. We used in situ proximity ligation assay to evaluate whether the receptors formed heteromeric complexes and to determine the expression level of these heteromers, also assessing the co-expression of heteromers in neurons, astroglia, or microglia cells. CB2r and GPR55 gene expressions were significantly lower (by 33 and 41%, respectively) in the DLPFC of suicide cases. CB2r protein expression was higher, as were CB2-GPR55 heteroreceptor complexes. The results also revealed the presence of CB2-GPR55 receptor heteromers in both neurons and astrocytes, whereas microglial cells showed no expression. We did not observe any significant alterations of GPR55 protein expression. Additional studies will be necessary to evaluate if these alterations are reproducible in suicide victims diagnosed with different psychiatric disorders. Taken together, the results suggest that CB2r and GPR55 may play a relevant role in the neurobiology of suicide.

Understanding the Neuroepigenetic Constituents of Suicide Brain

Stressful life incidents often cause a predisposition for developing mental disorders such as major depressive disorder (MDD). Impaired neurocognitive and neuro-vegetative functions of the central nervous system are the hallmarks of this mental illness. Blunted responses from emotionally salient regions of the brain including cortex, hippocampus, and amygdala have been associated with MDD-related behavioral changes. Moreover, improper signal processing and neuronal atrophy were held responsible for the overall dysfunctionality of these vulnerable regions in the MDD brain. The prevalence of genetic susceptibility along with adverse environmental stimuli often makes the situation worse for MDD patients, leading to an increased risk of suicidal behavior and eventually death by suicide. Despite considerable efforts to understand the complex neurobiology associated with MDD and suicidal behavior, their pathological determinants remain mostly elusive. Recent research, however, has shown that epigenetic perturbations have a formidable impact on the etiopathogenesis of MDD. Understanding the neuroepigenetic nature of this mental disorder may provide opportunities to devise more effective treatment strategies. Moreover, this can potentially lead to identifying predictive biomarkers associated with suicide risk. The present chapter critically reviews studies pertaining to epigenetic signatures of MDD and suicide brain.

Understanding epigenetic architecture of suicide neurobiology: A critical perspective

Current understanding of environmental cross-talk with genetic makeup is found to be mediated through an epigenetic interface which is associated with prominent reversible and heritable changes at gene expression level. Recent emergence of epigenetic modulation in shaping the genetic information has become a key regulatory factor in answering the underlying complexities associated with several mental disorders. A comprehensive understanding of the pertinent changes in the epigenetic makeup of suicide phenotype exhibits a characteristic signature with the possibility of using it as a biomarker to help predict the risk factors associated with suicide. Within the scope of this current review, the most sought after epigenetic changes of DNA methylation and histone modification are thoroughly scrutinized to understand their close functional association with the broad spectrum of suicide phenotype.

Association between FKBP5 Functional Polymorphisms and Completed Suicide

OBJECTIVES

Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis leads to impaired stress response. FK506-binding protein 51 (FKBP5), which influences HPA axis activity via glucocorticoid receptors, is supposed to play an important role in the regulation of negative feedback and glucocorticoid resistance. Since ineffective stress response mechanisms are considered as a biological background of suicide behavior, we aimed to analyze a possible association between FKBP5 functional polymorphisms and completed suicide.

METHODS

The selected FKBP5 polymorphisms rs1360780 and rs3800373 were genotyped in a sample of 563 suicide victims and 475 controls.

RESULTS

A significant association between the high-induction rs3800373 C allele and completed suicide was detected (OR = 1.36, p = 0.007). In this polymorphism, genotype distribution supported a codominant model of inheritance. The analyzed SNPs were in strong linkage disequilibrium (D' = 0.916 and r2 = 0.826) with the rs1360780 (T)-rs3800373 (C) haplotype apparently responsible for the observed association (OR = 1.34, p = 0.010).

CONCLUSION

The results of the present study indicate that genetic alterations in FKBP5 may influence vulnerability to suicide.

Ambient air pollution and suicide in Tokyo, 2001-2011

BACKGROUND

Some evidence suggests an association may exist between the level of air pollution and suicide mortality. However, this relation has been little studied to date. The current study examined the association in Tokyo, Japan.

METHODS

Suicide mortality data for Tokyo for the 11-year period 2001-2011 were obtained together with data on four air pollutants: fine particulate matter (PM2.5), suspended particulate matter (SPM), sulphur dioxide (SO2) and nitrogen dioxide (NO2). A time-stratified case-crossover study design was used to examine the daily association between the level of air pollution and suicide mortality.

RESULTS

During the study period there were 29,939 suicide deaths. In stratified analyses an interquartile range (IQR) increase in the same-day concentration of NO2 was linked to increased suicide mortality among those aged under 30 (percentage change: 6.73%, 95% CI: 0.69-13.12%). An IQR increase in PM2.5 and SO2 was associated with a 10.55% (95% CI: 2.05-19.75%) and 11.47% (95% CI: 3.60-19.93%) increase, respectively, in suicide mortality among widowed individuals for mean exposure on the first four days (average lags 0-3). Positive associations were observed for the air pollutants in the summer although associations were reversed in autumn.

LIMITATIONS

We relied on monitoring data to approximate individual exposure to air pollutants.

CONCLUSIONS

Higher levels of air pollution are associated with increased suicide mortality in some population subgroups in Tokyo. Further research is needed to elucidate the mechanisms linking air pollutants and suicide in this setting.

Suicide in males and females with cardiovascular disease and comorbid depression

BACKGROUND

Myocardial infarction (MI) has been associated with an increased risk of suicide, further increased among individuals with a comorbid psychiatric illness. A paucity of studies have examined details of suicide among individuals with cardiovascular disease (CVD) and comorbid depression. We aimed to compare demographic, clinical and suicide-specific characteristics between suicide victims with CVD with depression (CVD+D) and without comorbid depression (CVD-D).

METHODS

Coroner data on suicide decedents with CVD (n=413) occurring in Toronto, Canada from 1998 to 2012 were collected. Characteristics were compared between the CVD+D and CVD-D groups. Regression analysis examined for gender differences in these groups.

RESULTS

CVD+D subjects compared to CVD-D were more likely to have had a past suicide attempt (p=0.008), and to have experienced a bereavement (p=0.008) or financial stressor (p=0.005) in the past year. Each of these variables remained significantly associated with the presence of depression after the regression analysis. Within the CVD+D group, females were more likely to die from suicide by self-poisoning (p<0.0001) and males by shooting (p=0.001).

LIMITATIONS

Psychological autopsies were not available. The definition of CVD was broad and the accuracy of its diagnosis could not be confirmed.

CONCLUSION

Individuals with CVD+D who died from suicide had significant differences in clinical characteristics and specific stressors compared to those without depression. These data may help to better characterize suicide risk and prevention in this vulnerable population.

A Neural Basis for the Acquired Capability for Suicide

The high rate of fatal suicidal behavior (SB) in men is an urgent issue as highlighted in the public eye via news sources and media outlets. In this study, we have attempted to address this issue and understand the neural substrates underlying the gender differences in the rate of fatal SB. The Interpersonal-Psychological Theory of Suicide has proposed an explanation for the seemingly paradoxical relationship between gender and SB, i.e., greater non-fatal suicide attempts by women but higher number of deaths by suicide in men. This theory states that possessing suicidal desire (due to conditions such as depression) alone is not sufficient for a lethal suicide attempt. It is imperative for an individual to have the acquired capability for suicide (ACS) along with suicidal desire in order to die by suicide. Therefore, higher levels of ACS in men may explain why men are more likely to die by suicide than women, despite being less likely to experience suicidal ideation or depression. In this study, we used activation likelihood estimation meta-analysis to investigate a potential ACS network that involves neural substrates underlying emotional stoicism, sensation-seeking, pain tolerance, and fearlessness of death, along with a potential depression network that involves neural substrates that underlie clinical depression. Brain regions commonly found in ACS and depression networks for males and females were further used as seeds to obtain regions functionally and structurally connected to them. We found that the male-specific networks were more widespread and diverse than the female-specific ones. Also, while the former involved motor regions, such as the premotor cortex and cerebellum, the latter was dominated by limbic regions. This may support the fact that suicidal desire generally leads to fatal/decisive action in males, while, in females, it manifests as depression, ideation, and generally non-fatal actions. The proposed model is a first attempt to characterize the neural networks underlying gender differences in SB. Future studies should examine the proposed network to better characterize and refine this network using tasks specifically targeted toward constructs underlying ACS.