Editorial: Stress, depression and the immune system

Immunological correlates of suicidality among adolescents with internalizing symptoms

Background

Suicide is a leading cause of death in adolescents and young adults globally. Well-established risk factors for suicide are depression and past suicide attempts. People experiencing suicidality may represent a distinct neurobiological group of people with depression. Because converging evidence has implicated inflammation in depression, we sought to investigate relationships between suicidality and immune markers in youth experiencing diverse mood and anxiety symptoms. We hypothesized that adolescents with suicidality would exhibit a unique immune signature.

Methods

Adolescents underwent semi-structured interviews and completed self-reported measures to assess psychopathology, including suicidality (suicidal ideation, plans, or attempts). Fasting blood samples were collected, cultured with and without lipopolysaccharide (LPS) to stimulate an inflammatory response, and analyzed for 41 immune analytes. To assess how immune function related to suicidality categorically and dimensionally, we conducted group comparisons and correlations while controlling for multiple comparisons using false discovery rate (FDR). To further uncover subtle immune-suicidality relationships, we employed a data-driven approach using factor analysis to extract major immune factors, each of which was subsequently correlated with suicidality measures.

Results

Among 126 participants, 29 were healthy controls and 97 participants had internalizing symptoms; within the clinical group, 57 experienced suicidality. Three immune analytes differed between healthy controls, suicidal, and non-suicidal adolescents with internalizing symptoms in the LPS condition: Flt-3L (p FDR = 0.0246), GM-CSF (p FDR = 0.0246), and IFN-γ (p FDR = 0.0246). These analytes were negatively correlated with the Beck Scale for Suicide Ideation (BSSI): Flt-3L (ρ = -0.19, p = 0.04); GM-CSF (ρ = -0.26, p = 0.004); IFN-γ (ρ =-0.33, p = 0.0003). GM-CSF also negatively correlated with number of suicide attempts (ρ = -0.39, p = 0.003). Factor analysis reduced 41 analytes to several common immune factors across experimental conditions, with Flt-3L, GM-CSF, and IFN-γ all loading heavily onto immune factors that were hypoactive in suicidality. Through this data-driven approach, we detected further associations between suicidality and immune factors across all conditions.

Conclusions

Peripheral immune function may be distinctly altered in adolescent suicidality. Future work should examine immune-suicidality relationships longitudinally.

Pharmacological Mechanism of Ketamine in Suicidal Behavior Based on Animal Models of Aggressiveness and Impulsivity: A Narrative Review

Around 700,000 people die from suicide each year in the world. Approximately 90% of suicides have a history of mental illness, and more than two-thirds occur during a major depressive episode. Specific therapeutic options to manage the suicidal crisis are limited and measures to prevent acting out also remain limited. Drugs shown to reduce the risk of suicide (antidepressants, lithium, or clozapine) necessitate a long delay of onset. To date, no treatment is indicated for the treatment of suicidality. Ketamine, a glutamate NMDA receptor antagonist, is a fast-acting antidepressant with significant effects on suicidal ideation in the short term, while its effects on suicidal acts still need to be demonstrated. In the present article, we reviewed the literature on preclinical studies in order to identify the potential anti-suicidal pharmacological targets of ketamine. Impulsive-aggressive traits are one of the vulnerability factors common to suicide in patients with unipolar and bipolar depression. Preclinical studies in rodent models with impulsivity, aggressiveness, and anhedonia may help to analyze, at least in part, suicide neurobiology, as well as the beneficial effects of ketamine/esketamine on reducing suicidal ideations and preventing suicidal acts. The present review focuses on disruptions in the serotonergic system (5-HT_B receptor, MAO-A enzyme), neuroinflammation, and/or the HPA axis in rodent models with an impulsive/aggressive phenotype, because these traits are critical risk factors for suicide in humans. Ketamine can modulate these endophenotypes of suicide in human as well as in animal models. The main pharmacological properties of ketamine are then summarized. Finally, numerous questions arose regarding the mechanisms by which ketamine may prevent an impulsive-aggressive phenotype in rodents and suicidal ideations in humans. Animal models of anxiety/depression are important tools to better understand the pathophysiology of depressed patients, and in helping develop novel and fast antidepressant drugs with anti-suicidal properties and clinical utility.

Proinflammatory cytokines in the prefrontal cortex of teenage suicide victims

Teenage suicide is a major public health concern, but its neurobiology is not well understood. Proinflammatory cytokines play an important role in stress and in the pathophysiology of depression-two major risk factors for suicide. Cytokines are increased in the serum of patients with depression and suicidal behavior; however, it is not clear if similar abnormality in cytokines occurs in brains of suicide victims. We therefore measured the gene and protein expression levels of proinflammatory cytokines interleukin (IL)-1β, IL-6, and tissue necrosis factor (TNF)-α in the prefrontal cortex (PFC) of 24 teenage suicide victims and 24 matched normal control subjects. Our results show that the mRNA and protein expression levels of IL-1β, IL-6, and TNF-α were significantly increased in Brodmann area 10 (BA-10) of suicide victims compared with normal control subjects. These results suggest an important role for IL-1β, IL-6, and TNF-α in the pathophysiology of suicidal behavior and that proinflammatory cytokines may be an appropriate target for developing therapeutic agents.

Changes in the immune system in depression and dementia: causal or co-incidental effects?

It is now widely accepted that psychological stress and psychiatric illness can compromise immune function. Furthermore the mechanisms whereby such changes occur are probably associated with the activities of the cytokines and other inflammatory mediators of the immune system which are known to initiate changes in behaviour. This review aims to summarise the experimental and clinical evidence that implicates the pro-inflammatory cytokines in the pathological changes seen in major depression and in Alzheimer's disease (AD). In major depression, evidence is provided to show that both activation (e.g., macrophage activity, acute phase proteins) and inhibition (e.g., natural killer cell activity) of the immune system occur. Many of the behavioural changes seen in depression are simulated by three pro-inflammatory cytokines (IL-1, IL-6 and TNF-alpha), which may produce their impact on the brain by activating cyclooxygenase, nitric acid synthase and corticotrophin releasing factor. Effective antidepressant treatments largely attenuate the immune changes thereby raising the possibility that the normalisation of central biogenic amine function that are conventionally implicated in the cause of depression may be secondary to those of the pro-inflammatory cytokines. With respect to AD, while the cause(s) are unknown, there is both experimental and clinical evidence to suggest that inflammatory processes in the brain caused in particular by TNF-alpha together with the subsequent rise in free radicals, are instrumental in causing the pathological changes which underlie the disease. Evidence in favour of the inflammatory hypothesis is supported by the finding that nonsteroidal anti-inflammatory drugs slow down the progression of the disease.Although, more research is needed into the inter-relationships between the various pro-inflammatory cytokines and the behavioural changes invoked in major depression and AD, the immunological hypothesis has been important in stimulating new concepts regarding the causes of the pathological changes in these diseases and how effective drug treatments may attenuate them.