In a subset of patients, chronic exposure to stress is an etiological risk factor for neuroinflammation and depression. Neuroinflammation affects up to 27% of patients with MDD and is associated with a more severe, chronic, and treatment-resistant trajectory. Inflammation is not unique to depression and has transdiagnostic effects suggesting a shared etiological risk factor underlying psychopathologies and metabolic disorders. Research supports an association but not necessarily a causation with depression. Putative mechanisms link chronic stress to dysregulation of the HPA axis and immune cell glucocorticoid resistance resulting in hyperactivation of the peripheral immune system. The chronic extracellular release of DAMPs and immune cell DAMP-PRR signaling creates a feed forward loop that accelerates peripheral and central inflammation. Higher plasma levels of inflammatory cytokines, most consistently interleukin IL-1β, IL-6, and TNF-α, are correlated with greater depressive symptomatology. Cytokines sensitize the HPA axis, disrupt the negative feedback loop, and further propagate inflammatory reactions. Peripheral inflammation exacerbates central inflammation (neuroinflammation) through several mechanisms including disruption of the blood–brain barrier, immune cellular trafficking, and activation of glial cells. Activated glial cells release cytokines, chemokines, and reactive oxygen and nitrogen species into the extra-synaptic space dysregulating neurotransmitter systems, imbalancing the excitatory to inhibitory ratio, and disrupting neural circuitry plasticity and adaptation. In particular, microglial activation and toxicity plays a central role in the pathophysiology of neuroinflammation. Magnetic resonance imaging (MRI) studies most consistently show reduced hippocampal volumes. Neural circuitry dysfunction such as hypoactivation between the ventral striatum and the ventromedial prefrontal cortex underlies the melancholic phenotype of depression. Chronic administration of monoamine-based antidepressants counters the inflammatory response, but with a delayed therapeutic onset. Therapeutics targeting cell mediated immunity, generalized and specific inflammatory signaling pathways, and nitro-oxidative stress have enormous potential to advance the treatment landscape. Future clinical trials will need to include immune system perturbations as biomarker outcome measures to facilitate novel antidepressant development. In this overview, we explore the inflammatory correlates of depression and elucidate pathomechanisms to facilitate the development of novel biomarkers and therapeutics.

/pdf/chronic-stress-neuroinflammation-and-depression-an-overview-2yceu6pu.pdf

Chronic stress, neuroinflammation, and depression: an overview of pathophysiological mechanisms and emerging anti-inflammatories

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. 

The NLRP3 inflammasome in depression: Potential mechanisms and therapies.

Interleukin-18 (IL18) is an inflammatory cytokine that is related to psychiatric disorders such as depression and cognitive impairment. We previously found that IL18 deficiency may cause hippocampal impairment, resulting in depression-like behavioral changes. However, the potential role of IL18 in stressful conditions remains uncertain. In the present study, we examined the effect of IL18 on neural inflammation and stress tolerance during acute stress. Littermate Il18+/+ and Il18-/- mice were exposed to a single restraint stress for 6 h, and all assessments were performed 18 h after the mice were released from the restraint. In Il18-/- mice exposed to acute stress, the immobility times in both the forced swim test and tail suspension test were decreased, although no difference was observed in Il18+/+ mice. Il1β, Il6, and Tnfα expression levels in the hippocampus of stressed Il18-/- mice were significantly higher than those in the other groups. Moreover, the numbers of astrocytes and microglia, including those in the active form, were also increased compared with those in other groups. Regarding the molecular mechanism, the HSF5 and TTR genes were specifically expressed in stressed Il18-/- mice. As a potential treatment, intracerebral administration of IL18 to Il18-/- mice resulted in partial recovery of changes in behavioral assessments. Our results revealed that IL18-deficient mice were more sensitive and had a longer response to acute stress than that in normal mice. In addition, neural inflammation and augmentation of glucocorticoid signals caused by stress were more intense and remained longer in Il18-/- mice, resulting in behavioral changes. In conclusion, IL18 might be an indispensable factor that modulates the stress response and maintains balance between neural inflammation and glucocorticoid signaling. 

/pdf/acute-stress-induces-severe-neural-inflammation-and-1pxwbnhl.pdf

Acute stress induces severe neural inflammation and overactivation of glucocorticoid signaling in interleukin-18-deficient mice

Interleukin 18 (IL18) was originally identified as an inflammation-induced cytokine that is secreted by immune cells. An increasing number of studies have focused on its non-immunological functions, with demonstrated functions for IL18 in energy homeostasis and neural stability. IL18 is reportedly required for lipid metabolism in the liver and brown adipose tissue. Furthermore, IL18 (Il18) deficiency in mice leads to mitochondrial dysfunction in hippocampal cells, resulting in depressive-like symptoms and cognitive impairment. Microarray analyses of Il18−/− mice have revealed a set of genes with differential expression in liver, brown adipose tissue, and brain; however, the impact of IL18 deficiency in these tissues remains uncertain. In this review article, we discuss these genes, with a focus on their relationships with the phenotypic disease traits of Il18−/− mice.

Molecular Mechanisms of IL18 in Disease

Recent advances on the role of pro-inflammatory cytokine interleukin-18 in post-stroke depression

Abstract Background Interleukin-18 (IL-18) may participate in the development of major depressive disorder, but the specific mechanism remains unclear. This study aimed to explore whether IL-18 correlates with areas of the brain associated with depression. Methods Using a case–control design, 68 subjects (34 patients and 34 healthy controls) underwent clinical assessment, blood sampling, and resting-state functional Magnetic Resonance Imaging (fMRI). The total Hamilton depression-17 (HAMD-17) score was used to assess depression severity. Enzyme-linked immunosorbent assay (ELISA) was used to detect IL-18 levels. Rest-state fMRI was conducted to explore spontaneous brain activity. Results The level of IL-18 was higher in patients with depression in comparison with healthy controls. IL-18 was negatively correlated with degree centrality of the left posterior cingulate gyrus in the depression patient group, but no correlation was found in the healthy control group. Conclusion This study suggests the involvement of IL-18 in the pathophysiological mechanism for depression and interference with brain activity. 

/pdf/peripheral-interleukin-18-is-negatively-correlated-with-2go6zfmu.pdf

Peripheral Interleukin-18 is negatively correlated with abnormal brain activity in patients with depression: a resting-state fMRI study

Objective: The majority of non-small cell lung cancer (NSCLC) cases remain undiagnosed until advanced stages of the disease. Accumulating studies have highlighted the utility of palliative care as an effective treatment option, which relieves patients’ suffering by activating placebo effect in the body. To evaluate the clinical significance of palliative care, data from NSCLC drug-randomized controlled trials (RCTs) were collected and the effects of placebo treatment examined. Methods: PubMed (MEDLINE), Scopus, Web of Science, and China National Knowledge Infrastructure databases were searched from January 1,1978 to September 1,2020. Placebo-controlled phase II/III pharmaceutical RCTs enrolling patients with solely stage III/IV NSCLC were included. The quality of included studies was assessed using the Jadad method. Single-arm and two-arm meta-analyses of the therapeutic and adverse effects of placebo, that is, the primary and secondary outcome measures, were subsequently performed using either Bayesian or conventional models. Results: Five RCTs including 2245 drug-treated and 1510 placebo-treated patients at NSCLC stage III or IV were included for the study. Low risk of bias was observed for all five included studies using the Cochrane method. Following placebo treatment, controlled disease rate of 24.1% (95% credible interval [CrI], –0.126–0.609) and dropout rate of 2.1% (95% CrI, 0.007–0.039) were calculated, with a dose reduction rate of 3.0% (95% CrI, 0.017–0.045). Compared with active drug treatment, the placebo treatment group had a risk ratio of 0.81 (95% confidence interval, 0.68-0.97) and 0.85 (95% confidence interval, 0.76–0.96) for the achievement of progression-free survival and overall survival, respectively. Conclusion: In NSCLC drug RCTs, placebo treatment is indicated to generally induce low toxicity in patients by dropout and dose reduction rates and adverse events, although the therapeutic responses could not be precisely determined. The results suggest that under specific circumstances, palliative care which can activate placebo effect may have similar effects as active drugs (such as erlotinib, vandetanib, or pemetrexed) in terms of prolonging survival time. 

Placebo effect in the treatment of non-small cell lung cancer: a meta-analysis

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Peripheral Interleukin-18 is negatively correlated with abnormal brain activity in patients with depression: a resting-state fMRI study

Placebo effect in the treatment of non-small cell lung cancer: a meta-analysis