The importance of tryptophan as a precursor for neuroactive compounds has long been acknowledged. The metabolism of tryptophan along the kynurenine pathway and its involvement in mental disorders is ...an emerging area in psychiatry. We performed a meta-analysis to examine the differences in kynurenine metabolites in major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ). Electronic databases were searched for studies that assessed metabolites involved in the kynurenine pathway (tryptophan, kynurenine, kynurenic acid, quinolinic acid, 3-hydroxykynurenine, and their associate ratios) in people with MDD, SZ, or BD, compared to controls. We computed the difference in metabolite concentrations between people with MDD, BD, or SZ, and controls, presented as Hedges' g with 95% confidence intervals. A total of 101 studies with 10,912 participants were included. Tryptophan and kynurenine are decreased across MDD, BD, and SZ; kynurenic acid and the kynurenic acid to quinolinic acid ratio are decreased in mood disorders (i.e., MDD and BD), whereas kynurenic acid is not altered in SZ; kynurenic acid to 3-hydroxykynurenine ratio is decreased in MDD but not SZ. Kynurenic acid to kynurenine ratio is decreased in MDD and SZ, and the kynurenine to tryptophan ratio is increased in MDD and SZ. Our results suggest that there is a shift in the tryptophan metabolism from serotonin to the kynurenine pathway, across these psychiatric disorders. In addition, a differential pattern exists between mood disorders and SZ, with a preferential metabolism of kynurenine to the potentially neurotoxic quinolinic acid instead of the neuroprotective kynurenic acid in mood disorders but not in SZ.
Major depressive disorder (MDD) is a psychiatric condition that affects a large number of people in the world, and the treatment existents do not work for all individuals affected. Thus, it is ...believed that other systems or pathways which regulate brain networks involved in mood regulation and cognition are associated with MDD pathogenesis. Studies in humans and animal models have been shown that in MDD there are increased levels of inflammatory mediators, including cytokines and chemokines in both periphery and central nervous system (CNS). In addition, microglial activation appears to be a key event that triggers changes in signaling cascades and gene expression that would be determinant for the onset of depressive symptoms. Recent researches also point out that changes in the gut microbiota would lead to a systemic inflammation that in different ways would reach the CNS modulating inflammatory pathways and especially the microglia, which could influence responses to treatments. Moreover, pre‐ and probiotics have shown antidepressant responses and anti‐inflammatory effects. This review will focus on studies that show the relationship of inflammation with the gut microbiota–brain axis and its relation with MDD.
Stress situations could lead to an impairment in the gut microbiota that in turn lead to a production of inflammatory mediators and a decrease in SCFAs. Changes in the gut microbiota may impact the gut barrier and to produce higher levels of inflammatory cytokines in the blood. In the periphery, the kynurenine pathways, metabolic, mainly toxic metabolic, are influenced by changes in the gut microbiota and inflammatory mediators. Products from microbiota impairment or periphery pro‐inflammatory cytokines could disrupt BBB and cross to the brain increasing cytokines releasing in the brain‐resident cells, including microglia and astrocytes. Changes in these glial cells influence brain networks that could be behind the onset of MDD.
Recent studies have suggested that mitochondrial dysfunction and dysregulated neuroinflammatory pathways are involved in the pathophysiology of major depressive disorder (MDD). Here, we aimed to ...assess the differences in markers of mitochondrial dynamics, mitophagy, general autophagy, and apoptosis in peripheral blood mononuclear cells (PBMCs) of MDD patients (n = 77) and healthy controls (HCs, n = 24). Moreover, we studied inflammation engagement as a moderator of mitochondria dysfunctions on the severity of depressive symptoms. We found increased levels of Mfn-2 (p < 0.001), short Opa-1 (S-Opa-1) (p < 0.001) and Fis-1 (p < 0.001) in MDD patients, suggesting an increase in the mitochondrial fragmentation. We also found that MDD patients had higher levels of Pink-1 (p < 0.001), p62/SQSTM1 (p < 0.001), LC3B (p = 0.002), and caspase-3 active (p = 0.001), and lower levels of parkin (p < 0.001) compared with HCs. Moreover, we showed that that MDD patients with higher CRP levels had higher levels of Mfn-2 (p = 0.001) and LC3B (p = 0.002) when compared with MDD patients with low CRP. Another notable finding was that the severity of depressive symptoms in MDD is associated with changes in protein levels in pathways related to mitochondrial dynamics and mitophagy, and can be dependent on the inflammatory status. Overall, our study demonstrated that a disruption in the mitochondrial dynamics network could initiate a cascade of abnormal changes relevant to the critical pathological changes during the course of MDD and lead to poor outcomes.
The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) are important for the maintenance of brain homeostasis
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During sepsis, peripheral production of proinflammatory ...cytokines and reactive oxygen species are responsible for structural alterations in those brain barriers. Thus, an increasing permeability of these barriers can lead to the activation of glial cells such as microglia and the production of cytotoxic mediators which in turn act on the brain barriers, damaging them further. Thereby, in this review, we try to highlight how the brain barrier’s permeability is not only a cause but a consequence of brain injury in sepsis.
Studies investigating inflammatory markers in post-traumatic stress disorder (PTSD) have yielded mixed results. The aim of our study was to compare concentrations of inflammatory markers in patients ...with PTSD compared with healthy controls.
We did a meta-analysis and meta-regression of studies comparing inflammatory markers between patients with PTSD and healthy controls by searching PubMed, Embase, Scopus, Web of Science, and PsycINFO for articles published between Jan 1, 1960, and April 7, 2015. From eligible studies (ie, cross-sectional studies or baseline data from longitudinal studies of peripheral blood cytokine concentrations that compared adults with PTSD with healthy controls), we extracted outcomes of interest, such as mean and SD of peripheral blood cytokines, the time of day blood was collected, whether the study allowed patients with comorbid major depressive disorder in the PTSD group, whether patients were medication free, and severity of PTSD symptoms. We undertook meta-analyses whenever values of inflammatory markers were available in two or more studies. A random-effects model with restricted maximum-likelihood estimator was used to synthesise the effect size (assessed by standardised mean difference SMD) across studies.
8057 abstracts were identified and 20 studies were included. Interleukin 6 (SMD 0.88; p=0.0003), interleukin 1β (SMD 1.42; p=0.045), and interferon γ (SMD 0.49; p=0.002) levels were higher in the PTSD group than in healthy controls. Subgroup meta-analysis of patients who were not given medication showed higher tumour necrosis factor α (TNFα; SMD 0.69, 95% CI 0.35-1.02; p<0.0001) in the PTSD group than the control group in addition to the aforementioned cytokines. TNFα (SMD 1.32, 0.13-2.50; p=0.003), interleukin 1β (SMD 2.35, 0.01-4.68; p=0.048), and interleukin 6 (SMD 1.75, 0.97-2.53; p<0.0001) levels remained increased in the PTSD group in a subgroup meta-analysis of studies that excluded comorbid major depressive disorder. Illness duration was positively associated with interleukin 1β levels (b=0.33, p<0.0001) and severity with interleukin 6 (b=0.02, p=0.042). A model composed of several variables-presence of comorbid major depressive disorder, use of psychotropic medications, assay used, and time of day blood was collected-explained the large amount of heterogeneity between interleukin 1β, interleukin 6, and C-reactive protein studies. Egger's linear regression test revealed a potential publication bias for interleukin 1β. Additionally, for most inflammatory markers, study heterogeneity was reported to be high (I(2)>75%).
PTSD is associated with increased interleukin 6, interleukin 1β, TNFα, and interferon γ levels. This information might be useful for consideration of chronic low-grade inflammation as a potential target or biomarker in PTSD treatment. Use of psychotropic medication and presence of comorbid major depressive disorder were important moderators that might explain the inconsistency between results of previous studies. Our search strategy used a range of databases and we made exhaustive effort to acquire data by contacting the authors. Notably, high levels of between-study heterogeneity were recorded for most cytokine variables measured in our analysis. However, meta-regression analysis could explain a large amount of this heterogeneity.
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Bipolar disorder (BD) is a chronic psychiatric illness characterized by severe and biphasic changes in mood. Several pathophysiological mechanisms have been hypothesized to underpin the neurobiology ...of BD, including the presence of mitochondrial dysfunction. A confluence of evidence points to an underlying dysfunction of mitochondria, including decreases in mitochondrial respiration, high-energy phosphates and pH; changes in mitochondrial morphology; increases in mitochondrial DNA polymorphisms; and downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration. Mitochondria play a pivotal role in neuronal cell survival or death as regulators of both energy metabolism and cell survival and death pathways. Thus, in this review, we discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BD. The final part of this review discusses mitochondria as a potential target of therapeutic interventions in BD.
Abstract Objectives The first drug repurposed for the treatment of depression was the tuberculostatic iproniazid. At present, drugs belonging to new classes of antidepressants still have ...antimicrobial effects. Dysbiosis of gut microbiota was implicated in the development or exacerbation of mental disorders, such as major depressive disorder (MDD). Based on the current interest in the gut-brain axis, the focus of this narrative review is to compile the available studies regarding the influences of gut microbiota in behavior and depression and to show the antimicrobial effect of antidepressant drugs. A discussion regarding the possible contribution of the antimicrobial effect of antidepressant drugs to its effectiveness/resistance is included. Methods The search included relevant articles from PubMed, SciELO, LILACS, PsycINFO, and ISI Web of Knowledge. Results MDD is associated with changes in gut permeability and microbiota composition. In this respect, antidepressant drugs present antimicrobial effects that could also be related to the effectiveness of these drugs for MDD treatment. Conversely, some antimicrobials present antidepressant effects. Conclusion Both antidepressants and antimicrobials present neuroprotective/antidepressant and antimicrobial effects. Further studies are needed to evaluate the participation of antimicrobial mechanisms of antidepressants in MDD treatment as well as to determine the contribution of this effect to antidepressant resistance.
Severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2) causes the coronavirus disease 2019 (COVID-19), which has been declared a public health emergency of international interest, with ...confirmed cases in most countries. COVID-19 presents manifestations that can range from asymptomatic or mild infections up to severe manifestations that lead to hospitalization and death. A growing amount of evidence indicates that the virus may cause neuroinvasion. Postmortem brain study findings have included edema, hemorrhage, hydrocephalus, atrophy, encephalitis, infarcts, swollen axons, myelin loss, gliosis, neuronal satellitosis, hypoxic-ischemic damage, arteriolosclerosis, leptomeningeal inflammation, neuronal loss, and axon degeneration. In addition, the COVID-19 pandemic is causing dangerous effects on the mental health of the world population, some of which can be attributed to its social impact (social distancing, financial issues, and quarantine). There is also a concern that environmental stressors, enhanced by psychological factors, are contributing to the emergence of psychiatric outcomes during the pandemic. Although clinical studies and diagnosing SARS-CoV-2-related neurological disease can be challenging, they are necessary to help define the manifestations and burden of COVID-19 in neurological and psychiatric symptoms during and after the pandemic. This review aims to present the neurobiology of coronavirus and postmortem neuropathological hallmarks.
There is accumulating evidence demonstrating that dysfunction of glutamatergic neurotransmission, particularly via N-methyl-d-aspartate (NMDA) receptors, is involved in the pathophysiology of major ...depressive disorder (MDD). Several studies have revealed an altered expression of NMDA receptor subtypes and impaired NMDA receptor-mediated intracellular signaling pathways in brain circuits of patients with MDD. Clinical studies have demonstrated that NMDA receptor antagonists, particularly ketamine, have rapid antidepressant effects in treatment-resistant depression, however, neurobiological mechanisms are not completely understood. Growing body of evidence suggest that signal transduction pathways involved in synaptic plasticity play critical role in molecular mechanisms underlying rapidly acting antidepressant properties of ketamine and other NMDAR antagonists in MDD. Discovering the molecular mechanisms underlying the unique antidepressant actions of ketamine will facilitate the development of novel fast acting antidepressants which lack undesirable effects of ketamine. This review provides a critical examination of the NMDA receptor involvement in the neurobiology of MDD including analyses of alterations in NMDA receptor subtypes and their interactive signaling cascades revealed by postmortem studies. Furthermore, to elucidate mechanisms underlying rapid-acting antidepressant properties of NMDA receptor antagonists we discussed their effects on the neuroplasticity, mostly based on signaling systems involved in synaptic plasticity of mood-related neurocircuitries.
•Synaptic plasticity is critical for NMDA receptor antagonists effects.•Depressive patients show altered levels of NMDA receptor subunits in the brain.•Ketamine effects could be result of brain networks connectivity changes.
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