Neuroimmunology of depression

Exploratory studies of the antidepressant effect of Cordyceps sinensis polysaccharide and its potential mechanism

Cordyceps sinensis, a traditionally prized medicinal fungus, contains polysaccharides as one of its main bioactive constituents, known for their significant immunomodulatory properties. In this study, we systematically investigated the composition and structure of Cordyceps sinensis polysaccharide, followed by an evaluation of its therapeutic effect on depression using a chronic restraint stress-induced depression model. The polysaccharide CSWP-2, extracted via hot water, precipitated with ethanol, and purified using DEAE-cellulose column chromatography from Cordyceps sinensis, is primarily composed of glucose, mannose, and galactose, with α-1,4-D-glucan as its major structural component. Behavioral tests, immunological profiling, metabolomics, and gut microbiota analyses indicated a notable ameliorative effect of CSWP-2 on depressive-like symptoms in mice. Furthermore, the action of CSWP-2 may be attributed to the modulation of the gut microbiome's abundance and its metabolic impacts, thereby transmitting signals to the host immune system and exerting immunomodulatory activity, ultimately contributing to its antidepressant effects.

Peripheral CD4+ T helper lymphocytes alterations in major depressive disorder: A systematic review and meta-analysis

Previous research has shown that patients with major depressive disorder (MDD) develop immune dysfunction. However, the exact alterations of cluster of differentiation (CD)4+ T helper (Th) lymphocytes in MDD remains unclear. This meta-analysis aimed to examine the specific changes in CD4+ Th cells. A comprehensive search of PubMed, EMBASE, Web of Science, and PsycINFO databases was conducted to identify studies investigating CD4+ Th, Th1, Th2, Th17, and T regulatory (Treg) cell counts in the peripheral blood of MDD patients and healthy controls (HCs), covering the period up to June 22, 2024. Our findings revealed that patients with MDD might exhibit higher CD4+ Th cells (SMD=0.26, 95 %CI, 0.02 to 0.50), CD4+/CD8+ cell ratios (SMD=0.51, 95 %CI, 0.14 to 0.89), Th1/Th2 cell ratios (SMD=0.15, 95 %CI, 0.01 to 0.30) and lower Th1 (SMD=-0.17, 95 %CI, -0.30 to -0.03), Th2 (SMD=-0.25, 95 %CI, -0.40 to -0.11), and Treg cells (SMD=-0.69, 95 %CI, -1.27 to -0.11). However, no significant difference was observed in terms of Th17 cells and Th17/Treg cell ratios between MDD patients and the HCs. Heterogeneity was large (I2:18.1-95.2 %), and possible sources of heterogeneity were explored (e.g., age, depression scale, country, and antidepressant use). Our findings indicate that peripheral CD4+ T cells in depressed patients exhibit features of adaptive immune dysfunction, as evidenced by increased CD4+ Th cells and CD4+/CD8+ and decreased Treg cells. These findings offer insights into the underlying mechanism of MDD.

β-arrestin2 is indispensable for the antidepressant effects of fluoxetine via inhibiting astrocytic pyroptosis in chronic mild stress mouse model for depression

β-arrestin2 is a versatile protein for signaling transduction in brain physiology and pathology. Herein, we investigated the involvement of β-arrestin2 in pharmacological effects of fluoxetine for depression. A chronic mild stress (CMS) model was established using wild-type (WT) and β-arrestin2-/- mice. Behavioral results demonstrated that CMS mice showed increased immobility time in the tail suspension test and forced swimming test, elevated concentrations of pro-inflammatory factors in peripheral blood, increased expression of pyroptosis-related proteins, and increased co-labeling of glial fibrillary acidic protein and Caspase1 p10 in the hippocampus compared to the CON group. Treatment with fluoxetine (FLX) ameliorated these conditions. However, compared with the β-arrestin2-/- CMS group, these results of the β-arrestin2-/- CMS + FLX group showed no significant changes. These results suggested that the above effects of FLX could be eliminated by knocking out β-arrestin2. Mass spectrometry implying that FLX promoted the binding of β-arrestin2 to the NLRP2 inflammasome of depressed mice. Subsequently, the results of the cellular experiments suggested that the 5HT2B receptor antagonist may attenuate L-kynurenine + ATP-induced cell pyroptosis by attenuating NLRP2 binding to β-arrestin2. We further found that the lack of β-arrestin2 eliminated the anti-pyroptosis effect of fluoxetine. In conclusion, β-arrestin2 is an essential protein for fluoxetine to alleviate pyroptosis in the hippocampal astrocytes of CMS mice. Mechanistically, we found that the 5-HT2BR-β-arrestin2-NLRP2 axis is vital for maintaining the antidepressant effects of fluoxetine.

Depression, an unmet health need in Africa: Understanding the promise of ketamine

In Africa, there is currently a paucity of data on the epidemiology of depression, its treatment and management. The prevalence of depression is severely underestimated, with unique circumstances and societal risk factors associated with depression and its public awareness. Treating and managing depression is confounded by an inaccessibility to efficient and low-cost treatments for patients with depression. The aetiology of depression is multifactorial, with various theories implicating multiple neuronal networks. Despite this, the treatment of depression is one-dimensional focussing on outdated theories of depression and mainly targeting dysfunctional neurotransmitter pathways. Hence, it is not surprising that there is a significant increase in the prevalence of patients suffering from treatment resistant depression (TRD), with a large portion of patients deriving little clinical benefit from these traditional anti-depressant therapies. This highlights the need for more effective treatment strategies for depression, especially applicable to resource limited environments such as Africa, where there is little investment in public healthcare resources towards managing mental health disorders. The clinical potential of using ketamine in managing depression has received considerable attention in the past two decades, with the FDA approving esketamine for the management of TRD in 2019. This widespread attention has significantly increased ketamine's appeal as a novel antidepressant. Consequently, many ketamine infusion clinics have been established in Africa. However, there is little regulation or guidance for ketamine infusions. Furthermore, while esketamine is expensive and hence inaccessible to a large portion of the African population, racemic ketamine is significantly cheaper and has demonstrated clinical potential. However, there is currently a limited understanding of the neurological mechanisms of action of racemic ketamine in treating and managing depression, especially in a diverse African population. Therefore, this review aims to provide an African context of depression and the therapeutic potential of ketamine by highlighting aspects of its molecular mechanism of action.

Minocycline in depression not responding to first-line therapy: A systematic review and meta-analysis

BACKGROUND

Major depressive disorder is often resistant to first-line treatment, with around 30% failing to respond to traditional therapy. Treatment-resistant depression results in prolonged hospitalization and healthcare costs. Anti-inflammatory drugs have shown promising results in depression not responding to initial therapy. Minocycline has anti-inflammatory properties and crosses the blood-brain barrier. It has demonstrated varied results in several randomized controlled trials (RCTs).

METHODS

We assessed the efficacy of minocycline compared to placebo in depression not responding to one first-line antidepressant via a systematic review and meta-analysis. We performed a comprehensive literature search across PubMed, Cochrane, and Scopus for RCTs. We visualized the results using forest plots and drapery plots. We assessed and explored heterogeneity using I2, prediction interval, and meta-regression. Then, we rated the certainty of the evidence.

RESULTS

Four RCTs revealed a non-significant difference in depression severity [-3.93; 95% CI: -16.14 to 8.28], rate of response [1.15; 0.33-4.01], and rate of remission [0.94; 0.44-2.01]. However, the reduction in depression severity is significant at a trend of P < .1. The high between-study heterogeneity (I2 = 78%) for depression severity could be answered by meta-regression (P = .02) for the duration of therapy.

CONCLUSION

There is no significant difference with minocycline compared to placebo for depression not responding to first-line antidepressant therapy. However, the treatment response varies with treatment duration and patients' neuroinflammatory state. Thus, larger and longer RCTs, especially in diverse disease subgroups, are needed for further insight. This is needed to allow greater precision medicine in depression and avoid elevated healthcare expenditure associated with hit-and-trial regimens.

REGISTRATION

CRD42023398476 (PROSPERO).

Exploring the Relationship between Mood Disorders and Coexisting Health Conditions: The Focus on Nutraceuticals

Major depressive disorder and bipolar disorder are the leading causes of global disability. Approximately 50% of patients fail to attain remission, prompting a pronounced focus on the significance of dietary patterns and specific nutrients within the pathophysiology of mood disorders. The connection between chronic diseases and mood disorders follows a bidirectional pattern: physical ailments are interrelated with affective disorders, and, concurrently, mood symptoms often precede chronic diseases and have the potential to worsen their prognosis. Nutraceuticals affect factors that could potentially impact the onset of mood disorders: monoamines and brain-derived neurotrophic factor (BDNF) concentrations, neuroinflammation, oxidative stress, and sleep quality. Furthermore, mood disorders rarely manifest in isolation. Typically, such patients concurrently experience other mental disorders or somatic comorbidities: obesity, hypertension, diabetes, polycystic ovary syndrome (PCOS), etc., where providing nutritional support is also pertinent. To optimize the therapeutic approach for individuals with mood disorders, incorporating nutritional support may not solely ameliorate symptoms stemming directly from the mental condition, but also indirectly through interventions targeting comorbidities.

Harmine exerts anxiolytic effects by regulating neuroinflammation and neuronal plasticity in the basolateral amygdala

Increasing evidence indicates that an altered immune system is closely linked to the pathophysiology of anxiety disorders, and inhibition of neuroinflammation may represent an effective therapeutic strategy to treat anxiety disorders. Harmine, a beta-carboline alkaloid in various medicinal plants, has been widely reported to display anti-inflammatory and potentially anxiolytic effects. However, the exact underlying mechanisms are not fully understood. Our recent study has demonstrated that dysregulation of neuroplasticity in the basolateral amygdala (BLA) contributes to the pathological processes of inflammation-related anxiety. In this study, using a mouse model of anxiety challenged with Escherichia coli lipopolysaccharide (LPS), we found that harmine alleviated LPS-induced anxiety-like behaviors in mice. Mechanistically, harmine significantly prevented LPS-induced neuroinflammation by suppressing the expression of pro-inflammatory cytokines including IL-1β and TNF-α. Meanwhile, ex vivo whole-cell slice electrophysiology combined with optogenetics showed that LPS-induced increase of medial prefrontal cortex (mPFC)-driven excitatory but not inhibitory synaptic transmission onto BLA projection neurons, thereby alleviating LPS-induced shift of excitatory/inhibitory balance towards excitation. In addition, harmine attenuated the increased intrinsic neuronal excitability of BLA PNs by reducing the medium after-hyperpolarization. In conclusion, our findings provide new evidence that harmine may exert its anxiolytic effect by downregulating LPS-induced neuroinflammation and restoring the changes in neuronal plasticity in BLA PNs.

Memory impairments in rodent depression models: A link with depression theories

More than 80% of depressed patients struggle with learning new tasks, remembering positive events, or concentrating on a single topic. These neurocognitive deficits accompanying depression may be linked to functional and structural changes in the prefrontal cortex and hippocampus. However, their mechanisms are not yet completely understood. We conducted a narrative review of articles regarding animal studies to assess the state of knowledge. First, we argue the contribution of changes in neurotransmitters and hormone levels in the pathomechanism of cognitive dysfunction in animal depression models. Then, we used numerous neuroinflammation studies to explore its possible implication in cognitive decline. Encouragingly, we also observed a positive correlation between increased oxidative stress and a depressive-like state with concomitant memory deficits. Finally, we discuss the undeniable role of neurotrophin deficits in developing cognitive decline in animal models of depression. This review reveals the complexity of depression-related memory impairments and highlights the potential clinical importance of gathered findings for developing more reliable animal models and designing novel antidepressants with procognitive properties.

Brain regional pharmacokinetics of hydroxytyrosol and its molecular mechanism against depression assessed by multi-omics approaches

BACKGROUND

Hydroxytyrosol (HT), as the main compound in olive leaves with its potential ability to cross blood-brain barrier (BBB), has exhibited the advantaged antidepressant effect. However, no information is available regarding the brain regional uptake of HT, as well the underlying antidepressant mechanism remains unclear.

PURPOSE

To comprehensively reveal the brain uptake of HT and its specific mechanism on the accompanying antidepressant activity.

STUDY DESIGN AND METHODS

The BBB penetration and brain regional distribution of HT in the normal and chronic unpredictable mild stress (CUMS)-induced depressive mice in consideration with the BBB integrality were analyzed. Then, the hippocampal region-specific responses of biomolecules and concurrent alterations in the therapeutic effect of HT on depression were explored using untargeted metabolomics, spatial-resolved metabolomics and tissue proteomics, which were confirmed by LPS-induced BV-2 microglia and CUMS mice.

RESULTS

BBB permeability analysis in normal and CUMS mice confirmed that increased BBB permeability of CUMS mice was induced by the deficiency of tight junction-related proteins. Consistently, according to the established LC-MS/MS method, it was found that HT could not be largely detected in the cerebrospinal fluids and brains of normal mice after oral administration, while it could excessively penetrate the BBB (200-fold higher), and mostly distributed in the hippocampus of CUMS mice. Meanwhile, multi-omics analysis combined with targeted analysis discovered that HT could mainly improve fatty acid biosynthesis and metabolism in the hippocampus with region-specific responses and accompanying inhibition of C3-CD11b pathway in CUMS mice. Besides, in vitro experiments further confirmed the anti-complement ability of HT, which could inhibit C3-CD11b pathway for alleviating the LPS-induced BV-2 microglia activation.

CONCLUSION

HT can excessively penetrate the BBB and be mostly distributed in the hippocampus of depressive mice, which contribute to improve fatty acid biosynthesis and metabolism in the hippocampus with region-specific responses and accompanying inhibition of C3-CD11b pathway for microglia activation. These findings give the clearer understanding of brain regional pharmacokinetics of HT and its accompanying molecular mechanism against depression.

Clinical correlates of autoimmune thyroiditis and non-autoimmune hypothyroidism in treatment-naïve patients with major depressive disorders

BACKGROUND

Thyroid autoimmunity is a potentially critical factor that is often neglected in the association between subclinical hypothyroidism (SCH) and depressive disorders. This study aimed to investigate the clinical correlates of autoimmune thyroiditis (AIT) and non-autoimmune hypothyroidism (NAIH) in treatment-naïve patients with major depressive disorder (MDD).

METHOD

Using a cross-sectional design, we recruited a total of 1718 outpatients with treatment-naïve MDD. Demographic and relevant clinical information including duration of MDD, severity of depression and anxiety, psychotic symptoms, suicide attempts, thyroid function parameters, etc. were collected. According to thyroid function parameters, patients were classified as AIT, NAIH, latent Hashimoto's thyroiditis (LH) and euthyroidism (ET).

RESULTS

Patients with SCH (including AIT and NAIH) had older age at onset, and were more likely to have psychotic symptoms compared to those with ET. Multiple linear regression analysis showed that SCH was associated with duration of MDD and HAMD scores. Logistic regression analysis showed that the odds of having more severe anxiety and metabolic syndrome were greater among patients with SCH compared to those with ET. The odds of having suicide attempts were greater among patients with AIT than among those with ET.

LIMITATION

Because of the cross-sectional design of this study, we were unable to sort out causality between MDD and SCH.

CONCLUSION

Our findings suggested that AIT and NAIH were associated with duration of MDD, HAMD scores, severity of anxiety, and metabolic syndrome. However, only AIT in SCH was associated with suicide attempts.

Neuro-immune crosstalk in depressive symptoms of multiple sclerosis

Depressive disorders can occur in up to 50% of people with multiple sclerosis in their lifetime. If left untreated, comorbid major depressive disorders may not spontaneously remit and is associated with an increased morbidity and mortality. Conversely, epidemiological evidence supports increased psychiatric visit as a significant prodromal event prior to diagnosis of MS. Are there common molecular pathways that contribute to the co-development of MS and psychiatric illnesses? We discuss immune cells that are dysregulated in MS and how such dysregulation can induce or protect against depressive symptoms. This is not meant to be a comprehensive review of all molecular pathways but rather a framework to guide future investigations of immune responses in depressed versus euthymic people with MS. Currently, there is weak evidence supporting the use of antidepressant medication in comorbid MS patients. It is our hope that by better understanding the neuroimmune crosstalk in the context of depression in MS, we can enhance the potential for future therapeutic options.

Depression Pathophysiology: Astrocyte Mitochondrial Melatonergic Pathway as Crucial Hub

Major depressive disorder (MDD) is widely accepted as having a heterogenous pathophysiology involving a complex mixture of systemic and CNS processes. A developmental etiology coupled to genetic and epigenetic risk factors as well as lifestyle and social process influences add further to the complexity. Consequently, antidepressant treatment is generally regarded as open to improvement, undoubtedly as a consequence of inappropriately targeted pathophysiological processes. This article reviews the diverse array of pathophysiological processes linked to MDD, and integrates these within a perspective that emphasizes alterations in mitochondrial function, both centrally and systemically. It is proposed that the long-standing association of MDD with suppressed serotonin availability is reflective of the role of serotonin as a precursor for the mitochondrial melatonergic pathway. Astrocytes, and the astrocyte mitochondrial melatonergic pathway, are highlighted as crucial hubs in the integration of the wide array of biological underpinnings of MDD, including gut dysbiosis and permeability, as well as developmental and social stressors, which can act to suppress the capacity of mitochondria to upregulate the melatonergic pathway, with consequences for oxidant-induced changes in patterned microRNAs and subsequent patterned gene responses. This is placed within a development context, including how social processes, such as discrimination, can physiologically regulate a susceptibility to MDD. Future research directions and treatment implications are derived from this.

Will Sirtuin 2 Be a Promising Target for Neuroinflammatory Disorders?

Neuroinflammatory disorder is a general term that is associated with the progressive loss of neuronal structure or function. At present, the widely studied diseases with neuroinflammatory components are mainly divided into neurodegenerative and neuropsychiatric diseases, namely, Alzheimer’s disease, Parkinson’s disease, depression, stroke, and so on. An appropriate neuroinflammatory response can promote brain homeostasis, while excessive neuroinflammation can inhibit neuronal regeneration and damage the central nervous system. Apart from the symptomatic treatment with cholinesterase inhibitors, antidepressants/anxiolytics, and neuroprotective drugs, the treatment of neuroinflammation is a promising therapeutic method. Sirtuins are a host of class III histone deacetylases, that require nicotinamide adenine dinucleotide for their lysine residue deacetylase activity. The role of sirtuin 2 (SIRT2), one of the sirtuins, in modulating senescence, myelin formation, autophagy, and inflammation has been widely studied. SIRT2 is associated with many neuroinflammatory disorders considering it has deacetylation properties, that regulate the entire immune homeostasis. The aim of this review was to summarize the latest progress in regulating the effects of SIRT2 on immune homeostasis in neuroinflammatory disorders. The overall structure and catalytic properties of SIRT2, the selective inhibitors of SIRT2, the relationship between immune homeostasis and SIRT2, and the multitasking role of SIRT2 in several diseases with neuroinflammatory components were discussed.

Ketamine-New Possibilities in the Treatment of Depression: A Narrative Review

The SARS-CoV-2 coronavirus epidemic has led to an increase in the number of people with depression. Symptoms related to the mental sphere (mainly depression and anxiety) may be experienced by one third of the worldwide population. This entails the need for the effective and rapid treatment of depressive episodes. An effective drug seems to be s-ketamine, which was accepted in March 2019 by the Food and Drug Administration (FDA) for the treatment of drug-resistant depression. This drug provides a quick antidepressant effect with maximum effectiveness achieved after 24 h. It also appears to reduce the occurrence of suicidal thoughts. However, research into undesirable effects, especially in groups of people susceptible to psychotic episodes or those who use alcohol or psychoactive substances, is necessary.