Inflammation in the pathogenesis of depression: a disorder of neuroimmune origin

Sex differences in the microglial response to stress and chronic alcohol exposure in mice

BACKGROUND

Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of the neurobiological processes underlying this sex difference is still emerging. Neuroimmune signaling, particularly by microglia, the brain's macrophages, is known to contribute to dysregulation of limbic circuits following stress and alcohol exposure. Females exhibit heightened immune reactivity, so we set out to characterize sex differences in the microglial response to stress and alcohol exposure.

METHODS

Male and female C57BL/6J mice were administered alcohol over 15 or 22 trials of a modified Drinking in the Dark paradigm, with repeated exposure to inescapable footshock stress and the stress-paired context. Mice were perfused immediately after drinking and we performed immunohistochemical analyses of microglial density, morphology, and protein expression in subregions of the amygdala and hippocampus.

RESULTS

We observed dynamic sex differences in microglial phenotypes at baseline and in response to stress and alcohol. Microglia in the hippocampus displayed more prominent sex differences and heightened reactivity to stress and alcohol. Chronic alcohol exposure decreased density of amygdala microglia and lysosomal expression.

CONCLUSION

We analyzed multiple measures of microglial activation, resulting in a comprehensive assessment of microglial changes mediated by sex, stress, and alcohol. These findings highlight the complexity of microglial contributions to the development of AUD and comorbid mood and stress disorders in men and women.

Brain connectivity correlates of the impact of a digital intervention for individuals with subjective cognitive decline on depression and IL-18

Late-life depression represents a significant health concern, linked to disruptions in brain connectivity and immune functioning, mood regulation, and cognitive function. This pilot study explores a digital intervention targeting mental health, brain health, and immune functioning in individuals aged 55-60 with subjective cognitive decline, elevated stress and depressive symptoms. Seventeen participants engaged in a two-week intervention comprising spatial cognition, psychological techniques based on mindfulness, attention-training exercises, and cognitive behavioral therapy. Pre-and post-intervention changes in resting-state functional connectivity, inflammation, and psychological health were evaluated. Key findings include: (1) Reduced self-reported depression with a large effect size, (2) Decreased connectivity within the default mode network (DMN), (3) Enhanced anticorrelation between the DMN-Salience networks that was associated with improved depression scores (4) Reduced salivary IL-18 concentration with a medium effect size, correlated with decreased DMN-amygdala connectivity. There was a trend towards reduced anxiety, with no significant changes in quality of life. To our knowledge, this is the first study to investigate the effect of digital intervention on immune markers, clinical behavioral outcomes, and brain function, demonstrating positive synergistic potential across all three levels. These preliminary findings, which need replication in larger, controlled studies, have important implications for basic science and scalable digital interventions.

BDNF/BDNF-AS Gene Polymorphisms Modulate Treatment Response and Remission in Bipolar Disorder: A Randomized Clinical Trial

Background: Bipolar disorder (BD) is a chronic condition associated with treatment resistance, cognitive decline, structural brain changes, and an approximately 13-year reduction in life expectancy compared to the general population. Depression in BD substantially impairs quality of life, while neuroinflammation and excitotoxicity are thought to contribute to the recurrence of mood episodes and disease progression. Brain-derived neurotrophic factor (BDNF) plays a key role in neuronal growth and function, with its dysregulation being linked to various psychiatric disorders. This study is an extension of a previously published clinical trial and was conducted to assess the effects of three BDNF and BDNF-AS gene polymorphisms (rs1519480, rs6265, and rs10835210) on treatment outcomes and serum BDNF levels in patients with treatment-resistant bipolar disorder depression (TRBDD) over an eight-week period. Methods: This study included 41 participants from a previously conducted randomized clinical trial, all of whom had available BDNF serum samples and genotype data. The participants, aged 21 to 65, were diagnosed with bipolar disorder, and treatment-resistant depression was assessed using the Maudsley Staging Method. Participants were randomly assigned to receive either escitalopram plus a placebo (ESC+PBO) or escitalopram plus celecoxib (ESC+CBX) over an 8-week period. Statistical analyses included a mixed ANOVA and chi-square tests to compare the minor allele carrier status of three SNPs with treatment response and remission rates. Results: Non-carriers of the rs6265 A allele (p = 0.005) and carriers of the rs10835210 A allele (p = 0.007) showed a significantly higher response to treatment with adjunctive celecoxib compared to escitalopram alone. Additionally, remission rates after adjunctive celecoxib were significantly higher in both carriers and non-carriers across all three SNPs compared to escitalopram alone. However, remission rates were notably higher in non-carriers of the rs1519480 G allele and rs10835210 A allele, as well as in carriers of the rs6265 A allele. Conclusions: This study suggests that genetic variations in BDNF and BDNF-AS genes significantly influence treatment response to and remission with escitalopram and celecoxib in bipolar disorder.

Targeting Cytokine-Mediated Inflammation in Brain Disorders: Developing New Treatment Strategies

Cytokine-mediated inflammation is increasingly recognized for playing a vital role in the pathophysiology of a wide range of brain disorders, including neurodegenerative, psychiatric, and neurodevelopmental problems. Pro-inflammatory cytokines such as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) cause neuroinflammation, alter brain function, and accelerate disease development. Despite progress in understanding these pathways, effective medicines targeting brain inflammation are still limited. Traditional anti-inflammatory and immunomodulatory drugs are effective in peripheral inflammatory illnesses. Still, they face substantial hurdles when applied to the central nervous system (CNS), such as the blood-brain barrier (BBB) and unwanted systemic effects. This review highlights the developing treatment techniques for modifying cytokine-driven neuroinflammation, focusing on advances that selectively target critical cytokines involved in brain pathology. Novel approaches, including cytokine-specific inhibitors, antibody-based therapeutics, gene- and RNA-based interventions, and sophisticated drug delivery systems like nanoparticles, show promise with respect to lowering neuroinflammation with greater specificity and safety. Furthermore, developments in biomarker discoveries and neuroimaging techniques are improving our ability to monitor inflammatory responses, allowing for more accurate and personalized treatment regimens. Preclinical and clinical trial data demonstrate the therapeutic potential of these tailored techniques. However, significant challenges remain, such as improving delivery across the BBB and reducing off-target effects. As research advances, the creation of personalized, cytokine-centered therapeutics has the potential to alter the therapy landscape for brain illnesses, giving patients hope for better results and a higher quality of life.

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces depression-like phenotype

The etiology of major depressive disorder (MDD) remains poorly understood. Our previous studies suggest a role for the aryl hydrocarbon receptor (AhR) in depression. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental contaminant, with a high AhR binding affinity, and an established benchmark for assessing AhR activity. Therefore, this study examined the effect of TCDD on depression-like behaviors. Female mice were fed standard chow or a high-fat diet (HFD) for 11 weeks, and their weight was recorded. Subsequently, they were tested for baseline sucrose preference and splash test grooming. Then, TCDD (0.1 µg/kg/day) or vehicle was administered orally for 28 days, and mice were examined for their sucrose preference and performances in the splash test, forced swim test (FST), and Morris water maze (MWM) task. TCDD significantly decreased sucrose preference, increased FST immobility time, and decreased groom time in chow-fed mice. HFD itself significantly reduced sucrose preference. However, TCDD significantly increased FST immobility time and decreased groom time in HFD-fed mice. A small decrease in bodyweight was observed only at the fourth week of daily TCDD administration in chow-fed mice, and no significant effects of TCDD on bodyweights were observed in HFD-fed mice. TCDD did not have a significant effect on spatial learning in the MWM. Thus, this study demonstrated that TCDD induces a depression-like state, and the effects were not due to gross lethal toxicity. This study further suggests that more studies should examine a possible role for AhR and AhR-active environmental pollutants in precipitating or worsening MDD.

Use of Extracellular Monomeric Ubiquitin as a Therapeutic Option for Major Depressive Disorder

Major depressive disorder (MDD) is a mood disorder that has become a global health emergency according to the World Health Organization (WHO). It affects 280 million people worldwide and is a leading cause of disability and financial loss. Patients with MDD present immunoendocrine alterations like cortisol resistance and inflammation, which are associated with alterations in neurotransmitter metabolism. There are currently numerous therapeutic options for patients with MDD; however, some studies suggest a high rate of therapeutic failure. There are multiple hypotheses explaining the pathophysiological mechanisms of MDD, in which several systems are involved, including the neuroendocrine and immune systems. In recent years, inflammation has become an important target for the development of new therapeutic options. Extracellular monomeric ubiquitin (emUb) is a molecule that has been shown to have immunomodulatory properties through several mechanisms including cholinergic modulation and the generation of regulatory T cells. In this perspective article, we highlight the influence of the inflammatory response in MDD. In addition, we review and discuss the evidence for the use of emUb contained in Transferon as a concomitant treatment with selective serotonin reuptake inhibitors (SSRIs).

Role of microglia in stress-induced alcohol intake in female and male mice

Rates of alcohol use disorder (AUD) have escalated in recent years, with a particular increase among women. Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of sex-specific neurobiological substrates underlying this phenomenon is still emerging. Microglia, the resident macrophages of the brain, are essential for reshaping neuronal processes, and microglial activity contributes to overall neuronal plasticity. We investigated microglial dynamics and morphology in limbic brain structures of male and female mice following exposure to stress, alcohol or both challenges. In a modified paradigm of intermittent binge drinking (repeated "drinking in the dark"), we determined that female, but not male, mice increased their alcohol consumption after exposure to a physical stressor and re-exposure trials in the stress-paired context. Ethanol (EtOH) drinking and stress altered a number of microglial parameters, including overall number, in subregions of the amygdala and hippocampus, with effects that were somewhat more pronounced in female mice. We used the CSF1R antagonist PLX3397 to deplete microglia in female mice to determine whether microglia contribute to stress-induced escalation of EtOH intake. We observed that microglial depletion attenuated stress-induced alcohol intake with no effect in the unstressed group. These findings suggest that microglial activity can contribute to alcohol intake under stressful conditions, and highlight the importance of evaluating sex-specific mechanisms that could result in tailored interventions for AUD in women.

Targeting Large-Conductance Calcium-Activated Potassium Channels to Ameliorate Lipopolysaccharide-Induced Depressive-Like Behavior in Mice

Neuroinflammation plays crucial role in the development and progression of depression. Large conductance calcium- and voltage-dependent potassium (BK) channels mediate the activation of microglia. Herein, we investigated whether BK channels could serve as a target for the treatment of inflammation-associated depression. Lipopolysaccharide (LPS, 0.83 mg/kg) was injected intraperitoneally (i.p.) to induce neuroinflammation and depressive-like behavior in 6-8 week ICR mice. Adeno-associated virus (AAV) constructs (AAV9-Iba1p-BK shRNA-EGFP (BK shRNA-AAV) or AAV9-Iba1p-NC shRNA-EGFP (NC shRNA-AAV)) were unilaterally injected intracerebroventricularly to selectively knock down BK channels in microglia. The tail suspension test (TST) and forced-swim test (FST) were used to evaluate depressive-like behavior in mice 24 h after LPS challenge. The morphology of microglia, expression of BK channels, levels of cytokines, and expression and activity of indoleamine 2,3-dioxygenase (IDO) were measured by immunohistochemistry, western blot, quantitative real time PCR, and enzyme-linked immunosorbent assay (ELISA), respectively. Either paxilline (i.p.), a specific BK channel blocker, or BK shRNA-AAV effectively inhibited the activation of microglia, reduced the production of IL-1β in the hippocampus and suppressed the expression and activity of IDO in the hippocampus and prefrontal cortex, resulting in the amelioration of depressive-like behavior in mice. These data suggest for the first time that BK channels are involved in LPS-induced depressive-like behaviors. Thus, microglia BK channels may be a potential drug target for the depression treatment.

How inflammation influences psychiatric disease

Recent studies highlight the strong correlation between infectious diseases and the development of neuropsychiatric disorders. In this editorial, we comment on the article "Anti-infective therapy durations predict psychological stress and laparoscopic surgery quality in pelvic abscess patients" by Zhang et al, published in the recent issue of the World Journal of Psychiatry 2023; 13 (11): 903-911. Our discussion highlighted the potential consequences of anxiety, depression, and psychosis, which are all linked to bacterial, fungal, and viral infections, which are relevant to the impact of inflammation on the sequelae in mental health as those we are observing after the coronavirus disease 2019 pandemic. We focus specifically on the immune mechanisms triggered by inflammation, the primary contributor to psychiatric complications. Importantly, pathophysiological mechanisms such as organ damage, post-injury inflammation, and infection-induced endocrine alterations, including hypocortisolism or autoantibody formation, significantly contribute to the development of chronic low-grade inflammation, promoting the emergence or development of psychiatric alterations in susceptible individuals. As inflammation can have long-term effects on patients, a multidisciplinary treatment plan can avoid complications and debilitating health issues, and it is crucial to recognize and address the mental health implications.

Mood and microbes: a comprehensive review of intestinal microbiota's impact on depression

Depression is considered a multifaceted and intricate mental disorder of growing concern due to its significant impact on global health issues. The human gut microbiota, also known as the "second brain," has an important role in the CNS by regulating it through chemical, immunological, hormonal, and neurological processes. Various studies have found a significant bidirectional link between the brain and the gut, emphasizing the onset of depression therapies. The biological and molecular processes underlying depression and microbiota are required, as the bidirectional association may represent a novel study. However, profound insights into the stratification and diversity of the gut microbiota are still uncommon. This article investigates the emerging evidence of a bacterial relationship between the gut and the brain's neurological system and its potential pathogenicity and relevance. The interplay of microbiota, immune system, nervous system neurotransmitter synthesis, and neuroplasticity transitions is also widely studied. The consequences of stress, dietary fibers, probiotics, prebiotics, and antibiotics on the GB axis are being studied. Multiple studies revealed the processes underlying this axis and led to the development of effective microbiota-based drugs for both prevention and treatment. Therefore, the results support the hypothesis that gut microbiota influences depression and provide a promising area of research for an improved knowledge of the etiology of the disease and future therapies.

Understanding the Biological Relationship between Migraine and Depression

Migraine is a highly prevalent neurological disorder. Among the risk factors identified, psychiatric comorbidities, such as depression, seem to play an important role in its onset and clinical course. Patients with migraine are 2.5 times more likely to develop a depressive disorder; this risk becomes even higher in patients suffering from chronic migraine or migraine with aura. This relationship is bidirectional, since depression also predicts an earlier/worse onset of migraine, increasing the risk of migraine chronicity and, consequently, requiring a higher healthcare expenditure compared to migraine alone. All these data suggest that migraine and depression may share overlapping biological mechanisms. Herein, this review explores this topic in further detail: firstly, by introducing the common epidemiological and risk factors for this comorbidity; secondly, by focusing on providing the cumulative evidence of common biological aspects, with a particular emphasis on the serotoninergic system, neuropeptides such as calcitonin-gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P, neuropeptide Y and orexins, sexual hormones, and the immune system; lastly, by remarking on the future challenges required to elucidate the etiopathological mechanisms of migraine and depression and providing updated information regarding new key targets for the pharmacological treatment of these clinical entities.

Distinguishing features of depression in dementia from primary psychiatric disease

Depression is a common and devastating neuropsychiatric symptom in the elderly and in patients with dementia. In particular, nearly 80% of patients with Alzheimer's Disease dementia experience depression during disease development and progression. However, it is unknown whether the depression in patients with dementia shares the same molecular mechanisms as depression presenting as primary psychiatric disease or occurs and persists through alternative mechanisms. In this review, we discuss how the clinical presentation and treatment differ between depression in dementia and as a primary psychiatric disease, with a focus on major depressive disorder. Then, we hypothesize several molecular mechanisms that may be unique to depression in dementia such as neuropathological changes, inflammation, and vascular events. Finally, we discuss existing issues and future directions for investigation and treatment of depression in dementia.

Saffron extract interferes with lipopolysaccharide-induced brain activation of the kynurenine pathway and impairment of monoamine neurotransmission in mice

Background

Although activation of inflammatory processes is essential to fight infections, its prolonged impact on brain function is well known to contribute to the pathophysiology of many medical conditions, including neuropsychiatric disorders. Therefore, identifying novel strategies to selectively counter the harmful effects of neuroinflammation appears as a major health concern. In that context, this study aimed to test the relevance of a nutritional intervention with saffron, a spice known for centuries for its beneficial effect on health.

Methods

For this purpose, the impact of an acute oral administration of a standardized saffron extract, which was previously shown to display neuromodulatory properties and reduce depressive-like behavior, was measured in mice challenged with lipopolysaccharide (LPS, 830 μg/kg, ip).

Results

Pretreatment with saffron extract (6.5 mg/kg, per os) did not reduce LPS-induced sickness behavior, preserving therefore this adaptive behavioral response essential for host defense. However, it interfered with delayed changes of expression of cytokines, chemokines and markers of microglial activation measured 24 h post-LPS treatment in key brain areas for behavior and mood control (frontal cortex, hippocampus, striatum). Importantly, this pretreatment also counteracted by that time the impact of LPS on several neurobiological processes contributing to inflammation-induced emotional alterations, in particular the activation of the kynurenine pathway, assessed through the expression of its main enzymes, as well as concomitant impairment of serotonergic and dopaminergic neurotransmission.

Conclusion

Altogether, this study provides important clues on how saffron extract interferes with brain function in conditions of immune stimulation and supports the relevance of saffron-based nutritional interventions to improve the management of inflammation-related comorbidities.