A randomized controlled trial of the tumor necrosis factor antagonist infliximab for treatment-resistant depression: the role of baseline inflammatory biomarkers

Peripheral mitochondrial DNA as a neuroinflammatory biomarker for major depressive disorder

In the pathogenesis of major depressive disorder, chronic stress-related neuroinflammation hinders favorable prognosis and antidepressant response. Mitochondrial DNA may be an inflammatory trigger, after its release from stress-induced dysfunctional central nervous system mitochondria into peripheral circulation. This evidence supports the potential use of peripheral mitochondrial DNA as a neuroinflammatory biomarker for the diagnosis and treatment of major depressive disorder. Herein, we critically review the neuroinflammation theory in major depressive disorder, providing compelling evidence that mitochondrial DNA release acts as a critical biological substrate, and that it constitutes the neuroinflammatory disease pathway. After its release, mitochondrial DNA can be carried in the exosomes and transported to extracellular spaces in the central nervous system and peripheral circulation. Detectable exosomes render encaged mitochondrial DNA relatively stable. This mitochondrial DNA in peripheral circulation can thus be directly detected in clinical practice. These characteristics illustrate the potential for mitochondrial DNA to serve as an innovative clinical biomarker and molecular treatment target for major depressive disorder. This review also highlights the future potential value of clinical applications combining mitochondrial DNA with a panel of other biomarkers, to improve diagnostic precision in major depressive disorder.

Exploring the mechanisms of action of probiotics in depression: Results from a randomized controlled pilot trial

BACKGROUND

We previously reported greater reductions in depression and anxiety following probiotic supplementation in people with major depressive disorder (MDD) in a randomised double-blind placebo-controlled pilot trial (Nikolova et al., 2023). Here, we investigate the mechanisms underlying these effects.

METHODS

49 people with MDD received a multi-strain probiotic (n = 24) or placebo (n = 25) for 8 weeks in addition to their antidepressant. Stool and blood samples were collected to analyse gut microbiota composition and inflammatory cytokines. Stool samples from 25 matched healthy volunteers (HVs) were also obtained.

RESULTS

Within the probiotic group, there was a significant increase in richness according to Chao1(bias-corrected) (w4 p = 0.04) and a trend for increased Total count (w4 p = 0.06, w8 p = 0.09) compared to baseline, but not to placebo. When compared to HVs post-treatment, only the placebo group had a significant decrease in Shannon' entropy (p = 0.03) and a trend for decreased Total count (p = 0.08) and Simpson's index (p = 0.09). Between-group differences in beta diversity were observed at week 4 (p = 0.04), but not week 8. Consistent between-group differences were seen in family Bacilleceae post-treatment (FDR p < 0.05), which correlated with decreases in anxiety (FDR p < 0.05). There were no differences in inflammatory markers.

LIMITATIONS

This study was limited by data loss during the COVID-19 Pandemic.

CONCLUSION

Probiotics may positively impact the microbiota by normalising diversity and increasing levels of health-related taxa, which may partially account for their benefits in MDD. Understanding how these changes relate to symptom improvement can inform their targeted use in clinical practice. Larger trials incorporating functional multi-omics are needed.

TRIAL REGISTRATION

NCT03893162.

The (neuro)inflammatory system in anxiety disorders and PTSD: Potential treatment targets

Targeting the immune system has recently garnered attention in the treatment of stress- associated psychiatric disorders resistant to existing pharmacotherapeutics. While such approaches have been studied in considerable detail in depression, the role of (neuro)inflammation in anxiety-related disorders, or in anxiety as an important transdiagnostic symptom, is much less clear. In this review we first critically review clinical and in part preclinical evidence of central and peripheral immune dysregulation in anxiety disorders and post-traumatic stress disorder (PTSD) and briefly discuss proposed mechanisms of how inflammation can affect anxiety-related symptoms. We then give an overview of existing and potential future targets in inflammation-associated signal transduction pathways and discuss effects of different immune-modulatory drugs in anxiety-related disorders. Finally, we discuss key gaps in current clinical trials such as the lack of prospective studies involving anxiety patient stratification strategies based on inflammatory biomarkers. Overall, although evidence is rather limited so far, there is data to indicate that increased (neuro)inflammation is present in subgroups of anxiety disorder patients. Although exact identification of such immune subtypes of anxiety disorders and PTSD is still challenging, these patients will likely particularly benefit from therapeutic targeting of aspects of the inflammatory system. Different anti-inflammatory treatment approaches (microglia-directed treatments, pro-inflammatory cytokine inhibitors, COX-inhibitors, phytochemicals and a number of novel anti-inflammatory agents) have indeed shown some efficacy even in non-stratified anxiety patient groups and appear promising as novel alternative or complimentary therapeutic options in specific ("inflammatory") subtypes of anxiety disorder and PTSD patients.

Immunological drivers and potential novel drug targets for major psychiatric, neurodevelopmental, and neurodegenerative conditions

Immune dysfunction is implicated in the aetiology of psychiatric, neurodevelopmental, and neurodegenerative conditions, but the issue of causality remains unclear impeding attempts to develop new interventions. Using genomic data on protein and gene expression across blood and brain, we assessed evidence of a potential causal role for 736 immune response-related biomarkers on 7 neuropsychiatric conditions by applying Mendelian randomization (MR) and genetic colocalisation analyses. A systematic three-tier approach, grouping biomarkers based on increasingly stringent criteria, was used to appraise evidence of causality (passing MR sensitivity analyses, colocalisation, False Discovery Rate and Bonferroni thresholds). We provide evidence for a potential causal role of 29 biomarkers for 7 conditions. The identified biomarkers suggest a role of both brain specific and systemic immune response in the aetiology of schizophrenia, Alzheimer's disease, depression, and bipolar disorder. Of the identified biomarkers, 20 are therapeutically tractable, including ACE, TNFRSF17, SERPING1, AGER and CD40, with drugs currently approved or in advanced clinical trials. Based on the largest available selection of plasma immune-response related biomarkers, our study provides insight into possible influential biomarkers for the aetiology of neuropsychiatric conditions. These genetically prioritised biomarkers now require examination to further evaluate causality, their role in the aetiological mechanisms underlying the conditions, and therapeutic potential.

Systemic Inflammation and Anhedonic Responses to an Inflammatory Challenge in Adults With Major Depressive Disorder: A Randomized Controlled Trial

OBJECTIVE

The authors sought to determine whether an inflammatory challenge with lipopolysaccharide (LPS) differentially impacts symptoms of anhedonia in participants with major depressive disorder with high (≥3 mg/L) and low (≤1.5 mg/L) serum C-reactive protein (CRP) concentrations.

METHODS

Sixty-eight participants with major depressive disorder were randomly assigned, in a 1:1 ratio, to receive LPS (0.8 ng/kg body weight) or placebo (saline) in a parallel-group double-blind design. Participants were stratified according to baseline CRP concentrations, yielding four groups: high-CRP LPS (N=13), low-CRP LPS (N=19), high-CRP placebo (N=13), and low-CRP placebo (N=19). Blood was sampled at baseline, at 1, 1.5, 3.5, 6, and 24 hours, and 1 week after LPS or saline administration, with concurrent assessment of psychological outcomes. The primary outcome measure was the Snaith-Hamilton Pleasure Scale (SHAPS), and the primary contrast of interest was the change between baseline and 1.5 hours (peak of the inflammatory response) in the high-CRP versus low-CRP groups receiving LPS. Secondary outcomes included the Montgomery-Åsberg Depression Rating Scale (MADRS) and serum levels of three cytokines: interleukin-6 (IL-6), IL-10, and tumor necrosis factor (TNF). Data were analyzed with linear mixed models.

RESULTS

Significantly greater increases in self-reported anhedonia (on the SHAPS) and IL-6 levels were observed between baseline and 1.5 hours in the high-CRP versus low-CRP LPS groups. There were no significant differences for TNF and IL-10. The MADRS was not administered at 1.5 hours; secondary analyses showed a significant group-by-condition-by-time interaction driven by a greater decrease in MADRS scores between baseline and 24 hours in the high-CRP group.

CONCLUSIONS

Depressed individuals with systemic inflammation appeared to be biologically primed to respond more strongly to inflammatory stimuli, and psychologically, this sensitization impacted the symptom of anhedonia, the primary outcome.

Exploring the combined effects of serum tumor necrosis factor-alpha and serotonin on antidepressant efficacy in depression: A 12-week prospective analysis

BACKGROUND

This study investigated the interplay between serum tumor necrosis factor-alpha (sTNF-α) and serotonin (s5-HT) levels in predicting 12-week antidepressant treatment outcomes among patients with depressive disorders.

METHODS

We analyzed baseline sTNF-α and s5-HT levels in 1086 patients enrolled in a naturalistic study of stepwise antidepressant treatment. Remission was defined as achieving a Hamilton Depression Rating Scale score of 7 or less at 12 weeks. Logistic regression analyses adjusted for sociodemographic and clinical covariates were utilized to explore the relationships between biomarker levels and treatment outcomes.

RESULTS

Elevated sTNF-α levels were significantly associated with non-remission at 12 weeks in patients with lower s5-HT levels. Conversely, in patients with higher s5-HT levels, sTNF-α levels did not show a significant association with remission outcomes. The interaction between sTNF-α and s5-HT levels significantly predicted remission status even after adjusting for potential confounders.

CONCLUSIONS

The findings suggest that the combined assessment of immune and serotonergic biomarkers can enhance the prediction of antidepressant treatment outcomes. This underscores the potential of integrating biomarker profiles to tailor antidepressant strategies, thereby advancing personalized treatment approaches in depression. Future studies should explore the underlying mechanisms of these interactions to better understand their role in treatment responsiveness.

A randomized proof-of-mechanism trial of TNF antagonism for motivational deficits and related corticostriatal circuitry in depressed patients with high inflammation

Chronic, low-grade inflammation has been associated with motivational deficits in patients with major depression (MD). In turn, impaired motivation has been linked to poor quality of life across psychiatric disorders. We thus determined effects of the anti-inflammatory drug infliximab-a potent tumor necrosis factor (TNF) antagonist-on behavioral and neural measures of motivation in 42 medically stable, unmedicated MD patients with a C-reactive protein >3 mg/L. All patients underwent a double-blind, placebo-controlled, single-dose, randomized clinical trial with infliximab (5 mg/kg) versus placebo. Behavioral performance on an effort-based decision-making task, self-report questionnaires, and neural responses during event-related functional magnetic resonance imaging were assessed at baseline and 2 weeks following infusion. We found that relative to placebo, patients receiving infliximab were more willing to expend effort for rewards. Moreover, increase in effortful choices was associated with reduced TNF signaling as indexed by decreased soluble TNF receptor type 2 (sTNFR2). Changes in effort-based decision-making and sTNFR2 were also associated with changes in task-related activity in a network of brain areas, including dorsomedial prefrontal cortex (dmPFC), ventral striatum, and putamen, as well as the functional connectivity between these regions. Changes in sTNFR2 also mediated the relationships between drug condition and behavioral and neuroimaging measures. Finally, changes in self-reported anhedonia symptoms and effort-discounting behavior were associated with greater responses of an independently validated whole-brain predictive model (aka "neural signature") sensitive to monetary rewards. Taken together, these data support the use of anti-inflammatory treatment to improve effort-based decision-making and associated brain circuitry in depressed patients with high inflammation.

Transcriptomic profiles in major depressive disorder: the role of immunometabolic and cell-cycle-related pathways in depression with different levels of inflammation

Transcriptomic profiles are important indicators for molecular mechanisms and pathways involved in major depressive disorder (MDD) and its different phenotypes, such as immunometabolic depression. We performed whole-transcriptome and pathway analyses on 139 individuals from the observational, case-control, BIOmarkers in DEPression (BIODEP) study, 105 with MDD and 34 controls. We divided MDD participants based on levels of inflammation, as measured by serum high-sensitivity C-reactive protein (CRP), in n = 39 'not inflamed' (CRP < 1 mg/L), n = 31 with 'elevated CRP' (1-3 mg/L), and n = 35 with 'low-grade inflammation' (>3 mg/L). We performed whole-blood RNA sequencing using Illumina NextSeq 550 and statistical analyses with the Deseq2 package for R statistics (RUV-corrected) and subsequent pathway analyses with Ingenuity Pathway Analysis. Immunometabolic pathways were activated in individuals with CRP > 1 mg/L, although surprisingly the CRP 1-3 group showed stronger immune activation than the CRP > 3 group. The main pathways identified in the comparison between CRP < 1 group and controls were cell-cycle-related, which may be protective against immunometabolic abnormalities in this 'non-inflamed' depressed group. We further divided MDD participants based on exposure and response to antidepressants (n = 47 non-responders, n = 37 responders, and n = 22 unmedicated), and identified specific immunomodulatory and neuroprotective pathways in responders (especially vs. non-responders), which could be relevant to treatment response. In further subgroup analyses, we found that the specific transcriptional profile of responders is independent of CRP levels, and that the inhibition of cell-cycle-related pathways in MDD with CRP < 1 mg/L is present only in those who are currently depressed, and not in the responders. The present study demonstrates immunometabolic and cell-cycle-related transcriptomic pathways associated with MDD and different (CRP-based and treatment-based) MDD phenotypes, while shedding light on potential molecular mechanisms that could prevent or facilitate an individual's trajectory toward immunometabolic depression and/or treatment-non-responsive depression. The recognition and integration of these mechanisms will facilitate a precision-medicine approach in MDD.

The genetic association between major depressive disorder and coronary heart disease

Major depressive disorder (MDD) and coronary heart disease (CHD) can both cause significant morbidity and mortality. The association of MDD and CHD has long been identified, but the mechanisms still require further investigation. Seven mRNA microarray datasets containing samples from patients with MDD and CHD were downloaded from Gene Expression Omnibus. Combined matrixes of MDD and CAD were constructed for subsequent analysis. Differentially expressed genes (DEGs) were identified. Functional enrichment analyses based on shared DEGs were conducted to identify pivotal pathways. A protein-protein network was also applied to further investigate the functional interaction. Results showed that 24 overlapping genes were identified. Enrichment analysis indicated that the shared genes are mainly associated with immune function and ribosome biogenesis. The functional interactions of shared genes were also demonstrated by PPI network analysis. In addition, three hub genes including MMP9, S100A8, and RETN were identified. Our results indicate that MDD and CHD have a genetic association. Genes relevant to immune function, especially IL-17 signalling pathway may be involved in the pathogenesis of MDD and CHD.

Peripheral and central inflammation in depression: How large is the gap and can we bridge it with PET neuroimaging and neural-derived extracellular vesicles?

Major depressive disorder (MDD) presents as a multifaceted syndrome with complex pathophysiology and variable treatment responses, posing significant challenges in clinical management. Neuroinflammation is known to play pivotal mechanism in depression, linking immune responses with central nervous system (CNS) dysfunction. This review explores the interplay between peripheral and central inflammatory processes in MDD, emphasizing discrepancies in biomarker validity and specificity. While peripheral markers like cytokines have historically been investigated as proxies for neuroinflammation, their reliability remains contentious due to inconsistent findings, lack of correlation with neuroinflammatory markers, the influence of confounding variables, and the role of regulatory mechanism within the CNS. Additionally, the human brain shows a pattern of regionalized inflammation. Current methodologies for investigating neuroinflammation in humans in vivo, including neural-derived extracellular vesicles (EVs) and positron emission tomography (PET) neuroimaging using translocator protein, offer promising avenues while facing substantial limitations. We propose that future research in MDD may benefit from combined microglia-derived EV-TSPO PET neuroimaging analyses to leverage the strengths and mitigate the limitations of both individual methods.

The Association Among Bipolar Disorder, Mitochondrial Dysfunction, and Reactive Oxygen Species

Mitochondria, often known as the cell's powerhouses, are primarily responsible for generating energy through aerobic oxidative phosphorylation. However, their functions extend far beyond just energy production. Mitochondria play crucial roles in maintaining calcium balance, regulating apoptosis (programmed cell death), supporting cellular signaling, influencing cell metabolism, and synthesizing reactive oxygen species (ROS). Recent research has highlighted a strong link between bipolar disorder (BD) and mitochondrial dysfunction. Mitochondrial dysfunction contributes to oxidative stress, particularly through the generation of ROS, which are implicated in the pathophysiology of BD. Oxidative stress arises when there is an imbalance between the production of ROS and the cell's ability to neutralize them. In neurons, excessive ROS can damage various cellular components, including proteins in neuronal membranes and intracellular enzymes. Such damage may interfere with neurotransmitter reuptake and the function of critical enzymes, potentially affecting brain regions involved in mood regulation and emotional control, which are key aspects of BD. In this review, we will explore how various types of mitochondrial dysfunction contribute to the production of ROS. These include disruptions in energy metabolism, impaired ROS management, and defects in mitochondrial quality control mechanisms such as mitophagy (the process by which damaged mitochondria are selectively degraded). We will also examine how abnormalities in calcium signaling, which is crucial for synaptic plasticity, can lead to mitochondrial dysfunction. Additionally, we will discuss the specific mitochondrial dysfunctions observed in BD, highlighting how these defects may contribute to the disorder's pathophysiology. Finally, we will identify potential therapeutic targets to improve mitochondrial function, which could pave the way for new treatments to manage or mitigate symptoms of BD.

Inflammatory markers associated with electroconvulsive therapy response in patients with depression: A meta-analysis

Electroconvulsive therapy (ECT) is an effective intervention for severe unipolar and bipolar depression, yet its drawbacks often lead to its underutilization. Accurate prediction of ECT outcomes is crucial for optimizing patient care and increasing remission rates. This study synthesized existing evidence on the relationship between baseline inflammatory markers and ECT outcomes. Additionally, we explored whether changes in these markers during ECT correlated with symptom improvement. A correlation meta-analysis was conducted according to the PRISMA statement, including a total of fourteen studies (n = 556 patients). The analyses revealed that higher baseline CRP and IL-6 levels were significantly associated with greater depressive symptom reduction post-ECT. Additionally, our findings suggested that increases in kynurenine metabolites and IL-8 during treatment correlated with improved depressive symptoms, offering insights into the mechanistic aspects of depression and ECT. In conclusion, peripheral inflammation in depression, as measured by CRP and IL-6, is associated with better ECT outcomes and may guide treatment stratification. Further research on a broader range of cytokines and kynurenine metabolites is needed to confirm these findings.

Depressive symptoms mediate the association between dietary inflammatory index and sleep: A cross-sectional study of NHANES 2005-2014

BACKGROUND

Sleep pattern (sleep duration, trouble sleeping, sleep disorder) is associated with both energy density dietary inflammatory index (EDII) and depression. However, whether depression mediates the EDII-sleep pattern relationship is unclear.

METHODS

14,305 participants from the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2014 were included in this study. Weighted multivariable logistic regression and mediated effect analysis were conducted to analyze the associations between EDII, depression and sleep pattern.

RESULTS

In the regression model with full confounding variables adjusted, the OR (95 % CI) for the association between EDII and sleep pattern was 2.11 (1.44, 3.08). Similarly, comparing the highest to the lowest EDII scores, the association with depression yielded an identical OR of 2.62 (1.89, 3.64). Mediation models showed depressive symptoms mediated 24.06 % of the EDII-sleep pattern link. Analysis by sleep pattern subtypes found depressive symptoms mediated 18.22 % for sleep duration, 30.53 % for sleep disorder (both with substantial direct EDII effects), and 93.73 % for trouble sleeping, where EDII's direct impact was not considerable.

CONCLUSION

Positive association of EDII with unhealthy sleep pattern is partly mediated by depression, and anti-inflammatory diet could be beneficial.

Immune links in comorbid depression and psoriasis: A narrative mini-review and perspective

Evidence suggests a bidirectional association between psoriasis and depression, which is considered to reflect complex neuroimmunological and psychosocial interactions. Despite an early interest in the brain-skin axis and the role of stress in psoriasis immunopathogenesis, there is ongoing limited preclinical and clinical research into the inflammatory links between depression and psoriasis. Existing findings for serum inflammatory markers of depression in psoriasis are inconsistent and do not fully align with those in the general population, while brain imaging evidence is scarce and has not confirmed direct brain involvement in the systemic inflammation of psoriasis. The present paper reviews the available literature on the immune interplay of psoriasis with depression, highlights the significance of further work in the field and proposes avenues for future research.

Advancing precision psychiatry and targeted treatments: Insights from immunopsychiatry

Despite tremendous advancements in neuroscience, there has been limited impact on patient care. Current psychiatric treatments are largely non-specific, and drug development is hindered by outdated, overinclusive diagnostic categories and a "one-size-fits-all" approach. Additionally, mechanisms underlying psychiatric illnesses and their treatments with conventional medications remain poorly understood. Precision psychiatry is a strategy that holds great promise for novel therapies targeting specific pathophysiologic mechanisms in selected patients, ultimately contributing to more effective, personalized treatments. Immunopsychiatry, which focuses on the immune system's role in psychiatric disorders, exemplifies the challenges and potential solutions for precision psychiatry. Despite understanding how inflammation contributes to psychiatric illness, results of clinical trials with anti-inflammatory drugs have been inconsistent and underwhelming. Shortcomings of these trials include a lack of focus on subgroups of patients with increased inflammation, the use of non-specific outcome variables (e.g., not specific to inflammation's impact on the brain and behavior), and failure to establish target engagement of the inflammatory response. To advance anti-inflammatory treatments, clinical trials should: 1) enrich for patients using predictive biomarkers; 2) use clinical outcome assessments that align with inflammation's effects on the brain; 3) consider novel diagnostic constructs linked to inflammation; and 4) verify target engagement. Moreover, greater attention should be paid to efforts to repurpose available anti-inflammatory drugs while awaiting development of novel treatments targeting more specific immune pathways. Taken together, a collaborative approach involving academia, industry, funding agencies, patients, payors, and policymakers is required to advance Immunopsychiatry and ultimately provide a roadmap for successful implementation of precision psychiatry.

IUPHAR review: Drug repurposing in Schizophrenia - An updated review of clinical trials

There is an urgent need for mechanistically novel and more efficacious treatments for schizophrenia, especially those targeting negative and cognitive symptoms with a more favorable side-effect profile. Drug repurposing-the process of identifying new therapeutic uses for already approved compounds-offers a promising approach to overcoming the lengthy, costly, and high-risk process of traditional CNS drug discovery. This review aims to update our previous findings on the clinical drug repurposing pipeline in schizophrenia. We examined studies conducted between 2018 and 2024, identifying 61 trials evaluating 40 unique repurposed drug candidates. These encompassed a broad range of pharmacological mechanisms, including immunomodulation, cognitive enhancement, and hormonal, metabolic, and neurotransmitter modulation. A notable development is the combination of the muscarinic modulators xanomeline, a compound with antipsychotic properties, and trospium, included to mitigate peripheral side effects, now approved by the FDA as the first antipsychotic drug in decades with a fundamentally novel mechanism of action. Moving beyond the traditional dopaminergic paradigm of schizophrenia, such findings highlight opportunities to improve treatment-resistant symptoms and alleviate adverse effects. Overall, the evolving drug repurposing landscape illustrates a significant shift in the rationale for schizophrenia drug development, highlighting the potential of in silico strategies, biomarker-based patient stratification, and personalized treatments that align with underlying pathophysiological processes.

Markers of positive affect and brain state synchrony discriminate melancholic from non-melancholic depression using naturalistic stimuli

Melancholia has been proposed as a qualitatively distinct depressive subtype associated with a characteristic symptom profile (psychomotor retardation, profound anhedonia) and a better response to biological therapies. Existing work has suggested that individuals with melancholia are blunted in their display of positive emotions and differ in their neural response to emotionally evocative stimuli. Here, we unify these brain and behavioural findings amongst a carefully phenotyped group of seventy depressed participants, drawn from an established Australian database (the Australian Genetics of Depression Study) and further enriched for melancholia (high ratings of psychomotor retardation and anhedonia). Melancholic (n = 30) or non-melancholic status (n = 40) was defined using a semi-structured interview (the Sydney Melancholia Prototype Index). Complex facial expressions were captured whilst participants watched a movie clip of a comedian and classified using a machine learning algorithm. Subsequently, the dynamics of sequential changes in brain activity were modelled during the viewing of an emotionally evocative movie in the MRI scanner. We found a quantitative reduction in positive facial expressivity amongst participants with melancholia, combined with differences in the synchronous expression of brain states during positive epochs of the movie. In non-melancholic depression, the display of positive affect was inversely related to the activity of cerebellar regions implicated in the processing of affect. However, this relationship was reduced in those with a melancholic phenotype. Our multimodal findings show differences in evaluative and motoric domains between melancholic and non-melancholic depression through engagement in ecologically valid tasks that evoke positive emotion. These findings provide new markers to stratify depression and an opportunity to support the development of targeted interventions.

Unraveling the Complex Interplay Between Neuroinflammation and Depression: A Comprehensive Review

The relationship between neuroinflammation and depression is a complex area of research that has garnered significant attention in recent years. Neuroinflammation, characterized by the activation of glial cells and the release of pro-inflammatory cytokines, has been implicated in the pathophysiology of depression. The relationship between neuroinflammation and depression is bidirectional; not only can inflammation contribute to the onset of depressive symptoms, but depression itself can also exacerbate inflammatory responses, creating a vicious cycle that complicates treatment and recovery. The present comprehensive review aimed to explore the current findings on the interplay between neuroinflammation and depression, as well as the mechanisms, risk factors, and therapeutic implications. The mechanisms by which neuroinflammation induces depressive-like behaviors are diverse. Neuroinflammation can increase pro-inflammatory cytokines, activate the hypothalamus-pituitary-adrenal (HPA) axis, and impair serotonin synthesis, all of which contribute to depressive symptoms. Furthermore, the activation of microglia has been linked to the release of inflammatory mediators that can disrupt neuronal function and contribute to mood disorders. Stress-induced neuroinflammatory responses can lead to the release of pro-inflammatory cytokines that not only affect brain function but also influence behavior and mood. Understanding these mechanisms is crucial for developing targeted therapies that can mitigate the effects of neuroinflammation on mood disorders.

Emerging Medications for Treatment-Resistant Depression: A Review with Perspective on Mechanisms and Challenges

Background/Objectives: Non-response to initial treatment options for major depressive disorder (MDD) is a common clinical challenge with profound deleterious impacts for affected patients. Few treatments have received regulatory approval for treatment-resistant depression (TRD). Methods: A systematic search of United States and European Union clinical trials registries was conducted to identify Phase II, III, or IV clinical trials, with a last update posted on or after 1 January 2020, that were evaluating medications for TRD. For both the US and EU registries, the condition term "treatment resistant depression" and associated lower-level terms (per registry search protocol) were used. For the US registry, a secondary search using the condition term "depressive disorders" and the modifying term "inadequate" was also performed to capture registrations not tagged as TRD. Two additional searches were also conducted in the US registry for the terms "suicide" and "anhedonia" as transdiagnostic targets of investigational medications. Trials were categorized based on the primary mechanism of action of the trial's investigational medication. Results: Fifty clinical trials for TRD, 20 for anhedonia, and 25 for suicide were identified. Glutamate system modulation was the mechanism currently with the most compounds in development, including antagonists and allosteric modulators of NMDA receptors, AMPA receptors, metabotropic type 2/3 glutamate receptors, and intracellular effector molecules downstream of glutamate signaling. Psychedelics have seen the greatest surge among mechanistic targets in the past 5 years, however, with psilocybin in particular garnering significant attention. Other mechanisms included GABA modulators, monoamine modulators, anti-inflammatory/immune-modulating agents, and an orexin type 2 receptor antagonist. Conclusions: These investigations offer substantial promise for more efficacious and potentially personalized medication approaches for TRD. Challenges for detecting efficacy in TRD include the heterogeneity within the TRD population stemming from the presumed variety of biological dysfunctions underlying the disorder, comorbid disorders, chronic psychosocial stressors, and enduring effects of prior serotonergic antidepressant medication treatments.

Investigating the relationship between inflammatory cytokines and adolescent depression: a comparative analysis

Background

Major depressive disorder (MDD) in adolescents poses a significant threat to physical health. Previous studies have indicated that adolescents with MDD exhibit immune activation.

Objective

This study aimed to compare cytokine levels in adolescents with MDD to healthy controls and assess their diagnostic value.

Methods

This cross-sectional study included 58 adolescent patients with depression from Beijing Anding Hospital (outpatients and inpatients) and 40 healthy adolescents recruited from the community. Multiplex cytokine analysis (Luminex xMAP) was used to measure serum levels of several cytokines. Data analysis was performed using SPSS (version 26.0) to compare cytokine levels between adolescents with MDD and healthy controls and assess gender differences. Correlations between cytokine levels and demographic data, clinical features and depressive symptoms were also analyzed. The receiver operating characteristic (ROC) curves were used to evaluate the diagnostic value of cytokines.

Results

Serum IL-4, IFN-γ, and TNF-α levels were significantly elevated in MDD group compared with healthy controls (p < 0.05). In MDD group, the age of first onset of depression in females was significantly younger than that in males (p < 0.05), and female serum TNF-α levels were significantly higher than those in males (p < 0.05). BMI and serum IL-4 levels were significantly positively correlated in adolescents with MDD. The area under the ROC curve for serum IL-4 and TNF-α in diagnosing adolescent depression was 0.695 (95% confidence interval [CI]: 0.580 - 0.809; p < 0.05), with a sensitivity of 0.793 and specificity of 0.675.

Conclusion

Compared with healthy controls, adolescents with depression demonstrated significantly elevated serum cytokine levels, indicating immune activation which were higher in female. Cytokines may have promising diagnostic value in adolescent depression, but further validation with additional indicators is needed.

PKR Inhibition Prevents Neuroinflammation and Rescues Depressive-Like Behaviors via BDNF/TrkB Signaling

PKR, a kinase implicated in inflammation, accumulates in the brain, but its role in neuroinflammation-related depression is poorly understood. This study aimed to investigate whether pharmacological PKR inhibition using C16 (PKR inhibitor) could reverse LPS-induced neuroinflammation and depressive-like behaviors. Mice (C57BL/6J, 20-22 g, 6-8 weeks old) were administered LPS intraperitoneally for three days to induce depressive-like behavior and neuroinflammation. Simultaneously, mice were treated with C16 (a pharmacological PKR inhibitor) intraperitoneally for the same duration, followed by behavioral assessments. After euthanasia, brain-hippocampus tissues were collected for biochemical analysis. To validate these in vivo findings, BV2 and HT22 cells were cultured and subjected to pharmacological and biochemical analysis. LPS treatment significantly increased hippocampal neuroinflammation (GFAP/IBA-1 p < 0.001), cytokine production (IL-1β, IL-6, TNF-α, p < 0.05), PKR phosphorylation (p < 0.05), and inflammatory signaling (NLRP3/ASC, p < 0.001). Concomitantly, LPS exposure induced depressive-like symptoms (p < 0.001), impaired synaptic function (Synasin-1/SNAP25, p < 0.05), spine numbers (p < 0.001), and downregulated brain-derived neurotrophic factor (BDNF) /TrkB signaling (p < 0.001). Importantly, these effects were attenuated by C16, a PKR inhibitor. C16 also reduced LPS-induced ER stress markers in the hippocampus (p < 0.05). Interestingly, K252a, a BDNF/TrkB inhibitor, reversed the protective effects of C16, increasing both neuroinflammation (p < 0.001) and depressive symptoms (p < 0.001) in LPS-treated mice. Notably, in vitro studies using BV2 and HT22 cells corroborated these findings. In conclusion, these findings suggest that PKR is critical in mediating LPS-induced neuroinflammation and depressive-like behaviors, potentially through interactions with BDNF/TrkB signaling.

Extra-axial inflammatory signal and its relationship to peripheral and central immunity in depression

Although both central and peripheral inflammation have been observed consistently in depression, the relationship between the two remains obscure. Extra-axial immune cells may play a role in mediating the connection between central and peripheral immunity. This study investigates the potential roles of calvarial bone marrow and parameningeal spaces in mediating interactions between central and peripheral immunity in depression. PET was used to measure regional TSPO expression in the skull and parameninges as a marker of inflammatory activity. This measure was correlated with brain TSPO expression and peripheral cytokine concentrations in a cohort enriched for heightened peripheral and central immunity comprising 51 individuals with depression and 25 healthy controls. The findings reveal a complex relationship between regional skull TSPO expression and both peripheral and central immunity. Facial and parietal skull bone TSPO expression showed significant associations with both peripheral and central immunity. TSPO expression in the confluence of sinuses was also linked to both central and peripheral immune markers. Group-dependent elevations in TSPO expression within the occipital skull bone marrow were also found to be significantly associated with central inflammation. Significant associations between immune activity within the skull, parameninges, parenchyma and periphery highlight the role of the skull bone marrow and venous sinuses as pivotal sites for peripheral and central immune interactions.

Differences Between Adolescent Depression and Healthy Controls in Biomarkers Associated With Immune or Inflammatory Processes: A Systematic Review and Meta-Analysis

OBJECTIVE

Adolescent depression is a highly prevalent and disabling mental disorder with unclear pathophysiology and unfavorable treatment outcomes. Recent efforts have been focusing on searching for biomarkers as specific indicators of adolescent depression. We performed a systematic literature review and meta-analysis, specifically including studies with healthy control groups as an inclusion criterion. This approach helps to avoid confounding factors and provides more accurate results regarding the inflammatory and immune biomarkers associated with adolescent depression.

METHODS

Three electronic databases were searched for studies comparing the means and changes in the biomarkers between depressed adolescent patients and healthy controls published in English until February 2024. Two authors independently performed the screening, quality assessment, and data extraction of the studies. A meta-analysis was conducted on outcomes reported by two or more studies using a random-effects model and presented Forrest plots and test statistics (I2) for heterogeneity analysis.

RESULTS

Nine studies were included in the review, including seven case-control studies and two cross-sectional studies. These studies included 24 target biomarkers, 13 of which were quantified in 2 or more studies. Compared to the healthy controls, the depressed adolescents had significantly higher values in ten indicators. Additionally, the depressed adolescents had lower procalcitonin levels than the healthy controls. The two groups showed no significant differences in the remaining 13 biomarkers.

CONCLUSION

Our findings offer fresh insights into the pathophysiology of inflammatory and immune aspects of adolescent depression and provide helpful guidance in developing targeted and effective intervention and prevention strategies to address adolescent depression.

Lipids and C-reactive protein predict anhedonia and reward circuit functional connectivity responses to anti-cytokine and dopaminergic therapies in patients with depression

Increased inflammation and associated metabolic disturbances have been shown to affect neurotransmitters and brain circuits, contributing to an immunometabolic phenotype of anhedonic depression. To extend our previous findings on relationships between plasma lipids and antidepressant response to anti-cytokine therapy, we explored in secondary analyses whether lipid-related biomarkers similarly predicted change in anhedonia or functional connectivity (FC) in dopamine-rich corticostriatal reward circuitry in medically-stable, depressed patients with a range of inflammation levels (indexed by plasma C-reactive protein [CRP]) who were administered inflammation-targeted therapies. Relationships were examined between baseline lipids (plasma cholesterols, triglycerides and non-esterified fatty acids) and reduction of anhedonia symptoms in Study 1 (n = 60) after three infusions of infliximab or placebo and change in resting-state FC in Study 2 (n = 31) after acute, within-subject challenge with levodopa (L-DOPA) and placebo. A treatment by inflammation interaction revealed lower anhedonia after infliximab versus placebo (F[1,49] = 5.5, p < 0.05) in patients with, but not without, CRP>3 mg/L (n = 27). A composite score of lipid-related biomarkers (with increasing values reflecting higher concentrations) also precited anhedonia response (post-treatment minus baseline) to infliximab (r = -0.46, p < 0.05) but not placebo (r = 0.14, p = 0.56). Lipid scores similarly predicted CRP-related increases in reward circuit FC after L-DOPA (r = 0.53, p < 0.01) but not placebo (r = 0.20, p = 0.34). Responses to infliximab and L-DOPA were strongest in patients with versus without clinically elevated CRP (>3 mg/L) and/or cholesterol (>150 mg/dL)(p < 0.05). Results highlight a role for dyslipidemia in immunometabolic depression, biomarkers of which, together with CRP, have potential to classify patients indicated for therapies that block inflammation or its effects on neurotransmitters like dopamine.

Corticostriatal contributions to dysregulated motivated behaviors in stress, depression, and substance use disorders

Coordinated network activity, particularly in circuits arising from the prefrontal cortex innervating the ventral striatum, is crucial for normal processing of reward-related information which is perturbed in several psychiatric disorders characterized by dysregulated reward-related behaviors. Stress-induced depression and substance use disorders (SUDs) both share this common underlying pathology, manifested as deficits in perceived reward in depression, and increased attribution of positive valence to drug-predictive stimuli and dysfunctional cognition in SUDs. Here we review preclinical and clinical data that support dysregulation of motivated and reward-related behaviors as a core phenotype shared between these two disorders. We posit that altered processing of reward-related stimuli arises from dysregulated control of subcortical circuits by upstream regions implicated in executive control. Although multiple circuits are directly involved in reward processing, here we focus specifically on the role of corticostriatal circuit dysregulation. Moreover, we highlight the growing body of evidence indicating that such abnormalities may be due to heightened neuroimmune signaling by microglia, and that targeting the neuroimmune system may be a viable approach to treating this shared symptom.

Abnormal choroid plexus, hippocampus, and lateral ventricles volumes as markers of treatment-resistant major depressive disorder

AIM

One-third of patients with major depressive disorder (MDD) do not achieve full remission and have high relapse rates even after treatment, leading to increased medical costs and reduced quality of life and health status. The possible specificity of treatment-resistant depression (TRD) neurobiology is still under investigation, with risk factors such as higher inflammatory markers being identified. Given recent findings on the role of choroid plexus (ChP) in neuroinflammation and hippocampus in treatment response, the aim of the present study was to evaluate inflammatory- and trophic-related differences in these regions along with ventricular volumes among patients with treatment-sensitive depression (TSD), TRD, and healthy controls (HCs).

METHODS

ChP, hippocampal, and ventricular volumes were assessed in 197 patients with MDD and 58 age- and sex-matched HCs. Volumes were estimated using FreeSurfer 7.2. Treatment resistance status was defined as failure to respond to at least two separate antidepressant treatments. Region of interest volumes were then compared among groups.

RESULTS

We found higher ChP volumes in patients with TRD compared with patients with TSD and HCs. Our results also showed lower hippocampal volumes and higher lateral ventricular volumes in TRD compared with both patients without TRD and HCs.

CONCLUSIONS

These findings corroborate the link between TRD and neuroinflammation, as ChP volume could be considered a putative marker of central immune activity. The lack of significant differences in all of the region of interest volumes between patients with TSD and HCs may highlight the specificity of these features to TRD, possibly providing new insights into the specific neurobiological underpinnings of this condition.

Psoriasis management tree based on comorbidity

Psoriasis, a common chronic inflammatory skin disorder, encompasses various subtypes, including guttate, pustular, erythrodermic, and the most common type, plaque psoriasis. Irrespective of the subtype, psoriasis can manifest with multisystemic presentations, including psoriatic arthritis, metabolic disorders, cardiovascular disease, malignancies, chronic kidney disease (CKD), psychiatric illness, and inflammatory bowel disease (IBD). Many comorbidities and concomitant conditions must be considered when selecting the most appropriate therapy for a patient (Kaushik et al., 2019 and Monks et al., 2021) . Ongoing clinical trials and the development of new therapeutic targets contribute to the continuous improvement of available treatment options. Given the dynamic landscape of therapies, particularly when managing complex patients with multiple comorbidities, dermatologists are constantly challenged with the task of adeptly tailoring treatments to each psoriasis patient. This article systematically reviews the current evidence, presenting it as an updated Psoriasis Decision Tree to assist physicians in selecting tailored treatment options.

Can infliximab serve as a new therapy for neuropsychiatric symptoms?

Neuropsychiatric disorders present a global challenge to public health. Mechanisms associated with neuropsychiatric disorders etiology include apoptosis, oxidative stress, and neuroinflammation. Tumor necrosis factor alpha, an inflammatory cytokine, mediates pathophysiology of neuropsychiatric disorders. Therefore, its inhibition by infliximab might afford a valuable target for intervention. Infliximab is commonly used to treat inflammatory diseases, including ulcerative colitis, Crohn's disease, and rheumatoid arthritis. Recently, it has been shown that infliximab improves cognitive dysfunction, depression, anxiety, and life quality. Here, we review contemporary knowledge supporting the need to further characterize infliximab as a potential treatment for neuropsychiatric disorders.

Associations between IL-6 and trajectories of depressive symptoms across the life course: Evidence from ALSPAC and UK Biobank cohorts

BACKGROUND

Peripheral inflammatory markers, including serum interleukin 6 (IL-6), are associated with depression, but less is known about how these markers associate with depression at different stages of the life course.

METHODS

We examined the associations between serum IL-6 levels at baseline and subsequent depression symptom trajectories in two longitudinal cohorts: ALSPAC (age 10-28 years; N = 4,835) and UK Biobank (39-86 years; N = 39,613) using multilevel growth curve modeling. Models were adjusted for sex, BMI, and socioeconomic factors. Depressive symptoms were measured using the Short Moods and Feelings Questionnaire in ALSPAC (max time points = 11) and the Patient Health Questionnaire-2 in UK Biobank (max time points = 8).

RESULTS

Higher baseline IL-6 was associated with worse depression symptom trajectories in both cohorts (largest effect size: 0.046 [ALSPAC, age 16 years]). These associations were stronger in the younger ALSPAC cohort, where additionally higher IL-6 levels at age 9 years was associated with worse depression symptoms trajectories in females compared to males. Weaker sex differences were observed in the older cohort, UK Biobank. However, statistically significant associations (pFDR <0.05) were of smaller effect sizes, typical of large cohort studies.

CONCLUSIONS

These findings suggest that systemic inflammation may influence the severity and course of depressive symptoms across the life course, which is apparent regardless of age and differences in measures and number of time points between these large, population-based cohorts.

The interface of depression and diabetes: treatment considerations

This state-of-the-art review explores the relationship between depression and diabetes, highlighting the two-way influences that make treatment challenging and worsen the outcomes of both conditions. Depression and diabetes often co-occur and share genetic, lifestyle, and psychosocial risk factors. Lifestyle elements such as diet, physical activity, and sleep patterns play a role on the development and management of both conditions, highlighting the need for integrated treatment strategies. The evidence suggests that traditional management strategies focusing on either condition in isolation fall short of addressing the intertwined nature of diabetes and depression. Instead, integrated care models encompassing psychological support and medical management are recommended to improve treatment efficacy and patient adherence. Such models require collaboration across multiple healthcare disciplines, including endocrinology, psychiatry, and primary care, to offer a holistic approach to patient care. This review also identifies significant patient-related barriers to effective management, such as stigma, psychological resistance, and health literacy, which need to be addressed through patient-centered education and support systems. Future directions for research include longitudinal studies in diverse populations to further elucidate causal relationships and the exploration of novel therapeutic targets, as well as the effectiveness of healthcare models aimed at preventing the onset of one condition in individuals diagnosed with the other.

Associations between body mass index, high-sensitivity C-reactive protein, and depressive symptoms: NHANES 2015-2016

Objective

Studies have shown associations between Body Mass Index (BMI), High-Sensitivity C-reactive protein (HSCRP), and depressive symptoms(DP). However, the complex relationship between them remains uncertain. The objective of this research is to examine the correlation between them in a substantial sample that is representative of the national level.

Methods

Our analysis was based on the 2015-2016National Health and Nutrition Examination Survey (NHANES).DP was measured by the Patient Health Questionnaire-9 (PHQ-9). Using multivariable logistic regression analysis and stratified analysis, we examined the relationship between BMI, HSCRP, and DP. We applied generalized additive models to explore the non-linear relationships among variables.

Results

This study included a total of 4834 participants. The results revealed that BMI (P=0.002) and HSCRP (P=0.008) were risk factors for DP. The relationship between BMI and DP (P=0.035), BMI and HSCRP (P<0.001) were non-linear. The nonlinear association between HSCRP and DP (P=0.031), BMI and DP (P=9e-04) is significant in females when stratified by gender. No nonlinear association was found between BMI and DP (P =0.677) and between HSCRP and DP (P =0.439) in males. The results of the interaction test reveal a significant interaction between HSCRP and gender.

Conclusions

Research has found both BMI and HSCRP are risk factors for DP and the relationship between them was non-linear. The nonlinear associations between BMI and DP, as well as between HSCRP and DP, are gender-dependent.

Role of Inflammation and Cytokine Dysregulation in Depression in Patients with Inflammatory Skin Conditions

The growing field of psychodermatology examines the interplay between dermatological and psychiatric comorbidities. While current literature recognizes that cutaneous and psychiatric conditions often coexist within patients, the relationship between dysregulated inflammation and depression in patients with inflammatory skin conditions has not been thoroughly explored. This review seeks to describe the connection between cutaneous disease and depression via shared inflammatory cytokine pathways. A review of current literature was conducted, and studies addressing the co-occurrence of depression and inflammatory skin diseases were included. This review focuses on depression in patients with psoriasis, atopic dermatitis, and hidradenitis suppurativa. Studies that focused on the prevalence of depression in these populations, shared inflammatory pathways, and co-management of cutaneous and psychiatric disorders were chosen. The literature revealed a high prevalence of depression in individuals with inflammatory skin conditions compared with those without cutaneous disease. Recent studies described how proinflammatory cytokines in inflammatory skin diseases can elicit inflammation in the brain, leading to depressive symptoms. Certain subsets of cytokines that mediate inflammatory pathways were associated with both cutaneous inflammation and depression, highlighting shared pathology. Antiinflammatory medications targeting shared cytokines found reductions in both cutaneous and depressive symptoms. Practitioners have emphasized interdisciplinary approaches to treating both conditions, including psychotherapy and pharmacological methods. There is a clear association between inflammatory cutaneous diseases and depression. Co-management of these conditions, including interdisciplinary methods, is essential for patients' well-being. Future research addressing similar links between other cutaneous and psychiatric conditions could yield new treatment opportunities as well.

Psychoneuroimmunology of Mood Disorders

Recent research has shed light on the intricate relationship between mood disorders, such as major depressive disorder (MDD) and bipolar disorder (BD), and inflammation. This chapter explores the complex interplay involving immune and metabolic dysfunction in the pathophysiology of these disorders, emphasizing their association with autoimmunity/inflammatory conditions, chronic low-grade systemic inflammation, T cell overactivation, and immunosenescence. This perspective underscores the notion that MDD and BD are not solely brain disorders, highlighting their nature as multi-system conditions.

Towards a consensus roadmap for a new diagnostic framework for mental disorders

Current nosology claims to separate mental disorders into distinct categories that do not overlap with each other. This nosological separation is not based on underlying pathophysiology but on convention-based clustering of qualitative symptoms of disorders which are typically measured subjectively. Yet, clinical heterogeneity and diagnostic overlap in disease symptoms and dimensions within and across different diagnostic categories of mental disorders is huge. While diagnostic categories provide the basis for general clinical management, they do not describe the underlying neurobiology that gives rise to individual symptomatic presentations. The ability to incorporate neurobiology into the diagnostic framework and to stratify patients accordingly will be a critical step forward for the development of new treatments for mental disorders. Furthermore, it will also allow physicians to provide patients with a better understanding of their illness's complexities and management. To realize this ambition, a paradigm shift is needed to build an understanding of how neuropsychiatric conditions can be defined more precisely using quantitative (multimodal) biological processes and markers and thus to significantly improve treatment success. The ECNP New Frontiers Meeting 2024 set out to develop a consensus roadmap for building a new diagnostic framework for mental disorders by discussing its rationale, outlook, and consequences with all stakeholders involved. This framework would instantiate a set of principles and procedures by which research could continuously improve precision diagnostics while moving away from traditional nosology. In this meeting report, the speakers' summaries from their presentations are combined to address three key elements for generating such a roadmap, namely, the application of innovative technologies, understanding the biology of mental illness, and translating biological understanding into new approaches. In general, the meeting indicated a crucial need for a biology-informed framework to establish more precise diagnosis and treatment for mental disorders to facilitate bringing the right treatment to the right patient at the right time.

Network analysis of depressive symptoms and C-reactive protein levels in major depressive disorder

BACKGROUND

C-reactive protein (CRP) levels have been implicated in the severity and symptomatology of major depressive disorder (MDD). The aim of this study was to explore the structure of depressive symptoms in patients with MDD according to different groups of CRP levels using network analysis.

METHODS

The study included 864 individuals (mean age = 54.05, 67.48 % male) diagnosed with MDD from the 2015-2020 National Health and Nutrition Examination Survey (NHANES). Analyses examined how depressive symptoms and CRP level were related to each other, and how the network structure of depressive symptoms differed across groups with different CRP levels.

RESULTS

A direct positive correlation was observed between CRP levels and specific depressive symptoms (e.g., appetite change, energy loss, and feelings of worthlessness). Moreover, there was a stronger correlation between depressive symptoms in the medium CRP and high CRP groups compared to the low CRP group. Furthermore, it was observed that there were notable structural differences between the high-CRP and moderate-CRP groups.

LIMITATIONS

The study is based on cross-sectional data, which precludes the drawing of causal conclusions. Furthermore, it does not take into account confounding factors such as body mass index (BMI) and lifestyle.

CONCLUSIONS

The findings underscore the pivotal role of CRP as a marker of the severity of depressive symptoms. Routine CRP level testing and anti-inflammatory therapies may be beneficial for depressed patients with elevated CRP levels in clinical practice.

Blood-derived factors to brain communication in brain diseases

Brain diseases, mainly including acute brain injuries, neurodegenerative diseases, and mental disorders, have posed a significant threat to human health worldwide. Due to the limited regenerative capability and the existence of the blood-brain barrier, the brain was previously thought to be separated from the rest of the body. Currently, various cross-talks between the central nervous system and peripheral organs have been widely described, including the brain-gut axis, the brain-liver axis, the brain-skeletal muscle axis, and the brain-bone axis. Moreover, several lines of evidence indicate that leveraging systemic biology intervention approaches, including but not limited to lifestyle interventions, exercise, diet, blood administration, and peripheral immune responses, have demonstrated a significant influence on the progress and prognosis of brain diseases. The advancement of innovative proteomic and transcriptomic technologies has enriched our understanding of the nuanced interplay between peripheral organs and brain diseases. An array of novel or previously underappreciated blood-derived factors have been identified to play pivotal roles in mediating these communications. In this review, we provide a comprehensive summary of blood-to-brain communication following brain diseases. Special attention is given to the instrumental role of blood-derived signals, positing them as significant contributors to the complex process of brain diseases. The insights presented here aim to bridge the current knowledge gaps and inspire novel therapeutic strategies for brain diseases.

Immunological Approaches in the Diagnosis and Treatment of Psychiatric Disorders: A Historical Overview

BACKGROUND

For over 130 years, scientists have been suggesting that infection and inflammation may play a role in psychosis and other psychiatric disorders. First attempts to treat psychosis by immune-modulating therapies were made early in the last century; however, after the development of antipsychotics in the 1950s, scientific interest shifted away from immunological aspects of psychiatric disorders to the involvement of catecholamines, in particular dopamine, in psychosis.

SUMMARY

Antipsychotic treatment was not as successful as expected, so the 1990s saw renewed interest in inflammation and psychoneuroimmunological research in schizophrenia and beyond. In parallel, advances in immunological research methods allowed immunological and inflammatory mechanisms to be studied in more detail.

KEY MESSAGES

Clinical studies and meta-analyses have demonstrated positive effects of anti-inflammatory treatment in certain patients with psychiatric disorders. More research is needed to elucidate exactly how immunological mechanisms result in disease pathophysiology, with the aim to improve anti-inflammatory and personalized treatments.

Efficacy and safety of drugs for psoriasis patients with mental disorders: A systematic review

BACKGROUND

The emergence of biological agents and small molecule drugs has revolutionized the treatment landscape for psoriasis, yet there remains a lack of systematic reviews elucidating the efficacy and safety of drugs for patients with psoriasis and mental disorders (MDs). The aim was to systemically evaluate the efficacy and safety of FDA-approved psoriasis drugs on MD symptoms and MD drugs on psoriasis symptoms.

METHODS

We conducted comprehensive literature searches of the PubMed, Embase, and Cochrane Library from inception to March 24, 2024, identifying 116 relevant studies for inclusion.

RESULTS

Our review encompasses 62 clinical trials and 54 case reports/series. Analyses of clinical trials revealed a positive impact of psoriasis drugs on MD, with notable exceptions including lithium and benzodiazepine receptor agonists, which exhibited adverse effects on psoriasis. Furthermore, analysis of case reports/series highlighted the efficacy of drugs such as apremilast, etanercept, infliximab, and secukinumab in ameliorating MD symptoms, contrasting with detrimental effects observed with methotrexate (MTX), cyclosporine, adalimumab, and secukinumab. Notably, tumor necrosis factor alpha (TNF-α) inhibitors and interleukin inhibitors demonstrated superior efficacy compared to conventional treatments. In the anxiety group, secukinumab showed the largest effective size as assessed by the Hospital Anxiety and Depression Scale - Anxiety (HADS-A) index; In the depression group, ixekizumab showed the largest effective size assessed by the 16-item Quick Inventory of Depressive Symptomology - Self-Report (QIDS-SR16) index.

LIMITATIONS

The extracted data cannot be meta-analyzed, as the measurement scale is not uniform.

CONCLUSIONS

This systematic review provides robust evidence regarding treatment options for individuals with psoriasis and MD, emphasizing the potential benefits of specific drugs in managing both conditions concurrently.

The inflammatory underpinning of depression: An historical perspective

Over the last thirty years, substantial evidence has accumulated in support of the hypothesis that dysregulation of inflammatory processes plays a critical role in the pathophysiology of depression. This review traces the evolution of research supporting this link, discussing key findings from several major investigative fronts: Alterations in inflammatory markers associated with depression; Mood changes following the exogenous administration of inflammatory challenges; The anti-inflammatory properties of traditional antidepressants and the promising antidepressant effects of anti-inflammatory drugs. Additionally, it explores how inflammatory processes interact with specific brain regions and neurochemical systems to drive depressive pathology. A thorough analysis of the 100 most-cited experimental studies on the topic ensures a comprehensive, transparent and unbiased collection of references. This methodological approach offers a panoramic view of the inflammation-depression nexus, shedding light on the complexity of its mechanisms and their connections to psychiatric categorizations, symptoms, demographics, and life events. Synthesizing insights from this extensive research, the review presents an integrative model of the biological foundations of inflammation-associated depression. It posits that we have reached a critical juncture where the translation of this knowledge into personalized immunomodulatory treatments for depression is not just possible, but imperative.

Efficacy of inflammation-based stratification for add-on celecoxib or minocycline in major depressive disorder: Protocol of the INSTA-MD double-blind placebo-controlled randomised clinical trial

Introduction

Different lines of evidence confirm the involvement of the immune system in the pathophysiology of major depressive disorder. Up to 30% of depressed patients present with an immune-mediated subtype, characterized by peripheral inflammation (high-sensitive C-reactive protein (hsCRP) ≥ 3 mg/l) and an atypical symptom profile with fatigue, anhedonia, increased appetite, and hypersomnia. This immune-mediated subtype of MDD is associated with poorer response to first-line antidepressant treatment. Consequently, strategies for immune-targeted augmentation should be prioritised towards patients with this subtype. Meta-analyses have shown modest but heterogeneous treatment effects with immune-targeted augmentation in unstratified MDD cohorts, with celecoxib and minocycline as most promising first-line treatment options. However, no study has prospectively evaluated the effectiveness of a priori stratification by baseline inflammation levels for add-on celecoxib or minocycline in MDD.

Methods

The INSTA-MD trial is a multicentre, 12-week, randomised, double-blind, placebo-controlled, parallel-group stratified clinical trial of adjunctive minocycline or celecoxib to treatment-as-usual for patients with MDD. Two hundred forty adult patients with Major Depressive Disorder who failed to remit with one or two trials of antidepressant treatment will be enrolled and allocated to high-hsCRP (hsCRP ≥3 mg/L) or low-hsCRP (hsCRP <3 mg/L) strata, where disproportional stratified sampling will ensure equally sized strata. Participants in each hsCRP stratum will be randomised to augment their ongoing antidepressant treatment with either adjunctive minocycline, celecoxib or placebo for a duration of 12 weeks, resulting in six treatment arms of each 40 participants. The primary objective is to evaluate the efficacy of immune-targeted augmentation with minocycline or celecoxib versus placebo, and the use of baseline hsCRP stratification to predict treatment response. Additionally, we will perform a head-to-head analysis between the two active compounds. The primary outcome measure is change in the Hamilton Depression Rating Scale (HDRS-17) total score. Secondary outcome measures will be response and remission rates, and change in inflammation-specific symptoms, adverse events and therapy acceptability (adherence). Further exploratory analyses will be performed with an array of peripheral inflammatory biomarkers, metabolic outcomes and physiological data.

Expected impact

The aim of INSTA-MD is to advance the use of immune-targeted precision psychiatry, by supporting the implementation of targeted hsCRP screening and treatment of immune-mediated MDD as a cost-effective intervention in primary care settings. Based on previous studies, we expect immune-targeted augmentation with minocycline or celecoxib to yield a superior remission rate of 15-30% compared to treatment as usual for immune-mediated cases of MDD. By treating immune-related depression early in the treatment algorithm with repurposed first-line anti-inflammatory treatments, we can significantly improve the outcomes of these patients, and reduce the global societal and economic burden of depression.

Ethics and dissemination

This protocol has been approved by the Medical Ethics Review Board (CTR - 04/08/2023).

Registration details

Trial registration number NCT05644301 (Clinical trial.gov), EU-CT 2022-501692-35-00.

Review article: The role of the gut-brain axis in inflammatory bowel disease and its therapeutic implications

BACKGROUND

Treatments targeting the gut-brain axis (GBA) are effective at reducing symptom burden in irritable bowel syndrome (IBS). The prevalence of common mental disorders and IBS-type symptom reporting is significantly higher in inflammatory bowel disease (IBD) than would be expected, suggesting potential GBA effects in this setting. Manipulation of the GBA may offer novel treatment strategies in selected patients with IBD. We present a narrative review of the bi-directional effects of the GBA in IBD and explore the potential for GBA-targeted therapies in this setting.

METHODS

We searched MEDLINE, EMBASE, EMBASE Classic, PsychINFO, and the Cochrane Central Register of Controlled Trials for relevant articles published by March 2024.

RESULTS

The bi-directional relationship between psychological well-being and adverse longitudinal disease activity outcomes, and the high prevalence of IBS-type symptom reporting highlight the presence of GBA-mediated effects in IBD. Treatments targeting gut-brain interactions including brain-gut behavioural treatments, neuromodulators, and dietary interventions appear to be useful adjunctive treatments in a subset of patients.

CONCLUSIONS

Psychological morbidity is prevalent in patients with IBD. The relationship between longitudinal disease activity outcomes, IBS-type symptom reporting, and poor psychological health is mediated via the GBA. Proactive management of psychological health should be integrated into routine care. Further clinical trials of GBA-targeted therapies, conducted in selected groups of patients with co-existent common mental disorders, or those who report IBS-type symptoms, are required to inform effective integrated models of care in the future.

Plasminogen Activator Inhibitor-1 in the Pathophysiology of Late Life Depression

INTRODUCTION

Late life depression (LLD) is characterized by specific clinical features including a high frequency of vascular form and frequent antidepressant treatment resistance. The expression and functions of the serine protease inhibitor, Plasminogen Activator Inhibitor-1 (PAI-1) is known to be altered by aging, vascular damage, insulin levels associated with a sedentary lifestyle, chronic stress leading to hypercortisolemia, and inflammatory changes linked to stress responses. These phenomena would be implicated in LLD like vascular depression. This article thus aims to review the existing literature regarding the association between LLD and plasmatic levels of PAI-1, a marker of hypofibrinolysis. We hypothesize that increased age would be associated with changes in PAI-1 plasma level and function which influence LLD pathogenesis and its treatment.

RESULTS

Although a large number of studies on PAI-1 changes in the elderly exist, studies about its implications in LLD are sparse. Despite heterogeneous findings regarding the direction of variation in plasmatic PAI-1 levels among elderly participants with LLD, all studies demonstrated an association between PAI-1 levels and current or remitted depressive symptoms. Moreover, disruptions in the concentrations of other biological markers influencing PAI-1 expression, such as cytokines or adipokines, were also observed, notably an increase in the levels of interleukins 6 and 8.

DISCUSSION

LLD genesis appears to be influenced by PAI-1 regulatory loops which are implicated in senescence or cell death. The resistance to antidepressant treatment appears to be linked to distinct biological profiles involving inflammatory and fibrinolytic factors. Taken together these data suggest that PAI-1 pathway may be a promising target of treatment development efforts for LLD, and depression in general.

Treatment-resistant depression: molecular mechanisms and management

Due to the heterogeneous nature of depression, the underlying etiological mechanisms greatly differ among individuals, and there are no known subtype-specific biomarkers to serve as precise targets for therapeutic efficacy. The extensive research efforts over the past decades have not yielded much success, and the currently used first-line conventional antidepressants are still ineffective for close to 66% of patients. Most clinicians use trial-and-error treatment approaches, which seem beneficial to only a fraction of patients, with some eventually developing treatment resistance. Here, we review evidence from both preclinical and clinical studies on the pathogenesis of depression and antidepressant treatment response. We also discuss the efficacy of the currently used pharmacological and non-pharmacological approaches, as well as the novel emerging therapies. The review reveals that the underlying mechanisms in the pathogenesis of depression and antidepressant response, are not specific, but rather involve an interplay between various neurotransmitter systems, inflammatory mediators, stress, HPA axis dysregulation, genetics, and other psycho-neurophysiological factors. None of the current depression hypotheses sufficiently accounts for the interactional mechanisms involved in both its etiology and treatment response, which could partly explain the limited success in discovering efficacious antidepressant treatment. Effective management of treatment-resistant depression (TRD) requires targeting several interactional mechanisms, using subtype-specific and/or personalized therapeutic modalities, which could, for example, include multi-target pharmacotherapies in augmentation with psychotherapy and/or other non-pharmacological approaches. Future research guided by interaction mechanisms hypotheses could provide more insights into potential etiologies of TRD, precision biomarker targets, and efficacious therapeutic modalities.

Tocilizumab Reduces Depression Risk in Rheumatoid Arthritis Patients: A Systematic Review and Meta-Analysis

Depression is a possible cause of the increased mental health risks associated with rheumatoid arthritis (RA), including depression-related complications. Biological disease-modifying antirheumatic drug (bDMARDs) therapies have emerged as innovative anti-inflammatory drugs with positive effects on mental well-being. Tocilizumab is a bDMARDs commonly used to treat RA and its influence on depression needs to be studied. It targets interleukin-6 (IL-6) receptors, reducing inflammation, which may also alleviate depressive symptoms due to the role of inflammation in the pathophysiology of depression. Thus, its influence on depression needs to be studied. To assess the strength of the association between exposure to tocilizumab and the rate of development of depression in patients with RA and to evaluate tocilizumab as an exposure and depression as an outcome in these patients, a search was conducted in the MEDLINE, PreMEDLINE, Cochrane, and Scopus databases from January 1980 to April 2024. Inclusion criteria were studies that diagnosed RA according to the latest American College of Rheumatology/European League Against Rheumatism guidelines or a rheumatologist and provided information on tocilizumab exposure and diagnosed depression as an outcome. The present meta-analysis was conducted following the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement. These studies were assessed for eligibility by the author and an independent assessor. To summarize the findings, the meta-analysis combined the relative risk estimates from each study with raw data counts. Twelve studies in the meta-analysis fulfilled the inclusion criteria. Tocilizumab monotherapy exhibited a promising beneficial effect on the risk of depression, indicated by the decreased risk in RA patients (Relative risk 0.68, 95% CI 0.20, 2.31). Patients with RA on tocilizumab treatment had a lower risk of developing depression compared to those unexposed to tocilizumab treatment. Therefore, future longitudinal studies are needed to confirm the beneficial effect of tocilizumab on depression in the RA population.

Looking Back to Move Forward: Research in Stress, Behavior, and Immune Function

BACKGROUND

From the original studies investigating the effects of adrenal gland secretion to modern high-throughput multidimensional analyses, stress research has been a topic of scientific interest spanning just over a century.

SUMMARY

The objective of this review was to provide historical context for influential discoveries, surprising findings, and preclinical models in stress-related neuroimmune research. Furthermore, we summarize this work and present a current understanding of the stress pathways and their effects on the immune system and behavior. We focus on recent work demonstrating stress-induced immune changes within the brain and highlight studies investigating stress effects on microglia. Lastly, we conclude with potential areas for future investigation concerning microglia heterogeneity, bone marrow niches, and sex differences.

KEY MESSAGES

Stress is a phenomenon that ties together not only the central and peripheral nervous system, but the immune system as well. The cumulative effects of stress can enhance or suppress immune function, based on the intensity and duration of the stressor. These stress-induced immune alterations are associated with neurobiological changes, including structural remodeling of neurons and decreased neurogenesis, and these contribute to the development of behavioral and cognitive deficits. As such, research in this field has revealed important insights into neuroimmune communication as well as molecular and cellular mediators of complex behaviors relevant to psychiatric disorders.

Effect modification of tumor necrosis factor-α on the kynurenine and serotonin pathways in major depressive disorder on type 2 diabetes mellitus

Major depressive disorder (MDD) is strongly associated with type 2 diabetes mellitus (T2DM). The kynurenine and serotonin pathways, as well as chronic low-grade inflammation, are being considered potential links between them. MDD associated with T2DM is less responsive to treatment than that without T2DM; however, the underlying mechanism remains unknown. We aimed to investigate the effects of inflammatory cytokines on the kynurenine and serotonin pathways in patients with comorbid MDD and T2DM and those with only MDD. We recruited 13 patients with comorbid MDD and T2DM and 27 patients with only MDD. We measured interleukin-6 and tumor necrosis factor-α (TNF-α) levels as inflammatory cytokines and metabolites of the kynurenine pathway and examined the relationship between the two. TNF-α levels were significantly higher in patients with comorbid MDD and T2DM than in those with only MDD in univariate (p = 0.044) and multivariate (adjusted p = 0.036) analyses. TNF-α showed a statistically significant effect modification (interaction) with quinolinic acid/tryptophan and serotonin in patients from both groups (β = 1.029, adjusted p < 0.001; β =  - 1.444, adjusted p = 0.047, respectively). Limitations attributed to the study design and number of samples may be present. All patients were Japanese with mild to moderate MDD; therefore, the generalizability of our findings may be limited. MDD with T2DM has more inflammatory depression components and activations of the kynurenine pathway by inflammatory cytokines than MDD without T2DM. Hence, administering antidepressants and anti-inflammatory drugs in combination may be more effective in patients with comorbid MDD and T2DM.

The Role of Inflammation in Depression and Beyond: A Primer for Clinicians

PURPOSE OF REVIEW

We evaluate available evidence for the role of inflammation in depression. We reappraise literature involving systemic inflammation, neuroinflammation and neurotransmission and their association with depression. We review the connection between depression, autoimmunity and infectious diseases. We revise anti-inflammatory treatments used in depression.

RECENT FINDINGS

Peripheral inflammatory markers are present in a subset of patients with depression and can alter common neurotransmitters in this population but there is no clear causality between depression and systemic inflammation. Infectious conditions and autoimmune illnesses do not have a clear correlation with depression. Certain medications have positive evidence as adjunctive treatments in depression but studies are heterogenic, hence they are sparsely used in clinical settings. The current evidence does not fully support inflammation, infections or autoimmunity as possible etiologies of depression. The available studies have numerous confounders that obscure the findings. Anti-inflammatory agents may have potential for treatment of depression, but further research is needed to clarify their usefulness in routine clinical practice.

Glycolytic metabolism: Food for immune cells, fuel for depression?

Inflammation is one biological pathway thought to impact the brain to contribute to major depressive disorder (MDD) and is reliably associated with resistance to standard antidepressant treatments. While peripheral immune cells, particularly monocytes, have been associated with aspects of increased inflammation in MDD and symptom severity, significant gaps in knowledge exist regarding the mechanisms by which these cells are activated to contribute to behavioral symptoms in MDD. One concept that has gained recent appreciation is that metabolic rewiring to glycolysis in activated myeloid cells plays a crucial role in facilitating these cells' pro-inflammatory functions, which may underlie myeloid contribution to systemic inflammation and its effects on the brain. Given emerging evidence from translational studies of depression that peripheral monocytes exhibit signs of glycolytic activation, better understanding the immunometabolic phenotypes of monocytes which are known to be elevated in MDD with high inflammation is a critical step toward comprehending and treating the impact of inflammation on the brain. This narrative review examines the extant literature on glycolytic metabolism of circulating monocytes in depression and discusses the functional implications of immunometabolic shifts at both cellular and systemic levels. Additionally, it proposes potential therapeutic applications of existing immunomodulators that target glycolysis and related metabolic pathways in order to reverse the impact of elevated inflammation on the brain and depressive symptoms.

Inflammatory cytokines, cortisol, and anhedonia in patients with treatment-resistant depression after consecutive infusions of low-dose esketamine

Anhedonia, defined as a significant loss of interest or pleasure, is one of the core symptoms of treatment- resistant depression (TRD) and is often associated with poor prognosis. This article primarily investigates the changes in anhedonia symptoms, inflammatory markers, and cortisol levels in TRD patients after low-dose esketamine treatments. A total of sixty patients with TRD were enrolled in the clinical study of esketamine. We primarily assessed the severity of depressive symptoms and anhedonia using the Hamilton Rating Scale for Depression (HAMD) and the Snaith-Hamilton Pleasure Scal(SHAPS), respectively, before esketamine treatment and within 24 h after each treatment. Blood specimens were collected before the first treatment and within 1 h after the sixth treatment, measuring the levels of cortisol, interleukin-6(IL-6), interleukin-4(IL-4), and tumor necrosis factor-alpha(TNF-α) in plasma. We found that after six consecutive infusions of low-dose esketamine, patients' depressive symptoms and anhedonia showed improvement. After six treatments, plasma levels of cortisol, IL-6, and TNF-α decreased in patients with TRD, while the anti-inflammatory cytokine IL-4 increased. Multiple linear regression analysis revealed that baseline cortisol levels were correlated with anhedonia, while inflammatory factors showed no significant correlation. Add-on esketamine appears to be a good choice for the treament of the anhedonia in TRD. It has also shown promising effects on altering inflammatory markers in patients with TRD. Moreover, elevated plasma cortisol levels may serve as a potential biomarker for anhedonia in patients with TRD.

Pathogenesis and therapeutic strategies for cancer-related depression

Depression is a common co-morbidity among cancer cases, which has a detrimental influence on cancer treatment and prognosis. Recent advancements in the neurobiology of depression and cancer pathophysiology have revealed several shared biobehavioral mechanisms and introduced new therapeutic strategies. In this review, we summarize the biological mechanisms driving cancer-related depression, including psychosocial factors, immuno-inflammatory processes, chronic stress, dysbiosis of gut microbiota, and medically-induced factors. Interventions used for cancer-related depression may include psychosocial therapies, pharmacological therapies, immunotherapies, psychobiological medications, and dietary strategies. This review could inspire the elucidation of possible co-occurring mechanisms and complex interactions between cancer and depression, provide an opportunity to propose faster and more effective therapies for cancer-related depression, and well as new strategies for cancer in the future.