The effects of interleukin-6 neutralizing antibodies on symptoms of depressed mood and anhedonia in patients with rheumatoid arthritis and multicentric Castleman's disease

Quality of life after idiopathic multicentric Castleman disease in China: a cross-sectional, multi-center survey of patient reported outcome and caregiver reported outcome

The majority of multicentric Castleman disease (MCD) patients in China are of the idiopathic subtype (iMCD) with systemic manifestations. However, the impact of iMCD on life quality, mental and psychological status, social function, and caregiving burden is poorly understood. To address this gap, a cross-sectional web-based survey was conducted with 178 iMCD patients and 82 caregivers, including 42 patient-caregiver dyads. Patient-reported outcome measurements were performed using four self-administered questionnaires (MCD-SS, SF-36, PHQ-9, and WPAI:GH). Caregiver-reported outcome measurements were performed using three questionnaires (SF-36, Zarit-22, CRA) to assess the caregiving burden. Correlation analysis was performed in patient-caregiver dyads. Patients reported a median of nine symptoms by MCD-SS, with a high mean score of 4.34 for the Fatigue domain. Their SF-36 scores indicated significant declines in physical and mental health compared to the Chinese general population (p < 0.001). Based on PHQ-9, around 65% of patients exhibited depressive symptoms, with 28.6% of them experiencing mild to severe major depression. Only 47.2% (84/178) of the patients were employed, and 28.5% experienced impaired work time. Caregivers also reported lower SF-36 scores than the general population (p < 0.05) and expressed feeling of self-criticism, lack of family support and financial problems. Correlations were observed between patients' symptom burden, mental health impairment and caregiving burden (correlation coefficient: 0.31 ~ 0.55). Our study concluded that fatigue and depressive symptoms significantly impact the life quality and social well-being of iMCD patients. The disease also affect the physical and mental health of caregivers, leading to feelings of guilt and a lack of family support.

Possible association of elevated CSF IL-6 levels with anxiety and frustration in psychiatric disorders

AIM

Neuroinflammation is an important causal factor for a variety of psychiatric disorders. We previously reported increased cerebrospinal fluid interleukin-6 levels in patients with schizophrenia and major depressive disorder. The present study aimed to examine the possible association of interleukin-6 levels with anxiety and frustration, negative valence symptoms shared in various psychiatric disorders.

METHODS

We included 129 patients with psychiatric disorders and 70 controls. CSF and plasma interleukin-6 levels were measured by immunoassay kits, and psychological symptoms were assessed with the State-Trait Anxiety Inventory, and the Basic Psychological Need Satisfaction and Frustration Scale. To examine regional cerebral blood flow, patients underwent arterial spin labeling analysis using magnetic resonance imaging.

RESULTS

Cerebrospinal fluid interleukin-6 levels were significantly correlated with State-Trait Anxiety Inventory-trait anxiety (r = 0.25, P = 0.046) and Basic Psychological Need Satisfaction and Frustration Scale-autonomy frustration scores (r = 0.29, P = 0.018). Patients with abnormally high cerebrospinal fluid interleukin-6 levels (defined >97.5 percentile of the controls) had higher scores for trait anxiety (P = 0.035) and autonomy frustration (P = 0.026), and significantly increased regional cerebral blood flow in the left superior temporal gyrus, bilateral nucleus accumbens, and cerebellum than the remaining patients.

CONCLUSION

Patients with elevated cerebrospinal fluid interleukin-6 constitute a subpopulation of psychiatric disorders associated with anxiety and autonomy frustration, which may be related to altered functions in specific brain areas.

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.

Interdisciplinary Rheumatoid Arthritis Research and Patient Care: An Introduction and Critique of the Biopsychosocial Model of Disease Experience in Rheumatoid Arthritis

INTRODUCTION

Rheumatoid arthritis (RA), a debilitating autoimmune disease, affects approximately 78 million people globally. RA is often managed solely by rheumatology providers, but an interdisciplinary approach to RA may be the key to improving health equity and outcomes. An interdisciplinary model is an important step towards this goal. The Biopsychosocial Model of Disease Experience in RA (BDRA) is a conceptual approach that considers individual disease determinants in interdisciplinary research and care.

OBJECTIVE

To introduce and critique the evidence-based, interdisciplinary BDRA.

METHODS

Engel's Biopsychosocial Model of Health (BMH) and the Revised Symptom Management Conceptual Model (RSMCM) were blended in the BDRA. A literature search of articles published prior to December 2021 was completed using "disease exacerbation," "disease improvement," and "disease activity" in RA. Results were categorized as biological, psychological, and social determinants of disease activity in RA. These biopsychosocial factors alter biological function and result in the individual RA experience. Model development and critique were completed using guidelines established by Walker and Avant.

CONCLUSION

The BDRA is a visual depiction of RA biopsychosocial factors, disease activity, and individual experience. This model can guide interdisciplinary research and patient care, in efforts to improve RA health equity and rates of sustained remission.

Innate immunity-mediated neuroinflammation promotes the onset and progression of post-stroke depression

Post-stroke depression (PSD) is a prevalent psychiatric disorder after stroke, with the incidence of approximately one-third among stroke survivors. It is classified as an organic mental disorder and has a well-documented association with stroke affecting various aspects of patients, such as the recovery of limb motor function, daily living self-care ability, and increasing the mortality of stroke survivors. However, the pathogenesis of PSD is not yet fully understood. Currently, immune inflammation is a research hotspot. This review focuses on the pathogenesis of PSD, particularly elucidating the role of inflammation in mediating neuroinflammation through innate immunity. Simultaneously, we highlight that peripheral inflammation following a stroke may trigger a detrimental cycle of neuroinflammation by activating innate immune pathways within the central nervous system, which could potentially contribute to the development of PSD. Lastly, we summarize potential treatments for PSD and propose targeting cytokines and innate immune pathways as novel therapeutic approaches.

Monoclonal antibody precision therapy targeting inflammation for bipolar disorder: a narrative review

Bipolar disorder (BD) is a severe mental disorder with various hypotheses regarding its pathogenesis. This article provides a summary of numerous studies on the variations in inflammatory cytokine levels in patients with BD and the effects of treatment with antipsychotics, mood stabilizers, and antidepressants on these levels. In addition, patients with autoimmune diseases who use anti-inflammatory monoclonal antibodies experience symptoms, such as depression, anxiety, and insomnia. These pieces of evidence suggest a potential association between immune inflammation and BD and offer new possibilities for therapy. Building upon this relationship, the authors propose an innovative approach for treating BD through individualized and precise therapy using anti-inflammatory monoclonal antibody drugs. To support this proposal, the authors compile information on pharmacological effects and relevant studies, including trials of various anti-inflammatory therapeutic monoclonal antibody drugs (e.g. infliximab, tocilizumab, and canakinumab) for the potential treatment of BD and its associated side effects in psychiatry. The authors categorize these anti-inflammatory monoclonal antibody drugs into levels I-IV through a comprehensive analysis of their advantages and disadvantages. Their potential is examined, and the need for further exploration of their pharmaceutical effects is established.

Investigating the Potential Mechanisms and Therapeutic Targets of Inflammatory Cytokines in Post-stroke Depression

Post-stroke depression (PSD) affects approximately one-third of stroke survivors, severely impacting general recovery and quality of life. Despite extensive studies, the exact mechanisms underlying PSD remain elusive. However, emerging evidence implicates proinflammatory cytokines, including interleukin-1β, interleukin-6, tumor necrosis factor-alpha, and interleukin-18, play critical roles in PSD development. These cytokines contribute to PSD through various mechanisms, including hypothalamic-pituitary-adrenal (HPA) axis dysfunction, neurotransmitter alterations, neurotrophic factor changes, gut microbiota imbalances, and genetic predispositions. This review is aimed at exploring the role of cytokines in stroke and PSD while identifying their potential as specific therapeutic targets for managing PSD. A more profound understanding of the mechanisms regulating inflammatory cytokine expression and anti-inflammatory cytokines like interleukin-10 in PSD may facilitate the development of innovative interventions to improve outcomes for stroke survivors experiencing depression.

A review on linking stress, depression, and insulin resistance via low-grade chronic inflammation

Stress is a disturbance in homeostasis caused by psychological, physiological, or environmental factors. Prolonged reactions to chronic stress can be detrimental, resulting in various metabolic abnormalities, referred to as metabolic syndrome (MS). There is a reciprocal increased risk between MS and major depressive disorder. Recent studies established an association between inflammation and insulin signaling in type 2 diabetes mellitus with depression. In the present review, we discuss chronic low-grade inflammation, pathways of insulin resistance, and brain glucose metabolism in the context of neuroinflammation and depression. Specific attention is given to psychotropic drugs such as bupropion, mirtazapine, and nefazodone, anti-inflammatory drugs like Celecoxib (COX-2 inhibitor), Etanercept, adalimumab, IL-4Ra antagonist, Anti-IL- 17A antibody (Ixekizumab) and lifestyle modifications including exercise, dietary changes, and sleep hygiene. These therapeutic solutions offer potential in treating depression by targeting metabolic conditions like insulin resistance and inflammatory pathways. The article further explains the significance of a nutrition and antioxidants-rich diet, emphasizing the role of omega-3 fatty acids, vitamin D, zinc, and polyphenols, to improve immunity and activate anti-inflammatory signaling pathways.

Potential value of Interleukin-6 as a diagnostic biomarker in human MDD and the antidepressant effect of its receptor antagonist tocilizumab in lipopolysaccharide-challenged rats

Depression is a common mental disease with disastrous effect on the health and wealth globally. Focusing on the role for inflammation and immune activation in the pathogenesis of depression, many tries have been taken into effect targeting at the blockage of inflammatory cytokines, among which interleukin- 6 (IL-6) and its receptor antagonist tocilizumab attracts more attention, with inconsistent findings. Moderate to severe depressive disorder (MSDD) patients were enrolled and the serum concentrations of IL-6 and tumor necrosis factor-α (TNF-α) measured, their correlation with the Hamilton Depression Rating Scale-24 (HAMD-24) scores was analyzed, and their role in discriminating MSDD patients from the health controls were evaluated. Meanwhile, a depression rat model was established by intraperitoneal injection of LPS, and tocilizumab was administrated doing 50 mg/kg via intravenous injection. The behavioral performance was observed, the serum concentration of IL-6, TNF-α, and C-reactive protein (CRP) was measured, and the protein expression of IL-6 and TNF-α in the hippocampus were also detected. The activity of the Hypothalamic-pituitary-adrenal (HPA) axis was observed, and the protein expression levels in the hippocampus were detected via western blot. Moreover, the immunofluorescence staining (IF) technique was used to investigate the co-location of IL-6 and neuron (MAP2), astrocyte (GFAP), or microglial (IBA-1). The results showed that the serum IL-6 level was significantly increased in the MSDD patients and lipopolysaccharide (LPS)-challenged rats, with a significant correlation with the HAMD-24 scores or struggling time in the FST and corticosterone (CORT) abundance. Results of ROC analysis showed a significant diagnosis value of IL-6 in discriminating MSDD patients or depression rats from the controls in the present study. Tocilizumab could relieve the depression-like behaviors induced by LPS, together with a normal abundance of serum CORT and hypothalamic CRH expression. Moreover, tocilizumab could alleviate the "inflammatory storm" and impaired hippocampal synaptic plasticity in LPS-challenged depression rats, inhibiting the hyperactivation of astrocyte and microglia, decreasing the peripheral and central abundance of IL-6, CRP, and TNF-α, and balancing the hippocampal expression levels of synaptic plasticity-associated proteins and key molecular in Wnt/β-catenin signaling pathway. These results indicated a predictive role of IL-6 in discriminating depression from controls, and demonstrated an antidepressant effect of tocilizumab in LPS-challenged rats, targeting at the inflammatory storm and the subsequent impairments of hippocampal synaptic plasticity.

Increased prefrontal cortical cells positive for macrophage/microglial marker CD163 along blood vessels characterizes a neuropathology of neuroinflammatory schizophrenia

Transcript levels of cytokines and SERPINA3 have been used to define a substantial subset (40%) of individuals with schizophrenia with elevated inflammation and worse neuropathology in the dorsolateral prefrontal cortex (DLPFC). In this study, we tested if inflammatory proteins are likewise related to high and low inflammatory states in the human DLFPC in people with schizophrenia and controls. Levels of inflammatory cytokines (IL6, IL1β, IL18, IL8) and a macrophage marker (CD163 protein) were measured in brains obtained from the National Institute of Mental Health (NIMH) (N = 92). First, we tested for diagnostic differences in protein levels overall, then we determined the percentage of individuals that could be defined as "high" inflammation using protein levels. IL-18 was the only cytokine to show increased expression in schizophrenia compared to controls overall. Interestingly, two-step recursive clustering analysis showed that IL6, IL18, and CD163 protein levels could be used as predictors of "high and low" inflammatory subgroups. By this model, a significantly greater proportion of schizophrenia cases (18/32; 56.25%; SCZ) were identified as belonging to the high inflammatory (HI) subgroup compared to control cases (18/60; 30%; CTRL) [χ2(1) = 6.038, p = 0.014]. When comparing across inflammatory subgroups, IL6, IL1β, IL18, IL8, and CD163 protein levels were elevated in both SCZ-HI and CTRL-HI compared to both low inflammatory subgroups (all p < 0.05). Surprisingly, TNFα levels were significantly decreased (-32.2%) in schizophrenia compared to controls (p < 0.001), and were most diminished in the SCZ-HI subgroup compared to both CTRL-LI and CTRL-HI subgroups (p < 0.05). Next, we asked if the anatomical distribution and density of CD163+ macrophages differed in those with schizophrenia and high inflammation status. Macrophages were localized to perivascular sites and found surrounding small, medium and large blood vessels in both gray matter and white matter, with macrophage density highest at the pial surface in all schizophrenia cases examined. A higher density of CD163+ macrophages, that were also larger and more darkly stained, was found in the SCZ-HI subgroup (+154% p < 0.05). We also confirmed the rare existence of parenchymal CD163+ macrophages in both high inflammation subgroups (schizophrenia and controls). Brain CD163+ cell density around blood vessels positively correlated with CD163 protein levels. In conclusion, we find a link between elevated interleukin cytokine protein levels, decreased TNFα protein levels, and elevated CD163+ macrophage densities especially along small blood vessels in those with neuroinflammatory schizophrenia.

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

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

Association of plasma cytokines and antidepressant response following mild-intensity whole-body hyperthermia in major depressive disorder

Whole-body hyperthermia (WBH) shows promise for the treatment of major depressive disorder (MDD). Because MDD is associated with increased inflammation, and anti-inflammatory agents show some promise as antidepressants, the current study sought to identify the acute and longer-term immune effects of WBH in participants with MDD and to explore whether these effects associate with the procedure's antidepressant properties. Thirty participants who met DSM-IV-TR criteria for MDD were randomized to receive a single session of WBH (n = 16) or sham treatment (n = 14). Hamilton Depression Rating Scale (HDRS) scores were assessed at baseline and 1, 2, 4, and 6 weeks post-treatment (WBH vs. sham), and plasma cytokine concentrations were assessed at baseline, immediately post-treatment, and 1 and 4 weeks post-treatment. As previously reported, WBH produced a rapid and sustained antidepressant effect. When compared to sham, WBH increased plasma interleukin (IL)-6 immediately post-treatment (time by treatment: χ²_{(3, N=108)} = 47.33, p < 0.001), while having no effect on other cytokines acutely and no impact on IL-6, or any other cytokine, at 1 or 4 weeks post treatment. In the study sample as a whole, increased IL-6 post-treatment was associated with reduced HDRS depression scores over the 6 weeks of follow-up (F_{(1, 102.3)} = 6.74, p = 0.01). These results suggest a hitherto unrecognized relationship between hyperthermia, the immune system, and depression, and may point to WBH as a novel modality for exploring behavioral effects of IL-6 when the cytokine is activated in isolation from the inflammatory mediators with which it frequently travels.

The prevalence and the effect of interferon -γ in the comorbidity of rheumatoid arthritis and depression

BACKGROUND

Depression is the most common comorbidities associated with rheumatoid arthritis (RA). We aimed to explore the mechanism of association between RA and depression.

METHODS

120 subjects were enrolled and depression was diagnosed and assessed using DSM-5 and 24-item version of Hamilton Depression Scale. Pain intensity and joint function in patients with RA were assessed using the visual analog scale (VAS) and health assessment questionnaire (HAQ). Serum levels of interferon-gamma (IFN-γ), indoleamine 2,3-dioxygenase (IDO), kynurenine (KYN), tryptophan (TRP), and quinolinic acid (QUIN)were detected. In animal experiments, K/BxN mice with RA-like phenotype was used and depressive behavior was observed. The protein expression level of N-methyl -D- aspartate receptor 2B (NR2B) in the hippocampus was detected.

RESULTS

In this study, 36.67 % of patients with RA also had depression. The working status, month family income, tender joint count, the VAS and HAQ score were the main factors influencing the depression in RA patients. HAQ score was found to be an independent risk factor for depression in RA. Serum IDO, IFN-γ, KYN were increased and TRP contents were decreased in RA group. K/BxN mice with RA-like phenotype showed depressive behavior. However, injection of IFN-γ neutralizing antibody could inhibit kynurenine pathway and reverse the depressive behavior in mice. The levels of QUIN in the neurotoxic metabolic pathway were increased and N-methyl -D- aspartate receptors (NMDAR) were activated, which may be the mechanism behind the onset of depression.

CONCLUSIONS

From clinical and preclinical aspects, the occurrence of depression in RA was explored and the related mechanism was revealed.

Inflammation, Lifestyle Factors, and the Microbiome-Gut-Brain Axis: Relevance to Depression and Antidepressant Action

Depression is considered a major public health concern, where existing pharmacological treatments are not equally effective across all patients. The pathogenesis of depression involves the interaction of complex biological components, such as the immune system and the microbiota-gut-brain axis. Adjunctive lifestyle-oriented approaches for depression, including physical exercise and special diets are promising therapeutic options when combined with traditional antidepressants. However, the mechanisms of action of these strategies are incompletely understood. Accumulating evidence suggests that physical exercise and specific dietary regimens can modulate both the immune system and gut microbiota composition. Here, we review the current information about the strategies to alleviate depression and their crosstalk with both inflammatory mechanisms and the gut microbiome. We further discuss the role of the microbiota-gut-brain axis as a possible mediator for the adjunctive therapies for depression through inflammatory mechanisms. Finally, we review existing and future adjunctive strategies to manipulate the gut microbiota with potential use for depression, including physical exercise, dietary interventions, prebiotics/probiotics, and fecal microbiota transplantation.

Research progress on rheumatoid arthritis-associated depression

Depression is an independent mood disorder and one of the most common comorbidities of rheumatoid arthritis (RA). Growing evidence suggests that there is two-way regulation between RA and depression, resulting in a vicious cycle of RA, depression, poor outcomes, and disease burden. The rising prevalence of RA-associated depression warrants a re-examination of the relationships between them. Here we provide an overview of the etiology and pathological mechanisms of RA-associated depression, and recent advances in treatment with biologics, which will facilitate the development of new and effective prevention and treatment strategies.

Global and Dimensions of Mental Health in Arthritis Patients

Arthritis is one of the main clusters of long-lasting musculoskeletal and joint disorders. Recently, there has been increasing interest in the impact of arthritis patients' mental health, which has mainly focused on depression and anxiety in clinical samples. However, much less is known about how domains of mental health based on the widely used 12-item version of the general health survey (GHQ-12) are affected by arthritis. The current research answered this question using confirmatory factor analysis, general linear models, and one-sample t-tests on a nationally representative sample from the United Kingdom with 5588 arthritis patients and 8794 participants indicating that they were not clinically diagnosed with arthritis. The current study found that (1) a total of three factors of GHQ-12 that are labeled GHQ-12A (social dysfunction and anhedonia; six items), GHQ-12B (depression and anxiety; four items), and GHQ-12C (loss of confidence; two items), and (2) both the global mental health and dimensions of mental health are negatively affected by arthritis. Clinicians could use the results from the present study to make better treatment decisions for patients with arthritis.

The Role of Inflammation in the Pathophysiology of Depression and Suicidal Behavior: Implications for Treatment

Depression and suicidal behavior are 2 complex psychiatric conditions of significant public health concerns due to their debilitating nature. The need to enhance contemporary treatments and preventative approaches for these illnesses not only calls for distillation of current views on their pathogenesis but also provides an impetus for further elucidation of their novel etiological determinants. In this regard, inflammation has recently been recognized as a potentially important contributor to the development of depression and suicidal behavior. This review highlights key evidence that supports the presence of dysregulated neurometabolic and immunologic signaling and abnormal interaction with microbial species as putative etiological hallmarks of inflammation in depression as well as their contribution to the development of suicidal behavior. Furthermore, therapeutic insights addressing candidate mechanisms of pathological inflammation in these disorders are proposed.

Suicide and Inflammation

Suicide is a leading cause of death worldwide. Although the neurobiological dysfunction underlying suicidal behavior remains unclear, recent work suggests that the immune system may play a role in the pathophysiology of suicide. In this chapter, we discuss a nascent body of literature suggesting that peripheral and central nervous systems (CNS) inflammation are associated with suicidal behavior. Because early-life stress is a major risk factor for suicidal behavior and is also associated with immune dysregulation, we hypothesize that such immune dysregulation may be the mechanism by which childhood maltreatment leads to an increased risk of suicidal behavior and suicide. Targeting inflammatory processes may be a novel treatment strategy, especially in populations that have experienced childhood trauma and exhibit elevated inflammation. Future work should directly test the hypothesis that reducing inflammation would result in a reduction in suicidal behavior.

Evaluation of Inflammatory Response System (IRS) and Compensatory Immune Response System (CIRS) in Adolescent Major Depression

Purpose

Nowadays, the role of two tightly interconnected systems, the inflammatory response system (IRS) and the compensatory immune response system (CIRS) in depression, is increasingly discussed. Various studies indicate pro-inflammatory activity in adolescent depression; however, there is an almost complete lack of findings about IRS and CIRS balance. Thus, we aimed to assess different IRS and CIRS indices, profiles, and IRS/CIRS ratios in drug-naïve MDD patients at adolescent age, with respect to sex.

Patients and Methods

One hundred MDD adolescents (40 boys, average age: 15.4±1.2 yrs.) and 60 controls (28 boys, average age: 15.3±1.5 yrs.) were examined. Evaluated parameters were 1. plasma levels of interleukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, interferon gamma, tumor necrosis factor alpha (TNF-α), soluble receptor of IL-6 (sIL-6R), soluble receptors of TNF-α (sTNF-R1, sTNF-R2); 2. profiles: IL-6 trans-signaling, M1 macrophage signaling, helper T lymphocytes (Th) 1 profile, regulatory T lymphocytes (Treg)+Th2, allIRS, and allCIRS; 3. IRS vs CIRS activity ratios: TNF-α/TNF-R1, TNF-α/TNF-R2, TNF-α/sTNF-Rs (ie sTNF-R1+sTNF-R2), Th1/Th2, Th1/Treg, Th1/Th2+Treg, M1/Th2, M1/Treg, M1/Treg+Th2, allIRS/allCIRS.

Results

MDD patients showed increased IL-4, IL-10, TNF-α, sIL-6R, Treg+Th2, allIRS, allCIRS, and TNF-α/sTNF-Rs, and decreased Th1/Th2+Treg. MDD females showed increased IL-10 and TNF-α compared to control females. MDD males showed increased IL-4, IL-10, sIL-6R, Treg+Th2, and TNF-α/TNF-R1 compared to control males. Increased sTNF-R1 was found in MDD males compared to MDD females. Positive correlations were found between CDI score and sIL-6R and IL-10 in the total group and between CDI score and IL-10 in adolescent males.

Conclusion

Our study for the first time extensively evaluated IRS and CIRS interactions revealing enhanced pro-inflammatory TNF-α signaling and IL-6 trans-signaling in association with increased IL-10- and IL-4-mediated anti-inflammatory activity in first-episode depression at the adolescent age. Moreover, results reflect the sex-specific simultaneous activation of IRS and CIRS pathways in adolescent depression.

Microglial Inflammatory-Metabolic Pathways and Their Potential Therapeutic Implication in Major Depressive Disorder

Increasing evidence supports the notion that neuroinflammation plays a critical role in the etiology of major depressive disorder (MDD), at least in a subset of patients. By virtue of their capacity to transform into reactive states in response to inflammatory insults, microglia, the brain's resident immune cells, play a pivotal role in the induction of neuroinflammation. Experimental studies have demonstrated the ability of microglia to recognize pathogens or damaged cells, leading to the activation of a cytotoxic response that exacerbates damage to brain cells. However, microglia display a wide range of responses to injury and may also promote resolution stages of inflammation and tissue regeneration. MDD has been associated with chronic priming of microglia. Recent studies suggest that altered microglial morphology and function, caused either by intense inflammatory activation or by senescence, may contribute to depression and associated impairments in neuroplasticity. In this context, modifying microglia phenotype by tuning inflammatory pathways might have important translational relevance to harness neuroinflammation in MDD. Interestingly, it was recently shown that different microglial phenotypes are associated with distinct metabolic pathways and analysis of the underlying molecular mechanisms points to an instrumental role for energy metabolism in shaping microglial functions. Here, we review various canonical pro-inflammatory, anti-inflammatory and metabolic pathways in microglia that may provide new therapeutic opportunities to control neuroinflammation in brain disorders, with a strong focus on MDD.

Investigational Drugs for the Treatment of Depression (Part 1): Monoaminergic, Orexinergic, GABA-Ergic, and Anti-Inflammatory Agents

Therapeutic management of depression has currently important limitations, and its low efficacy is reflected in high rates of non-response even after multiple trials of antidepressants. Almost two-thirds of the patients diagnosed with major depression who received a 4–6 weeks trial of antidepressant could not reach remission, and more than 30% of these patients are considered treatment-resistant. In bipolar depression, the situation is also discouraging if we analyze the high suicide rate, the risk for the treatment-emergent affective switch when antidepressants are added, the high rate of treatment resistance (up to 25%), and the severe functional impairments associated with these episodes. Therefore, new therapeutic agents are needed, as well as new pathogenetic models for depression. The vast majority of the currently approved antidepressants are based on the monoamine hypothesis, although new drugs exploiting different neurotransmitter pathways have been recently approved by FDA. Brexanolone, an allopregnanolone analog, is an example of such new antidepressants, and its approval for post-partum depression inspired the search for a new generation of neurosteroids and GABA-ergic modulators, with an easier way of administration and superior tolerability profile. Orexin receptors antagonists are also extensively studied for different psychiatric disorders, depression included, in phase II trials. Antiinflammatory drugs, both cyclo-oxygenase 2 inhibitors and biological therapy, are investigated in patients with depressive disorders based on the proven correlation between inflammation and mood disorders in preclinical and clinical studies. Also, a new generation of monoamine-based investigational drugs is explored, ranging from triple reuptake inhibitors to atypical antipsychotics, in patients with major depression. In conclusion, there is hope for new treatments in uni- and bipolar depression, as it became clear, after almost seven decades, that new pathogenetic pathways should be targeted to increase these patients’ response rate.

Immune targets for therapeutic development in depression: towards precision medicine

Over the past two decades, compelling evidence has emerged indicating that immune mechanisms can contribute to the pathogenesis of major depressive disorder (MDD) and that drugs with primary immune targets can improve depressive symptoms. Patients with MDD are heterogeneous with respect to symptoms, treatment responses and biological correlates. Defining a narrower patient group based on biology could increase the treatment response rates in certain subgroups: a major advance in clinical psychiatry. For example, patients with MDD and elevated pro-inflammatory biomarkers are less likely to respond to conventional antidepressant drugs, but novel immune-based therapeutics could potentially address their unmet clinical needs. This article outlines a framework for developing drugs targeting a novel patient subtype within MDD and reviews the current state of neuroimmune drug development for mood disorders. We discuss evidence for a causal role of immune mechanisms in the pathogenesis of depression, together with targets under investigation in randomized controlled trials, biomarker evidence elucidating the link to neural mechanisms, biological and phenotypic patient selection strategies, and the unmet clinical need among patients with MDD.

Increased plasma levels of IL-6 are associated with striatal structural atrophy in major depressive disorder patients with anhedonia

BACKGROUND

Anhedonia, as the core endophenotype of major depressive disorder (MDD), is closely related to poor prognosis, but the mechanism of this feature remains to be understood. The aim of this study was to investigate the inflammatory factors and brain structural alterations in MDD patients with anhedonia and evaluate the relationship between these factors.

METHODS

We assessed the plasma levels of interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) in MDD patients with anhedonia (n = 22), MDD patients without anhedonia (n = 20), and age- and sex-matched healthy controls (HCs, n = 20) by enzyme-linked immunosorbent assay kits. All participants underwent high-resolution brain magnetic resonance imaging (MRI) scans, and voxel-based morphometry (VBM) was used to evaluate their gray matter volume (GMV). We compared inflammatory factors and GMV among the three groups and explored their relationships in MDD patients with anhedonia.

RESULTS

Compared with those of HCs, plasma levels of IL-1β were increased in patients with MDD independent of anhedonia features, while plasma levels of IL-6 were elevated in MDD patients with anhedonia only. Meanwhile, MDD patients with anhedonia exhibited reduced GMV in the left striatal structures compared to MDD patients without anhedonia and HCs. Moreover, a significant association was observed between increased plasma levels of IL-6 and decreased GMV of the left putamen in MDD patients with anhedonia.

CONCLUSIONS

The present research outcomes suggest that anhedonia is associated with increased plasma levels of IL-6 and decreased GMV in the left striatal structures. In addition, this study demonstrates that GMV loss in the left putamen is related to increased plasma levels of IL-6 in MDD with anhedonia, which provides further insights into the possible mechanisms of anhedonia.

The severity of inflammation in major neuropsychiatric disorders: comparison of neutrophil-lymphocyte and platelet-lymphocyte ratios between schizophrenia, bipolar mania, bipolar depression, major depressive disorder, and obsessive compulsive disorder

BACKGROUND

As non-specific markers of immune dysregulation, neutrophil-lymphocyte and platelet-lymphocyte ratios (NLR and PLR) have been consistently shown to be increased in major neuropsychiatric disorders. Although this increase seems to be trans-diagnostic, the extent to which its magnitude differs between disorders remains largely unclear.

AIM

The aim of this study was to directly compare the severity of inflammation (as reflected by NLR and PLR) between schizophrenia (Sch), bipolar mania (BD-M), bipolar depression (BD-D), major depressive disorder (MDD) and obsessive compulsive disorder (OCD).

METHODS

NLR and PLR were obtained for a total of 417 subjects (91 Sch, 70 BD-D, 37 BD-M, 93 MDD, 37 OCD, and 95 controls) and analyzed for group differences.

RESULTS

Sch, BD-M, BD-D and MDD presented with significantly higher NLR compared with both OCD and HC. NLR in BD-M was significantly higher than all the remaining groups, whereas Sch, BD-D and MDD presented with comparably elevated NLR. Moreover, BD-M, Sch and MDD had significantly higher PLR compared with HC.

CONCLUSION

These results suggest that the underlying inflammation may be most severe in BD-M, followed by Sch, BD-D and MDD. On the other hand, inflammation may be of negligible intensity in OCD, or at least undetectable by means of NLR or PLR.

Inflamed brain: Targeting immune changes and inflammation for treatment of depression

Although there are a number of clinically effective treatments for depression, many patients exhibit treatment resistance. Recent clinical and preclinical studies reveal that peripheral and brain immune changes and inflammation are involved in the pathophysiology of depression. This 'Inflamed Brain' research provides critical clues for understanding of disease pathophysiology and many candidate molecules that are potentially useful for identifying novel drug targets for the treatment of depression. In this review, we will present clinical evidence on the role of inflammation in the pathophysiology of depression. We will also summarize current clinical trials which test drugs targeting inflammation for the treatment of patients with depression. Furthermore, we will briefly provide preclinical evidence demonstrating altered immune system function and inflammation in stress-induced animal models and will discuss the future potential of inflammation-related drug targets. Collectively, inflammatory signatures identified in clinical and preclinical studies may allow us to stratify depressive patients based on biotypes, contributing to the development of novel mechanism-based interventions that target specific patient populations.

Unravelling the broader complexity of IL-6 involvement in health and disease

The classification of interleukin-6 (IL-6) as a pro-inflammatory cytokine undervalues the biological impact of this cytokine in health and disease. With broad activities affecting the immune system, tissue homeostasis and metabolic processes, IL-6 displays complex biology. The significance of these involvements has become increasingly important in clinical settings where IL-6 is identified as a prominent target for therapy. Here, clinical experience with IL-6 antagonists emphasises the need to understand the context-dependent properties of IL-6 within an inflammatory environment and the anticipated or unexpected consequences of IL-6 blockade. In this review, we will describe the immunobiology of IL-6 and explore the gamut of IL-6 bioactivity affecting the clinical response to biological drugs targeting this cytokine pathway.

Depression and interleukin-6 signaling: A Mendelian Randomization study

BACKGROUND

A large body of research has reported associations between depression and elevated interleukin-6 (IL-6), a cytokine with several roles including pro-inflammatory signaling. The nature and directionality of this relationship are not yet clear. In this study we use Mendelian Randomization to examine the possibility of a causal relationship between IL-6 and depressive symptoms, and to explore multiple signaling pathways that could serve as mechanisms for this relationship.

METHODS

This study uses a two-sample Mendelian Randomization design. Data come from the UK Biobank (n = 89,119) and published summary statistics from six existing GWAS analyses. The primary analysis focuses on the soluble interleukin-6 receptor (sIL-6R), which is involved in multiple signaling pathways. Exploratory analyses use C-reactive protein (CRP) and soluble glycoprotein 130 (sgp130) to further examine potential underlying mechanisms.

RESULTS

Results are consistent with a causal effect of sIL-6R on depression (PCA-IVW Odds Ratio: 1.023 (95% Confidence Interval: 1.006-1.039), p = 0.006). Exploratory analyses demonstrate that the relationship could be consistent with either decreased classical signaling or increased trans signaling as the underlying mechanism.

DISCUSSION

These results strengthen the body evidence implicating IL-6 signaling in depression. When compared with existing observational and animal findings, the direction of these results suggests involvement of IL-6 trans signaling. Further study is needed to examine whether IL6R genetic variants might influence IL-6 trans signaling in the brain, as well as to explore other potential pathways linking depression and inflammation.

Major Depressive Disorder in Older Patients as an Inflammatory Disorder: Implications for the Pharmacological Management of Geriatric Depression

Depression is a common and highly disabling condition in older adults. It is a heterogenous disorder and there is emerging evidence of a link between inflammation and depression in older patients, with a possible inflammatory subtype of depression. Persistent low-level inflammation, from several sources including psychological distress and chronic disease, can disrupt monoaminergic and glutaminergic systems to create dysfunctional brain networks. Despite the evidence for the role of inflammation in depression, there is insufficient evidence to recommend use of any putative anti-inflammatory agent in the treatment of depression in older adults at this stage. Further characterisation of markers of inflammation and stratification of participants with elevated rates of inflammatory markers in treatment trials is needed.

On inflammatory hypothesis of depression: what is the role of IL-6 in the middle of the chaos?

Many patients with major depressive disorder (MDD) are reported to have higher levels of multiple inflammatory cytokines including interleukin 6 (IL-6). Recent studies both pre-clinical and clinical have advocated for the functional role of IL-6 in development of MDD and suggested a great potential for targeting this cytokine to open new avenues in pharmacotherapy of depression. The purpose of the present narrative review was to provide an integrated account of how IL-6 may contribute to development of depression. All peer-reviewed journal articles published before July 2020 for each area discussed were searched by WOS, PubMed, MEDLINE, Scopus, Google Scholar, for original research, review articles, and book chapters. Publications between 1980 and July 2020 were included. Alterations in IL-6 levels, both within the periphery and the brain, most probably contribute to depression symptomatology in numerous ways. As IL-6 acts on multiple differing target tissues throughout the body, dysregulation of this particular cytokine can precipitate a multitude of events relevant to depression and blocking its effects can prevent further escalation of inflammatory responses, and potentially pave the way for opening new avenues in diagnosis, treatment, and prevention of this debilitating disorder.

Neurological risks and benefits of cytokine-based treatments in coronavirus disease 2019: from preclinical to clinical evidence

Immunodeficiency and hyperinflammation are responsible for the most frequent and life-threatening forms of coronavirus disease 2019 (COVID-19). Therefore, cytokine-based treatments targeting immuno-inflammatory mechanisms are currently undergoing clinical scrutiny in COVID-19-affected patients. In addition, COVID-19 patients also exhibit a wide range of neurological manifestations (neuro-COVID), which may also benefit from cytokine-based treatments. In fact, such drugs have shown some clinical efficacy also in neuroinflammatory diseases. On the other hand, anti-cytokine drugs are endowed with significant neurological risks, mainly attributable to their immunodepressant effects. Therefore, the aim of the present manuscript is to briefly describe the role of specific cytokines in neuroinflammation, to summarize the efficacy in preclinical models of neuroinflammatory diseases of drugs targeting these cytokines and to review the clinical data regarding the neurological effects of these drugs currently being investigated against COVID-19, in order to raise awareness about their potentially beneficial and/or detrimental neurological consequences.

The IL-6 antagonist tocilizumab is associated with worse depression and related symptoms in the medically ill

Because medical illness is associated with increased inflammation and an increased risk for treatment-resistant major depressive disorder, anti-cytokine therapy may represent a novel, and especially efficacious, treatment for depression. We hypothesized that blockade of the interleukin (IL)-6 signaling pathway with tocilizumab would decrease depression and related symptomatology in a longitudinal cohort of allogeneic hematopoietic stem cell transplantation (HCT) patients, a medically ill population with a significant inflammation and psychopathology. Patients undergoing allogeneic HCT received either a single dose of tocilizumab one day prior to HCT (n = 25), or HCT alone (n = 62). The primary outcome included depressive symptoms at 28 days post HCT; anxiety, fatigue, sleep, and pain were assessed at pretreatment baseline and days +28, +100, and +180 post HCT as secondary outcomes. Multivariate regression demonstrated that preemptive treatment with tocilizumab was associated with significantly higher depression scores at D28 vs. the comparison group (β = 5.74; 95% CI 0.75, 10.73; P = 0.03). Even after adjustment for baseline depressive symptoms, propensity score, and presence of acute graft-versus-host disease (grades II-IV) and other baseline covariates, the tocilizumab-exposed group continued to have significantly higher depression scores compared to the nonexposed group at D28 (β = 4.73; 95% CI 0.64, 8.81; P = 0.02). Despite evidence that IL-6 antagonism would be beneficial, blockade of the IL-6 receptor with tocilizumab among medically ill patients resulted in significantly more-not less-depressive symptoms.

Cytokine Imbalance in Schizophrenia. From Research to Clinic: Potential Implications for Treatment

Cytokines are one of the most important components of the immune system. They orchestrate the brain's response to infectious and other exogenous insults and are crucial mediators of the cross-talk between the nervous and immune systems. Epidemiological studies have demonstrated that severe infections and autoimmune disorders, in addition to genetic predisposition, are risk factors for schizophrenia. Furthermore, maternal infection during pregnancy appears to increase the risk of schizophrenia, and proinflammatory cytokines may be negatively involved in the neurodevelopmental process. A cytokine imbalance has been described in the blood and cerebrospinal fluid of schizophrenia patients, particularly in the T helper type 1 [Th1] and type 2 [Th2] cytokines, albeit the results of such studies appear to be contradictory. Chronic stress, likewise, appears to contribute to a lasting proinflammatory state and likely also promotes the disorder. The aim of this mini-review is to investigate the roles of different cytokines in the pathophysiology of schizophrenia and define how cytokines may represent key molecular targets to regulate for the prevention and treatment of schizophrenia. How current antipsychotic drugs impact cytokine networks is also evaluated. In this context, we propose to change the focus of schizophrenia from a traditionally defined brain disorder, to one that is substantially impacted by the periphery and immune system.

The Link Between Autonomic Nervous System and Rheumatoid Arthritis: From Bench to Bedside

Neuronal stimulation is an emerging field of research focused on the management and treatment of various diseases through the reestablishment of physiological homeostasis. Electrical vagus nerve stimulation has recently been proposed as a revolutionary therapeutic option for rheumatoid arthritis (RA) in combination with or even as a replacement for conventional and biological drugs. In the past few years, disruption of the autonomic system has been linked to RA onset and activity. Novel research on the link between the autonomic nervous system and the immune system (immune-autonomics) has paved the way for the development of innovative RA management strategies. Clinical evidence supports this approach. Cardiovascular involvement, in terms of reduced baroreflex sensitivity and heart rate variability-derived indices, and mood disorders, common comorbidities in patients with RA, have been linked to autonomic nervous system dysfunction, which in turn is influenced by increased levels of circulating pro-inflammatory cytokines. This narrative review provides an overview of the autonomic nervous system and RA connection, discussing most of the common cardiac and mental health-related RA comorbidities and their potential relationships to systemic and joint inflammation.

IL-6 Receptor Blockade by Tocilizumab Has Anti-absence and Anti-epileptogenic Effects in the WAG/Rij Rat Model of Absence Epilepsy

Increased expression of interleukin-6 (IL-6) both in cerebrospinal fluid (CSF) and plasma is closely associated with convulsive epilepsy and symptom severity of depression. By comparison, at present, little is known about the role of this cytokine in childhood (non-convulsive) absence epilepsy. The aim of this work was to investigate the potential effects of acute and chronic treatment with tocilizumab (TCZ, 10 and 30 mg/kg/day), on absence seizures, their development, and related psychiatric comorbidity in WAG/Rij rats. It is known that lipopolysaccharide (LPS)-induced changes in inflammatory processes increase absence epileptic activity. In order to study the central effects of TCZ, we investigated whether administration of this anti-IL-6R antibody could modulate the lipopolysaccharide (LPS) or IL-6-evoked changes in absence epileptic activity in WAG/Rij rats. Our results demonstrate that TCZ, at both doses, significantly reduced the development of absence seizures in adult WAG/Rij rats at 6 months of age (1 month after treatment suspension) compared with untreated controls, thus showing disease-modifying effects. Decreased absence seizure development at 6 months of age was also accompanied by reduced comorbid depressive-like behavior, whereas no effects were observed on anxiety-related behavior. Acute treatment with TCZ, at 30 mg/kg, had anti-absence properties lasting ~25 h. The co-administration TCZ with i.c.v. LPS or IL-6 showed that TCZ inhibited the worsening of absence seizures induced by both proinflammatory agents in the WAG/Rij rats, supporting a central anti-inflammatory-like protective action. These results suggest the possible role of IL-6 and consequent neuroinflammation in the epileptogenic process underlying the development and maintenance of absence seizures in WAG/Rij rats. Accordingly, IL-6 signaling could be a promising pharmacological target in absence epilepsy and depressive-like comorbidity.

The Bidirectional Relationship of Depression and Inflammation: Double Trouble

Depression represents the number one cause of disability worldwide and is often fatal. Inflammatory processes have been implicated in the pathophysiology of depression. It is now well established that dysregulation of both the innate and adaptive immune systems occur in depressed patients and hinder favorable prognosis, including antidepressant responses. In this review, we describe how the immune system regulates mood and the potential causes of the dysregulated inflammatory responses in depressed patients. However, the proportion of never-treated major depressive disorder (MDD) patients who exhibit inflammation remains to be clarified, as the heterogeneity in inflammation findings may stem in part from examining MDD patients with varied interventions. Inflammation is likely a critical disease modifier, promoting susceptibility to depression. Controlling inflammation might provide an overall therapeutic benefit, regardless of whether it is secondary to early life trauma, a more acute stress response, microbiome alterations, a genetic diathesis, or a combination of these and other factors.

Serum level of soluble interleukin 6 receptor is a useful biomarker for identification of treatment-resistant major depressive disorder

AIM

A substantial proportion of major depressive disorder patients are treatment-resistant to antidepressant therapy, who require augmentation drugs, or other treatments including electroconvulsive therapy or transcranial magnetic stimulation. Identifying treatment-resistant major depressive disorder patients before the actual administration of antidepressant is, however, often difficult. Accordingly, the serum biomarker to identify treatment-resistant patients will be helpful in clinical settings. This study aims to clarify the appropriate biomarkers for identification of treatment-resistant major depressive disorder.

METHOD

Given that immune-inflammatory processes are involved in the pathogenesis of major depressive disorder, it is possible that certain cytokine-related molecules could serve as clinically useful biomarkers of treatment-resistant major depressive disorder patients. In this study, we measured serum levels of tumor necrosis factor-α, interleukin 6, and soluble interleukin 6 receptor after major depressive disorder patients underwent antidepressant therapy.

RESULTS

The serum level of soluble interleukin 6 receptor, but not interleukin 6 or tumor necrosis factor-α, was significantly higher in treatment-resistant major depressive disorder patients than in remitted patients, suggesting that serum soluble interleukin 6 receptor could be a good biomarker of treatment-resistant major depressive disorder. Receiver operating characteristic analysis confirmed that serum soluble interleukin-6 receptor level measurement was useful for identification of treatment-resistant major depressive disorder patients. Multiple regression analysis using the serum levels of the aforementioned cytokines as explanatory variables and the Quick Inventory of Depressive Symptomatology-Self Report score (QIDS-SR16 ) as a target variable showed that only serum soluble interleukin-6 receptor level could explain the severity of major depressive disorder.

CONCLUSION

Based on these results, we recommend measurement of serum soluble interleukin-6 receptor level to discriminate treatment-resistant major depressive disorder patients. High serum soluble interleukin-6 receptor level is associated with the pathogenesis of treatment-resistant major depressive disorder, suggesting the involvement of the interleukin 6 trans-signaling system in onset of treatment-resistant major depressive disorder.

Update on the Pathomechanism, Diagnosis, and Treatment Options for Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease that involves multiple joints bilaterally. It is characterized by an inflammation of the tendon (tenosynovitis) resulting in both cartilage destruction and bone erosion. While until the 1990s RA frequently resulted in disability, inability to work, and increased mortality, newer treatment options have made RA a manageable disease. Here, great progress has been made in the development of disease-modifying anti-rheumatic drugs (DMARDs) which target inflammation and thereby prevent further joint damage. The available DMARDs are subdivided into (1) conventional synthetic DMARDs (methotrexate, hydrochloroquine, and sulfadiazine), (2) targeted synthetic DMARDs (pan-JAK- and JAK1/2-inhibitors), and (3) biologic DMARDs (tumor necrosis factor (TNF)-α inhibitors, TNF-receptor (R) inhibitors, IL-6 inhibitors, IL-6R inhibitors, B cell depleting antibodies, and inhibitors of co-stimulatory molecules). While DMARDs have repeatedly demonstrated the potential to greatly improve disease symptoms and prevent disease progression in RA patients, they are associated with considerable side-effects and high financial costs. This review summarizes our current understanding of the underlying pathomechanism, diagnosis of RA, as well as the mode of action, clinical benefits, and side-effects of the currently available DMARDs.

Fatigue in inflammatory rheumatic disorders: pathophysiological mechanisms

Today, inflammatory rheumatic disorders are effectively treated, but many patients still suffer from residual fatigue. This work presents pathophysiological mechanisms of fatigue. First, cytokines can interfere with neurotransmitter release at the preterminal ending. Second, a long-term increase in serum concentrations of proinflammatory cytokines increase the uptake and breakdown of monoamines (serotonin, noradrenaline and dopamine). Third, chronic inflammation can also decrease monoaminergic neurotransmission via oxidative stress (oxidation of tetrahydrobiopterin [BH4]). Fourth, proinflammatory cytokines increase the level of enzyme indoleamine-2, 3-dioxygenase activity and shunt tryptophan away from the serotonin pathway. Fifth, oxidative stress stimulates astrocytes to inhibit excitatory amino acid transporters. Sixth, astrocytes produce kynurenic acid that acts as an antagonist on the α7-nicotinic acetylcholine receptor to inhibit dopamine release. Jointly, these actions result in increased glutamatergic and decreased monoaminergic neurotransmission. The above-described pathophysiological mechanisms negatively affect brain functioning in areas that are involved in fatigue.

Role of Interleukin-6 in Depressive Disorder

Major depressive disorder (MDD), which is a leading psychiatric illness across the world, severely affects quality of life and causes an increased incidence of suicide. Evidence from animal as well as clinical studies have indicated that increased peripheral or central cytokine interleukin-6 (IL-6) levels play an important role in stress reaction and depressive disorder, especially physical disorders comorbid with depression. Increased release of IL-6 in MDD has been found to be a factor associated with MDD prognosis and therapeutic response, and may affect a wide range of depressive symptomatology. However, study results of the IL6 genetic effects in MDD are controversial. Increased IL-6 activity may cause depression through activation of hypothalamic-pituitary-adrenal axis or influence of the neurotransmitter metabolism. The important role of neuroinflammation in MDD pathogenesis has created a new perspective that the combining of blood IL-6 and other depression-related cytokine levels may help to classify MDD biological subtypes, which may allow physicians to identify the optimal treatment for MDD patients. To modulate the IL-6 activity by IL-6-related agents, current antidepressive agents, herb medication, pre-/probiotics or non-pharmacological interventions may hold great promise for the MDD patients with inflammatory features.

Innate Immunity: A Common Denominator between Neurodegenerative and Neuropsychiatric Diseases

The intricate relationships between innate immunity and brain diseases raise increased interest across the wide spectrum of neurodegenerative and neuropsychiatric disorders. Barriers, such as the blood–brain barrier, and innate immunity cells such as microglia, astrocytes, macrophages, and mast cells are involved in triggering disease events in these groups, through the action of many different cytokines. Chronic inflammation can lead to dysfunctions in large-scale brain networks. Neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are associated with a substrate of dysregulated immune responses that impair the central nervous system balance. Recent evidence suggests that similar phenomena are involved in psychiatric diseases, such as depression, schizophrenia, autism spectrum disorders, and post-traumatic stress disorder. The present review summarizes and discusses the main evidence linking the innate immunological response in neurodegenerative and psychiatric diseases, thus providing insights into how the responses of innate immunity represent a common denominator between diseases belonging to the neurological and psychiatric sphere. Improved knowledge of such immunological aspects could provide the framework for the future development of new diagnostic and therapeutic approaches.

Novel neuroimmunologic therapeutics in depression: A clinical perspective on what we know so far

Depression, one of the most common mental health disorders, is among the leading causes of health-related disability worldwide. Although antidepressant treatment has been available for decades, depression remains largely refractory to the prevailing limited treatment approach of monoamine transmission modulation. Fortunately, recent evidence points to a link between depression and inflammatory factors within the innate and the adaptive immune system. The purpose of this review is to evaluate current and potential clinical immunotherapies for depression, as contextually focused by an immunologic lens of the pathophysiologic mechanisms of depression. The utility of pro-inflammatory cytokines (primarily interleukin-1β, interleukin -6 and tumor necrosis factor-α) is considered in their role as screening biomarkers in prediction of treatment response or nonresponse. The evidence base of numerous recent clinical studies is discussed as related to their antidepressant efficacy and favorable safety profile, with consideration of multiple agents that target inflammatory mechanisms linked to depression including nonsteroidal anti-inflammatory pathways (i.e., aspirin, celecoxib), cytokine antagonism (i.e., etanercept, infliximab), N-methyl-D-aspartate receptor (NMDA) receptor antagonism (i.e., ketamine), and modulation of kynurenine pathways (i.e., minocycline). Additionally, new and exciting directions in targeting inflammatory mechanisms in the treatment of depression are underway, and future investigation is also warranted to explore the utility of inflammation in diagnosing depression, guiding clinical treatment decision-making, and monitoring disease burden and relapse risk.

Shared pathways for neuroprogression and somatoprogression in neuropsychiatric disorders

Activated immune-inflammatory, oxidative and nitrosative stress (IO&NS) pathways and consequent mitochondrial aberrations are involved in the pathophysiology of psychiatric disorders including major depression, bipolar disorder and schizophrenia. They offer independent and shared contributions to pathways underpinning medical comorbidities including insulin resistance, metabolic syndrome, obesity and cardiovascular disease - herein conceptualized as somatoprogression. This narrative review of human studies aims to summarize relationships between IO&NS pathways, neuroprogression and somatoprogression. Activated IO&NS pathways, implicated in the neuroprogression of psychiatric disorders, affect the pathogenesis of comorbidities including insulin resistance, dyslipidaemia, obesity and hypertension, and by inference, metabolic syndrome. These conditions activate IO&NS pathways, exacerbating neuroprogression in psychiatric disorders. The processes whereby proinflammatory cytokines, nitrosative and endoplasmic reticulum stress, NADPH oxidase isoforms, PPARγ inactivation, SIRT1 deficiency and intracellular signalling pathways impact lipid metabolism and storage are considered. Through associations between body mass index, chronic neuroinflammation and FTO expression, activation of IO&NS pathways arising from somatoprogression may contribute to neuroprogression. Early evidence highlights the potential of adjuvants targeting IO&NS pathways for treating somatoprogression and neuroprogression.

Prevalence of low-grade inflammation in depression: a systematic review and meta-analysis of CRP levels

BACKGROUND

Peripheral low-grade inflammation in depression is increasingly seen as a therapeutic target. We aimed to establish the prevalence of low-grade inflammation in depression, using different C-reactive protein (CRP) levels, through a systematic literature review and meta-analysis.

METHODS

We searched the PubMed database from its inception to July 2018, and selected studies that assessed depression using a validated tool/scale, and allowed the calculation of the proportion of patients with low-grade inflammation (CRP >3 mg/L) or elevated CRP (>1 mg/L).

RESULTS

After quality assessment, 37 studies comprising 13 541 depressed patients and 155 728 controls were included. Based on the meta-analysis of 30 studies, the prevalence of low-grade inflammation (CRP >3 mg/L) in depression was 27% (95% CI 21-34%); this prevalence was not associated with sample source (inpatient, outpatient or population-based), antidepressant treatment, participant age, BMI or ethnicity. Based on the meta-analysis of 17 studies of depression and matched healthy controls, the odds ratio for low-grade inflammation in depression was 1.46 (95% CI 1.22-1.75). The prevalence of elevated CRP (>1 mg/L) in depression was 58% (95% CI 47-69%), and the meta-analytic odds ratio for elevated CRP in depression compared with controls was 1.47 (95% CI 1.18-1.82).

CONCLUSIONS

About a quarter of patients with depression show evidence of low-grade inflammation, and over half of patients show mildly elevated CRP levels. There are significant differences in the prevalence of low-grade inflammation between patients and matched healthy controls. These findings suggest that inflammation could be relevant to a large number of patients with depression.

Interleukin 6 as a pathogenic factor mediating clinical manifestations and a therapeutic target for rheumatic diseases and depressive disorders

The review summarizes current idea on the key role of interleukin 6 (IL-6) in the pathogenesis of rheumatic diseases (RDs) and depressive disorders. It considers in detail the mechanisms by which IL6 induces the clinical and laboratory manifestations of RDs and depression; the influence of precipitating and predisposing stress factors, including childhood mental traumas, which increase the risk of RDs and depression, on IL-6 production. Particular attention is paid to the consideration of prospects for using IL-6 inhibitors in the therapy of depression.

Cytokine secretion and the risk of depression development in patients with connective tissue diseases

Research in the past two decades has revolutionized our understanding of depressive illnesses. Proinflammatory cytokines have become a point of interest in the interconnecting areas of neuropsychiatric and autoimmune diseases. The cytokine hypothesis of depression suggests that pro-inflammatory cytokines play a primary role in the mediation of the pathophysiological characteristics of major depression, in which an inflammatory process may be induced by external and internal stressors, such as psychological and inflammatory diseases, respectively. The higher prevalence of depression, particularly in patients with chronic autoimmune connective tissue disorders (CTD), suggests that depression may present a dysfunctional adaptation of cytokine-induced sickness, which could manifest in times of an exacerbated activation of the innate immune system. Inflammation is thought to contribute to the development of clinical depression through its ability to induce sickness behaviors corresponding to the neurovegetative features of depression, through the dysregulation of the hypothalamic-pituitary-adrenal axis, alterations in neurotransmitter synthesis and reuptake, and through its involvement in the neuroprogression pathways. This review explores the complex interrelationships in which inflammatory responses alter neuroendocrine and neuropsychological regulation contributing to depressive symptoms in CTD. The prevalence and characteristics of depression, and its correlation to the levels of inflammatory cytokines and disease activity among different CTD will be reviewed.

Longitudinal Association Between Depression and Inflammatory Markers: Results From the Netherlands Study of Depression and Anxiety

BACKGROUND

While cross-sectional associations of inflammatory markers interleukin-6 (IL-6) and C-reactive protein with major depressive disorder are well established, evidence for longitudinal associations mostly comes from studies on depression symptoms, not diagnoses. This study examined cross-sectional and bidirectional longitudinal associations between depression diagnosis and symptoms in an adult sample over a 6-year period.

METHODS

Data were obtained from the baseline (n = 2416) and 2- and 6-year follow-up assessments (n = 1925 and n = 1924, respectively) of the Netherlands Study of Depression and Anxiety. C-reactive protein and IL-6 were assessed at each wave, as were the Composite International Diagnostic Interview and Inventory of Depressive Symptomatology. Linear mixed models and generalized estimating equation models with a binomial distribution were used to study longitudinal associations between depression and inflammation and vice versa.

RESULTS

There was a consistent cross-sectional association between current depressive disorder (vs. no current disorder) and symptoms with IL-6 across all follow-up measurements (Cohen's d_{depression diagnosis} = 0.06, p = .017; B_{standardized Inventory of Depressive Symptomatology} = 0.029, SE = 0.011, p = .008). In longitudinal analyses, higher IL-6 levels predicted subsequent chronic course in those with a diagnosis at baseline in women but not in men (odds ratio_women = 1.13, 95% confidence interval = 1.04-1.23), and both depressive disorder and high severity predicted higher IL-6 levels at the subsequent follow-up (p values < .01). In contrast, C-reactive protein was not associated with current depression in cross-sectional and longitudinal analyses.

CONCLUSIONS

In this longitudinal study, cross-sectional and bidirectional longitudinal associations were found between depression and IL-6 levels. This underlines the importance of targeting inflammation pathways in the treatment of major depressive disorder. IL-6 could be a potential marker for patient profiling in personalized medicine approaches.