Therapeutic Implications of Brain-Immune Interactions: Treatment in Translation

Statins for major depressive disorder: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

The burden of depressive disorder is large and new treatment approaches are required. Repurposing widely available drugs such as statins may be a time- and cost-effective solution. Statins have anti-inflammatory and anti-oxidant properties which have been shown to be relevant to the pathophysiology of depression. This study assesses the efficacy, acceptability, tolerability, and safety of statins in major depressive disorder.

METHODS

Our study is an update and extension of a previous meta-analysis published in 2016 by Salagre et al. We performed a systematic review (PubMed/MEDLINE, Cochrane CENTRAL, ISI Web of Science, CINAHL, and ClinicalTrials.gov until the 1st September 2020) and meta-analysis of randomized controlled trials using any statin against placebo or any other statin in the treatment of major depressive disorder. Our primary efficacy outcome measure was the mean value on any standardized scale for depressive symptoms at 8 weeks of treatment. We also calculated outcomes for efficacy, response, and remission at 2, 4, and 12 weeks, as well as acceptability (dropouts for any cause), tolerability (dropouts due to any adverse event), and safety (any adverse event) outcomes at the studies' endpoints. Furthermore, we conducted an exploratory network meta-analysis for the primary efficacy outcome to identify potential differences between statins.

RESULTS

We retrieved five randomized controlled trials meeting our inclusion criteria: four used a statin in addition to an antidepressant and compared it to placebo plus antidepressant, and one compared two statins alone. and one comparing one statin with another. Statins compared to placebo in addition to antidepressants were efficacious at 8 weeks (N = 255, SMD = -0.48, 95% CI = -0.74 to -0. 22) and 12 weeks (N = 134, SMD = -0.47, 95% CI = -0.89 to -0.05, moderate certainty) with no difference for acceptability, tolerability, and safety (low certainty). An exploratory network meta-analysis suggested that the most lipophilic statins, especially simvastatin, could be more efficacious than less lipophilic or hydrophilic molecules.

CONCLUSIONS

This systematic review suggests the efficacy, acceptability, tolerability, and safety of statins in addition to antidepressants in patients with major depressive disorder. Further clinical trials in different settings are required to test this result.

TRIAL RGISTRATION

PROSPERO registration: CRD42020170938.

Variation rs6971 in the Translocator Protein Gene (TSPO) is Associated with Aggressiveness and Impulsivity but Not with Anxiety in a Population-Representative Sample of Young Adults

Expression of the 18-kDa translocator protein (TSPO), originally identified as a peripheral benzodiazepine receptor, has been found to be altered in several psychiatric disorders. A common single nucleotide polymorphism (rs6971) in the TSPO gene leads to an amino acid substitution, Ala147Thr, which dramatically alters the affinity with which TSPO binds drug ligands. As cholesterol also binds TSPO in the same transmembrane domain, it is suggested that this substitution may impair the ability of TSPO to bind or import cholesterol, and hence may affect steroid synthesis and hypothalamic-pituitary-adrenal function. The analysis was carried out on older birth cohort (n = 655) of the longitudinal Estonian Children Personality, Behavior and Health Study sample. Anxiety, aggressive behavior, impulsiveness, and history of stressful life events were self-reported in various data collection waves. Psychiatric assessment of lifetime prevalence of anxiety disorders was carried out at 25 years of age by experienced clinical psychologists. TSPO rs6971 was genotyped in all participants. TSPO rs6971 was not associated with self-reported levels of anxiety or lifetime prevalence of anxiety disorders. However, participants homozygous for the minor A allele displayed the highest aggressiveness and dysfunctional impulsivity scores. The positive, adaptive aspect of impulsivity was sensitive to stressful life events, as the AA genotype was associated with functional impulsivity only when the participants had experienced a low number of stressful life events during childhood. TSPO rs6971 polymorphism may be related to development of aggressiveness and impulsivity by adulthood, regardless of the participants' gender.

The hedgehog pathway suppresses neuropathogenesis in CD4 T cell-driven inflammation

The concerted actions of the CNS and the immune system are essential to coordinating the outcome of neuroinflammatory responses. Yet, the precise mechanisms involved in this crosstalk and their contribution to the pathophysiology of neuroinflammatory diseases largely elude us. Here, we show that the CNS-endogenous hedgehog pathway, a signal triggered as part of the host response during the inflammatory phase of multiple sclerosis and experimental autoimmune encephalomyelitis, attenuates the pathogenicity of human and mouse effector CD4 T cells by regulating their production of inflammatory cytokines. Using a murine genetic model, in which the hedgehog signalling is compromised in CD4 T cells, we show that the hedgehog pathway acts on CD4 T cells to suppress the pathogenic hallmarks of autoimmune neuroinflammation, including demyelination and axonal damage, and thus mitigates the development of experimental autoimmune encephalomyelitis. Impairment of hedgehog signalling in CD4 T cells exacerbates brain-brainstem-cerebellum inflammation and leads to the development of atypical disease. Moreover, we present evidence that hedgehog signalling regulates the pathogenic profile of CD4 T cells by limiting their production of the inflammatory cytokines granulocyte-macrophage colony-stimulating factor and interferon-γ and by antagonizing their inflammatory program at the transcriptome level. Likewise, hedgehog signalling attenuates the inflammatory phenotype of human CD4 memory T cells. From a therapeutic point of view, our study underlines the potential of harnessing the hedgehog pathway to counteract ongoing excessive CNS inflammation, as systemic administration of a hedgehog agonist after disease onset effectively halts disease progression and significantly reduces neuroinflammation and the underlying neuropathology. We thus unveil a previously unrecognized role for the hedgehog pathway in regulating pathogenic inflammation within the CNS and propose to exploit its ability to modulate this neuroimmune network as a strategy to limit the progression of ongoing neuroinflammation.

Prefrontal dopamine D1 receptor manipulation influences anxiety behavior and induces neuroinflammation within the hippocampus

Background

Prefrontal dopamine D1 receptor (D1R) mediates behavior related to anxiety, reward and memory, and is involved in inflammatory processes, all of which are affected in bipolar disorder. Interleukin-6 (IL-6), a pro-inflammatory cytokine, is increased in patients with bipolar disorder in plasma samples, imaging studies and postmortem tissue and is an indicator for an inflammatory state. We could previously show that lentiviral overexpression of D1R in the medial prefrontal cortex (mPFC) of male adult rats and its termination induces bipolar disorder-like behavior. The purpose of this study was to investigate anxiety and the role of the immune system, specifically IL-6 positive neurons in this animal model. Due to its high density of inflammatory mediator receptors and therewith sensibility to immune activation, the hippocampus was investigated.

Methods

Expression of the gene for D1R in glutamatergic neurons within the mPFC of male, adult rats was manipulated through an inducible lentiviral vector. Animals over-expressing the gene (mania-like state), after termination of the expression (depressive-like) and their respective control groups were investigated. Anxiety behavior was studied in the elevated plus maze and marble burying test. Furthermore, IL-6-positive cells were counted within several subregions of the hippocampus.

Results

D1R manipulation in the mPFC had only mild effects on anxiety behavior in the elevated plus maze. However, subjects after termination buried more marbles compared to D1R over-expressing animals and their respective control animals indicating elevated anxiety behavior. In addition, animals in the depressive-like state showed higher numbers of IL-6 positive cells reflecting an elevated pro-inflammatory state in the hippocampus, in the CA3 and dentate gyrus. Consistently, inflammatory state in the whole hippocampus and anxiety behavior correlated positively, indicating a connection between anxiety and inflammatory state of the hippocampus.

Conclusions

Behavioral and neurobiological findings support the association of manipulation of the D1R in the mPFC on anxiety and inflammation in the hippocampus. In addition, by confirming changes in the inflammatory state, the proposed animal model for bipolar disorder has been further validated.

Linking atypical depression and insulin resistance-related disorders via low-grade chronic inflammation: Integrating the phenotypic, molecular and neuroanatomical dimensions

Insulin resistance (IR) and related disorders, such as T2DM, increase the risk of major depressive disorder (MDD) and vice versa. Current evidence indicates that psychological stress and overeating can induce chronic low-grade inflammation that can interfere with glutamate metabolism in MDD as well as insulin signaling, particularly in the atypical subtype. Here we first review the interactive role of inflammatory processes in the development of MDD, IR and related metabolic disorders. Next, we describe the role of the anterior cingulate cortex in the pathophysiology of MDD and IR-related disorders. Furthermore, we outline how specific clinical features of atypical depression, such as hyperphagia, are more associated with inflammation and IR-related disorders. Finally, we examine the regional specificity of the effects of inflammation on the brain that show an overlap with the functional and morphometric brain patterns activated in MDD and IR-related disorders.

Reconsidering the reasons for heightened inflammation in major depressive disorder

BACKGROUND

Increased circulating pro-inflammatory markers have repeatedly been associated with major depressive disorder (MDD). However, it remains unclear whether inflammation represents a causal mechanism for MDD, or whether the association is influenced by confounding factors such as body mass index (BMI).

METHODS

To better understand this complex relationship, we generated polygenic risk scores (PRS) for MDD and BMI in a population cohort and attempted to isolate the impact these potential risk factors have on adulthood inflammation. Peripheral blood samples were collected as part of the South East London Community Health study, where we generated individualized PRS for MDD and BMI and quantified inflammatory markers using multiplex ELISA-based technology. We performed linear regressions to investigate the effects of PRS for MDD and BMI on inflammatory marker levels.

RESULTS

Out of 35 inflammatory markers, we found a nominal effect of PRS for MDD on interleukin-10. We also found a significant positive effect of BMI on nine inflammatory markers, of which the two most strongly affected markers, interleukin-6 (IL-6) and C-reactive protein (CRP), were also nominally predicted by BMI PRS.

LIMITATIONS

The study utilized a cross-sectional design with a moderately sized sample.

CONCLUSIONS

Our findings suggest there may not be a shared genetic mechanism contributing to MDD and higher inflammatory marker levels. However, there may be shared genetic etiology between BMI and adulthood levels of CRP and IL-6. Therefore, polygenic risk scores for BMI may represent a useful indicator for heightened levels of inflammation in adulthood.

Oxytocin Signaling as a Target to Block Social Defeat-Induced Increases in Drug Abuse Reward

There is huge scientific interest in the neuropeptide oxytocin (OXT) due to its putative capacity to modulate a wide spectrum of physiological and cognitive processes including motivation, learning, emotion, and the stress response. The present review seeks to increase the understanding of the role of OXT in an individual’s vulnerability or resilience with regard to developing a substance use disorder. It places specific attention on the role of social stress as a risk factor of addiction, and explores the hypothesis that OXT constitutes a homeostatic response to stress that buffers against its negative impact. For this purpose, the review summarizes preclinical and clinical literature regarding the effects of OXT in different stages of the addiction cycle. The current literature affirms that a well-functioning oxytocinergic system has protective effects such as the modulation of the initial response to drugs of abuse, the attenuation of the development of dependence, the blunting of drug reinstatement and a general anti-stress effect. However, this system is dysregulated if there is continuous drug use or chronic exposure to stress. In this context, OXT is emerging as a promising pharmacotherapy to restore its natural beneficial effects in the organism and to help rebalance the functions of the addicted brain.

Inflammatory Depression-Mechanisms and Non-Pharmacological Interventions

Treatment of depression is hampered by the failure to identify distinct symptom profiles with distinct pathophysiologies that differentially respond to distinct treatments. We posit that inflammatory depression is a meaningful depression subtype associated with specific symptoms and biological abnormalities. We review several upstream, potentially causative, mechanisms driving low-grade inflammation in this subtype of depression. We also discuss downstream mechanisms mediating the link between inflammation and symptoms of depression, including alterations in dopaminergic neurotransmission and tryptophan metabolism. Finally, we review evidence for several non-pharmacological interventions for inflammatory depression, including probiotics, omega-3 fatty acids, and physical exercise interventions. While some evidence suggests that these interventions may be efficacious in inflammatory depression, future clinical trials should consider enriching patient populations for inflammatory markers, or stratify patients by inflammatory status, to confirm or refute this hypothesis.

Neuronal activity increases translocator protein (TSPO) levels

The mitochondrial protein, translocator protein (TSPO), is a widely used biomarker of neuroinflammation, but its non-selective cellular expression pattern implies roles beyond inflammatory processes. In the present study, we investigated whether neuronal activity modifies TSPO levels in the adult central nervous system. First, we used single-cell RNA sequencing to generate a cellular landscape of basal TSPO gene expression in the hippocampus of adult (12 weeks old) C57BL6/N mice, followed by confocal laser scanning microscopy to verify TSPO protein in neuronal and non-neuronal cell populations. We then quantified TSPO mRNA and protein levels after stimulating neuronal activity with distinct stimuli, including designer receptors exclusively activated by designer drugs (DREADDs), exposure to a novel environment and acute treatment with the psychostimulant drug, amphetamine. Single-cell RNA sequencing demonstrated a non-selective and multi-cellular gene expression pattern of TSPO at basal conditions in the adult mouse hippocampus. Confocal laser scanning microscopy confirmed that TSPO protein is present in neuronal and non-neuronal (astrocytes, microglia, vascular endothelial cells) cells of cortical (medial prefrontal cortex) and subcortical (hippocampus) brain regions. Stimulating neuronal activity through chemogenetic (DREADDs), physiological (novel environment exposure) or psychopharmacological (amphetamine treatment) approaches led to consistent increases in TSPO gene and protein levels in neurons, but not in microglia or astrocytes. Taken together, our findings show that neuronal activity has the potential to modify TSPO levels in the adult central nervous system. These findings challenge the general assumption that altered TSPO expression or binding unequivocally mirrors ongoing neuroinflammation and emphasize the need to consider non-inflammatory interpretations in some physiological or pathological contexts.

Fatigue, depression, and pain in multiple sclerosis: How neuroinflammation translates into dysfunctional reward processing and anhedonic symptoms

Fatigue, depression, and pain affect the majority of multiple sclerosis (MS) patients, which causes a substantial burden to patients and society. The pathophysiology of these symptoms is not entirely clear, and current treatments are only partially effective. Clinically, these symptoms share signs of anhedonia, such as reduced motivation and a lack of positive affect. In the brain, they are associated with overlapping structural and functional alterations in areas involved in reward processing. Moreover, neuroinflammation has been shown to directly impede monoaminergic neurotransmission that plays a key role in reward processing. Here, we review recent neuroimaging and neuroimmunological findings, which indicate that dysfunctional reward processing might represent a shared functional mechanism fostering the symptom cluster of fatigue, depression, and pain in MS. We propose a framework that integrates these findings with a focus on monoaminergic neurotransmission and discuss its therapeutic implications, limitations, and perspectives.

Novel Pharmacological Targets for Combat PTSD-Metabolism, Inflammation, The Gut Microbiome, and Mitochondrial Dysfunction

INTRODUCTION

Current pharmacological treatments of post-traumatic stress disorder (PTSD) have limited efficacy. Although the diagnosis is based on psychopathological criteria, it is frequently accompanied by somatic comorbidities and perhaps "accelerated biological aging," suggesting widespread physical concomitants. Such physiological comorbidities may affect core PTSD symptoms but are rarely the focus of therapeutic trials.

METHODS

To elucidate the potential involvement of metabolism, inflammation, and mitochondrial function in PTSD, we integrate findings and mechanistic models from the DOD-sponsored "Systems Biology of PTSD Study" with previous data on these topics.

RESULTS

Data implicate inter-linked dysregulations in metabolism, inflammation, mitochondrial function, and perhaps the gut microbiome in PTSD. Several inadequately tested targets of pharmacological intervention are proposed, including insulin sensitizers, lipid regulators, anti-inflammatories, and mitochondrial biogenesis modulators.

CONCLUSIONS

Systemic pathologies that are intricately involved in brain functioning and behavior may not only contribute to somatic comorbidities in PTSD, but may represent novel targets for treating core psychiatric symptoms.

Depression Heterogeneity and Its Biological Underpinnings: Toward Immunometabolic Depression

Epidemiological evidence indicates the presence of dysregulated homeostatic biological pathways in depressed patients, such as increased inflammation and disrupted energy-regulating neuroendocrine signaling (e.g., leptin, insulin). Alterations in these biological pathways may explain the considerable comorbidity between depression and cardiometabolic conditions (e.g., obesity, metabolic syndrome, diabetes) and represent a promising target for intervention. This review describes how immunometabolic dysregulations vary as a function of depression heterogeneity by illustrating that such biological dysregulations map more consistently to atypical behavioral symptoms reflecting altered energy intake/expenditure balance (hyperphagia, weight gain, hypersomnia, fatigue, and leaden paralysis) and may moderate the antidepressant effects of standard or novel (e.g., anti-inflammatory) therapeutic approaches. These lines of evidence are integrated in a conceptual model of immunometabolic depression emerging from the clustering of immunometabolic biological dysregulations and specific behavioral symptoms. The review finally elicits questions to be answered by future research and describes how the immunometabolic depression dimension could be used to dissect the heterogeneity of depression and potentially to match subgroups of patients to specific treatments with higher likelihood of clinical success.

Efficacy of adjunctive infliximab vs. placebo in the treatment of anhedonia in bipolar I/II depression

We investigated the efficacy of tumour necrosis factor (TNF)-α antagonist infliximab on a measure of anhedonia amongst individuals with bipolar I/II depression (ClinicalTrials.gov identifier NCT02363738). Adults (ages 18-65) with bipolar I/II disorder currently experiencing a major depressive episode with a higher probability of inflammatory activity (i.e., meeting one or more of the following inflammatory/metabolic criteria: obesity and dyslipidemia/hypertension, daily cigarette smoking, diabetes mellitus, migraine, inflammatory bowel disease, and/or C-reactive protein level of ⩾5 mg/L) were enrolled in a double-blind, 12-week clinical trial of adjunctive infliximab (5 mg/kg) and saline control, which were administered at weeks 0, 2, and 6. The primary outcome measure for the present secondary analysis was change in the Snaith-Hamilton Pleasure Scale (SHAPS) total score between placebo- and infliximab-treated subjects from baseline to weeks 6 and 12. Plasma concentrations of TNF-α and soluble TNF receptors (sTNFR) 1 and 2 were assessed at weeks 0, 2, 6, and 12. Sixty eligible adults received treatment with infliximab (n=29) or placebo (n=31); 47 subjects completed the study (infliximab: n=21, placebo: n=26). Overall, infliximab-randomized subjects exhibited significantly larger increases in SHAPS total score, denoting greater reductions in anhedonic symptoms, when compared to placebo-randomized subjects (treatment × time interaction effect: χ²=7.15,df=2,p=0.03). Anti-anhedonic efficacy was moderated by baseline plasma levels of TNF-α and sTNFR1, but not by changes in TNF-α or sTNFR1 concentrations. Baseline and changes in sTNFR2 concentrations did not moderate anti-anhedonic efficacy. Infliximab significantly improved a measure of anhedonia relative to placebo in adults with bipolar I/II depression at week 6; intervention efficacy was not sustained 6 weeks after the final infusion.

Neuroimmune Mechanisms and Sex/Gender-Dependent Effects in the Pathophysiology of Mental Disorders

Innate and adaptive immune mechanisms have emerged as critical regulators of CNS homeostasis and mental health. A plethora of immunologic factors have been reported to interact with emotion- and behavior-related neuronal circuits, modulating susceptibility and resilience to mental disorders. However, it remains unclear whether immune dysregulation is a cardinal causal factor or an outcome of the pathologies associated with mental disorders. Emerging variations in immune regulatory pathways based on sex differences provide an additional framework for discussion in these psychiatric disorders. In this review, we present the current literature pertaining to the effects that disrupted immune pathways have in mental disorder pathophysiology, including immune dysregulation in CNS and periphery, microglial activation, and disturbances of the blood-brain barrier. In addition, we present the suggested origins of such immune dysregulation and discuss the gender and sex influence of the neuroimmune substrates that contribute to mental disorders. The findings challenge the conventional view of these disorders and open the window to a diverse spectrum of innovative therapeutic targets that focus on the immune-specific pathophenotypes in neuronal circuits and behavior. SIGNIFICANCE STATEMENT: The involvement of gender-dependent inflammatory mechanisms on the development of mental pathologies is gaining momentum. This review addresses these novel factors and presents the accumulating evidence introducing microglia and proinflammatory elements as critical components and potential targets for the treatment of mental disorders.

Antidepressant-Like Effects of Coumaroylspermidine Extract From Safflower Injection Residues

In this study, a total coumaroylspermidine extract (CSE), which included four coumaroylspermidine compounds, was prepared from safflower injection (a traditional Chinese medicine) residues for the first time. The total content of the four coumaroylspermidine compounds was determined to be 64.86 ± 0.41% using high-performance liquid chromatography. We then evaluated the anti-depressant effect of CSE by using a chronic unpredictable mild stress (CUMS) model in rats. Results of sucrose preference tests, open field tests, and forced swimming tests suggest that CSE exhibits a significant anti-depressant effect. In studies to explore the mechanism, CSE was found to inhibit the increases in levels of corticosterone and decreases in levels of 5-hydroxytryptamine, dopamine, and noradrenaline induced by CUMS. Metabolic profiling showed that 10 endogenous metabolites and four metabolic pathways were altered after CSE treatment. Thus, this study not only found a spermidine extract with antidepressant effect from safflower injection residue for the first time but also provided a way for the efficient utilize of safflower injection residue.

Childhood trauma, HPA axis activity and antidepressant response in patients with depression

Childhood trauma is among the most potent contributing risk factors for depression and is associated with poor treatment response. Hypothalamic-pituitary-adrenal (HPA) axis abnormalities have been linked to both childhood trauma and depression, but the underlying mechanisms are poorly understood. The present study aimed to investigate the link between childhood trauma, HPA axis activity and antidepressant response in patients with depression. As part of the Wellcome Trust NIMA consortium, 163 depressed patients and 55 healthy volunteers were included in this study. Adult patients meeting Structured Clinical Interview for Diagnostic and Statistical Manual Version-5 criteria for major depression were categorised into subgroups of treatment responder (n = 42), treatment non-responder (n = 80) and untreated depressed (n = 41) based on current depressive symptom severity measured by the 17-item Hamilton Rating Scale for Depression and exposure to antidepressant medications established by Antidepressant Treatment Response Questionnaire. Childhood Trauma Questionnaire was obtained. Baseline serum C-reactive protein was measured using turbidimetric detection. Salivary cortisol was analyzed at multiple time points during the day using the ELISA technique. Glucocorticoid resistance was defined as the coexistence of hypercortisolemia and inflammation. Our results show that treatment non-responder patients had higher exposure to childhood trauma than responders. No specific HPA axis abnormalities were found in treatment non-responder depressed patients. Untreated depressed showed increased diurnal cortisol levels compared with patients on antidepressant medication, and higher prevalence of glucocorticoid resistance than medicated patients and controls. The severity of childhood trauma was associated with increased diurnal cortisol levels only in individuals with glucocorticoid resistance. Therefore, our findings suggest that the severity of childhood trauma experience contributes to a lack of response to antidepressant treatment. The effects of childhood trauma on increased cortisol levels are specifically evident in patients with glucocorticoid resistance and suggest glucocorticoid resistance as a target for the development of personalized treatment for a subgroup of depressed patients with a history of childhood trauma rather than for all patients with resistance to antidepressant treatment.

Immuno-moodulin: A new anxiogenic factor produced by Annexin-A1 transgenic autoimmune-prone T cells

Patients suffering from autoimmune diseases are more susceptible to mental disorders yet, the existence of specific cellular and molecular mechanisms behind the co-morbidity of these pathologies is far from being fully elucidated. By generating transgenic mice overexpressing Annexin-A1 exclusively in T cells to study its impact in models of autoimmune diseases, we made the unpredicted observation of an increased level of anxiety. Gene microarray of Annexin-A1 CD4⁺ T cells identified a novel anxiogenic factor, a small protein of approximately 21 kDa encoded by the gene 2610019F03Rik which we named Immuno-moodulin. Neutralizing antibodies against Immuno-moodulin reverted the behavioral phenotype of Annexin-A1 transgenic mice and lowered the basal levels of anxiety in wild type mice; moreover, we also found that patients suffering from obsessive compulsive disorders show high levels of Imood in their peripheral mononuclear cells. We thus identify this protein as a novel peripheral determinant that modulates anxiety behavior. Therapies targeting Immuno-moodulin may lead to a new type of treatment for mental disorders through regulation of the functions of the immune system, rather than directly acting on the nervous system.

Inflammation as a treatment target in mood disorders: review

BACKGROUND

Mood disorders, i.e. major depressive disorder (MDD) and bipolar disorders, are leading sources of disability worldwide. Currently available treatments do not yield remission in approximately a third of patients with a mood disorder. This is in part because these treatments do not target a specific core pathology underlying these heterogeneous disorders. In recent years, abnormal inflammatory processes have been identified as putative pathophysiological mechanisms and treatment targets in mood disorders, particularly among individuals with treatment-resistant conditions.

AIMS

In this selective review, we aimed to summarise recent advances in the field of immunopsychiatry, including emerging pathophysiological models and findings from treatment ttrials of immunomodulatory agents for both MDD and bipolar disorders.

METHOD

We performed a literature review by searching Medline for clinical trials of immunomodulating agents as monotherapy or adjunctive treatments in MDD and bipolar disorders. Included studies are randomised controlled trials (RCTs), cluster RCTs or cross-over trials of immunomodulating agents that had an active comparator or a placebo-arm.

RESULTS

Current evidence shows an association between inflammation and mood symptoms. However, there is conflicting evidence on whether this link is causal.

CONCLUSIONS

Future studies should focus on identifying specific neurobiological underpinnings for the putative causal association between an activated inflammatory response and mood disorders. Results of these studies are needed before further treatment trials of immunomodulatory agents can be justified.

What does plasma CRP tell us about peripheral and central inflammation in depression?

Peripheral blood C-reactive protein (CRP) is a biomarker used clinically to measure systemic inflammation and is reproducibly increased in a subset of patients with major depressive disorder (MDD). Furthermore, increased peripheral blood CRP in MDD has been associated with altered reward circuitry and increased brain glutamate in relation with symptoms of anhedonia. Nevertheless, the relationship between peripheral CRP and other peripheral and central markers of inflammation in depressed patients has not been established. Plasma (n = 89) and CSF (n = 73) was collected from medically stable, currently unmedicated adult outpatients with MDD. Associations among plasma and CSF CRP and plasma and CSF inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor [TNF] and IL-1beta) and their soluble receptors/antagonists were examined. Relationships between plasma and CSF inflammatory markers and depressive symptoms including anhedonia and reduced motivation (RM) were also explored. Plasma CRP was correlated with multiple plasma inflammatory markers (all p < 0.05), and a strong correlation was found between plasma and CSF CRP (r = 0.855, p < 0.001). CSF CRP in turn correlated with CSF cytokine receptors/antagonists (all p < 0.05). Principal component analyses revealed clusters of CSF inflammatory markers that were associated with high plasma CRP (>3 mg/L) and correlated with depressive symptom severity. These findings were driven by CSF TNF, which correlated with RM (r = 0.236, p = 0.045), and CSF IL-6 soluble receptor, which correlated with anhedonia (r = 0.301, p = 0.010) in the sample as a whole and particularly females. CRP appears to be a peripheral biomarker that reflects peripheral and central inflammation and seems well-suited for guiding immunotherapies targeting TNF and IL-6 in patients with MDD.

Neutrophil-lymphocyte ratio, monocyte-lymphocyte ratio and platelet-lymphocyte ratio in non-affective psychosis: A meta-analysis and systematic review

Objectives: Neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR) and monocyte/lymphocyte ratio (MLR) are inexpensive and reproducible biomarkers of inflammation. This is the first meta-analysis exploring the role of NLR, MLR and PLR in non-affective psychosis.Methods: Eight studies have been identified from the main electronic databases. Meta-analyses based on random-effects models have been carried out generating pooled standardised mean differences (SMDs) between non-affective psychotic patients and healthy controls (HCs).Results: Subjects with non-affective psychosis had a significant higher NLR and MLR as compared with HC (respectively SMD = 0.715; P < 0.001; I²=57.565% and SMD = 0.417; P = 0.001; I²=65.754%), confirmed by heterogeneity-based sensitivity analysis. Subgroup analyses showed no differences in effect size across different study characteristics, including drug treatment status, diagnosis, and setting. Meta-regression showed that age influenced the relationship between non-affective psychosis and MLR. A trend of significance, not confirmed by heterogeneity-based sensitivity analysis, was observed in PLR with patients showing higher PLR than HC.Conclusions: Our meta-analysis supports the hypothesis that an inflammatory activation occurs in non-affective psychosis and inflammatory ratios, especially NLR and MLR, may be useful to detect this activation.

Modulation of the antidepressant effects of ketamine by the mTORC1 inhibitor rapamycin

Twenty-four hours after administration, ketamine exerts rapid and robust antidepressant effects that are thought to be mediated by activation of the mechanistic target of rapamycin complex 1 (mTORC1). To test this hypothesis, depressed patients were pretreated with rapamycin, an mTORC1 inhibitor, prior to receiving ketamine. Twenty patients suffering a major depressive episode were randomized to pretreatment with oral rapamycin (6 mg) or placebo 2 h prior to the intravenous administration of ketamine 0.5 mg/kg in a double-blind cross-over design with treatment days separated by at least 2 weeks. Depression severity was assessed using Montgomery-Åsberg Depression Rating Scale (MADRS). Rapamycin pretreatment did not alter the antidepressant effects of ketamine at the 24-h timepoint. Over the subsequent 2-weeks, we found a significant treatment by time interaction (F(8,245) = 2.02, p = 0.04), suggesting a prolongation of the antidepressant effects of ketamine by rapamycin. Two weeks following ketamine administration, we found higher response (41%) and remission rates (29%) following rapamycin + ketamine compared to placebo + ketamine (13%, p = 0.04, and 7%, p = 0.003, respectively). In summary, single dose rapamycin pretreatment failed to block the antidepressant effects of ketamine, but it prolonged ketamine's antidepressant effects. This observation raises questions about the role of systemic vs. local blockade of mTORC1 in the antidepressant effects of ketamine, provides preliminary evidence that rapamycin may extend the benefits of ketamine, and thereby potentially sheds light on mechanisms that contribute to depression relapse after ketamine administration.

Effects of exogenous ghrelin administration and ghrelin receptor blockade, in combination with alcohol, on peripheral inflammatory markers in heavy-drinking individuals: Results from two human laboratory studies

The ghrelin system has been garnering interest for its role in different neuropsychiatric disorders, including alcohol use disorder (AUD). Accordingly, targeting the ghrelin system is under investigation as a potential novel therapeutic approach. While alcohol provokes the immune system and inflammatory responses, ghrelin has potent immunomodulatory and anti-inflammatory properties. The present study aimed to shed light on the "crosstalk" between ghrelin and inflammation by examining the effects of exogenous ghrelin administration and ghrelin receptor blockade on peripheral inflammatory markers in the context of two human laboratory studies with alcohol administration. Non-treatment-seeking, heavy-drinking individuals with alcohol dependence, the majority of whom were African American males, were enrolled. In the first randomized, crossover, double-blind, placebo-controlled human laboratory study, participants underwent two experimental paradigms - an intravenous alcohol self-administration (IV-ASA) and an intravenous alcohol clamp (IV-AC) - each consisting of two counterbalanced sessions (ghrelin, placebo). A loading dose of intravenous ghrelin (3 mcg/kg) or placebo, followed by a continuous ghrelin (16.9 ng/kg/min) or placebo infusion was administered. In the second dose-escalating, single-blind, placebo-controlled human laboratory phase 1b study, participants were dosed with an oral ghrelin receptor blocker (PF-5190457) and underwent an oral alcohol challenge. Repeated blood samples were collected, and plasma concentrations of the following inflammatory markers were measured: C-reactive protein (CRP), interleukin (IL)-6, IL-10, IL-18, and tumor necrosis factor alpha (TNF-α). During the IV-ASA experiment, significant drug × time interaction effects were observed for IL-6 (F_3,36 = 3.345, p = 0.030) and IL-10 (F_3,53.2 = 4.638, p = 0.006), indicating that ghrelin, compared to placebo, significantly reduced blood concentrations of the proinflammatory cytokine IL-6, while increasing blood concentrations of the anti-inflammatory cytokine IL-10. No significant drug × time interaction effects were observed during the IV-AC experiment, possibly because of its much shorter duration and/or smaller sample. Treatment with PF-5190457, compared to placebo, had no significant effect on the inflammatory markers investigated. In conclusion, a supraphysiologic pharmacological challenge with exogenous ghrelin in heavy-drinking individuals produced anti-inflammatory effects in the context of intravenous alcohol administration. On the contrary, ghrelin receptor blockade did not lead to any change in the inflammatory markers included in this study. Mechanistic studies are required to better understand the interaction between ghrelin, alcohol, and inflammatory processes.

Brain eicosapentaenoic acid metabolism as a lead for novel therapeutics in major depression

The results of several meta-analyses suggest that eicosapentaenoic acid (EPA) supplementation is therapeutic in managing the symptoms of major depression. It was previously assumed that because EPA is extremely low in the brain it did not cross the blood-brain barrier and any therapeutic effects it exerted would be via the periphery. However, more recent studies have established that EPA does enter the brain, but is rapidly metabolised following entry. While EPA does not accumulate within the brain, it is present in microglia and homeostatic mechanisms may regulate its esterification to phospholipids that serve important roles in cell signaling. Furthermore, a variety of signaling molecules from EPA have been described in the periphery and they have the potential to exert effects within the brain. If EPA is confirmed to be therapeutic in major depression as a result of adequately powered randomized clinical trials, future research on brain EPA metabolism could lead to the discovery of novel targets for treating or preventing major depression.

Neural networks and the anti-inflammatory effect of transcutaneous auricular vagus nerve stimulation in depression

Transcutaneous auricular vagus nerve stimulation (taVNS) is a relatively non-invasive alternative treatment for patients suffering from major depressive disorder (MDD). It has been postulated that acupuncture may achieve its treatment effects on MDD through suppression of vagal nerve inflammatory responses. Our previous research established that taVNS significantly increases amygdala–dorsolateral prefrontal cortex connectivity, which is associated with a reduction in depression severity. However, the relationship between taVNS and the central/peripheral functional state of the immune system, as well as changes in brain neural circuits, have not as yet been elucidated. In the present paper, we outline the anatomic foundation of taVNS and emphasize that it significantly modulates the activity and connectivity of a wide range of neural networks, including the default mode network, executive network, and networks involved in emotional and reward circuits. In addition, we present the inflammatory mechanism of MDD and describe how taVNS inhibits central and peripheral inflammation, which is possibly related to the effectiveness of taVNS in reducing depression severity. Our review suggests a link between the suppression of inflammation and changes in brain regions/circuits post taVNS.

Scopoletin ameliorates anxiety-like behaviors in complete Freund's adjuvant-induced mouse model

Anxiety disorder is highly prevalent worldwide and represents a chronic and functionally disabling condition, with high levels of psychological stress characterized by cognitive and physiological symptoms. Scopoletin (SP), a main active compound in Angelica dahurica, is traditionally used for the treatment of headache, rhinitis, pain, and other conditions. Here, we evaluated the effects of SP in a mouse model of complete Freund’s adjuvant (CFA)-induced chronic inflammation anxiety. SP (2.0, 10.0, 50.0 mg/kg) administration for 2 weeks dose-dependently ameliorated CFA-induced anxiety-like behaviors in the open field test and elevated plus maze test. Moreover, we found that SP treatment inhibited microglia activation and decreased both peripheral and central IL-1β, IL-6, and TNF-α levels in a dose-dependent manner. Additionally, the imbalance in excitatory/inhibitory receptors and neurotransmitters in the basolateral nucleus after CFA injection was also modulated by SP administration. Our findings indicate that the inhibition of the nuclear factor-kappa B and mitogen-activated protein kinase signaling pathways involving anti-inflammatory activities and regulation of the excitatory/inhibitory balance can be attributed to the anxiolytic effects of SP. Moreover, our molecular docking analyses show that SP also has good affinity for gamma-aminobutyric acid (GABA) transaminase and GABA_A receptors. Therefore, these results suggest that SP could be a candidate compound for anxiolytic therapy and for use as a structural base for developing new drugs.

Inflammation and Negative Symptoms of Schizophrenia: Implications for Reward Processing and Motivational Deficits

Negative symptoms of schizophrenia are debilitating and chronic in nature, are difficult to treat, and contribute to poor functional outcomes. Motivational deficits are a core negative symptom and may involve alterations in reward processing, which involve subcortical regions such as the basal ganglia. More specifically, dopamine-rich regions like the ventral striatum, have been implicated in these reward-processing deficits. Inflammation is one mechanism that may underlie negative symptoms, and specifically motivational deficits, via the effects of inflammatory cytokines on the basal ganglia. Previous work has demonstrated that inflammatory stimuli decrease neural activity in the ventral striatum and decrease connectivity in reward-relevant neural circuitry. The immune system has been shown to be involved in the pathophysiology of schizophrenia, and inflammatory cytokines have been shown to be altered in patients with the disorder. This paper reviews the literature on associations between inflammatory markers and negative symptoms of schizophrenia as well as the role of anti-inflammatory drugs to target negative symptoms. We also review the literature on the role of inflammation and reward processing deficits in both healthy controls and individuals with depression. We use the literature on inflammation and depression as a basis for a model that explores potential mechanisms responsible for inflammation modulating certain aspects of negative symptoms in patients with schizophrenia. This approach may offer novel targets to treat these symptoms of the disorder that are significant barriers to functional recovery and do not respond well to available antipsychotic medications.

Higher S100B Levels Predict Persistently Elevated Anhedonia with Escitalopram Monotherapy Versus Antidepressant Combinations: Findings from CO-MED Trial

BACKGROUND

Elevated S100 calcium binding protein B (S100B) levels in systemic circulation may induce neuroinflammation and reflect greater blood-brain barrier (BBB) dysfunction. Neuroinflammation in patients with major depressive disorder (MDD), in turn, may reduce likelihood of improvement with serotonergic antidepressants.

METHODS

Levels of S100B were measured in plasma samples obtained prior to initiation of treatment with bupropion-plus-escitalopram, escitalopram-plus-placebo, or venlafaxine-plus-mirtazapine in participants of Combining Medications to Enhance Depression Outcomes trial (n = 153). Depression severity was measured with 16-item Quick Inventory of Depressive Symptomatology Self-Report and anhedonia was measured with 3 items of 30-item Inventory of Depressive Symptomatology. Differential changes in depression severity and anhedonia over acute-phase (baseline, weeks 1, 2, 4, 6, 8, 10, and 12) in the three treatment arms were tested with logS100B-by-treatment-arm interaction in mixed model analyses after controlling for age, gender, and body mass index.

RESULTS

There was a significant logS100B-by-treatment-arm interaction for anhedonia (F = 3.21; df = 2, 142; p = 0.04) but not for overall depression severity (F = 1.99; df = 2, 142; p = 0.14). Higher logS100B levels were associated with smaller reductions in anhedonia (effect size = 0.67, p = 0.047) in escitalopram monotherapy but not in the other two arms. Correlation coefficients of anhedonia severity averaged over acute-phase (including baseline) with baseline S100B levels were 0.57, -0.19, and 0.22 for escitalopram monotherapy, bupropion-plus-escitalopram and venlafaxine-plus-mirtazapine arms respectively.

CONCLUSION

Higher baseline S100B levels in depressed patients resulted in poorer response to escitalopram monotherapy. Addition of bupropion, a dopaminergic antidepressant, partially mitigated this effect.

Inflammation associated with coronary heart disease predicts onset of depression in a three-year prospective follow-up: A preliminary study

Depression frequently co-occurs with coronary heart disease (CHD), worsening clinical outcomes of both, and inflammation has been proposed as a biological link between these two disorders. The aim of the present study was to investigate the role of inflammation in the development of depression in CHD patients during a 3-year follow-up. We examined the inflammatory biomarker, high-sensitivity C-reactive protein (hsCRP), measured at baseline, as a potential predictor of later onset of depression. We recruited 89 CHD patients, who were assessed at baseline and then every 6 months, for three years. The sample included, at baseline, 25 depressed and 64 non-depressed CHD patients, as confirmed by Clinical Interview Schedule Revised (CIS-R). Depressive symptoms were assessed at baseline and all follow-up points by the Patient Health Questionnaire-9 (PHQ-9). In all CHD patients (n = 89), we found a significant positive correlation between hsCRP levels and the severity of depressive symptoms at baseline (PHQ-9, r = 0.23, p = 0.032). During follow-up, n = 21 patients (of the 64 non-depressed at baseline) developed depression, defined as being PHQ-9 positive (a score ≥ 10) in at least one follow-up assessment. Of these, n = 9 subjects were defined as developing clinically-significant depression, that is, having a positive PHQ-9 in at least 3 of the 6 follow-up assessments, implying a duration of symptoms of at least one year. We found that increased hsCRP values at baseline predicted future onset of depression. Specifically, baseline hsCRP values were higher in patients who later developed clinically-significant depression (mean ± SD; 6.76 ± 6.52 mg/L) compared with never-depressed (2.77 ± 3.13 mg/L; F(1,48) = 7.29, p = 0.010), even after controlling for baseline PHQ-9 scores. In conclusion, inflammation in CHD patients is associated with future development of clinically-significant depression. HsCRP, a reliable and ready-to-use biological marker of inflammation, may help to identify depression high-risk phenotypes even among CHD patients, who already have high baseline inflammation. Our study conveys important preliminary findings that will require further replication but that have the potential to affect the mental and physical health of a vulnerable group of individuals.

Inflammation and decreased functional connectivity in a widely-distributed network in depression: Centralized effects in the ventral medial prefrontal cortex

Major depressive disorder is a heterogeneous disease involving widespread disruptions in functional brain networks, the neurobiological mechanisms of which are poorly understood. Amassing evidence supports innate immune activation as one pathophysiologic mechanism contributing to depression in a subgroup of patients with elevated inflammatory markers. Although inflammation is known to alter monoamine and glutamate neurotransmitters, little work has been done to understand its role in network dysfunction in patients with depression. Here we conducted a large-scale network-based analyses of resting-state functional magnetic resonance imaging (rfMRI) data acquired from depressed patients with varying levels of inflammation to develop a comprehensive characterization of network alterations as an effect of inflammation. Complementary approaches of global brain connectivity and parcellation-based network analysis applied to the whole brain revealed that increased plasma C-reactive protein (CRP) was associated with reduced functional connectivity in a widely-distributed network including ventral striatum, parahippocampal gyrus/amygdala, orbitofrontal and insular cortices, and posterior cingulate cortex. These broad alterations were centralized in the ventral medial prefrontal cortex (vmPFC), representing a hub for the effects of inflammation on network function in the whole brain. When feeding the identified multivariate network features into a machine learning algorithm of support vector regression, we achieved high prediction accuracies for depressive symptoms that have been associated with inflammation in previous studies including anhedonia and motor slowing. These findings extend and broaden previous observations from hypothesis-driven studies, providing further support for inflammation as a distinct contributing factor to network dysfunction and symptom severity in depression.

Depression- and anxiogenic-like behaviors induced by lipopolysaccharide in mice are reversed by a selenium-containing indolyl compound: Behavioral, neurochemical and computational insights involving the serotonergic system

Major depression and anxiety are highly incapacitating psychiatric disorders often present simultaneously, and the causal relationship between these disorders and inflammation are under extensive investigation. The treatment for this comorbidity still relies on drugs acting on the serotonergic neurotransmission, but the modulation of immune-inflammatory pathways has attained an increasing interest in the drug discovery. We have previously demonstrated that the selenoorganic compound 3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole (CMI) possess antioxidant, anti-inflammatory, antinociceptive and antidepressant-like effect in mice. Considering these pharmacological properties and the structural similarities between tryptophan, serotonin and CMI, the aim of the present study was to investigate whether CMI ameliorates depression- and anxiogenic-like behavior induced by lipopolysaccharide (LPS) in Swiss male mice by modulating the serotonergic system and reducing neuroinflammation. The administration of CMI (1 mg/kg, i.g) reversed the behavioral deficits induced by LPS (0.83 mg/kg, i.p) in the tail suspension test, splash test and elevated plus maze. The pre-treatment of mice with WAY100635 (5-HT_1A receptor antagonist), ketanserin (5-HT_2A/2C receptor antagonist) and ondansetron (5-HT₃ receptor antagonist) prevented the antidepressant- and anxiolytic-like effect elicited by CMI treatment after the LPS challenge. The administration of CMI also counteracted the increased expression of pro-inflammatory cytokines and indoleamine 2,3-dioxygenase (IDO) in the prefrontal cortex and hippocampus of mice challenged with LPS. Additionally, a molecular docking analysis showed that CMI binds to the active site of the serotonin transporter and IDO. These findings suggest that CMI reversed behavioral and biochemical alterations in the depression-anxiety comorbidity induced by LPS, possibly by modulation of neuroinflammatory mediators and the serotonergic system.

Role of Soluble Epoxide Hydrolase in Metabolism of PUFAs in Psychiatric and Neurological Disorders

Inflammation plays a key role in the pathogenesis of a number of psychiatric and neurological disorders. Soluble epoxide hydrolases (sEH), enzymes present in all living organisms, metabolize epoxy fatty acids (EpFAs) to corresponding 1,2-diols by the addition of a molecule of water. Accumulating evidence suggests that sEH in the metabolism of polyunsaturated fatty acids (PUFAs) plays a key role in inflammation. Preclinical studies demonstrated that protein expression of sEH in the prefrontal cortex, striatum, and hippocampus from mice with depression-like phenotype was higher than control mice. Furthermore, protein expression of sEH in the parietal cortex from patients with major depressive disorder was higher than controls. Interestingly, Ephx2 knock-out (KO) mice exhibit stress resilience after chronic social defeat stress. Furthermore, the sEH inhibitors have antidepressant effects in animal models of depression. In addition, pharmacological inhibition or gene KO of sEH protected against dopaminergic neurotoxicity in the striatum after repeated administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in an animal model of Parkinson’s disease (PD). Protein expression of sEH in the striatum from MPTP-treated mice was higher than control mice. A number of studies using postmortem brain samples showed that the deposition of protein aggregates of α-synuclein, termed Lewy bodies, is evident in multiple brain regions of patients from PD and dementia with Lewy bodies (DLB). Moreover, the expression of the sEH protein in the striatum from patients with DLB was significantly higher compared with controls. Interestingly, there was a positive correlation between sEH expression and the ratio of phosphorylated α-synuclein to α-synuclein in the striatum. In the review, the author discusses the role of sEH in the metabolism of PUFAs in inflammation-related psychiatric and neurological disorders.

[Translational behavioral research using common marmosets in the psychiatric field]

The drug discovery activities for novel compounds with the superior efficacies to current drugs have been largely unsuccessful in the psychiatric field. One of the main reasons is the lack of appropriate behavioral assays and animal models for psychiatric disorders. Since the prefrontal cortex has great roles in their pathophysiology, non-human primate common marmosets with the well-developed prefrontal cortex would be useful as experimental animals in the future translational research. To measure objectively and quantitatively the psychiatric symptoms like motivational deficits, negative affective bias and cognitive impairments in patients with schizophrenia or major depressive disorder, the clinical laboratory tasks have been developed. The development of marmoset behavioral paradigms, which may correspond to the clinical laboratory tasks, have been progressed for the translational research. On the other hand, there are still limitations to develop the marmoset models resembling the pathophysiology of psychiatric disorders. We review the current state and future perspective of translational behavioral research using marmosets.

Role of Inflammation in Depression and Treatment Implications

Approximately one third of depressed patients fail to respond to currently available antidepressant therapies. Therefore, new conceptual frameworks are needed to identify pathophysiologic pathways and neurobiological targets for the development of novel treatment strategies. In this regard, recent evidence suggests that inflammation may contribute to symptoms relevant to a number of psychiatric disorders and particularly depression. Numerous studies (including meta-analyses) have found elevated peripheral and central inflammatory cytokines and acute phase proteins in depression. Chronic exposure to increased inflammation is thought to drive changes in neurotransmitters and neurocircuits that lead to depressive symptoms and that may also interfere with or circumvent the efficacy of antidepressants. Indeed, patients with high inflammation have been shown to exhibit poor response to conventional antidepressant therapies. Recent developments in our ability to understand and measure the effects of inflammation on the brain in patients have opened new doors for the testing of novel treatment strategies that target the immune system or its consequences on neurotransmitter systems. Such recent developments in the field of behavioral immunology and their translational implications for the treatment of depression are discussed herein.

Glucose and lipid-related biomarkers and the antidepressant response to infliximab in patients with treatment-resistant depression

The tumor necrosis factor (TNF) antagonist infliximab was previously found to reduce depressive symptoms in patients with treatment-resistant major depression (TRD) who exhibited high baseline inflammation, as reflected by plasma C-reactive protein (CRP) >5 mg/L. Further predictors of antidepressant response to infliximab included differential expression of peripheral blood gene transcripts that were related not only to inflammation but also to glucose and lipid metabolism. To determine whether plasma biomarkers of glucose and lipid metabolism were similarly associated with antidepressant response to infliximab and with relevant gene transcripts, we measured concentrations of glucose, insulin, and protein hormones that regulate glucose homeostasis and metabolism (leptin, resistin, and adiponectin), as well as cholesterols, triglycerides, and non-esterified fatty acids (NEFA), in medically-stable TRD outpatients at baseline and 2 weeks after the first infusion of infliximab (n = 26) or placebo (n = 26). Treatment response was defined as 50% reduction in depressive symptoms at any point during the 12-week trial. We found that baseline cholesterol (total, low-density lipoprotein [LDL], and non-high-density lipoprotein [non-HDL]), triglycerides and NEFA were elevated in patients who exhibited an antidepressant response to infliximab (all p < 0.05) but not placebo (all p > 0.299). HDL and non-HDL cholesterol concentrations also correlated with two lipid-related gene transcripts that were predictive of antidepressant response (r = 0.33 to 0.39, p < 0.05). Although not associated with response to infliximab, resistin correlated with numerous glucose-related transcripts (r = -0.32 to 0.37, p < 0.05) and was higher at 2 weeks post-infusion in patients treated with infliximab compared to placebo (p = 0.028). Concentrations of cholesterol (total, LDL, HDL, non-HDL) were also lower at 2 weeks in patients treated with infliximab compared to placebo, but only in those patients with CRP >5 mg/L at baseline (all p < 0.05). These results are consistent with previous work showing that high inflammation in patients with depression is associated with metabolic alterations, which together predict response to both traditional and experimental antidepressant therapies. Additionally, our findings suggest a causal relationship between increased inflammation and high cholesterol in depression, as a single infusion of infliximab reduced cholesterol in TRD patients with high CRP compared to placebo.

Emerging role of the P2X7-NLRP3-IL1β pathway in mood disorders

The science of neuroimmunopsychiatry has evolved rapidly in the last few years with the hope of tackling the unmet need in mood disorders. This article focuses on an inflammatory pathway, highly conserved in myeloid cells that may play a role in neuroinflammatory disorders including depression. Within the brain tissue, microglia are the myeloid cells that express the P2X7 ion channel that is connected through the NLRP3 inflammasome complex leading to release of IL-1β and IL-18. We present, in the way of reviewing relevant literature, the preclinical data and scientific rationale supporting the role of the P2X7-NLRP3-IL-1β pathway in mood disorders. We also highlight recent advances in drug discovery and development of P2X7 small molecule antagonists and P2X7 PET ligands which provide optimism that clinical tools are availableto address critical proof-of-concept experiments in mood disorders.

Essential Role of Keap1-Nrf2 Signaling in Mood Disorders: Overview and Future Perspective

Depression is one of the most common mood disorders with a high rate of relapse. Accumulating evidence suggests that the transcription factor Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1)-Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) system plays a key role in inflammation which is involved in depression. Preclinical studies demonstrated that the protein expressions of Keap1 and Nrf2 in the prefrontal cortex (PFC), CA3 and dentate gyrus (DG) of hippocampus in mice with depression-like phenotype were lower than control mice. In the learned helplessness paradigm, the protein levels of Keap1 and Nrf2 in the PFC and DG of hippocampus from rats with depression-like phenotype were also lower than control and resilient rats. Furthermore, rodents with depression-like phenotype have higher levels of pro-inflammatory cytokines. Interestingly, Nrf2 knock-out (KO) mice exhibit depression-like phenotype, and higher serum levels of pro-inflammatory cytokines compared with wild-type mice. Furthermore, Nrf2 KO mice have lower expression of brain-derived neurotrophic factor (BDNF) in the PFC, and CA3 and DG of hippocampus compared to wild-type mice. 7,8-Dihydroxyflavone, a TrkB agonist, showed antidepressant effects in Nrf2 KO mice, by stimulating BDNF-TrkB in the PFC, CA3, and DG. Pretreatment with sulforaphane, a naturally occurring Nrf2 activator, prevented depression-like phenotype in mice after inflammation, or chronic social defeat stress. Interestingly, dietary intake of 0.1% glucoraphanin (a precursor of sulforaphane) containing food during juvenile and adolescent stages of mice could prevent depression-like phenotype in adulthood after chronic social defeat stress. Moreover, the protein expressions of Keap1 and Nrf2 in the parietal cortex from major depressive disorder and bipolar disorder were lower than controls. These findings suggest that Keap1-Nrf2 system plays a key role in the stress resilience which is involved in the pathophysiology of mood disorders. It is, therefore, possible that dietary intake of cruciferous vegetables including glucoraphanin (or SFN) may prevent or minimize relapse from remission, induced by stress and/or inflammation in depressed patients. In the review, the author would like to discuss the role of Keap1-Nrf2 system in mood disorders.

Granulocyte Colony Stimulating Factor Enhances Reward Learning through Potentiation of Mesolimbic Dopamine System Function

Deficits in motivation and cognition are hallmark symptoms of multiple psychiatric diseases. These symptoms are disruptive to quality of life and often do not improve with available medications. In recent years there has been increased interest in the role of the immune system in neuropsychiatric illness, but to date no immune-related treatment strategies have come to fruition. The cytokine granulocyte-colony stimulating factor (G-CSF) is known to have trophic and neuroprotective properties in the brain, and we recently identified it as a modulator of neuronal and behavioral plasticity. By combining operant tasks that assess discrete aspects of motivated behavior and decision-making in male mice and rats with subsecond dopamine monitoring via fast-scan cyclic voltammetry, we defined the role of G-CSF in these processes as well as the neural mechanism by which it modulates dopamine function to exert these effects. G-CSF enhanced motivation for sucrose as well as cognitive flexibility as measured by reversal learning. These behavioral outcomes were driven by mesolimbic dopamine system plasticity, as systemically administered G-CSF increased evoked dopamine release in the nucleus accumbens independent of clearance mechanisms. Importantly, sustained increases in G-CSF were required for these effects as acute exposure did not enhance behavioral outcomes and decreased dopamine release. These effects seem to be a result of the ability of G-CSF to alter local inflammatory signaling cascades, particularly tumor necrosis factor α. Together, these data show G-CSF as a potent modulator of the mesolimbic dopamine circuit and its ability to appropriately attend to salient stimuli.SIGNIFICANCE STATEMENT Emerging evidence has highlighted the importance of the immune system in psychiatric diseases states. However, the effects of peripheral cytokines on motivation and cognitive function are largely unknown. Here, we report that granulocyte-colony stimulating factor (G-CSF), a pleiotropic cytokine with known trophic and neuroprotective properties in the brain, acts directly on dopaminergic circuits to enhance their function. These changes in dopaminergic dynamics enhance reward learning and motivation for natural stimuli. Together, these results suggest that targeting immune factors may provide a new avenue for therapeutic intervention in the multiple psychiatric disorders that are characterized by motivational and cognitive deficits.

Imaging the Role of Inflammation in Mood and Anxiety-related Disorders

Background

Studies investigating the impact of a variety of inflammatory stimuli on the brain and behavior have reported evidence that inflammation and release of inflammatory cytokines affect circuitry relevant to both reward and threat sensitivity to contribute to behavioral change. Of relevance to mood and anxiety-related disorders, biomarkers of inflammation such as inflammatory cytokines and acute-phase proteins are reliably elevated in a significant proportion of patients with major depressive disorder (MDD), bipolar disorder, anxiety disorders and post-traumatic stress disorder (PTSD).

Methods

This review summarized clinical and translational work demonstrating the impact of peripheral inflammation on brain regions and neurotransmitter systems relevant to both reward and threat sensitivity, with a focus on neuroimaging studies involving administration of inflammatory stimuli. Recent translation of these findings to further understand the role of inflammation in mood and anxiety-related disorders is also discussed.

Results

Inflammation was consistently found to affect basal ganglia and cortical reward and motor circuits to drive reduced motivation and motor activity, as well as anxiety-related brain regions including amygdala, insula and anterior cingulate cortex, which may result from cytokine effects on monoamines and glutamate. Similar relationships between inflammation and altered neurocircuitry have been observed in MDD patients with increased peripheral inflammatory markers, and such work is on the horizon for anxiety disorders and PTSD.

Conclusion

Neuroimaging effects of inflammation on reward and threat circuitry may be used as biomarkers of inflammation for future development of novel therapeutic strategies to better treat mood and anxiety-related disorders in patients with high inflammation.

Increased inflammation and brain glutamate define a subtype of depression with decreased regional homogeneity, impaired network integrity, and anhedonia

Combined increases in peripheral inflammation and brain glutamate may identify a subtype of depression with distinct neuroimaging signatures. Two contrasting subgroups of depressed subjects-with and without combined elevations in plasma C-reactive protein (CRP) and basal ganglia glutamate (high and low CRP-Glu, respectively) were identified by hierarchical clustering using plasma CRP (indexing peripheral inflammation) and magnetic resonance spectroscopy (MRS)-based measurement of left basal ganglia glutamate. High CRP-Glu group status was associated with greater severity of anhedonia and cognitive and motor slowing. Local- and network-level measures of functional integrity were determined using brain oxygen level-dependent (BOLD)-oscillatory activity and graph theory. Greater decreases in concordance of oscillatory activity between neighboring voxels (Regional Homogeneity 'ReHo', p < 0.01) within the MRS volume-of-interest was associated with the High CRP-Glu subgroup. Using brain-wide, CRP-Glu ReHo contrast maps, a covariance network of 41 regions-of-interest (ROIs) with similar ReHo decreases was identified in the High CRP-Glu group and was located to brain structures previously implicated in depression. The 41-ROI network was further decomposed into four subnetworks. ReHo decreases within Subnetwork4-comprised of reward processing regions -was associated with anhedonia. Subnetwork4 ReHo also predicted decreased network integrity, which mediated the link between local ReHo and anhedonia in the Low but not High CRP-Glu group. These findings suggest that decreased ReHo and related disruptions in network integrity may reflect toxic effects of inflammation-induced increases in extrasynaptic glutamate signaling. Moreover, local BOLD oscillatory activity as reflected in ReHo might be a useful measure of target-engagement in the brain for treatment of inflammation-induced behaviors.

Antidepressant treatment resistance is associated with increased inflammatory markers in patients with major depressive disorder

BACKGROUND

One third of patients with major depressive disorder (MDD) fail to respond to currently available antidepressant medications. Inflammation may contribute to treatment non-response through effects on neurotransmitter systems relevant to antidepressant efficacy. In post-hoc analyses, increased concentrations of inflammatory markers prior to treatment predict poor antidepressant response. However, limited data exists on whether depressed patients with multiple failed treatment trials in their current episode of depression exhibit increased inflammation.

METHODS

Plasma concentrations of inflammatory markers were measured in unmedicated, medically stable patients with MDD (n = 98) and varying numbers of adequate antidepressant treatment trials in the current depressive episode as measured by the Massachusetts General Hospital Antidepressant Treatment Response Questionnaire. Covariates including age, sex, race, education, body mass index (BMI) and severity of depression were included in statistical models where indicated.

RESULTS

A significant relationship was found between number of failed treatment trials and tumor necrosis factor (TNF), soluble TNF receptor 2 (sTNF-R2) and interleukin (IL)-6 (all p < 0.05 in multivariate analyses). Post hoc pairwise comparisons with correction for multiple testing revealed that patients with 3 or more failed trials in the current episode had significantly higher plasma TNF, sTNF-R2 and IL-6 compared to individuals with 0 or 1 trial (all p < 0.05). High sensitivity c-reactive protein was also associated with a greater number of treatment failures, but only in models with BMI excluded.

CONCLUSIONS

Measuring inflammatory markers and targeting inflammation or its downstream mediators may be relevant for depressed patients with multiple failed antidepressant treatment trials in their current depressive episode.

Functional neuroanatomy of peripheral inflammatory physiology: A meta-analysis of human neuroimaging studies

Communication between the brain and peripheral mediators of systemic inflammation is implicated in numerous psychological, behavioral, and physiological processes. Functional neuroimaging studies have identified brain regions that associate with peripheral inflammation in humans, yet there are open questions about the consistency, specificity, and network characteristics of these findings. The present systematic review provides a meta-analysis to address these questions. Multilevel kernel density analysis of 24 studies (37 statistical maps; 264 coordinates; 457 participants) revealed consistent effects in the amygdala, hippocampus, hypothalamus, striatum, insula, midbrain, and brainstem, as well as prefrontal and temporal cortices. Effects in some regions were specific to particular study designs and tasks. Spatial pattern analysis revealed significant overlap of reported effects with limbic, default mode, ventral attention, and corticostriatal networks, and co-activation analyses revealed functional ensembles encompassing the prefrontal cortex, insula, and midbrain/brainstem. Together, these results characterize brain regions and networks associated with peripheral inflammation in humans, and they provide a functional neuroanatomical reference point for future neuroimaging studies on brain-body interactions.

Translational control of depression-like behavior via phosphorylation of eukaryotic translation initiation factor 4E

Translation of mRNA into protein has a fundamental role in neurodevelopment, plasticity, and memory formation; however, its contribution in the pathophysiology of depressive disorders is not fully understood. We investigated the involvement of MNK1/2 (MAPK-interacting serine/threonine-protein kinase 1 and 2) and their target, eIF4E (eukaryotic initiation factor 4E), in depression-like behavior in mice. Mice carrying a mutation in eIF4E for the MNK1/2 phosphorylation site (Ser209Ala, Eif4e ki/ki), the Mnk1/2 double knockout mice (Mnk1/2^-/-), or mice treated with the MNK1/2 inhibitor, cercosporamide, displayed anxiety- and depression-like behaviors, impaired serotonin-induced excitatory synaptic activity in the prefrontal cortex, and diminished firing of the dorsal raphe neurons. In Eif4e ki/ki mice, brain IκBα, was decreased, while the NF-κB target, TNFα was elevated. TNFα inhibition in Eif4e ki/ki mice rescued, whereas TNFα administration to wild-type mice mimicked the depression-like behaviors and 5-HT synaptic deficits. We conclude that eIF4E phosphorylation modulates depression-like behavior through regulation of inflammatory responses.

Metabolism, Metabolomics, and Inflammation in Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is defined by classic psychological manifestations, although among the characteristics are significantly increased rates of serious somatic comorbidities, such as cardiovascular disease, immune dysfunction, and metabolic syndrome. In this review, we assess the evidence for disturbances that may contribute to somatic pathology in inflammation, metabolic syndrome, and circulating metabolites (implicating mitochondrial dysfunction) in individuals with PTSD and in animal models simulating features of PTSD. The clinical and preclinical data highlight probable interrelated features of PTSD pathophysiology, including a proinflammatory milieu, metabolomic changes (implicating mitochondrial and other processes), and metabolic dysregulation. These data suggest that PTSD may be a systemic illness, or that it at least has systemic manifestations, and the behavioral manifestations are those most easily discerned. Whether somatic pathology precedes the development of PTSD (and thus may be a risk factor) or follows the development of PTSD (as a result of either shared pathophysiologies or lifestyle adaptations), comorbid PTSD and somatic illness is a potent combination placing affected individuals at increased physical as well as mental health risk. We conclude with directions for future research and novel treatment approaches based on these abnormalities.

Recent Advances in CNS P2X7 Physiology and Pharmacology: Focus on Neuropsychiatric Disorders

The ATP-gated P2X7 ion channel is an abundant microglial protein in the CNS that plays an important pathological role in executing ATP-driven danger signal transduction. Emerging data has generated scientific interest and excitement around targeting the P2X7 ion channel as a potential drug target for CNS disorders. Over the past years, a wealth of data has been published on CNS P2X7 biology, in particular the role of P2X7 in microglial cells, and in vivo effects of brain-penetrant P2X7 antagonists. Likewise, significant progress has been made around the medicinal chemistry of CNS P2X7 ligands, as antagonists for in vivo target validation in models of CNS diseases, to identification of two clinical compounds (JNJ-54175446 and JNJ-55308942) and finally, discovery of P2X7 PET ligands. This review is an attempt to bring together the current understanding of P2X7 in the CNS with a focus on P2X7 as a drug target in neuropsychiatric disorders.

Personalized Antidepressant Selection and Pathway to Novel Treatments: Clinical Utility of Targeting Inflammation

Major depressive disorder (MDD) is a chronic condition that affects one in six adults in the US during their lifetime. The current practice of antidepressant medication prescription is a trial-and-error process. Additionally, over a third of patients with MDD fail to respond to two or more antidepressant treatments. There are no valid clinical markers to personalize currently available antidepressant medications, all of which have similar mechanisms targeting monoamine neurotransmission. The goal of this review is to summarize the recent findings of immune dysfunction in patients with MDD, the utility of inflammatory markers to personalize treatment selection, and the potential of targeting inflammation to develop novel antidepressant treatments. To personalize antidepressant prescription, a c-reactive protein (CRP)-matched treatment assignment can be rapidly implemented in clinical practice with point-of-care fingerstick tests. With this approach, 4.5 patients need to be treated for 1 additional remission as compared to a CRP-mismatched treatment assignment. Anti-cytokine treatments may be effective as novel antidepressants. Monoclonal antibodies against proinflammatory cytokines, such as interleukin 6, interleukin 17, and tumor necrosis factor α, have demonstrated antidepressant effects in patients with chronic inflammatory conditions who report significant depressive symptoms. Additional novel antidepressant strategies targeting inflammation include pharmaceutical agents that block the effect of systemic inflammation on the central nervous system. In conclusion, inflammatory markers offer the potential not only to personalize antidepressant prescription but also to guide the development of novel mechanistically-guided antidepressant treatments.

Nested positive feedback loops in the maintenance of major depression: An integration and extension of previous models

Several theories of Major Depressive Disorder (MDD) have previously been proposed, focusing largely on either a psychological (i.e., cognitive/affective), biological, or neural/computational level of description. These theories appeal to somewhat distinct bodies of work that have each highlighted separate factors as being of considerable potential importance to the maintenance of MDD. Such factors include a range of cognitive/attentional information-processing biases, a range of structural and functional brain abnormalities, and also dysregulation within the autonomic, endocrine, and immune systems. However, to date there have been limited efforts to integrate these complimentary perspectives into a single multi-level framework. Here we review previous work in each of these MDD research domains and illustrate how they can be synthesized into a more comprehensive model of how a depressive episode is maintained. In particular, we emphasize how plausible (but insufficiently studied) interactions between the various MDD-related factors listed above can lead to a series of nested positive feedback loops, which are each capable of maintaining an individual in a depressive episode. We also describe how these different feedback loops could be active to different degrees in different individual cases, potentially accounting for heterogeneity in both depressive symptoms and treatment response. We conclude by discussing how this integrative model might extend understanding of current treatment mechanisms, and also potentially guide the search for markers to inform treatment selection in individual cases.

Interleukin 17 selectively predicts better outcomes with bupropion-SSRI combination: Novel T cell biomarker for antidepressant medication selection

BACKGROUND

Interleukin 17 (IL-17) is produced by highly inflammatory Th17 cells and has been implicated in pathophysiology of depression. IL-17 putatively disrupts the blood brain barrier and affects dopamine synthesis whereas dopamine has been shown to decrease Th17 cell-mediated immune response. Nevertheless, whether IL-17 can predict differential treatment outcome with antidepressants modulating dopaminergic transmission is unknown.

METHODS

IL-17 and other T cell and non-T cell markers (Th1, Th2 and non-T cell markers) were measured with the Bioplex Pro™ human cytokine 27-plex kit in the Combining Medications to Enhance Depression Outcomes (CO-MED) trial participants who provided baseline plasma and were treated with either bupropion plus escitalopram (bupropion-SSRI), escitalopram plus placebo (SSRI monotherapy), or venlafaxine plus mirtazapine (n=166). Differential changes in symptom severity and side-effects based on levels of IL-17 and other T and non-T cell markers were tested using a treatment-arm-by-biomarker interaction in separate repeated measures mixed model analyses. Subsequent analyses stratified by treatment arm were conducted for those markers with a significant interaction.

RESULTS

There was a significant treatment-arm-by-IL-17 interaction for depression severity (p=0.037) but not for side-effects (p=0.28). Higher baseline IL-17 level was associated with greater reduction in depression severity (effect size=0.78, p=0.008) in the bupropion-SSRI but not the other two treatment arms. Other T and non-T cell markers were not associated with differential treatment outcomes.

CONCLUSION

Higher baseline levels of IL-17 are selectively associated with greater symptomatic reduction in depressed patients treated with bupropion-SSRI combination.