Severe depression is associated with increased microglial quinolinic acid in subregions of the anterior cingulate gyrus: evidence for an immune-modulated glutamatergic neurotransmission?

Kynurenine pathway: the link between depressive disorders and inflammation

Depression is highly prevalent worldwide and the leading cause of disability. It is believed that currently more than 300 million people of all ages suffer from depression. However, the unambiguous cause of the depression remains unknown. It is suggested that the occurrence of this disease is primarily affected by genetic factors, psychological factors and atypical brain structure or function. Recently, an increasingly important role is attributed to the inflammatory response, which is considered to be the main cause of depression. Activation of the kynurenine pathway (KP) is one of the described mechanisms by which inflammation can induce depression. Kynurenine pathway activation is associated with several neuropsychiatric diseases, including major depression disorder (MDD). The imbalance between the neuroprotective and neurotoxic metabolites in the kynurenine pathway and the associated serotonin and melatonin deficiency, may contribute to the manifestation of depressive symptoms. In this review we discuss the role of the major enzymes of the tryptophan KP: tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) and the role of selected kynurenic metabolites in the depressive disorders. Particular attention was also paid to the genetic basis of depressive disorders and to the summary of current knowledge on the effectiveness of treatment and supplementation with tryptophan and 5-hydroxytryptophan in depression.

The neurophysiology of ketamine: an integrative review

The drug ketamine has been extensively studied due to its use in anaesthesia, as a model of psychosis and, most recently, its antidepressant properties. Understanding the physiology of ketamine is complex due to its rich pharmacology with multiple potential sites at clinically relevant doses. In this review of the neurophysiology of ketamine, we focus on the acute effects of ketamine in the resting brain. We ascend through spatial scales starting with a complete review of the pharmacology of ketamine and then cover its effects on in vitro and in vivo electrophysiology. We then summarise and critically evaluate studies using EEG/MEG and neuroimaging measures (MRI and PET), integrating across scales where possible. While a complicated and, at times, confusing picture of ketamine’s effects are revealed, we stress that much of this might be caused by use of different species, doses, and analytical methodologies and suggest strategies that future work could use to answer these problems.

Microglia: A Central Player in Depression

Microglia are the major immune cells in the central nervous system and play a key role in the normal function of the brain. Microglia exhibit functional diversity, and they control the inflammation in central nervous system through releasing inflammatory cytokine, clearing apoptotic cells via phagocytosis, regulating synaptic plasticity and the formation of neural network by synapse pruning. Recent studies have strongly indicated that the microglial dysfunction is associated with a variety of neuropsychiatric diseases such as depression, which have been termed as "microgliopathy". The emergency of advanced technologies and tools has enabled us to comprehensively understand the role of microglia in physiology and pathology, and growing studies have targetted microglia to explore the treatment of neuropsychiatric diseases. Here, we describe the key progress of microglia research, and review the recent developments in the understanding of the role of microglia in physiology and etiology of depression.

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.

Prospective study of the effects of sport-related concussion on serum kynurenine pathway metabolites

Reports of neurodegenerative and psychiatric disease in former athletes have increased public concern about the acute and chronic effects of sport-related concussions (SRC). The biological factors underlying individual differences in the psychiatric sequalae of SRC and their role in potential long-term negative outcomes have not been determined. One understudied biological consequence of the known inflammatory response to concussion is the activation of a key immunoregulatory pathway, the kynurenine pathway (KP). Activation of the KP produces several neuroactive metabolites that have been associated with psychiatric and neurodegenerative diseases. We tested the hypothesis that SRC results in an elevation of serum KP metabolites with neurotoxic properties (quinolinic acid [QuinA], 3-hydroxykynurenine [3HK]) together with a reduction in the neuroprotective metabolite kynurenic acid (KynA), and that these metabolites would predict post-concussion psychological symptoms. Additionally, because brain injury is thought to prime the immune system, a secondary goal was to test the hypothesis that athletes with acute SRC and a history of prior SRC would have elevated neurotoxic relative to neuroprotective KP metabolites compared to athletes that were concussed for the first time. High school and collegiate football players (N = 1136) were enrolled at a preseason baseline visit that included clinical testing and blood specimen collection. Athletes that suffered a SRC (N = 59) completed follow-up visits within 6-hours (early-acute), at 24-48 h (late-acute) and at 8, 15, and 45 days post-injury. Uninjured contact sport (CC; N = 54) and non-contact sport athletes completed similar visits and served as controls (NCC; N = 30). SRC athletes had significantly elevated psychological symptoms, assessed using the Brief Symptom Inventory-18 (BSI), acutely following injury relative to both control groups. There was a group-by-visit interaction on the ratio of KynA to 3HK in serum, a neuroprotective index, with elevated KynA/3HK in athletes with SRC at the early-acute visit relative to later visits. Importantly, athletes with greater elevation in this neuroprotective index at the early-acute visit reported fewer depressive symptoms at the late-acute visit. Finally, SRC athletes with prior concussion had significantly lower serum KynA/QuinA at all visits compared to SRC athletes with no prior concussion, an effect driven by elevated QuinA in SRC athletes with prior concussion. These results suggest that early-acute activation of the KynA branch of the KP may protect against the development of depressive symptoms following concussion. Furthermore, they highlight the potential of serum QuinA as a biomarker for repetitive head injury and provide insight into possible mechanisms linking prior concussion with subsequent injury.

The Role of the Gut Microbiota in Dietary Interventions for Depression and Anxiety

There is emerging evidence that an unhealthy dietary pattern may increase the risk of developing depression or anxiety, whereas a healthy dietary pattern may decrease it. This nascent research suggests that dietary interventions could help prevent, or be an alternative or adjunct therapy for, depression and anxiety. The relation, however, is complex, affected by many confounding variables, and is also likely to be bidirectional, with dietary choices being affected by stress and depression. This complexity is reflected in the data, with sometimes conflicting results among studies. As the research evolves, all characteristics of the relation need to be considered to ensure that we obtain a full understanding, which can potentially be translated into clinical practice. A parallel and fast-growing body of research shows that the gut microbiota is linked with the brain in a bidirectional relation, commonly termed the microbiome-gut-brain axis. Preclinical evidence suggests that this axis plays a key role in the regulation of brain function and behavior. In this review we discuss possible reasons for the conflicting results in diet-mood research, and present examples of areas of the diet-mood relation in which the gut microbiota is likely to be involved, potentially explaining some of the conflicting results from diet and depression studies. We argue that because diet is one of the most significant factors that affects human gut microbiota structure and function, nutritional intervention studies need to consider the gut microbiota as an essential piece of the puzzle.

Characterization of kynurenine pathway in patients with diarrhea-predominant irritable bowel syndrome

Our objectives are to demonstrate whether the kynurenine pathway is activated in diarrhea-type irritable bowel syndrome (IBS-D) patients, and whether the neurotoxic metabolite quinolinic acid (QUIN) is out of balance with the neuroprotective metabolite kynurenic acid (KYNA), and further explore whether this can lead to increased expression of N-methyl D-aspartate receptor 2B (NMDAR2B) in the enteric nervous system and in turn leads to intestinal symptoms and mood disorders. All enrolled healthy controls and patients accepted IBS Symptom Severity Scale (IBS-SSS) score, Self-rating Depression Scale (SDS) and Self-rating Anxiety Scale (SAS) anxiety and depression scores, and also underwent colonoscopy to collect ileum and colonic mucosa specimens. The expression of NMDAR2B in intestinal mucosa was detected by immunofluorescence, and fasting serum was collected to detect the tryptophan, kynurenine (KYN), KYNA and QUIN by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Our results showed that the KYN pathway of IBS-D patients was activated. The production of QUIN and KYNA was imbalanced and resulting in an increased NMDAR2B for patients with IBS-D, which may be involved in intestinal symptoms and mood disorders of IBS-D.

Polyphenols selectively reverse early-life stress-induced behavioural, neurochemical and microbiota changes in the rat

There is a growing emphasis on the role of the microbiota-gut-brain axis as modulator of host behaviour and as therapeutic target for neuropsychiatric disorders. In addition, accumulating evidence suggests that early-life stress can exert long-lasting changes on the brain and microbiota, and this early adversity is associated with increased risk for developing depression in later life. The maternal separation (MS) model in rats is a robust paradigm to study the effects of early-life stress on the microbiota-gut-brain axis. Recently, we have shown that polyphenols, naturally occurring compounds associated with several health benefits, have anti-stress effects in in vitro models. In this study, we assess the therapeutic potential of a variety of both flavonoid and non-flavonoid polyphenols in reversing the impact of MS on behaviour and the microbiota-gut-brain axis. Rats underwent a dietary intervention with the naturally-derived polyphenols xanthohumol and quercetin, as well as with a phlorotannin extract for 8 weeks. Treatment with polyphenols prevented the depressive- and anxiety-like behaviours induced by MS, where xanthohumol effects were correlated with rescue of BDNF plasma levels. In addition, MS resulted in altered brain levels of 5-hydroxyindoleacetic acid (5-HIAA) and dopamine, accompanied by abnormal elevation of plasma corticosterone. Although polyphenols did not reverse neurotransmitter imbalance, xanthohumol normalised corticosterone levels in MS rats. Finally, we explored the impact of MS and polyphenolic diets on the gut microbiota. We observed profound changes in microbial composition and diversity produced by MS condition and by xanthohumol treatment. Moreover, functional prediction analysis revealed that MS results in altered enrichment of pathways associated with microbiota-brain interactions that are significantly reversed by xanthohumol treatment. These results suggest that naturally-derived polyphenols exert antidepressant-like effects in MS rats, which mechanisms could be potentially mediated by HPA regulation, BDNF levels rescue and modulation of the microbiota-gut-brain axis.

Cellular mechanisms and molecular signaling pathways in stress-induced anxiety, depression, and blood-brain barrier inflammation and leakage

Depression and anxiety are comorbid conditions in many neurological or psychopathological disorders. Stress is an underlying event that triggers development of anxiety and depressive-like behaviors. Recent experimental data indicate that anxiety and depressive-like behaviors occurring as a result of stressful situations can cause blood-brain barrier (BBB) dysfunction, which is characterized by inflammation and leakage. However, the underlying mechanisms are not completely understood. This paper sought to review recent experimental preclinical and clinical data that suggest possible molecular mechanisms involved in development of stress-induced anxiety and depression with associated BBB inflammation and leakage. Critical therapeutic targets and potential pharmacological candidates for treatment of stress-induced anxiety and depression with associated BBB dysfunctions are also discussed.

[Curcumin as an ajuvant treatment of depression: mechanisms of action and application prospects]

Curcumin, a natural compound found in the rhizomes of turmeric, has a pronounced anti-inflammatory activity. Rodent models of depression show that this activity is similar to the effect of antidepressants (AD). Experimental data indicate that this activity may be related to the effect of curcumin on the monoamine cycle, oxidative and nitrosative stress, neurogenesis, hypothalamic-pituitary-adrenal, and immune systems. A number of meta-analyzes indicate the effectiveness of the combined use of curcumin with antidepressants in the treatment of depression. The mechanism of action of curcumin, as well as the prospects for its further use are considered.

Targeting Inflammatory-Mitochondrial Response in Major Depression: Current Evidence and Further Challenges

The prevalence of psychiatric disorders has increased in recent years. Among existing mental disorders, major depressive disorder (MDD) has emerged as one of the leading causes of disability worldwide, affecting individuals throughout their lives. Currently, MDD affects 15% of adults in the Americas. Over the past 50 years, pharmacotherapy, psychotherapy, and brain stimulation have been used to treat MDD. The most common approach is still pharmacotherapy; however, studies show that about 40% of patients are refractory to existing treatments. Although the monoamine hypothesis has been widely accepted as a molecular mechanism to explain the etiology of depression, its relationship with other biochemical phenomena remains only partially understood. This is the case of the link between MDD and inflammation, mitochondrial dysfunction, and oxidative stress. Studies have found that depressive patients usually exhibit altered inflammatory markers, mitochondrial membrane depolarization, oxidized mitochondrial DNA, and thus high levels of both central and peripheral reactive oxygen species (ROS). The effect of antidepressants on these events remains unclear. Nevertheless, the effects of ROS on the brain are well known, including lipid peroxidation of neuronal membranes, accumulation of peroxidation products in neurons, protein and DNA damage, reduced antioxidant defenses, apoptosis induction, and neuroinflammation. Antioxidants such as ascorbic acid, tocopherols, and coenzyme Q have shown promise in some depressive patients, but without consensus on their efficacy. Hence, this paper provides a review of MDD and its association with inflammation, mitochondrial dysfunction, and oxidative stress and is aimed at thoroughly discussing the putative links between these events, which may contribute to the design and development of new therapeutic approaches for patients.

Rapid anti-depressant-like effects of ketamine and other candidates: Molecular and cellular mechanisms

Major depressive disorder takes at least 3 weeks for clinical anti‐depressants, such as serotonin selective reuptake inhibitors, to take effect, and only one‐third of patients remit. Ketamine, a kind of anaesthetic, can alleviate symptoms of major depressive disorder patients in a short time and is reported to be effective to treatment‐resistant depression patients. The rapid and strong anti‐depressant‐like effects of ketamine cause wide concern. In addition to ketamine, caloric restriction and sleep deprivation also elicit similar rapid anti‐depressant‐like effects. However, mechanisms about the rapid anti‐depressant‐like effects remain unclear. Elucidating the mechanisms of rapid anti‐depressant effects is the key to finding new therapeutic targets and developing therapeutic patterns. Therefore, in this review we summarize potential molecular and cellular mechanisms of rapid anti‐depressant‐like effects based on the pre‐clinical and clinical evidence, trying to provide new insight into future therapy.

GSK3β: A Master Player in Depressive Disorder Pathogenesis and Treatment Responsiveness

Glycogen synthase kinase 3β (GSK3β), originally described as a negative regulator of glycogen synthesis, is a molecular hub linking numerous signaling pathways in a cell. Specific GSK3β inhibitors have anti-depressant effects and reduce depressive-like behavior in animal models of depression. Therefore, GSK3β is suggested to be engaged in the pathogenesis of major depressive disorder, and to be a target and/or modifier of anti-depressants’ action. In this review, we discuss abnormalities in the activity of GSK3β and its upstream regulators in different brain regions during depressive episodes. Additionally, putative role(s) of GSK3β in the pathogenesis of depression and the influence of anti-depressants on GSK3β activity are discussed.

Accelerated immunosenescence in rheumatoid arthritis: impact on clinical progression

Patients with rheumatoid arthritis (RA) develop features of accelerated ageing, including immunosenescence. These changes include decreased thymic functionality, expansion of late-differentiated effector T cells, increased telomeric attrition, and excessive production of cytokines (senescence-associated secretory phenotype). The progression of RA has been associated with the early development of age-related co-morbidities, including osteoporosis, cardiovascular complications, and cognitive impairment. Here I review data supporting the hypothesis that immune-senescence contributes to the aggravation of both articular and extra-articular manifestations. Of note, poor cognitive functions in RA were associated with senescent CD28- T cells, inflammaging, and autoantibodies against brain antigens. The pathways of immune-to-brain communication are discussed and provide the rationale for the cognitive impairment reported in RA.

Atorvastatin ameliorates depressive behaviors and neuroinflammatory in streptozotocin-induced diabetic mice

Depression is a chronic and progressive syndrome and commonly associated with several neuropsychiatric comorbidities, of which depression is the most studied. It has been demonstrated that statins also have anti-inflammatory and immunomodulatory properties, which being explored for potential benefits in depression. However, the role of statins in the treatment of diabetes-related depression has not been well examined. Herein, we investigated the effects of atorvastatin on depressive behaviors and neuroinflammation in streptozotocin-induced diabetic mice. Our data indicated that oral administration of atorvastatin at 10 or 20 mg/kg for 3 weeks markedly ameliorated diabetes-associated depressive behaviors reflected by better performance in sucrose preference test (SPT), tail suspension test (TST), and novelty-suppressed feeding test (NSFT). The study further showed that atrovastatin decreased the expression of nucleus NF-κB p65 expression and ameliorated neuroinflammatory responses in prefrontal cortex as evidenced by less Iba-1-positive cells and lower inflammatory mediators including IL-1β and TNF-α. As expected, atorvastatin-treated diabetic mice exhibited significant improvement of hyperlipidemia rather than hyperglycemia. These results suggest that atorvastatin has the potential to be employed as a therapy for diabetes-related depression.

Physical exercise prevents mice from L-Kynurenine-induced depression-like behavior

BACKGROUND

Depression is a wide-spread disease that affects millions of people worldwide. Recent studies in neuroinflammation suggested that increased plasma kynurenine (KYN) level was related to depressive symptoms, while animal studies indicated that KYN increase could be caused by environmental stressor. Recent study reported that exercise may prevent stress-induced depression by enhancing KYN metabolism in muscle. This study seeks to test the effect of voluntary exercise on depressive-like behavior induced by stress and KYN in mice.

HYPOTHESIS

Exercise prevents depressive-like behavior induced by KYN.

RESULTS

Our study found that two weeks of voluntary exercise greatly reduced stress-induced helplessness in mice. On non-stressed mice, naïve mice injected with KYN showed increased immobile time in the TST (214 ± 30 s for KYN vs. 181 ± 33 s for saline; p < 0.05) and higher failure rate in the escape test (39 ± 31 % for KYN vs. 16 ± 13 % for saline; p < 0.05), while exercised mice were not affected by KYN injection in neither test. We also observed that exercised mice's plasma KYN concentration (3.29 ± 1.09 u M) was as low as a quarter of that of control (12.95 ± 3.44 u M) (P < 0.01) after KYN injection. Finally, we found that exercised mice expressed more kynurenine aminotransferase III (KAT3) in the muscle than control mice (1.62 ± 0.60 folds for exercise vs. 1.00 ± 0.22 folds for control; p = 0.005) CONCLUSION: Exercise promotes KAT3 expression, enhances KYN metabolism, and consequently prevents mice from stress or KYN-induced depressive-like behavior.

Systemic inflammation is associated with depressive symptoms differentially by sex and race: a longitudinal study of urban adults

Systemic inflammation may influence trajectories of depressive symptoms over time, perhaps differentially by sex and race. Inflammatory markers and the Center for Epidemiologic Studies-Depression scale [total score: CES-D_total and four distinctive domains: somatic complaints, depressed affect, positive affect and interpersonal problems] were examined among African-American (AA) and White urban adults participating in the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study [2004-2013, Age_base:30-64 y, mean ± SD follow-up time: 4.64 ± 0.93 y, N = 150 (with cytokine data) to N = 1,767 (with other inflammatory markers)]. Findings suggest that serum concentrations of high-sensitivity C-reactive protein (hsCRP), z-inflammation composite score [ICS, combining elevated hsCRP and ESR with low serum albumin and iron], and serum interleukin (IL) 1β were positively associated with ΔCES-D_total (Δ: annual rate of increase) among Whites only. IL-12 was directly related to ΔCES-D_total among men and AA. The race-specific associations of hsCRP, ICS, IL-1β and the sex-specific association of IL-12 with ΔCES-D_total were replicated for the "depressed affect" domain. Similarly, among men, lower serum albumin and higher ICS were linked with higher baseline "somatic complaints". IL-10 among AA and IL-12 among men were inversely related to Δ"positive affect", while "interpersonal problems" were cross-sectionally associated with IL-6 among AA and IL-10 among Whites. Finally, baseline ICS was positively associated with incident "elevated depressive symptoms" (EDS: CES-D_total ≥ 16) among AA (HR = 1.28, 95% CI: 1.04-1.56, P = 0.017). Overall, systemic inflammation was directly linked to increased depressive symptoms over time and at baseline, differentially across sex and race groups. More longitudinal research is needed to replicate our findings.

Ribosomal DNA transcription in prefrontal pyramidal neurons is decreased in suicide

Prefrontal cortical regions, which are crucial for the regulation of emotionally influenced behaviour, play most probably a dominant role in the pathogenesis of suicide. The study was carried out on paraffin-embedded brain tissue blocks containing specimens from the anterior cingulate cortex (dorsal and ventral parts), the orbitofrontal cortex, and the dorsolateral cortex obtained from 23 suicide completers (predominantly violent) with unknown psychiatric diagnosis and 25 non-suicidal controls. The transcriptional activity of ribosomal DNA (rDNA) as a surrogate marker of protein biosynthesis was evaluated separately in layers III and V pyramidal neurons in regions of interest (ROIs) mentioned above by the AgNOR silver staining method bilaterally. The overall statistical analysis revealed a decrease of AgNOR area suggestive of attenuated rDNA activity in suicide victims versus controls, particularly in male subjects. Further ROI-specific post-hoc analyses revealed decreases of the median AgNOR area in suicides compared to non-suicides in all 16 ROIs. However, this effect was only significant in the layer V pyramidal neurons of the right ventral anterior cingulate cortex. Our findings suggest that decreased rDNA transcription in prefrontal pyramidal neurons plays possibly an important role in suicide pathogenesis.

Inflammation as a Mechanism of Bipolar Disorder Neuroprogression

Bipolar disorder (BD) is a severe, debilitating psychiatric condition with onset in adolescence or young adulthood and often follows a relapsing and remitting course throughout life. The concept of neuroprogression in BD refers to the progressive path with an identifiable trajectory that takes place with recurrent mood episodes, which eventually leads to cognitive, functional, and clinical deterioration in the course of BD. Understanding the biological basis of neuroprogression helps to explain the subset of BD patients who experience worsening of their disorder over time. Additionally, the study of the neurobiological mechanisms underpinning neuroprogression will help BD staging based on systems biology. Replicated epidemiological studies have suggested inflammatory mechanisms as primary contributors to the neuroprogression of mood disorders. It is known that dysregulated inflammatory/immune pathways are often associated with BD pathophysiology. Hence, in this chapter, we focus on the evidence for the involvement of inflammation and immune regulated pathways in the neurobiological consequences of BD neuroprogression. Herein we put forth the evidence of immune markers from autoimmune disorders, chronic infections, and gut-brain axis that lead to BD neuroprogression. Further, we highlighted the peripheral and central inflammatory components measured along with BD progression.

Lateralization of increased density of Iba1-immunopositive microglial cells in the anterior midcingulate cortex of schizophrenia and bipolar disorder

There is increasing evidence from genetic, biochemical, pharmacological, neuroimaging and post-mortem studies that immunological dysregulation plays a crucial role in the pathogenesis of psychoses. The involvement of microglia in schizophrenia and bipolar disorder (BD) has remained controversial, however, since results from various post-mortem studies are still inconclusive. Here, we analyzed the estimated density of microglia of age-matched individuals with schizophrenia (n = 17), BD (n = 13), and non-psychiatric control subjects (n = 17) in the anterior midcingulate cortex (aMCC), a brain area putatively involved in the pathogenesis of psychoses, using ionized calcium binding adaptor molecule 1 (Iba1)-immunohistochemistry. The microglial cells displayed a homogenously distributed Iba1-staining pattern in the aMCC with slightly varying activation states in all three groups. The estimated microglial densities did not differ significantly between individuals with schizophrenia, BD and control subjects. Remarkably, when both hemispheres were investigated separately within the three groups, the density was significantly lateralized towards the right aMCC in schizophrenia (p = 0.01) and-even more evident-in BD subjects (p = 0.008). This left-right lateralization was not observed in the control group (p = 0.52). Of note, microglial density was significantly lower in BD individuals who did not commit suicide compared with BD individuals who died from suicide (p = 0.002). This difference was not observed between individuals with BD who committed suicide and controls. The results, tentatively interpreted, suggest a hitherto unknown increased lateralization of microglial density to the right hemisphere in both psychiatric groups. If confirmed in independent samples, lateralization should be considered in all post-mortem studies on microglia. Density differences between suicide and non-suicide individuals needs further elucidation.

Postmortem evidence of brain inflammatory markers in bipolar disorder: a systematic review

Bipolar disorder (BD) is a chronic affective disorder with extreme mood swings that include mania or hypomania and depression. Though the exact mechanism of BD is unknown, neuroinflammation is one of the numerous investigated etiopathophysiological causes of BD. This article presents a systematic review of the data regarding brain inflammation evaluating microglia, astrocytes, cytokines, chemokines, adhesion molecules, and other inflammatory markers in postmortem BD brain samples. This systematic review was performed according to PRISMA recommendations, and relevant studies were identified by searching the PubMed/MEDLINE, PsycINFO, EMBASE, LILACS, IBECS, and Web of Science databases for peer-reviewed journal articles published by March 2019. Quality of included studies appraised using the QUADAS-2 tool. Among the 1814 articles included in the primary screening, 51 articles measured inflammatory markers in postmortem BD brain samples. A number of studies have shown evidence of inflammation in BD postmortem brain samples. However, an absolute statement cannot be concluded whether neuroinflammation is present in BD due to the large number of studies did not evaluate the presence of infiltrating peripheral immune cells in the central nervous system (CNS) parenchyma, cytokines levels, and microglia activation in the same postmortem brain sample. For example, out of 15 studies that evaluated microglia cells markers, 8 studies found no effect of BD on these cells. Similarly, 17 out of 51 studies evaluating astrocytes markers, 9 studies did not find any effect of BD on astrocyte cells, whereas 8 studies found a decrease and 2 studies presented both increase and decrease in different brain regions. In addition, multiple factors account for the variability across the studies, including postmortem interval, brain area studied, age at diagnosis, undergoing treatment, and others. Future analyses should rectify these potential sources of heterogeneity and reach a consensus regarding the inflammatory markers in postmortem BD brain samples.

The kynurenine pathway: a finger in every pie

The kynurenine pathway (KP) plays a critical role in generating cellular energy in the form of nicotinamide adenine dinucleotide (NAD+). Because energy requirements are substantially increased during an immune response, the KP is a key regulator of the immune system. Perhaps more importantly in the context of psychiatry, many kynurenines are neuroactive, modulating neuroplasticity and/or exerting neurotoxic effects in part through their effects on NMDA receptor signaling and glutamatergic neurotransmission. As such, it is not surprising that the kynurenines have been implicated in psychiatric illness in the context of inflammation. However, because of their neuromodulatory properties, the kynurenines are not just additional members of a list of inflammatory mediators linked with psychiatric illness, but in preclinical studies have been shown to be necessary components of the behavioral analogs of depression and schizophrenia-like cognitive deficits. Further, as the title suggests, the KP is regulated by, and in turn regulates multiple other physiological systems that are commonly disrupted in psychiatric disorders, including endocrine, metabolic, and hormonal systems. This review provides a broad overview of the mechanistic pathways through which the kynurenines interact with these systems, thus impacting emotion, cognition, pain, metabolic function, and aging, and in so doing potentially increasing the risk of developing psychiatric disorders. Novel therapeutic approaches targeting the KP are discussed. Moreover, electroconvulsive therapy, ketamine, physical exercise, and certain non-steroidal anti-inflammatories have been shown to alter kynurenine metabolism, raising the possibility that kynurenine metabolites may have utility as treatment response or therapeutic monitoring biomarkers.

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.

Microglial Dysregulation and Suicidality: A Stress-Diathesis Perspective

According to the stress-diathesis model of suicidal behavior, completed suicide depends on the interaction between psychosocial stressors and a trait-like susceptibility. While there are likely multiple biological processes at play in suicidal behavior, recent findings point to over-activation of microglia, the resident macrophages of the central nervous system, as implicated in stress-induced suicidal behavior. However, it remains unclear how microglial dysregulation can be integrated into a clinical model of suicidal behavior. Therefore, this narrative review aims to (1) examine the findings from human post-mortem and neuroimaging studies that report a relationship between microglial activation and suicidal behavior, and (2) update the clinical model of suicidal behavior to integrate the role of microglia. A systematic search of SCOPUS, PubMed, PsycINFO, and Embase databases revealed evidence of morphological alterations in microglia and increased translocator protein density in the brains of individuals with suicidality, pointing to a positive relationship between microglial dysregulation and suicidal behavior. The studies also suggested several pathological mechanisms leading to suicidal behavior that may involve microglial dysregulation, namely (1) enhanced metabolism of tryptophan to quinolinic acid through the kynurenine pathway and associated serotonin depletion; (2) increased quinolinic acid leading to excessive N-methyl-D-aspartate-signaling, resulting in potential disruption of the blood brain barrier; (3) increased quinolinic acid resulting in higher neurotoxicity, and; (4) elevated interleukin 6 contributing to loss of inhibition of glutamatergic neurons, causing heightened glutamate release and excitotoxicity. Based on these pathways, we reconceptualized the stress-diathesis theory of suicidal behavior to incorporate the role of microglial activity.

Biological bases of suicidal behaviours: A narrative review

Suicidal behaviour is a multifaceted phenomenon that concerns all human populations. It has been suggested that a complex interaction between the individual genetic profile and environmental factors throughout life underlies the pathophysiology of suicidal behaviour. Although epidemiological and genetic studies suggest the existence of a genetic component, exposure to biological and psychosocial adversities, especially during critical developmental periods, also contributes to altering the biological responses to threat and pleasure. This results in amplified maladaptive cognitive and behavioural traits and states associated with suicidal behaviours. Alterations in the cognitive inhibition and decision-making capacity have been implicated in suicidal behaviours. Structural and functional changes in key brain regions and networks, such as prefrontal cortex, insula and default mode network, may underlie this relationship. Furthermore, the shift from health to suicidal behaviour incorporates complex and dynamic changes in the immune and stress responses, monoaminergic system, gonadal system and neuroplasticity. In this review, we describe the major findings of epidemiological, genetic, neuroanatomical, neuropsychological, immunological and neuroendocrinological studies on suicide behaviours to provide a solid background for future research in this field. This broad overview of the biological bases of suicide should promote neuroscience research on suicidal behaviours. This might lead to improved biological models and to the identification of evidence-based biomarkers, treatment options and preventive strategies.

Biomarkers of suicidal behaviors: A comprehensive critical review

Suicide is a relevant worldwide public health problem. Many studies have shown that different demographic and clinical factors are potentially associated with suicidal behavior. Other studies have reported data about the role of biomarkers in the onset of suicidal behaviors. Specifically, researchers have found that suicidal risk may be increased by abnormalities in serotonergic system, hypothalamic-pituitary-adrenal axis, lipid metabolism, immune system and neuronal plasticity. The identification of specific biological parameters associated with self-harm may be helpful to implement prevention strategies and also to detect new therapeutic strategies. In this review, we summarize and analyze the results of main studies about neurobiological mechanisms related to suicidal behavior, also exploring the possible interconnection between the different biological systems.

Role of the kynurenine pathway and the endocannabinoid system as modulators of inflammation and personality traits

BACKGROUND

Kynurenine pathway metabolites and endocannabinoids both exert potent regulatory effects on the immune system, but the relationship between these molecules is unknown. The role of these immunobiological mediators in emotionality and personality traits is not previously characterized.

METHODS

Interleukin-6 (IL-6), 2-arachidonoylglycerol (2-AG) and picolinic acid (PIC) were measured in the plasma of physically healthy individuals who had history of mood, anxiety, and personality disorders (n = 96) or who had no history of any psychiatric disorder (n = 56) by DSM-5 Criteria. Dimensional assessments of personality were performed using the Eysenck Personality Questionnaire (EPQ) and the Tridimensional Personality Questionnaire (TPQ).

RESULTS

Plasma IL-6 levels were significantly associated with plasma 2-AG levels and plasma PIC levels across all subjects. PIC levels were also negatively associated with 2-AG levels across all subjects, independent of IL-6 levels. In our analysis of the biological determinants of personality factors, we identified significant associations between IL-6 and novelty seeking assessment, and between PIC and neuroticism assessment.

CONCLUSIONS

These data provide evidence of a biological link between metabolites of the kynurenine pathway, the endocannabinoid system and IL-6 and suggest that these factors may influence personality traits.

The Gut Microbiota Links Dietary Polyphenols With Management of Psychiatric Mood Disorders

The pathophysiology of depression is multifactorial yet generally aggravated by stress and its associated physiological consequences. To effectively treat these diverse risk factors, a broad acting strategy is required and is has been suggested that gut-brain-axis signaling may play a pinnacle role in promoting resilience to several of these stress-induced changes including pathogenic load, inflammation, HPA-axis activation, oxidative stress and neurotransmitter imbalances. The gut microbiota also manages the bioaccessibility of phenolic metabolites from dietary polyphenols whose multiple beneficial properties have known therapeutic efficacy against depression. Although several potential therapeutic mechanisms of dietary polyphenols toward establishing cognitive resilience to neuropsychiatric disorders have been established, only a handful of studies have systematically identified how the interaction of the gut microbiota with dietary polyphenols can synergistically alleviate the biological signatures of depression. The current review investigates several of these potential mechanisms and how synbiotics, that combine probiotics with dietary polyphenols, may provide a novel therapeutic strategy for depression. In particular, synbiotics have the potential to alleviate neuroinflammation by modulating microglial and inflammasome activation, reduce oxidative stress and balance serotonin metabolism therefore simultaneously targeting several of the major pathological risk factors of depression. Overall, synbiotics may act as a novel therapeutic paradigm for neuropsychiatric disorders and further understanding the fundamental mechanisms of gut-brain-axis signaling will allow full utilization of the gut microbiota's as a therapeutic tool.

Kynurenine metabolism and inflammation-induced depressed mood: A human experimental study

Inflammation has an important physiological influence on mood and behavior. Kynurenine metabolism is hypothesized to be a pathway linking inflammation and depressed mood, in part through the impact of kynurenine metabolites on glutamate neurotransmission in the central nervous system. This study evaluated whether the circulating concentrations of kynurenine and related compounds change acutely in response to an inflammatory challenge (endotoxin administration) in a human model of inflammation-induced depressed mood, and whether such metabolite changes relate to mood change. Adults (n = 115) were randomized to receive endotoxin or placebo. Mood (Profile of Mood States), plasma cytokine (interleukin-6, tumor necrosis factor-α) and metabolite (kynurenine, tryptophan, kynurenic acid, quinolinic acid) concentrations were repeatedly measured before the intervention, and at 2 and 6 h post-intervention. Linear mixed models were used to evaluate relationships between mood, kynurenine and related compounds, and cytokines. Kynurenine, kynurenic acid, and tryptophan (but not quinolinic acid) concentrations changed acutely (p's all <0.001) in response to endotoxin as compared to placebo. Neither kynurenine, kynurenic acid nor tryptophan concentrations were correlated at baseline with cytokine concentrations, but all three were significantly correlated with cytokine concentrations over time in response to endotoxin. Quinolinic acid concentrations were not correlated with cytokine concentrations either before or following endotoxin treatment. In those who received endotoxin, kynurenine (p = 0.049) and quinolinic acid (p = 0.03) positively correlated with depressed mood, although these findings would not survive correction for multiple testing. Changes in tryptophan and kynurenine pathway metabolites did not mediate the relationship between cytokines and depressed mood. Further work is necessary to clarify the pathways leading from inflammation to depressed mood in humans.

Microglial production of quinolinic acid as a target and a biomarker of the antidepressant effect of ketamine

Major depressive disorder is a complex multifactorial condition with a so far poorly characterized underlying pathophysiology. Consequently, the available treatments are far from satisfactory as it is estimated that up to 30% of patients are resistant to conventional treatment. Recent comprehensive evidence has been accumulated which suggests that inflammation may be implied in the etiology of this disease. Here we investigated ketamine as an innovative treatment strategy due to its immune-modulating capacities. In a murine model of LPS-induced depressive-like behavior we demonstrated that a single dose of ketamine restores the LPS-induced depressive-like alterations. These behavioral effects are associated with i/ a reversal of anxiety and reduced self-care, ii/ a decrease in parenchymal cytokine production, iii/ a modulation of the microglial reactivity and iv/ a decrease in microglial quinolinic acid production that is correlated with plasmatic peripheral production. In a translational approach, we show that kynurenic acid to quinolinic acid ratio is a predictor of ketamine response in treatment-resistant depressed patients and that the reduction in quinolinic acid after a ketamine infusion is a predictor of the reduction in MADRS score. Our results suggest that microglia is a key therapeutic target and that quinolinic acid is a biomarker of ketamine response in major depressive disorder.

Markers of central inflammation in major depressive disorder: A systematic review and meta-analysis of studies examining cerebrospinal fluid, positron emission tomography and post-mortem brain tissue

BACKGROUND

Increased peripheral inflammation has been consistently reported in patients with major depressive disorder (MDD). However, only few studies have explored markers of central (brain) inflammation in patients with MDD. The aim of this study is to systematically review in vivo and post-mortem markers of central inflammation, including studies examining cerebrospinal fluid (CSF), positron emission tomography, and post-mortem brain tissues in subjects suffering with MDD compared with controls.

METHODS

PubMed and Medline databases were searched up to December 2018. We included studies measuring cerebrospinal fluid (CSF) cytokines and chemokines, positron emission tomography (PET) studies; and post-mortem studies measuring cytokines, chemokines and cell-specific markers of microglia and astrocytes, all in MDD. A meta-analysis was performed only for CSF and PET studies, as studies on post-mortem markers of inflammation had different cell-specific markers and analysed different brain regions.

RESULTS

A total of 69 studies met the inclusion criteria. CSF levels of IL-6 and TNF-α were higher in patients with MDD compared with controls (standardised mean difference SMD 0.37, 95%CI: 0.17-0.57 and SMD 0.58, 95%CI 0.26-0.90, respectively). CSF levels of IL-6 were increased in suicide attempters regardless of their psychiatric diagnosis. Translocator protein, a PET marker of central inflammation, was elevated in the anterior cingulate cortex and temporal cortex of patients with MDD compared with controls (SMD 0.78, 95%CI: 0.41-1.16 and SMD 0.52, 95%CI: 0.19-0.85 respectively). Abnormalities in CSF and PET inflammatory markers were not correlated with those in peripheral blood. In post-mortem studies, two studies found increased markers of microglia in MDD brains, while four studies found no MDD related changes. Of the studies investigating expression of cell-specific marker for astrocytes, thirteen studies reported a decreased expression of astrocytes specific markers, two studies reported increased expression of astrocytes specific markers, and eleven studies did not detect any difference. Four out of six studies reported decreased markers of oligodendrocytes in the prefrontal cortex. Post-mortem brain levels of tumor necrosis alpha (TNF-α) were also found increased in MDD.

CONCLUSIONS

Our review suggests the presence of an increase in IL-6 and TNF-alpha levels in CSF and brain parenchyma, in the context of a possible increased microglia activity and reduction of astrocytes and oligodendrocytes markers in MDD. The reduced number of astrocytes may lead to compromised integrity of blood brain barrier with increased monocyte recruitment and infiltration, which is partly supported by post-mortem studies and by PET studies showing an increased TSPO expression in MDD.

Kynurenine Pathway Metabolites as Biomarkers for Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) currently lacks a robust and well-defined biomarker that can 1) assess the progression of the disease, 2) predict and/or delineate the various clinical subtypes, and 3) evaluate or predict a patient's response to treatments. The kynurenine Pathway (KP) of tryptophan degradation represent a promising candidate as it is involved with several neuropathological features present in ALS including neuroinflammation, excitotoxicity, oxidative stress, immune system activation and dysregulation of energy metabolism. Some of the KP metabolites (KPMs) can cross the blood brain barrier, and many studies have shown their levels are dysregulated in major neurodegenerative diseases including ALS. The KPMs can be easily analyzed in body fluids and tissue and as they are small molecules, and are stable. KPMs have a Janus face action, they can be either or both neurotoxic and/or neuroprotective depending of their levels. This mini review examines and presents evidence supporting the use of KPMs as a relevant set of biomarkers for ALS, and highlights the criteria required to achieve a valid biomarker set for ALS.

HMGB1 involved in stress-induced depression and its neuroinflammatory priming role: a systematic review

Background

Evidence from clinical and preclinical studies has demonstrated that stress can cause depressive-like symptoms including anhedonia and psychomotor retardation, namely, the manifestation of motivational deficits in depression. The proximate mediator of linking social-environmental stress with internal motivational deficits remains elusive, although substantial studies proposed neural endocrine mechanisms. As an endogenous danger-associated molecule, high mobility group box-1 (HMGB1) is necessary and sufficient for stress-induced sensitization of innate immune cells and subsequent (neuro)inflammation.

Aim

This review aims to provide evidence to unveil the potential mechanism of the relationship between motivational deficits and stress in depression.

Methods

We reviewed original case-control studies investigating the association between HMGB1-mediated inflammation and stress-induced depression. The literature search of Pubmed and Web of Science electronic database from inception up to March 28th, 2019 were conducted by two independent authors. We performed a qualitative systematic review approach to explore the correlation between HMGB1-mediated inflammation and anhedonia/psychomotor retardation in depression.

Results

A total of 69 studies based on search strategy were retrieved and seven eligible studies met the inclusion criteria. Studies showed that HMGB1 was implicated with depressive-like behaviors, which are similar with motivational deficits. Furthermore, HMGB1-mediated inflammation in depressive-like behaviors may be involved in Nod-like receptor family pyrin domain containing three (NLRP3) inflammasome and proinflammatory cytokines, abnormal kynurenine pathway and imbalance between neuroprotective and neurotoxic factors.

Conclusions

We found that stress-induced inflammation mediated by HMGB1 may affect motivational deficits through regulating dopamine pathway in corticostriatal neurocircuitry. The systematic review may shed light on the novel neurobiological underpinning for treatment of motivation deficits in depression.

Effect of ultramicronized-palmitoylethanolamide and co-micronized palmitoylethanolamide/polydatin on chronic pelvic pain and quality of life in endometriosis patients: An open-label pilot study

Purpose

The aim of the present study was to evaluate the effectiveness of the ultramicronized-palmitoylethanolamide (um-PEA) and co-micronised palmitoylethanolamide/polydatin m(PEA/PLD) in the management of chronic pelvic pain related to endometriosis in patients desiring pregnancy.

Patients and methods

Thirty symptomatic women with laparoscopic diagnosis of endometriosis and pregnancy desire were enrolled. Patients were treated with um-PEA twice daily for 10 days followed by m(PEA/PLD) twice daily for 80 days. Intensity of chronic pelvic pain, dyspareunia, dysmenorrhea, dyschezia, and dysuria were evaluated at baseline, after 10, 30, 60, 90 days and after 30 days from the end of treatment, by VAS. Quality of life and women's psychological well-being were evaluated at baseline and at the end of the treatment after 90 days with 36-Item Short Form Health Survey questionnaire and Symptom Check list-90 questionnaire, respectively. All collected data were analyzed with the non-parametric Wilcoxon test.

Results

At the end of the treatment, all patients showed a significant improvement in chronic pelvic pain, deep dyspareunia, dysmenorrhea, dyschezia, as well as in quality of life and psychological well-being.

Conclusion

In spite of the study's limited sample size and the open-label design, this research suggests the efficacy of um-PEA and m(PEA/PLD) in reducing painful symptomatology and improving quality of life as well as psychological well-being in patients suffering from endometriosis. Additionally, this treatment did not show any serious side effect, proving particularly suitable for women with pregnancy desire and without other infertility factors.

Family-based analyses reveal novel genetic overlap between cytokine interleukin-8 and risk for suicide attempt

BACKGROUND

Suicide is major public health concern. It is imperative to find robust biomarkers so that at-risk individuals can be identified in a timely and reliable manner. Previous work suggests mechanistic links between increased cytokines and risk for suicide, but questions remain regarding the etiology of this association, as well as the roles of sex and BMI.

METHODS

Analyses were conducted using a randomly-ascertained extended-pedigree sample of 1882 Mexican-American individuals (60% female, mean age = 42.04, range = 18-97). Genetic correlations were calculated using a variance components approach between the cytokines TNF-α, IL-6 and IL-8, and Lifetime Suicide Attempt and Current Suicidal Ideation. The potentially confounding effects of sex and BMI were considered.

RESULTS

159 individuals endorse a Lifetime Suicide Attempt. IL-8 and IL-6 shared significant genetic overlap with risk for suicide attempt (ρg = 0.49, pFDR = 7.67 × 10-03; ρg = 0.53, pFDR = 0.01), but for IL-6 this was attenuated when BMI was included as a covariate (ρg = 0.37, se = 0.23, pFDR = 0.12). Suicide attempts were significantly more common in females (pFDR = 0.01) and the genetic overlap between IL-8 and risk for suicide attempt was significant in females (ρg = 0.56, pFDR = 0.01), but not in males (ρg = 0.44, pFDR = 0.30).

DISCUSSION

These results demonstrate that: IL-8 shares genetic influences with risk for suicide attempt; females drove this effect; and BMI should be considered when assessing the association between IL-6 and suicide. This finding represents a significant advancement in knowledge by demonstrating that cytokine alterations are not simply a secondary manifestation of suicidal behavior, but rather, the pathophysiology of suicide attempts is, at least partly, underpinned by the same biological mechanisms responsible for regulating inflammatory response.

Antidepressant and Antiaging Effects of Açaí (Euterpe oleracea Mart.) in Mice

Depression is a mental disorder that affects 300 million people of all ages worldwide, but fewer than half of those with the condition receive adequate treatment. In addition, the high pharmacological refractoriness (affecting 30%-50% of patients) and toxicity of some classical antidepressants support the pursuit of new therapies. People with this condition show depressed mood, loss of pleasure, high levels of oxidative stress, and accelerated biological aging (decreased telomere length and expression of the telomerase reverse transcriptase (TERT), the enzyme responsible for telomere maintenance). Because of the close relationship between depression and oxidative stress, nutraceuticals with antioxidant properties are excellent candidates for therapy. This study represents the first investigation of the possible antidepressant and antiaging effects of commercial samples of clarified açaí (Euterpe oleracea) juice (EO). This fruit is rich in antioxidants and widely consumed. In this study, mice were treated with saline or EO (10 μL/g, oral) for 4 days and then with saline or lipopolysaccharide (0.5 mg/kg, i.p.) to induce depressive-like behavior. Only four doses of EO were enough to abolish the despair-like and anhedonia behaviors and alterations observed in electromyographic measurements. The antidepression effect of EO was similar to that of imipramine and associated with antioxidant and antiaging effects (preventing lipid peroxidation and increasing TERT mRNA expression, respectively) in three major brain regions involved in depression (hippocampus, striatum, and prefrontal cortex). Additionally, EO significantly protected hippocampal cells, preventing neuronal loss associated with the depressive-like state and nitrite level increases (an indirect marker of nitric oxide production). Moreover, EO alone significantly increased TERT mRNA expression, revealing for the first time a potent antiaging action in the brain that suggests neuroprotection against long-term age-related consequences.

Systematic Review on the Involvement of the Kynurenine Pathway in Stroke: Pre-clinical and Clinical Evidence

Background: Stroke is the second leading cause of death after ischemic heart disease and the third leading cause of disability-adjusted life-years lost worldwide. There is a great need for developing more effective strategies to treat stroke and its resulting impairments. Among several neuroprotective strategies tested so far, the kynurenine pathway (KP) seems to be promising, but the evidence is still sparse.

Methods: Here, we performed a systematic review of preclinical and clinical studies evaluating the involvement of KP in stroke. We searched for the keywords: (“kynurenine” or “kynurenic acid” or “quinolinic acid”) AND (“ischemia” or “stroke” or “occlusion) in the electronic databases PubMed, Scopus, and Embase. A total of 1,130 papers was initially retrieved.

Results: After careful screening, forty-five studies were included in this systematic review, being 39 pre-clinical and six clinical studies. Despite different experimental models of cerebral ischemia, the results are concordant in implicating the KP in the pathophysiology of stroke. Preclinical evidence also suggests that treatment with kynurenine and KMO inhibitors decrease infarct size and improve behavioral and cognitive outcomes. Few studies have investigated the KP in human stroke, and results are consistent with the experimental findings that the KP is activated after stroke.

Conclusion: Well-designed preclinical studies addressing the expression of KP enzymes and metabolites in specific cell types and their potential effects at cellular levels alongside more clinical studies are warranted to confirm the translational potential of this pathway as a pharmacological target for stroke and related complications.

A Narrative Review of Cancer-Related Fatigue (CRF) and Its Possible Pathogenesis

Many cancer patients suffer from severe fatigue when treated with chemotherapy or radiotherapy; however, the etiology and pathogenesis of this kind of fatigue remains unknown. Fatigue is associated with cancer itself, as well as adjuvant therapies and can persist for a long time. Cancer patients present a high degree of fatigue, which dramatically affects the quality of their everyday life. There are various clinical research studies and reviews that aimed to explore the mechanisms of cancer-related fatigue (CRF). However, there are certain limitations in these studies: For example, some studies have only blood biochemical texts without histopathological examination, and there has been insufficient systemic evaluation of the dynamic changes in relevant indexes. Thus, we present this narrative review to summarize previous studies on CRF and explore promising research directions. Plenty of evidence suggests a possible association between CRF and physiological dysfunction, including skeletal muscular and mitochondrial dysfunction, peripheral immune activation and inflammation dysfunction, as well as central nervous system (CNS) disorder. Mitochondrial DNA (mtDNA), mitochondrial structure, oxidative pressure, and some active factors such as ATP play significant roles that lead to the induction of CRF. Meanwhile, several pro-inflammatory and anti-inflammatory cytokines in the peripheral system, even in the CNS, significantly contribute to the occurrence of CRF. Moreover, CNS function disorders, such as neuropeptide, neurotransmitter, and hypothalamic-pituitary-adrenal (HPA) axis dysfunction, tend to amplify the sense of fatigue in cancer patients through various signaling pathways. There have been few accurate animal models established to further explore the molecular mechanisms of CRF due to different types of cancer, adjuvant therapy schedules, living environments, and physical status. It is imperative to develop appropriate animal models that can mimic human CRF and to explore additional mechanisms using histopathological and biochemical methods. Therefore, the main purpose of this review is to analyze the possible pathogenesis of CRF and recommend future research that will clarify CRF pathogenesis and facilitate the formulation of new treatment options.

Neuroimmunology of the female brain across the lifespan: Plasticity to psychopathology

The female brain is highly dynamic and can fundamentally remodel throughout the normal ovarian cycle as well as in critical life stages including perinatal development, pregnancy and old-age. As such, females are particularly vulnerable to infections, psychological disorders, certain cancers, and cognitive impairments. We will present the latest evidence on the female brain; how it develops through the neonatal period; how it changes through the ovarian cycle in normal individuals; how it adapts to pregnancy and postpartum; how it responds to illness and disease, particularly cancer; and, finally, how it is shaped by old age. Throughout, we will highlight female vulnerability to and resilience against disease and dysfunction in the face of environmental challenges.

SCI and depression: Does inflammation commandeer the brain?

The incidence of depression is almost twice as high in the spinally injured population compared to the general population. While this incidence has long been attributed to the psychological, economic, and social burdens that accompany spinal cord injury (SCI), data from animal studies indicate that the biology of SCI may play an important role in the development of depression. Inflammation has been shown to impact stress response in rodents and humans, and inflammatory cytokines have been associated with depression for decades. The inflammation inherent to SCI may disrupt necessary mechanisms of mental homeostasis, such as serotonin production, dopamine production, and the hypothalamic pituitary adrenal axis. Additionally, gut dysbiosis that occurs after SCI can exacerbate inflammation and may cause further mood and behavior changes. These mediators combined may significantly contribute to the rise in depression seen after SCI. Currently, there are no therapies specific to depression after SCI. Elucidation of the molecular pathways that contribute to SCI-specific depression is crucial for the understanding of this disease and its potential treatments.

A Focus on the Functions of Area 25

Subcallosal area 25 is one of the least understood regions of the anterior cingulate cortex, but activity in this area is emerging as a crucial correlate of mood and affective disorder symptomatology. The cortical and subcortical connectivity of area 25 suggests it may act as an interface between the bioregulatory and emotional states that are aberrant in disorders such as depression. However, evidence for such a role is limited because of uncertainty over the functional homologue of area 25 in rodents, which hinders cross-species translation. This emphasizes the need for causal manipulations in monkeys in which area 25, and the prefrontal and cingulate regions in which it is embedded, resemble those of humans more than rodents. In this review, we consider physiological and behavioral evidence from non-pathological and pathological studies in humans and from manipulations of area 25 in monkeys and its putative homologue, the infralimbic cortex (IL), in rodents. We highlight the similarities between area 25 function in monkeys and IL function in rodents with respect to the regulation of reward-driven responses, but also the apparent inconsistencies in the regulation of threat responses, not only between the rodent and monkey literatures, but also within the rodent literature. Overall, we provide evidence for a causal role of area 25 in both the enhanced negative affect and decreased positive affect that is characteristic of affective disorders, and the cardiovascular and endocrine perturbations that accompany these mood changes. We end with a brief consideration of how future studies should be tailored to best translate these findings into the clinic.

Quinolinic Acid and Nuclear Factor Erythroid 2-Related Factor 2 in Depression: Role in Neuroprogression

Depression is an incapacitating neuropsychiatric disorder. The serotonergic system in the brain plays an important role in the pathophysiology of depression. However, due to delayed and/or poor performance of selective serotonin reuptake inhibitors in treating depressive symptoms, the role of the serotonergic system in depression has been recently questioned further. Evidence from recent studies suggests that increased inflammation and oxidative stress may play significant roles in the pathophysiology of depression. The consequences of these factors can lead to the neuroprogression of depression, involving neurodegeneration, astrocytic apoptosis, reduced neurogenesis, reduced plasticity (neuronal and synaptic), and enhanced immunoreactivity. Specifically, increased proinflammatory cytokine levels have been shown to activate the kynurenine pathway, which causes increased production of quinolinic acid (QA, an N-Methyl-D-aspartate agonist) and decreases the synthesis of serotonin. QA exerts many deleterious effects on the brain via mechanisms including N-methyl-D-aspartate excitotoxicity, increased oxidative stress, astrocyte degeneration, and neuronal apoptosis. QA may also act directly as a pro-oxidant. Additionally, the nuclear translocation of antioxidant defense factors, such as nuclear factor (erythroid-derived 2)-like 2 (Nrf2), is downregulated in depression. Hence, in the present review, we discuss the role of QA in increasing oxidative stress in depression by modulating the nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 and thus affecting the synthesis of antioxidant enzymes.

Memantine Is Protective against Cytotoxicity Caused by Lead and Quinolinic Acid in Cultured Rat Embryonic Hippocampal Cells

Quinolinic acid (QA) is an excitotoxic metabolite of the kynurenine pathway of tryptophan metabolism produced in response to inflammation and oxidative stress. Lead (Pb) causes oxidative stress and thus may produce neurotoxicity by increasing QA production. We investigated the in vitro cytotoxic effects of Pb and QA and the protective effects of the NMDA receptor antagonist memantine. Primary cultures of embryonic hippocampal cells from Wistar rats were treated with different concentrations of Pb, QA, and Pb + QA with and without memantine. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Apoptosis was analyzed by flow cytometry after Annexin-V/propidium iodide staining. The numbers of immunostained neurons (with β3-Tubulin; Tuj1) and astrocytes (with glial fibrillary acidic protein) were counted. Pb at 20 μg/dL (0.97 μM) and QA at 500 nM concentrations showed significant cytotoxic effects, as evidenced by decreased cell viability, increased apoptosis, and a decrease in the number of both astrocytes and neurons. The combination of Pb and QA showed significant synergistic apoptotic effects at lower doses. Memantine (500 nM) was largely protective against the cytotoxic effects of both Pb and QA, suggesting that Pb's and QA's cytotoxicity involves NMDA receptor activation. Whereas the neuroprotection by memantine from QA-induced toxicity has been previously reported, this is the first study reporting the protection by memantine against Pb-induced cytotoxicity in cultured hippocampal cells. Protection by memantine against these neurotoxicants in vivo needs to be investigated.