Network beyond IDO in psychiatric disorders: revisiting neurodegeneration hypothesis

Alterations of kynurenine pathway in alcohol use disorder and abstinence: a link with gut microbiota, peripheral inflammation and psychological symptoms

The gut-brain communication is mostly driven by the immune, metabolic and neural pathways which remained poorly explored in patients with alcohol use disorder (AUD). The metabolites arising from the tryptophan-kynurenine pathway have gained considerable attention since they are at the interface between intestinal bacteria, host immune response and brain functions. This study described the circulating levels of kynurenine metabolites in AUD patients, at the onset (T1) and end (T2) of a 3-week detoxification program, and tested correlations between those metabolites and inflammatory markers, the gut microbiota and the psychological symptoms. Increased concentration of the neurotoxic metabolite quinolinic acid (QUIN) and decreased levels of the neuroprotector metabolite kynurenic acid (KYNA) which both modulate glutamatergic neurotransmission were observed in AUD patients, particularly at T2. The inflammatory marker hsCRP was associated with several metabolic ratios of the kynurenine pathway. Tryptophan, KYNA and QUIN were correlated with depression, alcohol craving and reaction time, respectively. Analysis of gut microbiota revealed that bacteria known as short-chain fatty acid producers, as well as bacterial metabolites including butyrate and medium-chain fatty acids were associated with some metabolites of the tryptophan-kynurenine pathway. Targeting the glutamatergic neurotransmission through the modulation of the kynurenine pathway, by manipulating the gut microbiota, might represent an interesting alternative for modulating alcohol-related behavior.

Psychological Stresses in Children Trigger Cytokine- and Kynurenine Metabolite-Mediated Abdominal Pain and Proinflammatory Changes

Recurrent abdominal pain (RAP) is a common medically unexplained symptom among children worldwide. However, the biological mechanisms behind the development of functional and behavioral symptoms and changes in blood markers have not been well explored. This study aimed to assess changes in the concentrations of inflammatory markers, including cytokines and tryptophan catabolites, in the serum of children with RAP compared to those with subclinical infections. Children with RAP but without organic diseases were included, and those with asymptomatic intestinal parasitic infections were used as a subclinical infection cohort. Blood samples were collected and used to measure the cytokine profile using Multiplex Immunoassay and tryptophan catabolites using high performance liquid chromatography. Children with RAP showed significantly higher concentrations of serum tumor necrotic factor-α, p<0.05, but lower concentrations of IL-10, p<0.001, IL-6, p<0.001 and brain-derived neurotrophic factors (BDNF) p<0.01. In addition, a significant increase in the metabolite of the kynurenine pathway, 3-hydroxyanthranilic acid (3-HAA) p<0.01, a significant decrease in the concentrations of anthranilic acid (AA) p<0.001, together with an increased ratio of serum 3-HAA to AA (3-HAA/AA) p<0.001, was found in this cohort. These findings indicate the significant activation of the immune system and presence of inflammation in children with RAP than those with subclinical parasitic infections. Moreover, children with RAP tested with the Strengths and Difficulties Questionnaire (SDQ), displayed high psychological problems though these SDQ scores were not statistically associated with measured cytokines and kynurenine metabolites. We however could hypothesize that the pro-inflammatory state together with concomitant low concentrations of BDNF in those children with RAP could play a role in psychological stress and experiencing medically unexplained symptoms.

Kynurenine pathway in post-mortem prefrontal cortex and cerebellum in schizophrenia: relationship with monoamines and symptomatology

BACKGROUND

The cortico-cerebellar-thalamic-cortical circuit has been implicated in the emergence of psychotic symptoms in schizophrenia (SZ). The kynurenine pathway (KP) has been linked to alterations in glutamatergic and monoaminergic neurotransmission and to SZ symptomatology through the production of the metabolites quinolinic acid (QA) and kynurenic acid (KYNA).

METHODS

This work describes alterations in KP in the post-mortem prefrontal cortex (PFC) and cerebellum (CB) of 15 chronic SZ patients and 14 control subjects in PFC and 13 control subjects in CB using immunoblot for protein levels and ELISA for interleukins and QA and KYNA determinations. Monoamine metabolites were analysed by high-performance liquid chromatography and SZ symptomatology was assessed by Positive and Negative Syndrome Scale (PANSS). The association of KP with inflammatory mediators, monoamine metabolism and SZ symptomatology was explored.

RESULTS

In the PFC, the presence of the anti-inflammatory cytokine IL-10 together with IDO2 and KATII enzymes decreased in SZ, while TDO and KMO enzyme expression increased. A network interaction analysis showed that in the PFC IL-10 was coupled to the QA branch of the kynurenine pathway (TDO-KMO-QA), whereas IL-10 associated with KMO in CB. KYNA in the CB inversely correlated with negative and general PANSS psychopathology. Although there were no changes in monoamine metabolite content in the PFC in SZ, a network interaction analysis showed associations between dopamine and methoxyhydroxyphenylglycol degradation metabolite. Direct correlations were found between general PANSS psychopathology and the serotonin degradation metabolite, 5-hydroxyindoleacetic acid. Interestingly, KYNA in the CB inversely correlated with 5-hydroxyindoleacetic acid in the PFC.

CONCLUSIONS

Thus, this work found alterations in KP in two brain areas belonging to the cortico-cerebellar-thalamic-cortical circuit associated with SZ symptomatology, with a possible impact across areas in 5-HT degradation.

The Impact of Cardiovascular Rehabilitation on Psychophysiological Stress, Personality and Tryptophan Metabolism: A Randomized Pilot Feasibility Study

Multicomponent cardiac rehabilitation (CR) is a secondary prevention strategy for cardiac patients to tackle stress and psychosocial wellbeing. However, there is a lack of data on its psychoneuroimmunological effects and of biomarkers to determine individual risk and to develop treatment strategies. We conducted a pilot randomized controlled trial (RCT) to investigate the feasibility of deriving psychophysiological stress markers in patients with cardiovascular diseases. Thirty individuals with cardiovascular disease (mean age 58.8 years; 23.3% female) were enrolled and randomized into three treatment groups: standard rehabilitation, yoga, or transcendental meditation (TM). Depression, anxiety, sleep, stress perception, personality functioning, hair cortisol, serum tryptophan, kynurenine and neopterin concentrations were estimated at baseline and after a four-week intervention. Hair cortisol levels decreased significantly after rehabilitation in all groups (F = 15.98, p < 0.001). In addition, personality functioning improved in all patients over time. Participants with impairments in personality functioning showed a positive correlation with baseline neopterin that did not remain significant after Bonferroni correction. Concentrations of serum tryptophan and its metabolite kynurenine did not change significantly. This pilot RCT provides preliminary evidence of multicomponent CR leading to stabilization of hair cortisol levels and improved psychophysiological wellbeing and personality functioning. Impairments in personality functioning were correlated with neopterin levels, which may impact the symptomatology and outcome.

Depression, dementia and immune dysregulation

Major depression is a prevalent illness that increases the risk of several neurological conditions. These include stroke, cardiovascular disease, and dementia including Alzheimer's disease. In this review we ask whether certain types of depression and associated loneliness may be a harbinger of cognitive decline and possibly even dementia. We propose that chronic stress and inflammation combine to compromise vascular and brain function. The resulting increases in proinflammatory cytokines and microglial activation drive brain pathology leading to depression and mild cognitive impairment, which may progress to dementia. We present evidence that by treating the inflammatory changes, depression can be reversed in many cases. Importantly, there is evidence that anti-inflammatory and antidepressant treatments may reduce or prevent dementia in people with depression. Thus, we propose a model in which chronic stress and inflammation combine to increase brain permeability and cytokine production. This leads to microglial activation, white matter damage, neuronal and glial cell loss. This is first manifest as depression and mild cognitive impairment, but can eventually evolve into dementia. Further research may identify clinical subgroups with inflammatory depression at risk for dementia. It would then be possible to address in clinical trials whether effective treatment of the depression can delay the onset of dementia.

The role of the gut microbiome in the development of schizophrenia

Schizophrenia is a heterogeneous neurodevelopmental disorder involving the convergence of a complex and dynamic bidirectional interaction of genetic expression and the accumulation of prenatal and postnatal environmental risk factors. The development of the neural circuitry underlying social, cognitive and emotional domains requires precise regulation from molecular signalling pathways, especially during critical periods or "windows", when the brain is particularly sensitive to the influence of environmental input signalling. Many of the brain regions involved, and the molecular substrates sub-serving these domains are responsive to life-long microbiota-gut-brain (MGB) axis signalling. This intricate microbial signalling system communicates with the brain via the vagus nerve, immune system, enteric nervous system, enteroendocrine signalling and production of microbial metabolites, such as short-chain fatty acids. Preclinical data has demonstrated that MGB axis signalling influences neurotransmission, neurogenesis, myelination, dendrite formation and blood brain barrier development, and modulates cognitive function and behaviour patterns, such as, social interaction, stress management and locomotor activity. Furthermore, preliminary clinical studies suggest altered gut microbiota profiles in schizophrenia. Unravelling MGB axis signalling in the context of an evolving dimensional framework in schizophrenia may provide a more complete understanding of the neurobiological architecture of this complex condition and offers the possibility of translational interventions.

Infectious disease-associated encephalopathies

Infectious diseases may affect brain function and cause encephalopathy even when the pathogen does not directly infect the central nervous system, known as infectious disease-associated encephalopathy. The systemic inflammatory process may result in neuroinflammation, with glial cell activation and increased levels of cytokines, reduced neurotrophic factors, blood-brain barrier dysfunction, neurotransmitter metabolism imbalances, and neurotoxicity, and behavioral and cognitive impairments often occur in the late course. Even though infectious disease-associated encephalopathies may cause devastating neurologic and cognitive deficits, the concept of infectious disease-associated encephalopathies is still under-investigated; knowledge of the underlying mechanisms, which may be distinct from those of encephalopathies of non-infectious cause, is still limited. In this review, we focus on the pathophysiology of encephalopathies associated with peripheral (sepsis, malaria, influenza, and COVID-19), emerging therapeutic strategies, and the role of neuroinflammation.

Effects of sleeve gastrectomy on neutrophil-lymphocyte ratio

OBJECTIVES

Obesity and related diseases have become one of the most important health problems in the modern age. In addition to its clinical use in the treatment of obesity, bariatric surgery reduces obesity-induced inflammation. Neutrophil-lymphocyte ratio (NLR) is a cheap and easily attainable inflammatory marker. The purpose of this study is to show the effect of bariatric surgery on NLR at preoperative and postoperative 3rd, 6th, and 12th months after SG.

METHODS

298 patients, who underwent sleeve gastrectomy (SG) in general surgery clinic between 2015 and 2017, were included in the study. We excluded the patients younger than 18 years old, and did not have any inflammatory, infectious, hematological, and comorbide diseases such as diabetes mellitus, cardiovascular diseases, ischemic heart disease, hypertension, renal insufficiency, cancer, and respiratory problems like asthma, obstructive sleep apnea syndrome. We evaluated the levels of NLR at preoperative and postoperative 3rd, 6th, and 12th months visits.

RESULTS

There were a total of 298 adult patients (age: mean 38.6, minimum 18, maximum 69 years old). Of whom 247 were female (82.9%) and 51 were male (17.1%). We found that NLR levels decreased significantly at 3rd, 6th, and 12th month visits after SG (p<0.001).

CONCLUSIONS

We concluded that NLR levels decrease after surgery in a proportional reduction in adipose tissue. The decrease in NLR levels may also be associated with the protective effects of sleeve gastrectomy against low-grade inflammation-related diseases.

Metabolomics: Impact of Comorbidities and Inflammation on Sickness Behaviors for Individuals with Chronic Wounds

Significance: Approximately 6.5 million people in the United States suffer from chronic wounds. The chronic wound population is typically older and is characterized by a number of comorbidities associated with inflammation. In addition to experiencing wound-related pain, individuals with chronic wounds commonly experience multiple concurrent psychoneurological symptoms such as fatigue and depression, which delay wound healing. However, these distressing symptoms have been relatively overlooked in this population, although their adverse effects on morbidity are well established in other chronic disease populations. Recent Advances: Inflammation is involved in multiple pathways, which activate brain endothelial and innate immune cells that release proinflammatory cytokines, which produce multiple symptoms known as sickness behaviors. Inflammation-based activation of the kynurenine (KYN) pathway and its metabolites is a mechanism associated with chronic illnesses. Critical Issues: Although putative humoral and neuronal routes have been identified, the specific metabolic variations involved in sickness behaviors in chronic wound patients remain unclear. To improve health outcomes in the chronic wound population, clinicians need to have better understanding of the mechanisms underlying sickness behaviors to provide appropriate treatments. Future Directions: This article presents a synthesis of studies investigating associations between inflammation, metabolic pathways, and sickness behaviors in multiple chronic diseases. The presentation of a theoretical framework proposes a mechanism underlying sickness behaviors in the chronic wound population. By mediating the immune system response, dysregulated metabolites in the KYN pathway may play an important role in sickness behaviors in chronic inflammatory conditions. This framework may guide researchers in developing new treatments to reduce the disease burden in the chronic wound population.

A study of tryptophan, kynurenine and serotonin transporter in first-episode drug-naïve major depressive disorder

Major depressive disorder (MDD) is associated with the disharmonic functioning of the serotonin system. The serotonin system is mainly modulated by the serotonin transporter (SERT) which regulates serotonin uptake and the metabolism of its precursor, tryptophan and following kynurenine pathway. Currently, there is a lack of research examining both markers concurrently in MDD. This study evaluated the alterations and inter-relationships of both markers in first-episode drug-naïve MDD patients. Thirty-three MDD patients and 33 age- and sex-matched healthy controls (HC) were recruited. The SERT availability were comparable between two groups in the midbrain, thalamus, caudate, and putamen. The kynurenine/tryptophan ratio which indicates tryptophan metabolism was lower in MDD than HC with no group difference in the tryptophan or kynurenine concentration. A negative correlation between the midbrain SERT availability and kynurenine concentration in HC was found. For the subgroup of HC with high kynurenine/tryptophan ratio, the SERT availability was positively associated with the kynurenine/tryptophan ratio and negatively correlated with tryptophan or kynurenine concentration. This study demonstrated the altered tryptophan metabolism and the relationship between tryptophan metabolism and the SERT availability in first-episode drug-naïve MDD patients, which gave a new insight towards the future investigation of the pathophysiology of MDD.

Comprehensive Bibliometric Analysis of the Kynurenine Pathway in Mood Disorders: Focus on Gut Microbiota Research

Background: Emerging evidence implicates the dysregulated kynurenine pathway (KP), an immune-inflammatory pathway, in the pathophysiology of mood disorders (MD), including depression and bipolar disorder characterized by a low-grade chronic pro-inflammatory state. The metabolites of the KP, an important part of the microbiota-gut-brain axis, serve as immune system modulators linking the gut microbiota (GM) with the host central nervous system.

Aim: This bibliometric analysis aimed to provide a first glimpse into the KP in MD, with a focus on GM research in this field, to guide future research and promote the development of this field.

Methods: Publications relating to the KP in MD between the years 2000 and 2020 were retrieved from the Scopus and Web of Science Core Collection (WoSCC), and analyzed in CiteSpace (5.7 R5W), biblioshiny (using R-Studio), and VOSviewer (1.6.16).

Results: In total, 1,064 and 948 documents were extracted from the Scopus and WoSCC databases, respectively. The publications have shown rapid growth since 2006, partly owing to the largest research hotspot appearing since then, “quinolinic acid.” All the top five most relevant journals were in the neuropsychiatry field, such as Brain Behavior and Immunity. The United States and Innsbruck Medical University were the most influential country and institute, respectively. Journal co-citation analysis showed a strong tendency toward co-citation of research in the psychiatry field. Reference co-citation analysis revealed that the top four most important research focuses were “kynurenine pathway,” “psychoneuroimmunology,” “indoleamine 2,3-dioxygenase,” and “proinflammatory cytokines,” and the most recent focus was “gut-brain axis,” thus indicating the role of the KP in bridging the GM and the host immune system, and together reflecting the field’s research foundations. Overlap analysis between the thematic map of keywords and the keyword burst analysis revealed that the topics “Alzheimer’s disease,” “prefrontal cortex,” and “acid,” were research frontiers.

Conclusion: This comprehensive bibliometric study provides an updated perspective on research associated with the KP in MD, with a focus on the current status of GM research in this field. This perspective may benefit researchers in choosing suitable journals and collaborators, and aid in the further understanding of the field’s hotspots and frontiers, thus facilitating future research.

Effects of stress associated with academic examination on the kynurenine pathway profile in healthy students

The effects of stress on the neuroendocrine, central nervous and immune systems are extremely complex. The kynurenine pathway (KP) of the tryptophan metabolism is recognised as a cross-link between the neuroendocrine- and immune systems. However, the effects of acute stress from everyday life on KP activation have not yet been studied. This study aims to investigate changes in the levels of the KP neuroactive metabolites and cytokines in response to stress triggered by academic examinations. Ninety-two healthy first year medical students benevolently participated in the study. Parameters were measured pre- examination, which is considered to be a high-stress period, and post-examination, as a low-stress period. Stress induced by academic examinations significantly increases the perceived stress scores (p<0.001), serum cortisol levels (p<0.001) and brain-derived neurotrophic factor (BDNF) levels (p<0.01). It decreased IL-10 levels (p<0.05) but had no effect on IL-6 and TNF-alpha levels. Only the KP neuroactive metabolite, 3-hydroxykynurenine (3-HK) significantly increased (p<0.01) in the post-examination period. In addition, the stress scores positively correlated with the levels of cortisol (r² = 0.297, p<0.01) at post examination. Acute stress triggered by academic examinations increases cortisol and BDNF production and suppresses the anti-inflammatory cytokine, IL-10, but did not increase significantly the levels of other pro-inflammatory cytokines, tryptophan, kynurenine and downstream KP metabolites. The concomitant increased levels of BDNF under the duress of acute examination stress appear to limit the levels pro-inflammatory markers, which may attenuate the action of cortisol and the neuroinflammatory branch of the KP.

Tryptophan Catabolites in Bipolar Disorder: A Meta-Analysis

Objective

Tryptophan catabolites (TRYCATs) are implicated in the pathophysiology of mood disorders by mediating immune-inflammation and neurodegenerative processes. We performed a meta-analysis of TRYCAT levels in bipolar disorder (BD) patients compared to healthy controls.

Methods

A systematic literature search in seven electronic databases (PubMed, Embase, Web of Science, Cochrane, Emcare, PsycINFO, Academic Search Premier) was conducted on TRYCAT levels in cerebrospinal fluid or peripheral blood according to the PRISMA statement. A minimum of three studies per TRYCAT was required for inclusion. Standardized mean differences (SMD) were computed using random effect models. Subgroup analyses were performed for BD patients in a different mood state (depressed, manic). The methodological quality of the studies was rated using the modified Newcastle-Ottawa Quality assessment Scale.

Results

Twenty-one eligible studies were identified. Peripheral levels of tryptophan (SMD = -0.44; p < 0.001), kynurenine (SMD = - 0.3; p = 0.001) and kynurenic acid (SMD = -.45; p = < 0.001) were lower in BD patients versus healthy controls. In the only three eligible studies investigating TRP in cerebrospinal fluid, tryptophan was not significantly different between BD and healthy controls. The methodological quality of the studies was moderate. Subgroup analyses revealed no significant difference in TRP and KYN values between manic and depressed BD patients, but these results were based on a limited number of studies.

Conclusion

The TRYCAT pathway appears to be downregulated in BD patients. There is a need for more and high-quality studies of peripheral and central TRYCAT levels, preferably using longitudinal designs.

Neurogenic hypothesis of positive psychology in stress-induced depression: Adult hippocampal neurogenesis, neuroinflammation, and stress resilience

Stress is an important risk factor for depression. Emerging evidence supports the hypothesis that stress-mediated neuroinflammation destroys brain function and leads to anxiety-like and depression-like behaviors. Previous studies of stress-induced depression have mainly focused on pathological damage; however, the rise of positive psychology has attracted the interest of many researchers in environmental enrichment to promote stress resilience. The hippocampus is one of the most severely damaged brain regions in stress-induced depression. In addition, the hippocampus is one of the most unique regions in the brain, as new neurons are produced in the adult hippocampus, a process known as adult hippocampal neurogenesis (AHN). AHN is an important core component of the neurogenic hypothesis and has also become a major innovative breakthrough in positive psychology, in which environmental enrichment mediates stress resilience. Neuroinflammation, by activating microglia and releasing some proinflammatory cytokines, is increasingly shown to be one of the key determinant pathophysiological factors that negatively affects AHNand cognitive reserve. AHN is mainly related to remodeling stress response mechanisms, such as memory clearing, emotional control, and pattern separation, suggesting that a correlation may exist between neuroinflammation and AHN in stress resilience. Therefore, we summarized the previous research results to systematically expound on the relationship between AHN, stress resilience, and neuroinflammation. We hope this neurogenic hypothesis of positive psychology in stress-induced depression will provide a new perspective for the study of depression and antidepressant therapy.

The role of the kynurenine pathway and quinolinic acid in adolescent major depressive disorder

BACKGROUND

The biological mechanisms underlying major depressive disorder (MDD) are not yet sufficiently understood. The kynurenine pathway has been proposed to play a key role between peripheral inflammation and alterations in the central nervous system. This is because of reduced usability of tryptophan (TRP) and production of oxygen radicals and highly potent neurotoxic agents in this pathway.

OBJECTIVE

In this study, we aimed to compare the metabolites of the serum kynurenine pathway (tryptophan, kynurenine, quinolinic acid and kynurenic acid) and IFN-γ, IL-6, IL-1β and high-sensitivity C-reactive protein (hsCRP) levels in patients with major depressive disorder and in healthy controls and to evaluate the relationship between cytokine levels and the functioning of the kynurenine pathway.

METHODS

Clinical and biochemical data from the patients were obtained and assessed in a cross-sectional design. Serum samples were analysed for IL-6, IL-1β, interferon (IFN)-γ, tryptophan (TRP), quinolinic acid (QUIN), kynurenic acid (KYNA) and kynurenine (Kyn) levels by the enzyme-linked immunosorbent assay. hsCRP test was analysed by the immunoturbidimetric method.

RESULTS

In total, 48 adolescent patients with major depressive disorder (no drug use) and 31 healthy controls were included in the study. TRP levels were observed to be significantly lower in patients with MDD than in healthy controls (P = .046); the Kyn/TRP ratio was significantly higher in patients with MDD than in healthy controls (P = .032); the levels of QUIN were significantly higher in patients with MDD than in healthy controls (P = .003). No significant difference was found between the groups in terms of other kynurenine metabolites and cytokines levels.

CONCLUSION

These results suggest that the Kyn and related molecular pathways may play a role in the pathophysiology of MDD. The most important finding was the increased level of QUIN, which has a neurotoxic effect, in the kynurenine pathway.

Basal myokine levels are associated with quality of life and depressed mood in older adults

In an aging society, late-life depression has become an increasing problem. There is evidence that physical activity ameliorates depressive symptoms and increases the quality of life (QoL). However, the underlying mechanisms are still poorly understood. Myokines are molecules secreted in response to muscle contraction. Some of them can cross the blood-brain barrier, making them promising candidates for mediating the beneficial effects of physical activity on mood. The present study aims to compare circulating myokine levels to depression/QoL in older athletes and controls. 55 athletes, 57 controls >59 years were enrolled. The assessment included ergometry, magnetic resonance imaging, blood withdrawal, and neuropsychological testing. Serum interleukin-6 (IL-6), irisin, brain-derived neurotrophic factor (BDNF), kynurenine, and cathepsin B were analyzed and compared to surrogates of depression and quality of life. Athletes presented with higher levels of Cathepsin B. Among controls, all myokines but irisin were associated with age. Also, among controls, kynurenine and IL-6 correlated inversely with specific dimensions of quality of life questionnaires, and IL-6 further with depressive symptoms and decreased physical performance. No such associations could be found among athletes. Irisin levels were inversely associated with mild depression and low-grade white matter-lesions in the brain and predicted impaired QoL. The circulating levels of several myokines/muscle activity-related factors appear to be associated with depressive symptoms and impaired QoL among older adults. However, in athletes, some of these connections seem ameliorated, suggesting additional stressors (as f.e. age) or a different pathomechanism among athletes.

Association of the kynurenine pathway metabolites with clinical, cognitive features and IL-1β levels in patients with schizophrenia spectrum disorder and their siblings

OBJECTIVE

There is evidence suggesting that tryptophan (TRP)-kynurenine (KYN) pathway dysregulation is involved in the pathophysiology of schizophrenia and is regulated by inflammatory cytokines. The study investigate for the first time whether this dysregulation occurs in advanced stages of the disease as a byproduct or emerges as one of the early and inherited manifestations of schizophrenia.

METHOD

Sera of 148 patients with schizophrenia spectrum disorders (SCZ), 139 unaffected siblings (SIB) and 210 controls were investigated. Serum interleukin (IL)-1β levels were measured by ELISA, and TRP, KYN and kynurenic acid (KYNA) levels were measured by a high-performance liquid chromatography system. Also, we collected clinical data by applying Comprehensive Assessment of Symptoms and History in SCZ, and SIS-R in SIB and control groups.

RESULTS

Compared to controls, SCZ and SIB groups had lower TRP and higher KYNA levels. TRP levels showed significant differences only between SCZ and controls (p < 0.01). KYNA levels of both SCZ (p ≤ 0.001) and SIB (p < 0.05) were higher than controls. No statistical significance was found for KYN levels across groups. SCZ and SIB groups had higher serum IL-1β levels than controls (p ≤ 0.001).

CONCLUSIONS

Patients with SCZ and their siblings exhibited similar clinical features and TRP metabolite levels suggesting that TRP-KYN dysregulation may be an inherited component of the disease putatively conferring increased risk to schizophrenia. Elevation of IL-1β is one of the factors promoting overconsumption of the TRP-KYN pathway leading to increased production of neuroregulatory KYNA and presumably to neurodegeneration.

Early and late behavioral consequences of ethanol withdrawal: focus on brain indoleamine 2,3 dioxygenase activity

Anxiety and depression are symptoms associated with ethanol withdrawal that lead individuals to relapse. In the kynurenine pathway, the enzyme indoleamine 2,3 dioxygenase (IDO) is responsible for the conversion of tryptophan to kynurenine, and dysregulation of this pathway has been associated with psychiatric disorders, such as anxiety and depression. The present study evaluated the early and late behavioral and biochemical effects of ethanol withdrawal in rats. Male Wistar rats were submitted to increasing concentrations of ethanol in drinking water during 21 days. In experiment 1, both control and withdrawal groups were submitted to a battery of behavioral tests 3, 5, 10, 19, and 21 days following ethanol removal. In experiment 2, animals were euthanized 3 days (short-term) or 21 days (long-term) after withdrawal, and the brains were dissected altogether, following kynurenine concentration analysis in prefrontal cortex, hippocampus, and striatum. Short-term ethanol withdrawal decreased the exploration of the open arms in the elevated plus-maze. In the forced swimming test, long-term ethanol-withdrawn rats displayed higher immobility time than control animals. Ethanol withdrawal altered neither locomotion nor motor coordination of rats. In experiment 2, kynurenine concentrations were increased in the prefrontal cortex after a long-term period of withdrawal. In conclusion, short-term ethanol withdrawal produced anxiety-like behaviors, while long-term withdrawal favored depressive-like behaviors. Long-term ethanol withdrawal elevated kynurenine levels, specifically in the prefrontal cortex, suggesting that the depressive-like responses observed after long-term withdrawal might be related to the increased IDO activity.

Chemokines in post-traumatic stress disorder: A network meta-analysis

BACKGROUND

Previous studies on the association between chemokines concentrations and post-traumatic stress disorder (PTSD) yielded inconsistent results. Therefore, the purpose of this network meta-analysis was to summarize these results.

METHODS

The databases of PubMed, Web of Science, Psyc-ARTICLES, Embase and Cochrane Library were searched for relevant articles published not later than January 15, 2020. Then, eligible studies were selected based on predefined study selection criteria. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated as group differences in chemokines concentrations. Moreover, network meta-analysis was used to rank chemokines effect values according to their respective surface under cumulative ranking curve (SUCRA) probabilities.

FINDINGS

A total of 18 eligible studies that investigated the association between 9 different chemokines and PTSD were identified. They involved 1,510 patients and 2,012 controls. Results of the meta-analysis showed that the concentrations of CCL3, CCL4 and CCL5 in the PTSD patients were significantly higher than that in the controls (SMDs of 4.12, 6.11 and 1.53 respectively). However, although not statistically significant, concentrations of CCL2 tended to be lower in PTSD patients than in the controls (SMD = -0.76); whereas concentrations of CXCL12 tended to be higher in PTSD patients than in the controls (SMD = 0.37). SUCRA probabilities showed that, among all the chemokines studied, the effect of CCL5 was the highest in PTSD patients.

INTERPRETATION

Concentrations of CCL3, CCL4 and CCL5 may be associated with a trauma and/or PTSD. Also, CXCL12 and CCL2 may be the underlying biomarkers for trauma and/or PTSD. Thus, future studies with large population based samples are needed to further assess these associations. In addition, future research should explore possible mechanisms underlying these associations, with the aim to develop new diagnostics for PTSD. PROSPERO CRD42019147703.

Fractalkine, sICAM-1 and Kynurenine Pathway in Restrictive Anorexia Nervosa-Exploratory Study

The link between the kynurenine pathway and immunomodulatory molecules—fractalkine and soluble intercellular adhesion molecule-1 (sICAM-1)—in anorexia nervosa (AN) remains unknown. Fractalkine, sICAM-1, tryptophan (TRP), kynurenine (KYN), neuroprotective kynurenic acid (KYNA), neurotoxic 3-OH-kynurenine (3-OH-KYN), and the expression of mRNA for kynurenine aminotransferases (KAT1-3) were studied in 20 female patients with restrictive AN (mostly drug-free, all during first episode of the disease) and in 24 controls. In AN, serum fractalkine, but not sICAM-1, KYNA, KYN, TRP or 3-OH-KYN, was higher; ratios TRP/KYN, KYN/KYNA, KYN/3-OH-KYN and KYNA/3-OH-KYN were unaltered. The expression of the gene encoding KAT3, but not of genes encoding KAT1 and KAT2 (measured in blood mononuclear cells), was higher in patients with AN. In AN, fractalkine positively correlated with TRP, while sICAM-1 was negatively associated with 3-OH-KYN and positively linked with the ratio KYN/3-OH-KYN. Furthermore, TRP and fractalkine were negatively associated with the body mass index (BMI) in AN. Expression of KAT1, KAT2 and KAT3 did not correlate with fractalkine, sICAM-1 or BMI, either in AN or control. Increased fractalkine may be an independent factor associated with the restrictive type of AN. Excessive physical activity probably underlies increased expression of KAT3 observed among enrolled patients. Further, longitudinal studies on a larger cohort of patients should be aimed to clarify the contribution of fractalkine and KAT3 to the pathogenesis of AN.

Involvement of Kynurenine Metabolism in Bipolar Disorder: An Updated Review

Bipolar disorder (BD) is a severe affective disorder, mainly characterized by alternative depressive and manic or hypomanic episodes, yet the pathogenesis of BD has not been fully elucidated. Recent researches have implicated the altered kynurenine (KYN) metabolism involved in the neurobiology of BD. Excessive activation of the immune system also occurs in patients with BD, which further accelerates the KYN pathway for tryptophan metabolism. Changes of the KYN metabolites have effects on neuronal receptors and are involved in neuroendocrine transmissions. Interactions between KYN metabolism and the immune system may contribute to the neuropathogenesis of BD. Various studies have shown that alterations of the KYN metabolites were associated with mood, psychotic symptoms, and cognitive functions in patients with BD. In this review, we briefly introduce the KYN pathway and describe the immune dysregulation in BD as well as their interactions. We then focus on the research advances on the KYN metabolism in BD, which hold promise for identifying novel treatment targets in patients stricken with this disorder.

The role of anthranilic acid in the increase of depressive symptoms and major depressive disorder during treatment for hepatitis C with pegylated interferon-α2a and oral ribavirin

BACKGROUND

Tryptophan metabolism via the kynurenine pathway is considered the link between the immune and endocrine systems. Dysregulation of serotonergic transmission can stem from the direct influence of interferon-α on the activity of serotonergic receptors 5-HT1A and 5-HT2A, and from its indirect effect on tryptophan metabolism. Induction of the kynurenine pathway increases the concentration of neurotoxic kynurenine metabolites, and the activity of kynurenine derivatives is linked to the onset of depression. The aim of our study was to evaluate the relationships between depressive symptoms and kynurenine, tryptophan, anthranilic acid and kynurenic acid concentrations, indolamine 2,3-dioxygenase (IDO) activity and tryptophan availability to the brain.

METHODS

The study followed a prospective longitudinal cohort design. We evaluated 101 patients with chronic hepatitis C who were treated with pegylated interferon-α2a, and 40 controls who were awaiting treatment. We evaluated the relationships between total score on the Montgomery-Åsberg Depression Rating Scale and kynurenine, tryptophan, anthranilic acid and kynurenic acid concentrations, IDO activity and tryptophan availability to the brain. A logistic regression model was adapted for the diagnosis of major depressive disorder at each time point, taking into account changes in parameters of the kynurenine pathway between a given time point and the baseline measurement.

RESULTS

Of the treated patients, 44% fulfilled the criteria for major depressive disorder at least once during the 24 weeks of treatment. Anthranilic acid concentrations were significantly increased compared to baseline for all time points except week 2. Tryptophan availability showed a significant decrease (β = -0.09, p = 0.01) only in week 12 of treatment. Over time, kynurenine, tryptophan and anthranilic acid concentrations, as well as IDO activity and tryptophan availability to the brain, were significantly associated with total score on the Montgomery-Åsberg Depression Rating Scale. A logistic regression model revealed that participants with decreased tryptophan availability to the brain at 12 weeks of treatment and participants with increased anthranilic acid concentrations at week 24 of treatment were at increased risk for diagnosis of major depressive disorder (odds ratios 2.92 and 3.59, respectively).

LIMITATIONS

This study had an open-label design in a population receiving naturalistic treatment.

CONCLUSION

The present study provides the first direct evidence of the role of anthranilic acid in the pathogenesis of inflammation-induced major depressive disorder during treatment for hepatitis C with pegylated interferon-α2a.

Alpha7 nicotinic-N-methyl-D-aspartate hypothesis in the treatment of schizophrenia and beyond

Development of novel treatments for positive, cognitive, and negative symptoms continue to be a high-priority area of schizophrenia research and a major unmet clinical need. Given that all randomized controlled trials (RCTs) conducted to date failed with one add-on medication/mechanism of action, future RCTs with the same approach are not warranted. Even if the field develops a medication for cognition, others are still needed to treat negative and positive symptoms. Therefore, fixing one domain does not completely solve the problem. Also, targeting the cholinergic system, glutamatergic system, and cholinergic plus alpha7 nicotinic and N-methyl-D-aspartate (NMDA) receptors failed independently. Hence, targeting other less important pathophysiological mechanisms/targets is unlikely to be successful. Meta-analyses of RCTs targeting major pathophysiological mechanisms have found some efficacy signal in schizophrenia; thus, combination treatments with different mechanisms of action may enhance the efficacy signal. The objective of this article is to highlight the importance of conducting RCTs with novel combination treatments in schizophrenia to develop antischizophrenia treatments. Positive RCTs with novel combination treatments that target the alpha7 nicotinic and NMDA receptors simultaneously may lead to a disease-modifying therapeutic armamentarium in schizophrenia. Novel combination treatments that concurrently improve the three domains of psychopathology and several prognostic and theranostic biomarkers may facilitate therapeutic discovery in schizophrenia.

The next psychoactive drugs: From imipramine to ketamine

Since the 1950s, the therapeutic arsenal against depression has grown considerably. From the discovery of mono-amine oxidase inhibitors (MAOIs) to the antidepressant effect of ketamine, several pharmacological breakthroughs made the history of psychiatry. These discoveries oriented the research about the pathophysiology of depression, which is one of the most disabling diseases worldwide affecting 10 to 20% of general population. In this article, we offer a short historical review of the various therapeutic options developed over the past century and the consequences of these innovations. We then review the discovery of the antidepressant effects of ketamine (and its S-enantiomer, esketamine), the lastest development in depression treatment. Ketamine's effects are spectacular both in terms of their very short onset time, and because they are observed even in treatment-resistant depression. Just as MAOIs and tricyclic antidepressants allowed the "monoaminergic hypothesis of depression" to emerge, unravelling the mechanisms of ketamine's antidepressant effects should highlight the role of glutamatergic system and neuro-inflammation in the neurobiology of depression. Ketamine might also help to refine our understanding of the cognitive pathophysiology of depression and to deeply transform the clinical representations of depressive disorder.

Kynurenine Pathway of Tryptophan Metabolism in Neuropsychiatric Disorders: Pathophysiologic and Therapeutic Considerations

Under physiological conditions 95% of the ingested essential amino acid tryptophan is metabolized by the kynurenine pathway (KP) to yield the ubiquitous co-enzyme nicotinamide adenine dinucleotide, fulfilling cellular energy require-ments. Importantly, the intermediaries of KP exert crucial effects throughout the body, including the central nervous system. Besides, KP metabolites are implicated in diverse disease processes such as inflammation/immune disorders, endocrine/metabolic conditions, cancers and neuropsychiatric diseases. A burgeoning body of research indicates that the KP plays a pathogenic role in major psychiatric diseases like mood disorders and schizophrenia. Triggered by inflammatory processes, the balance between neurotoxic and neuroprotective branches of the KP is disturbed. In preclinical models these discrepancies result in behaviors reminiscent of depression and psychosis. In clinical samples, recent studies are discovering key kynurenine pathway abnormalities which incriminate it in the pathogenesis of the main psychiatric disorders. Harnessing this knowledge has the potential to find disease biomarkers helpful in identifying and prognosticating neuropsychiatric disorders. Concurrently, earnest research efforts directed towards manipulating the KP hold the promise of discovering novel pharmacological agents that have therapeutic value. In this manuscript, an in-depth appraisal of the extant literature is done to understand the working of KP as this applies to neuropsychiatric disorders. It is concluded that this pathway plays an overarching role in the development of major psychiatric disorders, the KP metabolites have the potential to serve as disease markers and new medications based on KP modulation can bring lasting cures for patients suffering from these intractable conditions.

Galantamine-Memantine combination in the treatment of Alzheimer's disease and beyond

Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly population worldwide. Despite the major unmet clinical need, no new medications for the treatment of AD have been approved since 2003. Galantamine is an acetylcholinesterase inhibitor that is also a positive allosteric modulator at the α4β2 and α7nACh receptors. Memantine is an N-methyl-d-aspartate receptor modulator/agonist. Both galantamine and memantine are FDA-approved medications for the treatment of AD. The objective of this review is to highlight the potential of the galantamine-memantine combination to conduct randomized controlled trials (RCTs) in AD. Several studies have shown the combination to be effective. Neurodegenerative diseases involve multiple pathologies; therefore, combination treatment appears to be a rational approach. Although underutilized, the galantamine-memantine combination is the standard of care in the treatment of AD. Positive RCTs with the combination with concurrent improvement in symptoms and biomarkers may lead to FDA approval, which may lead to greater utilization of this combination in clinical practice.

Arctigenin protects against depression by inhibiting microglial activation and neuroinflammation via HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB pathways

BACKGROUND AND PURPOSE

Arctigenin, a major bioactive component of Fructus arctii, has been reported to have antidepressant-like effects. However, the mechanisms underlying these effects are still unclear. Neuroinflammation can be caused by excessive production of proinflammatory cytokines in microglia via high-mobility group box 1 (HMGB1)/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways, leading to depression. In this study, we have investigated the antidepressant mechanism of arctigenin by conducting in vitro and in vivo studies.

EXPERIMENTAL APPROACH

The effects of chronic unpredictable mild stress (CUMS) on wild-type (WT) and TLR4^-/- mice were examined. Antidepressant-like effects of arctigenin were tested using the CUMS-induced model of depression in WT mice. The effects of arctigenin were assessed on the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways in the prefrontal cortex (PFC) of mouse brain and HMGB1- or TNF-α-stimulated primary cultured microglia. The interaction between HMGB1 and TLR4 or TNF-α and TNFR1 with or without arctigenin was examined by localized surface plasmon resonance (LSPR) and co-immunoprecipitation assays.

KEY RESULTS

The immobility times in the tail suspension test (TST) and forced swimming test (FST) were reduced in TLR4^-/- mice, compared with WT mice. Arctigenin exhibited antidepressant-like effects. Arctigenin also inhibited microglia activation and inflammatory responses in the PFC of mouse brain. Arctigenin inhibited HMGB1 and TLR4 or TNF-α and TNFR1 interactions, and suppressed both HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways.

CONCLUSIONS AND IMPLICATIONS

Arctigenin has antidepressant-like effects by attenuating excessive microglial activation and neuroinflammation through the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signalling pathways. This suggests that arctigenin has potential as a new drug candidate suitable for clinical trials to treat depression.

Alleviation of cognitive deficits and high copper levels by an NMDA receptor antagonist in a rat depression model

BACKGROUND

Major depressive disorder (MDD) is frequently associated with cognitive deficits and high copper levels. Dysfunction of N-methyl-d-aspartate (NMDA) receptors has been postulated to underlie MDD pathogenesis. This study sought to investigate the curative effect of the NMDA receptor antagonist memantine on cognitive deficits in depression and the underlying mechanisms.

METHODS

Adult male Sprague-Dawley rats received corticosterone (CORT) (20 mg/kg) bi-weekly via subcutaneous injection and/or copper gluconate (7 mg/kg) via daily intragastric administration. After 3 weeks, sucrose preference tests and open field tests showed anhedonia and high anxiety in both the CORT and CORT+Cu groups. Memantine intervention (20 mg/kg daily via intragastric administration for 14 days) led to recovery of anhedonia and anxiety behaviors. Memantine also remarkably suppressed serum copper ion levels. Moreover, memantine treatment effectively rescued depression-related spatial memory deficits as shown by the Morris water maze task.

RESULTS

Compared to the pre-memantine treatment results, the results of behavioral tests and cognitive function after memantine treatment were significantly normalized, and the copper concentration was decreased in all groups.

CONCLUSIONS

Collectively, our findings suggest that the NMDA receptor antagonist memantine may improve symptoms of anhedonia and anxiety and the cognitive deficits associated with depression, likely be related to suppress serum copper ion levels.

Prenatal IL-6 levels and activation of the tryptophan to kynurenine pathway are associated with depressive but not anxiety symptoms across the perinatal and the post-partum period in a low-risk sample

Depression and anxiety symptoms are highly prevalent among women during pregnancy and post-partum. Previous studies suggest that one of the pathophysiological underpinnings could be an enhanced metabolism of tryptophan (Trp) into kynurenine (Kyn) due to increased inflammation. However, the longitudinal changes in the Kyn pathway and the complex interplay with inflammation and stress in women with perinatal depressive or anxiety symptoms are incompletely understood. We examined a cohort of healthy women at 34-36 gestational weeks. One hundred and ten women were assessed for salivary cortisol and 97 participants were also assessed for serum levels of Trp, Kyn and Interleukin 6 (IL-6). Women filled in two screening questionnaires for depressive (Edinburgh Postnatal Depression Scale (EPDS)) and anxiety (State Trait Anxiety Inventory subscale (STAI-S)) symptoms at 34-36 gestational weeks, delivery, 3 and 12 months postpartum. Unexpectedly, lower prenatal Kyn levels were associated with higher depressive symptoms in late pregnancy. Furthermore, prenatal Trp levels and the Kyn/Trp ratio moderate the association between IL-6 levels and depressive symptoms during the perinatal and the post-partum period. We found no interactions between Trp and Kyn biomarkers and cortisol on depressive symptoms. The observed associations were more robustly found for depressive symptoms, whereas weak and non-significant effects were found for the trajectory of anxiety symptoms. Overall, our data support the involvement of the Trp to Kyn pathway and inflammation in the course of depressive but not anxiety symptoms in women from late pregnancy until one-year post-partum, providing new evidence on the mechanisms regulating emotions during pregnancy and after delivery in a low-risk sample.

Chronic fatigue and depression due to multiple sclerosis: Immune-inflammatory pathways, tryptophan catabolites and the gut-brain axis as possible shared pathways

Chronic fatigue and major depression (MDD)-like symptoms are common manifestations of multiple sclerosis (MS), both with huge impact on quality of life. Depression can manifest itself as fatigue, and depressive symptoms are often mistaken for fatigue, and vice versa. The two conditions are sometimes difficult to differentiate, and their relationship is unclear. Whether chronic fatigue and depression occur primarily, secondarily or coincidentally with activated immune-inflammatory pathways in MS is still under debate. We have carried out a descriptive review aiming to gain a deeper understanding of the relationship between chronic fatigue and depression in MS, and the shared pathways that underpin both conditions. This review focuses on immune-inflammatory pathways, the kynurenine pathway and the gut-brain axis. It seems likely that proinflammatory cytokines, tryptophan catabolites (the KYN pathway) and the gut-brain axis are involved in the mechanisms causing chronic fatigue and MDD-like symptoms in MS. However, the evidence base is weak, and more research is needed. In order to advance our understanding of the underlying pathological mechanisms, MS-related fatigue and depression should be examined using a longitudinal design and both immune-inflammatory and KYN pathway biomarkers should be measured, relevant clinical characteristics judiciously registered, and self-report instruments for both fatigue and depression should be used.

[The next psychoactive drugs: From imipramine to ketamine]

Depuis les années 1950, l’arsenal thérapeutique permettant de lutter contre la dépression s’est considérablement enrichi. De la découverte des inhibiteurs de la monoamine oxydase (IMAO) à celle de la kétamine, ces percées pharmacologiques ont marqué l’histoire de la psychiatrie et guidé la recherche sur la physiopathologie de la dépression, cette pathologie dévastatrice affectant entre 10 et 20 % de la population mondiale. Nous proposons dans cet article une courte revue historique des différentes options thérapeutiques développées au cours du siècle passé et des conséquences qu’ont eu ces innovations. Nous réalisons ensuite un état des lieux de la plus récente de ces découvertes, celle des effets antidépresseurs de la kétamine (et de son énantiomère S, l’eskétamine), spectaculaires de par leur délai d’apparition et leur efficacité même dans les formes les plus résistantes de dépression. De même que la découverte des IMAO et des tricycliques a permis de concevoir une théorie monoaminergique de la dépression, l’étude des mécanismes d’actions de la kétamine pourrait permettre de comprendre le rôle de la transmission glutamatergique ou de la neuro-inflammation dans la neurobiologie de cette pathologie, d’affiner nos connaissances sur sa physiopathologie cognitive ou encore de transformer en profondeur les représentations des cliniciens sur cette maladie.

Analyzing the Potential Biological Determinants of Autism Spectrum Disorder: From Neuroinflammation to the Kynurenine Pathway

Autism Spectrum Disorder (ASD) etiopathogenesis is still unclear and no effective preventive and treatment measures have been identified. Research has focused on the potential role of neuroinflammation and the Kynurenine pathway; here we review the nature of these interactions. Pre-natal or neonatal infections would induce microglial activation, with secondary consequences on behavior, cognition and neurotransmitter networks. Peripherally, higher levels of pro-inflammatory cytokines and anti-brain antibodies have been identified. Increased frequency of autoimmune diseases, allergies, and recurring infections have been demonstrated both in autistic patients and in their relatives. Genetic studies have also identified some important polymorphisms in chromosome loci related to the human leukocyte antigen (HLA) system. The persistence of immune-inflammatory deregulation would lead to mitochondrial dysfunction and oxidative stress, creating a self-sustaining cytotoxic loop. Chronic inflammation activates the Kynurenine pathway with an increase in neurotoxic metabolites and excitotoxicity, causing long-term changes in the glutamatergic system, trophic support and synaptic function. Furthermore, overactivation of the Kynurenine branch induces depletion of melatonin and serotonin, worsening ASD symptoms. Thus, in genetically predisposed subjects, aberrant neurodevelopment may derive from a complex interplay between inflammatory processes, mitochondrial dysfunction, oxidative stress and Kynurenine pathway overexpression. To validate this hypothesis a new translational research approach is necessary.

Neuroinflammation-Associated Alterations of the Brain as Potential Neural Biomarkers in Anxiety Disorders

Stress-induced changes in the immune system, which lead to neuroinflammation and consequent brain alterations, have been suggested as possible neurobiological substrates of anxiety disorders, with previous literature predominantly focusing on panic disorder, agoraphobia, and generalized anxiety disorder, among the anxiety disorders. Anxiety disorders have frequently been associated with chronic stress, with chronically stressful situations being reported to precipitate the onset of anxiety disorders. Also, chronic stress has been reported to lead to hypothalamic–pituitary–adrenal axis and autonomic nervous system disruption, which may in turn induce systemic proinflammatory conditions. Preliminary evidence suggests anxiety disorders are also associated with increased inflammation. Systemic inflammation can access the brain, and enhance pro-inflammatory cytokine levels that have been shown to precipitate direct and indirect neurotoxic effects. Prefrontal and limbic structures are widely reported to be influenced by neuroinflammatory conditions. In concordance with these findings, various imaging studies on panic disorder, agoraphobia, and generalized anxiety disorder have reported alterations in structure, function, and connectivity of prefrontal and limbic structures. Further research is needed on the use of inflammatory markers and brain imaging in the early diagnosis of anxiety disorders, along with the possible efficacy of anti-inflammatory interventions on the prevention and treatment of anxiety disorders.

Antidepressive Effect of Arctiin by Attenuating Neuroinflammation via HMGB1/TLR4- and TNF-α/TNFR1-Mediated NF-κB Activation

Inflammation is a potential factor in the pathophysiology of depression. A traditional Chinese herbal medicine, arctiin, and its aglycone, arctigenin, are the major bioactive components in Fructus arctii and exhibit neuroprotective and anti-inflammatory activities. Arctigenin has been reported to have antidepressant-like effects. However, the antidepressant-like effects of arctiin, its precursor, remain unknown. In this study, we investigated the antidepressant-like effects of arctiin and its underlying mechanisms by in vivo and in vitro experiments in mice. Our results showed that arctiin significantly attenuated sucrose consumption and increased the immobility time in tail suspension and forced swimming tests. Arctiin decreased neuronal damage in the prefrontal cortex (PFC) of the brain. Arctiin also attenuated the levels of three inflammatory mediators, indoleamine 2,3-dioxygenase, 5-hydroxytryptamine, and dopamine, that were elevated in the PFC or serum of chronic unpredictable mild stress (CUMS)-exposed mice. Arctiin reduced excessive activation of microglia and neuroinflammation by reducing high mobility group box 1 (HMGB1)/toll-like receptor 4 (TLR4)- and tumor necrosis factor-α (TNF-α)/TNF receptor 1 (TNFR1)-mediated nuclear factor-kappa B (NF-κB) activation in the PFC of CUMS-exposed mice and HMGB1- or TNF-α-stimulated primary cultured microglia. These findings demonstrate that arctiin ameliorates depression by inhibiting the activation of microglia and inflammation via the HMGB1/TLR4 and TNF-α/TNFR1 signaling pathways.

A mood state-specific interaction between kynurenine metabolism and inflammation is present in bipolar disorder

OBJECTIVES

Cytokines are thought to contribute to the pathogenesis of psychiatric symptoms by kynurenine pathway activation. Kynurenine metabolites affect neurotransmission and can cause neurotoxicity. We measured inflammatory markers in patients with bipolar disorder (BD) and studied their relation to kynurenine metabolites and mood.

METHODS

Patients with BD suffering from an acute mood episode were assigned to the depressive (n = 35) or (hypo)manic (n = 32) subgroup. Plasma levels of inflammatory markers [cytokines, C-reactive protein] and kynurenine metabolites [tryptophan (TRP), kynurenine (KYN), 3-hydroxykynurenine (3-HK), quinolinic acid (QA), kynurenic acid (KYNA)] were measured on 6 time points during 8 months follow-up. Biological marker levels in patients were compared to controls (n = 35) and correlated to scores on mood scales. Spearman correlations and linear mixed models were used for statistical analysis.

RESULTS

Twenty patients of the manic subgroup, 29 of the depressive subgroup, and 30 controls completed the study. The manic subgroup had a rapid remission of mood symptoms, but in the depressive subgroup subsyndromal symptoms persisted. No differences in inflammation were found between groups. A strong correlation between tumor necrosis factor-α and KYN, KYN/TRP, 3-HK and QA (ρ > 0.60) was specific for the manic group, but only at baseline (during mania). The depressive subgroup had a lower neuroprotective ratio (KYNA/3-HK, P = .0004) and a strong association between interferon-y and kynurenine pathway activation (P < .0001). KYNA was low in both patient groups versus controls throughout the whole follow-up (P = .0008).

CONCLUSIONS

Mania and chronic depressive symptoms in BD are accompanied by a strong interaction between inflammation and a potentially neurotoxic kynurenine metabolism.

Inhibition Mechanism of Indoleamine 2, 3-Dioxygenase 1 (IDO1) by Amidoxime Derivatives and Its Revelation in Drug Design: Comparative Molecular Dynamics Simulations

For cancer treatment, in addition to the three standard therapies of surgery, chemotherapy, and radiotherapy, immunotherapy has become the fourth internationally-recognized alternative treatment. Indoleamine 2, 3-dioxygenase 1 (IDO1) catalyzes the conversion of tryptophan to kynurenine causing lysine depletion, which is an important target in the research and development of anticancer drugs. Epacadostat (INCB024360) is currently one of the most potent IDO1 inhibitors, nevertheless its inhibition mechanism still remains elusive. In this work, comparative molecular dynamics simulations were performed to reveal that the high inhibitory activity of INCB024360 mainly comes from two aspects: disturbing the ligand delivery tunnel and then preventing small molecules such as oxygen and water molecules from accessing the active site, as well as hindering the shuttle of substrate tryptophan with product kynurenine through the heme binding pocket. The scanning of key residues showed that L234 and R231 residues both were crucial to the catalytic activity of IDO1. With the association with INCB024360, L234 forms a stable hydrogen bond with G262, which significantly affects the spatial position of G262-A264 loop and then greatly disturbs the orderliness of ligand delivery tunnel. In addition, the cleavage of hydrogen bond between G380 and R231 increases the mobility of the GTGG conserved region, leading to the closure of the substrate tryptophan channel. This work provides new ideas for understanding action mechanism of amidoxime derivatives, improving its inhibitor activity and developing novel inhibitors of IDO1.

Effect of selective serotonin reuptake inhibitor on prefrontal-striatal connectivity is dependent on the level of TNF-α in patients with major depressive disorder

BACKGROUND

We hypothesize that the tumor necrosis factor-α (TNF-α) may play a role in disturbing the effect of selective serotonin reuptake inhibitor (SSRI) on the striatal connectivity in patients with major depressive disorder (MDD).

METHODS

We performed a longitudinal observation by combining resting-state functional magnetic resonance imaging (rs-fMRI) and biochemical analyses to identify the abnormal striatal connectivity in MDD patients, and to evaluate the effect of TNF-α level on these abnormal connectivities during SSRI treatment. Eighty-five rs-fMRI scans were collected from 25 MDD patients and 35 healthy controls, and the scans were repeated for all the patients before and after a 6-week SSRI treatment. Whole-brain voxel-wise functional connectivity (FC) was calculated by correlating the rs-fMRI time courses between each voxel and the striatal seeds (i.e. spherical regions placed at the striatums). The level of TNF-α in serum was evaluated by Milliplex assay. Factorial analysis was performed to assess the interaction effects of 'TNF-α × treatment' in the regions with between-group FC difference.

RESULTS

Compared with controls, MDD patients showed significantly higher striatal FC in the medial prefrontal cortex (MPFC) and bilateral middle/superior temporal cortices before SSRI treatment (p < 0.001, uncorrected). Moreover, a significant interaction effect of 'TNF-α × treatment' was found in MPFC-striatum FC in MDD patients (p = 0.002), and the significance remained after adjusted for age, gender, head motion, and episode of disease.

CONCLUSION

These findings provide evidence that treatment-related brain connectivity change is dependent on the TNF-α level in MDD patients, and the MPFC-striatum connectivities possibly serve as an important target in the brain.

Reduced peripheral availability of tryptophan and increased activation of the kynurenine pathway and cortisol correlate with major depression and suicide

Objectives: Patients affected by major depression (MDD) are at high risk of suicide. The metabolism of tryptophan (Trp) along the serotonin (5-HT) and kynurenine (Kyn) pathways was found dysfunctional in MDD and in suicide. However, a clear biological framework linking dysfunctions in Trp metabolism via 5-HT and Kyn, cortisol, and the activities of tryptophan and indoleamino 2,3-dioxygenase (TDO, IDO) enzymes has not been yet clarified in MDD with or without suicidal behaviours.Methods: We analysed peripheral markers of Trp via 5-HT and Kyn pathways, Kyn/Trp ratio as a measure of TDO/IDO activities, cortisol, and psychopathology in 73 non-suicidal and 56 suicidal MDD patients, and in 40 healthy controls.Results: Plasma Trp levels were lower and the ratio Kyn/Trp higher in suicidal MDD than in non-suicidal MDD patients and controls. Trp levels and the ratio Kyn/Trp correlated with suicidal ideation, and cortisol with the Kyn/Trp ratio. Finally, Trp levels discriminated controls from non-suicidal and suicidal MDD patients, and also non-suicidal from suicidal MDD patients.Conclusions: Reduced availability of Trp for 5-HT synthesis and increased activation of the Kyn pathway and cortisol correlate with depression and suicide. Low plasma Trp levels may be a biomarker of MDD and suicide in MDD.

Kynurenines and the Endocannabinoid System in Schizophrenia: Common Points and Potential Interactions

Schizophrenia, which affects around 1% of the world’s population, has been described as a complex set of symptoms triggered by multiple factors. However, the exact background mechanisms remain to be explored, whereas therapeutic agents with excellent effectivity and safety profiles have yet to be developed. Kynurenines and the endocannabinoid system (ECS) play significant roles in both the development and manifestation of schizophrenia, which have been extensively studied and reviewed previously. Accordingly, kynurenines and the ECS share multiple features and mechanisms in schizophrenia, which have yet to be reviewed. Thus, the present study focuses on the main common points and potential interactions between kynurenines and the ECS in schizophrenia, which include (i) the regulation of glutamatergic/dopaminergic/γ-aminobutyric acidergic neurotransmission, (ii) their presence in astrocytes, and (iii) their role in inflammatory mechanisms. Additionally, promising pharmaceutical approaches involving the kynurenine pathway and the ECS will be reviewed herein.

Tryptophan in health and disease

Tryptophan (TRP), an essential amino acid in mammals, is involved in several physiological processes including neuronal function, immunity, and gut homeostasis. In humans, TRP is metabolized via the kynurenine and serotonin pathways, leading to the generation of biologically active compounds, such as serotonin, melatonin and niacin. In addition to endogenous TRP metabolism, resident gut microbiota also contributes to the production of specific TRP metabolites and indirectly influences host physiology. The variety of physiologic functions regulated by TRP reflects the complex pattern of diseases associated with altered homeostasis. Indeed, an imbalance in the synthesis of TRP metabolites has been associated with pathophysiologic mechanisms occurring in neurologic and psychiatric disorders, in chronic immune activation and in the immune escape of cancer. In this chapter, the role of TRP metabolism in health and disease is presented. Disorders involving the central nervous system, malignancy, inflammatory bowel and cardiovascular disease are discussed.

Nocturnal Gamma-Hydroxybutyrate Reduces Cortisol-Awakening Response and Morning Kynurenine Pathway Metabolites in Healthy Volunteers

BACKGROUND

Gamma-hydroxybutyrate (GHB; or sodium oxybate) is an endogenous GHB-/gamma-aminobutyric acid B receptor agonist. It is approved for application in narcolepsy and has been proposed for the potential treatment of Alzheimer's disease, Parkinson's disease, fibromyalgia, and depression, all of which involve neuro-immunological processes. Tryptophan catabolites (TRYCATs), the cortisol-awakening response (CAR), and brain-derived neurotrophic factor (BDNF) have been suggested as peripheral biomarkers of neuropsychiatric disorders. GHB has been shown to induce a delayed reduction of T helper and natural killer cell counts and alter basal cortisol levels, but GHB's effects on TRYCATs, CAR, and BDNF are unknown.

METHODS

Therefore, TRYCAT and BDNF serum levels, as well as CAR and the affective state (Positive and Negative Affect Schedule [PANAS]) were measured in the morning after a single nocturnal dose of GHB (50 mg/kg body weight) in 20 healthy male volunteers in a placebo-controlled, balanced, randomized, double-blind, cross-over design.

RESULTS

In the morning after nocturnal GHB administration, the TRYCATs indolelactic acid, kynurenine, kynurenic acid, 3-hydroxykynurenine, and quinolinic acid; the 3-hydroxykynurenine to kynurenic acid ratio; and the CAR were significantly reduced (P < 0.05-0.001, Benjamini-Hochberg corrected). The quinolinic acid to kynurenic acid ratio was reduced by trend. Serotonin, tryptophan, and BDNF levels, as well as PANAS scores in the morning, remained unchanged after a nocturnal GHB challenge.

CONCLUSIONS

GHB has post-acute effects on peripheral biomarkers of neuropsychiatric disorders, which might be a model to explain some of its therapeutic effects in disorders involving neuro-immunological pathologies. This study was registered at ClinicalTrials.gov as NCT02342366.

Physical activity and muscle-brain crosstalk

Neurological and mental illnesses account for a considerable proportion of the global burden of disease. Exercise has many beneficial effects on brain health, contributing to decreased risks of dementia, depression and stress, and it has a role in restoring and maintaining cognitive function and metabolic control. The fact that exercise is sensed by the brain suggests that muscle-induced peripheral factors enable direct crosstalk between muscle and brain function. Muscle secretes myokines that contribute to the regulation of hippocampal function. Evidence is accumulating that the myokine cathepsin B passes through the blood-brain barrier to enhance brain-derived neurotrophic factor production and hence neurogenesis, memory and learning. Exercise increases neuronal gene expression of FNDC5 (which encodes the PGC1α-dependent myokine FNDC5), which can likewise contribute to increased brain-derived neurotrophic factor levels. Serum levels of the prototype myokine, IL-6, increase with exercise and might contribute to the suppression of central mechanisms of feeding. Exercise also increases the PGC1α-dependent muscular expression of kynurenine aminotransferase enzymes, which induces a beneficial shift in the balance between the neurotoxic kynurenine and the neuroprotective kynurenic acid, thereby reducing depression-like symptoms. Myokine signalling, other muscular factors and exercise-induced hepatokines and adipokines are implicated in mediating the exercise-induced beneficial impact on neurogenesis, cognitive function, appetite and metabolism, thus supporting the existence of a muscle-brain endocrine loop.

Aberrant Expression of Intracellular let-7e, miR-146a, and miR-155 Correlates with Severity of Depression in Patients with Major Depressive Disorder and Is Ameliorated after Antidepressant Treatment

Chronic inflammation and abnormalities in Toll-like receptor (TLR) signaling pathways are associated with major depressive disorder (MDD). Our previous work reported that impaired negative regulators for the TLR pathways are associated with MDD. This study aimed to assess the association between the severity of depression and the intracellular microRNAs that regulate TLR4 signaling in both peripheral blood mononuclear cells (PBMCs) and monocytes from MDD patients. The severity of MDD before and after antidepressant treatment was determined by the 17-item Hamilton Depression Rating Scale, and quantitative RT-PCR was used to measure the levels of intracellular regulatory microRNAs, including let-7e, miR-21-5p miR-145, miR-223, miR-146a, and miR-155, in PBMCs and monocytes isolated from 43 healthy controls and 84 patients with MDD before and after treatment with antidepressants. Assays of PBMCs showed that the levels of let-7e, miR-146a, and miR-155 were lower in MDD patients than in healthy controls and were significantly higher after than before treatment in the 69 patients who completed treatment with antidepressants for four weeks. Levels of miR-146a and miR-155 in monocytes were lower in MDD patients than in controls and were increased in the former after antidepressant treatment. Multiple linear regression analyses found that let-7e and miR-146a expression before treatment was inversely correlated with severity of depression, whereas miR-155 before treatment was directly correlated with severity of depression. These findings suggest that intracellular regulatory microRNAs which regulate TLR4 signaling are aberrantly expressed in patients with MDD and that these levels are ameliorated by antidepressant treatment.

Antidepressant-Like Effect and Mechanism of Action of Honokiol on the Mouse Lipopolysaccharide (LPS) Depression Model

There is growing evidence that neuroinflammation is closely linked to depression. Honokiol, a biologically active substance extracted from Magnolia officinalis, which is widely used in traditional Chinese medicine, has been shown to exert significant anti-inflammatory effects and improve depression-like behavior caused by inflammation. However, the specific mechanism of action of this activity is still unclear. In this study, the lipopolysaccharide (LPS) mouse model was used to study the effect of honokiol on depression-like behavior induced by LPS in mice and its potential mechanism. A single administration of LPS (1 mg/kg, intraperitoneal injection) increased the immobility time in the forced swimming test (FST) and tail suspension test (TST), without affecting autonomous activity. Pretreatment with honokiol (10 mg/kg, oral administration) for 11 consecutive days significantly improved the immobility time of depressed mice in the FST and TST experiments. Moreover, honokiol ameliorated LPS-induced NF-κB activation in the hippocampus and significantly reduced the levels of the pro-inflammatory cytokines; tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and interferon γ (IFN-γ). In addition, honokiol inhibited LPS-induced indoleamine 2,3-dioxygenase (IDO) activation and quinolinic acid (a toxic product) increase and reduced the level of free calcium in brain tissue, thereby inhibiting calcium overload. In summary, our results indicate that the anti-depressant-like effects of honokiol are mediated by its anti-inflammatory effects. Honokiol may inhibit the LPS-induced neuroinflammatory response through the NF-κB signaling pathway, reducing the levels of related pro-inflammatory cytokines, and furthermore, this may affect tryptophan metabolism and increase neuroprotective metabolites.

Allopregnanolone Treatment Improves Plasma Metabolomic Profile Associated with GABA Metabolism in Fragile X-Associated Tremor/Ataxia Syndrome: a Pilot Study

Currently, there is no effective treatment for the fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder. In this pilot study, we evaluated whether allopregnanolone, a natural neurosteroid that exerts beneficial effects in neurodegenerative diseases, nervous system injury, and peripheral neuropathies, could improve lymphocytic bioenergetics and plasma pharmacometabolomics in six males with FXTAS (68 ± 3 years old; FMR1 CGG repeats 94 ± 4; FXTAS stages ranging from 3 to 5) enrolled in a 12-week open-label intervention study conducted at the University of California Davis from December 2015 through July 2016. Plasma pharmacometabolomics and lymphocytic mitochondria function were assessed at baseline (on the day of the first infusion) and at follow-up (within 48 h from the last infusion). In parallel, quantitative measurements of tremor and ataxia and neuropsychological evaluations of mental state, executive function, learning, memory, and psychological symptoms were assessed at the same time points. Allopregnanolone treatment impacted significantly GABA metabolism, oxidative stress, and some of the mitochondria-related outcomes. Notably, the magnitude of the individual metabolic response, as well as the correlation with some of the behavioral tests, was overwhelmingly carrier-specific. Based on this pilot study, allopregnanolone treatment has the potential for improving cognitive and GABA metabolism in FXTAS aligned with the concept of precision medicine.

A review on inflammatory cytokine-induced alterations of the brain as potential neural biomarkers in post-traumatic stress disorder

The heterogeneity of post-traumatic stress disorder (PTSD) symptoms indicates that multiple neurobiological mechanisms underlie the pathophysiology of the condition. However, no generally accepted PTSD biomarkers in clinical practice currently exist. The sequential responses to recurrent and chronic stress by the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS) system are considered to play a significant role in the onset and progression of PTSD. Decreased activity of the HPA axis and parasympathetic nervous system, along with increased activity of the sympathetic nervous system, have been observed in PTSD, which may lead to increased levels of proinflammatory cytokines. Such heightened activity of the immune system may cause alterations in the structure and function of brain regions-for example, the amygdala, hippocampus, medial prefrontal cortex, anterior cingulate cortex, and insula-through changes in levels of serotonin and kynurenine pathway metabolites, and direct neurotoxic effects of cytokines. Although chronic inflammation-induced alterations in brain regions critical in controlling emotional behavior and fear regulation may represent a strong candidate biomarker of PTSD, future studies are necessary to further elucidate inflammation-associated neural biomarkers of PTSD. Continued research on therapeutic methods that involve the normalization of the HPA axis, ANS, and immune system is expected to contribute to the development of novel ways to treat PTSD.

Early-life adversity-induced long-term epigenetic programming associated with early onset of chronic physical aggression: Studies in humans and animals

Objectives: To examine whether chronic physical aggression (CPA) in adulthood can be epigenetically programmed early in life due to exposure to early-life adversity. Methods: Literature search of public databases such as PubMed/MEDLINE and Scopus. Results: Children/adolescents susceptible for CPA and exposed to early-life abuse fail to efficiently cope with stress that in turn results in the development of CPA later in life. This phenomenon was observed in humans and animal models of aggression. The susceptibility to aggression is a complex trait that is regulated by the interaction between environmental and genetic factors. Epigenetic mechanisms mediate this interaction. Subjects exposed to stress early in life exhibited long-term epigenetic programming that can influence their behaviour in adulthood. This programming affects expression of many genes not only in the brain but also in other systems such as neuroendocrine and immune. Conclusions: The propensity to adult CPA behaviour in subjects experienced to early-life adversity is mediated by epigenetic programming that involves long-term systemic epigenetic alterations in a whole genome.

Simvastatin prevents and ameliorates depressive behaviors via neuroinflammatory regulation in mice

BACKGROUND

Statins play a beneficial role in the treatment of coronary artery disease and are widely prescribed to prevent hypercholesterolemia. Previous studies have demonstrated that statins also have anti-inflammatory and immunomodulatory properties, and these are being explored for potential benefits in depression. However, the role of statins in the treatment of depression has not been well examined.

METHODS

We investigated the effects of simvastatin on depressive behaviors and neuroinflammation in lipopolysaccharide (LPS) and chronic mild stress (CMS) induced depression model in mice. Sucrose preference test (SPT), forced swimming test (FST), novelty-suppressed feeding test (NSFT) were used to detect the depressive behaviors. The microglial activation was detected by immunohistochemistry analysis and the pro-inflammatory cytokines expressions including IL-1β, TNF-α and IL-6 were examined by Western blot analysis.

RESULTS

Our data indicated that oral administration of simvastatin at 20 mg/kg significantly prevented and ameliorated depressive behaviors reflected by better performance in the SPT, FST and NSFT. Moreover, simvastatin markedly prevented and ameliorated LPS and CMS-induced neuroinflammation, as shown by the suppressed activation of microglia in hippocampus and decreased hippocampal pro-inflammatory cytokines expressions including IL-1β, TNF-α, IL-6, which might be mediated via the inhibition of NF-κB pathway, as shown by the decreased nuclear NF-κB p65 expression.

LIMITATIONS

The interpretation of the evidence of a positive treatment effect of simvastatin on the depressive manifestations, multifaceted etiology of depression, and confirmation of this finding from animal models to humans is needed.

CONCLUSION

These results suggest that simvastatin has the potential to be employed as a therapy for depression associated with neuroinflammation.

[A role of the immune system in the pathogenesis of schizophrenia]

The review addresses immunological aspects of schizophrenia, a multifactor disease caused by genetic factors, innate disorders of the central nervous system (CNS), including the consequences of perinatal hypoxia and infections, and adverse environmental influences. Neuroinflammation as a part of the pathophysiology of schizophrenia is characterized by the higher transcription of CNS inflammatory mediators, excessive activation of microglia, inhibition of glutamatergic receptors that leads to the decrease in the number of cortical synapses and neuronal apoptosis. The authors discuss a role of genetic polymorphisms of cytokine genes, complement system components etc. The literature data on the changes in systemic immune response and imbalance in Th1/Th2 adaptive immune responses are analyzed as well. Some papers showed higher levels of proinflammatory mediators in CSF and blood of patients with schizophrenia that indicated the involvement of blood brain barrier (BBB) dysfunction. The authors present the recent data on BBB dysfunction in schizophrenia and its role in the pathogenesis of the disease, autoimmunity in patients comparing it with immune activation and genetic predisposition. An important and arguable issues about a role of parasite and viral infections in the pathogenesis of schizophrenia, initiation of immune responses and direct impacts on the brain, an influence of antipsychotic treatment on immunity are discussed. In author's opinion, conflicting results of genetic and immunological studies of schizophrenia may be explained by different methodological approaches to selection of patients and healthy controls and the differences in schizophrenia classification.