Kynurenines: from the perspective of major psychiatric disorders

Experiences with 99mTc-HMPAO in a Diagnostic Pathway for Violent Patients with Schizophrenic Spectrum Disorders

BACKGROUND AND OBJECTIVE

In a security ward we assessed the diagnostic contribution of single photon scintigraphy [SPECT] in our diagnostic pathway for patients with serious mental disease and a history of violence.

METHODS

Twenty patients were examined between 2012 and 2015 and the findings compared to those in nine patients with the same diagnosis, but no history of violence.

RESULTS

All violent patients had areas with reduced accumulation of 99mTc-HMPAO frontally and in the temporal lobe, in the non-violent group only two patients demonstrated these findings.

CONCLUSION

Traditionally, low accumulation of the tracer in SPECT is related to reduced perfusion of brain tissue. We discuss our findings in the light of other possible pathophysiological mechanisms.

Altered KYN/TRP, Gln/Glu, and Met/methionine sulfoxide ratios in the blood plasma of medication-free patients with major depressive disorder

Capillary electrophoresis-time-of-flight mass spectrometry (CE-TOFMS) is a comprehensive, quantitative, and high throughput tool used to analyze metabolite profiles. In the present study, we used CE-TOFMS to profile metabolites found in the blood plasma of 33 medication-free patients with major depressive disorder (MDD) and 33 non-psychiatric control subjects. We then investigated changes which occurred in the metabolite levels during an 8-week treatment period. The medication-free MDD patients and control subjects showed significant differences in their mean levels of 33 metabolites, including kynurenine (KYN), glutamate (Glu), glutamine (Gln), methionine sulfoxide, and methionine (Met). In particular, the ratios of KYN to tryptophan (TRP), Gln to Glu, and Met to methionine sulfoxide were all significantly different between the two groups. Among the 33 metabolites with altered levels in MDD patients, the levels of KYN and Gln, as well as the ratio of Gln to Glu, were significantly normalized after treatment. Our findings suggest that imbalances in specific metabolite levels may be involved in the pathogenesis of MDD, and provide insight into the mechanisms by which antidepressant agents work in MDD patients.

Kynurenic Acid in Schizophrenia: A Systematic Review and Meta-analysis

Kynurenic acid (KYNA) is an endogenous antagonist of N-methyl-D-aspartate and α7 nicotinic acetylcholine receptors that is derived from astrocytes as part of the kynurenine pathway of tryptophan degradation. Evidence suggests that abnormal KYNA levels are involved in the pathophysiology of schizophrenia. However, this has never been assessed through a meta-analysis. A literature search was conducted through Ovid using Embase, Medline, and PsycINFO databases (last search: December 2016) with the search terms: (kynuren* or KYNA) and (schizophreni* or psychosis). English language studies measuring KYNA levels using any method in patients with schizophrenia and healthy controls (HCs) were identified. Standardized mean differences (SMDs) were calculated to determine differences in KYNA levels between groups. Subgroup analyses were separately performed for nonoverlapping participant samples, KYNA measurement techniques, and KYNA sample source. The influences of patients' age, antipsychotic status (%medicated), and sex (%male) on study SMDs were assessed through a meta-regression. Thirteen studies were deemed eligible for inclusion in the meta-analysis. In the main analysis, KYNA levels were elevated in the patient group. Subgroup analyses demonstrated that KYNA levels were increased in nonoverlapping participant samples, and centrally (cerebrospinal fluid and brain tissue) but not peripherally. Patients' age, %medicated, and %male were each positively associated with study SMDs. Overall, KYNA levels are increased in patients with schizophrenia, specifically within the central nervous system. An improved understanding of KYNA in patients with schizophrenia may contribute to the development of novel diagnostic approaches and therapeutic strategies.

Genetic variants of the kynurenine-3-monooxygenase and postpartum depressive symptoms after cesarean section in Chinese women

BACKGROUND

New conceptualizations of depression have emphasized the role of the kynurenine pathway (KP) in the pathogenesis of postpartum depressive symptoms (PDS). Kynurenine 3-monooxygenase (KMO) is a rate-limiting enzyme of the KP, where it catalyzes the conversion of kynurenine (KYN) to 3-hydroxykynurenine (3-HK). Previous work indicates that KMO is closely linked to the pathophysiology of depressive disorders. The purpose of this study is to investigate whether variations in the KMO gene affect PDS development after cesarean section.

METHODS

A total of 710 Chinese women receiving cesarean section were enrolled in this study. PDS was determined by an Edinburgh Postnatal Depression Scale (EPDS) score ≥13. Subsequently, 24 women with PDS and 48 matched women without PDS were randomly selected for investigation of perinatal serum concentrations of KYN, 3-HK and the 3-HK/KYN ratio. The 3-HK/KYN ratio indicates the activity of KMO. In addition, 6 single nucleotide polymorphisms of the KMO gene were examined. Following this genotyping, 36 puerperant women carrying the KMO rs1053230 AG genotype and 72 matched puerperant women carrying the KMO rs1053230 GG genotype were selected for comparisons of KYN, 3-HK and 3-HK/KYN ratio levels.

RESULTS

The results show the incidence of PDS in the Chinese population to be 7.3%, with PDS characterized by increased serum 3-HK concentration and 3-HK/KYN ratio, versus matched postpartum women without PDS (P<0.05). Furthermore, polymorphisms of KMO rs1053230 are significantly associated with the incidence of PDS (P<0.05). The serum concentrations of 3-HK and the 3-HK/KYN ratio in postpartum women carrying the KMO rs1053230 AG genotype are significantly higher than those in matched postpartum women carrying the KMO rs1053230 GG genotype.

CONCLUSIONS

The presented data highlight the contribution of alterations in the KP to the pathogenesis of postpartum depression. Heightened KMO activity, including as arising from KMO rs1053230 G/A genetic variations, are indicated as one possible mechanism driving the biological underpinnings of PDS.

Increased breakdown of kynurenine towards its neurotoxic branch in bipolar disorder

INTRODUCTION

Bipolar disorder (BD) is a chronic psychiatric disease which can take most different and unpredictable courses. It is accompanied by unspecific brainstructural changes and cognitive decline. The neurobiological underpinnings of these processes are still unclear. Emerging evidence suggests that tryptophan catabolites (TRYCATs), which involve all metabolites of tryptophan towards the kynurenine (KYN) branch, are involved in the etiology as well as in the course of BD. They are proposed to be mediators of immune-inflammation and neurodegeneration. In this study we measured the levels of KYN and its main catabolites consisting of the neurotoxic hydroxykynurenine (3-HK), the more neuroprotective kynurenic acid (KYNA) and anthranilic acid (AA) and evaluated the ratios between end-products and substrates as proxies for the specific enzymatic activity (3-HK/KYN, KYNA/KYN, AA/KYN) as well as 3-HK/KYNA as a proxy for neurotoxic vs. neuroprotective end-product relation in individuals with BD compared to healthy controls (HC).

METHODS

We took peripheral TRYCAT blood levels of 143 euthymic to mild depressive BD patients and 101 HC. For statistical analyses MANCOVA's controlled for age, sex, body mass index, cardiovascular disease and smoking were performed.

RESULTS

The levels of KYNA (F = 5,579; p <.05) were reduced in BD compared to HC. The enzymatic activity of the kynurenine-3-monooxygenase (KMO) reflected by the 3-HK/KYN ratio was increased in BD individuals compared to HC (F = 5,394; p <.05). Additionally the ratio of 3-HK/KYNA was increased in individuals with BD compared to healthy controls (F = 11,357; p <.01).

DISCUSSION

In conclusion our findings subserve the concept of KYN -pathway alterations in the pathophysiology of BD. We present evidence of increased breakdown towards the neurotoxic branch in KYN metabolism even in a euthymic to mild depressive state in BD. From literature we know that depression and mania are accompanied by inflammatory states which should be capable to produce an even greater imbalance due to activation of key enzymes in the neurotoxic direction of KYN -conversion. These processes could finally be involved in the development of unspecific brain structural changes and cognitive deficits which are prevalent in BD. Further research should focus on state dependent changes in TRYCATs and its relation to cognition, brain structure and staging parameters.

The Obesity-Impulsivity Axis: Potential Metabolic Interventions in Chronic Psychiatric Patients

Pathological impulsivity is encountered in a broad range of psychiatric conditions and is thought to be a risk factor for aggression directed against oneself or others. Recently, a strong association was found between impulsivity and obesity which may explain the high prevalence of metabolic disorders in individuals with mental illness even in the absence of exposure to psychotropic drugs. As the overlapping neurobiology of impulsivity and obesity is being unraveled, the question asked louder and louder is whether they should be treated concomitantly. The treatment of obesity and metabolic dysregulations in chronic psychiatric patients is currently underutilized and often initiated late, making correction more difficult to achieve. Addressing obesity and metabolic dysfunction in a preventive manner may not only lower morbidity and mortality but also the excessive impulsivity, decreasing the risk for aggression. In this review, we take a look beyond psychopharmacological interventions and discuss dietary and physical therapy approaches.

A Simple HPLC-MS/MS Method for Determination of Tryptophan, Kynurenine and Kynurenic Acid in Human Serum and its Potential for Monitoring Antidepressant Therapy

The kynurenine pathway, in which tryptophan is metabolized to kynurenine and kynurenic acid, has been linked to depression. A rapid and highly reproducible liquid-chromatography-tandem mass spectrometry (LC-MS/MS) method were established for determining tryptophan, kynurenine and kynurenic acid in human serum. Biological samples were precipitated with methanol before separation on an Agilent Eclipse XDB-C18. The stable-isotope-labeled internal standards (kynurenine-¹³C₄¹⁵N and kynurenic acid-d₅) were used for quantification. Detection was performed using multiple reaction monitoring in electrospray ionization mode at m/z 205.1→188.1 for tryptophan, m/z 209.1→146.1 for kynurenine, m/z 190.1→144.1 for kynurenic acid. Good linearity of analyte to internal standard peak area ratios was seen in the concentration range 1,000-50,000 ng/mL for tryptophan, 100-5,000 ng/mL for kynurenine and 1-60 ng/mL for kynurenic acid. Pooled drug-free human serum was purified using activated charcoal and the method was shown to be linear, with validation parameters within acceptable limits. The newly developed method was successfully used to determine concentrations of tryptophan, kynurenine and kynurenic acid in serum from 26 healthy volunteers and 54 patients with depression. Concentrations of tryptophan and kynurenine were lower in serum from depressed individuals than from healthy individuals.

Inflammation-Associated Co-morbidity Between Depression and Cardiovascular Disease

Morbidity and mortality of cardiovascular disease (CVD) is exceedingly high worldwide. Depressive illness is a serious psychiatric illness that afflicts a significant portion of the world population. Epidemiological studies have confirmed the high co-morbidity between these two disease entities. The co-morbidity is bidirectional and the mechanisms responsible for it are complex and multifaceted. In addition to genetic, biological systems, psychosocial, and behavioral factors that are involved include the central and autonomic nervous systems, the neuroendocrine, immune, and the vascular and hematologic systems. Specific pathophysiologic factors across these systems include homeostatic imbalance between the sympathetic and the parasympathetic systems with loss of heart rate variability (HRV) in depression, sympathoadrenal activation, hypothalamic-pituitary-adrenal (HPA) axis activation, immune system dysregulation resulting in a pro-inflammatory status, platelet activation, and endothelial dysfunction. These abnormalities have been demonstrated in most individuals diagnosed with major depressive disorder (MDD), bipolar disorder (BPD), and probably in other psychiatric disorders. A likely common instigator underlying the co-morbidity between cardiovascular pathology and depression is mental stress. Chronic stress shifts the homeostatic balance in the autonomic nervous system with sustained sympathetic overdrive and diminished vagal tone. Diminished vagal tone contributes to a pro-inflammatory status with associated sequelae. Stress hormones and certain pro-inflammatory substances released by macrophages and microglia upregulate the rate-limiting enzymes in the metabolic pathway of tryptophan (TRP). This enzymatic upregulation stimulates the kynurenine (KYN) pathway resulting in the formation of neurotoxic metabolites. Inflammation occurs in cardiac, cardiovascular, and cerebrovascular pathology independent of the presence or absence of depression. Inflammation is closely associated with endothelial dysfunction, a preamble to atherosclerosis and atherothrombosis. Endothelial dysfunction has been detected in depression and may prove to be a trait marker for this illness. Thus understanding vascular biology in conjunction with psychiatric co-morbidity will be of critical importance. Antidepressant drug therapy is of definite benefit to patients with medical and psychiatric co-morbidity and may reverse the pro-inflammatory status associated with depression. There is, however, an urgent need to develop novel pharmacotherapeutic approaches to benefit a much larger proportion of patients suffering from these disease entities.

Progesterone Alters Kynurenine Pathway Activation in IFN-γ-Activated Macrophages - Relevance for Neuroinflammatory Diseases

We have previously demonstrated that the kynurenine pathway (KP), the major biochemical pathway for tryptophan metabolism, is dysregulated in many inflammatory disorders that are often associated with sexual dimorphisms. We aimed to identify a potential functional interaction between the KP and gonadal hormones. We have treated primary human macrophages with progesterone in the presence and absence of inflammatory cytokine interferon-gamma (interferon-γ) that is known to be a potent inducer of regulating the KP enzyme. We found that progesterone attenuates interferon-γ-induced KP activity, decreases the levels of the excitotoxin quinolinic acid, and increases the neuroprotective kynurenic acid levels. We also showed that progesterone was able to reduce the inflammatory marker neopterin. These results may shed light on the gender disparity in response to inflammation.

Effect of Coffee in Lipopolysaccharide-Induced Indoleamine 2,3-Dioxygenase Activation and Depressive-like Behavior in Mice

Research has identified a potential inverse correlation between coffee consumption and the risk of depression. The aim of this study was to investigate the effects of caffeinated coffee on lipopolysaccharide-induced depressive-like behaviors and inflammatory biomarkers in an in vivo model of depression in a C57BL/6J mouse model. The behavioral studies showed that caffeinated coffee decreased immobility time in both the tail suspension test (caffeinated coffee 56.60 ± 9.17; p < 0.0001) and the forced swimming test (caffeinated coffee 28.80 ± 5.93; p < 0.0001), suggesting antidepressant-like activity. The effects of caffeinated coffee on the inflammatory biomarkers associated with depression supported the results observed in the behavioral studies. Statistically significant decreases in indoleamine 2,3-dioxygenase activity (p < 0.001) and the neopterin/biopterin ratio (p < 0.001) were observed in animals pretreated with caffeinated coffee 24 h post-lipopolysaccharide exposure in comparison to the lipopolysaccharide control group. In conclusion, this study has provided evidence to suggest that caffeinated coffee has antidepressant-like activities; however, further studies are required to fully investigate these effects.

Chronic Treatment with the IDO1 Inhibitor 1-Methyl-D-Tryptophan Minimizes the Behavioural and Biochemical Abnormalities Induced by Unpredictable Chronic Mild Stress in Mice - Comparison with Fluoxetine

We demonstrated that confronting mice to the Unpredictable Chronic Mild Stress (UCMS) procedure-a validated model of stress-induced depression-results in behavioural alterations and biochemical changes in the kynurenine pathway (KP), suspected to modify the glutamatergic neurotransmission through the imbalance between downstream metabolites such as 3-hydroxykynurenine, quinolinic and kynurenic acids. We showed that daily treatment with the IDO1 inhibitor 1-methyl-D-tryptophan partially rescues UCMS-induced KP alterations as does the antidepressant fluoxetine. More importantly we demonstrated that 1-methyl-D-tryptophan was able to alleviate most of the behavioural changes resulting from UCMS exposure. We also showed that both fluoxetine and 1-methyl-D-tryptophan robustly reduced peripheral levels of proinflammatory cytokines in UCMS mice suggesting that their therapeutic effects might occur through anti-inflammatory processes. KP inhibition might be involved in the positive effects of fluoxetine on mice behaviour and could be a relevant strategy to counteract depressive-like symptoms.

Metabolomic Changes in Serum of Children with Different Clinical Diagnoses of Malnutrition

Background: Mortality in children with severe acute malnutrition (SAM) remains high despite standardized rehabilitation protocols. Two forms of SAM are classically distinguished: kwashiorkor and marasmus. Children with kwashiorkor have nutritional edema and metabolic disturbances, including hypoalbuminemia and hepatic steatosis, whereas marasmus is characterized by severe wasting. The metabolic changes underlying these phenotypes have been poorly characterized, and whether homeostasis is achieved during hospital stay is unclear.

Objectives: We aimed to characterize metabolic differences between children with marasmus and kwashiorkor at hospital admission and after clinical stabilization and to compare them with stunted and nonstunted community controls.

Methods: We studied children aged 9–59 mo from Malawi who were hospitalized with SAM (n = 40; 21 with kwashiorkor and 19 with marasmus) or living in the community (n = 157; 78 stunted and 79 nonstunted). Serum from patients with SAM was obtained at hospital admission and 3 d after nutritional stabilization and from community controls. With the use of targeted metabolomics, 141 metabolites, including amino acids, biogenic amines, acylcarnitines, sphingomyelins, and phosphatidylcholines, were measured.

Results: At admission, most metabolites (128 of 141; 91%) were lower in children with kwashiorkor than in those with marasmus, with significant differences in several amino acids and biogenic amines, including those of the kynurenine-tryptophan pathway. Several phosphatidylcholines and some acylcarnitines also differed. Patients with SAM had profiles that were profoundly different from those of stunted and nonstunted controls, even after clinical stabilization. Amino acids and biogenic amines generally improved with nutritional rehabilitation, but most sphingomyelins and phosphatidylcholines did not.

Conclusions: Children with kwashiorkor were metabolically distinct from those with marasmus, and were more prone to severe metabolic disruptions. Children with SAM showed metabolic profiles that were profoundly different from stunted and nonstunted controls, even after clinical stabilization. Therefore, metabolic recovery in children with SAM likely extends beyond discharge, which may explain the poor long-term outcomes in these children. This trial was registered at isrctn.org as ISRCTN13916953.

Non-Invasive, Focal Disconnection of Brain Circuitry Using Magnetic Resonance-Guided Low-Intensity Focused Ultrasound to Deliver a Neurotoxin

Disturbances in the function of neuronal circuitry contribute to most neurologic disorders. As knowledge of the brain's connectome continues to improve, a more refined understanding of the role of specific circuits in pathologic states will also evolve. Tools capable of manipulating identified circuits in a targeted and restricted manner will be essential not only to expand our understanding of the functional roles of such circuits, but also to therapeutically disconnect critical pathways contributing to neurologic disease. This study took advantage of the ability of low-intensity focused ultrasound (FUS) to transiently disrupt the blood-brain barrier (BBB) to deliver a neurotoxin with poor BBB permeability (quinolinic acid [QA]) in a guided manner to a target region in the brain parenchyma. Ten male Sprague-Dawley rats were divided into two groups receiving the following treatments: (i) magnetic resonance-guided FUS + microbubbles + saline (n = 5), or (ii) magnetic resonance-guided FUS + microbubbles + QA (n = 5). Systemic administration of QA was well tolerated. However, when QA and microbubbles were systemically administered in conjunction with magnetic resonance-guided FUS, the BBB was disrupted and primary neurons were destroyed in the targeted subregion of the hippocampus in all QA-treated animals. Administration of vehicle (saline) together with microbubbles and FUS also disrupted the BBB but did not produce neuronal injury. These findings indicate the feasibility of non-invasively destroying a targeted region of the brain parenchyma using low-intensity FUS together with systemic administration of microbubbles and a neurotoxin. This approach could be of therapeutic value in various disorders in which disturbances of neural circuitry contribute to neurologic disease.

The role of macrophage polarization on bipolar disorder: Identifying new therapeutic targets

OBJECTIVE

Bipolar disorder is a chronic, severe and disabling disease; however, its pathophysiology remains poorly understood. Recent evidence has suggested that inflammation and immune dysregulation play a significant role in the pathophysiology of bipolar disorder. This review is aimed to highlight the importance of systemic inflammation in modulating the inflammatory response of microglia and hence its potential involvement with bipolar disorder. We also discuss novel therapeutic strategies that emerge from this new research.

METHOD

This article presents a theoretical synthesis of the effects of systemic inflammation on the immune response of the central nervous system in bipolar disorder. The complex relationship between stress, pro-inflammatory cytokines and microglial dysfunction is summarized, emphasizing the role of the kynurenine pathway in this process and, consequently, their effects on neuronal plasticity.

RESULTS

Bipolar patients demonstrate increased serum levels of pro-inflammatory cytokines (interleukin-1β, interleukin-6 and tumor necrosis factor-α) and lower hypothalamic-pituitary-adrenal axis sensitivity. This imbalance in the immune system promotes a change in blood-brain barrier permeability, leading to an inflammatory signal spread in the central nervous system from the periphery, through macrophages activation (M1 polarization). Chronic microglial activation can result in neuronal apoptosis, neurogenesis inhibition, hippocampal volume reduction, lower neurotransmitters synthesis and cytotoxicity, by increasing glutamate production and kynurenine metabolism.

CONCLUSIONS

This review provides an overview of the mechanisms involved in the immune system imbalance and its potential involvement in the pathophysiology of bipolar disorder. Consequently, new strategies that normalize the immune-inflammatory pathways may provide a valuable therapeutic target for the treatment of these disorders.

Perturbational Profiling of Metabolites in Patient Fibroblasts Implicates α-Aminoadipate as a Potential Biomarker for Bipolar Disorder

Many studies suggest the presence of aberrations in cellular metabolism in bipolar disorder. We studied the metabolome in bipolar disorder to gain insight into cellular pathways that may be dysregulated in bipolar disorder and to discover evidence of novel biomarkers. We measured polar and nonpolar metabolites in fibroblasts from subjects with bipolar I disorder and matched healthy control subjects, under normal conditions and with two physiologic perturbations: low-glucose media and exposure to the stress-mediating hormone dexamethasone. Metabolites that were significantly different between bipolar and control subjects showed distinct separation by principal components analysis methods. The most statistically significant findings were observed in the perturbation experiments. The metabolite with the lowest p value in both the low-glucose and dexamethasone experiments was α-aminoadipate, whose intracellular level was consistently lower in bipolar subjects. Our study implicates α-aminoadipate as a possible biomarker in bipolar disorder that manifests under cellular stress. This is an intriguing finding given the known role of α-aminoadipate in the modulation of kynurenic acid in the brain, especially as abnormal kynurenic acid levels have been implicated in bipolar disorder.

Shared Immune and Repair Markers During Experimental Toxoplasma Chronic Brain Infection and Schizophrenia

Chronic neurologic infection with Toxoplasma gondii is relatively common in humans and is one of the strongest known risk factors for schizophrenia. Nevertheless, the exact neuropathological mechanisms linking T gondii infection and schizophrenia remain unclear. Here we utilize a mouse model of chronic T gondii infection to identify protein biomarkers that are altered in serum and brain samples at 2 time points during chronic infection. Furthermore, we compare the identified biomarkers to those differing between "postmortem" brain samples from 35 schizophrenia patients and 33 healthy controls. Our findings suggest that T gondii infection causes substantial and widespread immune activation indicative of neural damage and reactive tissue repair in the animal model that partly overlaps with changes observed in the brains of schizophrenia patients. The overlapping changes include increases in C-reactive protein (CRP), interleukin-1 beta (IL-1β), interferon gamma (IFNγ), plasminogen activator inhibitor 1 (PAI-1), tissue inhibitor of metalloproteinases 1 (TIMP-1), and vascular cell adhesion molecule 1 (VCAM-1). Potential roles of these factors in the pathogenesis of schizophrenia and toxoplasmosis are discussed. Identifying a defined set of markers shared within the pathophysiological landscape of these diseases could be a key step towards understanding their specific contributions to pathogenesis.

Multiprobe molecular imaging of an NMDA receptor hypofunction rat model for glutamatergic dysfunction

There are many indications of a connection between abnormal glutamate transmission through N-methyl-d-aspartate (NMDA) receptor hypofunction and the occurrence of schizophrenia. The importance of metabotropic glutamate receptor subtype 5 (mGluR5) became generally recognized due to its physical link through anchor proteins with NMDAR. Neuroinflammation as well as the kynurenine (tryptophan catabolite; TRYCAT) pathway are equally considered as major contributors to the pathology. We aimed to investigate this interplay between glutamate release, neuronal activation and inflammatory markers, by using small-animal positron emission tomography (PET) in a rat model known to induce schizophrenia-like symptoms. Daily intraperitoneal injection of MK801 or saline were administered to induce the model together with N-Acetyl-cysteine (NAc) or saline as the treatment in 24 male Sprague Dawley rats for one month. Biweekly in vivo [(11)C]-ABP688 microPET was performed together with mGluR5 immunohistochemistry. Simultaneously, weekly in vivo [(18)F]-FDG microPET imaging data for glucose metabolism was acquired and microglial activation was investigated with biweekly in vivo [(18)F]-PBR111 scans versus OX42 immunohistochemistry. Finally, plasma samples were analyzed for TRYCAT metabolites. We show that chronic MK801 administration (and thus elevated endogenous glutamate) causes significant tissue loss in rat brain, enhances neuroinflammatory pathways and may upregulate mGluR5 expression.

Maternal separation induces neuroinflammation and long-lasting emotional alterations in mice

Early life experiences play a key role in brain function and behaviour. Adverse events during childhood are therefore a risk factor for psychiatric disease during adulthood, such as mood disorders. Maternal separation is a validated mouse model for maternal neglect, producing negative early life experiences that result in subsequent emotional alteration. Mood disorders have been found to be associated with neurochemical changes and neurotransmitter deficits such as reduced availability of monoamines in discrete brain areas. Emotional alterations like depression result in reduced serotonin availability and enhanced kynurenine metabolism through the action of indoleamine 2, 3-dioxygenase in response to neuroinflammatory factors. This mechanism involves regulation of the neurotransmitter system by neuroinflammatory agents, linking mood regulation to neuroinmunological reactions. In this context, the aim of this study was to investigate the effects of maternal separation with early weaning on emotional behaviour in mice. We investigated neuroinflammatory responses and the state of the tryptophan-kynurenine metabolic pathway in discrete brain areas following maternal separation. We show that adverse events during early life increase risk of long-lasting emotional alterations during adolescence and adulthood. These emotional alterations are particularly severe in females. Behavioural impairments were associated with microglia activation and disturbed tryptophan-kynurenine metabolism in brain areas related to emotional control. This finding supports the preeminent role of neuroinflammation in emotional disorders.

Bipolar Disorder: Role of Inflammation and the Development of Disease Biomarkers

Bipolar disorder is a severe and enduring psychiatric condition which in many cases starts during early adulthood and follows a relapsing and remitting course throughout life. In many patients the disease follows a progressive path with brief periods of inter-episode recovery, sub-threshold symptoms, treatment resistance and increasing functional impairment in the biopsychosocial domains. Knowledge about the neurobiology of bipolar disorder is increasing steadily and evidence from several lines of research implicates immuno-inflammatory mechanisms in the brain and periphery in the etiopathogenesis of this illness and its comorbidities. The main findings are an increase in the levels of proinflammatory cytokines during acute episodes with a decrease in neurotrophic support. Related to these factors are glial cell dysfunction, neuro-endocrine abnormalities and neurotransmitter aberrations which together cause plastic changes in the mood regulating areas of the brain and neuroprogression of the bipolar diathesis. Research in the above mentioned areas is providing an opportunity to discover novel biomarkers for the disease and the field is reaching a point where major breakthroughs can be expected in the not too distant future. It is hoped that with new discoveries fresh avenues will be found to better treat an otherwise recalcitrant disease.

The Neurobiology of Bipolar Disorder: An Integrated Approach

Bipolar disorder is a heterogeneous condition with myriad clinical manifestations and many comorbidities leading to severe disabilities in the biopsychosocial realm. The objective of this review article was to underline recent advances in knowledge regarding the neurobiology of bipolar disorder. A further aim was to draw attention to new therapeutic targets in the treatment of bipolar disorder. To accomplish these goals, an electronic search was undertaken of the PubMed database in August 2015 of literature published during the last 10 years on the pathophysiology of bipolar disorder. A wide-ranging evaluation of the existing work was done with search terms such as "mood disorders and biology," "bipolar disorder and HPA axis," "bipolar disorder and cytokines," "mood disorders and circadian rhythm," "bipolar disorder and oxidative stress," etc. This endeavor showed that bipolar disorder is a diverse condition sharing neurobiological mechanisms with major depressive disorder and psychotic spectrum disorders. There is convincing evidence of crosstalk between different biological systems that act in a deleterious manner causing expression of the disease in genetically predisposed individuals. Inflammatory mediators act in concert with oxidative stress to dysregulate hormonal, metabolic, and circadian homeostasis in precipitating and perpetuating the illness. Stress, whether biologically or psychologically mediated, is responsible for the initiation and progression of the diathesis. Bipolar spectrum disorders have a strong genetic component; severe life stresses acting through various paths cause the illness phenotype.

Acute Psychological Stress Modulates the Expression of Enzymes Involved in the Kynurenine Pathway throughout Corticolimbic Circuits in Adult Male Rats

Tryptophan is an essential dietary amino acid that is necessary for protein synthesis, but also serves as the precursor for serotonin. However, in addition to these biological functions, tryptophan also serves as a precursor for the kynurenine pathway, which has neurotoxic (quinolinic acid) and neuroprotective (kynurenic acid) metabolites. Glucocorticoid hormones and inflammatory mediators, both of which are increased by stress, have been shown to bias tryptophan along the kynurenine pathway and away from serotonin synthesis; however, to date, there is no published data regarding the effects of stress on enzymes regulating the kynurenine pathway in a regional manner throughout the brain. Herein, we examined the effects of an acute psychological stress (120 min restraint) on gene expression patterns of enzymes along the kynurenine pathway over a protracted time-course (1–24 h post-stress termination) within the amygdala, hippocampus, hypothalamus, and medial prefrontal cortex. Time-dependent changes in differential enzymes along the kynurenine metabolism pathway, particularly those involved in the production of quinolinic acid, were found within the amygdala, hypothalamus, and medial prefrontal cortex, with no changes seen in the hippocampus. These regional differences acutely may provide mechanistic insight into processes that become dysregulated chronically in stress-associated disorders.

Quinolinic acid-immunoreactivity in the naïve mouse brain

Quinolinic acid (QUIN) has been suggested to be involved in infections, inflammatory neurological disorders and in the development of psychiatric disorders. In this view, several studies have been performed to investigate QUIN localization in the brain and its neurotoxic effects. However, evidence is lacking regarding QUIN in healthy, control conditions. The aim of this study was to investigate the region-specific distribution and pattern of QUIN expression in the naïve mouse brain. In addition, possible sex differences in QUIN-immunoreactivity and its link with affect-related behavioural observations were assessed. For this purpose, naïve mice were subjected to the forced swim test (FST) and 20 min open field (OF) testing to measure affect-related behaviour. Afterwards, brains were assessed for QUIN-immunoreactivity. QUIN-immunoreactivity was particularly observed in the cingulate cortex (CC), highlighting clearly delineated cells, and the thalamic reticular nucleus (TRN), showing a more diffuse staining pattern. Subsequently, QUIN-positive cells in the CC were counted, while QUIN-immunoreactivity in the TRN was examined using gray value measurements. No significant differences between sexes were observed for the number of QUIN-positive cells in the CC, neither in levels of QUIN-immunoreactivity in the TRN. A direct correlation was found between QUIN-positive cells in the CC and QUIN-immunoreactivity in the TRN. Moreover, in male mice, a very strong correlation (rsp=.943; p<.01) between QUIN-immunoreactivity at the level of the TRN and motor activity in the OF was observed. Thus, our results suggest that QUIN - detected in the CC and the TRN - may play a role in regulating motor activity in normal conditions.

Levels in neurotransmitter precursor amino acids correlate with mental health in patients with breast cancer

Breast cancer is the most common cancer among females. Approximately 30% of cancer patients develop depression or depressive adaptation disorder within 5 years post diagnosis. Low grade inflammation and subsequent changes in neurotransmitter levels could be the pathophysiological link. In the current study we investigated the association of neurotransmitter precursor amino acids with a diagnosis of depression or state anxiety in 154 subjects suffering from breast cancer (BCA(+)), depression (DPR(+)), both or neither. Sociodemographic parameters, severity of depressive symptoms, and state anxiety (ANX) were recorded. Neopterin, kynurenine/tryptophan and phenylalanine/tyrosine were analysed by HPLC or ELISA. Significantly higher serum neopterin values were found in DPR(+) patients (p = 0.034) and in ANX(+) subjects (p = 0.008), as a marker of Th1-related inflammation. The phenylalanine/tyrosine ratio (index of the catecholamine pathway) was associated with the factors "breast cancer" and "depression" and their interaction (all p < 0.001); it was highest in the DPR(+)BCA(+) group. The kynurenine/tryptophan ratio (index of the serotonin pathway) was significantly associated with the factors "breast cancer" and "state anxiety" and their interaction (p < 0.001, p = 0.026, p = 0.02, respectively); it was highest in the ANX(+)BCA(+) group. In BCA(+) patients kynurenine/tryptophan ratios correlated with severity of state anxiety (r = 0.226, p = 0.048, uncorrected) and phenylalanine/tyrosine ratios with severity of depressive symptoms (r = 0.376, p < 0.05, corrected). In conclusion, levels of neurotransmitter precursor amino acids correlate with mental health, an effect which was much more pronounced in BCA(+) patients than in BCA(-) subjects. Aside from identifying underlying pathophysiological mechanisms, these results could be the basis for future treatment studies: in BCA(+) patients with depression the use of serotonin-noradrenaline reuptake inhibitors might be recommended while in those with predominant anxiety selective serotonin reuptake inhibitors might be the treatment of choice.

Kynurenine pathway dysfunction in the pathophysiology and treatment of depression: Evidences from animal and human studies

Treatment-resistant depression affects up to 20% of individuals suffering from major depressive disorder (MDD). The medications currently available to treat depression, including serotonin re-uptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs) and tricyclic antidepressants (TCAs), fail to produce adequate remission of depressive symptoms for a large number of patients. The monoamine hypothesis upon which these medications are predicated should be expanded and revised as research elucidates alternative mechanisms of depression and effective methods to treat the underlying pathologic consequences. Research into the role of tryptophan degradation and the kynurenine pathway in the setting of inflammation has brought new insight into potential etiologies of MDD. Further investigation into the connection between inflammatory mediators, tryptophan degradation, and MDD can provide many targets for novel antidepressant therapies. Thus, this review will highlight the role of the kynurenine pathway in the pathophysiology of depression, as well as a novel therapeutic target to classic and new modulators to treat depression based on findings from preclinical and clinical studies.

The transcription factor nuclear factor interleukin 6 mediates pro- and anti-inflammatory responses during LPS-induced systemic inflammation in mice

The transcription factor nuclear factor interleukin 6 (NF-IL6) plays a pivotal role in neuroinflammation and, as we previously suggested, hypothalamus-pituitary-adrenal-axis-activation. Here, we investigated its contribution to immune-to-brain communication and brain controlled sickness symptoms during lipopolysaccharide (LPS)-induced (50 or 2500 μg/kg i.p.) systemic inflammation in NF-IL6-deficient (KO) or wildtype mice (WT). In WT LPS induced a dose-dependent febrile response and reduction of locomotor activity. While KO developed a normal fever after low-dose LPS-injection the febrile response was almost abolished 3-7 h after a high LPS-dose. High-dose LPS-stimulation was accompanied by decreased (8 h) followed by enhanced (24 h) inflammation in KO compared to WT e.g. hypothalamic mRNA-expression including microsomal prostaglandin E synthase, inducible nitric oxide synthase and further inflammatory mediators, neutrophil recruitment to the brain as well as plasma levels of inflammatory markers such as IL-6 and IL-10. Interestingly, KO showed reduced locomotor activity even under basal conditions, but enhanced locomotor activity to novel environment stress. Hypothalamic-pituitary-adrenal-axis-activity of KO was intact, but tryptophan-metabolizing enzymes were shifted to enhanced serotonin production and reuptake. Overall, we showed for the first time that NF-IL6 plays a dual role for sickness response and immune-to-brain communication: acting pro-inflammatory at 8h but anti-inflammatory at 24 h after onset of the inflammatory response reflecting active natural programming of inflammation. Moreover, reduced locomotor activity observed in KO might be due to altered tryptophan metabolism and serotonin reuptake suggesting some role for NF-IL6 as therapeutic target for depressive disorders.

The impact of electroconvulsive therapy on the tryptophan-kynurenine metabolic pathway

BACKGROUND

There is still limited knowledge about the mechanism of action of electroconvulsive therapy (ECT) in the treatment of depression. Substantial evidence suggests a role for the immune-moderated tryptophan (TRP)-kynurenine (KYN) pathway in depression; i.e. a depression-associated disturbance in the balance between the TRP-KYN metabolites towards a neurotoxic process. We, therefore, aimed to investigate the impact of ECT treatment on the TRP-KYN pathway, in association with ECT-related alterations in depressive symptoms.

METHOD

Twenty-three patients with unipolar or bipolar depression, treated with bilateral ECT twice a week were recruited. Blood serum samples, and depression scores using the Hamilton Depression Rating Scale-17 items (HDRS) as well as the Beck Depression Inventory (BDI) were collected repeatedly during the period of ECT and until 6 weeks after the last ECT session. TRP and KYN metabolites were analyzed in serum using the High Performance Liquid Chromatography. Four patients could not complete the study; thereby yielding data of 19 patients. Analyses were performed using multilevel linear regression analysis.

RESULTS

There was an increase in kynurenic acid (KYNA) (B=0.04, p=0.001), KYN/TRP ratio (B=0.14, p=0.001), KYNA/KYN ratio (B=0.07, p<0.0001), and KYNA/3-hydroxykynurenine ratio (B=0.01, p=0.008) over time during the study period. KYN (B=-0.02, p=0.003) and KYN/TRP (B=-0.19, p=0.003) were negatively associated with total HDRS over time. Baseline TRP metabolite concentrations did not predict time to ECT response.

CONCLUSION

Our findings show that ECT influences the TRP-KYN pathway, with a shift in TRP-KYN metabolites balance towards molecules with neuroprotective properties correlating with antidepressant effects of ECT; thereby providing a first line of evidence that the mechanism of action of ECT is (co)mediated by the TRP-KYN pathway.

Role of indoleamine 2,3-dioxygenase in health and disease

IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1’s catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.

Does escitalopram reduce neurotoxicity in major depression?

A pro-inflammatory state and a dysregulation in the tryptophan/kynurenine pathway have been documented in depression. This study examined whether treatment with the SSRI, escitalopram (ESC), could suppress inflammation and favorably shift metabolites of the kynurenine pathway in patients with major depressive disorder (MDD) within the utilized treatment period. Twenty seven healthy control subjects were included for comparison. Thirty patients were enrolled after completing baseline assessments. They received a 12-week ESC monotherapy. Twenty subjects were completers. Clinical assessments were carried out at each visit using the HAM-D, HAM-A, CGI and BDI rating scales. Blood samples were collected at each assessment and stored until analyzed. Cytokines were analyzed with Randox multiplex assay and tryptophan and kynurenine metabolites were analyzed using HPLC/GCMS. Baseline plasma concentrations of hsCRP, TNFα, IL6 and MCP-1 were significantly higher in patients compared to healthy controls. IL10 trended toward an increase. Baseline plasma IL1β correlated significantly with IL1α, and IL4. Patients showed significant improvement in all outcome measures with a high remission rate. Significant correlations were obtained between specific symptoms and certain biomarkers at baseline but these correlations must be viewed as very preliminary. During ESC treatment concentrations of inflammatory biomarkers did not change except for TNFα that trended lower. Metabolites and ratios of the tryptophan/kynurenine pathway showed reductions of the neurotoxic metabolites, 3-hydroxykynurenine and quinolinic acid, 3-hydroxykynurenine/kynurenine, quinolinic acid/tryptophan, kynurenic acid/quinolinic acid and quinolinic acid/3-hydroxykynurenine. The results indicate that ESC may exert its antidepressant effect in part through inhibition of synthesis of certain neurotoxic kynurenine metabolites and possibly also through reduction of the inflammatory response, although there was no concordance in the time course of changes between antidepressant efficacy and reversal of the pro-inflammatory status.

Coordinated messenger RNA/microRNA changes in fibroblasts of patients with major depression

BACKGROUND

Peripheral biomarkers for major psychiatric disorders have been an elusive target for the last half a century. Dermal fibroblasts are a simple, relevant, and much underutilized model for studying molecular processes of patients with affective disorders, as they share considerable similarity of signal transduction with neuronal tissue.

METHODS

Cultured dermal fibroblast samples from patients with major depressive disorder (MDD) and matched control subjects (n = 16 pairs, 32 samples) were assayed for genome-wide messenger RNA (mRNA) expression using microarrays. In addition, a simultaneous quantitative polymerase chain reaction-based assessment of >1000 microRNA (miRNA) species was performed. Finally, to test the relationship between the mRNA-miRNA expression changes, the two datasets were correlated with each other.

RESULTS

Our data revealed that MDD fibroblasts, when compared with matched control subjects, showed a strong mRNA gene expression pattern change in multiple molecular pathways, including cell-to-cell communication, innate/adaptive immunity, and cell proliferation. Furthermore, the same patient fibroblasts showed altered expression of a distinct panel of 38 miRNAs, which putatively targeted many of the differentially expressed mRNAs. The miRNA-mRNA expression changes appeared to be functionally connected, as the majority of the miRNA and mRNA changes were in the opposite direction.

CONCLUSIONS

Our data suggest that combined miRNA-mRNA assessments are informative about the disease process and that analyses of dermal fibroblasts might lead to the discovery of promising peripheral biomarkers of MDD that could be potentially used to aid the diagnosis and allow mechanistic testing of disturbed molecular pathways.

A randomised double-blind placebo-controlled 12- week feasibility trial of methotrexate added to treatment as usual in early schizophrenia: study protocol for a randomised controlled trial

Background

Methotrexate is a commonly used anti-inflammatory and immunosuppressive drug. There is growing evidence that inflammatory processes are involved in the pathogenesis of schizophrenia. In our recent randomised double-blind placebo-controlled clinical trial in Pakistan and Brazil, the addition of minocycline (antibiotic and anti-inflammatory drug) for 1 year to treatment as usual reduced negative symptoms and improved some cognitive measures. A meta-analysis of cytokine changes in the peripheral blood has identified IL-2, IFN-gamma, TNF-alpha and soluble IL-2 receptor as trait markers of schizophrenia because their levels were elevated during acute exacerbations and reduced in remission. This suggests immune activation and an inflammatory syndrome in schizophrenia. Based on the evidence of the strong anti-inflammatory properties of methotrexate, we propose that low-dose methotrexate may be an effective therapy in early schizophrenia.

Methods/Design

This is a double-blind placebo-controlled study of methotrexate added to treatment as usual for patients suffering from schizophrenia, schizoaffective disorder, psychosis not otherwise specified or schizophreniform disorder. This will be with 72 patients, 36 in each arm over 3 months. There will be screening, randomisation and follow-up visits. Full clinical assessments will be carried out at baseline, 2, 4, 8 and 12 weeks. Social and cognitive assessments will be carried out at baseline and 12 weeks. Methotrexate will be given at a dose of 10 mgs orally once a week for a 3-month period.

Discussion

Evidence suggests inflammatory processes are involved in the pathogenesis of schizophrenia and anti-inflammatory treatments have shown to have some beneficial effects. Methotrexate is a known immunosuppressant and anti-inflammatory drug. The aim of this study is to establish the degree of improvement in positive and negative symptoms, as well as cognitive functioning with the addition of methotrexate to treatment as usual.

ClinicalTrials.gov identifier: NCT02074319 (24 February 2014).

Enantiomeric Separation of Monosubstituted Tryptophan Derivatives and Metabolites by HPLC with a Cinchona Alkaloid-Based Zwitterionic Chiral Stationary Phase and Its Application to the Evaluation of the Optical Purity of Synthesized 6-Chloro-l-Tryptophan

6-Chlorotryptophan possesses unique bioactivity and can be used as a precursor for several bioactive compounds in medicinal chemistry. It was enantioselectively synthesized by condensing 6-chloroindole with racemic N-acetylserine, followed by enzymatic hydrolysis with l-aminoacylase (EC 3.5.1.14). The optical purity was examined by conducting high-performance liquid chromatography with a Cinchona alkaloid-based zwitterionic chiral stationary phase (CSP) [CHIRALPAK^® ZWIX(+)], which bears a chiral trans-2-aminocyclohexanesulfonic acid moiety tagged at C-9 of the Cinchona alka-loid. The zwitterionic CSP enabled efficient enantiomeric separations of monosubstituted tryptophan derivatives 1-methyltryptophan, 5-methyltryptophan, 6-methyltryptophan, 5-methoxytryptophan, and 6-chlorotryptophan with a methanol/H₂O (98/2) mobile phase containing formic acid (FA) and diethylamine (DEA) additives. The mobile phase contains 25–75 mM FA and 20–50 mM DEA, enabling good separation of the enantiomers of each tryptophan derivative (α > 1.25). Thus, the optical purity of the synthesized 6-chloro-l-tryptophan was easily determined (greater than 99.0%) using HPLC with the zwitterionic CSP.

Etiological classification of depression based on the enzymes of tryptophan metabolism

BACKGROUND

Viewed in terms of input and output, the mechanisms of depression are still akin to a black box. However, there must be main pivots for diverse types of depression. From recent therapeutic observations, both the serotonin (5-HT) and kynurenine pathways of tryptophan metabolism may be of particular importance to improved understanding of depression. Here, I propose an etiological classification of depression, based on key peripheral and central enzymes of tryptophan metabolism.

DISCUSSION

Endogenous depression is caused by a larger genetic component than reactive depression. Besides enterochromaffin and mast cells, tryptophan hydroxylase 1 (TPH1), primarily expressed in the gastrointestinal tract, is also found in 5-hydroxytryptophan-producing cells (5-HTP cells) in normal intestinal enterocytes, which are thought to essentially shunt 5-HT production in 5-HT-producing cells. Genetic studies have reported an association between TPH1 and depression, or the responsiveness of depression to antidepressive medication. Therefore, it is possible that hypofunctional 5-HTP cells (reflecting TPH1 dysfunction) in the periphery lead to deficient brain 5-HT levels. Additionally,it has been reported that higher TPH2 expression in depressed suicides may reflect a homeostatic response to deficient 5-HT levels. Subsequently, endogenous depression may be caused by TPH1 dysfunction combined with compensatory TPH2 activation. Reactive depression results from life stresses and involves the hypothalamic-pituitary-adrenal axis, with resulting cortisol production inducing tryptophan 2,3-dioxygenase (TDO) activation. In secondary depression, caused by inflammation, infection, or oxidative stress, indoleamine 2,3-dioxygenase (IDO) is activated. In both reactive and secondary depression, the balance between 3-hydroxykynurenine (3-HK) and kynurenic acid may shift towards 3-HK production via kynurenine-3-monooxygenase (KMO) activation. By shifting the equilibrium position of key enzymes of tryptophan metabolism, the classical classification of depression can be reorganized, as below. Peripheral classification of depression by key enzymes: TPH1 dysfunction, TDO activation, IDO activation. Central classification: TPH2 activation, KMO activation.

SUMMARY

Etiological classification of depression expressed by peripheral (TPH1, TDO, IDO) and central (TPH2, KMO)enzymes of tryptophan metabolism may enable depression to be viewed as a clear box, with the inner components available for inspection and treatment.

The impact of microbiota on brain and behavior: mechanisms & therapeutic potential

There is increasing evidence that host-microbe interactions play a key role in maintaining homeostasis. Alterations in gut microbial composition is associated with marked changes in behaviors relevant to mood, pain and cognition, establishing the critical importance of the bi-directional pathway of communication between the microbiota and the brain in health and disease. Dysfunction of the microbiome-brain-gut axis has been implicated in stress-related disorders such as depression, anxiety and irritable bowel syndrome and neurodevelopmental disorders such as autism. Bacterial colonization of the gut is central to postnatal development and maturation of key systems that have the capacity to influence central nervous system (CNS) programming and signaling, including the immune and endocrine systems. Moreover, there is now expanding evidence for the view that enteric microbiota plays a role in early programming and later response to acute and chronic stress. This view is supported by studies in germ-free mice and in animals exposed to pathogenic bacterial infections, probiotic agents or antibiotics. Although communication between gut microbiota and the CNS are not fully elucidated, neural, hormonal, immune and metabolic pathways have been suggested. Thus, the concept of a microbiome-brain-gut axis is emerging, suggesting microbiota-modulating strategies may be a tractable therapeutic approach for developing novel treatments for CNS disorders.

Metabolic consequences of interleukin-6 challenge in developing neurons and astroglia

Background

Maternal immune activation and subsequent interleukin-6 (IL-6) induction disrupt normal brain development and predispose the offspring to developing autism and schizophrenia. While several proteins have been identified as having some link to these developmental disorders, their prevalence is still small and their causative role, if any, is not well understood. However, understanding the metabolic consequences of environmental predisposing factors could shed light on disorders such as autism and schizophrenia.

Methods

To gain a better understanding of the metabolic consequences of IL-6 exposure on developing central nervous system (CNS) cells, we separately exposed developing neuron and astroglia cultures to IL-6 for 2 hours while collecting effluent from our gravity-fed microfluidic chambers. By coupling microfluidic technologies to ultra-performance liquid chromatography-ion mobility-mass spectrometry (UPLC-IM-MS), we were able to characterize the metabolic response of these CNS cells to a narrow window of IL-6 exposure.

Results

Our results revealed that 1) the use of this technology, due to its superb media volume:cell volume ratio, is ideally suited for analysis of cell-type-specific exometabolome signatures; 2) developing neurons have low secretory activity at baseline, while astroglia show strong metabolic activity; 3) both neurons and astroglia respond to IL-6 exposure in a cell type-specific fashion; 4) the astroglial response to IL-6 stimulation is predominantly characterized by increased levels of metabolites, while neurons mostly depress their metabolic activity; and 5) disturbances in glycerophospholipid metabolism and tryptophan/kynurenine metabolite secretion are two putative mechanisms by which IL-6 affects the developing nervous system.

Conclusions

Our findings are potentially critical for understanding the mechanism by which IL-6 disrupts brain function, and they provide information about the molecular cascade that links maternal immune activation to developmental brain disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0183-6) contains supplementary material, which is available to authorized users.

Reduced microglial immunoreactivity for endogenous NMDA receptor agonist quinolinic acid in the hippocampus of schizophrenia patients

Postmortem and positron emission tomography studies have indicated the pathophysiological involvement of microglial cells in schizophrenia. We hypothesized that the microglial production of quinolinic acid (QUIN), an endogenous N-methyl-d-aspartate receptor (NMDAR) agonist, may be linked to the previously described glutamatergic deficits in the hippocampus of schizophrenia patients. We performed a semi-quantitative assessment of QUIN-immunoreactive microglial cells in schizophrenia patients and matched controls in the CA1, CA2/3, and dentate gyrus (DG) area of the posterior hippocampal formation. Complementary immunostaining of the commonly used microglial surface marker HLA-DR was performed in adjacent histological sections. Fewer QUIN-immunoreactive microglial cells were observed in the CA1 hippocampal subregion of schizophrenia patients compared to controls (left p=0.028, right p=0.018). No significant diagnosis-dependent changes were observed in the CA2/3 and DG regions. These results were controlled for potential confounds by age, duration of disease, autolysis time, psychotropic medication, and hippocampal volume. No diagnosis-related differences were observed for the overall density of microglial cells (HLA-DR expression). Our findings suggest that reduced microglial QUIN content in the hippocampal CA1 region is associated with schizophrenia. We hypothesize that this association may contribute to impaired glutamatergic neurotransmission in the hippocampus of schizophrenia patients.

Quantitative analyses of schizophrenia-associated metabolites in serum: serum D-lactate levels are negatively correlated with gamma-glutamylcysteine in medicated schizophrenia patients

The serum levels of several metabolites are significantly altered in schizophrenia patients. In this study, we performed a targeted analysis of 34 candidate metabolites in schizophrenia patients (n = 25) and compared them with those in age- and gender-matched healthy subjects (n = 27). Orthogonal partial least square-discriminant analysis revealed that complete separation between controls and patients was achieved based on these metabolites. We found that the levels of γ-glutamylcysteine (γ-GluCys), linoleic acid, arachidonic acid, D-serine, 3-hydroxybutyrate, glutathione (GSH), 5-hydroxytryptamine, threonine, and tyrosine were significantly lower, while D-lactate, tryptophan, kynurenine, and glutamate levels were significantly higher in schizophrenia patients compared to controls. Using receiver operating characteristics (ROC) curve analysis, the sensitivity, specificity, and the area under curve of γ-GluCys, a precursor of GSH, and D-lactate, a terminal metabolite of methylglyoxal, were 88.00%, 81.48%, and 0.8874, and 88.00%, 77.78%, and 0.8415, respectively. In addition, serum levels of D-lactate were negatively correlated with γ-GluCys levels in patients, but not in controls. The present results suggest that oxidative stress-induced damage may be involved in the pathogenesis of schizophrenia.

Melanoma tumors alter proinflammatory cytokine production and monoamine brain function, and induce depressive-like behavior in male mice

Depression is a commonly observed disorder among cancer patients; however, the mechanisms underlying the relationship between these disorders are not well known. We used an animal model to study the effects of tumor development on depressive-like behavior manifestation, proinflammatory cytokine expression, and central monoaminergic activity. Male OF1 mice were inoculated with B16F10 melanoma tumor cells and subjected to a 21-day behavioral evaluation comprising the novel palatable food (NPF) test and tail suspension test (TST). The mRNA expression levels of proinflammatory cytokines, interleukin (IL)-1β and IL-6, and tumor necrosis factor-alpha (TNF-α), were measured in the hypothalamus and hippocampus and the levels of IL-6 and TNF-α were measured in the blood plasma. We similarly determined the monoamine turnover in various brain areas. The tumors resulted in increasing the immobility in TST and the expression level of IL-6 in the hippocampus. These increases corresponded with a decrease in dopaminergic activity in the striatum and a decrease in serotonin turnover in the prefrontal cortex. Similarly, a high level of tumor development produced increases in the brain expression levels of IL-6 and TNF-α and plasma levels of IL-6. Our findings suggest that these alterations in inflammatory cytokines and monoaminergic system function might be responsible for the manifestation of depressive-like behaviors in tumor-bearing mice.

The immune system and electroconvulsive therapy for depression

BACKGROUND

Electroconvulsive therapy (ECT) remains the most effective and fast-acting treatment option for several psychiatric conditions, including treatment-resistant depression. Although ECT has been in use for 75 years, the mechanism of action is unknown. There is emerging evidence that modulation of the hypothalamic-pituitary-adrenal axis may mediate, in part, the therapeutic action of ECT. A growing body of evidence points to links between disturbances in the immune system and depression. However, the impact of ECT on immune functioning and the possible role of alterations in the immune system as a mechanism of action of ECT remain elusive.

OBJECTIVES

To provide a literature overview on the effects of ECT on the immune system.

METHODS

Relevant articles and abstracts in English were retrieved from PubMed/Medline using search terms related to ECT, inflammation, and immune system. The results of studies examining ECT-induced changes in immune functioning as well as the degree to which these represent possible mechanisms mediating the therapeutic action of ECT were summarized.

RESULTS

Our search identified only a limited number of studies. The findings suggest that a single session of ECT induces an acute, transient immune activation, whereas repetitive ECT treatment results in long-term down-regulation of immune activation. However, inconsistency in findings and methodological issues, including sample size and lack of consideration of confounding factors affecting cytokine concentrations, precludes definitive conclusion.

CONCLUSIONS

To elucidate the possible role of immunological changes mediating the effect of ECT, more prospective controlled studies with larger sample sizes are required.

Tryptophan breakdown is increased in euthymic overweight individuals with bipolar disorder: a preliminary report

OBJECTIVES

Individuals with bipolar disorder (BD) are disproportionately affected by symptoms of being overweight and metabolic syndrome when compared to the general population. The pertinence of this observation is underscored by observations that excess weight is associated with a more complex illness presentation, course, and outcome in BD. We present the first preliminary report of our BIPFAT study, which explored shared hypothesized pathophysiological pathways between being overweight and having BD.

METHODS

We investigated the tryptophan-kynurenine metabolism pathway as a proxy of dysregulated inflammatory homeostasis in euthymic, overweight individuals with BD (n = 78) compared to healthy controls (n = 156).

RESULTS

Both blood kynurenine concentrations and the kynurenine to tryptophan ratio [(Kyn:Trp); an estimate of tryptophan breakdown] were significantly higher in the total sample of euthymic patients with BD, with greater increases noted in both parameters in the subsample of overweight patients with BD. When compared to controls, peripheral neopterin concentrations were significantly lower. Within the BD group, there were also significant between-group differences in neopterin concentrations, with higher levels in those who were overweight and in subjects with BD in the later stages of illness compared to earlier stages.

CONCLUSIONS

Increased tryptophan breakdown, as well as neopterin levels in BD, may be an indirect mediator of immune-mediated inflammation. In BD, this may account for the high prevalence of medical comorbidities and increased mortality. The observation of increased kynurenine levels and Kyn:Trp, and altered circulating neopterin levels provides indirect evidence of increased activity of tryptophan-degrading indoleamine 2,3-dioxygenase in euthymic individuals with BD, underscoring the role of inflammatory mediators as a causative and/or consequent factor. More robust abnormalities in the overweight subsample underscore the additional inflammatory burden of medical comorbidity and suggest a shared pathophysiology as well as a mechanism mediating BD and cardiovascular disease.

Activation of brain indoleamine 2,3-dioxygenase contributes to epilepsy-associated depressive-like behavior in rats with chronic temporal lobe epilepsy

BACKGROUND

Depression has most often been diagnosed in patients with temporal lobe epilepsy (TLE), but the mechanism underlying this association remains unclear. In this study, we report that indoleamine 2,3-dioxygenase 1 (IDO1), a rate-limiting enzyme in tryptophan metabolism, plays a key role in epilepsy-associated depressive-like behavior.

METHODS

Rats which develop chronic epilepsy following pilocarpine status epilepticus exhibited a set of interictal disorders consistent with depressive-like behavior. Changes of depressive behavior were examined by taste preference test and forced swim test; brain IL-1β, IL-6 and IDO1 expression were quantified using real-time reverse transcriptase PCR; brain kynurenine/tryptophan and serotonin/tryptophan ratios were analyzed by liquid chromatography-mass spectrometry. Oral gavage of minocycline or subcutaneous injection of 1-methyltryptophan (1-MT) were used to inhibite IDO1 expression.

RESULTS

We observed the induction of IL-1β and IL-6 expression in rats with chronic TLE, which further induced the upregulation of IDO1 expression in the hippocampus. The upregulation of IDO1 subsequently increased the kynurenine/tryptophan ratio and decreased the serotonin/tryptophan ratio in the hippocampus, which contributed to epilepsy-associated depressive-like behavior. The blockade of IDO1 activation prevented the development of depressive-like behavior but failed to influence spontaneous seizures. This effect was achieved either indirectly, through the anti-inflammatory tetracycline derivative minocycline, or directly, through the IDO antagonist 1-MT, which normalizes kynurenine/tryptophan and serotonin/tryptophan ratios.

CONCLUSION

Brain IDO1 activity plays a key role in epileptic rats with epilepsy-associated depressive-like behavior.

Impact of inflammation on neurotransmitter changes in major depression: an insight into the action of antidepressants

This review summarises the evidence that chronic low grade inflammation plays an important role in the pathology of depression. Evidence is provided that pro-inflammatory cytokines, together with dysfunctional endocrine and neurotransmitter systems, provide a network of changes that underlie depression and may ultimately contribute to the neurodegenerative changes that characterise depression in the elderly. Antidepressants attenuate the inflammatory changes and hypercortisolaemia by reducing the release of the pro-inflammatory cytokines from activated microglia, and by sensitizing the glucocorticoids receptors in the HPA axis. These effects correlate with an improvement in monoamine neurotransmitter function. The possible mechanisms whereby this cascade of changes occurs are outlined. In conclusion, the mechanisms whereby antidepressants act should now consider the involvement of the immune and endocrine systems in addition to the central neurotransmitters. This may open up possibilities for a new generation of antidepressants in the future.

Network beyond IDO in psychiatric disorders: revisiting neurodegeneration hypothesis

The involvement of immune system activation in the pathophysiology of certain psychiatric disorders is well documented. Inflammatory molecules such as pro-inflammatory cytokines could enhance the activity of the indoleamine 2,3-dioxygenase (IDO) enzyme which is the first rate-limiting enzyme of the tryptophan degradation pathway, the kynurenine pathway. The increased tryptophan degradation could induce serotonin depletion and depressive mood. On the other hand, the downstream metabolites from this pathway, such as 3-hydroxykynurenine, quinolinic acid and kynurenic acid, are neuroactive metabolites which can modulate several neurotransmissions, such as glutamatergic, GABAergic, dopaminergic and noradrenergic neurotransmissions, which in turn induce changes in neuronal-glial network and neuropsychiatric consequences. In this issue, we have revised the previous 'neurodegeneration hypothesis,' which explained the involvement of cytokines and IDO pathway interaction in depression, with a further extended view related to the network beyond IDO, the network between immune molecules, tryptophan metabolites and different neurotransmitters, in depression and other major psychiatric disorders such as schizophrenia, bipolar disorder and childhood psychiatric disorders.

Immune system and glucose metabolism interaction in schizophrenia: a chicken-egg dilemma

Impaired glucose metabolism and the development of metabolic syndrome contribute to a reduction in the average life expectancy of individuals with schizophrenia. It is unclear whether this association simply reflects an unhealthy lifestyle or whether weight gain and impaired glucose tolerance in patients with schizophrenia are directly attributable to the side effects of atypical antipsychotic medications or disease-inherent derangements. In addition, numerous previous studies have highlighted alterations in the immune system of patients with schizophrenia. Increased concentrations of interleukin (IL)-1, IL-6, and transforming growth factor-beta (TGF-β) appear to be state markers, whereas IL-12, interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and soluble IL-2 receptor (sIL-2R) appear to be trait markers of schizophrenia. Moreover, the mononuclear phagocyte system (MPS) and microglial activation are involved in the early course of the disease. This review illustrates a "chicken-egg dilemma", as it is currently unclear whether impaired cerebral glucose utilization leads to secondary disturbances in peripheral glucose metabolism, an increased risk of cardiovascular complications, and accompanying pro-inflammatory changes in patients with schizophrenia or whether immune mechanisms may be involved in the initial pathogenesis of schizophrenia, which leads to disturbances in glucose metabolism such as metabolic syndrome. Alternatively, shared underlying factors may be responsible for the co-occurrence of immune system and glucose metabolism disturbances in schizophrenia.