Kynurenine Pathway Of Tryptophan Metabolism Research Articles

VEEV TC-83 Triggers Dysregulation of the Tryptophan-Kynurenine Pathway in the Central Nervous System That Correlates with Cognitive Impairment in Tg2576 Mice.

Neurodegenerative diseases are chronic conditions affecting the central nervous system (CNS). Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid beta in the limbic and cortical brain regions. AD is presumed to result from genetic abnormalities or environmental factors, including viral infections, which may have deleterious, long-term effects. In this study, we demonstrate that the Venezuelan equine encephalitis virus (VEEV) commonly induces neurodegeneration and long-term neurological or cognitive sequelae. Notably, the effects of VEEV infection can persistently influence gene expression in the mouse brain, suggesting a potential link between the observed neurodegenerative outcomes and long-term alterations in gene expression. Additionally, we show that alphavirus encephalitis exacerbates the neuropathological profile of AD through crosstalk between inflammatory and kynurenine pathways, generating a range of metabolites with potent effects. Using a mouse model for β-amyloidosis, Tg2576 mice, we found that cognitive deficits and brain pathology were more severe in Tg2576 mice infected with VEEV TC-83 compared to mock-infected controls. Thus, during immune activation, the kynurenine pathway plays a more active role in the VEEV TC-83-infected cells, leading to increases in the abundance of transcripts related to the kynurenine pathway of tryptophan metabolism. This pathway generates several metabolites with potent effects on neurotransmitter systems as well as on inflammation, as observed in VEEV TC-83-infected animals.

Abstract 3421: Associations of circulating levels of tryptophan-kynurenine metabolites and inflammation biomarker neopterin with overall survival among patients with stage I-III colorectal cancer

Abstract Introduction: Dysregulation of the kynurenine pathway of tryptophan metabolism has been linked to the development of inflammation-related chronic diseases, such as colorectal cancer (CRC). Circulating concentrations of certain kynurenine metabolites, the kynurenine/tryptophan ratio (KTR), and the pro-inflammatory marker neopterin increase during inflammation, particularly in response to interferon-gamma. However, comprehensive data on the associations between inflammation markers and kynurenine metabolites and clinical outcomes in CRC patients are lacking. To address this gap in knowledge, we investigated associations of circulating kynurenine metabolites and neopterin with overall survival (OS) in prospectively followed non-metastatic CRC patients. Methods: Pre-surgery blood samples from 2,101 stage I-III CRC patients participating in the international FOCUS consortium were used to measure circulating levels of nine tryptophan-kynurenine pathway metabolites and neopterin using liquid chromatography-tandem mass spectrometry. Multivariable linear regression models and Spearman partial correlation analyses were conducted to quantify associations between kynurenine metabolites and neopterin. Based on the results from correlation analyses, a subset of patients (n=984) was categorized into different groups (‘kynurenine metabolite/neopterin‘: i.e. ‘low/high‘, ‘high/high‘) using the median biomarker concentration as cut-off. Associations of biomarkers with OS were assessed using Cox proportional hazards regression models. All models were adjusted for age at diagnosis, sex, tumor stage, tumor site, circulating creatine levels and cohort. Results: Tryptophan was inversely correlated with neopterin (r=−0.21, β=−0.48, Plinear<0.001). Neopterin was positively correlated with kynurenine (kyn) (r=0.25, β=0.57, Plinear<0.001), the KTR (r=0.42, β=0.87, Plinear<0.001), 3-hydroxykynurenine (r=0.26, β=0.32, Plinear<0.001), anthranilic acid (r=0.29, β=0.36, Plinear<0.001), and quinolinic acid (QA) (r=0.41, β=0.56, Plinear<0.001). After a median follow-up of 3.2 years for OS, 14% (141) patients deceased. While patients with ‘high neopterin’ levels had a 43% increased risk of death (HR, 1.43, 95%CI 0.95-2.16), the ‘high kyn/high neopterin‘ patient group had a 52% increased risk of death (HR, 1.52, 95%CI 1.04-2.22). Similarly, the ‘high QA/high neopterin‘ and ‘high KTR/high neopterin‘ patient groups had a 85% and 89% increased risk of death, respectively (HRQA/Neopt, 1.85, 95%CI 1.24-2.75, HRKTR/Neopt, 1.89, 95%CI 1.27-2.80). Conclusion: Tryptophan-kynurenine pathway activation correlates with inflammation marker neopterin in CRC. Combined associations of kynurenine metabolites and neopterin may be a promising predictor for OS among stage I-III CRC patients. Citation Format: Victoria Damerell, Eline H. van Roekel, Stefanie Brezina, Dieuwertje E. Kok, Tengda Lin, Daniëlle D. Holthuijsen, Jennifer Ose, Caroline Himbert, Simone J. P. Eussen, Arve Ulvik, Fränzel J. van Duijnhoven, Jane C. Figueiredo, Christopher I. Li, Erin M. Siegel, Martin Schneider, David Shibata, Adetunji A. Toriola, Alexis B. Ulrich, Per M. Ueland, Matty P. Weijenberg, Andrea Gsur, Ellen Kampman, Cornelia M. Ulrich, Biljana Gigic. Associations of circulating levels of tryptophan-kynurenine metabolites and inflammation biomarker neopterin with overall survival among patients with stage I-III colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3421.

Unveiling the neuroprotection effects of Volvalerenic acid A: Mitochondrial fusion induction via IDO1-mediated Stat3-Opa1 signaling pathway

BackgroundIschemic stroke is a leading cause of death and long-term disability worldwide. Studies have suggested that cerebral ischemia induces massive mitochondrial damage. Valerianic acid A (VaA) is the main active ingredient of valerianic acid with neuroprotective activity. PurposeThis study aimed to investigate the neuroprotective effects of VaA with ischemic stroke and explore the underlying mechanisms. MethodIn this study, we established the oxygen-glucose deprivation and reperfusion (OGD/R) cell model and the middle cerebral artery occlusion and reperfusion (MCAO/R) animal model in vitro and in vivo. Neurological behavior score, 2, 3, 5-triphenyl tetrazolium chloride (TTC) staining and Hematoxylin and Eosin (HE) Staining were used to detect the neuroprotection of VaA in MCAO/R rats. Also, the levels of ROS, mitochondrial membrane potential (MMP), and activities of NAD+ were detected to reflect mitochondrial function. Mechanistically, gene knockout experiments, transfection experiments, immunofluorescence, DARTS, and molecular dynamics simulation experiments showed that VaA bound to IDO1 regulated the kynurenine pathway of tryptophan metabolism and prevented Stat3 dephosphorylation, promoting Stat3 activation and subsequent transcription of the mitochondrial fusion-related gene Opa1. ResultsWe showed that VaA decreased the infarct volume in a dose-dependent manner and exerted neuroprotective effects against reperfusion injury. Furthermore, VaA promoted Opa1-related mitochondrial fusion and reversed neuronal mitochondrial damage and loss after reperfusion injury. In SH-SY5Y cells, VaA (5, 10, 20 μM) exerted similar protective effects against OGD/R-induced injury. We then examined the expression of significant enzymes regulating the kynurenine (Kyn) pathway of the ipsilateral brain tissue of the ischemic stroke rat model, and these enzymes may play essential roles in ischemic stroke. Furthermore, we found that VaA can bind to the initial rate-limiting enzyme IDO1 in the Kyn pathway and prevent Stat3 phosphorylation, promoting Stat3 activation and subsequent transcription of the mitochondrial fusion-related gene Opa1. Using in vivo IDO1 knockdown and in vitro IDO1 overexpressing models, we demonstrated that the promoted mitochondrial fusion and neuroprotective effects of VaA were IDO1-dependent. ConclusionVaA administration improved neurological function by promoting mitochondrial fusion through the IDO1-mediated Stat3-Opa1 pathway, indicating its potential as a therapeutic drug for ischemic stroke.

Changes in kynurenine metabolites in the gray and white matter of the dorsolateral prefrontal cortex of individuals affected by schizophrenia

Alterations in the kynurenine pathway of tryptophan metabolism have been implicated in the pathophysiology of schizophrenia. Here, we performed an in-depth analysis of all metabolites of the kynurenine pathway, i.e., tryptophan (TRY), kynurenic acid (KYNA), L-kynurenine (KYN), 3-hydroxykynurenine (3-HK), anthranylic acid (ANA), 3-hydroxyanthranylic acid (3-HANA), xanthurenic acid (XA) and quinolinic acid (QUINA), in postmortem samples of the dorsolateral prefrontal cortex (DLPFC, Brodmann area 46, 9) of individuals affected by schizophrenia and non-schizophrenic controls. The analysis was carried out in the gray and white matter. Levels of KYN, 3-HK, ANA, and 3-HANA were significantly increased in both the gray and white matter of the DLPFC of individuals affected by schizophrenia, whereas levels of TRY, KYNA, and QUINA were increased exclusively in the white matter and remained unchanged in the gray matter. These increases in kynurenine metabolites did not correlate with age, sex, duration of the disease, and duration and type of antipsychotic medication. These findings suggest that the two major branches of the kynurenine pathway, i.e., the transamination of KYN into KYNA, and hydroxylation of KYN into 3-HK are activated in the white matter of individuals affected by schizophrenia, perhaps as a result of neuroinflammation, and support the evidence that abnormalities of the white matter are consistenly associated with schizophrenia.

Surgical resection of lung cancer inhibits mRNA expression of GOT2 gene encoding kynurenine aminotransferase in leukocytes.

Lung cancer is the most common malignant tumour. More than 80% of all diagnosed cases are non-small cell carcinoma which can be effectively treated by radical resection. Despite significant progress in the field of diagnostic and therapeutic methods, the results of lung cancer treatment are still unsatisfactory. Lung cancer is detected relatively late, which leads to an unfavourable prognosis. Kynurenine aminotransferases are an important element of the kynurenine pathway of tryptophan metabolism, which has recently aroused great interest from the aspect of possible use as a target point of personalized therapies in malignant tumours.The aim of the study was to analyze the expression of the selected gene of kynurenine aminotransferases GOT 2 at the mRNA level in peripheral blood leukocytes of patients with lung cancer. The mRNA expression of the GOT 2 gene was tested on blood samples from 50 patients treated surgically for non-small cell lung cancer.The control group consisted of 15 healthy individuals.The determination of mRNA expression of the GOT 2 gene was performed using the real-time PCR method.The GAPDH gene was used as the endogenous reference level. The mRNA expression of the GOT2 gene on the 6th day after surgery was statistically significantly lower than before surgery (p = 0,05). In the study group, the average LogRQ mRNA expression of the GOT2 gene before the procedure was 0.192082±0.292174 in woman. This was statistically significantly higher than in men whose average LogRQ mRNA expression of the GOT2 gene before the procedure was 0.004210±0.235065 (p=0.0183). Surgical resection of lung cancer results in inhibition of GOT2 mRNA expression in leukocytes. Further studies are expected to show whether it may be used as a target point for personalized therapies in lung cancer.

Lipopolysaccharide aggravates depressive‐like behavior via increasing microglial inflammation, decreasing microglial ramification, and altering tryptophan level in obese rats

AbstractBackgroundLong‐term high‐fat diet consumption has been shown to induce endotoxemia, microglial dysmorphology, and depressive‐like behavior (1, 2). Previous studies demonstrated that the kynurenine pathway of tryptophan metabolism plays an important role on mediating the depressive‐like behavior in response to inflammation (3, 4). However, the effects of lipopolysaccharide as endotoxin on the alterations of microglial profiles/morphologies, changes in brain metabolites, as well as depressive‐like behavior in obese condition have never been investigated.MethodSixteen male Wistar rats were randomly divided into two groups to fed with either normal diet (ND, n = 8) or the high‐fat diet (HFD, n = 8) for 12 weeks. At week 12, animals in each dietary group were subsequently divided into two subgroups (n = 4 per subgroup) to receive either a single dose of vehicle (1 ml of 0.9% normal saline solution, intraperitoneal (i.p) injection, or lipopolysaccharide (LPS, 0.5 mg/kg, i.p. injection). After the injections for 12‐16 hours, all animals were measured depressive‐like behaviors and blood was collected. Then, animals were sacrificed, and brains were obtained for further molecular investigation.ResultWe found that LPS‐treated HFD‐fed rats, not LPS‐treated ND‐fed rats and vehicle‐treated HFD‐fed rats, increased microglial IL‐1β mRNA level (p<0.05, Figure 1). In addition, LPS‐treated ND‐fed rats and vehicle‐treated HFD‐fed rats significantly decreased microglial ramification as indicated by decreasing branch points, whereas LPS‐treated HFD‐fed rats showed the lowest microglial branch points (p<0.05, Figure 1). The level of brain tryptophan and depressive‐like behavior increased in both LPS‐treated ND‐fed rats and vehicle‐treated HFD‐fed rats, when compared with those of vehicle‐treated ND‐fed rats (p<0.05, Figure 1). Interestingly, LPS‐treated HFD‐fed rats showed the highest brain tryptophan level and freezing duration during Force Swimming Test (FST) (p<0.05, Figure 1).ConclusionThese findings indicate that LPS aggravates depressive‐like behavior in obese condition by increased microglial hyperactivation, and possibly be related to its regulation of kynurenine metabolism.

A systematic review and meta-analysis of the kynurenine pathway of tryptophan metabolism in rheumatic diseases.

https://www.crd.york.ac.uk/prospero, identifier CRD CRD42023443718.

The kynurenine pathway of tryptophan metabolism: a neglected therapeutic target of COVID-19 pathophysiologyand immunotherapy.

SARS-CoV-2 (COVID-19) exerts profound changes in the kynurenine (Kyn) pathway (KP) of tryptophan (Trp) metabolism that may underpin its pathophysiology. The KP is the main source of the vital cellular effector NAD+ and intermediate metabolites that modulate immune and neuronal functions. Trp metabolism is the top pathway influenced by COVID-19. Sixteenstudies established virus-induced activation of the KPmediated mainly by induction of indoleamine 2,3-dioxygenase(IDO1) in most affected tissues and of IDO2 in lung by the increased release of proinflammatory cytokines, but could additionally involve increased flux of plasma free Trp and induction of Trp 2,3-dioxygenase (TDO) by cortisol. The major Kyn metabolite targeted by COVID-19 is kynurenic acid (KA), the Kyn metabolite with the greatest affinity for the aryl hydrocarbon receptor (AhR), which is also activated by COVID-19. AhR activation initiates two important series of events: a vicious circle involving IDO1induction, KA accumulation and further AhR activation, and activation of poly (ADP-ribose)polymerase (PARP) leading to NAD+ depletion and cell death. The virus further deprives the host of NAD+ by inhibiting its main biosynthetic pathway from quinolinic acid, while simultaneously acquiring NAD+ by promoting its synthesis from nicotinamide in the salvage pathway. Additionally, the protective effects of sirtuin 1 are minimised by the PARP activation. KP dysfunction may also underpin the mood and neurological disorders acutely and during "long COVID". More studies of potential effects of vaccination therapy on the KP are required andexploration of therapeutic strategies involving modulation of the KP changes are proposed.

LC–MS/MS-based quantification of tryptophan, kynurenine, and kynurenic acid in human placental, fetal membranes, and umbilical cord samples

Tryptophan breakdown metabolites formed along the kynurenine pathway play a significant role in pregnancy and fetal development. To understand their involvement, it is crucial to quantify the levels of tryptophan (TRP), kynurenine (KYN), and kynurenic acid (KYNA) in relevant biological samples such as the placenta, fetal membranes, and umbilical cord. This study used liquid chromatography-tandem mass spectrometry (LC–MS/MS) to determine TRP, KYN, and KYNA levels. The LC–MS/MS method was optimized for high sensitivity and specificity, demonstrating good reproducibility with a precision of < 10% CV and an accuracy of 85–115%. The lower limit of quantification for both TRP and KYN was 0.5 µg/ml, while for KYNA, it was 0.5 ng/mL. The method exhibited linearity within the examined range of concentrations in the homogenate, ranging from 0.5 to 30 µg/ml for TRP and KYN and from 0.5 to 25 ng/ml for KYNA. Using this method, we found significant differences in the concentrations of these substances in investigated maternal–fetal compartments. Placenta samples exhibited higher KYN and lower KYNA concentrations than the umbilical cord and fetal membrane, indicating a potentially important role for kynurenines in late pregnancy. Collectively, this finding may facilitate further research and provide inside into the involvement of the kynurenine pathway of TRP metabolism in fetal development.

Behavior, Neural Structure, and Metabolism in Adult Male Mice Exposed to Environmentally Relevant Doses of Di(2-ethylhexyl) Phthalate Alone or in a Phthalate Mixture.

We have previously shown that chronic exposure of adult male mice to low doses of di(2-ethylhexyl) phthalate (DEHP) altered male sexual behavior and induced down-regulation of the androgen receptor (AR) in the neural circuitry controlling this behavior. The cellular mechanisms induced by chronic exposure of adult male mice to low doses of DEHP alone or in an environmental phthalate mixture were studied. Two-month-old C57BL/6J males were exposed orally for 8 wk to DEHP alone (0, 5, or ) or to DEHP () in a phthalate mixture. Behavior, dendritic density per length, pre-/postsynaptic markers, synapse ultrastructure, and bioenergetic activity were analyzed. Mice exposed to DEHP either alone or in a phthalate mixture differed in mating, emission of ultrasonic vocalizations, and the ability to attract receptive females in urinary preference tests from control mice. Analyses in the medial preoptic area, the key hypothalamic region involved in male sexual behavior, showed lower dendritic spine density and protein levels of glutamate receptors and differences in other postsynaptic components and presynaptic markers between the treated groups. Ultrastructural observation of dendritic synapses by electron microscopy showed comparable morphology between the treated groups. Metabolic analyses highlighted differences in hypothalamic metabolites of males exposed to DEHP alone or in a phthalate mixture compared to control mice. These differences included lower tryptophan and higher levels, respectively, a precursor and end product of the kynurenine pathway of tryptophan metabolism. The protein amounts of the xenobiotic aryl hydrocarbon receptor, one of the targets of this metabolic pathway and known negative regulator of the AR, were higher in the medial preoptic area of exposed male mice. Differences in behavior of male mice exposed to environmental doses of phthalates were associated with differences in neural structure and metabolism, with possibly a key role of the kynurenine pathway of tryptophan metabolism in the effects mediated by these substances. https://doi.org/10.1289/EHP11514.

Helicobacter pylori promotes gastric intestinal metaplasia through activation of IRF3-mediated kynurenine pathway

BackgroundMetabolic reprogramming is a critical event for cell fate and function, making it an attractive target for clinical therapy. The function of metabolic reprogramming in Helicobacter pylori (H. pylori)-infected gastric intestinal metaplasia remained to be identified.MethodsXanthurenic acid (XA) was measured in gastric cancer cells treated with H. pylori or H. pylori virulence factor, respectively, and qPCR and WB were performed to detect CDX2 and key metabolic enzymes expression. A subcellular fractionation approach, luciferase and ChIP combined with immunofluorescence were applied to reveal the mechanism underlying H. pylori mediated kynurenine pathway in intestinal metaplasia in vivo and in vitro.ResultsHerein, we, for the first time, demonstrated that H. pylori contributed to gastric intestinal metaplasia characterized by enhanced Caudal-related homeobox transcription factor-2 (CDX2) and mucin2 (MUC2) expression, which was attributed to activation of kynurenine pathway. H. pylori promoted kynurenine aminotransferase II (KAT2)-mediated kynurenine pathway of tryptophan metabolism, leading to XA production, which further induced CDX2 expression in gastric epithelial cells. Mechanically, H. pylori activated cyclic guanylate adenylate synthase (cGAS)-interferon regulatory factor 3 (IRF3) pathway in gastric epithelial cells, leading to enhance IRF3 nuclear translocation and the binding of IRF3 to KAT2 promoter. Inhibition of KAT2 could significantly reverse the effect of H. pylori on CDX2 expression. Also, the rescue phenomenon was observed in gastric epithelial cells treated with H. pylori after IRF3 inhibition in vitro and in vivo. Most importantly, phospho-IRF3 was confirmed to be a clinical positive relationship with CDX2.ConclusionThese finding suggested H. pylori contributed to gastric intestinal metaplasia through KAT2-mediated kynurenine pathway of tryptophan metabolism via cGAS-IRF3 signaling, targeting the kynurenine pathway could be a promising strategy to prevent gastric intestinal metaplasia caused by H. pylori infection.2STnY-xvxhAA5nGkWu7hrzVideo

Kynurenine pathway of tryptophan metabolism in pathophysiology and therapy of major depressive disorder

Serotonin deficiency in major depressive disorder (MDD) has formed the basis of antidepressant drug development and was originally attributed to induction of the major tryptophan (Trp)-degrading enzyme, liver Trp 2,3-dioxygenase (TDO), by cortisol, leading to decreased Trp availability to the brain for serotonin synthesis. Subsequently, the serotonin deficiency was proposed to involve induction of the extrahepatic Trp-degrading enzyme indoleamine 2,3-dioxygenase (IDO) by proinflammatory cytokines, with inflammation being the underlying cause. Recent evidence, however, challenges this latter concept, as not all MDD patients are immune-activated and, when present, inflammation is mild and/or transient. A wide range of antidepressant drugs inhibit the activity of liver TDO and bind specifically to the enzyme, but not to IDO. IDO induction is not a major event in MDD, but, when it occurs, its metabolic consequences may be masked and overridden by upregulation of kynurenine monooxygenase (KMO), the gateway to production of modulators of immune and neuronal functions. KMO appears to be activated in MDD by certain proinflammatory cytokines and antidepressants with anti-inflammatory properties may block this activation. We demonstrate the ability of the antidepressant ketamine to dock (bind) to KMO. The pathophysiology of MDD may be underpinned by both the serotonin deficiency and glutamatergic activation mediated respectively by TDO induction and N-methyl-D-aspartate receptor activation. Inhibition of TDO and KMO should be the focus of MDD pharmacotherapy.

Brain-Derived Neurotrophic Factor, Kynurenine Pathway, and Lipid-Profiling Alterations as Potential Animal Welfare Indicators in Dairy Cattle

Complete animal welfare evaluation in intensive farming is challenging. With this study, we investigate new biomarkers for animal physical and mental health by comparing plasma expression of biochemical indicators in dairy cows reared in three different systems: (A) semi-intensive free-stall, (B) non-intensive tie-stall, and (C) intensive free-stall. Additionally, protein levels of mature brain-derived neurotrophic factor (mBDNF) and its precursor form (proBDNF) and indoleamine 2,3-dioxygenase (IDO1) specific activity were evaluated in brain samples collected from 12 cattle culled between 73 and 138 months of age. Alterations in plasma lipid composition and in the kynurenine pathway of tryptophan metabolism were observed in the tie-stall-reared animals. The total plasma BDNF concentration was higher in tie-stall group compared to the two free-housing groups. Brain analysis of the tie-stall animals revealed a different mBDNF/proBDNF ratio, with a higher level of proBDNF (p < 0.001). Our data are similar to previous studies on animal models of depression, which reported that inhibition of the conversion of proBDNF in its mature form and/or elevated peripheral kynurenine pathway activation may underlie cerebral biochemical changes and induce depressive-like state behavior in animals.

Cognitive and hippocampal effects of adult male mice exposure to environmentally relevant doses of phthalates

We recently showed that chronic exposure of adult male mice to environmental doses of DEHP alone or in a phthalate mixture altered blood brain barrier integrity and induced an inflammatory profile in the hippocampus. Here, we investigate whether such exposure alters hippocampus-dependent behavior and underlying cellular mechanisms. Adult C57BL/6 J male mice were continuously exposed orally to the vehicle or DEHP alone (5 or 50 μg/kg/d) or to DEHP (5 μg/kg/d) in a phthalate mixture. In the Morris water maze, males showed reduced latencies across days to find the platform in the cue and spatial reference memory tasks, regardless of their treatment group. In the probe test, DEHP-50 exposed males displayed a higher latency to find the platform quadrant. In the temporal order memory test, males exposed to DEHP alone or in a phthalate mixture were unable to discriminate between the most recently and previously seen objects. They also displayed reduced ability to show a preference for the new object in the novel object recognition test. These behavioral alterations were associated with a lowered dendritic spine density and protein levels of glutamate receptors and postsynaptic markers, and increased protein levels of the presynaptic synaptophysin in the hippocampus. Metabolomic analysis of the hippocampus indicated changes in amino acid levels including reduced tryptophan and L-kynurenine and elevated NAD + levels, respectively, a precursor, intermediate and endproduct of the kynurenine pathway of tryptophan metabolism. Interestingly, the protein amounts of the xenobiotic aryl hydrocarbon receptor, a target of this metabolic pathway, were elevated in the CA1 area. These data indicate that chronic exposure of adult male mice to environmental doses of DEHP alone or in a phthalate mixture impacted hippocampal function and structure, associated with modifications in amino acid metabolites with a potential involvement of the kynurenine pathway of tryptophan metabolism.

Cognitive impairments correlate with increased central nervous system immune activation after allogeneic haematopoietic stem cell transplantation

Murine studies indicate that, after allogeneic haematopoietic stem cell transplantation (aHSCT), donor-derived macrophages replace damaged microglia and alloreactive T-cells invade the central nervous system (CNS). The clinical relevance of this is unknown. We assessed CNS immune surveillance and metabolic activity involved in neuronal survival, in relation to fatigue and cognitive dysfunction in 25 long-term survivors after aHSCT. Patients with cognitive dysfunction exhibited increased proportions of activated T-cells and CD16 + NK-cells in the cerebrospinal fluid (CSF). Immune cell activation was paralleled with reduced levels of anti-inflammatory factors involved in T-cell suppression (transforming growth factor-β, programmed death ligand-1), NK-cell regulation (poliovirus receptor, nectin-2), and macrophage and microglia activation (CD200, chemokine [C-X3-C motif] ligand-1). Additionally, the CSF mRNA expression pattern was associated with neuroinflammation and oxidative stress. Furthermore, proteomic, and transcriptomic studies demonstrated decreased levels of neuroprotective factors, and an upregulation of apoptosis pathway genes. The kynurenine pathway of tryptophan metabolism was activated in the CNS of all aHSCT patients, resulting in accumulation of neurotoxic and pro-inflammatory metabolites. Cognitive decline and fatigue are overlooked but frequent complications of aHSCT. This study links post-transplant CNS inflammation and neurotoxicity to our previously reported hypoactivation in the prefrontal cortex during cognitive testing, suggesting novel treatment targets.A) The kynurenine pathway of tryptophan metabolism was activated in all aHSCT patients. The levels of KYN and 3-HK, that readily cross the BBB, were increased in both plasma and CSF, while QUIN, that do not cross the BBB, was exclusively elevated in CSF, suggesting intrathecal production in microglia. QUIN and 3-HK have documented neurotoxic properties and may contribute to an underlying neurotoxic environment after aHSCT. B-D) Activated T-cells and CD16 + NK-cells were increased in the CSF of aHSCT patients with fatigue (C, D), coupled with decreased amounts of immune regulatory (green and blue dots) and neurotrophic (grey dots) proteins in the subgroup with cognitive dysfunction (D). In contrast, patients with normal cognition (B, C) had increased levels of reparative and anti-inflammatory factors, possibly counteracting the toxic environment highlighted by the increased apoptosis activity and signs of ongoing neuroinflammation observed in the mRNA sequencing analysis.

Maternal Stress during Pregnancy in Mice Induces Sex-Dependent Behavioral Alterations in Offspring along with Impaired Serotonin and Kynurenine Pathways of Tryptophan Metabolism

Maternal stress during pregnancy results in increased risk of developing psychiatric disorders in the offspring including anxiety, depression, schizophrenia, and autism. However, the mechanisms underlying this disease susceptibility remain largely to be determined. In this study, the involvement of the serotonin (5-HT) and kynurenine (KYN) pathways of tryptophan metabolism on the behavioral deficits induced by maternal stress during the late phase of gestation in mice was investigated. Adult offspring born to control or restraint-stressed dams were exposed to the elevated plus-maze and tail suspension tests. Metabolites of the KYN and 5-HT pathways were measured in the hippocampus and brainstem by ultra-performance liquid chromatography tandem mass spectrometry. Female, but not male, prenatally stressed (PNS) offspring displayed a depressive-like phenotype, mainly when in proestrus/diestrus, along with reduced hippocampal 5-HT levels and high 5-HT turnover rate in the hippocampus and brainstem. In contrast, male PNS mice showed enhanced anxiety-like behaviors and higher hippocampal and brainstem quinolinic acid levels compared to male offspring born to nonstressed dams. These results indicate that maternal stress affects the behavior and brain metabolism of tryptophan in the offspring in a sex-dependent manner and suggest that alterations in both the 5-HT and KYN pathways may underlie the emotional dysfunctions observed in individuals exposed to stress during in utero development.

Kynurenine Pathway of Tryptophan Metabolism Is Associated with Hospital Mortality in Patients with Acute Respiratory Distress Syndrome: A Prospective Cohort Study.

Acute respiratory distress syndrome (ARDS) involves dysregulated immune-inflammatory responses, characterized by severe oxidative stress and high mortality. Metabolites modulating the inflammatory and immune responses may play a central role in the pathogenesis of ARDS. Most biogenic amines may induce the production of reactive oxygen species, oxidative stress, mitochondrial dysfunction, and programmed cell death. We conducted a prospective study on metabolic profiling specific to the amino acids and biogenic amines of 69 patients with ARDS. Overall, hospital mortality was 52.2%. Between day 1 and day 7 after ARDS onset, plasma kynurenine levels and the kynurenine/tryptophan ratio were significantly higher among non-survivors than in survivors (all p < 0.05). Urine metabolic profiling revealed a significantly higher prevalence of tryptophan degradation and higher concentrations of metabolites downstream of the kynurenine pathway among non-survivors than among survivors upon ARDS onset. Cox regression models revealed that plasma kynurenine levels and the plasma kynurenine/tryptophan ratio on day 1 were independently associated with hospital mortality. The activation of the kynurenine pathway was associated with mortality in patients with ARDS. Metabolic phenotypes and modulating metabolic perturbations of the kynurenine pathway could perhaps serve as prognostic markers or as a target for therapeutic interventions aimed at reducing oxidative stress and mortality in ARDS.

Kynurenine pathway metabolites and therapeutic response to olanzapine in female patients with schizophrenia: Alongitudinal study.

AimA metabolomics approach has recently been used to identify metabolites associated with response to antipsychotic treatment. This study was designed to identify the predictive biomarkers of response to olanzapine monotherapy using a metabolomics‐based strategy.MethodsTwenty‐five first‐episode and drug‐naïve female patients with schizophrenia were recruited and treated with olanzapine for 4 weeks. Psychiatric symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS) at baseline and 4‐week follow‐up.ResultsPositive subscore, general psychopathology subscore, and PANSS total score were significantly decreased after treatment. An ultra‐performance liquid chromatography‐mass spectrometry (UPLC‐MS)‐based metabolomics approach identified 72 differential metabolites after treatment. In addition, the baseline levels of methyl n‐formylanthranilate (MNFT) were correlated with the rate of reduction in the positive subscore or PANSS total score. However, increase in MNFT after treatment was not associated with the rate of reduction in the PANSS total score or its subscores. Subsequent regression analysis revealed that the baseline MNFT levels predicted the treatment outcomes after olanzapine monotherapy for 4 weeks in patients with schizophrenia.ConclusionsOur study results suggest that the baseline MNFT levels in the kynurenine pathway of tryptophan metabolism may be predictive of the treatment response to olanzapine in schizophrenia.

Structure-based optimization of type III indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors

The haem enzyme indoleamine 2,3-dioxygenase 1 (IDO1) catalyses the rate-limiting step in the kynurenine pathway of tryptophan metabolism and plays an essential role in immunity, neuronal function, and ageing. Expression of IDO1 in cancer cells results in the suppression of an immune response, and therefore IDO1 inhibitors have been developed for use in anti-cancer immunotherapy. Here, we report an extension of our previously described highly efficient haem-binding 1,2,3-triazole and 1,2,4-triazole inhibitor series, the best compound having both enzymatic and cellular IC50 values of 34 nM. We provide enzymatic inhibition data for almost 100 new compounds and X-ray diffraction data for one compound in complex with IDO1. Structural and computational studies explain the dramatic drop in activity upon extension to pocket B, which has been observed in diverse haem-binding inhibitor scaffolds. Our data provides important insights for future IDO1 inhibitor design.

Metabolism of tryptophan in non-small lung cancer patients with different effect of PD-1 / PD-L1 inhibitors immunotherapy

Introduction. In the structure of cancer incidence, lung cancer ranks first among men. In order to study the molecular mechanisms of the initiation and progression of lung cancer, it is necessary to study not only the tumor cells themselves, but also the features of the systemic tryptophan metabolism. Tryptophan catabolites, being to a large extent product of the metabolic activity of the intestinal microbiota, can affect the effectiveness of immunotherapy with checkpoint inhibitors. The kynurenine pathway of tryptophan metabolism is intensified in the body of cancer patients; its products have a pro-oncogenic and immunosuppressive effect, which may hinder the effectiveness of immunotherapy.Objective – to study the dynamics of changes in various metabolites of tryptophan metabolism in the blood serum and feces of patients with non-small cell lung cancer with various effects of immunotherapy with inhibitors of PD-1 (programmed cell death receptor 1) / PD-L1 (programmed cell death receptor 1 ligand).Materials and methods. The study included blood serum and stool samples obtained from 20 patients with non-small cell lung cancer treated with PD-1 / PD-L1 inhibitors. Using high-performance liquid chromatography with mass spectrometric analysis, the levels of 13 tryptophan metabolites were assessed in patients with various effects of immunotherapy. The significance of differences between the samples was assessed using a nonparametric method according to the Mann – Whitney test. They were considered statistically significant at p &lt;0.05.Results. In fecal analyzes of patients in whom a positive effect of immunotherapy was observed, baseline levels of 5-hydroxyindole acetate and quinolinic acid were lower than in patients with tumor progression. Positive clinical dynamics was accompanied by a decrease in the content of indole-3-lactate, kynurenine and indole-3-carboxaldehyde in the feces of patients. In the serum of patients with a positive response, the initial content of 5-hydroxyindole acetate, indole-3-acetate, indole-3-butyrate and quinoline acid was lower than in patients with progression of non-small cell lung cancer. A positive response to immunotherapy was characterized by an increase in the levels of indole-3-butyrate and indole-3-propionate, and a negative response was not accompanied by statistically significant changes in the studied tryptophan metabolites.Conclusion. Profiling tryptophan metabolites in feces and serum of patients with non-small cell lung cancer can be used to predict the effectiveness of immunotherapy with PD-1 / PD-L1 inhibitors.