Tryptophan-kynurenine Pathway Research Articles

The Intersection between Tryptophan-Kynurenine Pathway Metabolites and Immune Inflammation, Hormones, and Gut Microbiota in Perinatal Depression.

Perinatal depression is a prevalent mental disorder among pregnant women, characterized by sleep disturbances, appetite changes, negative emotions, cognitive impairment, and suicidal or homicidal tendencies. These symptoms severely compromise personal well-being, disrupt family life, and burden society. Early detection and intervention are thus crucial. The tryptophan-kynurenine (TRP-KYN) pathway is central to the inflammatory hypothesis of depression and has gained significant attention in perinatal depression research. This pathway encompasses numerous metabolic enzymes and neuroactive metabolites that interact with other physiological systems, influencing neurotransmitter synthesis and neuronal development. Through these interactions, the TRP-KYN pathway exerts psychotropic effects. This article reviews the key metabolites and enzymes of the TRP-KYN pathway and examines its intersection with immune inflammation, hormones, and gut microbiota.

α-Amino-β-carboxymuconate-ε-semialdehyde decarboxylase catalyzes Enol/Keto tautomerization of oxaloacetate

ACMSD (α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase) is a key metalloenzyme critical for regulating de novo endogenous NAD+/NADH biosynthesis through the tryptophan-kynurenine pathway. This decarboxylase is a recognized target implicated in mitochondrial diseases and neurodegenerative disorders. However, unraveling its enzyme-substrate complex has been challenging due to its high catalytic efficiency. Here, we present a combined biochemical and structural study wherein we determined the crystal structure of ACMSD in complex with malonate. Our analysis revealed significant rearrangements in the active site, particularly in residues crucial for ACMS decarboxylation, including Arg51, Arg239* (a residue from an adjacent subunit), His228, and Trp194. Docking modeling studies proposed a putative ACMS binding mode. Additionally, we found that ACMSD catalyzes oxaloacetic acid (OAA) tautomerization at a rate of 6.51 ± 0.42 s-1 but not decarboxylation. The isomerase activity of ACMSD on OAA warrants further investigation in future biological studies. Subsequent mutagenesis studies and crystallographic analysis of W194A variant shed light on the roles of specific second-coordination sphere residues. Our findings indicate that Arg51 and Arg239* are crucial for OAA tautomerization. Moreover, our comparative analysis with related isomerase superfamily members underscores a general strategy employing arginine residues to promote OAA isomerization. Given the observed isomerase activity of ACMSD on OAA and its structural similarity to ACMS, we propose that ACMSD may facilitate isomerization to ensure ACMS is in the optimal tautomeric form for subsequent decarboxylation initiated by the zinc-bound hydroxide ion. Overall, these findings deepen the understanding of the structure and function of ACMSD, offering insights into potential therapeutic interventions.

Circulating tryptophan–kynurenine pathway metabolites are associated with all‐cause mortality among patients with stage I–III colorectal cancer

AbstractAlterations within the tryptophan–kynurenine metabolic pathway have been linked to the etiology of colorectal cancer (CRC), but the relevance of this pathway for prognostic outcomes in CRC patients needs further elucidation. Therefore, we investigated associations between circulating concentrations of tryptophan–kynurenine pathway metabolites and all‐cause mortality among CRC patients. This study utilizes data from 2102 stage I–III CRC patients participating in six prospective cohorts involved in the international FOCUS Consortium. Preoperative circulating concentrations of tryptophan, kynurenine, kynurenic acid (KA), 3‐hydroxykynurenine (HK), xanthurenic acid (XA), 3‐hydroxyanthranilic acid (HAA), anthranilic acid (AA), picolinic acid (PA), and quinolinic acid (QA) were measured by liquid chromatography–tandem mass spectrometry. Using Cox proportional hazards regression, we examined associations of above‐mentioned metabolites with all‐cause mortality, adjusted for potential confounders. During a median follow‐up of 3.2 years (interquartile range: 2.2–4.9), 290 patients (13.8%) deceased. Higher blood concentrations of tryptophan, XA, and PA were associated with a lower risk of all‐cause mortality (per doubling in concentrations: tryptophan: HR = 0.56; 95%CI:0.41,0.76, XA: HR = 0.74; 95%CI:0.64,0.85, PA: HR = 0.76; 95%CI:0.64,0.92), while higher concentrations of HK and QA were associated with an increased risk of death (per doubling in concentrations: HK: HR = 1.80; 95%CI:1.47,2.21, QA: HR = 1.31; 95%CI:1.05,1.63). A higher kynurenine‐to‐tryptophan ratio, a marker of cell‐mediated immune activation, was associated with an increased risk of death (per doubling: HR = 2.07; 95%CI:1.52,2.83). In conclusion, tryptophan–kynurenine pathway metabolites may be prognostic markers of survival in CRC patients.

The correlation of inflammation, tryptophan-kynurenine pathway, and suicide risk in adolescent depression.

Accumulating evidence suggests a role for the tryptophan-kynurenine pathway (TKP) in the psychopathology of major depressive disorder (MDD). Abnormal inflammatory profile and production of TKP neurotoxic metabolites appear more pronounced in MDD with suicidality. Progress in understanding the neurobiology of MDD in adolescents lags significantly behind that in adults due to limited empirical evidence. Aims of this study was to investigate the association between inflammation, TKP, and suicidality in adolescent depression. Seventy-three adolescents with MDD were assessed for serum levels of interleukin (IL)-1β, IL-6, IL-18, IL-10, tumor necrosis factor-α (TNF-α), tryptophan (TRP), kynurenine (KYN), 3-hydroxykynurenine (3-HK), and kynurenine acid (KA). Correlations between cytokines and TKP measures were examined. Patients were divided into high- (n = 42) and non-high-suicide-risk groups (n = 31), and serum levels of cytokines and TKP metabolites were compared. Significant negative correlations were found between TRP and IL-8 (r = - 0.27, P < 0.05) and IL-10 (r = - 0.23, P < 0.05), while a significant positive correlation was observed between 3-HK and IL-8 (r = 0.39, P < 0.01) in depressed adolescents. The KYN/TPR (index of indoleamine 2,3-dioxygenase, IDO) was positively correlated with IL-1β (r = 0.34), IL-6 (r = 0.32), IL-10 (r = 0.38) and TNF-α (r = 0.35) levels (P < 0.01); and 3-HK/KYN (index of kynurenine3-monooxidase, KMO) was positively correlated with IL-8 level (r = 0.31, P < 0.01). Depressed adolescents at high suicide risk exhibited significantly higher levels of IL-1β (Z = 2.726, P < 0.05), IL-10 (Z = 2.444, P < 0.05), and TNF-α (Z = 2.167, P < 0.05) and lower levels of 3-HK (Z = 2.126, P < 0.05) compared to their non-high suicide risk counterparts. Our findings indicated that serum inflammatory cytokines were robustly associated with IDO and KMO activity, along with significantly decreased serum level of TRP, increased level of 3-HK, and higher suicide risk in adolescent depression.

The association between HIV-1 Tat and Vif amino acid sequence variation, inflammation and Trp-Kyn metabolism: an exploratory investigation

BackgroundHIV-1 has well-established mechanisms to disrupt essential pathways in people with HIV, such as inflammation and metabolism. Moreover, diversity of the amino acid sequences in fundamental HIV-1 proteins including Tat and Vif, have been linked to dysregulating these pathways, and subsequently influencing clinical outcomes in people with HIV. However, the relationship between Tat and Vif amino acid sequence variation and specific immune markers and metabolites of the tryptophan-kynurenine (Trp-Kyn) pathway remains unclear. Therefore, this study aimed to investigate the relationship between Tat/Vif amino acid sequence diversity and Trp-Kyn metabolites (quinolinic acid (QUIN), Trp, kynurenic acid (KA), Kyn and Trp/Kyn ratio), as well as specific immune markers (sCD163, suPAR, IL-6, NGAL and hsCRP) in n = 67 South African cART-naïve people with HIV.MethodsSanger sequencing was used to determine blood-derived Tat/Vif amino acid sequence diversity. To measure Trp-Kyn metabolites, a LC–MS/MS metabolomics platform was employed using a targeted approach. To measure immune markers, Enzyme-linked immunosorbent assays and the Particle-enhanced turbidimetric assay was used.ResultsAfter adjusting for covariates, sCD163 (p = 0.042) and KA (p = 0.031) were higher in participants with Tat signatures N24 and R57, respectively, and amino acid variation at position 24 (adj R2 = 0.048, β = -0.416, p = 0.042) and 57 (adj R2 = 0.166, β = 0.535, p = 0.031) of Tat were associated with sCD163 and KA, respectively.ConclusionsThese preliminary findings suggest that amino acid variation in Tat may have an influence on underlying pathogenic HIV-1 mechanisms and therefore, this line of work merits further investigation.

Tryptophan-Kynurenine Pathway Activation and Cognition in Virally Suppressed Women With HIV.

Immune and cognitive dysfunction persists even in virally suppressed women with HIV (VS-WWH). Since inflammation and HIV proteins induce the enzyme indoleamine 2,3-dioxygenase (IDO), converting tryptophan (T) to kynurenine (K) while producing downstream neurotoxic metabolites, we investigated IDO activation (KT ratio) in relation to cognition in VS-WWH and demographically similar women without HIV (WWoH). Ninety-nine VS-WWH on stable antiretroviral therapy and 102 WWoH (median age 52 vs 54 years; 73% vs 74% Black, respectively) from the New York and Chicago sites of the Women's Interagency HIV Study (WIHS) completed a neuropsychological test battery assessing motor function, processing speed, attention/working memory, verbal fluency, verbal learning and memory, and executive function and had plasma measured for tryptophan-kynurenine metabolites through liquid chromatography-tandem mass spectrometry and monocyte-derived [soluble cluster of differentiation-14 (sCD14), soluble cluster of differentiation-163 (sCD163), monocyte chemoattractant protein-1 (MCP-1)] plus general inflammatory markers [tumor necrosis factor alpha-2 receptor (TNF-R2), high-sensitivity C-reactive protein, high-sensitivity interleukin-6] through enzyme-linked immunosorbent assays between 2017 and 2020. VS-WWH had a higher KT ratio (P < 0.01) and higher sCD14 levels (P < 0.05) compared with WWoH. Higher sCD163 was associated with higher KT ratio (R = 0.29, P < 0.01) and worse fine motor function in VS-WWH; after adjusting for sCD163 and sCD14 in multivariable regressions, higher KT ratio remained significantly associated with impaired fine motor function in VS-WWH only (standardized β = -0.29, P < 0.05). IDO activation was not associated with cognition in WWoH. IDO activation (K:T) was associated with worse fine motor control in VS-WWH independent of measured systemic inflammation. Further studies investigating biological mechanisms linking IDO activation to fine motor function among VS-WWH are warranted.

Ido2 Deficiency Exacerbates Motor Impairment and Reduces Aryl Hydrocarbon Receptor Activity through Decreased Kynurenine in a Chronic Demyelinating Mouse Model.

Demyelinating diseases including multiple sclerosis (MS) are chronic inflammatory diseases of the central nervous system. Indoleamine 2,3-dioxygenase 2 (Ido2) is a recently identified as catalytic enzyme involved in the rate-limiting step of the tryptophan-kynurenine pathway that influences susceptibility to inflammatory diseases. However, the pathological role of Ido2 in demyelination remains unclear. In this study, we investigated whether Ido2 deficiency influences the pathogenesis of proteolipid protein transgenic (Plp tg) mice, an animal model of chronic demyelination. Ido2 deficiency exacerbates impairments of motor function in the locomotor activity test, wire hanging test, and rotarod test. Ido2 deficiency caused severe demyelination associated with CD68-positive microglial activation in Plp tg mice. In the cerebellum of Plp tg mice, Ido2 deficiency significantly increased the expression of Tnfα. Ido2 deficiency reduced tryptophan metabolite kynurenine (KYN) levels and subsequent aryl hydrocarbon receptor (AhR) activity, which play an important role in anti-inflammatory response. These results suggest that Ido2 has an important role in preventing demyelination through AhR. Taken together, Ido2 could be a potential therapeutic target for demyelinating diseases.

Qingfei mixture mitigates immunosuppression of tumor microenvironment in non-small cell lung cancer by blocking stat1/Ido1-mediated tryptophan-kynurenine pathway

Programmed death-1 (PD-1) acts as a T cell checkpoint and is important in controlling T cell exhaustion. Blocking the intercommunication across PD-1 and PD-L1 is promising for advanced lung cancer treatment. However, the response rate requires being strengthened. This study aimed to determine whether the combination treatment of Qingfei mixture (QFM) and PD-1 inhibitor could improve the sensitivity of monoclonal antibody by regulating STAT1/IDO1-mediated tryptophan (Trp)-kynurenine (Kyn) pathway. The in vivo imaging system, immunofluorescence, hematoxylin-eosin staining, TUNEL, flow cytometry, HPLC, and ELISA were used to estimate the anti-tumor effects in LLC-luc tumor-bearing C57BL/6 mice treated with QFM, PD-1 inhibitor, 2-NP (enhancer of STAT1 transcription), and FICZ (AhR agonist) alone or in combination. IFN-γ-mediated A549 and LLC cells were treated with QFM-containing serum and fludarabine (FLU, STAT1 inhibitor), and cell viability, apoptosis, and Kyn content were then evaluated using CCK-8 assays, flow cytometry, and HPLC assays, respectively. Additionally, the expressions of STAT1, IDO1, AhR, NFATc1, TRIP12, PD-1, and PD-L1 were measured in vivo and in vitro. We found QFM increased the anti-cancer actions of PD-1 inhibitors by increasing the CD8+IFNγ+ T cells infiltration and decreasing the ratio of Kyn/Trp. Besides, QFM-containing serum suppressed the proliferation and promoted apoptosis in A549 and LLC cells, meanwhile, FLU boosted the effects of QFM-containing serum. Moreover, the suppression of tumor growth in the combination therapy was attenuated in the mice receiving 2-NP or FICZ. The occurrence of the above results was accompanied by a decrease in STAT1, IDO1, AhR, PD-1, and PD-L1 expressions. Collectively, the findings suggested that QFM may increase the influences of PD-1 inhibitors at least partially by blocking the STAT1/IDO1-mediated tryptophan-kynurenine pathway in lung cancer.

PET Imaging of Neurofibromatosis Type 1 with a Fluorine-18 Labeled Tryptophan Radiotracer.

Neurofibromatosis type 1 (NF1) is a neurocutaneous disorder. Plexiform neurofibromas (PNFs) are benign tumors commonly formed in patients with NF1. PNFs have a high incidence of developing into malignant peripheral nerve sheath tumors (MPNSTs) with a 5-year survival rate of only 30%. Therefore, the accurate diagnosis and differentiation of MPNSTs from benign PNFs are critical to patient management. We studied a fluorine-18 labeled tryptophan positron emission tomography (PET) radiotracer, 1-(2-[18F]fluoroethyl)-L-tryptophan (L-[18F]FETrp), to detect NF1-associated tumors in an animal model. An ex vivo biodistribution study of L-[18F]FETrp showed a similar tracer distribution and kinetics between the wild-type and triple mutant mice with the highest uptake in the pancreas. Bone uptake was stable. Brain uptake was low during the 90-min uptake period. Static PET imaging at 60 min post-injection showed L-[18F]FETrp had a comparable tumor uptake with [1⁸F]fluorodeoxyglucose (FDG). However, L-[18F]FETrp showed a significantly higher tumor-to-brain ratio than FDG (n = 4, p < 0.05). Sixty-minute-long dynamic PET scans using the two radiotracers showed similar kidney, liver, and lung kinetics. A dysregulated tryptophan metabolism in NF1 mice was further confirmed using immunohistostaining. L-[18F]FETrp is warranted to further investigate differentiating malignant NF1 tumors from benign PNFs. The study may reveal the tryptophan-kynurenine pathway as a therapeutic target for treating NF1.

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&amp;lt;0.001). Neopterin was positively correlated with kynurenine (kyn) (r=0.25, β=0.57, Plinear&amp;lt;0.001), the KTR (r=0.42, β=0.87, Plinear&amp;lt;0.001), 3-hydroxykynurenine (r=0.26, β=0.32, Plinear&amp;lt;0.001), anthranilic acid (r=0.29, β=0.36, Plinear&amp;lt;0.001), and quinolinic acid (QA) (r=0.41, β=0.56, Plinear&amp;lt;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.

Kynurenine 3-monooxygenase limits de novo NAD+ synthesis through dietary tryptophan in renal proximal tubule epithelial cell models.

Nicotinamide adenine dinucleotide (NAD+) is a pivotal coenzyme, essential for cellular reactions, metabolism, and mitochondrial function. Depletion of kidney NAD+ levels and reduced de novo NAD+ synthesis through the tryptophan-kynurenine pathway are linked to acute kidney injury (AKI), whereas augmenting NAD+ shows promise in reducing AKI. We investigated de novo NAD+ biosynthesis using in vitro, ex vivo, and in vivo models to understand its role in AKI. Two-dimensional (2-D) cultures of human primary renal proximal tubule epithelial cells (RPTECs) and HK-2 cells showed limited de novo NAD+ synthesis, likely due to low pathway enzyme gene expression. Using three-dimensional (3-D) spheroid culture model improved the expression of tubular-specific markers and enzymes involved in de novo NAD+ synthesis. However, de novo NAD+ synthesis remained elusive in the 3-D spheroid culture, regardless of injury conditions. Further investigation revealed that 3-D cultured cells could not metabolize tryptophan (Trp) beyond kynurenine (KYN). Intriguingly, supplementation of 3-hydroxyanthranilic acid into RPTEC spheroids was readily incorporated into NAD+. In a human precision-cut kidney slice (PCKS) ex vivo model, de novo NAD+ synthesis was limited due to substantially downregulated kynurenine 3-monooxygenase (KMO), which is responsible for KYN to 3-hydroxykynurenine conversion. KMO overexpression in RPTEC 3-D spheroids successfully reinstated de novo NAD+ synthesis from Trp. In addition, in vivo study demonstrated that de novo NAD+ synthesis is intact in the kidney of the healthy adult mice. Our findings highlight disrupted tryptophan-kynurenine NAD+ synthesis in in vitro cellular models and an ex vivo kidney model, primarily attributed to KMO downregulation.NEW & NOTEWORTHY Nicotinamide adenine dinucleotide (NAD+) is essential in regulating mitochondrial function. Reduced NAD+ synthesis through the de novo pathway is associated with acute kidney injury (AKI). Our study reveals a disruption in de novo NAD+ synthesis in proximal tubular models, but not in vivo, attributed to downregulation of enzyme kynurenine 3-monooxygenase (KMO). These findings highlight a crucial role of KMO in governing de novo NAD+ biosynthesis within the kidney, shedding light on potential AKI interventions.

Tryptophan-kynurenine metabolic pathway and daytime dysfunction in women with HIV.

Sleep disturbances are prevalent in women with HIV (WWH). Tryptophan-kynurenine (T-K) pathway metabolites are associated with alterations in actigraphy derived sleep measures in WWH, although may not always correlate with functional impairment. We investigated the relationship between T-K pathway metabolites and self-reported daytime dysfunction in WWH and women without HIV (WWoH). 141 WWH on stable antiretroviral therapy and 140 demographically similar WWoH enrolled in the IDOze Study had targeted plasma T-K metabolites measured using liquid chromatography-tandem mass spectrometry. We utilized the daytime dysfunction component of the Pittsburgh Sleep Quality Index (PSQI) to assess functional impairment across HIV-serostatus. Lower levels of 5-hydroxytryptophan and serotonin were associated with greater daytime dysfunction in all women. In WWH, daytime dysfunction was associated with increased kynurenic acid (R = 0.26, p < 0.05), and kynurenic acid-tryptophan (KA-T) ratio (R = 0.28, p < 0.01). WWH with daytime dysfunction had a 0.7 log fold increase in kynurenic acid compared to WWH without daytime dysfunction. Kynurenic acid levels and the KA-T ratio were associated with daytime dysfunction in WWH but not in WWoH. Longitudinal studies are needed to establish a causal relationship and directionality between T-K metabolic changes and sleep impairment in WWH.

A pilot investigation of the association between HIV-1 Vpr amino acid sequence diversity and the tryptophan-kynurenine pathway as a potential mechanism for neurocognitive impairment

HIV infection compromises both the peripheral and central immune systems due to its pathogenic and neuropathogenic features. The mechanisms driving HIV-1 pathogenesis and neuropathogenesis involve a series of events, including metabolic dysregulation. Furthermore, HIV-subtype-specific variations, particularly alterations in the amino acid sequences of key viral proteins, are known to influence the severity of clinical outcomes in people living with HIV. However, the impact of amino acid sequence variations in specific viral proteins, such as Viral protein R (Vpr), on metabolites within the Tryptophan (Trp)-kynurenine (Kyn) pathway in people living with HIV remains unclear. Our research aimed to explore the relationship between variations in the Vpr amino acid sequence (specifically at positions 22, 41, 45, and 55, as these have been previously linked to neurocognitive function) and peripheral Trp-Kyn metabolites. Additionally, we sought to clarify the systems biology of Vpr sequence variation by examining the link between Trp-Kyn metabolism and peripheral inflammation, as a neuropathogenic mechanism. In this preliminary study, we analyzed a unique cohort of thirty-two (n = 32) South African cART naïve people living with HIV. We employed Sanger sequencing to ascertain blood-derived Vpr amino acid sequence variations and a targeted LC-MS/MS metabolomics platform to assess Trp-Kyn metabolites, such as Trp, Kyn, kynurenic acid (KA), and quinolinic acid (QUIN). Particle-enhanced turbidimetric assay and Enzyme-linked immunosorbent assays were used to measure immune markers, hsCRP, IL-6, suPAR, NGAL and sCD163. After applying Bonferroni corrections (p =.05/3) and adjusting for covariates (age and sex), only the Vpr G41 and A55 groups was nearing significance for higher levels of QUIN compared to the Vpr S41 and T55 groups, respectively (all p =.023). Multiple regression results revealed that Vpr amino acid variations at position 41 (adj R2 = 0.049, β = 0.505; p =.023), and 55 (adj R2 = 0.126, β = 0.444; p =.023) displayed significant associations with QUIN after adjusting for age and sex. Lastly, the higher QUIN levels observed in the Vpr G41 group were found to be correlated with suPAR (r =.588, p =.005). These results collectively underscore the importance of specific Vpr amino acid substitutions in influencing QUIN and inflammation (specifically suPAR levels), potentially contributing to our understanding of their roles in the pathogenesis and neuropathogenesis of HIV-1.

Metabolomic changes in adults with status epilepticus: Ahuman case-control study.

Status epilepticus (SE) is a life-threatening prolonged epileptic seizure that affects ~40 per 100 000 people yearly worldwide. The persistence of seizures may lead to excitotoxic processes, neuronal loss, and neuroinflammation, resulting in long-term neurocognitive and functional disabilities. A better understanding of the pathophysiological mechanisms underlying SE consequences is crucial for improving SE management and preventing secondary neuronal injury. We conducted a comprehensive untargeted metabolomic analysis, using liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS), on plasma and cerebrospinal fluid (CSF) samples from 78 adult patients with SE and 107 control patients without SE, including 29 with CSF for both groups. The metabolomic fingerprints were compared between patients with SE and controls. Metabolites with differences in relative abundances that could not be attributed to treatment or nutrition provided in the intensive care unit were isolated. Enrichment analysis was performed on these metabolites to identify the most affected pathways. We identified 76 metabolites in the plasma and 37 in the CSF that exhibited differential expression in patients with SE compared to controls. The enrichment analysis revealed that metabolic dysregulations in patients with SE affected primarily amino acid metabolism (including glutamate, alanine, tryptophan, glycine, and serine metabolism), pyrimidine metabolism, and lipid homeostasis. Specifically, patients with SE had elevated levels of pyruvate, quinolinic acid, and keto butyric acid levels, along with lower levels of arginine, N-acetylaspartylglutamate (NAAG), tryptophan, uracil, and uridine. The tryptophan kynurenine pathway was identified as the most significantly altered in SE, resulting in the overproduction of quinolinic acid, an N-methyl-d-aspartate (NMDA) receptor agonist with pro-inflammatory properties. This study has identified several pathways that may play pivotal roles in SE consequences, such as the tryptophan kynurenine pathway. These findings offer novel perspectives for the development of neuroprotective therapeutics.

Association between metabolites in tryptophan-kynurenine pathway and inflammatory bowel disease: a two-sample Mendelian randomization

Previous observational studies have suggested an association between tryptophan (TRP)–kynurenine (KYN) pathway and inflammatory bowel disease (IBD). However, whether there is a causal relationship among them remains unclear. Therefore, a two-sample Mendelian randomization (MR) study was conducted to explore the potential causal effects of crucial metabolites in TRP–KYN pathway on IBD and its subtypes. Using summary data from genome-wide association studies, a two-sample MR was employed to evaluate the genetic associations between TRP and KYN as exposures and IBD as an outcome. The inverse variance weighted method was used as the primary MR analysis, with MR-Egger, weighted mode, simple mode, and weighted median methods as complementary analyses. The odds ratios (OR) and 95% confidence intervals (CI) were determined for TRP–IBD (OR 0.739, 95% CI [0.697; 0.783]), TRP–UC (OR 0.875, 95% CI [0.814; 0.942]), TRP–CD (OR 0.685, 95% CI [0.613; 0.765]), KYN–IBD (OR 4.406, 95% CI [2.247; 8.641]), KYN–UC (OR 2.578, 95% CI [1.368; 4.858], and KYN–CD (OR 13.516, 95% CI [4.919; 37.134]). Collectively, the MR analysis demonstrated a significant protective association between TRP and IBD, whereas KYN was identified as a risk factor for IBD.

Indoleamine 2,3-dioxygenase 2 deficiency associates withautism-like behavior via dopaminergic neuronal dysfunction.

Indoleamine 2,3-dioxygenase 2 (IDO2) is an enzyme of the tryptophan-kynurenine pathway that is constitutively expressed in the brain. To provide insight into the physiological role of IDO2 in the brain, behavioral and neurochemical analyses in IDO2 knockout (KO) mice were performed. IDO2 KO mice showed stereotyped behavior, restricted interest and social deficits, traits that are associated with behavioral endophenotypes of autism spectrum disorder (ASD). IDO2 was colocalized immunohistochemically with tyrosine-hydroxylase-positive cells in dopaminergic neurons. In the striatum and amygdala of IDO2 KO mice, decreased dopamine turnover was associated with increased α-synuclein level. Correspondingly, levels of downstream dopamine D1 receptor signaling molecules such as brain-derived neurotrophic factor and c-Fos positive proteins were decreased. Furthermore, decreased abundance of ramified-type microglia resulted in increased dendritic spine density in the striatum of IDO2 KO mice. Both chemogenetic activation of dopaminergic neurons and treatment with methylphenidate, a dopamine reuptake inhibitor, ameliorated the ASD-like behavior of IDO2 KO mice. Sequencing analysis of exon regions in IDO2 from 309 ASD samples identified a rare canonical splice site variant in one ASD case. These results suggest that the IDO2 gene is, at least in part, a factor closely related to the development of psychiatric disorders.

Structure–activity relationship studies of 5-(Pyridin-3-yl)-1H-indole-4,7-diones as indoleamine 2,3-dioxygenase 1 inhibitors

Indoleamine 2,3-dioxygenase 1 (IDO1) is the key enzyme that catalyzes the conversion of l-tryptophan (Trp) to N-formyl-kynurenine in the tryptophan-kynurenine (Trp-Kyn) pathway. Overexpression of IDO1 contributes to the depletion of Trp and the accumulation of Kyn, which can result in tumor immune escape. Inhibition of IDO1 can restore the host immune response to eradicate cancer cells. 5-(Pyridin-3-yl)-1H-indole-4,7-dione was developed as the scaffold for a type of IDO1 inhibitors from simplification of the structure of exiguamine A in our previous work. In the present study, we designed and synthesized a series of compounds with different side-chain substituents, and linkers of varying lengths, at the 3-position, to design compounds with an aryl motif that can occupy pocket B of the IDO1 protein. Most compounds exhibited potent IDO1 inhibitory activity with IC50 values at the micromolar level, and 3-(2-((4-fluorobenzyl)amino)ethyl)-5-(3-pyridyl)-1H-indole-4,7-dione (1d) displayed the most potent inhibition with a half-maximal inhibitory concentration (IC50) value of 0.125 μM in an enzymatic assay and a half-maximal effective concentration (EC50) value of 0.821 μM in a cellular assay. Compound 1d showed higher selectivity for IDO1 over indoleamine 2,3-dioxygenase 2 and tryptophan 2,3-dioxygenase at the effective concentration. Molecular docking studies and molecular dynamic simulations suggested that the phenyl ring of these inhibitors can enter into pocket B of IDO1 and interact with the residue Phe 226 through hydrophobic interactions.

Longitudinal associations of macronutrient and micronutrient intake with plasma kynurenines in colorectal cancer survivors up to 12 months posttreatment

BackgroundThe tryptophan-kynurenine pathway is increasingly recognized to play a role in health-related quality of life (HRQoL) after cancer. Because tryptophan is an essential amino acid, and vitamins and minerals act as enzymatic cofactors in the tryptophan-kynurenine pathway, a link between diet and kynurenines is plausible. ObjectivesThis study aimed to investigate the longitudinal associations of macronutrient and micronutrient intake with metabolites of the kynurenine pathway in colorectal cancer (CRC) survivors up to 12 mo posttreatment. MethodsIn a prospective cohort of stage I–III CRC survivors (n = 247), repeated measurements were performed at 6 wk, 6 mo, and 12 mo posttreatment. Macronutrient and micronutrient intake was measured by 7-d dietary records. Plasma concentrations of tryptophan and kynurenines were analyzed using liquid chromatography tandem mass spectrometry (LC/MS-MS). Longitudinal associations were analyzed using linear mixed models adjusted for sociodemographic, clinical, and lifestyle factors. ResultsAfter adjustment for multiple testing, higher total protein intake was positively associated with kynurenic acid (KA) (β as standard deviation [SD] change in KA concentration per 1 SD increase in total protein intake: 0.12; 95% CI: 0.04, 0.20), xanthurenic acid (XA) (standardized β: 0.22; 95% CI: 0.11, 0.33), 3-hydroxyanthranilic acid (HAA) (standardized β: 0.15; 95% CI: 0.04, 0.27) concentrations, and the kynurenic acid-to-quinolinic acid ratio (KA/QA) (standardized β: 0.12; 95% CI: 0.02,0.22). In contrast, higher total carbohydrate intake was associated with lower XA concentrations (standardized β: −0.18; 95% CI: −0.30, −0.07), a lower KA/QA (standardized β: −0.23; 95% CI: −0.34, −0.13), and a higher kynurenine-to-tryptophan ratio (KTR) (standardized β: 0.20; 95% CI: 0.10, 0.30). Higher fiber intake was associated with a higher KA/QA (standardized β: 0.11; 95% CI: 0.02, 0.21) and a lower KTR (standardized β: −0.12; 95% CI: −0.20, −0.03). Higher total fat intake was also associated with higher tryptophan (Trp) concentrations (standardized β: 0.18; 95% CI: 0.06, 0.30) and a lower KTR (standardized β: −0.13; 95% CI: −0.22, −0.03). For micronutrients, positive associations were observed for zinc with XA (standardized β: 0.13; 95% CI: 0.04, 0.21) and 3-hydroxykynurenine (HK) (standardized β: 0.12; 95% CI: 0.03, 0.20) concentrations and for magnesium with KA/QA (standardized β: 0.24; 95% CI: 0.13, 0.36). ConclusionsOur findings show that intake of several macronutrients and micronutrients is associated with some metabolites of the kynurenine pathway in CRC survivors up to 12 mo posttreatment. These results may be relevant for enhancing HRQoL after cancer through potential diet-induced changes in kynurenines. Further studies are necessary to confirm our findings.

Plasma Tryptophan-Kynurenine Pathway Metabolites and Risk for Progression to End-Stage Kidney Disease in Patients With Type 2 Diabetes.

We sought to study the associations between plasma metabolites in the tryptophan-kynurenine pathway and the risk of progression to end-stage kidney disease (ESKD) in patients with type 2 diabetes. Plasma tryptophan, kynurenine, 3-hydroxykynurenine, kynurenic acid, and xanthurenic acid concentrations were measured in discovery (n = 1,915) and replication (n = 346) cohorts. External validation was performed in Chronic Renal Insufficiency Cohort (CRIC) participants with diabetes (n = 1,312). The primary outcome was a composite of incident ESKD (progression to estimated glomerular filtration rate [eGFR] <15 mL/min/1.73 m2, sustained dialysis, or renal death). The secondary outcome was annual eGFR decline. In the discovery cohort, tryptophan was inversely associated with risk for ESKD, and kynurenine-to-tryptophan ratio (KTR) was positively associated with risk for ESKD after adjustment for clinical risk factors, including baseline eGFR and albuminuria (adjusted hazard ratios [HRs] 0.62 [95% CI 0.51, 0.75] and 1.48 [1.20, 1.84] per 1 SD). High levels of kynurenic acid and xanthurenic acid were associated with low risks of ESKD (0.74 [0.60, 0.91] and 0.74 [0.60, 0.91]). Consistently, high levels of tryptophan, kynurenic acid, and xanthurenic acid were independently associated with a slower eGFR decline, while a high KTR was predictive of a faster eGFR decline. Similar outcomes were obtained in the replication cohort. Furthermore, the inverse association between kynurenic acid and risk of ESKD was externally validated in CRIC participants with diabetes (adjusted HR 0.78 [0.65, 0.93]). Accelerated catabolism of tryptophan in the kynurenine pathway may be involved in progressive loss of kidney function. However, shunting the kynurenine pathway toward the kynurenic acid branch may potentially slow renal progression.