Kynurenine Levels Research Articles

Therapeutic effects of in vivo administration of an inhibitor of tryptophan 2,3-dioxygenase (680c91) for the treatment of fibroids: a preclinical study

ObjectiveFibroids are characterized by marked overexpression of Tryptophan 2,3 dioxygenase (TDO2). The objective of this study was to determine the effectiveness of in vivo administration of an inhibitor of TDO2 (680C91) on fibroid size and gene expression. DesignAnimal and ex vivo human study. SubjectsSCID mice bearing human fibroid xenografts treated with vehicle and TDO2 inhibitor. InterventionDaily intraperitoneal administration of 680C91 or vehicle for two months and in vitro studies with fibroid explants. Main Outcome MeasuresTumor weight and gene expression profile of xenografts and in vitro mechanistic experiments using fibroid explants. ResultsCompound 680C91 was well-tolerated with no effects on blood chemistry and body weight. Treatment of mice with 680C91 resulted in 30% reduction in the weight of fibroid xenografts after two months of treatment and as expected lower levels of kynurenine, the byproduct of tryptophan degradation and an endogenous ligand of AhR (aryl hydrocarbon receptor) in the xenografts. The expression of CYP1B1 (cytochrome P450 family 1 subfamily B member 1), TGF-β3 (transforming growth factor beta 3), FN1 (fibronectin), CDK2 (cyclin-dependent kinase 2), E2F1 (E2F transcription factor 1), IL-8 (interleukin 8) and SPARC (secreted protein acidic and cysteine rich) mRNA, were lower in the xenografts of mice treated with 680C91 as compared with vehicle controls. Similarly, the protein abundance of collagen, FN1, CYP1B1 and SPARC were lower in the xenografts of 680C91 treated mice as compared with vehicle controls. Immunohistochemical analysis of xenografts indicated decreased expression of collagen, Ki67 and E2F1 but no significant changes in cleaved caspase 3 expression in mice treated with 680C91. The levels of kynurenine in the xenografts showed a direct correlation with the tumor weight and FN1 levels. In vitro studies with fibroid explants showed a significant induction of CYP1B1, TGF-β3, FN1, CDK2, E2F1, IL8 and SPARC mRNA by tryptophan which could be blocked by co-treatment with 680C91 and the AhR antagonist CH-223191. ConclusionThe results indicate that correction of aberrant tryptophan catabolism in fibroids could be an effective treatment through its effect to reduce cell proliferation and ECM accumulation.

Antidepressant effects of Peiyuan Jieyu formula in a mouse model of chronic stress in conjunction with lipopolysaccharide-induced depression

ObjectiveTo explore the mechanism of the Peiyuan Jieyu formula in treating depression by assessing its impact on a lipopolysaccharide-induced (LPS-induced) depression mouse model. MethodsWe created a mouse model of depression by exposing mice that had previously received chronic stress to intraperitoneal LPS injections. The mice were divided into the following groups: control, model, fluoxetine, Tiansi Yin, Sini powder, and low-, medium-, and high-dose Peiyuan Jieyu formula groups. Forced swim and tail suspension tests were used to assess the efficacy of the depression (despair) model, and weight gain rates were also measured. Furthermore, serum levels of various depression and inflammation-associated molecules, including tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), tryptophan, 5-hydroxytryptamine, kynurenine (KYN), and kynurenic acid (KA) were assessed. Furthermore, the expression levels of ionic calcium-binding adaptor molecule-1 (IBA-1) and indoleamine 2,3-dioxygenase (IDO) mRNA in hippocampal microglia were measured. ResultsThe model group displayed greater despair-associated immobility, which was shortened in response to various doses of Peiyuan Jieyu formula. Furthermore, formula administration significantly reduced serum TNF-α levels and hippocampal IDO mRNA expression. The high formula dose also reduced IFN-γ and IBA-1 levels, the latter was also decreased in response to the medium formula dose. However, the low formula dose reduced serum KYN level and KYN/tryptophan (TRP) and KYN/KA ratios. ConclusionThe Peiyuan Jieyu formula holds immense potential in treating depression in a mouse model, potentially inhibiting inflammation and improving TRP-KYN metabolic disorders.

Relation of the kynurenine pathway with normal age: A systematic review

BackgroundThe kynurenine pathway (KP) is gaining more attention as a common pathway involved in age-related conditions. However, which changes in the KP occur due to normal ageing is still largely unclear. The aim of this systematic review was to summarize the available evidence for associations of KP metabolites with age. MethodsWe used an broad search strategy and included studies up to October 2023. ResultsOut of 8795 hits, 55 studies were eligible for the systematic review. These studies suggest that blood levels of tryptophan decrease with age, while blood and cerebrospinal fluid levels of kynurenine and its ratio with tryptophan increase. Studies investigating associations between cerebrospinal fluid and blood levels of kynurenic acid and quinolinic acid with age reported either positive or non-significant findings. However, there is a large heterogeneity across studies. Additionally, most studies were cross-sectional, and only few studies investigated associations with other downstream kynurenines. ConclusionsThis systematic review suggests that levels of kynurenines are positively associated with age. Larger and prospective studies are needed that also investigate a more comprehensive panel of KP metabolites and changes during the life-course.

Verification studies of tryptophan and kynurenine determination using HPLC and evaluation of the kynurenine pathway and neopterin levels in human colostrum samples.

Colostrum, the first breast fluid produced by mammals after giving birth, is followed by breast milk, which serves as the sole source of nutrients for breastfed newborns and infants. Tryptophan, an essential amino acid, plays a crucial role in the development and maturation of the central nervous system in infants. Tryptophan is primarily degraded through the kynurenine pathway. Owing to its sensitivity to dietary intake, immune-mediated tryptophan degradation is assessed by the kynurenine-to-tryptophan ratio, with a focus on one of the rate-limiting enzymes in the pathway. This study involved the validation of the simultaneous determination of tryptophan and kynurenine using HPLC. The validated method was then used to detect levels of tryptophan and kynurenine, as well as to calculate the kynurenine-to-tryptophan ratio in colostrum samples. Simultaneously, these results were compared with colostrum neopterin levels measured using commercial enzyme-linked immunosorbent assay kits. The mean levels for tryptophan, kynurenine, and neopterin were 17.3 ± 62.4 μM, 0.45 ± 0.03 μM, and 28.9 ± 2.6 nM, respectively. This study is among the few that have evaluated these parameters in colostrum samples. Neopterin levels secreted by the mammary gland were found not to be correlated with tryptophan degradation, a process influenced by the mother's nutritional status.

Distinct Temporal Dynamic Serum Metabolite Profiles Characterize Treatment Response and Early Toxicity after B-Cell Lymphoma Directed CAR-T-Cell Therapy

Introduction: CD19 chimeric antigen receptor T-cell therapy (CD19.CAR-T) has profoundly improved treatment options for patients with relapsed/refractory B-cell lymphomas (r/r BCL), but is also associated with distinct toxicities. To elucidate host-intrinsic immunometabolic factors contributing to clinical benefit or immunotoxicity, we recently demonstrated that an increase of metabolically high-risk adipose tissue mass is associated with an elevated cytokine release syndrome (CRS) risk but also with improved survival (Haematologica 2022, CIR 2023). To gain further insights into the underlying immunometabolic mechanisms, we analyzed temporal dynamic changes of serum metabolites in r/r BCL patients during the first 14 days of CD19.CAR-T treatment. Methods: In this single-center analysis, we studied patients receiving CD19.CAR-T for r/r large BCL or mantle cell lymphoma (MCL) between 01/2019 and 12/2021 in a real-world setting. All patients were consecutively treated in our department (LMU University Hospital) and serum was prospectively collected in the morning hours from fasted patients beginning at the day of CAR-T infusion (D0), and 3-5 and 14 days later. Using liquid chromatography mass-spectrometry, we quantitatively analyzed a total of 305 water-soluble metabolites and 734 lipids. Metabolomic data was integrated with clinical patient records including CRS, 1-year progression-free survial (PFS) and amount of visceral adipose tissue (VAT). Results: In total, we measured 170 serum samples from 55 r/r LBCL and 4 r/r MCL patients, of which 52 had serial samples at all three time points (D0: 55, D3-5: 59, D14: 56). The following CAR-T products were administered: axi-cel (n = 26), tisa-cel (n = 29) and brexu-cel (n = 4). 25 (42.4%) patients developed a CRS grade ≥ 2, while 34 patients had a CRS grade 0-1. The best 90-day overall response rate was 52.5%, with a complete remission rate of 42.4%. At 1 year, 67.8% of patients progressed. From the 1039 metabolites measured, 525 metabolites passed quality control. Metabolite values were normalized and auto-scaled for further analysis. A partial least square differential analysis based on the collected time points led to a clear separation of samples with uric acid, desoxy-ribose-5-phosphate (dRibose-P), essential amino acids and (phospho)lipids having the strongest impact. Whereas 56 metabolites showed a significant increase from D0 to D14 led by uric and essential amino acids, 34 metabolites decreased over the course of treatment with the strongest reduction in dRibose-P and sphingosine phosphate. Performing a metabolic pathway enrichment analysis based on the most altered metabolite levels, we detected 22 significantly affected metabolic pathways and programs including aerobic glycolysis, urea cycle, amino acid and lipid metabolism (FDR < 0.1, Fig. 1A). To further delineate metabolite changes in regards to CRS, 1-year PFS and amount of VAT, we conducted a multivariate empirical bayes analysis of variance to specifically detect metabolites with differential temporal dynamics and considered all metabolites with an FDR < 0.1. Patients who developed a CRS ≥ 2° showed increased levels of kynurenine, phosphatidylethanolamides and lysophosphatidylserines, and decreased levels of ornithine and phosphatidylinositols. 1-year progressors showed a significant increase of several phosphatidylinositols beginning at D3-5 after CAR-T infusion, and decreased levels of phosphatidylcholines. For VAT, we used a threshold of 144 cm² which was derived from previously conducted computer tomography segmentation analyses. As expected, VAT cohorts mostly differed in fatty acid metabolism-associated metabolites including (acyl)carnitines, cholesterol esters, triglycerides and xanthine. In order to identify metabolites being associated with multiple outcomes, we looked for mutual metabolites among distinct cohort profiles. Here, one example is phosphatidylinositol-(22:5/16:0), which was increased in CRS 0-1° and 1y-progressors ( Fig. 1B). Conclusions: Our study highlights that CD19.CAR-T treatment is accompanied by broad changes in the serum metabolome of r/r BCL patients, which can be used to profile patients being affected by CAR-T-related immunotoxicity and their response to treatment. In ongoing analyses, we evaluate the use of these profiles for predictive models, and assess their impact on CAR-T cell function in-vitro.

Systemic perturbations in amino acids/amino acid derivatives and tryptophan pathway metabolites associated with murine influenza A virus infection

BackgroundInfluenza A virus (IAV) is the only influenza virus causing flu pandemics (i.e., global epidemics of flu disease). Influenza (the flu) is a highly contagious disease that can be deadly, especially in high-risk groups. Worldwide, these annual epidemics are estimated to result in about 3 to 5 million cases of severe illness and in about 290,000 to 650,000 respiratory deaths. We intend to reveal the effect of IAV infection on the host′s metabolism, immune response, and neurotoxicity by using a mouse IAV infection model.Methods51 metabolites of murine blood plasma (33 amino acids/amino acid derivatives (AADs) and 18 metabolites of the tryptophan pathway) were analyzed by using Ultra-High-Performance Liquid Chromatography-Mass Spectrometry with Electrospray Ionization at the acute (7 days post-infection (dpi)), resolution (14 dpi), and recovery (21 dpi) stages of the virus infection in comparison with controls.ResultsAmong the 33 biogenic amino acids/AADs, the levels of five amino acids/AADs (1-methylhistidine, 5-oxoproline, α-aminobutyric acid, glutamine, and taurine) increased by 7 dpi, whereas the levels of ten amino acids/AADs (4-hydroxyproline, alanine, arginine, asparagine, cysteine, citrulline, glycine, methionine, proline, and tyrosine) decreased. By 14 dpi, the levels of one AAD (3-methylhistidine) increased, whereas the levels of five amino acids/AADs (α-aminobutyric acid, aminoadipic acid, methionine, threonine, valine) decreased. Among the 18 metabolites from the tryptophan pathway, the levels of kynurenine, quinolinic acid, hydroxykynurenine increased by 7 dpi, whereas the levels of indole-3-acetic acid and nicotinamide riboside decreased.ConclusionsOur data may facilitate understanding the molecular mechanisms of host responses to IAV infection and provide a basis for discovering potential new mechanistic, diagnostic, and prognostic biomarkers and therapeutic targets for IAV infection.

Regulation of kynurenine metabolism by blood donor genetics and biology impacts red cell hemolysis in vitro and in vivo

AbstractIn the field of transfusion medicine, the clinical relevance of the metabolic markers of the red blood cell (RBC) storage lesion is incompletely understood. Here, we performed metabolomics of RBC units from 643 donors enrolled in the Recipient Epidemiology and Donor Evaluation Study, REDS RBC Omics. These units were tested on storage days 10, 23, and 42 for a total of 1929 samples and also characterized for end-of-storage hemolytic propensity after oxidative and osmotic insults. Our results indicate that the metabolic markers of the storage lesion poorly correlated with hemolytic propensity. In contrast, kynurenine was not affected by storage duration and was identified as the top predictor of osmotic fragility. RBC kynurenine levels were affected by donor age and body mass index and were reproducible within the same donor across multiple donations from 2 to 12 months apart. To delve into the genetic underpinnings of kynurenine levels in stored RBCs, we thus tested kynurenine levels in stored RBCs on day 42 from 13 091 donors from the REDS RBC Omics study, a population that was also genotyped for 879 000 single nucleotide polymorphisms. Through a metabolite quantitative trait loci analysis, we identified polymorphisms in SLC7A5, ATXN2, and a series of rate-limiting enzymes (eg, kynurenine monooxygenase, indoleamine 2,3-dioxygenase, and tryptophan dioxygenase) in the kynurenine pathway as critical factors affecting RBC kynurenine levels. By interrogating a donor-recipient linkage vein-to-vein database, we then report that SLC7A5 polymorphisms are also associated with changes in hemoglobin and bilirubin levels, suggestive of in vivo hemolysis in 4470 individuals who were critically ill and receiving single-unit transfusions.

IMMU-27. NON-TUMOR CELL IDO1 NON-ENZYMATICALLY DECREASES RT + PD-1 MAB TREATMENT EFFICACY IN OLDER ADULTS WITH GLIOBLASTOMA

Abstract Checkmate 498 is a large, randomized, phase 3 clinical trial that demonstrated an improved hazard ratio for younger but not older adults with MGMT unmethylated GBM treated with RT + PD-1 mAb. In an effort to better understand the biological determinant, indoleamine 2,3 dioxygenase 1 (IDO1), and its relationship with reducing RT + PD-1 mAb treatment efficacy in older adults with GBM, we created and/or compared 20-26 month-old C57BL/6 background mice that were IDO1-T2A-GFP [wild-type (WT); negative control (n=16)], IDO1 enzyme null [with normal IDO1 expression potential but incapable of tryptophan metabolism (n=16)], IDO1KO (n=4), Ido1fl/fl (n=14), Lysm-Cre+→Ido1fl/fl [IDO1-deficient in monocytes, macrophages, and microglia (n=20)], CD11c-Cre+→Ido1fl/fl [IDO1-deficient in dendritic cells (n=23)], Tie2-Cre+→Ido1fl/fl [IDO1-deficient in endothelial cells (n=14)]. Mice were intracranially (ic.) engrafted with 5×103 syngeneic GL261 followed by treatment with radiation (RT) + PD-1 mAb beginning at 14-days post ic. IDO1 WT and IDO1 enzyme null mice had a survival rate of 12.5% and 18.75% at 90-day post ic., respectively, which was significantly reduced as compared to IDO1KO mice with a 75% survival rate (p< 0.05). Tie2-Cre+→Ido1fl/fl mice, CD11c-Cre+→Ido1fl/fl, and Lysm-Cre+→Ido1fl/fl mice had a 100%, 96%, and 70% survival rate at 90-day post ic., respectively, as compared to Ido1fl/fl mice with a 42% survival rate (p< 0.05). Significantly reduced kynurenine (KYN) levels were found in IDO1 enzyme null and IDO1KO mice as compared to WT mice (p< 0.001). Unexpectedly, kynurenine levels were also reduced in Tie2-Cre+→Ido1fl/fl but not in CD11c-Cre+→Ido1fl/fl, Lysm-Cre+→Ido1fl/fl or Ido1fl/fl mice (p< 0.05). Tryptophan (TRP) levels did not change between mouse groups. These data support the hypothesis that non-tumor cell IDO1 reduces immunotherapeutic efficacy in older adults with GBM through a TRP-KYN pathway-independent mechanism.

The tryptophan catabolite or kynurenine pathway in autism spectrum disorder; a systematic review and meta-analysis.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social communication and interaction, as well as rigid and unchanging interests and behaviors. Several studies have reported that activated immune-inflammatory and nitro-oxidative pathways are accompanied by depletion of plasma tryptophan (TRP), increased competing amino acid (CAAs) levels, and activation of the TRP catabolite (TRYCAT) pathway. This study aims to systematically review and meta-analyze data on peripheral TRP, CAAs, TRYCAT pathway activity, and individual TRYCATs, including kynurenine (KYN) and kynurenic acid (KA) levels, in the blood and urine of ASD patients. After extensively searching PubMed, Google Scholar, and SciFinder, a total of 25 full-text papers were included in the analysis, with a total of 6653 participants (3557 people with ASD and 3096 healthy controls). Our results indicate that blood TRP and the TRP/CAAs ratio were not significantly different between ASD patients and controls (standardized mean difference, SMD = -0.227, 95% confidence interval, CI: -0.540; 0.085, and SMD = 0.158, 95% CI: -0.042; 0.359), respectively. The KYN/TRP ratio showed no significant difference between ASD and controls (SMD = 0.001, 95% CI: -0.169; 0.171). Blood KYN and KA levels were not significantly changed in ASD. Moreover, there were no significant differences in urine TRP, KYN, and KA levels between ASD and controls. We could not establish increases in neurotoxic TRYCATs in ASD. In conclusion, this study demonstrates no abnormalities in peripheral blood TRP metabolism, indoleamine 2,3-dioxygenase enzyme (IDO) activity, or TRYCAT production in ASD. Reduced TRP availability and elevated neurotoxic TRYCAT levels are not substantial contributors to ASD's pathophysiology.

Kynurenine, Kynurenic Acid, Quinolinic Acid and Interleukin-6 Levels in the Serum of Patients with Autism Spectrum Disorder.

Background and Objectives: It is known that inflammatory processes play a role in the pathogenesis of autism spectrum disorder (ASD). It is also reported that immune activation induces the kynurenine pathway (KP), as known as the tryptophan destruction pathway. In our study, we aimed to investigate whether the serum levels of KP products and interleukin (IL)-6 activating indolamine 2-3 dioxygenase (IDO) enzyme are different in healthy developing children and children with ASD. Materials and Methods: Forty-three ASD children aged 2-9 were included in this study. Forty-two healthy developing children, similar to the patient group in terms of age and gender, were selected as the control group. Serum levels of kynurenic acid, kynurenine, quinolinic acid and IL-6 were analyzed using the ELISA method. ASD severity was evaluated with the Autism Behavior Checklist (ABC). Results: The mean age of children with ASD was 42.4 ± 20.5 months, and that of healthy controls was 48.1 ± 15.8 months. While the serum levels of kynurenic acid, kynurenine and interleukin-6 were higher in the group with ASD (p < 0.05), there was no significant difference (p > 0.05) in terms of the quinolinic acid level. There was no significant difference between the ABC total and subscale scores of children with ASD and biochemical parameters (p > 0.05). Conclusions: We conclude that these biomarkers must be measured in all ASD cases. They may be important for the diagnosis of ASD.

Lifelong exposure to n-3 PUFA deficiency leads to anxiety-like profile in male and female adolescent rats: Impact on spleen-brain axis

Low consumption of n-3 polyunsaturated fatty acids (PUFA) during the developmental period has been increasingly associated with an increased risk of depressive-like symptoms in both male and female sexes. Therefore, here we performed behavioral and biochemical quantifications in adolescent rats to evaluate possible sex-driven differences in the development of anxiety-like disorders related to life-long n-3 PUFA low intake. Male and female adolescent rats fed for their entire life with n-3 PUFA poor diet showed an anxiety-like profile compared to n6/n-3 PUFA balanced diet. However, such deficiency led to reduced cortical serotonin (5-HT) in females, while increased GABA levels were retrieved in males. Conversely, in amygdala, 5-HT and noradrenaline (NA) were increased in n-3 PUFA poor treated rats. In male rats, n-3 PUFA poor diet induced significant increase in systemic kynurenine levels, while the pro-oxidant metabolite 3-Hydroxy kynurenine was higher in both sexes. In addition, considering the recent involvement of spleen-brain axis on mood disorders and neuroimmune communication, we evaluated biomarkers in the spleen. N-3 PUFA deprivation reduced NA content and increased the indoleamine 2,3-dioxygenase-1 expression in females, while acetylcholine and tumor necrosis factor alpha were higher in males. Taken together, our data indicated that deficiency of n-3 PUFA in diet induced mood disorders in adolescent animals, however this behavioral phenotype is accompanied by a different immune activation in male and female rats.

Tryptophan metabolites and incident cardiovascular disease: The EPIC-Norfolk prospective population study

Background and aimsCardiovascular disease (CVD) remains the largest cause of death globally due to various risk factors. One novel potential contributor to CVD might be the metabolism of the essential amino acid tryptophan (Trp), which through many pathways can produce immunomodulatory metabolites such as kynurenine, indole-3-propionate and serotonin. We aim to identify the metabolites with the strongest association with cardiovascular disease, utilizing a substantial and diverse cohort of individuals. In our pursuit of this aim, our primary focus is to validate and reinforce the findings from previous cross-sectional studies. MethodsWe used the community-based EPIC-Norfolk cohort (46.3 % men, age 59.8 ± 9.0) with a median follow-up of 22.1 (17.6–23.3) years to study associations between the relative levels of Trp metabolites measured with untargeted metabolomics and incident development of CVD. Serum from n = 11,972 apparently healthy subjects was analysed, of which 6982 individuals had developed CVD at the end of follow-up. Cox proportional hazard models were used to study associations, adjusted for sex, age, conventional cardiovascular risk factors and CRP. All metabolites were Ln-normalised prior to analysis. ResultsHigher levels of Trp were inversely associated with mortality (HR 0.73; CI 0.64–0.83) and fatal CVD (HR 0.76; CI 0.59–0.99). Higher levels of kynurenine (HR 1.33; CI 1.19–1.49) and the [Kynurenine]/[Tryptophan]-ratio (HR 1.24; CI 1.14–1.35) were associated with a higher incident development of CVD. Serotonin was not associated with overall CVD, but we did find associations for myocardial infarction and stroke. Adjustment for CRP did not yield any discernible differences in effect size. ConclusionsTryptophan levels were inversely correlated with CVD, while several of its major metabolites (especially kynurenine and serotonin) were positively correlated. These findings indicate that mechanistic studies are required to understand the role of Trp metabolism in CVD with the goal to identify new therapeutic targets.

The possible role of quinolinic acid as a predictive marker in patients with SARS-CoV-2

Background and aimsQuinolinic acid (QA) is a metabolite of the kynurenine pathway, which is activated by inflammatory stimuli during viral infection. We investigated the role of QA in patients infected with SARS-CoV-2, particularly its prognostic value for survival. MethodsOverall, 104 unvaccinated inpatients were included, divided into a survival (N = 80) and a deceased group (N = 24). Plasma levels of tryptophan, kynurenine, QA, C-reactive protein (CRP) and procalcitonin (PCT) were measured on admission and after seven days. The QA/TRP ratio and the relative differences between the measurements for QA (QA-Diff) and QA/TRP (Diff-QA/TRP) were calculated. ResultsAmong the kynurenine pathway markers, QA-Diff showed the highest discriminatory power for the survival prognosis (Youden index 0.467, cut-off −1.3 %, AUC 0.733, p < 0.001, sensitivity 0.79, specificity 0.675). Among the inflammatory markers, CRP showed the highest discriminatory power (Youden index 0.533, cut-off 25.0 mg/L, AUC 0.794, p < 0.001, sensitivity 0.958, specificity 0.575). A significant correlation between QA and PCT was found on admission and after one week (Spearman‘s rho 0.455 and 0.539, all p-values < 0.001). ConclusionsQA may serve as prognostic marker for survival in patients with SARS-CoV-2. The repeated measurements during the first week of the disease may enhance the prognostic power.

Organic cation transporter 2 contributes to SSRI antidepressant efficacy by controlling tryptophan availability in the brain

Selective serotonin reuptake inhibitors (SSRI) are common first-line treatments for major depression. However, a significant number of depressed patients do not respond adequately to these pharmacological treatments. In the present preclinical study, we demonstrate that organic cation transporter 2 (OCT2), an atypical monoamine transporter, contributes to the effects of SSRI by regulating the routing of the essential amino acid tryptophan to the brain. Contrarily to wild-type mice, OCT2-invalidated mice failed to respond to prolonged fluoxetine treatment in a chronic depression model induced by corticosterone exposure recapitulating core symptoms of depression, i.e., anhedonia, social withdrawal, anxiety, and memory impairment. After corticosterone and fluoxetine treatment, the levels of tryptophan and its metabolites serotonin and kynurenine were decreased in the brain of OCT2 mutant mice compared to wild-type mice and reciprocally tryptophan and kynurenine levels were increased in mutants’ plasma. OCT2 was detected by immunofluorescence in several structures at the blood-cerebrospinal fluid (CSF) or brain-CSF interface. Tryptophan supplementation during fluoxetine treatment increased brain concentrations of tryptophan and, more discreetly, of 5-HT in wild-type and OCT2 mutant mice. Importantly, tryptophan supplementation improved the sensitivity to fluoxetine treatment of OCT2 mutant mice, impacting chiefly anhedonia and short-term memory. Western blot analysis showed that glycogen synthase kinase-3β (GSK3β) and mammalian/mechanistic target of rapamycin (mTOR) intracellular signaling was impaired in OCT2 mutant mice brain after corticosterone and fluoxetine treatment and, conversely, tryptophan supplementation recruited selectively the mTOR protein complex 2. This study provides the first evidence of the physiological relevance of OCT2-mediated tryptophan transport, and its biological consequences on serotonin homeostasis in the brain and SSRI efficacy.

Study of the association between serum levels of kynurenine and cardiovascular outcomes and overall mortality in chronic kidney disease.

Kynurenine is a protein-bound uremic toxin. Its circulating levels are increased in chronic kidney disease (CKD). Experimental studies showed that it exerted deleterious cardiovascular effects. We sought to evaluate an association between serum kynurenine levels and adverse fatal or nonfatal cardiovascular events and all-cause mortality in CKD patients. The CKD-REIN study is a prospective cohort of people with CKD having an estimated glomerular filtration rate (eGFR) <60ml/min/1.73m². Baseline frozen samples of total and free fractions of kynurenine and tryptophan were measured using a validated liquid chromatography tandem mass spectrometry technique. Cause-specific Cox models were used to estimate hazard ratios (HRs) for each outcome. Of the 2406 included patients (median age: 68 years; median eGFR: 25ml/min/1.73m2), 52% had a history of cardiovascular disease. A doubling of serum-free kynurenine levels was associated with an 18% increased hazard of cardiovascular events [466 events, HR (95%CI):1.18(1.02,1.33)], independently of eGFR, serum-free tryptophan level or other uremic toxins, cardioprotective drugs, and traditional cardiovascular risk factors. Serum-free kynurenine was significantly associated with non-atheromatous cardiovascular events [HR(95%CI):1.26(1.03,1.50)], but not with atheromatous cardiovascular events [HR(95%CI):1.15(0.89,1.50)]. The association of serum-free kynurenine with cardiovascular mortality was also independently significant [87 events; adjusted HR(95%CI):1.64(1.10,2.40)]. However, the association of serum-free kynurenine with all-cause mortality was no more significant after adjustment on serum-free tryptophan [311 events, HR(95%CI):1.12(0.90, 1.40)]. Our findings imply that serum-free kynurenine, independently of other cardiovascular risk factors (including eGFR), is associated with fatal or nonfatal cardiovascular outcomes, particularly non-atheromatous cardiovascular events; in patients with CKD. Strategies to reduce serum kynurenine levels should be evaluated in further studies.

Attenuation of Chronic Stress-Induced Depressive-like Symptoms by Fish Oil via Alleviating Neuroinflammation and Impaired Tryptophan Metabolism in Aging Rats.

The prevalence of depression is increasing, and geriatric depression, in particular, is difficult to recognize and treat. Depression in older adults is often accompanied by neuroinflammation in the central nervous system (CNS). Neuroinflammation affects the brain's physiological and immune functions through several pathways and induces depressive symptoms. This study investigated the relationship among depression, neuroinflammation, and fish oil supplementation. Thirty-six male Sprague-Dawley rats were used in an aging-related depression animal model to simulate geriatric depression. Cognitive function, depressive-like symptoms, peripheral nervous system and CNS inflammation status, and the tryptophan-related metabolic pathway were analyzed. The geriatric depression animal model was associated with depressive-like behaviors and cognitive impairment. The integrity of the blood-brain barrier was compromised, resulting in increased expression of ionized calcium-binding adapter molecule 1 and the glial fibrillary acidic protein in the brain, indicating increased neuroinflammation. Tryptophan metabolism was also negatively affected. The geriatric-depressive-like rats had high levels of neurotoxic 5-hydroxyindoleacetic acid and kynurenine in their hippocampus. Fish oil intake improved depressive-like symptoms and cognitive impairment, reduced proinflammatory cytokine expression, activated the brain's glial cells, and increased the interleukin-10 level in the prefrontal cortex. Thus, fish oil intervention could ameliorate abnormal neurobehaviors and neuroinflammation and elevate the serotonin level in the hippocampus.

IDO-Kynurenine pathway mediates NLRP3 inflammasome activation-induced postoperative cognitive impairment in aged mice

Aim Postoperative cognitive dysfunction (POCD) is a common postoperative complication, especially in elderly patients. It extends hospital stay, increases the mortality rate and are heavy burdens to the family and society. Accumulating research has indicated that overactivation of pyrin domain-containing protein 3 (NLRP3) inflammasomes is related to POCD andplays a critical role in activating pro-inflammatory cytokines. According to existing studies, indoleamine 2,3-dioxygenase (IDO) is potently up-regulated by inflammatory factors, tryptophan in brain is mainly catalyzed by IDO to kynurenine (KYN), KYN metabolism may contribute to the development of depressive disorder and memory deficits. Hence, this study elucidated whether IDO-Kynurenine pathway mediates NLRP3 inflammasome activation-induced postoperative cognitive impairment in aged mice. Material and Methods POCD model was established in aged C57BL/6J mice by exploratory laparotomy under isoflurane anesthesia. Learning and memory were determined using Morris water maze. Results The data showed that IDO and kynurenine aminotransferase-II (KAT-II) mRNA in hippocampus was up-regulated, and NLRP3, caspase recruitment domain (ASC), interleukin-1b (IL-1b) and IDO overexpressed, KYN levels increased after anesthesia and surgery. NLRP3 inflammasome inhibitor (MCC950) reversed NLRP3, ASC, IL-1b and IDO overexpression, and the elevation of KYN levels. To clarify the role of IDO-Kynurenine pathway in postoperative cognitive impairment, IDO inhibitor (1-methyl-Ltryptophan 1-MT) reduced the elevation of KYN and kynurenic acid (KYNA) levels, reduction of tryptophan (TRP), as well as improved learning and memory abilities. Finally, KAT-II inhibitor (PF-04859989) reduced brain KYNA levels and restored the cognitive impairment. Conclusion These results reveal that IDO-Kynurenine pathway mediates NLRP3 inflammasome activation-induced postoperative cognitive impairment.

Ochratoxin A induces abnormal tryptophan metabolism in the intestine and liver to activate AMPK signaling pathway

BackgroundOchratoxin A (OTA) is a mycotoxin widely present in raw food and feed materials and is mainly produced by Aspergillus ochraceus and Penicillium verrucosum. Our previous study showed that OTA principally induces liver inflammation by causing intestinal flora disorder, especially Bacteroides plebeius (B. plebeius) overgrowth. However, whether OTA or B. plebeius alteration leads to abnormal tryptophan-related metabolism in the intestine and liver is largely unknown. This study aimed to elucidate the metabolic changes in the intestine and liver induced by OTA and the tryptophan-related metabolic pathway in the liver.Materials and methodsA total of 30 healthy 1-day-old male Cherry Valley ducks were randomly divided into 2 groups. The control group was given 0.1 mol/L NaHCO3 solution, and the OTA group was given 235 μg/kg body weight OTA for 14 consecutive days. Tryptophan metabolites were determined by intestinal chyme metabolomics and liver tryptophan-targeted metabolomics. AMPK-related signaling pathway factors were analyzed by Western blotting and mRNA expression.ResultsMetabolomic analysis of the intestinal chyme showed that OTA treatment resulted in a decrease in intestinal nicotinuric acid levels, the downstream product of tryptophan metabolism, which were significantly negatively correlated with B. plebeius abundance. In contrast, OTA induced a significant increase in indole-3-acetamide levels, which were positively correlated with B. plebeius abundance. Simultaneously, OTA decreased the levels of ATP, NAD+ and dipeptidase in the liver. Liver tryptophan metabolomics analysis showed that OTA inhibited the kynurenine metabolic pathway and reduced the levels of kynurenine, anthranilic acid and nicotinic acid. Moreover, OTA increased the phosphorylation of AMPK protein and decreased the phosphorylation of mTOR protein.ConclusionOTA decreased the level of nicotinuric acid in the intestinal tract, which was negatively correlated with B. plebeius abundance. The abnormal metabolism of tryptophan led to a deficiency of NAD+ and ATP in the liver, which in turn activated the AMPK signaling pathway. Our results provide new insights into the toxic mechanism of OTA, and tryptophan metabolism might be a target for prevention and treatment.Graphical

Reducing brain kynurenic acid synthesis precludes kynurenine-induced sleep disturbances.

Patients with neurocognitive disorders often battle sleep disturbances. Kynurenic acid is a tryptophan metabolite of the kynurenine pathway implicated in the pathology of these illnesses. Modest increases in kynurenic acid, an antagonist at glutamatergic and cholinergic receptors, result in cognitive impairments and sleep dysfunction. We explored the hypothesis that inhibition of the kynurenic acid synthesising enzyme, kynurenine aminotransferase II, may alleviate sleep disturbances. At the start of the light phase, adult male and female Wistar rats received systemic injections of either: (i) vehicle; (ii) kynurenine (100 mg kg-1; i.p.); (iii) the kynurenine aminotransferase II inhibitor, PF-04859989 (30 mg kg-1; s.c.); or (iv) PF-04859989 and kynurenine in combination. Kynurenine and kynurenic acid levels were evaluated in the plasma and brain. Separate animals were implanted with electroencephalogram and electromyogram telemetry devices to record polysomnography, and evaluate the vigilance states wake, rapid eye movement sleep and non-rapid eye movement sleep following each treatment. Kynurenine challenge increased brain kynurenic acid and resulted in reduced rapid eye movement sleep duration, non-rapid eye movement sleep delta power and sleep spindles. PF-04859989 reduced brain kynurenic acid formation when given prior to kynurenine, prevented disturbances in rapid eye movement sleep and sleep spindles, and enhanced non-rapid eye movement sleep. Our findings suggest that reducing kynurenic acid in conditions where the kynurenine pathway is activated may serve as a potential strategy for improving sleep dynamics.

Abnormal kynurenine-pathway metabolites in gout: Biomarkers exploration based on orthogonal partial least squares-discriminant analysis

BackgroundThis study aims to investigate serological characteristics of kynurenine pathway (KP) metabolites in healthy controls (HC) and gout patients and explore possible differential metabolites. MethodsA total of 191 individual fresh residual sera was collected from 129 HC and 62 gout patients. A liquid chromatography-tandem mass spectrometry method was fully validated to measure 6 metabolites, including tryptophan (TRP), kynurenine (KYN), 5-hydroxytryptamine (5HT), kynurenic acid (KA), xanthurenic acid (XA), and neopterin (NEO). Supervised orthogonal partial least squares-discriminant analysis (OPLS-DA) and differential metabolite screening with fold change (FC) were performed to identify intrinsic variations and differential levels of KP metabolites between the HC and gout groups. Logistic regression was used to assess the contributions of KP metabolites to gout. ResultsThere were significant decreases of TRP, 5HT, XA, and NEO and increases of KYN, KA, KA/KYN, and KYN/TRP in gout patients compared to the HC group (all p < 0.05). KP metabolites of the gout group showed good discrimination from those of the HC group (Q2: 0.892). Two distinct different metabolites were identified in gout, i.e., XA (FC: 0.56, p < 0.01) and NEO (FC: 0.34, p < 0.01). Of the KP metabolites, KYN was strongly associated with gout (OR: 7.91, p < 0.01). ConclusionsAbnormal levels of serum KP metabolites were observed in gout. XA and NEO are promising biomarkers that were relevant to the status of gout. The level of KYN could be an attractive checkpoint for the management of gout. Continuous monitoring of KP metabolism in gout provides new opportunities to predict therapeutic efficacy and prognosis.