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It is well-known that the pregnane X receptor (PXR)/Nr1i2 is a critical xenobiotic-sensing nuclear receptor enriched in liver and intestine and is responsible for drug-drug interactions, due to its versatile ligand binding domain (LBD) and target genes involved in xenobiotic biotransformation. PXR can be modulated by various xenobiotics including pharmaceuticals, nutraceuticals, dietary factors, and environmental chemicals. Microbial metabolites such as certain secondary bile acids (BAs) and the tryptophan metabolite indole-3-propionic acid (IPA) are endogenous PXR activators. Gut microbiome is increasingly recognized as an important regulator for host xenobiotic biotransformation and intermediary metabolism. PXR regulates and is regulated by the gut-liver axis. This review summarizes recent research advancements leveraging pharmaco- and toxico-metagenomic approaches that have redefined the previous understanding of PXR. Key topics covered in this review include: (1) genome-wide investigations on novel PXR-target genes, novel PXR-DNA interaction patterns, and novel PXR-targeted intestinal bacteria; (2) key PXR-modulating activators and suppressors of exogenous and endogenous sources; (3) novel bidirectional interactions between PXR and gut microbiome under physiologic, pathophysiological, pharmacological, and toxicological conditions; and (4) modifying factors of PXR-signaling including species and sex differences and time (age, critical windows of exposure, and circadian rhythm). The review also discusses critical knowledge gaps and important future research topics centering around PXR. SIGNIFICANCE STATEMENT: This review summarizes recent research advancements leveraging O'mics approaches that have redefined the previous understanding of the xenobiotic-sensing nuclear receptor pregnane X receptor (PXR). Key topics include: (1) genome-wide investigations on novel PXR-targeted host genes and intestinal bacteria as well as novel PXR-DNA interaction patterns; (2) key PXR modulators including microbial metabolites under physiological, pathophysiological, pharmacological, and toxicological conditions; and (3) modifying factors including species, sex, and time.

Objective The aryl hydrocarbon receptor (AHR) plays a key role in obesity. In vitro studies revealed that the tryptophan metabolite kynurenine (Kyn) activates AHR signaling in cultured hepatocytes. The objective of this study was to determine whether Kyn activated the AHR in mice to induce obesity. Methods Mice were fed a low-fat diet and the same diet supplemented with Kyn. Body mass, liver status, and the expression of identified relevant genes were determined. Results Kyn caused mice to gain significant body mass, develop fatty liver and hyperglycemia, and increase expression levels of cytochrome P450 1B1 and stearoyl-CoA desaturase 1. The hyperglycemia was accompanied with decreased insulin levels, which may have been due to the repression of genes involved in insulin secretion. Kyn plasma concentrations and BMI were measured in female patients, and a significant association was observed between Kyn and age in patients with obesity but not in patients who were lean. Conclusions Results show that (1) Kyn or a metabolite thereof is a ligand responsible for inducing AHR-based obesity, fatty liver, and hyperglycemia in mice; (2) plasma Kyn levels increase with age in women with obesity but not in lean women; and (3) an activated AHR is necessary but not sufficient to attain obesity, a status that also requires fat in the diet.

Polydextrose (PDX) is a branched glucose polymer, utilized as a soluble dietary fiber. Recently, PDX was found to have hypolipidemic effects and effects on the gut microbiota. To investigate these findings more closely, a non-targeted metabolomics approach, was exploited to determine metabolic alterations in blood and epididymal adipose tissue samples that were collected from C57BL/6 mice fed with a Western diet, with or without oral administration of PDX. Metabolomic analyses revealed significant differences between PDX- and control mice, which could be due to differences in diet or due to altered microbial metabolism in the gut. Some metabolites were found in both plasma and adipose tissue, such as the bile acid derivative deoxycholic acid and the microbiome-derived tryptophan metabolite indoxyl sulfate, both of which increased by PDX. Additionally, PDX increased the levels of glycine betaine and l-carnitine in plasma samples, which correlated negatively with plasma TG and positively correlated with bacterial genera enriched in PDX mice. The results demonstrated that PDX caused differential metabolite patterns in blood and adipose tissues and that one-carbon metabolism, associated with glycine betaine and l-carnitine, and bile acid and tryptophan metabolism are associated with the hypolipidemic effects observed in mice that were given PDX.

Several risk factors are known to be involved in the initiation and development of gastric cancer. Among them, H. pylori is one of the most prominent with multiple virulence factors contributing to its pathogenicity. In this study, we have discussed an interesting immunological cycle exploring the interplay between H. pylori, aryl hydrocarbon receptor (AHR), tryptophan, arginine, and the metabolites of these two amino acids in the development of gastric cancer. AHR is a ligand-activated transcription factor which acts as a regulator for a diverse set of genes and has various types of exogenous and endogenous ligands. The tryptophan metabolite, kynurenine, is one of these ligands that can interact with AHR, leading to immune suppression and subsequently, susceptibility to gastric cancer. On the other hand, H. pylori downregulates the expression of AHR and AHR repressor (AHRR), leading to increased inflammatory cytokine production. A metabolite of the kynurenine pathway, xanthurenic acid, is a potent inhibitor of a terminal enzyme in the synthetic pathway of tetrahydrobiopterin (BH4). BH4, itself, is a cofactor in the process of nitric oxide (NO) production from arginine that has been shown to have immune-enhancing properties. Arginine has also been evidenced to have anti-tumoral function through inducing apoptosis in gastric cell lines; however, controversy exists regarding the anti-tumor role of arginine and BH4, since they are also associated with increased NO production, subsequently promoting tumor angiogenesis. Hence, although several synergistic connections result in immunity improvement, these correlations can also act as a double-edged sword, promoting tumor development. This emphasizes on the need for further investigations to better understand this complex interplay.

Tryptophan and metabolites have important biological functions in humans. Milk is an important source of tryptophan intake. In this study, we developed a method to detect levels of tryptophan and 12 metabolites in milk. The analytes were extracted by using the QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure and analyzed by liquid chromatography-tandem mass spectrometry with electrospray ionization. The proposed method resulted in suitable accuracy (standard deviation ≤10.31%) and high sensitivity (the limits of quantification were between 0.05 and 5 ng/mL). Recoveries were in the range of 44 to 126%. Finally, the developed method was successfully applied to compare the content of tryptophan and metabolites in 4 milk products produced by different processes: pasteurized milk, UHT milk, milk powder, and yogurt. The results of partial least squares-discriminant analysis (PLS-DA) showed that different types of processed milk could be distinguished clearly according to the method used here. The determined tryptophan and metabolites levels in milk can provide a new reference for evaluation of milk.

Kynurenic acid, a tryptophan metabolite, acts as antagonist or agonist of several receptors. Hypobromous acid (HOBr) and hypochlorous acid (HOCl) are generated by eosinophils and neutrophils. At inflammation sites, kynurenic acid may encounter HOBr and HOCl to generate products. When kynurenic acid was incubated with HOBr under neutral conditions, kynurenic acid generated a single product almost exclusively. This was identified as 3-bromokynurenic acid. Kynurenic acid reacted with HOCl, generating two products. The major product was identified as 3-chlorokynurenic acid with its oxidative decarboxylation product, 3-chloro-4-hydroxy-2(1H)-quinolinone as a by-product. Free amino acids suppressed the reactions of kynurenic acid with HOBr and HOCl. Taurine suppressed the HOCl reaction but not the HOBr reaction. An eosinophil peroxidase system containing H2O2, NaCl, and NaBr reacted with kynurenic acid, generating 3-bromokynurenic acid under mildly acidic conditions. Although a myeloperoxidase system containing H2O2 and NaCl reacted with kynurenic acid to generate 3-chlorokynurenic acid under mildly acidic conditions, the product was altered to 3-bromokynurenic acid by addition of NaBr to the system. These results suggest that 3-bromokynurenic acid and 3-chlorokynurenic acid may be generated from kynurenic acid at inflammation sites in humans, although their formation will be suppressed by coexistent amino acids.

Recent advances in our understanding of the pathophysiology of atopic dermatitis (AD) have revealed that skin microbiome dysbiosis plays an important role in the disease. In this review, we describe how changes in the structure and function of the microbiome are involved in the pathogenesis of AD. We highlight recent data showing that differential changes in microbial diversity, both within and across communities from different body habitats (including the skin, gut, and oral mucosa), are associated with the development and severity of AD. We also describe recent evidence demonstrating that the metabolic activity of the skin microbiome can act as a regulator of inflammation, with alterations in the level of a skin microbiome-derived tryptophan metabolite, indole-3-aldehyde (IAId), being shown to play a role in AD. The various mechanisms by which interactions between the microbiome and components of the non-histaminergic pathway result in itch in AD are also discussed.

Tryptophan catabolism by the enzymes indoleamine 2,3-dioxygenase 1 and tryptophan 2,3-dioxygenase 2 (IDO/TDO) promotes immunosuppression across different cancer types. The tryptophan metabolite L-Kynurenine (Kyn) interacts with the ligand-activated transcription factor aryl hydrocarbon receptor (AHR) to drive the generation of Tregs and tolerogenic myeloid cells and PD-1 up-regulation in CD8+ T cells. Here, we show that the AHR pathway is selectively active in IDO/TDO-overexpressing tumors and is associated with resistance to immune checkpoint inhibitors. We demonstrate that IDO-Kyn-AHR-mediated immunosuppression depends on an interplay between Tregs and tumor-associated macrophages, which can be reversed by AHR inhibition. Selective AHR blockade delays progression in IDO/TDO-overexpressing tumors, and its efficacy is improved in combination with PD-1 blockade. Our findings suggest that blocking the AHR pathway in IDO/TDO expressing tumors would overcome the limitation of single IDO or TDO targeting agents and constitutes a personalized approach to immunotherapy, particularly in combination with immune checkpoint inhibitors., The tryptophan metabolite kynurenine is an endogenous ligand of the aryl hydrocarbon receptor (AHR). Here, the authors show that AHR targeting in IDO/TDO-expressing tumours counteracts a regulatory T cell/macrophage suppressive axis and synergizes with immune checkpoint blockade to hinder tumour growth.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy and is refractory to available treatments. Delineating the regulatory mechanisms of metabolic reprogramming, a key event in pancreatic cancer progression, may identify candidate targets with potential therapeutic significance. We hypothesized that inflammatory signaling pathways regulate metabolic adaptations in pancreatic cancer. Metabolic profiling of tumors from PDAC patients with a high‐ (>median, N=31) and low‐NOS2 (inducible nitric oxide synthase) (•(nitric oxide)‐mediated signaling pathway was elucidated. The level of kynurenine, a tryptophan metabolite, was associated with high NOS2 expression, and a higher level of kynurenine predicted poor survival in patients (N=63,P= 0.01). Gene expression analysis in PDAC tumors (N=63) showed a positive correlation between the expression of NOS2 and the tryptophan/kynurenine pathway genes, including indoleamine‐2,3‐dioxygenase 1 (IDO1) and several aryl hydrocarbon receptor (AHR)‐target genes includingNFE2L2(NRF2),SERPINB2, IL1b,IL6andIL8, which are implicated in pancreatic cancer. Consistently, treatment of pancreatic cancer cell lines with NO•donor induced IDO1, kynurenine production, and the expression of AHR‐target genes. Furthermore, kynurenine treatment enhanced spheroid growth and invasive potential of pancreatic cancer cell lines. Mechanistically, NO•‐induced IDO1/Kynurenine/AHR signaling was mediated by RUNX3 transcription factor. Our findings identified a novel NO•/RUNX3/Kynurenine metabolic axis, which enhances disease aggressiveness in pancreatic cancer and may have potential translational significance in improving disease outcome.

RATIONALE: Stress is related to cognitive impairments which are observed in most major brain diseases. Prior studies showed that the brain concentration of the tryptophan metabolite kynurenic acid (KYNA) is modulated by stress, and that changes in cerebral KYNA levels impact cognition. However, the link between these phenomena has not been tested directly so far. OBJECTIVES: To investigate a possible causal relationship between acute stress, KYNA and fear discrimination. METHODS: Adult rats were exposed to one of three acute stressors - restraint, predator odor, or inescapable foot shocks (ISS) - and KYNA in the prefrontal cortex was measured using microdialysis. Corticosterone was analyzed in a subset of rats. Another cohort underwent a fear discrimination procedure immediately after experiencing stress. Different auditory conditioned stimuli (CSs) were either paired with foot shock (CS+) or non-reinforced (CS−). One week later, fear was assessed by re-exposing rats to each CS. Finally, to test whether stress-induced changes in KYNA causally impacted fear discrimination, a group of rats that received ISS were pre-treated with the selective KYNA synthesis inhibitor PF-04859989. RESULTS: ISS caused the greatest increase in circulating corticosterone levels and raised extracellular KYNA levels by ~85%. The two other stressors affected KYNA much less (

In allergen-specific immunotherapy for asthma, antigens attached to dendritic cells increase the tryptophan metabolism in these cells and alter the Th17/Treg balance in the airways. Tryptophan metabolism has long been suggested to be relevant in the pathophysiology of allergic disorders, including asthma. Our study investigated whether tryptophan metabolites are responsible for the changes in Th17/Treg balance and decreases in airway hyperreactivity and inflammation seen during allergen-specific immunotherapy in an asthma model. Ovalbumin was injected intraperitoneally into mice to establish an asthma model, and then high dose ovalbumin allergen-specific immunotherapy was administered to induce immune tolerance. Airway hyperreactivity and serum ovalbumin-specific immunoglobulin E were measured to assess whether the animal model was successfully established. We then examined the influence of inhibition of tryptophan metabolism and the addition of tryptophan metabolites on allergen-specific immunotherapy-induced changes in the Th17/Treg balance and decreases in airway inflammation and inflammatory cytokines. Production of tryptophan metabolites was partly responsible for the allergen-specific immunotherapy-induced increase in Tregs, decrease in airway inflammation, and decrease in inflammatory cytokines. Ovalbumin-specific immunoglobulin E and airway hyperreactivity were not affected. In the context of asthma, an increase in tryptophan metabolites is one of the mechanisms by which allergen-specific immunotherapy achieves immune tolerance.

Tryptophan is an essential amino acid for the human body, whose intake is through the diet. Several studies support the theory that microbiota-derived tryptophan metabolite played a crucial role in maintaining the balance between gut microbiota and the mucosal immune system. Previously, we selected the Lactobacillus plantarum KLDS 1.0386 strain with high tryptophan-metabolic activity after the screening of 16 Lactobacillus strains. The current study aimed to assess the effects of L. plantarum KLDS 1.0386 combination with tryptophan in improving ulcerative colitis (UC) induced by dextran sodium sulfate (DSS) and the potential mechanisms involved. Our results showed that L. plantarum KLDS 1.0386 combined with tryptophan (LAB + Trp) decreased DAI score, MPO level, and pro-inflammatory cytokine (TNF-α, IL-1β, and IL-6) concentration. It also increased anti-inflammatory cytokine (IL-10) production, tight junction proteins (claudin-1, occludin, and ZO-1), and mucin (MUC1 and MUC2) mRNA expressions. The level of indole-3-acetic acid (IAA), an important tryptophan metabolite in the liver, serum, and colon, was elevated after LAB + Trp treatment, which further upregulated aryl hydrocarbon receptor (AHR) mRNA expression to activate the IL-22/STAT3 signaling pathway. Moreover, the supplementation with LAB + Trp modulated gut microbiota composition. The present study provided novel insights that can be used to reduce the number of UC patients by employing a method utilizing tryptophan-catabolizing Lactobacillus strains.

Tryptophan and kynurenine pathway (KP) metabolites are implicated in the pathophysiology of depression. We aimed to investigate their plasma concentrations in medicated patients with depression (n = 94) compared to age- and sex-matched healthy controls (n = 57), and in patients with depression after electroconvulsive therapy (ECT) in a real-world clinical setting, taking account of co-variables including ECT modality and heterogenous psychopathology. Depression severity was assessed using the Hamilton Depression Rating Scale (HAM-D24). Tryptophan (TRP) and kynurenine (KYN) metabolite concentrations [anthranilic acid (AA), 3-hydroxyanthranilic acid (3HAA), picolinic acid (PA), kynurenic acid (KYNA), and xanthurenic acid (XA)] and KYNA/KYN and KYNA/quinolinic acid (QUIN) ratios were lower in patients compared to controls. For the total group there was no significant change in KP metabolites post-ECT or correlations with mood ratings. However, improvements in mood score were correlated with increased KYN, 3-hydroxykynurenine (3HK), 3HAA, QUIN, and KYN/TRP in a subgroup of unipolar depressed patients. Additionally, in remitters baseline KYN, 3HK, and QUIN were associated with baseline HAM-D24 scores, and changes in 3HK and 3HAA concentrations post-ECT correlated with improvement in mood. KYN, KYNA, AA, 3HK, XA, PA, and QUIN were increased in a smaller 3-month follow-up group (n = 19) compared to pre-ECT concentrations. Overall, the results indicate that ECT mobilizes the KP, where a moderate association between selected metabolites and treatment response in unipolar depressed patients is evident.

The aryl hydrocarbon receptor (AhR) plays an important role in intestinal homeostasis, and some microbial metabolites of tryptophan are known AhR agonists. In this study, we assessed the impact of tryptophan supplementation on the formation of tryptophan metabolites, AhR activation, and microbiota composition in the simulator of the human intestinal microbial ecosystem (SHIME). AhR activation, microbial composition, and tryptophan metabolites were compared during high tryptophan supplementation (4 g/L tryptophan), control, and wash-out periods. During tryptophan supplementation, the concentration of several tryptophan metabolites was increased compared to the control and wash-out period, but AhR activation by fermenter supernatant was significantly decreased. This was due to the higher levels of tryptophan, which was found to be an antagonist of AhR signaling. Tryptophan supplementation induced most microbial changes in the transverse colon including increased relative abundance of lactobacillus. We conclude that tryptophan supplementation leads to increased formation of AhR agonists in the colon.

AimsNeutrophil granulocytes are the major cells involved in Chlamydia trachomatis (C. trachomatis)-mediated inflammation and histopathology. A key protein in human intracellular antichlamydial defense is the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) which limits the growth of the tryptophan auxotroph Chlamydia. Despite its importance, the role of IDO in the intracellular defense against Chlamydia in neutrophils is not well characterized.MethodsGlobal gene expression screen was used to evaluate the effect of C. trachomatis serovar D infection on the transcriptome of human neutrophil granulocytes. Tryptophan metabolite concentrations in the Chlamydia-infected and/or interferon-gamma (IFNG)-treated neutrophils were measured by ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS).ResultsOur results indicate that the C. trachomatis infection had a major impact on neutrophil gene expression, inducing 1,295 genes and repressing 1,510 genes. A bioinformatics analysis revealed that important factors involved in the induction of neutrophil gene expression were the interferon-related transcription factors such as IRF1-5, IRF7-9, STAT2, ICSB, and ISGF3. One of the upregulated genes was ido1, a known infection- and interferon-induced host gene. The tryptophan-degrading activity of IDO1 was not induced significantly by Chlamydia infection alone, but the addition of IFNG greatly increased its activity. Despite the significant IDO activity in IFNG-treated cells, C. trachomatis growth was not affected by IFNG. This result was in contrast to what we observed in HeLa human cervical epithelial cells, where the IFNG-mediated inhibition of C. trachomatis growth was significant and the IFNG-induced IDO activity correlated with growth inhibition.ConclusionsIDO activity was not able to inhibit chlamydial growth in human neutrophils. Whether the IDO activity was not high enough for inhibition or other chlamydial growth-promoting host mechanisms were induced in the infected and interferon-treated neutrophils needs to be further investigated.

Tranilast (TRL), a synthetic derivative of a tryptophan metabolite, is an anti-allergic drug used to treat bronchial asthma. We investigated how TRL activated the nuclear factor-erythroid 2 p45-related factor 2 (Nrf2)-hemeoxygenase-1 (HO-1) pathway based on the electrophilic chemistry of the drug and whether TRL activity contributed to the treatment of rat colitis. In human colon carcinoma cells, TRL activated Nrf2, as represented by an increase in nuclear Nrf2 and induction of Nrf2-dependent luciferase and, subsequently, HO-1, a target gene product of Nrf2. TRL activation of Nrf2 and induction of HO-1 were completely prevented by chemical reduction of the electrophilic functional group (α, β-unsaturated carbonyl group) in the drug. In parallel, TRL was reactive with the nucleophilic thiol group in N-acetylcysteine, forming a covalent adduct. Moreover, TRL, but not reduced TRL, binds to Kelch-like ECH-associated protein 1 (KEAP1), releasing Nrf2. TRL administration ameliorated colonic damage and inflammation in rats with dinitrobenzene sulfonic acid-induced colitis, which was partly compromised by the chemical reduction of TRL or co-treatment with an HO-1 inhibitor. Our results suggest that TRL activated the Nrf2-HO-1 pathway via covalent binding to KEAP1, partly contributing to TRL amelioration in rat colitis.

The moust symptoms of piglets infected with Encephalomyocarditis virus (EMCV) are related to breeding difficulty, circulation insufficiency, depression and occurrence of high lethality. An increase of tryptophan metabolism in the periphery and in the central nervous system (CNS) in human and non-human subjects with inflammatory diseases has been suggested. We investigated an alterations of tryptophan metabolite i.e. kynurenic acid (KYNA) level in the serum of piglets after EMC virus infection. In addition, we investigated the markers of immune stimulation i.e. neopterin and β2-microglobulin.KYNA was determined by high performance liquid chromatography method, while neopterin and β2-microglobulin by ELISA method. Piglets with an age of 8 weeks were infected intranasal and orally with the EMC virus. Blood samples were collected before virus inoculation at day 0 (control) and at 1, 2, 3 and 4 days post inoculation (DPI) and piglets as control subjects were used, too.In EMCV infected piglets we observed a time dependent alteration of investigated parameters. KYNA level increased significantly and at 3 DPI was 341% of CO, p0.001 and at 4 DPI an enhancement was 242% of CO, p0.001, respectively. Neopterin increased moderately after EMCV infection and at 4 DPI was 130% of CO, p0.05. Serum β2-microglobulin was slightly lowered and at 4 DPI was 86% of CO, p0.05. Present data indicate an marked increase of kynurenine metabolism in the periphery after EMCV infection and an moderate activation of immune system.A marked increase of KYNA and a moderate enhancement of neopterin indicate sensibility of kynurenine metabolism to EMCV infection. Lowering of ß2-microgobulin might relate to development of events leading to the lethality. We suggest that due to viral infection an increase of KYNA might contribute to the inpairment of organs in the periphery and CNS function and might participate by sudden death.

Background: The incidence of renal cell carcinoma (RCC) is increasing year by year. It is difficult to have complete treatment so far. Studies have shown that tryptophan metabolite Kynurenine (Kyn) affects cell proliferation, migration, apoptosis, adhesion, and differentiation. Our aim is to explore whether Kyn activates aromatic hydrocarbon receptor (AhR) to mediate RCC metastasis.Methods: We collected RCC tissues and feces from RCC patients. 16S rRNA technology was performed to analyze the gut microbial composition of RCC patients. LC-MS/MS was used to analyze the gut microbial metabolites. The AhR was inhibited and treated with Kyn. Immunofluorescence was used to measure the degree of AhR activation. The migration and invasion ability of 786-O cells was tested by Transwell assay. Flow cytometry and cell cycle assay were utilized to observe the apoptosis and cycle of 786-O cells. CCK-8 assay was used to detect 786-O cells proliferation. qRT-PCR and Western blot were used to detect AhR and EMT-related genes expression level.Results: AhR expression was up-regulated in RCC tissues. RCC gut microbiota was disordered. The proportion of Kyn was increased in RCC. After being treated with Kyn, the migration, invasion, and proliferation ability of 786-O cells were decreased. Furthermore, the expression of EMT-related protein E-cadherin decreased, and the expression of N-cadherin and Vimentin increased. The proportion of 786-O cells in the S phase increased. The apoptosis rate of 786-O cells was inhibited.Conclusion: The tryptophan metabolite Kyn could activate AhR. Kyn could promote 786-O cells migration and invasion. Gut microbiota could activate AhR through its tryptophan metabolite Kyn to mediate RCC metastasis.

Objective: Lithium is a cornerstone treatment option in bipolar disorder. Currently, only clinical findings are used to predict the response of lithium treatment but reliable biological marker has not yet been identified. With this background, it was aimed to compare tryptophan metabolite levels between bipolar patients and healthy control group and to investigate the relationship between lithium treatment response and tryptophan metabolite levels of euthymic bipolar patients(BP). Materials and Methods: 52 euthymic BP patients on lithium were included in the study. Sociodemographic and clinical information were recorded and lithium treatment response status was determined according to the Alda scale. Age and gender matched Healthy controls(HC) were selected from the people who admitted to Selcuk University Medical Faculty Hospital Health Board. Plasma tryptophan metabolite levels were compared between BP and HC. The correlation and association between the lithium response levels of the patients and the plasma tryptophan metabolites were evaluated. Results: Plasma tryptophan(TRP), kynurenine(KYN), kynurenine/tryptophan ratio(KYN/TRP), 3-hydroxy-kynurenine(3-HK) and kynurenic acid(KYNA) levels were significantly lower in BP than HC. In the regression analysis, only plasma KYNA concentrations were found to be significantly lower in the responding well to lithium treatment and TRP levels. None of the tryptophan metabolites were found to be associated well response to lithium treatment after the logistic regression analysis. Conclusion: Our findings indicate that KYNA levels might be used as a screening test for discriminating bipolar patients from the HC. TRP levels might be used to predict lithium treatment response in spite of low specifity and low sensitivity levels. Key words: Tryptophan metabolites, lithium treatment response, bipolar disorder

Cage layer fatigue is a common metabolic disease associated with a calcium and phosphorus imbalance, but recently we found this disease can be led by high fat diet. In order to elucidate the pathogenesis induced by a high fat diet, we randomly divided 88 White Shell Roman layers into 2 groups. There were 44 layers in each group. The control group was fed by a standard layer rations, and the high fat group was fed by completed rations mixing with 3% soybean oil. This study successfully constructed an animal model of osteoporosis caused by high fat. Bone samples were collected for bone mineral density, bone biomechanical properties which are all decreased at 26, 30, 34, and 38 wk old. We found the pathway of tryptophan-ERK-CREB from the perspective of metabonomics which promote the bone absorption. By metabolomics, we screened the significantly activated tryptophan pathway in high fat feed and detected the elevated tryptophan metabolite serum 5-HT at 26, 30, 34 and 38 wk old in the high fat group. At 38 wk old, we detected significantly elevated protein and mRNA levels of ERK/CREB/C-fos in bone tissue in the high fat group. So we concluded that high-fat were associated with a decrease in bone density and bone biomechanical index by disrupting tryptophan-5-HT-ERK1/2-CREB metabolism signaling pathways.

The lack of effective treatments and a high rate of relapse in cocaine addiction constitute a major health problem. The present study was conducted to examine the expression of tryptophan-derived metabolites in the context of cocaine addiction and psychiatric comorbidity, which is common in addicted subjects. Abstinent patients with cocaine use disorder (CUD) and control subjects were recruited for a cross-sectional study. Participants were assessed with a semi-structured diagnostic interview (PRISM) based on DSM-IV-TR for substance and mental disorders. Plasma concentrations of tryptophan metabolites and their association with relevant CUD-related variables and psychiatric comorbidity were explored. We observed decreased plasma kynurenic acid concentrations in the cocaine group, however no associations between CUD-related variables and tryptophan-derived metabolites were found. In contrast, 5-HT concentrations were increased in CUD-patients and the diagnosis of different psychiatric disorders in the cocaine group was related to higher plasma 5-HT concentrations compared with non-comorbid patients. Therefore, while changes in plasma kynurenic acid concentrations appear to be directly associated with lifetime CUD, changes in 5-HT concentrations are associated with psychiatric comorbidity. These results emphasize the need to find potential biomarkers for a better stratification of cocaine-addicted patients in order to develop therapeutic approaches to prevent cocaine relapse.

The cellular and molecular mechanisms underlying loss of muscle mass with age (sarcopenia) are not well-understood; however, heterochronic parabiosis experiments show that circulating factors are likely to play a role. Kynurenine (KYN) is a circulating tryptophan metabolite that is known to increase with age and is a ligand of the aryl hydrocarbon receptor (Ahr). Here, we tested the hypothesis that KYN activation of Ahr plays a role in muscle loss with aging. Results indicate that KYN treatment of mouse and human myoblasts increased levels of reactive oxygen species (ROS) 2-fold and KYN treatment in vivo reduced muscle size and strength and increased muscle lipid peroxidation in young mice. PCR array data indicate that muscle fiber size reduction with KYN treatment reduces protein synthesis markers whereas ubiquitin ligase gene expression is not significantly increased. KYN is generated by the enzyme indoleamine 2,3-dioxygenase (IDO), and aged mice treated with the IDO inhibitor 1-methyl-D-tryptophan showed an increase in muscle fiber size and muscle strength. Small-molecule inhibition of Ahr in vitro, and Ahr knockout in vivo, did not prevent KYN-induced increases in ROS, suggesting that KYN can directly increase ROS independent of Ahr activation. Protein analysis identified very long-chain acyl-CoA dehydrogenase as a factor activated by KYN that may increase ROS and lipid peroxidation. Our data suggest that IDO inhibition may represent a novel therapeutic approach for the prevention of sarcopenia and possibly other age-associated conditions associated with KYN accumulation such as bone loss and neurodegeneration.

Tumors display increased uptake and processing of nutrients to fulfill the demands of rapidly proliferating cancer cells. Seminal studies have shown that the proto-oncogene MYC promotes metabolic reprogramming by altering glutamine uptake and metabolism in cancer cells. How MYC regulates the metabolism of other amino acids in cancer is not fully understood. Using high-performance liquid chromatography (HPLC)-tandem mass spectrometry (LC-MS/MS), we found that MYC increased intracellular levels of tryptophan and tryptophan metabolites in the kynurenine pathway. MYC induced the expression of the tryptophan transporters SLC7A5 and SLC1A5 and the enzyme arylformamidase (AFMID), involved in the conversion of tryptophan into kynurenine. SLC7A5, SLC1A5, and AFMID were elevated in colon cancer cells and tissues, and kynurenine was significantly greater in tumor samples than in the respective adjacent normal tissue from patients with colon cancer. Compared with normal human colonic epithelial cells, colon cancer cells were more sensitive to the depletion of tryptophan. Blocking enzymes in the kynurenine pathway caused preferential death of established colon cancer cells and transformed colonic organoids. We found that only kynurenine and no other tryptophan metabolite promotes the nuclear translocation of the transcription factor aryl hydrocarbon receptor (AHR). Blocking the interaction between AHR and kynurenine with CH223191 reduced the proliferation of colon cancer cells. Therefore, we propose that limiting cellular kynurenine or its downstream targets could present a new strategy to reduce the proliferation of MYC-dependent cancer cells.