Indole Pathway Research Articles

Dual Transcriptome of Post-Germinating Mutant Lines of Arabidopsis thaliana Infected by Alternaria brassicicola

Alternaria brassicicola is a seed-borne pathogen that causes black spot disease in Brassica crops, yet the seed defense mechanisms against this fungus remain poorly understood. Building upon recent reports that highlighted the involvement of indole pathways in seeds infected by Alternaria, this study provides transcriptomic resources to further elucidate the role of these metabolic pathways during the interaction between seeds and fungal pathogens. Using RNA sequencing, we examined the gene expression of glucosinolate-deficient mutant lines (cyp79B2/cyp79B3 and qko) and a camalexin-deficient line (pad3), generating a dataset from 14 samples. These samples were inoculated with Alternaria or water, and collected at 3, 6, and 10 days after sowing to extract total RNA. Sequencing was performed using DNBseq™ technology, followed by bioinformatics analyses with tools such as FastQC (version 0.11.9), multiQC (version 1.13), Venny (version 2.0), Salmon software (version 0.14.1), and R packages DESeq2 (version 1.36.0), ClusterProfiler (version 4.12.6) and ggplot2 (version 3.4.0). By providing this valuable dataset, we aim to contribute to a deeper understanding of seed defense mechanisms against Alternaria, leveraging RNA-seq for various analyses, including differential gene expression and co-expression correlation. This work serves as a foundation for a more comprehensive grasp of the interactions during seed infection and highlights potential targets for enhancing crop protection and management.

Vinegar-processed Schisandra Chinensis enhanced therapeutic effects on colitis-induced depression through tryptophan metabolism

BackgroundUlcerative colitis (UC) is an inflammatory bowel disease characterized by its incurable nature and undefined etiology, which is often accompanied by a high prevalence of comorbid depression. The gut-brain axis has emerged as a promising treatment target in recent years. Purpose: This study aimed to investigate how vinegar-processed Schisandra Chinensis (VSC) enhances therapeutic effects on depressive behavior in chronic UC mice. Methods: A chronic UC model was induced in mice using dextran sulfate sodium. The therapeutic effects of both raw and vinegar-processed Schisandra Chinensis on UC and associated depressive symptoms were assessed. Colonic mucosal damage was evaluated using hematoxylin and eosin (H&E) and Alcian blue staining. The integrity of the blood-brain barrier (BBB) and synaptic structures was visualized via transmission electron microscopy (TEM). Enzyme-linked immunosorbent assay (ELISA) was employed to quantify inflammatory cytokine levels in the colon, serum, and brain, while western blotting was performed for protein expression analysis. Additionally, metagenomic analysis was conducted to investigate gut microbiota composition. Nissl staining and immunofluorescence were used to assess hippocampal neuronal damage, and behavioral assessments including the morris water maze, open field test, forced swimming test and tail suspension test, were implemented to evaluate depressive states. Serum metabolites were analyzed using UPLC-MS/MS. Results: Both raw and vinegar-processed Schisandra Chinensis significantly upregulated aryl hydrocarbon receptor (AhR), inhibited NF-κB p-p65 activation, and reduced levels of pro-inflammatory cytokine. These treatments also enhanced the expression of tight junction proteins, restored colonic mucosal and BBB integrity, alleviated damage to hippocampal neurons, and improved synaptic structure. Behavioral assessments indicated that VSC was particularly effective in ameliorating depressive-like behaviors in chronic UC mice. In the gut, both treatments reshaped the gut microbial composition, restoring the relative abundance of Duncaniella, Candidatus_Amulumruptor, Alistipes, Parabacteroides, Lachnospiraceae_bacterium, uncultured_Bacteroides_sp., Candidatus_Amulumruptor_caecigallinarius, with VSC showing more pronounced effects. Serum metabolomics revealed an increase in tryptophan levels and a decrease in kynurenine and xanthurenic acid levels with VSC, indicating that tryptophan metabolism shifted from the kynurenine pathway to the 5-HT or indole pathway. However, this phenomenon did not occur with Schisandra Chinensis (SC). Conclusion: This study demonstrated that the disruption of tryptophan metabolic balance served as a biological mechanism underlying the occurrence of depressive behaviors induced by UC. The application of SC following vinegar processing enhanced its regulatory effects on gut microbiota and tryptophan metabolism. This findings provided a new insight for the clinical management of gut-brain comorbidities.

Assessment of Urinary Dopamine and Serotonin Metabolites in Relation to Dysbiosis Indicators in Patients with Functional Constipation.

The causes of functional constipation (FC) in adults are unclear, but changes in the gut microbiome may play an important role. The present study aimed to assess the relationship between urinary metabolites of dopamine and serotonin and some dysbiosis indicators in patients with FC. The study included 40 healthy women and 40 women with FC aged 21-46 years. Urinary levels of homovanillic acid (HVA), 5-hydoxyindoleacetic acid (5-HIAA), p-hydroxyphenylacetic acid (PhAc), and 3-indoxyl sulfate, as final metabolites of dopamine, serotonin, and indole pathway, respectively, were determined using the LC-Ms/Ms method. However, hydrogen-methane and ammonia breath tests were performed. The GA-map Dysbiosis Test was used to identify and characterize the dysbiosis index (DI). In patients with FC, the DI was significantly higher than in the control group: 4.05 ± 0.53 vs. 1.52 ± 0.81 points (p < 0.001), but the number of many types of bacteria varied among individuals. The levels of HVA were higher, while 5-HIAA levels were lower in patients. Moreover, the HVA/5-HIAA ratio had a positive correlation with DI as well as with the severity of symptoms. In patients with functional constipation, the balance in dopamine and serotonin secretion is disturbed, which is associated with changes in the gut microbiome.

Fast Targeted Metabolomics for Analyzing Metabolic Diversity of Bacterial Indole Derivatives in ME/CFS Gut Microbiome.

Disruptions in microbial metabolite interactions due to gut microbiome dysbiosis and metabolomic shifts may contribute to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and other immune-related conditions. The aryl hydrocarbon receptor (AhR), activated upon binding various tryptophan metabolites, modulates host immune responses. This study investigates whether the metabolic diversity-the concentration distribution-of bacterial indole pathway metabolites can differentiate bacterial strains and classify ME/CFS samples. A fast targeted liquid chromatography-parallel reaction monitoring method at a rate of 4 minutes per sample was developed for large-scale analysis. This method revealed significant metabolic differences in indole derivatives among B. uniformis strains cultured from human isolates. Principal component analysis identified two major components (PC1, 68.9%; PC2, 18.7%), accounting for 87.6% of the variance and distinguishing two distinct B. uniformis clusters. The metabolic difference between clusters was particularly evident in the relative contributions of indole-3-acrylate and indole-3-aldehyde. We further measured concentration distributions of indole derivatives in ME/CFS by analyzing fecal samples from 10 patients and 10 healthy controls using the fast targeted metabolomics method. An AdaBoost-LOOCV model achieved moderate classification success with a mean LOOCV accuracy of 0.65 (Control: precision of 0.67, recall of 0.60, F1-score of 0.63; ME/CFS: precision of 0.64, recall of 0.7000, F1-score of 0.67). These results suggest that the metabolic diversity of indole derivatives from tryptophan degradation, facilitated by the fast targeted metabolomics and machine learning, is a potential biomarker for differentiating bacterial strains and classifying ME/CFS samples. Mass spectrometry datasets are accessible at the National Metabolomics Data Repository (ST002308, DOI: 10.21228/M8G13Q; ST003344, DOI: 10.21228/M8RJ9N; ST003346, DOI: 10.21228/M8RJ9N).

Auto-inducible synthetic pathway in E. coli enhanced sustainable indigo production from glucose

Indigo is widely used in textile industries for denim garments dyeing and is mainly produced by chemical synthesis which, however, raises environmental sustainability issues. Bio-indigo may be produced by fermentation of metabolically engineering bacteria, but current methods are economically incompetent due to low titer and the need for an inducer. To address these problems, we first characterized several synthetic promoters in E. coli and demonstrated the feasibility of inducer-free indigo production from tryptophan using the inducer-free promoter. We next coupled the tryptophan-to-indigo and glucose-to-tryptophan pathways to generate a de novo glucose-to-indigo pathway. By rational design and combinatorial screening, we identified the optimal promoter-gene combinations, which underscored the importance of promoter choice and expression levels of pathway genes. We thus created a new E. coli strain that exploited an indole pathway to enhance the indigo titer to 123 mg/L. We further assessed a panel of heterologous tryptophan synthase homologs and identified a plant indole lyase (TaIGL), which along with modified pathway design, improved the indigo titer to 235 mg/L while reducing the tryptophan byproduct accumulation. The optimal E. coli strain expressed 8 genes essential for rewiring carbon flux from glucose to indole and then to indigo: mFMO, ppsA, tktA, trpD, trpC, TaIGL and feedback-resistant aroG and trpE. Fed-batch fermentation in a 3-L bioreactor with glucose feeding further increased the indigo titer (≈965 mg/L) and total quantity (≈2183 mg) at 72 h. This new synthetic glucose-to-indigo pathway enables high-titer indigo production without the need of inducer and holds promise for bio-indigo production.

Identification of Gut Microbiome Signatures Associated with Indole Pathway in Tryptophan Metabolism in Patients Undergoing Hemodialysis.

Microbiota tryptophan metabolism and the biosynthesis of indole derivatives play an important role in homeostasis and pathogenesis in the human body and can be affected by the gut microbiota. However, studies on the interplay between gut microbiota and tryptophan metabolites in patients undergoing dialysis are lacking. This study aimed to identify the gut microbiota, the indole pathway in tryptophan metabolism, and significant functional differences in ESRD patients with regular hemodialysis. We performed the shotgun metagenome sequencing of stool samples from 85 hemodialysis patients. Using the linear discriminant analysis effect size (LEfSe), we examined the composition of the gut microbiota and metabolic features across varying concentrations of tryptophan and indole metabolites. Higher tryptophan levels promoted tyrosine degradation I and pectin degradation I metabolic modules; lower tryptophan levels were associated with glutamate degradation I, fructose degradation, and valine degradation modules. Higher 3-indoxyl sulfate concentrations were characterized by alanine degradation I, anaerobic fatty acid beta-oxidation, sulfate reduction, and acetyl-CoA to crotonyl-CoA. Contrarily, lower 3-indoxyl sulfate levels were related to propionate production III, arabinoxylan degradation, the Entner-Doudoroff pathway, and glutamate degradation II. The present study provides a better understanding of the interaction between tryptophan, indole metabolites, and the gut microbiota as well as their gut metabolic modules in ESRD patients with regular hemodialysis.

Multiomic Signatures of Traffic-Related Air Pollution in London Reveal Potential Short-Term Perturbations in Gut Microbiome-Related Pathways.

This randomized crossover study investigated the metabolic and mRNA alterations associated with exposure to high and low traffic-related air pollution (TRAP) in 50 participants who were either healthy or were diagnosed with chronic pulmonary obstructive disease (COPD) or ischemic heart disease (IHD). For the first time, this study combined transcriptomics and serum metabolomics measured in the same participants over multiple time points (2 h before, and 2 and 24 h after exposure) and over two contrasted exposure regimes to identify potential multiomic modifications linked to TRAP exposure. With a multivariate normal model, we identified 78 metabolic features and 53 mRNA features associated with at least one TRAP exposure. Nitrogen dioxide (NO2) emerged as the dominant pollutant, with 67 unique associated metabolomic features. Pathway analysis and annotation of metabolic features consistently indicated perturbations in the tryptophan metabolism associated with NO2 exposure, particularly in the gut-microbiome-associated indole pathway. Conditional multiomics networks revealed complex and intricate mechanisms associated with TRAP exposure, with some effects persisting 24 h after exposure. Our findings indicate that exposure to TRAP can alter important physiological mechanisms even after a short-term exposure of a 2 h walk. We describe for the first time a potential link between NO2 exposure and perturbation of the microbiome-related pathways.

Dupilumab therapy improves gut microbiome dysbiosis and tryptophan metabolism in Chinese patients with atopic dermatitis

BackgroundDupilumab has demonstrate its potential to orchestrate inflammatory skin microenvironment, enhance skin barrier and shift skin microbiome dysbiosis, collectively contributing to clinical improvement in patients with atopic dermatitis (AD). As the second genome of human body, growing evidence suggests that the gut microbiome might relate to the host response to treatments. Little is known about the association between dupilumab treatment and gut microbiome in AD patients. ObjectiveWe aimed to characterize the gut microbiome among Chinese subjects with or without AD and determine the potential effect of dupilumab on the gut microbiome. ResultsThe 16 s rRNA gene sequencing was conducted on 48 healthy controls (HC), 44 AD patients and 27 AD patients who received dupilumab for 16 weeks. Prior to treatment, we identified the changed beta-diversity, increased Firmicutes/Bacteroidetes ratio, decreased Bifidobacterium and expanded Faecalibacterium among the AD patients compared to HC. After 16 weeks of dupilumab treatment, gut microbiome dysbiosis of the AD patients improved with reversed beta-diversity, closer bacterial connections, increased colonization of Bifidobacterium, Ruminococcus gnavus, and Coprococcus, which were negatively correlated with disease severity indicators. This shift was largely independent of the degree of clinical improvement. Bacterial function analysis revealed further metabolic alterations following dupilumab treatment, including up-regulated expression of genes involved in the indole pathway of tryptophan metabolism, corroborated by quantitative UHPLC-MS/MS analysis. ConclusionDupilumab treatment tends to help shift the gut microbial dysbiosis in AD patients to a healthier state, along with improved intestinal tryptophan metabolism, suggesting the gut flora and its metabolites may mediate part of the synergistic therapeutic effects on the host.

Host transcriptome response to heat stress and Eimeria maxima infection in meat-type chickens.

Eimeria (E.) maxima parasite infects chickens' midgut disrupting the jejunal and ileal mucosa causing high morbidity and mortality. Heat stress (HS) is a seasonal stressor that impacts biological functions leading to poor performance. This study elucidates how HS, E. maxima infection, and their combination affect the ileum transcriptome. Two-hundred and forty 2-week-old males Ross708 chickens were randomly allocated into four treatment groups: thermoneutral-control (TNc), thermoneutral-infected (TNi), heat-stress control (HSc), and heat stress-infected (HSi), with 6 replicates each of 10 birds. Infected groups received 200x103 sporulated E. maxima oocysts/bird, and heat-treated groups were raised at 35°C. At 6-day post-treatment, ileums of five randomly selected chickens per group were sampled, RNA was extracted and sequenced. A total of 413, 3377, 1908, and 2304 DEGs were identified when applying the comparisons: TNc vs HSc, TNc vs TNi, HSi vs HSc, and TNi vs HSi, respectively, at cutoff ≥1.2-fold change (FDR: q<0.05). HSc vs TNc showed upregulation of lipid metabolic pathways and degradation/metabolism of multiple amino acids; and downregulation of most immune-related and protein synthesis pathways. TNc vs TNi displayed upregulation of most of immune-associated pathways and eukaryotic mRNA maturation pathways; and downregulation of fatty acid metabolism and multiple amino acid metabolism pathways including tryptophan. Comparing HSi versus HSc and TNi revealed that combining the two stressors restored the expression of some cellular functions, e.g., oxidative phosphorylation and protein synthesis; and downregulate immune response pathways associated with E. maxima infection. During E. maxima infection under HS the calcium signaling pathway was downregulated, including genes responsible for increasing the cytoplasmic calcium concentration; and tryptophan metabolism was upregulated, including genes that contribute to catabolizing tryptophan through serotonin and indole pathways; which might result in reducing the cytoplasmic pool of nutrients and calcium available for the parasite to scavenge and consequently might affect the parasite's reproductive ability.

Biosynthesis of melatonin from l-tryptophan by an engineered microbial cell factory

BackgroundThe demand for melatonin is increasing due to its health-promoting bioactivities such as antioxidant and sleep benefits. Although melatonin is present in various organisms, its low content and high extraction cost make it unsustainable. Biosynthesis is a promising alternative method for melatonin production. However, the ectopic production of melatonin in microorganisms is very difficult due to the low or insoluble expression of melatonin synthesis genes. Hence, we aim to explore the biosynthesis of melatonin using Escherichia coli as a cell factory and ways to simultaneously coordinated express genes from different melatonin synthesis pathways.ResultsIn this study, the mXcP4H gene from Xanthomonas campestris, as well as the HsAADC, HsAANAT and HIOMT genes from human melatonin synthesis pathway were optimized and introduced into E. coli via a multi-monocistronic vector. The obtained strain BL7992 successfully synthesized 1.13 mg/L melatonin by utilizing L-tryptophan (l-Trp) as a substrate in a shake flask. It was determined that the rate-limiting enzyme for melatonin synthesis is the arylalkylamine N-acetyltransferase, which is encoded by the HsAANAT gene. Targeted metabolomics analysis of l-Trp revealed that the majority of l-Trp flowed to the indole pathway in BL7992, and knockout of the tnaA gene may be beneficial for increasing melatonin production.ConclusionsA metabolic engineering approach was adopted and melatonin was successfully synthesized from low-cost l-Trp in E. coli. This study provides a rapid and economical strategy for the synthesis of melatonin.

“Indole-gence” for the mind

Surging depression rates highlight the need for innovative strategies beyond the traditional focus on the brain. In this issue of Cell Host & Microbe, Cheng etal. uncover a role for the gut microbiota in depression through the intestinal receptor Grp35 and indole pathway, offering hope in fighting against depression.

A novel preliminary metabolomic panel for IHD diagnostics and pathogenesis

Cardiovascular disease (CVD) represents one of the main causes of mortality worldwide and nearly a half of it is related to ischemic heart disease (IHD). The article represents a comprehensive study on the diagnostics of IHD through the targeted metabolomic profiling and machine learning techniques. A total of 112 subjects were enrolled in the study, consisting of 76 IHD patients and 36 non-CVD subjects. Metabolomic profiling was conducted, involving the quantitative analysis of 87 endogenous metabolites in plasma. A novel regression method of age-adjustment correction of metabolomics data was developed. We identified 36 significantly changed metabolites which included increased cystathionine and dimethylglycine and the decreased ADMA and arginine. Tryptophan catabolism pathways showed significant alterations with increased levels of serotonin, intermediates of the kynurenine pathway and decreased intermediates of indole pathway. Amino acid profiles indicated elevated branched-chain amino acids and increased amino acid ratios. Short-chain acylcarnitines were reduced, while long-chain acylcarnitines were elevated. Based on these metabolites data, machine learning algorithms: logistic regression, support vector machine, decision trees, random forest, and gradient boosting, were used for IHD diagnostic models. Random forest demonstrated the highest accuracy with an AUC of 0.98. The metabolites Norepinephrine; Xanthurenic acid; Anthranilic acid; Serotonin; C6-DC; C14-OH; C16; C16-OH; GSG; Phenylalanine and Methionine were found to be significant and may serve as a novel preliminary panel for IHD diagnostics. Further studies are needed to confirm these findings.

Pharmacokinetics, quorum-sensing signal molecules and tryptophan-related metabolomics of the novel anti-virulence drug Fluorothiazinon in a Pseudomonas aeruginosa-induced pneumonia murine model

Pseudomonas aeruginosa (PA) infection is commonly associated with hospital-acquired infections in patients with immune deficiency and/or severe lung diseases. Managing this bacterium is complex due to drug resistance and high adaptability. Fluorothiazinon (FT) is an anti-virulence drug developed to suppress the virulence of bacteria as opposed to bacterial death increasing host’s immune response to infection and improving treatment to inhibit drug resistant bacteria. We aimed to evaluate FT pharmacokinetics, quorum sensing signal molecules profiling and tryptophan-related metabolomics in blood, liver, kidneys, and lungs of mice. Study comprised three groups: a group infected with PA that was treated with 400 mg/kg FT (“infected treated group”); a non-infected group, but also treated with the same single drug dose (“non-infected treated group”); and an infected group that received a vehicle (“infected non-treated group”). PA-mediated infection blood pharmacokinetics profiling was indicative of increased drug concentrations as shown by increased Cmax and AUCs. Tissue distribution in liver, kidneys, and lungs, showed that liver presented the most consistently higher concentrations of FT in the infected versus non-infected mice. FT showed that HHQ levels were decreased at 1 h after dosing in lungs while PQS levels were lower across time in lungs of infected treated mice in comparison to infected non-treated mice. Metabolomics profiling performed in lungs and blood of infected treated versus infected non-treated mice revealed drug-associated metabolite alterations, especially in the kynurenic and indole pathways.

Multitargeted Internal Calibration for the Quantification of Chronic Kidney Disease-Related Endogenous Metabolites Using Liquid Chromatography-Mass Spectrometry.

Accurate quantitative analysis in liquid chromatography-mass spectrometry (LC-MS) benefits from calibration curves generated in the same matrix as the study sample. In the case of endogenous compound quantification, as no blank matrix exists, the multitargeted internal calibration (MTIC) is an attractive and straightforward approach to avoid the need for extensive matrix similarity evaluation. Its principle is to take advantage of stable isotope labeled (SIL) standards as internal calibrants to simultaneously quantify authentic analytes using a within sample calibration. An MTIC workflow was developed for the simultaneous quantification of metabolites related to chronic kidney disease (CKD) using a volumetric microsampling device to collect 20 μL of serum or plasma, followed by a single-step extraction with acetonitrile/water and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Since a single concentration of internal calibrant is necessary to calculate the study sample concentration, the instrument response function was investigated to determine the best SIL concentration. After validation, the trueness of 16 endogenous analytes in authentic human serum ranged from 72.2 to 116.0%, the repeatability from 1.9 to 11.3%, and the intermediate precision ranged overall from 2.1 to 15.4%. The proposed approach was applied to plasma samples collected from healthy control participants and two patient groups diagnosed with CKD. Results confirmed substantial concentration differences between groups for several analytes, including indoxyl sulfate and cortisone, as well as metabolite enrichment in the kynurenine and indole pathways. Multitargeted methodologies represent a major step toward rapid and straightforward LC-MS/MS absolute quantification of endogenous biomarkers, which could change the paradigm of MS use in clinical laboratories.

Microbial-Derived Tryptophan Metabolites and Their Role in Neurological Disease: Anthranilic Acid and Anthranilic Acid Derivatives.

The gut microbiome provides the host access to otherwise indigestible nutrients, which are often further metabolized by the microbiome into bioactive components. The gut microbiome can also shift the balance of host-produced compounds, which may alter host health. One precursor to bioactive metabolites is the essential aromatic amino acid tryptophan. Tryptophan is mostly shunted into the kynurenine pathway but is also the primary metabolite for serotonin production and the bacterial indole pathway. Balance between tryptophan-derived bioactive metabolites is crucial for neurological homeostasis and metabolic imbalance can trigger or exacerbate neurological diseases. Alzheimer's, depression, and schizophrenia have been linked to diverging levels of tryptophan-derived anthranilic, kynurenic, and quinolinic acid. Anthranilic acid from collective microbiome metabolism plays a complex but important role in systemic host health. Although anthranilic acid and its metabolic products are of great importance for host-microbe interaction in neurological health, literature examining the mechanistic relationships between microbial production, host regulation, and neurological diseases is scarce and at times conflicting. This narrative review provides an overview of the current understanding of anthranilic acid's role in neurological health and disease, with particular focus on the contribution of the gut microbiome, the gut-brain axis, and the involvement of the three major tryptophan pathways.

The Involvement of Intestinal Tryptophan Metabolism in Inflammatory Bowel Disease Identified by a Meta-Analysis of the Transcriptome and a Systematic Review of the Metabolome.

Evidence is emerging for the role of intestinal tryptophan metabolism in the development of inflammatory bowel disease (IBD). In order to identify the role of altered intestinal tryptophan metabolism in IBD pathogenesis, a meta-analysis of the transcriptome was performed to identify differentially expressed genes involved in the tryptophan metabolism pathways in intestinal biopsies of IBD as compared to non-IBD controls. Moreover, a systematic review of the metabolome was performed to identify the concurrent changes in tryptophan metabolites. Integration of the transcriptome and metabolome identified various alterations in intestinal tryptophan metabolism during active disease in IBD patients, including decreased intestinal tryptophan absorption, enhanced kynurenine pathway, increased interstitial serotonin availability, changed indole pathway, and activated aryl hydrocarbon receptor signaling. Therefore, a network of intestinal tryptophan metabolism pathways in IBD could be established, helping to assess the potential of genes and metabolites involved in these pathways as diagnostic markers and targets for IBD management.

The Engagement of Cytochrome P450 Enzymes in Tryptophan Metabolism

Tryptophan is metabolized along three main metabolic pathways, namely the kynurenine, serotonin and indole pathways. The majority of tryptophan is transformed via the kynurenine pathway, catalyzed by tryptophan-2,3-dioxygenase or indoleamine-2,3-dioxygenase, leading to neuroprotective kynurenic acid or neurotoxic quinolinic acid. Serotonin synthesized by tryptophan hydroxylase, and aromatic L-amino acid decarboxylase enters the metabolic cycle: serotonin → N-acetylserotonin → melatonin → 5-methoxytryptamine→serotonin. Recent studies indicate that serotonin can also be synthesized by cytochrome P450 (CYP), via the CYP2D6-mediated 5-methoxytryptamine O-demethylation, while melatonin is catabolized by CYP1A2, CYP1A1 and CYP1B1 via aromatic 6-hydroxylation and by CYP2C19 and CYP1A2 via O-demethylation. In gut microbes, tryptophan is metabolized to indole and indole derivatives. Some of those metabolites act as activators or inhibitors of the aryl hydrocarbon receptor, thus regulating the expression of CYP1 family enzymes, xenobiotic metabolism and tumorigenesis. The indole formed in this way is further oxidized to indoxyl and indigoid pigments by CYP2A6, CYP2C19 and CYP2E1. The products of gut-microbial tryptophan metabolism can also inhibit the steroid-hormone-synthesizing CYP11A1. In plants, CYP79B2 and CYP79B3 were found to catalyze N-hydroxylation of tryptophan to form indole-3-acetaldoxime while CYP83B1 was reported to form indole-3-acetaldoxime N-oxide in the biosynthetic pathway of indole glucosinolates, considered to be defense compounds and intermediates in the biosynthesis of phytohormones. Thus, cytochrome P450 is engaged in the metabolism of tryptophan and its indole derivatives in humans, animals, plants and microbes, producing biologically active metabolites which exert positive or negative actions on living organisms. Some tryptophan-derived metabolites may influence cytochrome P450 expression, affecting cellular homeostasis and xenobiotic metabolism.

Abstract 644: Gut microbiota-derived metabolites as regulators of immunity in pre-cancer

Abstract Introduction: Tryptophan (Trp) as an essential amino acid that can only be obtained through diet and is a precursor of serotonin and melatonin and required for protein and niacin biosynthesis. In addition, Trp is appreciated for its influence on both host and microbial metabolism. Trp is shunted into the Kyn pathway (mostly) and indolic pathway (bacterial degradation), especially in the immune cells. Both Kyn and Indole/indole derivatives, in part by activating the ligand-dependent transcription factor aryl hydrocarbon receptor (AHR), can become dysfunctional in cancer. Most individuals with cancer such as colon cancer, exhibit increased L-kynurenine levels, which in part is explained by progression of immunosuppressive phenotype and excessive inflammatory signaling molecules. To date, studies in mice and humans have linked Kyn and AHR as potent modulators of host immunity to colon cancer (CRC). Nothing is yet known about their role in pre-cancer, during the development of adenomatous polyps. We hypothesized that increases in plasma Kyn and I3A and their receptor AHR on immune cells would be detected in patients with pre-malignant polyps, suggesting dysbiosis and increased colon cancer risk due to immune modulation. Methods: We measured with mass spectrometry Kyn and I3A in plasma samples of 88 polyp patients and compared to 22 colon cancer patients. We analyzed by flow cytometry PBMCs from 64 newly diagnosed advanced polyp patients (40-70 years old) and 9 age-matched colon cancer patients in order to evaluate AHR expression in different subsets of T cells, NKT cells and NK cells, and their possible association with exhaustion markers Tim-3, LAG-3 and PD-1, as well as Granzyme K, and the presence of immunosuppressive Treg and MDSC. Results: We showed high level of expression of gut microbiota-derived metabolites in plasma of colon pre-cancer compared to cancer patients. We identified CD8+ T effector memory cells (TEM) as primary T cell population expressing their receptor AHR in polyp patients, which had a statistically significant association with Granzyme K expression, which is a hallmark of inflammaging. Conclusions: Our results suggest gut microbiota-derived metabolites as potential mediators of immunosuppression in the setting of premalignancy, which could increase cancer risk and be targets of cancer-preventing strategies. Citation Format: Amir Hossein Mohseni, Sedigheh Taghinezhad-S, Pamela L. Beatty, Olivera J. Finn. Gut microbiota-derived metabolites as regulators of immunity in pre-cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 644.

Indole-3-pyruvic acid alleviates rheumatoid arthritis via the aryl hydrocarbon receptor pathway.

In previous studies, we found that smoking may participate in the pathogenesis of rheumatoid arthritis (RA) via the aryl hydrocarbon receptor (AhR) pathway. However, when we conducted a subgroup analysis, the expression of AhR and CYP1A1 in healthy people was higher than that in RA patients. We considered that endogenous AhR ligands may exist in vivo that activate AhR to play a protective role. Indole-3-pyruvic acid (IPA) is a tryptophan (Trp) metabolite produced by the indole pathway and serves as a ligand of AhR. This study aimed to reveal the effect and mechanism of IPA in RA. A total of 14 patients with RA and 14 healthy volunteers were enrolled. The differential metabolites were screened with liquid chromatography-mass spectrometry (LC-MS) metabolomics technology. We also treated peripheral blood mononuclear cells (PBMCs) with IPA to evaluate the effect on the differentiation of T helper 17 (Th17) cells or regulatory T (Treg) cells. To determine whether IPA can be used to alleviate RA, we administered IPA to rats with collagen-induced arthritis (CIA). Methotrexate was used as a standard drug for CIA. When the dose reached 20 mg/kg/d, the severity of CIA was significantly reduced. In vitro experiments verified that IPA inhibited the differentiation of Th17 cells and promoted the differentiation of Treg cells, but this effect was weakened by CH223191. IPA is a protective factor for RA; it can restore the Th17/Treg cell balance through the AhR pathway, which can alleviate RA.

RELATIONSHIP OF THE LEVELS OF TRYPTOFAN METABOLITES WITH ADIPOKINES AND MYOKINES IN PATIENTS WITH VARIOUS OBESITY PHENOTYPES

Relevance. In the last 10 years, there has been an active study of the system of conjugation of the metabolism of a macroorganism and its microbiome. The microbiotic conversion of tryptophan into biologically active signaling molecules is a potential regulatory mechanism by which the intestinal microbiota can change the metabolism of both intestinal cells and the entire macroorganism. However, the content of tryptophan metabolism metabolites in patients with metabolically healthy (MHO) and metabolically unhealthy obesity (MUHO), as well as the relationship of these metabolites with adipokines and myokines, has not yet been studied. Purpose of the study. To study the content of metabolites of tryptophan metabolism in the blood serum of obese patients and to evaluate the relationship between the content of adipokines and myokines and the content of tryptophan metabolism metabolites of bacterial and non-bacterial origin in the blood serum of patients with MSO and MNSO. Material and methods. 266 patients were examined, including 138 healthy non-obese volunteers and 128 obese patients, of whom two subgroups were formed: 30 patients with MHO and 41 patients with MUHO. Metabolite concentrations in blood and feces were determined using high performance liquid chromatography. Quantitative analysis of adipokines and myokines was performed by multiplex enzyme immunoassay. The content of metabolites of tryptophan metabolism in blood serum was assessed by high performance liquid chromatography with mass spectrometric detection. Results. For patients with obesity, an increase in the serum concentration of kynurenine, kynurenic and quinoline acids, indole-3-lactate, indole-3-butyrate and indole-3-acetate was established. Patients with MHO and MUHO were statistically significantly different only in terms of serum tryptamine concentration. Regardless of the presence/absence of metabolic disorders in obese patients, it has been established that xanthurenic and quinoline acids are interrelated with the concentration of myostatin in the blood serum. At the same time, for patients with MHO, it was shown that the serum concentration of the dominant catabolite of the indole pathway, indole-3-acetate, is interconnected with the content of insulin and leptin in the blood serum. Whereas in patients with MUHO, leptinemia is consistent with a high concentration of anthranilic acid in the blood serum, and hyperinsulinemia, on the contrary, is associated with a low concentration of indole-3-propionate in the blood serum