The tryptophan metabolite picolinic acid suppresses proliferation and metabolic activity of CD4+ T cells and inhibits c-Myc activation

Inflammation, the kynurenines, and mucosal injury during human experimental enterotoxigenic Escherichia coli infection

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea in children and travelers, especially in low- and middle-income countries. ETEC is a non-invasive gut pathogen colonizing the small intestinal wall before secreting diarrhea-inducing enterotoxins. We sought to investigate the impact of ETEC infection on local and systemic host defenses by examining plasma markers of inflammation and mucosal injury as well as kynurenine pathway metabolites. Plasma samples from 21 volunteers experimentally infected with ETEC were collected before and 1, 2, 3, and 7 days after ingesting the ETEC dose, and grouped based on the level of intestinal ETEC proliferation: 14 volunteers experienced substantial proliferation (SP) and 7 had low proliferation (LP). Plasma markers of inflammation, kynurenine pathway metabolites, and related cofactors (vitamins B2 and B6) were quantified using targeted mass spectrometry, whereas ELISA was used to quantify the mucosal injury markers, regenerating islet-derived protein 3A (Reg3a), and intestinal fatty acid-binding protein 2 (iFABP). We observed increased concentrations of plasma C-reactive protein (CRP), serum amyloid A (SAA), neopterin, kynurenine/tryptophan ratio (KTR), and Reg3a in the SP group following dose ingestion. Vitamin B6 forms, pyridoxal 5'-phosphate and pyridoxal, decreased over time in the SP group. CRP, SAA, and pyridoxic acid ratio correlated with ETEC proliferation levels. The changes following experimental ETEC infection indicate that ETEC, despite causing a non-invasive infection, induces systemic inflammation and mucosal injury when proliferating substantially, even in cases without diarrhea. It is conceivable that ETEC infections, especially when repeated, contribute to negative health impacts on children in ETEC endemic areas.

Polyphenols: Chemoprevention and therapeutic potentials in hematological malignancies

Polyphenols are one of the largest plant-derived natural product and they play an important role in plants' defense as well as in human health and disease. A number of them are pleiotropic molecules and have been shown to regulate signaling pathways, immune response and cell growth and proliferation which all play a role in cancer development. Hematological malignancies on the other hand, are cancers of the blood. While current therapies are efficacious, they are usually expensive and with unwanted side effects. Thus, the search for newer less toxic agents. Polyphenols have been reported to possess antineoplastic properties which include cell cycle arrest, and apoptosis via multiple mechanisms. They also have immunomodulatory activities where they enhance T cell activation and suppress regulatory T cells. They carry out these actions through such pathways as PI3K/Akt/mTOR and the kynurenine. They can also reverse cancer resistance to chemotherapy agents. In this review, i look at some of the molecular mechanism of action of polyphenols and their potential roles as therapeutic agents in hematological malignancies. Here i discuss their anti-proliferative and anti-neoplastic activities especially their abilities modulate signaling pathways as well as immune response in hematological malignancies. I also looked at clinical studies done mainly in the last 10-15 years on various polyphenol combination and how they enhance synergism. I recommend that further preclinical and clinical studies be carried out to ensure safety and efficacy before polyphenol therapies be officially moved to the clinics.

PicR as a MarR Family Transcriptional Repressor Multiply Controls the Transcription of Picolinic Acid Degradation Gene Cluster pic in Alcaligenes faecalis JQ135

Picolinic acid (PA) is a natural toxic pyridine derivative as well as an important intermediate used in the chemical industry. In a previous study, we identified a gene cluster, pic, that responsible for the catabolism of PA in Alcaligenes faecalis JQ135. However, the transcriptional regulation of the pic cluster remains known. This study showed that the entire pic cluster was composed of 17 genes and transcribed as four operons: picR, picCDEF, picB4B3B2B1, and picT1A1A2A3T2T3MN. Deletion of picR, encoding a putative MarR-type regulator, greatly shortened the lag phase of PA degradation. An electrophoretic mobility shift assay and DNase I footprinting showed that PicR has one binding site in the picR-picC intergenic region and two binding sites in the picB-picT1 intergenic region. The DNA sequences of the three binding sites have the palindromic characteristics of TCAG-N₄-CTNN: the space consists of four nonspecific bases, and the four palindromic bases on the left and the first two palindromic bases on the right are strictly conserved, while the last two bases on the right vary among the three binding sites. An in vivo β-galactosidase activity reporter assay indicated that 6-hydroxypicolinic acid but not PA acted as a ligand of PicR, preventing PicR from binding to promoter regions and thus derepressing the transcription of the pic cluster. This study revealed the negative transcriptional regulation mechanism of PA degradation by PicR in A. faecalis JQ135 and provides new insights into the structure and function of the MarR-type regulator. IMPORTANCE The pic gene cluster was found to be responsible for PA degradation and widely distributed in Alpha-, Beta-, and Gammaproteobacteria. Thus, it is very necessary to understand the regulation mechanism of the pic cluster in these strains. This study revealed that PicR binds to three sites of the promoter regions of the pic cluster to multiply regulate the transcription of the pic cluster, which enables A. faecalis JQ135 to efficiently utilize PA. Furthermore, the study also found a unique palindrome sequence for binding of the MarR-type regulator. This study enhanced our understanding of microbial catabolism of environmental toxic pyridine derivatives.

Kynurenine Pathway Metabolites as Biomarkers in Alzheimer’s Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that deteriorates cognitive function. Patients with AD generally exhibit neuroinflammation, elevated beta-amyloid (Aβ), tau phosphorylation (p-tau), and other pathological changes in the brain. The kynurenine pathway (KP) and several of its metabolites, especially quinolinic acid (QA), are considered to be involved in the neuropathogenesis of AD. The important metabolites and key enzymes show significant importance in neuroinflammation and AD. Meanwhile, the discovery of changed levels of KP metabolites in patients with AD suggests that KP metabolites may have a prominent role in the pathogenesis of AD. Further, some KP metabolites exhibit other effects on the brain, such as oxidative stress regulation and neurotoxicity. Both analogs of the neuroprotective and antineuroinflammation metabolites and small molecule enzyme inhibitors preventing the formation of neurotoxic and neuroinflammation compounds may have potential therapeutic significance. This review focused on the KP metabolites through the relationship of neuroinflammation in AD, significant KP metabolites, and associated molecular mechanisms as well as the utility of these metabolites as biomarkers and therapeutic targets for AD. The objective is to provide references to find biomarkers and therapeutic targets for patients with AD.

Predicting lupus membranous nephritis using reduced picolinic acid to tryptophan ratio as a urinary biomarker

The current gold standard for classifying lupus nephritis (LN) progression is a renal biopsy, which is an invasive procedure. Undergoing a series of biopsies for monitoring disease progression and treatments is unlikely suitable for patients with LN. Thus, there is an urgent need for non-invasive alternative biomarkers that can facilitate LN class diagnosis. Such biomarkers will be very useful in guiding intervention strategies to mitigate or treat patients with LN. Urine samples were collected from two independent cohorts. Patients with LN were classified into proliferative (class III/IV) and membranous (class V) by kidney histopathology. Metabolomics was performed to identify potential metabolites, which could be specific for the classification of membranous LN. The ratio of picolinic acid (Pic) to tryptophan (Trp) ([Pic/Trp] ratio) was found to be a promising candidate for LN diagnostic and membranous classification. It has high potential as an alternative biomarker for the non-invasive diagnosis of LN.

Tryptophan and Its Metabolites in Lung Cancer: Basic Functions and Clinical Significance

Lung cancer is the most lethal malignancy worldwide. Recently, it has been recognized that metabolic reprogramming is a complex and multifaceted factor, contributing to the process of lung cancer. Tryptophan (Try) is an essential amino acid, and Try and its metabolites can regulate the progression of lung cancer. Here, we review the pleiotropic functions of the Try metabolic pathway, its metabolites, and key enzymes in the pathogenic process of lung cancer, including modulating the tumor environment, promoting immune suppression, and drug resistance. We summarize the recent advance in therapeutic drugs targeting the Try metabolism and kynurenine pathway and their clinical trials.

Neuroinflammation and the Kynurenine Pathway in CNS Disease: Molecular Mechanisms and Therapeutic Implications

Diseases of the central nervous system (CNS) remain a significant health, social and economic problem around the globe. The development of therapeutic strategies for CNS conditions has suffered due to a poor understanding of the underlying pathologies that manifest them. Understanding common etiological origins at the cellular and molecular level is essential to enhance the development of efficacious and targeted treatment options. Over the years, neuroinflammation has been posited as a common link between multiple neurological, neurodegenerative and neuropsychiatric disorders. Processes that precipitate neuroinflammatory conditions including genetics, infections, physical injury and psychosocial factors, like stress and trauma, closely link dysregulation in kynurenine pathway (KP) of tryptophan metabolism as a possible pathophysiological factor that 'fuel the fire' in CNS diseases. In this study, we aim to review emerging evidence that provide mechanistic insights between different CNS disorders, neuroinflammation and the KP. We provide a thorough overview of the different branches of the KP pertinent to CNS disease pathology that have therapeutic implications for the development of selected and efficacious treatment strategies.

Targeting Dietary and Microbial Tryptophan-Indole Metabolism as Therapeutic Approaches to Colon Cancer

Tryptophan metabolism, via the kynurenine (Kyn) pathway, and microbial transformation of tryptophan to indolic compounds are fundamental for host health; both of which are altered in colon carcinogenesis. Alterations in tryptophan metabolism begin early in colon carcinogenesis as an adaptive mechanism for the tumor to escape immune surveillance and metastasize. The microbial community is a key part of the tumor microenvironment and influences cancer initiation, promotion and treatment response. A growing awareness of the impact of the microbiome on tryptophan (Trp) metabolism in the context of carcinogenesis has prompted this review. We first compare the different metabolic pathways of Trp under normal cellular physiology to colon carcinogenesis, in both the host cells and the microbiome. Second, we review how the microbiome, specifically indoles, influence host tryptophan pathways under normal and oncogenic metabolism. We conclude by proposing several dietary, microbial and drug therapeutic modalities that can be utilized in combination to abrogate tumorigenesis.

Comprehensive assessment of multiple tryptophan metabolites as potential biomarkers for immune checkpoint inhibitors in patients with non-small cell lung cancer

Purpose

Tryptophan metabolites have immunomodulatory functions, suggesting possible roles in cancer immunity.

Methods

Plasma tryptophan metabolites were measured using liquid chromatography/mass spectrometry before immune checkpoint inhibitors (ICIs) in patients with non-small cell lung cancer (NSCLC).

Results

The 19 patients with NSCLC had significantly lower levels of tryptophan (p = 0.002) and xanthurenic acid (p = 0.032), and a significantly higher level of 3-hydroxyanthranilic acid (3-HAA) (p = 0.028) compared with the 10 healthy volunteers. The patients achieving objective responses had significantly lower levels of 3-HAA than those who did not (p = 0.045). Receiver operating characteristic analyses determined that the cutoff value of 3-HAA for objective response was 35.4 pmol/mL (sensitivity: 87.5% and specificity: 83.3%). The patients with 3-HAA < 35.4 pmol/mL had significantly longer median progression-free survival (7.0 months) than those without (1.6 months, p = 0.022).

Conclusions

Tryptophan metabolites may have a potential for predicting the efficacy of ICIs.

Registration number

University Hospital Medical Information Network Clinical Trial Registry 000026140.

Electronic supplementary material

The online version of this article (10.1007/s12094-020-02421-8) contains supplementary material, which is available to authorized users.

Metabolite Profile Differences Among Different Storage Time in Beef Preserved at Low Temperature

Storage temperature influences meat color stability and quality. This study was performed to quality change-associated metabolites profiles using a nontargeted liquid chromatography-mass spectrometry (LC-MS/MS)-based method. Beef longissimus dorsi samples were purchased immediately after slaughter, and then stored at room temperature, 4 °C and 0 °C. Water holding capacity (WHC), moisture content and pH value of the muscle samples were detected. Muscle samples and quality control samples were then prepared for nontargeted LC-MS/MS system, followed by identification of distinct metabolites. Pearson correlation coefficients between metabolites and quality indexes were calculated. Storage reduced pH values of beef, and room temperature and 4 °C displayed the lowest pH value. Moisture content and WHC in beef muscles, especially WHC declined obviously during the first 24 hr. The significantly altered metabolites profiles in meat samples at 0, 3.5, and 7 days during 4 °C storage were identified using LC-MS/MS. Most metabolites showed linear changes during storage (0 to 7 days). Using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, we found 1(α)-naphthol, urocanic acid, tyramine, guanine, histamine, picolinic acid, 4-hydroxybenzaldehyde, and hypoxanthine were increased, and 2-(S-glutathionyl)acetyl glutathione and glutathione were decreased in beef during 4 °C storage. Correlation analysis showed there were significantly correlations between metabolites and meat quality indexes (WHC, moisture content, and pH). In summary, 1(α)-naphthol, urocanic acid, tyramine, guanine, histamine, picolinic acid, 4-hydroxybenzaldehyde, and hypoxanthine, proved to be harmful to human body, accumulated gradually, especially after 3.5 days during storage at 4 °C. While the contents of beneficial substances, including 2-(S-glutathionyl)acetyl glutathione and glutathione, were decreased, which provided reference for the nutrition guidance of using beef meat.

Identification and Characterization of a Novel pic Gene Cluster Responsible for Picolinic Acid Degradation in Alcaligenes faecalis JQ135

Picolinic acid (PA) is a natural toxic pyridine derivative. Microorganisms can degrade and utilize PA for growth. However, the full catabolic pathway of PA and its physiological and genetic foundation remain unknown. In this study, we identified a gene cluster, designated picRCEDFB4B3B2B1A1A2A3, responsible for the degradation of PA from Alcaligenes faecalis JQ135. Our results suggest that PA degradation pathway occurs as follows: PA was initially 6-hydroxylated to 6-hydroxypicolinic acid (6HPA) by PicA (a PA dehydrogenase). 6HPA was then 3-hydroxylated by PicB, a four-component 6HPA monooxygenase, to form 3,6-dihydroxypicolinic acid (3,6DHPA), which was then converted into 2,5-dihydroxypyridine (2,5DHP) by the decarboxylase PicC. 2,5DHP was further degraded to fumaric acid through PicD (2,5DHP 5,6-dioxygenase), PicE (N-formylmaleamic acid deformylase), PicF (maleamic acid amidohydrolase), and PicG (maleic acid isomerase). Homologous pic gene clusters with diverse organizations were found to be widely distributed in Alpha-, Beta-, and Gammaproteobacteria Our findings provide new insights into the microbial catabolism of environmental toxic pyridine derivatives.IMPORTANCE Picolinic acid is a common metabolite of l-tryptophan and some aromatic compounds and is an important intermediate in organic chemical synthesis. Although the microbial degradation/detoxification of picolinic acid has been studied for over 50 years, the underlying molecular mechanisms are still unknown. Here, we show that the pic gene cluster is responsible for the complete degradation of picolinic acid. The pic gene cluster was found to be widespread in other Alpha-, Beta-, and Gammaproteobacteria These findings provide a new perspective for understanding the catabolic mechanisms of picolinic acid in bacteria.

Ironing out Macrophage Immunometabolism

Over the last decade, increasing evidence has reinforced the key role of metabolic reprogramming in macrophage activation. In addition to supporting the specific immune response of different subsets of macrophages, intracellular metabolic pathways also directly control the specialized effector functions of immune cells. In this context, iron metabolism has been recognized as an important component of macrophage plasticity. Since macrophages control the availability of this essential metal, changes in the expression of genes coding for the major proteins of iron metabolism may result in different iron availability for the macrophage itself and for other cells in the microenvironment. In this review, we discuss how macrophage iron can also play a role in immunometabolism.

Novel 3,6-Dihydroxypicolinic Acid Decarboxylase-Mediated Picolinic Acid Catabolism in Alcaligenes faecalis JQ135

Picolinic acid (PA), a typical C-2-carboxylated pyridine derivative, is a metabolite of l-tryptophan and many other aromatic compounds in mammalian and microbial cells. Microorganisms can degrade and utilize PA for growth. However, the precise mechanism of PA metabolism remains unknown. Alcaligenes faecalis strain JQ135 utilizes PA as its carbon and nitrogen source for growth. In this study, we screened a 6-hydroxypicolinic acid (6HPA) degradation-deficient mutant through random transposon mutagenesis. The mutant hydroxylated 6HPA into an intermediate, identified as 3,6-dihydroxypicolinic acid (3,6DHPA), with no further degradation. A novel decarboxylase, PicC, was identified to be responsible for the decarboxylation of 3,6DHPA to 2,5-dihydroxypyridine. Although, PicC belonged to the amidohydrolase 2 family, it shows low similarity (<45%) compared to other reported amidohydrolase 2 family decarboxylases. Moreover, PicC was found to form a monophyletic group in the phylogenetic tree constructed using PicC and related proteins. Further, the genetic deletion and complementation results demonstrated that picC was essential for PA degradation. The PicC was Zn²⁺-dependent nonoxidative decarboxylase that can specifically catalyze the irreversible decarboxylation of 3,6DHPA to 2,5-dihydroxypyridine. The K_m and k _cat toward 3,6DHPA were observed to be 13.44 μM and 4.77 s^-1, respectively. Site-directed mutagenesis showed that His163 and His216 were essential for PicC activity. This study provides new insights into the microbial metabolism of PA at molecular level.IMPORTANCE Picolinic acid is a natural toxic pyridine derived from l-tryptophan metabolism and other aromatic compounds in mammalian and microbial cells. Microorganisms can degrade and utilize picolinic acid for their growth, and thus a microbial degradation pathway of picolinic acid has been proposed. Picolinic acid is converted into 6-hydroxypicolinic acid, 3,6-dihydroxypicolinic acid, and 2,5-dihydroxypyridine in turn. However, there was no physiological and genetic validation for this pathway. This study demonstrated that 3,6-dihydroxypicolinic acid was an intermediate in picolinic acid catabolism and further identified and characterized a novel amidohydrolase 2 family decarboxylase PicC. PicC was also shown to catalyze the decarboxylation of 3,6-dihydroxypicolinic acid into 2,5-dihydroxypyridine. This study provides a basis for understanding picolinic acid degradation and its underlying molecular mechanism.

Prospective study of blood metabolites associated with colorectal cancer risk

Few prospective studies, and none in Asians, have systematically evaluated the relationship between blood metabolites and colorectal cancer risk. We conducted a nested case-control study to search for risk-associated metabolite biomarkers for colorectal cancer in an Asian population using blood samples collected prior to cancer diagnosis. Conditional logistic regression was performed to assess associations of metabolites with cancer risk. In this study, we included 250 incident cases with colorectal cancer and individually matched controls nested within two prospective Shanghai cohorts. We found 35 metabolites associated with risk of colorectal cancer after adjusting for multiple comparisons. Among them, 12 metabolites were glycerophospholipids including nine associated with reduced risk of colorectal cancer and three with increased risk [odds ratios per standard deviation increase of transformed metabolites: 0.31-1.98; p values: 0.002-1.25 × 10^-10 ]. The other 23 metabolites associated with colorectal cancer risk included nine lipids other than glycerophospholipid, seven aromatic compounds, five organic acids and four other organic compounds. After mutual adjustment, nine metabolites remained statistically significant for colorectal cancer. Together, these independently associated metabolites can separate cancer cases from controls with an area under the curve of 0.76 for colorectal cancer. We have identified that dysregulation of glycerophospholipids may contribute to risk of colorectal cancer.

The Role of Indoleamine-2,3-Dioxygenase in Cancer Development, Diagnostics, and Therapy

Tumors are composed of abnormally transformed cell types and tissues that differ from normal tissues in their genetic and epigenetic makeup, metabolism, and immunology. Molecular compounds that modulate the immune response against neoplasms offer promising new strategies to combat cancer. Inhibitors targeting the indoleamine-2,3-dioxygenase 1 enzyme (IDO1) represent one of the most potent therapeutic opportunities to inhibit tumor growth. Herein, we assess the biochemical role of IDO1 in tumor metabolism and immune surveillance, and review current diagnostic and therapeutic approaches that are intended to increase the effectiveness of immunotherapies against highly aggressive and difficult-to-treat IDO-expressing cancers.

The role of indoleamine-2,3-dioxygenase in normal and pathological pregnancies

The survival of allogeneic fetus during pregnancy contradicts the laws of immune responses. Behind this paradoxical phenomenon, the mechanism is quite complex. Indoleamine-2,3-dioxygenase (IDO) is the first and rate-limiting enzyme of tryptophan catabolism. Emerging evidence shows that IDO is expressed at the maternal-fetal interface, including trophoblast cells, decidual stroma cells, decidual immune cells (eg, natural killer cells, T cells, and macrophages), and vascular endothelial cells of decidua and chorion. Moreover, the expression and activity of IDO are different among non-pregnant, normal pregnant, and pathological pregnant conditions. IDO plays important roles in normal pregnancy through immune suppression and regulation of fetal invasion and circulation. However, the abnormal expression and dysfunction of IDO are associated with some pathological pregnancies (including recurrent spontaneous abortion, preeclampsia, preterm labor, and fetal growth restriction).

Chloroquine inhibits human CD4+ T-cell activation by AP-1 signaling modulation

Chloroquine (CQ) is widely used as an anti-inflammatory therapeutic for rheumatic diseases. Although its modes of action on the innate immune system are well described, there is still insufficient knowledge about its direct effects on the adaptive immune system. Thus, we evaluated the influence of CQ on activation parameters of human CD4⁺ T-cells. CQ directly suppressed proliferation, metabolic activity and cytokine secretion of T-cells following anti-CD3/anti-CD28 activation. In contrast, CQ showed no effect on up-regulation of T-cell activation markers. CQ inhibited activation of all T helper cell subsets, although IL-4 and IL-13 secretion by Th2 cells were less influenced compared to other Th-specific cytokines. Up to 10 μM, CQ did not reduce cell viability, suggesting specific suppressive effects on T-cells. These properties of CQ were fully reversible in re-stimulation experiments. Analyses of intracellular signaling showed that CQ specifically inhibited autophagic flux and additionally activation of AP-1 by reducing phosphorylation of c-JUN. This effect was mediated by inhibition of JNK catalytic activity. In summary, we characterized selective and reversible immunomodulatory effects of CQ on human CD4⁺ T-cells. These findings provide new insights into the biological actions of JNK/AP-1 signaling in T-cells and may help to expand the therapeutic spectrum of CQ.

The Interactions Between Kynurenine, Folate, Methionine and Pteridine Pathways in Obesity

Obesity activates both innate and adaptive immune responses in adipose tissue. Elevated levels of eosinophils with depression of monocyte and neutrophil indicate the deficiencies in the immune system of morbidly obese individuals. Actually, adipose tissue macrophages are functional antigen-presenting cells that promote the proliferation of interferon-gamma (IFN-gamma)-producing CD4+ T cells in adipose tissue of obese subjects. Eventually, diet-induced obesity is associated with the loss of tissue homeostasis and development of type 1 inflammatory responses in visceral adipose tissue. Activity of inducible indoleamine 2,3-dioxygenase-1 (IDO-1) plays a major role under pro-inflammatory, IFN-gamma dominated settings. One of the two rate-limiting enzymes which can metabolize tryptophan to kynurenine is IDO-1. Tumor necrosis factor-alpha (TNF-alpha) correlates with IDO-1 in adipose compartments. Actually, IDO-1-mediated tryptophan catabolism due to chronic immune activation is the cause of reduced tryptophan plasma levels and be considered as the driving force for food intake in morbidly obese patients. Thus, decrease in plasma tryptophan levels and subsequent reduction in serotonin (5-HT) production provokes satiety dysregulation that leads to increased caloric uptake and obesity. However, after bariatric surgery, weight reduction does not lead to normalization of IDO-1 activity. Furthermore, there is a connection between arginine and tryptophan metabolic pathways in the generation of reactive nitrogen intermediates. Hence, abdominal obesity is associated with vascular endothelial dysfunction and reduced nitric oxide (NO) availability. IFN-gamma-induced activation of the inducible nitric oxide synthase (iNOS) and dissociation of endothelial adenosine monophosphate activated protein kinase (AMPK)- phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt)- endothelial NO synthase (eNOS) pathway enhances oxidative stress production secondary to high-fat diet. Thus, reduced endothelial NO availability correlates with the increase in plasma non-esterified fatty acids and triglycerides levels. Additionally, in obese patients, folate-deficiency leads to hyperhomocysteinemia. Folic acid confers protection against hyperhomocysteinemia-induced oxidative stress.

Resveratrol intake enhances indoleamine-2,3-dioxygenase activity in humans

BACKGROUND

Resveratrol is a polyphenol compound found in various nutrients that was shown to have immunomodulatory, anti-cancerogenic, and cardioprotective effects. The regulation of indoleamine-2,3-dioxygenase (IDO), the rate-limiting enzyme in inflammatory tryptophan metabolism, has been proposed to be involved in resveratrol's biological effects. These observations, however, rely on in vitro findings and animal studies. Therefore, we assessed the impact of resveratrol on tryptophan metabolism after oral intake in humans.

METHODS

Healthy volunteers were orally administrated 5g resveratrol (n=8) or placebo (n=2) in a pilot study. IDO activity was determined by analyzing plasma levels of tryptophan and kynurenine. Determination of the immune activation marker neopterin was included in the analysis.

RESULTS

Resveratrol administration significantly reduced tryptophan levels 2.5h (p<0.001) and 5h (p<0.001) after treatment. Kynurenine levels were slightly, but not significantly, elevated 2.5h after the intervention, which resulted in an 1.33- and 1.30-fold increase of the kynurenine to tryptophan ratio at 2.5h (p<0.01) and 5h (p<0.01), respectively. Neopterin levels were not affected by resveratrol administration.

CONCLUSION

This is the first evidence of a modulatory effect of orally administered resveratrol on tryptophan metabolism in humans. Since IDO has been shown to play a crucial role in immunity, cancer development and regulation of vascular tone, the modulation of this enzyme might be involved in resveratrol's diverse biological effects.