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Kynurenine Pathway (kynurenine + pathway)
Selected AbstractsAltered kynurenine metabolism correlates with infarct volume in strokeEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2007L. G. Darlington Abstract Inflammation and oxidative stress are involved in brain damage following stroke, and tryptophan oxidation along the kynurenine pathway contributes to the modulation of oxidative stress partly via the glutamate receptor agonist quinolinic acid and antagonist kynurenic acid, and via redox-active compounds such as 3-hydroxyanthranilic acid. We have confirmed that following a stroke, patients show early elevations of plasma neopterin, S100B and peroxidation markers, the latter two correlating with infarct volume assessed from computed tomography (CT) scans, and being consistent with a rapid inflammatory response. We now report that the kynurenine pathway of tryptophan metabolism was also activated, with an increased kynurenine : tryptophan ratio, but with a highly significant decrease in the ratio of 3-hydroxyanthranilic acid : anthranilic acid, which was strongly correlated with infarct volume. Levels of kynurenic acid were significantly raised in patients who died within 21 days compared with those who survived. The results suggest that increased tryptophan catabolism is initiated before or immediately after a stroke, and is related to the inflammatory response and oxidative stress, with a major change in 3-hydroxyanthranilic acid levels. Together with previous evidence that inhibiting the kynurenine pathway reduces brain damage in animal models of stroke and cerebral inflammation, and that increased kynurenine metabolism directly promotes oxidative stress, it is proposed that oxidative tryptophan metabolism may contribute to the oxidative stress and brain damage following stroke. Some form of anti-inflammatory intervention between the rise of S100B and the activation of microglia, including inhibition of the kynurenine pathway, may be valuable in modifying patient morbidity and mortality. [source] Tryptophan metabolism and oxidative stress in patients with Huntington's diseaseJOURNAL OF NEUROCHEMISTRY, Issue 3 2005N. Stoy Abstract Abnormalities in the kynurenine pathway may play a role in Huntington's disease (HD). In this study, tryptophan depletion and loading were used to investigate changes in blood kynurenine pathway metabolites, as well as markers of inflammation and oxidative stress in HD patients and healthy controls. Results showed that the kynurenine : tryptophan ratio was greater in HD than controls in the baseline state and after tryptophan depletion, indicating increased indoleamine dioxygenase activity in HD. Evidence for persistent inflammation in HD was provided by elevated baseline levels of C-reactive protein, neopterin and lipid peroxidation products compared with controls. The kynurenate : kynurenine ratio suggested lower kynurenine aminotransferase activity in patients and the higher levels of kynurenine in patients at baseline, after depletion and loading, do not result in any differences in kynurenic acid levels, providing no supportive evidence for a compensatory neuroprotective role for kynurenic acid. Quinolinic acid showed wide variations in blood levels. The lipid peroxidation data indicate a high level of oxidative stress in HD patients many years after disease onset. Levels of the free radical generators 3-hydroxykynurenine and 3-hydroxyanthranilic acid were decreased in HD patients, and hence did not appear to contribute to the oxidative stress. It is concluded that patients with HD exhibit abnormal handling of tryptophan metabolism and increased oxidative stress, and that these factors could contribute to ongoing brain dysfunction. [source] Understanding the role of tryptophan and serotonin metabolism in gastrointestinal functionNEUROGASTROENTEROLOGY & MOTILITY, Issue 12 2009D. Keszthelyi Abstract, Tryptophan is the precursor of a wide array of metabolites, which are involved in a variety of aspects of human nutrition and metabolism. Accumulating evidence suggests a role of tryptophan metabolites, especially serotonin (5-hydroxytryptamin) in intestinal (patho) physiology, although mechanisms of action are still poorly understood. Alterations of serotonin metabolism may give rise to gastrointestinal dysfunction. Recently, it has been postulated that other metabolites of tryptophan, mostly of the kynurenine pathway, also play a role in regulating gut function. This review analyses the current knowledge of the interrelationship between tryptophan metabolic pathways and summarizes the existing scientific evidence regarding the role of tryptophan metabolites in intestinal function and in the pathogenesis of gastrointestinal diseases. [source] Crystal structure of 3-hydroxyanthranilic acid 3,4-dioxygenase from Saccharomyces cerevisiae: A special subgroup of the type III extradiol dioxygenasesPROTEIN SCIENCE, Issue 4 2006Xiaowu Li Abstract 3-Hydroxyanthranilic acid 3,4-dioxygenase (3HAO) is a non-heme ferrous extradiol dioxygenase in the kynurenine pathway from tryptophan. It catalyzes the conversion of 3-hydroxyanthranilate (HAA) to quinolinic acid (QUIN), an endogenous neurotoxin, via the activation of N-methyl-D-aspartate (NMDA) receptors and the precursor of NAD+ biosynthesis. The crystal structure of 3HAO from S. cerevisiae at 2.4 Å resolution shows it to be a member of the functionally diverse cupin superfamily. The structure represents the first eukaryotic 3HAO to be resolved. The enzyme forms homodimers, with two nickel binding sites per molecule. One of the bound nickel atoms occupies the proposed ferrous-coordinated active site, which is located in a conserved double-strand ,-helix domain. Examination of the structure reveals the participation of a series of residues in catalysis different from other extradiol dioxygenases. Together with two iron-binding residues (His49 and Glu55), Asp120, Asn51, Glu111, and Arg114 form a hydrogen-bonding network; this hydrogen-bond network is key to the catalysis of 3HAO. Residues Arg101, Gln59, and the substrate-binding hydrophobic pocket are crucial for substrate specificity. Structure comparison with 3HAO from Ralstonia metallidurans reveals similarities at the active site and suggests the same catalytic mechanism in prokaryotic and eukaryotic 3HAO. Based on sequence comparison, we suggest that bicupin of human 3HAO is the first example of evolution from a monocupin dimer to bicupin monomer in the diverse cupin superfamilies. Based on the model of the substrate HAA at the active site of Y3HAO, we propose a mechanism of catalysis for 3HAO. [source] Indoleamine 2,3 dioxygenase,mediated tryptophan catabolism regulates accumulation of Th1/Th17 cells in the joint in collagen-induced arthritisARTHRITIS & RHEUMATISM, Issue 5 2009Gabriel Criado Objective Indoleamine 2,3 dioxygenase (IDO) is a catabolic enzyme that initiates the kynurenine pathway of tryptophan degradation and has immunomodulatory properties. The aim of this study was to investigate the regulation of collagen-induced arthritis by tryptophan catabolism mediated by IDO. Methods Arthritis was induced by immunization with type II collagen. After induction of arthritis, the expression of IDO was analyzed by quantitative reverse transcription,polymerase chain reaction. The effect of IDO deficiency on collagen-induced arthritis was assessed in vivo by administration of 1-methyltryptophan and clinical and histologic evaluation of IDO-deficient mice. The requirement for IDO activation was bypassed by administration of L -kynurenine. Results IDO was induced in lymph node dendritic cells after collagen immunization. Systemic inhibition of tryptophan catabolism during active arthritis increased disease severity. Conversely, bypassing the requirement for tryptophan degradation by the administration of L -kynurenine resulted in amelioration of arthritis. Furthermore, IDO-deficient mice showed a higher incidence of arthritis and exacerbated disease severity compared with IDO-competent mice. Such increased disease activity in IDO-deficient mice correlated early with increased production of the proinflammatory cytokines interferon-, and interleukin-17 by lymph node T cells and later with increased infiltration of Th1 and Th17 cells in the inflamed joints. Conclusion Our data indicate that the induction of IDO controls the accumulation of Th1 and Th17 pathogenic T cells at the site of inflammation during collagen-induced arthritis. Therefore, manipulation of the kynurenine pathway of tryptophan degradation provides the potential for therapeutic intervention in rheumatoid arthritis. [source] Crystallization and preliminary crystallographic studies of human indoleamine 2,3-dioxygenaseACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2006Shun-ichiro Oda Indoleamine 2,3-dioxygenase (IDO) is a haem-containing dioxygenase that catalyzes the oxidative cleavage of the pyrrole ring of indoleamines by the insertion of molecular oxygen. This reaction is the first and the rate-limiting step in the kynurenine pathway, the major Trp catabolic pathway in mammals. Recombinant human IDO was crystallized by the vapour-diffusion technique. The addition of 4-phenylimidazole as a haem ligand was essential for crystallization. The crystals belong to space group P212121, with unit-cell parameters a = 86.1, b = 98.0, c = 131.0,Å. Diffraction data were collected to 2.3,Å resolution. [source] 2125: High glucose sensitizes human retinal endothelial cells for IFN-g-mediated apoptosisACTA OPHTHALMOLOGICA, Issue 2010R NAGARAJ Purpose The biochemical mechanisms by which inflammatory cytokines cause damage in the diabetic retina are poorly understood. Indoelamine 2, 3-dioxygenase (IDO) is an inducible by IFN-, enzyme and is the first enzyme of the kynurenine pathway, which produces cytotoxic kynurenines. In this study we have investigated the role of IDO in apoptosis of human retinal capillary endothelial cells (HREC) under hyperglycemic conditions. Methods HREC were cultured in medium containing high glucose (25 mM) or low glucose (7.5 mM) and incubated with 1-100 U/ml of IFN-,. IDO activity was measured by an HPLC assay. Expression of IFN-, receptor 1, and activation of the JAK-STAT signaling pathway along with activation of PKC-, was assessed by Western blotting. HREC apoptosis was measured by Hoechst staining. The role of IDO in HREC apoptosis was evaluated in the presence specific chemical inhibitors of the kynurenine pathway. Results IFN-, dose-dependently activated JAK-STAT signaling and PKC-,, and upregulated IDO. The IDO-mediated tryptophan oxidation led to formation of kynurenines, which was followed by chemical modification of proteins by kynurenines in HREC. These changes were accompanied by production of reactive oxygen species (ROS) and depletion of protein-free thiols. IFN-, inhibited cell cycle at low concentrations and caused caspase-3-mediated apoptosis and at higher concentrations, and those effects were amplified in the presence of high glucose in HREC. We found that IFN-, mediated cytotoxicity in HREC was primarily due to ROS generated by 3-hydroxykynurenine. Conclusion Our results suggest that high glucose sensitizes HREC to deleterious effects IFN-, and provide a novel mechanistic pathway for retinal capillary endothelial cell death in diabetes. [source] KYNURENINE METABOLITES AND INFLAMMATION MARKERS IN DEPRESSED PATIENTS TREATED WITH FLUOXETINE OR COUNSELLINGCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2009Gillian M Mackay SUMMARY 1Depression could result from changes in tryptophan availability caused by activation of the kynurenine pathway as a result of inflammation. In the present study, we examined patients newly diagnosed with depression to determine whether kynurenines and related factors change in parallel with improvements in mood. 2Concentrations of 5-hydroxytryptamine (5-HT; serotonin), 5-hydroxyindoleacetic acid (5-HIAA), oxidized tryptophan metabolites, brain-derived neurotrophic factor (BDNF) and inflammatory mediators (interleukin (IL)-2, C-reactive protein (CRP), neopterin) were measured in peripheral blood during an 18 week period of treatment with fluoxetine, fluoxetine plus tri-iodothyronine (T3) or psychiatric counselling. 3The results showed significant improvements in mood, with reduced 5-HT concentrations in patients given fluoxetine and a rise in plasma tryptophan in patients given counselling or fluoxetine and T3. The addition of T3 to the fluoxetine regimen appeared to slow recovery from depression, although the use of T3 was associated with a fall in thyroxine concentrations. Changes in 5-HT concentrations did not correlate with psychiatric scores and were seen only in drug-treated groups, not those given counselling. There were no associated changes in absolute concentrations of kynurenines, BDNF, CRP, neopterin or IL-2. With fluoxetine treatment, there were correlations between the concentrations of kynurenine metabolites and the psychiatric rating scores, whereas no correlations were found with BDNF or inflammatory markers. 4It is concluded that depression scores are largely independent of inflammatory status, but kynurenine metabolism may be related to the degree of depression after fluoxetine treatment. [source] KYNURENINE PATHWAY METABOLISM IN PATIENTS WITH OSTEOPOROSIS AFTER 2 YEARS OF DRUG TREATMENTCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 11 2006Caroline M Forrest ABSTRACT 1Metabolism of tryptophan along the oxidative pathway via kynurenine results in the production of quinolinic acid and kynurenic acid, which can act on glutamate receptors in peripheral tissues. We have now measured the concentrations of kynurenine pathway metabolites in the plasma of patients with osteoporosis before treatment with drugs, throughout and after 2 years of treatment with the drugs raloxifene or etidronate. Oxidative stress was assessed by measuring levels of the lipid peroxidation products malondialdehyde and 4-hydroxynonenal. Kynurenines were analysed by HPLC. Bone density was measured using dual-energy X-ray absorptiometry scans. 2Patients with osteoporosis showed significantly lower baseline levels of 3-hydroxyanthranilic acid compared with healthy controls, but significantly higher levels of anthranilic acid and lipid peroxidation products. After 2 years treatment with etidronate and calcium, we observed significant therapeutic responses quantified by bone densitometric scanning. Significant improvements were not seen in patients treated with raloxifene. 3In parallel, the levels of 3-hydroxyanthranilic acid, anthranilic acid and lipid peroxidation products were restored to control values by both drug treatments studied and tryptophan levels were increased significantly compared with baseline values. 4The results suggest that tryptophan metabolism is altered in osteoporosis in a manner that could contribute to the oxidative stress and, thus, to progress of the disease. The oxidative metabolism of tryptophan (the kynurenine pathway) could represent a novel target for the development of new drugs for the treatment of osteoporosis. In addition, we noted that etidronate is a more effective drug than raloxifene, but that the simultaneous use of non-steroidal anti-inflammatory drugs may reduce the efficacy of etidronate. [source] | ||||||||||||||||