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1
Chen, Yiquan, and Gilles J. Guillemin. "Kynurenine Pathway Metabolites in Humans: Disease and Healthy States." International Journal of Tryptophan Research 2 (January 2009): IJTR.S2097. http://dx.doi.org/10.4137/ijtr.s2097.
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Tryptophan is an essential amino acid that can be metabolised through different pathways, a major route being the kynurenine pathway. The first enzyme of the pathway, indoleamine-2,3-dioxygenase, is strongly stimulated by inflammatory molecules, particularly interferon gamma. Thus, the kynurenine pathway is often systematically up-regulated when the immune response is activated. The biological significance is that 1) the depletion of tryptophan and generation of kynurenines play a key modulatory role in the immune response; and 2) some of the kynurenines, such as quinolinic acid, 3-hydroxykynurenine and kynurenic acid, are neuroactive. The kynurenine pathway has been demonstrated to be involved in many diseases and disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, AIDS dementia complex, malaria, cancer, depression and schizophrenia, where imbalances in tryptophan and kynurenines have been found. This review compiles most of these studies and provides an overview of how the kynurenine pathway might be contributing to disease development, and the concentrations of tryptophan and kynurenines in the serum, cerebrospinal fluid and brain tissues in control and patient subjects.
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Majláth, Zsófia, and László Vécsei. "A kinureninrendszer és a stressz." Orvosi Hetilap 156, no. 35 (August 2015): 1402–5. http://dx.doi.org/10.1556/650.2015.30246.
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The kynurenine pathway is the main route of tryptophan degradation which gives rise to several neuroactive metabolites. Kynurenic acid is an endogenous antagonist of excitatory receptors, which proved to be neuroprotective in the preclinical settings. Kynurenines have been implicated in the neuroendocrine regulatory processes. Stress induces several alterations in the kynurenine metabolism and this process may contribute to the development of stress-related pathological processes. Irritable bowel disease and gastric ulcer are well-known disorders which are related to psychiatric comorbidity and stress. In experimental conditions kynurenic acid proved to be beneficial by reducing inflammatory processes and normalizing microcirculation in the bowel. Further investigations are needed to better understand the relations of stress and the kynurenines, with the aim of developing novel therapeutic tools for stress-related pathologies. Orv. Hetil., 2015, 156(35), 1402–1405.
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Zakharov, Gennady A., Alexander V. Zhuravlev, Tatyana L. Payalina, Nikolay G. Kamyshev, and Elena V. Savvateeva-Popova. "The influence of D. melanogaster mutations of the kynurenine pathway of tryptophan metabolism on locomotor behavior and expression of genes belonging to glutamatergic and cholinergic systems." Ecological genetics 9, no. 2 (June 15, 2011): 65–73. http://dx.doi.org/10.17816/ecogen9265-73.
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Disbalance of kynurenines produced by Drosophila mutations of the kynurenine pathway of tryptophan metabolism influences the locomotor behavior in larvae. The most pronounced is the effect of accumulation of kynurenic acid in the mutant cinnabar manifested as sharp reduction of general level of locomotor activity. The mutations seem to act through modulatory influences of kynurenines on signal cascades governed by ionotropic glutamatergic and cholinergic receptors. Expression of receptor genes in the mutants shows age-related changes pointing to gradual evolvement of consequences of kynurenines disbalance.
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Büki, Alexandra, Gabriella Kekesi, Gyongyi Horvath, and László Vécsei. "A Potential Interface between the Kynurenine Pathway and Autonomic Imbalance in Schizophrenia." International Journal of Molecular Sciences 22, no. 18 (September 16, 2021): 10016. http://dx.doi.org/10.3390/ijms221810016.
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Schizophrenia is a neuropsychiatric disorder characterized by various symptoms including autonomic imbalance. These disturbances involve almost all autonomic functions and might contribute to poor medication compliance, worsened quality of life and increased mortality. Therefore, it has a great importance to find a potential therapeutic solution to improve the autonomic disturbances. The altered level of kynurenines (e.g., kynurenic acid), as tryptophan metabolites, is almost the most consistently found biochemical abnormality in schizophrenia. Kynurenic acid influences different types of receptors, most of them involved in the pathophysiology of schizophrenia. Only few data suggest that kynurenines might have effects on multiple autonomic functions. Publications so far have discussed the implication of kynurenines and the alteration of the autonomic nervous system in schizophrenia independently from each other. Thus, the coupling between them has not yet been addressed in schizophrenia, although their direct common points, potential interfaces indicate the consideration of their interaction. The present review gathers autonomic disturbances, the impaired kynurenine pathway in schizophrenia, and the effects of kynurenine pathway on autonomic functions. In the last part of the review, the potential interaction between the two systems in schizophrenia, and the possible therapeutic options are discussed.
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Hafstad Solvang, Stein-Erik, Jan Erik Nordrehaug, Dag Aarsland, Johannes Lange, Per Magne Ueland, Adrian McCann, Øivind Midttun, Grethe S. Tell, and Lasse Melvaer Giil. "Kynurenines, Neuropsychiatric Symptoms, and Cognitive Prognosis in Patients with Mild Dementia." International Journal of Tryptophan Research 12 (January 2019): 117864691987788. http://dx.doi.org/10.1177/1178646919877883.
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Introduction: Circulating tryptophan (Trp) and its downstream metabolites, the kynurenines, are potentially neuroactive. Consequently, they could be associated with neuropsychiatric symptoms and cognitive prognosis in patients with dementia. Objective: The objective of this study was to assess associations between circulating kynurenines, cognitive prognosis, and neuropsychiatric symptoms. Methods: We measured baseline serum Trp, neopterin, pyridoxal 5′-phosphate (PLP), and 9 kynurenines in 155 patients with mild dementia (90 with Alzheimer’s disease, 65 with Lewy body dementia). The ratios between kynurenine and Trp and kynurenic acid (KA) to kynurenine (KKR) were calculated. The Mini-Mental State Examination (MMSE) and the Neuropsychiatric Inventory (NPI) were administered at baseline and annually over 5 years. Associations between baseline metabolite concentrations with MMSE and the NPI total score were assessed using a generalized structural equation model (mixed-effects multiprocess model), adjusted for age, sex, current smoking, glomerular filtration rate, and PLP. Post hoc associations between KKRs and individual NPI items were assessed using logistic mixed-effects models. False discovery rate (0.05)–adjusted P values ( Q values) are reported. Results: Kynurenine had a nonlinear quadratic relationship with the intercept of the MMSE scores over 5 years ( Q < 0.05), but not with the slope of MMSE decline. Kynurenine was associated with a higher NPI total score over time ( Q < 0.001). Post hoc, both KKR and KA were associated with more hallucinations ( Q < 0.05). Conclusions: Kynurenine has a complex relationship with cognition, where both low and high levels were associated with poor cognitive performance. A higher KKR indicated risk for neuropsychiatric symptoms, especially hallucinations.
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Szűcs, Edina, Azzurra Stefanucci, Marilisa Pia Dimmito, Ferenc Zádor, Stefano Pieretti, Gokhan Zengin, László Vécsei, Sándor Benyhe, Marianna Nalli, and Adriano Mollica. "Discovery of Kynurenines Containing Oligopeptides as Potent Opioid Receptor Agonists." Biomolecules 10, no. 2 (February 12, 2020): 284. http://dx.doi.org/10.3390/biom10020284.
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Kynurenine (kyn) and kynurenic acid (kyna) are well-defined metabolites of tryptophan catabolism collectively known as “kynurenines”, which exert regulatory functions in host-microbiome signaling, immune cell response, and neuronal excitability. Kynurenine containing peptides endowed with opioid receptor activity have been isolated from natural organisms; thus, in this work, novel opioid peptide analogs incorporating L-kynurenine (L-kyn) and kynurenic acid (kyna) in place of native amino acids have been designed and synthesized with the aim to investigate the biological effect of these modifications. The kyna-containing peptide (KA1) binds selectively the μ-opioid receptor with a Ki = 1.08 ± 0.26 (selectivity ratio μ/δ/κ = 1:514:10,000), while the L-kyn-containing peptide (K6) shows a mixed binding affinity for μ, δ, and κ-opioid receptors, with efficacy and potency (Emax = 209.7 + 3.4%; LogEC50 = −5.984 + 0.054) higher than those of the reference compound DAMGO. This novel oligopeptide exhibits a strong antinociceptive effect after i.c.v. and s.c. administrations in in vivo tests, according to good stability in human plasma (t1/2 = 47 min).
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Theofylaktopoulou, Despoina, Arve Ulvik, Øivind Midttun, Per Magne Ueland, Stein Emil Vollset, Ottar Nygård, Steinar Hustad, Grethe S. Tell, and Simone J. P. M. Eussen. "Vitamins B2and B6as determinants of kynurenines and related markers of interferon-γ-mediated immune activation in the community-based Hordaland Health Study." British Journal of Nutrition 112, no. 7 (August 8, 2014): 1065–72. http://dx.doi.org/10.1017/s0007114514001858.
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Vitamins B2and B6are cofactors in the kynurenine pathway. Many of the kynurenines are neuroactive compounds with immunomodulatory effects. In the present study, we aimed to investigate plasma concentrations of vitamins B2and B6as determinants of kynurenines and two markers of interferon-γ-mediated immune activation (kynurenine:tryptophan ratio (KTR) and neopterin). We measured the concentrations of vitamins B2and B6vitamers, neopterin, tryptophan and six kynurenines (i.e. kynurenine, anthranilic acid, kynurenic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid and xanthurenic acid) in plasma from 7051 individuals. Dietary intake of vitamins B2and B6was assessed using a validated FFQ. Associations were investigated using partial Spearman's correlations, generalised additive models, and segmented or multiple linear regression. The B2vitamer, riboflavin, was positively associated with 3-hydroxyanthranilic acid and xanthurenic acid, with correlation coefficients, as obtained by segmented regression, of 0·20 (95 % CI 0·16, 0·23) and 0·24 (95 % CI 0·19, 0·28), at riboflavin concentrations below the median value (13·0 nmol/l). The vitamin B6vitamer, pyridoxal 5′-phosphate (PLP), was positively associated with most kynurenines at PLP concentrations < 39·3–47·0 nmol/l, and inversely associated with 3-hydroxykynurenine with the association being more prominent at PLP concentrations < 18·9 nmol/l. Riboflavin and PLP were associated with xanthurenic acid only at relatively low, but normal concentrations of both vitamers. Lastly, PLP was negatively correlated with neopterin and KTR. These results demonstrate the significant and complex determination of kynurenine metabolism by vitamin status. Future studies on B-vitamins and kynurenines in relation to chronic diseases should therefore integrate data on relevant biomarkers related to B-vitamins status and tryptophan metabolism.
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Ervik, Arne Olav, Stein-Erik Hafstad Solvang, Jan Erik Nordrehaug, Per Magne Ueland, Øivind Midttun, Audun Hildre, Adrian McCann, Ottar Nygård, Dag Aarsland, and Lasse Melvaer Giil. "The Associations Between Cognitive Prognosis and Kynurenines Are Modified by the Apolipoprotein ε4 Allele Variant in Patients With Dementia." International Journal of Tryptophan Research 12 (January 2019): 117864691988563. http://dx.doi.org/10.1177/1178646919885637.
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Background: The apolipoprotein E ε4 gene variant (APOEε4) confers considerable risk for dementia and affects neuroinflammation, brain metabolism, and synaptic function. The kynurenine pathway (KP) gives rise to neuroactive metabolites, which have inflammatory, redox, and excitotoxic effects in the brain. Aim: To assess whether the presence of at least one APOEε4 allele modifies the association between kynurenines and the cognitive prognosis. Methods: A total of 152 patients with sera for metabolite measurements and APOE genotype were included from the Dementia Study of Western Norway. The participants had mild Alzheimer disease and Lewy body dementia. Apolipoprotein E ε4 gene variant allele status was classified as one or more ε4 versus any other. Mini-Mental State Examination (MMSE) was measured at baseline and for 5 consecutive years. Mann-Whitney U tests and linear mixed-effects models were used for statistical analysis. Results: There were no significant differences in serum concentrations of tryptophan and kynurenine according to the presence or absence of APOEε4. High serum concentrations of kynurenic acid, quinolinic acid, and picolinic acid, and a higher kynurenine-to-tryptophan ratio, were all associated with more cognitive decline in patients without APOEε4 compared to those with the APOEε4 allele ( P-value of the interactions < .05). Conclusions: Kynurenic acid, quinolinic acid, picolinic acid, and the kynurenine-to-tryptophan ratio were associated with a significant increase in cognitive decline when the APOEε4 variant was absent, whereas there was a relatively less decline when the APOEε4 variant was present.
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Fukuwatari, Tsutomu. "Possibility of Amino Acid Treatment to Prevent the Psychiatric Disorders via Modulation of the Production of Tryptophan Metabolite Kynurenic Acid." Nutrients 12, no. 5 (May 13, 2020): 1403. http://dx.doi.org/10.3390/nu12051403.
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Kynurenic acid, a metabolite of the kynurenine pathway of tryptophan catabolism, acts as an antagonist for both the α7 nicotinic acetylcholine receptor and glycine coagonist sites of the N-methyl-d-aspartic acid receptor at endogenous brain concentrations. Elevation of brain kynurenic acid levels reduces the release of neurotransmitters such as dopamine and glutamate, and kynurenic acid is considered to be involved in psychiatric disorders such as schizophrenia and depression. Thus, the control of kynurenine pathway, especially kynurenic acid production, in the brain is an important target for the improvement of brain function or the effective treatment of brain disorders. Astrocytes uptake kynurenine, the immediate precursor of kynurenic acid, via large neutral amino acid transporters, and metabolize kynurenine to kynurenic acid by kynurenine aminotransferases. The former transport both branched-chain and aromatic amino acids, and the latter have substrate specificity for amino acids and their metabolites. Recent studies have suggested the possibility that amino acids may suppress kynurenic acid production via the blockade of kynurenine transport or via kynurenic acid synthesis reactions. This approach may be useful in the treatment and prevention of neurological and psychiatric diseases associated with elevated kynurenic acid levels.
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Ruddick, Jon P., Andrew K. Evans, David J. Nutt, Stafford L. Lightman, Graham A. W. Rook, and Christopher A. Lowry. "Tryptophan metabolism in the central nervous system: medical implications." Expert Reviews in Molecular Medicine 8, no. 20 (August 2006): 1–27. http://dx.doi.org/10.1017/s1462399406000068.
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The metabolism of the amino acid l-tryptophan is a highly regulated physiological process leading to the generation of several neuroactive compounds within the central nervous system. These include the aminergic neurotransmitter serotonin (5-hydroxytryptamine, 5-HT), products of the kynurenine pathway of tryptophan metabolism (including 3-hydroxykynurenine, 3-hydroxyanthranilic acid, quinolinic acid and kynurenic acid), the neurohormone melatonin, several neuroactive kynuramine metabolites of melatonin, and the trace amine tryptamine. The integral role of central serotonergic systems in the modulation of physiology and behaviour has been well documented since the first description of serotonergic neurons in the brain some 40 years ago. However, while the significance of the peripheral kynurenine pathway of tryptophan metabolism has also been recognised for several decades, it has only recently been appreciated that the synthesis of kynurenines within the central nervous system has important consequences for physiology and behaviour. Altered kynurenine metabolism has been implicated in the pathophysiology of conditions such as acquired immunodeficiency syndrome (AIDS)-related dementia, Huntington's disease and Alzheimer's disease. In this review we discuss the molecular mechanisms involved in regulating the metabolism of tryptophan and consider the medical implications associated with dysregulation of both serotonergic and kynurenine pathways of tryptophan metabolism.
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Trepci, Ada, Sophie Imbeault, Victoria L. Wyckelsma, Håkan Westerblad, Sigurd Hermansson, Daniel C. Andersson, Fredrik Piehl, et al. "Quantification of Plasma Kynurenine Metabolites Following One Bout of Sprint Interval Exercise." International Journal of Tryptophan Research 13 (January 2020): 117864692097824. http://dx.doi.org/10.1177/1178646920978241.
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The kynurenine pathway of tryptophan degradation produces several neuroactive metabolites suggested to be involved in a wide variety of diseases and disorders, however, technical challenges in reliably detecting these metabolites hampers cross-comparisons. The main objective of this study was to develop an accurate, robust and precise bioanalytical method for simultaneous quantification of ten plasma kynurenine metabolites. As a secondary aim, we applied this method on blood samples taken from healthy subjects conducting 1 session of sprint interval exercise (SIE). It is well accepted that physical exercise is associated with health benefits and reduces risks of psychiatric illness, diabetes, cancer and cardiovascular disease, but also influences the peripheral and central concentrations of kynurenines. In line with this, we found that in healthy old adults ( n = 10; mean age 64 years), levels of kynurenine increased 1 hour ( P = .03) after SIE, while kynurenic acid (KYNA) concentrations were elevated after 24 hours ( P = .02). In contrast, no significant changes after exercise were seen in young adults ( n = 10; mean age 24 years). In conclusion, the described method performs well in reliably detecting all the analyzed metabolites in plasma samples. Furthermore, we also detected an age-dependent effect on the degree by which a single intense training session affects kynurenine metabolite levels.
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Nozaki, Kazuhiko, and M. Flint Beal. "Neuroprotective Effects of L-Kynurenine on Hypoxia—Ischemia and NMDA Lesions in Neonatal Rats." Journal of Cerebral Blood Flow & Metabolism 12, no. 3 (May 1992): 400–407. http://dx.doi.org/10.1038/jcbfm.1992.57.
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Kynurenic acid is the only known endogenous excitatory amino acid receptor antagonist in the central nervous system. In the present study, we examined whether increasing brain concentrations of kynurenic acid by loading with its precursor l-kynurenine, or blocking its excretion with probenecid, could exert neuroprotective effects. Neuroprotective effects were examined in a neonatal model of hypoxia–ischemia, and following intrastriatal injection of N-methyl-d-aspartate (NMDA). Seven-day-old rats underwent unilateral ligation of the carotid artery, followed by exposure to 8% oxygen for 1.5 h. l-kynurenine administered 1 h before the hypoxia–ischemia showed a dose-dependent significant neuroprotective effect, with complete protection at a dose of 300 mg kg−1. The induction of c-fos immunoreactivity in cerebral cortex was also blocked by this dose of l-kynurenine. Probenecid alone had moderate neuroprotective effects, while a combination of a low dose of probenecid with doses of 50–200 mg kg−1 of l-kynurenine showed significant dose-dependent neuroprotection. Kynurenine dose-dependently protected against NMDA neurotoxicity in 7-day-old rats. Neurochemical analysis confirmed that l-kynurenine with or without probenecid markedly increased concentrations of kynurenic acid in cerebral cortex of 7-day-old rats. These results show for the first time that pharmacologic manipulation of endogenous concentrations of kynurenic acid can exert neuroprotective effects.
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Maget, Alexander, Martina Platzer, Susanne A. Bengesser, Frederike T. Fellendorf, Armin Birner, Robert Queissner, Carlo Hamm, et al. "Differences in Kynurenine Metabolism During Depressive, Manic, and Euthymic Phases of Bipolar Affective Disorder." Current Topics in Medicinal Chemistry 20, no. 15 (June 1, 2020): 1344–52. http://dx.doi.org/10.2174/1568026619666190802145128.
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Background & Objectives: The kynurenine pathway is involved in inflammatory diseases. Alterations of this pathway were shown in psychiatric entities as well. The aim of this study was to determine whether specific changes in kynurenine metabolism are associated with current mood symptoms in bipolar disorder. Methods: Sum scores of the Hamilton Depression Scale, Beck Depression Inventory, and Young Mania Rating Scale were collected from 156 bipolar individuals to build groups of depressive, manic and euthymic subjects according to predefined cut-off scores. Severity of current mood symptoms was correlated with activities of the enzymes kynurenine 3-monooxygenase (ratio of 3-hydroxykynurenine/ kynurenine), kynurenine aminotransferase (ratio of kynurenic acid/ kynurenine) and kynureninase (ratio of 3-hydroxyanthranilic acid/ 3-hydroxykynurenine), proxied by ratios of serum concentrations. Results: Individuals with manic symptoms showed a shift towards higher kynurenine 3-monooxygenase activity (χ2 = 7.14, Df = 2, p = .028), compared to euthymic as well as depressed individuals. There were no differences between groups regarding activity of kynurenine aminotransferase and kynureninase. Within the group of depressed patients, Hamilton Depression Scale and kynurenine aminotransferase showed a significant negative correlation (r = -0.41, p = .036), displaying lower metabolism in the direction of kynurenic acid. Conclusion: Depression severity in bipolar disorder seems to be associated with a decreased synthesis of putative neuroprotective kynurenic acid. Furthermore, higher kynurenine 3-monooxygenase activity in currently manic individuals indicates an increased inflammatory state within bipolar disorder with more severe inflammation during manic episodes. The underlying pathophysiological mechanisms of the different affective episodes could represent parallel mechanisms rather than opposed processes.
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Baran, H., J. A. Hainfellner, and B. Kepplinger. "Kynurenic Acid Metabolism in Various Types of Brain Pathology in HIV-1 Infected Patients." International Journal of Tryptophan Research 5 (January 2012): IJTR.S10627. http://dx.doi.org/10.4137/ijtr.s10627.
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Kynurenic acid, an intermediate metabolite of L-kynurenine, is a competitive antagonist of inotropic excitatory amino acid (EAA) receptors as well as a non competitive antagonist of 7 alpha nicotine cholinergic receptors and its involvement in memory deficit and cognition impairment has been suggested. Alterations of kynurenic acid metabolism in the brain after HIV-1 (human immunodeficiency virus type-1) infection have been demonstrated. The present study evaluates the biosynthetic machinery of kynurenic acid e.g. the content of L-kynurenine and kynurenic acid, as well as the activity of enzymes synthesizing kynurenic acid, kynurenine aminotransferase I (KAT I) and kynurenine aminotransferase II (KAT II) in the frontal cortex and cerebellum of HIV-1 infected patients in relation to different types of pathology classified as follows: HIV in brain (HIV); opportunistic infection (OPP); infarction of brain (INF); malignant lymphoma of brain (LY); and glial dystrophy (GD) and of control (CO) subjects. Of all investigated pathologies the most frequent was OPP (65%), followed by HIV (26%), LY, INF, and GD (each 22%, respectively). Further, 68% of HIV-1 patients had bronchopneumonia, the highest incidence of which, at 60%, was seen in the OPP and LY group. Kynurenic acid was increased significantly in the frontal cortex of LY (392% of CO, P < 0.001), HIV (231% of CO, P < 0.01) and GD (193% of CO, P < 0.05), as well as in the cerebellum of GD (261% of CO, P < 0.01). A significant increase of L-kynurenine was observed in the frontal cortex of LY (385% of CO, P < 0.001) and INF (206% of CO, P < 0.01), and in the cerebellum of GD, LY, OPP and HIV (between 177% and 147% of CO). The KAT I activity increased significantly in the frontal cortex of all pathological subgroups, ie OPP = 420% > INF > LY > HIV > GD = 192% of CO. In the cerebellum, too, all pathological subgroups showed marked increase of KAT I activity (OPP = 320% > LY, HIV > GD > INF = 176% of CO). On contrary, the activity of KAT II was moderately, but significantly, higher in the frontal cortex of INF and OPP; in the cerebellum of HIV, OPP and LY it was comparable to the control, while mildly reduced in INF and GD. Interestingly, normal subjects with the diagnosis of bronchopneumonia were characterized by high kynurenic acid metabolism in the brain, too. Correlation analyses between kynurenine parameters revealed association between high ratio KAT I/KAT II and increased kynurenic acid level and lower L-kynurenine in the frontal cortex and cerebellum of HIV and LY subgroups. The present study revealed a different pattern of alteration of kynurenic acid metabolism in frontal cortex and cerebellum among investigated pathological subgroups of HIV-1 infected patients. Interestingly, a marked enhancement of kynurenic acid metabolism in the brain has been found with occurrence of bronchopneumonia. This finding indicates a notable association between impaired conditions of oxygen availability and enhancement of kynurenic acid formation in the human brain. These observation(s) might have an impact on the understanding of pathological processes in the brain after HIV-1 infection involving the development of neuropsychiatric and neurological symptoms, including memory and cognition impairment.
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Martin, Kyle S., Michele Azzolini, and Jorge Lira Ruas. "The kynurenine connection: how exercise shifts muscle tryptophan metabolism and affects energy homeostasis, the immune system, and the brain." American Journal of Physiology-Cell Physiology 318, no. 5 (May 1, 2020): C818—C830. http://dx.doi.org/10.1152/ajpcell.00580.2019.
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Tryptophan catabolism through the kynurenine pathway generates a variety of bioactive metabolites. Physical exercise can modulate kynurenine pathway metabolism in skeletal muscle and thus change the concentrations of select compounds in peripheral tissues and in the central nervous system. Here we review recent advances in our understanding of how exercise alters tryptophan-kynurenine metabolism in muscle and its subsequent local and distal effects. We propose that the effects of kynurenine pathway metabolites on skeletal muscle, adipose tissue, immune system, and the brain suggest that some of these compounds could qualify as exercise-induced myokines. Indeed, some of the more recently discovered biological activities for kynurenines include many of the best-known benefits of exercise: improved energy homeostasis, promotion of an anti-inflammatory environment, and neuroprotection. Finally, by considering the tissue expression of the different membrane and cytosolic receptors for kynurenines, we discuss known and potential biological activities for these tryptophan metabolites.
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Wickström, Ronny, Åsa Fowler, Michel Goiny, Vincent Millischer, Sofia Ygberg, and Lilly Schwieler. "The Kynurenine Pathway is Differentially Activated in Children with Lyme Disease and Tick-Borne Encephalitis." Microorganisms 9, no. 2 (February 4, 2021): 322. http://dx.doi.org/10.3390/microorganisms9020322.
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In children, tick-borne encephalitis and neuroborreliosis are common infections affecting the central nervous system. As inflammatory pathways including cytokine expression are activated in these children and appear to be of importance for outcome, we hypothesized that induction of the kynurenine pathway may be part of the pathophysiological mechanism. Inflammatory biomarkers were analyzed in cerebrospinal fluid from 22 children with tick-borne encephalitis (TBE), 34 children with neuroborreliosis (NB) and 6 children with no central nervous system infection. Cerebrospinal fluid levels of kynurenine and kynurenic acid were increased in children with neuroborreliosis compared to the comparison group. A correlation was seen between expression of several cerebrospinal fluid cytokines and levels of kynurenine and kynurenic acid in children with neuroborreliosis but not in children with tick-borne encephalitis. These findings demonstrate a strong induction of the kynurenine pathway in children with neuroborreliosis which differs from that seen in children with tick-borne encephalitis. The importance of brain kynurenic acid (KYNA) in both immune modulation and neurotransmission raises the possibility that abnormal levels of the compound in neuroborreliosis might be of importance for the pathophysiology of the disease. Drugs targeting the enzymes of this pathway may open the venue for novel therapeutic interventions.
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Berthon, Céline, Michaela Fontenay, Selim Corm, Isabelle Briche, Michel Lhermitte, and Bruno Quesnel. "Metabolites of Tryptophan Catabolism Are Elevated in Sera of Patients with Myelodysplastic Syndromes and Inhibit Hematopoietic Progenitor Amplification." Blood 120, no. 21 (November 16, 2012): 3843. http://dx.doi.org/10.1182/blood.v120.21.3843.3843.
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Abstract Abstract 3843 Introduction: Tryptophan catabolism, which is mediated by the enzymes indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO), produces kynurenine, which blocks T-cell activation and induces immunosuppression. Kynurenine itself is converted by downstream enzymes into secondary catabolites that also have toxic effects on T cells. Tryptophan catabolism is elevated in many cancers, including acute myeloid leukemia (AML). However, tryptophan catabolites that are downstream of kynurenine have never been investigated in hematological malignancies. Methods: We evaluated the serum levels of primary and secondary tryptophan catabolites in a cohort of patients with myelodysplastic syndromes (MDS). Sera were isolated from 132 adult MDS patients after informed consent was obtained in accordance with the Helsinki Declaration. The levels of tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, and anthranilic acid in the sera were quantified using HPLC. For erythroid cell expansion, CD34+ cells were collected and isolated from the mononuclear cell fractions of cytapheresis products from 3 healthy donors and cultured in liquid medium under erythroid conditions with tryptophan catabolites. Results: The MDS patients showed significantly lower levels of tryptophan and higher levels of kynurenine, kynurenic acid, 3-hydroxyanthranilic acid, and anthranilic acid compared with the healthy controls. We also compared the kynurenine and tryptophan levels in the MDS patients with our previous cohort of 112 patients with primary AML. The kynurenine/tryptophan ratios were significantly higher in the MDS patients (median 0.0468 vs. 0.0676). The tryptophan catabolites correlated with cytopenia; higher kynurenine levels were associated with lower hemoglobin levels and higher blast counts and were associated with presence of dysgranulopoiesis. Lower tryptophan levels were found in patients with platelet transfusion dependency. Kynurenic acid levels were higher in patients with dysmegakaryopoiesis. High 3-hydroxyanthranilic and kynurenic acid levels were associated with severe thrombopenia below 20 G/L. IPSS score, cytogenetic, and WHO diagnosis did not associated with any tryptophan catabolite level. The tryptophan catabolites inhibited progenitor expansion during the in vitro culture of hematopoietic cells and reduced the numbers of granulocytes and erythroblasts. Conclusions: Thus, MDS patients are characterized by high tryptophan catabolism resulting in elevated primary and secondary metabolites, which both have inhibitory effects on hematopoiesis. These results suggest that IDO or TDO inhibitors should be investigated in MDS. Disclosures: No relevant conflicts of interest to declare.
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Pawlak, Krystyna, Michal Mysliwiec, and Dariusz Pawlak. "Hypercoagulability is independently associated with kynurenine pathway activation in dialysed uraemic patients." Thrombosis and Haemostasis 102, no. 07 (2009): 49–55. http://dx.doi.org/10.1160/th08-10-0696.
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SummaryPatients with end-stage renal disease (ESRD) exhibit features of a hypercoagulable state, which may contribute to atherosclerosis. Kynurenines are the metabolites of tryptophan degradation in mammals. We examined the relationship between coagulation activation and kynurenines in 92 patients with ESRD on maintenance haemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) and 20 healthy controls. We measured the plasma levels of: tissue factor (TF), its pathway inhibitor (TFPI), the marker of coagulation activation – prothrombin fragments 1+2 (F1+2), kynurenine (KYN) and its metabolites: kynurenic (KYNA), anthranilic (AA) and quinolinic (QA) acids. The ratio of KYNA to KYN (kyna/kyn), AA to KYN (aa/kyn) and QA to KYN (qa/kyn), reflecting intensified activity of enzymes which converted KYN to its metabolites, were also determined. Measured coagulation parameters and kynurenines were significantly elevated in ESRD patients compared to controls. TF, TFPI and F1+2 were significantly associated with AA, aa/kyn, QA and qa/kyn ratio. Multiple regression analysis showed that fibrinogen (p<0.01) and above mentioned KYN metabolites (all p<0.05) were the independent variables significantly associated with increased F1+2 levels, reflecting hypercoagulability in ESRD patients. In conclusion, this study represents the first to investigate both the coagulation system and KYN pathway in ESRD patients. The coagulation was enhanced in dialysed uraemic patients compared with the healthy controls demonstrated by increased TF, TFPI and F1+2 levels. These changes were correlated with activation of the KYN pathway. Finally, fibrinogen and KYN metabolites are independently and significantly associated with the hypercoagulable state in uraemic patients on CAPD and HD treatment.
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Kepplinger, Berthold, Halina Baran, Brenda Sedlnitzky-Semler, Nagy-Roland Badawi, and Helene Erhart. "Stochastic Resonance Activity Influences Serum Tryptophan Metabolism in Healthy Human Subjects." International Journal of Tryptophan Research 4 (January 2011): IJTR.S7986. http://dx.doi.org/10.4137/ijtr.s7986.
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Background Stochastic resonance therapy (SRT) is used for rehabilitation of patients with various neuropsychiatric diseases. An alteration in tryptophan metabolism along the kynurenine pathway has been identified in the central and peripheral nervous systems in patients with neuroinflammatory and neurodegenerative diseases and during the aging process. This study investigated the effect of SRT as an exercise activity on serum tryptophan metabolites in healthy subjects. Methods Serum L-tryptophan, L-kynurenine, kynurenic acid, and anthranilic acid levels were measured one minute before SRT and at one, 5, 15, 30, and 60 minutes after SRT. We found that SRT affected tryptophan metabolism. Serum levels of L-tryptophan, L-kynurenine, and kynurenic acid were significantly reduced for up to 60 minutes after SRT. Anthranilic acid levels were characterized by a moderate, non significant transient decrease for up to 15 minutes, followed by normalization at 60 minutes. Tryptophan metabolite ratios were moderately altered, suggesting activation of metabolism after SRT. Lowering of tryptophan would generally involve activation of tryptophan catabolism and neurotransmitter, protein, and bone biosynthesis. Lowering of kynurenic acid by SRT might be relevant for improving symptoms in patients with neuropsychiatric disorders, such as Parkinson's disease, Alzheimer's disease, schizophrenia, and depression, as well as certain pain conditions.
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Baran, Halina, Gabriele Amann, Barbara Lubec, and Gert Lubec. "Kynurenic Acid and Kynurenine Aminotransferase in Heart." Pediatric Research 41, no. 3 (March 1997): 404–10. http://dx.doi.org/10.1203/00006450-199703000-00017.
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Stone, Trevor W. "Kynurenic acid antagonists and kynurenine pathway inhibitors." Expert Opinion on Investigational Drugs 10, no. 4 (April 2001): 633–45. http://dx.doi.org/10.1517/13543784.10.4.633.
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Allison, David J., Joshua P. Nederveen, Tim Snijders, Kirsten E. Bell, Dinesh Kumbhare, Stuart M. Phillips, Gianni Parise, and Jennifer J. Heisz. "Exercise training impacts skeletal muscle gene expression related to the kynurenine pathway." American Journal of Physiology-Cell Physiology 316, no. 3 (March 1, 2019): C444—C448. http://dx.doi.org/10.1152/ajpcell.00448.2018.
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Exercise positively impacts mood and symptoms of depression; however, the mechanisms underlying these effects are not fully understood. Recent evidence highlights a potential role for skeletal muscle-derived transcription factors to influence tryptophan metabolism, along the kynurenine pathway, which has important implications in depression. This has important consequences for older adults, whose age-related muscle deterioration may influence this pathway and may increase their risk for depression. Although exercise training has been shown to improve skeletal muscle mass in older adults, whether this also translates into improvements in transcription factors and metabolites related to the kynurenine pathway has yet to be examined. The aim of the present study was to examine the influence of a 12-wk exercise program on skeletal muscle gene expression of transcription factors, kynurenine aminotransferase (KAT) gene expression, and plasma concentrations of tryptophan metabolites (kynurenines) in healthy older men over 65 yr of age. Exercise training significantly increased skeletal muscle gene expression of transcription factors (peroxisome proliferator-activated receptor-γ coactivator 1α, peroxisome proliferator-activated receptor-α, and peroxisome proliferator-activated receptor-δ: 1.77, 1.99, 2.18-fold increases, respectively, P < 0.01] and KAT isoforms 1–4 (6.5, 2.1, 2.2, and 2.6-fold increases, respectively, P ≤ 0.01). Concentrations of plasma kynurenines were not altered. These results demonstrate that 12 wk of exercise training significantly altered skeletal muscle gene expression of transcription factors and gene expression related to the kynurenine pathway, but not circulating kynurenine metabolites in older men. These findings warrant future research to determine whether distinct exercise modalities or varying intensities could induce a shift in the kynurenine pathway in depressed older adults.
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Schlittler, Maja, Michel Goiny, Leandro Z. Agudelo, Tomas Venckunas, Marius Brazaitis, Albertas Skurvydas, Sigitas Kamandulis, et al. "Endurance exercise increases skeletal muscle kynurenine aminotransferases and plasma kynurenic acid in humans." American Journal of Physiology-Cell Physiology 310, no. 10 (May 15, 2016): C836—C840. http://dx.doi.org/10.1152/ajpcell.00053.2016.
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Physical exercise has emerged as an alternative treatment for patients with depressive disorder. Recent animal studies show that exercise protects from depression by increased skeletal muscle kynurenine aminotransferase (KAT) expression which shifts the kynurenine metabolism away from the neurotoxic kynurenine (KYN) to the production of kynurenic acid (KYNA). In the present study, we investigated the effect of exercise on kynurenine metabolism in humans. KAT gene and protein expression was increased in the muscles of endurance-trained subjects compared with untrained subjects. Endurance exercise caused an increase in plasma KYNA within the first hour after exercise. In contrast, a bout of high-intensity eccentric exercise did not lead to increased plasma KYNA concentration. Our results show that regular endurance exercise causes adaptations in kynurenine metabolism which can have implications for exercise recommendations for patients with depressive disorder.
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Guo, Song, L. Vecsei, and Messoud Ashina. "The L-kynurenine signalling pathway in trigeminal pain processing: A potential therapeutic target in migraine?" Cephalalgia 31, no. 9 (May 18, 2011): 1029–38. http://dx.doi.org/10.1177/0333102411404717.
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Introduction: In recent years the kynurenine family of compounds, metabolites of tryptophan, has become an area of intensive research because of its neuroactive properties. Two metabolites of this family have become of interest in relation to migraine and pain processing. Discussion: Experimental studies have shown that kynurenic acid (KYNA) plays an important role in the transmission of sensory impulses in the trigeminovascular system and that increased levels of KYNA decrease the sensitivity of the cerebral cortex to cortical spreading depression. Furthermore, another metabolite of the kynurenine family, L-kynurenine, exerts vasodilating effects similar to nitric oxide by increasing cyclic guanosine monophosphate. Conclusion: This review summarizes current knowledge of the role of kynurenine signalling in trigeminal and central pain processing, including its therapeutic prospects in migraine treatment.
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Naz, Bhat, Ståhl, Forsslund, Sköld, Wheelock, and Wheelock. "Dysregulation of the Tryptophan Pathway Evidences Gender Differences in COPD." Metabolites 9, no. 10 (October 1, 2019): 212. http://dx.doi.org/10.3390/metabo9100212.
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Increased activity of indoleamine 2,3-dioxygenase (IDO) and tryptophan hydroxylase (TPH) have been reported in individuals with chronic obstructive pulmonary disease (COPD). We therefore investigated the effect of gender stratification upon the observed levels of tryptophan metabolites in COPD. Tryptophan, serotonin, kynurenine, and kynurenic acid were quantified in serum of never-smokers (n = 39), smokers (n = 40), COPD smokers (n = 27), and COPD ex-smokers (n = 11) by liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). The individual metabolite associations with lung function, blood, and bronchoalveolar lavage (BAL) immune-cell composition, as well as chemokine and cytokine levels, were investigated. Stratification by gender and smoking status revealed that the observed alterations in kynurenine and kynurenic acid, and to a lesser extent serotonin, were prominent in males, irrespective of COPD status (kynurenine p = 0.005, kynurenic acid p = 0.009, and serotonin p = 0.02). Inferred serum IDO activity and kynurenine levels decreased in smokers relative to never-smokers (p = 0.005 and p = 0.004, respectively). In contrast, inferred tryptophan hydroxylase (TPH) activity and serotonin levels showed an increase with smoking that reached significance with COPD (p = 0.01 and p = 0.01, respectively). Serum IDO activity correlated with blood CXC chemokine ligand 9 (CXCL9, p = 0.0009, r = 0.93) and chemokine (C-C motif) ligand 4 (CCL4.(p = 0.04, r = 0.73) in female COPD smokers. Conversely, serum serotonin levels correlated with BAL CD4+ T-cells (%) (p = 0.001, r = 0.92) and CD8+ T-cells (%) (p = 0.002, r = −0.90) in female COPD smokers, but not in male COPD smokers (p = 0.1, r = 0.46 and p = 0.1, r = −0.50, respectively). IDO- and TPH-mediated tryptophan metabolites showed gender-based associations in COPD, which were primarily driven by smoking status.
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Badawy, Abdulla A. B., and Donald M. Dougherty. "Assessment of the Human Kynurenine Pathway: Comparisons and Clinical Implications of Ethnic and Gender Differences in Plasma Tryptophan, Kynurenine Metabolites, and Enzyme Expressions at Baseline and after Acute Tryptophan Loading and Depletion." International Journal of Tryptophan Research 9 (January 2016): IJTR.S38189. http://dx.doi.org/10.4137/ijtr.s38189.
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Tryptophan (Trp) metabolism via the kynurenine pathway (KP) was assessed in normal healthy US volunteers at baseline and after acute Trp depletion (ATD) and acute Trp loading (ATL) using amino acid formulations. The hepatic KP accounts for ~90% of overall Trp degradation. Liver Trp 2,3-dioxygenase (TDO) contributes ~70% toward Trp oxidation, with the remainder achieved by subsequent rate-limiting enzymes in the KP. TDO is not influenced by a 1.15 g Trp load, but is maximally activated by a 5.15 g dose. We recommend a 30 mg/kg dose for future ATL studies. ATD activates TDO and enhances the Trp flux down the KP via its leucine component. Higher plasma free [Trp] and lower total [Trp] are observed in women, with no gender differences in kynurenines. Kynurenic acid is lower in female Caucasians, which may explain their lower incidence of schizophrenia. African-American and Hispanic women have a lower TDO and Trp oxidation relative to free Trp than the corresponding men. African-American women have a potentially higher 3-hydroxyanthranilic acid/anthranilic acid ratio, which may protect them against osteoporosis. Future studies of the KP in relation to health and disease should focus on gender and ethnic differences.
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Ciapała, Katarzyna, and Ewelina Rojewska. "Kinurenines in Central Nervous System under neuropathic pain – clinical implications from basic research." BÓL 20, no. 3 (January 16, 2020): 32–39. http://dx.doi.org/10.5604/01.3001.0013.7396.
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Central nervous system disorders are often accompanied by changes in tryptophan metabolism. Kynurenine pathway is known to be the main route by which this essential amino acid is catabolized to a plenty of metabolites. Intermediates of this cascade are responsible for a wide spectrum of effects, including endogenous regulation of neuronal excitability and immune cells response. Excessive or disrupted activation of the pathway can lead to the accumulation of neurotoxic compounds, and in consequence, contributes to the development of various type of pathologies. These aspects shed new light on the kynurenine pathway as a promising target for development of new therapeutic strategies. Following work briefly characterizes the kynurenine pathway and discusses the neurobiological functions of kynurenines, with particular focus on their role in the development and persistence of neuropathic pain. It is also presenting the potential clinical implications of modulation of the kynurenine pathway in pharmacological therapy of chronic pain.
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Yu, Edward, Christopher Papandreou, Miguel Ruiz-Canela, Marta Guasch-Ferre, Clary B. Clish, Courtney Dennis, Liming Liang, et al. "Association of Tryptophan Metabolites with Incident Type 2 Diabetes in the PREDIMED Trial: A Case–Cohort Study." Clinical Chemistry 64, no. 8 (August 1, 2018): 1211–20. http://dx.doi.org/10.1373/clinchem.2018.288720.
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Abstract BACKGROUND Metabolites of the tryptophan–kynurenine pathway (i.e., tryptophan, kynurenine, kynurenic acid, quinolinic acid, 3-hydroxyanthranilic) may be associated with diabetes development. Using a case–cohort design nested in the Prevención con Dieta Mediterránea (PREDIMED) study, we studied the associations of baseline and 1-year changes of these metabolites with incident type 2 diabetes (T2D). METHODS Plasma metabolite concentrations were quantified via LC-MS for n = 641 in a randomly selected subcohort and 251 incident cases diagnosed during 3.8 years of median follow-up. Weighted Cox models adjusted for age, sex, body mass index, and other T2D risk factors were used. RESULTS Baseline tryptophan was associated with higher risk of incident T2D (hazard ratio = 1.29; 95% CI, 1.04–1.61 per SD). Positive changes in quinolinic acid from baseline to 1 year were associated with a higher risk of T2D (hazard ratio = 1.39; 95% CI, 1.09–1.77 per SD). Baseline tryptophan and kynurenic acid were directly associated with changes in homeostatic model assessment for insulin resistance (HOMA-IR) from baseline to 1 year. Concurrent changes in kynurenine, quinolinic acid, 3-hydroxyanthranilic acid, and kynurenine/tryptophan ratio were associated with baseline-to-1-year changes in HOMA-IR. CONCLUSIONS Baseline tryptophan and 1-year increases in quinolinic acid were positively associated with incident T2D. Baseline and 1-year changes in tryptophan metabolites predicted changes in HOMA-IR. Tryptophan levels may initially increase and then deplete as diabetes progresses in severity.
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Nicholas, Dequina A., Lorena M. Salto, Kristen Lavelle, Joy Wilson, W. Lawrence Beeson, Anthony Firek, William H. R. Langridge, Zaida Cordero-MacIntyre, and Marino De Leon. "En Balance: The Contribution of Physical Activity to the Efficacy of Spanish Diabetes Education of Hispanic Americans with Type 2 Diabetes." Journal of Diabetes Research 2020 (April 21, 2020): 1–8. http://dx.doi.org/10.1155/2020/4826704.
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Purpose. En Balance, a culturally sensitive diabetes education program, improves glycemic control in Hispanics with type 2 diabetes. The program emphasized diet, physical activity, and other factors important for glycemic control. However, the individual contributions of these education factors are unclear. The purpose of this study is to assess the contribution of physical activity to the success of En Balance in improving the health of Mexican Americans with type 2 diabetes. Methods. A retrospective study was conducted with plasma samples collected pre- and post-3-month study. Samples from 58 (18 males and 40 females) Hispanic subjects with type 2 diabetes were analyzed for the concentration of kynurenines, known to decrease in response to exercise. After three months, health outcomes for the active group (decreased kynurenines) and the rest of the cohort were evaluated by paired Wilcoxon signed-rank test. Results. Half of the subjects had increased kynurenine levels at the end of the educational program. We found that the subjects in the active group with decreased kynurenine concentrations displayed statistically greater improvements in fasting blood glucose, A1C, cholesterol, and triglycerides despite weight loss being higher in the group with increased kynurenine concentrations. Conclusions. En Balance participants with decreased kynurenine levels had significantly improved glycemic control. These data suggest that physical activity significantly contributes to the success of the En Balance education program. This analysis indicates that diabetes public health educators should emphasize the benefit of physical activity on glycemic control even in the absence of major weight loss.
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Noakes, Rowland R. "Effects of Tranilast on the Urinary Excretion of Kynurenic and Quinolinic Acid under Conditions of L Tryptophan Loading." International Journal of Tryptophan Research 6 (January 2013): IJTR.S12797. http://dx.doi.org/10.4137/ijtr.s12797.
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The pathogenesis of morphea and other cutaneous sclerosing disorders remain poorly understood. Although they are considered to be autoimmune disorders, abnormal tryptophan metabolism may be involved. Current therapy is directed to supressing the autoimmune response. Demonstration of a therapeutic response to manipulation of the kynurenine pathway would both support a role for abnormal tryptophan metabolism and offer additional targets for therapy. Tranilast is a 3-hydroxyanthranilic acid derivative known to target the kynurenine pathway. The aim of this study was to see if tranilast lowered the urinary excretion of the kynurenine metabolites kynurenic and quinolinic acid under condition of L tryptophan loading in a volunteer. Mean baseline value for kynurenic acid and quinolinic acid were 1.1 and 2.1 mmol/mol creatinine, respectively. This rose to 5.6 and 3.8 mmol/mol creatinine respectively under conditions of L tryptophan loading 2 grams daily. Adding 1 g of tranilast daily lowered the values to 2.0 and 2.9 mmol/mol creatinine, respectively. These data suggest that tranilast acts as a competitive inhibitor of either indoleamine 2, 3-dioxygenase (IDO), tryptophan 2, 3 di-oxygenase (TDO) or both. As it involved only 1 subject, the results may not be representative of the larger population and must be considered preliminary.
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Bhat, Abid, Ananda Staats Pires, Vanessa Tan, Saravana Babu Chidambaram, and Gilles J. Guillemin. "Effects of Sleep Deprivation on the Tryptophan Metabolism." International Journal of Tryptophan Research 13 (January 2020): 117864692097090. http://dx.doi.org/10.1177/1178646920970902.
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Sleep has a regulatory role in maintaining metabolic homeostasis and cellular functions. Inadequate sleep time and sleep disorders have become more prevalent in the modern lifestyle. Fragmentation of sleep pattern alters critical intracellular second messengers and neurotransmitters which have key functions in brain development and behavioral functions. Tryptophan metabolism has also been found to get altered in SD and it is linked to various neurodegenerative diseases. The kynurenine pathway is a major regulator of the immune response. Adequate sleep alleviates neuroinflammation and facilitates the cellular clearance of metabolic toxins produced within the brain, while sleep deprivation activates the enzymatic degradation of tryptophan via the kynurenine pathway, which results in an increased accumulation of neurotoxic metabolites. SD causes increased production and accumulation of kynurenic acid in various regions of the brain. Higher levels of kynurenic acid have been found to trigger apoptosis, leads to cognitive decline, and inhibit neurogenesis. This review aims to link the impact of sleep deprivation on tryptophan metabolism and associated complication in the brain.
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Nagy, Bence M., Chandran Nagaraj, Andreas Meinitzer, Neha Sharma, Rita Papp, Vasile Foris, Bahil Ghanim, et al. "Importance of kynurenine in pulmonary hypertension." American Journal of Physiology-Lung Cellular and Molecular Physiology 313, no. 5 (November 1, 2017): L741—L751. http://dx.doi.org/10.1152/ajplung.00517.2016.
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The tryptophan metabolite kynurenine is significantly increased in pulmonary arterial hypertension (PAH) patients, and it is a potent vasodilator of systemic arteries. Our aim was to investigate the role of kynurenine in the pulmonary circulation. Serum tryptophan, kynurenine, and kynurenic acid levels were measured in 20 idiopathic PAH (IPAH) patients, 20 healthy controls, and 20 patients with chronic lung disease or metabolic syndrome without PH. Laser-dissected pulmonary arteries from IPAH and control lungs were tested for the expression of indoleamine-2, 3-dioxygenase (IDO), the rate-limiting enzyme for the conversion from tryptophan to kynurenine. Acute effects of kynurenine were tested in pulmonary vascular preparations, two different models of chronic pulmonary hypertension (PH), and in human pulmonary arterial smooth muscle cells (hPASMCs). In IPAH vs. control serum, kynurenine was significantly elevated (3.6 ± 0.2 vs. 2.6 ± 0.1 µM, P < 0.0001), and strongly associated with PH (area under the curve = 0.86), but kynurenine levels were not elevated in lung disease and metabolic syndrome. Among all investigated tryptophan metabolites, kynurenine displayed the strongest correlation with mean pulmonary arterial pressure (mPAP) (ρ: 0.770, P < 0.0001). Tryptophan was significantly decreased in IPAH lungs; however, IDO expression was not changed. In hPASMCs, kynurenine increased both cAMP and cGMP; in intrapulmonary arteries, it relaxed the preconstriction via NO/cGMP and cAMP pathways, and in two models of established PH, it acutely decreased the mPAP. Our data suggest that kynurenine elevation might be specifically associated with mPAP; kynurenine acts on hPASMCs in synergy with NO and exerts acute pulmonary vasodilatation in chronic PH models. Kynurenine might provide both a new biomarker and a new therapeutic option for PH.
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Badawy, Abdulla A. B., and Samina Bano. "Tryptophan Metabolism in Rat Liver after Administration of Tryptophan, Kynurenine Metabolites, and Kynureninase Inhibitors." International Journal of Tryptophan Research 9 (January 2016): IJTR.S38190. http://dx.doi.org/10.4137/ijtr.s38190.
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Rat liver tryptophan (Trp), kynurenine pathway metabolites, and enzymes deduced from product/substrate ratios were assessed following acute and/or chronic administration of kynurenic acid (KA), 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid (3-HAA), Trp, and the kynureninase inhibitors benserazide (BSZ) and carbidopa (CBD). KA activated Trp 2,3-dioxygenase (TDO), possibly by increasing liver 3-HAA, but inhibited kynurenine aminotransferase (KAT) and kynureninase activities with 3-HK as substrate. 3-HK inhibited kynureninase activity from 3-HK. 3-HAA stimulated TDO, but inhibited kynureninase activity from K and 3-HK. Trp (50 mg/kg) increased kynurenine metabolite concentrations and KAT from K, and exerted a temporary stimulation of TDO. The kynureninase inhibitors BSZ and CBD also inhibited KAT, but stimulated TDO. BSZ abolished or strongly inhibited the Trp-induced increases in liver Trp and kynurenine metabolites. The potential effects of these changes in conditions of immune activation, schizophrenia, and other disease states are discussed.
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Mor, Adrian, Krystyna Pawlak, Bartlomiej Kalaska, Tomasz Domaniewski, Beata Sieklucka, Marta Zieminska, Bogdan Cylwik, and Dariusz Pawlak. "Modulation of the Paracrine Kynurenic System in Bone as a New Regulator of Osteoblastogenesis and Bone Mineral Status in an Animal Model of Chronic Kidney Disease Treated with LP533401." International Journal of Molecular Sciences 21, no. 17 (August 19, 2020): 5979. http://dx.doi.org/10.3390/ijms21175979.
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An increase in the peripheral synthesis of serotonin and kynurenine, observed during the chronic kidney disease (CKD) course, is negatively associated with bone health. Serotonin and kynurenine are connected by the common precursor, tryptophan. LP533401 is an inhibitor of peripheral serotonin synthesis. This study aimed to establish if the inhibition of serotonin synthesis by LP533401 may affect the kynurenine pathway activity in bone tissue and its potential consequence with regard to osteogenesis and bone mineral status. Nephrectomized rats were treated with LP533401 at a dose of 30 and 100 mg/kg daily for eight weeks. Tryptophan and kynurenine concentrations were determined, and tryptophan 2,3-dioxygenase (TDO) expression was assessed. We discovered the presence of a TDO-dependent, paracrine kynurenic system in the bone of rats with CKD. Its modulation during LP533401 treatment was associated with impaired bone mineral status. Changes in TDO expression affecting the kynurenine pathway activity were related to the imbalance between peripheral serotonin and 25-hydroxyvitamin D. There were also close associations between the expression of genes participating in osteoblastogenesis and activation of the kynurenine pathway in the bones of LP53301-treated rats. Our results represent the next step in studying the role of tryptophan metabolites in renal osteodystrophy.
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Vecchiarelli, Haley A., Chaitanya P. Gandhi, and Matthew N. Hill. "Acute Psychological Stress Modulates the Expression of Enzymes Involved in the Kynurenine Pathway throughout Corticolimbic Circuits in Adult Male Rats." Neural Plasticity 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/7215684.
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Tryptophan is an essential dietary amino acid that is necessary for protein synthesis, but also serves as the precursor for serotonin. However, in addition to these biological functions, tryptophan also serves as a precursor for the kynurenine pathway, which has neurotoxic (quinolinic acid) and neuroprotective (kynurenic acid) metabolites. Glucocorticoid hormones and inflammatory mediators, both of which are increased by stress, have been shown to bias tryptophan along the kynurenine pathway and away from serotonin synthesis; however, to date, there is no published data regarding the effects of stress on enzymes regulating the kynurenine pathway in a regional manner throughout the brain. Herein, we examined the effects of an acute psychological stress (120 min restraint) on gene expression patterns of enzymes along the kynurenine pathway over a protracted time-course (1–24 h post-stress termination) within the amygdala, hippocampus, hypothalamus, and medial prefrontal cortex. Time-dependent changes in differential enzymes along the kynurenine metabolism pathway, particularly those involved in the production of quinolinic acid, were found within the amygdala, hypothalamus, and medial prefrontal cortex, with no changes seen in the hippocampus. These regional differences acutely may provide mechanistic insight into processes that become dysregulated chronically in stress-associated disorders.
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Hertelendy, Péter, József Toldi, Ferenc Fülöp, and László Vécsei. "Ischemic Stroke and Kynurenines: Medicinal Chemistry Aspects." Current Medicinal Chemistry 25, no. 42 (February 6, 2019): 5945–57. http://dx.doi.org/10.2174/0929867325666180313113411.
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Ischemic stroke is one of the leading causes of mortality and permanent disability in developed countries. Stroke induces massive glutamate release, which in turn causes N-Methyl-D-aspartate (NMDA) receptor over-excitation and thus, calcium overload in neurons leading to cell death via apoptotic cascades. The kynurenine pathway is a complex enzymatic cascade of tryptophan catabolism, generating various neuroactive metabolites. One metabolite, kynurenic acid (KYNA), is a potent endogenous NMDA glutamate receptor antagonist, making it a possible therapeutic tool to decrease excitotoxicity and neuroinflammation. Recently, clinical investigations have shown that during the acute phase of ischemic stroke, kynurenine pathway is activated and peripheral levels of metabolites correlated with worse outcome. In this review, we set out to summarize the current literature on the connection of the kynurenine pathway and ischemic stroke and set a course for future investigations and potential drug development.
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HITTER (BURU), Timea, Éva KÁLLAY, Loredana E. OLAR, Răzvan ŞTEFAN, Erzsebet BUTA, Silvia CHIOREAN, Maria CANTOR, and Ionel PAPUC. "The Effect of Therapeutic Horticulture on Depression and Kynurenine Pathways." Notulae Botanicae Horti Agrobotanici Cluj-Napoca 47, no. 3 (July 24, 2019): 804–12. http://dx.doi.org/10.15835/nbha47311544.
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The article presents the results of a study conducted to assess change in depression severity, and modification in the kynurenine pathway at participants. Presently, depression is one of the most regularly encountered mental illnesses. Research based on experimental studies indicated the beneficial effects of activities conducted in nature are reducing self-reported anger, fatigue, anxiety, stress and depression. The present study was conducted by measuring depression on both the subjective (Beck Depression Inventory) and the objective (spectrophotometric analysis) levels, to obtain more relevant information regarding the real change in depression levels, during the therapeutic horticulture intervention. Consequently, depression is assessed with the BDI doubled the data by assessing the levels of kynurenine and kynurenic acid obtained from biological samples. Results indicate that the levels of depression measured with the BDI have significantly decreased after the Therapeutic Horticulture Sesions. An even better result regards the fact that the significance of this change was not only statistical, but also clinical. Analysing the kynurerine and kynurenic acid concentrations, differences were observed amongst subject during the research study.
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Badawy, Abdulla A.-B., Sarah L. Lake, and Donald M. Dougherty. "Mechanisms of the Pellagragenic Effect of Leucine: Stimulation of Hepatic Tryptophan Oxidation by Administration of Branched-Chain Amino Acids to Healthy Human Volunteers and the Role of Plasma Free Tryptophan and Total Kynurenines." International Journal of Tryptophan Research 7 (January 2014): IJTR.S18231. http://dx.doi.org/10.4137/ijtr.s18231.
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The pellagragenic effect of leucine (Leu) has been proposed to involve modulation of L-tryptophan (Trp) metabolism along the hepatic kynurenine pathway. Here, we discuss some of the mechanisms suggested and report the effects in healthy volunteers of single doses of Leu (4.05–6.75 g) administered in a 16-amino acid mixture on concentrations of plasma Trp and its kynurenine metabolites. Flux of Trp through Trp 2,3-dioxygenase (TDO) is dose-dependently enhanced most probably by Leu and can be attributed to TDO activation. Trp oxidation is better expressed using plasma total kynurenines, rather than kynurenine, and free, rather than total, Trp. Increased hepatic Trp oxidation may be an additional mechanism of action of branched-chain amino acids in the acute Trp depletion test. Inhibition of intestinal absorption or hepatic uptake of Trp by Leu can be excluded. Potential mechanisms of the aggravation of pellagra symptoms by Leu are discussed.
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Dehhaghi, Mona, Hamed Kazemi Shariat Panahi, and Gilles J. Guillemin. "Microorganisms, Tryptophan Metabolism, and Kynurenine Pathway: A Complex Interconnected Loop Influencing Human Health Status." International Journal of Tryptophan Research 12 (January 2019): 117864691985299. http://dx.doi.org/10.1177/1178646919852996.
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The kynurenine pathway is important in cellular energy generation and limiting cellular ageing as it degrades about 90% of dietary tryptophan into the essential co-factor NAD+ (nicotinamide adenine dinucleotide). Prior to the production of NAD+, various intermediate compounds with neuroactivity (kynurenic acid, quinolinic acid) or antioxidant activity (3-hydroxykynurenine, picolinic acid) are synthesized. The kynurenine metabolites can participate in numerous neurodegenerative disorders (Alzheimer disease, amyotrophic lateral sclerosis, Huntington disease, and Parkinson disease) or other diseases such as AIDS, cancer, cardiovascular diseases, inflammation, and irritable bowel syndrome. Recently, the role of gut in affecting the emotional and cognitive centres of the brain has attracted a great deal of attention. In this review, we focus on the bidirectional communication between the gut and the brain, known as the gut-brain axis. The interaction of components of this axis, namely, the gut, its microbiota, and gut pathogens; tryptophan; the kynurenine pathway on tryptophan availability; the regulation of kynurenine metabolite concentration; and diversity and population of gut microbiota, has been considered.
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Goeden, Nick, Francesca M. Notarangelo, Ana Pocivavsek, Sarah Beggiato, Alexandre Bonnin, and Robert Schwarcz. "Prenatal Dynamics of Kynurenine Pathway Metabolism in Mice: Focus on Kynurenic Acid." Developmental Neuroscience 39, no. 6 (2017): 519–28. http://dx.doi.org/10.1159/000481168.
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The kynurenine pathway (KP), the major catabolic route of tryptophan in mammals, contains several neuroactive metabolites, including kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK). KP metabolism, and especially the fate of KYNA, during pregnancy is poorly understood, yet it may play a significant role in the development of psychiatric disorders later in life. The present study was designed to investigate the prenatal features of KP metabolism in vivo, with special focus on KYNA. To this end, pregnant CD-1 mice were treated systemically with kynurenine (100 mg/kg), KYNA (10 mg/kg), or saline on embryonic day 18. As expected, administration of either kynurenine or KYNA increased KYNA levels in the maternal plasma and placenta. Maternal kynurenine treatment also raised kynurenine levels in the fetal plasma and brain, demonstrating the ability of this pivotal KP metabolite to cross the placenta and increase the levels of both KYNA and 3-HK in the fetal brain. In contrast, maternal administration of KYNA caused only a small, nonsignificant elevation in KYNA levels in fetal plasma and brain. Complementary experiments using an ex vivo placental perfusion procedure confirmed the significant transplacental transfer of kynurenine and demonstrated that only a very small fraction of maternal kynurenine is converted to KYNA in the placenta and released into the fetal compartment under physiological conditions. Jointly, these results help to clarify the contributions of the maternal circulation and the placenta to fetal KYNA in the late prenatal period.
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Baranyi, Andreas, Omid Amouzadeh-Ghadikolai, Dirk von Lewinski, Robert J. Breitenecker, Hans-Bernd Rothenhäusler, Christoph Robier, Maria Baranyi, Simon Theokas, and Andreas Meinitzer. "Revisiting the tryptophan-serotonin deficiency and the inflammatory hypotheses of major depression in a biopsychosocial approach." PeerJ 5 (November 2, 2017): e3968. http://dx.doi.org/10.7717/peerj.3968.
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Background The aim of this cross-sectional study was to identify important biopsychosocial correlates of major depression. Biological mechanisms, including the inflammatory and the tryptophan-serotonin deficiency hypotheses of major depression, were investigated alongside health-related quality of life, life satisfaction, and social support. Methods The concentrations of plasma tryptophan, plasma kynurenine, plasma kynurenic acid, serum quinolinic acid, and the tryptophan breakdown to kynurenine were determined alongside health-related quality of life (Medical Outcome Study Form, SF-36), life satisfaction (Life Satisfaction Questionnaire, FLZ), and social support (Social Support Survey, SSS) in 71 depressive patients at the time of their in-patient admittance and 48 healthy controls. Results Corresponding with the inflammatory hypothesis of major depression, our study results suggest a tryptophan breakdown to kynurenine in patients with major depression, and depressive patients had a lower concentration of neuroprotective kynurenic acid in comparison to the healthy controls (Mann–Whitney-U: 1315.0; p = 0.046). Contradicting the inflammatory theory, the concentrations of kynurenine (t: −0.945; df = 116; p = 0.347) and quinolinic acid (Mann-Whitney-U: 1376.5; p = 0.076) in depressive patients were not significantly different between depressed and healthy controls. Our findings tend to support the tryptophan-serotonin deficiency hypothesis of major depression, as the deficiency of the serotonin precursor tryptophan in depressive patients (t: −3.931; df = 116; p < 0.001) suggests dysfunction of serotonin neurotransmission. A two-step hierarchical linear regression model showed that low tryptophan concentrations, low social support (SSS), occupational requirements (FLZ), personality traits (FLZ), impaired physical role (SF-36), and impaired vitality (SF-36) predict higher Beck Depression Inventory (BDI-II) scores. Discussion Our study results argue for the validity of a biopsychosocial model of major depression with multiple pathophysiological mechanisms involved.
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Biernacki, Tamás, Dániel Sandi, Krisztina Bencsik, and László Vécsei. "Kynurenines in the Pathogenesis of Multiple Sclerosis: Therapeutic Perspectives." Cells 9, no. 6 (June 26, 2020): 1564. http://dx.doi.org/10.3390/cells9061564.
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Over the past years, an increasing amount of evidence has emerged in support of the kynurenine pathway’s (KP) pivotal role in the pathogenesis of several neurodegenerative, psychiatric, vascular and autoimmune diseases. Different neuroactive metabolites of the KP are known to exert opposite effects on neurons, some being neuroprotective (e.g., picolinic acid, kynurenic acid, and the cofactor nicotinamide adenine dinucleotide), while others are toxic to neurons (e.g., 3-hydroxykynurenine, quinolinic acid). Not only the alterations in the levels of the metabolites but also disturbances in their ratio (quinolinic acid/kynurenic acid) have been reported in several diseases. In addition to the metabolites, the enzymes participating in the KP have been unearthed to be involved in modulation of the immune system, the energetic upkeep of neurons and have been shown to influence redox processes and inflammatory cascades, revealing a sophisticated, intertwined system. This review considers various methods through which enzymes and metabolites of the kynurenine pathway influence the immune system, the roles they play in the pathogenesis of neuroinflammatory diseases based on current evidence with a focus on their involvement in multiple sclerosis, as well as therapeutic approaches.
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Zádor, Ferenc, Gábor Nagy-Grócz, Gabriella Kekesi, Szabolcs Dvorácskó, Edina Szűcs, Csaba Tömböly, Gyongyi Horvath, Sándor Benyhe, and László Vécsei. "Kynurenines and the Endocannabinoid System in Schizophrenia: Common Points and Potential Interactions." Molecules 24, no. 20 (October 15, 2019): 3709. http://dx.doi.org/10.3390/molecules24203709.
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Schizophrenia, which affects around 1% of the world’s population, has been described as a complex set of symptoms triggered by multiple factors. However, the exact background mechanisms remain to be explored, whereas therapeutic agents with excellent effectivity and safety profiles have yet to be developed. Kynurenines and the endocannabinoid system (ECS) play significant roles in both the development and manifestation of schizophrenia, which have been extensively studied and reviewed previously. Accordingly, kynurenines and the ECS share multiple features and mechanisms in schizophrenia, which have yet to be reviewed. Thus, the present study focuses on the main common points and potential interactions between kynurenines and the ECS in schizophrenia, which include (i) the regulation of glutamatergic/dopaminergic/γ-aminobutyric acidergic neurotransmission, (ii) their presence in astrocytes, and (iii) their role in inflammatory mechanisms. Additionally, promising pharmaceutical approaches involving the kynurenine pathway and the ECS will be reviewed herein.
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Kegel, Magdalena E., Maria Bhat, Elisabeth Skogh, Martin Samuelsson, Kristina Lundberg, Marja-Liisa Dahl, Carl Sellgren, et al. "Imbalanced Kynurenine Pathway in Schizophrenia." International Journal of Tryptophan Research 7 (January 2014): IJTR.S16800. http://dx.doi.org/10.4137/ijtr.s16800.
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Several studies suggest a role for kynurenic acid (KYNA) in the pathophysiology of schizophrenia. It has been proposed that increased brain KYNA levels in schizophrenia result from a pathological shift in the kynurenine pathway toward enhanced KYNA formation, away from the other branch of the pathway leading to quinolinic acid (QUIN). Here we investigate the levels of QUIN in cerebrospinal fluid (CSF) of patients with schizophrenia and healthy controls, and relate those to CSF levels of KYNA and other kynurenine metabolites from the same individuals. CSF QUIN levels from stable outpatients treated with olanzapine (n = 22) and those of controls (n = 26) were analyzed using liquid chromatography-mass spectrometry. No difference in CSF QUIN levels between patients and controls was observed (20.6 ± 1.5 nM vs. 18.2 ± 1.1 nM, P = 0.36). CSF QUIN was positively correlated to CSF kynurenine and CSF KYNA in patients but not in controls. The CSF QUIN/KYNA ratio was lower in patients than in controls ( P = 0.027). In summary, the present study offers support for an over-activated and imbalanced kynurenine pathway, favoring the production of KYNA over QUIN in patients with schizophrenia.
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Yamashita, Masatoshi. "Potential Role of Neuroactive Tryptophan Metabolites in Central Fatigue: Establishment of the Fatigue Circuit." International Journal of Tryptophan Research 13 (January 2020): 117864692093627. http://dx.doi.org/10.1177/1178646920936279.
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Central fatigue leads to reduced ability to perform mental tasks, disrupted social life, and impaired brain functions from childhood to old age. Regarding the neurochemical mechanism, neuroactive tryptophan metabolites are thought to play key roles in central fatigue. Previous studies have supported the “tryptophan-serotonin enhancement hypothesis” in which tryptophan uptake into extensive brain regions enhances serotonin production in the rat model of exercise-induced fatigue. However, serotonin was transiently released after 30 minutes of treadmill running to exhaustion, but this did not reflect the duration of fatigue. In addition, as the vast majority of tryptophan is metabolized along the kynurenine pathway, possible involvement of the tryptophan-kynurenine pathway in the mechanism of central fatigue induction has been pointed out. More recently, our study demonstrated that uptake of tryptophan and kynurenine derived from the peripheral circulation into the brain enhances kynurenic acid production in rat brain in sleep deprivation–induced central fatigue, but without change in serotonin activity. In particular, dynamic change in glial-neuronal interactive processes within the hypothalamus-hippocampal circuit causes central fatigue. Furthermore, increased tryptophan-kynurenine pathway activity in this circuit causes reduced memory function. This indicates a major potential role for the endogenous tryptophan-kynurenine pathway in central fatigue, which supports the “tryptophan-kynurenine enhancement hypothesis.” Here, we review research on the basic neuronal mechanism underlying central fatigue induced by neuroactive tryptophan metabolites. Notably, these basic findings could contribute to our understanding of latent mental problems associated with central fatigue.
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Rentschler, Katherine M., Annalisa M. Baratta, Audrey L. Ditty, Nathan T. J. Wagner, Courtney J. Wright, Snezana Milosavljevic, Jessica A. Mong, and Ana Pocivavsek. "Prenatal Kynurenine Elevation Elicits Sex-Dependent Changes in Sleep and Arousal During Adulthood: Implications for Psychotic Disorders." Schizophrenia Bulletin 47, no. 5 (April 5, 2021): 1320–30. http://dx.doi.org/10.1093/schbul/sbab029.
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Abstract Dysregulation of the kynurenine pathway (KP) of tryptophan catabolism has been implicated in psychotic disorders, including schizophrenia and bipolar disorder. Kynurenic acid (KYNA) is a KP metabolite synthesized by kynurenine aminotransferases (KATs) from its biological precursor kynurenine and acts as an endogenous antagonist of N-methyl-D-aspartate and α7-nicotinic acetylcholine receptors. Elevated KYNA levels found in postmortem brain tissue and cerebrospinal fluid of patients are hypothesized to play a key role in the etiology of cognitive symptoms observed in psychotic disorders. Sleep plays an important role in memory consolidation, and sleep disturbances are common among patients. Yet, little is known about the effect of altered KP metabolism on sleep–wake behavior. We presently utilized a well-established experimental paradigm of embryonic kynurenine (EKyn) exposure wherein pregnant dams are fed a diet laced with kynurenine the last week of gestation and hypothesized disrupted sleep–wake behavior in adult offspring. We examined sleep behavior in adult male and female offspring using electroencephalogram and electromyogram telemetry and determined sex differences in sleep and arousal in EKyn offspring. EKyn males displayed reduced rapid eye movement sleep, while female EKyn offspring were hyperaroused compared to controls. We determined that EKyn males maintain elevated brain KYNA levels, while KYNA levels were unchanged in EKyn females, yet the activity levels of KAT I and KAT II were reduced. Our findings indicate that elevated prenatal kynurenine exposure elicits sex-specific changes in sleep–wake behavior, arousal, and KP metabolism.
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Rejdak, Robert, Anselm Junemann, Paweł Grieb, Sebastian Thaler, Frank Schuettauf, Tomasz Chorągiewicz, Tomasz Żarnowski, Waldemar A. Turski, and Eberhart Zrenner. "Kynurenic acid and kynurenine aminotransferases in retinal aging and neurodegeneration." Pharmacological Reports 63, no. 6 (November 2011): 1324–34. http://dx.doi.org/10.1016/s1734-1140(11)70697-1.
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Zelentsova, Ekaterina A., Peter S. Sherin, Olga A. Snytnikova, Robert Kaptein, Eric Vauthey, and Yuri P. Tsentalovich. "Photochemistry of aqueous solutions of kynurenic acid and kynurenine yellow." Photochem. Photobiol. Sci. 12, no. 3 (2013): 546–58. http://dx.doi.org/10.1039/c2pp25357g.
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Myint, A. M. "Role of Tryptophan-kynurenine Pathway in Depression: Psychopathological Aspect." European Psychiatry 24, S1 (January 2009): 1. http://dx.doi.org/10.1016/s0924-9338(09)70521-8.
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It was reported that cytokines such as IFN-γ reduce the synthesis of 5-HT by stimulating the activity of indoleamine 2,3 dioxygenase (IDO) enzyme which degrades tryptophan to kynurenine. Kynurenine is further metabolized to kynurenic acid (KYNA), 3-hydroxykynurenine (3OHK) and quinolinic acid (QA) by kynurenine aminotransferase (KAT), kynurenine 3-monooxygenase (KMO) and kynureninase. Both KMO and kynureninase are also shown to be activated by IFNγ. The 3OHK is neurotoxic apoptotic while QA is the excitotoxic N-methyl-D-aspartate (NMDA) receptor agonist. Conversely KYNA is an antagonist of all three ionotropic excitatory amino acid receptors and considered neuroprotective. In the brain, tryptophan catabolism occurs in the astrocytes and. The astrocytes are shown to produce mainly KYNA whereas microglia and macrophages produced mainly 3OHK and QA. The astrocytes have been demonstrated to metabolise the QA produced by the neighbouring microglia.Tryptophan breakdown has been found to be increased but KYNA, the neuroprotective metabolite is decreased in both blood and cerebrospinal fluid of the patients with major depression compared to healthy controls. Moreover, the ratio between KYNA and 3OHK showed significant correlation with response to treatment. These findings lead to the hypothesis an imbalance neuroprotection-neurodegener-ation in terms of kynurenine metabolites and their immunological and biochemical interactions in the brain might further induce the apoptosis of the neuroprotective astrocytes and the vulnerability to stress is thereby enhanced.
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Blesl, C., A. Tmava, A. Baranyi, A. Meinitzer, A. Painold, A. Holl, V. Stadlbauer-Köllner, H. P. Kapfhammer, and S. Mörkl. "The Kynurenine pathway in pancreatic carcinoma." European Psychiatry 41, S1 (April 2017): S480. http://dx.doi.org/10.1016/j.eurpsy.2017.01.564.
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IntroductionPancreatic carcinoma (PC) belongs to the most aggressive tumours worldwide, with a five year survival of 7%. Mostly, diagnosis is made in late stages, as by now no early detection method is available. Symptoms of depression occur frequently before diagnosis of PC. PC and depression are both known to go along with changes in the kynurenine-pathway.ObjectivesThis study aimed to examine the kynurenine pathway (Figure 1) and evaluate a possible depression in newly diagnosed PC patients in comparison to healthy controls (HC).Methods26 PC patients and 26 age and sex matched HC participated in this study. We investigated serum-levels of kynurenine, kynurenic-acid, quinolinic-acid and tryptophan. To diagnose features of depression SKID-II and BDI were used.ResultsNone of the participants fulfilled criteria of a depressive episode. Regarding BDI-scores, 2 PC-patients showed features of mild depression. PC patients showed significantly lower tryptophan-levels (P = 0.05) and significantly increased quinolinic-acid levels (P = 0.01) compared to HC. Quinolinic-acid levels were correlated with BDI (r = 0.23, P = 0.02).ConclusionsOur study results imply IDO-activation and kynurenine-pathway activation by showing decreased tryptophan and high quinolonic-acid levels in our PC patients compared to HC. Larger studies are needed to gather further insight in the kynurenine pathway in PC.Disclosure of interestThe authors have not supplied their declaration of competing interest.Figure 1