Kynurenine Pathway Of Tryptophan Metabolism Research Articles

The relationship of alcohol use disorders and depressive symptoms to tryptophan metabolism: cross-sectional data from a Nepalese alcohol treatment sample.

Activation of the kynurenine pathway of tryptophan metabolism results in increased production of potentially depressogenic tryptophan catabolites and a reduction in tryptophan availability for serotonin synthesis. As alcohol consumption affects tryptophan metabolism and disposition, we determined serum levels of tryptophan, kynurenine, and an index of tryptophan degradation (kynurenine/tryptophan ratio) in patients with alcohol-use disorder (AUD) and compared their levels considering abstinence duration, AUD severity, and comorbid depression. The study sample included 169 AUD inpatients from 8 alcohol treatment facilities in Kathmandu, Nepal. The Composite International Diagnostic Interview was administered to generate the AUD diagnosis. The Alcohol Use Disorder Identification Test (AUDIT) captured AUD severity and patterns of alcohol use. The Hopkins Symptom Checklist-25 was used to reveal current depressive symptoms. Serum kynurenine and tryptophan levels were determined by high-performance liquid chromatography, and tryptophan degradation was measured by KT ratio (kynurenine/tryptophan × 10(3)). Patients with above average AUDIT scores had higher mean serum levels of kynurenine (2.1 μM ± 0.7 vs. 1.8 μM ± 0.6, p = 0.006) and KT ratios (48.6 ± 17.6 vs. 40.4 ± 14.3, p = 0.002) than those with below average scores. Patients with current depressive symptoms had higher mean tryptophan concentrations (49.9 μM ± 13 vs. 45.7 μM ± 14.1, p = 0.047) and lower KT ratios (41.4 ± 14 vs. 47.5 ± 17.6, p = 0.028) compared to patients whose reported depressive symptoms were below the standard cutoff. Higher tryptophan levels and lower KT ratios in the depressed group were specific to patients with longer abstinence and higher AUD severity. Depression-related deregulation in tryptophan metabolism was found to depend on length of abstinence and on AUD severity. Together, results suggest that in AUD populations, peripheral tryptophan metabolism is subject to interactions between AUD severity and depressive symptoms.

Biochemical, histopathological and morphological profiling of a rat model of early immune stimulation: relation to psychopathology.

Perinatal immune challenge leads to neurodevelopmental dysfunction, permanent immune dysregulation and abnormal behaviour, which have been shown to have translational validity to findings in human neuropsychiatric disorders (e.g. schizophrenia, mood and anxiety disorders, autism, Parkinson’s disease and Alzheimer’s disease). The aim of this animal study was to elucidate the influence of early immune stimulation triggered by systemic postnatal lipopolysaccharide administration on biochemical, histopathological and morphological measures, which may be relevant to the neurobiology of human psychopathology. In the present study of adult male Wistar rats we examined the brain and plasma levels of monoamines (dopamine, serotonin), their metabolites, the levels of the main excitatory and inhibitory neurotransmitters glutamate and γ-aminobutyric acid and the levels of tryptophan and its metabolites from the kynurenine catabolic pathway. Further, we focused on histopathological and morphological markers related to pathogenesis of brain diseases - glial cell activation, neurodegeneration, hippocampal volume reduction and dopaminergic synthesis in the substantia nigra. Our results show that early immune stimulation in adult animals alters the levels of neurotransmitters and their metabolites, activates the kynurenine pathway of tryptophan metabolism and leads to astrogliosis, hippocampal volume reduction and a decrease of tyrosine hydroxylase immunoreactivity in the substantia nigra. These findings support the crucial pathophysiological role of early immune stimulation in the above mentioned neuropsychiatric disorders.

The role of the kynurenine pathway of tryptophan metabolism in cardiovascular disease. An emerging field.

Coronary heart disease and stroke, the deadliest forms of cardiovascular disease (CVD), are mainly caused by atherosclerosis, a chronic inflammatory disease of the artery wall driven by maladaptive immune responses in the vessel wall. Various risk factors for CVD influence this pathogenic process, including diabetes mellitus, hypertension, dyslipidaemia, and obesity. Indoleamine 2,3-dioxygenase (IDO), an enzyme catalyzing the rate-limiting step in the kynurenine pathway of tryptophan degradation, is strongly induced by inflammation in several tissues, including the artery wall. An increasing body of evidence indicates that IDO promotes immune tolerance, decreases inflammation, and functions as a homeostatic mechanism against excessive immune reactions. This review provides an overview of the emerging field of the kynurenine pathway of tryptophan degradation in CVD, emphasizing the role of IDO-mediated tryptophan metabolism and its metabolites in the modulation of 'classical' cardiovascular risk factors, such as hypertension, obesity, lipid metabolism, diabetes mellitus, and in the development of atherosclerotic CVD.

Kynurenic Acid Is a Nutritional Cue that Enables Behavioral Plasticity

The kynurenine pathway of tryptophan metabolism is involved in the pathogenesis of several braindiseases, but its physiological functions remain unclear. We report that kynurenic acid, ametabolite in this pathway, functions as a regulator of food-dependent behavioral plasticity inC.elegans. The experience of fasting in C.elegans alters a variety of behaviors, including feeding rate, when food is encountered post-fast.Levels of neurally produced kynurenic acid are depleted by fasting, leading to activation of NMDA-receptor-expressing interneurons and initiation of a neuropeptide-y-like signaling axis that promotes elevated feeding through enhanced serotonin release when animals re-encounter food. Upon refeeding, kynurenic acid levels are eventually replenished, ending the elevated feeding period. Because tryptophan is an essential amino acid, these findings suggest that a physiological role of kynurenic acid is in directly linking metabolism to activity of NMDA and serotonergic circuits, which regulate a broad range of behaviors and physiologies.

Antidepressants may lead to a decrease in niacin and NAD in patients with poor dietary intake

The term niacin is the generic name for the two compounds nicotinic acid and nicotinamide, the major dietary precursors for two important coenzymes, nicotinamide adenine dinucleotide (NAD) and its phosphorylated form, NADP. Niacin is important for the maintenance of cellular integrity and energy production and is involved in more than 500 intracellular reactions. Deficiencies of niacin may contribute to neuropsychiatric and neurodegenerative disorders. Patients who develop nutritional deficiencies as a result of poor dietary intake, especially inadequate intake of proteins and vitamins, could potentially suffer from niacin deficiency and NAD depletion. However, de novo synthesis of niacin and NAD in the kynurenine pathway of tryptophan metabolism may compensate for impaired dietary intake. The rate of synthesis of NAD and niacin from tryptophan oxidation depends on the induction of the enzyme indoleamine 2,3-dioxygenase (IDO) by pro-inflammatory cytokines such as interferon-gamma. Niacin synthesis is not limited by a decrease in tryptophan and excessive IDO activity may therefore lead to a decline in tryptophan levels. Antidepressants have an anti-inflammatory effect, including reduction of interferon-gamma and therefore inhibition of IDO, the rate-limiting enzyme of the kynurenine pathway. In theory, this could account for increased serotonin as more tryptophan becomes available for serotonin synthesis. However, the downside may be that less NAD and niacin are synthesised downstream, which could exacerbate common psychiatric problems. It is our hypothesis that patients with poor dietary intake, who are treated with antidepressants, are at risk of developing niacin/NAD deficiency with possible development of associated neuropsychiatric symptoms.We therefore propose that niacin supplementation be considered in patients with inadequate diets who are treated with antidepressants. We believe that if this does not happen, a subclinical niacin deficiency may result, which would be difficult to detect as it would cause the same symptoms of the original illness (e.g. depression). Niacin deficiency should be considered and ruled out in all patients with treatment-resistant depression, who have a poor response to antidepressants. This is potentially a cost-effective and easy intervention, which could be examined in a randomized controlled trial.

Etiological classification of depression based on the enzymes of tryptophan metabolism.

BackgroundViewed in terms of input and output, the mechanisms of depression are still akin to a black box. However, there must be main pivots for diverse types of depression. From recent therapeutic observations, both the serotonin (5-HT) and kynurenine pathways of tryptophan metabolism may be of particular importance to improved understanding of depression. Here, I propose an etiological classification of depression, based on key peripheral and central enzymes of tryptophan metabolism.DiscussionEndogenous depression is caused by a larger genetic component than reactive depression. Besides enterochromaffin and mast cells, tryptophan hydroxylase 1 (TPH1), primarily expressed in the gastrointestinal tract, is also found in 5-hydroxytryptophan-producing cells (5-HTP cells) in normal intestinal enterocytes, which are thought to essentially shunt 5-HT production in 5-HT-producing cells. Genetic studies have reported an association between TPH1 and depression, or the responsiveness of depression to antidepressive medication. Therefore, it is possible that hypofunctional 5-HTP cells (reflecting TPH1 dysfunction) in the periphery lead to deficient brain 5-HT levels. Additionally, it has been reported that higher TPH2 expression in depressed suicides may reflect a homeostatic response to deficient 5-HT levels. Subsequently, endogenous depression may be caused by TPH1 dysfunction combined with compensatory TPH2 activation. Reactive depression results from life stresses and involves the hypothalamic-pituitary-adrenal axis, with resulting cortisol production inducing tryptophan 2,3-dioxygenase (TDO) activation. In secondary depression, caused by inflammation, infection, or oxidative stress, indoleamine 2,3-dioxygenase (IDO) is activated. In both reactive and secondary depression, the balance between 3-hydroxykynurenine (3-HK) and kynurenic acid may shift towards 3-HK production via kynurenine-3-monooxygenase (KMO) activation. By shifting the equilibrium position of key enzymes of tryptophan metabolism, the classical classification of depression can be reorganized, as below.Peripheral classification of depression by key enzymesTPH1 dysfunctionTDO activationIDO activationCentral classification of depression by key enzymesTPH2 activationKMO activationSummaryEtiological classification of depression expressed by peripheral (TPH1, TDO, IDO) and central (TPH2, KMO) enzymes of tryptophan metabolism may enable depression to be viewed as a clear box, with the inner components available for inspection and treatment.

Influence of kynurenine 3-monooxygenase (KMO) gene polymorphism on cognitive function in schizophrenia

BackgroundCognitive deficits compromise quality of life and productivity for individuals with schizophrenia and have no effective treatments. Preclinical data point to the kynurenine pathway of tryptophan metabolism as a potential target for pro-cognitive drug development. We have previously demonstrated association of a kynurenine 3-monooxygenase (KMO) gene variant with reduced KMO gene expression in postmortem schizophrenia cortex, and neurocognitive endophenotypic deficits in a clinical sample. KMO encodes kynurenine 3-monooxygenase (KMO), the rate-limiting microglial enzyme of cortical kynurenine metabolism. Aberration of the KMO gene might be the proximal cause of impaired cortical kynurenine metabolism observed in schizophrenia. However, the relationship between KMO variation and cognitive function in schizophrenia is unknown. This study examined the effects of the KMO rs2275163C>T C (risk) allele on cognitive function in schizophrenia. MethodsWe examined the association of KMO polymorphisms with general neuropsychological performance and P50 gating in a sample of 150 schizophrenia and 95 healthy controls. ResultsConsistent with our original report, the KMO rs2275163C>T C (risk) allele was associated with deficits in general neuropsychological performance, and this effect was more marked in schizophrenia compared with controls. Additionally, the C (Arg452) allele of the missense rs1053230C>T variant (KMO Arg452Cys) showed a trend effect on cognitive function. Neither variant affected P50 gating. ConclusionsThese data suggest that KMO variation influences a range of cognitive domains known to predict functional outcome. Extensive molecular characterization of this gene would elucidate its role in cognitive function with implications for vertical integration with basic discovery.

LC-MS-based urinary metabolite signatures in idiopathic Parkinson's disease.

Increasing evidence has shown that abnormal metabolic phenotypes in body fluids reflect the pathogenesis and pathophysiology of Parkinson's disease (PD). These body fluids include urine; however, the relationship between, specifically, urinary metabolic phenotypes and PD is not fully understood. In this study, urinary metabolites from a total of 401 clinical urine samples collected from 106 idiopathic PD patients and 104 normal control subjects were profiled by using high-performance liquid chromatography coupled to high-resolution mass spectrometry. Our study revealed significant correlation between clinical phenotype and urinary metabolite profile. Metabolic profiles of idiopathic PD patients differed significantly and consistently from normal controls, with related metabolic pathway variations observed in steroidogenesis, fatty acid beta-oxidation, histidine metabolism, phenylalanine metabolism, tryptophan metabolism, nucleotide metabolism, and tyrosine metabolism. In the fruit fly Drosophila melanogaster, the alteration of the kynurenine pathway in tryptophan metabolism corresponded with pathogenic changes in the alpha-synuclein overexpressed Drosophila model of PD. The results suggest that LC-MS-based urinary metabolomic profiling can reveal the metabolite signatures and related variations in metabolic pathways that characterize PD. Consistent PD-related changes across species may provide the basis for understanding metabolic regulation of PD at the molecular level.

Cerebrolysin Accelerates Metamorphosis and Attenuates Aging-Accelerating Effect of High Temperature in Drosophila Melanogaster.

Cerebrolysin® (CBL) is a neuroprotective drug used for the treatment of neurodegenerative diseases. CBL's mechanisms of action remain unclear. Involvement of tryptophan (TRP)-kynurenine (KYN) pathway in neuroprotective effect of CBL might be suggested considering that modulation of KYN pathway of TRP metabolism by CBL, and protection against eclosion defect and prolongation of life span of Drosophila melanogaster with pharmacologically or genetically-induced down-regulation of TRP conversion into KYN. To investigate possible involvement of TRP-KYN pathway in mechanisms of neuroprotective effect of CBL, we evaluated CBL effects on metamorphosis and life span of Drosophila melanogaster maintained at 23 °C and 28 °C ambient temperature. CBL accelerated metamorphosis, exerted strong tendency (p = 0.04) to prolong life span in female but not in male flies, and attenuated aging-accelerating effect of high (28 °C) ambient temperature in both female and male flies. Further research of CBL effects on metamorphosis and resistance to aging-accelerating effect of high temperature might offer new insights in mechanisms of its neuroprotective action and expand its clinical applications.

Modified neocortical and cerebellar protein expression and morphology in adult rats following prenatal inhibition of the kynurenine pathway

Inhibition of the kynurenine pathway of tryptophan metabolism during gestation can lead to changes in synaptic transmission, neuronal morphology and plasticity in the rat hippocampus. This suggests a role for the kynurenine pathway in early brain development, probably caused by kynurenine modulation of N-methyl-d-aspartate (NMDA) glutamate receptors which are activated by the tryptophan metabolite quinolinic acid and blocked by kynurenic acid. We have now examined samples of neocortex and cerebellum of adult animals to assess the effects of a prenatally administered kynurenine-3-monoxygenase inhibitor (Ro61-8048) on protein and mRNA expression, dendritic structure and immuno-histochemistry. No changes were seen in mRNA expression using quantitative real-time polymerase chain reaction. Changes were detected in the expression of several proteins including the GluN2A subunit, unco-ordinated-5H3 (unc5H3), doublecortin, cyclo-oxygenase, sonic hedgehog and Disrupted in schizophrenia-1 (DISC1), although no differences in immunoreactive cell numbers were observed. In the midbrain, dependence receptor expression was also changed. The numbers and lengths of individual dendritic regions were not changed but there were significant increases in the overall complexity values of apical and basal dendritic trees. The data support the hypothesis that constitutive kynurenine metabolism plays a critical role in early, embryonic brain development, although fewer effects are produced in the neocortex and cerebellum than in the hippocampus and the nature of the changes seen are qualitatively different. The significant changes in DISC1 and unc5H3 may be relevant to cerebellar dysfunction and schizophrenia respectively, in which these proteins have been previously implicated.

Molecular pharmacodynamics of new oral drugs used in the treatment of multiple sclerosis.

New oral drugs have considerably enriched the therapeutic armamentarium for the treatment of multiple sclerosis. This review focuses on the molecular pharmacodynamics of fingolimod, dimethyl fumarate (BG-12), laquinimod, and teriflunomide. We specifically comment on the action of these drugs at three levels: 1) the regulation of the immune system; 2) the permeability of the blood–brain barrier; and 3) the central nervous system. Fingolimod phosphate (the active metabolite of fingolimod) has a unique mechanism of action and represents the first ligand of G-protein-coupled receptors (sphingosine-1-phosphate receptors) active in the treatment of multiple sclerosis. Dimethyl fumarate activates the nuclear factor (erythroid-derived 2)-related factor 2 pathway of cell defense as a result of an initial depletion of reduced glutathione. We discuss how this mechanism lies on the border between cell protection and toxicity. Laquinimod has multiple (but less defined) mechanisms of action, which make the drug slightly more effective on disability progression than on annualized relapse rate in clinical studies. Teriflunomide acts as a specific inhibitor of the de novo pyrimidine biosynthesis. We also discuss new unexpected mechanisms of these drugs, such as the induction of brain-derived neurotrophic factor by fingolimod and the possibility that laquinimod and teriflunomide regulate the kynurenine pathway of tryptophan metabolism.

Prenatal inhibition of the kynurenine pathway leads to structural changes in the hippocampus of adult rat offspring

Glutamate receptors for N-methyl-d-aspartate (NMDA) are involved in early brain development. The kynurenine pathway of tryptophan metabolism includes the NMDA receptor agonist quinolinic acid and the antagonist kynurenic acid. We now report that prenatal inhibition of the pathway in rats with 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulphonamide (Ro61-8048) produces marked changes in hippocampal neuron morphology, spine density and the immunocytochemical localisation of developmental proteins in the offspring at postnatal day 60. Golgi–Cox silver staining revealed decreased overall numbers and lengths of CA1 basal dendrites and secondary basal dendrites, together with fewer basal dendritic spines and less overall dendritic complexity in the basal arbour. Fewer dendrites and less complexity were also noted in the dentate gyrus granule cells. More neurons containing the nuclear marker NeuN and the developmental protein sonic hedgehog were detected in the CA1 region and dentate gyrus. Staining for doublecortin revealed fewer newly generated granule cells bearing extended dendritic processes. The number of neuron terminals staining for vesicular glutamate transporter (VGLUT)-1 and VGLUT-2 was increased by Ro61-8048, with no change in expression of vesicular GABA transporter or its co-localisation with vesicle-associated membrane protein-1. These data support the view that constitutive kynurenine metabolism normally plays a role in early embryonic brain development, and that interfering with it has profound consequences for neuronal structure and morphology, lasting into adulthood.

Bacterial expression of human kynurenine 3-monooxygenase: Solubility, activity, purification

Kynurenine 3-monooxygenase (KMO) is an enzyme central to the kynurenine pathway of tryptophan metabolism. KMO has been implicated as a therapeutic target in several disease states, including Huntington’s disease. Recombinant human KMO protein production is challenging due to the presence of transmembrane domains, which localise KMO to the outer mitochondrial membrane and render KMO insoluble in many in vitro expression systems. Efficient bacterial expression of human KMO would accelerate drug development of KMO inhibitors but until now this has not been achieved. Here we report the first successful bacterial (Escherichia coli) expression of active FLAG™-tagged human KMO enzyme expressed in the soluble fraction and progress towards its purification.

Abstract A196: Downregulation of kynurenine 3-monooxygenase (KMO) function prohibits canine mammary gland tumor (cMGT) cells from going wild.

Abstract Kynurenine 3-monooxygenase (KMO), mainly found on the outer membrane of the mitochondria, is one of the enzymes in the kynurenine pathway of tryptophan metabolism. KMO catalyzes L-kynurenine (KYN) to form 3-hydroxy kynurenine (3-HK) and further generates the downstream metabolite quinolinic acid (QA) which is an N-methyl-D-aspartate (NMDA) agonist. In the past, KMO was considered to be associated with neurodegenerative diseases because the downstream metabolites demonstrate excitotoxicity to CNS and act as factors in neurodegenerative diseases. In our previous study has shown that overexpression of KMO is related to tumor malignancy and survival time of cMGT-suffering dogs (in progress). In this study, we investigated function of KMO in cMGT cells. First of all, KMO expression of cMGT cells (CMT-1, MPG and CF41.mg) was identified in mRNA and protein level. Second, the application of KMO inhibitor reduced proliferation and migration of cMGT cells. The reduced proliferation, not migration, could be restored by NMDA or QA. Third, the application of KMO inhibitor also decreased the activity of Erk, Akt and STAT3 in cMGT cells. However, the decreased activity of Erk and STAT3 in cMGT cells could be restored through the application of NMDA of QA. Our data suggest that KMO is involved in the proliferation and migration of cMGT cells. Furthermore, the inhibition of proliferation by KMO inhibitor is mainly through Erk and STAT3 signaling cascades and the signaling pathway may be activated through the NMDA receptor. The inhibition of migration by KMO inhibitor is mainly through Akt signaling cascades. In conclusions, KMO might be a new therapeutic target of cMGT due to the downregulation of KMO reduces proliferation and migration of cMGT cells. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A196. Citation Format: Albert T. Liao, Chen-Si Lin, Mei-Hsien Chang. Downregulation of kynurenine 3-monooxygenase (KMO) function prohibits canine mammary gland tumor (cMGT) cells from going wild. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A196.

Changes in synaptic transmission and protein expression in the brains of adult offspring after prenatal inhibition of the kynurenine pathway

During early brain development, N-methyl-d-aspartate (NMDA) receptors are involved in cell migration, neuritogenesis, axon guidance and synapse formation, but the mechanisms which regulate NMDA receptor density and function remain unclear. The kynurenine pathway of tryptophan metabolism includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at NMDA receptors and we have previously shown that inhibition of the pathway using the kynurenine-3-monoxygenase inhibitor Ro61-8048 in late gestation produces rapid changes in protein expression in the embryos and effects on synaptic transmission lasting until postnatal day 21 (P21). The present study sought to determine whether any of these effects are maintained into adulthood. After prenatal injections of Ro61-8048 the litter was allowed to develop to P60 when some offspring were euthanized and the brains removed for examination. Analysis of protein expression by Western blotting revealed significantly reduced expression of the GluN2A subunit (32%) and the morphogenetic protein sonic hedgehog (31%), with a 29% increase in the expression of doublecortin, a protein associated with neurogenesis. No changes were seen in mRNA abundance using quantitative real-time polymerase chain reaction. Neuronal excitability was normal in the CA1 region of hippocampal slices but paired-pulse stimulation revealed less inhibition at short interpulse intervals. The amount of long-term potentiation was decreased by 49% in treated pups and recovery after low-frequency stimulation was delayed. The results not only strengthen the view that basal, constitutive kynurenine metabolism is involved in normal brain development, but also show that changes induced prenatally can affect the brains of adult offspring and those changes are quite different from those seen previously at weaning (P21). Those changes may be mediated by altered expression of NMDAR subunits and sonic hedgehog.

The kynurenine pathway as a therapeutic target in cognitive and neurodegenerative disorders

Understanding the neurochemical basis for cognitive function is one of the major goals of neuroscience, with a potential impact on the diagnosis, prevention and treatment of a range of psychiatric and neurological disorders. In this review, the focus will be on a biochemical pathway that remains under-recognized in its implications for brain function, even though it can be responsible for moderating the activity of two neurotransmitters fundamentally involved in cognition - glutamate and acetylcholine. Since this pathway - the kynurenine pathway of tryptophan metabolism - is induced by immunological activation and stress, it also stands in a unique position to mediate the effects of environmental factors on cognition and behaviour. Targeting the pathway for new drug development could, therefore, be of value not only for the treatment of existing psychiatric conditions, but also for preventing the development of cognitive disorders in response to environmental pressures.

Prenatal inhibition of the tryptophan–kynurenine pathway alters synaptic plasticity and protein expression in the rat hippocampus

Glutamate receptors sensitive to N-methyl-d-aspartate (NMDA) are important in early brain development, influencing cell proliferation and migration, neuritogenesis, axon guidance and synapse formation. The kynurenine pathway of tryptophan metabolism includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at these receptors. Rats were treated in late gestation with 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]-benzene-sulphonamide (Ro61-8048), an inhibitor of kynurenine-3-monoxygenase which diverts kynurenine metabolism to kynurenic acid. Within 5h of drug administration, there was a significant decrease in GluN2A expression and increased GluN2B in the embryo brains, with changes in sonic hedgehog at 24h. When injected dams were allowed to litter normally, the brains of offspring were removed at postnatal day 21 (P21). Recordings of hippocampal field excitatory synaptic potentials (fEPSPs) showed that prenatal exposure to Ro61-8048 increased neuronal excitability and paired-pulse facilitation. Long-term potentiation was also increased, with no change in long-term depression. At this time, levels of GluN2A, GluN2B and postsynaptic density protein PSD-95 were all increased. Among several neurodevelopmental proteins, the expression of sonic hedgehog was increased, but DISC1 and dependence receptors were unaffected, while raised levels of doublecortin and Proliferating Cell Nuclear Antigen (PCNA) suggested increased neurogenesis. The results reveal that inhibiting the kynurenine pathway in utero leads to molecular and functional synaptic changes in the embryos and offspring, indicating that the pathway is active during gestation and plays a significant role in the normal early development of the embryonic and neonatal nervous system.

Biochemical identification and crystal structure of kynurenine formamidase fromDrosophila melanogaster

KFase (kynurenine formamidase), also known as arylformamidase and formylkynurenine formamidase, efficiently catalyses the hydrolysis of NFK (N-formyl-L-kynurenine) to kynurenine. KFase is the second enzyme in the kynurenine pathway of tryptophan metabolism. A number of intermediates formed in the kynurenine pathway are biologically active and implicated in an assortment of medical conditions, including cancer, schizophrenia and neurodegenerative diseases. Consequently, enzymes involved in the kynurenine pathway have been considered potential regulatory targets. In the present study, we report, for the first time, the biochemical characterization and crystal structures of Drosophila melanogaster KFase conjugated with an inhibitor, PMSF. The protein architecture of KFase reveals that it belongs to the α/β hydrolase fold family. The PMSF-binding information of the solved conjugated crystal structure was used to obtain a KFase and NFK complex using molecular docking. The complex is useful for understanding the catalytic mechanism of KFase. The present study provides a molecular basis for future efforts in maintaining or regulating kynurenine metabolism through the molecular and biochemical regulation of KFase.

Vitamin B6 status and interferon‐γ‐mediated immune activation in primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) has been associated with low-grade inflammation and elevated risk of cardiovascular disease (CVD). In inflammatory conditions, interferon-γ (IFN-γ) activity is enhanced and a decreased circulating concentration of vitamin B6 is often observed. Such changes in IFN-γ activity or vitamin B6 levels have been associated with increased incidence of CVD. The aim of the study was to investigate systemic markers of IFN-γ-mediated immune activation, such as neopterin, the kynurenine-to-tryptophan ratio (KTR) and kynurenine pathway metabolites, as well as B6 vitamers in patients with PHPT. A total of 57 patients with PHPT and a control group of 20 healthy blood donors were included in this study. PHPT patients who responded positively to parathyroidectomy were followed for 6months. Forty-three patients participated in the longitudinal study in which blood samples were taken at inclusion and 1, 3 and 6months after surgery. Plasma concentrations of the B6 vitamers pyridoxal 5'-phosphate (PLP) (P=0.007) and pyridoxal (P=0.013) were significantly lower in the patient group compared to healthy control subjects. An increase in the KTR indicated that the kynurenine pathway of tryptophan metabolism was altered in PHPT patients (P=0.015). During the initial 6months after surgery, levels of PLP (P<0.001) and anthranilic acid (P<0.001) increased significantly, whereas neopterin decreased (P=0.018). The results of this study demonstrate altered levels of vitamin B6 and the KTR in PHPT patients, both of which may reflect cellular immune activation. These abnormalities should be considered in relation to the increased risk of CVD previously observed in patients with PHPT.

The effect of mutations of the kynurenine pathway of tryptophan metabolism on locomotor behavior and gene expression in glutamatergic and cholinergic systems of D. melanogaster

Kynurenine disbalance induced by mutations of the kynurenine path of tryptophan metabolism in drosophilae has an effect on the locomotor behavior of larvae. Excessive concentrations of kynurenic acid in the cinnabar mutant caused a dramatic decline in the activity. The effects of mutations apparently depend on the modulatory effect of kynurenines on the signal pathways regulated by ionotropic glutamatergic and cholinergic receptors. The age dynamics of their genes’ expression is evidence for progressive development of disorders induced by kynurenine disbalance.