NAD Biosynthesis Evolution in Bacteria: Lateral Gene Transfer of Kynurenine Pathway in Xanthomonadales and Flavobacteriales

The biosynthesis of quinolinate, the de novo precursor of nicotinamide adenine dinucleotide (NAD), may be performed by two distinct pathways, namely, the bacterial aspartate (aspartate-to-quinolinate) and the eukaryotic kynurenine (tryptophan-to-quinolinate). Even though the separation into eukaryotic and bacterial routes is long established, recent genomic surveys have challenged this view, because certain bacterial species also carry the genes for the kynurenine pathway. In this work, both quinolinate biosynthetic pathways were investigated in the Bacteria clade and with special attention to Xanthomonadales and Bacteroidetes, from an evolutionary viewpoint. Genomic screening has revealed that a small number of bacterial species possess some of the genes for the kynurenine pathway, which is complete in the genus Xanthomonas and in the order Flavobacteriales, where the aspartate pathway is absent. The opposite pattern (presence of the aspartate pathway and absence of the kynurenine pathway) in close relatives (Xylella ssp. and the order Bacteroidales, respectively) points to the idea of a recent acquisition of the kynurenine pathway through lateral gene transfer in these bacterial groups. In fact, sequence similarity comparison and phylogenetic reconstruction both suggest that at least part of the genes of the kynurenine pathway in Xanthomonas and Flavobacteriales is shared by eukaryotes. These results reinforce the idea of the role that lateral gene transfer plays in the configuration of bacterial genomes, thereby providing alternative metabolic pathways, even with the replacement of primary and essential cell functions, as exemplified by NAD biosynthesis.

Inhibition of the kynurenine-NAD+ pathway leads to energy failure and exacerbates apoptosis in pneumococcal meningitis

Pneumococcal meningitis causes neurological sequelae, including learning and memory deficits in up to half of the survivors. In both humans and in animal models of the disease, there is apoptotic cell death in the hippocampus, a brain region involved in learning and memory function. We previously demonstrated that in an infant rat model of pneumococcal meningitis, there is activation of the kynurenine (KYN) pathway in the hippocampus, and that there was a positive correlation between the concentration of 3-hydroxykynurenine and the extent of hippocampal apoptosis. To clarify the role of the KYN pathway in the pathogenesis of hippocampal apoptosis in pneumococcal meningitis, we specifically inhibited 2 key enzymes of the KYN pathway and assessed hippocampal apoptosis, KYN pathway metabolites, and nicotinamide adenine dinucleotide (NAD) concentrations by high-performance liquid chromatography. Pharmacological inhibition of kynurenine 3-hydroxylase and kynureninase led to decreased cellular NAD levels and increased apoptosis in the hippocampus. The cerebrospinal fluid levels of tumor necrosis factor and interleukin-1? and -? were not affected. Our data suggest that activation of the KYN pathway in pneumococcal meningitis is neuroprotective by compensating for an increased NAD demand caused by infection and inflammation;this mechanism may prevent energy failure and apoptosis in the hippocampus.

Attention-deficit hyperactivity disorder (ADHD) and glial integrity: an exploration of associations of cytokines and kynurenine metabolites with symptoms and attention

In contrast to studies of depression and psychosis, the first part of this study showed no major differences in serum levels of cytokines and tryptophan metabolites between healthy children and those with attention-deficit/hyperactivity disorder of the combined type (ADHD). Yet, small decreases of potentially toxic kynurenine metabolites and increases of cytokines were evident in subgroups. Therefore we examined predictions of biochemical associations with the major symptom clusters, measures of attention and response variability.

Attention-deficit hyperactivity disorder (ADHD) and glial integrity: S100B, cytokines and kynurenine metabolism--effects of medication

Children with attention-deficit/hyperactivity disorder (ADHD) show a marked temporal variability in their display of symptoms and neuropsychological performance. This could be explained in terms of an impaired glial supply of energy to support neuronal activity.

Association of kynurenine aminotransferase II gene C401T polymorphism with immune response in patients with meningitis

The kynurenine (KYN) pathway has been shown to be altered in several diseases which compromise the central nervous system (CNS) including infectious diseases such as bacterial meningitis (BM). The aim of this study was to assess single nucleotide polymorphisms (SNPs) in four genes of KYN pathway in patients with meningitis and their correlation with markers of immune response in BM.

Pneumococcal meningitis causes accumulation of neurotoxic kynurenine metabolites in brain regions prone to injury

Pneumococcal meningitis (PM) is characterized by an intense inflammatory host reaction that contributes to the development of cortical necrosis and hippocampal apoptosis. Inflammatory conditions in the brain are known to induce tryptophan degradation along the kynurenine pathway, resulting in accumulation of neurotoxic metabolites. In the present study, we investigated the contribution of the kynurenine pathway to brain injury in experimental PM by measuring the concentration of its metabolites and the enzymatic activities and mRNA levels of its major enzymes in the vulnerable brain regions. In the late phase of acute PM, we found a significant transcriptional upregulation of kynurenine-3-hydroxylase and an accumulation of the neurotoxic metabolites 3-hydroxykynurenine (3-HKYN) and 3-hydroxyanthranilic acid in cortex and hippocampus. The positive correlation between the concentration of 3-HKYN and the extent of hippocampal apoptosis adds support to the concept that 3-HKYN contributes to brain injury in PM.

Inhibition by interferon-gamma of human mononuclear cell-mediated low density lipoprotein oxidation. Participation of tryptophan metabolism along the kynurenine pathway

In this study we examined the potential inhibition by interferon-gamma (IFN gamma) of the early stages of low density lipoprotein (LDL) oxidation mediated by human peripheral blood mononuclear cells (PBMC) and monocyte-derived macrophages (MDM) in Ham's F-10 medium supplemented with physiological amounts of L-tryptophan (Trp). We assessed LDL oxidation by measuring the consumption of LDL's major antioxidant (i.e., alpha-tocopherol) and targets for oxidation (cholesteryllinoleate and cholesterylarachidonate), together with the accumulation of cholesterylester hydroperoxides and the increase in relative electrophoretic mobility of the lipoprotein particle. Exposure of PBMC or MDM to IFN gamma induced the degradation of extracellular Trp with concomitant accumulation of kynurenine, anthranilic and 3-hydroxyanthranilic acid (3HAA) in the culture medium. Formation of 3HAA, but neither Trp degradation nor formation of kynurenine and anthranilic acid, was inhibited by low amounts of diphenylene iodonium (DPI) in a concentration-dependent manner. In contrast to oxidative Trp metabolism, exposure of human PBMC or MDM to IFN gamma failed to induce degradation of arginine, and nitrite was not detected in the cell supernatant, indicating that nitric oxide synthase was not induced under these conditions. Incubation of LDL in Trp-supplemented F-10 medium resulted in a time-dependent oxidation of the lipoprotein that was accelerated in the presence of PBMC or MDM but inhibited strongly in the presence of both cells and IFN gamma, i.e., when Trp degradation and formation of 3HAA were induced. In contrast, when IFN gamma was added to PBMC or MDM in F-10 medium that was virtually devoid of Trp, inhibition of cell-accelerated LDL oxidation was not observed. Exogenous 3HAA added to PBMC or purified monocytes in the absence of IFN gamma also strongly and in a concentration-dependent manner inhibited LDL oxidation. Selective inhibition of IFN gamma-induced formation of 3HAA by DPI caused reversion of the inhibitory action of this cytokine on both PBMC- and MDM-mediated LDL oxidation. These results show that IFN gamma treatment of human PBMC or MDM in vitro attenuates the extent of LDL oxidation caused by these cells, and indicate that Trp degradation with formation of 3HAA is a major contributing factor to this inhibitory activity.

The kynurenine pathway is involved in bacterial meningitis.

BackgroundBacterial meningitis (BM) is characterized by an intense host inflammatory reaction, which contributes to the development of brain damage and neuronal sequelae. Activation of the kynurenine (KYN) pathway (KP) has been reported in various neurological diseases as a consequence of inflammation. Previously, the KP was shown to be activated in animal models of BM, and the association of the SNP AADAT¿+¿401C/T (kynurenine aminotransferase II - KAT II) with the host immune response to BM has been described. The aim of this study was to investigate the involvement of the KP during BM in humans by assessing the concentrations of KYN metabolites in the cerebrospinal fluid (CSF) of BM patients and their relationship with the inflammatory response compared to aseptic meningitis (AM) and non-meningitis (NM) groups.MethodsThe concentrations of tryptophan (TRP), KYN, kynurenic acid (KYNA) and anthranilic acid (AA) were assessed by HPLC from CSF samples of patients hospitalized in the Giselda Trigueiro Hospital in Natal (Rio Grande do Norte, Brazil). The KYN/TRP ratio was used as an index of indoleamine 2,3-dioxygenase (IDO) activity, and cytokines were measured using a multiplex cytokine assay. The KYNA level was also analyzed in relation to AADAT¿+¿401C/T genotypes.ResultsIn CSF from patients with BM, elevated levels of KYN, KYNA, AA, IDO activity and cytokines were observed. The cytokines INF-¿ and IL-1Ra showed a positive correlation with IDO activity, and TNF-¿ and IL-10 were positively correlated with KYN and KYNA, respectively. Furthermore, the highest levels of KYNA were associated with the AADAT¿+¿401 C/T variant allele.ConclusionThis study suggests a downward modulatory effect of the KP on CSF inflammation during BM.

Antidepressant effects of exercise: a role for the adiponectin-PGC-1α-kynurenine triad?

It is well-recognized that exercise improves mental health, e.g., by decreasing depressive behaviors, improving hippocampal-dependent learning and neurogenesis, and increasing dendritic plasticity. Yet how exercise influences the brain at the molecular level is not clearly understood. Yau et al recently reported that the antidepressant effects of physical exercise are mainly mediated by adiponectin, an adipocyte-secreted hormone ('adipocytokine') with neuroprotective effects at the central nervous system level (Yau et al., 2014). This article is protected by copyright. All rights reserved

Effect of phenolic-rich plant materials on protein and lipid oxidation reactions

The antioxidant activity of natural plant materials rich in phenolic compounds is being widely investigated for protection of food products sensitive to oxidative reactions. In this thesis plant materials rich in phenolic compounds were studied as possible antioxidants to prevent protein and lipid oxidation reactions in different food matrixes such as pork meat patties and corn oil-in water emulsions. Loss of anthocyanins was also measured during oxidation in corn oil-in-water emulsions. In addition, the impact of plant phenolics on amino acid level was studied using tryptophan as a model compound to elucidate their role in preventing the formation of tryptophan oxidation products. A high-performance liquid chromatography (HPLC) method with ultraviolet and fluorescence detection (UV-FL) was developed that enabled fast investigation of formation of tryptophan derived oxidation products. Byproducts of oilseed processes such as rapeseed (Brassica rapa L.), camelina (Camelina sativa) and soy meal (Glycine max L.) as well as Scots pine bark (Pinus sylvestris) and several reference compounds were shown to act as antioxidants toward both protein and lipid oxidation in cooked pork meat patties. In meat, the antioxidant activity of camelina, rapeseed and soy meal were more pronounced when used in combination with a commercial rosemary extract (Rosmarinus officinalis). Berry phenolics such as black currant (Ribes nigrum) anthocyanins and raspberry (Rubus idaeus) ellagitannins showed potent antioxidant activity in corn oil-in-water emulsions toward lipid oxidation with and without β-lactoglobulin. The antioxidant effect was more pronounced in the presence of β-lactoglobulin. The berry phenolics also inhibited the oxidation of tryptophan and cysteine side chains of β-lactoglobulin. The results show that the amino acid side chains were oxidized prior the propagation of lipid oxidation, thereby inhibiting fatty acid scission. In addition, the concentration and color of black currant anthocyanins decreased during the oxidation. Oxidation of tryptophan was investigated in two different oxidation models with hydrogen peroxide (H2O2) and hexanal/FeCl2. Oxidation of tryptophan in both models resulted in oxidation products such as 3a-hydroxypyrroloindole-2-carboxylic acid, dioxindolylalanine, 5-hydroxy-tryptophan, kynurenine, N-formylkynurenine and β-oxindolylalanine. However, formation of tryptamine was only observed in tryptophan oxidized in the presence of H2O2. Pine bark phenolics, black currant anthocyanins, camelina meal phenolics as well as cranberry proanthocyanidins (Vaccinium oxycoccus) provided the best antioxidant effect toward tryptophan and its oxidation products when oxidized with H2O2. The tryptophan modifications formed upon hexanal/FeCl2 treatment were efficiently inhibited by camelina meal followed by rapeseed and soy meal. In contrast, phenolics from raspberry, black currant, and rowanberry (Sorbus aucuparia) acted as weak prooxidants. This thesis contributes to elucidating the effects of natural phenolic compounds as potential antioxidants in order to control and prevent protein and lipid oxidation reactions. Understanding the relationship between phenolic compounds and proteins as well as lipids could lead to the development of new, effective, and multifunctional antioxidant strategies that could be used in food, cosmetic and pharmaceutical applications.

Tryptophan degradation in irritable bowel syndrome: evidence of indoleamine 2,3-dioxygenase activation in a male cohort

Background: Irritable bowel syndrome (IBS) is a common disorder that affects 10–15% of the population. Although characterised by a lack of reliable biological markers, the disease state is increasingly viewed as a disorder of the brain-gut axis. In particular, accumulating evidence points to the involvement of both the central and peripheral serotonergic systems in disease symptomatology. Furthermore, altered tryptophan metabolism and indoleamine 2,3-dioxygenase (IDO) activity are hallmarks of many stress-related disorders. The kynurenine pathway of tryptophan degradation may serve to link these findings to the low level immune activation recently described in IBS. In this study, we investigated tryptophan degradation in a male IBS cohort (n = 10) and control subjects (n = 26). Methods: Plasma samples were obtained from patients and healthy controls. Tryptophan and its metabolites were measured by high performance liquid chromatography (HPLC) and neopterin, a sensitive marker of immune activation, was measured using a commercially available ELISA assay. Results: Both kynurenine levels and the kynurenine:tryptophan ratio were significantly increased in the IBS cohort compared with healthy controls. Neopterin was also increased in the IBS subjects and the concentration of the neuroprotective metabolite kynurenic acid was decreased, as was the kynurenic acid:kynurenine ratio. Conclusion: These findings suggest that the activity of IDO, the immunoresponsive enzyme which is responsible for the degradation of tryptophan along this pathway, is enhanced in IBS patients relative to controls. This study provides novel evidence for an immune-mediated degradation of tryptophan in a male IBS population and identifies the kynurenine pathway as a potential source of biomarkers in this debilitating condition.

Análise de polimorfismos dos genes da rota quinureniana em pacientes com meningite bacteriana.

Bacterial meningitis (BM) is still an important infectious disease causing death and disability. Invasive bacterial infections of the central nervous systems (CNS) generate some of the most powerful inflammatory responses known, which contributes to neuronal damage. The DNA microarray technology showed alterations in the kynurenine (KYN) pathway that is induced in BM and other diseases associated with inflammation, leading to brain injury. Our main aim was to search SNPs previously described in the KYN path enzymes to investigate a putative association of this SNPs with imbalanced in this pathway in patients with BM. The patients included in this study were 33 males and 24 females, with ages varying from 02 months to 68 years. SNPs were located inside of the domain conserved in KYNU, IDO, KATI and KATII. Primers were designed for analysis of SNPs already described by PIRA-PCR followed by RFLP. The analysis of KYNU+715G/A SNP found a heterozygous frequency of 0.033. We did not found the variant allele of SNP KYNU+693G/A, KATI+164T/C, KATII+650C/T and IDO+434T/G. Despite of previews studies showing the importance of KYN pathway we did not found one association of these SNPs analyzed with susceptibility or severity of MB in study population.

Ativação local da rota da quinurenina por moduladores inflamatórios durante a meningite bacteriana.

Activation of the kynurenine (KYN) pathway (KP) by modulators of immune system has been observed during several neurological diseases. Here we assessed the association of chemo-/cytokine levels with the concentration of KP metabolites in cerebrospinal fluid (CSF) and plasma samples from patients with bacterial meningitis (BM). All samples were collected from 42 patients diagnosed with acute bacterial meningitis (ABM), aseptic meningitis, tuberculous meningitis and patients without infection neurological disorders. CSF and plasma concentration of metabolites from the KP was assessed by high pressure liquid chromatography (HPLC) and cytokines and chemokines by Bio-plex 200 suspension array system. Concentrations of the KP metabolites KYN and kynurenic acid (KYNA) were significantly higher in CSF of patients with ABM compared to other groups. Tryptophan (TRP), anthranilic acid (AA), 3-hydroxykynurenine (3HK) and 3-hydroxyanthranilic acid (3HAA) did not show statistical significance, although some of them presented a good accumulation during ABM. The expression of TNF-alpha, IL-6, IL-1beta, IFN-gamma, IL-10, IL-1 receptor antagonist (IL-1Ra), MIP-1alpha, MIP-1beta, MCP-1 and G-CSF was about 100-fold higher in CSF from ABM patients than other infected groups. In all CSF and plasma samples, the concentration of IL-2, IL-12(p70), IL-4, IL-8 and GM-CSF was not significant. ABM still showed significant concentrations of IL-6, IL-10, IL-1Ra and MCP-1 in plasma samples. Based on the comparison of KP metabolites concentrations between plasma and CSF samples we conclude that the activation of the tryptophan pathway upon BM occurs within the brain. This increase in KP metabolites is most due to activation of the KP by molecules as IFN-gamma and TNF-alpha in response to infection.