Inhibition Of Kynurenine Pathway Research Articles

The tryptophan-kynurenine pathway in immunomodulation and cancer metastasis.

The activation of the kynurenine pathway in cancer progression and metastasis through immunomodulatory pathways has drawn attention to the potential for kynurenine pathway inhibition. The activation of the kynurenine pathway, which results in the production of kynurenine metabolites through the degradation of tryptophan, promotes the development of intrinsically malignant properties in cancer cells while facilitating tumour immune escape. In addition, kynurenine metabolites act as biologically active substances to promote cancer development and metastasis. A literature review was conducted to investigate the role of the tryptophan-kynurenine pathway in immunomodulation and cancer metastasis. Evidence suggests that several enzymes and metabolites implicated in the kynurenine pathway are overexpressed in various cancers. As such, the tryptophan pathway represents a promising target for cancer treatment. However, downstream signalling pathways, including aryl hydrocarbon receptor activation, have previously induced diverse biological effects in various malignancies, which resulted in either the promotion or the inhibition of metastasis. As a result, a thorough investigation of the kynurenine pathway and its regulatory mechanisms is necessary in order to properly comprehend the effects of kynurenine pathway activation involved in cancer development and metastasis.

Low-dose sumatriptan improves the outcome of acute mesenteric ischemia in rats via downregulating kynurenine.

Mesenteric ischemia has remained without effective pharmacological management for many years. Sumatriptan, an abortive medication for migraine and cluster headaches, has potent anti-inflammatory properties and ameliorated organ ischemia in previous animal studies. Similarly, inhibition of the kynurenine pathway ameliorated renal and myocardial ischemia/reperfusion (I/R) in many preclinical studies. Herein, we assessed the effect of sumatriptan on experimental mesenteric I/R and investigated whether kynurenine pathway inhibition is a mechanism underlying its action. Ischemia was induced by ligating the origin of the superior mesenteric artery (SMA) and its anastomosis with the inferior mesenteric artery (IMA) with bulldog clamps for 30min. Ischemia was followed by 1h of reperfusion. Sumatriptan (0.1, 0.3, and 1mg/kg ip) was injected 5min before the reperfusion phase, 1-methyltryptophan (1-MT) (100mg/kg iv) was used to inhibit kynurenine production. At the end of the reperfusion phase, samples were collected from the jejunum of rats for H&E staining and molecular assessments. Sumatriptan improved the integrity of intestinal mucosa after I/R, and 0.1mg/kg was the most effective dose of sumatriptan in this study. Sumatriptan decreased the increased levels of TNF-α, kynurenine, and p-ERK but did not change the decreased levels of NO. Furthermore, sumatriptan significantly increased the decreased ratio of Bcl2/Bax. Similarly, 1-MT significantly decreased TNF-α and kynurenine and protected against mucosal damage. This study demonstrated that sumatriptan has protective effects against mesenteric ischemia and the kynurenine inhibition is potentially involved in this process. Therefore, it can be assumed that sumatriptan has the potential to be repurposed as a treatment for acute mesenteric ischemia.

Genomic Analysis Of NAD+ Synthesis Pathways Involved In Aging and Cancer

Cancer cells have elevated energy demands to sustain continuous growth and other malignant processes and undergo extensive metabolic reprogramming to meet these demands. One element of this reprogramming in many cancer subtypes is elevated synthesis of nicotinamide adenine dinucleotide (NAD+), a critical co-enzyme that supports energy production through both glycolysis and the TCA cycle. The kynurenine metabolic pathway is the evolutionarily conserved means by which cells produce NAD+ de novo from tryptophan. NAD+ levels drop with age, a contributing factor to many forms of age-related disease. While interventions that increase NAD+ have been shown to extend lifespan, previous work from our lab demonstrates that knockdown of several kynurenine pathway enzymes, thus decreasing de novo NAD+ production, results in increased longevity of Caenorhabditis elegans by 20-30%. To address this apparent contradiction, we propose that kynurenine pathway inhibition may produce metabolic feedback that results in upregulation of NAD+ recycling. Eukaryotic cells recycle NAD+ from nicotinamide (NAM) through one of two pathways: the Salvage pathway in mammalian cells and the Preiss-Handler pathway in C. elegans and related invertebrates species. We are using tools in C. elegans and human cell culture to examine the interaction between kynurenine/de novo NAD+ synthesis and NAD+ recycling through Salvage and Preiss-Handler. In particular, we are interested in how combining interventions between these pathways will influence activity throughout the NAD+ metabolic networks (measured via mass spectrometry), physiological phenotypes, and transcriptomic changes (via RNA sequence data) involved in aging and age-associated disease.

Kynurenine Metabolism Lifespan Extension Mediated by Oxidative Stress Response and Hypoxic Response in C. elegans

Abstract Aging is characterized by a progressive decline in the normal physiological functions of an organism, ultimately leading to mortality. Metabolic changes throughout the aging process disrupt the balance and homeostasis of the cell. The kynurenine metabolic pathway is the sole de novo biosynthetic pathway for producing NAD+ from ingested tryptophan. Altered kynurenine pathway activity is associated with both aging and a variety of age-associated diseases, and kynurenine-based interventions can extend lifespan in Caenorhabditis elegans. Our laboratory recently demonstrated knockdown of the kynurenine pathway enzymes kynureninase (KYNU) or 3-hydroxyanthranilic acid dioxygenase (HAAO) increases lifespan by 20-30% in C elegans. However, the mechanism of how these interventions may modulate response against different stressors during the aging process has yet to be explored. Fluorescent reporter strains show the stress-responsive transcription factors skn-1 (ortholog of NRF2/NFE2L2; oxidative stress response) and hif-1 (ortholog of HIF1A; hypoxic stress response) to be highly upregulated when the kynurenine pathway is inhibited. We also demonstrated the increase expression of gst-4 and gcs-1 (transcriptional targets skn-1), which are involved in production of the antioxidant glutathione (GSH), as well as upregulation of cysl-2 (transcriptional target of hif-1), a regulator of cysteine biosynthesis from serine. We hypothesize that lifespan extension resulting from kynurenine pathway inhibition is mediated, at least in part, by upregulation of these transcription factors, providing elevated defense against oxidative stress and hypoxic stress.

Genomic Analysis Of NAD+ Synthesis Pathways Involved In Aging and Cancer

Age-related changes in DNA methylation are potent regulators of gene expression and may in part explain the onset of disease and disability. Vervet monkeys are a well-described model of neurocognitive and physical aging. Like humans, gait speed declines with age in vervets, and variability in gait speed in older animals is associated with age-related musculoskeletal and cognitive decline. To identify methylation patterns linked to aging-related physical decline, we investigated differentially methylated loci in vastus lateralis biopsies of 29 female vervets aged 8-28 years (~25-90 years in humans). We evaluated 107,490 loci on the Illumina Infinium Methylation EPIC Human Array that aligned with high fidelity to the vervet genome using the R package minfi and fit generalized linear mixed models to account for underlying genetic relatedness. We found 13 CpG methylation sites associated with 12 genes (CALCR, EBF4, GDNF, GMCL1, HAND1, HOXC10, IRX2, LBX2, MPPED2, SHISA6, SOX2, and WNT2) significantly differentially methylated with gait speed. Increased methylation was negatively associated with gait speed for all loci except GMCL1, reflecting the pattern of global hypermethylation of skeletal muscle tissue with age. Several of the associated genes are involved in development and differentiation including HOXC10 and LBX2, which regulates myoblast migration. CACNG8 regulates voltage-dependent calcium gated channels, and GDNF promotes motor neuron innervation of skeletal muscle. Most associations with muscle phenotypes are novel, but several have been linked to age-related bone diseases. We are currently evaluating the relationships of these differentially methylated loci with muscle mRNA expression and protein abundance.

Abstract 14258: Modulation of Kynurenine Pathway to Prevent Brain Injury After Cardiac Arrest and Cardiopulmonary Resuscitation in Mice

Introduction: Kynurenine pathway (KP) is emerging as one of the potential components affecting cardiac arrest (CA) outcomes. The aim of this study is to evaluate the effects of KP inhibition through genetic deletion of the rate-limiting enzyme of the KP, indoleamine-2,3-dyoxygenase (IDO) on survival and neurological outcome after CA. Methods and Results: Sixteen adult male wild-type (WT) and IDO-deleted (IDO -/- ) mice were subjected to 8 min untreated CA followed by resuscitation. At baseline heart rate and mean arterial pressure (MAP) did not differ among groups. At the time of return of spontaneous circulation, 30 and 60 min later, MAP was higher in the IDO -/- group compared to the WT one (p=0.0005). IDO -/- mice showed higher survival compared to WT at 7 days after CA (68.5% in IDO -/- vs 37.5% in WT; log rank p=0.036). Neurological function was higher in IDO -/- than in WT mice during the 7 days following CA (p=0.0124). IDO -/- mice also showed an improved locomotor function compared to WT mice (p=0.037). Brain magnetic resonance imaging (MRI) with diffusion tensor imaging (DTI) sequences showed a reduction in fractional anisotropy in the external capsule of the corpus callosum in WT mice compared to IDO -/- mice at 7 days after resuscitation (p=0.015). We then treated additional IDO -/- mice with L-kyn 15 min before CA, to revert the IDO -/- phenotype. Brain MRI with diffusion-weighted imaging (DWI) sequences and histological analysis were performed 24h after CA in WT, IDO -/- , and IDO -/- +L-Kyn mice. Brain MRI revealed restriction of water diffusivity 24h after CA in WT mice. IDO-deletion reduced water diffusion abnormalities while the beneficial effect was reverted in the L-kyn group (p=0.01). Degenerating neurons in the frontal cortex, represented as Fluoro-Jade B positive cells, were more numerous in WT compared to IDO -/- mice; L-kyn halted this IDO deletion-induced reduction in degenerating cells (p=0.05). Conclusion: KP inhibition improves survival and neurological outcome after CA. The neuroprotective effect of IDO-deletion was associated with preservation of brain white matter microintegrity and with reduction of cerebral cytotoxic edema. Reversal of these beneficial effects by L-kyn administration in IDO -/- mice further confirm the KP role in CA outcome.

Inhibition of Kynurenine Metabolism and Its Effect in Mitochondrial Function in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent cancer in the liver. The majority of ingested tryptophan is processed in the liver through the kynurenine pathway, the endpoint of which is de novo NAD+ biosynthesis. Dysregulation of tryptophan-kynurenine metabolism and NAD+ synthesis may promote mitochondrial malfunction, tumor reprogramming, and carcinogenesis. Using a publicly available gene expression dataset from liver hepatocellular carcinoma (LIHC) samples available through The Cancer Genome Atlas (TCGA; n = 371), we employed Principal Component Analysis (PCA), hierarchical clustering, gene-pattern expression profiling, and survival analysis to cluster patients and determine overall survival. Our analysis of genes encoding kynurenine pathway enzymes determined that patients with high QPRT expression had a poor prognosis with decreased median survival, with no effect on the maximum survival. There is a significant difference in the survival between patients with high QPRT expression relative to patients with high HAAO/AFMID expression (HR = 1.2, [95% CI 0.5-1.8] P = 0.0181, Gehan-Breslow-Wilcoxon Test). Patients with high QPRT expression have higher survival rates compared with low QPRT expression (HR = 1.4, [95% CI 0.9-2.2] P = 0.0344, Gehan-Breslow-Wilcoxon Test). To test the consequences of kynurenine-pathway inhibition in mitochondrial function and morphology we use 4-Cl-3HAA, an irreversible HAAO inhibitor, and observed a small increase in mitochondrial fragmentation in HepG2 cells after 24 hours of treatment. We conclude that kynurenine metabolism may be useful as a biomarker to predict patient prognosis among HCC patients. In ongoing work, we are testing QPRT inhibitors in cell culture as a potential adjuvant for chemotherapies.

Abstract 15237: Inhibition of the Kynurenine Pathway Improves Neurological Recovery in a Rat Model of Cardiac Arrest

Introduction: Kynurenine pathway (KP), the major route of the tryptophan (TRP) catabolism, is involved in the pathogenesis of numerous cerebral disorders. We have previously demonstrated that KP is activated following cardiac arrest (CA) and correlates with neurological injury both in animals and humans. We thus hypothesized that inhibition of the enzyme initiating the TRP catabolism into kynurenine (KYN), i.e. indoleamine-2,3-dioxygenase (IDO), could prevent KP activation and improve neurological recovery. Methods: Twenty-two rats received oral administration of 1-Methyl-Tryptophan (1-MT, 800mg/Kg of racemate) (n=10) or corresponding vehicle (n=12), 24h and 2h before CA. Ventricular fibrillation was induced and untreated for 8 min. CPR was then performed for additional 8 min prior to defibrillation. Blood samples were obtained for assay of plasma levels of: 1-MT, TRP, KYN, high-sensitive cardiac troponin T (hs-cTnT), and neuron specific enolase (NSE). Rats were observed up to 96h for assessment of neurological recovery by the neurological deficit score (NDS). Results: High plasma levels of 1-MT were observed up to 96h after drug administration (Fig). CA induced a significant and long-lasting KP activation (reported as KYN/TRP) and this was significantly reduced in rats treated with 1-MT (Fig). 90% of animals treated with 1-MT were successfully resuscitated compared to 75% of those treated with vehicle. Lower levels of hs-cTnT (5186 vs. 9207 ng/L) and NSE (0.44 vs. 0.76 ng/mL) were observed in treated animals compared to vehicles. 1-MT also significantly reduced the KP activation in the hippocampus, restoring the KYN/TRP ratio to the values observed in naïve rats. The severity of CA-induced neurological deficit was significantly reduced by 1-MT (Fig), and correlated with level of KP activation, both in plasma (Fig) and in the hippocampus (r=0.73, p=0.019). Conclusions: In this model, inhibition of KP was feasible and improved neurological recovery after CA.

96. Anti-depressants and kynurenine pathway inhibition: A therapeutic strategy for neuroprotection in vitro?

The kynurenine pathway (KP) is the main pathway by which tryptophan is metabolized. Its rate limiting enzyme indolamine 2, 3-dioxygenase (IDO) catalyses the production of kynurenine, which in turn is metabolised by either kynurenine 3-hydroxylase (KMO) which leads to the production of quinolinic acid (neurotoxic), or by kynurenine aminotransferase (KAT II) which yields kynurenic acid (neuroprotective). These enzymes are localised in microglia and astrocytes respectively. The present studies demonstrated that IFN- γ induces expression of IDO, KMO and kynase along with the production of neurotoxic molecules from BV-2 microglia. This was determined using a cell culture system whereby microglia were activated with IFN- γ and this conditioned medium was then placed on primary cortical neurons. Inhibition of the kynurenine pathway with 1-(D)-methyl-tryptophan (IDO inhibitor) and Ro 61-8048 (KMO inhibitor) completely attenuated this microglial-mediated neurotoxicity, as did the NMDA antagonist MK-801. Furthermore the anti-depressant fluoxetine partially attenuated this neurotoxicity and IFN- γ induced increases in IDO and kynase mRNA expression. Inhibition of classical neurotoxic factors released from microglia i.e. iNOS and the enzyme NADPH oxidase had no effect on this microglial mediated neurotoxicity, and neither did the anti-inflammatory agent dexamethasone. These results propose IFN- γ activated microglia induce neurotoxicity by activating the KP, and this can be attenuated using fluoxetine, suggesting a possible role for anti-depressants in ameliorating neuronal damage and in influencing the KP balance.

Kynurenine pathway inhibition as a therapeutic strategy for neuroprotection

The oxidative pathway for the metabolism of tryptophan along the kynurenine pathway generates quinolinic acid, an agonist at N-methyl-D-aspartate receptors, as well as kynurenic acid which is an antagonist at glutamate and nicotinic receptors. The pathway has become recognized as a key player in the mechanisms of neuronal damage and neurodegenerative disorders. As a result, manipulation of the pathway, so that the balance between the levels of components of the pathway can be modified, has become an attractive target for the development of pharmacological agents with the potential to treat those disorders. This review summarizes some of the relevant background information on the pathway itself before identifying some of the chemical strategies for its modification, with examples of their successful application in animal models of infection, stroke, traumatic brain damage, cerebral malaria and cerebral trypanosomiasis.

Effects of Kynurenine Pathway Inhibition on NAD+Metabolism and Cell Viability in Human Primary Astrocytes and Neurons

The kynurenine pathway (KP) is the principle route of L-Tryptophan (TRP) metabolism, producing several neurotoxic and neuroprotective metabolic precursors before complete oxidation to the essential pyridine nucleotide nicotinamide adenine dinucleotide (NAD+). KP inhibition may prove therapeutic in central nervous system (CNS) inflammation by reducing the production of excitotoxins such as quinolinic acid (QUIN). However, KP metabolism may also be cytoprotective through the de novo synthesis of intracellular NAD+. We tested the hypothesis that the KP is directly involved in the maintenance of intracellular NAD+ levels and SIRT1 function in primary astrocytes and neurons through regulation of NAD+ synthesis. Competitive inhibition of indoleamine 2,3 dioxygenase (IDO), and quinolinic acid phosphoribosyltransferase (QPRT) activities with 1-methyl-L-Tryptophan (1-MT), and phthalic acid (PA) respectively, resulted in a dose-dependent decrease in intracellular NAD+ levels and sirtuin deacetylase-1 (SIRT1) activity, and correlated directly with reduced cell viability. These results support the hypothesis that the primary role of KP activation during neuroinflammation is to maintain NAD+ levels through de novo synthesis from TRP. Inhibition of KP metabolism under these conditions can compromise cell viability, NAD-dependent SIRT1 activity and CNS function, unless alternative precursors for NAD+ synthesis are made available.

Kynurenine pathway – a new link between endothelial dysfunction and carotid atherosclerosis in chronic kidney disease patients

The endothelium dysfunction is an important component of atherosclertic cardiovascular disease. It has been also suggested that kynurenine pathway activation may be involved in the pathogenesis of this disease. This is a cross-sectional study in chronic kidney disease (CKD) patients (n=106; 60 Males). The plasma markers of endothelial dysfunction and kynurenine (KYN), 3-hydroxykynurenine (3-HKYN), kynurenic acid (KYNA), anthranilic acid (AA) and quinolinic acid (QA) were measured in relation to an early indicator of the systemic atherosclerosis - intima-media thickness (IMT). Kynurenines, von Willebrand factor (vWF), thrombomodulin (TM), soluble adhesion molecules (sICAM-1, sVCAM-1) and IMT in each uraemic group were significantly higher than in healthy people. In contrast, no significant differences in sE-selectin and sP-selectin concentrations were observed between CKD patients and controls. Kynurenines were positively associated with vWF, TM, sICAM-1 and sVCAM-1, whereas sP-selectin was inversely associated with the most of kynurenines. IMT was positively correlated both with kynurenines: KYN, 3-HKYN, QA as well as with endothelial markers: TM, vWF, sICAM-1 and sVCAM-1 (all p<0.01). Finally, multiple regression analysis identified age, vWF, sVCAM-1 and QA levels as the independent variables significantly associated with increased IMT in this population (adjusted r² = 0.51). This study suggests a relationship between kynurenine pathway activation, endothelial dysfunction and the progression of atherosclerosis in CKD patients. It opens a new idea that the inhibition of kynurenine pathway may provide an effective strategy to slow down endothelial dysfunction and thereby the prevalence of atherosclerosis in this population.

Effect of indoleamine dioxygenase-1 deficiency and kynurenine pathway inhibition on murine cerebral malaria

Cerebral malaria (CM) can be a fatal manifestation of Plasmodium falciparum infection. In this study, two different approaches were used to examine the role of indoleamine 2,3-dioxygenase-1 (IDO-1) and its metabolites in the development of murine CM. Mice genetically deficient in IDO-1 were not protected against CM, but partial protection was observed in C57BL/6 mice treated with Ro 61-8048, an inhibitor of kynurenine-3-hydroxylase. This protection was associated with suppressed levels of picolinic acid (PA) within the brain, but not with changes in the levels of kynurenic acid (KA) or quinolinic acid (QA). These data suggest that although IDO-1 is not directly involved in the pathogenesis of CM in C57BL/6 mice, the production of the kynurenine pathway metabolite PA may contribute to the development of murine CM.

Prolonged Survival of a Murine Model of Cerebral Malaria by Kynurenine Pathway Inhibition

C57BL/6J mice infected with Plasmodium berghei ANKA develop neurological dysfunction and die within 7 days of infection. We show that treatment of infected mice with a kynurenine-3-hydroxylase inhibitor prevents them from developing neurological symptoms and extends their life span threefold until severe anemia develops.

Kynurenine pathway inhibition reduces neurotoxicity of HIV-1-infected macrophages.

The AIDS dementia complex (ADC) is a consequence of excessive immune activation driven at least in part by systemic HIV infection and probably brain infection. Quinolinic acid (QUIN) is a neurotoxic tryptophan metabolite produced by macrophages in response to stimulation with cytokines or infection with HIV-1. Consequently it has been implicated in ADC pathogenesis. However, macrophages infected with HIV-1 synthesize numerous neurotoxic substances. Therefore we conducted experiments using human fetal brain tissue to determine the relative importance of QUIN as a neurotoxin in ADC. Human macrophages were infected with HIV-1 in vitro using a viral isolate from a demented patient. 6-Chloro-D-tryptophan, an inhibitor of QUIN biosynthesis, was added to half the macrophage cultures to block formation of QUIN. Supernatants containing QUIN (SQpos) or in which QUIN biosynthesis had been inhibited (SQneg) were then added to human fetal brain aggregate cultures. Toxicity was evaluated using lactate dehydrogenase efflux, trypan blue exclusion, immunohistochemistry, image analysis, and electron microscopy. Each technique showed a reduction of toxicity in SQneg-treated cultures. These studies confirm the significance of QUIN as a neurotoxin in ADC and suggest that neuroprotective strategies may have a place in the treatment of this disease.