On the antioxidant properties of kynurenic acid: free radical scavenging activity and inhibition of oxidative stress

Neuroprotection effects of kynurenic acid-loaded micelles for the Parkinson's disease models

Anti-glutamatergic agents may have neuroprotective effects against excitotoxicity that is known to be involved in the pathogenesis of Parkinson's disease (PD). One of these agents is kynurenic acid (KYNA), a tryptophan metabolite, which is an endogenous N-methyl-D-aspartic acid (NMDA) receptor antagonist. However, its pharmacological properties of poor water solubility and limited blood-brain barrier (BBB) permeability rules out its systemic administration in disorders affecting the central nervous system. Our aim in the present study was to investigate the neuroprotective effects of KYNA-loaded micelles (KYNA-MICs) against PD in vitro and in vivo. Lipid-based micelles (MICs) in conjunction with KYNA drug delivery have the potential to enhance the penetration of therapeutic drugs into a diseased brain without BBB obstacles. KYNA-MICs were characterized by particle size (105.8 ± 12.1 nm), loading efficiency (78.3 ± 4.23%), and in vitro drug release (approximately 30% at 24 h). The in vitro experiments showed that KYNA-MICs effectively reduced 2-fold protein aggregation. The in vivo studies revealed that KYNA was successfully delivered by 5-fold increase in neurotoxin-induced PD brains. The results showed significant enhancement of KYNA delivery into brain. We also found that the KYNA-MICs exhibited several therapeutic effects. The KYNA-MICs reduced protein aggregation of an in vitro PD model, ameliorated motor functions, and prevented loss of the striatal neurons in a PD animal model. The beneficial effects of KYNA-MICs are probably explained by the anti-excitotoxic activity of the treatment's complex. As the KYNA-MICs did not induce any appreciable side-effects at the protective dose applied to a chronic PD mouse model, our results demonstrate that KYNA provides neuroprotection and attenuates PD pathology.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Hydrogels containing KYNA promote angiogenesis and inhibit inflammation to improve the survival rate of multi-territory perforator flaps

BACKGROUND

A new spray adhesive (KYNA-PF127) was established through the combination of thermosensitive hydrogel (Pluronic F127) and KYNA, aimed to investigate the effect of KYNA-PF127 on multi-territory perforator flaps and its possible molecular mechanism.

MATERIALS AND METHODS

36 SD male rats with 250-300 g were randomly divided into 3 groups (n = 12): control group, blank glue group and KYNA-PF127 group. KYNA-PF127 hydrogel was prepared and characterized for its morphology and properties using scanning electron microscopy. CCK-8 assay, scratch wound assay, transwell assay, tube formation assay and Ki67 staining were used to study the effect of KYNA-PF127 on the proliferation, migration, and tube formation of HUVECs. VEGF and FGF2 were measured by qPCR to evaluate the angiogenesis capacity of HUVECs in vitro. In vivo, the effect of each group on the survival area of the cross-zone perforator flap was evaluated, and angiogenesis was evaluated by HE and immunofluorescence (CD31 and MMP-9). The effect of inflammation on skin collagen fibers was assessed by Masson. Immunohistochemistry (SOD1, IL-1β, TNF-α) was used to evaluate the effects of oxidative stress and inflammatory factors on multi-territory flaps.

RESULTS

KYNA-PF127 has good sustained release and biocompatibility at 25% concentration. KYNA-PF127 promoted the proliferation, migration, and angiogenesis of HUVECs in vitro. In vivo, the survival area of multi-territory perforator flaps and angiogenic capability have increased after KYNA-PF127 intervention. KYNA-PF127 could effectively reduce the oxidative stress and inflammation of multi-territory perforator flaps.

CONCLUSION

KYNA-PF127 promotes angiogenesis through its antioxidant stress and anti-inflammatory effects, and shows potential clinical value in promoting the survival viability and drug delivery of multi-territory perforator flaps.

Different Kynurenine Pathway Dysregulation in Systemic Sclerosis in Men and Women

Systemic sclerosis (SSc), a predominantly female-affected systemic autoimmune disease, requires tailored treatment strategies contingent on organ involvement and symptom severity. Given SSc's inflammatory nature, the involvement of the kynurenine pathway (KP) in its pathophysiology is underexplored. Our study aimed to investigate sex-related differences in KP activation among SSc patients and assess the impact of angiotensin-converting enzyme (ACE) inhibitors and estimated glomerular filtration rate (eGFR) on KP metabolite concentrations. We enrolled 48 SSc patients and 53 healthy controls, quantifying KP metabolites (tryptophan (TRP), kynurenine (KYN), and kynurenic acid (KYNA)) in serum via high-performance liquid chromatography. Separate multivariate analyses of covariance (MANCOVAs) for women and men were performed to ascertain mean differences between patients and healthy controls while correcting for age. For our secondary objective, we conducted a MANCOVA to explore disparities in ACE inhibitor users and non-users among patients, with BMI correction. Our findings revealed decreased TRP concentrations but increased KYNA/TRP ratio and KYN/TRP ratio in both male and female SSc patients compared to their respective controls. Unlike women, SSc males exhibited higher KYN concentrations and decreased KYNA/KYN ratio relative to their controls. Additionally, SSc patients using ACE inhibitors had higher serum KYNA levels than non-users. Notably, we established a significant correlation between eGFR and KYNA in SSc patients. These results indicate differential KP activation in male and female SSc patients, with males demonstrating heightened KP activation. While ACE inhibitors may influence the KP in SSc patients, further research is necessary to comprehensively understand their impact on symptoms and prognosis in the context of these KP alterations.

The Probiotic Lactobacillus reuteri Preferentially Synthesizes Kynurenic Acid from Kynurenine

The gut-brain axis is increasingly understood to play a role in neuropsychiatric disorders. The probiotic bacterium Lactobacillus (L.) reuteri and products of tryptophan degradation, specifically the neuroactive kynurenine pathway (KP) metabolite kynurenic acid (KYNA), have received special attention in this context. We, therefore, assessed relevant features of KP metabolism, namely, the cellular uptake of the pivotal metabolite kynurenine and its conversion to its primary products KYNA, 3-hydroxykynurenine and anthranilic acid in L. reuteri by incubating the bacteria in Hank's Balanced Salt solution in vitro. Kynurenine readily entered the bacterial cells and was preferentially converted to KYNA, which was promptly released into the extracellular milieu. De novo production of KYNA increased linearly with increasing concentrations of kynurenine (up to 1 mM) and bacteria (107 to 109 CFU/mL) and with incubation time (1-3 h). KYNA neosynthesis was blocked by two selective inhibitors of mammalian kynurenine aminotransferase II (PF-048559989 and BFF-122). In contrast to mammals, however, kynurenine uptake was not influenced by other substrates of the mammalian large neutral amino acid transporter, and KYNA production was not affected by the presumed competitive enzyme substrates (glutamine and α-aminoadipate). Taken together, these results reveal substantive qualitative differences between bacterial and mammalian KP metabolism.

Tryptophan metabolism and small fibre neuropathy: a correlation study

Small nerve fibres located in the epidermis sense pain. Dysfunction of these fibres decreases the pain threshold known as small fibre neuropathy. Diabetes mellitus is accompanied by metabolic changes other than glucose, synergistically eliciting small fibre neuropathy. These findings suggest that various metabolic changes may be involved in small fibre neuropathy. Herein, we explored the correlation between pain sensation and changes in plasma metabolites in healthy Japanese subjects. The pain threshold evaluated from the intraepidermal electrical stimulation was used to quantify pain sensation in a total of 1021 individuals in the 2017 Iwaki Health Promotion Project. Participants with a pain threshold evaluated from the intraepidermal electrical stimulation index <0.20 mA were categorized into the pain threshold evaluated from the intraepidermal electrical stimulation index-low group (n = 751); otherwise, they were categorized into the pain threshold evaluated from the intraepidermal electrical stimulation index-high group (n = 270). Metabolome analysis of plasma was conducted using capillary electrophoresis time-of-flight mass spectrometry. The metabolite set enrichment analysis revealed that the metabolism of tryptophan was significantly correlated with the pain threshold evaluated from the intraepidermal electrical stimulation index in all participants (P < 0.05). The normalized level of tryptophan was significantly decreased in participants with a high pain threshold evaluated from the intraepidermal electrical stimulation index. In addition to univariate linear regression analyses, the correlation between tryptophan concentration and the pain threshold evaluated from the intraepidermal electrical stimulation index remained significant after adjustment for multiple factors (β = -0.07615, P < 0.05). These findings indicate that specific metabolic changes are involved in the deterioration of pain thresholds. Here, we show that abnormal tryptophan metabolism is significantly correlated with an elevated pain threshold evaluated from the intraepidermal electrical stimulation index in the Japanese population. This correlation provides insight into the pathology and clinical application of small fibre neuropathy.

Novel Activity of Oral Hypoglycemic Agents Linked with Decreased Formation of Tryptophan Metabolite, Kynurenic Acid

Kynurenic acid is a tryptophan (Trp) metabolite formed along the kynurenine (KYN) pathway in the brain and in peripheral tissues. The disturbed formation of kynurenic acid, which targets glutamate-mediated neurotransmission, GPR35, and aryl hydrocarbon receptors of immune or redox status, was implicated in the development of neuropsychiatric and metabolic disorders among others. Kynurenic acid exerts neuroprotective and immunomodulatory effects, yet its high brain levels may negatively impact cognition. Changes in the Trp-KYN pathway are also linked with the pathogenesis of diabetes mellitus, which is an established risk factor for cardiovascular and neurological diseases or cognitive deficits. Here, the effects of metformin and glibenclamide on the brain synthesis of kynurenic acid were evaluated. Acute exposure of rat cortical slices in vitro to either of the drugs reduced kynurenic acid production de novo. Glibenclamide, but not metformin, inhibited the activity of kynurenic acid biosynthetic enzymes, kynurenine aminotransferases (KATs) I and II, in semi-purified cortical homogenates. The reduced availability of kynurenic acid may be regarded as an unwanted effect, possibly alleviating the neuroprotective action of oral hypoglycemic agents. On the other hand, considering that both compounds ameliorate the cognitive deficits in animal and human studies and that high brain kynurenic acid may hamper learning and memory, its diminished synthesis may improve cognition.

rTMS reduces spatial learning and memory deficits induced by sleep deprivation possibly via suppressing the expression of kynurenine 3-monooxygenase in rats

INTRODUCTION

Impairment of learning and memory caused by sleep deprivation is a common symptom that significantly affects quality of life. Repetitive transcranial magnetic stimulation (rTMS) is a promising approach to exert a positive effect on cognitive impairment. However, there is less known about the mechanism of rTMS for learning and memory induced by chronic REM sleep deprivation (CRSD). This study was to detect the effects of rTMS on spatial learning and memory deficits by CRSD and explore possible mechanism.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into four groups: wide platform (Control), sleep deprivation (SD), sleep deprivation + rTMS (TMS), and sleep deprivation + sham rTMS (Sham-TMS). Morris water maze (MWM) and open field test (OFT) assessed spatial learning and memory and anxiety of rats with pre/post-intervention. Golgi staining and transmission electron microscope (TEM) were used to observe structural variations of synapses in the hippocampus. The alteration in gene expression of different groups was analyzed by RNA-sequencing (RNA-Seq), and the key gene was screened and identified by quantitative polymerase chain reaction (qPCR) and subsequently verified with western blotting and immunofluorescence.

RESULTS

The behavioral test showed spatial learning and memory decreased and anxiety increased in the SD group compared to the Control and TMS groups. Moreover, rTMS improved spine density, ultrastructural damage, and quantities of synapses. In accordance with RNA-Seq, 56 differentially expressed genes (DEGs) were identified by comparing alternations in four groups and concentrated on kynurenine 3-monooxygenase (KMO). The expression of KMO increased significantly in rats of the SD group compared to the Control and TMS groups identified by qPCR, western blotting, and immunofluorescence.

CONCLUSION

1 Hz rTMS alleviated spatial learning and memory deficits induced by CRSD probably via down-regulating the expression of KMO and improving the structure and quantity of synapses in the hippocampus of rats.

Plasma Tryptophan-Kynurenine Pathway Metabolites and Risk for Progression to End-Stage Kidney Disease in Patients With Type 2 Diabetes

OBJECTIVE

We sought to study the associations between plasma metabolites in the tryptophan-kynurenine pathway and the risk of progression to end-stage kidney disease (ESKD) in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Plasma tryptophan, kynurenine, 3-hydroxykynurenine, kynurenic acid, and xanthurenic acid concentrations were measured in discovery (n = 1,915) and replication (n = 346) cohorts. External validation was performed in Chronic Renal Insufficiency Cohort (CRIC) participants with diabetes (n = 1,312). The primary outcome was a composite of incident ESKD (progression to estimated glomerular filtration rate [eGFR] <15 mL/min/1.73 m2, sustained dialysis, or renal death). The secondary outcome was annual eGFR decline.

RESULTS

In the discovery cohort, tryptophan was inversely associated with risk for ESKD, and kynurenine-to-tryptophan ratio (KTR) was positively associated with risk for ESKD after adjustment for clinical risk factors, including baseline eGFR and albuminuria (adjusted hazard ratios [HRs] 0.62 [95% CI 0.51, 0.75] and 1.48 [1.20, 1.84] per 1 SD). High levels of kynurenic acid and xanthurenic acid were associated with low risks of ESKD (0.74 [0.60, 0.91] and 0.74 [0.60, 0.91]). Consistently, high levels of tryptophan, kynurenic acid, and xanthurenic acid were independently associated with a slower eGFR decline, while a high KTR was predictive of a faster eGFR decline. Similar outcomes were obtained in the replication cohort. Furthermore, the inverse association between kynurenic acid and risk of ESKD was externally validated in CRIC participants with diabetes (adjusted HR 0.78 [0.65, 0.93]).

CONCLUSIONS

Accelerated catabolism of tryptophan in the kynurenine pathway may be involved in progressive loss of kidney function. However, shunting the kynurenine pathway toward the kynurenic acid branch may potentially slow renal progression.

Effect of Quinolinic Acid on Behavior, Morphology, and Expression of Inflammatory/oxidative Status in Rats' Striatum: Is Coenzyme Q10 a Good Protector?

Quinolinic acid (QUIN) is a toxic compound with pro-oxidant, pro-inflammatory, and pro-apoptotic actions found at high levels in the central nervous system (CNS) in several pathological conditions. Due to the toxicity of QUIN, it is important to evaluate strategies to protect against the damage caused by this metabolite in the brain. In this context, coenzyme Q10 (CoQ10) is a provitamin present in the mitochondria with a protective role in cells through several mechanisms of action. Based on these, the present study was aimed at evaluating the possible neuroprotective role of CoQ10 against damage caused by QUIN in the striatum of young Wistar rats. Twenty-one-day-old rats underwent a 10-day pretreatment with CoQ10 or saline (control) intraperitoneal injections and on the 30th day of life received QUIN intrastriatal or saline (control) administration. The animals were submitted to behavior tests or euthanized, and the striatum was dissected to neurochemical studies. Results showed that CoQ10 was able to prevent behavioral changes (the open field, object recognition, and pole test tasks) and neurochemical parameters (alteration in the gene expression of IL-1β, IL-6, SOD, and GPx, as well as in the immunocontent of cytoplasmic Nrf2 and nuclear p-Nf-κβ) caused by QUIN. These findings demonstrate the promising therapeutic effects of CoQ10 against QUIN toxicity.

Quantitative LC-MS study of compounds found predictive of COVID-19 severity and outcome

INTRODUCTION

Since the beginning of the SARS-CoV-2 pandemic in December 2019 multiple metabolomics studies have proposed predictive biomarkers of infection severity and outcome. Whilst some trends have emerged, the findings remain intangible and uninformative when it comes to new patients.

OBJECTIVES

In this study, we accurately quantitate a subset of compounds in patient serum that were found predictive of severity and outcome.

METHODS

A targeted LC-MS method was used in 46 control and 95 acute COVID-19 patient samples to quantitate the selected metabolites. These compounds included tryptophan and its degradation products kynurenine and kynurenic acid (reflective of immune response), butyrylcarnitine and its isomer (reflective of energy metabolism) and finally 3',4'-didehydro-3'-deoxycytidine, a deoxycytidine analogue, (reflective of host viral defence response). We subsequently examine changes in those markers by disease severity and outcome relative to those of control patients' levels.

RESULTS & CONCLUSION

Finally, we demonstrate the added value of the kynurenic acid/tryptophan ratio for severity and outcome prediction and highlight the viral detection potential of ddhC.

Crosstalk between Exercise-Derived Endocannabinoidome and Kynurenines: Potential Target Therapies for Obesity and Depression Symptoms

The kynurenine pathway (KP) and the endocannabinoid system (ECS) are known to be deregulated in depression and obesity; however, it has been recognized that acute physical exercise has an important modulating role inducing changes in the mobilization of their respective metabolites-endocannabinoids (eCBs) and kynurenines (KYNs)-which overlap at some points, acting as important antidepressant, anti-nociceptive, anti-inflammatory, and antioxidant biomarkers. Therefore, the aim of this review is to analyze and discuss some recently performed studies to investigate the potential interactions between both systems, particularly those related to exercise-derived endocannabinoidome and kynurenine mechanisms, and to elucidate how prescription of physical exercise could represent a new approach for the clinical management of these two conditions.

Kynurenine pathway dynamics in patients with schizophrenia spectrum disorders across the disease trajectory

The aim of this study was to evaluate how schizophrenia spectrum disorders (SSD) and applied long-term (5.1 years) antipsychotic (AP) treatment affect the serum levels of tryptophan (Trp) metabolites. A total of 112 adults (54 first-episode psychosis [FEP] patients and 58 control subjects [CSs]) participated in the study. The investigated changes in the metabolite levels appeared against a background of persistent increase in BMI and waist circumference among the patients. Regarding the kynurenine (KYN) pathway, the strongest changes were seen in AP-naïve FEP patients. Trp, KYN, kynurenic acid (KYNA), and anthranilic acid (ANT) levels were significantly reduced in blood samples from patients in the early stage of the disease. Furthermore, 3-OH-kynurenine (3-HK) and quinolinic acid (QUIN) levels were somewhat lower in these patients. Most of these changes in the KYN pathway became weaker with AP treatment. The levels of serotonin and its metabolite 5-HIAA tended to be higher at 5.1 years in patients showing the relation of elevated serotonin turnover to increased BMI and waist circumference. The similar trend was evident for the ratio between xanthurenic acid (XA) and KYNA with strong link to the elevated BMI. Altogether, the present study supports the role of Trp-metabolites in the development of obesity and metabolic syndrome in SSD patients.

Kynurenic Acid: A Novel Player in Cardioprotection against Myocardial Ischemia/Reperfusion Injuries

BACKGROUND

Myocardial infarction is one of the leading causes of mortality worldwide; hence, there is an urgent need to discover novel cardioprotective strategies. Kynurenic acid (KYNA), a metabolite of the kynurenine pathway, has been previously reported to have cardioprotective effects. However, the mechanisms by which KYNA may be protective are still unclear. The current study addressed this issue by investigating KYNA's cardioprotective effect in the context of myocardial ischemia/reperfusion.

METHODS

H9C2 cells and rats were exposed to hypoxia/reoxygenation or myocardial infarction, respectively, in the presence or absence of KYNA. In vitro, cell death was quantified using flow cytometry analysis of propidium iodide staining. In vivo, TTC-Evans Blue staining was performed to evaluate infarct size. Mitochondrial respiratory chain complex activities were measured using spectrophotometry. Protein expression was evaluated by Western blot, and mRNA levels by RT-qPCR.

RESULTS

KYNA treatment significantly reduced H9C2-relative cell death as well as infarct size. KYNA did not exhibit any effect on the mitochondrial respiratory chain complex activity. SOD2 mRNA levels were increased by KYNA. A decrease in p62 protein levels together with a trend of increase in PARK2 may mark a stimulation of mitophagy. Additionally, ERK1/2, Akt, and FOXO3α phosphorylation levels were significantly reduced after the KYNA treatment. Altogether, KYNA significantly reduced myocardial ischemia/reperfusion injuries in both in vitro and in vivo models.

CONCLUSION

Here we show that KYNA-mediated cardioprotection was associated with enhanced mitophagy and antioxidant defense. A deeper understanding of KYNA's cardioprotective mechanisms is necessary to identify promising novel therapeutic targets and their translation into the clinical arena.

Effect of Yarrowia lipolytica yeast biomass with increased kynurenic acid content on selected metabolic indicators in mice

Background

The unconventional yeast species Yarrowia lipolytica is a valuable source of protein and many other nutrients. It can be used to produce hydrolytic enzymes and metabolites, including kynurenic acid (KYNA), an endogenous metabolite of tryptophan with a multidirectional effect on the body. The administration of Y. lipolytica with an increased content of KYNA in the diet may have a beneficial effect on metabolism, which was evaluated in a nutritional experiment on mice.

Methods

In the dry biomass of Y. lipolytica S12 enriched in KYNA (high-KYNA yeast) and low-KYNA (control) yeast, the content of KYNA was determined by high-performance liquid chromatography. Then, proximate and amino acid composition and selected indicators of antioxidant status were compared. The effect of 5% high-KYNA yeast content in the diet on the growth, hematological and biochemical indices of blood and the redox status of the liver was determined in a 7-week experiment on adult male mice from an outbred colony derived from A/St, BALB/c, BN/a and C57BL/6J inbred strains.

Results

High-KYNA yeast was characterized by a greater concentration of KYNA than low-KYNA yeast (0.80 ± 0.08 vs. 0.29 ± 0.01 g/kg dry matter), lower content of crude protein with a less favorable amino acid composition and minerals, higher level of crude fiber and fat and lower ferric-reducing antioxidant power, concentration of phenols and glutathione. Consumption of the high-KYNA yeast diet did not affect the cumulative body weight gain per cage, cumulative food intake per cage and protein efficiency ratio compared to the control diet. A trend towards lower mean corpuscular volume and hematocrit, higher mean corpuscular hemoglobin concentration and lower serum total protein and globulins was observed, increased serum total cholesterol and urea were noted. Its ingestion resulted in a trend towards greater ferric-reducing antioxidant power in the liver and did not affect the degree of liver lipid and protein oxidation.

Conclusions

The improvement of the quality of Y. lipolytica yeast biomass with increased content of KYNA, including its antioxidant potential, would be affected by the preserved level of protein and unchanged amino acid profile. It will be worth investigating the effect of such optimized yeast on model animals, including animals with metabolic diseases.

Differential Effects of Hypothermia and SZR72 on Cerebral Kynurenine and Kynurenic Acid in a Piglet Model of Hypoxic-Ischemic Encephalopathy

Kynurenic acid (KYNA), an endogenous neuroprotectant with antiexcitotoxic, antioxidant, and anti-inflammatory effects, is synthesized through the tryptophan-kynurenine (KYN) pathway. We investigated whether brain KYN or KYNA levels were affected by asphyxia in a translational piglet model of hypoxic-ischemic encephalopathy (HIE). We also studied brain levels of the putative blood-brain barrier (BBB) permeable neuroprotective KYNA analogue SZR72, and whether SZR72 or therapeutic hypothermia (TH) modified KYN or KYNA levels. KYN, KYNA, and SZR72 levels were determined using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry in five brain regions 24 h after 20 min of asphyxia in vehicle-, SZR72- and TH-treated newborn piglets (n = 6-6-6) and naive controls (n = 4). Endogenous brain KYN levels (median range 311.2-965.6 pmol/g) exceeded KYNA concentrations (4.5-6.0 pmol/g) ~100-fold. Asphyxia significantly increased cerebral KYN and KYNA levels in all regions (1512.0-3273.9 and 16.9-21.2 pmol/g, respectively), increasing the KYN/Tryptophan-, but retaining the KYNA/KYN ratio. SZR72 treatment resulted in very high cerebral SZR72 levels (13.2-33.2 nmol/g); however, KYN and KYNA levels remained similar to those of the vehicle-treated animals. However, TH virtually ameliorated asphyxia-induced elevations in brain KYN and KYNA levels. The present study reports for the first time that the KYN pathway is altered during HIE development in the piglet. SZR72 readily crosses the BBB in piglets but fails to affect cerebral KYNA levels. Beneficial effects of TH may include restoration of the tryptophan metabolism to pre-asphyxia levels.

The Role of the Kynurenine/AhR Pathway in Diseases Related to Metabolism and Cancer

The Aryl hydrocarbon receptor (AhR) is a xenobiotic and endobiotic receptor, which regulates many cellular processes from contaminant metabolism to immunomodulation. Consequently, it is also involved in pathophysiological pathways and now represents a potential therapeutical target. In this review, we will highlight the ancestral function of the protein together with an illustration of its ligand's battery, emphasizing the different responses triggered by these high diverse molecules. Among them, several members of the kynurenine pathway (one key process of tryptophan catabolism) are AhR agonists and are subsequently involved in regulatory functions. We will finally display the interplay between Tryptophan (Trp) catabolism and dysregulation in metabolic pathways drawing hypothesis on the involvement of the AhR pathway in these cancer-related processes.

Kynurenic acid, a key L-tryptophan-derived metabolite, protects the heart from an ischemic damage

BACKGROUND

Renal injury induces major changes in plasma and cardiac metabolites. Using a small- animal in vivo model, we sought to identify a key metabolite whose levels are significantly modified following an acute kidney injury (AKI) and to analyze whether this agent could offer cardiac protection once an ischemic event has occurred.

METHODS AND RESULTS

Metabolomics profiling of cardiac lysates and plasma samples derived from rats that underwent AKI 1 or 7 days earlier by 5/6 nephrectomy versus sham-operated controls was performed. We detected 26 differential metabolites in both heart and plasma samples at the two selected time points, relative to sham. Out of which, kynurenic acid (kynurenate, KYNA) seemed most relevant. Interestingly, KYNA given at 10 mM concentration significantly rescued the viability of H9C2 cardiac myoblast cells grown under anoxic conditions and largely increased their mitochondrial content and activity as determined by flow cytometry and cell staining with MitoTracker dyes. Moreover, KYNA diluted in the drinking water of animals induced with an acute myocardial infarction, highly enhanced their cardiac recovery according to echocardiography and histopathology.

CONCLUSION

KYNA may represent a key metabolite absorbed by the heart following AKI as part of a compensatory mechanism aiming at preserving the cardiac function. KYNA preserves the in vitro myocyte viability following exposure to anoxia in a mechanism that is mediated, at least in part, by protection of the cardiac mitochondria. A short-term administration of KYNA may be highly beneficial in the treatment of the acute phase of kidney disease in order to attenuate progression to reno-cardiac syndrom and to reduce the ischemic myocardial damage following an ischemic event.

Optimizing human performance in extreme environments through precision medicine: From spaceflight to high-performance operations on Earth

Humans operating in extreme environments often conduct their operations at the edges of the limits of human performance. Sometimes, they are required to push these limits to previously unattained levels. As a result, their margins for error in execution are much smaller than that found in the general public. These same small margins for error that impact execution may also impact risk, safety, health, and even survival. Thus, humans operating in extreme environments have a need for greater refinement in their preparation, training, fitness, and medical care. Precision medicine (PM) is uniquely suited to address the needs of those engaged in these extreme operations because of its depth of molecular analysis, derived precision countermeasures, and ability to match each individual (and his or her specific molecular phenotype) with any given operating context (environment). Herein, we present an overview of a systems approach to PM in extreme environments, which affords clinicians one method to contextualize the inputs, processes, and outputs that can form the basis of a formal practice. For the sake of brevity, this overview is focused on molecular dynamics, while providing only a brief introduction to the also important physiologic and behavioral phenotypes in PM. Moreover, rather than a full review, it highlights important concepts, while using only selected citations to illustrate those concepts. It further explores, by demonstration, the basic principles of using functionally characterized molecular networks to guide the practical application of PM in extreme environments. At its core, PM in extreme environments is about attention to incremental gains and losses in molecular network efficiency that can scale to produce notable changes in health and performance. The aim of this overview is to provide a conceptual overview of one approach to PM in extreme environments, coupled with a selected suite of practical considerations for molecular profiling and countermeasures.

Untargeted metabonomic analysis of non-alcoholic fatty liver disease with iron overload in rats via UPLC/MS

BACKGROUND/AIMS

In recent years, many metabolites specific to nonalcoholic fatty liver disease (NAFLD) have been identified thanks to the application of metabolomics techniques. This study aimed to investigate the candidate targets and potential molecular pathways involved in NAFLD in the presence of iron overload.

METHODS

Male Sprague Dawley rats were fed with control or high-fat diet with or without excess iron. After 8,16,20 weeks of treatment, urine samples of rats were collected for metabolomics analysis using ultra-performance liquid chromatography/mass spectrometry (UPLC-MS). Blood and liver samples were also collected.

RESULTS

High-fat, high-iron diet resulted in increased triglyceride accumulation and increased oxidative damage. A total of 13 metabolites and four potential pathways were identified. Compared to the control group, the intensities of adenine, cAMP, hippuric acid, kynurenic acid, xanthurenic acid, uric acid, and citric acid were significantly lower (P < 0.05) and the concentration of other metabolites was significantly higher in the high-fat diet group. In the high-fat, high-iron group, the differences in the intensities of the above metabolites were amplified.

CONCLUSION

Our findings suggest that NAFLD rats have impaired antioxidant system and liver function, lipid disorders, abnormal energy, and glucose metabolism, and that iron overload may further exacerbate these disorders.

Lysophosphatidic acid modulates CD8 T cell immunosurveillance and metabolism to impair anti-tumor immunity

Lysophosphatidic acid (LPA) is a bioactive lipid which increases in concentration locally and systemically across different cancer types. Yet, the exact mechanism(s) of how LPA affects CD8 T cell immunosurveillance during tumor progression remain unknown. We show LPA receptor (LPAR) signaling by CD8 T cells promotes tolerogenic states via metabolic reprogramming and potentiating exhaustive-like differentiation to modulate anti-tumor immunity. We found LPA levels predict response to immunotherapy and Lpar5 signaling promotes cellular states associated with exhausted phenotypes on CD8 T cells. Importantly, we show that Lpar5 regulates CD8 T cell respiration, proton leak, and reactive oxygen species. Together, our findings reveal that LPA serves as a lipid-regulated immune checkpoint by modulating metabolic efficiency through LPAR5 signaling on CD8 T cells. Our study offers key insights into the mechanisms governing adaptive anti-tumor immunity and demonstrates LPA could be exploited as a T cell directed therapy to improve dysfunctional anti-tumor immunity.

Markers of arterial stiffness and urinary metabolomics in young adults with early cardiovascular risk: the African-PREDICT study

INTRODUCTION

Increased exposure to risk factors in the young and healthy contributes to arterial changes, which may be accompanied by an altered metabolism.

OBJECTIVES

To increase our understanding of early metabolic alterations and how they associate with markers of arterial stiffness, we profiled urinary metabolites in young adults with cardiovascular disease (CVD) risk factor(s) and in a control group without CVD risk factors.

METHODS

We included healthy black and white women and men (N = 1202), aged 20-30 years with a detailed CVD risk factor profile, reflecting obesity, physical inactivity, smoking, excessive alcohol intake, masked hypertension, hyperglycemia, dyslipidemia and low socio-economic status, forming the CVD risk group (N = 1036) and the control group (N = 166). Markers of arterial stiffness, central systolic blood pressure (BP) and pulse wave velocity were measured. A targeted metabolomics approach was followed by measuring amino acids and acylcarnitines using a liquid chromatography-tandem mass spectrometry method.

RESULTS

In the CVD risk group, central systolic BP (adjusted for age, sex, ethnicity) was negatively associated with histidine, arginine, asparagine, serine, glutamine, dimethylglycine, threonine, GABA, proline, methionine, pyroglutamic acid, aspartic acid, glutamic acid, branched chain amino acids (BCAAs) and butyrylcarnitine (all P ≤ 0.048). In the same group, pulse wave velocity (adjusted for age, sex, ethnicity, mean arterial pressure) was negatively associated with histidine, lysine, threonine, 2-aminoadipic acid, BCAAs and aromatic amino acids (AAAs) (all P ≤ 0.044). In the control group, central systolic BP was negatively associated with pyroglutamic acid, glutamic acid and dodecanoylcarnitine (all P ≤ 0.033).

CONCLUSION

In a group with increased CVD risk, markers of arterial stiffness were negatively associated with metabolites related to AAA and BCAA as well as energy metabolism and oxidative stress. Our findings may suggest that metabolic adaptations may be at play in response to increased CVD risk to maintain cardiovascular integrity.

Therapeutic potential of targeting kynurenine pathway in neurodegenerative diseases

Kynurenine pathway (KP), the primary pathway of L-tryptophan (Trp) metabolism in mammals, contains several neuroactive metabolites such as kynurenic acid (KA) and quinolinic acid (QA). Its imbalance involved in aging and neurodegenerative diseases (NDs) has attracted much interest in therapeutically targeting KP enzymes and KP metabolite-associated receptors, especially kynurenine monooxygenase (KMO). Currently, many agents have been discovered with significant improvement in animal models but only one aryl hydrocarbon receptor (AHR) agonist 30 (laquinimod) has entered clinical trials for treating Huntington's disease (HD). In this review, we describe neuroactive KP metabolites, discuss the dysregulation of KP in aging and NDs and summarize the development of KP regulators in preclinical and clinical studies, offering an outlook of targeting KP for NDs treatment in future.

Modulating the Kynurenine pathway or sequestering toxic 3-hydroxykynurenine protects the retina from light-induced damage in Drosophila

Tissue health is regulated by a myriad of exogenous or endogenous factors. Here we investigated the role of the conserved Kynurenine pathway (KP) in maintaining retinal homeostasis in the context of light stress in Drosophila melanogaster. cinnabar, cardinal and scarlet are fly genes that encode different steps in the KP. Along with white, these genes are known regulators of brown pigment (ommochrome) biosynthesis. Using white as a sensitized genetic background, we show that mutations in cinnabar, cardinal and scarlet differentially modulate light-induced retinal damage. Mass Spectrometric measurements of KP metabolites in flies with different genetic combinations support the notion that increased levels of 3-hydroxykynurenine (3OH-K) and Xanthurenic acid (XA) enhance retinal damage, whereas Kynurenic Acid (KYNA) and Kynurenine (K) are neuro-protective. This conclusion was corroborated by showing that feeding 3OH-K results in enhanced retinal damage, whereas feeding KYNA protects the retina in sensitized genetic backgrounds. Interestingly, the harmful effects of free 3OH-K are diminished by its sub-cellular compartmentalization. Sequestering of 3OH-K enables the quenching of its toxicity through conversion to brown pigment or conjugation to proteins. This work enabled us to decouple the role of these KP genes in ommochrome formation from their role in retinal homeostasis. Additionally, it puts forward new hypotheses on the importance of the balance of KP metabolites and their compartmentalization in disease alleviation.

Dysregulation of tryptophan metabolism and distortion of cell signaling after oral exposure to ethanol and Kynurenic acid

Kynurenic acid (KYNA), an unavoidable tryptophan metabolite during fermentation is naturally blended with alcohol in all alcoholic beverages. Thus, alcohol drinking inevitably results in co-intake of KYNA. Effects of alcohol or KYNA on human health have been widely studied. However, the combined effects of both remain unknown. Here we report that alcohol and KYNA have a synergistic impact of on global gene expression, especially the gene sets related to tryptophan metabolism and cell signaling. Adult mice were exposed to alcohol (ethanol) and/or KYNA daily for a week. Transcriptomes of the brain, kidney and liver were profiled via bulk RNA sequencing. Results indicate that while KYNA alone largely promotes, and alcohol alone mostly inhibits gene expression, alcohol and KYNA co-administration has a stronger inhibition of global gene expression. Tryptophan metabolism is severely skewed towards kynurenine pathway by decreasing tryptophan hydroxylase 2 and increasing tryptophan dioxygenase. Quantification of tryptophan metabolic enzymes corroborates the transcriptional changes of these enzymes. Furthermore, the co-administration greatly enhances the GnRH signaling pathway. This research provides critical data to better understand the effects of alcohol and KYNA in mix on human health.

Kynurenine Pathway in Diabetes Mellitus-Novel Pharmacological Target?

The tryptophan-kynurenine pathway (Trp-KYN) is the major route for tryptophan conversion in the brain and in the periphery. Kynurenines display a wide range of biological actions (which are often contrasting) such as cytotoxic/cytoprotective, oxidant/antioxidant or pro-/anti-inflammatory. The net effect depends on their local concentration, cellular environment, as well as a complex positive and negative feedback loops. The imbalance between beneficial and harmful kynurenines was implicated in the pathogenesis of various neurodegenerative disorders, psychiatric illnesses and metabolic disorders, including diabetes mellitus (DM). Despite available therapies, DM may lead to serious macro- and microvascular complications including cardio- and cerebrovascular disease, peripheral vascular disease, chronic renal disease, diabetic retinopathy, autonomic neuropathy or cognitive impairment. It is well established that low-grade inflammation, which often coincides with DM, can affect the function of KP and, conversely, that kynurenines may modulate the immune response. This review provides a detailed summary of findings concerning the status of the Trp-KYN pathway in DM based on available animal, human and microbiome studies. We highlight the importance of the molecular interplay between the deranged (functionally and qualitatively) conversion of Trp to kynurenines in the development of DM and insulin resistance. The Trp-KYN pathway emerges as a novel target in the search for preventive and therapeutic interventions in DM.

The Role of Inflammation in the Pathophysiology of Depression and Suicidal Behavior: Implications for Treatment

Depression and suicidal behavior are 2 complex psychiatric conditions of significant public health concerns due to their debilitating nature. The need to enhance contemporary treatments and preventative approaches for these illnesses not only calls for distillation of current views on their pathogenesis but also provides an impetus for further elucidation of their novel etiological determinants. In this regard, inflammation has recently been recognized as a potentially important contributor to the development of depression and suicidal behavior. This review highlights key evidence that supports the presence of dysregulated neurometabolic and immunologic signaling and abnormal interaction with microbial species as putative etiological hallmarks of inflammation in depression as well as their contribution to the development of suicidal behavior. Furthermore, therapeutic insights addressing candidate mechanisms of pathological inflammation in these disorders are proposed.

PTSD, Immune System, and Inflammation

Posttraumatic stress disorder (PTSD) is a severe trauma and stress-related disorder associated with different somatic comorbidities, especially cardiovascular and metabolic disorders, and with chronic low-grade inflammation. Altered balance of the hypothalamic-pituitary-adrenal (HPA) axis, cytokines and chemokines, C-reactive protein, oxidative stress markers, kynurenine pathways, and gut microbiota might be involved in the alterations of certain brain regions regulating fear conditioning and memory processes, that are all altered in PTSD. In addition to the HPA axis, the gut microbiota maintains the balance and interaction of the immune, CNS, and endocrine pathways forming the gut-brain axis. Disbalance in the HPA axis, gut-brain axis, oxidative stress pathways and kynurenine pathways, altered immune signaling and disrupted homeostasis, as well as the association of the PTSD with the inflammation and disrupted cognition support the search for novel strategies for treatment of PTSD. Besides potential anti-inflammatory treatment, dietary interventions or the use of beneficial bacteria, such as probiotics, can potentially improve the composition and the function of the bacterial community in the gut. Therefore, bacterial supplements and controlled dietary changes, with exercise, might have beneficial effects on the psychological and cognitive functions in patients with PTSD. These new treatments should be aimed to attenuate inflammatory processes and consequently to reduce PTSD symptoms but also to improve cognition and reduce cardio-metabolic disorders associated so frequently with PTSD.

Attenuation of hexaconazole induced oxidative stress by folic acid, malic acid and ferrocenecarboxaldehyde in an invertebrate model Bombyx mori

Fungicides are a class of pesticides used to ward off fungal diseases from agricultural crops to achieve maximum productivity. These chemicals are quite efficient in controlling diseases; however, the excessive use of these affects non-target organisms as well. In this study, Bombyx mori was utilized to investigate the effect of the pesticide hexaconazole (HEX) on the antioxidant system of this organism and also to find ways to mitigate it. On oral exposure to this chemical, a significant reduction in antioxidants, CAT, GPX, GSH, and SOD in the gut, fat body, and silk gland was observed. The HEX treatment also resulted in lipid peroxidation (LPO) in all the three tissues. To mitigate this toxicity and protect the silkworm from oxidative stress, we tested three compounds, namely folic acid, ferrocenecarboxaldehyde, and malic acid having known antioxidant potential. Folic acid provided significant protection against HEX-induced toxicity. Ferrocenecarboxaldehyde and malic acid proved to be ill-efficient in controlling oxidative stress, with ferrocenecarboxaldehyde being the least effective of the three. Folic acid was also efficient in controlling LPO up to a considerable level. Ferrocenecarboxaldehyde and malic acid also prevented LPO less efficiently than folic acid. Overall folic acid was the only compound that mitigated HEX-induced oxidative stress in silkworm with statistical significance in all the tissues viz. gut, fat body, and silk gland.

Central Stimulatory Effect of Kynurenic Acid on BDNF-TrkB Signaling and BER Enzymatic Activity in the Hippocampal CA1 Field in Sheep

Deficiency of neurotrophic factors and oxidative DNA damage are common causes of many neurodegenerative diseases. Recently, the importance of kynurenic acid (KYNA), an active metabolite of tryptophan, has increased as a neuroprotective molecule in the brain. Therefore, the present study tested the hypothesis that centrally acting KYNA would positively affect: (1) brain-derived neurotrophic factor (BDNF)-tyrosine receptor kinase B (TrkB) signaling and (2) selected base excision repair (BER) pathway enzymes activities in the hippocampal CA1 field in sheep. Both lower (20 μg in total) and higher (100 μg in total) doses of KYNA infused into the third brain ventricle differentially increased the abundance of BDNF and TrkB mRNA in the CA1 field; additionally, the higher dose increased BDNF tissue concentration. The lower dose of KYNA increased mRNA expression for 8-oxoguanine glycosylase (OGG1), N-methylpurine DNA glycosylase (MPG), and thymine DNA glycosylase and stimulated the repair of 1,N6-ethenodeoxyadenosine and 3,N4-ethenodeoxy-cytosine as determined by the excision efficiency of lesioned nucleobases. The higher dose increased the abundance of OGG1 and MPG transcripts, however, its stimulatory effect on repair activity was less pronounced in all cases compared to the lower dose. The increased level of AP-endonuclease mRNA expression was dose-dependent. In conclusion, the potential neurotrophic and neuroprotective effects of KYNA in brain cells may involve stimulation of the BDNF-TrkB and BER pathways.

Temporal Profile of Kynurenine Pathway Metabolites in a Rodent Model of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is an early onset genetic disorder characterized by numerous renal cysts resulting in end stage renal disease. Our study aimed to determine if metabolic reprogramming and tryptophan (Trp) metabolism via the kynurenine pathway (KP) is a critical dysregulated pathway in PKD. Using the Lewis polycystic kidney (LPK) rat model of PKD and Lewis controls, we profiled temporal trends for KP metabolites in plasma, urine, and kidney tissues from 6- and 12-week-old mixed sex animals using liquid and gas chromatography, minimum n = 5 per cohort. A greater kynurenine (KYN) concentration was observed in LPK kidney and plasma of 12-week rats compared to age matched Lewis controls (P ⩽ .05). LPK kidneys also showed an age effect (P ⩽ .05) with KYN being greater in 12-week versus 6-week LPK. The metabolites xanthurenic acid (XA), 3-hydroxykynurenine (3-HK), and 3-hydroxyanthranilic acid (3-HAA) were significantly greater in the plasma of 12-week LPK rats compared to age matched Lewis controls (P ⩽ .05). Plasma XA and 3-HK also showed an age effect (P ⩽ .05) being greater in 12-week versus 6-week LPK. We further describe a decrease in Trp levels in LPK plasma and kidney (strain effect P ⩽ .05). There were no differences in KP metabolites in urine between cohorts. Using the ratio of product and substrates in the KP, a significant age-strain effect (P ⩽ .05) was observed in the activity of the KYN/Trp ratio (tryptophan-2,3-dioxygenase [TDO] or indoleamine-2,3-dioxygenase [IDO] activity), kynurenine 3-monooxygenase (KMO), KAT A (kynurenine aminotransferase A), KAT B, total KAT, total KYNU (kynureninase), KYNU A, KYNU B, and total KYNU within LPK kidneys, supporting an activated KP. Confirmation of the activation of these enzymes will require verification through orthogonal techniques. In conclusion, we have demonstrated an up-regulation of the KP in alignment with progression of renal impairment in the LPK rat model, suggesting that KP activation may be a critical contributor to the pathobiology of PKD.

A multiple-metabolites model to predict preliminary renal injury induced by iodixanol based on UHPLC/Q-Orbitrap-MS and 1H-NMR

BACKGROUND & AIMS

There are some problems, such as unclear pathological mechanism, delayed diagnosis, and inaccurate therapeutic target of Contrast-induced acute kidney injury (CI-AKI). It is significantly important to find biomarkers and therapeutic targets that can indicate renal injury in the early stage of CI-AKI. This study aims to establish a multiple-metabolites model to predict preliminary renal injury induced by iodixanol and explore its pathogenesis.

METHODS

Both UHPLC/Q-Orbitrap-MS and ¹H-NMR methods were applied for urine metabolomics studies on two independent cohorts who suffered from a preliminary renal injury caused by iodixanol, and the multivariate statistical analysis and random forest (RF) algorithm were used to process the related date.

RESULTS

In the discovery cohort (n = 169), 6 metabolic markers (leucine, indole, 5-hydroxy-L-tryptophan, N-acetylvaline, hydroxyhexanoycarnine, and kynurenic acid) were obtained by the cross-validation between the RF and liquid chromatography-mass spectrometry (LC-MS). Secondly, the 6 differential metabolites were confirmed by comparison of standard substance and structural identification of ¹H-NMR. Subsequently, the multiple-metabolites model composed of the 6 biomarkers was validated in a validation cohort (n = 165).

CONCLUSIONS

The concentrations of leucine, indole, N-acetylvaline, 5-hydroxy-L-tryptophan, hydroxyhexanoycarnitine and kynurenic acid in urine were proven to be positively correlated with the degree of renal injury induced by iodixanol. The multiple-metabolites model based on these 6 biomarkers has a good predictive ability to predict early renal injury caused by iodixanol, provides treatment direction for injury intervention and a reference for reducing the incidence of clinical CI-AKI further.

Kynurenic acid ameliorates NLRP3 inflammasome activation by blocking calcium mobilization via GPR35

The inflammasome has been linked to diverse inflammatory and metabolic diseases, and tight control of inflammasome activation is necessary to avoid excessive inflammation. Kynurenic acid (KA) is a tryptophan metabolite in the kynurenine pathway. However, the roles and mechanisms of the regulation of inflammasome activation by KA have not yet been fully elucidated. Here, we found that KA suppressed caspase-1 activation and IL-1β production in macrophages by specifically inhibiting canonical and noncanonical activation of the NLRP3 inflammasome. Mechanistically, KA reduced calcium mobilization through G-protein receptor 35 (GPR35), resulting in reduced mitochondrial damage and decreased mtROS production, thus blocking NLRP3 inflammasome assembly and activation. Importantly, KA prevented lipopolysaccharide-induced systemic inflammation, monosodium urate-induced peritoneal inflammation, and high-fat diet-induced metabolic disorder. Thus, KA ameliorated inflammation and metabolic disorders by blocking calcium mobilization-mediated NLRP3 inflammasome activation via GPR35. Our data reveal a novel mechanism for KA in the modulation of inflammasome activation and suggest that GPR35 might be a promising target for improving NLRP3 inflammasome-associated diseases by regulating calcium mobilization.

Decreased cerebrospinal fluid kynurenic acid in epileptic spasms: A biomarker of response to corticosteroids

Background

Epileptic (previously infantile) spasms is the most common epileptic encephalopathy occurring during infancy and is frequently associated with abnormal neurodevelopmental outcomes. Epileptic spasms have a diverse range of known (genetic, structural) and unknown aetiologies. High dose corticosteroid treatment for 4 weeks often induces remission of spasms, although the mechanism of action of corticosteroid is unclear. Animal models of epileptic spasms have shown decreased brain kynurenic acid, which is increased after treatment with the ketogenic diet. We quantified kynurenine pathway metabolites in the cerebrospinal fluid (CSF) of infants with epileptic spasms and explored clinical correlations.

Methods

A panel of nine metabolites in the kynurenine pathway (tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, anthranilic acid, 3-hydroxyanthranilic acid, quinolinic acid, and picolinic acid) were measured using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). CSF collected from paediatric patients less than 3 years of age with epileptic spasms (n=34, 19 males, mean age 0.85, median 0.6, range 0.3–3 yrs) were compared with other epilepsy syndromes (n=26, 9 males, mean age 1.44, median 1.45, range 0.3–3 yrs), other non-inflammatory neurological diseases (OND) (n=29, 18 males, mean age 1.47, median 1.6, range 0.1–2.9 yrs) and inflammatory neurological controls (n=12, 4 males, mean age 1.80, median 1.80, range 0.8–2.5 yrs).

Findings

There was a statistically significant decrease of CSF kynurenic acid in patients with epileptic spasms compared to OND (p<0.0001). In addition, the kynurenic acid/kynurenine (KYNA/KYN) ratio was lower in the epileptic spasms subgroup compared to OND (p<0.0001). Epileptic spasms patients who were steroid responders or partial steroid responders had lower KYNA/KYN ratio compared to patients who were refractory to steroids (p<0.005, p<0.05 respectively).

Interpretation

This study demonstrates decreased CSF kynurenic acid and KYNA/KYN in epileptic spasms, which may also represent a biomarker for steroid responsiveness. Given the anti-inflammatory and neuroprotective properties of kynurenic acid, further therapeutics able to increase kynurenic acid should be explored.

Funding

Financial support for the study was granted by Dale NHMRC Investigator grant APP1193648, Petre Foundation, Cerebral Palsy Alliance and Department of Biochemistry at the Children's Hospital at Westmead. Prof Guillemin is funded by NHMRC Investigator grant APP1176660 and Macquarie University.

Melatonin ameliorates disease severity in a mouse model of multiple sclerosis by modulating the kynurenine pathway

Melatonin (MT), a neurohormone with immunomodulatory properties, is one of the metabolites produced in the brain from tryptophan (TRP) that has already strong links with the neuropathogenesis of Multiple sclerosis (MS). However, the exact molecular mechanisms behind that are not fully understood. There is some evidence showing that MS and MT are interconnected via different pathways: Relapses of MS has a direct correlation with a low level of MT secretion and a growing body of evidence suggest that MT be therapeutic in Experimental Autoimmune Encephalomyelitis (EAE, a recognise animal model of MS) severity. Previous studies have demonstrated that the kynurenine pathway (KP), the main pathway of TRP catabolism, plays a key role in the pathogenesis of MS in humans and in EAE. The present study aimed to investigate whether MT can improve clinical signs in the EAE model by modulating the KP. C57BL/6 mice were induced with EAE and received different doses of MT. Then the onset and severity of EAE clinical symptoms were recorded. Two biological factors, aryl hydrocarbon receptor (AhR) and NAD+ which closely interact in the KP were also assessed. The results indicated that MT treatment at all tested doses significantly decrease the EAE clinical scores and the number of demyelinating plaques. Furthermore, MT treatment reduced the mRNA expression of the KP regulatory enzyme indoleamine 2,3-dioxygenase 1(IDO-1) and other KP enzymes. We also found that MT treatment reduces the mRNA expression of the AhR and inhibits the enzyme Nicotinamide N-Methyltransferase (Nnmt) overexpression leading to an increase in NAD+ levels. Collectively, this study suggests that MT treatment may significantly attenuates the severity of EAE by altering the KP, AhR and NAD+ metabolism.

The role and mechanism of tryptophan - kynurenine metabolic pathway in depression

Major depressive disorder (MDD) is a common mental illness characterized by persistent low mood and anhedonia, normally accompanied with cognitive impairment. Due to its rising incidence and high rate of recurrence and disability, MDD poses a substantial threat to patients' physical and mental health, as well as a significant economic cost to society. However, the etiology and pathogenesis of MDD are still unclear. Chronic inflammation may cause indoleamine-2,3-dioxygenase (IDO) to become overactive throughout the body and brain, resulting in excess quinolinic acid (QUIN) and less kynuric acid (KYNA) in the brain. QUIN's neurotoxicity damages glial cells and neurons, accelerates neuronal apoptosis, hinders neuroplasticity, and causes depression due to inflammation. Therefore, abnormal TRP-KYN metabolic pathway and its metabolites have been closely related to MDD, suggesting changes in the TRP-KYN metabolic pathway might contribute to MDD. In addition, targeting TRP-KYN with traditional Chinese medicine showed promising treatment effects for MDD. This review summarizes the recent studies on the TRP-KYN metabolic pathway and its metabolites in depression, which would provide a theoretical basis for exploring the etiology and pathogenesis of depression.

The microbial production of kynurenic acid using Yarrowia lipolytica yeast growing on crude glycerol and soybean molasses

Yarrowia lipolytica yeast are able to produce kynurenic acid—a very valuable compound acting as a neuroprotective and antioxidant agent in humans. The recent data proved the existence of the kynurenine biosynthesis pathway in this yeast cells. Due to this fact, the aim of this work was to enhance kynurenic acid production using crude glycerol and soybean molasses as cheap and renewable carbon and nitrogen sources. The obtained results showed that Y. lipolytica GUT1 mutants are able to produce kynurenic acid in higher concentrations (from 4.5 mg dm⁻³ to 14.1 mg dm⁻³) than the parental strain (3.6 mg dm⁻³) in the supernatant in a medium with crude glycerol. Moreover, the addition of soybean molasses increased kynurenic acid production by using wild type and transformant strains. The A-101.1.31 GUT1/1 mutant strain produced 17.7 mg dm⁻³ of kynurenic acid in the supernatant during 150 h of the process and 576.7 mg kg⁻¹ of kynurenic acid in dry yeast biomass. The presented work proves the great potential of microbial kynurenic acid production using waste feedstock. Yeast biomass obtained in this work is rich in protein, with a low content of lipid, and can be a healthy ingredient of animal and human diet.

Chromosomal-level assembly of Bactericera cockerelli reveals rampant gene family expansions impacting genome structure, function and insect-microbe-plant-interactions

Lineage specific expansions and gene duplications are some of the most important sources of evolutionary novelty in eukaryotes. Although not as prevalent in eukaryotes compared to bacteria, horizontal gene transfer events can also result in key adaptations for insects, especially for those involved in insect-microbe interactions. In this study we assemble the first chromosomal assembly of the psyllid Bactericera cockerelli and reveal that the B. cockerelli genome has experienced significantly more gene expansion events compared to other Hemipteran representatives with fully sequenced genomes. We also reveal that B. cockerelli's genome is the largest psyllid genome (567 Mb) sequenced to date and is ~15% larger than the other two psyllid species genomes sequenced (Pachypsylla venusta and Diaphorina citri). Structurally, B. cockerelli appears to have an additional chromosome compared to the distantly related psyllid species P. venusta due to a previous chromosomal fission or fusion event. The increase in genome size and dynamic nature of the B. cockerelli genome may largely be contributed to the widespread expansion of type I and type II repeat elements that are rampant across all of B. cockerelli's. chromosomes. These repeat elements are distributed near equally in both euchromatic and heterochromatic regions. Furthermore, significant gene family expansions and gene duplications were uncovered for genes that are expected to be important in its adaptation to insect-plant and microbe interactions, which include transcription factors, proteases, odorant receptors, and horizontally transferred genes that are involved in the nutritional symbioses with their long-term nutritional endosymbiont Carsonella.

The tryptophan catabolite or kynurenine pathway in COVID-19 and critical COVID-19: a systematic review and meta-analysis

Background

Coronavirus disease 2019 (COVID-19) is accompanied by activated immune-inflammatory pathways and oxidative stress, which both induce indoleamine-2,3-dioxygenase (IDO), a key enzyme of the tryptophan (TRP) catabolite (TRYCAT) pathway. The aim of this study was to systematically review and meta-analyze the status of the TRYCAT pathway, including the levels of TRP and kynurenine (KYN) and the activity of IDO, as measured by the ratio of KYN/TRP.

Methods

This systematic review searched PubMed, Google Scholar, and Web of Sciences and included 14 articles that compared TRP and tryptophan catabolites (TRYCATs) in COVID-19 patients versus non-COVID-19 controls, as well as severe/critical versus mild/moderate COVID-19. The analysis was done on a total of 1269 people, including 794 COVID-19 patients and 475 controls.

Results

The results show a significant (p < 0.0001) increase in the KYN/TRP ratio (standardized mean difference, SMD = 1.099, 95% confidence interval, CI: 0.714; 1.484) and KYN (SMD = 1.123, 95% CI: 0.730; 1.516) and significantly lower TRP (SMD = − 1.002, 95%CI: − 1.738; − 0.266) in COVID-19 versus controls. The KYN/TRP ratio (SMD = 0.945, 95%CI: 0.629; 1.262) and KYN (SMD = 0.806, 95%CI: 0.462; 1.149) were also significantly (p < 0.0001) higher and TRP lower (SMD = − 0.909, 95% CI: − 1.569; − 0.249) in severe/critical versus mild/moderate COVID-19. No significant difference was detected in kynurenic acid (KA) and the KA/KYN ratio between COVID-19 patients and controls.

Conclusions

Our results indicate increased activity of the IDO enzyme in COVID-19 and severe/critical patients. The TRYCAT pathway is implicated in the pathophysiology and progression of COVID-19 and may signal a worsening outcome of the disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07582-1.

Characterization of Redox Environment and Tryptophan Catabolism through Kynurenine Pathway in Military Divers’ and Swimmers’ Serum Samples

Endurance and resistance exercises, alone or in combination, induce metabolic changes that affect tryptophan (Trp) catabolism. The kynurenine pathway (KP) is the main route of Trp degradation, and it is modulated by the inflammatory and redox environments. Previous studies have shown that KP metabolites work as myokines that mediate the positive systemic effects related to exercise. However, it is poorly understood how different exercise modalities and intensities impact the KP. The aim of this study was to characterize the effect of two different exercise modalities, military diving and swimming, on the KP and the redox environment. A total of 34 healthy men from the Mexican Navy were included in the study, 20 divers and 14 swimmers, who started and stayed in military training consistently during the six months of the study; 12 Mexican men without fitness training were used as the control group. Physical fitness was determined at the beginning and after 6 months of training; criteria included body composition; serum levels of Trp, kynurenine (KYN), kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK); the glutathione ratio (GSH/GSSG); and malondialdehyde (MDA).. Results showed a significant loss of body fat in both the diver and swimmer groups. Compared with the control group, divers showed a decrease in Trp and 3-HK levels, but no changes were observed in the KYN/Trp, KYNA/Trp or 3-HK/Trp ratios, while swimmers showed a decrease in KYN levels and an increase in the KYNA and 3-HK levels. Additionally, divers showed a decrease in the GSH/GSSG ratio and an increase in MDA levels, in contrast to the swimmers, who showed a decrease in MDA levels and an increase in GSH/GSSG levels. Our findings suggest a differential shift in the KP and redox environment induced by diving and swimming. Swimming promotes an antioxidant environment and a peripheral overactivation of the KP.

The immunosuppressive role of indoleamine 2, 3-dioxygenase in glioblastoma: mechanism of action and immunotherapeutic strategies

Glioblastoma multiforme (GBM) is a fatal brain tumor in adults with a bleak diagnosis. Expansion of immunosuppressive and malignant CD4 + FoxP3 + GITR + regulatory T cells is one of the hallmarks of GBM. Importantly, most of the patients with GBM expresses the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO). While IDO1 is generally not expressed at appreciable levels in the adult central nervous system, it is rapidly stimulated and highly expressed in response to ongoing immune surveillance in cancer. Increased levels of immune surveillance in cancer are thus related to higher intratumoral IDO expression levels and, as a result, a worse OS in GBM patients. Conversion of the important amino acid tryptophan into downstream catabolite known as kynurenines is the major function of IDO. Decreasing tryptophan and increasing the concentration of immunomodulatory tryptophan metabolites has been shown to induce T-cell apoptosis, increase immunosuppressive programming, and death of tumor antigen-presenting dendritic cells. This observation supported the immunotherapeutic strategy, and the targeted molecular therapy that suppresses IDO1 activity. We review the current understanding of the role of IDO1 in tumor immunological escape in brain tumors, the immunomodulatory effects of its primary catabolites, preclinical research targeting this enzymatic pathway, and various issues that need to be overcome to increase the prospective immunotherapeutic relevance in the treatment of GBM malignancy.

An Emerging Cross-Species Marker for Organismal Health: Tryptophan-Kynurenine Pathway

Tryptophan (TRP) is an essential dietary amino acid that, unless otherwise committed to protein synthesis, undergoes metabolism via the Tryptophan-Kynurenine (TRP-KYN) pathway in vertebrate organisms. TRP and its metabolites have key roles in diverse physiological processes including cell growth and maintenance, immunity, disease states and the coordination of adaptive responses to environmental and dietary cues. Changes in TRP metabolism can alter the availability of TRP for protein and serotonin biosynthesis as well as alter levels of the immune-active KYN pathway metabolites. There is now considerable evidence which has shown that the TRP-KYN pathway can be influenced by various stressors including glucocorticoids (marker of chronic stress), infection, inflammation and oxidative stress, and environmental toxicants. While there is little known regarding the role of TRP metabolism following exposure to environmental contaminants, there is evidence of linkages between chemically induced metabolic perturbations and altered TRP enzymes and KYN metabolites. Moreover, the TRP-KYN pathway is conserved across vertebrate species and can be influenced by exposure to xenobiotics, therefore, understanding how this pathway is regulated may have broader implications for environmental and wildlife toxicology. The goal of this narrative review is to (1) identify key pathways affecting Trp-Kyn metabolism in vertebrates and (2) highlight consequences of altered tryptophan metabolism in mammals, birds, amphibians, and fish. We discuss current literature available across species, highlight gaps in the current state of knowledge, and further postulate that the kynurenine to tryptophan ratio can be used as a novel biomarker for assessing organismal and, more broadly, ecosystem health.

The tryptophan metabolism, kynurenine pathway and oxidative stress - Implications for glioma pathobiology

The kynurenine pathway receives increasing attention due to its involvement in central nervous system pathologies, i.a. neurodegenerative and psychiatric disorders, but also due to the contribution to the pathomechanism of neoplasms, including brain tumors.The present review focuses on kynurenine pathway activity in gliomas, brain tumors of glial origin. The upregulation of kynurenine pathway enzyme, indoleamine 2,3-dioxygenase (IDO), resulting in a decreased level of tryptophan and augmented kynurenine synthesis (increased (KYN/Trp ratio) are the most recognised hallmark of malignant transformation, characterised with immunomodulatory adaptations, providing an escape from defence mechanisms of the host, growth-beneficial milieu and resistance to some therapeutics. The review addresses, however, the oxidative/nitrosative stress-associated mechanisms of tryptophan catabolism, mainly the kynurenine pathway activity, linking them with glioma pathobiology.

Influence of periodontal inflammation on tryptophan-kynurenine metabolism: a cross-sectional study

OBJECTIVES

Kynurenine pathway (KP) is the primary way of degrading tryptophan (TRP) and generates several bioactive metabolites (such as kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxykynurenine (3OHKYN)) to regulate biological processes that include host-microbiome signaling and immune cell response. This study is aimed to determine the relationship between periodontal inflammation and tryptophan-kynurenine metabolism and identify their association with periodontal clinical parameters.

MATERIALS AND METHODS

Saliva and serum samples were collected from 20 stage III, grade B generalized periodontitis patients, and 20 periodontally healthy control individuals. Samples were analyzed for IL-6, KYN, TRP, KYN/TRP ratio, KYNA, 3OHKYN, picolinic acid (PA), and quinolinic acid (QA) by liquid chromatography-mass spectrometry. Clinical periodontal parameters (plaque index (PI), probing pocket depth (PPD), gingival recession (GR), clinical attachment loss (CAL), and bleeding on probing (BOP)) were recorded.

RESULTS

Clinical parameters were significantly higher in the periodontitis group (p < 0.001). Salivary IL-6, TRP, KYN, KYNA, PA, and QA levels were significantly higher and KYN/TRP ratio was significantly lower in periodontitis group than control group (p < 0.05). Serum KYN, KYN/TRP ratio and PA levels were significantly higher in periodontitis group than control group (p < 0.05). PPD, BOP, PI, and CAL had significantly positive correlations with salivary IL-6, TRP, PA, QA, and serum KYN and significantly negative correlations with salivary KYN/TRP ratio.

CONCLUSIONS

Our results suggest that periodontal inflammation plays a role in local and systemic tryptophan-kynurenine metabolism.

CLINICAL RELEVANCE

Due to their effects on the immune and inflammatory systems, kynurenines may be potential agents for diagnosis and treatment of periodontal diseases.

Untargeted Metabolomic Profiling and Antioxidant Capacities of Different Solvent Crude Extracts of Ephedra foeminea

Ephedra foeminea is a traditional medicinal plant used in the Eastern Mediterranean region. This study aims to investigate the chemical profiles of different solvent extracts of E. foeminea via an untargeted metabolomics approach, alongside determining their antioxidant capacities. E. foeminea samples collected from Jordan were macerated in solvents of varying polarities; dichloromethane/methanol, methanol, ethanol, ethyl acetate, and acetone. The crude extracts were subjected to comprehensive chemical profiling and metabolomics study using Gas chromatography–Mass spectrometry (GC–MS), Liquid chromatography–Mass spectrometry (LC–MS), and Nuclear Magnetic Resonance (NMR). The obtained data were analyzed using Venn diagrams, Principle Component Analysis (PCA), and Metabolite Enrichment Set Analysis (MESA). ABTS assay was performed to measure the crude extracts’ antioxidant activity. MESA revealed the dominant chemical groups as amino acids, fatty acids, carboxylic acids, and carbohydrates. Results indicated that dichloromethane/methanol and methanolic extracts had the most distinct composition as well as the most unique compounds. The methanolic extract had the most potency (IC50 249.6 µg/mL) in the ABTS assay. However, no significant differences were found. In conclusion, solvents influenced the recovery of metabolites in E. foeminea and the antioxidant activity of the E. foeminea methanolic extract could be correlated to the abundant presence of diverse bioactive compounds.

Isatis tinctoria L. Leaf Extract Inhibits Replicative Senescence in Dermal Fibroblasts by Regulating mTOR-NF-κB-SASP Signaling

Senescent fibroblasts progressively deteriorate the functional properties of skin tissue. Senescent cells secrete senescence-associated secretory phenotype (SASP) factor, which causes the aging of surrounding non-senescent cells and accelerates aging in the individuals. Recent findings suggested the senomorphic targeting of the SASP regulation as a new generation of effective therapeutics. We investigated whether Isatis tinctoria L. leaf extract (ITE) inhibited senescence biomarkers p53, p21^CDKN1A, and p16^INK4A gene expression, and SASP secretions by inhibiting cellular senescence in the replicative senescent human dermal fibroblast (RS-HDF). ITE has been demonstrated to inhibit the secretion of SASP factors in several senomorphic types by regulating the MAPK/NF-κB pathway via its inhibitory effect on mTOR. ITE suppressed the inflammatory response by inhibiting mTOR, MAPK, and IκBα phosphorylation, and blocking the nuclear translocation of NF-κB. In addition, we observed that autophagy pathway was related to inhibitory effect of ITE on cellular senescence. From these results, we concluded that ITE can prevent and restore senescence by blocking the activation and secretion of senescence-related factors generated from RS-HDFs through mTOR-NF-κB regulation.

Pomegranate and Its Components, Punicalagin and Ellagic Acid, Promote Antidepressant, Antioxidant, and Free Radical-Scavenging Activity in Ovariectomized Rats

Previous reports described the antidepressant-like action of the aqueous extract of pomegranate (Punica granatum: AEPG). Thus we evaluated the effect of AEPG and the main compounds found in the extract, punicalagin (PNCG) and ellagic acid (EA), on forced swimming test and the redox environment (reactive oxygen species [ROS] production, lipoperoxidation [LPX], and cellular function) in the brain of rats treated with 3 weeks post ovariectomy exposed ex vivo to pro-oxidants. Also, we selected PNCG and EA to study their antidepressant-like effects (0.001, 0.01, 0.1, 1.0, and 10 mg/kg) in the forced swimming test and their scavenging capacities in chemical combinatorial assays (expressed as IC₅₀ values). We observed a 2-fold increase in the formation of ROS and LPX in the brain after exposure to FeSO₄. However, these effects were significantly attenuated when rats were treated with AEPG, PNCG, and EA (1 mg/kg and 0.010 mg/kg for 14 days). AEPG and EA significantly increased the cellular function values of brains that had been affected by the effect of FeSO₄ and with ONOO^–. PNCG and EA significantly reduced immobility behavior at the lower doses used in this study. The capacity of scavenging compounds to eliminate radicals was for hydroxyl radical (^⋅OH), superoxide anion (O2^⋅⁣–), and peroxynitrite (ONOO^–) as follows: AEPG > punicalagin > ellagic acid. In conclusion, the AEPG and their active compounds PNCG and EA promote antidepressant-like actions and antioxidant activity as they attenuate oxidative damage and prevent cellular dysfunction in ovariectomized rat brains.

Synthesis and Investigation of the G-Quadruplex Binding Properties of Kynurenic Acid Derivatives with a Dihydroimidazoquinoline-3,5-dione Core

G-quadruplexes are secondary structures originating from nucleic acid regions rich in guanines, which are well known for their involvement in gene transcription and regulation and DNA damage repair. In recent studies from our group, kynurenic acid (KYNA) derivative 1 was synthesized and found to share the structural features typical of G-quadruplex binders. Herein, structural modifications were conducted on this scaffold in order to assist the binding with a G-quadruplex, by introducing charged hydrophilic groups. The antiproliferative activity of the new analogues was evaluated on an IGROV-1 human ovarian cancer cell line, and the most active compound, compound 9, was analyzed with NMR spectrometry in order to investigate its binding mode with DNA. The results indicated that a weak, non-specific interaction was set with duplex nucleotides; on the other hand, titration in the presence of a G-quadruplex from human telomere d(TTAGGGT)4 showed a stable, although not strong, interaction at the 3'-end of the nucleotidic sequence, efficiently assisted by salt bridges between the quaternary nitrogen and the external phosphate groups. Overall, this work can be considered a platform for the development of a new class of potential G-quadruplex stabilizing molecules, confirming the crucial role of a planar system and the ability of charged nitrogen-containing groups to facilitate the binding to G-quadruplex grooves and loops.

Therapeutic Targets for Regulating Oxidative Damage Induced by Ischemia-Reperfusion Injury: A Study from a Pharmacological Perspective

Ischemia-reperfusion (I-R) injury is damage caused by restoring blood flow into ischemic tissues or organs. This complex and characteristic lesion accelerates cell death induced by signaling pathways such as apoptosis, necrosis, and even ferroptosis. In addition to the direct association between I-R and the release of reactive oxygen species and reactive nitrogen species, it is involved in developing mitochondrial oxidative damage. Thus, its mechanism plays a critical role via reactive species scavenging, calcium overload modulation, electron transport chain blocking, mitochondrial permeability transition pore activation, or noncoding RNA transcription. Other receptors and molecules reduce tissue and organ damage caused by this pathology and other related diseases. These molecular targets have been gradually discovered and have essential roles in I-R resolution. Therefore, the current study is aimed at highlighting the importance of these discoveries. In this review, we inquire about the oxidative damage receptors that are relevant to reducing the damage induced by oxidative stress associated with I-R. Several complications on surgical techniques and pathology interventions do not mitigate the damage caused by I-R. Nevertheless, these therapies developed using alternative targets could work as coadjuvants in tissue transplants or I-R-related pathologies