Effects Of Kynurenic Acid Research Articles

IL-33 Induces a Switch in Intestinal Metabolites Revealing the Tryptophan Pathway as a Target for Inducing Allograft Survival.

IL-33, a pleiotropic cytokine, has been associated with a plethora of immune-related processes, both inflammatory and anti-inflammatory. T regulatory (Treg) cells, the main leukocyte population involved in immune tolerance, can be induced by the administration of IL-33, the local microbiota, and its metabolites. Here, we demonstrate that IL-33 drastically induces the production of intestinal metabolites involved on tryptophan (Trp) metabolism. naïve mice were treated with IL-33 for 4 days and leukocyte populations were analyzed by flow cytometry, and feces were processed for microbiota and intestinal metabolites studies. Using a murine skin transplantation model, the effect of Kynurenic acid (KA) on allograft survival was tested. Under homeostatic conditions, animals treated with IL-33 showed an increment in Treg cell frequencies. Intestinal bacterial abundance analysis indicates that IL-33 provokes dysbiosis, demonstrated by a reduction in Enterobacteria and an increment in Lactobacillus genera. Furthermore, metabolomics analysis showed a dramatic IL-33 effect on the abundance of intestinal metabolites related to amino acid synthesis pathways, highlighting molecules linked to Trp metabolism, such as kynurenic acid (KA), 5-Hydroxyindoleacetic acid (5-HIAA), and 6-Hydroxynicotinic acid (6-HNA), which was supported by an enhanced expression of Ido and Kat mRNA in MLN cells, which are two enzymes involved on KA synthesis. Interestingly, animals receiving KA in drinking water and subjected to skin transplantation showed allograft acceptance, which is associated with an increment in Treg cell frequencies. Our study reveals a new property for IL-33 as a modulator of the intestinal microbiota and metabolites, especially those involved with Trp metabolism. In addition, we demonstrate that KA favors Tregs in vivo, positively affecting skin transplantation survival.

The Effects of Kynurenic Acid in Zebrafish Embryos and Adult Rainbow Trout.

Kynurenic acid (KYNA) is a metabolite of tryptophan formed on the kynurenine pathway. Its pharmacological effects are relatively well characterized in mammals, whereas its role in fish is poorly understood. Therefore, the aim of the study was to expand the knowledge of KYNA's presence inside a fish's body and its impact on fish development and function. The study was performed on zebrafish larvae and adult rainbow trout. We provide evidence that KYNA is present in the embryo, larva and mature fish and that its distribution in organs varies considerably. A study of KYNA's effect on early larval development suggests that it can accelerate larval maturation, especially under conditions that are suboptimal for fish growth. Moreover, KYNA in concentrations over 1 mM caused morphological impairment and death of larvae. However, long-lasting exposure of larvae to subtoxic concentrations of KYNA does not affect the behavior of 5-day-old larvae kept under standard optimal conditions. We also show that ingestion of KYNA-supplemented feed can lead to KYNA accumulation, particularly in the pyloric caeca of mature trout. These results shed new light on the relevance of KYNA and provide new impulse for further research on the importance of the kynurenine pathway in fish.

Loop diuretics inhibit kynurenic acid production and kynurenine aminotransferases activity in rat kidneys.

Loop diuretics became a cornerstone in the therapy of hypervolemia in patients with chronic kidney disease or heart failure. Apart from the influence on water and electrolyte balance, these drugs were shown to inhibit tissue fibrosis and renin-angiotensin-system activity. The kynurenine (KYN) pathway products are suggested to be uremic toxins. Kynurenic acid (KYNA) is synthesized by kynurenine aminotransferases (KATs) in the brain and periphery. The cardiovascular and renal effects of KYNA are well documented. However, high KYNA levels have been correlated with the rate of kidney damage and its complications. Our study aimed to assess the effect of loop diuretics, ethacrynic acid, furosemide, and torasemide on KYNA synthesis and KATs activity in rat kidneys in vitro. Quantitative analyses of KYNA were performed using fluorimetric HPLC detection. Additionally, molecular docking studies determined the possible interactions of investigated compounds with an active site of KAT I and KAT II. All studied drugs inhibited KYNA production in rat kidneys in vitro at 0.5-1.0mmol/l concentrations. Only ethacrynic acid at 1.0mmol/l concentration significantly lowered KAT I and KAT II activity in kidney homogenates, whereas other drugs were ineffective. Molecular docking results indicated the common binding site for each of the studied loop diuretics and KYNA. They suggested possible residues involved in their binding to the active site of both KAT I and KAT II model. Our study reveals that loop diuretics may decrease KYNA synthesis in rat kidneys in vitro. The presented results warrant further research in the context of KYN pathway activity regulation by loop diuretics.

Kynurenic acid protects against ischemia/reperfusion injury by modulating apoptosis in cardiomyocytes

Acute myocardial infarction, often associated with ischemia/reperfusion injury (I/R), is a leading cause of death worldwide. Although the endogenous tryptophan metabolite kynurenic acid (KYNA) has been shown to exert protection against I/R injury, its mechanism of action at the cellular and molecular level is not well understood yet. Therefore, we examined the potential involvement of antiapoptotic mechanisms, as well as N-methyl-D-aspartate (NMDA) receptor modulation in the protective effect of KYNA in cardiac cells exposed to simulated I/R (SI/R). KYNA was shown to attenuate cell death induced by SI/R dose-dependently in H9c2 cells or primary rat cardiomyocytes. Analysis of morphological and molecular markers of apoptosis (i.e., membrane blebbing, apoptotic nuclear morphology, DNA double-strand breaks, activation of caspases) revealed considerably increased apoptotic activity in cardiac cells undergoing SI/R. The investigated apoptotic markers were substantially improved by treatment with the cytoprotective dose of KYNA. Although cardiac cells were shown to express NMDA receptors, another NMDA antagonist structurally different from KYNA was unable to protect against SI/R-induced cell death. Our findings provide evidence that the protective effect of KYNA against SI/R-induced cardiac cell injury involves antiapoptotic mechanisms, that seem to evoke independently of NMDA receptor signaling.

Effect of kynurenic acid on enzymatic activity of the DNA base excision repair pathway in specific areas of the sheep brain

Relatively low levels of antioxidant enzymes coupled with high oxygen metabolism result in the formation of numerous oxidative DNA damages in the tissues of the central nervous system. Recently, kynurenic acid (KYNA), knowns for its neuroprotective properties, has gained increasing attention in this context. Therefore, our hypothesis assumed that increased KYNA levels in the brain would positively influence mRNA expression of selected enzymes of the base excision repair pathway as well as enhance their efficiency in excising damaged nucleobases in specific areas of the sheep brain. The study was conducted on adult anestrous sheep (n = 18), in which two different doses of KYNA (20 and 100 μg/day) were infused into the third brain ventricle for three days. Molecular and biochemical analysis included the hypothalamus (preoptic and mediol-basal areas), hippocampus (CA3 field) and amygdala (central amygdaloid nucleus), dissected from the brain of sheep euthanized immediately after the last infusion. The results revealed a significant increase P < 0.001) in the relative mRNA abundance of N-methylpurine DNA glycosylase (MPG) following administration of both dose of KYNA across all examined tissues. The transcription of thymine-DNA glycosylase (TDG) increased significantly (P < 0.001) in all tissues in response to the lower KYNA dose compared to the control group. Moreover, 8-oxoguanine (8-oxoG) DNA glycosylase (OGG1) mRNA levels were also higher in both animal groups (P < 0.001). In addition, in the hypothalamus, hippocampus and amygdala, AP endonuclease 1 (APE1) mRNA expression increased under both doses of KYNA. Moreover, the both dose of KYNA significantly stimulated the efficiency of 8-oxoG excision in hypothalamus and amygdala (P < 0.05–0.001). The lower and higher doses of KYNA significantly influenced the effectiveness of εA and εC in all structures (P < 0.01–0.001). In conclusion, the favorable effect of KYNA in the brain may include the protection of genetic material in nerve and glial cells by stimulating the expression and efficiency of BER pathway enzymes.

The kynurenic acid analog SZR104 induces cytomorphological changes associated with the anti-inflammatory phenotype in cultured microglia

We previously showed the anti-inflammatory effects of kynurenic acid (KYNA) and its brain-penetrable analog N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-hydroxyquinoline-2-carboxamide (SZR104) both in vivo and in vitro. Here, we identified the cytomorphological effects of KYNA and SZR104 in secondary microglial cultures established from newborn rat forebrains. We quantitatively analyzed selected morphological aspects of microglia in control (unchallenged), lipopolysaccharide (LPS)-treated (challenged), KYNA- or SZR104-treated, and LPS + KYNA or LPS + SZR104-treated cultures. Multicolor immunofluorescence labeling followed by morphometric analysis (area, perimeter, transformation index, lacunarity, density, span ratio, maximum span across the convex hull, hull circularity, hull area, hull perimeter, max/min radii, mean radius, diameter of bounding circle, fractal dimension, roughness, circularity) on binary (digital) silhouettes of the microglia revealed their morphological plasticity under experimental conditions. SZR104 and, to a lesser degree, KYNA inhibited proinflammatory phenotypic changes. For example, SZR104 treatment resulted in hypertrophied microglia characterized by a swollen cell body, enlarged perimeter, increased transformation index/decreased circularity, increased convex hull values (area, perimeter, mean radius, maximum span, diameter of the bounding circle and hull circularity), altered box-counting parameters (such as fractal dimension), and increased roughness/decreased density. Taken together, analysis of cytomorphological features could contribute to the characterization of the anti-inflammatory activity of SZR104 on cultured microglia.

Effects of kynurenic acid and choline on lipopolysaccharide-induced cyclooxygenase pathway

Abstract Objectives Inflammation can be endogenously modulated by the cholinergic anti-inflammatory pathway via calcium (Ca2+)-permeable alpha-7 nicotinic acetylcholine receptor (α7nAChR) ion channel expressed in immune cells. α7nAChR agonist choline and tryptophan metabolite kynurenic acid (KYNA) produces immunomodulatory effects. This study aimed to determine the effects of the choline and KYNA on the lipopolysaccharide (LPS)-induced cyclooxygenase (COX)-2 pathway. Methods In vitro inflammation model was produced via LPS administration in macrophage cells. To determine the effective concentrations, choline and KYNA were applied with increasing concentrations and LPS-induced inflammatory parameters investigated. The involvement of nAChR mediated effects was investigated with the use of non-selective nAChR and selective α7nAChR antagonists. The effects of choline and KYNA on COX-2 enzyme, PGE2, TNFα, NF-κB and intracellular Ca2+ levels were analyzed. Results LPS-induced COX-2 expression, PGE2 TNFα and NF-κB levels were decreased with choline treatment while intracellular calcium levels via α7nAChRs increased. KYNA also showed an anti-inflammatory effect on the same parameters. Additionally, KYNA administration increased the effectiveness of choline on these inflammatory mediators. Conclusions Our data suggest a possible interaction between the kynurenine pathway and the cholinergic system on the modulation of LPS-induced inflammatory response in macrophages.

Extension of life span by down-regulation of enzymes catalyzing tryptophan conversion into kynurenine: Possible implications for mechanisms of aging.

The end products of catabolism of tryptophan (Trp), an essential amino acid, are known to affect mechanism(s) of aging, a neurodegenerative condition. This review focuses on the possible role of the initial step of Trp catabolism, kynurenine (Kyn) formation from Trp, in aging mechanism(s). Rate-limiting enzymes of Trp conversion into Kyn are tryptophan 2,3-dioxygenase 2 (TDO) or indoleamine 2,3-dioxygenase (IDO). Aging is associated with up-regulated production of cortisol, an activator of TDO, and pro-inflammatory cytokines, inducers of IDO. The other rate-limiting enzyme of Kyn formation from Trp is ATP-binding cassette (ABC) transporter that regulates Trp availability as a substrate for TDO. Inhibitors of TDO (alpha-methyl tryptophan) and ABC transporter (5-methyltryptophan) extended life span of wild-type Drosophila. Life span prolongation was observed in TDO knockdown of Caenorhabditis elegans and in TDO or ABC transporter-deficient Drosophila mutants. Down-regulation of enzymes catalyzing Kyn conversion into kynurenic acid (KYNA) and 3-hydroxykynurenine decreases life span. Considering that down-regulation of Methuselah (MTH) gene prolonged life span, aging-accelerating effect of KYNA, a GPR35/MTH agonist, might depend on MTH gene activation. Mice treated with TDO inhibitor, benserazide, an ingredient of anti-Parkinson medication carbidopa, and TDO-deficient Drosophila mutants were resistant to inducement of aging-associated Metabolic Syndrome by high-sugar or high-fat diets. Up-regulation of Kyn formation was associated with accelerated aging and increased mortality in human subjects. Trp-Kyn pathway is evolutionary conserved (from yeasts, through insects, worms, vertebrates to humans). Further studies might explore possible antiaging effect of down-regulation of Kyn formation from Trp by dietary, pharmacological, and genetic interventions.

Kinureninski put katabolizma triptofana i shizofrenija

The development of new therapeutic options focused on the recovery of patients with schizophrenia is primarily conditioned by elucidating the biological underpinnings of the disorder. The kynurenine pathway of tryptophan catabolism is the focus of psychiatric research since its catabolites have neuroactive properties, and one of the most important is the effect of kynurenic acid as the only endogenous NMDA receptor antagonist. According to the kynurenine hypothesis, there is an imbalance of excitatory and neuroprotective metabolites of the kynurenine pathway in patients with schizophrenia. It is postulated that excessive production of kynurenic acid leads to excessive blockade of NMDA glutamate and alpha-7 nicotinic receptors, acting as a trigger for the development of psychotic symptoms and neurocognitive deficits. This paper aims to review the kynurenine hypothesis of schizophrenia, important findings of studies exploring metabolites of the kynurenine pathway in patients with schizophrenia, and findings from the research on the potential impact of proinflammatory cytokines on the kynurenine pathway.

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.

Perivascular brown adipocytes-derived kynurenic acid relaxes blood vessel via endothelium PI3K-Akt-eNOS pathway.

Several metabolites from the kynurenine pathway of tryptophan metabolism play a critical role in vascular function and vascular wall remodeling. This study aimed to test whether metabolite kynurenic acid (KYNA) from the kynurenine pathway relaxes blood vessels. We employed histological staining, in vitro cell culture, Western blotting, real-time PCR, and nitric oxide detection to validate kynurenine aminotransferase (KAT) localization in the vasculature as well as KYNA action on endothelial cells. We also detected vascular reactivity by organ chamber and monitored blood pressure by telemetry to investigate the regulation effect of KYNA on vascular tone. The results presented that perivascular adipose tissue (PVAT) from mice thoracic aorta had robust staining of anti-KAT1 and KYNA than PVAT from the abdominal aorta and mesenteric artery, which is consistent with the expression profile of brown adipocyte marker uncoupling protein 1. KYNA, metabolized from kynurenine by KAT, relaxed pre-contracted both aortic ring and mesenteric artery. In addition, KYNA derived from KAT in PVAT participates in the cross-talk between PVAT and vessel by mediating PVAT inhibition on agonist-induced thoracic aorta contraction. Furthermore, intraperitoneal injection of KYNA in mice reduced blood pressure. The vessel relaxation effect of KYNA was through the endothelium-dependent PI3K-Akt-eNOS pathway. Finally, the high-fat diet decreased KAT1 expression in perithoracic aortic fat and led to KYNA reduction in blood. Our research identified KYNA generated by KAT as a novel perivascular brown adipocyte-derived vascular relaxation factor and suggests that KYNA reduction is a critical event in vascular dysfunction under obese condition.

Memory Enhancement with Kynurenic Acid and Its Mechanisms in Neurotransmission.

Kynurenic acid (KYNA) is an endogenous tryptophan (Trp) metabolite known to possess neuroprotective property. KYNA plays critical roles in nociception, neurodegeneration, and neuroinflammation. A lower level of KYNA is observed in patients with neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases or psychiatric disorders such as depression and autism spectrum disorders, whereas a higher level of KYNA is associated with the pathogenesis of schizophrenia. Little is known about the optimal concentration for neuroprotection and the threshold for neurotoxicity. In this study the effects of KYNA on memory functions were investigated by passive avoidance test in mice. Six different doses of KYNA were administered intracerebroventricularly to previously trained CFLP mice and they were observed for 24 h. High doses of KYNA (i.e., 20–40 μg/2 μL) significantly decreased the avoidance latency, whereas a low dose of KYNA (0.5 μg/2 μL) significantly elevated it compared with controls, suggesting that the low dose of KYNA enhanced memory function. Furthermore, six different receptor blockers were applied to reveal the mechanisms underlying the memory enhancement induced by KYNA. The series of tests revealed the possible involvement of the serotonergic, dopaminergic, α and β adrenergic, and opiate systems in the nootropic effect. This study confirmed that a low dose of KYNA improved a memory component of cognitive domain, which was mediated by, at least in part, four systems of neurotransmission in an animal model of learning and memory.

Kynurenic Acid Acts as a Signaling Molecule Regulating Energy Expenditure and Is Closely Associated With Metabolic Diseases.

Kynurenic acid (KYNA) is an important bio-active product of tryptophan metabolism. In addition to its well-known neuroprotective effects on mental health disorders, it has been proposed as a bio-marker for such metabolic diseases as atherosclerosis and diabetes. Emerging evidence suggests that KYNA acts as a signaling molecule controlling the networks involved in the balance of energy store and expenditure through GPR35 and AMPK signaling pathway. KYNA plays an important role in the pathogenesis and development of several endocrine and metabolic diseases. Exercise training promotes KYNA production in skeletal muscles and increases thermogenesis in the long term and limits weight gain, insulin resistance and inflammation. Additionally, KYNA is also present in breast milk and may act as an anti-obesity agent in infants. Although we are far from fully understanding the role of KYNA in our body, administration of KYNA, enzyme inhibitors or metabolites may serve as a potential therapeutic strategy for treating metabolic diseases. The present review provides a perspective on the current knowledge regarding the biological effects of KYNA in metabolic diseases and perinatal nutrition.

Kynurenic acid ameliorates lipopolysaccharide-induced endometritis by regulating the GRP35/NF-κB signaling pathway

Endometritis is a serious reproductive disease in mammals that commonly results in reproductive loss and even permanent infertility. Kynurenic acid (KYNA) is the main bioactive metabolite of tryptophan degradation and exhibits neuroprotective and anticonvulsant properties. However, little is known about the role of KYNA in achieving endometritis remission. This study investigated the protective effects and mechanisms of KYNA using a mouse model of against lipopolysaccharide (LPS)-induced endometritis. The endometritis model was induced by an intrauterine injection of LPS, and KYNA was intraperitoneally injected before and two hours after LPS treatment. Twenty-four hours after LPS administration, pathological changes in uterine tissues were observed by hematoxylin- and eosin (H&E) staining. The levels of the inflammatory factors, TNF-α and IL-1β, were measured by ELISA. The myeloperoxidase (MPO) activity in uterine tissues was detected using MPO kits and immunohistochemistry. Furthermore, the expression of signaling pathway proteins and tight junction proteins occludin and ZO-1 in uterine tissues was detected by western blot. KYNA prominently inhibited uterine pathological injury and neutrophil infiltration and restricted the secretion of TNF-α and IL-1β in the uteri of subjects with endometritis. Furthermore, KYNA upregulated the levels of the tight junction proteins (TJPs)occludin and ZO-1 in the uterus. In vitro, KYNA inhibited LPS-induced TNF-α and IL-1β production, and NF-κB activation in mouse endometrial epithelial cells (mEECs). In addition, KYNA increased the expression of G protein-coupled receptor 35 (GPR35) and inhibition of GPR35 reversed the anti-inflammatory effects of KYNA. In conclusion, KYNA protected against LPS-induced endometritis by maintaining epithelial barrier permeability and suppressing proinflammatory responses via the GRP35/NF-κB signaling pathway.

Kynurenic Acid and Its Analog SZR104 Exhibit Strong Antiinflammatory Effects and Alter the Intracellular Distribution and Methylation Patterns of H3 Histones in Immunochallenged Microglia-Enriched Cultures of Newborn Rat Brains.

Kynurenic acid (KYNA) is implicated in antiinflammatory processes in the brain through several cellular and molecular targets, among which microglia-related mechanisms are of paramount importance. In this study, we describe the effects of KYNA and one of its analogs, the brain-penetrable SZR104 (N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-hydroxyquinoline-2-carboxamide), on the intracellular distribution and methylation patterns of histone H3 in immunochallenged microglia cultures. Microglia-enriched secondary cultures made from newborn rat forebrains were immunochallenged with lipopolysaccharide (LPS). The protein levels of selected inflammatory markers C–X–C motif chemokine ligand 10 (CXCL10) and C–C motif chemokine receptor 1 (CCR1), histone H3, and posttranslational modifications of histone H3 lys methylation sites (H3K9me3 and H3K36me2, marks typically associated with opposite effects on gene expression) were analyzed using quantitative fluorescent immunocytochemistry and western blots in control or LPS-treated cultures with or without KYNA or SZR104. KYNA and SZR104 reduced levels of the inflammatory marker proteins CXCL10 and CCR1 after LPS-treatment. Moreover, KYNA and SZR104 favorably affected histone methylation patterns as H3K9me3 and H3K36me2 immunoreactivities, and histone H3 protein levels returned toward control values after LPS treatment. The cytoplasmic translocation of H3K9me3 from the nucleus indicated inflammatory distress, a process that could be inhibited by KYNA and SZR104. Thus, KYNA signaling and metabolism, and especially brain-penetrable KYNA analogs such as SZR104, could be key targets in the pathway that connects chromatin structure and epigenetic mechanisms with functional consequences that affect neuroinflammation and perhaps neurodegeneration.

The Mechanism of the Neuroprotective Effect of Kynurenic Acid in the Experimental Model of Neonatal Hypoxia-Ischemia: The Link to Oxidative Stress.

The over-activation of NMDA receptors and oxidative stress are important components of neonatal hypoxia–ischemia (HI). Kynurenic acid (KYNA) acts as an NMDA receptor antagonist and is known as a reactive oxygen species (ROS) scavenger, which makes it a potential therapeutic compound. This study aimed to establish the neuroprotective and antioxidant potential of KYNA in an experimental model of HI. HI on seven-day-old rats was used as an experimental model. The animals were injected i.p. with different doses of KYNA 1 h or 6 h after HI. The neuroprotective effect of KYNA was determined by the measurement of brain damage and elements of oxidative stress (ROS and glutathione (GSH) level, SOD, GPx, and catalase activity). KYNA applied 1 h after HI significantly reduced weight loss of the ischemic hemisphere, and prevented neuronal loss in the hippocampus and cortex. KYNA significantly reduced HI-increased ROS, GSH level, and antioxidant enzyme activity. Only the highest used concentration of KYNA showed neuroprotection when applied 6 h after HI. The presented results indicate induction of neuroprotection at the ROS formation stage. However, based on the presented data, it is not possible to pinpoint whether NMDA receptor inhibition or the scavenging abilities are the dominant KYNA-mediated neuroprotective mechanisms.

Kynurenic Acid Accelerates Healing of Corneal Epithelium In Vitro and In Vivo

Kynurenic acid (KYNA) is an endogenous compound with a multidirectional effect. It possesses antiapoptotic, anti-inflammatory, and antioxidative properties that may be beneficial in the treatment of corneal injuries. Moreover, KYNA has been used successfully to improve the healing outcome of skin wounds. The aim of the present study is to evaluate the effects of KYNA on corneal and conjunctival cells in vitro and the re-epithelization of corneal erosion in rabbits in vivo. Normal human corneal epithelial cell (10.014 pRSV-T) and conjunctival epithelial cell (HC0597) lines were used. Cellular metabolism, cell viability, transwell migration, and the secretion of IL-1β, IL-6, and IL-10 were determined. In rabbits, after corneal de-epithelization, eye drops containing 0.002% and 1% KYNA were applied five times a day until full recovery. KYNA decreased metabolism but did not affect the proliferation of the corneal epithelium. It decreased both the metabolism and proliferation of conjunctival epithelium. KYNA enhanced the migration of corneal but not conjunctival epithelial cells. KYNA reduced the secretion of IL-1β and IL-6 from the corneal epithelium, leaving IL-10 secretion unaffected. The release of all studied cytokines from the conjunctival epithelium exposed to KYNA was unchanged. KYNA at higher concentration accelerated the healing of the corneal epithelium. These favorable properties of KYNA suggest that KYNA containing topical pharmaceutical products can be used in the treatment of ocular surface diseases.

Kynurenic acid protects against mastitis in mice by ameliorating inflammatory responses and enhancing blood-milk barrier integrity

Mastitis is one of the most serious diseases in humans and animals, especially in the modern dairy industry. Seeking safe and effective mastitis prevention strategies is urgent since food safety and drug residues in milk remain an enormous concern, despite the contribution of antibiotics to control mastitis. Kynurenic acid (KYNA), derived from the kynurenine pathway of tryptophan metabolism, has been shown to exhibit anti-inflammatory and immunomodulatory effects in many diseases. Recently, it was reported that impaired KYNA levels were associated with mastitis. However, the physiological role of KYNA in mastitis has not yet been elucidated. Therefore, the aim of this study was to investigate the protective role of KYNA in pathogen-induced mastitis in mice, as well as the underlying mechanism of this effect. We first evaluated the effects of KYNA on LPS-induced mastitis in mice. Additionally, the underlying anti-inflammatory mechanism of KYNA was investigated in mammary epithelial cells (MMECs). Furthermore, we examined the effects of KYNA on S. aureus and E. coli induced mastitis in mice. Our results demonstrated that KYNA alleviated LPS-induced mastitis by reducing inflammatory responses and enhancing blood-milk barrier integrity. The fundamental mechanisms involved the inhibition of NF-κB and activation of Nrf2/Ho-1, which is probably mediated by G protein-coupled receptor 35 but not aryl hydrocarbon receptor. Notably, KYNA also protected against S. aureus and E. coli induced mastitis in mice. In conclusion, our results highlight the role of KYNA in mastitis and serve as a basis for using endogenous metabolite as a novel preventative or therapeutic strategy for disease intervention.

Effects of Kynurenic Acid on the Rat Aorta Ischemia-Reperfusion Model: Pharmacological Characterization and Proteomic Profiling.

Kynurenic acid (KYNA) is derived from tryptophan, formed by the kynurenic pathway. KYNA is being widely studied as a biomarker for neurological and cardiovascular diseases, as it is found in ischemic conditions as a protective agent; however, little is known about its effect after ischemia-reperfusion in the vascular system. We induced ischemia for 30 min followed by 5 min reperfusion (I/R) in the rat aorta for KYNA evaluation using functional assays combined with proteomics. KYNA recovered the exacerbated contraction induced by phenylephrine and relaxation induced by acetylcholine or sodium nitroprussiate in the I/R aorta, with vessel responses returning to values observed without I/R. The functional recovery can be related to the antioxidant activity of KYNA, which may be acting on the endothelium-injury prevention, especially during reperfusion, and to proteins that regulate neurotransmission and cell repair/growth, expressed after the KYNA treatment. These proteins interacted in a network, confirming a protein profile expression for endothelium and neuron repair after I/R. Thus, the KYNA treatment had the ability to recover the functionality of injured ischemic-reperfusion aorta, by tissue repairing and control of neurotransmitter release, which reinforces its role in the post-ischemic condition, and can be useful in the treatment of such disease.

P0016EFFECT OF GEMFIBROZIL ON KYNURENINE AMINOTRANSFERASE ACTIVITY AND KYNURENIC ACID PRODUCTION IN RAT KIDNEY

Abstract Background and Aims Hypertriglyceridemia is the most common lipid disorder in chronic kidney disease. Lifestyle changes and fibrates administration are main methods of lowering triglycerides’ level. PPARα (peroxisome proliferator-activated receptor-α) activation is the primary mechanism of action of fibrates. A tryptophan metabolite, kynurenic acid (KYNA), is produced from L-kynurenine (L-KYN) by kynurenine aminotransferases (KATs). KAT I and KAT II isoenzymes are the best analyzed KATs. KYNA acts predominantly as a nonselective antagonist of ionotropic glutamatergic receptors, particularly N-methyl-D-aspartate (NMDA) type, which are highly expressed in the kidney. Natriuretic and hypotensive effects of KYNA are well described. Diet rich in fatty acids was reported to elevate central and peripheral KYNA level. The goal of presented study was to analyze the influence of gemfibrozil, one of the fibrates given to treat hypertriglyceridemia, on KYNA production and the activity of KAT isoenzymes: KAT I and KAT II, in rat kidney in vitro. Additionally, the molecular docking of gemfibrozil to KAT I and KAT II structures was performed to study drug-enzyme interaction. On the final step the microarray datamining was carried out to investigate whether gemfibrozil affects the expression of KAT-coding genes. Method The effect of gemfibrozil on KYNA synthesis together with KAT I and KAT II activity was tested in rat kidney homogenates in vitro after 2 hours incubation in the presence of L-KYN and gemfibrozil. The drug was examined at the concentration of 1 µM, 10 µM, 50 µM, 100 µM, 500 µM and 1 mM. Production of KYNA was analyzed using the high performance liquid chromatography (HPLC) with fluorometric detector. Results Gemfibrozil at 100 µM, 500 µM and 1 mM decreased KYNA production in kidney homogenates in vitro to 66% (P &amp;lt; 0.05), 58% (P &amp;lt; 0.01) and 41% (P &amp;lt; 0.01) of control value, respectively. At 100 µM, 500 µM and 1 mM concentration gemfibrozil lowered renal KAT I activity in vitro to 68% (P &amp;lt; 0.05), 56% (P &amp;lt; 0.01) and 52% (P &amp;lt; 0.01) of control value, respectively. Moreover, gemfibrozil at 500 µM and 1 mM concentration decreased kidney KAT II activity in vitro to 47% (P &amp;lt; 0.001) and 26% (P &amp;lt; 0.001) of control value, respectively. Results of the molecular docking suggested that gemfibrozil may affect the active site of both KAT I and KAT II. Publicly available microarray datasets suggested that the expression of KAT-coding genes does not change after gemfibrozil administration. Conclusion Gemfibrozil decreases KYNA production in rat kidney in vitro through inhibition of KAT I and KAT II isoenzymes. Presented results indicate a novel mechanism of gemfibrozil’s action in the kidney. Its potential role in nephrotoxicity needs verification in upcoming studies.