The pharmacological manipulation of glutamate receptors and neuroprotection

Involvement of kynurenine pathway between inflammation and glutamate in the underlying etiopathology of CUMS-induced depression mouse model

Inflammation and glutamate (GLU) are widely thought to participate in the pathogenesis of depression, and current evidence suggests that the development of depression is associated with the activation of the kynurenine pathway (KP). However, the exact mechanism of KP among the inflammation, GLU and depression remain poorly understood. In this study, we examined the involvement of KP, inflammation and GLU in depressive phenotype induced by chronic unpredictable mild stress (CUMS) in C57B/6 J mice. Our results showed that CUMS caused depressive like-behavior in the sucrose preference test, tail suspension test and forced swimming test. From a molecular perspective, CUMS upregulated the peripheral and central inflammatory response and activated indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme of KP, which converts tryptophan (TRP) into kynurenine (KYN). KYN is a precursor for QA in microglia, which could activate the N-methyl-D-aspartate receptor (NMDAR), increasing the GLU release, mirrored by increased IDO activity, quinolinic acid and GLU levels in the hippocampus, prefrontal cortex and serum. However, intervention with IDO inhibitor 1-methyl-DL-tryptophan (50 mg/kg/s.c.) and 1-methyl-L-tryptophan (15 mg/kg/i.p.) reversed the depressive-like behaviors and adjusted central and peripheral KP’s metabolisms levels as well as GLU content, but the inflammation levels were not completely affected. These results provide certain evidence that KP may be a vital pathway mediated by IDO linking inflammation and glutamate, contributing to depression.

Urinary metabolomics identified metabolic disturbance associated with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disorder. Nevertheless, its accurate mechanisms remain unclear. Metabolomics is a powerful technique to identify small molecules that could be used to discover pathogenesis and therapeutical targets of disease. In the present study, a urinary untargeted metabolomics combined with targeted quantification analysis was performed to uncover metabolic disturbance associated with PCOS. A total of thirty-eight metabolites were obtained between PCOS patients and healthy controls, which were mainly involved in lipids (39.5%), organic acids and derivatives (23.7%), and organic oxygen compounds (18.4%). Based on enrichment analysis, fourteen metabolic pathways were found to be perturbed in PCOS, particularly glycerophospholipid metabolism and tryptophan metabolism. Targeted quantification profiling of tryptophan metabolism demonstrated that seven compounds (tryptophan, kynurenine, kynurenic acid, quinolinic acid, xanthurenic acid, 3-hydroxyanthranilic acid and 3-hydroxykynurenine) were up-regulated in PCOS. And these tryptophan-kynurenine metabolites showed significant correlations with PCOS clinical features, such as positively associated with testosterone, free androgen index, and the ratio of luteinizing hormone to follicle stimulating hormone. Thus, this study disclosed urinary metabolome changes associated with PCOS, and might provide new insights into PCOS pathogenesis elucidation and therapeutical target development.

Brain Kynurenine Pathway and Functional Outcome of Rats Resuscitated From Cardiac Arrest

Background Brain injury and neurological deficit are consequences of cardiac arrest (CA), leading to high morbidity and mortality. Peripheral activation of the kynurenine pathway (KP), the main catabolic route of tryptophan metabolized at first into kynurenine, predicts poor neurological outcome in patients resuscitated after out-of-hospital CA. Here, we investigated KP activation in hippocampus and plasma of rats resuscitated from CA, evaluating the effect of KP modulation in preventing CA-induced neurological deficit. Methods and Results Early KP activation was first demonstrated in 28 rats subjected to electrically induced CA followed by cardiopulmonary resuscitation. Hippocampal levels of the neuroactive metabolites kynurenine, 3-hydroxy-anthranilic acid, and kynurenic acid were higher 2 hours after CA, as in plasma. Further, 36 rats were randomized to receive the inhibitor of the first step of KP, 1-methyl-DL-tryptophan, or vehicle, before CA. No differences were observed in hemodynamics and myocardial function. The CA-induced KP activation, sustained up to 96 hours in hippocampus (and plasma) of vehicle-treated rats, was counteracted by the inhibitor as indicated by lower hippocampal (and plasmatic) kynurenine/tryptophan ratio and kynurenine levels. 1-Methyl-DL-tryptophan reduced the CA-induced neurological deficits, with a significant correlation between the neurological score and the individual kynurenine levels, as well as the kynurenine/tryptophan ratio, in plasma and hippocampus. Conclusions These data demonstrate the CA-induced lasting activation of the first step of the KP in hippocampus, showing that this activation was involved in the evolving neurological deficit. The degree of peripheral activation of KP may predict neurological function after CA.

GluA3-containing AMPA receptors: From physiology to synaptic dysfunction in brain disorders

In the mammalian brain, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) play a fundamental role in the activation of excitatory synaptic transmission and the induction of different forms of synaptic plasticity. The modulation of the AMPAR tetramer subunit composition at synapses defines the functional properties of the receptor. During the last twenty years, several studies have evaluated the roles played by each subunit, from GluA1 to GluA4, in both physiological and pathological conditions. Here, we have focused our attention on GluA3-containing AMPARs, addressing their functional role in synaptic transmission and synaptic plasticity and their involvement in a variety of brain disorders. Although several aspects remain to be fully understood, GluA3 is a widely expressed and functionally relevant subunit in AMPARs involved in several brain circuits, and its pharmacological modulation could represent a novel approach for the rescue of altered glutamatergic synapses associated with neurodegenerative and neurodevelopmental disorders.

Kynurenine Pathway in Chronic Kidney Disease: What’s Old, What’s New, and What’s Next?

Impaired kidney function and increased inflammatory process occurring in the course of Chronic Kidney Disease (CKD) contribute to the development of complex amino-acid alterations. The essential amino-acid tryptophan (TRP) undergoes extensive metabolism along several pathways, resulting in the production of many biologically active compounds. The results of many studies have shown that its metabolism via the kynurenine pathway is potently increased in the course of CKD. Metabolites of this pathway exhibit differential, sometimes opposite, roles in several biological processes. Their accumulation in the course of CKD may induce oxidative cell damage which stimulates inflammatory processes. They can also modulate the activity of numerous cellular signaling pathways through activation of the aryl hydrocarbon receptor, leading to the disruption of homeostasis of various organs. As a result, they can contribute to the development of the systemic disorders accompanying the course of chronic renal failure. This review gathers and systematizes reports concerning the knowledge connecting the kynurenine pathway metabolites to systemic disorders accompanying the development of CKD.

The kynurenine connection: how exercise shifts muscle tryptophan metabolism and affects energy homeostasis, the immune system, and the brain

Tryptophan catabolism through the kynurenine pathway generates a variety of bioactive metabolites. Physical exercise can modulate kynurenine pathway metabolism in skeletal muscle and thus change the concentrations of select compounds in peripheral tissues and in the central nervous system. Here we review recent advances in our understanding of how exercise alters tryptophan-kynurenine metabolism in muscle and its subsequent local and distal effects. We propose that the effects of kynurenine pathway metabolites on skeletal muscle, adipose tissue, immune system, and the brain suggest that some of these compounds could qualify as exercise-induced myokines. Indeed, some of the more recently discovered biological activities for kynurenines include many of the best-known benefits of exercise: improved energy homeostasis, promotion of an anti-inflammatory environment, and neuroprotection. Finally, by considering the tissue expression of the different membrane and cytosolic receptors for kynurenines, we discuss known and potential biological activities for these tryptophan metabolites.

Does kynurenic acid act on nicotinic receptors? An assessment of the evidence

As a major metabolite of kynurenine in the oxidative metabolism of tryptophan, kynurenic acid is of considerable biological and clinical importance as an endogenous antagonist of glutamate in the central nervous system. It is most active as an antagonist at receptors sensitive to N-methyl-D-aspartate (NMDA) which regulate neuronal excitability and plasticity, brain development and behaviour. It is also thought to play a causative role in hypo-glutamatergic conditions such as schizophrenia, and a protective role in several neurodegenerative disorders, notably Huntington's disease. An additional hypothesis, that kynurenic acid could block nicotinic receptors for acetylcholine in the central nervous system has been proposed as an alternative mechanism of action of kynurenate. However, the evidence for this alternative mechanism is highly controversial, partly because at least eight earlier studies concluded that kynurenic acid blocked NMDA receptors but not nicotinic receptors and five subsequent, independent studies designed to repeat the results have failed to do so. Many studies considered to support the alternative 'nicotinic' hypothesis have been based on the use of analogs of kynurenate such as 7-chloro-kynurenic acid, or putatively nicotinic modulators such as galantamine, but a detailed analysis of the pharmacology of these compounds suggests that the results have often been misinterpreted, especially since the pharmacology of galantamine itself has been disputed. This review examines the evidence in detail, with the conclusion that there is no confirmed, reliable evidence for an antagonist activity of kynurenic acid at nicotinic receptors. Therefore, since there is overwhelming evidence for kynurenate acting at ionotropic glutamate receptors, especially NMDAR glutamate and glycine sites, with some activity at GPR35 sites and Aryl Hydrocarbon Receptors, results with kynurenic acid should be interpreted only in terms of these confirmed sites of action.

Microorganisms, Tryptophan Metabolism, and Kynurenine Pathway: A Complex Interconnected Loop Influencing Human Health Status

The kynurenine pathway is important in cellular energy generation and limiting cellular ageing as it degrades about 90% of dietary tryptophan into the essential co-factor NAD⁺ (nicotinamide adenine dinucleotide). Prior to the production of NAD⁺, various intermediate compounds with neuroactivity (kynurenic acid, quinolinic acid) or antioxidant activity (3-hydroxykynurenine, picolinic acid) are synthesized. The kynurenine metabolites can participate in numerous neurodegenerative disorders (Alzheimer disease, amyotrophic lateral sclerosis, Huntington disease, and Parkinson disease) or other diseases such as AIDS, cancer, cardiovascular diseases, inflammation, and irritable bowel syndrome. Recently, the role of gut in affecting the emotional and cognitive centres of the brain has attracted a great deal of attention. In this review, we focus on the bidirectional communication between the gut and the brain, known as the gut-brain axis. The interaction of components of this axis, namely, the gut, its microbiota, and gut pathogens; tryptophan; the kynurenine pathway on tryptophan availability; the regulation of kynurenine metabolite concentration; and diversity and population of gut microbiota, has been considered.

Influence of Cyclooxygenase-2 Inhibitors on Kynurenic Acid Production in Rat Brain in Vitro

Significant body of evidence suggests that abnormal kynurenic acid (KYNA) level is involved in the pathophysiology of central nervous system disorders. In the brain, KYNA is synthesized from kynurenine (KYN) by kynurenine aminotransferases (KATs), predominantly by KAT II isoenzyme. Blockage of ionotropic glutamate (GLU) receptors is a main cellular effect of KYNA. High KYNA levels have been linked with psychotic symptoms and cognitive dysfunction in animals and humans. As immunological imbalance and impaired glutamatergic neurotransmission are one of the crucial processes in neurological pathologies, we aimed to analyze the effect of anti-inflammatory agents, inhibitors of cyclooxygenase-2 (COX-2): celecoxib, niflumic acid, and parecoxib, on KYNA synthesis and KAT II activity in rat brain in vitro. The influence of COX-2 inhibitors was examined in rat brain cortical slices and on isolated KAT II enzyme. Niflumic acid and parecoxib decreased in a dose-dependent manner KYNA production and KAT II activity in rat brain cortex in vitro, whereas celecoxib was ineffective. Molecular docking results suggested that niflumic acid and parecoxib interact with an active site of KAT II. In conclusion, niflumic acid and parecoxib are dual COX-2 and KAT II inhibitors.

Angiotensin II type 1 receptor blockers decrease kynurenic acid production in rat kidney in vitro

Glutamate (GLU) mainly through N-methyl-D-aspartate (NMDA) receptors plays pivotal role in kidney function regulation. Kynurenic acid (KYNA), a GLU receptors antagonist, is synthesized from kynurenine by kynurenine aminotransferases (KATs). Previously, it was shown that angiotensin II type 1 receptor blockers (ARBs) decrease KYNA production in rat brain in vitro. The aim of this study was to examine the influence of six ARBs: candesartan, irbesartan, losartan, olmesartan, telmisartan, and valsartan on KYNA production on rat kidney in vitro. The effect of ARBs was determined in kidney homogenates and on isolated KAT II enzyme. Among tested ARBs, irbesartan was the most effective KYNA synthesis inhibitor with IC₅₀ of 14.4 μM. Similar effects were observed after losartan (IC₅₀ 45.9 μM) and olmesartan administration (IC₅₀ 108.1 μM), whereas candesartan (IC₅₀ 475.3 μM), valsartan (IC₅₀ 513.9 μM), and telmisartan (IC₅₀ 669.5 μM) displayed lower activity in KYNA synthesis inhibition in rat kidney homogenates in vitro. On the other hand, valsartan (IC₅₀ 27.5 μM) was identified to be the strongest KAT II inhibitor in rat kidney in vitro. Candesartan, losartan, and telmisartan suppressed KAT II activity with IC₅₀ equal to 83.2, 83.3, and 108.3 μM, respectively. Olmesartan and irbesartan were the weakest KAT II inhibitors with IC₅₀ values of 237.4 and 809.9 μM, respectively. Moreover, molecular docking suggested that studied ARBs directly bind to an active site of KAT II. In conclusion, our results indicate that ARBs decrease KYNA synthesis in rat kidney through enzymatic inhibition of KAT II, which may have impact on kidney function.

Knockdown of RTN1-C attenuates traumatic neuronal injury through regulating intracellular Ca2+ homeostasis

Reticulons (RTNs) are a family of membrane-bound proteins that are dominantly localized to the endoplasmic reticulum (ER) membrane. RTN1-C is one member of RTNs abundantly expressed in the brain and has been shown to mediate neuronal injury in cerebral ischemia models. In the present study, we investigated the role of RTN1-C in an in vitro brain trauma model mimicked by traumatic neuronal injury (TNI) in primary cultured cortical neurons. TNI increased the expression of RTN1-C in cortical neurons but had no effect on RTN1-A and RTN1-B. Knockdown of RTN1-C with specific siRNA (Si-RTN1-C) significantly decreased cytotoxicity and apoptosis after TNI. The results of Ca²⁺ imaging showed that intracellular Ca²⁺ overload induced by TNI was attenuated by RTN1-C knockdown. Furthermore, the activation of metabotropic glutamate receptor 1 (mGluR1)-induced Ca²⁺ response was partially prevented by Si-RTN1-C transfection. We also evaluated the role of RTN1-C in store-operated Ca²⁺ entry (SOCE) in cortical neurons using the ER Ca²⁺ inducer thapsigargin (Tg). The results showed that knockdown of RTN1-C alleviated the SOCE-mediated Ca²⁺ influx and decreased the expression of stromal interactive molecule 1 (STIM1). In summary, the present study found that knockdown of RTN1-C protected neurons against TNI via preservation of intracellular Ca²⁺ homeostasis, which was associated with the inhibition of mGluR1-mediated ER Ca²⁺ release and suppression of STIM1-related SOCE. Thus, RTN1-C might represent a therapeutic target for traumatic brain injury (TBI) research.

Pharmacological characterisation of S 47445, a novel positive allosteric modulator of AMPA receptors

S 47445 is a novel positive allosteric modulator of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors (AMPA-PAM). S 47445 enhanced glutamate’s action at AMPA receptors on human and rat receptors and was inactive at NMDA and kainate receptors. Potentiation did not differ among the different AMPA receptors subtypes (GluA1/2/4 flip and flop variants) (EC₅₀ between 2.5–5.4 μM), except a higher EC₅₀ value for GluA4 flop (0.7 μM) and a greater amount of potentiation on GluA1 flop. A low concentration of S 47445 (0.1 μM) decreased receptor response decay time of GluA1flop/GluA2flip AMPA receptors and increased the sensitivity to glutamate. Furthermore, S 47445 (0.1 and 0.3 μM) in presence of repetitive glutamate pulses induced a progressive potentiation of the glutamate-evoked currents from the second pulse of glutamate confirming a rapid-enhancing effect of S 47445 at low concentrations. The potentiating effect of S 47445 (1 μM) was concentration-dependently reversed by the selective AMPA receptor antagonist GYKI52466 demonstrating the selective modulatory effect of S 47445 on AMPA receptors. Using an AMPA-kainate chimera approach, it was confirmed that S 47445 binds to the common binding pocket of AMPA-PAMs. S 47445 did not demonstrate neurotoxic effect against glutamate-mediated excitotoxicity in vitro, in contrast significantly protected rat cortical neurons at 10 μM. S 47445 was shown to improve both episodic and spatial working memory in adult rodents at 0.3 mg/kg, as measured in the natural forgetting condition of object recognition and T-maze tasks. Finally, no deleterious effect on spontaneous locomotion and general behavior was observed up to 1000 mg/kg of S 47445 given acutely in rodents, neither occurrence of convulsion or tremors. Collectively, these results indicate that S 47445 is a potent and selective AMPA-PAM presenting procognitive and potential neuroprotective properties. This drug is currently evaluated in clinical phase 2 studies in Alzheimer’s disease and in Major Depressive Disorder.

Cloning, Expression and Characterization of NAD Kinase from Staphylococcus aureus Involved in the Formation of NADP (H): A Key Molecule in the Maintaining of Redox Status and Biofilm Formation

BACKGROUND

Staphylococcus aureus has the ability to form biofilms on any niches, a key pathogenic factor of this organism and this phenomenon is directly related to the concentration of NADPH. The formation of NADP is catalyzed by NAD kinase (NADK) and this gene of S. aureus ATCC 12600 was cloned, sequenced, expressed and characterized.

MATERIALS AND METHODS

The NADK gene was polymerase chain reaction amplified from the chromosomal DNA of S. aureus ATCC 12600 and cloned in pQE 30 vector, sequenced and expressed in Escherichia coli DH5α. The pure protein was obtained by passing through nickel metal chelate agarose column. The enzyme kinetics of the enzyme and biofilm assay of the S. aureus was carried out in both aerobic and anaerobic conditions. The kinetics was further confirmed by the ability of the substrates to dock to the NADK structure.

RESULTS

The recombinant NADK exhibited single band with a molecular weight of 31kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the gene sequence (GenBank: JN645814) revealed presence of only one kind of NADK in all S. aureus strains. The enzyme exhibited very high affinity for NAD compared to adenosine triphosphate concurring with the docking results. A root-mean-square deviation value 14.039Å observed when NADK structure was superimposed with its human counterpart suggesting very low homology. In anaerobic conditions, higher biofilm units were found with decreased NADK activity.

CONCLUSION

The results of this study suggest increased NADPH concentration in S. aureus plays a vital role in the biofilm formation and survival of this pathogen in any environmental conditions.

Quinolinic acid injection in mouse medial prefrontal cortex affects reversal learning abilities, cortical connectivity and hippocampal synaptic plasticity

Intracerebral injection of the excitotoxic, endogenous tryptophan metabolite, quinolinic acid (QA), constitutes a chemical model of neurodegenerative brain disease. Complementary techniques were combined to examine the consequences of QA injection into medial prefrontal cortex (mPFC) of C57BL6 mice. In accordance with the NMDAR-mediated synapto- and neurotoxic action of QA, we found an initial increase in excitability and an augmentation of hippocampal long-term potentiation, converting within two weeks into a reduction and impairment, respectively, of these processes. QA-induced mPFC excitotoxicity impaired behavioral flexibility in a reversal variant of the hidden-platform Morris water maze (MWM), whereas regular, extended MWM training was unaffected. QA-induced mPFC damage specifically affected the spatial-cognitive strategies that mice use to locate the platform during reversal learning. These behavioral and cognitive defects coincided with changes in cortical functional connectivity (FC) and hippocampal neuroplasticity. FC between various cortical regions was assessed by resting-state fMRI (rsfMRI) methodology, and mice that had received QA injection into mPFC showed increased FC between various cortical regions. mPFC and hippocampus (HC) are anatomically as well as functionally linked as part of a cortical network that controls higher-order cognitive functions. Together, these observations demonstrate the central functional importance of rodent mPFC as well as the validity of QA-induced mPFC damage as a preclinical rodent model of the early stages of neurodegeneration.

Mystixin-7 Peptide Protects Ionotropic Glutamatergic Mechanisms against Glutamate-Induced Excitotoxicity In Vitro

Hyperactivation of the N-methyl-D-aspartic acid type glutamate receptors (NMDARs) causes glutamate excitotoxicity, a process potentially important for many neurological diseases. This study aims to investigate protective effects of the synthetic corticotrophin-releasing factor-like peptide, mystixin-7 (MTX), on model glutamate-induced excitotoxicity in vitro. The technique online monitoring of electrophysiological parameters (excitatory glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPAR) and NMDAR-dependent postsynaptic mechanisms) in the olfactory cortex slices was used. Application of L-glutamate in toxic concentration (20 mM) on slices evoked hyperactivation of NMDARs and weaker activation of the AMPARs. Upon further action agonist, the excessive activation of glutamate receptors was replaced by their irreversible blockade. Pretreatment of the slices using MTX in different concentrations (50 and 100 mg/mL) protected both NMDARs and AMPARs from glutamate-induced damage. An enzymatic treatment of MTX reduced hyperactivation of both NMDARs and AMPARs. The present study demonstrated that MTX minipeptide protected the functioning of both NMDARs and AMPARs against glutamate-induced damage. The MTX peptide is a prospective candidate for elaborated medication in treatment of neurological diseases.

Mystixin-7 mini-peptide protects ionotropic glutamatergic mechanisms against oxygen-glucose deprivation in vitro

The aim of the present study was to explore the neuroprotective effects of the mystixin-7 mini-peptide (MTX, a synthetic corticotropin-releasing-factor-like, 7-amino-acid peptide) on an in vitro oxygen glucose deprivation model (OGD, 10min). The study used a technique of on-line monitoring of changes in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) and N-methyl-d-aspartic acid receptor (NMDAR)-mediated field excitatory postsynaptic potentials (fEPSPs) in the olfactory cortex slices in the OGD model. OGD resulted in an irreversible blockade of both AMPAR and NMDAR activity. Pretreatment of slices by MTX and their subsequent exposure to OGD resulted in decreased activity of these postsynaptic mechanisms (AMPARs, 71%; NMDARs, 68% as compared to baseline), but they were not blocked altogether. The degree protection of activity of both AMPARs and NMDARs had dose-dependent manner, with a maximal effect at 100mg/mL. These protective effects were retained after the removal of MTX from the bathing medium. To evaluate the protective efficacy of MTX on NMDARs, the slices were pretreated by MTX and exposed to OGD and then treated with l-glutamate (1mM). NMDARs' response to application of l-glutamate was minimal at higher concentrations of MTX and maximal at lower concentrations. These findings indicate that the molecules of MTX interact with a certain amount of NMDARs, and thereby protect them from the OGD. Pretreatment of slices with MTX contributed to the protection of network activity against OGD and promoted the development of the learning process in the form of long-term potentiation. To specify the protective effects of MTX, it was denatured by trypsin. The proteolytic cleavage of MTX resulted to a significant decrease in the activity of both AMPARs and NMDARs against OGD as compared with that of the native peptide. Together, these findings provide further insight into the protective potential of the MTX mini-peptide. We believe that the data presented can be the basis for the development of therapeutics MTX-based medications for the treatment of the ischemic stroke.

Altered Expression of Human Mitochondrial Branched Chain Aminotransferase in Dementia with Lewy Bodies and Vascular Dementia

Cytosolic and mitochondrial human branched chain aminotransferase (hBCATc and hBCATm, respectively) play an integral role in brain glutamate metabolism. Regional increased levels of hBCATc in the CA1 and CA4 region of Alzheimer’s disease (AD) brain together with increased levels of hBCATm in frontal and temporal cortex of AD brains, suggest a role for these proteins in glutamate excitotoxicity. Glutamate toxicity is a key pathogenic feature of several neurological disorders including epilepsy associated dementia, AD, vascular dementia (VaD) and dementia with Lewy bodies (DLB). To further understand if these increases are specific to AD, the expression profiles of hBCATc and hBCATm were examined in other forms of dementia including DLB and VaD. Similar to AD, levels of hBCATm were significantly increased in the frontal and temporal cortex of VaD cases and in frontal cortex of DLB cases compared to controls, however there were no observed differences in hBCATc between groups in these areas. Moreover, multiple forms of hBCATm were observed that were particular to the disease state relative to matched controls. Real-time PCR revealed similar expression of hBCATm mRNA in frontal and temporal cortex for all cohort comparisons, whereas hBCATc mRNA expression was significantly increased in VaD cases compared to controls. Collectively our results suggest that hBCATm protein expression is significantly increased in the brains of DLB and VaD cases, similar to those reported in AD brain. These findings indicate a more global response to altered glutamate metabolism and suggest common metabolic responses that might reflect shared neurodegenerative mechanisms across several forms of dementia.

Propargylamine as functional moiety in the design of multifunctional drugs for neurodegenerative disorders: MAO inhibition and beyond

Much progress has been made in designing analogues that can potentially confer neuroprotection against debilitating neurodegenerative disorders, yet the multifactorial pathogenesis of this cluster of diseases remains a stumbling block for the successful design of an 'ultimate' drug. However, with the growing popularity of the "one drug, multiple targets" paradigm, many researchers have successfully synthesized and evaluated drug-like molecules incorporating a propargylamine function that shows potential to serve as multifunctional drugs or multitarget-directed ligands. It is the aim of this review to highlight the reported activities of these propargylamine derivatives and their prospect to serve as drug candidates for the treatment of neurodegenerative disorders.

Prevention of postoperative fatigue syndrome in rat model by ginsenoside Rb1 via down-regulation of inflammation along the NMDA receptor pathway in the hippocampus

Postoperative fatigue syndrome (POFS) is a common complication which decelerates recovery after surgery. The present study investigated the anti-fatigue effect of ginsenoside Rb1 (GRb1) through the inflammatory cytokine-mediated N-methyl-D-aspartate (NMDA) receptor pathway. A POFS rat model was created by major small intestinal resection and assessed with an open field test. Real-time quantitative polymerase chain reaction, western blot analysis, high performance liquid chromatography and a transmission electron microscopic analysis were used to determine typical biochemical parameters in the hippocampus. Our results showed that POFS rats exhibited fatigue associated with an increased expression of inflammatory cytokines and NMDA receptor 1, higher (kynurenine)/(tryptophan) and (kynurenine)/(kynurenic acid) on postoperative days 1 and 3, and an increased expression of indoleamine 2,3-dioxygenase (IDO) on postoperative day 1. Degenerated neurons were found in the hippocampus of POFS rats. The NMDA receptor antagonist MK801 had a significant effect on central fatigue on postoperative day 1. GRb1 had no effect on IDO or tryptophan metabolism, but exhibited a significant effect on POFS by inhibiting the expression of inflammatory cytokines and NMDA receptor 1. These data suggested that inflammatory cytokines could activate tryptophan metabolism to cause POFS through the NMDA receptor pathway. GRb1 had an anti-fatigue effect on POFS by reducing inflammatory cytokines and NMDA receptors.

Cardiovascular afferents cause the release of 5-HT in the nucleus tractus solitarii; this release is regulated by the low- (PMAT) not the high-affinity transporter (SERT)

The nucleus tractus solitarii (NTS) integrates inputs from cardiovascular afferents and thus is crucial for cardiovascular homeostasis. These afferents primarily release glutamate, although 5-HT has also been shown to play a role in their actions. Using fast-cyclic voltammetry, an increase in 5-HT concentrations (range 12-50 nm) could be detected in the NTS in anaesthetized rats in response to electrical stimulation of the vagus and activation of cardiopulmonary, chemo- and baroreceptor reflexes. This 5-HT signal was not potentiated by the serotonin transporter (SERT) or the noradrenaline transporter (NET) inhibitors citalopram and desipramine (1 mg kg(-1) ). However, decynium-22 (600 μg kg(-1) ), an organic cation 3 transporter (OCT3)/plasma membrane monoamine transporter (PMAT) inhibitor, increased the 5-HT signal by 111 ± 21% from 29 ± 10 nm. The effectiveness of these inhibitors was tested against the removal time of 5-HT and noradrenaline applied by microinjection to the NTS. Citalopram and decynium-22 attenuated the removal of 5-HT but not noradrenaline, whereas desipramine had the reverse action. The OCT3 inhibitor corticosterone (10 mg kg(-1) ) had no effect. Blockade of glutamate receptors with topical kynurenate (10-50 nm) reduced the vagally evoked 5-HT signal by 50%, indicating that this release was from at least two sources. It is concluded that vagally evoked 5-HT release is under the regulation of the high-capacity, low-affinity transporter PMAT, not the low-capacity, high-affinity transporter SERT. This is the first demonstration that PMAT may be playing a physiological role in the regulation of 5-HT transmission and this could indicate that 5-HT is acting, in part, as a volume transmitter within the NTS.

The Role of NMDA Receptors in the Development of Brain Resistance through Pre- and Postconditioning

Brain tolerance or resistance can be achieved by interventions before and after injury through potential toxic agents used in low stimulus or dose. For brain diseases, the neuroprotection paradigm desires an attenuation of the resulting motor, cognitive, emotional, or memory deficits following the insult. Preconditioning is a well-established experimental and clinical translational strategy with great beneficial effects, but limited applications. NMDA receptors have been reported as protagonists in the adjacent cellular mechanisms contributing to the development of brain tolerance. Postconditioning has recently emerged as a new neuroprotective strategy, which has shown interesting results when applied immediately, i.e. several hours to days, after a stroke event. Investigations using chemical postconditioning are still incipient, but nevertheless represent an interesting and promising clinical strategy. In the present review pre- and postconditioning are discussed as neuroprotective paradigms and the focus of our attention lies on the participation of NMDA receptors proteins in the processes related to neuroprotection.

Involvement of the kynurenine pathway in human glioma pathophysiology

The kynurenine pathway (KP) is the principal route of L-tryptophan (TRP) catabolism leading to the production of kynurenine (KYN), the neuroprotectants, kynurenic acid (KYNA) and picolinic acid (PIC), the excitotoxin, quinolinic acid (QUIN) and the essential pyridine nucleotide, nicotinamide adenine dinucleotide (NAD(+)). The enzymes indoleamine 2,3-dioxygenase-1 (IDO-1), indoleamine 2,3-dioxygenase-2 (IDO-2) and tryptophan 2,3-dioxygenase (TDO-2) initiate the first step of the KP. IDO-1 and TDO-2 induction in tumors are crucial mechanisms implicated to play pivotal roles in suppressing anti-tumor immunity. Here, we report the first comprehensive characterisation of the KP in 1) cultured human glioma cells and 2) plasma from patients with glioblastoma (GBM). Our data revealed that interferon-gamma (IFN-γ) stimulation significantly potentiated the expression of the KP enzymes, IDO-1 IDO-2, kynureninase (KYNU), kynurenine hydroxylase (KMO) and significantly down-regulated 2-amino-3-carboxymuconate semialdehyde decarboxylase (ACMSD) and kynurenine aminotransferase-I (KAT-I) expression in cultured human glioma cells. This significantly increased KP activity but significantly lowered the KYNA/KYN neuroprotective ratio in human cultured glioma cells. KP activation (KYN/TRP) was significantly higher, whereas the concentrations of the neuroreactive KP metabolites TRP, KYNA, QUIN and PIC and the KYNA/KYN ratio were significantly lower in GBM patient plasma (n = 18) compared to controls. These results provide further evidence for the involvement of the KP in glioma pathophysiology and highlight a potential role of KP products as novel and highly attractive therapeutic targets to evaluate for the treatment of brain tumors, aimed at restoring anti-tumor immunity and reducing the capacity for malignant cells to produce NAD(+), which is necessary for energy production and DNA repair.

Knockdown of STIM1 improves neuronal survival after traumatic neuronal injury through regulating mGluR1-dependent Ca(2+) signaling in mouse cortical neurons

Activation of glutamate receptors and followed increase of intracellular calcium concentration is a key pathological mechanism involved in secondary neuronal injury after traumatic brain injury (TBI). Stromal interaction molecule (STIM) proteins are considered to be important players in regulating neuronal Ca(2+) homeostasis under normal aging and pathological conditions. Here, we investigated the role of STIM1 in regulating metabotropic glutamate receptor 1 (mGluR1)-related Ca(2+) signaling and neuronal survival by using an in vitro traumatic neuronal injury (TNI) model. The expression of STIM1 was significantly increased at both mRNA and protein levels after TNI. Down-regulation of STIM1 by specific small interfere RNA significantly preserved neuronal viability, decreased lactate dehydrogenase release, and inhibited apoptotic cell death after traumatic injury. Moreover, knockdown of STIM1 significantly alleviated the mGluR1-related increase of cytoplasmic Ca(2+) levels after TNI. By analyzing Ca(2+) imaging in Ca(2+)-free conditions, we demonstrated that the mGluR1-dependent inositol trisphosphate receptor and/or ryanodine receptor-mediated Ca(2+) release from the endoplasmic reticulum after TNI is strongly attenuated in the absence of STIM1. Together, our results demonstrate that in the mammalian nervous system, STIM1 is a key regulator of mGluR1-dependent Ca(2+) signaling and knockdown of STIM1 might be an effective intervention target in TBI.

Parthanatos: mitochondrial-linked mechanisms and therapeutic opportunities

Cells die by a variety of mechanisms. Terminally differentiated cells such as neurones die in a variety of disorders, in part, via parthanatos, a process dependent on the activity of poly (ADP-ribose)-polymerase (PARP). Parthanatos does not require the mediation of caspases for its execution, but is clearly mechanistically dependent on the nuclear translocation of the mitochondrial-associated apoptosis-inducing factor (AIF). The nuclear translocation of this otherwise beneficial mitochondrial protein, occasioned by poly (ADP-ribose) (PAR) produced through PARP overactivation, causes large-scale DNA fragmentation and chromatin condensation, leading to cell death. This review describes the multistep course of parthanatos and its dependence on PAR signalling and nuclear AIF translocation. The review also discusses potential targets in the parthanatos cascade as promising avenues for the development of novel, disease-modifying, therapeutic agents.

Molecular and cellular mechanisms underlying anti-neuronal antibody mediated disorders of the central nervous system

Over the last decade multiple autoantigens located on the plasma membrane of neurons have been identified. Neuronal surface antigens include molecules directly involved in neurotransmission and excitability. Binding of the antibody to the antigen may directly alter the target protein's function, resulting in neurological disorders. The often striking reversibility of symptoms following early aggressive immunotherapy supports a pathogenic role for autoantibodies to neuronal surface antigens. In order to better understand and treat these neurologic disorders it is important to gain insight in the underlying mechanisms of antibody pathogenicity. In this review we discuss the clinical, circumstantial, in vitro and in vivo evidence for neuronal surface antibody pathogenicity and the possible underlying cellular and molecular mechanisms. This review shows that antibodies to neuronal surface antigens are often directed at conformational epitopes located in the extracellular domain of the antigen. The conformation of the epitope can be affected by specific posttranslational modifications. This may explain the distinct clinical phenotypes that are seen in patients with antibodies to antigens that are expressed throughout the brain. Furthermore, it is likely that there is a heterogeneous antibody population, consisting of different IgG subtypes and directed at multiple epitopes located in an immunogenic region. Binding of these antibodies may result in different pathophysiological mechanisms occurring in the same patient, together contributing to the clinical syndrome. Unraveling the predominant mechanism in each distinct antigen could provide clues for therapeutic interventions.

Targeting α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors in epilepsy

INTRODUCTION

Despite epilepsies being between the oldest and most studied neurological diseases, new treatment remains an unmet need of scientific research due to the high percentage of refractory patients. Several studies have identified new suitable anti-seizure targets. Glutamate activation of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) have long ago been identified as suitable targets for the development of anti seizure drugs.

AREAS COVERED

Here, we describe: i) AMPARs' structure and their involvement and role during seizures and in epilepsy and ii) the efficacy of AMPAR antagonists in preclinical models of seizures and epilepsy.

EXPERT OPINION

The physiological and pathological role of AMPAR in the CNS and the development of AMPAR antagonists have recently gained attention considering their recent involvement in status epilepticus and the marketing of perampanel. The need for new anti-seizure drugs represents a major challenge in both preclinical and clinical epilepsy. The introduction into the market of perampanel for the treatment of epilepsy will shed new light on the real potential of AMPAR antagonism in clinical settings outside the limited world of clinical trials. While research will go on in this area, fundamental will be the post-marketing evaluation of perampanel efficacy and tolerability and a better definition of the role of this receptor in the epileptic brain.

Synergistic effect of the L-tryptophan and kynurenic acid with dipyrone or paracetamol in mice

PURPOSE

Our great interest in this work was study the synergism between l-tryptophan and dipyrone or paracetamol as well as the interaction of kynurenic acid (l-tryptophan metabolite) and these analgesics agents utilizing a robust methodology.

METHODS

We performed the writhing test induced by acetic acid in mice to evaluate the antinociceptive effect of the treatments isolated and combined (p.o. and i.p.). Dose-response curves were constructed and the values of ED50 for treatment alone and combined were statistically compared. In addition, isobolographic analysis was performed and the experimental values were compared with the theoretical values for simple additive effect.

RESULTS

The combined treatment with l-tryptophan and dipyrone or paracetamol reduced significantly the ED50 of these analgesics when compared to the isolated treatments. l-tryptophan alone has no antinociceptive effect. l-Tryptophan increases the central amount of 5-HT and the synergism with dipyrone is antagonized by the 5-HT depletion. The kyna has an antinociceptive dose-related effect and a synergistic interaction with dipyrone and paracetamol verified by isobolographic analyses and confirmed by experimental values of ED50 of combined treatments were statistically lower than theoretical calculated values for simple additive effect. Melatonin antagonist receptor attenuates the antinociceptive synergism between l-tryptophan and dipyrone.

CONCLUSION

Our results demonstrate that the increased 5-HT amount on the central nervous system is not per se capable to induce antinociception. The l-tryptophan interacts synergistically with dipyrone and paracetamol both orally and by i.p. route. This effect is dependent on the biotransformation of l-tryptophan to 5-HT and involves kynurenic acid and melatonin receptors.

Treatment of status epilepticus with ketamine, are we there yet?

Status epilepticus (SE), a neurological emergency both in adults and in children, could lead to brain damage and even death if untreated. Generalized convulsive SE (GCSE) is the most common and severe form, an example of which is that induced by organophosphorus nerve agents. First- and second-line pharmacotherapies are relatively consensual, but if seizures are still not controlled, there is currently no definitive data to guide the optimal choice of therapy. The medical community seems largely reluctant to use ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate glutamate receptor. However, a review of the literature clearly shows that ketamine possesses, in preclinical studies, antiepileptic properties and provides neuroprotection. Clinical evidences are scarcer and more difficult to analyze, owing to a use in situations of polytherapy. In absence of existing or planned randomized clinical trials, the medical community should make up its mind from well-conducted preclinical studies performed on appropriate models. Although potentially active, ketamine has no real place for the treatment of isolated seizures, better accepted drugs being used. Its best usage should be during GCSE, but not waiting for SE to become totally refractory. Concerns about possible developmental neurotoxicity might limit its pediatric use for refractory SE.

Post-ischemic treatment with L-kynurenine sulfate exacerbates neuronal damage after transient middle cerebral artery occlusion

Since brain ischemia is one of the leading causes of adult disability and death, neuroprotection of the ischemic brain is of particular importance. Acute neuroprotective strategies usually have the aim of suppressing glutamate excitotoxicity and an excessive N-methyl-d-aspartate (NMDA) receptor function. Clinically tolerated antagonists should antagonize an excessive NMDA receptor function without compromising the normal synaptic function. Kynurenic acid (KYNA) an endogenous metabolite of the tryptophan metabolism, may be an attractive neuroprotectant in this regard. The manipulation of brain KYNA levels was earlier found to effectively enhance the histopathological outcome of experimental ischemic/hypoxic states. The present investigation of the neuroprotective capacity of L-kynurenine sulfate (L-KYNs) administered systemically after reperfusion in a novel distal middle cerebral artery occlusion (dMCAO) model of focal ischemia/reperfusion revealed that in contrast with earlier results, treatment with L-KYNs worsened the histopathological outcome of dMCAO. This contradictory result indicates that post-ischemic treatment with L-KYNs may be harmful.

The L-kynurenine-probenecid combination reduces neuropathic pain in rats

BACKGROUND

l-Kynurenine has antinociceptive effects in acute and inflammatory pain. This study determined the effect of l-kynurenine and its metabolite (kynurenic acid) on rats subjected to neuropathic pain.

METHODS

L5/L6 spinal nerve ligation induced tactile allodynia as measured with von Frey filaments using the up-down method. High-performance liquid chromatography and Western blot analysis determined kynurenic acid levels and expression of kynurenine amino transferase II (KAT II), respectively.

RESULTS

l-Kynurenine (50-200 mg/kg, i.p.) or probenecid (100 mg/kg, i.p.) did not affect allodynia in neuropathic rats. In contrast, l-kynurenine (50-200 mg/kg, i.p.) in combination with probenecid (100 mg/kg, i.p.), an inhibitor of organic anion transport, reversed allodynia. Furthermore, intrathecal kynurenic acid (1-30 μg) reversed allodynia. Probenecid (100 mg/kg, i.p.) supplementation enhanced the maximal antiallodynic effect of intrathecal kynurenic acid (10 μg). Only the combined administration of l-kynurenine (200 mg/kg)/probenecid (100 mg/kg) increased the kynurenic acid concentration in cerebrospinal fluid. KAT II is expressed in dorsal root ganglia and dorsal spinal cord. KAT II expression was unchanged by the spinal nerve ligation or l-kynurenine/probenecid combination. The kynurenine/probenecid combination did not affect motor activity.

CONCLUSIONS

l-Kynurenine produces its antiallodynic effect in the central nervous system through kynurenic acid. This effect may result from blockade of N-methyl-d-aspartate receptors. KAT II is expressed in dorsal root ganglion and dorsal spinal cord. Combined l-kynurenine and probenecid therapy has the potential to reduce neuropathic pain in humans.

The neuroprotector kynurenic acid increases neuronal cell survival through neprilysin induction

Kynurenic acid (KYNA), one of the main product of the kynurenine pathway originating from tryptophan, is considered to be neuroprotective. Dysregulation of KYNA activity is thought to be involved in neurodegenerative diseases, the physiopathology of which evokes excitotoxicity, oxidative stress and/or protein aggregation. The neuroprotective effect of KYNA is generally attributed to its antagonistic action on NMDA receptors. However, this single target action appears insufficient to support KYNA beneficial effects against complex neurodegenerative processes including neuroinflammation, β-amyloid peptide (Aβ) toxicity and apoptosis. Novel insights are therefore required to elucidate KYNA neuroprotective mechanisms. Here, we combined cellular, biochemical, molecular and pharmacological approaches to demonstrate that low micromolar concentrations of KYNA strongly induce neprilysin (NEP) gene expression, protein level and enzymatic activity increase in human neuroblastoma SH-SY5Y cells. Furthermore, our studies revealed that KYNA exerts a protective effect on SH-SY5Y cells by increasing their viability through a mechanism independent from NMDA receptors. Interestingly, KYNA also induced NEP activity and neuroprotection in mouse cortical neuron cultures the viability of which was more promoted than SH-SY5Y cell survival under KYNA treatment. KYNA-evoked neuroprotection disappeared in the presence of thiorphan, an inhibitor of NEP activity. NEP is a well characterized metallopeptidase whose deregulation leads to cerebral Aβ accumulation and neuronal death in Alzheimer's disease. Therefore, our results suggest that a part of the neuroprotective role of KYNA may depend on its ability to induce the expression and/or activity of the amyloid-degrading enzyme NEP in nerve cells.

Kynurenine Pathway in Skin Cells: Implications for UV-Induced Skin Damage

The kynurenine pathway (KP) is the principle route of catabolism of the essential amino acid tryptophan, leading to the production of several neuroactive and immunoregulatory metabolites. Alterations in the KP have been implicated in various neuropsychiatric and neurodegenerative diseases, immunological disorders, and many other diseased states. Although the role of the KP in the skin has been evaluated in small niche fields, limited studies are available regarding the effect of acute ultra violet exposure and the induction of the KP in human skin-derived fibroblasts and keratinocytes. Since UV exposure can illicit an inflammatory component in skin cells, it is highly likely that the KP may be induced in these cells in response to UV exposure. It is also possible that some KP metabolites may act as pro-inflammatory and anti-inflammatory mediators, since the KP is important in immunomodulation.

Quinolinic acid, the inescapable neurotoxin

Over the last two decades, evidence for the involvement of quinolinic acid (QUIN) in neuroinflammatory diseases has been exponentially increasing. Within the brain, QUIN is produced and released by infiltrating macrophages and activated microglia, the very cells that are prominent during neuroinflammation. QUIN acts as an agonist of the N-methyl-D-aspartate receptor and as such is considered to be a brain endogenous excitotoxin. Since the discovery of the excitotoxic activity of QUIN in the early 1980s, several other cytotoxic mechanisms have been identified. We know today that QUIN acts as a neurotoxin, gliotoxin, proinflammatory mediator, pro-oxidant molecule and can alter the integrity and cohesion of the blood-brain barrier. This paper aims to review some of the most recent findings about the effects of QUIN and its mode of action.

Biochemical and structural characterization of mouse mitochondrial aspartate aminotransferase, a newly identified kynurenine aminotransferase-IV

Mammalian mAspAT (mitochondrial aspartate aminotransferase) is recently reported to have KAT (kynurenine aminotransferase) activity and plays a role in the biosynthesis of KYNA (kynurenic acid) in rat, mouse and human brains. This study concerns the biochemical and structural characterization of mouse mAspAT. In this study, mouse mAspAT cDNA was amplified from mouse brain first stand cDNA and its recombinant protein was expressed in an Escherichia coli expression system. Sixteen oxo acids were tested for the co-substrate specificity of mouse mAspAT and 14 of them were shown to be capable of serving as co-substrates for the enzyme. Structural analysis of mAspAT by macromolecular crystallography revealed that the cofactor-binding residues of mAspAT are similar to those of other KATs. The substrate-binding residues of mAspAT are slightly different from those of other KATs. Our results provide a biochemical and structural basis towards understanding the overall physiological role of mAspAT in vivo and insight into controlling the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.

In vivo detection of excitotoxicity by manganese-enhanced MRI: comparison with physiological stimulation

Manganese-enhanced MRI (MEMRI) is a powerful technique for the in vivo monitoring of brain function in animals. Manganese enters into cells through calcium channels, i.e., voltage-gated calcium channels and activated glutamate receptors (e.g., N-methyl-D-aspartate receptors). N-methyl-D-aspartate receptors are activated both in normal physiological and pathophysiological conditions. Consistent with these mechanisms, we showed that in the olfactory bulb, the MEMRI signal strongly increases when excitotoxic mechanisms are induced by an administration of a N-methyl-D-aspartate receptor agonist, quinolinate. We found that the intensity of the MEMRI signal in excitotoxic conditions is similar to the odor-evoked signal in normal physiological conditions. Finally, we showed that the dynamics of the MEMRI signal are determined by the early phase of manganese in the olfactory bulb. Overall, these data show that, in addition to physiological studies, MEMRI can be used as an in vivo method to follow-up the dynamics of excitotoxic events.

Behavioural studies with a newly developed neuroprotective KYNA-amide

The neuroactive properties and neuroprotective potential of endogenous L: -kynurenine, kynurenic acid (KYNA) and its derivatives are well established. KYNA acts as an antagonist on the obligatory co-agonist glycine site, and has long been at the focus of neuroprotective trials. Unfortunately, KYNA is barely able to cross the blood-brain barrier. Accordingly, the development and synthesis of KYNA analogs which can readily cross the BBB have been at the focus of research interest with the aim of neuroprotection. Earlier we reported a new KYNA-amide crosses the BBB and proved neuroprotective in several experiments. In the present study, we investigated the locomotor activity, working memory performance, and also the long-lasting, consolidated reference memory of animals treated intraperitoneally (i.p.) with the novel analog. The effects of the novel analog on the spatial orientation and learning ability of rats were assessed in the Morris water maze (MWM) paradigm. The effects on locomotor activity of mice was assessed in the open field (OF) paradigm, and those on the spatial orientation and learning ability of mice were investigated in the radial arm maze (RAM) paradigm. It emerged that there is a dose of this KYNA-amide which is neuroprotective, but does not worsen the cognitive function of the brain. This result is significant in that a putative neuroprotectant without adverse cognitive side-effects is of great benefit.

Cell signaling in NMDA preconditioning and neuroprotection in convulsions induced by quinolinic acid

The search for novel, less invasive therapeutic strategies to treat neurodegenerative diseases has stimulated scientists to investigate the mechanisms involved in preconditioning. Preconditioning has been report to occur in many organs and tissues. In the brain, the modulation of glutamatergic transmission is an important and promising target to the use of effective neuroprotective agents. The glutamatergic excitotoxicity is a factor common to neurodegenerative diseases and acute events such as cerebral ischemia, traumatic brain injury and epilepsy. In this review we focus on the neuroprotection and preconditioning by chemical agents. Specially, chemical preconditioning models using N-methyl-d-aspartate (NMDA) pre-treatment, which has demonstrated to lead to neuroprotection against seizures and damage to neuronal tissue induced by quinolinic acid (QA). Here we attempted to gather important results obtained in the study of cellular and molecular mechanisms involved in NMDA preconditioning and neuroprotection.

Neuroprotection with a new kynurenic acid analog in the four-vessel occlusion model of ischemia

Global forebrain ischemia results in damage to the pyramids in the CA1 hippocampal subfield, which is particularly vulnerable to excitotoxic processes. Morphological and functional disintegration of this area leads to a cognitive dysfunction and neuropsychiatric disorders. Treatment with N-methyl-d-aspartate receptor antagonists is a widely accepted method with which to stop the advance of excitotoxic processes and concomitant neuronal death. From a clinical aspect, competitive glycine- and polyamine-site antagonists with relatively low affinity and moderate side-effects are taken into account. Endogenous kynurenic acid acts as an antagonist on the obligatory co-agonist glycine site, and has long been at the focus of neuroprotective trials. In the present study, we estimated the neuroprotective capability of a novel kynurenic acid analog in transient global forebrain ischemia, measuring the rate of hippocampal CA1 pyramidal cell loss and the preservation of long-term potentiation at Schaffer collateral-CA1 synapses. The neuroprotective potential was reflected by a significantly diminished hippocampal CA1 cell loss and preserved long-term potentiation expression. The neuroprotective effect was robust in the event of pretreatment, and also when the drug was administered at the time of reperfusion. This result is beneficial since a putative neuroprotectant proven to be effective as post-treatment is of much greater benefit.

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

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

Characterization of the kynurenine pathway in NSC-34 cell line: implications for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common type of motor neuron degenerative disease for which the aetiology is still unknown. The kynurenine pathway (KP) is a major degradative pathway of tryptophan ultimately leading to the production of NAD(+) and is also one of the major regulatory mechanisms of the immune response. The KP is known to be involved in several neuroinflammatory disorders. Among the KP intermediates, quinolinic acid (QUIN) is a potent excitotoxin, while kynurenic acid and picolinic acid are both neuroprotectant. This study aimed to (i) characterize the components of the KP in NSC-34 cells (a rodent motor neuron cell line) and (ii) assess the effects of QUIN on the same cells. RT-PCR and immunocytochemistry were used to characterize the KP enzymes, and lactate dehydrogenase (LDH) test was used to assess the effect of QUIN in the absence and presence of NMDA receptor antagonists, kynurenines and 1-methyl tryptophan. Our data demonstrate that a functional KP is present in NSC-34 cells. LDH tests showed that (i) QUIN toxicity on NSC-34 cells increases with time and concentration; (ii) NMDA antagonists, 2-amino-5-phosphonopentanoic acid, MK-801 and memantine, can partially decrease QUIN toxicity; (iii) kynurenic acid can decrease LDH release in a linear manner, whereas picolinic acid does the same but non-linearly; and (iv) 1-methyl tryptophan is effective in decreasing QUIN release by the rodent microglial cell line BV-2 and thus protects NSC-34 from cell death. There is currently a lack of effective treatment for ALS and our in vitro results provide a novel therapeutic strategy for ALS patients.

A biological pathway linking inflammation and depression: activation of indoleamine 2,3-dioxygenase

This article highlights the evidence linking depression to increased inflammatory drive and explores putative mechanisms for the association by reviewing both preclinical and clinical literature. The enzyme indoleamine 2,3-dioxygenase is induced by proinflammatory cytokines and may form a link between immune functioning and altered neurotransmission, which results in depression. Increased indoleamine 2,3-dioxygenase activity may cause both tryptophan depletion and increased neurotoxic metabolites of the kynurenine pathway, two alterations which have been hypothesized to cause depression. The tryptophan-kynurenine pathway is comprehensively described with a focus on the evidence linking metabolite alterations to depression. The use of immune-activated groups at high risk of depression have been used to explore these hypotheses; we focus on the studies involving chronic hepatitis C patients receiving interferon-alpha, an immune activating cytokine. Findings from this work have led to novel strategies for the future development of antidepressants including inhibition of indoleamine 2,3-dioxygenase, moderating the cytokines which activate it, or addressing other targets in the kynurenine pathway.

Pharmacological characterization of some selected 4,5-dihydro-4-oxo-1,2,4-triazolo[1,5-a]quinoxaline-2-carboxylates and 3-hydroxyquinazoline-2,4-diones as (S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)-propionic acid receptor antagonists

In the present study, some selected, previously reported 4,5-dihydro-4-oxo-1,2,4-triazolo[1,5-a]quinoxaline-2-carboxylates (TQXs) and 3-hydroxy-quinazoline-2,4-diones (QZs), were evaluated for their affinity at the (S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)-propionic acid (AMPA) receptor in the [(3)H]-6-cyano-7-nitroquinoxaline-2,3-dione ([(3)H]-CNQX) binding assay. Electrophysiological experiments were performed in oocytes expressing rat homomeric GluR3 subunits in order to assess the pharmacological profile of the tested compounds. The binding data, together with those regarding the functional activity, confirmed that most of the TQXs and QZs reported herein are potent AMPA receptor antagonists. When tested for their ability to prevent sound-induced seizures in DBA/2 mice, some of these derivatives showed anticonvulsant properties.