Enmein Decreases Synaptic Glutamate Release and Protects against Kainic Acid-Induced Brain Injury in Rats

This study investigated the effects of enmein, an active constituent of Isodon japonicus Hara, on glutamate release in rat cerebrocortical nerve terminals (synaptosomes) and evaluated its neuroprotective potential in a rat model of kainic acid (KA)-induced glutamate excitotoxicity. Enmein inhibited depolarization-induced glutamate release, FM1-43 release, and Ca2+ elevation in cortical nerve terminals but had no effect on the membrane potential. Removing extracellular Ca2+ and blocking vesicular glutamate transporters, N- and P/Q-type Ca2+ channels, or protein kinase C (PKC) prevented the inhibition of glutamate release by enmein. Enmein also decreased the phosphorylation of PKC, PKC-α, and myristoylated alanine-rich C kinase substrates in synaptosomes. In the KA rat model, intraperitoneal administration of enmein 30 min before intraperitoneal injection of KA reduced neuronal cell death, glial cell activation, and glutamate elevation in the hippocampus. Furthermore, in the hippocampi of KA rats, enmein increased the expression of synaptic markers (synaptophysin and postsynaptic density protein 95) and excitatory amino acid transporters 2 and 3, which are responsible for glutamate clearance, whereas enmein decreased the expression of glial fibrillary acidic protein (GFAP) and CD11b. These results indicate that enmein not only inhibited glutamate release from cortical synaptosomes by suppressing Ca2+ influx and PKC but also increased KA-induced hippocampal neuronal death by suppressing gliosis and decreasing glutamate levels by increasing glutamate uptake.

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Baicalein, a Constituent of Scutellaria baicalensis, Reduces Glutamate Release and Protects Neuronal Cell Against Kainic Acid-Induced Excitotoxicity in Rats

The American Journal of Chinese Medicine ◽

10.1142/s0192415x1650052x ◽

2016 ◽

Vol 44 (05) ◽

pp. 943-962 ◽

Cited By ~ 13

Author(s):

Yi Chang ◽

Cheng Wei Lu ◽

Tzu Yu Lin ◽

Shu Kuei Huang ◽

Su Jane Wang

Keyword(s):

Kainic Acid ◽

Natural Compound ◽

Glutamate Release ◽

Protective Action ◽

Neuronal Cell ◽

Scutellaria Baicalensis ◽

Glutamate Excitotoxicity ◽

Flavonoid Compound ◽

Nerve Terminals

Interest in the health benefits of flavonoids, particularly their effects on neurodegenerative disease, is increasing. This study evaluated the role of baicalein, a flavonoid compound isolated from the traditional Chinese medicine Scutellaria baicalensis, in glutamate release and glutamate neurotoxicity in the rat hippocampus. In the rat hippocampal nerve terminals (synaptosomes), baicalein inhibits depolarization-induced glutamate release, and this phenomenon is prevented by chelating the extracellular Ca[Formula: see text] ions and blocking presynaptic Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel activity. In slice preparations, whole cell patch-clamp experiments revealed that baicalein reduced the frequency of miniature excitatory postsynaptic currents, without affecting their amplitude. In a kainic acid rat model, intraperitoneally administering baicalein to rats before the kainic acid intraperitoneal injection substantially attenuated kainic acid-induced neuronal cell death, c-Fos expression, and the activation of the mammalian target of rapamycin in the hippocampus. This study is the first to demonstrate that the natural compound baicalein inhibits glutamate release from hippocampal nerve terminals, and executes a protective action against kainic acid-induced excitotoxicity in vivo. The findings enhance the understanding of baicalein’s action in the brain, and suggest that this natural compound is valuable for treating brain disorders related to glutamate excitotoxicity.

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NLRX1 Enhances Glutamate Uptake and Inhibits Glutamate Release by Astrocytes

Cells ◽

10.3390/cells8050400 ◽

2019 ◽

Vol 8 (5) ◽

pp. 400 ◽

Cited By ~ 6

Author(s):

Shaimaa Mahmoud ◽

Marjan Gharagozloo ◽

Camille Simard ◽

Abdelaziz Amrani ◽

Denis Gris

Keyword(s):

Glutamate Uptake ◽

Glutamate Release ◽

Neuronal Firing ◽

Glutamate Excitotoxicity ◽

Cns Inflammation ◽

Atp Production ◽

Inflammatory Conditions ◽

Mitochondrial Functions ◽

The Central Nervous System ◽

First Time

Uptake of glutamate from the extracellular space and glutamate release to neurons are two major processes conducted by astrocytes in the central nervous system (CNS) that protect against glutamate excitotoxicity and strengthen neuronal firing, respectively. During inflammatory conditions in the CNS, astrocytes may lose one or both of these functions, resulting in accumulation of the extracellular glutamate, which eventually leads to excitotoxic neuronal death, which in turn worsens the CNS inflammation. NLRX1 is an innate immune NOD-like receptor that inhibits the major inflammatory pathways. It is localized in the mitochondria and was shown to inhibit cell death, enhance ATP production, and dampen oxidative stress. In the current work, using primary murine astrocyte cultures from WT and Nlrx1-/- mice, we demonstrate that NLRX1 potentiates astrocytic glutamate uptake by enhancing mitochondrial functions and the functional activity of glutamate transporters. Also, we report that NLRX1 inhibits glutamate release from astrocytes by repressing Ca2+-mediated glutamate exocytosis. Our study, for the first time, identified NLRX1 as a potential regulator of glutamate homeostasis in the CNS.

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Ghrelin attenuates kainic acid-induced neuronal cell death in the mouse hippocampus

Journal of Endocrinology ◽

10.1677/joe-10-0040 ◽

2010 ◽

Vol 205 (3) ◽

pp. 263-270 ◽

Cited By ~ 69

Author(s):

Jiyeon Lee ◽

Eunjin Lim ◽

Yumi Kim ◽

Endan Li ◽

Seungjoon Park

Keyword(s):

Cell Death ◽

Kainic Acid ◽

Hippocampal Neurons ◽

Therapeutic Potential ◽

Excitatory Amino Acid ◽

Neuroprotective Effect ◽

Neuronal Cell Death ◽

Neuronal Cell ◽

Proinflammatory Mediators ◽

Hippocampal Neurodegeneration

Ghrelin is an endogenous ligand for GH secretagogue receptor type 1a (GHSR1a), and is produced and released mainly from the stomach. It has been recently demonstrated that ghrelin can function as a neuroprotective factor by inhibiting apoptotic pathways. Kainic acid (KA), an excitatory amino acid l-glutamate analog, causes neuronal death in the hippocampus; previous studies suggest that activated microglia and astrocytes actively participate in the pathogenesis of KA-induced hippocampal neurodegeneration. However, it is unclear whether ghrelin has neuroprotective effect in KA-induced hippocampal neurodegeneration. I.p. injection of KA produced typical neuronal cell death in the CA1 and CA3 pyramidal layers of the hippocampus, and the systemic administration of ghrelin significantly attenuated KA-induced neuronal cell death in these regions through the activation of GHSR1a. Ghrelin prevents KA-induced activation of microglia and astrocytes, and the expression of proinflammatory mediators tumor necrosis factor α, interleukin-1β, and cyclooxygenase-2. The inhibitory effect of ghrelin on the activation of microglia and astrocytes appears to be associated with the inhibition of matrix metalloproteinase-3 expression in damaged hippocampal neurons. Our data suggest that ghrelin has a therapeutic potential for suppressing KA-induced pathogenesis in the brain.

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Permanent dynamic transporter-mediated turnover of glutamate across the plasma membrane of presynaptic nerve terminals: arguments in favor and against

Reviews in the Neurosciences ◽

10.1515/revneuro-2015-0023 ◽

2016 ◽

Vol 27 (1) ◽

pp. 71-81 ◽

Cited By ~ 26

Author(s):

Tatiana Borisova

Keyword(s):

Plasma Membrane ◽

Glutamate Uptake ◽

Glutamate Release ◽

Glutamate Transporter ◽

Long Term Potentiation ◽

Nerve Terminals ◽

Model Calculations ◽

New Vision ◽

Ambient Glutamate ◽

Energy Deprivation

AbstractMechanisms for maintenance of the extracellular level of glutamate in brain tissue and its regulation still remain almost unclear, and criticism of the current paradigm of glutamate transport and homeostasis has recently appeared. The main premise for this study is the existence of a definite and non-negligible concentration of ambient glutamate between the episodes of exocytotic release in our experiments with rat brain nerve terminals (synaptosomes), despite the existence of a very potent Na+-dependent glutamate uptake. Glutamate transporter reversal is considered as the main mechanisms of glutamate release under special conditions of energy deprivation, hypoxia, hypoglycemia, brain trauma, and stroke, underlying an increase in the ambient glutamate concentration and development of excitotoxicity. In the present study, a new vision on transporter-mediated release of glutamate as one of the main mechanisms involved in the maintenance of definite concentration of ambient glutamate under normal energetical status of nerve terminals is forwarded. It has been suggested that glutamate transporters act effectively in outward direction in a non-pathological manner, and this process is thermodynamically synchronized with uptake and provides effective outward glutamate current, thereby establishing and maintaining permanent and dynamic glutamatein/glutamateout gradient and turnover across the plasma membrane. In this context, non-transporter tonic glutamate release by diffusion, spontaneous exocytosis, cystine-glutamate exchanger, and leakage through anion channels can be considered as a permanently added ‘new’ exogenous substrate using two-substrate kinetic model calculations. Permanent glutamate turnover is of value for tonic activation of post/presynaptic glutamate receptors, long-term potentiation, memory formation, etc. Counterarguments against this mechanism are also considered.

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Evaluation of GABAergic Transmission Modulation as a Novel Functional Target for Management of Multiple Sclerosis: Exploring Inhibitory Effect of GABA on Glutamate-Mediated Excitotoxicity

Advances in Pharmacological Sciences ◽

10.1155/2014/632376 ◽

2014 ◽

Vol 2014 ◽

pp. 1-6 ◽

Cited By ~ 3

Author(s):

Ankit A. Gilani ◽

Ranjeet Prasad Dash ◽

Mehul N. Jivrajani ◽

Sandeep Kumar Thakur ◽

Manish Nivsarkar

Keyword(s):

Multiple Sclerosis ◽

Sodium Valproate ◽

Glutamate Release ◽

Inhibitory Effect ◽

Glutamate Excitotoxicity ◽

Nerve Terminals ◽

Moderate Activity ◽

Gamma Aminobutyric Acid ◽

Metabotropic Receptors ◽

Potential Implication

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system (CNS) where the communication ability of nerve cells in the brain and spinal cord with each other gets impaired. Some current findings suggest the role of glutamate excitotoxicity in the development and progression of MS. An excess release of glutamate leads to the activation of ionotropic and metabotropic receptors, thus resulting in accumulation of toxic cytoplasmic Ca2+and cell death. However, it has been observed that gamma-aminobutyric acid-A (GABAA) receptors located in the nerve terminals activate presynaptic Ca2+/calmodulin-dependent signaling to inhibit depolarization-evoked Ca2+influx and glutamate release from isolated nerve terminals, which suggest a potential implication of GABAAreceptor in management of MS. With this proof of concept, we tried to explore the potential of selective GABAAreceptor agonists or positive allosteric modulators (diazepam and phenobarbitone sodium) and GABAAlevel enhancer (sodium valproate) for management of MS by screening them for their activity in experimental autoimmune encephalomyelitis (EAE) model in rats and cuprizone-induced demyelination model in mice. In this study, sodium valproate was found to show the best activity in the animal models whereas phenobarbitone sodium showed moderate activity. However, diazepam was found to be ineffective.

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Astrocytes Maintain Glutamate Homeostasis in the CNS by Controlling the Balance between Glutamate Uptake and Release

Cells ◽

10.3390/cells8020184 ◽

2019 ◽

Vol 8 (2) ◽

pp. 184 ◽

Cited By ~ 51

Author(s):

Shaimaa Mahmoud ◽

Marjan Gharagozloo ◽

Camille Simard ◽

Denis Gris

Keyword(s):

Molecular Mechanisms ◽

Glutamate Uptake ◽

Glutamate Release ◽

Neuronal Firing ◽

Glutamate Excitotoxicity ◽

Dual Function ◽

Cns Diseases ◽

Glutamate Homeostasis ◽

Neuronal Functions ◽

Uptake And Release

Glutamate is one of the most prevalent neurotransmitters released by excitatory neurons in the central nervous system (CNS); however, residual glutamate in the extracellular space is, potentially, neurotoxic. It is now well-established that one of the fundamental functions of astrocytes is to uptake most of the synaptically-released glutamate, which optimizes neuronal functions and prevents glutamate excitotoxicity. In the CNS, glutamate clearance is mediated by glutamate uptake transporters expressed, principally, by astrocytes. Interestingly, recent studies demonstrate that extracellular glutamate stimulates Ca2+ release from the astrocytes’ intracellular stores, which triggers glutamate release from astrocytes to the adjacent neurons, mostly by an exocytotic mechanism. This released glutamate is believed to coordinate neuronal firing and mediate their excitatory or inhibitory activity. Therefore, astrocytes contribute to glutamate homeostasis in the CNS, by maintaining the balance between their opposing functions of glutamate uptake and release. This dual function of astrocytes represents a potential therapeutic target for CNS diseases associated with glutamate excitotoxicity. In this regard, we summarize the molecular mechanisms of glutamate uptake and release, their regulation, and the significance of both processes in the CNS. Also, we review the main features of glutamate metabolism and glutamate excitotoxicity and its implication in CNS diseases.

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Potential Treatment of Amyotrophic Lateral Sclerosis with Gabapentin: A Hypothesis

Annals of Pharmacotherapy ◽

10.1177/106002809502901118 ◽

1995 ◽

Vol 29 (11) ◽

pp. 1164-1167 ◽

Cited By ~ 19

Author(s):

Devin F Welty ◽

Gerald P Schielke ◽

Jeffrey D Rothstein

Keyword(s):

Amyotrophic Lateral Sclerosis ◽

Motor Neurons ◽

Excitatory Amino Acid ◽

Glutamate Uptake ◽

Glutamate Release ◽

Glutamate Toxicity ◽

Potential Treatment ◽

Glutamate Metabolism ◽

Lateral Sclerosis

Objective: To provide the biochemical rationale for the use of the new anticonvulsant agent gabapentin as a treatment for amyotrophic lateral sclerosis (ALS). Background: ALS is a neuropathologic disorder of the central nervous system characterized by a progressive loss of upper and lower motor neurons. Although the etiopathology of ALS is incompletely known, it is hypothesized that glutamatergic neurotransmission is related to neuropathology. Glutamate is an excitatory amino acid neurotransmitter that is cytotoxic when overexpressed at synaptic terminals, probably through a calcium-related mechanism. The concentration of glutamate in cerebrospinal fluid is increased in patients with ALS. The increased extracellular concentrations of glutamate may be caused by a decreased capacity of glutamate transport in brain tissue and/or abnormal glutamate metabolism. Recent success with the glutamate release inhibitor riluzole in well-controlled clinical trials supports the excitotoxic mechanism of neuropathology in patients with ALS. Potential Treatment For Als: Gabapentin has demonstrated neuroprotective properties in a model of chronic glutamate toxicity in vitro. Although the neuroprotective mechanism of action of gabapentin is currently unknown, it is hypothesized here that gabapentin decreases the rate of formation of glutamate derived from the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine. The proposed decrease in formation of glutamate from BCAAs may decrease the pool of releasable glutamate and therefore compensate for diminished glutamate uptake capacity and/or abnormal glutamate metabolism in patients with ALS. Conclusions: Based on this rationale, it is proposed that gabapentin may provide a beneficial effect in the treatment of patients with ALS.

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Regulation of Amino Acid Transport in Glioma

Neurosurgery ◽

10.1093/neuros/nyz310_315 ◽

2019 ◽

Vol 66 (Supplement_1) ◽

Author(s):

Stephanie Robert ◽

Robyn Umans ◽

Joelle Martin ◽

Harald Sontheimer

Keyword(s):

Tumor Growth ◽

Glutamate Uptake ◽

Glutamate Release ◽

Brain Slices ◽

Glutamate Excitotoxicity ◽

Transcriptional Level ◽

Pharmacological Inhibition ◽

Electrophysiological Recordings ◽

Elevated Expression

Abstract INTRODUCTION Glutamate is an important molecule in the biology of brain tumors. Glutamate reaches toxic concentrations in peritumoral tissue, contributing to tumor growth and peritumoral excitotoxicity. Mediated by the cystine-glutamate exchanger, System xc- (SXC), glutamate uptake allows production of the antioxidant glutathione (GSH), which protects cells from damage and cell death. We have shown SXC is variably expressed among glioma patients, with ∼50% demonstrating elevated expression, associated seizures, and glutamate excitotoxicity. In a clinical pilot study, we found pharmacological inhibition of SXC reduces glutamate release in gliomas with elevated SXC. We now hypothesize that differences in SXC expression is due to transcriptional and co-receptor regulation, specifically, by p53 and CD44. METHODS This study utilizes in Vivo propagated glioma xenolines to test the consequences of p53 and CD44 loss on SXC function. We use siRNA/shRNA against p53/CD44, and glutamate assays to test SXC function, as well as chromatin immunopreciptiation (ChIP) assay and immunofluorescence to detail the relationship between between p53/CD44 and SXC. Lastly, using electrophysiological recordings in live brain slices, we test peritumoral excitotoxicity due to SXC function in setting of p54/CD44 loss to determine glutamate excitotoxicity on the surrounding brain. RESULTS SXC activity and glutamate release is altered by p53 and CD44 expression, altering peritumoral excitotoxicity, invasion, and tumor growth. P53 activity transcriptionally suppresses SXC and prevents glutamate release. Furthermore, SXC is also regulated by the hyaluronan receptor CD44. CD44 appears to be a membrane co-receptor of SXC, and loss of CD44 results in decreased SXC function, and consequently the ability of glioma cells to invade and grow. CONCLUSION These studies explore new strategies to alter the abnormal glutamate biology of gliomas at a transcriptional level, which is advantageous given poor options for pharmacological inhibition of SXC. Furthermore, the expression of p53 and CD44 may have predictive value regarding treatment and prognosis of glioma.

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Role of EphrinA3 in HIV-1 Neuropathogenesis

ASN NEURO ◽

10.1177/17590914211044359 ◽

2021 ◽

Vol 13 ◽

pp. 175909142110443

Author(s):

Chitra Mohinder Singh Singal ◽

Paritosh Jaiswal ◽

Anuradha Mehta ◽

Kanza Saleem ◽

Pankaj Seth

Keyword(s):

Excitatory Amino Acid ◽

Neuronal Damage ◽

Glutamate Uptake ◽

Synaptic Activity ◽

Glutamate Excitotoxicity ◽

Amino Acid Transporters ◽

Extracellular Glutamate ◽

Hiv 1

Glial cells perform important supporting functions for neurons through a dynamic crosstalk. Neuron–glia communication is the major phenomenon to sustain homeostatic functioning of the brain. Several interactive pathways between neurons and astrocytes are critical for the optimal functioning of neurons, and one such pathway is the ephrinA3–ephA4 signaling. The role of this pathway is essential in maintaining the levels of extracellular glutamate by regulating the excitatory amino acid transporters, EAAT1 and EAAT2 on astrocytes. Human immunodeficiency virus-1 (HIV-1) and its proteins cause glutamate excitotoxicity due to excess glutamate levels at sites of high synaptic activity. This study unravels the effects of HIV-1 transactivator of transcription (Tat) from clade B on ephrinA3 and its role in regulating glutamate levels in astrocyte–neuron co-cultures of human origin. It was observed that the expression of ephrinA3 increases in the presence of HIV-1 Tat B, while the expression of EAAT1 and EAAT2 was attenuated. This led to reduced glutamate uptake and therefore high neuronal death due to glutamate excitotoxicity. Knockdown of ephrinA3 using small interfering RNA, in the presence of HIV-1 Tat B reversed the neurotoxic effects of HIV-1 Tat B via increased expression of glutamate transporters that reduced the levels of extracellular glutamate. The in vitro findings were validated in autopsy brain sections from acquired immunodeficiency syndrome patients and we found ephrinA3 to be upregulated in the case of HIV-1-infected patients. This study offers valuable insights into astrocyte-mediated neuronal damage in HIV-1 neuropathogenesis.

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Redistribution of Glutamate and Glutamine in Slices of Human Neocortex Exposed to Combined Hypoxia and Glucose Deprivation in vitro

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.1993.65 ◽

1993 ◽

Vol 13 (3) ◽

pp. 503-515 ◽

Cited By ~ 30

Author(s):

Jan-Erik Aas ◽

Jon Berg-Johnsen ◽

Elisabeth Hegstad ◽

Jon H. Laake ◽

Iver A. Langmoen ◽

...

Keyword(s):

Glial Cells ◽

Glutamate Uptake ◽

Polyclonal Antibodies ◽

Glutamate Release ◽

Glucose Deprivation ◽

Nerve Terminals ◽

Neuronal Somata ◽

Human Neocortex ◽

Axon Terminals

This study was undertaken to elucidate the roles of neurons and glial cells in the handling of glutamate and glutamine, a glutamate precursor, during cerebral ischemia. Slices (400–600 μm) from human neocortex obtained during surgery for epilepsy or brain tumors were incubated in artificial cerebrospinal fluid and subjected to 30 min of combined hypoxia and glucose deprivation (an in vitro model of brain ischemia). These slices, and control slices that had not been subjected to “ischemic” conditions, were then fixed and embedded. Ultrathin sections were processed according to a postembedding immunocytochemical method with polyclonal antibodies raised against glutamate or glutamine, followed by colloidal gold-labeled secondary antibodies. The gold particle densities over various tissue profiles were calculated from electron micrographs using a specially designed computer program. Combined hypoxia and glucose deprivation caused a reduced glutamate immunolabeling in neuronal somata, while that of glial processes increased. Following 1 h of recovery, the glutamate labeling of neuronal somata declined further to very low values, compared to control slices. The glutamate labeling of glial cells returned to normal levels following recovery. In axon terminals, no consistent change in the level of glutamate immunolabeling was observed. Immunolabeling of glutamine was low in both nerve terminals and neuronal somata in normal slices and was reduced to nondetectable levels in nerve terminals upon hypoxia and glucose deprivation. This treatment was also associated with a reduced glutamine immunolabeling in glial cells. Reversed glutamate uptake due to perturbations of the transmembrane ion concentrations and membrane potential probably contributes to the loss of neuronal glutamate under “ischemic” conditions. The increased glutamate labeling of glial cells under the same conditions can best be explained by assuming that glial cells resist a reversal of glutamate uptake, and that their ability to convert glutamate into glutamine is compromised due to the energy failure. The persistence of a nerve terminal pool of glutamate is compatible with recent biochemical data indicating that the exocytotic glutamate release is contingent on an adequate energy supply and therefore impeded during ischemia.

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