Glutamate-induced Neuronal Damage Research Articles

Epigallocatechin gallate improves neuronal damage in animal model of ischemic stroke and glutamate-exposed neurons via modulation of hippocalcin expression.

Epigallocatechin gallate (EGCG) is a polyphenolic component of green tea that has anti-oxidative and anti-inflammatory effects in neurons. Ischemic stroke is a major neurological disease that causes irreversible brain disorders. It increases the intracellular calcium concentration and induces apoptosis. The regulation of intracellular calcium concentration is important to maintain the function of the nervous system. Hippocalcin is a neuronal calcium sensor protein that controls intracellular calcium concentration. We investigated whether EGCG treatment regulates the expression of hippocalcin in stroke animal model and glutamate-induced neuronal damage. We performed middle cerebral artery occlusion (MCAO) to induce cerebral ischemia. EGCG (50 mg/kg) or phosphate buffered saline was injected into the abdominal cavity just before MCAO surgery. The neurobehavioral tests were performed 24 h after MCAO surgery and cerebral cortex tissue was collected. MCAO damage induced severe neurobehavioral disorders, increased infarct volume, and decreased the expression of hippocalcin in the cerebral cortex. However, EGCG treatment improved these deficits and alleviated the decrease in hippocalcin expression in cerebral cortex. In addition, EGCG dose-dependently alleviated neuronal cell death and intracellular calcium overload in glutamate-exposed neurons. Glutamate exposure reduced hippocalcin expression, decreased Bcl-2 expression, and increased Bax expression. However, EGCG treatment mitigated these changes caused by glutamate toxicity. EGCG also attenuated the increase in caspase-3 and cleaved caspase-3 expressions caused by glutamate exposure. The effect of EGCG was more pronounced in non-transfected cells than in hippocalcin siRNA-transfected cells. These findings demonstrate that EGCG protects neurons against glutamate toxicity through the regulation of Bcl-2 family proteins and caspase-3. It is known that hippocalcin exerts anti-apoptotic effect through the modulation of apoptotic pathway. Thus, we can suggest evidence that EGCG has a neuroprotective effect by regulating hippocalcin expression in ischemic brain damage and glutamate-exposed cells.

Lutein inhibits glutamate-induced apoptosis in HT22 cells via the Nrf2/HO-1 signaling pathway.

Excessive glutamate levels induce oxidative stress, resulting in neuronal damage, and cell death. While natural antioxidants show promise for neuroprotection, their effectiveness in the central nervous system (CNS) is limited by the blood -brain barrier. Lutein, a neuroprotective carotenoid, has gained attention for its ability to traverse this barrier and accumulate in various brain regions. This study aimed to elucidate the mechanisms underlying the protective effects of lutein against glutamateinduced cell death in HT22 cells. HT22 cells were treated with lutein (1.25-20 μM) for 24 hours. Cell viability, ROS levels, apoptosis, and mitochondrial membrane potential were assessed following lutein pretreatment and glutamate exposure. Protein expression of apoptotic markers was analyzed using Western blotting. Lutein effectively attenuated glutamate-induced apoptosis due to its antioxidant properties. Additionally, lutein inhibited glutamate-induced mitochondrial-mediated apoptosis. We observed that lutein modulated the nuclear translocation of nuclear factor erythroid 2 -related factor 2 (Nrf2) and upregulated the expression of heme oxygenase-1 (HO-1). Inhibition of HO-1 by tin protoporphyrin (SnPP), a synthetic inhibitor, weakened the protective effect of lutein. Furthermore, we demonstrated that lutein prevented the aberrant activation of MAPKs induced by glutamate, including ERK1/2, p38, and JNK, thereby conferring oxidative protection. Our study highlights the potent antioxidant properties of lutein, which effectively safeguards against glutamate-induced mitochondrial apoptotic cell death through the Nrf2/HO-1 signaling pathway and inhibition of MAPK activation. These findings demonstrate that lutein exerts a neuroprotective effect against glutamate-induced neuronal cell damage.

Protective Effects of 3'-Epilutein and 3'-Oxolutein against Glutamate-Induced Neuronal Damage.

Dietary lutein can be naturally metabolized to 3'-epilutein and 3'-oxolutein in the human body. The epimerization of lutein can happen in acidic pH, and through cooking, 3'-epilutein can be the product of the direct oxidation of lutein in the retina, which is also present in human serum. The 3'-oxolutein is the main oxidation product of lutein. Thus, the allylic oxidation of dietary lutein can result in the formation of 3'-oxolutein, which may undergo reduction either to revert to dietary lutein or epimerize to form 3'-epilutein. We focused on the effects of 3'-epilutein and 3'-oxolutein itself and on glutamate-induced neurotoxicity on SH-SY5Y human neuroblastoma cells to identify the possible alterations in oxidative stress, inflammation, antioxidant capacity, and iron metabolism that affect neurological function. ROS measurements were performed in the differently treated cells. The inflammatory state of cells was followed by TNFα, IL-6, and IL-8 cytokine ELISA measurements. The antioxidant status of the cells was determined by the total antioxidant capacity kit assay. The alterations of genes related to ferroptosis and lipid peroxidation were followed by gene expression measurements; then, thiol measurements were performed. Lutein metabolites 3'-epilutein and 3'-oxolutein differently modulated the effect of glutamate on ROS, inflammation, ferroptosis-related iron metabolism, and lipid peroxidation in SH-SY5Y cells. Our results revealed the antioxidant and anti-inflammatory features of 3'-epilutein and 3'-oxolutein as possible protective agents against glutamate-induced oxidative stress in SH-SY5Y cells, with greater efficacy in the case of 3'-epilutein.

Blocking ERK-DAPK1 Axis Attenuates Glutamate Excitotoxicity in Epilepsy.

Glutamate excitotoxicity induces neuronal cell death during epileptic seizures. Death-associated protein kinase 1 (DAPK1) expression is highly increased in the brains of epilepsy patients; however, the underlying mechanisms by which DAPK1 influences neuronal injury and its therapeutic effect on glutamate excitotoxicity have not been determined. We assessed multiple electroencephalograms and seizure grades and performed biochemical and cell death analyses with cellular and animal models. We applied small molecules and peptides and knocked out and mutated genes to evaluate the therapeutic efficacy of kainic acid (KA), an analog of glutamate-induced neuronal damage. KA administration increased DAPK1 activity by promoting its phosphorylation by activated extracellular signal-regulated kinase (ERK). DAPK1 activation increased seizure severity and neuronal cell death in mice. Selective ERK antagonist treatment, DAPK1 gene ablation, and uncoupling of DAPK1 and ERK peptides led to potent anti-seizure and anti-apoptotic effects in vitro and in vivo. Moreover, a DAPK1 phosphorylation-deficient mutant alleviated glutamate-induced neuronal apoptosis. These results provide novel insight into the pathogenesis of epilepsy and indicate that targeting DAPK1 may be a potential therapeutic strategy for treating epilepsy.

Icaritin Alleviates Glutamate-Induced Neuronal Damage by Inactivating GluN2B-Containing NMDARs Through the ERK/DAPK1 Pathway

Excitatory toxicity due to excessive glutamate release is considered the core pathophysiological mechanism of cerebral ischemia. It is primarily mediated by N-methyl-D-aspartate receptors (NMDARs) on neuronal membranes. Our previous studies have found that icaritin (ICT) exhibits neuroprotective effects against cerebral ischemia in rats, but the underlying mechanism is unclear. This study aims to investigate the protective effect of ICT on glutamate-induced neuronal injury and uncover its possible molecular mechanism. An excitatory toxicity injury model was created using rat primary cortical neurons treated with glutamate and glycine. The results showed that ICT has neuroprotective effects on glutamate-treated primary cortical neurons by increasing cell viability while reducing the rate of lactate dehydrogenase (LDH) release and reducing apoptosis. Remarkably, ICT rescued the changes in the ERK/DAPK1 signaling pathway after glutamate treatment by increasing the expression levels of p-ERK, p-DAPK1 and t-DAPK1. In addition, ICT also regulates NMDAR function during glutamate-induced injury by decreasing the expression level of the GluN2B subunit and enhancing the expression level of the GluN2A subunit. As cotreatment with the ERK-specific inhibitor U0126 and ICT abolishes the beneficial effects of ITC on the ERK/DAPK1 pathway, NMDAR subtypes and neuronal cell survival, ERK is recognized as a crucial mediator in the protective mechanism of ICT. In conclusion, our findings demonstrate that ICT has a neuroprotective effect on neuronal damage induced by glutamate, and its mechanism may be related to inactivating GluN2B-containing NMDAR through the ERK/DAPK1 pathway. This study provides a new clue for the prevention and treatment of clinical ischemic cerebrovascular diseases.

Quercetin Reduces Ischemic Brain Injury by Preventing Ischemia-induced Decreases in the Neuronal Calcium Sensor Protein Hippocalcin

Calcium acts as a second messenger that mediates physiologic functions, such as metabolism, cell proliferation, and apoptosis. Hippocalcin is a neuronal calcium sensor protein that regulates intracellular calcium concentration. Moreover, it prevents neuronal cell death from oxidative stress. Quercetin has excellent antioxidant properties and preventative effects. We studied modulation of hippocalcin expression by quercetin treatment in cerebral ischemic injury and glutamate-induced neuronal cell damage. Focal cerebral ischemia was induced by permanent middle cerebral artery occlusion (pMCAO). Male Sprague-Dawley rats were injected with vehicle or quercetin (10 mg/kg) 1 h prior to pMCAO, and cerebral cortical tissues were isolated 24 h after pMCAO. Quercetin improved pMCAO-induced neuronal movement deficit and infarction. pMCAO induced a decrease in hippocalcin expression in the cerebral cortex. However, quercetin treatment attenuated this pMCAO-induced decrease. In cultured hippocampal cells, glutamate excitotoxicity dramatically increased the intracellular calcium concentration, whereas quercetin alleviated intracellular calcium overload. Moreover, Western blot and immunocytochemical studies showed reduction of hippocalcin expression in glutamate-exposed cells. Quercetin prevented this glutamate-induced decrease. Furthermore, caspase-3 expression in hippocalcin siRNA transfection conditions is higher than caspase-3 expression in un-transfection conditions. Quercetin treatment attenuated the increase of caspase-3. Taken together, these results suggest that quercetin exerts a preventative effect through attenuation of intracellular calcium overload and restoration of down-regulated hippocalcin expression during ischemic injury.

4,5 caffeoylquinic acid and scutellarin, identified by integrated metabolomics and proteomics approach as the active ingredients of Dengzhan Shengmai, act against chronic cerebral hypoperfusion by regulating glutamatergic and GABAergic synapses

Dengzhan Shengmai (DZSM) is a proprietary Chinese medicine for remarkable curative effect as a treatment of cerebrovascular diseases, such as chronic cerebral hypoperfusion (CCH) and dementia based on evidence-based medicine, which have been widely used in the recovery period of ischemic cerebrovascular diseases. The purpose of this study was to investigate the active substances and mechanism of DZSM against CCH. Integrative metabolomic and proteomic studies were performed to investigate the neuroprotective effect of DZSM based on CCH model rats. The exposed components of DZSM in target brain tissue were analysed by a high-sensitivity HPLC-MS/MS method, and the exposed components were tested on a glutamate-induced neuronal excitatory damage cell model for the verification of active ingredients and mechanism of DZSM. Upon proteomic and metabolomic analysis, we observed a significant response in DZSM therapy from the interconnected neurotransmitter transport pathways including glutamatergic and GABAergic synapses. Additionally, DZSM had a significant regulatory effect on glutamate and GABA-related proteins including vGluT1 and vIAAT, suggested that DZSM could be involved in the vesicle transport of excitatory and inhibitory neurotransmitters in the pre-synaptic membrane. DZSM could also regulated the metabolism of arachidonic acid (AA), phospholipids, lysophospholipids and the expression of phospholipase A2 in post-synaptic membrane. The results of glutamate-induced neuronal excitatory injury cell model experiment for verification of active ingredients and mechanism of DZSM showed that there are five active ingredients, and among them, 4,5 caffeoylquinic acid (4,5-CQA) and scutellarin (SG) could simultaneously affect the GABAergic and glutamatergic synaptic metabolism as well as the related receptors, the NR2b subunit of NMDA and the α1 subunit of GABAA. The active ingredients of DZSM could regulate the over-expression of the NMDA receptor, enhance the expression of the GABAA receptor, resist glutamate-induced neuronal excitatory damage, and finally maintain the balance of excitatory and inhibitory synaptic metabolism dominated by glutamate and GABA. Furtherly, we compared the efficacy of DZSM, 4,5-CQA, SG and the synergistic effect of 4,5-CQA and SG, and the results showed that all the groups significantly improved cell viability compared with the model group (p < 0.001). The western blot results showed that DZSM, 4,5-CQA, SG and 4,5-CQA/SG co-administration groups could significantly regulate the expression of receptors (GABAA α1 and NR2b subunit of NMDA) and synaptic-related proteins, such as Sv2a, Syp, Slc17a7, bin1 and Prkca, respectively. These results proved DZSM and its active ingredients (4,5-CQA and SG) had the effect of regulating glutamatergic and GABAergic synapses. Finally, membrane potential FLIPR assay of 4,5-CQA and SG was used for GABRA1 activity test, and it was found that the two compounds could increase GABA-induced activation of GABRA1 receptor (GABA 10 μM) in a dose-dependent manner with EC50 value of 48.74 μM and 29.77 μM, respectively. Manual patch clamp method was used to record NMDA NR1/NR2B subtype currents, and scutellarin could cause around 10 % blockade at 10 μM (p＜0.05 compared with the control group). These studies provided definitive clues of the mechanism for the neuroprotective effect of DZSM for CCH treatment and the active compounds regulating glutamatergic and GABAergic synapses. Additionally, 4,5-CQA and SG might be potential drugs for the treatment of neurodegenerative disease related to CCH.

Quercetin Attenuates Decrease of Thioredoxin Expression Following Focal Cerebral Ischemia and Glutamate-induced Neuronal Cell Damage

Quercetin is a bioactive flavonoid which abundantly exists in vegetables and fruits. Quercetin exerts a neuroprotective effect against cerebral ischemia. Thioredoxin acts as antioxidant by regulating redox signaling. This study investigated whether quercetin regulates thioredoxin expression in focal cerebral ischemia and glutamate-induced neuronal cell death. Male Sprague Dawley rats (210–230 g) were intraperitoneally injected with vehicle or quercetin (10 mg/kg) 1 h prior to middle cerebral artery occlusion (MCAO). Cerebral cortex was collected 24 h after MCAO. MCAO led to neurological movement deficits, brain edema, and serious histopathological damages in cerebral cortex, and quercetin alleviated these damages following MCAO. We observed the change of thioredoxin expression in MCAO animals with quercetin using proteomic approach, reverse-transcription PCR, and Western blot analyses. Thioredoxin expression decreased in vehicle-treated MCAO animals, while quercetin attenuated this decrease. Moreover, quercetin treatment alleviated the decrease in the number of thioredoxin-positive cells in cerebral cortex of MCAO animals. Furthermore, immunoprecipitation analysis demonstrated that interaction of apoptosis signal-regulating kinase 1 (ASK1) and thioredoxin was decreased in MCAO animals with vehicle, while quercetin prevented MCAO-induced decrease in these binding. In addition, quercetin also alleviated the reduction of cell viability and the decrease in thioredoxin expression in glutamate-treated hippocampal cell line and primary cultures of cortical neurons. However in thioredoxin-silenced cortical neuron, anti-apoptotic effect of quercetin was decreased. Thus, changes of thioredoxin expression by quercetin may contribute to the neuroprotective effect of quercetin in focal cerebral ischemia. Our findings suggest that quercetin mediates its neuroprotective function by regulation of thioredoxin expression and maintenance of interaction between ASK1 and thioredoxin.

Xiaoyaosan exerts antidepressant-like effects by regulating the functions of astrocytes and EAATs in the prefrontal cortex of mice

BackgroundMounting evidence indicates that the cerebral cortex is an important physiological system of emotional activity, and its dysfunction may be the main cause of stress. Glutamate is the primary excitatory neurotransmitter in the central nervous system (CNS), which initiates rapid signal transmission in the synapse before its reuptake into the surrounding glia, specifically astrocytes (ASTs). The astrocytic excitatory amino acid transporters 1 (EAAT1) and 2 (EAAT2) are the major transporters that take up synaptic glutamate to maintain optimal extracellular glutamic levels, thus preventing accumulation in the synaptic cleft and ensuing excitotoxicity. Growing evidence has shown that excitotoxicity is associated with depression. Therefore, we hypothesized that the underlying antidepressant-like mechanism of Xiaoyaosan (XYS), a Chinese herbal formula, may be related to the regulation of astrocytic EAATs. Therefore, we studied the antidepressant mechanism of XYS on the basis of EAAT dysfunction in ASTs.MethodsEighty adult C57BL/6 J mice were randomly divided into 4 groups: a control group, a chronic unpredictable mild stress (CUMS) group, a Xiaoyaosan (XYS) treatment group and a fluoxetine hydrochloride (Flu) treatment group. Except for the control group, mice in the other groups all received chronic unpredictable mild stress for 21 days. Mice in the control and CUMS groups received gavage administration with 0.5 mL of normal saline (NS) for 21 days, and mice in the XYS and Flu treatment groups were administered dosages of 0.25 g/kg/d and 2.6 mg/kg/d by gavage. The effects of XYS on the depressive-like behavioral tests, including the open field test (OFT), forced swimming test (FST) and sucrose preference test (SPT), were examined. The glutamate (Glu) concentrations of the prefrontal cortex (PFC) were detected with colorimetry. The morphology of neurons in the PFC was observed by Nissl staining. The expression of glial fibrillary acidic protein (GFAP), NeuN, EAAT1 and EAAT2 proteins in the PFC of mice was detected by using Western blotting and immunohistochemistry. Quantitative real-time PCR (qPCR) was used to detect the expression of the GFAP, NeuN, EAAT1 and EAAT2 genes in the PFC of mice.ResultsThe results of behavioral tests showed that CUMS-induced mice exhibited depressive-like behavior, which could be improved in some tests with XYS and Flu treatment. Immunohistochemistry and Western blot analysis showed that the protein levels of GFAP, NeuN, EAAT1 and EAAT2 in the PFC of CUMS mice were significantly lower than those in the control group, and these changes could be reversed by XYS and Flu. The results of qPCR analysis showed that the expression of GFAP, NeuN, EAAT1 and EAAT2 mRNAs in the PFC of CUMS mice was not significantly changed, with the exception of EAAT2, compared with that of the control group, while the expression of the above mRNAs was significantly higher in the XYS and Flu groups than that in the CUMS group.ConclusionXYS may exert antidepressant-like effects by improving the functions of AST and EAATs and attenuating glutamate-induced neuronal damage in the frontal cortex.

A Novel Tetramethylpyrazine Derivative Protects Against Glutamate-Induced Cytotoxicity Through PGC1α/Nrf2 and PI3K/Akt Signaling Pathways.

Glutamate-induced excitotoxicity is one of the main causes of neuronal cell death in stroke. Compound 22a has been previously reported as a promising neuroprotective compound derived from tetramethylpyrazine, which is a widely used active ingredient of traditional Chinese medicine Chuanxiong (Ligusticum wallichii Franchat). Compound 22a can protect neurons from oxidative stress-induced PC12 cell death and alleviates the infarct areas and brain edema in a rat permanent middle cerebral artery occlusion model. In the current work, we further investigated the neuroprotective effects and underlying mechanisms of compound 22a against glutamate-induced excitotoxicity in primary culture of rat cerebellar granule neurons (CGNs). We found that pretreatment with compound 22a prevented glutamate-induced neuronal damage by maintaining mitochondrial membrane potential and attenuating cellular apoptosis. Compound 22a could also enhance peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) transcriptional activity and induce nuclear accumulation of Nrf2 in PC12 cells. Accordingly, pretreatment with compound 22a reversed the glutamate-induced down-regulation of expression of the proteins PGC1α, transcriptional factor NF-E2-related factor 2 (Nrf2), and hemooxygenase 1 (HO-1). In addition, compound 22a increased the phosphorylation of phosphoinositide 3-kinase (p-PI3K), phosphorylated protein kinase B (p-Akt), and glycogen synthase kinase 3β (p-GSK3β). Meanwhile, the small interfering RNA-mediated silencing of PGC1α expression and selective inhibitors targeting PI3K/Akt (LY294002 and Akt-iv) could significantly attenuate the neuroprotective effect of compound 22a. Taken together, compound 22a protected against glutamate-induced CGN injury possibly in part through regulation of PGC1α/Nrf2 and PI3K/Akt pathways.

Therapeutic window for YC‑1 following glutamate‑induced neuronal damage and transient focal cerebral ischemia.

3-(5′-Hydroxymethyl-2′-furyl)-1-benzylindazole (YC-1), has been demonstrated to inhibit platelet aggregation, vascular contraction and hypoxia-inducible factor 1 activity in vitro and in vivo. The present study investigated the neuroprotective efficacy of YC-1 in cultured neurons exposed to glutamate-induced excitotoxicity and in an animal model of stroke. In a cortical neuronal culture model, YC-1 demonstrated neurotoxicity at a concentration >100 µM, and YC-1 (10–30 µM) achieved potent cytoprotection against glutamate-induced neuronal damage. Additionally, YC-1 (30 µM) effectively attenuated the increase in intracellular Ca2+ levels. Delayed treatment of YC-1 (30 µM) also protected against glutamate-induced neuronal damage and cell swelling in cultured neurons, though only at 4 h post-treatment. In addition, immediate treatment of YC-1 (30 µM) following the exposure of cortical neurons to glutamate (300 µM) produced a marked reduction in intracellular pH. Delayed treatment of YC-1 (25 mg/kg) protected against ischemic brain damage in vivo, though only when administered at 3 h post-insult. Thus, YC-1 exhibited neuroprotection against glutamate-induced neuronal damage and in mice subjected to transient focal cerebral ischemia. This neuroprotection may be mediated via its ability to limit the glutamate-induced excitotoxicity. However, the neuroprotective therapeutic window of YC-1 is only at 3 h in vivo and 4 h in vitro, which may, at least in part, be attributed to its ability to reduce the intracellular pH in the early phase of ischemic stroke. Although YC-1 provided the potential for clinical therapy, the treatment time point must be carefully evaluated following ischemia.

Controlled Release of Ursodeoxycholic Acid from Pullulan Acetate Nanoparticles to Modulate Glutamate-Induced Excitotoxicity in PC-12 Cells

The neuroprotective effects of the ursodeoxycholic acid- (UDCA-) loaded pullulan acetate (PA) (UDCA-PA) nanospheres stabilized by poly(vinyl alcohol) (PVA) were identified by in vitro study. The UDCA-PA nanospheres were constructed by nanoemulsion process. The UDCA-PA nanospheres were analyzed using Fourier transform-infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). Then, the UDCA-PA nanospheres were used to treat PC-12 neuronal cells, which were formerly triggered by glutamate-induced excitotoxicity. As a result, the cells treated with the UDCA-PA nanospheres showed higher survival rate against glutamate-induced excitotoxicity. Furthermore, the UDCA-PA nanospheres decreased immunoreactivity of Annexin V, a membrane marker for apoptotic cells, in PC-12 with glutamate-induced injury. Particularly, the UDCA-PA nanospheres decreased the level of apoptosis-related proteins such as caspase-3. Taken together, the UDCA-PA nanospheres increased neuroprotective effects against glutamate-induced neuronal damage via inhibition of apoptosis at low concentration.

Ecdysterones from Rhaponticum carthamoides (Willd.) Iljin reduce hippocampal excitotoxic cell loss and upregulate mTOR signaling in rats

Glutamate-induced excitotoxicity is a key pathological mechanism in many neurological disease states. Ecdysterones derived from Rhaponticum carthamoides (Willd.) Iljin (RCI) have been shown to alleviate glutamate-induced neuronal damage; although their mechanism of action is unclear, some data suggest that they enhance signaling in the mechanistic target of rapamycin (mTOR) signaling pathway. This study sought to elucidate the mechanisms underlying ecdysterone-mediated neuroprotection. We used in silico target prediction and simulation methods to identify putative ecdysterone binding targets, and to specifically identify those that represent nodes where several neurodegenerative diseases converge. We then used histological analyses in a rat hippocampal excitotoxicity model to test the effectiveness of ecdysterones in vivo. We found that RCI-derived ecdysterones should bind to glutamatergic NMDA-type receptors (NMDARs); specifically, in vivo modeling showed binding to the GRIN2B subunit of NMDARs, which was found also to be a node of convergence in several neurodegenerative disease pathways. Computerized network construction by using pathway information from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database showed putative links between GRIN2B and mTOR pathway elements including phosphoinositide-3kinase (PI3K), mTOR, and protein kinase C (PKC); these elements are associated with neuronal survival. Brain tissue western blots of ecdysterone-treated rats showed upregulated PI3K, Akt, mTOR, and phosphorylated Akt and mTOR, and down regulated GRIN2B and the apoptotic enzyme cleaved caspase-3. Ecdysterone treatment also prevented glutamate-induced rat hippocampal cell loss. In summary, RCI-derived ecdysterones appear to prevent glutamatergic excitotoxicity by increasing mTOR/Akt/PI3K signaling activity.

Anti-oxidative and anti-inflammatory effects of 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride on glutamate-induced neurotoxicity in rat brain

In a previous in vitro study, we demonstrated the protective effects of a new drug, 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride (KHG26377), against glutamate-induced excitotoxicity in cultured glial cells. In this study, we explored the possible mechanisms underlying the neuroprotective and anti-inflammatory effects of this compound against glutamate-induced excitotoxicity in rat brain. Our results showed that pretreatment with KHG26377 significantly attenuated glutamate-induced elevation of lipid peroxidation, TNF-α, IFN-γ, nitric oxide, reactive oxygen species, NADPH oxidase, and Ca2+ levels, as well as the expression of caspase-3, neuronal nitric oxide synthase, and pERK. Furthermore, KHG26377 pretreatment attenuated key antioxidant parameters such as levels of superoxide dismutase, catalase, glutathione, glutathione peroxidase, and glutathione reductase, and also mitigated suppression of mitochondrial transmembrane potential by glutamate toxicity. Thus, through its antioxidant and anti-inflammatory activities in rat brain, KHG26377 may help protect against glutamate-induced neuronal damage.

Lanthionine Synthetase C-like Protein 1 Interacts with and Inhibits Cystathionine β-Synthase: A TARGET FOR NEURONAL ANTIOXIDANT DEFENSE

The finding that eukaryotic lanthionine synthetase C-like protein 1 (LanCL1) is a glutathione-binding protein prompted us to investigate the potential relationship between LanCL1 and cystathionine β-synthase (CBS). CBS is a trans-sulfuration enzyme critical for the reduced glutathione (GSH) synthesis and GSH-dependent defense against oxidative stress. In this study we found that LanCL1 bound to CBS in mouse cortex and HEK293 cells. Mapping studies revealed that the binding region in LanCL1 spans amino acids 158-169, and that in CBS contains N-terminal and C-terminal regulatory domains. Recombinant His-LanCL1 directly bound endogenous CBS from mouse cortical lysates and inhibited its activity. Overexpression of LanCL1 inhibited CBS activity in HEK293 cells. CBS activity is reported to be regulated by oxidative stress. Here we found that oxidative stress induced by H(2)O(2) or glutamate lowered the GSH/GSSG ratio, dissociated LanCL1 from CBS, and elevated CBS activity in primary rat cortical neurons. Decreasing the GSH/GSSG ratio by adding GSSG to cellular extracts also dissociated LanCL1 from CBS. Either lentiviral knockdown of LanCL1 or specific disruption of the LanCL1-CBS interaction using the peptide Tat-LanCL1(153-173) released CBS activity in neurons but occluded CBS activation in response to oxidative stress, indicating the major contribution of the LanCL1-CBS interaction to the regulation of CBS activity. Furthermore, LanCL1 knockdown or Tat-LanCL1(153-173) treatment reduced H(2)O(2) or glutamate-induced neuronal damage. This study implies potential therapeutic value in targeting the LanCL1-CBS interaction for neuronal oxidative stress-related diseases.

Neuroprotection of Ilex latifolia and caffeoylquinic acid derivatives against excitotoxic and hypoxic damage of cultured rat cortical neurons

Ilex latifolia (Aquifoliaceae), one of the primary components of "Ku-ding-cha", has been used in Chinese folk medicine to treat headaches and various inflammatory diseases. A previous study demonstrated that the ethanol extract of I. latifolia could protect against ischemic apoptotic brain damage in rats. The present study investigated the protective activity of I. latifolia against glutamate-induced neurotoxicity using cultured rat cortical neurons in order to explain a possible mechanism related to its inhibitory effect on ischemic brain damage and identified potentially active compounds from it. Exposure of cultured cortical neurons to 500 μM glutamate for 12 h triggered neuronal cell death. I. latifolia (10-100 μg/mL) inhibited glutamate-induced neuronal death, elevation of intracellular calcium ([Ca(2+)](i)), generation of reactive oxygen species (ROS), the increase of a pro-apoptotic protein, BAX, and the decrease of an anti-apoptotic protein, BcL-2. Hypoxia-induced neuronal cell death was also inhibited by I. latifolia. 3,4-Dicaffeoylquinic acid (diCQA), 3,5-diCQA, and 3,5-diCQA methyl ester isolated from I. latifolia also inhibited the glutamate-induced increase in [Ca(2+)](i), generation of ROS, the change of apoptosis-related proteins, and neuronal cell death; and hypoxia-induced neuronal cell death. These results suggest that I. latifolia and its active compounds prevented glutamate-induced neuronal cell damage by inhibiting increase of [Ca(2+)](i), generation of ROS, and resultantly apoptotic pathway. In addition, the neuroprotective effects of I. latifolia on ischemia-induced brain damage might be associated with the anti-excitatory and anti-oxidative actions and could be attributable to these active compounds, CQAs.

NMDA receptor signaling: death or survival?

Glutamate-induced neuronal damage is mainly caused by overactivation of N-methyl-D-aspartate (NMDA) receptors. Conversely, normal physiological brain function and neuronal survival require adequate activation of NMDA receptors. Studies have revealed that NMDA receptor-induced neuronal death or survival is mediated through distinct subset of NMDA receptors triggering different intracellular signaling pathways. Here we discuss recent advances in the characterization of NMDA receptors in neuronal protection, emphasizing subunit-specific role, which contributes to temporal-spatial distribution, subcellular localization and diverse channel properties of NMDA receptors.

Dammarane derivatives protect cultured rat cortical cells from glutamate-induced neurotoxicity.

We previously reported that ginsenosides Rb1 and Rg3, dammarane glycosides, of Panax ginseng C. A. Meyer (Araliaceae), significantly attenuated glutamate-induced neurotoxicity in primary cultures of rat cortical cells. To seek more potent neuroprotective compounds, we attempted to modify the chemical structure of dammarane glycosides and obtained six derivatives, MA-11, PT-11, PT-111, POA-101, POA-111 and N-001. The neuroprotective activity of these dammarane derivatives were evaluated employing primary cultures of rat corticoid cells. The glutamate-induced neuronal cell damage was significantly reduced by a pre-treatment with protopanaxadiol, MA-11 or PT-11 at concentrations ranging from 100 nM to 10 microM. Both MA-11 and PT-11, preserved the levels of catalase and inhibited decreases in glutathione reductase in glutamate-injured cells. Furthermore, the dammarane derivatives reduced the content of intracellular peroxide in glutamate-intoxicated cells. Finally, they inhibited the formation of malondialdehyde, a compound produced during lipid peroxidation, in glutamate-insulted cells. These results show that the dammarane derivatives, MA-11 and PT-11, exert significant neuroprotective effects on cultured cortical cells by a mechanism seemingly distinct from that afforded by ginsenosides Rb1 and Rg3. As such, the dammarane derivatives may be efficacious in protecting neurons from oxidative damage caused by exposure to excess glutamate.

Platelet-derived Growth Factor Selectively Inhibits NR2B-containing N-Methyl-D-aspartate Receptors in CA1 Hippocampal Neurons

Platelet-derived growth factor (PDGF) beta receptor activation inhibits N-methyl-d-aspartate (NMDA)-evoked currents in hippocampal and cortical neurons via the activation of phospholipase Cgamma, PKC, the release of intracellular calcium, and a rearrangement of the actin cytoskeleton. In the hippocampus, the majority of NMDA receptors are heteromeric; most are composed of 2 NR1 subunits and 2 NR2A or 2 NR2B subunits. Using NR2B- and NR2A-specific antagonists, we demonstrate that PDGF-BB treatment preferentially inhibits NR2B-containing NMDA receptor currents in CA1 hippocampal neurons and enhances long-term depression in an NR2B subunit-dependent manner. Furthermore, treatment of hippocampal slices or cultures with PDGF-BB decreases the surface localization of NR2B but not of NR2A subunits. PDGFbeta receptors colocalize to a higher degree with NR2B subunits than with NR2A subunits. After neuronal injury, PDGFbeta receptors and PDGF-BB are up-regulated and PDGFbeta receptor activation is neuroprotective against glutamate-induced neuronal damage in cultured neurons. We demonstrate that the neuroprotective effects of PDGF-BB are occluded by the NR2B antagonist, Ro25-6981, and that PDGF-BB promotes NMDA signaling to CREB and ERK1/2. We conclude that PDGFbetaR signaling, by preferentially targeting NR2B receptors, provides an important mechanism for neuroprotection by growth factors in the central nervous system.

Achyranthes bidentata Blume extract protects cultured hippocampal neurons against glutamate-induced neurotoxicity

We have prepared an aqueous extract of Achyranthes bidentata Blume, a Chinese medicinal herb commonly prescribed for arthritis treatment or immnopotentiation, and have found that Achyranthes bidentata extract promotes nerve growth and prevents neuronal apoptosis. Aim of the study To investigate the protective effect of Achyranthes bidentata extract against glutamate-induced neurotoxicity in primary culture of rat hippocampal neurons. Materials and methods We accomplished MTT assay for cell viability, Hoechst 33342 staining, and flow cytometry for cell apoptosis analysis to examine the effects of Achyranthes bidentata extract on glutamate-induced neurotoxicity, and also used Fluo 4-AM measurement, RT-PCR and Western blot analysis to determine the changes in intracellular calcium concentration [Ca 2+] I, and mRNA and protein levels of Bcl-2, respectively, concurrently accompanied with the influences of Achyranthes bidentata extract. Results Achyranthes bidentata extract was found to inhibit glutamate-induced neuronal damage in a dose- and time-dependent manner. On the other hand, Achyranthes bidentata extract depressed glutamate-induced elevation of intracellular calcium concentration [Ca 2+] i , and also antagonized glutamate-evoked decreases in Bcl-2 expression at mRNA and protein levels. Conclusion The results suggest that Achyranthes bidentata extract prevents glutamate-induced cell damage in primarily cultured hippocampal neurons by inhibiting an increase in [Ca 2+] i , and reversing the down-regulation of Bcl-2.