Attenuation of Glutamate-Induced Excitotoxicity by Withanolide-A in Neuron-Like Cells: Role for PI3K/Akt/MAPK Signaling Pathway

Withania somnifera (L.) Dunal, a Potential Source of Phytochemicals for Treating Neurodegenerative Diseases: A Systematic Review

Withania somnifera (L.) Dunal is a medicinal plant belonging to the traditional Indian medical system, showing various therapeutic effects such as anti-cancer, anti-inflammatory, anti-microbial, anti-diabetic, and hepatoprotective activity. Of great interest is W. somnifera's potential beneficial effect against neurodegenerative diseases, since the authorized medicinal treatments can only delay disease progression and provide symptomatic relief and are not without side effects. A systematic search of PubMed and Scopus databases was performed to identify preclinical and clinical studies focusing on the applications of W. somnifera in preventing neurodegenerative diseases. Only English articles and those containing the keywords (Withania somnifera AND "neurodegenerative diseases", "neuroprotective effects", "Huntington", "Parkinson", "Alzheimer", "Amyotrophic Lateral Sclerosis", "neurological disorders") in the title or abstract were considered. Reviews, editorials, letters, meta-analyses, conference papers, short surveys, and book chapters were not considered. Selected articles were grouped by pathologies and summarized, considering the mechanism of action. The quality assessment and the risk of bias were performed using the Cochrane Handbook for Systematic Reviews of Interventions checklist. This review uses a systematic approach to summarize the results from 60 investigations to highlight the potential role of W. somnifera and its specialized metabolites in treating or preventing neurodegenerative diseases.

Computational investigation of Moringa oleifera phytochemicals targeting EGFR: molecular docking, molecular dynamics simulation and density functional theory studies

Epidermal growth factor receptor (EGFR) is a prominent target for anticancer therapy due to its role in activating several cell signaling cascades. Clinically approved EGFR inhibitors are reported to show treatment resistance and toxicity, this study, therefore, investigates Moringa oleifera phytochemicals to find potent and safe anti-EGFR compounds. For that, phytochemicals were screened based on drug-likeness and molecular docking analysis followed by molecular dynamics simulation, density functional theory analysis and ADMET analysis to identify the effective inhibitors of EGFR tyrosine kinase (EGFR-TK) domain. Known EGFR-TK inhibitors (1-4 generations) were used as control. Among 146 phytochemicals, 136 compounds showed drug-likeness, of which Delta 7-Avenasterol was the most potential EGFR-TK inhibitor with a binding energy of -9.2 kcal/mol followed by 24-Methylenecholesterol (-9.1 kcal/mol), Campesterol (-9.0 kcal/mol) and Ellagic acid (-9.0 kcal/mol). In comparison, the highest binding affinity from control drugs was displayed by Rociletinib (-9.0 kcal/mol). The molecular dynamics simulation (100 ns) exhibited the structural stability of native EGFR-TK and protein-inhibitor complexes. Further, MM/PBSA computed the binding free energies of protein complex with Delta 7-Avenasterol, 24-Methylenecholesterol, Campesterol and Ellagic acid as -154.559 ± 18.591 kJ/mol, -139.176 ± 19.236 kJ/mol, -136.212 ± 17.598 kJ/mol and -139.513 ± 23.832 kJ/mol, respectively. Non-polar interactions were the major contributors to these energies. The density functional theory analysis also established the stability of these inhibitor compounds. ADMET analysis depicted acceptable outcomes for all top phytochemicals without displaying any toxicity. In conclusion, this report has identified promising EGFR-TK inhibitors to treat several cancers that can be further investigated through laboratory and clinical tests.

Modulation of Multidrug Resistance Protein 1-mediated Transport Processes by the Antiviral Drug Ritonavir in Cultured Primary Astrocytes

The Multidrug Resistance Protein 1 (Mrp1) is an ATP-dependent efflux transporter and a major facilitator of drug resistance in mammalian cells during cancer and HIV therapy. In brain, Mrp1-mediated GSH export from astrocytes is the first step in the supply of GSH precursors to neurons. To reveal potential mechanisms underlying the drug-induced modulation of Mrp1-mediated transport processes, we investigated the effects of the antiviral drug ritonavir on cultured rat primary astrocytes. Ritonavir strongly stimulated the Mrp1-mediated export of glutathione (GSH) by decreasing the Km value from 200 nmol/mg to 28 nmol/mg. In contrast, ritonavir decreased the export of the other Mrp1 substrates glutathione disulfide (GSSG) and bimane-glutathione. To give explanation for these apparently contradictory observations, we performed in silico docking analysis and molecular dynamics simulations using a homology model of rat Mrp1 to predict the binding modes of ritonavir, GSH and GSSG to Mrp1. The results suggest that ritonavir binds to the hydrophilic part of the bipartite binding site of Mrp1 and thereby differently affects the binding and transport of the Mrp1 substrates. These new insights into the modulation of Mrp1-mediated export processes by ritonavir provide a new model to better understand GSH-dependent detoxification processes in brain cells.

Molecular targets and mechanisms of anti-cancer effects of withanolides

Withanolides are a class of natural products with a steroidal lactone structure that exhibit a broad spectrum of anti-cancer effects. To date, several studies have shown that their possible mechanisms in cancer development and progression are associated with the regulation of cell proliferation, apoptosis, metastasis, and angiogenesis. Withanolides can also attenuate inflammatory responses, as well as modulate the genomic instability and energy metabolism of cancer cells. In addition, they may improve the safety and efficacy of cancer treatments as adjuvants to traditional cancer therapeutics. Herein, we summarize the molecular targets and mechanisms of withanolides in different cancers, as well as their current clinical studies on them.

Phytotherapeutic alternatives for neurodegenerative dementias: Scientific review, discussion and therapeutic proposal

The incidence and prevalence of age-related neurodegenerative dementias have been increasing. There is no curative therapy and conventional drug treatment can cause problems for patients. Medicinal plants traditionally used for problems associated with ageing are emerging as a therapeutic resource. The main aim is to give a proposal for use and future research based on scientific knowledge and tradition. A literature search was conducted in several searchable databases. The keywords used were related to neurodegenerative dementias, ageing and medicinal plants. Boolean operators and filters were used to focus the search. As a result, there is current clinical and preclinical scientific information on 49 species used in traditional medicine for ageing-related problems, including neurodegenerative dementias. There are preclinical and clinical scientific evidences on their properties against protein aggregates in the central nervous system and their effects on neuroinflammation, apoptosis dysregulation, mitochondrial dysfunction, gabaergic, glutamatergic and dopaminergic systems alterations, monoamine oxidase alterations, serotonin depletion and oestrogenic protection. In conclusion, the potential therapeutic effect of the different medicinal plants depends on the type of neurodegenerative dementia and its stage of development, but more clinical and preclinical research is needed to find better, safer and more effective treatments.

Extraction and Quantitation of Phytosterols from Edible Brown Seaweeds: Optimization, Validation, and Application

Brown seaweeds are known as important marine food sources, from which phytosterols have been recognized as functional food components with multiple health-beneficial effects. However, studies on phytosterol extraction and quantitation from edible brown seaweeds are limited. In the present work, extraction methods for seaweed phytosterols were compared and optimized by one-factor-at-one-time method and response surface methodology. Moreover, the quantitation method of total sterols and major sterol components, including fucosterol, saringosterol, and ostreasterol, was established and validated using ¹H NMR. Furthermore, the developed extraction and determination methods were applied to investigate three common edible seaweeds from Japan (Hijiki, Wakame, and Kombu). As a result, the finally optimized conditions were ultrasound-assisted extraction with CHCl₃-MeOH 2:3 for 15 min followed by saponification with 1.65 mL of 1.85 M KOH for 14.5 h. Based on the developed methods, phytosterols in three seaweeds were compared, and Hijiki showed an abundant total sterol amount (2.601 ± 0.171 mg/g DW), significantly higher than Wakame (1.845 ± 0.137 mg/g DW) and Kombu (1.171 ± 0.243 mg/g DW). Notably, the composition of the sterol components varied in different seaweeds. These findings might help the nutritional investigation and functional food development concerning phytosterols from seaweeds.

Ashwagandha-loaded nanocapsules improved the behavioral alterations, and blocked MAPK and induced Nrf2 signaling pathways in a hepatic encephalopathy rat model

Ashwagandha (ASH), a vital herb in Ayurvedic medicine, demonstrated potent preclinical hepato- and neuroprotective effects. However, its efficacy is limited due to low oral bioavailability. Accordingly, we encapsulated ASH extract in chitosan-alginate bipolymeric nanocapsules (ASH-BPNCs) to enhance its physical stability and therapeutic effectiveness in the gastrointestinal tract. ASH-BPNC was prepared by emulsification followed by sonication. The NCs showed small particle size (< 220 nm), zeta-potential of 25.2 mV, relatively high entrapment efficiency (79%), physical stability at acidic and neutral pH, and in vitro release profile that extended over 48 h. ASH-BPNC was then investigated in a thioacetamide-induced hepatic encephalopathy (HE) rat model. Compared with free ASH, ASH-BPNC improved survival, neurological score, general motor activity, and cognitive task-performance. ASH-BPNC restored ALT, AST and ammonia serum levels, and maintained hepatic and brain architecture. ASH-BPNC also restored GSH, MDA, and glutathione synthetase levels, and Nrf2 and MAPK signaling pathways in liver and brain tissues. Moreover, ASH-BPNC downregulated hepatic NF-κB immunohistochemical expression. Moreover, the in vivo biodistribution studies demonstrated that most of the administered ASH-BPNC is accumulated in the brain and hepatic tissues. In conclusion, chitosan-alginate BPNCs enhanced the hepatoprotective and neuroprotective effects of ASH, thus providing a promising therapeutic approach for HE.

Therapeutic potential and molecular mechanisms of salidroside in ischemic diseases

Rhodiola is an ancient wild plant that grows in rock areas in high-altitude mountains with a widespread habitat in Asia, Europe, and America. From empirical belief to research studies, Rhodiola has undergone a long history of discovery, and has been used as traditional medicine in many countries and regions for treating high-altitude sickness, anoxia, resisting stress or fatigue, and for promoting longevity. Salidroside, a phenylpropanoid glycoside, is the main active component found in all species of Rhodiola. Salidroside could enhance cell survival and angiogenesis while suppressing oxidative stress and inflammation, and thereby has been considered a potential compound for treating ischemia and ischemic injury. In this article, we highlight the recent advances in salidroside in treating ischemic diseases, such as cerebral ischemia, ischemic heart disease, liver ischemia, ischemic acute kidney injury and lower limb ischemia. Furthermore, we also discuss the pharmacological functions and underlying molecular mechanisms. To our knowledge, this review is the first one that covers the protective effects of salidroside on different ischemia-related disease.

Glutamate excitotoxicity: Potential therapeutic target for ischemic stroke

Glutamate-mediated excitotoxicity is an important mechanism leading to post ischemic stroke damage. After acute stroke, the sudden reduction in cerebral blood flow is most initially followed by ion transport protein dysfunction and disruption of ion homeostasis, which in turn leads to impaired glutamate release, reuptake, and excessive N-methyl-D-aspartate receptor (NMDAR) activation, promoting neuronal death. Despite extensive evidence from preclinical studies suggesting that excessive NMDAR stimulation during ischemic stroke is a central step in post-stroke damage, NMDAR blockers have failed to translate into clinical stroke treatment. Current treatment options for stroke are very limited, and there is therefore a great need to develop new targets for neuroprotective therapeutic agents in ischemic stroke to extend the therapeutic time window. In this review, we highlight recent findings on glutamate release, reuptake mechanisms, NMDAR and its downstream cellular signaling pathways in post-ischemic stroke damage, and review the pathological changes in each link to help develop viable new therapeutic targets. We then also summarize potential neuroprotective drugs and therapeutic approaches for these new targets in the treatment of ischemic stroke.

Functional Deficits of 5×FAD Neural Stem Cells Are Ameliorated by Glutathione Peroxidase 4

Alzheimer's disease (AD) is the most common cause of dementia affecting millions of people around the globe. Impaired neurogenesis is reported in AD as well as in AD animal models, although the underlying mechanism remains unclear. Elevated lipid peroxidation products are well-documented in AD. In current study, the role of lipid peroxidation on neural stem cell (NSCs) function is tested. Neural stem cells (NSCs) from 5×FAD mice, a widely used AD model with impaired neurogenesis, were observed to have increased levels of lipid reactive oxygen species compared to NSCs from control WT mice. 5×FAD NSCs exhibited altered differentiation potential as revealed by their propensity to differentiate into astrocytic lineage instead of neuronal lineage compared to WT NSCs. In addition, 5×FAD NSCs showed a reduced level of Gpx4, a key enzyme in reducing hydroperoxides in membrane lipids, and this reduction appeared to be caused by enhanced autophagy-lysosomal degradation of Gpx4 protein. To test if increasing Gpx4 could restore differentiation potential, NSCs from 5×FAD and Gpx4 double transgenic mice, i.e., 5×FAD/GPX4 mice were studied. Remarkably, upon differentiation, neuronal linage cells increased significantly in 5×FAD/GPX4 cultures compared to 5×FAD cultures. Taken together, the findings suggest that deficiency of lipid peroxidation defense contributes to functional decline of NSCs in AD.

Isolation and structure elucidation of a steroidal moiety from Withania somnifera and in silico evaluation of antimalarial efficacy against artemisinin resistance Plasmodium falciparum kelch 13 protein

According to the 2021 Malaria report, 241 million clinical episodes with 627000 deaths penalty was estimated across the worldwide. However, mutation in the propeller domain of Plasmodium falciparum kelch 13 protein resulted in longer parasite clearance time following an artemisinin-based treatment and had a greater survival rate of ring-stage parasites even after a brief exposure to a high dose of artesunate. Clinical manifestations become more complex and worse with the emerging trend of drug resistance against artemisinin derivatives and the poor effectiveness of malaria vaccination drive. Steroidal lactone (withanolide) moiety (C-28) isolated from methanolic leaf extract Withania somnifera show a greater affinity towards Pfkelch 13 protein in comparison to the artemisinin derivatives (artesunate, artemether). The isolated compound was characterized to be withaferin A with a percentage yield of 29.01% w/w in chloroform fraction, 1.75% w/w in methanolic extract, and 0.29% w/w in raw leaf powder. Structure-based analysis shows that withaferin A (docking score -8.253, -9.802) has a higher affinity for two distinct binding pockets I and II of the Plasmodium falciparum kelch 13 protein than artesunate (docking score -4.470, -3.656). Further, Gibbs binding free energy signifies thermodynamic stability of the docked complex of withaferin A (-43.25, -43.76 Kcal/mol) in comparison to artesunate docked complex (-8.49, -5.75 Kcal/mol). The pharmacokinetic profile of withaferin A shows more drug-likeness characteristics without violating Jorgensen's rule of three, and Lipinski's rule of five. Hence above experimental findings suggest withaferin A could be a suitable therapeutic adjunct for preclinical evaluation of antimalarial potentiality in artemisinin-resistant malaria.

Effect of Withanolide A on 7-Ketocholesterol Induced Cytotoxicity in hCMEC/D3 Brain Endothelial Cells

Withanolide A is a naturally occurring phytochemical that is found in Ashwagandha (Withania somnifera, fam. Solanaceae) or Indian Ginseng. In the current study, we elucidated the effect of withanolide A on 7-ketocholesterol (7KC) induced injury in hCMEC/D3 human brain endothelial cells. 7KC is a cholesterol oxidation product or oxysterol that is present in atherosclerotic plaques and is elevated in the plasma of patients with hypercholesterolemia and/or diabetes mellitus. Results showed that withanolide A significantly reduced the effects of 7KC, which include loss of endothelial cell viability, increase in expression of pro-inflammatory genes-IL-1β, IL-6, IL-8, TNF-α, cyclooxygenase-2 (COX-2), increased COX-2 enzyme activity, increased ROS formation, increased expression of inducible nitric oxide synthase and genes associated with blood clotting, including Factor 2/thrombin, Factor 8, von Willebrand factor, and thromboxane A synthase, and increased human thrombin enzyme activity. Some of the above effects of withanolide A on 7KC were reduced in the presence of the glucocorticoid receptor antagonist, mifepristone (RU486). These findings suggest that the glucocorticoid receptor could play a role in the cytoprotective, antioxidant, and anti-clotting effects of withanolide A against 7KC. Further studies are necessary to elucidate the detailed mechanisms of action of withanolide A against oxysterol-induced injury.

Drosophila Trachea as a Novel Model of COPD

COPD, a chronic obstructive pulmonary disease, is one of the leading causes of death worldwide. Clinical studies and research in rodent models demonstrated that failure of repair mechanisms to cope with increased ROS and inflammation in the lung leads to COPD. Despite this progress, the molecular mechanisms underlying the development of COPD remain poorly understood, resulting in a lack of effective treatments. Thus, an informative, simple model is highly valued and desired. Recently, the cigarette smoke-induced Drosophila COPD model showed a complex set of pathological phenotypes that resemble those seen in human COPD patients. The Drosophila trachea has been used as a premier model to reveal the mechanisms of tube morphogenesis. The association of these mechanisms to structural changes in COPD can be analyzed by using Drosophila trachea. Additionally, the timeline of structural damage, ROS, and inflammation can be studied in live organisms using fluorescently-tagged proteins. The related function of human COPD genes identified by GWAS can be screened using respective fly homologs. Finally, the Drosophila trachea can be used as a high-throughput drug screening platform to identify novel treatments for COPD. Therefore, Drosophila trachea is an excellent model that is complementary to rodent COPD models.

Engineering of Saccharomyces cerevisiae for 24-Methylene-Cholesterol Production

24-Methylene-cholesterol is a necessary substrate for the biosynthesis of physalin and withanolide, which show promising anticancer activities. It is difficult and costly to prepare 24-methylene-cholesterol via total chemical synthesis. In this study, we engineered the biosynthesis of 24-methylene-cholesterol in Saccharomyces cerevisiae by disrupting the two enzymes (i.e., ERG4 and ERG5) in the yeast’s native ergosterol pathway, with ERG5 being replaced with the DHCR7 (7-dehydrocholesterol reductase) enzyme. Three versions of DHCR7 originating from different organisms—including the DHCR7 from Physalis angulata (PhDHCR7) newly discovered in this study, as well as the previously reported OsDHCR7 from Oryza sativa and XlDHCR7 from Xenopus laevis—were assessed for their ability to produce 24-methylene-cholesterol. XlDHCR7 showed the best performance, producing 178 mg/L of 24-methylene-cholesterol via flask-shake cultivation. The yield could be increased up to 225 mg/L, when one additional copy of the XlDHCR7 expression cassette was integrated into the yeast genome. The 24-methylene-cholesterol-producing strain obtained in this study could serve as a platform for characterizing the downstream enzymes involved in the biosynthesis of physalin or withanolide, given that 24-methylene-cholesterol is a common precursor of these chemicals.

Natural Product Isoliquiritigenin Activates GABAB Receptors to Decrease Voltage-Gate Ca2+ Channels and Glutamate Release in Rat Cerebrocortical Nerve Terminals

Reduction in glutamate release is a key mechanism for neuroprotection and we investigated the effect of isoliquiritigenin (ISL), an active ingredient of Glycyrrhiza with neuroprotective activities, on glutamate release in rat cerebrocortical nerve terminals (synaptosomes). ISL produced a concentration-dependent inhibition of glutamate release and reduced the intraterminal [Ca²⁺] increase. The inhibition of glutamate release by ISL was prevented after removing extracellular Ca²⁺ or blocking P/Q-type Ca²⁺ channels. This inhibition was mediated through the γ-aminobutyric acid type B (GABA_B) receptors because ISL was unable to inhibit glutamate release in the presence of baclofen (an GABA_B agonist) or CGP3548 (an GABA_B antagonist) and docking data revealed that ISL interacted with GABA_B receptors. Furthermore, the ISL inhibition of glutamate release was abolished through the inhibition of G_i/o-mediated responses or G_βγ subunits, but not by 8-bromoadenosine 3′,5′-cyclic monophosphate or adenylate cyclase inhibition. The ISL inhibition of glutamate release was also abolished through the inhibition of protein kinase C (PKC), and ISL decreased the phosphorylation of PKC. Thus, we inferred that ISL, through GABA_B receptor activation and G_βγ-coupled inhibition of P/Q-type Ca²⁺ channels, suppressed the PKC phosphorylation to cause a decrease in evoked glutamate release at rat cerebrocortical nerve terminals.

Natural products attenuate PI3K/Akt/mTOR signaling pathway: A promising strategy in regulating neurodegeneration

BACKGROUND

As common, progressive, and chronic causes of disability and death, neurodegenerative diseases (NDDs) significantly threaten human health, while no effective treatment is available. Given the engagement of multiple dysregulated pathways in neurodegeneration, there is an imperative need to target the axis and provide effective/multi-target agents to tackle neurodegeneration. Recent studies have revealed the role of phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) in some diseases and natural products with therapeutic potentials.

PURPOSE

This is the first systematic and comprehensive review on the role of plant-derived secondary metabolites in managing and/or treating various neuronal disorders via the PI3K/Akt/mTOR signaling pathway.

STUDY DESIGN AND METHODS

A systematic and comprehensive review was done based on the PubMed, Scopus, Web of Science, and Cochrane electronic databases. Two independent investigators followed the PRISMA guidelines and included papers on PI3K/Akt/mTOR and interconnected pathways/mediators targeted by phytochemicals in NDDs.

RESULTS

Natural products are multi-target agents with diverse pharmacological and biological activities and rich sources for discovering and developing novel therapeutic agents. Accordingly, recent studies have shown increasing phytochemicals in combating Alzheimer's disease, aging, Parkinson's disease, brain/spinal cord damages, depression, and other neuronal-associated dysfunctions. Amongst the emerging targets in neurodegeneration, PI3K/Akt/mTOR is of great importance. Therefore, attenuation of these mediators would be a great step towards neuroprotection in such NDDs.

CONCLUSION

The application of plant-derived secondary metabolites in managing and/or treating various neuronal disorders through the PI3K/Akt/mTOR signaling pathway is a promising strategy towards neuroprotection.

Lyciumamide A, a dimer of phenolic amide, protects against NMDA-induced neurotoxicity and potential mechanisms in vitro

Currently, the excessive activation of N-methyl-D-aspartate receptors (NMDARs) is considered to be a crucial mechanism of brain injury. Lycium barbarum A (LyA) is a dimer of phenol amides isolated from the fruit of Lycium barbarum. Our previous studies have shown that LyA has potential antioxidant activity. This study aimed to explore the neuroprotective effect of LyA and its potential mechanism. Firstly, the molecular docking was used to preliminarily explore the potential function of LyA to block NMDAR. Then, the ability of LyA was further verified by NMDA-induced human neuroblastoma SH-SY5Y cells in vivo. Treatment with LyA significantly attenuated NMDA-induced neuronal insults by increasing cell viability, reducing lactate dehydrogenase (LDH) release, and increasing cell survival. Meanwhile, LyA significantly reversed the increase in intracellular calcium and in ROS production induced by NMDA. Finally, the western blot indicated that LyA could suppress the Ca²⁺ influx and increase the p-NR2B, p-CaMKII, p-JNK, and p-p38 level induced by NMDA. These above findings provide evidence that LyA protect against brain injury, and restraining NMDARs and suppressing mitochondrial oxidative stress and inhibiting cell apoptosis may be involved in the protective mechanism.

Withanolides isolated from Tubocapsicum anomalum and their antiproliferative activity

Seven undescribed withanolides (1-7) and six artificial withanolides (8-13), along with 20 known compounds (14-33) were isolated from the aerial parts of Tubocapsicum anomalum. Their structures were confirmed by comprehensive spectroscopic analyses. The absolute configuration of compound 1 was defined by single-crystal X-ray crystallography. All isolates were evaluated for their antiproliferative effects against five human tumor cell lines (Hep3B, MDA-MB-231, SW480, HCT116 and A549), among which compound 24 (tubocapsanolide A) exhibited the highest activities against the MDA-MB-231 cells with an IC₅₀ value of 1.89 ± 1.03 μM. Further studies showed that 24 exhibited significant damage to mitochondria in MDA-MB-231 cells, including excess reactive oxygen species, decreased mitochondrial membrane potential, and apoptosis initiation. In addition, compound 24 also inhibited cell migration. These findings show that tubocapsanolide A may be a promising molecule for triple-negative breast cancer treatment and merit further evaluation.

Therapeutic modulation of the phosphatidylinositol 3-kinases (PI3K) pathway in cerebral ischemic injury

The cerebral ischemic reperfusion injury may leads to morbidity and mortality in patients. phosphatidylinositol 3-kinase (PI3K) signaling pathway has been believed to work in association with its downstream targets, other receptors, and pathways that may offer antioxidant, anti-inflammatory, anti-apoptotic effects, neuroprotective role in neuronal excitotoxicity. This review elaborates the mechanistic interventions of the PI3K pathway in cerebral ischemic injury in context to nuclear factor erythroid 2-related factor 2 (Nrf2) regulation, Hypoxia-inducible factor 1 signaling (HIF-1), growth factors, Endothelial NOS (eNOS) proinflammatory cytokines, Erythropoietin (EPO), Phosphatase and tensin homologous protein of chromosome 10 gene (PTEN) signaling, NF-κB/Notch signaling, c-Jun N-terminal kinase (JNK) and Glycogen synthase kinase-3β (GSK-3β) signaling pathway. Evidences showing the activation of PI3K inhibits apoptotic pathway, which results in its neuroprotective effect in ischemic injury. Despite discussing the therapeutic role of the PI3K pathway in treating cerebral ischemic injury, the review also enlighten the selective modulation of PI3K pathway with activators and inhibitors which may provide promising results in clinical and preclinical settings.

Improving the inhibition of β-amyloid aggregation by withanolide and withanoside derivatives

Here, we have studied the ameliorative effects of Withania somnifera derivatives (Withanolide A, Withanolide B, Withanoside IV, and Withanoside V) on the fibril formation of amyloid-β ₄₂ for Alzheimer's disease. We analyzed reduction in the aggregation of β amyloid protein with these Ashwagandha derivatives by Thioflavin T assay in the oligomeric and fibrillar state. We have tested the cytotoxic activity of these compounds against human SK-N-SH cell line for 48 h, and the IC ₅₀ value found to be 28.61 ± 2.91, 14.84 ± 1.45, 18.76 ± 0.76 and 30.14 ± 2.59 μM, respectively. After the treatment of the cells with half the concentration of IC ₅₀ value, there was a remarkable decrease in the number of apoptotic cells stained by TUNEL assay indicating the DNA damage and also observed significant decrease of reactive oxygen species. Also, the binding and molecular stability of these derivatives with amyloid β was also studied using bioinformatics tools where these molecules were interacted at LVFFA region which is inhibition site of amyloid-β1 ₄₂. These studies revealed that the Withanolides and Withanosides interact with the hydrophobic core of amyloid-β _1-42 in the oligomeric stage, preventing further interaction with the monomers and diminishing aggregation.

The protective effects of memantine against inflammation and impairment of endothelial tube formation induced by oxygen-glucose deprivation/reperfusion

Acute myocardial infarction (AMI) is one of the leading causes of death and disability. The dysregulation of cardiac endothelial cells plays a significant role in the pathogenesis of AMI. In the present study, we investigated the potential of memantine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist used in the treatment of Alzheimer's disease, to mitigate the effects of ischemia-reperfusion injury in the peripheral vasculature using human umbilical cord endothelial cells (HUVECs). Previous studies have identified anti-inflammatory and antioxidant effects of memantine, but the effects of memantine on angiogenesis and microtubule formation have not been fully elucidated. Our findings indicate that pretreatment with memantine significantly reduced the expression of interleukin (IL)-6 and IL-8, which are both serum markers if AMI severity. We also demonstrate that memantine could prevent mitochondrial dysfunction and oxidative stress by rescuing mitochondrial membrane potential and reducing the production of reactive oxygen species (ROS) by NADPH oxidase-4 (NOX-4). Importantly, memantine also promoted the expression of the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) antioxidant signaling pathway. Importantly, memantine pretreatment improved cell viability and prevented the decrease in microtubule formation induced by OGD/R. Through a phosphoinositide-3-kinase (PI3K) inhibition experiment, we determined that the PI3K/protein kinase B (Akt) pathway is essential for the effects of memantine on angiogenesis. Together, our findings suggest a potential role for memantine in the prevention and treatment of AMI.

Neurodegenerative diseases and Withania somnifera (L.): An update

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera (L.) Dunal also known as 'Ashwaghanda' in Sanskrit and as 'Indian Winter Cherry' in english. is an important medicinal herb in India. It is widely used in Indian systems of medicine as an adaptogen, nerve tonic, anti-stress, memory enhancer and against cognitive deficits, insomnia, anxiety, infectious diseases, infertility, rheumatoid arthritis and gout over thousands of years. Its formulations are mainly used in Unani and Ayurvedic system of medicine. It is a remarkable centuries old herbal Rasayana used to treat neuronal ailments and is known as ''Sattvic Kapha Rasayana.

AIM OF THE STUDY

To review neuroprotective properties of Withania somnifera (L.)extract as well as its active constituents in neurodegenerative diseases and other neurological ailments.

MATERIALS AND METHODS

The sources of information used in present article include Indian system of Medicine reports on the use of natural products, Medicinal books, research articles and scientific databases like PubMed, Google Scholar, Web of Science, Science-Direct, SciFinder, ACS Publications and Wiley Online Library.

RESULTS

Research reports based largely on preclinical studies as well as few clinical trials have highlighted the neuroprotective role of Ashwagandha against many neurodegenerative diseases including Alzheimer's, Huntington's and Parkinson's disease. The protective effects of Ashwagandha were accomplished by restoring mitochondrial and endothelial function, mitigation of apoptosis, inflammation and oxidative stress mechanisms.

CONCLUSION

In this review, we recapitulated neuroprotective properties of Ashwagandha extracts and/or its major constituents and discussed their mechanisms of action and potential therapeutic applications. The pre-clinical as well as clinical studies suggest the use of Withania somnifera (L.) against neurodegenerative disease. However, extensive studies are warranted to validate the use of extract or its single constituents for its clinical use.

Naringenin Upregulates AMPK-Mediated Autophagy to Rescue Neuronal Cells From β-Amyloid (1-42) Evoked Neurotoxicity

Deposition of an amyloid-β peptide is one of the first events in the pathophysiology of Alzheimer's disease (AD) and is clinically characterized by Aβ plaques, tau tangles, and behavioral impairments that lead to neuronal death. A substantial number of studies encourage targeting the skewness in the production and degradation of amyloid-β could be among the promising therapies in the disease. Neuronal autophagy has emerged for an essential role in the degradation of such toxic aggregate-prone proteins in various neurodegenerative diseases. We profiled a small library of common dietary compounds and identified those that can enhance autophagy in neuronal cells. Here we noted naringenin in silico exhibits a robust affinity with AMP-activated protein kinase (AMPK) and upregulated AMPK-mediated autophagy signaling in neurons. Naringenin can induce autophagy promoting proteins such as ULK1, Beclin1, ATG5, and ATG7 in Neuro2a cells and primary mouse neurons as well. The knockdown of AMPK by siRNA-AMPK was complemented by naringenin that restored transcript levels of AMPK. Further, naringenin can reduce the levels of Aβ at a nontoxic concentration from neuronal cells. Moreover, it maintained the mitochondrial membrane potential and resisted reactive oxygen species production, which led to the protection against Aβ_1-42 evoked neurotoxicity. This highlights the neuroprotective potential of naringenin that can be developed as an anti-amyloidogenic nutraceutical.

Ginsenoside Rg1 alleviates repeated alcohol exposure-induced psychomotor and cognitive deficits

Background

Chronic alcohol consumption disrupts psychomotor and cognitive functions, most of which are subserved by the dysfunction of hippocampus. Dysregulated excitatory glutamatergic transmission is implicated in repeated alcohol induced psychomotor and cognitive impairment. Ginsenoside Rg1, one of the main active ingredient of the traditional tonic medicine Panax ginseng C.A. Meyer (Araliaceae), has been used to treat cognitive deficits. Particularly, Rg1 has been demonstrated to improve hippocampus-dependent learning in mice and attenuate glutamate-induced excitotoxicity in vitro. Thus, in the present research, we sought to investigate the therapeutic effects of Ginsenoside Rg1 on repeated alcohol induced psychomotor and cognitive deficits in hippocampal-dependent behavioral tasks and unravel the underpinnings of its neuroprotection.

Methods

Male ICR (CD-1) mice were consecutively intragastrically treated with 20% (w/v) alcohol for 21 days. Then, behavior tests were conducted to evaluate repeated alcohol induced psychomotor and cognitive deficits. Histopathological changes, and biochemical and molecular alterations were assessed to determine the potential neuroprotective mechanism of Rg1.

Results

The results suggested that Rg1, at the optimal dose of 6 mg/kg, has the potential to ameliorate repeated alcohol induced cognitive deficits by regulating activities of NR2B containing NMDARs and excitotoxic signaling.

Conclusion

Our findings further provided a new strategy to treat chronic alcohol exposure induced adverse consequences.

Multifunctional memantine nitrate significantly protects against glutamate-induced excitotoxicity via inhibiting calcium influx and attenuating PI3K/Akt/GSK3beta pathway

Overactivation of N-methyl-D-aspartate (NMDA) receptors has been associated with neurodegenerative disorders such as Alzheimer's disease (AD), cerebral vascular disorders and amyotrophic lateral sclerosis (ALS). We have previously designed and synthesized a series of memantine nitrate and some of them have shown vessel dilatory effects and neuroprotective effects; however, the detailed mechanisms have not been elucidated. In this study, we further demonstrated that memantine nitrate-06 (MN-06), one of the novel compounds derived from memantine, possessed significant neuroprotective effects against glutamate-induced excitotoxicity in rat primary cerebellar granule neurons (CGNs). Pretreatment of MN-06 reversed the activation of GSK3b and the suppression of phosphorylated Akt induced by glutamate. In addition, the neuroprotective effects of MN-06 could be abolished by LY294002, the specific phosphatidylinositol 3-kinase (PI3-K) inhibitor. Ca²⁺ imaging shown that pretreatment of MN-06 prevented Ca²⁺ influx induced by glutamate. Moreover, MN-06 might inhibit the NMDA-mediated current by antagonizing NDMA receptors, which was further confirmed by molecular docking simulation. Taken together, MN-06 protected against glutamate-induced excitotoxicity by blocking calcium influx and attenuating PI3-K/Akt/GSK-3b pathway, indicating that MN-06 might be a potential drug for treating neurodegenerative disorders.

Radioprotective effects and mechanisms of animal, plant and microbial polysaccharides

Ionizing radiation is increasingly used to successfully diagnose many human health problems, but ionizing radiation may cause damage to organs/tissues in the living organisms such as the spleen, liver, skin, and brain. Many radiation protective agents have been discovered, with the deepening of radiation research. Unfortunately, these protective agents have many side effects, which cause drug resistance, nausea, vomiting, osteoporosis, etc. The polysaccharides extracted from natural sources are widely available and low in toxicity. In vivo and in vitro experiments have demonstrated that polysaccharides have anti-radiation activity through anti-oxidation, immune regulation, protection of hematopoietic system and protection against DNA damage. Recently, some studies have shown that polysaccharides were resistant to radiation. In the review, the anti-radiation activities of polysaccharides from different sources are summarized, and the anti-radiation mechanisms are discussed as well. It can be used to develop more effective anti-radiation management drugs.

The key role of macrophage depolarization in the treatment of COPD with ergosterol both in vitro and in vivo

Macrophages are the most abundant immune cells in the lung, which play an important role in COPD. The anti-inflammatory and anti-oxidation of ergosterol are well documented. However, the effect of ergosterol on macrophage polarization has not been studied. The objective of this work was to investigate the effect of ergosterol on macrophage polarization in CSE-induced RAW264.7 cells and Sprague-Dawley (SD) rats COPD model. Our results demonstrate that CSE-induced macrophages tend to the M1 polarization via increasing ROS, IL-6 and TNF-α, as well as increasing MMP-9 to destroy the lung construction in both RAW264.7 cells and SD rats. However, treatment of RAW264.7 cells and SD rats with ergosterol inhibited CSE-induced inflammatory by decreasing ROS, IL-6 and TNF-α, and increasing IL-10 and TGF-β, shuffling the dynamic polarization of macrophages from M1 to M2 both in vitro and in vivo. Ergosterol also decreased the expression of M1 marker CD40, while increased that of M2 marker CD163. Moreover, ergosterol improved the lung characters in rats by decreasing MMP-9. Furthermore, ergosterol elevated HDAC3 activation and suppressed P300/CBP and PCAF activation as well as acetyl NF-κB/p65 and IKKβ, demonstrating that HDAC3 deacetylation was involved in the effect of ergosterol on macrophage polarization. These results also provide a proof in immunoregulation of ergosterol for therapeutic effects of cultured C. sinensis on COPD patients.

Ergosterol attenuates cigarette smoke extract-induced COPD by modulating inflammation, oxidative stress and apoptosis in vitro and in vivo

Cigarette smoke (CS) is the major cause of chronic obstructive pulmonary disease (COPD). CS heightens inflammation, oxidative stress and apoptosis. Ergosterol is the main bioactive ingredient in Cordyceps sinensis (C. sinensis), a traditional medicinal herb for various diseases. The objective of this work was to investigate the effects of ergosterol on anti-inflammatory and antioxidative stress as well as anti-apoptosis in a cigarette smoke extract (CSE)-induced COPD model both in vitro and in vivo Our results demonstrate that CSE induced inflammatory and oxidative stress and apoptosis with the involvement of the Bcl-2 family proteins via the nuclear factor kappa B (NF-κB)/p65 pathway in both 16HBE cells and Balb/c mice. CSE induced epithelial cell death and increased the expression of nitric oxide (NO), interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), malondialdehyde (MAD) and the apoptosis-related proteins cleaved caspase 3/7/9 and cleaved-poly-(ADP)-ribose polymerase (PARP) both in vitro and in vivo, whereas decreased the levels of superoxide dismutase (SOD) and catalase (CAT). Treatment of 16HBE cells and Balb/c mice with ergosterol inhibited CSE-induced inflammatory and oxidative stress and apoptosis by inhibiting the activation of NF-κB/p65. Ergosterol suppressed apoptosis by inhibiting the expression of the apoptosis-related proteins both in vitro and in vivo Moreover, the usage of QNZ (an inhibitor of NF-κB) also partly demonstrated that NF-κB/p65 pathway was involved in the ergosterol protective progress. These results show that ergosterol suppressed COPD inflammatory and oxidative stress and apoptosis through the NF-κB/p65 pathway, suggesting that ergosterol may be partially responsible for the therapeutic effects of cultured C. sinensis on COPD patients.

Influence of laser needle-knife on PI-3K, AKT and VEGF mRNA expression in cervical spondylotic arteriopathy model rabbits

Objective

To determine the effect of laser needle-knife on PI-3K, AKT and VEGF mRNA expression of vertebral arteries in a rabbit model of cervical spondylotic arteriopathy (CSA) and the mechanism of action involved.

Methods

Forty healthy general-grade rabbits were divided into a normal control group, model group, acupuncture group, and laser needle-knife group (n = 10 rabbits per group), and the CSA rabbit model was established in all but groups but the normal control group. CSA model rabbits in the acupuncture group were treated by acupuncture at the Fengchi (GB 20) and Cervical Jiaji (EX-B 2) points, whereas rabbits in the laser needle-knife group were treated with laser needle-knife targeting the Jiaji points near the C5 spinous process. Rabbits in the normal control and model groups were fixed using similar methods. Behavioral characteristics of all rabbits were evaluated before and after treatment. Peak systolic velocity (PSV) of the right carotid and vertebral arteries in each group were examined using beside B ultrasound, and PI-3K, AKT, VEGF mRNA expression in vertebral arteries were determined by real-time PCR.

Results

The behavioral signs of rabbits were improved after treatment in both the acupuncture and laser needle-knife groups. In comparison with control group, PSV of right carotid arteries in acupuncture group and laser needle-knife group were enhanced significantly (P < 0.05 and P < 0.01), PSV of right vertebral arteries in acupuncture group and laser needle-knife group were enhanced significantly too (P < 0.01 and P < 0.05). PI-3K mRNA expression in laser needle-knife and acupuncture group was significantly higher than that in control group (P < 0.01, P < 0.05). AKT mRNA expression in laser needle-knife and acupuncture group was significantly higher than that in control group (P < 0.01). VEGF mRNA expression in laser needle-knife and acupuncture group was significantly higher than that in control group too (P < 0.01, P < 0.05). No significant differences were found in PI-3K, AKT and VEGF mRNA expression levels among acupuncture and laser needle-knife groups (P > 0.05).

Conclusion

Laser needle-knife could effectively intervene the mRNA expression of PI-3K, AKT and VEGF, this may be one of the mechanisms of the effect of laser needle-knife in treating CSA in rabbits.

Donepezil improves neuropathy through activation of AMPK signalling pathway in streptozotocin-induced diabetic mice

Diabetic neuropathy (DN) is a common complication of diabetes mellitus and is associated with structural changes in the nerves. However, the molecular basis for DN is poorly understood. Adenosine monophosphate activated protein kinase (AMPK) has been shown to regulate the activity of some kinases including protein kinase B (AKT), mitogen-activated protein kinases (MAPK) and mammalian target of rapamycin complex 1 (mTORC1) that represent important signalling pathways modulating the function of peripheral nociceptive neuron. Donepezil can activate AMPK and exerts neuroprotective effects. In this study, streptozotocin (45 mg/kg for 5 Day, i.p.) was used to induce experimental DN. After confirmation of development of neuropathy, mice were randomly distributed into five groups: Group 1; negative control group received saline (0.9%NaCl), Group 2; diabetic mice received saline, Group (3-5); diabetic mice received daily donepezil (1, 2 or 4 mg/kg, p.o.) respectively for 20 days. Mice were then sacrificed under anesthesia then their sciatic nerve and spinal cord were dissected out and processed for biochemical and histopathological studies. Diabetic mice revealed severe histological abnormalities including degenerated neurons in the spinal cord and swollen myelin sheath with inflammatory edema observed in sciatic nerves. In addition, diabetic mice showed reduced expression of p-AMPK in sciatic nerves with consequent activation of AKT/MAPK/4EBP1. A significant upregulation of the N-Methyl-d-aspartate (NMDA) receptors in both cervical and lumbar regions of spinal cord of diabetic mice was also demonstrated. Donepezil, an AMPK activator, blocked the phosphorylation of AKT/MAPK/4EBP1, down regulate the expression of NMDA receptors and reversed hyperalgesia developed in diabetic mice. Therefore, Donepezil could be a potential pharmacological agent for management of DN.

Standardized phytotherapic extracts rescue anomalous locomotion and electrophysiological responses of TDP-43 Drosophila melanogaster model of ALS

Findings from studies using animal models expressing amyotrophic lateral sclerosis (ALS) mutations in RNA-binding proteins, such as Transactive Response DNA-binding protein-43 (TDP-43), indicate that this protein, which is involved in multiple functions, including transcriptional regulation and pre-mRNA splicing, represents a key candidate in ALS development. This study focuses on characterizing, in a Drosophila genetic model of ALS (TDP-43), the effects of Mucuna pruriens (Mpe) and Withania somnifera (Wse). Electrophysiological and behavioural data in TDP-43 mutant flies revealed anomalous locomotion (i.e. impaired climbing with unexpected hyperactivity) and sleep dysregulation. These features, in agreement with previous findings with a different ALS model, were at least partially, rescued by treatment with Mpe and Wse. In addition, electrophysiological recordings from dorsal longitudinal muscle fibers and behavioral observations of TDP-43 flies exposed to the volatile anaesthetics, diethyl ether or chloroform, showed paradoxical responses, which were normalized upon Mpe or Wse treatment. Hence, given the involvement of some potassium channels in the effects of anaesthetics, our results also hint toward a possible dysregulation of some potassium channels in the ALS-TDP-43 Drosophila model, that might shed new light on future therapeutic strategies pertaining to ALS.

Humanin Attenuates NMDA-Induced Excitotoxicity by Inhibiting ROS-dependent JNK/p38 MAPK Pathway

Humanin (HN) is a novel 24-amino acid peptide that protects neurons against N-methyl-d-aspartate (NMDA)-induced toxicity. However, the contribution of the different mitogen-activated protein kinases (MAPKs) signals to HN neuroprotection against NMDA neurotoxicity remains unclear. The present study was therefore aimed to investigate neuroprotective mechanisms of HN. We analyzed intracellular Ca²⁺ levels, reactive oxygen species (ROS) production, and the MAPKs signal transduction cascade using an in vitro NMDA-mediated excitotoxicity of cortical neurons model. Results showed that: (1) HN attenuated NMDA-induced neuronal insults by increasing cell viability, decreasing lactate dehydrogenase (LDH) release, and increasing cell survival; (2) HN reversed NMDA-induced increase in intracellular calcium; (3) pretreatment by HN or 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA-AM), an intracellular calcium chelator, decreased ROS generation after NMDA exposure; (4) administration of HN or N-Acetyl-l-cysteine (NAC), a ROS scavenger, inhibited NMDA-induced JNK and p38 MAPK activation. These results indicated that HN reduced intracellular elevation of Ca²⁺ levels, which, in turn, inhibited ROS generation and subsequent JNK and p38 MAPK activation that are involved in promoting cell survival in NMDA-induced excitotoxicity. Therefore, the present study suggests that inhibition of ROS-dependent JNK/p38 MAPK signaling pathway serves an effective strategy for HN neuroprotection against certain neurological diseases.

Relationship between Cytotoxicity in the Hippocampus and an Abnormal High Intensity Area on the Diffusion-weighted Images of Three Patients with Transient Global Amnesia

Objective An abnormal high intensity area (HIA) on diffusion-weighted imaging (DWI) indicates the presence of cytotoxic edema and has been reported to be observed in the hippocampus of patients with transient global amnesia (TGA). The appearance of an HIA on DWI is usually delayed after the onset of patients with amnesia in TGA; thus, the significance of the HIA was evaluated in patients with TGA. Methods Three adult TGA patients who had a unilateral HIA on DWI (right, n=2; left, n=1) were enrolled. These patients were hospitalized due to acute-onset amnesia. Amnesia subsided within 24 hours of hospitalization in all three patients. Results The HIA was confined to the upper lateral zone of the body in the unilateral hippocampus where the CA1 region exists. The lesions were confirmed after the improvement of amnesia in the three patients. The location of the lesions corresponded to the watershed area where the upper and lower hippocampal arteries were anastomosed. Conclusion Cytotoxicity caused by glutamate-mediated calcium influx in the neurons of the CA1 region was recently reported in the pathogenesis of TGA. Based on the pathogenesis, the cytotoxicity was considered to have been caused by calcium overload throughout the entire CA1 region, and amnesia occurred due to this cytotoxicity. The cytotoxicity was more marked in the lesions because of the lower blood flow in the watershed area and was prolonged after the function of the CA1 region (excluding the watershed area) improved, which led to cytotoxic edema in the lesions.

A Novel Tetramethylpyrazine Derivative Prophylactically Protects against Glutamate-Induced Excitotoxicity in Primary Neurons through the Blockage of N-Methyl-D-aspartate Receptor

The over-activation of NMDA receptor via the excessive glutamate is believed to one of the most causal factors associated with Alzheimer’s disease (AD), a progressive neurodegenerative brain disorder. Molecules that could protect against glutamate-induced neurotoxicity may hold therapeutic values for treating AD. Herein, the neuroprotective mechanisms of dimeric DT-010, a novel derivative of naturally occurring danshensu and tetramethylpyrazine, were investigated using primary rat cerebellar granule neurons (CGNs) and hippocampal neurons. It was found that DT-010 (3–30 μM) markedly prevented excitotoxicity of CGNs caused by glutamate, as evidenced by the promotion of neuronal viability as well as the reversal of abnormal morphological changes. While its parent molecules did not show any protective effects even when their concentration reached 50 μM. Additionally, DT-010 almost fully blocked intracellular accumulation of reactive oxygen species caused by glutamate and exogenous oxidative stimulus. Moreover, Western blot results demonstrated that DT-010 remarkably attenuated the inhibition of pro-survival PI3K/Akt/GSK3β pathway caused by glutamate. Ca²⁺ imaging with Fluo-4 fluorescence analysis further revealed that DT-010 greatly declined glutamate-induced increase in intracellular Ca²⁺. Most importantly, with the use of whole-cell patch clamp electrophysiology, DT-010 directly inhibited NMDA-activated whole-cell currents in primary hippocampal neurons. Molecular docking simulation analysis further revealed a possible binding mode that inhibited NMDA receptor at the ion channel, showing that DT-010 favorably binds to Asn602 of NMDA receptor via arene hydrogen bond. These results suggest that DT-010 could be served as a novel NMDA receptor antagonist and protect against glutamate-induced excitotoxicity from blocking the upstream NMDA receptors to the subsequent Ca²⁺ influx and to the downstream GSK3β cascade.

Ceftriaxone- and N-acetylcysteine-induced brain tolerance to ischemia: Influence on glutamate levels in focal cerebral ischemia

One of the major players in the pathophysiology of cerebral ischemia is disrupted homeostasis of glutamatergic neurotransmission, resulting in elevated extracellular glutamate (Glu) concentrations and excitotoxicity-related cell death. In the brain, Glu concentrations are regulated by Glu transporters, including Glu transporter-1 (GLT-1) and cystine/Glu antiporter (system x_c^-). Modulation of these transporters by administration of ceftriaxone (CEF, 200 mg/kg, i.p.) or N-acetylcysteine (NAC, 150 mg/kg, i.p.) for 5 days before focal cerebral ischemia may induce brain tolerance to ischemia by significantly limiting stroke-related damage and normalizing Glu concentrations. In the present study, focal cerebral ischemia was induced by 90-minute middle cerebral artery occlusion (MCAO). We compared the effects of CEF and NAC pretreatment on Glu concentrations in extracellular fluid and cellular-specific expression of GLT-1 and xCT with the effects of two reference preconditioning methods, namely, ischemic preconditioning and chemical preconditioning in rats. Both CEF and NAC significantly reduced Glu levels in the frontal cortex and hippocampus during focal cerebral ischemia, and this decrease was comparable with the Glu level achieved with the reference preconditioning strategies. The results of immunofluorescence staining of GLT-1 and xCT on astrocytes, neurons and microglia accounted for the observed changes in extracellular Glu levels to a certain extent. Briefly, after MCAO, the expression of GLT-1 on astrocytes decreased, but pretreatment with CEF seemed to prevent this downregulation. In addition, every intervention used in this study seemed to reduce xCT expression on astrocytes and neurons. The results of this study indicate that modulation of Glu transporter expression may restore Glu homeostasis. Moreover, our results suggest that CEF and NAC may induce brain tolerance to ischemia by influencing GLT-1 and system x_c^- expression levels. These transporters are presumably good targets for the development of novel therapies for brain ischemia.