Insulin blocks glutamate-induced neurotoxicity in differentiated SH-SY5Y neuronal cells

Effects of quercetin and derivatives on NAMPT/Sirtuin-1 metabolic pathway in neuronal cells: an approach to mitigate chemotherapy-induced cognitive impairment

BACKGROUND

 The cognitive alterations observed in individuals undergoing cancer treatments have garnered more attention recently. Chemotherapy can reduce nicotinamide adenine dinucleotide (NAD+) levels by inhibiting nicotinamide phosphoribosyl transferase (NAMPT). This reduction can make cancer cells more susceptible to oxidative damage and death and may also affect non-cancerous cells, particularly the brain cells. During chemotherapy-induced suppression, the downregulation of the NAMPT-mediated NAD+/Sirtuin 1 (SIRT1) pathway may cause dyscognition. Objective: This study aimed to assess the role of quercetin and analogues in chemobrain and the associated mechanisms. Methods: The potential of quercetin and its derivatives interaction with NAMPT and SIRT1 proteins was performed using computational studies followed by their in vitro evaluation in SH-SY5Y cells. Molecular docking and simulation studies of human SIRT1 and NAMPT proteins with quercetin and its derivatives were performed. Differentiated SH-SY5Y cell lines were treated with quercetin and selected derivatives against Methotrexate and 5-Fluorouracil (MF) toxicity, by subjecting to cytotoxicity assay, flow cytometry, and RT-PCR analysis. Results: Quercetin, Rutin, and Isoquercetin showed interactions necessary in the activation process of both proteins. Cytotoxicity and flow cytometric studies demonstrated that the phytochemicals shield the differentiated SH-SY5Y cells from MF toxicity. As determined by RT-PCR investigations, NAMPT and SIRT1 gene mRNA expression was higher in test drug-treated cells at quercetin (0.12, 0.6 µM), rutin, and isoquercetin (16, 80 µM) and lower in MF-treated cells. Conclusion: The treatment of phytochemicals alleviated CICI by targeting NAMPT and SIRT1 proteins, which could lead to the identification of effective treatment strategies for the chemobrain.

Sarcococca saligna ameliorated D-galactose induced neurodegeneration through repression of neurodegenerative and oxidative stress biomarkers

Sarcococca saligna is a valuable source of bioactive secondary metabolites exhibiting antioxidant, anti-inflammatory and acetylcholinesterase inhibitory activities. The study was intended to explore the therapeutic pursuits of S. saligna in amelioration of cognitive and motor dysfunctions induced by D-galactose and linked mechanistic pathways. Alzheimer's disease model was prepared by administration of D-galactose subcutaneous injection100 mg/kg and it was treated with rivastigmine (100 mg/kg, orally) and plant extract for 42 days. Cognitive and motor functions were evaluated by behavioral tasks and oxidative stress biomarkers. Level of acetylcholinesterase, reduced level of glutathione, protein and nitrite level, and brain neurotransmitters were analyzed in brain homogenate. The level of apoptosis regulator Bcl-2, Caspases 3 and heat shock protein HSP-70 in brain homogenates were analyzed by ELISA and colorimetric method, respectively. AChE, IL-1β, TNF-α, IL-1α and β secretase expressions were analyzed by RT-PCR. S. saligna dose dependently suppressed the neurodegenerative effects of D-galactose induced behavioral and biochemical impairments through modulation of antioxidant enzymes and acetylcholinesterase inhibition. S. saligna markedly (P < 0.05) ameliorated the level of brain neurotransmitters, Bcl-2, HSP-70 and Caspases-3 level. S. saligna at 500-1000 mg/kg considerably recovered the mRNA expression of neurodegenerative and neuro-inflammatory biomarkers, also evident from histopathological analysis. These findings suggest that S. saligna could be applicable in cure of Alzheimer's disease.

Insulin Diminishes Superoxide Increase in Cytosol and Mitochondria of Cultured Cortical Neurons Treated with Toxic Glutamate

Glutamate excitotoxicity is involved in the pathogenesis of many disorders, including stroke, traumatic brain injury, and Alzheimer’s disease, for which central insulin resistance is a comorbid condition. Neurotoxicity of glutamate (Glu) is primarily associated with hyperactivation of the ionotropic N-methyl-D-aspartate receptors (NMDARs), causing a sustained increase in intracellular free calcium concentration ([Ca²⁺]_i) and synchronous mitochondrial depolarization and an increase in intracellular superoxide anion radical (O₂^–•) production. Recently, we found that insulin protects neurons against excitotoxicity by decreasing the delayed calcium deregulation (DCD). However, the role of insulin in O₂^–• production in excitotoxicity still needs to be clarified. The present study aims to investigate insulin’s effects on glutamate-evoked O₂^–• generation and DCD using the fluorescent indicators dihydroethidium, MitoSOX Red, and Fura-FF in cortical neurons. We found a linear correlation between [Ca²⁺]_i and [O₂^–•] in primary cultures of the rat neuron exposed to Glu, with insulin significantly reducing the production of intracellular and mitochondrial O₂^–• in the primary cultures of the rat neuron. MK 801, an inhibitor of NMDAR-gated Ca²⁺ influx, completely abrogated the glutamate effects in both the presence and absence of insulin. In experiments in sister cultures, insulin diminished neuronal death and O₂ consumption rate (OCR).

Urokinase-Type Plasminogen Activator Enhances the Neuroprotective Activity of Brain-Derived Neurotrophic Factor in a Model of Intracerebral Hemorrhage

Brain-derived neurotrophic factor (BDNF) is a classic neuroprotective and pro-regenerative factor in peripheral and central nervous tissue. Its ability to stimulate the restoration of damaged nerve and brain tissue after ischemic stroke and intraventricular hemorrhage has been demonstrated. However, the current concept of regeneration allows us to assert that one factor, even if essential, cannot be the sole contributor to this complex biological process. We have previously shown that urokinase-type plasminogen activator (uPA) complements BDNF activity and stimulates restoration of nervous tissue. Using a model of intracerebral hemorrhage in rats, we investigated the neurotrophic and neuroprotective effect of BDNF combined with uPA. The local simultaneous administration of BDNF and uPA provided effective neuroprotection of brain tissue after intracerebral hemorrhage, promoted survival of experimental animals and their neurological recovery, and decreased lesion volume. The study of cellular mechanisms of the observed neurotrophic effect of BDNF and uPA combination revealed both known mechanisms (neuronal survival and neurite growth) and new ones (microglial activation) that had not been shown for BDNF and uPA. Our findings support the concept of using combinations of biological factors with diverse but complementary mechanisms of action as a promising regenerative approach.

Is L-Glutamate Toxic to Neurons and Thereby Contributes to Neuronal Loss and Neurodegeneration? A Systematic Review

L-glutamate (L-Glu) is a nonessential amino acid, but an extensively utilised excitatory neurotransmitter with critical roles in normal brain function. Aberrant accumulation of L-Glu has been linked to neurotoxicity and neurodegeneration. To investigate this further, we systematically reviewed the literature to evaluate the effects of L-Glu on neuronal viability linked to the pathogenesis and/or progression of neurodegenerative diseases (NDDs). A search in PubMed, Medline, Embase, and Web of Science Core Collection was conducted to retrieve studies that investigated an association between L-Glu and pathology for five NDDs: Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Together, 4060 studies were identified, of which 71 met eligibility criteria. Despite several inadequacies, including small sample size, employment of supraphysiological concentrations, and a range of administration routes, it was concluded that exposure to L-Glu in vitro or in vivo has multiple pathogenic mechanisms that influence neuronal viability. These mechanisms include oxidative stress, reduced antioxidant defence, neuroinflammation, altered neurotransmitter levels, protein accumulations, excitotoxicity, mitochondrial dysfunction, intracellular calcium level changes, and effects on neuronal histology, cognitive function, and animal behaviour. This implies that clinical and epidemiological studies are required to assess the potential neuronal harm arising from excessive intake of exogenous L-Glu.

Study of the potential neuroprotective effect of Dunaliella salina extract in SH-SY5Y cell model

Alzheimer’s disease (AD) is the most common form of dementia caused by a progressive loss of neurons from different regions of the brain. This multifactorial pathophysiology has been widely characterized by neuroinflammation, extensive oxidative damage, synaptic loss, and neuronal cell death. In this sense, the design of multi-target strategies to prevent or delay its progression is a challenging goal. In the present work, different in vitro assays including antioxidant, anti-inflammatory, and anti-cholinergic activities of a carotenoid-enriched extract from Dunaliella salina microalgae obtained by supercritical fluid extraction are studied. Moreover, its potential neuroprotective effect in the human neuron-like SH-SY5Y cell model against remarkable hallmarks of AD was also evaluated. In parallel, a comprehensive metabolomics study based on the use of charged-surface hybrid chromatography (CSH) and hydrophilic interaction liquid chromatography (HILIC) coupled to high-resolution tandem mass spectrometry (Q-TOF MS/MS) was applied to evaluate the effects of the extract on the metabolism of the treated cells. The use of advanced bioinformatics and statistical tools allowed the identification of more than 314 metabolites in SH-SY5Y cells, of which a great number of phosphatidylcholines, triacylglycerols, and fatty acids were significantly increased, while several phosphatidylglycerols were decreased, compared to controls. These lipidomic changes in cells along with the possible role exerted by carotenoids and other minor compounds on the cell membrane might explain the observed neuroprotective effect of the D. salina extract. However, future experiments using in vivo models to corroborate this hypothesis must be carried out.

MSC Secretome as a Promising Tool for Neuroprotection and Neuroregeneration in a Model of Intracerebral Hemorrhage

Multipotent mesenchymal stromal cells (MSCs) are considered to be critical contributors to injured tissue repair and regeneration, and MSC-based therapeutic approaches have been applied to many peripheral and central neurologic disorders. It has been demonstrated that the beneficial effects of MSC are mainly mediated by the components of their secretome. In the current study, we have explored the neuroprotective potential of the MSC secretome in a rat model of intracerebral hemorrhage and shown that a 10-fold concentrated secretome of human MSC and its combination with the brain-derived neurotrophic factor (BDNF) provided a better survival and neurological outcome of rats within 14 days of intracerebral hemorrhage compared to the negative (non-treated) and positive (BDNF) control groups. We found that it was due to the ability of MSC secretome to stimulate neuron survival under conditions of glutamate-induced neurotoxicity. However, the lesion volume did not shrink in these rats, and this also correlated with prominent microglia activation. We hypothesize that this could be caused by the species-specificity of the used MSC secretome and provide evidence to confirm this. Thus, we have found that allogenic rat MSC secretome was more effective than xenogenic human MSC secretome in the rat intracerebral hemorrhage model: it reduced the volume of the lesion and promoted excellent survival and neurological outcome of the treated rats.

Neuroprotective effects of Bhilawanol and Anacardic acid during glutamate-induced neurotoxicity

Bhilawanol (Bh) and anacardic acid (AA) are two lipid-soluble compounds mostly found in the nut of Semecarpus anacardium (SA). This herb has many medicinal properties including enhancing learning and memory, yet its active compounds have not been studied for neuroprotective effects. We investigated the neuroprotective effects of Bh and AA against glutamate induced cell death in the adrenal pheochromocytoma cell line of rats (PC12 cells). Cell viability, toxicity and calcium influx were determined by MTT assay, LDH release assay and Fluo-3 imaging while apoptosis was assayed by caspase-3 and Bcl-2 gene expression. Our results showed that Bh and AA treatments significantly increased cell viability, reduced cell toxicity and calcium influx in PC12 cells in addition to suppressing the reactive oxygen species. Furthermore, AA treatment decreased caspase-3 expression level whereas both Bh and AA enhanced the expression of anti-apoptotic gene Bcl-2 in PC12 cells. Both compounds potently inhibited acetylcholinesterase enzyme (AChE) in a dose and time dependent manner. These findings suggest that the traditional use of SA may be explained on the basis of both Bh and AA showing neuroprotective potential due to their effects on enhancing cell viability, reducing cell toxicity most probably by reducing excessive calcium influx and suppression of ROS as well as by decreasing the expression of proapoptotic caspase 3 gene and increasing the expression of antiapoptotic gene Bcl2. Traditional use in enhancing learning and memory was justified in part by inhibition of AChE.

Clinical Evidence of Antidepressant Effects of Insulin and Anti-Hyperglycemic Agents and Implications for the Pathophysiology of Depression-A Literature Review

Close connections between depression and type 2 diabetes (T2DM) have been suggested by many epidemiological and experimental studies. Disturbances in insulin sensitivity due to the disruption of various molecular pathways cause insulin resistance, which underpins many metabolic disorders, including diabetes, as well as depression. Several anti-hyperglycemic agents have demonstrated antidepressant properties in clinical trials, probably due to their action on brain targets based on the shared pathophysiology of depression and T2DM. In this article, we review reports of clinical trials examining the antidepressant effect of these medications, including insulin, metformin, glucagon like peptide-1 receptor agonists (GLP-1RA), and peroxisome proliferator-activated receptor (PPAR)-γ agonists, and briefly consider possible molecular mechanisms underlying the associations between amelioration of insulin resistance and improvement of depressive symptoms. In doing so, we intend to suggest an integrative perspective for understanding the pathophysiology of depression.

Gateways for Glutamate Neuroprotection in Parkinson's Disease (PD): Essential Role of EAAT3 and NCX1 Revealed in an In Vitro Model of PD

Increasing evidence suggests that metabolic alterations may be etiologically linked to neurodegenerative disorders such as Parkinson's disease (PD) and in particular empathizes the possibility of targeting mitochondrial dysfunctions to improve PD progression. Under different pathological conditions (i.e., cardiac and neuronal ischemia/reperfusion injury), we showed that supplementation of energetic substrates like glutamate exerts a protective role by preserving mitochondrial functions and enhancing ATP synthesis through a mechanism involving the Na⁺-dependent excitatory amino acid transporters (EAATs) and the Na⁺/Ca²⁺ exchanger (NCX). In this study, we investigated whether a similar approach aimed at promoting glutamate metabolism would be also beneficial against cell damage in an in vitro PD-like model. In retinoic acid (RA)-differentiated SH-SY5Y cells challenged with α-synuclein (α-syn) plus rotenone (Rot), glutamate significantly improved cell viability by increasing ATP levels, reducing oxidative damage and cytosolic and mitochondrial Ca²⁺ overload. Glutamate benefits were strikingly lost when either EAAT3 or NCX1 expression was knocked down by RNA silencing. Overall, our results open the possibility of targeting EAAT3/NCX1 functions to limit PD pathology by simultaneously favoring glutamate uptake and metabolic use in dopaminergic neurons.

NCX1 and EAAC1 transporters are involved in the protective action of glutamate in an in vitro Alzheimer's disease-like model

Increasing evidence suggests that metabolic dysfunctions are at the roots of neurodegenerative disorders such as Alzheimer's disease (AD). In particular, defects in cerebral glucose metabolism, which have been often noted even before the occurrence of clinical symptoms and histopathological lesions, are now regarded as critical contributors to the pathogenesis of AD. Hence, the stimulation of energy metabolism, by enhancing the availability of specific metabolites, might be an alternative way to improve ATP synthesis and to positively affect AD progression. For instance, glutamate may serve as an intermediary metabolite for ATP synthesis through the tricarboxylic acid (TCA) cycle and the oxidative phosphorylation. We have recently shown that two transporters are critical for the anaplerotic use of glutamate: the Na⁺-dependent Excitatory Amino Acids Carrier 1 (EAAC1) and the Na⁺-Ca²⁺ exchanger 1 (NCX1). Therefore, in the present study, we established an AD-like phenotype by perturbing glucose metabolism in both primary rat cortical neurons and retinoic acid (RA)-differentiated SH-SY5Y cells, and we explored the potential of glutamate to halt cell damage by monitoring neurotoxicity, AD markers, ATP synthesis, cytosolic Ca²⁺ levels and EAAC1/NCX1 functional activities. We found that glutamate significantly increased ATP production and cell survival, reduced the increase of AD biomarkers (amyloid β protein and the hyperphosphorylated form of tau protein), and recovered the increase of NCX reverse-mode activity. The RNA silencing of either EAAC1 or NCX1 caused the loss of the beneficial effects of glutamate, suggesting the requirement of a functional interplay between these transporters for glutamate-induced protection. Remarkably, our results indicate, as proof-of-principle, that facilitating the use of alternative fuels, like glutamate, may be an effective approach to overcome deficits in glucose utilization and significantly slow down neuronal degenerative process in AD.

Enolase inhibition alters metabolic hormones and inflammatory factors to promote neuroprotection in spinal cord injury

Enolase inhibition is a potential therapeutic strategy currently being investigated for treatment of spinal cord injury (SCI) as it reduces pro-inflammatory cytokines and chemokines, alters metabolic factors, and reduces gliosis in acute SCI. Herein, the role of enolase in SCI has been examined to better understand the effects of this enzyme on inflammation, metabolic hormones, glial cell activation, and neuroprotection under these shorter injury conditions. Immunohistochemical analyses of inflammatory markers vimentin, Cox-2, and caspase-1 indicated that enolase inhibition attenuated the elevated levels of inflammation seen following SCI. Iba1, GFAP, NFP, and CSPG staining indicated that enolase inhibition with prolonged administration of ENOblock reduced microglia/astrocyte activation and lead to enhanced neuroprotection in SCI. An analysis of metabolic hormones revealed that ENOblock treatment significantly upregulated plasma concentrations of peptide YY, glucagon-like peptide 1, glucose-dependent insulinotropic peptide, glucagon, and insulin hormones as compared to vehicle-treated controls (Mann-Whitney, p ≤ 0.05). ENOblock did not have a significant effect on plasma concentrations of pancreatic polypeptide. Interestingly, ENOblock treatment inhibited chondroitin sulfate proteoglycan (CSPG), which is produced by activated glia and serves to block regrowth of axons across the lesion site following injury. An increased level of NeuN and MBP with reduced caspase-1 was detected in SCI tissues after ENOblock treatment, suggesting preservation of myelin and induction of neuroprotection. ENOblock also induced improved motor function in SCI rats, indicating a role for enolase in modulating inflammatory and metabolic factors in SCI with important implications for clinical consideration.

Vitamins D and E Stimulate the PI3K-AKT Signalling Pathway in Insulin-Resistant SK-N-SH Neuronal Cells

This study investigated the effects of vitamins D and E on an insulin-resistant model and hypothesized that this treatment would reverse the effects of Alzheimer’s disease (AD) and improves insulin signalling. An insulin-resistant model was induced in SK-N-SH neuronal cells with a treatment of 250 nM insulin and re-challenged with 100 nM at two different incubation time (16 h and 24 h). The effects of vitamin D (10 and 20 ng/mL), vitamin E in the form of tocotrienol-rich fraction (TRF) (200 ng/mL) and the combination of vitamins D and E on insulin signalling markers (IR, PI3K, GLUT3, GLUT4, and p-AKT), glucose uptake and AD markers (GSK3β and TAU) were determined using quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). The results demonstrated an improvement of the insulin signalling pathway upon treatment with vitamin D alone, with significant increases in IR, PI3K, GLUT3, GLUT4 expression levels, as well as AKT phosphorylation and glucose uptake, while GSK3β and TAU expression levels was decreased significantly. On the contrary, vitamin E alone, increased p-AKT, reduced the ROS as well as GSK3β and TAU but had no effect on the insulin signalling expression levels. The combination of vitamins D and E only showed significant increase in GLUT4, p-AKT, reduced ROS as well as GSK3β and TAU. Thus, the universal role of vitamin D, E alone and in combinations could be the potential nutritional agents in restoring the sensitivity of neuronal cells towards insulin and delaying the pathophysiological progression of AD.

Insulin Protects Cortical Neurons Against Glutamate Excitotoxicity

Glutamate excitotoxicity is implicated in the pathogenesis of numerous diseases, such as stroke, traumatic brain injury, and Alzheimer's disease, for which insulin resistance is a concomitant condition, and intranasal insulin treatment is believed to be a promising therapy. Excitotoxicity is initiated primarily by the sustained stimulation of ionotropic glutamate receptors and leads to a rise in intracellular Ca²⁺ ([Ca²⁺] _i ), followed by a cascade of intracellular events, such as delayed calcium deregulation (DCD), mitochondrial depolarization, adenosine triphosphate (ATP) depletion that collectively end in cell death. Therefore, cross-talk between insulin and glutamate signaling in excitotoxicity is of particular interest for research. In the present study, we investigated the effects of short-term insulin exposure on the dynamics of [Ca²⁺] _i and mitochondrial potential in cultured rat cortical neurons during glutamate excitotoxicity. We found that insulin ameliorated the glutamate-evoked rise of [Ca²⁺] _i and prevented the onset of DCD, the postulated point-of-no-return in excitotoxicity. Additionally, insulin significantly improved the glutamate-induced drop in mitochondrial potential, ATP depletion, and depletion of brain-derived neurotrophic factor (BDNF), which is a critical neuroprotector in excitotoxicity. Also, insulin improved oxygen consumption rates, maximal respiration, and spare respiratory capacity in neurons exposed to glutamate, as well as the viability of cells in the MTT assay. In conclusion, the short-term insulin exposure in our experiments was evidently a protective treatment against excitotoxicity, in a sharp contrast to chronic insulin exposure causal to neuronal insulin resistance, the adverse factor in excitotoxicity.

The Protective Effect of Insulin on Rat Cortical Neurons in Oxidative Stress and Its Dependence on the Modulation of Akt, GSK-3beta, ERK1/2, and AMPK Activities

Insulin is a promising drug for the treatment of diseases associated with brain damage. However, the mechanism of its neuroprotective action is far from being understood. Our aim was to study the insulin-induced protection of cortical neurons in oxidative stress and its mechanism. Immunoblotting, flow cytometry, colorimetric, and fluorometric techniques were used. The insulin neuroprotection was shown to depend on insulin concentration in the nanomolar range. Insulin decreased the reactive oxygen species formation in neurons. The insulin-induced modulation of various protein kinase activities was studied at eight time-points after neuronal exposure to prooxidant (hydrogen peroxide). In prooxidant-exposed neurons, insulin increased the phosphorylation of GSK-3beta at Ser⁹ (thus inactivating it), which resulted from Akt activation. Insulin activated ERK1/2 in neurons 5–30 min after cell exposure to prooxidant. Hydrogen peroxide markedly activated AMPK, while it was for the first time shown that insulin inhibited it in neurons at periods of the most pronounced activation by prooxidant. Insulin normalized Bax/Bcl-2 ratio and mitochondrial membrane potential in neurons in oxidative stress. The inhibitors of the PI3K/Akt and MEK1/2/ERK1/2 signaling pathways and the AMPK activator reduced the neuroprotective effect of insulin. Thus, the protective action of insulin on cortical neurons in oxidative stress appear to be realized to a large extent through activation of Akt and ERK1/2, GSK-3beta inactivation, and inhibition of AMPK activity increased by neuronal exposure to prooxidant.

Neurometabolic Evidence Supporting the Hypothesis of Increased Incidence of Type 3 Diabetes Mellitus in the 21st Century

The most recent evidence supports the existence of a link between type 2 diabetes (T2DM) and Alzheimer's Disease (AD), described by the new term: type 3 diabetes (T3D). The increasing incidence of T2DM in the 21st century and accompanying reports on the higher risk of AD in diabetic patients prompts the search for pathways linking glycemia disturbances and neurodegeneration. It is suggested that hyperglycemia may lead to glutamate-induced excitotoxicity, a pathological process resulting from excessive depolarization of membrane and uncontrolled calcium ion influx into neuronal cells. On the other hand, it has been confirmed that peripheral insulin resistance triggers insulin resistance in the brain, which may consequently contribute to AD by amyloid beta accumulation, tau phosphorylation, oxidative stress, advanced glycation end products, and apoptosis. Some literature sources suggest significant amylin involvement in additional amyloid formation in the central nervous system, especially under hyperamylinemic conditions. It is particularly important to provide early diagnostics in people with metabolic disturbances, especially including fasting insulin and HOMA-IR, which are necessary to reveal insulin resistance. The present review reveals the most recent and important evidence associated with the phenomenon of T3D and discusses the potential lacks of prevention and diagnostics for diabetes which might result in neurometabolic disorders, from a pharmacotherapy perspective.

Neuroprotective effects of Scrophularia buergeriana extract against glutamate-induced toxicity in SH-SY5Y cells

The aim of this study was to investigate the antioxidant and anti-apoptotic activities, as well as the underlying mechanisms of action, of Scrophularia buergeriana (S. buergeriana) extract (SBE) in glutamate-induced SH-SY5Y cell death. The roots of S. buergeriana were extracted with 70% ethanol, and standardized SBE was used in this study. To induce cytotoxicity, the SH-SY5Y cells were exposed to glutamate for 3 h, or pre-treated with SBE for 1 h, and subsequently incubated with glutamate for 3 h. The neuro-protective effects were assessed by measuring cell viability and the total glutathione contents using commercial kits. The antioxidant and anti-apoptotic mechanisms of action of SBE were evaluated by western blot analysis. The results confirmed that glutamate-induced toxicity was caused by reactive oxygen species (ROS) production, leading to oxidative stress and DNA damage, thus leading to cell death. However, treatment of the SH-SY5Y cells with SBE significantly increased the viability of the cells exposed to glutamate by upregulating the levels of antioxidant proteins, such as superoxide dismutase (SOD)1, SOD2 and glutathione peroxidase-1 (GPx-1), and directly enhancing the total glutathione contents. Furthermore, SBE attenuated DNA impairment and decreased B-cell lymphoma-2 (Bcl-2)-associated X protein (Bax), cleaved caspase-3 and cleaved poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) activation. In addition, SBE upregulated Bcl-2 expression via p38 mitogen-activated protein kinases (MAPKs). On the whole, the findings of this study demonstrated that SBE exerts neuroprotective effects against glutamate-induced cell toxicity through its antioxidant and anti-apoptotic activities.

Protective effect of 5-HT7 receptor activation against glutamate-induced neurotoxicity in human neuroblastoma SH-SY5Y cells via antioxidative and antiapoptotic pathways

Serotonin exerts anti-inflammatory, antioxidant and antiapoptotic effects through 5-HT7 receptors. The present study determined the role of 5-HT7 receptors in glutamate-induced neurotoxicity by using human SH-SY5Y neuroblastoma cells. The cells were pretreated with different concentrations of 5-HT7 receptor agonist LP44 and antagonist SB269970 for 60 min, followed by treatment with glutamate. Cell proliferation was measured using xCELLigence system. Treatment with all the concentrations of LP44 significantly protected the cells from the toxic effects of glutamate after 24, 48 and 72 h. Although 5-HT7 receptor expression was significantly upregulated in glutamate-treated cells, it was downregulated in LP44-pretreated cells. Furthermore, LP44 treatment significantly decreased malondialdehyde levels and increased superoxide dismutase activities and glutathione levels. Moreover, LP44 treatment significantly decreased tumor necrosis factor alpha (TNF-α) levels and inhibited caspase 3 and caspase 9 mRNA expression. In contrast, SB269970 treatment exerted an insignificant effect on oxidative stress, inflammation and apoptosis. These findings suggest that exogenous stimulation of the 5-HT7 receptors may be protective in glutamate-induced neurotoxicity and that 5-HT7 receptor agonists can be used as therapeutic agents for preventing glutamate-induced neurological disorders.

Neurotoxic Agent-Induced Injury in Neurodegenerative Disease Model: Focus on Involvement of Glutamate Receptors

Glutamate receptors play a crucial role in the central nervous system and are implicated in different brain disorders. They play a significant role in the pathogenesis of neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Although many studies on NDDs have been conducted, their exact pathophysiological characteristics are still not fully understood. In in vivo and in vitro models of neurotoxic-induced NDDs, neurotoxic agents are used to induce several neuronal injuries for the purpose of correlating them with the pathological characteristics of NDDs. Moreover, therapeutic drugs might be discovered based on the studies employing these models. In NDD models, different neurotoxic agents, namely, kainic acid, domoic acid, glutamate, β-N-Methylamino-L-alanine, amyloid beta, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridinium, rotenone, 3-Nitropropionic acid and methamphetamine can potently impair both ionotropic and metabotropic glutamate receptors, leading to the progression of toxicity. Many other neurotoxic agents mainly affect the functions of ionotropic glutamate receptors. We discuss particular neurotoxic agents that can act upon glutamate receptors so as to effectively mimic NDDs. The correlation of neurotoxic agent-induced disease characteristics with glutamate receptors would aid the discovery and development of therapeutic drugs for NDDs.

The involvement of tau in nucleolar transcription and the stress response

Tau is known for its pathological role in neurodegenerative diseases, including Alzheimer's disease (AD) and other tauopathies. Tau is found in many subcellular compartments such as the cytosol and the nucleus. Although its normal role in microtubule binding is well established, its nuclear role is still unclear. Here, we reveal that tau localises to the nucleolus in undifferentiated and differentiated neuroblastoma cells (SHSY5Y), where it associates with TIP5, a key player in heterochromatin stability and ribosomal DNA (rDNA) transcriptional repression. Immunogold labelling on human brain sample confirms the physiological relevance of this finding by showing tau within the nucleolus colocalises with TIP5. Depletion of tau results in an increase in rDNA transcription with an associated decrease in heterochromatin and DNA methylation, suggesting that under normal conditions tau is involved in silencing of the rDNA. Cellular stress induced by glutamate causes nucleolar stress associated with the redistribution of nucleolar non-phosphorylated tau, in a similar manner to fibrillarin, and nuclear upsurge of phosphorylated tau (Thr231) which doesn't colocalise with fibrillarin or nucleolar tau. This suggests that stress may impact on different nuclear tau species. In addition to involvement in rDNA transcription, nucleolar non-phosphorylated tau also undergoes stress-induced redistribution similar to many nucleolar proteins.

Insulin signaling pathway protects neuronal cell lines by Sirt3 mediated IRS2 activation

Cellular stress like ER and oxidative stress are the principle causative agents of various proteinopathies. Multifunctional protein PARK7/DJ-1 provides protection against cellular stress. Recently, insulin/IGF also has emerged as a neuro-protective molecule. However, it is not known whether DJ-1 and insulin/IGF complement each other for cellular protection in response to stress. In this study, we show for the first time, that in human and mouse neuronal cell lines, down regulation of DJ-1 for 48 h leads to compensatory upregulation of insulin/IGF signaling (IIS) pathway genes, namely, insulin receptor, insulin receptor substrate, and Akt under normal physiological conditions as well as in cellular stress conditions. Moreover, upon exogenous supply of insulin there is a marked increase in the IIS components both at gene and protein levels leading to down regulation and inactivation of GSK3β. By immunoprecipitation, it was observed that Sirt3 mediated deacetylation and activation of FoxO3a could not occur under DJ-1 downregulation. Transient DJ-1 downregulation also led to Akt mediated increased phosphorylation and nuclear exclusion of FoxO3a. When DJ-1 was downregulated increased interaction of Sirt3 with IRS2 was observed leading to its activation resulting in IIS upregulation. Thus, transient downregulation of DJ-1 leads to stimulation of IIS pathway by Sirt3 mediated IRS2 activation. Consequently, antiapoptotic program is triggered in neuronal cells via Akt-GSK3β-FoxO3a axis. © 2018 BioFactors, 44(3):224-236, 2018.

Effect of insulin on spatial memory in aluminum chloride-induced dementia in rats

Latest reports suggest the involvement of insulin in modulating memory. A few published in-vitro studies favor the antidementia effect of insulin. Thus, the present study aimed to evaluate the prophylactic role of insulin and its combination with glucose and its possible mechanism(s) in an aluminum chloride (AlCl3)-induced cognitive dysfunction model in rodents, with a special focus on memory centers namely, the hippocampus and the frontal cortex. Male Wistar rats were exposed to AlCl3 (175 mg/kg orally) for 60 days. Insulin (0.5 IU/kg), Insulin (0.5 IU/kg) in combination with glucose (200 mg/kg), and rivastigmine (1 mg/kg) were administered intraperitoneally 45 min before the administration of AlCl3 for 60 days. Spatial memory was assessed using the Morris water-maze test. After 60 days of treatment, animals were killed, and the hippocampus and frontal cortex were collected and analyzed for acetylcholinesterase activity and antioxidant enzyme level. Blood glucose levels were also analyzed. Treatment with the standard drug, rivastigmine (1 mg/kg), produced a significant reduction in escape latency and increased the time spent in the target quadrant compared with the AlCl3-treated group. Insulin and its combination with glucose could not inhibit the behavioral impairments in aluminum-exposed rats. Treatment with insulin alone and its combination with glucose reversed the increased glucose levels. Insulin alone and its combination with glucose could not inhibit aluminum-induced oxidative stress and impaired cholinergic transmission in the hippocampus and frontal cortex regions. The study suggests the inability of prophylactic insulin administration against cognitive dysfunction induced by environmental toxin (AlCl3) in the hippocampus and the frontal cortex.

Is Glaucoma a Neurodegeneration caused by Central Insulin Resistance: Diabetes Type 4?

How to cite this article: Dada T. Is Glaucoma a Neurodegeneration caused by Central Insulin Resistance: Diabetes Type 4? J Curr Glaucoma Pract 2017;11(3):77-79.

Catechin ameliorates doxorubicin-induced neuronal cytotoxicity in in vitro and episodic memory deficit in in vivo in Wistar rats

Cognitive dysfunction by chemotherapy compromises the quality of life in cancer patients. Tea polyphenols are known chemopreventive agents. The present study was designed to evaluate the neuroprotective potential of (+) catechin hydrate (catechin), a tea polyphenol, in IMR-32 neuroblastoma cells in vitro and alleviation of episodic memory deficit in Wistar rats in vivo against a widely used chemotherapeutic agent, Doxorubicin (DOX). In vitro, neuroprotective studies were assessed in undifferentiated IMR-32 cells using percentage viability and in differentiated cells by neurite length. These studies showed catechin increased percentage viability of undifferentiated IMR-32 cells. Catechin pretreatment also showed an increase in neurite length of differentiated cells. In vivo neuroprotection of catechin was evaluated using novel object recognition task in time-induced memory deficit model at 50, 100 and 200 mg/kg dose and DOX-induced memory deficit models at 100 mg/kg dose. The latter model was developed by injection of DOX (2.5 mg/kg, i.p.) in 10 cycles over 50 days in Wistar rats. Catechin showed a significant reversal of time-induced memory deficit in a dose-dependent manner and prevention of DOX-induced memory deficit at 100 mg/kg. In addition, catechin treatment showed a significant decrease in oxidative stress, acetylcholine esterase and neuroinflammation in the hippocampus and cerebral cortex in DOX-induced toxicity model. Hence, catechin may be a potential adjuvant therapy for the amelioration of DOX-induced cognitive impairment which may improve the quality of life of cancer survivors. This improvement might be due to the elevation of antioxidant defense, prevention of neuroinflammation and inhibition of acetylcholine esterase enzyme.

Rutin protects against neuronal damage in vitro and ameliorates doxorubicin-induced memory deficits in vivo in Wistar rats

Doxorubicin (DOX) is the most widely used broad-spectrum anticancer agent, either alone or in combination, for most cancers including breast cancer. Long-term use of chemotherapeutic agents to treat breast cancer patients results in cognitive complications with a negative impact on survivors’ quality of life. The study objective was to evaluate rutin (RUT) for its neuroprotective effect against DOX in human neuroblastoma (IMR32) cells in vitro and study its potential to ameliorate DOX-induced cognitive dysfunction in Wistar rats. Cell viability assay (3-[4,5 dimethyl thiazol-2-yl]-2,5-diphenyl tetrazolium bromide), neurite growth assay, detection of apoptosis by (acridine orange/ethidium bromide) staining, intracellular reactive oxygen species (ROS) assay, and flowcytometric analysis were carried out to assess neuroprotective potential against DOX. An in vivo study was conducted for assessing protective effect of RUT against memory deficit associated with DOX-induced chemobrain using object recognition task (ORT). Locomotion was assessed using open field test. Serum biochemistry, acetylcholinesterase, oxidative stress markers in hippocampus, and frontal cortex were assessed. Histopathological analysis of major organ systems was also carried out. Prior exposure to RUT at 100 µM protected IMR32 cells from DOX (1 µM) neurotoxicity. DOX exposure resulted in increased cellular death, apoptosis, and intracellular ROS generation with inhibition of neurite growth in differentiated IMR32 cells, which was significantly ameliorated by RUT. Cognitive dysfunction was induced in Wistar rats by administering ten cycles of DOX (2.5 mg/kg, intra-peritoneal, once in 5 days), as we observed significant impairment of episodic memory in ORT. Coadministration with RUT (50 mg/kg, per os) significantly prevented memory deficits in vivo without any confounding influence on locomotor activity. RUT also offered protection against DOX-induced myelosuppression, cardiotoxicity, and nephrotoxicity. In conclusion, RUT may be a possible adjuvant therapeutic intervention to alleviate cognitive and other complications associated with DOX chemotherapy.

Quinolinic acid induces neuritogenesis in SH-SY5Y neuroblastoma cells independently of NMDA receptor activation

Glutamate and nicotinamide adenine dinucleotide (NAD⁺ ) have been implicated in neuronal development and several types of cancer. The kynurenine pathway of tryptophan metabolism includes quinolinic acid (QA) which is both a selective agonist at N-methyl-D-aspartate (NMDA) receptors and also a precursor for the formation of NAD⁺ . The effect of QA on cell survival and differentiation has therefore been examined on SH-SY5Y human neuroblastoma cells. Retinoic acid (RA, 10 μm) induced differentiation of SH-SY5Y cells into a neuronal phenotype showing neurite growth. QA (50-150 nm) also caused a concentration-dependent increase in the neurite/soma ratio, indicating differentiation. Both RA and QA increased expression of the neuronal marker β3-tubulin in whole-cell homogenates and in the neuritic fraction assessed using a neurite outgrowth assay. Expression of the neuronal proliferation marker doublecortin revealed that, unlike RA, QA did not decrease the number of mitotic cells. QA-induced neuritogenesis coincided with an increase in the generation of reactive oxygen species. Neuritogenesis was prevented by diphenylene-iodonium (an inhibitor of NADPH oxidase) and superoxide dismutase, supporting the involvement of reactive oxygen species. NMDA itself did not promote neuritogenesis and the NMDA antagonist dizocilpine (MK-801) did not prevent quinolinate-induced neuritogenesis, indicating that the effects of QA were independent of NMDA receptors. Nicotinamide caused a significant increase in the neurite/soma ratio and the expression of β3-tubulin in the neuritic fraction. Taken together, these results suggest that QA induces neuritogenesis by promoting oxidizing conditions and affecting the availability of NAD⁺ , independently of NMDA receptors.

Neuroprotective Effect of Puerarin on Glutamate-Induced Cytotoxicity in Differentiated Y-79 Cells via Inhibition of ROS Generation and Ca(2+) Influx

Glutamate toxicity is estimated to be the key cause of photoreceptor degeneration in the pathogenesis of retinal degenerative diseases. Oxidative stress and Ca(2+) influx induced by glutamate are responsible for the apoptosis process of photoreceptor degeneration. Puerarin, a primary component of Kudzu root, has been widely used in the clinical treatment of retinal degenerative diseases in China for decades; however, the detailed molecular mechanism underlying this effect remains unclear. In this study, the neuroprotective effect of puerarin against glutamate-induced cytotoxicity in the differentiated Y-79 cells was first investigated through cytotoxicity assay. Then the molecular mechanism of this effect regarding anti-oxidative stress and Ca(2+) hemostasis was further explored with indirect immunofluorescence, flow cytometric analysis and western blot analysis. Our study showed that glutamate induced cell viability loss, excessive reactive oxygen species (ROS) generation, calcium overload and up-regulated cell apoptosis in differentiated Y-79 cells, which effect was significantly attenuated with the pre-treatment of puerarin in a dose-dependent manner. Furthermore, our data indicated that the neuroprotective effect of puerarin was potentially mediated through the inhibition of glutamate-induced activation of mitochondrial-dependent signaling pathway and calmodulin-dependent protein kinase II (CaMKII)-dependent apoptosis signal-regulating kinase 1(ASK-1)/c-Jun N-terminal kinase (JNK)/p38 signaling pathway. The present study supports the notion that puerarin may be a promising neuroprotective agent in the prevention of retinal degenerative diseases.

Neuroprotective and Cytotoxic Phthalides from Angelicae Sinensis Radix

Seven phthalides, including a new dimeric one named tokinolide C (7), were isolated from Angelicae Sinensis Radix and characterized. The structures of these compounds were elucidated on the basis of comprehensive analysis of spectroscopic data and comparison with literature data. All of the compounds were evaluated for their cytotoxic activities against the A549, HCT-8, and HepG2 cancer cell lines. Riligustilide (4) showed cytotoxicity against three cancer cell lines, with IC50 values of 13.82, 6.79, and 7.92 μM, respectively. Tokinolide A (6) and tokinolide C (6) exerted low cytotoxicity in these cancer cell lines, while the remaining compounds were inactive. Flow cytometry analysis was employed to evaluate the possible mechanism of cytotoxic action of riligustilide (4). We observed that compound 4 was able to arrest the cell cycle in the G1, S phases and induce apoptosis in a time-dependent manner in HCT-8 cell lines. In addition, these compounds were evaluated for neuroprotective effect against SH-SY5Y cells injured by glutamate. The result showed that ligustilide (1), Z-butylidenephthalide (3) and tokinolide A (6) exhibited significant neuroprotective effects.

Stimulus-dependent neuronal cell responses in SH-SY5Y neuroblastoma cells

The aim of the present study was to elucidate the intracellular mechanisms that cause neuronal cell death following exposure to excitatory neurotransmitter‑induced neurotoxicity, neurotoxins and oxidative stress. Human SH‑SY5Y neuroblastoma cells were exposed to various stimuli, including glutamate, 6‑hydroxydopamine (6‑OHDA), and glucose oxidase, and cell viability was determined by MTT assay. Early apoptosis and necrosis were examined by Annexin V/propidium iodide double staining and flow cytometric analysis. Intracellular calcium ion concentration and mitochondrial membrane potential were assessed by Fluo‑3a and JC‑1 staining, respectively. In addition, protein expression of receptor‑interacting protein (RIP) kinase 1 and RIP kinase 3 were evaluated by western blotting. Glutamate, 6‑OHDA and glucose oxidase treatment decreased cell viability. Glutamate induced apoptosis and necrosis, whereas, 6‑OHDA induced cell necrosis and glucose oxidase induced apoptosis. Furthermore, glutamate, 6‑OHDA or glucose oxidase treatment significantly increased intracellular calcium concentrations (P<0.05). The effect of glutamate on mitochondrial membrane potential varied with high and low concentrations, whereas 6‑OHDA and glucose oxidase significantly increased the mitochondrial membrane potential in the SH‑SY5Y cells (P<0.05). Glutamate significantly upregulated expression levels of RIP kinase 1 (P<0.05), but not RIP kinase 3. These findings demonstrate that the response of SH‑SY5Y cells varies with the stimuli. Furthermore, RIP kinase 1 may specifically regulate programmed necrosis in glutamate‑mediated excitatory toxicity, but not in cell damage induced by either 6-OHDA or glucose oxidase.

Sesamol, a lipid lowering agent, ameliorates aluminium chloride induced behavioral and biochemical alterations in rats

Background:

Sesame oil from the seeds of Sesamum indicum Linn. (Pedaliaceae) has been used traditionally in Indian medical practice of Ayurveda in the treatment of central nervous system disorders and insomnia. A few published reports favor the anti-dementia effect of sesamol (SML), an active constituent of sesame oil.

Objective:

Thus, the present study was aimed to explore the anti-dementia effect and possible mechanism (s) of SML in aluminium chloride (AlCl₃)-induced cognitive dysfunction model in rodents with special emphasis on memory centers viz., hippocampus and frontal cortex.

Methods:

Male Wistar rats were exposed to AlCl₃ (175 mg/kg p.o.) for 60 days. SML (10 and 20 mg/kg) and rivastigmine (1 mg/kg) were administered orally 45 min before administration of AlCl₃ for 60 days. Spatial memory was assessed using Morris water maze test. After 60 days of treatment animals were sacrificed, hippocampus and frontal cortex were collected and analyzed for acetylcholinesterase (AChE) activity, tumor necrosis factor (TNF-α) level, antioxidant enzymes (Glutathione, catalase), lipid peroxidation, and nitrite level. The circulating triglycerides, total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels were also analyzed.

Results:

SML significantly prevented behavioral impairments in aluminium-exposed rats. Treatment with SML reversed the increased cholesterol, triglycerides and LDL while raised the HDL levels. SML significantly corrected the effect of AlCl₃ on AChE activity. Further, SML reversed the elevated nitric oxide, TNF-α and reduced antioxidant enzymes in hippocampus and frontal cortex.

Conclusion:

The present study suggests the neuro-protection by SML against cognitive dysfunction induced by environmental toxin (AlCl₃) in hippocampus and frontal cortex.

Researching glutamate - induced cytotoxicity in different cell lines: a comparative/collective analysis/study

Although glutamate is one of the most important excitatory neurotransmitters of the central nervous system, its excessive extracellular concentration leads to uncontrolled continuous depolarization of neurons, a toxic process called, excitotoxicity. In excitotoxicity glutamate triggers the rise of intracellular Ca²⁺ levels, followed by up regulation of nNOS, dysfunction of mitochondria, ROS production, ER stress, and release of lysosomal enzymes. Excessive calcium concentration is the key mediator of glutamate toxicity through over activation of ionotropic and metabotropic receptors. In addition, glutamate accumulation can also inhibit cystine (CySS) uptake by reversing the action of the CySS/glutamate antiporter. Reversal of the antiporter action reinforces the aforementioned events by depleting neurons of cysteine and eventually glutathione’s reducing potential. Various cell lines have been employed in the pursuit to understand the mechanism(s) by which excitotoxicity affects the cells leading them ultimately to their demise. In some cell lines glutamate toxicity is exerted mainly through over activation of NMDA, AMPA, or kainate receptors whereas in other cell lines lacking such receptors, the toxicity is due to glutamate induced oxidative stress. However, in the greatest majority of the cell lines ionotropic glutamate receptors are present, co-existing to CySS/glutamate antiporters and metabotropic glutamate receptors, supporting the assumption that excitotoxicity effect in these cells is accumulative. Different cell lines differ in their responses when exposed to glutamate. In this review article the responses of PC12, SH-SY5Y, HT-22, NT-2, OLCs, C6, primary rat cortical neurons, RGC-5, and SCN2.2 cell systems are systematically collected and analyzed.

Modulatory role of simvastatin against aluminium chloride-induced behavioural and biochemical changes in rats

Objectives. Aluminium, a neurotoxic agent in humans, has been implicated in the pathogenesis of neurodegenerative disorders. In this study, we examined the behavioral and biochemical effects of aluminium in rats with special emphasis on memory centres, namely, hippocampus and frontal cortex. Further, the effect of simvastatin treatment on aluminium intoxication was evaluated. Methods. Rats were exposed to aluminium chloride (AlCl₃) for 60 days. Simvastatin (10 mg/kg/p.o.) and rivastigmine (1 mg/kg/p.o.) were administered daily prior to AlCl₃. Behavioral parameters were assessed using Morris water maze test and actophotometer followed by biochemical investigations, namely, acetylcholinesterase (AChE) activity, TNF-α level, antioxidant enzymes (GSH, catalase), lipid peroxidation, and nitrite level in hippocampus and frontal cortex. Triglycerides, total cholesterol, LDL, and HDL levels in serum were also determined. Key Findings. Simvastatin treatment improved cognitive function and locomotor activity in rats. Simvastatin reversed hyperlipidemia and significantly rectified the deleterious effect of AlCl₃ on AChE activity. Further, in hippocampus and frontal cortex, aluminium-induced elevation in nitrite and TNF-α and reduction in antioxidant enzymes were inhibited by simvastatin. Conclusion. To conclude, the present study suggests that simvastatin per se protects the neurons in hippocampus and frontal cortex from AlCl₃, an environmental toxin.