Roles of glutamine synthetase inhibition in epilepsy

Sodium Houttuyfonate Prevents Seizures and Neuronal Cell Loss by Maintaining Glutamatergic System Stability in Male Rats with Kainic Acid-Induced Seizures

The present study evaluated the antiseizure and neuroprotective effects of sodium houttuyfonate (SH), a derivative of Houttuynia cordata Thunb. (H. cordata), in a kainic acid (KA)- induced seizure rat model and its underlying mechanism. Sprague Dawley rats were administered normal saline, SH (50 or 100 mg/kg), or carbamazepine (300 mg/kg) by oral gavage for seven consecutive days before the intraperitoneal administration of KA (15 mg/kg). SH showed antiseizure effects at a dose of 100 mg/kg; it prolonged seizure latency and decreased seizure scores. SH also significantly decreased neuronal loss in the hippocampi of KA-treated rats, which was associated with the prevention of glutamate level increase, the upregulation of glutamate reuptake-associated proteins (excitatory amino acid transporters 1-3), glutamate metabolism enzyme glutamine synthetase, the downregulation of the glutamate synthesis enzyme glutaminase, and significant alterations in the expression of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor) and NMDA (N-methyl-D-aspartic acid receptor) receptor subunits in the hippocampus. Furthermore, the effects of SH were similar to those of the antiseizure drug carbamazepine. Therefore, the results of the present study suggest that SH has antiseizure effects on KA-induced seizures, possibly through the prevention of glutamatergic alterations. Our findings suggest that SH is a potential alternative treatment that may prevent seizures by preserving the normal glutamatergic system.

Ursolic acid inhibits the synaptic release of glutamate and prevents glutamate excitotoxicity in rats

The present study evaluated the effect of ursolic acid, a natural pentacyclic triterpenoid, on glutamate release in rat cortical nerve terminals (synaptosomes) and its neuroprotection in a kainic acid-induced excitotoxicity rat model. In cortical synaptosomes, ursolic acid produced a concentration-dependent inhibition of evoked glutamate release with a half-maximum inhibition of release value of 9.5 μM, and calcium-free medium and the P/Q -type Ca2+ channel blocker, ω-agatoxin IVA, but not ω-conotoxin GVIA, an N-type Ca2+ channel blocker, prevented the ursoloic acid effect. The molecular docking study indicated that ursolic acid interacted with P/Q-type Ca2+ channels. Ursolic acid also significantly decreased the depolarization-induced activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and the subsequent phosphorylation of synapsin I, and the ursolic acid effect on evoked glutamate release was inhibited by the CaMKII inhibitor KN 62 in synaptosomes. In addition, in rats that were intraperitoneally injected with ursolic acid 30 min before kainic acid intraperitoneal injection, cortical neuronal degeneration was attenuated. This effect of ursolic acid in the improvement of kainic acid-induced neuronal damage was associated with the reduction of kainic acid-induced glutamate increase in the cortex of rats; this was characterized by the reduction of glutamate and glutaminase levels and elevation of glutamate dehydrogenase, glutamate transporter 1, glutamate-aspartate transporter, and glutamine synthetase protein levels. These results suggest that ursolic acid inhibits glutamate release from cortical synaptosomes by decreasing P/Q-type Ca2+ channel activity and subsequently suppressing CaMKII and exerts a preventive effect against glutamate neurotoxicity by controlling glutamate levels.

Prominent and conspicuous astrocyte atrophy in human sporadic and familial Alzheimer's disease

Pathophysiology of sporadic Alzheimer's disease (SAD) and familial Alzheimer's disease (FAD) remains poorly known, including the exact role of neuroglia and specifically astroglia, in part because studies of astrocytes in human Alzheimer's disease (AD) brain samples are scarce. As far as we know, this is the first study of a 3-D immunohistochemical and microstructural analysis of glial fibrillary acidic protein (GFAP)- and glutamine synthetase (GS)-positive astrocytes performed in the entorhinal cortex (EC) of human SAD and FAD samples. In this study, we report prominent atrophic changes in GFAP and GS astrocytes in the EC of both SAD and FAD characterised by a decrease in area and volume when compared with non-demented control samples (ND). Furthermore, we did not find neither astrocytic loss nor astrocyte proliferation or hypertrophy (gliosis). In contrast with the astrogliosis classically accepted hypothesis, our results show a highly marked astrocyte atrophy that could have a major relevance in AD pathological processes being fundamental and key for AD mnesic and cognitive alterations equivalent in both SAD and FAD.

Neurological Phenotypes in Mouse Models of Mitochondrial Disease and Relevance to Human Neuropathology

Mitochondrial diseases represent the most common inherited neurometabolic disorders, for which no effective therapy currently exists for most patients. The unmet clinical need requires a more comprehensive understanding of the disease mechanisms and the development of reliable and robust in vivo models that accurately recapitulate human disease. This review aims to summarise and discuss various mouse models harbouring transgenic impairments in genes that regulate mitochondrial function, specifically their neurological phenotype and neuropathological features. Ataxia secondary to cerebellar impairment is one of the most prevalent neurological features of mouse models of mitochondrial dysfunction, consistent with the observation that progressive cerebellar ataxia is a common neurological manifestation in patients with mitochondrial disease. The loss of Purkinje neurons is a shared neuropathological finding in human post-mortem tissues and numerous mouse models. However, none of the existing mouse models recapitulate other devastating neurological phenotypes, such as refractory focal seizures and stroke-like episodes seen in patients. Additionally, we discuss the roles of reactive astrogliosis and microglial reactivity, which may be driving the neuropathology in some of the mouse models of mitochondrial dysfunction, as well as mechanisms through which cellular death may occur, beyond apoptosis, in neurons undergoing mitochondrial bioenergy crisis.

A role of GABAA receptor α1 subunit in the hippocampus for rapid-acting antidepressant-like effects of ketamine

Ketamine can produce rapid-acting antidepressant effects in treatment-resistant patients with depression. Although alterations in glutamatergic and GABAergic neurotransmission in the brain play a role in depression, the precise molecular mechanisms in these neurotransmission underlying ketamine's antidepressant actions remain largely unknown. Mice exposed to FSS (forced swimming stress) showed depression-like behavior and decreased levels of GABA (γ-aminobutyric acid), but not glutamate, in the hippocampus. Ketamine increased GABA levels and decreased glutamate levels in the hippocampus of mice exposed to FSS. There was a correlation between GABA levels and depression-like behavior. Furthermore, ketamine increased the levels of enzymes and transporters on the GABAergic neurons (SAT1, GAD67, GAD65, VGAT and GAT1) and astrocytes (EAAT2 and GAT3), without affecting the levels of enzymes and transporters (SAT2, VGluT1 and GABA_AR γ2) on glutamatergic neurons. Moreover, ketamine caused a decreased expression of GABA_AR α1 subunit, which was specifically expressed on GABAergic neurons and astrocytes, an increased GABA synthesis and metabolism in GABAergic neurons, a plasticity change in astrocytes, and an increase in ATP (adenosine triphosphate) contents. Finally, GABA_AR antagonist bicuculline or ATP exerted a rapid antidepressant-like effect whereas pretreatment with GABA_AR agonist muscimol blocked the antidepressant-like effects of ketamine. In addition, pharmacological activation and inhibition of GABA_AR modulated the synthesis and metabolism of GABA, and the plasticity of astrocytes in the hippocampus. The present data suggest that ketamine could increase GABA synthesis and astrocyte plasticity through downregulation of GABA_AR α1, increases in GABA, and conversion of GABA into ATP, resulting in a rapid-acting antidepressant-like action. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Regulation of the Volume-Regulated Anion Channel Pore-Forming Subunit LRRC8A in the Intrahippocampal Kainic Acid Model of Mesial Temporal Lobe Epilepsy

Volume-regulated anion channels (VRACs) are a group of ubiquitously expressed outwardly-rectifying anion channels that sense increases in cell volume and act to return cells to baseline volume through an efflux of anions and organic osmolytes, including glutamate. Because cell swelling, increased extracellular glutamate levels, and reduction of the brain extracellular space (ECS) all occur during seizure generation, we set out to determine whether VRACs are dysregulated throughout mesial temporal lobe epilepsy (MTLE), the most common form of adult epilepsy. To accomplish this, we employed the IHKA experimental model of MTLE, and probed for the expression of LRRC8A, the essential pore-forming VRAC subunit, at acute, early-, mid-, and late-epileptogenic time points (1-, 7-, 14-, and 30-days post-IHKA, respectively). Western blot analysis revealed the upregulation of total dorsal hippocampal LRRC8A 14-days post-IHKA in both the ipsilateral and contralateral hippocampus. Immunohistochemical analyses showed an increased LRRC8A signal 7-days post-IHKA in both the ipsilateral and contralateral hippocampus, along with layer-specific changes 1-, 7-, and 30-days post-IHKA bilaterally. LRRC8A upregulation 1 day post-IHKA was observed primarily in astrocytes; however, some upregulation was also observed in neurons. Glutamate-GABA/glutamine cycle enzymes glutamic acid decarboxylase, glutaminase, and glutamine synthetase were also dysregulated at the 7-day timepoint post status epilepticus. The timepoint-dependent upregulation of total hippocampal LRRC8A and the possible subsequent increased efflux of glutamate in the epileptic hippocampus suggest that the dysregulation of astrocytic VRAC may play an important role in the development of epilepsy.

Ellagic acid and allopurinol decrease H2O2 concentrations, epileptiform activity and astrogliosis after status epilepticus in the hippocampus of adult rats

Status epilepticus (SE) can result in an overproduction of hydrogen peroxide (H₂O₂), which contributes to oxidative stress and brain injury during different phases of epileptogenesis and seizures. The purpose of this study was to evaluate the effects of ellagic acid and allopurinol administered after SE on H₂O₂ concentrations, electrical activity and GFAP immunoreactivity in the hippocampus of rats evaluated on Day 18 after SE. H₂O₂ levels were measured using an online technique with high temporal resolution and simultaneous electrical activity recording. For this purpose, the lateral ventricles of male Wistar rats (200-250 g) were injected with pilocarpine (2.4 mg/2 µl) to induce SE. After SE, rats were injected with ellagic acid (50 mg/kg i.p., and two additional doses at 24 and 48 h) or allopurinol (50 mg/kg i.p., single dose). Administration of ellagic acid or allopurinol after SE significantly reduced the H₂O₂ concentrations and decreased the presence of epileptiform activity and GFAP immunoreactivity in the hippocampus 18 days after SE. In conclusion, the administration of antioxidants potentially reduces oxidative stress, which indicates the possible attenuation of the neurobiological consequences after SE.

Novel test strategies for in vitro seizure liability assessment

INTRODUCTION

The increasing incidence of mental illnesses and neurodegenerative diseases results in a high demand for drugs targeting the central nervous system (CNS). These drugs easily reach the CNS, have a high affinity for CNS targets, and are prone to cause seizures as an adverse drug reaction. Current seizure liability assessment heavily depends on in vivo or ex vivo animal models and is therefore ethically debated, labor intensive, expensive, and not always predictive for human risk.

AREAS COVERED

The demand for CNS drugs urges the development of alternative safety assessment strategies. Yet, the complexity of the CNS hampers reliable detection of compound-induced seizures. This review provides an overview of the requirements of in vitro seizure liability assays and highlights recent advances, including micro-electrode array (MEA) recordings using rodent and human cell models.

EXPERT OPINION

Successful and cost-effective replacement of in vivo and ex vivo models for seizure liability screening can reduce animal use for drug development, while increasing the predictive value of the assays, particularly if human cell models are used. However, these novel test strategies require further validation and standardization as well as additional refinements to better mimic the human in vivo situation and increase their predictive value.

Female mice lacking ERβ display excitatory/inhibitory synaptic imbalance to drive the pathogenesis of temporal lobe epilepsy

Epilepsy is a highly prevalent and drug-refractory neurological disorder characterized by spontaneous recurrent seizures. Estrogen is identified to be proconvulsant and lowers the seizure threshold of female epilepsy. Estrogen receptor β (ERβ) has been proposed to mediate neuroprotection in epilepsy, although the underlying mechanism remains unknown. Rationale: In this study, we investigated the role of ERβ in the epileptogenesis of female temporal lobe epilepsy (TLE). Methods: Immunohistochemistry, immunofluorescence, western blots, Golgi staining, ¹H MRS and whole-cell patch-clamp were used to evaluate ERβ expression, pathological changes, and synaptic excitation /inhibition (E/I) balance in female TLE patients and ovariectomized (OVX) chronic epileptic mice. Electroencephalogram (EEG) recordings were recorded to evaluate the epileptic susceptibility in OVX WT and ERβ^-/- mice. And high-throughput RNA-sequence was performed to identify differential expression genes (DEGs) which can elucidate the potential mechanism of ERβ regulating the seizure susceptibility. Results: ERβ expression was decreased in the brains of female TLE patients and OVX chronic epileptic mice. ERβ deletion enhanced seizure susceptibility and exacerbated the imbalance of synaptic E/I in hippocampal CA1 area of OVX epileptic mice. In line with these observations, RNA-sequence data further identified glutamine ligase (GLUL) as the target of ERβ involved in regulating synaptic E/I in CA1. Furthermore, ERβ agonist WAY-200070 markedly suppressed epileptic phenotypes and normalized GLUL expression in CA1 region of kainic acid (KA) induced OVX chronic epileptic model. Conclusions: Our data provide novel insight into the pathogenesis of female TLE, and indicate ERβ provides a new therapeutic strategy for female TLE patients.

Mechanism of Fully Reversible, pH-Sensitive Inhibition of Human Glutamine Synthetase by Tyrosine Nitration

Glutamine synthetase (GS) catalyzes an ATP-dependent condensation of glutamate and ammonia to form glutamine. This reaction-and therefore GS-are indispensable for the hepatic nitrogen metabolism. Nitration of tyrosine 336 (Y336) inhibits human GS activity. GS nitration and the consequent loss of GS function are associated with a broad range of neurological diseases. The mechanism by which Y336 nitration inhibits GS, however, is not understood. Here, we show by means of unbiased MD simulations, binding, and configurational free energy computations that Y336 nitration hampers ATP binding but only in the deprotonated and negatively charged state of residue 336. By contrast, for the protonated and neutral state, our computations indicate an increased binding affinity for ATP. pK_a computations of nitrated Y336 within GS predict a pK_a of ∼5.3. Thus, at physiological pH, nitrated Y336 exists almost exclusively in the deprotonated and negatively charged state. In vitro experiments confirm these predictions, in that, the catalytic activity of nitrated GS is decreased at pH 7 and 6 but not at pH 4. These results indicate a novel, fully reversible, pH-sensitive mechanism for the regulation of GS activity by tyrosine nitration.

Loss of insulin-like growth factor-1 signaling in astrocytes disrupts glutamate handling

Insulin-like Growth Factor-1 (IGF-1) has been studied extensively for its ability to promote neuronal growth and excitability. Declining levels of IGF-1 have been correlated with impaired learning and memory as well as an increased risk of neurodegenerative diseases. While neuronal regulation by IGF-1 is well understood, the role of IGF-1 in influencing astrocyte function requires further exploration. Astrocytes regulate many aspects of the brain microenvironment, including controlling glutamate-glutamine cycling, which ultimately supports neuronal metabolism, neurotransmission, and protection from over stimulation. In this study, we examined whether IGF-1 acts through its cognate receptor, IGFR, to alter astrocytic glutamate handling. We utilized both small molecule IGFR inhibitors and Cre-driven genetic approaches to reduce IGFR in vivo and in cultured rodent astrocytes. When IGFR was knocked out of primary astrocytes derived from igfr^f/f mice using AAV5-CMV-Cre, significant reductions in glutamate uptake were observed. Similarly, inhibition of IGFR with picropodophyllotoxin for 2 h, as well as 24 h, reduced glutamate uptake in vitro. Mechanistically, short-term inhibition of IGFR resulted in a significant decrease in glutamate transporter availability on the cell surface, as assessed by biotinylation. Long-term inhibition of IGFR led to significant reductions in mRNA expression of glutamate transport machinery, as assessed with qPCR. Reduced glutamate transporter mRNA was also observed in the brains of astrocyte-specific IGFR-deficient mice, three to four months after knock-out was induced with tamoxifen. Interestingly, long-term IGF-1 inhibition also resulted in an increase in adenosine triphosphate-stimulated glutamate release, though no change in adenosine triphosphate-stimulated calcium flux was observed nor were any changes in purinergic receptor protein expression. Together, these data suggest that reduced IGF-1 signaling will favor an accumulation of extrasynaptic glutamate, which may contribute to neurodegeneration in disease states where IGF-1 levels are low. Cover Image for this issue: doi: 10.1111/jnc.14534.

Can we 'seize' the gut microbiota to treat epilepsy?

The gut-microbiota, the complex intestinal microbial ecosystem essential to health, is an emerging concept in medicine. Several studies demonstrate a microbiota-gut-brain bidirectional connection via neural, endocrine, metabolic and immune pathways. Accordingly, the gut microbiota has a crucial role in modulating intestinal permeability, to alter local/peripheral immune responses and in production of essential metabolites and neurotransmitters. Its alterations may consequently influence all these pathways that contribute to neuronal hyper-excitability and mirrored neuroinflammation in epilepsy and similarly other neurological conditions. Indeed, pre- and clinical studies support the role of the microbiome in pathogenesis, seizure modulation and responses to treatment in epilepsy. Up to now, researchers have focussed attention above all on the brain to develop antiepileptic treatments, but considering the microbiome, could extend our possibilities for developing novel therapies in the future. We provide here a comprehensive overview of the available data on the potential role of gut microbiota in the physiopathology and therapy of epilepsy and the supposed underlying mechanisms.

Loss of insulin-like growth factor-1 signaling in astrocytes disrupts glutamate handling

Insulin-like Growth Factor-1 (IGF-1) has been studied extensively for its ability to promote neuronal growth and excitability. Declining levels of IGF-1 have been correlated with impaired learning and memory as well as an increased risk of neurodegenerative diseases. While neuronal regulation by IGF-1 is well understood, the role of IGF-1 in influencing astrocyte function requires further exploration. Astrocytes regulate many aspects of the brain microenvironment, including controlling glutamate-glutamine cycling, which ultimately supports neuronal metabolism, neurotransmission, and protection from over stimulation. In this study, we examined whether IGF-1 acts through its cognate receptor, IGFR, to alter astrocytic glutamate handling. We utilized both small molecule IGFR inhibitors and Cre-driven genetic approaches to reduce IGFR in vivo and in cultured rodent astrocytes. When IGFR was knocked out of primary astrocytes derived from igfr^f/f mice using AAV5-CMV-Cre, significant reductions in glutamate uptake were observed. Similarly, inhibition of IGFR with picropodophyllotoxin for 2 h, as well as 24 h, reduced glutamate uptake in vitro. Mechanistically, short-term inhibition of IGFR resulted in a significant decrease in glutamate transporter availability on the cell surface, as assessed by biotinylation. Long-term inhibition of IGFR led to significant reductions in mRNA expression of glutamate transport machinery, as assessed with qPCR. Reduced glutamate transporter mRNA was also observed in the brains of astrocyte-specific IGFR-deficient mice, three to four months after knock-out was induced with tamoxifen. Interestingly, long-term IGF-1 inhibition also resulted in an increase in adenosine triphosphate-stimulated glutamate release, though no change in adenosine triphosphate-stimulated calcium flux was observed nor were any changes in purinergic receptor protein expression. Together, these data suggest that reduced IGF-1 signaling will favor an accumulation of extrasynaptic glutamate, which may contribute to neurodegeneration in disease states where IGF-1 levels are low. Cover Image for this issue: doi: 10.1111/jnc.14534.

The role of astrocytes in seizure generation: insights from a novel in vitro seizure model based on mitochondrial dysfunction

Approximately one-quarter of patients with mitochondrial disease experience epilepsy. Their epilepsy is often severe and resistant towards conventional antiepileptic drugs. Despite the severity of this epilepsy, there are currently no animal models available to provide a mechanistic understanding of mitochondrial epilepsy. We conducted neuropathological studies on patients with mitochondrial epilepsy and found the involvement of the astrocytic compartment. As a proof of concept, we developed a novel brain slice model of mitochondrial epilepsy by the application of an astrocytic-specific aconitase inhibitor, fluorocitrate, concomitant with mitochondrial respiratory inhibitors, rotenone and potassium cyanide. The model was robust and exhibited both face and predictive validity. We then used the model to assess the role that astrocytes play in seizure generation and demonstrated the involvement of the GABA-glutamate-glutamine cycle. Notably, glutamine appears to be an important intermediary molecule between the neuronal and astrocytic compartment in the regulation of GABAergic inhibitory tone. Finally, we found that a deficiency in glutamine synthetase is an important pathogenic process for seizure generation in both the brain slice model and the human neuropathological study. Our study describes the first model for mitochondrial epilepsy and provides a mechanistic insight into how astrocytes drive seizure generation in mitochondrial epilepsy.

Phosphorylation of Glutamine Synthetase on Threonine 301 Contributes to Its Inactivation During Epilepsy

The astrocyte-specific enzyme glutamine synthetase (GS), which catalyzes the amidation of glutamate to glutamine, plays an essential role in supporting neurotransmission and in limiting NH₄⁺ toxicity. Accordingly, deficits in GS activity contribute to epilepsy and neurodegeneration. Despite its central role in brain physiology, the mechanisms that regulate GS activity are poorly defined. Here, we demonstrate that GS is directly phosphorylated on threonine residue 301 (T301) within the enzyme’s active site by cAMP-dependent protein kinase (PKA). Phosphorylation of T301 leads to a dramatic decrease in glutamine synthesis. Enhanced T301 phosphorylation was evident in a mouse model of epilepsy, which may contribute to the decreased GS activity seen during this trauma. Thus, our results highlight a novel molecular mechanism that determines GS activity under both normal and pathological conditions.

Effects of dexamethasone on the Li-pilocarpine model of epilepsy: protection against hippocampal inflammation and astrogliosis

Background

Temporal lobe epilepsy (TLE) is the most common form of partial epilepsy and is accompanied, in one third of cases, by resistance to antiepileptic drugs (AED). Most AED target neuronal activity modulated by ionic channels, and the steroid sensitivity of these channels has supported the use of corticosteroids as adjunctives to AED. Assuming the importance of astrocytes in neuronal activity, we investigated inflammatory and astroglial markers in the hippocampus, a key structure affected in TLE and in the Li-pilocarpine model of epilepsy.

Methods

Initially, hippocampal slices were obtained from sham rats and rats subjected to the Li-pilocarpine model of epilepsy, at 1, 14, and 56 days after status epilepticus (SE), which correspond to the acute, silent, and chronic phases. Dexamethasone was added to the incubation medium to evaluate the secretion of S100B, an astrocyte-derived protein widely used as a marker of brain injury. In the second set of experiments, we evaluated the in vivo effect of dexamethasone, administrated at 2 days after SE, on hippocampal inflammatory (COX-1/2, PGE2, and cytokines) and astroglial parameters: GFAP, S100B, glutamine synthetase (GS) and water (AQP-4), and K⁺ (Kir 4.1) channels.

Results

Basal S100B secretion and S100B secretion in high-K⁺ medium did not differ at 1, 14, and 56 days for the hippocampal slices from epileptic rats, in contrast to sham animal slices, where high-K⁺ medium decreased S100B secretion. Dexamethasone addition to the incubation medium per se induced a decrease in S100B secretion in sham and epileptic rats (1 and 56 days after SE induction). Following in vivo dexamethasone administration, inflammatory improvements were observed, astrogliosis was prevented (based on GFAP and S100B content), and astroglial dysfunction was partially abrogated (based on Kir 4.1 protein and GSH content). The GS decrease was not prevented by dexamethasone, and AQP-4 was not altered in this epileptic model.

Conclusions

Changes in astroglial parameters emphasize the importance of these cells for understanding alterations and mechanisms of epileptic disorders in this model. In vivo dexamethasone administration prevented most of the parameters analyzed, reinforcing the importance of anti-inflammatory steroid therapy in the Li-pilocarpine model and possibly in other epileptic conditions in which neuroinflammation is present.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1109-5) contains supplementary material, which is available to authorized users.

Review: Roles for astrocytes in epilepsy: insights from malformations of cortical development

Malformations of cortical development (MCDs), such as cortical dysplasia and tuberous sclerosis complex, are common causes of intractable epilepsy, especially in paediatric patients. Recently, mounting evidence points to a common pathology of these disorders. Hyperactivation of mammalian target of rapamycin (mTOR) has been proposed as a central mechanism in most, if not all, MCDs. The transition from mTOR hyperactivation and cellular abnormalities to large-scale functional changes and seizure is, however, not fully understood. In this article we set out to review currently available information regarding MCD pathology, focusing on glial cells - especially astrocytes - and their interactions with the brain vascular system. A large body of evidence points to these elements as potential targets in MCD. Here, we attempt to provide a review of this evidence and propose some hypotheses regarding the possible chain of events linking primary glial dysfunction and epilepsy. We focus on extracellular matrix remodelling, blood-brain barrier leakage and failure of astrocyte-dependent removal of extracellular debris. We posit that the failure of these systems results in a chronically pro-inflammatory environment, maintaining local astrocytes in a state of gliosis, with increased susceptibility to seizures as a consequence.

Faster flux of neurotransmitter glutamate during seizure - Evidence from 13C-enrichment of extracellular glutamate in kainate rat model

The objective is to examine how the flux of neurotransmitter glutamate from neurons to the extracellular fluid, as measured by the rate of ¹³C enrichment of extracellular glutamate (GLU_ECF), changes in response to seizures in the kainate-induced rat model of temporal-lobe epilepsy. Following unilateral intrahippocampal injection of kainate, GLU_ECF was collected by microdialysis from the CA1/CA3 region of awake rats, in combination with EEG recording of chronic-phase recurrent seizures and intravenous infusion of [2,5-¹³C]glucose. The ¹³C enrichment of GLU_ECF C5 at ~ 10 picomol level was measured by gas-chromatography mass-spectrometry. The rate of ¹³C enrichment, expressed as the increase of the fractional enrichment/min, was 0.0029 ± 0.0001/min in frequently seizing rats (n = 4); this was significantly higher (p < 0.01) than in the control (0.00167 ± 0.0001/min; n = 6) or in rats with infrequent seizures (0.00172 ± 0.0001/min; n = 6). This result strongly suggests that the flux of the excitatory neurotransmitter from neurons to the extracellular fluid is significantly increased by frequent seizures. The extracellular [¹²C + ¹³C]glutamate concentration increased progressively in frequently seizing rats. Taken together, these results strongly suggest that the observed seizure-induced high flux of glutamate overstimulated glutamate receptors, which triggered a chain reaction of excitation in the CA3 recurrent glutamatergic networks. The rate of ¹³C enrichment of extracellular glutamine (GLN_ECF) at C5 was 0.00299 ± 0.00027/min in frequently seizing rats, which was higher (p < 0.05) than in controls (0.00227 ± 0.00008/min). For the first time in vivo, this study examined the effects of epileptic seizures on fluxes of the neurotransmitter glutamate and its precursor glutamine in the extracellular fluid of the hippocampus. The advantages, limitations and the potential for improvement of this approach for pre-clinical and clinical studies of temporal-lobe epilepsy are discussed.

Human astrocytes in the diseased brain

Astrocytes are key active elements of the brain that contribute to information processing. They not only provide neurons with metabolic and structural support, but also regulate neurogenesis and brain wiring. Furthermore, astrocytes modulate synaptic activity and plasticity in part by controlling the extracellular space volume, as well as ion and neurotransmitter homeostasis. These findings, together with the discovery that human astrocytes display contrasting characteristics with their rodent counterparts, point to a role for astrocytes in higher cognitive functions. Dysfunction of astrocytes can thereby induce major alterations in neuronal functions, contributing to the pathogenesis of several brain disorders. In this review we summarize the current knowledge on the structural and functional alterations occurring in astrocytes from the human brain in pathological conditions such as epilepsy, primary tumours, Alzheimer's disease, major depressive disorder and Down syndrome. Compelling evidence thus shows that dysregulations of astrocyte functions and interplay with neurons contribute to the development and progression of various neurological diseases. Targeting astrocytes is thus a promising alternative approach that could contribute to the development of novel and effective therapies to treat brain disorders.

Minireview on Glutamine Synthetase Deficiency, an Ultra-Rare Inborn Error of Amino Acid Biosynthesis

Glutamine synthetase (GS) is a cytosolic enzyme that produces glutamine, the most abundant free amino acid in the human body. Glutamine is a major substrate for various metabolic pathways, and is thus an important factor for the functioning of many organs; therefore, deficiency of glutamine due to a defect in GS is incompatible with normal life. Mutations in the human GLUL gene (encoding for GS) can cause an ultra-rare recessive inborn error of metabolism—congenital glutamine synthetase deficiency. This disease was reported until now in only three unrelated patients, all of whom suffered from neonatal onset severe epileptic encephalopathy. The hallmark of GS deficiency in these patients was decreased levels of glutamine in body fluids, associated with chronic hyperammonemia. This review aims at recapitulating the clinical history of the three known patients with congenital GS deficiency and summarizes the findings from studies done along with the work-up of these patients. It is the aim of this paper to convince the reader that (i) this disorder is possibly underdiagnosed, since decreased concentrations of metabolites do not receive the attention they deserve; and (ii) early detection of GS deficiency may help to improve the outcome of patients who could be treated early with metabolites that are lacking in this condition.

Molecular Mechanisms of Glutamine Synthetase Mutations that Lead to Clinically Relevant Pathologies

Glutamine synthetase (GS) catalyzes ATP-dependent ligation of ammonia and glutamate to glutamine. Two mutations of human GS (R324C and R341C) were connected to congenital glutamine deficiency with severe brain malformations resulting in neonatal death. Another GS mutation (R324S) was identified in a neurologically compromised patient. However, the molecular mechanisms underlying the impairment of GS activity by these mutations have remained elusive. Molecular dynamics simulations, free energy calculations, and rigidity analyses suggest that all three mutations influence the first step of GS catalytic cycle. The R324S and R324C mutations deteriorate GS catalytic activity due to loss of direct interactions with ATP. As to R324S, indirect, water-mediated interactions reduce this effect, which may explain the suggested higher GS residual activity. The R341C mutation weakens ATP binding by destabilizing the interacting residue R340 in the apo state of GS. Additionally, the mutation is predicted to result in a significant destabilization of helix H8, which should negatively affect glutamate binding. This prediction was tested in HEK293 cells overexpressing GS by dot-blot analysis: Structural stability of H8 was impaired through mutation of amino acids interacting with R341, as indicated by a loss of masking of an epitope in the glutamate binding pocket for a monoclonal anti-GS antibody by L-methionine-S-sulfoximine; in contrast, cells transfected with wild type GS showed the masking. Our analyses reveal complex molecular effects underlying impaired GS catalytic activity in three clinically relevant mutants. Our findings could stimulate the development of ATP binding-enhancing molecules by which the R324S mutant can be repaired extrinsically.

Glutamine synthetase (GS) catalyzes the ATP-dependent ligation of ammonia and glutamate to glutamine, which makes the enzyme essential for human nitrogen metabolism. Three mutations in human GS, R324C, R324S, and R341C, had been identified previously that lead to a glutamine deficiency, resulting in neonatal death in the case of R324C and R341C. However, the molecular mechanisms underlying this impairment of GS activity have remained elusive. Our results from computational biophysics approaches suggest that all three mutants influence the first step of GS’ catalytic cycle, namely ATP or glutamate binding. The analyses reveal a complex set of effects including the loss of direct interactions to substrates, the involvement of water-mediated interactions that alleviate part of the mutation effect, and long-range effects between the catalytic site and structural parts distant from it. As to the latter, experimental validation is in line with our prediction of a significant destabilization of helix H8 in the R341C mutant, which should negatively affect glutamate binding. Finally, our findings could stimulate the development of ATP-binding enhancing molecules for the R324S mutant, which has been suggested to have residual activity, that way extrinsically “repairing” the mutant.

Transporter-mediated L-glutamate elimination from cerebrospinal fluid: possible involvement of excitatory amino acid transporters expressed in ependymal cells and choroid plexus epithelial cells

BACKGROUND

L-Glutamate (L-Glu) is the major excitatory neurotransmitter in the CNS, and its level in cerebrospinal fluid (CSF) is reported to be increased in neuroexcitatory diseases such as epilepsy. Since L-Glu concentration in the CSF is reported to be lower than that in plasma, it has been proposed that some mechanisms of L-Glu clearance from the CSF operate in the brain. The purpose of this study was to elucidate the major pathway of L-Glu elimination from rat CSF and the transporters responsible.

METHODS

Protein expression and localization of excitatory amino acid transporters were examined by immunohistochemical analysis using specific antibodies. In vivo elimination of L-Glu from rat CSF was evaluated by intracerebroventricular administration. An L-Glu uptake study by using primary-cultured rat ependymal cells and isolated rat choroid plexus was performed to characterize L-Glu transport mechanisms.

RESULTS

An immunohistochemical analysis has shown that excitatory amino acid transporter (EAAT) 1 and EAAT3, which are D-aspartate-sensitive and kainate-insensitive L-Glu transporters, are localized on the CSF-side of rat ependymal cells and choroid plexus epithelial cells, respectively. In contrast, the kainate-sensitive L-Glu transporter, EAAT2, is not expressed in these cells. In vivo L-Glu elimination clearance from the rat CSF (189 μL/(min · rat)) was 23-fold higher than the CSF bulk flow rate, indicating that facilitative process(es) are involved in L-Glu elimination from the CSF. The in vivo [(3)H]L-Glu elimination from the CSF was significantly inhibited by unlabeled L-Glu and D-aspartate, but not kainate. Moreover, unlabeled L-Glu and D-aspartate inhibited [(3)H]L-Glu uptake by rat ependymal cells and choroid plexus epithelial cells, whereas kainate had little effect.

CONCLUSION

It is suggested that EAAT1 in ependymal cells and EAAT3 in choroid plexus epithelial cells participate in L-Glu elimination from the CSF.

Chronic SSRI stimulation of astrocytic 5-HT2B receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift

It is firmly believed that the mechanism of action of SSRIs in major depression is to inhibit the serotonin transporter, SERT, and increase extracellular concentration of serotonin. However, this undisputed observation does not prove that SERT inhibition is the mechanism, let alone the only mechanism, by which SSRI's exert their therapeutic effects. It has recently been demonstrated that 5-HT2B receptor stimulation is needed for the antidepressant effect of fluoxetine in vivo. The ability of all five currently used SSRIs to stimulate the 5-HT2B receptor equipotentially in cultured astrocytes has been known for several years, and increasing evidence has shown the importance of astrocytes and astrocyte-neuronal interactions for neuroplasticity and complex brain activity. This paper reviews acute and chronic effects of 5-HT2B receptor stimulation in cultured astrocytes and in astrocytes freshly isolated from brains of mice treated with fluoxetine for 14 days together with effects of anti-depressant therapy on turnover of glutamate and GABA and metabolism of glucose and glycogen. It is suggested that these events are causally related to the mechanism of action of SSRIs and of interest for development of newer antidepressant drugs.

Seizure-induced oxidative stress in temporal lobe epilepsy

An insult to the brain (such as the first seizure) causes excitotoxicity, neuroinflammation, and production of reactive oxygen/nitrogen species (ROS/RNS). ROS and RNS produced during status epilepticus (SE) overwhelm the mitochondrial natural antioxidant defense mechanism. This leads to mitochondrial dysfunction and damage to the mitochondrial DNA. This in turn affects synthesis of various enzyme complexes that are involved in electron transport chain. Resultant effects that occur during epileptogenesis include lipid peroxidation, reactive gliosis, hippocampal neurodegeneration, reorganization of neural networks, and hypersynchronicity. These factors predispose the brain to spontaneous recurrent seizures (SRS), which ultimately establish into temporal lobe epilepsy (TLE). This review discusses some of these issues. Though antiepileptic drugs (AEDs) are beneficial to control/suppress seizures, their long term usage has been shown to increase ROS/RNS in animal models and human patients. In established TLE, ROS/RNS are shown to be harmful as they can increase the susceptibility to SRS. Further, in this paper, we review briefly the data from animal models and human TLE patients on the adverse effects of antiepileptic medications and the plausible ameliorating effects of antioxidants as an adjunct therapy.

Glutamine synthetase stability and subcellular distribution in astrocytes are regulated by γ-aminobutyric type B receptors

Emerging evidence suggests that functional γ-aminobutyric acid B receptors (GABABRs) are expressed by astrocytes within the mammalian brain. GABABRs are heterodimeric G-protein-coupled receptors that are composed of R1/R2 subunits. To date, they have been characterized in neurons as the principal mediators of sustained inhibitory signaling; however their roles in astrocytic physiology have been ill defined. Here we reveal that the cytoplasmic tail of the GABABR2 subunit binds directly to the astrocytic protein glutamine synthetase (GS) and that this interaction determines the subcellular localization of GS. We further demonstrate that the binding of GS to GABABR2 increases the steady state expression levels of GS in heterologous cells and in mouse primary astrocyte culture. Mechanistically this increased stability of GS in the presence of GABABR2 occurs via reduced proteasomal degradation. Collectively, our results suggest a novel role for GABABRs as regulators of GS stability. Given the critical role that GS plays in the glutamine-glutamate cycle, astrocytic GABABRs may play a critical role in supporting both inhibitory and excitatory neurotransmission.

Restoration of glutamine synthetase activity, nitric oxide levels and amelioration of oxidative stress by propolis in kainic acid mediated excitotoxicity

BACKGROUND

Propolis has been proposed to be protective on neurodegenerative disorders. To understand the neuroprotective effects of honeybee propolis, glutamine synthetase (GS) activity, nitric oxide (NO), thiobarbituric acid reactive substances (TBARS) and total antioxidant status (TAS) were studied in different brain regions-cerebral cortex (CC), cerebellum (CB) and brain stem (BS) of rats supplemented with propolis and subjected to kainic acid (KA) mediated excitotoxicity.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into four groups; Control group and KA group received vehicle and saline. Propolis group and propolis + KA group were orally administered with propolis (150mg/kg body weight), five times every 12 hours. KA group and propolis + KA group were injected subcutaneously with kainic acid (15mg/kg body weight) and were sacrificed after 2 hrs and CC, CB and BS were separated homogenized and used for estimation of GS activity, NO, TBARS, and TAS concentrations by colorimetric methods. Results were analyzed by one-way ANOVA, reported as mean + SD from 6 animals, and p<0.05 considered statistically significant.

RESULTS

NO was increased (p< 0.001) and GS activity was decreased (p< 0.001) in KA treated group compared to control group as well as propolis + KA treated group. TBARS was decreased and TAS was increased (p< 0.001) in propolis + KA treated group compared KA treated group.

CONCLUSION

This study clearly demonstrated the restoration of GS activity, NO levels and decreased oxidative stress by propolis in kainic acid mediated excitotoxicity. Hence the propolis can be a possible potential candidate (protective agent) against excitotoxicity and neurodegenerative disorders.

Cerebral glucose metabolism in an immature rat model of pediatric traumatic brain injury

Altered cerebral metabolism and mitochondrial function have been identified in experimental and clinical studies of pediatric traumatic brain injury (TBI). Metabolic changes detected using (1)H (proton) magnetic resonance spectroscopy correlate with long-term outcomes in children after severe TBI. We previously identified early (4-h) and sustained (24-h and 7-day) abnormalities in brain metabolites after controlled cortical impact (CCI) in immature rats. The current study aimed to identify specific alterations of cerebral glucose metabolism at 24 h after TBI in immature rats. Rats (postnatal days 16-18) underwent CCI to the left parietal cortex. Sham rats underwent craniotomy only. Twenty-four hours after CCI, rats were injected (intraperitoneally) with [1,6-(13)C]glucose. Brains were removed, separated into hemispheres, and frozen. Metabolites were extracted with perchloric acid and analyzed using (1)H and (13)C-nuclear magnetic resonance spectroscopy. TBI resulted in decreases in N-acetylaspartate in both hemispheres, compared to sham contralateral. At 24 h after TBI, there was significant decrease in the incorporation of (13)C label into [3-(13)C]glutamate and [2-(13)C]glutamate in the injured brain. There were no differences in percent enrichment of [3-(13)C]glutamate, [4-(13)C]glutamate, [3-(13)C]glutamine, or [4-(13)C]glutamine. There was significantly lower percent enrichment of [2-(13)C]glutamate in both TBI sides and the sham craniotomy side, compared to sham contralateral. No differences were detected in enrichment of (13)C glucose label in [2-(13)C]glutamine, [2-(13)C]GABA (gamma-aminobutyric acid), [3-(13)C]GABA, or [4-(13)C]GABA, [3-(13)C]lactate, or [3-(13)C]alanine between groups. Results suggest that overall oxidative glucose metabolism in the immature brain recovers at 24 h after TBI. Specific reductions in [2-(13)C]glutamate could be the result of impairments in either neuronal or astrocytic metabolism. Future studies should aim to identify pathways leading to decreased metabolism and develop cell-selective "metabolic rescue."

Role of astrocytes in major neurological disorders: the evidence and implications

Given the huge amount and great complexity of astrocyte functions in the maintenance of brain homeostasis, it is easily understood how alterations in their physiology may be involved in the pathogenesis of many, if not all, neurological disorders. This assumption is strongly supported by accumulated evidence produced in humans and in experimental models of pathology. Based on these considerations, it is reasonable to encourage studies aimed at improving the knowledge about the implicated mechanisms, and astroglial cells can be considered as the innovative target for new, and possibly more effective, drug therapies.

Electrographic seizures are significantly reduced by in vivo inhibition of neuronal uptake of extracellular glutamine in rat hippocampus

Rats were given unilateral kainate injection into hippocampal CA3 region, and the effect of chronic electrographic seizures on extracellular glutamine (GLNECF) was examined in those with low and steady levels of extracellular glutamate (GLUECF). GLNECF, collected by microdialysis in awake rats for 5h, decreased to 62±4.4% of the initial concentration (n=6). This change correlated with the frequency and magnitude of seizure activity, and occurred in the ipsilateral but not in contralateral hippocampus, nor in kainate-injected rats that did not undergo seizure (n=6). Hippocampal intracellular GLN did not differ between the Seizure and No-Seizure Groups. These results suggested an intriguing possibility that seizure-induced decrease of GLNECF reflects not decreased GLN efflux into the extracellular fluid, but increased uptake into neurons. To examine this possibility, neuronal uptake of GLNECF was inhibited in vivo by intrahippocampal perfusion of 2-(methylamino)isobutyrate, a competitive and reversible inhibitor of the sodium-coupled neutral amino acid transporter (SNAT) subtypes 1 and 2, as demonstrated by 1.8±0.17 fold elevation of GLNECF (n=7). The frequency of electrographic seizures during uptake inhibition was reduced to 35±7% (n=7) of the frequency in pre-perfusion period, and returned to 88±9% in the post-perfusion period. These novel in vivo results strongly suggest that, in this well-established animal model of temporal-lobe epilepsy, the observed seizure-induced decrease of GLNECF reflects its increased uptake into neurons to sustain enhanced glutamatergic epileptiform activity, thereby demonstrating a possible new target for anti-seizure therapies.

The Glutamate-Glutamine (GABA) Cycle: Importance of Late Postnatal Development and Potential Reciprocal Interactions between Biosynthesis and Degradation

The gold standard for studies of glutamate-glutamine (GABA) cycling and its connections to brain biosynthesis from glucose of glutamate and GABA and their subsequent metabolism are the elegant in vivo studies by (13)C magnetic resonance spectroscopy (NMR), showing the large fluxes in the cycle. However, simpler experiments in intact brain tissue (e.g., immunohistochemistry), brain slices, cultured brain cells, and mitochondria have also made important contributions to the understanding of details, mechanisms, and functional consequences of glutamate/GABA biosynthesis and degradation. The purpose of this review is to attempt to integrate evidence from different sources regarding (i) the enzyme(s) responsible for the initial conversion of α-ketoglutarate to glutamate; (ii) the possibility that especially glutamate oxidation is essentially confined to astrocytes; and (iii) the ontogenetically very late onset and maturation of glutamine-glutamate (GABA) cycle function. Pathway models based on the functional importance of aspartate for glutamate synthesis suggest the possibility of interacting pathways for biosynthesis and degradation of glutamate and GABA and the use of transamination as the default mechanism for initiation of glutamate oxidation. The late development and maturation are related to the late cortical gliogenesis and convert brain cortical function from being purely neuronal to becoming neuronal-astrocytic. This conversion is associated with huge increases in energy demand and production, and the character of potentially incurred gains of function are discussed. These may include alterations in learning mechanisms, in mice indicated by lack of pairing of odor learning with aversive stimuli in newborn animals but the development of such an association 10-12 days later. The possibility is suggested that analogous maturational changes may contribute to differences in the way learning is accomplished in the newborn human brain and during later development.

Temporospatial expression and cellular localization of glutamine synthetase following traumatic spinal cord injury in adult rats

Glutamine synthetase (GS) is an enzyme involved in an endogenous mechanism of protection against glutamate neurotoxicity and is important in the regulation of astrocyte migration. To date, limited information is available concerning the expression of GS in normal spinal cords and following injury. In the present study, GS expression was identified in astrocytes, oligodendrocytes and microglia in normal rat spinal cords. Following traumatic spinal cord injury (SCI), the glutamate concentration increased rapidly at 1 h and returned to baseline rapidly. However, the GS activity and protein levels were found to decrease at 4 h and then increase gradually from day 3 following SCI. The quantification of astrocytes, oligodendrocytes and activated microglia/macrophages, as well as immunohistochemistry staining of day 7 post‑injured spinal cords, indicated that the astrocytes and microglia/macrophages contributed to the increase in GS. Collectively, the results provided evidence for the temporospatial expression and location of GS following SCI and suggested that the changes in GS levels may contribute to glutamate neurotoxicity and glial cell response following SCI.

Gene expression of glutamate metabolizing enzymes in the hippocampal formation in human temporal lobe epilepsy

PURPOSE

Increased interictal concentrations of extracellular hippocampal glutamate have been implicated in the pathophysiology of temporal lobe epilepsy (TLE). Recent studies suggest that perturbations of the glutamate metabolizing enzymes glutamine synthetase (GS) and phosphate activated glutaminase (PAG) may underlie the glutamate excess in TLE. However, the molecular mechanism of the enzyme perturbations remains unclear. A better understanding of the regulatory mechanisms of GS and PAG could facilitate the discovery of novel therapeutics for TLE.

METHODS

We used in situ hybridization on histologic sections to assess the distribution and quantity of messenger RNA (mRNA) for GS and PAG in subfields of hippocampal formations from the following: (1) patients with TLE and concomitant hippocampal sclerosis, (2) patients with TLE and no hippocampal sclerosis, and (3) nonepilepsy autopsy subjects.

KEY FINDINGS

GS mRNA was increased by ~50% in the CA3 in TLE patients without hippocampal sclerosis versus in TLE patients with sclerosis and in nonepilepsy subjects. PAG mRNA was increased by >100% in the subiculum in both TLE patient categories versus in nonepilepsy subjects. PAG mRNA was also increased in the CA1, CA2, CA3, and dentate hilus in TLE without hippocampal sclerosis versus in TLE with sclerosis. Finally, PAG mRNA was increased in the dentate gyrus in TLE with sclerosis versus in nonepilepsy subjects, and also increased in the hilus in TLE without sclerosis versus in TLE with sclerosis.

SIGNIFICANCE

These findings demonstrate complex changes in the expression of mRNAs for GS and PAG in the hippocampal formation in TLE, and raise the possibility that both transcriptional and posttranscriptional mechanisms may underlie the regulation of GS and PAG proteins in the epileptic brain.

Glia and epilepsy: excitability and inflammation

Epilepsy is characterized by recurrent spontaneous seizures due to hyperexcitability and hypersynchrony of brain neurons. Current theories of pathophysiology stress neuronal dysfunction and damage, and aberrant connections as relevant factors. Most antiepileptic drugs target neuronal mechanisms. However, nearly one-third of patients have seizures that are refractory to available medications; a deeper understanding of mechanisms may be required to conceive more effective therapies. Recent studies point to a significant contribution by non-neuronal cells, the glia--especially astrocytes and microglia--in the pathophysiology of epilepsy. This review critically evaluates the role of glia-induced hyperexcitability and inflammation in epilepsy.

Grape seed and skin extract prevents high-fat diet-induced brain lipotoxicity in rat

Obesity is related to an elevated risk of dementia and the physiologic mechanisms whereby fat adversely affects the brain are poorly understood. The present investigation analyzed the effect of a high fat diet (HFD) on brain steatosis and oxidative stress and the intracellular mediators involved in signal transduction, as well as the protection offered by grape seed and skin extract (GSSE). HFD induced ectopic deposition of cholesterol and phospholipid but not triglyceride. Moreover brain lipotoxicity is linked to an oxidative stress characterized by increased lipoperoxidation and carbonylation, inhibition of glutathione peroxidase and superoxide dismutase activities, depletion of manganese and a concomitant increase in ionizable calcium and acetylcholinesterase activity. Importantly GSSE alleviated all the deleterious effects of HFD treatment. Altogether our data indicated that HFD could find some potential application in the treatment of manganism and that GSSE should be used as a safe anti-lipotoxic agent in the prevention and treatment of fat-induced brain injury.