Metabolic and Homeostatic Changes in Seizures and Acquired Epilepsy-Mitochondria, Calcium Dynamics and Reactive Oxygen Species

The Alteration of Chloride Homeostasis/GABAergic Signaling in Brain Disorders: Could Oxidative Stress Play a Role?

In neuronal precursors and immature neurons, the depolarizing (excitatory) effect of γ-Aminobutyric acid (GABA) signaling is associated with elevated [Cl⁻]_i; as brain cells mature, a developmental switch occurs, leading to the decrease of [Cl⁻]_i and to the hyperpolarizing (inhibitory) effect of GABAergic signaling. [Cl⁻]_i is controlled by two chloride co-transporters: NKCC1, which causes Cl⁻ to accumulate into the cells, and KCC2, which extrudes it. The ontogenetic upregulation of the latter determines the above-outlined switch; however, many other factors contribute to the correct [Cl⁻]_i in mature neurons. The dysregulation of chloride homeostasis is involved in seizure generation and has been associated with schizophrenia, Down’s Syndrome, Autism Spectrum Disorder, and other neurodevelopmental disorders. Recently, much effort has been put into developing new drugs intended to inhibit NKCC1 activity, while no attention has been paid to the origin of [Cl⁻]_i dysregulation. Our study examines the pathophysiology of Cl⁻ homeostasis and focuses on the impact of oxidative stress (OS) and inflammation on the activity of Cl⁻ co-transporters, highlighting the relevance of OS in numerous brain abnormalities and diseases. This hypothesis supports the importance of primary prevention during pregnancy. It also integrates the therapeutic framework addressed to restore normal GABAergic signaling by counteracting the alteration in chloride homeostasis in central nervous system (CNS) cells, aiming at limiting the use of drugs that potentially pose a health risk.

Dietary medium chain triglycerides for management of epilepsy: New data from human, dog, and rodent studies

Many studies show that glucose metabolism in epileptic brain areas can be impaired. Energy is crucial to maintain normal brain function, including ion and neurotransmitter balances. Energy deficits can lead to disruption of ion gradients, which can trigger neuronal depolarization and generation of seizures. Thus, perturbed metabolic processing of glucose in epileptogenic brain areas indicates a specific nutritional need for people and animals with epilepsy, as they are likely to benefit from auxiliary brain fuels other than glucose. Ketogenic diets provide the ketone bodies acetoacetate and β-hydroxybutyrate, which can be used as auxiliary fuel by the brain. In approximately 50% children and adults with certain types of epilepsy, who can tolerate and maintain these dietary regimens, seizure frequency can be effectively reduced. More recent data demonstrate that addition of medium chain triglycerides (MCTs), which provide the medium chain fatty acids octanoic and decanoic acid, as well as ketone bodies as auxiliary brain energy, can be beneficial in rodent seizure models, and dogs and humans with epilepsy. Here, this evidence is reviewed, including tolerance in 65% of humans, efficacy studies in dogs, possible anticonvulsant mechanisms of actions of MCTs, and specifically decanoic acid as well as metabolic and antioxidant mechanisms. In conclusion, MCTs are a promising adjunct to standard pharmacological treatment for both humans and dogs with epilepsy, as they lack central nervous system side effects found with current antiepileptic drugs. There is now a need for larger clinical trials in children, adults, and dogs to find the ideal composition and doses of MCTs and the types of epilepsy that respond best.

Advancement in research on the role of the transient receptor potential vanilloid channel in cerebral ischemic injury (Review)

Stroke is a common critical disease occurring in middle-aged and elderly individuals, and is characterized by high morbidity, lethality and mortality. As such, it is of great concern to medical professionals. The aim of the present review was to investigate the effects of transient receptor potential vanilloid (TRPV) subtypes during cerebral ischemia in ischemia-reperfusion animal models, oxygen glucose deprivation and in other administration cell models in vitro to explore new avenues for stroke research and clinical treatments. TRPV1, TRPV2 and TRPV4 employ different methodologies by which they confer protection against cerebral ischemic injury. TRPV1 and TRPV4 are likely related to the inhibition of inflammatory reactions, neurotoxicity and cell apoptosis, thus promoting nerve growth and regulation of intracellular calcium ions (Ca2+). The mechanisms of neuroprotection of TRPV1 are the JNK pathway, N-methyl-D-aspartate (NMDA) receptor and therapeutic hypothermia. The mechanisms of neuroprotection of TRPV4 are the PI3K/Akt pathways, NMDA receptor and p38 MAPK pathway, amongst others. The mechanisms by which TRPV2 confers its protective effects are predominantly connected with the regulation of nerve growth factor, MAPK and JNK pathways, as well as JNK-dependent pathways. Thus, TRPVs have the potential for improving outcomes associated with cerebral ischemic or reperfusion injuries. The protection conferred by TRPV1 and TRPV4 is closely related to cellular Ca2+ influx, while TRPV2 has a different target and mode of action, possibly due to its expression sites. However, in light of certain contradictory research conclusions, further experimentation is required to clarify the mechanisms and specific pathways by which TRPVs act to alleviate nerve injuries.

Effects of Lacosamide Treatment on Epileptogenesis, Neuronal Damage and Behavioral Comorbidities in a Rat Model of Temporal Lobe Epilepsy

Clinically, temporal lobe epilepsy (TLE) is the most prevalent type of partial epilepsy and often accompanied by various comorbidities. The present study aimed to evaluate the effects of chronic treatment with the antiepileptic drug (AED) lacosamide (LCM) on spontaneous motor seizures (SMS), behavioral comorbidities, oxidative stress, neuroinflammation, and neuronal damage in a model of TLE. Vehicle/LCM treatment (30 mg/kg, p.o.) was administered 3 h after the pilocarpine-induced status epilepticus (SE) and continued for up to 12 weeks in Wistar rats. Our study showed that LCM attenuated the number of SMS and corrected comorbid to epilepsy impaired motor activity, anxiety, memory, and alleviated depressive-like responses measured in the elevated plus maze, object recognition test, radial arm maze test, and sucrose preference test, respectively. This AED suppressed oxidative stress through increased superoxide dismutase activity and glutathione levels, and alleviated catalase activity and lipid peroxidation in the hippocampus. Lacosamide treatment after SE mitigated the increased levels of IL-1β and TNF-α in the hippocampus and exerted strong neuroprotection both in the dorsal and ventral hippocampus, basolateral amygdala, and partially in the piriform cortex. Our results suggest that the antioxidant, anti-inflammatory, and neuroprotective activity of LCM is an important prerequisite for its anticonvulsant and beneficial effects on SE-induced behavioral comorbidities.

Reviving mitochondrial bioenergetics: A relevant approach in epilepsy

Epileptogenesis is most commonly associated with neurodegeneration and a bioenergetic defect attributing to the fact that mitochondrial dysfunction plays a key precursor for neuronal death. Mitochondria are the essential organelle of neuronal cells necessary for certain neurophysiological processes like neuronal action potential activity and synaptic transmission. The mitochondrial dysfunction disrupts calcium homeostasis leading to inhibitory interneuron dysfunction and increasing the excitatory postsynaptic potential. In epilepsy, the prolonged repetitive neuronal activity increases the excessive demand for energy and acidosis in the brain further increasing the intracellular calcium causing neuronal death. Similarly, the mitochondrial damage also leads to the decline of energy by dysfunction of the electron transport chain and abnormal production of the ROS triggering the apoptotic neuronal death. Thus, the elevated level of cytosolic calcium causes the mitochondria DNA damage coinciding with mtROS and releasing the cytochrome c binding to Apaf protein further initiating the apoptosis resulting in epileptic encephalopathies. The various genetic and mRNA studies of epilepsy have explored the various pathogenic mutations of genes affecting the mitochondria functioning further initiating the neuronal excitotoxicity. Based on the results of previous studies, the recent therapeutic approaches are targeting basic mitochondrial processes, such as energy metabolism or free-radical generation, or specific interactions of disease-related proteins with mitochondria and hold great promise to attenuate epileptogenesis. Therefore, the current review emphasizes the emerging insights to uncover the relation between mitochondrial dysfunction and ROS generation contributing to mechanisms underlying epileptic seizures.

Extracellular Vesicles in Neurological Disorders

The role of extracellular vesicles (EVs) in the central nervous system, and in particular the brain, is a rapidly growing research area. Importantly, the role for EVs in the nervous system spans from early development through to old age, with EVs being associated with several different neurological disorders. To date, researchers have been studying the function of EVs in the nervous system in three major areas: (i) the role of EVs in promoting disease pathways, (ii) the ability of EVs to be used as a diagnostic tool to identify cellular changes in the nervous system, and (iii) the potential use of EVs as therapeutic tools for the delivery of biomolecules or drugs to the nervous system. In each of these settings the analysis and use of EVs performs a different function, highlighting the breadth of areas in which the EV field is applicable. A key aspect of EV biology is the ability of vesicles to cross biological barriers, in particular the blood brain barrier. This allows for the measurement of serum EVs that contain information about cells in the brain, or alternatively, allows for the delivery of biomolecules that are packaged within EVs for therapeutic use.

Roles of four feedback loops in mitochondrial permeability transition pore opening induced by Ca^{2+} and reactive oxygen species

Transient or sustained permeability transition pore (PTP) opening is important in normal physiology or cell death, respectively. These are closely linked to Ca^{2+} and reactive oxygen species (ROS). The entry of Ca^{2+} into mitochondria regulates ROS production, and both Ca^{2+} and ROS trigger PTP opening. In addition to this feedforward loop, there exist four feedback loops in the Ca^{2+}-ROS-PTP system. ROS promotes Ca^{2+} entering (F1) and induces further ROS generation (F2), forming two positive feedback loops. PTP opening results in the efflux of Ca^{2+} (F3) and ROS (F4) from the mitochondria, forming two negative feedback loops. Owing to these complexities, we construct a mathematical model to dissect the roles of these feedback loops in the dynamics of PTP opening. The qualitative agreement between simulation results and recent experimental observations supports our hypothesis that under physiological conditions the PTP opens in an oscillatory state, while under pathological conditions it opens in a high steady state. We clarify that the negative feedback loops are responsible for producing oscillations, wherein F3 plays a more prominent role than F4; whereas the positive feedback loops are beneficial for maintaining oscillation robustness, wherein F1 has a more dominant role than F2. Furthermore, we manifest that the proper increase in negative feedback strength or decrease in positive feedback strength not only facilitates the occurrence of oscillations and thus protects the system against a high steady state, but also assists in lowering the oscillation peak. This study may provide potential therapeutic strategies in treating neurodegenerative diseases due to PTP dysfunction.

Role of oxidative stress in epileptogenesis and potential implications for therapy

In a state of balance between oxidants and antioxidants, free radicals play an advantageous role of “redox messengers”. In a state of oxidative stress, they trigger a cascade of events leading to epileptogenesis. During this latent, free of seizures period, a cascade of neurological changes takes place and finally leads to spontaneous recurrent seizures. The main processes involved in seizure generation are: neuroinflammation, neurodegeneration with anomalous neuroregeneration and lowering seizure threshold. Time of epileptogenesis offers a unique therapeutic window to prevent or at least attenuate seizure development. Animal data indicate that some antioxidants (for instance, resveratrol) may bear an anti-epileptogenic potential.

The roles of ER stress in epilepsy: Molecular mechanisms and therapeutic implications

Epilepsies are a diverse group of neurological disorders, which are characterized by spontaneous recurrent seizures. Although a wide range of pathogenic mechanisms such as alterations in ion channels, inflammation and neuronal loss have been reported to be implicated in the epileptogenesis, the underlying pathogenesis of epilepsy remains unclear currently. Endoplasmic reticulum (ER) stress is regarded as a condition that unfolded or misfolded proteins accumulate in the ER lumen. Excessive or prolonged ER stress causes the activation of the unfolded protein response (UPR) to buffer ER stress and restore ER homeostasis. Increasing evidence has indicated dysregulated ER stress during epileptogenesis, which may participate in various pathological processes associated with epilepsy. In this present review, we summarized recent advances in the involvement of ER stress in the pathogenesis of epilepsy. Additionally, the antiepileptic and neuroprotective effects of interventions targeting ER stress were also discussed.

Modulating neuroinflammation and oxidative stress to prevent epilepsy and improve outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in young adults worldwide. TBI survival is associated with persistent neuropsychiatric and neurological impairments, including posttraumatic epilepsy (PTE). To date, no pharmaceutical treatment has been found to prevent PTE or ameliorate neurological/neuropsychiatric deficits after TBI. Brain trauma results in immediate mechanical damage to brain cells and blood vessels that may never be fully restored given the limited regenerative capacity of brain tissue. This primary insult unleashes cascades of events, prominently including neuroinflammation and massive oxidative stress that evolve over time, expanding the brain injury, but also clearing cellular debris and establishing homeostasis in the region of damage. Accumulating evidence suggests that oxidative stress and neuroinflammatory sequelae of TBI contribute to posttraumatic epileptogenesis. This review will focus on possible roles of reactive oxygen species (ROS), their interactions with neuroinflammation in posttraumatic epileptogenesis, and emerging therapeutic strategies after TBI. We propose that inhibitors of the professional ROS-generating enzymes, the NADPH oxygenases and myeloperoxidase alone, or combined with selective inhibition of cyclooxygenase mediated signaling may have promise for the treatment or prevention of PTE and other sequelae of TBI. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Nuclear Factor-Erythroid 2-Related Factor 2 (Nrf2) and Mitochondrial Dynamics/Mitophagy in Neurological Diseases

Mitochondria play an essential role in bioenergetics and respiratory functions for cell viability through numerous biochemical processes. To maintain mitochondria quality control and homeostasis, mitochondrial morphologies change rapidly in response to external insults and changes in metabolic status through fusion and fission (so called mitochondrial dynamics). Furthermore, damaged mitochondria are removed via a selective autophagosomal process, referred to as mitophagy. Although mitochondria are one of the sources of reactive oxygen species (ROS), they are themselves vulnerable to oxidative stress. Thus, endogenous antioxidant defense systems play an important role in cell survival under physiological and pathological conditions. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that maintains redox homeostasis by regulating antioxidant-response element (ARE)-dependent transcription and the expression of antioxidant defense enzymes. Although the Nrf2 system is positively associated with mitochondrial biogenesis and mitochondrial quality control, the relationship between Nrf2 signaling and mitochondrial dynamics/mitophagy has not been sufficiently addressed in the literature. This review article describes recent clinical and experimental observations on the relationship between Nrf2 and mitochondrial dynamics/mitophagy in various neurological diseases.

Granule Cell Dispersion in Human Temporal Lobe Epilepsy: Proteomics Investigation of Neurodevelopmental Migratory Pathways

Granule cell dispersion (GCD) is a common pathological feature observed in the hippocampus of patients with Mesial Temporal Lobe Epilepsy (MTLE). Pathomechanisms underlying GCD remain to be elucidated, but one hypothesis proposes aberrant reactivation of neurodevelopmental migratory pathways, possibly triggered by febrile seizures. This study aims to compare the proteomes of basal and dispersed granule cells in the hippocampus of eight MTLE patients with GCD to identify proteins that may mediate GCD in MTLE. Quantitative proteomics identified 1,882 proteins, of which 29% were found in basal granule cells only, 17% in dispersed only and 54% in both samples. Bioinformatics analyses revealed upregulated proteins in dispersed samples were involved in developmental cellular migratory processes, including cytoskeletal remodeling, axon guidance and signaling by Ras homologous (Rho) family of GTPases (P < 0.01). The expression of two Rho GTPases, RhoA and Rac1, was subsequently explored in immunohistochemical and in situ hybridization studies involving eighteen MTLE cases with or without GCD, and three normal post mortem cases. In cases with GCD, most dispersed granule cells in the outer-granular and molecular layers have an elongated soma and bipolar processes, with intense RhoA immunolabeling at opposite poles of the cell soma, while most granule cells in the basal granule cell layer were devoid of RhoA. A higher percentage of cells expressing RhoA was observed in cases with GCD than without GCD (P < 0.004). In GCD cases, the percentage of cells expressing RhoA was significantly higher in the inner molecular layer than the granule cell layer (P < 0.026), supporting proteomic findings. In situ hybridization studies using probes against RHOA and RAC1 mRNAs revealed fine peri- and nuclear puncta in granule cells of all cases. The density of cells expressing RHOA mRNAs was significantly higher in the inner molecular layer of cases with GCD than without GCD (P = 0.05). In summary, our study has found limited evidence for ongoing adult neurogenesis in the hippocampus of patients with MTLE, but evidence of differential dysmaturation between dispersed and basal granule cells has been demonstrated, and elevated expression of Rho GTPases in dispersed granule cells may contribute to the pathomechanisms underpinning GCD in MTLE.

A Multimodal Ca(II) Responsive Near IR-MR Contrast Agent Exhibiting High Cellular Uptake

Ca(II) ions are critical for the proper function of neurons by contributing to synaptic signaling and regulating neuronal plasticity. Dysregulation of Ca(II) is associated with a number of pathologies that cause neurodegeneration; therefore the ability to monitor Ca(II) intracellularly is an important target for molecular imaging. Contrast-enhanced MR imaging is a promising modality for imaging changes in Ca(II) concentrations. However, the majority of Ca(II) responsive MR agents are limited to the extracellular space or hindered by poor cellular uptake. Here, we describe a new class of multimodal, bioresponsive Ca(II) magnetic resonance agents that are coupled to the NIR probe IR-783. This new design is based on previous generations of our Ca(II) MR agents but overcomes two significant challenges: (1) the presence of the NIR probe dramatically increases cellular uptake of the agent and (2) provides histological validation of the MR signal using NIR fluorescence imaging. IR-783 targets organic anion transporter polypeptides, and we demonstrate that the agents are not toxic in HT-22 or U-87 MG cells up to 20 μM. The cellular uptake of complex 1 was measured to be greater than 16 femtomoles per cell (where ∼1 femtomole/cell is detectable in acquired MR images). Complex 1 is simultaneously detectable by both MR and NIR fluorescence imaging in vitro and is activated (turned on) by intracellular Ca(II) at concentrations between 1 and 10 μM.

Role of the mitochondrial calcium uniporter in Mg2+-free-induced epileptic hippocampal neuronal apoptosis

PURPOSE

Mitochondrial Ca²⁺ overload is closely associated with seizure-induced neuronal damage. The mitochondrial calcium uniporter (MCU) plays a crucial role in regulating mitochondrial Ca²⁺ homeostasis. However, the role of the MCU in seizure-induced neuronal damage remains elusive. Materials and methods: In this study, the hippocampal neuronal culture (HNC) model of acquired epilepsy (AE) was used to investigate the role of the MCU in seizure-induced neuronal injury. Results: We found an increase in mitochondrial Ca²⁺ concentration in the HNC model of AE. The MCU inhibitor, Ru360, significantly reduced the rate of seizure-induced cell apoptosis and mitochondrial reactive oxygen species (ROS) production; whereas, the MCU agonist, spermine, exacerbated these processes. In addition, Ru360 significantly attenuated seizure-induced endoplasmic reticulum (ER) stress, which is characterized by the expression of glucose-regulated protein 78 (GRP78) and C/-EBP homologous protein (CHOP), while spermine had the opposite effect. We also found that pre-treatment with the mitochondria-targeted antioxidant, mitoquinone, decreased GRP78 and CHOP expression. Moreover, knockdown of CHOP using CHOP-specific small interfering RNA reduced neuronal seizure-induced apoptosis. Conclusions: Taken together, our data indicate that MCU inhibition has a neuroprotective effect against seizure-induced neuronal damage and that this mechanism may involve reduction of ROS-mediated ER stress.

Phosphoproteomic analysis reveals Akt isoform-specific regulation of cytoskeleton proteins in human temporal lobe epilepsy with hippocampal sclerosis

Akt is one of the most important downstream effectors of phosphatidylinositol 3-kinase/mTOR pathway. Hyperactivation and expression of this pathway are seen in a variety of neurological disorders including human temporal lobe epilepsy with hippocampal sclerosis (TLE-HS). Nevertheless, the expression and activation profiles of the Akt isoforms, Akt1, Akt2, and Akt3 and their functional roles in human TLE-HS have not been studied. We examined the protein expression and activation (phosphorylation) patterns of Akt and its isoforms in human hippocampal tissue from TLE and non-TLE patients. A phosphoproteomic approach followed by interactome analysis of each Akt isoform was used to understand protein-protein interactions and their role in TLE-HS pathology. Our results demonstrated activation of the Akt/mTOR pathway as well as activation of Akt downstream substrates like GSK3β, mTOR, and S6 in TLE-HS samples. Akt1 isoform levels were significantly increased in the TLE-HS samples as compared to the non-TLE samples. Most importantly, different isoforms were activated in different TLE-HS samples, Akt2 was activated in three samples, Akt2 and Akt1 were simultaneously activated in one sample and Akt3 was activated in two samples. Our phosphoproteomic screen across six TLE-HS samples identified 183 proteins phosphorylated by Akt isoforms, 29 of these proteins belong to cytoskeletal modification. Also, we were able to identify proteins of several other classes involved in glycolysis, neuronal development, protein folding and excitatory amino acid transport functions as Akt substrates. Taken together, our data offer clues to understand the role of Akt and its isoforms in underlying the pathology of TLE-HS and further, modulation of Akt/mTOR pathway using Akt isoforms specific inhibitors may offer a new therapeutic window for treatment of human TLE-HS.

Reactive oxygen species in status epilepticus

There has been growing evidence for a critical role of oxidative stress in neurodegenerative disease, providing novel targets for disease modifying treatments. Although antioxidants have been suggested and tried in the treatment of epilepsy, it is only recently that the pivotal role of oxidative stress in the pathophysiology of status epilepticus has been recognized. Although conventionally thought to be generated by mitochondria, reactive oxygen species during status epilepticus and prolonged seizure are generated mainly by NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (stimulated by NMDA receptor activation). Excessive production of reactive oxygen species results in lipid peroxidation, DNA damage, enzyme inhibition, and mitochondrial damage, culminating in neuronal death. Antioxidant therapy has been hampered by poor CNS penetration and rapid consumption by oxidants. However, alternative approaches such as inhibiting NADPH oxidase or increasing endogenous antioxidant defenses through activation of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) could avoid these problems. Small molecules that increase Nrf2 activation have proven to be not only effective neuroprotectants following status epilepticus, but also potently antiepileptogenic. There are "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Succinate accumulation induces mitochondrial reactive oxygen species generation and promotes status epilepticus in the kainic acid rat model

Though succinate accumulation is associated with reactive oxygen species (ROS) production and neuronal injury, which play critical roles in epilepsy, it is unclear whether succinate accumulation contributes to the onset of epilepsy or seizures. We sought to investigate changes in succinate, oxidative stress, and mito-SOX levels, as well as mitophagy and neuronal change, in different status epilepticus (SE) rat models. Our results demonstrate that KA-induced SE was accompanied by increased levels of succinate, oxidative stress, and mito-SOX, as well as mitophagy and neuronal degeneration. The similarly increased levels of succinate, oxidative stress, and mito-SOX were also found in pilocarpine-induced SE. Moreover, the reduction of succinate accumulation by the inhibition of succinate dehydrogenase (SDH), malate/aspartate shuttle (MAS), or purine nucleotide cycle (PNC) served to reduce succinate, oxidative stress, and mito-SOX levels, thereby preventing oxidative stress-related neuronal damage and lessening seizure severity. Interestingly, simulating succinate accumulation with succinic acid dimethyl ester may induce succinate accumulation and increased oxidative stress and mito-SOX levels, as well as behavior and seizures in electroencephalograms similar to those observed in rats exposed to KA. Our results indicate that succinate accumulation may contribute to the increased oxidative stress/mitochondrial ROS levels, neuronal degeneration, and SE induced by KA administration. Furthermore, we found that succinate accumulation was mainly due to the inverse catalysis of SDH from fumarate, which was supplemented by the MAS and PNC pathways. These results reveal new insights into the mechanisms underlying SE and that reducing succinate accumulation may be a clinically useful therapeutic target in SE.

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KA- or pilocarpine-induced SE was accompanied by succinate accumulation.

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Succinate accumulation caused elevated ROS/mito-ROS levels and neuronal injury.

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Inverse catalysis of SDH from fumarate mainly caused succinate accumulation.

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Inhibiting succinate accumulation relieved oxidative stress level, neuronal injury, and seizure.

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Simulating succinate accumulation induced elevated oxidative stress level and seizure.

Ketone Bodies in Neurological Diseases: Focus on Neuroprotection and Underlying Mechanisms

There is growing evidence that ketone bodies, which are derived from fatty acid oxidation and usually produced in fasting state or on high-fat diets have broad neuroprotective effects. Although the mechanisms underlying the neuroprotective effects of ketone bodies have not yet been fully elucidated, studies in recent years provided abundant shreds of evidence that ketone bodies exert neuroprotective effects through possible mechanisms of anti-oxidative stress, maintaining energy supply, modulating the activity of deacetylation and inflammatory responses. Based on the neuroprotective effects, the ketogenic diet has been used in the treatment of several neurological diseases such as refractory epilepsy, Parkinson's disease, Alzheimer's disease, and traumatic brain injury. The ketogenic diet has great potential clinically, which should be further explored in future studies. It is necessary to specify the roles of components in ketone bodies and their therapeutic targets and related pathways to optimize the strategy and efficacy of ketogenic diet therapy in the future.

Functional Nutrients for Epilepsy

Epilepsy is a common neurological disorder of which seizures are a core symptom. Approximately one third of epileptic patients are resistant to antiepileptic drugs and therefore require alternative therapeutic options. Dietary and nutritional supplements can in some cases replace drugs, but with the exception of ketogenic diets, there are no officially recommended dietary considerations for patients with epilepsy. In this review we summarize a selection of nutritional suggestions that have proved beneficial in treating different types of epilepsy. We describe the types of seizures and epilepsy and follow this with an introduction to basic molecular mechanisms. We then examine several functional nutrients for which there is clinical evidence of therapeutic efficacy in reducing seizures or epilepsy-associated sudden death. We also discuss experimental results that demonstrate possible molecular mechanisms elicited by the administration of various nutrients. The availability of multiple dietary and nutritional candidates that show favorable outcomes in animals implies that assessing the clinical potential of these substances will improve translational medicine, ultimately benefitting epilepsy patients.

Activation of nicotinamide adenine dinucleotide phosphate oxidase is the primary trigger of epileptic seizures in rodent models

OBJECTIVE

Despite decades of epilepsy research, 30% of focal epilepsies remain resistant to antiseizure drugs, with effective drug development impeded by lack of understanding on how seizures are initiated. Here, we report the mechanism of seizure onset relevant to most seizures that are characteristic of focal epilepsies.

METHODS

Electric and metabolic network parameters were measured using several seizure models in mouse hippocampal slices and acutely induced seizures in rats in vivo to determine metabolic events occurring at seizure onset.

RESULTS

We show that seizure onset is associated with a rapid release of H₂ O₂ resulting from N-methyl-D-aspartate (NMDA) receptor-mediated activation of nicotinamide adenine dinucleotide phosphate oxidase (NOX). NOX blockade prevented the fast H₂ O₂ release as well as the direct current shift and seizurelike event induction in slices. Similarly, intracerebroventricular injection of NOX antagonists prevented acutely induced seizures in rats.

INTERPRETATION

Our results show that seizures are initiated by NMDA receptor-mediated NOX-induced oxidative stress and can be arrested by NOX inhibition. We introduce a novel use for blood-brain barrier-permeable NOX inhibitor with a significant potential to become the first seizure-specific medication. Thus, targeting NOX may provide a breakthrough treatment for focal epilepsies. ANN NEUROL 2019;85:907-920.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

Altered Proteins in the Hippocampus of Patients with Mesial Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (MTLE) is usually associated with drug-resistant seizures and cognitive deficits. Efforts have been made to improve the understanding of the pathophysiology of MTLE for new therapies. In this study, we used proteomics to determine the differential expression of proteins in the hippocampus of patients with MTLE compared to control samples. By using the two-dimensional electrophoresis method (2-DE), the proteins were separated into spots and analyzed by LC-MS/MS. Spots that had different densitometric values for patients and controls were selected for the study. The following proteins were found to be up-regulated in patients: isoform 1 of serum albumin (ALB), proton ATPase catalytic subunit A (ATP6V1A), heat shock protein 70 (HSP70), dihydropyrimidinase-related protein 2 (DPYSL2), isoform 1 of myelin basic protein (MBP), and dihydrolipoamide S-acethyltransferase (DLAT). The protein isoform 3 of the spectrin alpha chain (SPTAN1) was down-regulated while glutathione S-transferase P (GSTP1) and protein DJ-1 (PARK7) were found only in the hippocampus of patients with MTLE. Interactome analysis of the nine proteins of interest revealed interactions with 20 other proteins, most of them involved with metabolic processes (37%), presenting catalytic activity (37%) and working as hydrolyses (25%), among others. Our results provide evidence supporting a direct link between synaptic plasticity, metabolic disturbance, oxidative stress with mitochondrial damage, the disruption of the blood–brain barrier and changes in CNS structural proteins with cell death and epileptogenesis in MTLE. Besides this, the presence of markers of cell survival indicated a compensatory mechanism. The over-expression of GSTP1 in MTLE could be related to drug-resistance.

Mitochondrial damage in hippocampal neurons of rats with epileptic protein expression of Fas and caspase-3

Epilepsy model in rats was established to observe the behavior and pathological changes, and to detect mitochondrial dysfunction, exploring its possible molecular mechanisms. The epileptic status of Sprague-Dawley (SD) rats was induced by intraperitoneal injection of lithium chloride, and the change of behavior was recorded. Electroencephalogram (EEG) was used to measure the abnormal discharge of neurons in rats. The brain tissue was fixed with polyformaldehyde and the paraffin sections were prepared, and the damage of the hippocampal neurons was observed with Nissl staining. Mitochondrial ATP and mitochondrial DNA were examined to assess mitochondrial dysfunction. Finally, qPCR and western blot analysis were used to detect mRNA and protein expression of fatty acid synthetase (Fas), Fas ligand (FasL) and caspase-3 in rat hippocampal neurons. The correlation between the mitochondrial dysfunction of rat hippocampal neurons and Fas and caspase-3 was analyzed. Compared with the normal group rats, the model group showed typical seizures, which were determined by the Racine attack score. EEG of the hippocampus of the model group was recorded in cluster in model group rats. Nissl staining showed a different degree of damage to the hippocampal neurons in the model group compared with normal rats. The mitochondrial ATP content and DNA content of rat hippocampal neurons in the model group were significantly lower than that of normal rats (P<0.01). The qPCR and western blot results showed that the mRNA and protein expression levels of Fas, FasL and caspase-3 were significantly increased in the hippocampus of rat model group (P<0.01). The expression level of Fas and caspase-3 in hippocampal tissues of rats was negatively correlated with mitochondrial DNA content. In conclusion, seizures cause damage of neuron mitochondria in rat hippocampus leading to death of hippocampal neurons, the mitochondrial damage of hippocampal neurons in epileptic rats was closely related to the expression of Fas and caspase-3.

Impairments in Oxidative Glucose Metabolism in Epilepsy and Metabolic Treatments Thereof

There is mounting evidence that oxidative glucose metabolism is impaired in epilepsy and recent work has further characterized the metabolic mechanisms involved. In healthy people eating a traditional diet, including carbohydrates, fats and protein, the major energy substrate in brain is glucose. Cytosolic glucose metabolism generates small amounts of energy, but oxidative glucose metabolism in the mitochondria generates most ATP, in addition to biosynthetic precursors in cells. Energy is crucial for the brain to signal "normally," while loss of energy can contribute to seizure generation by destabilizing membrane potentials and signaling in the chronic epileptic brain. Here we summarize the known biochemical mechanisms that contribute to the disturbance in oxidative glucose metabolism in epilepsy, including decreases in glucose transport, reduced activity of particular steps in the oxidative metabolism of glucose such as pyruvate dehydrogenase activity, and increased anaplerotic need. This knowledge justifies the use of alternative brain fuels as sources of energy, such as ketones, TCA cycle intermediates and precursors as well as even medium chain fatty acids and triheptanoin.

Impaired Bioenergetics in Mutant Mitochondrial DNA Determines Cell Fate During Seizure-Like Activity

Mutations in genes affecting mitochondrial proteins are increasingly recognised in patients with epilepsy, but the factors determining cell fate during seizure activity in these mutations remain unknown. Fluorescent dye imaging techniques were applied to fibroblast cell lines from patients suffering from common mitochondrial mutations and to age-matched controls. Using live cell imaging techniques in fibroblasts, we show that fibroblasts with mutations in the mitochondrial genome had reduced mitochondrial membrane potential and NADH pools and higher redox indices, indicative of respiratory chain dysfunction. Increasing concentrations of ferutinin, a Ca²⁺ ionophore, led to oscillatory Ca²⁺ signals in fibroblasts resembling dynamic Ca²⁺ changes that occur during seizure-like activity. Co-monitoring of mitochondrial membrane potential (ΔΨ_m) changes induced by ferutinin showed accelerated membrane depolarisation and cell collapse in fibroblasts with mutations in the mitochondrial genome when compared to controls. Ca²⁺ flash photolysis using caged Ca²⁺ confirmed impaired Ca²⁺ handling in fibroblasts with mitochondrial mutations. Findings indicate that intracellular Ca²⁺ levels cannot be compensated during periods of hyperexcitability, leading to Ca²⁺ overload and subsequent cell death in mitochondrial diseases.

Metabolic Dysfunction and Oxidative Stress in Epilepsy

The epilepsies are a heterogeneous group of disorders characterized by the propensity to experience spontaneous recurrent seizures. Epilepsies can be genetic or acquired, and the underlying mechanisms of seizure initiation, seizure propagation, and comorbid conditions are incompletely understood. Metabolic changes including the production of reactive species are known to result from prolonged seizures and may also contribute to epilepsy development. In this review, we focus on the evidence that metabolic and redox disruption is both cause and consequence of epileptic seizures. Additionally, we discuss the promise of targeting redox processes as a therapeutic option in epilepsy.