A Metabolic Paradigm for Epilepsy

Molecular Insights of Drug Resistance in Epilepsy: Multi-omics Unveil

Epilepsy is a devastating neurological disorder mainly associated with impaired synchronic discharge that leads to sensory, motor, and psychomotor impairments. Till now, about 30 anti-seizure medications (ASMs) have been approved for the management of epilepsy, yet one-third of individuals still have uncontrollable epilepsy and develop resistance. Drug resistance epilepsy (DRE) is defined as the condition where two ASMs fail to control the seizure in epileptic patients. The leading cause of the resistance was the extended use of ASMs. According to various studies, alterations in some genes and their expressions, along with specific metabolic impairments, are suggested to be associated with ASMs resistance and DRE pathophysiology. Several factors aid in the pathophysiology of DRE, such as alterations in protein-encoding genes such as neurotransmitter receptors, drug transporters, ion channels, and drug targets. Furthermore, the altered metabolite levels of metabolites implicated in neurotransmitter signaling, energetic pathways, oxidative stress, and neuroinflammatory signaling differentiate the epileptic patient from the DRE patient. Various DRE biomarkers can be identified using the "integrated omics approach," which includes the study of genomics, transcriptomics, and metabolomics. The current review has been compiled to understand the pathophysiological mechanisms of DRE by focusing on genomics, transcriptomics, and metabolomics. An effort has also been made to identify the therapeutic targets based on identifying significant markers by a multi-omics approach. This has the potential to develop novel therapeutic interventions in the future.

Metabolic aspects of genetic ion channel epilepsies

Nowadays, particularly in countries with high incomes, individual mutations in people affected by genetic epilepsies are identified, and genetic therapies are being developed. In addition, drugs are being screened to directly target specific mutations, and personalised medicine is possible. However, people with epilepsy do not yet benefit from these advances, and many types of epilepsies are medication-resistant, including Dravet syndrome. Thus, in the meantime, alternative and effective treatment options are needed. There is increasing evidence that metabolic deficits contribute to epileptic seizures and that such metabolic impairments may be amenable to treatment, with metabolic treatment options like the ketogenic diet being employed with some success. However, the brain metabolic alterations that occur in ion channel epilepsies are not well-understood, nor how these may differ from epilepsies that are of acquired and unknown origins. Here, we provide an overview of studies investigating metabolic alterations in epilepsies caused by mutations in the SCN1A and KCNA1 genes, which are currently the most studied ion channel epilepsies in animal models. The metabolic changes found in these models are likely to contribute to seizures. A metabolic basis of these ion channel epilepsies is supported by human and/or animal studies that show beneficial effects of the ketogenic diet, which may be mediated by the provision of auxiliary brain fuel in the form of ketone bodies. Other potentially more preferred dietary therapies including medium-chain triglycerides and triheptanoin have also been tested in a limited number of studies, but their efficacies remain to be clearly established. The extent to which brain metabolism is affected in people with Dravet syndrome, KCNA1 epilepsy and the models thereof still requires clarification. This requires more experiments that yield functional insight into metabolism.

Inflammation and oxidative stress in epileptic children: from molecular mechanisms to clinical application of ketogenic diet

Childhood epilepsy affects up to 1 % of children. It has been shown that 30 % of patients are resistant to drug treatments, making further investigation of other potential treatment strategies necessary. One such approach is the ketogenic diet (KD) showing promising results and potential benefits beyond the use of current antiepileptic drugs. This study aims to investigate the effects of KD on inflammation and oxidative stress, as one of the main suggested mechanisms of neuroprotection, in children with epilepsy. This narrative review was conducted using the Medline and Google Scholar databases, and by searching epilepsy, drug-resistant epilepsy, child, children, ketogenic, ketogenic diet, diet, ketogenic, keto, ketone bodies (BHB), PUFA, gut microbiota, inflammation, inflammation mediators, neurogenic inflammation, neuroinflammation, inflammatory marker, adenosine modulation, mitochondrial function, MTOR pathway, Nrf2 pathway, mitochondrial dysfunction, PPARɣ, oxidative stress, ROS/RNS, and stress oxidative as keywords. Compelling evidence underscores inflammation and oxidative stress as pivotal factors in epilepsy, even in cases with genetic origins. The ketogenic diet effectively addresses these factors by reducing ROS and RNS, enhancing antioxidant defenses, improving mitochondrial function, and regulating inflammatory genes. Additionally, KD curbs pro-inflammatory cytokine and chemokine production by dampening NF-κB activation, inhibiting the NLRP3 inflammasome, increasing brain adenosine levels, mTOR pathway inhibition, upregulating PPARɣ expression, and promoting a healthy gut microbiota while emphasizing the consumption of healthy fats. KD could be considered a promising therapeutic intervention in patients with epilepsy particularly in drug-resistant epilepsy cases, due to its targeted approach addressing oxidative stress and inflammatory mechanisms.

Sex differences in physiological response to increased neuronal excitability in a knockin mouse model of pediatric epilepsy

BACKGROUND

Epilepsy is a common neurological disease; however, few if any of the currently marketed antiseizure medications prevent or cure epilepsy. Discovery of pathological processes in the early stages of epileptogenesis has been challenging given the common use of preclinical models that induce seizures in physiologically normal animals. Moreover, despite known sex dimorphism in neurological diseases, females are rarely included in preclinical epilepsy models.

METHODS

We characterized sex differences in mice carrying a pathogenic knockin variant (p.N1768D) in the Scn8a gene that causes spontaneous tonic-clonic seizures (TCs) at ∼3 months of age and found that heterozygous females are more resilient than males in mortality and morbidity. To investigate the cellular mechanisms that underlie female resilience, we utilized blood-brain barrier (BBB) and hippocampal transcriptomic analyses in heterozygous mice before seizure onset (pre-TC) and in mice that experienced ∼20 TCs (post-TC).

RESULTS

In the pre-TC latent phase, both sexes exhibited leaky BBB; however, patterns of gene expression were sexually dimorphic. Females exhibited enhanced oxidative phosphorylation and protein biogenesis, while males activated gliosis and CREB signaling. After seizure onset (chronic phase), females exhibited a metabolic switch to lipid metabolism, while males exhibited increased gliosis and BBB dysfunction and a strong activation of neuroinflammatory pathways.

CONCLUSION

The results underscore the central role of oxidative stress and BBB permeability in the early stages of epileptogenesis, as well as sex dimorphism in response to increasing neuronal hyperexcitability. Our results also highlight the need to include both sexes in preclinical studies to effectively translate results of drug efficacy studies.

Integrative analysis of epilepsy-associated genes reveals expression-phenotype correlations

Epilepsy is a highly prevalent neurological disorder characterized by recurrent seizures. Patients exhibit broad genetic, molecular, and clinical diversity involving mild to severe comorbidities. The factors that contribute to this phenotypic diversity remain unclear. Here we used publicly available datasets to systematically interrogate the expression pattern of 230 epilepsy-associated genes across human tissues, developmental stages, and central nervous system (CNS) cellular subtypes. We grouped genes based on their curated phenotypes into 3 broad classes: core epilepsy genes (CEG), where seizures are the dominant phenotype, developmental and epileptic encephalopathy genes (DEEG) that are associated with developmental and epileptic encephalopathy, and seizure-related genes (SRG), which are characterized by the presence of seizures and gross brain malformations. We find that compared to the other two groups of genes, DEEGs are highly expressed within the adult CNS, exhibit the highest and most dynamic expression in various brain regions across development, and are significantly enriched in GABAergic neurons. Our analysis provides an overview of the expression pattern of epilepsy-associated genes with spatiotemporal resolution and establishes a broad expression-phenotype correlation in epilepsy.

Developing Peripheral Biochemical Biomarkers of Brain Disorders: Insights from Zebrafish Models

High prevalence of human brain disorders necessitates development of the reliable peripheral biomarkers as diagnostic and disease-monitoring tools. In addition to clinical studies, animal models markedly advance studying of non-brain abnormalities associated with brain pathogenesis. The zebrafish (Danio rerio) is becoming increasingly popular as an animal model organism in translational neuroscience. These fish share some practical advantages over mammalian models together with high genetic homology and evolutionarily conserved biochemical and neurobehavioral phenotypes, thus enabling large-scale modeling of human brain diseases. Here, we review mounting evidence on peripheral biomarkers of brain disorders in zebrafish models, focusing on altered biochemistry (lipids, carbohydrates, proteins, and other non-signal molecules, as well as metabolic reactions and activity of enzymes). Collectively, these data strongly support the utility of zebrafish (from a systems biology standpoint) to study peripheral manifestations of brain disorders, as well as highlight potential applications of biochemical biomarkers in zebrafish models to biomarker-based drug discovery and development.

Identification of metabolic biomarkers of chronic vagus nerve stimulation (VNS) in subjects with drug-resistant epilepsy (DRE)

Neuromodulation by means of vagus nerve stimulation (VNS) therapy, reduces seizure frequency and improves quality of life in subjects with drug-resistant epilepsy (DRE), yet its molecular mechanism remains unclear. This study investigates the impact of chronic VNS on lipid bioactive metabolites and fatty acids (FA) in the plasma and red blood cells of seven subjects with DRE. By measuring expression levels of peroxisome proliferator-activated receptor α (PPARα) and sirtuin1 (SIRT1) genes-key regulators in energy and lipid metabolism-and lipid profiles before and after various stages of VNS, this study identifies potential mechanisms by which VNS may reduce seizure frequency. Blood samples collected before VNS device implantation, after acute VNS stimulus, and following gradual intensity increments up to therapeutic levels revealed that VNS increases SIRT1 and PPARα expression and erythrocyte concentrations of PPARα ligands. Additionally, we observe reduced de novo lipogenesis biomarkers in erythrocytes, indicating that VNS may influence systemic lipid and energy metabolism. Our findings suggest that VNS could enhance neuronal function by modulating energy metabolism, thus potentially reducing seizure frequency in subjects with DRE. Future research targeting SIRT1 and PPARα may provide innovative therapeutic strategies for managing DRE. Plain Language Summary: The exact mechanism of VNS is still unknown. This study investigated the effects of VNS Therapy on energetic metabolism, suggesting possible novel biomarkers for DRE subjects and neuromodulation therapies.

Differential microRNA editing may drive target pathway switching in human temporal lobe epilepsy

MicroRNAs have emerged as important regulators of the gene expression landscape in temporal lobe epilepsy. The mechanisms that control microRNA levels and influence target choice remain, however, poorly understood. RNA editing is a post-transcriptional mechanism mediated by the adenosine acting on RNA (ADAR) family of proteins that introduces base modification that diversifies the gene expression landscape. RNA editing has been studied for the mRNA landscape but the extent to which microRNA editing occurs in human temporal lobe epilepsy is unknown. Here, we used small RNA-sequencing data to characterize the identity and extent of microRNA editing in human temporal lobe epilepsy brain samples. This detected low-to-high editing in over 40 of the identified microRNAs. Among microRNA exhibiting the highest editing was miR-376a-3p, which was edited in the seed region and this was predicted to significantly change the target pool. The edited form was expressed at lower levels in human temporal lobe epilepsy samples. We modelled the shift in editing levels of miR-376a-3p in human-induced pluripotent stem cell-derived neurons. Reducing levels of the edited form of miR-376a-3p using antisense oligonucleotides resulted in extensive gene expression changes, including upregulation of mitochondrial and metabolism-associated pathways. Together, these results show that differential editing of microRNAs may re-direct targeting and result in altered functions relevant to the pathophysiology of temporal lobe epilepsy and perhaps other disorders of neuronal hyperexcitability.

Glycaemic Imbalances in Seizures and Epilepsy of Paediatric Age: A Literature Review

Cerebral excitability and systemic metabolic balance are closely interconnected. Energy supply to neurons depends critically on glucose, whose fluctuations can promote immediate hyperexcitability resulting in acute symptomatic seizures. On the other hand, chronic disorders of sugar metabolism (e.g., diabetes mellitus) are often associated with long-term epilepsy. In this paper, we aim to review the existing knowledge on the association between acute and chronic glycaemic imbalances (hyper- and hypoglycaemia) with seizures and epilepsy, especially in the developing brain, focusing on clinical and instrumental features in order to optimize the care of children and adolescents and prevent the development of chronic neurological conditions in young patients.

Ketamine administration in idiopathic epileptic and healthy control dogs: Can we detect differences in brain metabolite response with spectroscopy?

Introduction

In recent years ketamine has increasingly become the focus of multimodal emergency management for epileptic seizures. However, little is known about the effect of ketamine on brain metabolites in epileptic patients. Magnetic resonance spectroscopy (MRS) is a non-invasive technique to estimate brain metabolites in vivo. Our aim was to measure the effect of ketamine on thalamic metabolites in idiopathic epileptic (IE) dogs using 3 Tesla MRS. We hypothesized that ketamine would increase the glutamine-glutamate (GLX)/creatine ratio in epileptic dogs with and without antiseizure drug treatment, but not in control dogs. Furthermore, we hypothesized that no different responses after ketamine administration in other measured brain metabolite ratios between the different groups would be detected.

Methods

In this controlled prospective experimental trial IE dogs with or without antiseizure drug treatment and healthy client-owned relatives of the breeds Border Collie and Greater Swiss Mountain Dog, were included. After sedation with butorphanol, induction with propofol and maintenance with sevoflurane in oxygen and air, a single voxel MRS at the level of the thalamus was performed before and 2 min after intravenous administration of 1 mg/kg ketamine. An automated data processing spectral fitting linear combination model algorithm was used to estimate all commonly measured metabolite ratios. A mixed ANOVA with the independent variables ketamine administration and group allocation was performed for all measured metabolites. A p < 0.05 was considered statistically significant.

Results

Twelve healthy control dogs, 10 untreated IE and 12 treated IE dogs were included. No significant effects for GLX/creatine were found. However, increased glucose/creatine ratios were found (p < 0.001) with no effect of group allocation. Furthermore, increases in the GABA/creatine ratio were found in IEU dogs.

Discussion

MRS was able to detect changes in metabolite/creatine ratios after intravenous administration of 1 mg/kg ketamine in dogs and no evidence was found that excitatory effects are induced in the thalamus. Although it is beyond the scope of this study to investigate the antiseizure potential of ketamine in dogs, results of this research suggest that the effect of ketamine on the brain metabolites could be dependent on the concentrations of brain metabolites before administration.

MMF induces antioxidative and anaplerotic pathways and is neuroprotective in hyperexcitability in vitro

Hyperexcitability-induced neuronal damage plays a role both in epilepsy as well as in inflammatory brain diseases such as multiple sclerosis (MS) and as such represents an important disease pathway which potentially can be targeted to mitigate neuronal damage. Dimethyl fumarate (DMF) and its pharmacologically active metabolite monomethyl fumarate (MMF) are FDA-approved therapeutics for MS, which can induce immunosuppressive and antioxidant pathways, and their neuroprotective capacity has been demonstrated in other preclinical neurological disease models before. In this study, we used an unbiased proteomic approach to identify potential new targets upon the treatment of MMF in glio-neuronal hippocampal cultures. MMF treatment results in induction of antioxidative (HMOX1, NQO1) and anaplerotic metabolic (GAPDH, PC) pathways, which correlated with reduction in ROS production, increased mitochondrial NADH-redox index and decreased NADH pool, independent of glutathione levels. Additionally, MMF reduced glycolytic capacity indicating individual intra-cellular metabolic programs within different cell types. Furthermore, we demonstrate a neuroprotective effect of MMF upon hyperexcitability in vitro (low magnesium model), where MMF prevents glio-neuronal death via reduced ROS production. These results highlight MMF as a potential new therapeutic opportunity in hyperexcitability-induced neurodegeneration.

Astrocytes in the initiation and progression of epilepsy

Epilepsy affects ~65 million people worldwide. First-line treatment options include >20 antiseizure medications, but seizure control is not achieved in approximately one-third of patients. Antiseizure medications act primarily on neurons and can provide symptomatic control of seizures, but do not alter the onset and progression of epilepsy and can cause serious adverse effects. Therefore, medications with new cellular and molecular targets and mechanisms of action are needed. Accumulating evidence indicates that astrocytes are crucial to the pathophysiological mechanisms of epilepsy, raising the possibility that these cells could be novel therapeutic targets. In this Review, we discuss how dysregulation of key astrocyte functions - gliotransmission, cell metabolism and immune function - contribute to the development and progression of hyperexcitability in epilepsy. We consider strategies to mitigate astrocyte dysfunction in each of these areas, and provide an overview of how astrocyte activation states can be monitored in vivo not only to assess their contribution to disease but also to identify markers of disease processes and treatment effects. Improved understanding of the roles of astrocytes in epilepsy has the potential to lead to novel therapies to prevent the initiation and progression of epilepsy.

Tailoring Materials for Epilepsy Imaging: From Biomarkers to Imaging Probes

Excising epileptic foci (EF) is the most efficient approach for treating drug-resistant epilepsy (DRE). However, owing to the vast heterogeneity of epilepsies, EF in one-third of patients cannot be accurately located, even after exhausting all current diagnostic strategies. Therefore, identifying biomarkers that truly represent the status of epilepsy and fabricating probes with high targeting specificity are prerequisites for identifying the "concealed" EF. However, no systematic summary of this topic has been published. Herein, the potential biomarkers of EF are first summarized and classified into three categories: functional, molecular, and structural aberrances during epileptogenesis, a procedure of nonepileptic brain biasing toward epileptic tissue. The materials used to fabricate these imaging probes and their performance in defining the EF in preclinical and clinical studies are highlighted. Finally, perspectives for developing the next generation of probes and their challenges in clinical translation are discussed. In general, this review can be helpful in guiding the development of imaging probes defining EF with improved accuracy and holds promise for increasing the number of DRE patients who are eligible for surgical intervention.

An Integrated Multi-Omic Network Analysis Identifies Seizure-Associated Dysregulated Pathways in the GAERS Model of Absence Epilepsy

Absence epilepsy syndromes are part of the genetic generalized epilepsies, the pathogenesis of which remains poorly understood, although a polygenic architecture is presumed. Current focus on single molecule or gene identification to elucidate epileptogenic drivers is unable to fully capture the complex dysfunctional interactions occurring at a genetic/proteomic/metabolomic level. Here, we employ a multi-omic, network-based approach to characterize the molecular signature associated with absence epilepsy-like phenotype seen in a well validated rat model of genetic generalized epilepsy with absence seizures. Electroencephalographic and behavioral data was collected from Genetic Absence Epilepsy Rats from Strasbourg (GAERS, n = 6) and non-epileptic controls (NEC, n = 6), followed by proteomic and metabolomic profiling of the cortical and thalamic tissue of rats from both groups. The general framework of weighted correlation network analysis (WGCNA) was used to identify groups of highly correlated proteins and metabolites, which were then functionally annotated through joint pathway enrichment analysis. In both brain regions a large protein-metabolite module was found to be highly associated with the GAERS strain, absence seizures and associated anxiety and depressive-like phenotype. Quantitative pathway analysis indicated enrichment in oxidative pathways and a downregulation of the lysine degradation pathway in both brain regions. GSTM1 and ALDH2 were identified as central regulatory hubs of the seizure-associated module in the somatosensory cortex and thalamus, respectively. These enzymes are involved in lysine degradation and play important roles in maintaining oxidative balance. We conclude that the dysregulated pathways identified in the seizure-associated module may be involved in the aetiology and maintenance of absence seizure activity. This dysregulated activity could potentially be modulated by targeting one or both central regulatory hubs.

Novel mutation of SIK1 gene causing a mild form of pediatric epilepsy in a Chinese patient

Developmental and Epileptic Encephalopathy (DEE) is a group of disorders affecting children at early stages of infancy, which is characterized by frequent seizures, epileptiform activity on EEG, and developmental delayor regression. Developmental and epileptic encephalopathy-30 (DEE30) is a severe neurologic disorder characterized by onset of refractory seizures soon after birth or in the first months of life. Which was recently found to be caused by heterozygous mutations in the salt-inducible kinase SIK1. In this study, we investigated a patient with early onset epilepsy. DNA sequencing of the whole coding region revealed a de novel heterozygous nucleotide substitution (c.880G > A) causing a missense mutation (p.A294T). This mutation was classified as variant of unknown significance (VUS) by American College of Medical Genetics and Genomics (ACMG). To further investigate the pathogenicity and pathogenesis of this mutation, we established a human neuroblastoma cell line (SH-SY5Y) stably-expressing wild type SIK1 and A294T mutant, and compared the transcriptome and metabolomics profiles. We presented a pediatric patient suffering from infantile onset epilepsy. Early EEG showed a boundary dysfunction of activity and MRI scan of the brain was normal. The patient responded well to single anti-epileptic drug treatment. Whole-exome sequencing found a missense mutation of SIK1 gene (c.880G > A chr21: 43,420,326 p. A294T). Dysregulated transcriptome and metabolome in cell models expressing WT and MUT SIK1 confirmed the pathogenicity of the mutation. Specifically, we found MEF2C target genes, certain epilepsy causing genes and metabolites are dysregulated by SIK1 mutation. We found MEF2C target genes, certain epilepsy causing genes and metabolites are dysregulated by SIK1 mutation. Our finding further expanded the disease spectrum and provided novel mechanistic insights of DEE30.

Metabonomic analysis of cerebrospinal fluid in epilepsy

Background

We sought to explore the relationship between epilepsy and cerebrospinal fluid metabolomics and identify biomarkers for the diagnosis, treatment, and prognosis of epilepsy.

Methods

In total, 23 epileptic patients treated at The First Affiliated Hospital of Dalian Medical University from April 2019 to September 2019 were selected for the disease group and 13 non-epileptic patients were selected for the control group. Cerebrospinal fluid samples were collected from both groups, and the metabolites were analyzed by gas chromatography–mass spectrometry. The metabolites differentially expressed in the cerebrospinal fluid samples were identified. A differential metabolite enrichment analysis was performed to determine the metabolic pathways.

Results

Using a variable importance in the projection value >1 and a P value <0.05 as the screening criteria, we found that 3 metabolites (i.e., alpha-ketoisocaproic acid 1, xylose 1, and glycine 2) were differentially expressed in the cerebrospinal fluid of the 23 epileptic patients compared to the 13 non-epileptic patients. Alpha-ketoisocaproic acid 1 and xylose 1 were highly expressed in the epileptic cerebrospinal fluid samples, while glycine 2 was lowly expressed in the epileptic cerebrospinal fluid samples. Additionally, the 3 metabolites were significantly enriched in the 5 metabolic pathways of primary bile acid biosynthesis, valine, leucine, and isoleucine degradation, glutathione metabolism, glyoxylate and dicarboxylate metabolism, and glycine, serine, and threonine metabolism.

Conclusions

The present study examined the metabolites of the cerebrospinal fluid of epileptic patients and non-epileptic patients. Our findings provide insights that may inform the discovery of therapeutic targets and diagnostic markers for epilepsy.

Modeling Epilepsy Using Human Induced Pluripotent Stem Cells-Derived Neuronal Cultures Carrying Mutations in Ion Channels and the Mechanistic Target of Rapamycin Pathway

Epilepsy is a neurological disorder that affects over 65 million people globally. It is characterized by periods of seizure activity of the brain as a result of excitation and inhibition (E/I) imbalance, which is regarded as the core underpinning of epileptic activity. Both gain- and loss-of-function (GOF and LOF) mutations of ion channels, synaptic proteins and signaling molecules along the mechanistic target of rapamycin (mTOR) pathway have been linked to this imbalance. The pathogenesis of epilepsy often has its roots in the early stage of brain development. It remains a major challenge to extrapolate the findings from many animal models carrying these GOF or LOF mutations to the understanding of disease mechanisms in the developing human brain. Recent advent of the human pluripotent stem cells (hPSCs) technology opens up a new avenue to recapitulate patient conditions and to identify druggable molecular targets. In the following review, we discuss the progress, challenges and prospects of employing hPSCs-derived neural cultures to study epilepsy. We propose a tentative working model to conceptualize the possible impact of these GOF and LOF mutations in ion channels and mTOR signaling molecules on the morphological and functional remodeling of intrinsic excitability, synaptic transmission and circuits, ultimately E/I imbalance and behavioral phenotypes in epilepsy.

Unifying mechanism behind the onset of acquired epilepsy

Acquired epilepsy (AE) can result from a number of brain insults and neurological diseases with wide etiological diversity sharing one common outcome of brain epileptiform activity. This implies that despite their disparity, all these initiating pathologies affect the same fundamental brain functions underlying network excitability. Identifying such mechanisms and their availability as therapeutic targets would help develop an effective strategy for epileptogenesis prevention. In this opinion article, we propose that the vicious cycle of NADPH oxidase (NOX)-mediated oxidative stress and glucose hypometabolism is the underlying cause of AE, as available data reveal a critical role for both pathologies in epileptogenesis and the process of seizure initiation. Altogether, here we present a novel view on the mechanisms behind the onset of AE and identify therapeutic targets for potential clinical applications.

Generation and Characterization of the Drosophila melanogaster paralytic Gene Knock-Out as a Model for Dravet Syndrome

Dravet syndrome is a severe rare epileptic disease caused by mutations in the SCN1A gene coding for the Nav1.1 protein, a voltage-gated sodium channel alpha subunit. We have made a knock-out of the paralytic gene, the single Drosophila melanogaster gene encoding this type of protein, by homologous recombination. These flies showed a heat-induced seizing phenotype, and sudden death in long term seizures. In addition to seizures, neuromuscular alterations were observed in climbing, flight, and walking tests. Moreover, they also manifested some cognitive alterations, such as anxiety and problems in learning. Electrophysiological analyses from larval motor neurons showed a decrease in cell capacitance and membrane excitability, while persistent sodium current increased. To detect alterations in metabolism, we performed an NMR metabolomic profiling of heads, which revealed higher levels in some amino acids, succinate, and lactate; and also an increase in the abundance of GABA, which is the main neurotransmitter implicated in Dravet syndrome. All these changes in the paralytic knock-out flies indicate that this is a good model for epilepsy and specifically for Dravet syndrome. This model could be a new tool to understand the pathophysiology of the disease and to find biomarkers, genetic modifiers and new treatments.

Experimental Epileptogenesis in a Cell Culture Model of Primary Neurons from Rat Brain: A Temporal Multi-Scale Study

Understanding seizure development requires an integrated knowledge of different scales of organization of epileptic networks. We developed a model of “epilepsy-in-a-dish” based on dissociated primary neuronal cells from neonatal rat hippocampus. We demonstrate how a single application of glutamate stimulated neurons to generate spontaneous synchronous spiking activity with further progression into spontaneous seizure-like events after a distinct latency period. By computational analysis, we compared the observed neuronal activity in vitro with intracranial electroencephalography (EEG) data recorded from epilepsy patients and identified strong similarities, including a related sequence of events with defined onset, progression, and termination. Next, a link between the neurophysiological changes with network composition and cellular structure down to molecular changes was established. Temporal development of epileptiform network activity correlated with increased neurite outgrowth and altered branching, increased ratio of glutamatergic over GABAergic synapses, and loss of calbindin-positive interneurons, as well as genome-wide alterations in DNA methylation. Differentially methylated genes were engaged in various cellular activities related to cellular structure, intracellular signaling, and regulation of gene expression. Our data provide evidence that a single short-term excess of glutamate is sufficient to induce a cascade of events covering different scales from molecule- to network-level, all of which jointly contribute to seizure development.

Spatio-temporal heterogeneity in hippocampal metabolism in control and epilepsy conditions

The hippocampus's dorsal and ventral parts are involved in different operative circuits, the functions of which vary in time during the night and day cycle. These functions are altered in epilepsy. Since energy production is tailored to function, we hypothesized that energy production would be space- and time-dependent in the hippocampus and that such an organizing principle would be modified in epilepsy. Using metabolic imaging and metabolite sensing ex vivo, we show that the ventral hippocampus favors aerobic glycolysis over oxidative phosphorylation as compared to the dorsal part in the morning in control mice. In the afternoon, aerobic glycolysis is decreased and oxidative phosphorylation increased. In the dorsal hippocampus, the metabolic activity varies less between these two times but is weaker than in the ventral. Thus, the energy metabolism is different along the dorsoventral axis and changes as a function of time in control mice. In an experimental model of epilepsy, we find a large alteration of such spatiotemporal organization. In addition to a general hypometabolic state, the dorsoventral difference disappears in the morning, when seizure probability is low. In the afternoon, when seizure probability is high, the aerobic glycolysis is enhanced in both parts, the increase being stronger in the ventral area. We suggest that energy metabolism is tailored to the functions performed by brain networks, which vary over time. In pathological conditions, the alterations of these general rules may contribute to network dysfunctions.

Focal corticarl dysplasia in epilepsy is associated with GABA increase

PURPOSE

Focal cortical dysplasia (FCD) is a major cause of drug-resistant epilepsy; however the underlying epileptogenic mechanisms of FCD metabolism in epilepsy patients remain unclear. The aim of this study is to detect alterations of γ-aminobutyric acid (GABA), glutathione (GSH), and the composite of glutamate and glutamine (Glx) in MRI-typical and neuropathologically confirmed FCD-associated epilepsy using Hadamard Encoding and Reconstruction of Mega-Edited Spectroscopy (HERMES).

MATERIALS AND METHODS

Fourteen epileptic patients suspected to be caused by FCD and 14 healthy controls were enrolled prospectively in this study; all subjects underwent a 3 T MRI scan, including 3D T1 weighted imaging and HERMES. The GABA signal detected by HERMES also contains signals from macromolecules and homocarnosine, so it is referred as GABA+. Signals of GABA+, GSH and Glx detected by HERMES from tumor foci, contralateral cerebral regions, and healthy controls were quantified using Gannet. Fitting errors and signal to noise ratios (SNRs) of GABA + signals were also recorded. Differences of GABA+, GSH, Glx, fitting error and SNR of GABA + among three groups were analyzed using linear mixed effects models.

RESULTS

Twelve FCD-associated epilepsy patients (7 females, aged 21.9 ± 9.3 years) and 12 matched healthy controls (7 females, aged 22.8 ± 9.8 years) were finally enrolled in this study. ANOVA results indicated that GABA levels were significantly increased in FCD foci compared with contralateral regions (p = 0.008) and with healthy controls (p = 0.003), while no difference was found in GSH and Glx levels. No difference of fitting errors or SNR of GABA + was found among FCD foci, contralateral regions and healthy controls.

CONCLUSIONS

Increased GABA levels were found in FCD foci that indicated GABA may play a central role in the pathophysiology of FCD patients with epilepsy.

Metabolomic signature of the Dravet syndrome: A genetic mouse model study

OBJECTIVE

Alterations in metabolic homeostasis can contribute to neuronal hyperexcitability and seizure susceptibility. Although the pivotal role of impaired bioenergetics is obvious in metabolic epilepsies, there is a gap of knowledge regarding secondary changes in metabolite patterns as a result of genetic Scn1a deficiency and ketogenic diet in the Dravet syndrome.

METHODS

A comprehensive untargeted metabolomics analysis, along with assessment of epileptiform activity and behavioral tests, was completed in a Dravet mouse model. Data sets were compared between animals on a control and a ketogenic diet, and metabolic alterations associated with Dravet mice phenotype and ketogenic diet were identified.

RESULTS

Hippocampal metabolomic data revealed complex alterations in energy metabolism with an effect of the genotype on concentrations of glucose and several glycolysis and tricarboxylic acid (TCA) cycle intermediates. Although low glucose, lactate, malate, and citrate concentrations became evident, the increase of several intermediates suggested a genotype-associated activation of catabolic processes with enhanced glycogenolysis and glycolysis. Moreover, we observed an impact on the glutamate/γ-aminobutyric acid (GABA)-glutamine cycle with reduced levels of all components along with a shift toward an increased GABA-to-glutamate ratio. Further alterations comprised a reduction in hippocampal levels of noradrenaline, corticosterone, and of two bile acids.

SIGNIFICANCE

Considering that energy depletion can predominantly compromise the function of GABAergic interneurons, the changes in energy metabolism may contribute to seizure susceptibility and ictogenesis. They may also explain the therapeutic potential of the ketogenic diet, which aims to shift energy metabolism toward a more fat-based energy supply. Conversely, the increased GABA-to-glutamate ratio might serve as an endogenous compensatory mechanism, which can be further supported by GABAergic drugs, representing the mainstay of therapeutic management of Dravet syndrome. In view of a possible neuroprotective function of bile acids, it might be of interest to explore a possible therapeutic potential of bile acid-mediated therapies, already in discussion for neurodegenerative disorders.

Enhancing glucose metabolism via gluconeogenesis is therapeutic in a zebrafish model of Dravet syndrome

Energy-producing pathways are novel therapeutic targets for the treatment of neurodevelopmental disorders. Here, we focussed on correcting metabolic defects in a catastrophic paediatric epilepsy, Dravet syndrome which is caused by mutations in sodium channel NaV1.1 gene, SCN1A. We utilized a translatable zebrafish model of Dravet syndrome (scn1lab) which exhibits key characteristics of patients with Dravet syndrome and shows metabolic deficits accompanied by down-regulation of gluconeogenesis genes, pck1 and pck2. Using a metabolism-based small library screen, we identified compounds that increased gluconeogenesis via up-regulation of pck1 gene expression in scn1lab larvae. Treatment with PK11195, a pck1 activator and a translocator protein ligand, normalized dys-regulated glucose levels, metabolic deficits, translocator protein expression and significantly decreased electrographic seizures in mutant larvae. Inhibition of pck1 in wild-type larvae mimicked metabolic and behaviour defects observed in scn1lab mutants. Together, this suggests that correcting dys-regulated metabolic pathways can be therapeutic in neurodevelopmental disorders such as Dravet syndrome arising from ion channel dysfunction.

Metabolic Control of Epilepsy: A Promising Therapeutic Target for Epilepsy

Epilepsy is a common neurological disease that is not always controlled, and the ketogenic diet shows good antiepileptic effects drug-resistant epilepsy or seizures caused by specific metabolic defects via regulating the metabolism. The brain is a vital organ with high metabolic demands, and epileptic foci tend to exhibit high metabolic characteristics. Accordingly, there has been growing interest in the relationship between brain metabolism and epilepsy in recent years. To date, several new antiepileptic therapies targeting metabolic pathways have been proposed (i.e., inhibiting glycolysis, targeting lactate dehydrogenase, and dietary therapy). Promising strategies to treat epilepsy via modulating the brain's metabolism could be expected, while a lack of thorough understanding of the role of brain metabolism in the control of epilepsy remains. Herein, this review aims to provide insight into the state of the art concerning the brain's metabolic patterns and their association with epilepsy. Regulation of neuronal excitation via metabolic pathways and antiepileptic therapies targeting metabolic pathways are emphasized, which could provide a better understanding of the role of metabolism in epilepsy and could reveal potential therapeutic targets.

Variability of seizure-like activity in an in vitro model of epilepsy depends on the electrical recording method

Background

Hippocampal and cortical slice-based models are widely used to study seizures and epilepsy. Seizure detection and quantification are essential components for studying mechanisms of epilepsy and assessing therapeutic interventions. To obtain meaningful signals and maximize experimental throughput, variability should be minimized. Some electrical recording methods require insertion of an electrode into neuronal tissue, change in slice chemical microenvironment, and transients in temperature and pH. These perturbations can cause acute and long-term alterations of the neuronal network which may be reflected in the variability of the recorded signal.

New method

In this study we investigated the effect of experimental perturbations in three local field potential (LFP) recording methods including substrate micro-wires (s-MWs), multiple electrode arrays (MEAs), and inserted micro wire electrodes (i-MW). These methods enabled us to isolate effects of different perturbations. We used organotypic hippocampal slices (OHCs) as an in-vitro model of posttraumatic epilepsy. To investigate the effect of the disturbances caused by the recording method on the paroxysmal events, we introduced jitter analysis, which is sensitive to small differences in the seizure spike timing.

Results

Medium replacement can introduce long-lasting perturbations. Electrode insertion increased variability on a shorter time scale. OHCs also underwent spontaneous state transitions characterized by transient increases in variability.

Comparison with existing methods

This new method of seizure waveform analysis allows for more sensitive assessment of variability of ictal events than simply measuring seizure frequency and duration.

Conclusion

We demonstrated that some of the variability in OHC recordings are due to experimental perturbations while some are spontaneous and independent of recording method.

Glucose-Sparing Action of Ketones Boosts Functions Exclusive to Glucose in the Brain

The ketogenic diet (KD) has been successfully used for a century for treating refractory epilepsy and is currently seen as one of the few viable approaches to the treatment of a plethora of metabolic and neurodegenerative diseases. Empirical evidence notwithstanding, there is still no universal understanding of KD mechanism(s). An important fact is that the brain is capable of using ketone bodies for fuel. Another critical point is that glucose's functions span beyond its role as an energy substrate, and in most of these functions, glucose is irreplaceable. By acting as a supplementary fuel, ketone bodies may free up glucose for its other crucial and exclusive function. We propose that this glucose-sparing effect of ketone bodies may underlie the effectiveness of KD in epilepsy and major neurodegenerative diseases, which are all characterized by brain glucose hypometabolism.

In vivo assessment of mechanisms underlying the neurovascular basis of postictal amnesia

Long-lasting confusion and memory difficulties during the postictal state remain a major unmet problem in epilepsy that lacks pathophysiological explanation and treatment. We previously identified that long-lasting periods of severe postictal hypoperfusion/hypoxia, not seizures per se, are associated with memory impairment after temporal lobe seizures. While this observation suggests a key pathophysiological role for insufficient energy delivery, it is unclear how the networks that underlie episodic memory respond to vascular constraints that ultimately give rise to amnesia. Here, we focused on cellular/network level analyses in the CA1 of hippocampus in vivo to determine if neural activity, network oscillations, synaptic transmission, and/or synaptic plasticity are impaired following kindled seizures. Importantly, the induction of severe postictal hypoperfusion/hypoxia was prevented in animals treated by a COX-2 inhibitor, which experimentally separated seizures from their vascular consequences. We observed complete activation of CA1 pyramidal neurons during brief seizures, followed by a short period of reduced activity and flattening of the local field potential that resolved within minutes. During the postictal state, constituting tens of minutes to hours, we observed no changes in neural activity, network oscillations, and synaptic transmission. However, long-term potentiation of the temporoammonic pathway to CA1 was impaired in the postictal period, but only when severe local hypoxia occurred. Lastly, we tested the ability of rats to perform object-context discrimination, which has been proposed to require temporoammonic input to differentiate between sensory experience and the stored representation of the expected object-context pairing. Deficits in this task following seizures were reversed by COX-2 inhibition, which prevented severe postictal hypoxia. These results support a key role for hypoperfusion/hypoxia in postictal memory impairments and identify that many aspects of hippocampal network function are resilient during severe hypoxia except for long-term synaptic plasticity.

Epilepsy Benchmarks Area II: Prevent Epilepsy and Its Progression

Area II of the 2014 Epilepsy Research Benchmarks aims to establish goals for preventing the development and progression of epilepsy. In this review, we will highlight key advances in Area II since the last summary of research progress and opportunities was published in 2016. We also highlight areas of investigation that began to develop before 2016 and in which additional progress has been made more recently.

Mom Controls the Thermostat: Mitochondria Influence the Neuronal Firing Set Point

Mitochondrial Regulation of the Hippocampal Firing Rate Set Point and Seizure Susceptibility

Styr B, Gonen N, Zarhin D, Ruggiero A, Atsmon R, Gazit N, Braun G, Frere S, Vertkin I, Shapira I, Harel M, Heim LR, Katsenelson M, Rechnitz O, Fadila S, Derdikman D, Rubinstein M, Geiger T, Ruppin E, Slutsky I. Neuron. 2019. pii: S0896-6273(19)30334-4. doi:10.1016/j.neuron.2019.03.045. [Epub ahead of print] PMID: 31047779.

Maintaining average activity within a set-point range constitutes a fundamental property of central neural circuits. However, whether and how activity set points are regulated remains unknown. Integrating genome-scale metabolic modeling and experimental study of neuronal homeostasis, we identified mitochondrial dihydroorotate dehydrogenase (DHODH) as a regulator of activity set points in hippocampal networks. The DHODH inhibitor teriflunomide stably suppressed mean firing rates via synaptic and intrinsic excitability mechanisms by modulating mitochondrial Ca2+ buffering and spare respiratory capacity. Bidirectional activity perturbations under DHODH blockade triggered firing rate compensation, while stabilizing firing to the lower level, indicating a change in the firing rate set point. In vivo, teriflunomide decreased CA3–CA1 synaptic transmission and CA1 mean firing rate and attenuated susceptibility to seizures, even in the intractable Dravet syndrome epilepsy model. Our results uncover mitochondria as a key regulator of activity set points, demonstrate the differential regulation of set points and compensatory mechanisms, and propose a new strategy to treat epilepsy.

Pediatric Epilepsy Mechanisms: Expanding the Paradigm of Excitation/Inhibition Imbalance

Mechanisms underlying seizures and epilepsy have traditionally been considered to involve abnormalities of ion channels or synaptic function. Those considerations gave rise to the excitation/inhibition (E/I) imbalance theory, whereby increased excitation, decreased inhibition, or both favor a hyperexcitable state and an increased propensity for seizure generation and epileptogenesis. Several recent findings warrant reconsideration and expansion of the E/I hypothesis: novel genetic mutations have been identified that do not overtly affect E/I balance; neurotransmitters may exert paradoxical effects, especially during development; anti-seizure medications do not necessarily work by decreasing excitation or increasing inhibition; and metabolic factors participate in the regulation of neuronal and network excitability. These novel conceptual and experimental advances mandate expansion of the E/I paradigm, with the expectation that new and exciting therapies will emerge from this broadened understanding of how seizures and epilepsy arise and progress.