A novel, noninvasive, predictive epilepsy biomarker with clinical potential

Identification of common core ion channel genes in epilepsy and Alzheimer's disease

BACKGROUND

Although available literature indicates that the incidence of dementia in the epilepsy population and the risk of seizures in the Alzheimer's disease (AD) population are high, the specific genetic risk factors and the interaction mechanism are unclear, rendering rational genetic interpretation rather challenging.

AIMS

Our work aims to identify the common core ion channel genes in epilepsy and AD.

METHODS

In this study, we first integrated gene expression omnibus datasets (GSE48350 and GSE6834) on AD and epilepsy to identify differentially expressed genes (DEGs), performing Gene Ontology function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs. The related protein-protein interaction (PPI) network was constructed for DEGs, and the hub gene was evaluated.

RESULTS

A total of 2800 and 35 genes were identified in GSE48350 and GSE6834, and 12 DEGs were significantly differentially expressed between the datasets. KEGG pathway analysis showed that DEGs were primarily enriched in glutamatergic synapse and dopaminergic synapse pathways. SCN2A, GRIA1, and KCNJ9 were the hub genes with high connectivity.

CONCLUSIONS

The findings suggest that the three genes, SCN2A, GRIA1, and KCNJ9, may serve as potential targets for treating AD comorbid with epilepsy.

Serum concentration of high-mobility group box 1, Toll-like receptor 4 as biomarker in epileptic patients

Epilepsy is one of the most common neurological diseases with severe outcome. High-mobility Group Box 1/Toll-like Receptor 4 axis is proposed to participate in the epileptogenesis and correlate with seizure severity in animal models. To explore whether HMGB1 and TLR4 could serve as clinical biomarkers in epileptic patients, we recruited a total of 72 epilepsy patients and measured the serum level of HMGB1 and TLR4 by flow fluorescence technology and ELISA respectively. We found that the serum levels of HMGB1 and TLR4 were elevated in epileptic patients. The serum levels of HMGB1 and TLR4 were also significantly higher in drug-resistant group compared with drug-effective group. There was a positive linear correlation between HMGB1 and TLR4 in the study group (R2 = 0.479). The HMGB1 level was found to be related to seizures frequency (F = 6.71, P = 0.012), the duration of disease (F = 6.55, P = 0.013) and drug reactivity (F = 3.96, P = 0.024) in epileptic patients, while TLR4 level was related to seizures frequency (F = 4.68, P = 0.034) and drug reactivity (F = 3.80, P = 0.027). Our result provides experimental evidences that the expression of HMGB1 and TLR4 was correlated with clinical symptom in epileptic patients, which could be used as clinical biomarkers to monitor therapeutic effect.

Vascular topology and blood flow are acutely impacted by experimental febrile status epilepticus

Febrile status epilepticus (FSE) is an important risk factor for temporal lobe epilepsy and early identification of those at high risk for epilepsy is vital. In a rat model of FSE, we identified an acute (2 hrs) novel MRI signal where reduced T2 relaxation values in the basolateral amygdala (BLA) predicted epilepsy in adulthood; this T2 signal remains incompletely understood and we hypothesized that it may be influenced by vascular topology. Experimental FSE induced in rat pups reduced blood vessel density of the cortical vasculature in a lateralized manner at 2 hrs post FSE. Middle cerebral artery (MCA) exhibited abnormal topology in FSE pups but not in controls. In the BLA, significant vessel junction reductions and decreased vessel diameter were observed, together with a strong trend for reduced vessel length. Perfusion weighted MRI (PWI) was acutely increased cerebral blood flow (CBF) in cortex, amygdala and hippocampus of FSE pups that correlated to decreased T2 relaxation values compared to controls. This is consistent with increased levels of deoxyhemoglobin associated with increased metabolic demand. In summary, FSE acutely modifies vascular topological and CBF in cortex and BLA that may underlie acute MRI signal changes that predict progression to future epilepsy.

Human herpesvirus 6 DNA was not detected in a brain specimen from a patient with mesial temporal sclerosis after status epilepticus due to human herpesvirus 6 infection

We performed virological analysis of resected brain tissues from a patient with temporal lobe epilepsy associated with mesial temporal sclerosis after febrile status epilepticus caused by human herpesvirus 6 infection. The patient had febrile status epilepticus at 9 months of age associated with human herpesvirus 6 infection. Magnetic resonance imaging revealed reduced water diffusion in the right temporal lobe and hippocampus. Polymerase chain reaction analysis detected 1.6 × 10⁵ copies/μg of human herpesvirus 6 DNA in whole blood, but none in the cerebrospinal fluid. The patient developed temporal lobe epilepsy associated with mesial temporal sclerosis at 67 months of age, necessitating surgical treatment. Anterior temporal lobectomy was performed at 171 months of age. Real-time polymerase chain reaction analysis of resected brain tissues revealed no viral DNA. In our patient, human herpesvirus 6 infection triggered febrile status epilepticus, while direct evidence to prove contribution of HHV-6 to the development of MTS was not obtained.

Recent Developments in Diagnosis of Epilepsy: Scope of MicroRNA and Technological Advancements

Epilepsy is one of the most common neurological disorders, characterized by recurrent seizures, resulting from abnormally synchronized episodic neuronal discharges. Around 70 million people worldwide are suffering from epilepsy. The available antiepileptic medications are capable of controlling seizures in around 60-70% of patients, while the rest remain refractory. Poor seizure control is often associated with neuro-psychiatric comorbidities, mainly including memory impairment, depression, psychosis, neurodegeneration, motor impairment, neuroendocrine dysfunction, etc., resulting in poor prognosis. Effective treatment relies on early and correct detection of epileptic foci. Although there are currently a few well-established diagnostic techniques for epilepsy, they lack accuracy and cannot be applied to patients who are unsupportive or harbor metallic implants. Since a single test result from one of these techniques does not provide complete information about the epileptic foci, it is necessary to develop novel diagnostic tools. Herein, we provide a comprehensive overview of the current diagnostic tools of epilepsy, including electroencephalography (EEG) as well as structural and functional neuroimaging. We further discuss recent trends and advances in the diagnosis of epilepsy that will enable more effective diagnosis and clinical management of patients.

Repeated hippocampal seizures lead to brain-wide reorganization of circuits and seizure propagation pathways

Repeated seizure activity can lead to long-term changes in seizure dynamics and behavior. However, resulting changes in brain-wide dynamics remain poorly understood. This is due partly to technical challenges in precise seizure control and in vivo whole-brain mapping of circuit dynamics. Here, we developed an optogenetic kindling model through repeated stimulation of ventral hippocampal CaMKII neurons in adult rats. We then combined fMRI with electrophysiology to track brain-wide circuit dynamics resulting from non-afterdischarge (AD)-generating stimulations and individual convulsive seizures. Kindling induced widespread increases in non-AD-generating stimulation response and ipsilateral functional connectivity and elevated anxiety. Individual seizures in kindled animals showed more significant increases in brain-wide activity and bilateral functional connectivity. Onset time quantification provided evidence for kindled seizure propagation from the ipsilateral to the contralateral hemisphere. Furthermore, a core of slow-migrating hippocampal activity was identified in both non-kindled and kindled seizures, revealing a novel mechanism of seizure sustainment and propagation.

Update on the Neuroimaging and Electroencephalographic Biomarkers of Epileptogenesis: A Literature Review

Epilepsy is one of the most common debilitating neurological disorders that lead to severe socio-cognitive dysfunction. While there are currently more than 30 antiseizure medications available for the treatment and prevention of seizures, none address the prevention of epileptogenesis that leading to the development of epilepsy following a potential brain insult. Hence, there is a growing need for the identification of accurate biomarkers of epileptogenesis that enable the prediction of epilepsy following a known brain insult. Although recent studies using various neuroimages and electroencephalography have found promising biomarkers of epileptogenesis, their utility needs to be further validated in larger clinical trials. In this literature review, we searched the Medline, Pubmed, and Embase databases using the following search algorithm: "epileptogenesis" and "biomarker" and "EEG" or "electroencephalography" or "neuroimaging" limited to publications in English. We presented a comprehensive overview of recent innovations in the role of neuroimaging and EEG in identifying reliable biomarkers of epileptogenesis.

New approaches for developing multi-targeted drug combinations for disease modification of complex brain disorders. Does epilepsy prevention become a realistic goal?

Over decades, the prevailing standard in drug discovery was the concept of designing highly selective compounds that act on individual drug targets. However, more recently, multi-target and combinatorial drug therapies have become an important treatment modality in complex diseases, including neurodegenerative diseases such as Alzheimer's and Parkinson's disease. The development of such network-based approaches is facilitated by the significant advance in our understanding of the pathophysiological processes in these and other complex brain diseases and the adoption of modern computational approaches in drug discovery and repurposing. However, although drug combination therapy has become an effective means for the symptomatic treatment of many complex diseases, the holy grail of identifying clinically effective disease-modifying treatments for neurodegenerative and other brain diseases remains elusive. Thus, despite extensive research, there remains an urgent need for novel treatments that will modify the progression of the disease or prevent its development in patients at risk. Here we discuss recent approaches with a focus on multi-targeted drug combinations for prevention or modification of epilepsy. Over the last ~10 years, several novel promising multi-targeted therapeutic approaches have been identified in animal models. We envision that synergistic combinations of repurposed drugs as presented in this review will be demonstrated to prevent epilepsy in patients at risk within the next 5-10 years.

Identification of clinically relevant biomarkers of epileptogenesis - a strategic roadmap

Onset of many forms of epilepsy occurs after an initial epileptogenic insult or as a result of an identified genetic defect. Given that the precipitating insult is known, these epilepsies are, in principle, amenable to secondary prevention. However, development of preventive treatments is difficult because only a subset of individuals will develop epilepsy and we cannot currently predict which individuals are at the highest risk. Biomarkers that enable identification of these individuals would facilitate clinical trials of potential anti-epileptogenic treatments, but no such prognostic biomarkers currently exist. Several putative molecular, imaging, electroencephalographic and behavioural biomarkers of epileptogenesis have been identified, but clinical translation has been hampered by fragmented and poorly coordinated efforts, issues with inter-model reproducibility, study design and statistical approaches, and difficulties with validation in patients. These challenges demand a strategic roadmap to facilitate the identification, characterization and clinical validation of biomarkers for epileptogenesis. In this Review, we summarize the state of the art with respect to biomarker research in epileptogenesis and propose a five-phase roadmap, adapted from those developed for cancer and Alzheimer disease, that provides a conceptual structure for biomarker research.

Multiple Disruptions of Glial-Neuronal Networks in Epileptogenesis That Follows Prolonged Febrile Seizures

Background and Rationale: Bi-directional neuronal-glial communication is a critical mediator of normal brain function and is disrupted in the epileptic brain. The potential role of aberrant microglia and astrocyte function during epileptogenesis is important because the mediators involved provide tangible targets for intervention and prevention of epilepsy. Glial activation is intrinsically involved in the generation of childhood febrile seizures (FS), and prolonged FS (febrile status epilepticus, FSE) antecede a proportion of adult temporal lobe epilepsy (TLE). Because TLE is often refractory to treatment and accompanied by significant memory and emotional difficulties, we probed the role of disruptions of glial-neuronal networks in the epileptogenesis that follows experimental FSE (eFSE).

Methods: We performed a multi-pronged examination of neuronal-glia communication and the resulting activation of molecular signaling cascades in these cell types following eFSE in immature mice and rats. Specifically, we examined pathways involving cytokines, microRNAs, high mobility group B-1 (HMGB1) and the prostaglandin E2 signaling. We aimed to block epileptogenesis using network-specific interventions as well as via a global anti-inflammatory approach using dexamethasone.

Results: (A) eFSE elicited a strong inflammatory response with rapid and sustained upregulation of pro-inflammatory cytokines. (B) Within minutes of the end of the eFSE, HMGB1 translocated from neuronal nuclei to dendrites, en route to the extracellular space and glial Toll-like receptors. Administration of an HMGB1 blocker to eFSE rat pups did not decrease expression of downstream inflammatory cascades and led to unacceptable side effects. (C) Prolonged seizure-like activity caused overall microRNA-124 (miR-124) levels to plunge in hippocampus and release of this microRNA from neurons via extra-cellular vesicles. (D) Within hours of eFSE, structural astrocyte and microglia activation was associated not only with cytokine production, but also with activation of the PGE₂ cascade. However, administration of TG6-10-1, a blocker of the PGE₂ receptor EP2 had little effect on spike-series provoked by eFSE. (E) In contrast to the failure of selective interventions, a 3-day treatment of eFSE–experiencing rat pups with the broad anti-inflammatory drug dexamethasone attenuated eFSE-provoked pro-epileptogenic EEG changes.

Conclusions: eFSE, a provoker of TLE-like epilepsy in rodents leads to multiple and rapid disruptions of interconnected glial-neuronal networks, with a likely important role in epileptogenesis. The intricate, cell-specific and homeostatic interplays among these networks constitute a serious challenge to effective selective interventions that aim to prevent epilepsy. In contrast, a broad suppression of glial-neuronal dysfunction holds promise for mitigating FSE-induced hyperexcitability and epileptogenesis in experimental models and in humans.

Augmented seizure susceptibility and hippocampal epileptogenesis in a translational mouse model of febrile status epilepticus

OBJECTIVE

Prolonged fever-induced seizures (febrile status epilepticus [FSE]) during early childhood increase the risk for later epilepsy, but the underlying mechanisms are incompletely understood. Experimental FSE (eFSE) in rats successfully models human FSE, recapitulating the resulting epileptogenesis in a subset of affected individuals. However, the powerful viral and genetic tools that may enhance mechanistic insights into epileptogenesis and associated comorbidities, are better-developed for mice. Therefore, we aimed to determine if eFSE could be generated in mice and if it provoked enduring changes in hippocampal-network excitability and the development of spontaneous seizures.

METHODS

We employed C57BL/6J male mice, the strain used most commonly in transgenic manipulations, and examined if early life eFSE could be sustained and if it led to hyperexcitability of hippocampal networks and to epilepsy. Outcome measures included vulnerability to the subsequent administration of the limbic convulsant kainic acid (KA) and the development of spontaneous seizures. In the first mouse cohort, adult naive and eFSE-experiencing mice were exposed to KA. A second cohort of control and eFSE-experiencing young adult mice was implanted with bilateral hippocampal electrodes and recorded using continuous video-electroencephalography (EEG) for 2 to 3 months to examine for spontaneous seizures (epileptogenesis).

RESULTS

Induction of eFSE was feasible and eFSE increased the susceptibility of adult C57BL/6J mice to KA, thereby reducing latency to seizure onset and increasing seizure severity. Of 24 chronically recorded eFSE mice, 4 (16.5%) developed hippocampal epilepsy with a latent period of ~3 months, significantly different from the expectation by chance (P = .04). The limbic epilepsy that followed eFSE was progressive.

SIGNIFICANCE

eFSE promotes pro-epileptogenic network changes in a majority of C57BL/6J male mice and frank "temporal lobe-like" epilepsy in one sixth of the cohort. Mouse eFSE may thus provide a useful tool for investigating molecular, cellular, and circuit changes during the development of temporal lobe epilepsy and its comorbidities.

High Mobility Group Box-1 and Blood-Brain Barrier Disruption

Increasing evidence suggests that inflammatory responses are involved in the progression of brain injuries induced by a diverse range of insults, including ischemia, hemorrhage, trauma, epilepsy, and degenerative diseases. During the processes of inflammation, disruption of the blood–brain barrier (BBB) may play a critical role in the enhancement of inflammatory responses and may initiate brain damage because the BBB constitutes an interface between the brain parenchyma and the bloodstream containing blood cells and plasma. The BBB has a distinct structure compared with those in peripheral tissues: it is composed of vascular endothelial cells with tight junctions, numerous pericytes surrounding endothelial cells, astrocytic endfeet, and a basement membrane structure. Under physiological conditions, the BBB should function as an important element in the neurovascular unit (NVU). High mobility group box-1 (HMGB1), a nonhistone nuclear protein, is ubiquitously expressed in almost all kinds of cells. HMGB1 plays important roles in the maintenance of chromatin structure, the regulation of transcription activity, and DNA repair in nuclei. On the other hand, HMGB1 is considered to be a representative damage-associated molecular pattern (DAMP) because it is translocated and released extracellularly from different types of brain cells, including neurons and glia, contributing to the pathophysiology of many diseases in the central nervous system (CNS). The regulation of HMGB1 release or the neutralization of extracellular HMGB1 produces beneficial effects on brain injuries induced by ischemia, hemorrhage, trauma, epilepsy, and Alzheimer’s amyloidpathy in animal models and is associated with improvement of the neurological symptoms. In the present review, we focus on the dynamics of HMGB1 translocation in different disease conditions in the CNS and discuss the functional roles of extracellular HMGB1 in BBB disruption and brain inflammation. There might be common as well as distinct inflammatory processes for each CNS disease. This review will provide novel insights toward an improved understanding of a common pathophysiological process of CNS diseases, namely, BBB disruption mediated by HMGB1. It is proposed that HMGB1 might be an excellent target for the treatment of CNS diseases with BBB disruption.

Genome-wide microRNA profiling of plasma from three different animal models identifies biomarkers of temporal lobe epilepsy

Epilepsy diagnosis is complex, requires a team of specialists and relies on in-depth patient and family history, MRI-imaging and EEG monitoring. There is therefore an unmet clinical need for a non-invasive, molecular-based, biomarker to either predict the development of epilepsy or diagnose a patient with epilepsy who may not have had a witnessed seizure. Recent studies have demonstrated a role for microRNAs in the pathogenesis of epilepsy. MicroRNAs are short non-coding RNA molecules which negatively regulate gene expression, exerting profound influence on target pathways and cellular processes. The presence of microRNAs in biofluids, ease of detection, resistance to degradation and functional role in epilepsy render them excellent candidate biomarkers. Here we performed the first multi-model, genome-wide profiling of plasma microRNAs during epileptogenesis and in chronic temporal lobe epilepsy animals. From video-EEG monitored rats and mice we serially sampled blood samples and identified a set of dysregulated microRNAs comprising increased miR-93-5p, miR-142-5p, miR-182-5p, miR-199a-3p and decreased miR-574-3p during one or both phases. Validation studies found miR-93-5p, miR-199a-3p and miR-574-3p were also dysregulated in plasma from patients with intractable temporal lobe epilepsy. Treatment of mice with common anti-epileptic drugs did not alter the expression levels of any of the five miRNAs identified, however administration of an anti-epileptogenic microRNA treatment prevented dysregulation of several of these miRNAs. The miRNAs were detected within the Argonuate2-RISC complex from both neurons and microglia indicating these miRNA biomarker candidates can likely be traced back to specific brain cell types. The current studies identify additional circulating microRNA biomarkers of experimental and human epilepsy which may support diagnosis of temporal lobe epilepsy via a quick, cost-effective rapid molecular-based test.

Quantitative T2 MRI is predictive of neurodegeneration following organophosphate exposure in a rat model

Organophosphorus compounds, such as chemical warfare nerve agents and pesticides, are known to cause neurological damage. This study measured nerve agent-related neuropathology and determined whether quantitative T₂ MRI could be used as a biomarker of neurodegeneration. Quantitative T₂ MRI was performed using a 9.4 T MRI on rats prior to and following soman exposure. T₂ images were taken at least 24 h prior, 1 h and 18-24 h after soman exposure. Rats were pre- and post-treated with HI-6 dimethanesulfonate and atropine methyl nitrate. A multicomponent T₂ acquisition and analysis was performed. Brains were stained with Fluoro-Jade C to assess neurodegeneration. Rats exposed to soman developed behavioral expression of electrographic seizures. At 18-24 h after soman exposure, significant increases in T₂, a possible marker of edema, were found in multiple regions. The largest changes were in the piriform cortex (before: 47.7 ± 1.4 ms; 18-24 h: 82.3 ± 13.4 ms). Fluoro-Jade C staining showed significant neurodegeneration 18-24 h post exposure. The piriform cortex had the strongest correlation between the change in relaxation rate and percent neurodegeneration (r = 0.96, p < 0.001). These findings indicate there is regionally specific neurodegeneration 24 h after exposure to soman. The high correlation between T₂ relaxivity and histopathology supports the use of T₂ as a marker of injury.

Biomarkers for epileptogenesis and its treatment

There are no pharmacological interventions to prevent the development of epilepsy, although many promising compounds have been identified in the animal laboratory. Clinical trials to validate their effectiveness, however, would currently be prohibitively expensive due to the large subject population and duration of follow-up necessary. There is, therefore, the need to identify biomarkers of epileptogenesis that could identify patients at high risk for epilepsy following a potential epileptogenic insult to enrich the subject population, as well as biomarkers that could determine the effectiveness of therapeutic intervention without the need to wait for seizures to occur. Putative biomarkers under investigation for epileptogenesis and its treatment include genetic, molecular, cellular, imaging, and electrophysiological measures that might reliably predict the development or progression of an epileptic condition, the effects of antiepileptogenic treatment, or cure after surgery. To be clinically useful for most purposes, ideal biomarkers should be noninvasive, and it is anticipated that a profile of multiple biomarkers will likely be required. Ongoing animal research involves a number of experimental models of epileptogenesis, with traumatic brain injury, offering the best potential for translational clinical investigations. Collaborative and multicenter research efforts by multidisciplinary teams of basic and clinical neuroscientists with access to robust, well-defined animal models, extensive patient populations, standardized protocols, and cutting-edge analytical methodologies are likely to be most successful. Such biomarker research should also provide insights into fundamental neuronal mechanisms of epileptogenesis suggesting novel targets for antiepileptogenic treatments. 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'.

Dexamethasone Attenuates Hyperexcitability Provoked by Experimental Febrile Status Epilepticus

The role of neuroinflammation in the mechanisms of epilepsy development is important because inflammatory mediators provide tractable targets for intervention. Inflammation is intrinsically involved in the generation of childhood febrile seizures (FSs), and prolonged FS [febrile status epilepticus (FSE)] precedes a large proportion of adult cases of temporal lobe epilepsy (TLE). As TLE is often refractory to therapy and is associated with serious cognitive and emotional problems, we investigated whether its development can be prevented using anti-inflammatory strategies. Using an immature rat model of FSE [experimental FSE (eFSE)], we administered dexamethasone (DEX), a broad anti-inflammatory agent, over 3 d following eFSE. We assessed eFSE-provoked hippocampal network hyperexcitability by quantifying the presence, frequency, and duration of hippocampal spike series, as these precede and herald the development of TLE-like epilepsy. We tested whether eFSE provoked hippocampal microgliosis, astrocytosis, and proinflammatory cytokine production in male and female rats and investigated blood–brain barrier (BBB) breaches as a potential contributor. We then evaluated whether DEX attenuated these eFSE sequelae. Spike series were not observed in control rats given vehicle or DEX, but occurred in 41.6% of eFSE-vehicle rats, associated with BBB leakage and elevated hippocampal cytokines. eFSE did not induce astrocytosis or microgliosis but provoked BBB disruption in 60% of animals. DEX significantly reduced spike series prevalence (to 7.6%) and frequency, and abrogated eFSE-induced cytokine production and BBB leakage (to 20%). These findings suggest that a short, postinsult intervention with a clinically available anti-inflammatory agent potently attenuates epilepsy-predicting hippocampal hyperexcitability, potentially by minimizing BBB disruption and related neuroinflammation.

Juvenile mild traumatic brain injury elicits distinct spatiotemporal astrocyte responses

Mild-traumatic brain injury (mTBI) represents ~80% of all emergency room visits and increases the probability of developing long-term cognitive disorders in children. To date, molecular and cellular mechanisms underlying post-mTBI cognitive dysfunction are unknown. Astrogliosis has been shown to significantly alter astrocytes' properties following brain injury, potentially leading to significant brain dysfunction. However, such alterations have never been investigated in the context of juvenile mTBI (jmTBI). A closed-head injury model was used to study jmTBI on postnatal-day 17 mice. Astrogliosis was evaluated using glial fibrillary acidic protein (GFAP), vimentin, and nestin immunolabeling in somatosensory cortex (SSC), dentate gyrus (DG), amygdala (AMY), and infralimbic area (ILA) of prefrontal cortex in both hemispheres from 1 to 30 days postinjury (dpi). In vivo T2-weighted-imaging (T2WI) and diffusion tensor imaging (DTI) were performed at 7 and 30 dpi to examine tissue level structural alterations. Increased GFAP-labeling was observed up to 30 dpi in the ipsilateral SSC, the initial site of the impact. However, vimentin and nestin expression was not perturbed by jmTBI. The morphology of GFAP positive cells was significantly altered in the SSC, DG, AMY, and ILA up to 7 dpi that some correlated with magnetic resonance imaging changes. T2WI and DTI values were significantly altered at 30 dpi within these brain regions most prominently in regions distant from the impact site. Our data show that jmTBI triggers changes in astrocytic phenotype with a distinct spatiotemporal pattern. We speculate that the presence and time course of astrogliosis may contribute to pathophysiological processes and long-term structural alterations following jmTBI.

Anti-HMGB1 monoclonal antibody therapy for a wide range of CNS and PNS diseases

High mobility group box-1 (HMGB1), a representative damage associated-molecular pattern (DAMP), has been reported to be involved in many inflammatory diseases. Several drugs are thought to have potential to control the translocation and secretion of HMGB1, or to neutralize extracellular HMGB1 by binding to it. One of these drugs, anti-HMGB1 monoclonal antibody (mAb), is highly specific for HMGB1 and has been shown to be effective for the treatment of a wide range of CNS diseases when modeled in animals, including stroke, traumatic brain injury, Parkinson's disease, epilepsy and Alzheimer's disease. Thus, anti-HMGB1 mAb not only is useful for target validation but also has extensive potential for the treatment of the above-mentioned diseases. In this review, we summarize existing knowledge on the effects of anti-HMGB1 mAb on CNS and PNS diseases, the common features of translocation and secretion of HMGB1 and the functional roles of HMGB1 in these diseases. The existing literature suggests that anti-HMGB1 mAb therapy would be effective for a wide range of CNS and PNS diseases.

Neuroimaging Biomarkers of Experimental Epileptogenesis and Refractory Epilepsy

This article provides an overview of neuroimaging biomarkers in experimental epileptogenesis and refractory epilepsy. Neuroimaging represents a gold standard and clinically translatable technique to identify neuropathological changes in epileptogenesis and longitudinally monitor its progression after a precipitating injury. Neuroimaging studies, along with molecular studies from animal models, have greatly improved our understanding of the neuropathology of epilepsy, such as the hallmark hippocampus sclerosis. Animal models are effective for differentiating the different stages of epileptogenesis. Neuroimaging in experimental epilepsy provides unique information about anatomic, functional, and metabolic alterations linked to epileptogenesis. Recently, several in vivo biomarkers for epileptogenesis have been investigated for characterizing neuronal loss, inflammation, blood-brain barrier alterations, changes in neurotransmitter density, neurovascular coupling, cerebral blood flow and volume, network connectivity, and metabolic activity in the brain. Magnetic resonance imaging (MRI) is a sensitive method for detecting structural and functional changes in the brain, especially to identify region-specific neuronal damage patterns in epilepsy. Positron emission tomography (PET) and single-photon emission computerized tomography are helpful to elucidate key functional alterations, especially in areas of brain metabolism and molecular patterns, and can help monitor pathology of epileptic disorders. Multimodal procedures such as PET-MRI integrated systems are desired for refractory epilepsy. Validated biomarkers are warranted for early identification of people at risk for epilepsy and monitoring of the progression of medical interventions.

Pharmacological targeting of brain inflammation in epilepsy: Therapeutic perspectives from experimental and clinical studies

Increasing evidence supports a pathogenic role of unabated neuroinflammation in various central nervous system (CNS) diseases, including epilepsy. Neuroinflammation is not a bystander phenomenon of the diseased brain tissue, but it may contribute to neuronal hyperexcitability underlying seizure generation, cell loss, and neurologic comorbidities. Several molecules, which constitute the inflammatory milieu in the epileptogenic area, activate signaling pathways in neurons and glia resulting in pathologic modifications of cell function, which ultimately lead to alterations in synaptic transmission and plasticity. Herein we report the up-to-date experimental and clinical evidence that supports the neuromodulatory role of inflammatory mediators, their related signaling pathways, and involvement in epilepsy. We discuss how these mechanisms can be harnessed to discover and validate targets for novel therapeutics, which may prevent or control pharmacoresistant epilepsies.

Epilepsy-predictive magnetic resonance imaging changes following experimental febrile status epilepticus: Are they translatable to the clinic?

OBJECTIVE

A subset of children with febrile status epilepticus (FSE) are at risk for development of temporal lobe epilepsy later in life. We sought a noninvasive predictive marker of those at risk that can be identified soon after FSE, within a clinically realistic timeframe.

METHODS

Longitudinal T₂ -weighted magnetic resonance imaging (T₂ WI MRI) of rat pups at several time points after experimental FSE (eFSE) was performed on a high-field scanner followed by long-term continuous electroencephalography. In parallel, T₂ WI MRI scans were performed on a 3.0-T clinical scanner. Finally, chronic T₂ WI MRI signal changes were examined in rats that experienced eFSE and were imaged months later in adulthood.

RESULTS

Epilepsy-predicting T₂ changes, previously observed at 2 hours after eFSE, persisted for at least 6 hours, enabling translation to the clinic. Repeated scans, creating MRI trajectories of T₂ relaxation times following eFSE, provided improved prediction of epileptogenesis compared with a single MRI scan. Predictive signal changes centered on limbic structures, such as the basolateral and medial amygdala. T₂ WI MRI changes, originally described on high-field scanners, can also be measured on clinical MRI scanners. Chronically elevated T₂ relaxation times in hippocampus were observed months after eFSE in rats, as noted for post-FSE changes in children.

SIGNIFICANCE

Early T₂ WI MRI changes after eFSE provide a strong predictive measure of epileptogenesis following eFSE, on both high-field and clinical MRI scanners. Importantly, the extension of the acute signal changes to at least 6 hours after the FSE enables its inclusion in clinical studies. Chronic elevations of T₂ relaxation times within the hippocampal formation and related structures are common to human and rodent FSE, suggesting that similar processes are involved across species.

Dysregulation of Astrocytic HMGB1 Signaling in Amyotrophic Lateral Sclerosis

Astrocytes have emerged as critical elements for the maintenance and function of the central nervous system. The expression on their cell membrane of RAGE and TLR4 receptors makes astrocytes susceptible to High-mobility group box 1 (HMGB1), a nuclear protein typically released in the extracellular milieu by living cells experiencing physiological stress conditions or by damaged cells. Here, we show that the interaction of HMGB1 with normal spinal cord astrocytes induces the astrocytic production of neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). Multiple investigations suggest a role for HMGB1 in amyotrophic lateral sclerosis (ALS). Yet, no mechanistic information on the implication of HMGB1 signaling in this disorder is currently available. We demonstrate that non-transgenic and transgenic SOD1^WT spinal motor neurons exhibit only a basal nucleus-to-cytoplasm shuttling of the HMGB1 protein. Conversely, in SOD1^G93A ALS mouse spinal cords, HMGB1 significantly translocates from the nucleus to the cytoplasm of motor neurons, thereby suggesting that it may be eventually released in the extracellular environment during the progression of the disease. We postulate that extracellular HMGB1 can paracrinally interact with the neighboring astrocytes in an attempt to counteract the neurodegenerative process. Yet, at variance with normal cells, SOD1^G93A-expressing astrocytes show impaired capacity to raise BDNF and GDNF levels upon HMGB1 stimulation. Our data suggest that HMGB1 have a potential to promote neuroprotective actions by healthy astrocytes. However, this neurotrophic response is disrupted in ALS astrocytes. This indicates that diseased astroglial cells may exacerbate motor neuron degeneration in ALS because of the loss of their neurosupportive functions.

Role of inflammation in epilepsy and neurobehavioral comorbidities: Implication for therapy

Epilepsy is a devastating condition affecting around 70 million people worldwide. Moreover, the quality of life of people with epilepsy (PWE) is worsened by a series of comorbidities. The neurobehavioral comorbidities discussed herein share a reciprocal and complex relationship with epilepsy, which ultimately complicates the treatment process in PWE. Understanding the mechanistic pathway by which these comorbidities are associated with epilepsy might be instrumental in developing therapeutic interventions. Inflammatory cytokine signaling in the brain regulates important brain functions including neurotransmitter metabolism, neuroendocrine function, synaptic plasticity, dopaminergic transmission, the kynurenine pathway, and affects neurogenesis as well as the neural circuitry of moods. In this review, we hypothesize that the complex relationship between epilepsy and its related comorbidities (cognitive impairment, depression, anxiety, autism, and schizophrenia) can be unraveled through the inflammatory mechanism that plays a prominent role in all these individual conditions. An ample amount of evidence is available reporting the role of inflammation in epilepsy and all individual comorbid condition but their complex relationship with epilepsy has not yet been explored through the prospective of inflammatory pathway. Our review suggests that epilepsy and its neurobehavioral comorbidities are associated with elevated levels of several key inflammatory markers. This review also sheds light on the mechanistic association between epilepsy and its neurobehavioral comorbidities. Moreover, we analyzed several anti-inflammatory therapies available for epilepsy and its neurobehavioral comorbidities. We suggest, these anti-inflammatory therapies might be a possible intervention and could be a promising strategy for preventing epileptogenesis and its related neurobehavioral comorbidities.

High Mobility Group Box 1 is a novel pathogenic factor and a mechanistic biomarker for epilepsy

Approximately 30% of epilepsy patients experience seizures that are not controlled by the available drugs. Moreover, these drugs provide mainly a symptomatic treatment since they do not interfere with the disease's mechanisms. A mechanistic approach to the discovery of key pathogenic brain modifications causing seizure onset, recurrence and progression is instrumental for designing novel and rationale therapeutic interventions that could modify the disease course or prevent its development. In this regard, increasing evidence shows that neuroinflammation is a pathogenic factor in drug-resistant epilepsies. The High Mobility Group Box 1 (HMGB1)/Toll-like receptor 4 axis is a key initiator of neuroinflammation following brain injuries leading to epilepsy, and its activation contributes to seizure mechanisms in animal models. Recent findings have shown dynamic changes in HMGB1 and its isoforms in the brain and blood of animals exposed to acute brain injuries and undergoing epileptogenesis, and in surgically resected epileptic foci in humans. HMGB1 isoforms reflect different pathophysiological processes, and the disulfide isoform, which is generated in the brain during oxidative stress, is implicated in seizures, cell loss and cognitive dysfunctions. Interfering with disulfide HMGB1-activated cell signaling mediates significant therapeutic effects in epilepsy models. Moreover, both clinical and experimental data suggest that HMGB1 isoforms may serve as mechanistic biomarkers for epileptogenesis and drug-resistant epilepsy. These novel findings suggest that the HMGB1 system could be targeted to prevent seizure generation and may provide clinically useful prognostic biomarkers which may also predict the patient's response to therapy.

Epilepsy biomarkers - Toward etiology and pathology specificity

A biomarker is a characteristic that is measured as an indicator of normal biologic processes, pathogenic processes, or responses to an exposure or intervention, including therapeutic interventions. Biomarker modalities include molecular, histologic, radiographic, or physiologic characteristics. In 2015, the FDA-NIH Joint Leadership Council developed the BEST Resource (Biomarkers, EndpointS, and other Tools) to improve the understanding and use of biomarker terminology in biomedical research, clinical practice, and medical product development. The BEST biomarker categories include: (a) susceptibility/risk biomarkers, (b) diagnostic biomarkers, (c) monitoring biomarkers, (d) prognostic biomarkers, (e) predictive biomarkers, (f) pharmacodynamic/response biomarkers, and (g) safety biomarkers. Here we review 30 epilepsy biomarker studies that have identified (a) diagnostic biomarkers for epilepsy, epileptogenesis, epileptogenicity, drug-refractoriness, and status epilepticus - some of the epileptogenesis and epileptogenicity biomarkers can also be considered prognostic biomarkers for the development of epilepsy in subjects with a given brain insult, (b) predictive biomarkers for epilepsy surgery outcome, and (c) a response biomarker for therapy outcome. The biomarker modalities include plasma/serum/exosomal and cerebrospinal fluid molecular biomarkers, brain tissue molecular biomarkers, imaging biomarkers, electrophysiologic biomarkers, and behavioral/cognitive biomarkers. Both single and combinatory biomarkers have been described. Most of the reviewed biomarkers have an area under the curve >0.800 in receiver operating characteristics analysis, suggesting high sensitivity and specificity. As discussed in this review, we are in the early phase of the learning curve in epilepsy biomarker discovery. Many of the seven biomarker categories lack epilepsy-related biomarkers. There is a need for epilepsy biomarker discovery using proper, statistically powered study designs with validation cohorts, and the development and use of novel analytical methods. A strategic roadmap to discuss the research priorities in epilepsy biomarker discovery, regulatory issues, and optimization of the use of resources, similar to those devised in the cancer and Alzheimer's disease research areas, is also needed.

Immunity and inflammation in status epilepticus and its sequelae: possibilities for therapeutic application

Status epilepticus (SE) is a life-threatening neurological emergency often refractory to available treatment options. It is a very heterogeneous condition in terms of clinical presentation and causes, which besides genetic, vascular and other structural causes also include CNS or severe systemic infections, sudden withdrawal from benzodiazepines or anticonvulsants and rare autoimmune etiologies. Treatment of SE is essentially based on expert opinions and antiepileptic drug treatment per se seems to have no major impact on prognosis. There is, therefore, urgent need of novel therapies that rely upon a better understanding of the basic mechanisms underlying this clinical condition. Accumulating evidence in animal models highlights that inflammation ensuing in the brain during SE may play a determinant role in ongoing seizures and their long-term detrimental consequences, independent of an infection or auto-immune cause; this evidence encourages reconsideration of the treatment flow in SE patients.

High mobility group box 1 enhances hyperthermia-induced seizures and secondary epilepsy associated with prolonged hyperthermia-induced seizures in developing rats

Levels of high mobility group box 1 (HMGB1), an important inflammatory mediator, are high in the serum of febrile seizure (FS) patients. However, its roles in FS and secondary epilepsy after prolonged FS are poorly understood. We demonstrate HMGB1's role in the pathogenesis of hyperthermia-induced seizures (HS) and secondary epilepsy after prolonged hyperthermia-induced seizures (pHS). In the first experiment, 14-15-day-old male rats were divided into four groups: high-dose HMGB1 (100 μg), moderate-dose (10 μg), low-dose (1 μg), and control. Each rat was administered HMGB1 intranasally 1 h before inducing HS. Temperature was measured at seizure onset with electroencephalography (EEG). In the second experiment, 10-11-day-old rats were divided into four groups: pHS + HMGB1 (10 μg), pHS, HMGB1, and control. HMGB1 was administered 24 h after pHS. Video-EEGs were recorded for 24 h at 90 and 120 days old; histological analysis was performed at 150 days old. In the first experiment, the temperature at seizure onset was significantly lower in the high- and moderate-dose HMGB1 groups than in the control group. In the second experiment, the incidence of spontaneous epileptic seizure was significantly higher in the pHS + HMGB1 group than in the other groups. Comparison between pHS + HMGB1 groups with and without epilepsy revealed that epileptic rats had significantly enhanced astrocytosis in the hippocampus and corpus callosum. In developing rats, HMGB1 enhanced HS and secondary epilepsy after pHS. Our findings suggest that HMGB1 contributes to FS pathogenesis and plays an important role in the acquired epileptogenesis of secondary epilepsy associated with prolonged FS.

Kainic Acid-Induced Post-Status Epilepticus Models of Temporal Lobe Epilepsy with Diverging Seizure Phenotype and Neuropathology

The aim of epilepsy models is to investigate disease ontogenesis and therapeutic interventions in a consistent and prospective manner. The kainic acid-induced status epilepticus (KASE) rat model is a widely used, well-validated model for temporal lobe epilepsy (TLE). As we noted significant variability within the model between labs potentially related to the rat strain used, we aimed to describe two variants of this model with diverging seizure phenotype and neuropathology. In addition, we evaluated two different protocols to induce status epilepticus (SE). Wistar Han (Charles River, France) and Sprague-Dawley (Harlan, The Netherlands) rats were subjected to KASE using the Hellier kainic acid (KA) and a modified injection scheme. Duration of SE and latent phase were characterized by video-electroencephalography (vEEG) in a subgroup of animals, while animals were sacrificed 1 week (subacute phase) and 12 weeks (chronic phase) post-SE. In the 12 weeks post-SE groups, seizures were monitored with vEEG. Neuronal loss (neuronal nuclei), microglial activation (OX-42 and translocator protein), and neurodegeneration (Fluorojade C) were assessed. First, the Hellier protocol caused very high mortality in WH/CR rats compared to SD/H animals. The modified protocol resulted in a similar SE severity for WH/CR and SD/H rats, but effectively improved survival rates. The latent phase was significantly shorter (p < 0.0001) in SD/H (median 8.3 days) animals compared to WH/CR (median 15.4 days). During the chronic phase, SD/H rats had more seizures/day compared to WH/CR animals (p < 0.01). However, neuronal degeneration and cell loss were overall more extensive in WH/CR than in SD/H rats; microglia activation was similar between the two strains 1 week post-SE, but higher in WH/CR rats 12 weeks post-SE. These neuropathological differences may be more related to the distinct neurotoxic effects of KA in the two rat strains than being the outcome of seizure burden itself. The divergences in disease progression and seizure outcome, in addition to the histopathological dissimilarities, further substantiate the existence of strain differences for the KASE rat model of TLE.

Neuroinflammation imaging markers for epileptogenesis

Epilepsy can be a devastating disorder. In addition to debilitating seizures, epilepsy can cause cognitive and emotional problems with reduced quality of life. Therefore, the major aim is to prevent the disorder in the first place: identify, detect, and reverse the processes responsible for its onset, and monitor and treat its progression. Epilepsy often occurs following a latent period of months to years (epileptogenesis) as a consequence of a brain insult, such as head trauma, stroke, or status epilepticus. Although this latent period clearly represents a therapeutic window, we are not able to stratify patients at risk for long-term epilepsy, which is prerequisite for preventative clinical trials. Moreover, because of the length of the latent period, an early biomarker for treatment response would be of high value. Finally, mechanistic biomarkers of epileptogenesis may provide more profound insight in the process of disease development.

Early tissue damage and microstructural reorganization predict disease severity in experimental epilepsy

Mesial temporal lobe epilepsy (mTLE) is the most common focal epilepsy in adults and is often refractory to medication. So far, resection of the epileptogenic focus represents the only curative therapy. It is unknown whether pathological processes preceding epilepsy onset are indicators of later disease severity. Using longitudinal multi-modal MRI, we monitored hippocampal injury and tissue reorganization during epileptogenesis in a mouse mTLE model. The prognostic value of MRI biomarkers was assessed by retrospective correlations with pathological hallmarks Here, we show for the first time that the extent of early hippocampal neurodegeneration and progressive microstructural changes in the dentate gyrus translate to the severity of hippocampal sclerosis and seizure burden in chronic epilepsy. Moreover, we demonstrate that structural MRI biomarkers reflect the extent of sclerosis in human hippocampi. Our findings may allow an early prognosis of disease severity in mTLE before its first clinical manifestations, thus expanding the therapeutic window.

Imaging blood-brain barrier dysfunction as a biomarker for epileptogenesis

A biomarker that will enable the identification of patients at high-risk for developing post-injury epilepsy is critically required. Microvascular pathology and related blood-brain barrier dysfunction and neuroinflammation were shown to be associated with epileptogenesis after injury. Here we used prospective, longitudinal magnetic resonance imaging to quantitatively follow blood-brain barrier pathology in rats following status epilepticus, late electrocorticography to identify epileptic animals and post-mortem immunohistochemistry to confirm blood-brain barrier dysfunction and neuroinflammation. Finally, to test the pharmacodynamic relevance of the proposed biomarker, two anti-epileptogenic interventions were used; isoflurane anaesthesia and losartan. Our results show that early blood-brain barrier pathology in the piriform network is a sensitive and specific predictor (area under the curve of 0.96, P < 0.0001) for epilepsy, while diffused pathology is associated with a lower risk. Early treatments with either isoflurane anaesthesia or losartan prevented early microvascular damage and late epilepsy. We suggest quantitative assessment of blood-brain barrier pathology as a clinically relevant predictive, diagnostic and pharmaco!dynamics biomarker for acquired epilepsy.

HMGB1 regulates P-glycoprotein expression in status epilepticus rat brains via the RAGE/NF-κB signaling pathway

Overexpression of P-glycoprotein (P-gp) in the brain is an important mechanism involved in drug-resistant epilepsy (DRE). High-mobility group box 1 (HMGB1), an inflammatory cytokine, significantly increases following seizures and may be involved in upregulation of P-gp. However, the underlying mechanisms remain elusive. The aim of the present study was to evaluate the role of HMGB1 and its downstream signaling components, receptor for advanced glycation end-product (RAGE) and nuclear factor-κB (NF-κB), on P-gp expression in rat brains during status epilepticus (SE). Small interfering RNA (siRNA) was administered to rats prior to induction of SE by pilocarpine, to block transcription of the genes encoding HMGB1 and RAGE, respectively. An inhibitor of NF-κB, pyrrolidinedithiocarbamic acid (PDTC), was utilized to inhibit activation of NF-κB. The expression levels of HMGB1, RAGE, phosphorylated-NF-κB p65 (p-p65) and P-gp were detected by western blotting. The relative mRNA expression levels of the genes encoding these proteins were measured using reverse transcription-quantitative polymerase chain reaction and the cellular localization of the proteins was determined by immunofluorescence. Pre-treatment with HMGB1 siRNA reduced the expression levels of RAGE, p-p65 and P-gp. PDTC reduced the expression levels of P-gp. These findings suggested that overexpression of P-gp during seizures may be regulated by HMGB1 via the RAGE/NF-κB signaling pathway, and may be a novel target for treating DRE.

Advances in the development of biomarkers for epilepsy

Over 50 million people worldwide have epilepsy. In nearly 30% of these cases, epilepsy remains unsatisfactorily controlled despite the availability of over 20 antiepileptic drugs. Moreover, no treatments exist to prevent the development of epilepsy in those at risk, despite an increasing understanding of the underlying molecular and cellular pathways. One of the major factors that have impeded rapid progress in these areas is the complex and multifactorial nature of epilepsy, and its heterogeneity. Therefore, the vision of developing targeted treatments for epilepsy relies upon the development of biomarkers that allow individually tailored treatment. Biomarkers for epilepsy typically fall into two broad categories: diagnostic biomarkers, which provide information on the clinical status of, and potentially the sensitivity to, specific treatments, and prognostic biomarkers, which allow prediction of future clinical features, such as the speed of progression, severity of epilepsy, development of comorbidities, or prediction of remission or cure. Prognostic biomarkers are of particular importance because they could be used to identify which patients will develop epilepsy and which might benefit from preventive treatments. Biomarker research faces several challenges; however, biomarkers could substantially improve the management of people with epilepsy and could lead to prevention in the right person at the right time, rather than just symptomatic treatment.

Therapeutic effects of anti-HMGB1 monoclonal antibody on pilocarpine-induced status epilepticus in mice

Inflammatory processes in brain tissue have been described in human epilepsy of various etiologies and in experimental models of seizures. High mobility group box-1 (HMGB1) is now recognized as representative of damage-associated molecular patterns (DAMPs). In the present study, we focused on whether anti-HMGB1 antibody treatment could relieve status epilepticus- triggered BBB breakdown and inflammation response in addition to the seizure behavior itself. Pilocarpine and methyl-scopolamine were used to establish the acute seizure model. Anti-HMGB1 mAb showed inhibitory effects on leakage of the BBB, and on the HMGB1 translocation induced by pilocarpine. The expression of inflammation-related factors, such as MCP-1, CXCL-1, TLR-4, and IL-6 in hippocampus and cerebral cortex were down-regulated by anti-HMGB1 mAb associated with the number of activated astrocytes, microglial cells as well as the expression of IL-1β. Both hematoxylin & eosin and TUNEL staining showed that the apoptotic cells could be reduced after anti-HMGB1 mAb treatment. The onset and latency of Racine stage five were significantly prolonged in the anti-HMGB1 mAb group. These results suggested that anti-HMGB1 mAb prevented the BBB permeability, reduced HMGB1 translocation while inhibiting the expression of inflammation-related factors, protected against neural cell apoptosis and prolonged Racine stage 5 seizure onset and latency.

Non-invasive PET imaging of brain inflammation at disease onset predicts spontaneous recurrent seizures and reflects comorbidities

Brain inflammation is an important factor in the conversion of a healthy brain into an epileptic one, a phenomenon known as epileptogenesis, offering a new entry point for prognostic tools. The development of anti-epileptogenic therapies to treat before or at disease onset is hampered by our inability to predict the severity of the disease outcome. In a rat model of temporal lobe epilepsy we aimed to assess whether in vivo non-invasive imaging of brain inflammation at disease onset was predictive of spontaneous recurrent seizures (SRS) frequency and severity of depression-like and sensorimotor-related comorbidities. To this end, translocator protein, a biomarker of inflammation, was imaged by means of positron emission tomography (PET) 2 and 4weeks post-status epilepticus using [¹⁸F]-PBR111. Translocator protein was highly upregulated 2weeks post-status epilepticus in limbic structures (up to 2.1-fold increase compared to controls in temporal lobe, P<0.001), whereas 4weeks post-status epilepticus, upregulation decreased (up to 1.6-fold increase compared to controls in temporal lobe, P<0.01) and was only apparent in a subset of these regions. Animals were monitored with video-electroencephalography during all stages of disease (acute, latent - first seizures appearing around 2weeks post-status epilepticus - and chronic phases), for a total of 12weeks, in order to determine SRS frequency for each subject (range 0.00-0.83SRS/day). We found that regional PET uptake at 2 and 4weeks post-status epilepticus correlated with the severity of depression-like and sensorimotor-related comorbidities during chronic epilepsy (P<0.05 for each test). Regional PET imaging did not correlate with SRS frequency, however, by applying a multivariate data-driven modeling approach based on translocator protein PET imaging at 2weeks post-status epilepticus, we accurately predicted the frequency of SRS (R=0.92; R²=0.86; P<0.0001) at the onset of epilepsy. This study not only demonstrates non-invasive imaging of translocator protein as a prognostic biomarker to ascertain SRS frequency, but also shows its capability to reflect the severity of depression-like and sensorimotor-related comorbidities. Our results are an encouraging step towards the development of anti-epileptogenic treatments by providing early quantitative assessment of SRS frequency and severity of comorbidities with high clinical relevance.

microRNAs in the pathophysiology of epilepsy

Temporal lobe epilepsy is a common and often drug-resistant seizure disorder. The underlying pathological processes which give rise to the development of spontaneous seizures include neuroinflammation, cell loss, neurogenesis and dendritic abnormalities and many of these are driven by insult-induced changes in gene expression and gene expression regulation. MicroRNAs are powerful modulators of post-transcriptional gene expression which are dysregulated during epileptogenesis. The advent of locked nucleic acid (LNA) based inhibitory methods and mimic technology has facilitated in vivo functional assessment of these molecules in epilepsy. Here we review recent advances in our understanding of the role of these short non-coding RNAs in the pathophysiology of epilepsy.

WONOEP appraisal: Imaging biomarkers in epilepsy

Neuroimaging offers a wide range of opportunities to obtain information about neuronal activity, brain inflammation, blood-brain barrier alterations, and various molecular alterations during epileptogenesis or for the prediction of pharmacoresponsiveness as well as postoperative outcome. Imaging biomarkers were examined during the XIII Workshop on Neurobiology of Epilepsy (XIII WONOEP) organized in 2015 by the Neurobiology Commission of the International League Against Epilepsy (ILAE). Here we present an extended summary of the discussed issues and provide an overview of the current state of knowledge regarding the biomarker potential of different neuroimaging approaches for epilepsy.

Optogenetic study of networks in epilepsy

Currently, approximately 30% of patients with epilepsy do not have adequate seizure control. A greater understanding of the underlying mechanisms by which seizures start or propagate could lead to new therapeutic strategies. The recent development of optogenetics, because of its unprecedented precision for controlling activity within distinct neuronal populations, has revolutionized neuroscience, including epilepsy research. This Review discusses recent breakthroughs made with optogenetics in epilepsy research. These breakthroughs include new insights into the key roles that different cell types play in mediating seizures as well as in the development of epilepsy. Subsequently, we discuss how targeting different brain regions and cell populations has opened up the possibility of highly specific therapies that can stop seizures on demand. Finally, we illustrate how combining newly available neuroscience tools with whole-brain imaging techniques will allow researchers to understand better the spread of seizures on a network level. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

The Diathesis-Epilepsy Model: How Past Events Impact the Development of Epilepsy and Comorbidities

In epilepsy, seizures and comorbidities (e.g., cognitive deficits and depression) occur when specific thresholds are crossed. These thresholds depend on the diathesis (or vulnerability) of a given individual. The diathesis is controlled by multiple genetic and environmental factors. Diathesis changes over multiple timescales: on a daily basis, and as part of the development/aging processes, etc. The diathesis-epilepsy model introduced here provides a conceptual framework to understand how past events (e.g., a very stressful event) can directly influence the occurrence of epilepsy and comorbidities later in life. Experimental evidence supports this model, and the existence of biomarkers predictive of a vulnerability state have led to the development of preventive therapeutic strategies. Epigenetic modifications could be a key determinant of diathesis. Their role is discussed.

Differential detection of impact site versus rotational site injury by magnetic resonance imaging and microglial morphology in an unrestrained mild closed head injury model

Seventy‐five percent of all traumatic brain injuries are mild and do not cause readily visible abnormalities on routine medical imaging making it difficult to predict which individuals will develop unwanted clinical sequelae. Microglia are brain‐resident macrophages and early responders to brain insults. Their activation is associated with changes in morphology or expression of phenotypic markers including P2Y12 and major histocompatibility complex class II. Using a murine model of unrestrained mild closed head injury (mCHI), we used microglia as reporters of acute brain injury at sites of impact versus sites experiencing rotational stress 24 h post‐mCHI. Consistent with mild injury, a modest 20% reduction in P2Y12 expression was detected by quantitative real‐time PCR (qPCR) analysis but only in the impacted region of the cortex. Furthermore, neither an influx of blood‐derived immune cells nor changes in microglial expression of CD45, TREM1, TREM2, major histocompatibility complex class II or CD40 were detected. Using magnetic resonance imaging (MRI), small reductions in T2 weighted values were observed but only near the area of impact and without overt tissue damage (blood deposition, edema). Microglial morphology was quantified without cryosectioning artifacts using ScaleA² clarified brains from CX3CR1‐green fluorescence protein (GFP) mice. The cortex rostral to the mCHI impact site receives greater rotational stress but neither MRI nor molecular markers of microglial activation showed significant changes from shams in this region. However, microglia in this rostral region did display signs of morphologic activation equivalent to that observed in severe CHI. Thus, mCHI‐triggered rotational stress is sufficient to cause injuries undetectable by routine MRI that could result in altered microglial surveillance of brain homeostasis.

Acute changes in microglial morphology reveal brain responses to unrestrained mild traumatic brain injury

In areas subjected to rotational stress distant from impact site

In the absence of detectable changes in standard molecular indicators of brain damage, inflammation or microglial activation.

That might result in decreased surveillance of brain function and increased susceptibility to subsequent brain insults.

ACTH Prevents Deficits in Fear Extinction Associated with Early Life Seizures

Objective

Early life seizures (ELS) are often associated with cognitive and psychiatric comorbidities that are detrimental to quality of life. In a rat model of ELS, we explored long-term cognitive outcomes in adult rats. Using ACTH, an endogeneous HPA-axis hormone given to children with severe epilepsy, we sought to prevent cognitive deficits. Through comparisons with dexamethasone, we sought to dissociate the corticosteroid effects of ACTH from other potential mechanisms of action.

Results

Although rats with a history of ELS were able to acquire a conditioned fear learning paradigm and controls, these rats had significant deficits in their ability to extinguish fearful memories. ACTH treatment did not alter any seizure parameters but nevertheless was able to significantly improve this fear extinction, while dexamethasone treatment during the same period did not. This ACTH effect was specific for fear extinction deficits and not for spatial learning deficits in a water maze. Additionally, ACTH did not alter seizure latency or duration suggesting that cognitive and seizure outcomes may be dissociable. Expression levels of melanocortin receptors, which bind ACTH, were found to be significantly lower in animals that had experienced ELS than in control animals, potentially implicating central melanocortin receptor dysregulation in the effects of ELS, and suggesting a mechanism of action for ACTH.

Interpretation

Taken together, these data suggest that early treatment with ACTH can have significant long-term consequences for cognition in animals with a history of ELS independently of seizure cessation and may act in part through a CNS melanocortin receptor pathway.

Temporal Coordination of Hippocampal Neurons Reflects Cognitive Outcome Post-febrile Status Epilepticus

The coordination of dynamic neural activity within and between neural networks is believed to underlie normal cognitive processes. Conversely, cognitive deficits that occur following neurological insults may result from network discoordination. We hypothesized that cognitive outcome following febrile status epilepticus (FSE) depends on network efficacy within and between fields CA1 and CA3 to dynamically organize cell activity by theta phase. Control and FSE rats were trained to forage or perform an active avoidance spatial task. FSE rats were sorted by those that were able to reach task criterion (FSE-L) and those that could not (FSE-NL). FSE-NL CA1 place cells did not exhibit phase preference in either context and exhibited poor cross-theta interaction between CA1 and CA3. FSE-L and control CA1 place cells exhibited phase preference at peak theta that shifted during active avoidance to the same static phase preference observed in CA3. Temporal coordination of neuronal activity by theta phase may therefore explain variability in cognitive outcome following neurological insults in early development.

Effect of Seizures on the Developing Brain and Cognition

Epilepsy is a complex disorder, which involves much more than seizures, encompassing a range of associated comorbid health conditions that can have significant health and quality-of-life implications. Of these comorbidities, cognitive impairment is one of the most common and distressing aspects of epilepsy. Clinical studies have demonstrated that refractory seizures, resistant to antiepileptic drugs, and occurring early in life have significant adverse effects on cognitive function. Much of what has been learned about the neurobiological underpinnings of cognitive impairment following early-life seizures has come from animal models. Although early-life seizures in rodents do not result in cell loss, seizures cause in changes in neurogenesis and synaptogenesis and alteration of excitatory or inhibitory balance, network connectivity and temporal coding. These morphological and physiological changes are accompanied by parallel impairment in cognitive skills. This increased understanding of the pathophysiological basis of seizure-induced cognitive deficits should allow investigators to develop novel targets for therapeutic interventions.