Brain inflammation in epilepsy: experimental and clinical evidence

Hippocampal FGF-2 and BDNF overexpression attenuates epileptogenesis-associated neuroinflammation and reduces spontaneous recurrent seizures

Under certain experimental conditions, neurotrophic factors may reduce epileptogenesis. We have previously reported that local, intrahippocampal supplementation of fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF) increases neurogenesis, reduces neuronal loss, and reduces the occurrence of spontaneous seizures in a model of damage-associated epilepsy. Here, we asked if these possibly anti-epileptogenic effects might involve anti-inflammatory mechanisms. Thus, we used a Herpes-based vector to supplement FGF-2 and BDNF in rat hippocampus after pilocarpine-induced status epilepticus that established an epileptogenic lesion. This model causes intense neuroinflammation, especially in the phase that precedes the occurrence of spontaneous seizures. The supplementation of FGF-2 and BDNF attenuated various parameters of inflammation, including astrocytosis, microcytosis and IL-1β expression. The effect appeared to be most prominent on IL-1β, whose expression was almost completely prevented. Further studies will be needed to elucidate the molecular mechanism(s) for these effects, and for that on IL-1β in particular. Nonetheless, the concept that neurotrophic factors affect neuroinflammation in vivo may be highly relevant for the understanding of the epileptogenic process.

Evaluation of the innate and adaptive immunity in type I and type II focal cortical dysplasias

PURPOSE

Induction of inflammatory pathways has been reported in epileptic patients with focal malformations of cortical development. In the present study we examined the innate and adaptive immune responses in focal cortical dysplasia (FCD) with different histopathologic and pathogenetic features.

METHODS

The inflammatory cell components and the induction of major proinflammatory pathways and molecules [complement pathway, interleukin (IL)-1β, and chemokine monocyte chemotactic protein-1 (MCP1)] was investigated in surgical specimens of sporadic type IA and type IIB FCD using immunocytochemical methods.

RESULTS

FCD II but not FCD I cases exhibit activation of the mammalian target of rapamycin (mTOR) cascade with strong neuronal expression of the phosphorylated isoform of S6 protein. Microglia reactivity was increased in all lesions (FCD I and II) compared to control tissue; however, the number of HLA-DR-positive cells was significantly higher in FCD II than in FCD I. In FCD II specimens we also observed perivascular and parenchymal T lymphocytes (CD3(+) ), with a predominance of CD8(+) T-cytotoxic/suppressor lymphocytes, as well as a few dendritic cells. Expression of components of the complement cascade, IL-1β, and MCP1 was prominent in FCD II cases.

DISCUSSION

Our findings indicate a prominent activation of both innate and adaptive immunity, with involvement of different inflammatory pathways in FCD II cases, supporting the possible involvement of inflammation in the epileptogenesis of these lesions, as well as the notion that FCD II is pathologically distinct from FCD I.

Role of CCR5 and its ligands in the control of vascular inflammation and leukocyte recruitment required for acute excitotoxic seizure induction and neural damage

Chemokines may play a role in leukocyte migration across the blood-brain barrier (BBB) during neuroinflammation and other neuropathological processes, such as epilepsy. We investigated the role of the chemokine receptor CCR5 in seizures. We used a rat model based on intraperitoneal kainic acid (KA) administration. Four months before KA injection, adult rats were given femoral intramarrow inoculations of SV (RNAiR5-RevM10.AU1), which carries an interfering RNA (RNAi) against CCR5, plus a marker epitope (AU1), or its monofunctional RNAi-carrying homologue, SV(RNAiR5). This treatment lowered expression of CCR5 in circulating cells. In control rats, seizures induced elevated expression of CCR5 ligands MIP-1α and RANTES in the microvasculature, increased BBB leakage and CCR5(+) cells, as well as neuronal loss, inflammation, and gliosis in the hippocampi. Animals given either the bifunctional or the monofunctional vector were largely protected from KA-induced seizures, neuroinflammation, BBB damage, and neuron loss. Brain CCR5 mRNA was reduced. Rats receiving RNAiR5-bearing vectors showed far greater repair responses: increased neuronal proliferation, and decreased production of MIP-1α and RANTES. Controls received unrelated SV(BUGT) vectors. Decrease in CCR5 in circulating cells strongly protected from excitotoxin-induced seizures, BBB leakage, CNS injury, and inflammation, and facilitated neurogenic repair.

Celecoxib treatment restores pharmacosensitivity in a rat model of pharmacoresistant epilepsy

BACKGROUND AND PURPOSE

A functional link between seizure-induced P-glycoprotein overexpression at the blood-brain barrier and therapeutic failure has been suggested by several studies using rodent epilepsy models and human epileptic tissue. Recently, we reported that interference with the mechanisms that up-regulate P-glycoprotein in response to seizure activity might provide a novel approach to control its expression in the epileptic brain. Based on these data, we hypothesized that blocking the appropriate signalling cascade by cyclooxygenase-2 inhibition should improve brain penetration of antiepileptic drugs and help to overcome drug resistance.

EXPERIMENTAL APPROACH

Effects of the selective cyclooxygenase-2 inhibitor celecoxib on the response to the P-glycoprotein substrate, phenobarbital, was evaluated in a chronic model of drug-resistant temporal lobe epilepsy in rats. Drug-resistant rats selected from this model exhibit a marked overexpression of P-glycoprotein in the hippocampus and other limbic brain regions.

KEY RESULTS

Responders and non-responders were selected from a group of rats with spontaneous recurrent seizures after prolonged treatment with phenobarbital at maximum tolerated doses. The efficacy of phenobarbital was re-evaluated following a 6 day treatment with celecoxib and the frequency of spontaneous recurrent seizures was significantly reduced in both groups of rats, phenobarbital responders or non-responders selected from the previous drug trial.

CONCLUSIONS AND IMPLICATIONS

Pretreatment with the cyclooxygenase-2 inhibitor restored the anticonvulsant activity of phenobarbital in rats that failed to exhibit a relevant response before celecoxib treatment. Our data provide further support for a novel therapeutic approach to overcome transporter-mediated drug resistance in epilepsies.

Neuropsychopharmacological understanding for therapeutic application of morphinans

Morphinans are a class of compounds containing the basic structure of morphine. It is well-known that morphinans possess diverse pharmacological effects on the central nervous system. This review will demonstrate novel neuroprotective effects of several morphinans such as, dextromethorphan, its analogs and naloxone on the models of multiple neurodegenerative disease by modulating glial activation associated with the production of a host of proinflammatory and neurotoxic factors, although dextromethorphan possesses neuropsychotoxic potentials. The neuroprotective effects and the therapeutic potential for the treatment of excitotoxic and inflammatory neurodegenerative diseases, and underlying mechanism of morphinans are discussed.

Can Immune Disorders Influence Therapeutical Approach in Treatment of Epilepsy among Neurologists? A First Co-Operative National Recognition in Italy

Functional disturbances of the immune system have been detected more often among persons affected by epilepsy than in the general population. In the February-July period of 2007 a specific questionnaire on the relationship between epilepsy and immunological response was sent to 27 specialized Centres for Epilepsy in nine Italian regions. 15,388 epileptic patients attended twenty-seven Centers during this six-month period. 3.3% (n=502) of these patients suffered an immune disease. This is the first national survey on the relationship between epilepsy and immunological response in current clinical practice.

Inflammation enhances epileptogenesis in the developing rat brain

In many experimental systems, proinflammatory stimuli exhibit proconvulsant properties. There are also accumulating data suggesting that inflammation may contribute to epileptogenesis in experimental models as well as in humans. Using two different models (Lithium-pilocarpine induced-status epilepticus (SE) and rapid kindling), we address this issue in the developing brain. Using P14 Wistar rat pups, we showed that inflammation induced by LPS results, after SE, into a more severe disease in adulthood. The main histological feature was an active gliosis that was observed only when inflammation and SE was combined. The use of a kindling model at P14, a model where seizure progress without any neurodegeneration, permits to show that systemic inflammation is responsible of an enhancement of epileptogenesis. The role of inflammation should be further explored in immature brain to identify therapeutic targets that may be relevant to clinical practice where the association of inflammation and epileptic events is common.

Treatment of refractory epilepsy with natalizumab in a patient with multiple sclerosis. Case report

BACKGROUND

Multiple sclerosis (MS) is considered an autoimmune disease of the central nervous system and therapeutic inhibition of leukocyte migration with natalizumab, an anti-alpha4 integrin antibody, is highly effective in patients with MS. Recent studies performed in experimental animal models with relevance to human disease suggested a key role for blood-brain barrier damage and leukocyte trafficking mechanisms also in the pathogenesis of epilepsy. In addition, vascular alterations and increased leukocyte accumulation into the brain were recently documented in patients with refractory epilepsy independently on the disease etiology.

CASE REPORT

Here we describe the clinical course of a 24-year-old patient with MS in whom abrupt tonic-clonic generalized seizures manifested at disease onset. Although MS had a more favorable course, treatment with glatiramer acetate and antiepileptic drugs for 7 years had no control on seizure generation and the patient developed severe refractory epilepsy. Interestingly, generalized seizures preceded new MS relapses suggesting that seizure activity may contribute to MS worsening creating a positive feedback loop between the two disease conditions. Notably, treatment with natalizumab for 12 months improved MS condition and led to a dramatic reduction of seizures.

CONCLUSION

Our case report suggests that inhibition of leukocyte adhesion may represent a new potential therapeutic approach in epilepsy and complement the traditional therapy with anti-epileptic drugs.

Role of glia in epilepsy-associated neuropathology, neuroinflammation and neurogenesis

The black reaction allowed Golgi to describe with amazing detail the morphology of glial cells as well as their proximal location and intimate connections with neurons and blood vessels. Based on this location, Golgi hypothesized that glial cells were functional units in the nervous system and were not merely a structural support medium. Relatively recent advances have confirmed the importance of glial cells in nervous system function and disease. The occurrence of gliosis is considered the hallmark of damaged tissue. Gliosis can differentially influence disease development and it is a prevailing characteristic of temporal lobe epilepsy. Its presence in the epileptic hippocampi might contribute to hyperexcitability, the development of aberrant neurogenic changes and inflammatory processes related to seizures. Considering the accumulating data regarding the pathological role of glial cells in epilepsy, novel therapeutic approaches that target glial cells are being explored. Such therapeutic approaches directed to glial cells present a novel perspective for the management of refractory pathologies.

Kainic acid and 3-Nitropropionic acid induced expression of laminin in vascular elements of the rat brain

Laminin is a glycoprotein component of the basement membrane and has been reported to be found in different areas of the nervous system including brain endothelial cells, Schwann cells and peripheral nerves. Although the in-vitro studies suggest that laminin plays an important role in growth and neurite extension of cultured neurons, localization of laminin in the brain has been controversial and inconsistent results have been reported. Recently, laminin immunoreactivity has been used as a marker for vascular elements in the brain. In this study, we have investigated the effect of two mechanistically different neurotoxins, kainic acid (KA), an NMDA agonist and 3-Nitropropionic acid (3-NPA), an inhibitor of mitochondrial respiration, on brain vascular elements revealed by laminin immunolabeling. We also explored whether administration of these two neurotoxic drugs correlate with the neuronal degeneration observed after neurotoxic insult by staining with Fluoro-Jade C dye. We have employed single immunolabeling to localize laminin in the brains. In KA treated rats, most of the laminin immunoreactivity is present in the piriform cortex, corpus callosum (myelinated tracts) amygdala, hippocampus, ventral thalamus and tenia tacta. In 3-NPA treated animals, laminin immunoreactivity was confined mostly to the striatum. In contrast, saline treated rats showed very little laminin immunolabeling around capillaries, arteries and in the meningeal membranes. To determine the effects of these neurotoxins on the integrity of the blood brain barrier (BBB), endothelial brain barrier antigen (EBA) immunolabeling was also performed. In addition, we performed CD11b immunolabeling to evaluate the effect of 3-NPA and KA on the activation of microglia in the brain. CD11b was dramatically increased in KA and 3-NPA treated animals. We have also combined laminin immunolabeling with Fluoro-Jade C labeling to evaluate the spatio-temporal association of degenerating neurons and the expression of laminin containing microvessels. Areas which showed intense laminin immunolabeling following KA or 3-NPA exposure correlated with those exhibiting the greatest number of degenerating neurons observed after Fluoro-Jade C staining. EBA-laminin double immunolabeling demonstrated that the expressions of laminin were predominantly localized in the areas (cortex, thalamus and hippocampus) where EBA has been either reduced or is absent. Our results from these experiments demonstrate that vascular laminin expression increases after treatment with KA or 3-NPA, suggesting the occurrence of neovascularization. Microglia may also contribute to the neurotoxic induced neovascularization and neurodegeneration.

Inflammation induced by LPS enhances epileptogenesis in immature rat and may be partially reversed by IL1RA

Inflammatory signaling in the central nervous system (CNS) has been shown to exacerbate both seizure activity and seizure-induced neuronal injury. However, it has not been firmly established whether neurodegeneration is a prerequisite of proconvulsant effect of neuroinflammation, or whether the latter may facilitate seizures without involving neuronal injury. We examined effects of inflammation in the rapid kindling model, where seizure progression occurs in the absence of neurodegeneration. P14 male Wistar rats were subjected to a rapid kindling procedure: 60 electrical stimulations of the hippocampus delivered every 5 min at the current that had been established to induce afterdischarge. Lipopolysaccharide (LPS) was injected (50 microg/kg, i.p., 2 h prior to the rapid kindling protocol [RKP]); IL-1Ra was injected (25 mg/kg, i.p., 2 h prior to the RKP). The effects of treatments were examined on baseline hippocampal excitability, on the progression of rapid kindling, and on the retention of rapid kindling. LPS increased baseline hippocampal excitability, evident as the decrease of hippocampal ADT. LPS also increased kindling progression. Twenty-four hours after the completion of kindling procedure, LPS-treated animals exhibited increased excitability as compared with saline-treated kindling controls. The kindling progression was blocked by IL1RA when given in combination with LPS. IL1RA was able to reverse the effect of LPS on afterdischarge duration (ADD) while IL1RA alone decreased ADT. We showed that inflammation provoked by LPS enhanced rapid kindling epileptogenesis in immature rat brains. IL1RA was also able to mitigate this augmentation of epileptogenesis enhanced by LPS.

Chronic exposure to the chemokine CCL3 enhances neuronal network activity in rat hippocampal cultures

We examined the effect of chronic CCL3 treatment on the properties of cultured rat hippocampal neurons to gain an understanding of the neuronal effects of CCL3 during neuroinflammatory disorders. Western blot assays showed that chronic exposure to CCL3 altered the level of specific neuronal and glial proteins and that CCL3 had no effect on neuronal survival. CCL3 treatment also altered intracellular Ca(2+) dynamics and increased Ca(2+) levels in hippocampal neurons, measured by fura-2 imaging techniques. Additionally, chronic CCL3 increased NMDA-evoked Ca(2+) signals in the hippocampal neurons and increased NMDA receptor levels. These CCL3-induced neuroadaptive changes could play an important role in the CNS dysfunction associated with CNS disorders with a neuroinflammatory component.

Amyloid-beta-induced neuronal dysfunction in Alzheimer's disease: from synapses toward neural networks

Alzheimer's disease is the most frequent neurodegenerative disorder and the most common cause of dementia in the elderly. Diverse lines of evidence suggest that amyloid-beta (Abeta) peptides have a causal role in its pathogenesis, but the underlying mechanisms remain uncertain. Here we discuss recent evidence that Abeta may be part of a mechanism controlling synaptic activity, acting as a positive regulator presynaptically and a negative regulator postsynaptically. The pathological accumulation of oligomeric Abeta assemblies depresses excitatory transmission at the synaptic level, but also triggers aberrant patterns of neuronal circuit activity and epileptiform discharges at the network level. Abeta-induced dysfunction of inhibitory interneurons likely increases synchrony among excitatory principal cells and contributes to the destabilization of neuronal networks. Strategies that block these Abeta effects may prevent cognitive decline in Alzheimer's disease. Potential obstacles and next steps toward this goal are discussed.

The acute phase response and soman-induced status epilepticus: temporal, regional and cellular changes in rat brain cytokine concentrations

Background

Neuroinflammation occurs following brain injury, including soman (GD) induced status epilepticus (SE), and may contribute to loss of neural tissue and declined behavioral function. However, little is known about this important pathological process following GD exposure. Limited transcriptional information on a small number of brain-expressed inflammatory mediators has been shown following GD-induced SE and even less information on protein upregulation has been elucidated. The purpose of this study is to further characterize the regional and temporal progression of the neuroinflammatory process following acute GD-induced SE.

Methods

The protein levels of 10 cytokines was quantified using bead multiplex immunoassays in damaged brain regions (i.e., piriform cortex, hippocampus and thalamus) up to 72 hours following seizure onset. Those factors showing significant changes were then localized to neural cells using fluorescent IHC.

Results

A significant concentration increase was observed in all injured brain regions for four acute phase response (APR) induction cytokines: interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor (TNF)-α. Increases in these APR cytokines corresponded both temporally and regionally to areas of known seizure damage and neuronal death. Neurotoxic cytokines IL-1α and IL-1β were primarily expressed by activated microglia whereas the potentially neuroprotective cytokine IL-6 was expressed by neurons and hypertrophic astrocytes.

Conclusions

Increases in neurotoxic cytokines likely play an active role in the progression of GD-induced SE neuropathology though the exact role that these and other cytokines play in this process require further study.

Immune therapy in autism: historical experience and future directions with immunomodulatory therapy

Autism affects 1 in 110 new births, and it has no single etiology with uniform agreement. This has a significant impact on the quality of life for individuals who have been diagnosed with autism. Although autism has a spectrum quality with a shared diagnosis, it presents a uniquely different clinical appearance in each individual. Recent research of suspected immunological factors have provided more support for a probable immunological process or for processes that may play a role in the acquisition of an autistic condition. These factors include prenatal, genetic, and postnatal findings, as well as the discovery of a dysfunctional chronic pro-inflammatory state in brain tissue and cerebrospinal fluid in subsets of autistic patients. These findings offer new theories that may lead to the development of disease modification or preventative therapeutic options in the near future. This article reviews prenatal, genetic, and observed immune aspects of the autism condition that may be risk factors in the presentation of the autistic clinical phenotype. Historical immune interventions in autism are reviewed and potential new therapies and interventions are discussed.

Breaching the barrier and inflaming epilepsy research

A Role for Leukocyte-Endothelial Adhesion Mechanisms in Epilepsy. Fabene PF, Navarro Mora G, Martinello M, Rossi B, Merigo F, Ottoboni L, Bach S, Angiari S, Benati D, Chakir A, Zanetti L, Schio F, Osculati A, Marzola P, Nicolato E, Homeister JW, Xia L, Lowe JB, McEver RP, Osculati F, Sbarbati A, Butcher EC, Constantin G. Nat Med 2008;14(12):1377–1383. The mechanisms involved in the pathogenesis of epilepsy, a chronic neurological disorder that affects approximately one percent of the world population, are not well understood. 1 – 3 Using a mouse model of epilepsy, we show that seizures induce elevated expression of vascular cell adhesion molecules and enhanced leukocyte rolling and arrest in brain vessels mediated by the leukocyte mucin P-selectin glycoprotein ligand-1 (PSGL-1, encoded by Selplg) and leukocyte integrins α4β1 and αLβ2. Inhibition of leukocyte-vascular interactions, either with blocking antibodies or by genetically interfering with PSGL-1 function in mice, markedly reduced seizures. Treatment with blocking antibodies after acute seizures prevented the development of epilepsy. Neutrophil depletion also inhibited acute seizure induction and chronic spontaneous recurrent seizures. Blood-brain barrier (BBB) leakage, which is known to enhance neuronal excitability, was induced by acute seizure activity but was prevented by blockade of leukocyte-vascular adhesion, suggesting a pathogenetic link between leukocyte-vascular interactions, BBB damage and seizure generation. Consistent with the potential leukocyte involvement in epilepsy in humans, leukocytes were more abundant in brains of individuals with epilepsy than in controls. Our results suggest leukocyte-endothelial interaction as a potential target for the prevention and treatment of epilepsy.

Myelomonocytic Cell Recruitment Causes Fatal CNS Vascular Injury during Acute Viral Meningitis. Kim JV, Kang SS, Dustin ML, McGavern DB. Nature 2009;457(7226):191–195. Lymphocytic choriomeningitis virus1 infection of the mouse central nervous system (CNS) elicits fatal immunopathology through blood–brain barrier breakdown2 and convulsive seizures3. Although lymphocytic-choriomeningitis-virus-specific cytotoxic T lymphocytes (CTLs) are essential for disease4, their mechanism of action is not known. To gain insights into disease pathogenesis, we observed the dynamics of immune cells in the meninges by two-photon microscopy. Here we report visualization of motile CTLs and massive secondary recruitment of pathogenic monocytes and neutrophils that were required for vascular leakage and acute lethality. CTLs expressed multiple chemoattractants capable of recruiting myelomonocytic cells. We conclude that a CD8+ T-cell-dependent disorder can proceed in the absence of direct T-cell effector mechanisms and rely instead on CTL-recruited myelomonocytic cells.

Leukocyte-endothelial adhesion mechanisms in epilepsy: cheers and jeers

A Role for Leukocyte-Endothelial Adhesion Mechanisms in Epilepsy. Fabene PF, Navarro MG, Martinello M, Rossi B, Merigo F, Ottoboni L, Bach S, Angiari S, Benati D, Chakir A, Zanetti L, Schio F, Osculati A, Marzola P, Nicolato E, Homeister JW, Xia L, Lowe JB, McEver RP, Osculati F, Sbarbati A, Butcher EC, Constantin G. Nat Med 2008;14(12):1377–1383. The mechanisms involved in the pathogenesis of epilepsy, a chronic neurological disorder that affects approximately one percent of the world population, are not well understood1,2,3. Using a mouse model of epilepsy, we show that seizures induce elevated expression of vascular cell adhesion molecules and enhanced leukocyte rolling and arrest in brain vessels mediated by the leukocyte mucin P-selectin glycoprotein ligand-1 (PSGL-1, encoded by Selplg) and leukocyte integrins41 and L2. Inhibition of leukocyte-vascular interactions, either with blocking antibodies or by genetically interfering with PSGL-1 function in mice, markedly reduced seizures. Treatment with blocking antibodies after acute seizures prevented the development of epilepsy. Neutrophil depletion also inhibited acute seizure induction and chronic spontaneous recurrent seizures. Blood-brain barrier (BBB) leakage, which is known to enhance neuronal excitability, was induced by acute seizure activity but was prevented by blockade of leukocyte-vascular adhesion, suggesting a pathogenetic link between leukocyte-vascular interactions, BBB damage and seizure generation. Consistent with the potential leukocyte involvement in epilepsy in humans, leukocytes were more abundant in brains of individuals with epilepsy than in controls. Our results suggest leukocyte-endothelial interaction as a potential target for the prevention and treatment of epilepsy.

VEGF as a target for neuroprotection

Vascular Endothelial Growth Factor Is Up-Regulated after Status Epilepticus and Protects against Seizure-Induced Neuronal Loss in Hippocampus. Nicoletti JN, Shah SK, McCloskey DP, Goodman JH, Elkady A, Atassi H, Hylton D, Rudge JS, Scharfman HE, Croll SD. Neuroscience 2008;151(1):232–241. Vascular endothelial growth factor (VEGF) is a protein factor which has been found to play a significant role in both normal and pathological states. Its role as an angiogenic factor is well-established. More recently, VEGF has been shown to protect neurons from cell death both in vivo and in vitro. While VEGF's potential as a protective factor has been demonstrated in hypoxia–ischemia, in vitro excitotoxicity, and motor neuron degeneration, its role in seizure-induced cell loss has received little attention. A potential role in seizures is suggested by Newton et al.'s [Newton SS, Collier EF, Hunsberger J, Adams D, Terwilliger R, Selvanayagam E, Duman RS (2003) Gene profile of electroconvulsive seizures: Induction of neurotrophic and angiogenic factors. J Neurosci 23:10841–10851] finding that VEGF mRNA increases in areas of the brain that are susceptible to cell loss after electroconvulsive-shock induced seizures. Because a linear relationship does not always exist between expression of mRNA and protein, we investigated whether VEGF protein expression increased after pilocarpine-induced status epilepticus. In addition, we administered exogenous VEGF in one experiment and blocked endogenous VEGF in another to determine whether VEGF exerts a neuroprotective effect against status epilepticus-induced cell loss in one vulnerable brain region, the rat hippocampus. Our data revealed that VEGF is dramatically up-regulated in neurons and glia in hippocampus, thalamus, amygdala, and neocortex 24 h after status epilepticus. VEGF induced significant preservation of hippocampal neurons, suggesting that VEGF may play a neuroprotective role following status epilepticus.

Blood-brain barrier damage, but not parenchymal white blood cells, is a hallmark of seizure activity

It has long been held that chronic seizures cause blood-brain barrier (BBB) damage. Recent studies have also demonstrated that BBB damage triggers seizures. We have used the BBB osmotic disruption procedure (BBBD) to examine the correlation between BBB opening, pattern of white blood cell (WBCs) entry into the brain and seizure occurrence. These findings were compared to results from resected epileptic brain tissue from temporal lobe epilepsy (TLE) patients. We confirmed that a successful BBB osmotic opening (BBBD) leads to the occurrence of acute epileptiform discharges. Electroencephalography (EEG) and time-joint frequency analysis reveal EEG slowing followed by an increase in the 10-20Hz frequency range. Using green fluorescent protein (GFP)-labeled WBCs (GFP-WBCs) suspended in Evans Blue we found that, at time of BBB-induced epileptiform discharges, WBCs populated the perivascular space of a leaky BBB. Similar results were obtained at time of pilocarpine seizure. No frank WBCs extravasation in the brain parenchyma was observed. In TLE brain specimens, CD45-positive leukocytes were detected only in the vascular and perivascular spaces while albumin and IgG extravasates were parenchymal. The pattern was similar to those observed in rats. Our data suggest that neither acute-induced nor chronic seizures correlate with WBC brain parenchymal migration while albumin and IgG brain leakage is a hallmark of acute and chronic seizures.

Epileptogenic role of astrocyte dysfunction

Astrocytes Are a Specific Immunological Target in Rasmussen's Encephalitis. Bauer J, Elger CE, Hans VH, Schramm J, Urbach H, Lassmann H, Bien CH. Ann Neurol 2007;62(1):67–80.

Objective

The current histopathological criteria of Rasmussen's encephalitis (RE) include the presence of T-cell-dominated inflammation, microglial activation, neuronal loss, and astrocytic activation. An in vitro study, however, suggested glutamate receptor 3 (GluR3) antibody-mediated astrocytic loss. Therefore, we investigated astrocytic apoptosis and loss in situ.

Methods

Histochemical, immunohistochemical, terminal deoxynucleotidyltransferase-mediated biotin-dUTP nick end labeling, and in situ hybridization techniques were applied to paraffin sections of 20 RE cases, 6 healthy control subjects, and 6 paraneoplastic encephalomyelitis, 10 Ammon's horn sclerosis, and 5 focal cortical dysplasia cases.

Results

Astrocytic apoptosis and subsequent loss of these cells is a specific feature of RE. Such lesions are not found in the control groups. In RE, astrocytic apoptosis and loss was present both in cortical and in white matter areas. Astrocytes in these tissues showed major histocompatibility complex class I expression. Furthermore, granzyme-B+ lymphocytes were found in close apposition to astrocytes bordering astrocyte-deficient lesions. Granzyme-B+ granules in these lymphocytes were polarized and faced the astrocytic membranes. No evidence was found for an antibody-mediated destruction.

Interpretation

We suggest a specific attack by cytotoxic T lymphocytes as a possible mechanism responsible for astrocytic degeneration in RE. The loss of astrocytes might play a role in neuronal dysfunction, seizure induction, and enhancement of neuronal cell death.

New roles for interleukin-1 Beta in the mechanisms of epilepsy

The mechanisms that transform a normal brain to an epileptic one are not fully understood. Interleukin-1 beta (IL-1beta) contributes to neuronal degeneration observed in several neurological disorders and recently has been implicated in neuronal injury that may accompany the process of epileptogenesis. This review presents the hypothesis that IL-1beta may contribute to the development of epilepsy via several mechanisms, including classical effects on neuronal survival and transcription pathways; novel rapid effects on receptor-gated ion channels; and long-lasting effects on expression of selective gene families. Thus, evidence that IL-1beta actions in epilepsy can be independent from the neurotoxic effects of this cytokine is presented.

Blood-brain barrier breakdown as a therapeutic target in traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death in young adults and children. The treatment of TBI in the acute phase has improved substantially; however, the prevention and management of long-term complications remain a challenge. Blood-brain barrier (BBB) breakdown has often been documented in patients with TBI, but the role of such vascular pathology in neurological dysfunction has only recently been explored. Animal studies have demonstrated that BBB breakdown is involved in the initiation of transcriptional changes in the neurovascular network that ultimately lead to delayed neuronal dysfunction and degeneration. Brain imaging data have confirmed the high incidence of BBB breakdown in patients with TBI and suggest that such pathology could be used as a biomarker in the clinic and in drug trials. Here, we review the neurological consequences of TBI, focusing on the long-term complications of such injuries. We present the clinical evidence for involvement of BBB breakdown in TBI and examine the primary and secondary mechanisms that underlie such pathology. We go on to consider the consequences of BBB injury, before analyzing potential mechanisms linking vascular pathology to neuronal dysfunction and degeneration, and exploring possible targets for treatment. Finally, we highlight areas for future basic research and clinical studies into TBI.

The toll receptor family: from microbial recognition to seizures

Toll-like Receptor 4 on Nonhematopoietic Cells Sustains CNS Inflammation during Endotoxemia, Independent of Systemic Cytokines

Chakravarty S, Herkenham M

J Neurosci 2005;25(7):1788–1796

Inflammatory agonists such as lipopolysaccharide (LPS) induce robust systemic as well as CNS responses after peripheral administration. Responses in the innate immune system require triggering of toll-like receptor 4 (TLR4), but the origin of CNS sequelae has been controversial. We demonstrate expression of TLR4 transcripts in mouse brain in the meninges, ventricular ependyma, circumventricular organs, along the vasculature, and in parenchymal microglia. The contribution of TLR4 expressed in CNS resident versus hematopoietic cells to the development of CNS inflammation was examined using chimeric mice. Reciprocal bone marrow chimeras between wild-type and TLR4 mutant mice show that TLR4 on CNS resident cells is critically required for sustained inflammation in the brain after systemic LPS administration. Hematopoietic TLR4 alone supported the systemic release of acute phase cytokines, but transcription of proinflammatory genes in the CNS was reduced in duration. In contrast, TLR4 function in radiation-resistant cells was sufficient for inflammatory progression in the brains of chimeric mice, despite the striking absence of cytokine elevations in serum. Surprisingly, a temporal rise in serum corticosterone was also dependent on TLR4 signaling in nonhematopoietic cells. Our findings demonstrate a requirement for TLR4 function in CNS-resident cells, independent of systemic cytokine effects, for sustained CNS-specific inflammation and corticosterone rise during endotoxemia.

Innate Immune Reaction in Response to Seizures: Implications for the Neuropathology Associated with Epilepsy

Turrin NP, Rivest S

Neurobiol Dis 2004;16(2):321–334

In the present study, the expression of proinflammatory transcripts was assessed across the brain of mice having undertaken pilocarpine-induced seizures. Pilocarpine-induced marked neurodegeneration and demyelination in multiple regions of the forebrain. The pattern of genes encoding toll-like receptor type 2 (TLR2) and I κB α (index of NF- κB activation) was associated with the neurodegenerating areas, but this was not the case for the mRNA encoding other inflammatory proteins. Scattered tumor necrosis factor-alpha (TNF- α)-expressing cells were found across brain, whereas the signals for monocytechemoattractant protein-1 and microsomal prostaglandin mPGES E synthase were robust in thalamus and cerebral cortex and weak in the hippocampus and amygdala. TLR2 and TNF- α transcripts were expressed mainly in microglia/macrophages. Cyclooxygenase-2 was induced specifically in the hippocampus and piriform cortex. A low increase in interleukin-12 mRNA was detected in the brain, but the signal for interferon-gamma (IFN- γ) remained undetectable. Although proinflammatory markers were induced in a different manner across the CNS, their patterns were not characteristic of those caused by other inflammatory challenges, such as endotoxin. These data suggest a different mechanism involved in regulating the innate immune reaction in response to seizures and could have direct implications for the neuropathology associated with epilepsy.

The emerging role for chemokines in epilepsy

Epilepsy has been considered mainly a neuronal disease, without much attention to non-neuronal cells. In recent years growing evidence suggest that astrocytes, microglia, blood leukocytes and blood-brain barrier breakdown are involved in the pathogenesis of epilepsy. In particular, leukocyte-endothelium interactions and eventually subsequent leukocyte recruitment in the brain parenchyma seem to represent key players in the epileptogenic cascade. Chemokines are chemotactic factors controlling leukocyte migration under physiological and pathological conditions. In the light of recent advances in our understanding of the role of inflammation mechanisms in the pathogenesis of epilepsy, pro-inflammatory chemokines may play a critical role in epileptogenesis.

Epileptogenesis provoked by prolonged experimental febrile seizures: mechanisms and biomarkers

Whether long febrile seizures (FSs) can cause epilepsy in the absence of genetic or acquired predisposing factors is unclear. Having established causality between long FSs and limbic epilepsy in an animal model, we studied here if the duration of the inciting FSs influenced the probability of developing subsequent epilepsy and the severity of the spontaneous seizures. We evaluated if interictal epileptifom activity and/or elevation of hippocampal T2 signal on magnetic resonance image (MRI) provided predictive biomarkers for epileptogenesis, and if the inflammatory mediator interleukin-1beta (IL-1beta), an intrinsic element of FS generation, contributed also to subsequent epileptogenesis. We found that febrile status epilepticus, lasting an average of 64 min, increased the severity and duration of subsequent spontaneous seizures compared with FSs averaging 24 min. Interictal activity in rats sustaining febrile status epilepticus was also significantly longer and more robust, and correlated with the presence of hippocampal T2 changes in individual rats. Neither T2 changes nor interictal activity predicted epileptogenesis. Hippocampal levels of IL-1beta were significantly higher for >24 h after prolonged FSs. Chronically, IL-1beta levels were elevated only in rats developing spontaneous limbic seizures after febrile status epilepticus, consistent with a role for this inflammatory mediator in epileptogenesis. Establishing seizure duration as an important determinant in epileptogenesis and defining the predictive roles of interictal activity, MRI, and inflammatory processes are of paramount importance to the clinical understanding of the outcome of FSs, the most common neurological insult in infants and children.

Modulating P-glycoprotein regulation: future perspectives for pharmacoresistant epilepsies?

Enhanced brain efflux of antiepileptic drugs by the blood-brain barrier transporter P-glycoprotein is discussed as one mechanism contributing to pharmacoresistance of epilepsies. P-glycoprotein overexpression has been proven to occur as a consequence of seizure activity. Therefore, blocking respective signaling events should help to improve brain penetration and efficacy of P-glycoprotein substrates. A series of recent studies revealed key signaling factors involved in seizure-associated transcriptional activation of P-glycoprotein. These data suggested several interesting targets, including the N-methyl-d-aspartate (NMDA) receptor, the inflammatory enzyme cyclooxygenase-2, and the prostaglandin E2 EP1 receptor. These targets have been further evaluated in rodent models, demonstrating that targeting these factors can control P-glycoprotein expression, improve antiepileptic drug brain penetration, and help to overcome pharmacoresistance. In general, the approach offers particular advantages over transporter inhibition as it preserves basal transporter function. In this review the different strategies for blocking P-glycoprotein upregulation, including their therapeutic promise and drawbacks are discussed. Moreover, pros and cons of the approach are compared to those of alternative strategies to overcome transporter-associated resistance. Regarding future perspectives of the novel approach, there is an obvious need to more clearly define the clinical relevance of transporter overexpression. In this context current efforts are discussed, including the development of imaging tools that allow an evaluation of P-glycoprotein function in individual patients.

ECoG studies of valproate, carbamazepine and halothane in frontal-lobe epilepsy induced by head injury in the rat

The use of electrocorticography (ECoG) with etiologically realistic epilepsy models promises to facilitate the discovery of better anti-epileptic drugs (AEDs). However, this novel approach is labor intensive, and must be optimized. To this end, we employed rostral parasagittal fluid percussion injury (rpFPI) in the adolescent rat, which closely replicates human contusive closed head injury and results in posttraumatic epilepsy (PTE). We systematically examined variables affecting the power to detect anti-epileptic effects by ECoG and used a non-parametric bootstrap strategy to test several different statistics, study designs, statistical tests, and impact of non-responders. We found that logarithmically transformed data acquired in repeated-measures experiments provided the greatest statistical power to detect decreases in seizure frequencies of preclinical interest with just 8 subjects and with up to approximately 40% non-responders. We then used this optimized design to study the anti-epileptic effects of acute exposure to halothane, and chronic (1 week) exposures to carbamazepine (CBZ) and valproate (VPA) 1 month post-injury. While CBZ was ineffective in all animals, VPA induced, during treatment, a progressive decrease in seizure frequency in animals primarily suffering from non-spreading neocortical seizures, but was ineffective in animals with a high frequency of spreading seizures. Halothane powerfully blocked all seizure activity. The data show that rpFPI and chronic ECoG can conveniently be employed for the evaluation of AEDs, suggest that VPA may be more effective than CBZ to treat some forms of PTE, and support the theory that pharmacoresistance may depend on the severity of epilepsy. The data also demonstrate the utility of chronic exposures to experimental drugs in preclinical studies and highlight the need for greater attention to etiology in clinical studies of AEDs.

Excitotoxicity of TNFalpha derived from KA activated microglia on hippocampal neurons in vitro and in vivo

Highly activated microglia and followed excessive expression of inflammatory cytokines are associated with neuroexcitotoxic injuries. We use electrophysiological techniques, ELISA, western-blot, RT-PCR assay and TUNEL method to explore whether over-produced tumor necrosis factor alpha (TNFalpha) released from activated microglia results in neuronal injuries, and further causes apoptosis through increasing excitotoxicity of hippocampal neurons. Our data showed that kainic acid (KA) activated microglia highly expressed TNFalpha, mRNA and protein. KA activated microglia conditioned media ((KA-MCM) significantly enhanced the amplitude of the population spike at rat's hippocampal CA3 region. It also increased the Ca(2+) current amplitude and density in cultured hippocampal neurons, as well as the high expression of NMDAR1, iNOS, and caspase 3 mRNA and protein at both hippocampal neurons and tissues. KA-MCM also increased TUNEL-positive cells in hippocampal neurons, whereas addition of anti-TNFalpha to the KA-MCM before its application significantly reduced those effects. These studies suggest that TNFalpha derived from KA activated microglia increases excitotoxicity of hippocampal neurons, and might induce neuronal apoptosis in vitro and in vivo.

The COX-2 inhibitor parecoxib is neuroprotective but not antiepileptogenic in the pilocarpine model of temporal lobe epilepsy

The enzyme cyclooxygenase-2 (COX-2), which catalyzes the production of pro-inflammatory prostaglandins, is induced in the brain after various insults, thus contributing to brain inflammatory processes involved in the long-term consequences of such insults. Mounting evidence supports that inflammation may contribute to epileptogenesis and neuronal injury developing after brain insults. Anti-inflammatory treatments, such as selective COX-2 inhibitors, may thus constitute a novel approach for anti-epileptogenesis or disease-modification after brain injuries such as head trauma, cerebral ischemia or status epilepticus (SE). However, recent rat experiments with prophylactic administration of two different COX-2 inhibitors after SE resulted in conflicting results. In the present study, we evaluated whether treatment with parecoxib, a pro-drug of the highly potent and selective COX-2 inhibitor valdecoxib, alters the long-term consequences of a pilocarpine-induced SE in rats. Parecoxib was administered twice daily at 10 mg/kg for 18 days following SE. Five weeks after termination of treatment, spontaneous recurrent seizures were recorded by continuous video/EEG monitoring. Prophylactic treatment with parecoxib prevented the SE-induced increase in prostaglandin E(2) and reduced neuronal damage in the hippocampus and piriform cortex. However, the incidence, frequency or duration of spontaneous seizures developing after SE or the behavioral and cognitive alterations associated with epilepsy were not affected by parecoxib. Only the severity of spontaneous seizures was reduced, indicating a disease-modifying effect. These results substantiate that COX-2 contributes to neuronal injury developing after SE, but inhibition of COX-2 is no effective means to modify epileptogenesis.

Toll-like receptor 4 and high-mobility group box-1 are involved in ictogenesis and can be targeted to reduce seizures

Brain inflammation is a major factor in epilepsy, but the impact of specific inflammatory mediators on neuronal excitability is incompletely understood. Using models of acute and chronic seizures in C57BL/6 mice, we discovered a proconvulsant pathway involving high-mobility group box-1 (HMGB1) release from neurons and glia and its interaction with Toll-like receptor 4 (TLR4), a key receptor of innate immunity. Antagonists of HMGB1 and TLR4 retard seizure precipitation and decrease acute and chronic seizure recurrence. TLR4-defective C3H/HeJ mice are resistant to kainate-induced seizures. The proconvulsant effects of HMGB1, like those of interleukin-1beta (IL-1beta), are partly mediated by ifenprodil-sensitive N-methyl-d-aspartate (NMDA) receptors. Increased expression of HMGB1 and TLR4 in human epileptogenic tissue, like that observed in the mouse model of chronic seizures, suggests a role for the HMGB1-TLR4 axis in human epilepsy. Thus, HMGB1-TLR4 signaling may contribute to generating and perpetuating seizures in humans and might be targeted to attain anticonvulsant effects in epilepsies that are currently resistant to drugs.

Innate but not adaptive immune responses contribute to behavioral seizures following viral infection

PURPOSE

To examine the role of innate immunity in a novel viral infection-induced seizure model.

METHODS

C57BL/6 mice, mouse strains deficient in interleukin (IL)-1RI, IL-6, tumor necrosis factor (TNF)-RI, or myeloid differentiation primary response gene 88 (MyD88), or transgenic mice (OT-I) were infected with Theiler's murine encephalomyelitis virus (TMEV) or were mock infected. Mice were followed for acute seizures. Tissues were examined for neuron loss, the presence of virus (viral RNA and antigen), perivascular cuffs, macrophages/microglia, and gliosis, and mRNA expression of IL-1, TNF-alpha, and IL-6.

RESULTS

IL-1 does not play a major role in seizures, as IL-1RI- and MyD88-deficient mice displayed a comparable seizure frequency relative to controls. In contrast, TNF-alpha and IL-6 appear to be important in the development of seizures, as only 10% and 15% of TNF-RI- and IL-6-deficient mice, respectively, showed signs of seizure activity. TNF-alpha and IL-6 mRNA levels also increased in mice with seizures. Inflammation (perivascular cuffs, macrophages/microglia, and gliosis) was greater in mice with seizures. OT-I mice (virus persists) had a seizure rate that was comparable to controls (no viral persistence), thereby discounting a role for TMEV-specific T cells in seizures.

DISCUSSION

We have implicated the innate immune response to viral infection, specifically TNF-alpha and IL-6, and concomitant inflammatory changes in the brain as contributing to the development of acute seizures. This model is a potential infection-driven model of mesial temporal lobe epilepsy with hippocampal sclerosis.

Expression pattern of miR-146a, an inflammation-associated microRNA, in experimental and human temporal lobe epilepsy

Increasing evidence supports the involvement of inflammatory and immune processes in temporal lobe epilepsy (TLE). MicroRNAs (miRNA) represent small regulatory RNA molecules that have been shown to act as negative regulators of gene expression controlling different biological processes, including immune-system homeostasis and function. We investigated the expression and cellular distribution of miRNA-146a (miR-146a) in a rat model of TLE as well as in human TLE. miR-146a analysis in rat hippocampus was performed by polymerase chain reaction and immunocytochemistry at 1 week and 3-4 months after induction of status epilepticus (SE). Prominent upregulation of miR-146a activation was evident at 1 week after SE and persisted in the chronic phase. The miR-146a expression was confirmed to be present in reactive astrocytes. In human TLE with hippocampal sclerosis, increased astroglial expression of miR-146a was observed mainly in regions where neuronal cell loss and reactive gliosis occurred. The increased and persistent expression of miR-146a in reactive astrocytes supports the possible involvement of miRNAs in the modulation of the astroglial inflammatory response occurring in TLE and provides a target for future studies aimed at developing strategies against pro-epileptogenic inflammatory signalling.

Tissue plasminogen activator and urokinase plasminogen activator in human epileptogenic pathologies

A growing body of evidence demonstrates the involvement of plasminogen activators (PAs) in a number of physiologic and pathologic events in the CNS. Induction of both tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA) has been observed in different experimental models of epilepsy and tPA has been implicated in the mechanisms underlying seizure activity. We investigated the expression and the cellular distribution of tPA and uPA in several epileptogenic pathologies, including hippocampal sclerosis (HS; n=6), and developmental glioneuronal lesions, such as focal cortical dysplasia (FCD, n=6), cortical tubers in patients with the tuberous sclerosis complex (TSC; n=6) and in gangliogliomas (GG; n=6), using immuno-cytochemical, western blot and real-time quantitative PCR analysis. TPA and uPA immunostaining showed increased expression within the epileptogenic lesions compared to control specimens in both glial and neuronal cells (hippocampal neurons in HS and dysplastic neurons in FCD, TSC and GG specimens). Confocal laser scanning microscopy confirmed expression of both proteins in astrocytes and microglia, as well as in microvascular endothelium. Immunoblot demonstrated also up-regulation of the uPA receptor (uPAR; P<0.05). Increased expression of tPA, uPA, uPAR and tissue PA inhibitor type mRNA levels was also detected by PCR analysis in different epileptogenic pathologies (P<0.05). Our data support the role of PA system components in different human focal epileptogenic pathologies, which may critically influence neuronal activity, inflammatory response, as well as contributing to the complex remodeling of the neuronal networks occurring in epileptogenic lesions.

Comorbidity between epilepsy and depression: role of hippocampal interleukin-1beta

Depression is a frequent comorbidity of temporal lobe epilepsy (TLE); however, its mechanisms remain poorly understood and effective therapies are lacking. Augmentation of hippocampal interleukin-1beta (IL-1beta) signaling may be a mechanistic factor of both TLE and clinical depression. We examined whether pharmacological blockade of hippocampal interleukin-1 receptor exerts antidepressant effects in an animal model of comorbidity between TLE and depression, which developed in Wistar rats following pilocarpine status epilepticus (SE). In post-SE animals, depression-like state was characterized by behavioral equivalents of anhedonia and despair; dysregulation of the hypothalamo-pituitary-adrenocortical axis; compromised raphe-hippocampal serotonergic transmission. Two-week long bilateral intrahippocampal infusion of human recombinant Interleukin-1 receptor antagonist (IL-1ra) improved all of the examined depressive impairments, without modifying spontaneous seizure frequency and without affecting normal parameters in naïve rats. These findings implicate hippocampal IL-1beta in epilepsy-associated depression and provide a rationale for the introduction of IL-1beta blockers in the treatment of depression in TLE.

Lymphocyte infiltration of neocortex and hippocampus after a single brief seizure in mice

Various immune responses have been described in epileptic patients and animal models of epilepsy, but immune responses in brain after a single seizure are poorly understood. We studied immune responses in brain after a single brief generalized tonic-clonic seizure in mice. C57bl/6 mice, either unanesthetized or anesthetized (pentobarbital, ethyl chloride) received either electrical (15-30 mA, 100 Hz, 1s) or sham stimulation (subcutaneous electrodes over frontal lobe, no current). Electrical stimulation of unanesthetized mice resulted in tonic-clonic convulsions with hind-limb extension (maximal seizure), tonic-clonic convulsions without hind-limb extension (submaximal seizure), or no seizure. In contrast, such stimulation of anesthetized mice did not result in seizure. Mice were killed at 1h-7 days after seizure. Brains or regions dissected from brain (neocortex, hippocampus, midbrain, cerebellum) of each group were pooled, single cell suspensions prepared, and cells separated according to density. CD4(+) (CD3(+)CD45(Hi)) and CD8(+) (CD3(+)CD45(Hi)) T cell and CD45R(+) (CD45(Hi)) B cell numbers were determined by flow cytometry. At 24h after a maximal seizure, CD4(+) and CD8(+) T cells and CD45R(+) B cells appeared in brain, reaching peak numbers at 48 h, but were no longer detected at 7days. CD4(+) T cells and CD45R(+) B cells were preferentially found in neocortex compared with hippocampus, whereas CD8(+) T cells were preferentially found in hippocampus at 24h after a maximal seizure. In contrast, virtually no lymphocytes were detected in brains of unstimulated or sham stimulated mice, unanesthetized stimulated mice after submaximal or no seizure, and anesthetized stimulated mice at 1 h-7 day. Neither Ly6-G+ neutrophils nor erythrocytes were detected in brains of any animals, nor was there any detectable increase of blood-brain barrier permeability by uptake of Evans Blue dye. The results indicate that lymphocyte entry into brain after a single brief seizure is due to a selective process of recruitment into cortical regions.

Acute p38-mediated inhibition of NMDA-induced outward currents in hippocampal CA1 neurons by interleukin-1beta

Interleukin-1beta (IL-1beta) is a potent pro-inflammatory cytokine that is primarily produced by microglia in the brain. IL-1beta inhibits N-methyl-d-aspartate (NMDA)-induced outward currents (I(NMDA-OUT)) through IL-1 type I receptor (IL-1RI) in hippocampal CA1 neurons (Zhang, R., Yamada, J., Hayashi, Y., Wu, Z, Koyama, S., Nakanishi, H., 2008. Inhibition of NMDA-induced outward currents by interleukin-1beta in hippocampal neurons, Biochem. Biophys. Res. Commun. 372, 816-820). Although IL-1RI is associated with mitogen-activated protein kinases, their involvement in the effect of IL-1beta on I(NMDA-OUT) remains unclear. In the present study, we demonstrate that IL-1beta caused activation of p38 mitogen-activated protein kinase and that the p38 inhibitor SB203580 significantly blocked the effect of IL-1beta on I(NMDA-OUT) in hippocampal CA1 neurons. Furthermore, the intracellular perfusion of active recombinant p38alpha significantly decreased the mean amplitude of I(NMDA-OUT). In neurons prepared from inflamed hippocampus, the mean amplitude of I(NMDA-OUT) was significantly reduced. In the inflamed hippocampus, IL-1beta and IL-1RI were expressed mainly in microglia and neurons, respectively. These results suggest that IL-1beta increases the excitability of hippocampal CA1 neurons in the p38-dependent inhibition of I(NMDA-OUT).

Epileptic encephalopathy in children possibly related to immune-mediated pathogenesis

Severe epilepsy in the paediatric population negatively influences neurological and cognitive development. Different etiological factors could be responsible of these severe epilepsies, and an early diagnosis could change, in some cases, the neurological and cognitive development. Immune mechanisms have been reported in epilepsy. Epilepsy has been associated with systemic lupus erythematosus, with the presence of anti-phospholipid antibodies (aPL), anti-cardiolipin antibodies, anti-nuclear antibodies, Beta2-glycoprotein antibodies, and anti-glutamic acid decarboxylase (anti-GAD) antibodies. CNS inflammation and markers of adaptive immunity have been, also, associated with some epileptic syndromes, such as West syndrome, temporal lobe epilepsy, febrile seizures, tonic-clonic seizures, and tuberous sclerosis. Inflammation and blood-brain barrier (BBB) disruption could be one of the mechanisms responsible for seizure recurrence. Recently clinical entities, characterized by severe epilepsy with a febrile, acute or sub-acute onset, sometimes associated with status epilepticus, followed by drug-resistant, partial epilepsy have been described. Some of these publications also suggested acronyms for the condition described: Acute Encephalitis with Refractory, Repetitive Partial Seizures (AERRPS) reported by Japanese authors, Devastating Epileptic Encephalopathy in School-aged Children (DESC) reported by French authors. Among children with acquired symptomatic severe epilepsy, we identified a group of previously normal children who had developed severe partial epilepsy after an acute/sub-acute illness resembling encephalitis. The etiological factors for those patients seems to remain unknown, and a possible immune-mediating or inflammatory process as pathogenesis of the disease could be hypothesized. More studies need to be addressed to finally define this peculiar epileptic entity.

Chemokine CCL2 and its receptor CCR2 are increased in the hippocampus following pilocarpine-induced status epilepticus

Background

Neuroinflammation occurs after seizures and is implicated in epileptogenesis. CCR2 is a chemokine receptor for CCL2 and their interaction mediates monocyte infiltration in the neuroinflammatory cascade triggered in different brain pathologies. In this work CCR2 and CCL2 expression were examined following status epilepticus (SE) induced by pilocarpine injection.

Methods

SE was induced by pilocarpine injection. Control rats were injected with saline instead of pilocarpine. Five days after SE, CCR2 staining in neurons and glial cells was examined using imunohistochemical analyses. The number of CCR2 positive cells was determined using stereology probes in the hippocampus. CCL2 expression in the hippocampus was examined by molecular assay.

Results

Increased CCR2 was observed in the hippocampus after SE. Seizures also resulted in alterations to the cell types expressing CCR2. Increased numbers of neurons that expressed CCR2 was observed following SE. Microglial cells were more closely apposed to the CCR2-labeled cells in SE rats. In addition, rats that experienced SE exhibited CCR2-labeling in populations of hypertrophied astrocytes, especially in CA1 and dentate gyrus. These CCR2+ astroctytes were not observed in control rats. Examination of CCL2 expression showed that it was elevated in the hippocampus following SE.

Conclusion

The data show that CCR2 and CCL2 are up-regulated in the hippocampus after pilocarpine-induced SE. Seizures also result in changes to CCR2 receptor expression in neurons and astrocytes. These changes might be involved in detrimental neuroplasticity and neuroinflammatory changes that occur following seizures.