Felbamate in experimental model of status epilepticus

Research Status, Synthesis and Clinical Application of Antiepileptic Drugs

According to the 2017 ILAE's official definition, epilepsy is a slow brain disease state characterized by recurrent episodes. Due to information released by ILAE in 2017, it can be divided into four types, including focal epilepsy, generalized epilepsy, combined generalized, and focal epilepsy, and unknown epilepsy. Since 1989, 24 new antiepileptic drugs have been approved to treat different types of epilepsy. Besides, there are a variety of antiepileptic medications under clinical monitoring. These novel antiepileptic drugs have plenty of advantages. Over the past 33 years, there have been many antiepileptic drugs on the mearket, but no one has been found that can completely cure epilepsy. In this paper, the mentioned drugs were classified according to their targets, and the essential information, and clinical studies of each drug were described. The structure-activity relationship of different chemical structures was summarized. This paper provides help for the follow-up research on epilepsy drugs.

In the fast lane: Receptor trafficking during status epilepticus

Status epilepticus (SE) remains a significant cause of morbidity and mortality and often is refractory to standard first-line treatments. A rapid loss of synaptic inhibition and development of pharmacoresistance to benzodiazepines (BZDs) occurs early during SE, while NMDA and AMPA receptor antagonists remain effective treatments after BZDs have failed. Multimodal and subunit-selective receptor trafficking within minutes to an hour of SE involves GABA-A, NMDA, and AMPA receptors and contributes to shifts in the number and subunit composition of surface receptors with differential impacts on the physiology, pharmacology, and strength of GABAergic and glutamatergic currents at synaptic and extrasynaptic sites. During the first hour of SE, synaptic GABA-A receptors containing γ2 subunits move to the cell interior while extrasynaptic GABA-A receptors with δ subunits are preserved. Conversely, NMDA receptors containing N2B subunits are increased at synaptic and extrasynaptic sites, and homomeric GluA1 ("GluA2-lacking") calcium permeant AMPA receptor surface expression also is increased. Molecular mechanisms, largely driven by NMDA receptor or calcium permeant AMPA receptor activation early during circuit hyperactivity, regulate subunit-specific interactions with proteins involved with synaptic scaffolding, adaptin-AP2/clathrin-dependent endocytosis, endoplasmic reticulum (ER) retention, and endosomal recycling. Reviewed here is how SE-induced shifts in receptor subunit composition and surface representation increase the excitatory to inhibitory imbalance that sustains seizures and fuels excitotoxicity contributing to chronic sequela such as "spontaneous recurrent seizures" (SRS). A role for early multimodal therapy is suggested both for treatment of SE and for prevention of long-term comorbidities.

Does status epilepticus modify the effect of ifenprodil on cortical epileptic afterdischarges in immature rats?

BACKGROUND

Ifenprodil as a specific antagonist of NMDA receptors containing a dominant NR2B subunit exhibits age-dependent anticonvulsant action. Possible changes of this action due to status epilepticus (SE) elicited at early stage of development were studied using cortical epileptic afterdischarges (ADs) as a model.

METHODS

Lithium-pilocarpine SE was induced at postnatal day 12 and effects of ifenprodil were studied 3, 6, 9, and 13 days after SE in rat pups with implanted epidural electrodes. Controls (LiPAR) received saline instead of pilocarpine. ADs were elicited by low frequency stimulation of sensorimotor cortex. Intensity of stimulation current increased in 18 steps from 0.2 to 15 mA. Ifenprodil (20 mg/kg) was administered intraperitoneally (ip) after the stimulation with 3.5-mA current. Threshold for four different phenomena as well as duration of ADs were evaluated.

RESULTS

The threshold for the transition into the limbic type of ADs was higher in 15-day-old SE rats than in LiPAR controls. Opposite difference was found in 18-day-old animals, older rats did not exhibit any difference. Isolated significant changes in total duration of ADs were found after high stimulation intensities. These changes appeared in 18-day-old rats where ADs were shorter in SE than in control LiPAR rats.

CONCLUSIONS

Changes in ifenprodil action were found only in the first week after SE but not in the second week. Interpretation of the results is complicated by failure of significant differences between SE and LiPAR rats probably due to a high dose of paraldehyde.

Trafficking of NMDA receptors during status epilepticus: therapeutic implications

We used two models of status epilepticus (SE) to study trafficking of N-methyl-d-aspartate (NMDA) receptors. SE is associated with increased surface expression of NR1 subunits of NMDA receptors, and with an increase of NMDA synaptic and extrasynaptic currents suggesting an increase in number of functional NMDA receptors on dentate granule cells. The therapeutic implications of these results are discussed.

Rapid surface accumulation of NMDA receptors increases glutamatergic excitation during status epilepticus

After 1h of lithium-pilocarpine status epilepticus (SE), immunocytochemical labeling of NMDA receptor NR1 subunits reveals relocation of subunits from the interior to the cell surface of dentate gyrus granule cells and CA3 pyramidal cells. Simultaneously, an increase in NMDA-miniature excitatory postsynaptic currents (mEPSC) as well as an increase in NMDA receptor-mediated tonic currents is observed in hippocampal slices after SE. Mean-variance analysis of NMDA-mEPSCs estimates that the number of functional postsynaptic NMDA receptors per synapse increases 38% during SE, and antagonism by ifenprodil suggests that an increase in the surface representation of NR2B-containing NMDA receptors is responsible for the augmentation of both the phasic and tonic excitatory currents with SE. These results provide a potential mechanism for an enhancement of glutamatergic excitation that maintains SE and may contribute to excitotoxic injury during SE. Therapies that directly antagonize NMDA receptors may be a useful therapeutic strategy during refractory SE.

The acute and chronic effects of the novel anticonvulsant lacosamide in an experimental model of status epilepticus

The effective management of status epilepticus (SE) continues to be a therapeutic challenge. The aim of this study was to investigate the efficacy of lacosamide treatment in an experimental model of self-sustaining SE. Rats were treated with lacosamide (3, 10, 30 or 50mg/kg) either 10 min (early treatment) or 40 min (late treatment) after the initiation of perforant path stimulation. Early lacosamide treatment significantly and dose-dependently reduced acute SE seizure activity; late treatment showed only a non-significant trend toward reduced seizure activity. Early lacosamide treatment also dose-dependently reduced the number of spontaneous recurrent seizures following a 6-week waiting period, with 70% reduction at the highest dose tested (50mg/kg); there was also a significant reduction in the number of spikes and the cumulative time spent in seizures. Late treatment with high-dose lacosamide (30-50mg/kg) reduced the number of animals that developed spontaneous recurrent seizures (33% vs 100% in controls, P<.05), but did not significantly reduce seizure severity or frequency in rats that developed spontaneous recurrent seizures. The results presented here suggest that lacosamide deserves investigation for the clinical treatment of SE. Potential for disease modification in this rat model of self-sustaining SE will require further studies.

Status epilepticus: pathophysiology and management in adults

As in Clark and Prout's classic work, we identify three phases of generalised convulsive status epilepticus, which we call impending, established, and subtle. We review physiological and subcellular changes that might play a part in the transition from single seizures to status epilepticus and in the development of time-dependent pharmacoresistance. We review the principles underlying the treatment of status epilepticus and suggest that prehospital treatment is beneficial, that therapeutic drugs should be used in rapid sequence according to a defined protocol, and that refractory status epilepticus should be treated with general anaesthesia. We comment on our preference for drugs with a short elimination half-life and discuss some therapeutic choices.

Animal models for the development of new neuropharmacological therapeutics in the status epilepticus

Status epilepticus (SE) is a major medical emergency associated with significant morbidity and mortality. SE is best defined as a continuous, generalized, convulsive seizure lasting > 5 min, or two or more seizures during which the patient does not return to baseline consciousness. The relative efficacy and safety of different drugs in the treatment of human SE should be determined in a prospective, randomized, blinded study. However, complementary animal models of SE are required to answer important questions concerning the treatment of SE because of the obvious difficulties of setting up such studies in clinical emergency conditions. This review offers an overview of the implementation and characteristics of some of the most prevalent animal models of SE currently in use. A description is also provide about how animal models of SE may facilitate the use of neurobiological techniques to successfully address critical questions in the drug treatment of SE. In particular, the experience with recently introduced drugs such as intravenous valproate will be addressed. Finally, the importance of some animal models and pharmacological approaches is explained and we discuss their impact in the development of therapeutic strategies to improve pharmacological treatment for SE is discussed.

Isobolographic and subthreshold analysis of interactions among felbamate and four conventional antiepileptic drugs in pentylenetetrazole-induced seizures in mice

PURPOSE

Despite possibility of idiosyncratic reaction development, felbamate (FBM) is recommended in Lennox-Gastaut syndrome and partial refractory epilepsy. The aim of this study was to evaluate the profile of interactions between FBM and four conventional antiepileptic drugs (AEDs): clonazepam (CZP), ethosuximide (ESM), phenobarbital (PB), and valproate (VPA), in pentylenetetrazole (PTZ)-induced convulsions in mice, a model of myoclonic seizures in humans.

METHODS

Data obtained from PTZ-evoked seizures were compared by use of two basic procedures, the subthreshold method and isobolographic analysis. Results of the chimney test (evaluating motor coordination) also were elaborated isobolographically. Thus it was possible to determine both median toxic dose (TD50) and protective index (PI) for each drug combination.

RESULTS

FBM reduced the clonic seizure activity [with an ED50 of 9.7 mg/kg; TD50, 439.1 mg/kg; and PI, 45.3]. FBM at the dose of 10 mg/kg, but not 7.5 mg/kg, significantly reduced PTZ-induced convulsions in mice. In the subthreshold method, FBM (7.5 mg/kg) did not affect the protective activity of conventional AEDs used in the study. However, when applied at 10 mg/kg, it enhanced the protective activity of PB and ESM, but not that of VPA or CZP. The nature of these interactions could not be precisely estimated with this method. The exact profile of drug interactions was determined with the use of isobolography. In terms of seizure inhibition, antagonism was found between FBM and VPA applied at the fixed-dose ratio of 3:1. Synergy was detected between FBM and PB (1:3). Combinations of FBM with VPA (1:3, 1:1), PB (1:1, 3:1), and ESM or CZP (1:3, 1:1, 3:1) led to additive interactions. As regards motor impairment, the combinations of FBM with VPA (1:3) or CZP (1:1, 3:1) were synergistic. Remaining combinations exhibited pure additivity. Pharmacokinetic events may influence FBM/ESM and FBM/CZP interactions, because FBM lowered the brain concentration of ESM and increased that of CZP.

CONCLUSIONS

The profitable benefit index was found only for the combination of FBM with PB (1:3). Conversely, the combinations of FBM with either VPA (1:3) or CZP (1:1, 3:1) do not seem promising for the therapy of refractory myoclonic convulsions. Isobolographic analysis provides more reliable clues to be considered by the clinicians willing to introduce AED combinations for the therapy of epilepsy.

Anticonvulsant effects of levetiracetam and levetiracetam-diazepam combinations in experimental status epilepticus

Status epilepticus (SE) is a neurological emergency, with high mortality and high morbidity among survivors, and novel therapeutic agents are needed to improve this picture. We examined the effects of the antiepileptic drug levetiracetam (LEV) in an experimental model of self-sustaining status epilepticus (SSSE), induced in rats by electrical stimulation of the perforant path. LEV's unique spectrum of anticonvulsant activity, very high therapeutic index, and neuroprotective properties, make it a potentially interesting agent in the treatment of SE. Pretreatment with LEV intravenously reduced (30 mg/kg) or prevented (50-1000 mg/kg) the development of self-sustaining seizures. Treatment during the maintenance phase of SSSE diminished (at 200 mg/kg) or aborted seizures (in doses of 500 or 1000 mg/kg). Addition of LEV significantly enhanced the anticonvulsant effects of diazepam (DZP), even when both drugs where given in doses far below their therapeutic level. We conclude that LEV deserves further evaluation in the treatment of status epilepticus.

Antiepileptic drugs in neuroprotection

Antiepileptic drugs (AEDs) are designed to prevent and suppress seizure activity. Their effects on calcium influx and molecular cascades contributing to necrotic and apoptotic neuronal death, however, suggests that they have functions other than just suppression of excitability. The neuroprotective effects of 20 AEDs currently in use or being investigated in Phase II - III clinical trials for treatment of epilepsy are reviewed. Data analyses is complicated by several factors. Firstly, the available data on the neuroprotective effects of different AEDs varies largely. Secondly, most of the evidence demonstrating neuroprotective effects comes from stroke models and it is uncertain whether these data can be extrapolated to other conditions, such as status epilepticus (SE) or traumatic brain injury. Thirdly, data obtained in adult animals cannot be extrapolated to young animals without caution. For example, AEDs protecting adult brain from stroke or SE-induced injury can cause apoptosis in immature brain. Finally, data comparison is complicated by the variability in study designs and methodologies between studies. With these caveats in mind, an analysis of the available data suggests that AEDs with different mechanisms of action can have mild-to-moderate neuroprotective effects. It is difficult, however, to associate the neuroprotective effects with a favourable functional outcome. For example, it is difficult to conclude that administration of AEDs during the latency phase would have an effect on the molecular cascades underlying epileptogenesis. The few favourable data demonstrating a decrease in the incidence of epilepsy after SE are probably related to the administration of AEDs during SE, which resulted in modification/alleviation of the insult itself and consequently, reduced its epileptogenecity. These experimental data, however, are clinically important because they show that early intervention of SE has an effect on long-term functional outcome. These observations emphasise the need to use additional outcome measures, such as markers of normal development or cognitive performance, when the benefits of neuroprotection achieved by the use of neuroprotective AEDs are assessed.

Neuroprotection and epilepsy

During the last years it has become obvious that the current way of treating epilepsy with antiepeileptic drugs is insufficient concerning the modification of the underlying disesease and provides merely a symptomatic treatment, without clear influence on the course of the disease. There is a pressing need to find alternative strategies and to find possibilities to intervene either into the basic processes determining the development of epilepsies or to promote compensatory processes in repairing these dysfunctions. The increasing knowledge about the basic neuronal changes underlying epilepsies allows now to analyse the potential role of neuroprotective agents in in epileptogenesis. In epilepsy the most frequent constellation is the presence of damage and overexcitation together. Increase in excitability may develop after a primary damage as in posttraumatic epilepsy, or outburst of epileptic excitability may cause neuronal damage as in cell loss after status epilepticus or in any case of the so called cytotoxic damage from extensive glutamatergic involvement. Epilepsy in certain forms is a progressive disease. The factors determining the progressive course and the possibe prevention of it is obviously an overlaping field with neuroprotection. Therefore although neuroprotection works only against certain aspects of a complex cascade of pathological events, might be a promising option in several stadiums during the development and course of epilepsy. We provide evidences that some of the new antiepileptic drugs have neuroprotective effect on different animal models of chronic partial epilepsies, and how this effect is fitting to the antiepileptogenic, and seizure supressing effect of the same drugs.

Antagonists and agonists at the glycine site of the NMDA receptor for therapeutic interventions

For decades neuroreceptor research has focused on the development of NMDA glycine-site antagonists, after Johnson and Ascher found out in 1987 about the co-agonistic character of this achiral amino acid at the NMDA receptor. Contrary to the inhibitory glycine receptor (glycine(A)) the glycine binding site on the NMDA receptor (glycine(B)) is strychnine-insensitive. A great diversity of diseases showing a disturbed glutamate neurotransmission have been linked to the NMDA receptor. Glycine site antagonists have been investigated for acute diseases like stroke and head trauma as well as chronic ones like dementia and chronic pain.

Anticonvulsant and antiepileptogenic effects of fluorofelbamate in experimental status epilepticus

PURPOSE

To examine the seizure-protective properties of fluorofelbamate, a felbamate analog, on acute and chronic seizures in an experimental model of self-sustaining status epilepticus (SSSE).

METHODS

SSSE was induced by stimulation of the perforant path for 30 min (PPS) through chronically implanted electrodes in free-running adult male Wistar rats. Fluorofelbamate was injected intravenously (i.v.) either 10 min, or 40 min after SSSE induction. Seizure and spike profiles were analyzed off-line.

RESULTS

Fluorofelbamate injected during the early stages of SSSE (10 min after the end of PPS), shortened the duration of seizures in a dose-dependent manner. While a dose of 50 mg kg(-1) was ineffective, 100 and 200 mg kg(-1) reduced cumulative seizure time from 393 +/- 10 min to 15 +/- 8 min and 2.4 +/- 0.5 min respectively. Administration of fluorofelbamate (200 and 300 mg kg (-1)) at a late stage of SSSE, which is refractory to treatment with conventional anticonvulsants, also significantly attenuated seizures. Acute fluorofelbamate treatment (200 mg kg(-1) 10 min after PPS) significantly decreased the frequency of spontaneous seizures which follow SSSE after a 'latent' interval. Moreover, in contrast to control animals, fluorofelbamate-treated rats showed regression of spontaneous seizures, and an apparent remission of epilepsy within 2 months after SSSE.

CONCLUSIONS

Acute treatment of SSSE with fluorofelbamate showed strong anticonvulsant effects even during the late stages of SSSE. In this model, it also displayed antiepileptogenic properties: it reduced the severity of chronic epilepsy after SSSE and lead to apparent remissions of that epilepsy.

Efficacy of current antiepileptics to prevent neurodegeneration in epilepsy models

Results of experiments performed in animal epilepsy models and human epilepsy during the past decade indicate that the epileptic brain is not a stable neuronal network, but undergoes modifications caused by the underlying etiology and/or recurrent seizures. In many forms of epilepsy, such as temporal lobe epilepsy, the underlying etiologic factor triggers a cascade of events (epileptogenesis) leading to spontaneous seizures and cognitive decline. In some patients, the condition progresses, due in part to recurrent seizures. The current treatment of epilepsy focuses exclusively on preventing or suppressing seizures, which are symptoms of the underlying disease. Now, however, we are beginning to understand the underlying neurobiology of the epileptic process, as well as factors that might predict the risk of progression in individual patients. Thus, there are new opportunities to develop neuroprotective and antiepileptogenic treatments for patients who, if untreated, would develop drug-refractory epilepsy associated with cognitive decline. These treatments might improve the long-term outcome and quality-of-life of patients with epilepsy. Here we review the available data regarding the neuroprotective effects of antiepileptic drugs (AEDs) at different phases of the epileptic process. Analysis of published data suggests that initial-insult modification and prevention of the progression of seizure-induced damage are candidate indications for treatment with AEDs. An understanding of the molecular mechanisms underlying the progression of epileptic process will eventually show what role AEDs have in the neuroprotective and antiepileptogenic treatment regimen.

Therapy of status epilepticus in adults and children

Clinical studies of the treatment of status epilepticus are extremely difficult to carry out, therefore a paucity of new clinical studies have been reported. Much of the progress regarding the therapy of status epilepticus has come from a better understanding of the epidemiology of status epilepticus and its consequences and from laboratory studies of experimental status. Status epilepticus has been used as an experimental tool to study epileptogenesis, but from such studies have come insights that can be applied to the therapy of status epilepticus itself. This review will focus on information from epidemiological, experimental, and clinical studies of status epilepticus, which may contribute to the improved treatment of this life-threatening disorder.