Protective effects of felbamate against hypoxia in the rat hippocampal slice

The therapeutic and neuroprotective effects of an antiepileptic drug valproic acid in glioma patients

Glioma is the most common primary malignant brain tumor in adults and the patients have poor prognosis despite treatment with surgery, radiotherapy and chemotherapy. The anti-epileptic drug, valproic acid (VPA) as a HDAC inhibitors is often used in glioma patients even if the patients don't have brain tumors associated epilepsy (BAE). Some previous studies have found that VPA not only has anti-epileptic effect, but also has anti-glioma growth effect through enhance radiotherapy sensitivity or other mechanism. Then VPA is reported to improve the survival of glioma patients receiving chemoradiation therapy. In addition, there are limited researches have shown that VPA has a neuroprotective effect in protect normal cells and tissues from the deleterious effects of treatment of glioma, especially radiotherapy. We'll give a brief overview of these effects of VPA in glioma patients.

Neuroprotection Against Diisopropylfluorophosphate in Acute Hippocampal Slices

Diisopropylfluorophosphate (DFP) is an irreversible inhibitor of acetylcholine esterase and a surrogate of the organophosphorus (OP) nerve agent sarin. The neurotoxicity of DFP was assessed as a reduction of population spike (PS) area elicited by synaptic stimulation in acute hippocampal slices. Two classical antidotes, atropine, and pralidoxime, and two novel antidotes, 4R-cembranotriene-diol (4R) and a caspase nine inhibitor, were tested. Atropine, pralidoxime, and 4R significantly protected when applied 30 min after DFP. The caspase inhibitor was neuroprotective when applied 5-10 min before or after DFP, suggesting that early synaptic apoptosis is responsible for the loss of PSs. It is likely that apoptosis starts at the synapses and, if antidotes are not applied, descends to the cell bodies, causing death. The acute slice is a reliable tool for mechanistic studies, and the assessment of neurotoxicity and neuroprotection with PS areas is, in general, pharmacologically congruent with in vivo results and predicts the effect of drugs in vivo. 4R was first found to be neuroprotective in slices and later we demonstrated that 4R is neuroprotective in vivo. The mechanism of neurotoxicity of OPs is not well understood, and there is a need for novel antidotes that could be discovered using acute slices.

Characteristics of selected second-generation antiepileptic drugs used in dogs

A significant number of cases of clinical canine epilepsy remain difficult to control in spite of the applied treatment. At the same time, the range of antiepileptic drugs is increasingly wide, which allows efficient treatment. In the present paper we describe the pharmacodynamics and pharmacokinetics of the newer antiepileptic drugs which were licensed after 1990 but are still not widely used in veterinary medicine. The pharmacokinetic profiles of six of these drugs were tested on dogs. The results of experimental studies suggest that second generation antiepileptic drugs may be applied in mono- as well as in poli- treatment of canine epilepsy because of the larger safety margin and more advantageous pharmacokinetic parameters. Knowledge of the drugs' pharmacokinetics allows its proper clinical appliance, which, in turn, gives the chance to improve the efficiency of pharmacotherapy of canine epilepsy.

Epileptogenesis in the immature brain: emerging mechanisms

Epileptogenesis is defined as the process of developing epilepsy-a disorder characterized by recurrent seizures-following an initial insult. Seizure incidence during the human lifespan is at its highest in infancy and childhood. Animal models of epilepsy and human tissue studies suggest that epileptogenesis involves a cascade of molecular, cellular and neuronal network alterations. Within minutes to days following the initial insult, there are acute early changes in neuronal networks, which include rapid alterations to ion channel kinetics as a result of membrane depolarization, post-translational modifications to existing functional proteins, and activation of immediate early genes. Subacute changes occur over hours to weeks, and include transcriptional events, neuronal death and activation of inflammatory cascades. The chronic changes that follow over weeks to months include anatomical changes, such as neurogenesis, mossy fiber sprouting, network reorganization, and gliosis. These epileptogenic processes are developmentally regulated and might contribute to differences in epileptogenesis between adult and developing brains. Here we review the factors responsible for enhanced seizure susceptibility in the developing brain, and consider age-specific mechanisms of epileptogenesis. An understanding of these factors could yield potential therapeutic targets for the prevention of epileptogenesis and also provide biomarkers for identifying patients at risk of developing epilepsy or for monitoring disease progression.

NMDA receptor antagonist felbamate reduces behavioral deficits and blood-brain barrier permeability changes after experimental subarachnoid hemorrhage in the rat

Increased levels of glutamate and aspartate have been detected after subarachnoid hemorrhage (SAH) that correlate with neurological status. The NMDA receptor antagonist felbamate (FBM; 2-phenyl-1,3-propanediol dicarbamate) is an anti-epileptic drug that elicits neuroprotective effects in different experimental models of hypoxia-ischemia. The aim of this dose-response study was to evaluate the effect of FBM after experimental SAH in rats on (1) behavioral deficits (employing a battery of assessment tasks days 1-5 post-injury) and (2) blood-brain barrier (BBB) permeability changes (quantifying microvascular alterations according to the extravasation of protein-bound Evans Blue by a spectrophotofluorimetric technique 2 days post-injury). Animals were injected with 400 muL of autologous blood into the cisterna magna. Within 5 min, rats received daily oral administration of FBM (15, 30, or 45 mg/kg) for 2 or 5 days. Results were compared with sham-injured controls treated with oral saline or FBM (15, 30, or 45 mg/kg). FBM administration significantly ameliorated SAH-related changes in Beam Balance scores on days 1 and 2 and Beam Balance time on days 1-3, Beam Walking performance on days 1 and 2, and Body Weight on days 3-5. FBM also decreased BBB permeability changes in frontal, temporal, parietal, occipital, and cerebellar cortices; subcortical and cerebellar gray matter; and brainstem. This study demonstrates that, in terms of behavioral and microvascular effects, FBM is beneficial in a dose-dependent manner after experimental SAH in rats. These results reinforce the concept that NMDA excitotoxicity is involved in the cerebral dysfunction that follows SAH.

Emerging experimental therapeutics for bipolar disorder: clues from the molecular pathophysiology

Bipolar affective disorder (manic-depressive illness) is a common, severe, chronic, and often life-threatening illness, associated with significant comorbidity. The recognition of the significant morbidity and mortality of patients with bipolar disorder, as well as the growing appreciation that a high percentage of patients respond poorly to existing treatments, has made the task of discovering new therapeutic agents, that are both efficacious and have few side effects increasingly more important. Most recent agents introduced into the pharmacopeia for the treatment of bipolar disorder have been anticonvulsants and atypical antipsychotics. We propose that novel treatments developed specifically for bipolar disorder will arise from (1) understanding more precisely the molecular mechanisms of treatments that are clearly efficacious or (2) developing medications based on the knowledge obtained of the underlying pathophysiology of bipolar disorder. Knowledge with regard to the underlying pathophysiology of bipolar disorder is increasing at a rapid pace, including alterations in intracellular signaling cascades as well as impairments of cellular plasticity and resilience in critical neuronal circuits. We propose that therapeutics designed to enhance cellular plasticity and resilience and that counter maladaptive stress-responsive systems may have considerable utility for the treatment of bipolar disorder. Therapeutic strategies designed to address cellular resilience and plasticity include the regulation of neurotrophic pathways, glucocorticoid signaling, phosphodiesterase activity, and glutamatergic throughput and mitochondrial function. While the task of developing novel medications for bipolar disorder is truly daunting, these and similar approaches will ultimately lead to better medications for the millions who suffer from this devastating illness.

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.

A self-complementary, self-assembling microsphere system: application for intravenous delivery of the antiepileptic and neuroprotectant compound felbamate

Felbamate (FBM) is a novel antiepileptic drug (AED) and neuroprotectant (NP) compound that interacts with strychnine-insensitive (SI) glycine receptors in brain (IC(50) = 374 microM). FBM concentrations required to interact with SI glycine receptors are consistent with brain levels following oral and intraperitoneal administration of AED and NP doses. Because of the solubility limits of FBM, an intravenous (iv) form has not been developed. Nevertheless, an iv form could be important for the treatment of disorders such as status epilepticus and neuronal damage due to hypoxic/ischemic events. Substituted diketopiperazines precipitate in acid to form microspherical particles of uniform size ( approximately 2 microm). The microsphere system entraps drugs on precipitation and dissolves near physiological pH to release the drug cargo. Therefore, microspheres were used to produce an iv formulation of FBM. Mice were administered the FBM/microsphere (20-60 mg/kg FBM) and tested for protection against tonic extension seizures using maximal electroshock. The FBM/microsphere was effective in a time- and dose-dependent manner following iv administration. The median effective dose (ED(50)) for protection against MES seizures at 30 min was 27.2 mg/kg [95% confidence interval (CI) = 20.8-33.4, slope = 6.5]. The ED(50) for minimal motor impairment at 30 min was 167 mg/kg (95% CI = 155-177, slope = 28.1). Thus, the feasibility of encapsulating FBM or similar aqueous insoluble compounds in a microsphere system with delivery by the iv route for treatment of epilepsy and various central nervous system disorders has been clearly demonstrated. Studies were performed in accordance with the Guide for the Care and Use of Laboratory Animals.

HIF-1alpha and p53 promote hypoxia-induced delayed neuronal death in models of CNS ischemia

Brain ischemia is a cause of substantial morbidity and mortality during the later decades of life. In light of this, many studies have used in vitro and in vivo models of acute necrosis to test candidate therapeutic agents. More recently, the existence of a genetically programmed component of ischemic death has become widely accepted. We have used molecular genetic approaches to investigate the potential link between hypoxia-induced gene transcription and the delayed death of ischemic neurons. Hypoxia-induced gene expression is an evolutionarily conserved response comprising both transcriptional activation and posttranscriptional and posttranslational stabilization events. Members of the PER-ARNT-SIM (PAS) family of basic helix-loop-helix transcription factors have been shown to regulate hypoxic transcripts in nonneuronal cultured lines. However, evidence for ischemic activation of PAS proteins within the neuronal compartment or possible involvement in neuronal death is lacking. The tumor-suppressor protein p53 is a known transcriptional activator within the central nervous system that is clearly involved in the pathologic response to ischemia. This article will provide data that implicate the coordinate activities of p53 and the PAS protein HIF-1alpha in driving ischemia-induced delayed neuronal death. Background regarding mechanisms of ischemic neuronal death will also be provided with special attention paid to the role of de novo gene expression in promoting this pathologic sequence. The identification of the HIF-1alpha/p53-mediated signaling pathway in neurons highlights a novel target toward which anti-ischemic neuroprotective drug discovery can be applied.

Changes in somatosensory evoked potentials following forebrain ischemia in the gerbils: effects of felbamate

Somatosensory evoked potentials (SEPs) as well as change following transient cerebral ischemia in the gerbil were characterized in this study. SEPs were measured in each gerbil before ischemia (day -1), during ischemia, 10 min, 2, 4, 8, 24, 48 h and 8 days after recirculation. During bilateral carotid occlusion, SEP amplitude was dramatically reduced and central conduction time was significantly increased. During recirculation these values showed an improvement when compared to ischemic but not to control values. Moreover at 8 days of recirculation they were still statistically different from control values. Felbamate administration at the dose of 150 mg kg(-1), immediately after recirculation was shown to ameliorate neurophysiological recovery following cerebral ischemia.

Electrophysiological effects of felbamate

Felbamate is a broad spectrum antiepileptic drug recently introduced into clinical practice for controlling seizures in patients affected by Lennox-Gastaut epilepsy, complex partial seizures or otherwise intractable epilepsies. However, the cellular mechanisms by which the drug exerts its anticonvulsant actions are not fully understood. The aim of the present article is to outline the possible mechanisms of action of felbamate as suggested by findings obtained with electrophysiological approaches.

Effects of felbamate on veratridine- and K(+)-stimulated release of glutamate from mouse cortex

Felbamate is a novel anticonvulsant which may modulate the strychnine-insensitive glycine site of the N-methyl-D-aspartate (NMDA) receptor complex. This study examined the effect of felbamate and 5,7-dichlorokynurenic acid on veratridine (20 microM)- and K+ (60 mM)-stimulated release of amino acids in mouse cortical slices. Felbamate significantly decreased veratridine-induced release of glutamate at 400 microM and 800 microM but had no effect on K(+)-stimulated release. 5,7-Dichlorokynurenic acid had no effect on amino-acid release in concentrations up to 200 microM. The inhibitory effect of felbamate on veratridine-induced release of glutamate may be due to inactivation of voltage-sensitive Na+ channels.

Neuroprotection with felbamate: a 7- and 28-day study in transient forebrain ischemia in gerbils

The use of glutamate antagonists and GABA agonists may protect neurons from the effects of transient ischemia. Felbamate is a new antiepileptic drug with glutamate antagonist and GABA agonist properties. We tested the efficacy of felbamate in a gerbil model of transient forebrain ischemia. Damage assessment was done with silver staining at 7 and 28 days after 5 min of bilateral carotid occlusion. Cerebral cortex, hippocampus (CA1 and CA4), thalamus and striatum were evaluated on a 4-point scoring system. The animals sacrificed at 28 days were also tested in a water-maze task to assess recovery of function. The initial dose of felbamate (300 mg/kg) was given 30 min before the ischemic insult in one set of animals and 30 min after the insult in another set of animals. There were 8 animals tested per group (total: 48 animals). There was significant neuronal protection with the use of felbamate, both before and after ischemia in all regions of the brain. Protection was seen in animals sacrificed at 7 and 28 days. Protection was moderate when felbamate was used before ischemia. It was highly significant when felbamate was given 30 min after the insult. Behavioral studies however did not show any difference in the felbamate treated animals versus the saline treated controls. The structural protection with felbamate was very significant when used in the post-ischemic period. This window for protection merits further evaluation in relation to the clinical setting of stroke.

Azelastine protects against CA1 traumatic neuronal injury in the hippocampal slice

Activation of NMDA receptors appears to play a important role in traumatic neuronal injury. Additionally, N-methyl-D-aspartate (NMDA) excitotoxicity may involve leukotriene production. Therefore, we investigated whether azelastine, an anti-allergic agent inhibiting the synthesis and release of leukotrienes, could protect against CA1 traumatic neuronal injury in the hippocampal slice. Fluid percussion trauma produced evidence of severe neuronal injury with CA1 antidromic population spike amplitude recovering after 95 min to only a mean 16 +/- 1 % S.E. of initial amplitude. With 15 microM azelastine treatment given after trauma for 35 min this recovery improved to 112 +/- 17%. The azelastine EC50 for this protection was 10 microM. Significant protection was also seen with azelastine application begun 15 min after trauma. Azelastine also protected the ability to induce long-term potentiation after trauma. The specific leukotriene inhibitors, MK-571 and MK-886, similarly provided significant neuroprotection. These findings suggest that CA1 traumatic neuronal injury may be mediated by leukotriene production.

Distribution of felbamate in brain

We studied the distribution of felbamate (FBM) in rat brain using a br ain imaging scanner to analyze thaw-mount autoradiographs. After intravenous injection of 14 C FBM in rats, the autoradiograph distribution of isotope labeling patterns in brain was captured on x-ray film. Densitometric differences on the x-ray film were converted into color-code variations representing the different concentrations of FBM in regions of the brain. We demonstrated that relatively uniform concentrations of FBM were detected throughout the brain. In all brain regions examined, there were no specifically high or low concentrations of FBM. We conclude that the FBM distributes uniformly.

Felbamate neuroprotection against CA1 traumatic neuronal injury

Traumatic brain injury is a leading cause of disability and death. Since the anticonvulsant felbamate provides hypoxic neuroprotection, we investigated whether felbamate would provide protection against traumatic neuronal injury as well. Traumatic injury to CA1 neurons in hippocampal slices was induced by fluid percussion, and CA1 evoked response was monitored. Pre-treatment with felbamate was strongly protective against neuronal injury, and permitted CA1 antidromic population spike recovery to a mean 94 +/- 1% (S.E.M.) of initial amplitude, compared to unmedicated slices which regained only 15 +/- 6%. The felbamate EC50 for this protection was 136 mg/1, and significant protection was found at felbamate concentrations similar to those reported in felbamate monotherapy for seizures. Significant protection was also detected when felbamate was initiated 15 min after trauma. Slices given brief post-trauma felbamate treatment could demonstrate long-term potentiation when assessed 8 h after trauma. These studies indicate that felbamate is neuroprotective against CA1 traumatic neuronal injury.

Excitoprotective effect of felbamate in cultured cortical neurons

The effect of felbamate on excitatory amino acid-induced biochemical changes was investigated in cultured cortical neurons. Felbamate inhibited NMDA- and glutamate-induced neuronal injury in a dose-dependent manner, but it did not rescue cells from kainate-induced neurotoxicity. The neuroprotective effect was accompanied by a decrease in NMDA- and glutamate-induced neuronal calcium (Ca2+) influx. Exogenous addition of glycine failed to modulate the effect of felbamate on NMDA-induced neurotoxicity or Ca2+ influx, although corresponding changes induced by the strychnine-insensitive glycine antagonist, 5,7-dichlorokynurenic acid could be modulated with glycine. Taken together, these results suggest that felbamate acts through a site on the NMDA receptor that is distinct from the strychinine-insensitive site, and that the effect of the drug on neuronal Ca2+ may be pivotal to its neuroprotective mechanism.

Electrophysiological actions of felbamate on rat striatal neurones

1. We have investigated the effects of the anticonvulsant drug, felbamate (FBM), on striatal neurones, recorded in vitro by using both intracellular and extracellular conventional recordings in slices and whole-cell recordings in acutely isolated neurones. 2. FBM, at therapeutically relevant concentrations (30-300 microM) showed multiple mechanisms of action. Like other antiepileptic drugs, FBM (30-300 microM) showed a direct inhibitory action on current-evoked firing discharge of striatal neurones. A patch-clamp analysis of this effect revealed a dose-related reduction of voltage-dependent sodium (Na+) currents (10-100 microM), with a half inhibiton dose (IC50) value of 28 microM. 3. We also tested whether FBM affected corticostriatal glutamate transmission. In control medium (1.2 mM external magnesium), both extracellularly recorded field potentials and intracellularly recorded excitatory postsynaptic potentials (e.p.s.ps) evoked by cortical stimulation were no affected by bath application of 30-300 microM FBM. 4. When magnesium was removed from the perfusing solution, a procedure which reveals a N-methyl-D-aspartate (NMDA)-mediated component in the corticostriatal synaptic potential, FBM (30-300 microM) produced a dose-dependent reduction of the amplitude of both the field potential and the e.p.s.p. 5. FBM reduced the inward currents produced either by bath or by focal applications of 30 microM NMDA, finding consistent with the hypothesis that the observed reduction of the NMDA-mediated component of the synaptic potentials may be caused at postsynaptic level. 6. The reduction of the NMDA-mediated component of the synaptic transmission by FBM and its depressant effect on the voltage-dependent Na+ channels, may account for the antiepileptic action of this drug. Moreover, the pharmacological properties of FBM might render this drug interesting as a neuroprotectant agent.

Felbamate, a novel antiepileptic drug, reverses N-methyl-D-aspartate/glycine-stimulated increases in intracellular Ca2+ concentration

Felbamate, 2-phenyl-1,3-propanediol dicarbamate, is a novel, orally active anticonvulsant that has recently been approved for the treatment of Lennox-Gastaut syndrome and partial onset seizures in the United States. Felbamate is active in a broad range of animal anticonvulsant tests. Although its mechanism of action has yet to be fully elucidated, felbamate appears to act by inhibiting the spread of seizures and elevating seizure threshold. One proposed mechanism of action for felbamate is via the NMDA receptor complex. Previous studies have demonstrated the ability of felbamate to inhibit glycine binding at the NMDA receptor complex. The present study examined the effects of felbamate on NMDA/glycine-stimulated increases in intracellular calcium (Ca2+) using cultured rat hippocampal neurons. The results of these experiments demonstrate that felbamate inhibits NMDA/glycine-stimulated increases in intracellular Ca2+ with a minimal effective concentration of 100 microM.

Delayed neuronal injury induced by sub-lethal NMDA exposure in the hippocampal slice

Stroke produces neuronal death by two general processes which differ in their temporal course. Acute neuronal death occurs within minutes, while delayed neuronal death evolves within 24 h. To better examine mechanisms of delayed death, we developed a new in vitro model of delayed neuronal injury using extended electrophysiological recordings in paired hippocampal slices. We exposed one hippocampal slice of each pair to 10 microM N-methyl-D-aspartate (NMDA) until the orthodromic CA1 PS disappeared. Thereafter, NMDA-treated slices regained near full recovery of PS amplitude within one hour. However, 10 h later, NMDA-treated slices demonstrated a rapid decline in PS amplitude of 82% +/- 15. CA1 orthodromic evoked PS was lost completely at an average 12.4 +/- 1.6 h after NMDA exposure. This sudden loss of response contrasted with paired, untreated slices, where CA1 PS could be elicited for 22.6 +/- 4.0 h (P < 0.05). Treatment with 10 mM MgCl2 begun after NMDA exposure and continued for 35 min, prevented delayed loss of CA1 orthodromic PS, which then could be elicited for 20.3 +/- 2.1 h. These results indicate that delayed injury can be evaluated using the hippocampal slice. They also suggest that activation of NMDA receptors can induce delayed neuronal injury in CA1 neurons, and that magnesium treatment after NMDA can prevent this injury.

Felbamate modulates the strychnine-insensitive glycine receptor

Felbamate (2-phenyl-1,3-propanediol dicarbamate) is a novel anticonvulsant substance whose mechanism of action is not clearly understood. The present investigation examined its ability to modulate the strychnine-insensitive glycine receptor associated with the N-methyl-D-aspartate (NMDA) receptor. Felbamate decreased the magnitude of glycine (100 microM)-enhanced NMDA (100 microM)-induced intracellular calcium ([Ca2+]i) transients in mouse cerebellar granule cells which had been loaded with the Ca(2+)-sensitive fluorescent probe indo-1 acetoxymethyl ester (indo-1/AM). This effect of felbamate was concentration dependent, with a maximal effect observed at 300 microM (65 +/- 4% of control). In the Frings audiogenic seizure-susceptible mouse model of reflex epilepsy, the glycine agonist D-serine (150 nmol, i.c.v.) completely blocked the anticonvulsant activity of a maximally effective dose of felbamate (19 mg/kg, i.p.). This effect of D-serine could be reversed by increasing the administered dose of felbamate to 29 mg/kg. Furthermore, administration of D-serine (300 nmol, i.c.v.) to felbamate-treated Frings mice produced a parallel right shift in felbamate's anticonvulsant dose-response curve (ED50s: 9.4 mg/kg for felbamate vs. 17.7 mg/kg for felbamate + D-serine). The results obtained in this investigation suggest that the ability of felbamate to modulate the strychnine-insensitive glycine receptor may be physiologically and behaviorally relevant to its anticonvulsant mechanism of action.

Felbamate displays in vitro antiepileptic effects as a broad spectrum excitatory amino acid receptor antagonist

The in vitro antiepileptic activity of the novel anticonvulsant drug felbamate was tested in rat hippocampal slices on the CA1 epileptiform bursting induced by different chemical epileptogenic agents. The effects of felbamate were compared with those of the anticonvulsant drugs diphenylhydantoin and pentobarbitone and with the effects of excitatory amino acid antagonists acting at both N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Like the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), felbamate at a minimum effective concentration of 1 mM induced a significant (P < 0.01) reduction of the duration of the CA1 epileptiform bursting due to the K+ channel blocker, 4-aminopyridine, and the excitatory amino acids, kainate and quisqualate. Like the NMDA receptor antagonist ketamine, felbamate (1.6 mM) significantly (P < 0.01) decreased the duration of the CA1 epileptiform bursting caused by 'Mg(2+)-free' solutions. Conversely, felbamate (1.6 mM), CNQX (100 microM) and ketamine (100 microM) failed to affect the epileptiform bursting induced by the GABA antagonist penicillin. Pentobarbitone (100 microM) significantly (P < 0.01) decreased the duration of the CA1 epileptiform bursting caused by 'Mg(2+)-free' solutions, 4-aminopyridine or penicillin, while diphenylhydantoin (up to concentrations of 100 microM) failed to have an effect. The results indicate that felbamate displays a unique profile of in vitro antiepileptic effects as a broad spectrum antagonist of excitatory amino acid transmission.

Glycine-induced CA1 excitotoxicity in the rat hippocampal slice

We evaluated the effects of glycine exposure upon CA1-evoked response in the rat hippocampal slice. Exposure to 10 mM glycine for 16 min produced rapid neuronal firing and increased orthodromic population spike (PS), followed by loss of CA1 neural transmission. Upon recovery, CA1 orthodromic and antidromic PS regained a mean of only 12 +/- 6% and 8 +/- 5%, of initial amplitude. The electrophysiological pattern of glycine injury was similar to the excitotoxic damage produced by 8 min exposure to sodium glutamate (9 mM). L-Histidine, an inhibitor of glycine transport, exacerbated glycine-induced injury, just as dihydrokainic acid, a glutamate transport inhibitor, exacerbated glutamate-induced injury. The anticonvulsant felbamate (1.3 mM), as well as 100 microM zinc chloride, provided excellent protection from glycine-induced injury: 7-clorokynurenic acid appeared to be toxic. Blockers of the NMDA-associated ionic channel and methyl arginine prevented loss of neural transmission, but did not prevent accompanying hyper-excitability. Only 10 mM magnesium sulfate provided full protection against 9 mM glutamate exposure. Perfusion with low calcium ACSF protected against both glycine- and glutamate-induced injury. Thus, exposure to glycine resembled the excitotoxic effects of glutamate, but showed a different profile of protection. These results suggest that glycine elevations, as occur under physiologic and pathologic conditions, may modulate neuronal activity.

Excitatory amino acid neurotransmission through both NMDA and non-NMDA receptors is involved in the anticonvulsant activity of felbamate in DBA/2 mice

The anticonvulsant activity of felbamate against sound-induced seizures was studied in the DBA/2 mouse model. Felbamate (10-300 mg/kg, i.p.) produced dose-dependent effects with ED50 values for the suppression of tonic, clonic and wild running phases of 23.1, 48.8 and 114.6 mg/kg, respectively. Felbamate also protected DBA/2 mice from N-methyl-D-aspartate (NMDA)-induced seizures with ED50 values of 12.1 and 29 mg/kg for tonus and clonus, respectively. Pretreatment with glycine, an agonist to the glycine/NMDA receptors, shifted the dose-response effect of felbamate to the right (ED50 = 56.8 against tonus and 94.8 mg/kg versus clonus). Similarly, D-serine, an agonist at the glycine site, shifted the ED50 of felbamate against the tonic component of audiogenic seizures from 23.1 to 78.1, and that against clonus from 48.8 to 90.3 mg/kg. Felbamate was also potent to prevent seizures induced by administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), an AMPA/kainate receptor agonist (ED50 = 11.8 and 20.9 mg/kg, against tonus and clonus, respectively). The data indicate that felbamate is an effective anticonvulsant drug in the genetic model of seizure-prone DBA/2 mice. Our findings suggest that the anticonvulsant properties of felbamate depend upon its interaction with neurotransmission mediated by both the glycine/NMDA and the AMPA/kainate receptor complex.

Comparative effects of felbamate and other compounds on N-methyl-D-aspartic acid-induced convulsions and lethality in mice

Felbamate and selected compounds were evaluated for their ability to protect against N-methyl-D-aspartic acid (NMDA)-induced convulsions and lethality in mice. Convulsions produced by intracerebroventricular administration of NMDA (0.8 micrograms per mouse) were antagonized by felbamate, phenytoin, carbamazepine, phenobarbital, valproate, diazepam, 2-amino-5-phosphonovalergic acid (APV), dextromethorphan and ketamine. NMDA (350 mg kg-1 intraperitoneally) produced 100% lethality in mice. Felbamate, phenytoin, and phenobarbital were ineffective in preventing NMDA-induced lethalities, whereas diazepam, APV, ketamine and dextromethorphan were the most potent compounds in preventing lethalities. Any relationship between the protective effects of felbamate against NMDA-induced seizures and competitive or non-competitive antagonism of NMDA receptor sites, however, cannot be established until further experimentation is carried out.

Felbamate

OBJECTIVE

To provide an up-to-date review of the current literature on felbamate (FBM) and its use as an antiepileptic medication (AEM).

DATA SOURCES

All published literature (manuscripts and abstracts) on FBM was reviewed. The initial bibliography (up to September 1992) was provided by the manufacturer (Carter-Wallace Laboratories); subsequent literature was obtained from American Epilepsy Society presentations in December 1992 and manuscripts published up to January 1993.

STUDY SELECTION/DATA EXTRACTION

All pertinent literature was reviewed. Information from the publications was abstracted and organized by the author.

DATA SYNTHESIS

FBM is effective in complex partial seizures either as monotherapy or as an adjunct in patients receiving other AEMs. In addition, it has shown efficacy in some seizures associated with the Lennox-Gastaut syndrome. Adverse effects appear to be mild. When FBM is given as monotherapy, the primary adverse effects are insomnia and weight loss. Patients receiving multiple AEMs may have increased adverse effects.

CONCLUSIONS

FBM appears to be an effective new AEM. Additional studies as to its role in newly diagnosed and pregnant patients are needed. Pharmacokinetic studies in children, patients with renal failure, and patients on nonepilepsy drugs also are needed.

Protection from hypoxic and N-methyl-D-aspartate injury with azelastine, a leukotriene inhibitor

The 5-lipoxygenase metabolites, leukotrienes, increase in concentration during cerebral ischemia. Azelastine is a new anti-allergic agent which inhibits leukotriene C4 synthesis and release. We examined the neuroprotective properties of azelastine using the hippocampal slice. Azelastine 15 microM significantly protected CA1 evoked responses from hypoxic injury, with CA1 population spike amplitude recovering to a mean 76 +/- 13% in azelastine treated slices, compared to 4 +/- 3% recovery in paired unmedicated slices. The EC50 for this azelastine hypoxic protection was 9.8 microM. Azelastine additionally protected against injury induced by N-methyl-D-aspartate (NMDA), but not non-NMDA glutamate receptor agonists. No hypoxic protection was afforded by diphenhydramine 50 microM, suggesting that azelastine protection did not occur through histamine H1 receptor blockade. The finding of protection with azelastine against hypoxic and NMDA-induced injury suggests that leukotriene production is a common pathway in these forms of neuronal injury, and that leukotriene inhibition may be a useful neuroprotective strategy.