Pharmacological Profile of the Novel Antiepileptic Drug Candidate Padsevonil: Characterization in Rodent Seizure and Epilepsy Models.

The antiepileptic drug (AED) candidate, (4R)-4-(2-chloro-2,2-difluoroethyl)-1-{[2-(methoxymethyl)-6-(trifluoromethyl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl]methyl}pyrrolidin-2-one (padsevonil), is the first in a novel class of drugs that bind to synaptic vesicle protein 2 (SV2) proteins and the GABAA receptor benzodiazepine site, allowing for pre- and postsynaptic activity, respectively. In acute seizure models, padsevonil provided potent, dose-dependent protection against seizures induced by administration of pilocarpine or 11-deoxycortisol, and those induced acoustically or through 6 Hz stimulation; it was less potent in the pentylenetetrazol, bicuculline, and maximal electroshock models. Padsevonil displayed dose-dependent protective effects in chronic epilepsy models, including the intrahippocampal kainate and Genetic Absence Epilepsy Rats from Strasbourg models, which represent human mesial temporal lobe and absence epilepsy, respectively. In the amygdala kindling model, which is predictive of efficacy against focal to bilateral tonic-clonic seizures, padsevonil provided significant protection in kindled rodents; in mice specifically, it was the most potent AED compared with nine others with different mechanisms of action. Its therapeutic index was also the highest, potentially translating into a favorable efficacy and tolerability profile in humans. Importantly, in contrast to diazepam, tolerance to padsevonil's antiseizure effects was not observed in the pentylenetetrazol-induced clonic seizure threshold test. Further results in the 6 Hz model showed that padsevonil provided significantly greater protection than the combination of diazepam with either 2S-(2-oxo-1-pyrrolidinyl)butanamide (levetiracetam) or 2S-2-[(4R)-2-oxo-4-propylpyrrolidin-1-yl] butanamide (brivaracetam), both selective SV2A ligands. This observation suggests that padsevonil's unique mechanism of action confers antiseizure properties beyond the combination of compounds targeting SV2A and the benzodiazepine site. Overall, padsevonil displayed robust efficacy across validated seizure and epilepsy models, including those considered to represent drug-resistant epilepsy. SIGNIFICANCE STATEMENT: Padsevonil, a first-in-class antiepileptic drug candidate, targets SV2 proteins and the benzodiazepine site of GABAA receptors. It demonstrated robust efficacy across a broad range of rodent seizure and epilepsy models, several representing drug-resistant epilepsy. Furthermore, in one rodent model, its efficacy extended beyond the combination of drugs interacting separately with SV2 or the benzodiazepine site. Padsevonil displayed a high therapeutic index, potentially translating into a favorable safety profile in humans; tolerance to antiseizure effects was not observed.

Brivaracetam does not modulate ionotropic channels activated by glutamate, γ-aminobutyric acid, and glycine in hippocampal neurons.

Brivaracetam (BRV) is a selective, high-affinity ligand for synaptic vesicle protein 2A (SV2A), recently approved as adjunctive treatment for drug-refractory partial-onset seizures in adults. BRV binds SV2A with higher affinity than levetiracetam (LEV), and was shown to have a differential interaction with SV2A. Because LEV was reported to interact with multiple excitatory and inhibitory ligand-gated ion channels and that may impact its pharmacological profile, we were interested in determining whether BRV directly modulates inhibitory and excitatory ionotropic receptors in central neurons. Voltage-clamp experiments were performed in primary cultures of mouse hippocampal neurons. At a supratherapeutic concentration of 100 µm, BRV was devoid of any direct effect on currents gated by γ-aminobutyric acidergic type A, glycine, kainate, N-methyl-d-aspartate, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid. Similarly to LEV, BRV reveals a potent ability to oppose the action of negative modulators on the inhibitory receptors. In conclusion, these results show that BRV contrasts with LEV by not displaying any direct action on inhibitory or excitatory postsynaptic ligand-gated receptors at therapeutic concentrations and thereby support BRV's role as a selective SV2A ligand. These findings add further evidence to the validity of SV2A as a relevant antiepileptic drug target and emphasize the potential for exploring further presynaptic mechanisms as a novel approach to antiepileptic drug discovery.

Acute and long-term effects of brivaracetam and brivaracetam-diazepam combinations in an experimental model of status epilepticus.

OBJECTIVE: To evaluate acute and long-term effects of intravenous brivaracetam (BRV) and BRV + diazepam (DZP) combination treatment in a rat model of self-sustaining status epilepticus (SSSE). METHODS: Rats were treated with BRV (10 mg/kg) 10 min after initiation of perforant path stimulation (PPS) as early treatment; or BRV (10-300 mg/kg), DZP (1 mg/kg), or BRV (0.3-10 mg/kg) + DZP (1 mg/kg) 10 min after the end of PPS (established SSSE). Seizure activity was recorded electrographically for 24 h posttreatment (acute effects), and for 1 week at 6-8 weeks or 12 months' posttreatment (long-term effects). All treatments were compared with control rats using one-way analysis of variance (ANOVA) and Bonferroni's test, or Kruskal--Wallis and Dunn's multiple comparison tests, when appropriate. RESULTS: Treatment of established SSSE with BRV (10-300 mg/kg) resulted in dose-dependent reduction in SSSE duration and cumulative seizure time, achieving statistical significance at doses ≥100 mg/kg. Lower doses of BRV (0.3-10 mg/kg) + low-dose DZP (1 mg/kg) significantly reduced SSSE duration and number of seizures. All control rats developed spontaneous recurrent seizures (SRS) 6-8 weeks after SSSE, whereas seizure freedom was noted in 2/10, 5/10, and 6/10 rats treated with BRV 200 mg/kg, 300 mg/kg, and BRV 10 mg/kg + DZP, respectively. BRV (10-300 mg/kg) showed a dose-dependent trend toward reduction of SRS frequency, cumulative seizure time, and spike frequency, achieving statistical significance at 300 mg/kg. Combination of BRV (10 mg/kg) + DZP significantly reduced SRS frequency, cumulative seizure time, and spike frequency. In the 12-month follow-up study, BRV (0.3-10 mg/kg) + low-dose DZP markedly reduced SRS frequency, cumulative seizure time, and spike frequency, achieving statistical significance at some doses. Early treatment of SSSE with BRV 10 mg/kg significantly reduced long-term SRS frequency. SIGNIFICANCE: These findings support clinical evaluation of BRV for treatment of status epilepticus or acute repetitive seizures.

Brivaracetam, a selective high-affinity synaptic vesicle protein 2A (SV2A) ligand with preclinical evidence of high brain permeability and fast onset of action.

OBJECTIVE: Rapid distribution to the brain is a prerequisite for antiepileptic drugs used for treatment of acute seizures. The preclinical studies described here investigated the high-affinity synaptic vesicle glycoprotein 2A (SV2A) antiepileptic drug brivara-cetam (BRV) for its rate of brain penetration and its onset of action. BRV was compared with levetiracetam (LEV). METHODS: In vitro permeation studies were performed using Caco-2 cells. Plasma and brain levels were measured over time after single oral dosing to audiogenic mice and were correlated with anticonvulsant activity. Tissue distribution was investigated after single dosing to rat (BRV and LEV) and dog (LEV only). Positron emission tomography (PET) displacement studies were performed in rhesus monkeys using the SV2A PET tracer [11C]UCB-J. The time course of PET tracer displacement was measured following single intravenous (IV) dosing with LEV or BRV. Rodent distribution data and physiologically based pharmacokinetic (PBPK) modeling were used to compute blood-brain barrier permeability (permeability surface area product, PS) values and then predict brain kinetics in man. RESULTS: In rodents, BRV consistently showed a faster entry into the brain than LEV; this correlated with a faster onset of action against seizures in audiogenic susceptible mice. The higher permeability of BRV was also demonstrated in human cells in vitro. PBPK modeling predicted that, following IV dosing to human subjects, BRV might distribute to the brain within a few minutes compared with approximately 1 h for LEV (PS of 0.315 and 0.015 ml/min/g for BRV and LEV, respectively). These data were supported by a nonhuman primate PET study showing faster SV2A occupancy by BRV compared with LEV. SIGNIFICANCE: These preclinical data demonstrate that BRV has rapid brain entry and fast brain SV2A occupancy, consistent with the fast onset of action in the audiogenic seizure mice assay. The potential benefit of BRV for treatment of acute seizures remains to be confirmed in clinical studies.

Brivaracetam: Rationale for discovery and preclinical profile of a selective SV2A ligand for epilepsy treatment.

Despite availability of effective antiepileptic drugs (AEDs), many patients with epilepsy continue to experience refractory seizures and adverse events. Achievement of better seizure control and fewer side effects is key to improving quality of life. This review describes the rationale for the discovery and preclinical profile of brivaracetam (BRV), currently under regulatory review as adjunctive therapy for adults with partial-onset seizures. The discovery of BRV was triggered by the novel mechanism of action and atypical properties of levetiracetam (LEV) in preclinical seizure and epilepsy models. LEV is associated with several mechanisms that may contribute to its antiepileptic properties and adverse effect profile. Early findings observed a moderate affinity for a unique brain-specific LEV binding site (LBS) that correlated with anticonvulsant effects in animal models of epilepsy. This provided a promising molecular target and rationale for identifying selective, high-affinity ligands for LBS with potential for improved antiepileptic properties. The later discovery that synaptic vesicle protein 2A (SV2A) was the molecular correlate of LBS confirmed the novelty of the target. A drug discovery program resulted in the identification of anticonvulsants, comprising two distinct families of high-affinity SV2A ligands possessing different pharmacologic properties. Among these, BRV differed significantly from LEV by its selective, high affinity and differential interaction with SV2A as well as a higher lipophilicity, correlating with more potent and complete seizure suppression, as well as a more rapid brain penetration in preclinical models. Initial studies in animal models also revealed BRV had a greater antiepileptogenic potential than LEV. These properties of BRV highlight its promising potential as an AED that might provide broad-spectrum efficacy, associated with a promising tolerability profile and a fast onset of action. BRV represents the first selective SV2A ligand for epilepsy treatment and may add a significant contribution to the existing armamentarium of AEDs.

Anti-ictogenic and antiepileptogenic properties of brivaracetam in mature and immature rats.

OBJECTIVE: Brivaracetam (BRV) is a new antiepileptic drug candidate rationally designed for high affinity and selectivity for the synaptic vesicle protein 2A. This study explored anti-ictogenic and antiepileptogenic effects of BRV in rats at different stages of development. METHODS: Using a rapid kindling model in P14, P21, P28, and P60 rats, we studied two doses of BRV: 10 and 100 mg/kg injected intraperitoneally 30 min before afterdischarge assessment. We also assessed blood and brain concentrations of BRV 30 min after the injection. RESULTS: BRV 100 mg/kg significantly increased the afterdischarge threshold (ADT) at all ages, whereas BRV at 10 mg/kg increased ADT in P60, P28, and P21 rats. BRV also shortens the afterdischarge duration (ADD), achieving statistical significance with 10 and 100 mg/kg at P60 and with 100 mg/kg at P21. At P60, BRV increases the number of stimulations required to achieve a stage 4-5 seizure in a dose-dependent manner. At P28 and P21, BRV increased the number of stimulations required to develop a stage 4-5 seizure in a dose-dependent manner with almost complete elimination of stage 4-5 seizures. In contrast, at P14, BRV had no effect on the number of stage 4-5 seizures. An age-related decrease in blood and brain concentrations of BRV was observed 30 min after injection of BRV 10 mg/kg, whereas with 100 mg/kg there were no significant age-correlated differences in brain and serum BRV concentrations. SIGNIFICANCE: BRV exerted dose-dependent anti-ictogenic effects from P60 to P14 independent of brain maturation. BRV also exhibited antiepileptogenic effects at P60, whereas this effect need to be further evaluated at P28 and P21. We did not observe any effect on epileptogenesis at P14 at either dose.

Lacosamide treatment following status epilepticus attenuates neuronal cell loss and alterations in hippocampal neurogenesis in a rat electrical status epilepticus model.

PURPOSE: The antiepileptic drug, lacosamide, exerts its therapeutic activity by enhancing slow inactivation of voltage-gated sodium channels. Because putative preventive or disease-modifying effects of drugs may affect epileptogenesis, intrinsic severity, and comorbidities, it is of particular interest to assess the effect of lacosamide on the development of epilepsy and associated cellular alterations. METHODS: The effect of lacosamide was evaluated in an electrical rat status epilepticus (SE) model with a 24-day treatment phase following induction of SE. The impact of lacosamide on the development of spontaneous seizures based on continuous video-electroencephalography (EEG) monitoring, as well as the impact on neuronal cell loss and alterations in hippocampal neurogenesis, was assessed. KEY FINDINGS: Neither low-dose nor high-dose lacosamide affected the development of spontaneous seizures. A dose-dependent neuroprotective effect of lacosamide with significant reduction of neuronal cell loss was observed in the hippocampal CA1 region, as well as in the piriform cortex. In addition, lacosamide attenuated the impact of SE on the rate of hippocampal cell neurogenesis. Moreover, lacosamide prevented a significant rise in the number of persistent basal dendrites. SIGNIFICANCE: Our data do not support an antiepileptogenic effect of lacosamide. However, because lacosamide reduced SE-associated cellular alterations, it would be of interest to determine whether these effects indicate a putative disease-modifying effect of lacosamide in future studies.

Synergism of lacosamide with established antiepileptic drugs in the 6-Hz seizure model in mice.

PURPOSE: Lacosamide (LCM, Vimpat) is an anticonvulsant with a unique mode of action. This provides lacosamide with the potential to act additively or even synergistically with other antiepileptic drugs (AEDs). The objective of this study was to determine the presence of such interactions by isobolographic analysis. METHODS: The anticonvulsant effect of LCM in combination with other AEDs including carbamazepine (CBZ), phenytoin (PHT), valproate (VPA), lamotrigine (LTG), topiramate (TPM), gabapentin (GBP), and levetiracetam (LEV) at fixed dose ratios of 1:3, 1:1, and 3:1, was evaluated in the 6-Hz-induced seizure model in mice. In addition, the impact of the combinations of LCM with the other AEDs on motor coordination was assessed in the rotarod test. Finally, AED concentrations were measured in blood and brain to evaluate potential pharmacokinetic drug interactions. KEY FINDINGS: All studied AEDs produced dose-dependent anticonvulsant effects against 6-Hz-induced seizures. Combinations of LCM with CBZ, LTG, TPM, GBP, or LEV were synergistic. All other LCM/AED combinations displayed additive effects with a tendency toward synergism. Furthermore, no enhanced adverse effects were observed in the rotarod test by combining LCM with other AEDs. No pharmacokinetic interactions were seen on brain AED concentrations. Coadministration of LCM and TPM led to an increase in plasma levels of LCM, whereas the plasma concentration of PHT was increased by coadministration of LCM. SIGNIFICANCE: The synergistic anticonvulsant interaction of LCM with various AEDs, without exacerbation of adverse motor effects, highlights promising properties of LCM as add-on therapy for drug refractory epilepsy.

Benefit of combination therapy in epilepsy: a review of the preclinical evidence with levetiracetam.

Levetiracetam (Keppra) is an antiepileptic drug (AED) characterized by a novel mechanism of action, unique profile of activity in seizure models, and broad-spectrum clinical efficacy. The present report critically reviews several preclinical studies focused on combination therapy with levetiracetam and other anticonvulsants in various seizure and epilepsy models. Administration of levetiracetam together with many different clinically used AEDs or other anticonvulsants generally enhances their protective activity and, among existing AEDs, this was particularly prevalent with valproate. The protective activity of other AEDs was also enhanced by levetiracetam, which seems to be a universal finding that is independent of seizure model or drug combination studied. However, particularly strong enhancement was observed when levetiracetam was combined with agents either enhancing GABAergic or reducing glutamatergic neurotransmission. Importantly, these combinations were not associated with exacerbation of side effects or pharmacokinetic interactions. Based on the available preclinical data, it appears that combination treatment with levetiracetam and other anticonvulsants provides additional therapeutic benefit that may be attributed to its novel and distinct mechanism of action. Moreover, combinations of levetiracetam with clinically used AEDs that enhance GABAergic inhibition may be considered for rational polytherapy, which is often necessary in drug-resistant patients.

Proepileptic phenotype of SV2A-deficient mice is associated with reduced anticonvulsant efficacy of levetiracetam.

PURPOSE: Synaptic vesicle protein 2A (SV2A) constitutes a distinct binding site for an antiepileptic drug levetiracetam (Keppra). In the present study we characterized SV2A (+/-) heterozygous mice in several seizure models and tested if the anticonvulsant efficacy of levetiracetam is reduced in these mice. METHODS: Seizure thresholds of male SV2A (+/-) mice and their wild-type littermates were assessed in pilocarpine (i.p.), kainic acid (s.c.), pentylenetetrazol (i.v.), 6-Hz and maximal electroshock models. Kindling development was compared in amygdala and corneal kindling models. Ex vivo binding of levetiracetam to SV2A was also performed. RESULTS: Long-term electroencephalography (EEG) monitoring and behavioral observations of SV2A (+/-) mice did not reveal any spontaneous seizure activity. However, a reduced seizure threshold of SV2A (+/-) mice was observed in pilocarpine, kainic acid, pentylenetetrazol, and 6-Hz models, but not in maximal electroshock seizure model. Accelerated epileptogenesis development was also demonstrated in amygdala and corneal kindling models. Anticonvulsant efficacy of levetiracetam, defined as its ability to increase seizure threshold for 6 Hz electrical stimulation, was significantly reduced (approx. 50%) in the SV2A (+/-) mice, consistently with reduced binding to SV2A in these mice. In contrast, valproate produced the same anticonvulsant effect in both SV2A (+/+) and SV2A (+/-) mice. DISCUSSION: The present results evidence that SV2A is involved in mediation of the in vivo anticonvulsant activity of levetiracetam, in accordance with its previously proposed mechanism of action. Furthermore, the present data also indicate that even partial SV2A deficiency may lead to increased seizure vulnerability and accelerated epileptogenesis.

Visualization of SV2A conformations in situ by the use of Protein Tomography.

The synaptic vesicle protein 2A (SV2A), the brain-binding site of the anti-epileptic drug levetiracetam (LEV), has been characterized by Protein Tomography. We identified two major conformations of SV2A in mouse brain tissue: first, a compact, funnel-structure with a pore-like opening towards the cytoplasm; second, a more open, V-shaped structure with a cleft-like opening towards the intravesicular space. The large differences between these conformations suggest a high degree of flexibility and support a valve-like mechanism consistent with the postulated transporter role of SV2A. These two conformations are represented both in samples treated with LEV, and in saline-treated samples, which indicates that LEV binding does not cause a large-scale conformational change of SV2A, or lock a specific conformational state of the protein. This study provides the first direct structural data on SV2A, and supports a transporter function suggested by sequence homology to MFS class of transporter proteins.

SV2A protein is a broad-spectrum anticonvulsant target: functional correlation between protein binding and seizure protection in models of both partial and generalized epilepsy.

SV2A, a synaptic vesicle protein, has been recently identified as a binding target for levetiracetam (Keppra). The specific mechanism by which SV2A binding leads to seizure protection has not yet been fully elucidated. However, a functional correlation between SV2A binding affinity and anticonvulsant potency has been observed in the mouse audiogenic seizure model. The present study was undertaken to test whether similar correlations exist in rodent models of partial and generalized epilepsies. As expected, there was a high degree of correlation between anticonvulsant potency and SV2A binding affinity in the mouse audiogenic seizure model (r(2)=0.77; p<0.001). A similar correlation was also observed in the mouse corneal kindling (r(2)=0.80; p<0.01) and in the rat model of generalized absence epilepsy (GAERS) (r(2)=0.72; p<0.01). Moreover, there were no significant differences between the slopes and intercepts of regression lines in these models. Interestingly, the protective potencies in these three epilepsy models were also well correlated with each other. As such, protective doses of a given SV2A ligand in one model could be easily predicted based on the data obtained in another model. Taken together, these results support the concept that SV2A protein is an important target for both partial and generalized epilepsies and thereby relevant for the generation of new antiepileptic drugs with potential broad-spectrum efficacy.

Current understanding of the mechanism of action of the antiepileptic drug lacosamide.

The antiepileptic drug lacosamide [(R)-2-acetamido-N-benzyl-3-methoxypropanamide], a chiral functionalized amino acid, was originally identified by virtue of activity in the mouse and rat maximal electroshock (MES) test. Attention was drawn to lacosamide because of its high oral potency and stereoselectivity. Lacosamide is also active in the 6 Hz seizure model but inactive against clonic seizures in rodents induced by subcutaneous pentylenetetrazol, bicuculline and picrotoxin. It is also ineffective in genetic models of absence epilepsy. At doses greater than those required to confer protection in the MES test, lacosamide inhibits behavioral and electrographic seizures in hippocampal kindled rats. It also effectively terminates seizures in the rat perforant path stimulation status epilepticus model when administered early after the onset of seizures. Lacosamide does not exhibit antiepileptogenic effects in kindling or post-status epilepticus models. The profile of lacosamide in animal seizure and epilepsy models is similar to that of sodium channel blocking antiepileptic drugs, such as phenytoin and carbamazepine. However, unlike these agents, lacosamide does not affect sustained repetitive firing (SRF) on a time scale of hundreds of milliseconds or affect fast inactivation of voltage-gated sodium channels; however, it terminates SRF on a time scale of seconds by an apparent effect on sodium channel slow inactivation. Lacosamide shifts the slow inactivation curve to more hyperpolarized potentials and enhances the maximal fraction of channels that are in the slow inactivated state. Currently, lacosamide is the only known antiepileptic drug in clinical practice that exerts its anticonvulsant activity predominantly by selectively enhancing slow sodium channel inactivation.

Discovery of 4-substituted pyrrolidone butanamides as new agents with significant antiepileptic activity.

(S)-alpha-ethyl-2-oxopyrrolidine acetamide 2 (levetiracetam, Keppra, UCB S.A.), a structural analogue of piracetam, has recently been approved as an add-on treatment of refractory partial onset seizures in adults. This drug appears to combine significant efficacy and high tolerability due to a unique mechanism of action. The latter relates to a brain-specific binding site for 2 (LBS for levetiracetam binding site) that probably plays a major role in its antiepileptic properties. Using this novel molecular target, we initiated a drug-discovery program searching for ligands with significant affinity to LBS with the aim to characterize their therapeutic potential in epilepsy and other central nervous system diseases. We systematically investigated the various positions of the pyrrolidone acetamide scaffold. We found that (i) the carboxamide moiety on 2 is essential for affinity; (ii) among 100 different side chains, the preferred substitution alpha to the carboxamide is an ethyl group with the (S)-configuration; (iii) the 2-oxopyrrolidine ring is preferred over piperidine analogues or acyclic compounds; (iv) substitution of positions 3 or 5 of the lactam ring decreases the LBS affinity; and (v) 4-substitution of the lactam ring by small hydrophobic groups improves the in vitro and in vivo potency. Six interesting candidates substituted in the 4-position have been shown to be more potent antiseizure agents in vivo than 2. Further pharmacological studies from our group led to the selection of (2S)-2-[(4R)-2-oxo-4-propylpyrrolidin-1-yl]butanamide 83alpha (ucb 34714) as the most interesting candidate. It is approximately 10 times more potent than 2 as an antiseizure agent in audiogenic seizure-prone mice. A clinical phase I program has been successfully concluded and 83alpha will commence several phase II trials during 2003.

Use of epileptic animals for adverse effect testing.

A crucial parameter deciding the clinical utility of new antiepileptic drugs (AEDs) is the therapeutic index expressing the margin between anticonvulsant and adverse effects. The latter is commonly quantified during preclinical testing in the rotarod test in normal, healthy rodents. However, the validity of using normal animals for adverse effect predictions in epilepsy patients is questionable. Limbic kindling of rodents induced by corneal kindling of mice and amygdala kindling of rats confirm that epileptic animals are more susceptible to the behavioral and cognitive alterations following acute administration of NMDA antagonists and certain established AEDs. This appears to represent a permanent reactivity specific for limbic kindling since it is absent in rats after chemical kindling with pentylenetetrazole. Animal species with inborn epilepsy, including audiogenic and photosensitive animals, are not revealing an enhanced susceptibility to the behavioral alterations induced by NMDA antagonists. In contrast, these induce severe adverse effects in genetic absence epilepsy rats where certain AEDs also are associated with a more marked deterioration of motor function than in normal animals. This appears in line with several complications with AED use in man being linked to an interaction with the dysfunction of the brain imposed by the epileptic condition. Thus, it is important to involve epileptic animals in preclinical adverse effect testing, in particular when evaluating new AED candidates with novel or unknown mechanisms. In that respect, limbic kindling appears to represent a sensitive and relevant approach.

Pilocarpine-induced epileptogenesis in the rat: impact of initial duration of status epilepticus on electrophysiological and neuropathological alterations.

This study characterized the electrophysiological and neuropathological changes in rat brains caused by pilocarpine (PILO)-induced status epilepticus (SE) of different duration. SE induced by PILO (375 mg/kg, i.p. adm.) were terminated with a bolus dose of diazepam (10 mg/kg, i.v. adm.) injected 7.5, 15, 30, 60 or 120 min after initiation of the secondary generalization of the SE. Three weeks later, the gain in body weight was significantly reduced in the rats exposed to PILO-induced SE lasting 30 min or more, when compared to controls. Spontaneous seizures were not detected in rats with PILO-induced SE of 7.5 min duration whereas 50 and 25% of the rats exposed to seizure durations of 30 and 120 min expressed motor seizures. Significant alterations reflecting hyperexcitability (increased number of population spikes (PSs)) and reduced paired-pulse inhibition were observed in recordings of hippocampal field potentials from rats with PILO-induced SE of at least 30 min duration. This was substantiated by brain lesions (necrosis in olfactory cortex, hippocampus, amygdala and thalamus) in all rats manifesting a SE of at least 30 min duration. Thus, the results of the present study demonstrate that rats exposed to PILO-induced SE of at least 30 min duration manifest an epileptogenic process, revealed 3 weeks later by several parameters. Among these, hippocampal field potentials appear to represent the most sensitive marker, potentially useful for pharmacological evaluation of drugs with putative antiepileptogenic properties.

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.

Electrophysiological, neurochemical and regional effects of levetiracetam in the rat pilocarpine model of temporal lobe epilepsy.

This study compared levetiracetam (Keppra) with reference antiepileptic drugs (AEDs) in the rat pilocarpine model of temporal lobe epilepsy. Electroencephalogram (EEG) recordings showed that i.p. administration of valproate (300 mg/kg), phenobarbital (5 mg/kg) and clonazepam (0.5 mg/kg) all significantly delayed the appearance of the first epileptic spike discharge in hippocampus as well as synchronous epileptiform activity in hippocampus and cortex. In contrast, i.p. administration of levetiracetam (17 mg/kg) only significantly delayed the appearance of the latter. This was corroborated by findings showing that i.p. administration of levetiracetam (17 mg/kg) significantly opposed pilocarpine-induced increases in the amplitude of the orthodromic population spike in the hippocampal CA3 area of urethane-anaesthetised rats, while valproate (200 mg/kg), phenobarbital (10 mg/kg) and clonazepam (1 mg/kg) had no effect. Pre-treatment i.p. with phenobarbital (10 mg/kg) and clonazepam (0.5 mg/kg) significantly reversed seizure-induced changes in aspartate and GABA concentrations while valproate (300 mg/kg) significantly reduced aspartate concentrations further. In contrast, levetiracetam (34 mg/kg) significantly counteracted all seizure-induced alterations in amino acid concentrations. Midazolam induced significant seizure protection after microinjection into substantia nigra pars reticulata (SNR, 50 nmol), nucleus accumbens (NA, 25 nmol) and caudate putamen (CP, 25 nmol), whereas phenytoin (50 nmol) only showed significant seizure protection after injection into the latter area. Levetiracetam differed by significant seizure protection after injection into SNR (1,000 nmol) and NA (3,000 nmol). These results suggest that levetiracetam is distinct from other AEDs by its ability to selectively suppress synchronisation of neuronal spike and burst firing in hippocampus.

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.

Binding characteristics of brivaracetam, a selective, high affinity SV2A ligand in rat, mouse and human brain: relationship to anti-convulsant properties.

Brivaracetam is a novel synaptic vesicle protein 2A (SV2A) ligand reported to be 10 fold more potent than levetiracetam in animal models of epilepsy. This study reports the binding profile of brivaracetam in the brain of several species in relation to its anticonvulsant properties. The affinity, kinetics and selectivity of brivaracetam and its tritiated form [(3)H]ucb 34714 have been determined by in vitro binding experiments in rat, human and mouse brain and on recombinant human SV2A. Brivaracetam and levetiracetam ex vivo binding to SV2A and anticonvulsant activities in audiogenic mice were compared in relation to dose and time. Brivaracetam bound selectively with 20 fold higher affinity than levetiracetam to SV2A. [(3)H]ucb 34714 bound reversibly and with high affinity to an homogenous population of binding sites in rat and human brain and to human SV2A expressed in CHO cells. The binding sites labeled by [(3)H]ucb 34714 in brain had the pharmacological characteristics of SV2A and no specific binding could be detected in the brain of SV2A(-/-) knock-out mice. The time- and dose-dependency of brivaracetam and levetiracetam for binding to brain SV2A and for providing seizure protection in audiogenic mice correlated well; brivaracetam being more potent and faster than levetiracetam. Brivaracetam is a potent and selective SV2A ligand. From its affinity and pharmacokinetics, simulations predicted that at therapeutically relevant doses, brivaracetam should occupy more than 80% of SV2A in human brain, in line with levels of occupancy observed in pre-clinical models of epilepsy.