Nifedipine affects the anticonvulsant activity of topiramate in various animal models of epilepsy

Influence of levetiracetam on the anticonvulsant efficacy of conventional antiepileptic drugs against audiogenic seizures in DBA/2 mice

Levetiracetam (LEV, [S]-alpha-ethyl-2-oxo-1-pyrrolidine acetamide) is a new antiepileptic that has been used as adjunctive therapy to treat patients with intractable epilepsy. Systemic administration of levetiracetam (2.5-30 mg/kg, intraperitoneally (i.p.)) was able to produce a dose-dependent decrease in DBA/2 audiogenic seizure severity score. In combination with conventional antiepileptic drugs, levetiracetam, 5mg/kg, i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, potentiated the anticonvulsant activity of some antiepileptic drugs studied against sound-induced seizures in DBA/2 mice. The degree of potentiation induced by levetiracetam was greater, approximately twice, for carbamazepine, diazepam, felbamate, topiramate, gabapentin, and valproate, less for lamotrigine, phenobarbital and phenytoin. This increase was associated with a comparable impairment in motor activity; however, the therapeutic index of combined treatment of antiepileptic drugs with levetiracetam was more favourable than the combination with saline with the exception of lamotrigine, phenytoin and phenobarbital. Since levetiracetam did not significantly influence the total and free plasma and the brain levels of antiepileptics studied. In addition, levetiracetam did not significantly affect the hypothermic effects of the anticonvulsants tested. In conclusion, levetiracetam showed an additive anticonvulsant effect when administered in combination with some classical anticonvulsants, most notably carbamazepine, diazepam, felbamate, gabapentin, topiramate and valproate, implicating a possible therapeutic relevance of such drug combinations.

Topiramate or valproate in patients with juvenile myoclonic epilepsy: a randomized open-label comparison

Few randomized, controlled trials evaluating antiepileptic drug (AED) efficacy and tolerability have focused solely on patients with juvenile myoclonic epilepsy (JME). We conducted a pilot, randomized controlled trial comparing topiramate (N=19) and valproate (N=9) in adolescents/adults with JME to evaluate clinical response when these broad-spectrum agents are titrated to optimal effect. Rating scales were used to systematically assess tolerability. Among patients completing 26 weeks of treatment, 8 of 12 (67%) in the topiramate group and 4 of 7 (57%) in the valproate group were seizure-free during the 12-week maintenance period. Median daily dose was 250mg topiramate or 750mg valproate. Two (11%) topiramate-treated patients and one (11%) valproate-treated patient discontinued due to adverse events. Systemic toxicity scores, but not neurotoxicity scores, differed substantially between the two groups; greater systemic toxicity was associated with valproate. Our preliminary findings that topiramate may be an effective, well-tolerated alternative to valproate warrant validation in a double-blind trial.

Amino acid levels in some brain areas of inducible nitric oxide synthase knock out mouse (iNOS−/−) before and after pentylenetetrazole kindling

Inducible nitric oxide synthase knock-out (iNOS(-/-)) mice are valid models of investigation for the role of iNOS in patho-physiological conditions. There are no available data concerning neuroactive amino acid levels of iNOS(-/-) mice and their behaviour in response to pentylenetetrazole (PTZ). We found no significant differences in the convulsive dose 50 (CD(50)) between iNOS(-/-) and control (iNOS(+/+)) mice, however, iNOS(-/-) mice reach the kindled status more slowly than control, suggesting that in basal condition the GABA-benzodiazepine inhibitory inputs are unaltered by iNOS mutation. Clear differences between iNOS(+/+) and iNOS(-/-) mice amino acid concentrations were evident both in basal conditions and after kindling. Our results show that aspartate was significantly lower in all brain areas studied except the brain stem whereas glutamate and glutamine were significantly higher in the cortex, hippocampus and brain stem. GABA was slightly and not significantly higher in the cortex, hippocampus and brain stem, whereas taurine was significantly higher in all areas except diencephalon and glycine was significantly lower in the diencephalon and cerebellum. In this context, the inability of iNOS(-/-) mice to increase the NO levels following PTZ administrations indicate that NO might play a pro-epileptogenic role in the genesis and development of some types of epilepsy. Since there is no correlation between neurotransmitter levels and the development of kindling, it is possible to exclude that the difference between the two strains is due to an imbalance between the considered neurotransmitters, and it is then possible that this difference is due to the presence of iNOS, which might be involved in long term plasticity of the brain.

The combination of topiramate and diazepam is partially neuroprotective in the hippocampus but not antiepileptogenic in the lithium-pilocarpine model of temporal lobe epilepsy

Lithium-pilocarpine induces status epilepticus (SE), leading to extensive damage and spontaneous recurrent seizures (SRS). Neuroprotective and antiepileptogenic effects of topiramate (TPM) associated with diazepam (DZP) were investigated in this model. SE was induced by LiCl and pilocarpine. TPM (10, 30 or 60 mg/kg) was injected at the onset of SE and 10h later and DZP (2.5 and 1.25mg/kg) at 2 and 10h after SE. TPM treatment was continued twice daily for 6 days. Other rats received two injections of DZP on the day of SE. Cell counting was performed on thionine-stained sections 14 days after SE and after 2 months of epilepsy. Occurrence and frequency of SRS were video-recorded. The MRI T2-weighted signal was quantified in hippocampus and ventral cortices. DZP-TPM treatment induced partial neuroprotection in CA1 and hilus, and tended to increase the percentage of rats with protected neurons in layer III/IV of the ventral entorhinal cortex. The latency to and frequency of SRS were not modified by DZP-TPM. T2-weighted signal was decreased in hippocampus 3 days after SE at all TPM doses and in ventral hippocampus after epilepsy onset. In conclusion, although DZP-TPM treatment was able to partially protect two areas critical for epileptogenesis, the hippocampus and ventral entorhinal cortex, it was not sufficient to prevent epileptogenesis.

Effects of non-competitive AMPA receptor antagonists injected into some brain areas of WAG/Rij rats, an animal model of generalized absence epilepsy

CFM-2 [1-(4-aminophenyl)-3,5-dihydro-7,8-dimethoxy-4H-2,3-benzodiazepin-4-one] and THIQ-10c [N-acetyl-1-(4-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline], are two non-competitive 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionic acid (AMPA) receptor antagonists, which demonstrated to antagonize generalized tonic-clonic seizures in different animal models. We have evaluated the effects of such compounds in a genetic animal model of absence epilepsy, the WAG/Rij rat. Animals were focally microinjected into specific brain areas of the cortico-thalamic circuit in order to evaluate the effects of these compounds on the number and duration of epileptic spike-wave discharges (SWDs) and better characterize the role of AMPA neurotransmission in this animal model. The focal microinjection of the two AMPA antagonists into some thalamic nuclei (ventralis posteromedialis (VPM), reticularis (NRT), ventralis posterolateralis (VPL) and the primary somatosensory forelimb region (S1FL)) was, generally, not able to significantly modify the occurrence of SWDs. Whereas, both compounds were able to reduce the number and duration of SWDs dose-dependently when microinjected into the peri-oral region of the primary somatosensory cortex (S1po). These findings suggest that AMPA receptor antagonists might play a role in absence epilepsies and that it might depend on the involvement of specific neuronal areas.

Development of aDrosophilaseizure model forin vivohigh-throughput drug screening

An important application of model organisms in neurological research has been to identify and characterise therapeutic approaches for epilepsy, a recurrent seizure disorder that affects > 1% of the human population. Proconvulsant-treated rodent models have been widely used for antiepileptic drug discovery and development, but are not suitable for high-throughput screening. To generate a genetically tractable model that would be suitable for large-scale, high-throughput screening for antiepileptic drug candidates, we characterized a Drosophila chemical treatment model using the GABA(A) receptor antagonist picrotoxin. This proconvulsant, delivered to Drosophila larvae via simple feeding methods suitable for automated screening, generated robust generalised seizures with lethality occurring at doses between 0.3 and 0.5 mg/mL. Electrophysiological analysis of CNS motor neuron output in picrotoxin-treated larvae revealed generalised seizures within minutes of drug exposure. At subthreshold doses for seizure induction, picrotoxin produced an increased frequency of motor neuron action potential bursting, indicating that CNS GABAergic transmission regulates patterned activity. Mutants in the Drosophila Rdl GABA(A) receptor are resistant to picrotoxin, confirming that seizure induction occurs via a conserved GABA(A) receptor pathway. To validate the usefulness of this model for in vivo drug screening, we identified several classes of neuroactive antiepileptic compounds in a pilot screen, including phenytoin and nifedipine, which can rescue the seizures and lethal neurotoxicity induced by picrotoxin. The well-defined actions of picrotoxin in Drosophila and the ease with which compounds can be assayed for antiseizure activity makes this genetically tractable model attractive for high-throughput in vivo screens to identify novel anticonvulsants and seizure susceptibility loci.

Effects of some neurosteroids injected into some brain areas of WAG/Rij rats, an animal model of generalized absence epilepsy

Neurosteroids are synthesized in the brain and have been demonstrated to modulate various cerebral functions. Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), a naturally occurring neurosteroid, and ganaxolone (3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one), a synthetic derivative, are two neurosteroids acting as positive allosteric modulators of the GABA(A) receptor complex acting on a specific steroid recognition site. Both agents antagonize generalized tonic-clonic seizures in various animal models of epilepsy. Pregnenolone sulphate (3beta-hydroxy-5alpha-pregnen-20-one 3-sulphate; PS) is a negative allosteric modulator of GABA(A) receptors and a positive modulator of the NMDA receptors. We have evaluated the effects of such compounds in a genetic animal model of absence epilepsy, the WAG/Rij rat. Animals were chronically implanted with five frontoparietal cortical electrodes for electrocorticogram (EEG) recordings and bilateral guide cannulae into specific brain areas of the cortico-thalamic circuit in order to evaluate the effects of these compounds on the number and duration of epileptic spike-wave discharges (SWDs). The focal and bilateral microinjection of the two GABA(A) positive modulators into some thalamic nuclei (nucleus ventralis posteromedialis, nucleus reticularis thalami, nucleus ventralis posterolateralis was usually able to significantly worsen the occurrence of SWDs in WAG/Rij rats. Whereas both compounds were able to reduce the number and duration of SWDs when microinjected into the peri-oral region of the primary somatosensory cortex. The effects of PS were more complex depending on both the dose and the site of administration, generally, at low doses in thalamic nuclei and cortex, PS induced an increase of absence activity and a reduction at higher doses. These findings suggest that neurosteroids might play a role in absence epilepsies and that it might depend on the involvement of specific neuronal areas.

Evidence supporting a role of serotonin in modulation of sudden death induced by seizures in DBA/2 mice

PURPOSE

Sudden unexpected death in epilepsy (SUDEP) is a serious concern for epilepsy patients. DBA/2 mice are proposed as a SUDEP model, because these mice exhibit respiratory arrest (RA) after audiogenic seizures (AGSs), and RA is also implicated in human SUDEP. Respiratory mechanisms are modulated, in part, by serotonin. Therefore we evaluated the effects of serotoninergic agents on RA incidence in DBA/2 mice.

METHODS

DBA/2 mice (75%) exhibited AGS and RA, and approximately 99% of animals could be resuscitated. The mice exhibiting RA were given a selective serotonin reuptake inhibitor, fluoxetine, 24 h after the initial AGS, and RA susceptibility was evaluated 30 min later. Ten percent of DBA/2 mice exhibited tonic hindlimb extension (TE) without RA, and a serotonin antagonist (cyproheptadine) was administered to these mice.

RESULTS

Fluoxetine (15-25 mg/kg, i.p.) significantly reduced the incidence of RA in DBA/2 mice after AGSs, and this effect was reversible by 72 h. Only the 25-mg/kg dose reduced AGS severity. In mice exhibiting TE without RA, the incidence of RA was significantly increased 30 min after cyproheptadine (1-2 mg/kg i.p.). Most of these mice exhibited AGSs without RA again by 72 h.

CONCLUSIONS

These findings indicate that fluoxetine reduced RA in DBA/2 mice at doses that did not reduce seizure severity. Because DBA/2 mice are a proposed model for human SUDEP, these data support evaluation of fluoxetine for SUDEP prevention in the patient population most susceptible to SUDEP. The data raise concern about the use of serotonin antagonists in this patient population.

Activity profile of pregabalin in rodent models of epilepsy and ataxia

Pregabalin (Lyrica) is a novel amino acid compound that binds with high affinity to the alpha2-delta (alpha2-delta) auxiliary protein of voltage-gated calcium channels. In vivo, it potently prevents seizures, pain-related behaviors and has anxiolytic-like activity in rodent models. The present studies were performed to determine the profile of pregabalin anticonvulsant activity in a variety of mouse and rat models. In the high-intensity electroshock test, pregabalin potently inhibited tonic extensor seizures in rats (ED50 = 1.8 mg/kg, PO), and low-intensity electroshock seizures in mice. It prevented tonic extensor seizures in the DBA/2 audiogenic mouse model (ED50 = 2.7 mg/kg, PO). Its time course of action against electroshock induced seizures in rats roughly followed the pharmacokinetics of radiolabeled drug in the brain compartment. At higher dosages (ED50 1= 31 mg/kg, PO), pregabalin prevented clonic seizures from pentylenetetrazole in mice. In a kindled rat model of partial seizures, pregabalin prevented stages 4-5 behavioral seizures (lowest effective dose = 10 mg/kg, IP), and also reduced the duration of electrographic seizures. Pregabalin was not active to prevent spontaneous absence-like seizures in the Genetic Absence Epilepsy in Rats from Strasbourg (GAERS) inbred Wistar rat strain. Pregabalin caused ataxia and decreased spontaneous locomotor activity at dosages 10-30-fold higher than those active to prevent seizures. These findings suggest that pregabalin has an anticonvulsant mechanism different from the prototype antiepileptic drugs and similar to that of gabapentin except with increased potency and bioavailability. In summary, our results show that pregabalin has several properties that favor treatment of partial seizures in humans.

Facilitation of spike-wave discharge activity by lipopolysaccharides in Wistar Albino Glaxo/Rijswijk rats

In normal rats the proinflammatory cytokines like interleukin-1beta, interleukin-6, which are induced by bacterial lipopolysaccharides, are able to control thalamo-cortical excitability by exerting strong effects on physiological synchronization such as sleep and on pathological synchronization like that in epileptic discharges. To investigate whether proinflammatory cytokines or lipopolysaccharides could modulate absence seizures resulting from a very different generator mechanism than the already investigated bicuculline-, kindling- and kainate-induced seizures, we used a genetically epileptic Wistar Albino Glaxo/Rijswijk rat strain, which is spontaneously generating high voltage spike-wave discharges. Wistar Albino Glaxo/Rijswijk rats responded with an increase of the number of spike-wave discharges to lipopolysaccharide injection (from 10 microg/kg to 350 microg/kg). Repetitive administration of 350 microg/kg lipopolysaccharides daily for 5 days increased the number of spike-wave discharges on the first, second and third days but the number of spike-wave discharges returned to the control value on day 5, at the 5th injection of lipopolysaccharides, showing a tolerance to lipopolysaccharides. The lipopolysaccharide-induced increase in spike-wave discharges was not directly correlated with the elevation of the core body temperature, as it is in febrile seizures, although lipopolysaccharide induced prostaglandin and is clearly pyrogenic at the doses used. Indomethacin, the prostaglandin synthesis inhibitor, efficiently blocked lipopolysaccharide-induced enhancement of spike-wave discharge genesis suggesting that the spike-wave discharge facilitating effect of lipopolysaccharides involves induction of cyclooxygenase 2 and subsequent synthesis and actions of prostaglandin E2. Low dose (40 mg/kg, i.p.) of competitive N-methyl-d-aspartate receptor antagonist 2-amino-5-phosphonopentanoic acid, and low dose of lipopolysaccharide (20 microg/kg) showed a synergistic interaction to increase the number of spike-wave discharges, whereas at supramaximal doses of lipopolysaccharide and the N-methyl-D-aspartate antagonist no synergy was present. The data reveal a functional connection between absence epileptic activity and lipopolysaccharide induction of prostaglandin synthesis and prostaglandin action and suggest some common cellular targets in epilepsy and lipopolysaccharide-induced inflammation.

Biphasic actions of topiramate on monoamine exocytosis associated with both soluble N-ethylmaleimide-sensitive factor attachment protein receptors and Ca(2+)-induced Ca(2+)-releasing systems

To explore the pharmacological mechanisms of topiramate (TPM), we determined the effects of TPM on monoamine (dopamine and serotonin) exocytosis associated with N-ethylmaleimide-sensitive factor attachment protein receptors and Ca(2+)-induced Ca(2+)-releasing systems, including inositol-triphosphate receptor and ryanodine receptor in freely moving rat pre-frontal cortex using in vivo microdialysis. During resting stage, Ca(2+) output from endoplasmic reticulum Ca(2+) store via inositol-triphosphate receptor regulates syntaxin-associated monoamine exocytosis mechanism, whereas during neuronal hyperexcitable stage, Ca(2+) output via ryanodine receptor regulates synaptobrevin-associated monoamine exocytosis mechanism. Basal monoamine releases were increased and decreased by therapeutically relevant and supratherapeutic concentration of TPM, respectively. The therapeutic-relevant concentration of TPM increased Ca(2+)-evoked release concentration-dependently; however, its stimulatory effect was attenuated in the supratherapeutic range. The K(+)-evoked releases were reduced by TPM concentration-dependently (from therapeutic to supratherapeutic ranges). The therapeutic-relevant concentration of TPM-induced elevation of basal release was reduced by cleavage with syntaxin and inhibition of inositol-triphosphate receptor predominantly, by cleavage with SNAP-25 and synaptobrevin weakly, but not by ryanodine receptor inhibitor. The therapeutic-relevant concentration of TPM-induced elevation of Ca(2+)-evoked release was reduced by cleavage with syntaxin and inositol-triphosphate receptor inhibitor selectively. The therapeutic-relevant concentration of TPM-induced reduction of K(+)-evoked monoamine release was abolished by cleavage with synaptobrevin, but was not affected by cleavage with SNAP-25 or synaptobrevin. The stimulatory effect of ryanodine receptor agonist on K(+)-evoked monoamine release was reduced by TPM, whereas that of inositol-triphosphate receptor agonist was not affected by TPM. Therefore, these results indicate that the combination of the effects of TPM on exocytosis mechanisms associated with SNARE and Ca(2+)-induced Ca(2+)-releasing systems, enhancement of inositol-triphosphate receptor/syntaxin and inhibition of ryanodine receptor/synaptobrevin in pre-frontal cortex, may be involved in clinical actions of TPM.

Preclinical Profiling and Safety Studies of ABT-769: A Compound with Potential for Broad-spectrum Antiepileptic Activity

PURPOSE

The objective of this study was to characterize the antiseizure and safety profiles of ABT-769 [(R)-N-(2 amino-2-oxoethyl)spiro[2,5]octane-1-carboxamide].

METHODS

ABT-769 was tested for protection against maximal electroshock and pentylenetetrazol-induced seizures in the mouse and for suppression of electrically kindled amygdala seizures and spontaneous absence-like seizures in the rat. The central nervous system safety profile was evaluated by using tests of motor coordination and inhibitory avoidance. The potential for liver toxicity was assessed in vitro by using a mitochondrial fatty acid beta-oxidation assay. Teratogenic potential was assessed in the mouse.

RESULTS

ABT-769 blocked maximal electroshock, subcutaneous pentylenetetrazol and intravenous pentylenetetrazol-induced seizures with median effective dose (ED50) values of 0.25, 0.38, and 0.11 mmol/kg, p.o., respectively. No tolerance was evident in the intravenous pentylenetetrazol test after twice-daily dosing of ABT-769 (0.3 mmol/kg, p.o.) for 4 days. ABT-769 blocked absence-like spike-wave discharge (ED50, 0.15 mmol/kg, p.o.) and shortened the cortical and amygdala afterdischarge duration of kindled seizures (1 and 3 mmol/kg, p.o.). The protective indices (ED50 rotorod impairment/ED50 seizure protection) were 4.8, 3.2, and 10.9 in the maximal electroshock, subcutaneous pentylenetetrazol and intravenous pentylenetetrazol seizure tests, respectively. ABT-769 did not affect inhibitory avoidance performance (0.1-1 mmol/kg, p.o.). ABT-769 did not affect mitochondrial fatty acid beta-oxidation or induce neural tube defects.

CONCLUSIONS

ABT-769 is an efficacious antiseizure agent in animal models of convulsive and nonconvulsive epilepsy and has a favorable safety profile. ABT-769 has a broad-spectrum profile like that of valproic acid. Its profile is clearly different from those of carbamazepine, phenytoin, lamotrigine, topiramate, vigabatrin, and tiagabine.

Amino acid levels in some lethargic mouse brain areas before and after pentylenetetrazole kindling

Genetic animal models have contributed significantly to our understanding of epilepsy causes. Lethargic mice are considered a valid model of absence epilepsy, which have been shown to possess behavioral, electrographic and pharmacological profiles similar to those of humans with absence epilepsies. Single gene mutations that comprise the beta4 subunit of voltage-sensitive Ca2+ channels underlie the spontaneous discharges of the absence, non-convulsive seizures of lethargic mice. There are no available data concerning how the mutant channels actually behave at terminals in response to chemical activation by subconvulsant stimulation with pentylenetetrazole. In this study, we found no significant difference in the convulsive dose 50 between lethargic and control mice. Lethargic mice showed a more rapid development of kindling to pentylenetetrazole than control animals. No significant differences were observed between the groups of mice rechallenged with pentylenetetrazole 30 or 60 days after the end of the chronic treatment. Marked differences in brain amino acid levels were found between the two strains of mice in basal conditions and after kindling. In conclusion, our results indicate that lethargic mice show a range of biochemical and behavioral changes, correlated in particular with a higher susceptibility to develop kindled seizures.

Molecular Pharmacology of Topiramate: Managing Seizures and Preventing Migraine

Topiramate is a neuromodulatory compound with stabilizing properties that was initially introduced for the management of partial seizures. Topiramate has been demonstrated to modify several receptor-gated and voltage-sensitive ion channels, including voltage-activated Na+ and Ca2+ channels and non-NMDA receptors. These receptors have been implicated in the pathophysiology of both epilepsy and migraine. The pharmacological mechanisms of action for topiramate that may explain its antiepileptic and migraine preventive activities will be discussed in this review. In addition, the potential relationship between the molecular activities of topiramate and its efficacy in epilepsy and migraine prevention will be emphasized.