Will brain damage after status epilepticus be history in 2010?

Fit for purpose application of currently existing animal models in the discovery of novel epilepsy therapies

Animal seizure and epilepsy models continue to play an important role in the early discovery of new therapies for the symptomatic treatment of epilepsy. Since 1937, with the discovery of phenytoin, almost all anti-seizure drugs (ASDs) have been identified by their effects in animal models, and millions of patients world-wide have benefited from the successful translation of animal data into the clinic. However, several unmet clinical needs remain, including resistance to ASDs in about 30% of patients with epilepsy, adverse effects of ASDs that can reduce quality of life, and the lack of treatments that can prevent development of epilepsy in patients at risk following brain injury. The aim of this review is to critically discuss the translational value of currently used animal models of seizures and epilepsy, particularly what animal models can tell us about epilepsy therapies in patients and which limitations exist. Principles of translational medicine will be used for this discussion. An essential requirement for translational medicine to improve success in drug development is the availability of animal models with high predictive validity for a therapeutic drug response. For this requirement, the model, by definition, does not need to be a perfect replication of the clinical condition, but it is important that the validation provided for a given model is fit for purpose. The present review should guide researchers in both academia and industry what can and cannot be expected from animal models in preclinical development of epilepsy therapies, which models are best suited for which purpose, and for which aspects suitable models are as yet not available. Overall further development is needed to improve and validate animal models for the diverse areas in epilepsy research where suitable fit for purpose models are urgently needed in the search for more effective treatments.

Unprovoked status epilepticus: the prognosis for otherwise normal children with focal epilepsy

OBJECTIVE

To document the effect of unprovoked status epilepticus (SE) on the prognosis for otherwise normal children with focal epilepsy.

METHODS

From the Nova Scotia Childhood Epilepsy Study (population-based), we identified patients with focal epilepsy, normal intelligence, and neurologic examination and follow-up ≥ 10 years. We compared those with and without unprovoked SE.

RESULTS

One hundred eighty-eight cases had a mean follow-up of 27 ± 5 years with no deaths from SE. Thirty-nine (20%) had SE, 19 of whom experienced their first seizure. The number of episodes of SE was 1 in 27 patients (69%) and 2 to 10 in 12 patients. At onset 9 of 39 (23%) SE patients and 35 of 149 (23%) no-SE patients had specific learning disorders. At follow-up, 11 (28%) SE and 49 (33%) no-SE patients had learning disorders (P = not statistically different [ns]). Grades repeated, high school graduation, and advanced education did not differ. The number of antiepileptic drug (AED) used throughout the clinical course was the same: 22/39 (56%). SE patients used ≤ 2 AEDs versus 99 of 149 (64%) no-SE patients (P = .2). The distribution of patients using 3 to 11 AEDs was similar. The remission rate (seizure-free without AEDs at the end of follow-up) for SE patients was 24 of 39 (61%) versus 99 of 149 (66%) in no-SE (P = .5). Intractable epilepsy occurred in 15% SE and 11% of no-SE cases.

CONCLUSIONS

SE often recurs but apparently has little influence on long-term intellectual and seizure outcome in normally intelligent children with focal epilepsy.

[Generalized convulsive status epilepticus in emergency situations in and out of hospital]

Generalized convulsive status epilepticus (GCSE) must be rapidly identified and managed according to pre-established protocols developed by the teams that treat such patients. Close collaboration between emergency specialists, critical-care specialists, electrophysiologists, and neurologists is essential. Overt GCSE, by far the most frequent, is generally easy to diagnose: it must nonetheless be distinguished from pseudo-status epilepticus. Subtle GCSE is difficult to recognize. The initial antiepileptic treatments are fairly well classified but their efficacy is unreliable. If the patient is treated within 5 to 30 minutes after convulsions begin, clonazepam should be administered alone; if the convulsions persist, follow it 5 minutes later with a second injection of clonazepam together with phosphenytoin or phenobarbital. If convulsions began more than 30 minutes before treatment, the initial clonazepam dose should be combined with phosphenytoin or phenobarbital. Relay antiepileptic treatment is essential in the short term as well, unless the cause is immediately reversible. This relay must be immediate if diazepam or midazolam is used alone, because of the high risk of recurrence. Refractory GCSE must be diagnosed very cautiously. Its treatment requires resuscitation using anesthetic agents guided if possible by continuous electroencephalography (EEG), without ever stopping the basic antiepileptic treatment. The cerebral aggression that results from either the status epilepticus itself or its cause must be treated with precision. Treatment of the cause is primordial and, when possible, always the main priority. The etiological investigation must be conducted with tenacity, speed, and perspicacity. GCSE may occur in known epileptics or be the first presentation. The investigation will be negative in 5-10% of cases. Although sometimes difficult to interpret, EEG is essential in numerous situations, in particular, atypical clinical pictures, vigilance disorders that persist after convulsions, and refractory status epilepticus. Overall mortality is on the order of 10%. Prognosis is above all a function of the cause. Age, duration of GCSE symptoms, and the speed and quality of management also affect prognosis. Current guidelines are based only very partially on data and evidence. Defining GCSE at its different stages is an essential prerequisite for the treatment trials that are necessary.

Effect of novel AMPA antagonist, NS1209, on status epilepticus

The current first line treatment of status epilepticus (SE) is based on the use of compounds that enhance GABAergic transmission or block sodium channels. These treatments discontinue SE in only two-thirds of patients, and therefore new therapeutic approaches are needed. We investigated whether a novel water-soluble AMPA antagonist, NS1209, discontinues SE in adult rats. SE was induced by electrical stimulation of the amygdala or subcutaneous administration of kainic acid. Animals were monitored continuously with video-electroencephalography during SE and drug treatment. We found that NS1209 could be safely administered to rats undergoing electrically induced SE at doses up to 50mg/kg followed by intravenous infusion of 5mg/kg for up to 24h. NS1209 administered as a bolus dose of 10-50mg/kg (i.p. or i.v.) followed by infusion of 4 or 5mg/kg h (i.v.) for 2-24h effectively discontinued electrically induced SE in all animals within 30-60 min, and there was no recurrence of SE after a 24-h infusion. Kainate-induced SE was similarly blocked by 10 or 30 mg/kg NS1209 (i.v.). To compare the efficacy and neuroprotective effects of NS1209 with those of diazepam (DZP), one group of rats received DZP (20mg/kg, i.p. and another dose of 10 mg/kg 6h later). By using the administration protocols described, the anticonvulsant effect of NS1209 was faster and more complete than that of DZP. NS1209 treatment (20 mg/kg bolus followed by 5mg/kg h infusion for 24 h) was neuroprotective against SE-induced hippocampal neurodegeneration, but to a lesser extent than DZP. These findings suggest that AMPA receptor blockade by NS1209 provides a novel and mechanistically complimentary addition to the armamentarium of drugs used to treat SE in humans.

Epileptic seizures cause extended postictal cerebral vascular dysfunction that is prevented by HO-1 overexpression

The extended postictal state is characterized by neurological problems in patients. Inadequate blood supply to the brain and impaired cerebral autoregulation may contribute to seizure-induced neuronal damage. Recent evidence in newborn pigs indicates that activation of the antioxidative enzyme heme oxygenase (HO) at the onset of seizures is necessary for increased cerebral blood flow during the ictal episode and for normal cerebral vascular functioning during the immediate postictal period. We hypothesized that seizures cause prolonged postictal cerebral vascular dysfunction that can be accentuated by HO inhibition and rescued by HO overexpression. Cerebral vascular responses to endothelium-dependent (hypercapnia, bradykinin) and -independent (isoproterenol, sodium nitroprusside) stimuli were assessed 48 h after bicuculline-induced seizures in: 1) saline-control newborn piglets, 2) HO-inhibited animals (HO was inhibited by tin protoporphyrin, SnPP, 3 mg/kg iv), and 3) HO-overexpressing piglets (HO-1 was upregulated by cobalt protoporphyrin, CoPP, 50 mg/kg ip). Extended alterations of HO expression in cerebral microvessels were confirmed by measuring CO production and inducible HO (HO-1) and constitutive HO (HO-2) proteins. Our data provide evidence that seizures cause a severe, sustained, postictal cerebral vascular dysfunction as reflected by impaired vascular reactivity to physiologically relevant dilators. During the delayed postictal state, vascular reactivity to all dilator stimuli was reduced in saline control and, to a greater extent, in HO-inhibited animals. In CoPP-treated piglets, no reduction in postictal cerebral vascular reactivity was observed. These findings may indicate that CoPP prevents postictal cerebral vascular dysfunction by upregulating HO-1, a finding that might have implications for preventing postictal neurological complications.