Prophylactic treatment with levetiracetam after status epilepticus: Lack of effect on epileptogenesis, neuronal damage, and behavioral alterations in rats
Introduction
Epileptogenesis, i.e., the process leading to epilepsy, is a common sequel of brain insults such as head trauma, cerebrovascular disease, brain tumors, neurosurgical procedures, neurodegenerative conditions, status epilepticus, and febrile seizures (Herman, 2002, Pitkänen, 2004). Following such brain insults, there is a cascade of morphologic and functional changes in the injured area over months to years before the occurrence of spontaneous recurrent seizures (SRS), i.e., the hallmark of epilepsy. This latent period may offer a therapeutic window for the prevention of epileptogenesis and the development of unprovoked seizures and epilepsy (Pitkänen, 2004). However, in clinical trials, administration of conventional antiepileptic drugs (AEDs) such as phenytoin, carbamazepine or valproate following acute brain insults has thus far failed to prevent epileptogenesis (Temkin, 2001, Temkin, 2004).
Based on data from the kindling model of temporal lobe epilepsy (TLE), the novel AED levetiracetam (LEV; Keppra®) has been suggested to exert antiepileptogenic properties (Klitgaard and Pitkänen, 2003). LEV seems to act by a unique mechanism, i.e. modulation of synaptic release of neurotransmitters by binding to the synaptic vesicle protein, SV2A (Lynch et al., 2004, Gillard et al., 2006). In the kindling model, LEV was reported to markedly suppress kindling development at doses devoid of visible adverse effects (Löscher et al., 1998). After termination of treatment, all rats developed fully kindled seizures, but the duration of these seizures was significantly lower compared to controls, indicating a disease-modifying effect of the treatment (Löscher et al., 1998). Our initial observation was subsequently confirmed by Stratton et al. (2003) who reported that, while both treatment with LEV or lamotrigine retarded kindling, only prior treatment with LEV prevented the increase in seizure duration upon further kindling following cessation of treatment. However, whether this effect of LEV really represents an antiepileptogenic or disease-modifying action is difficult to ascertain, because traditional kindling does not lead to epilepsy with SRS. More recently, Yan et al. (2005) reported that LEV retarded the development of SRS in a spontaneously epileptic rat mutant and suggested that LEV possesses not only antiseizure effects but also antiepileptogenic properties.
For further evaluating whether LEV exerts antiepileptogenic activity, we used a rat model in which SRS develop after a status epilepticus (SE) induced by sustained electrical stimulation of the basolateral amygdala (BLA) (Brandt et al., 2003a). Our goal was to evaluate LEV by a clinically driven study design. Such a design should ideally satisfy the following criteria: (1) the chosen animal model should recapitulate most, if not all, features of a given type of epilepsy such as TLE, including its progressiveness and its pathological landmark, i.e. hippocampal sclerosis; (2) administration of the drug candidate should begin shortly after the epileptogenesis-inducing brain insult to mimic the clinical setting; and (3) the dosing protocol of the drug candidate should take the differences in pharmacokinetics between rodents and humans into account. Based on these considerations, LEV was tested by two experimental protocols. In the first protocol, which was based on a previous study by Bolanos et al. (1998) with valproate in the kainate model, LEV treatment was started 24 h after onset of electrical BLA stimulation without prior termination of the SE. In the second protocol, the SE was interrupted after 4 h by diazepam, immediately followed by onset of treatment with LEV. This duration of SE has been shown to be sufficient for inducing development of SRS and histological damage in the hippocampal formation, particularly in the dentate hilus (Brandt et al., 2003a). Treatment with LEV was continued for 8 weeks (experiment #1) or 5 weeks (experiment #2) after SE, using continuous drug administration via osmotic minipumps. The occurrence of SRS was recorded during and after treatment. In addition to recording SRS, the rats were tested in a battery of behavioral tests, including the elevated-plus-maze and the Morris water maze. Finally, the brains of the animals were analyzed for histological lesions in the hippocampal formation.
Section snippets
Animals
Fifty-nine female Sprague–Dawley rats were purchased at a body weight of 200–220 g (Harlan-Winkelmann Versuchstierzucht, Borchen, Germany). Following arrival, the rats were kept under controlled environmental conditions (24–25 °C; 50–60% humidity; 12:12 h light/dark cycle; lights on at 06:00 h) with free access to standard laboratory chow (Altromin 1324 standard diet) and tap water. All experiments were done in compliance with the European Communities Council Directive of 24th November 1986
Results
Drug-associated adverse effects were not observed in the two experiments with LEV. Furthermore, the body weight gain was comparable in LEV-treated and saline-treated groups (not illustrated). Because of the differences in the two protocols used for evaluating the effects of LEV, all other findings will be separately described for the two experiments.
Discussion
In contrast to our expectations, LEV did not exert any significant effect on the long-term consequences of SE, i.e., the development of spontaneous seizures, behavioral alterations and hippocampal damage in this experimental model. In contrast, independent of whether rats were treated with saline or LEV after SE, all rats developed SRS without significant intergroup differences in frequency, severity or duration. Furthermore, hyperexcitability and impairment of spatial learning were observed in
Acknowledgements
We thank Maria Hausknecht, Christiane Bartling and Michael Weissing for technical assistance in the histology. The study was supported by UCB Pharma (Braine l'Alleud, Belgium).
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- 1
Present address: Sanofi-Aventis Pharma Deutschland, Frankfurt am Main, Germany.
- 2
Present address: Department of Veterinary Clinical Sciences, Neurology, The Royal Veterinary College, University of London, London, UK.
- 3
Present address: Institute of Pharmacology, Toxicology and Pharmacy, University of Munich, Munich, Germany.