Abstracts

Rationale: Epilepsy is a common neurological disease, affecting nearly 70 million people worldwide. Dravet syndrome (DS) is one of the most severe epilepsy forms, characterized by drug-resistant seizures and numerous comorbidities. More than 80% of the DS patients carry a mutation in the SCN1A gene, which is also the most prominent epilepsy gene (Gataullina, S. & Dulac, O. Seizure 44, 58–64 (2017)). Recent data of fenfluramine (FA), a serotonin releaser, emphasize its successful use in treating drug-resistant seizures in DS patients (Schoonjans, A.-S., Lagae, L. & Ceulemans. B. Ther. Adv. Neurol. Disord. 8 (6), 328–338 (2015)). Nevertheless, the efficacy of FA to treat other seizures or epilepsy syndromes is currently unknown. Methods: We examined the effects of FA by using three different models of seizures and epilepsy: (1) a genetic zebrafish (ZF) model of DS, i.e. homozygous scn1Lab-/- mutants (Sourbron, J. et al. Front. Pharmacol. 8, 191 (2017)); (2) a chemical ZF model of seizures induced by pentylenetetrazole (PTZ) (Afrikanova, T. et al. PLoS One 8, e54166 (2013)); (3) a mouse model of electrically induced seizures (6-Hz) (Leclercq, K., Matagne, A. & Kaminski R.M. Epilepsy Res. 108, 675–683 (2014)). ZF larvae were treated on 6 dpf with vehicle (VHC; 0.1% dimethyl sulfoxide, DMSO) or FA (25, 50 or 100 µM) for 24 h. Thereafter, the locomotor activity (behavior) was examined by an automated tracking device. Subsequently, we measured forebrain local field potentials (LFPs, brain activity) to confirm anticonvulsant effects of FA treatment, if indicated by the behavioral assays. The efficacy of FA in the mouse 6-Hz model was examined by behavioral characterization after intraperitoneal injection of NMRI mice (30-35 g) with VHC (50/50 DMSO/PEG200) or FA (5 or 20 mg/kg). Seizures were transcorneal-induced 1 h after injection (6-Hz, 0.2 ms pulse width, 44 mA). Results: Our results show that FA treatment significantly decreased epileptiform behavior in homozygous scn1Lab-/- mutants (One-way ANOVA; p < 0.05 vs. VHC). Consistently, we confirmed this anti-epileptiform activity by LFP recordings (Mann-Whitney test; p < 0.05 vs. VHC). In addition, we observed a concentration-dependent effect (more pronounced anticonvulsant activities in case of a higher concentration). There were no significant antiseizure effects observed by FA treatment in the PTZ-induced ZF model of seizures (One-way ANOVA; p > 0.05 vs. VHC+PTZ). Conversely, we demonstrated a dose-dependent, significant reduction of seizures by FA in the mouse 6-Hz model (Mann-Whitney test; p < 0.05 vs. VHC). Conclusions: The efficacy of FA was confirmed in the ZF model of DS, in line with the clinical efficacy of FA in treating drug-resistant seizures of DS patients. Of interest, FA was not active in a widely used ZF model of seizures induced by PTZ, an antagonist of the γ-aminobutyric acid subtype A receptor (GABAA R), and known to be most sensitive to GABAergic ASDs. Importantly, we show a significant seizure reduction by FA in the mouse 6-Hz model demonstrated to be a model for drug-resistant seizures. These findings suggest the possible applicability of FA in the treatment of other epilepsies, beyond DS. Funding: This research was funded by the Agentschap voor innovatie door wetenschap en technologie (IWT) and Zogenix.