Abstracts

Rationale: Dravet syndrome (DS) is a devastating childhood-onset epilepsy caused by loss-of-function mutations in SCN1A, the gene encoding the Na_v 1.1 sodium channel α-subunit. This epilepsy is often non-responsive to most current anti-epileptic drug treatments. Ketogenic diet (KD), a high fat dietary regimen, is one of the most effective treatments for DS and other intractable epilepsies. But the mechanisms of the diet anti-epileptic properties are not completely understood. Previous studies, in our lab and others, demonstrated that selective decrease in excitability of interneurons in the hippocampus and resulting increased network excitability in this brain region play a key role in the pathogenesis of epilepsy in our mouse model of DS. In addition, KD provides protection against flurothyl-induced seizure in this mouse model. Here, we hypothesized that this therapeutic effect is due to the diet ability to reverse the hippocampal network dysfunction. To test this hypothesis, we first investigated which of the main metabolites of the diet is responsible for seizure protection and evaluated their ability to suppress hippocampal hyperexcitability, a marker of seizure susceptibility in DS mice. Methods: The ability of the main metabolites of KD (Beta-hydroxybutyrate (BHB), acetoacetate (ACA), Arachidonic acid (AA), docosahexaenic acid (DHA) to protect against hyperthermia-induced seizures in DS mice was assessed under video/ EEG as described in our previous work. Field potentials were recorded from hippocampi of DS mice in brain slice preparations in normal and high K⁺ conditions. BHB was added to the high K⁺ ACSF to test its effect on hippocampal excitability. Results: Of the four KD metabolites tested, only BHB and DHA rendered DS mice more resistant to hyperthermia-induced seizures. These seizures were induced at higher temperatures when mice were treated with BHB or DHA than with vehicle. In addition, larger proportions of mice treated with the metabolites were seizure-free at elevated temperatures. In brain slices of both WT and DS mice, BHB reduced the hyperexcitibility of hippocampal network. Both the frequency and amplitude of population spikes were dramatically reduced in the presence of extracellular BHB. Conclusions: These findings suggest that BHB and DHA may serve as key components of future effective anti-seizure drugs for DS. BHB mechanism of action includes suppression of abnormal hippocampal excitability, a predicted important biomarker of this epilepsy. Future studies will determine whether DHA has similar mode of action.