Abstracts

Rationale:
The use of AEDs with multiple mechanisms of action may confer certain advantages when treating patients with multiple seizure types or in whom the diagnosis is initially unclear (Sills,2015). Stiripentol (Diacomit ®) is an antiepileptic drug indicated for the treatment of Dravet syndrome, a rare epileptic encephalopathy characterized by the presence of multiple seizure types, mainly generalized convulsive seizures, focal seizures and absence seizures. Stiripentol (STP) has a strong anticonvulsant effect on generalized clonic or tonic-clonic seizures and has also been reported to be beneficial in reducing the frequency of focal and absence seizures. To better characterize its impact on absence seizures, we studied specifically the effects of STP on spike-and-wave discharges (SWD) in two different animal models of absence seizures: rats treated with a low dose of pentylenetetrazol, and WAG/Rij rats, a genetic model of absence seizures. In addition, using electrophysiological recordings, we studied STP activity on T-type calcium channels, as these ionic channels are strongly involved in abnormal thalamo-cortical oscillations underlying absence seizures generation.
Method:
Adult (7-9 weeks) Sprague-Dawley rats were administered with 20 mg/kg intraperitoneal (i.p.) pentylenetetrazol and either STP (150, 300 mg/kg, i.p.) or vehicle; cortical activity was continuously recorded by EEG. WAG/Rij rats were implanted at six weeks of age, and their EEG activity was recorded 3 times a week. At 12 weeks of age, spike-and-waves discharges were visualized, and the effects of STP (150, 300 mg/kg, i.p.) administration were analyzed between 20 and 22 weeks of age. Stiripentol effects were quantified on three parameters: total duration, mean duration and number of SWD. In electrophysiological studies, the effect of STP at seven different concentrations were analyzed on peak currents recorded with manual patch-clamp, from CHO transiently transfected with cDNA encoding for the human isoform for Cav3.1 and Cav3.3, and in HEK393 for Cav3.2 channels.
Results:
STP administration at the dose of 150 and 300 mg/kg significantly decreased the total duration and number of SWD induced by PTZ. In the WAG Rij strain, i.p. administration of STP 300 mg/kg significantly decreased the total duration, the number and the mean duration of seizures. At the dose of 150mg/kg, only the mean duration of seizures was significantly decreased. Patch-clamp recordings showed that STP induced an inhibition of the peak current amplitude with IC50 values of respectively 69.2, 64.3, 36.6µM for Cav3.1, Cav3.2 or Cav3.2.
Conclusion:
Stiripentol administration induced a strong antiepileptic effect on two different models of absence seizures in the rat: PTZ-induced absence seizures and spontaneous absence seizures in WAG/Rij rats. Electrophysiological recordings showed that STP inhibits T-Type calcium channels peak activity, more specifically the Cav3.3 subtype. These data highlight a new mechanism of action of STP on T-type calcium channels, correlated with a strong anti-absence effect.
Funding:
:Biocodex