Stiripentol inhibits spike-and-wave discharges in animal models of absence seizures: A new mechanism of action involving T-type calcium channels

Objective Stiripentol (STP; Diacomit (R)) is an antiepileptic drug indicated for Dravet syndrome that has been identified as a gamma-aminobutyric acid (GABAergic) positive allosteric modulator. Dravet syndrome is characterized by multiple seizure types: generalized tonic-clonic, focal, myoclonic, and absence seizures. In addition to its antiepileptic effects on tonic-clonic seizures, STP has also been reported to reduce the frequency of atypical absence seizures in patients. Our study focused on STP potential effects on absence seizures, to better characterize its full spectrum of mechanisms of action. Methods STP effects on absence seizures were quantified by electroencephalographic recording in two animal models: rats treated with a low dose of pentylenetetrazol (20 mg/kg ip) and rats from the WAG/Rij strain. In addition, we characterized STP effects on T-type calcium channel activity. Peak currents were recorded with manual patch clamp on cells transfected with cDNA encoding for the human isoform for Ca(v)3.1, Ca(v)3.2, and Ca(v)3.3. Results STP administered before pentylenetetrazol almost completely abolished the generation of spike-and-wave discharges (SWDs) at the dose of 300 mg/kg. At this dose, STP also statistically significantly decreased SWD cumulated duration and number in WAG/Rij rats. Its antiepileptic effect was maintained in WAG/Rij rats, whose seizures were aggravated by the GABA agonist THIP (gaboxadol hydrochloride). Furthermore, electrophysiological recordings showed that STP inhibits T-type calcium channel peak activity, with a higher specificity for the Ca(v)3.3 subtype. Significance In addition to its previously characterized anticonvulsive properties, these data highlight a new mechanism of action of STP on abnormal thalamocortical activity. This strong antiabsence effect on seizures is correlated with an inhibition of T-type calcium channels. This new mechanism of action could be implicated in the specificity of STP therapeutic effects in Dravet syndrome.