Abstract
Objective
Many early-onset epilepsies present as Developmental and Epileptic Encephalopathy associating refractory seizures, altered psychomotor development and disorganized interictal cortical activity. Abnormal upregulation of specific NMDA receptor subunits is being disentangled as one of the mechanisms of severe early-onset epilepsies. In Tuberous sclerosis complex, upregulation of the GluN2C subunit of the NMDA receptor with slow deactivation kinetic results in increased neuronal excitation and synchronization.
Methods
Starting from an available GluN2C/D antagonist, NMDA receptor modulating compounds were developed and screened using a patch clamp on neuronal culture in order to select those with the strongest inhibitory effect on glutamatergic NMDA currents. For these selected compounds, blood pharmacokinetics and passage through the blood-brain barrier were studied. We tested the effect of the most promising compounds on epileptic activity in Tsc1
+/-
mice brain slices with multielectrode array, then in vivo, at post-natal ages P14-P17, comparable to the usual age of epilepsy onset in humans.
Results
Using a double electrode voltage clamp on isolated NMDA currents, we identified the most prominent antagonists of the GluN2C subunit with no effect on GluN2A as means of preventing side effects. The best compound passing through the blood-brain barrier was selected. Applied in vivo in 6 Tsc1
+/-
mice at P14-P17, this compound reduced or completely stopped spontaneous seizures in 4 of them, and decreased the background activity disorganization. Furthermore, ictal-like discharges stopped on a human brain sample from an infant with epilepsy due to TSC.
Interpretation
Subunit-selective inhibition is a valuable target to develop drugs for severe epilepsies resulting from an upregulation of NMDA-receptor subunit-mediated transmission.
AGO