Rationale:
There are a number of anti-epileptic drugs (AEDs) on the market, however, up to 30% of patients are still resistant to these available therapies. Drug-resistant epilepsy mostly concerns mesial temporal lobe epilepsy (mTLE), the most common form of focal epilepsy (80%) and involves structures of the limbic system such as the hippocampus and the amygdala. This reinforces the need for the discovery of new AEDs with improved efficacy and tolerance.
Epileptic-like activity can be induced chemically or electrically in various models to facilitate the screening of potential new anti-epileptic drug candidates.
In vitro models provide a valuable first line screening approach for new drug candidates, allowing for higher throughput testing of several compounds, while ex vivo models are usually used to confirm efficacy of the most promising compounds and better understand their mechanism of action. At a more advanced stage, acute in vivo models provide proof of concept in a more integrated setting by reproducing generalized tonic-clonic seizures, as is seen with the maximal electroshock (MES) test or partial seizure observed in the 6Hz test. The electrical amygdala kindling test remains the gold standard, as it closely mimics various aspects of mTLE with the induction of partial seizures with secondary generalization.
The aim of our experiment was to compare the effects of two well-known AEDs: Retigabine (RET), a Kv7 potassium channel opener, and Levetiracetam (LEV) in different models.
Methods:
For in vitro and ex-vivo experiments, epileptiform activity was induced by the convulsive agent 4-Aminopyridine (4-AP), a voltage-dependent potassium channel blocker and detected by calcium oscillations on rat cortical primary cultures and by firing rate and bursts frequency on mouse hippocampal slices using a multi electrode array (MEA).
In Vivo Experiments:
Maximal Electroshock and 6Hz seizure model in mice. Electrical Amygdala Kindling in the rat.
Results:
In Vitro & Ex Vivo Experiments:
Levetiracetam at 200 µM partially inhibited epileptiform activity on hippocampal slices while RET (10 µM) fully abolished epileptic-like activity in both models.
For in-vivo experiments, RET at 5-10 mg/kg, i.p. decreased the number of mice showing tonic convulsions in the MES model while LEV was not active. Partial seizure induced by 6 Hz stimulation were inhibited by LEV from 100 m/kg, i.p. and in the lesser extent with RET. In the rat kindling test, RET at 5-10 mg/kg decreased the seizure score and reduced after-discharge duration on the amygdala and cortical signals, while LEV at 500 mg/kg, was only efficacious on the seizure score.
Conclusions:
While clear anticonvulsant activity was observed with RET and LEV in in vitro, ex vivo or in vivo models, there were some differences in terms of efficacy that may be linked to their own mechanism of action. This data confirms the importance of testing a compound across a variety of models to assess anti-convulsant efficacy.
Funding: N/A