Safinamide modulates striatal glutamatergic signalling in a rat model of levodopa-induced dyskinesia

Safinamide (Xadago®) is a novel dual mechanism drug which has been approved in the EU and US as add-on treatment to levodopa in Parkinson's disease (PD) therapy. In addition to its selective and reversible monoamine oxidase B (MAO-B) inhibition, safinamide through use-dependent sodium channel blockade reduces overactive glutamatergic transmission in basal ganglia, which is believed to contribute to motor symptoms and complications including levodopa-induced dyskinesia (LID). The present study investigated the effects of safinamide on the development of LID in 6-hydroxydopamine (6-OHDA) lesioned rats, evaluating behavioural, molecular and neurochemical parameters associated with LID appearance. 6-OHDA lesioned rats were treated with either saline, levodopa (6 mg/Kg) or levodopa plus safinamide (15 mg/Kg) for 21 days. Abnormal involuntary movements, motor performance, molecular composition of the striatal glutamatergic synapse, glutamate and GABA release were analysed. 
In the striatum, safinamide prevented the rearrangement of the subunit composition of NMDA receptors and the levodopa-induced increase of glutamate release, associated with dyskinesia, without affecting the levodopa-stimulated motor performance and dyskinesia. Overall, these findings suggest that the striatal glutamate-modulating component of safinamide's activity may contribute to its clinical effects where its long-term use as levodopa add-on therapy, significantly improves motor function and ON time without troublesome dyskinesia.