Abstracts

Rationale: Brivaracetam (BRV), currently in Phase III development for epilepsy, is a novel high-affinity synaptic vesicle protein 2A (SV2A) ligand that also displays inhibitory activity at neuronal voltage-dependent sodium channels. The purpose of this study was to characterize the effect of BRV on the biophysical properties of the fast voltage-gated sodium current. This was performed in the N1E-115 mouse neuroblastoma cell line and compared with carbamazepine (CBZ). Methods: The effects of BRV and of CBZ, 1µM - 100µM, were studied on the biophysical properties of the endogenous voltage-activated Na⁺ current expressed in N1E-115 mouse neuroblastoma cells plated on glass coverslips. Membrane currents were recorded in the whole-cell configuration of the patch-clamp method. Results: Similarly to CBZ, BRV did not affect the voltage-dependence of the activation curve of voltage-gated Na⁺ currents expressed in N1E-115 cells and induced a significant shift of the steady-state fast inactivation curve toward hyperpolarized potential values. In cells depolarized from a holding potential (HP = -80mV), close to the half-potential of the fast steady-state inactivation curve of the Na⁺ current, both drugs produced a dose-dependent inhibition of the current. This effect was already significant at 1µM (BRV: 19% ± 9%, n=5; CBZ: 19% ± 4%, n=5), inhibition increased up to 30% ± 6% and 40% ± 6%, with BRV and CBZ, at 100µM, respectively. In contrast, when cells were held at more hyperpolarized potential (HP = -120mV), promoting the resting state of Na⁺ channels, BRV did not affect the current amplitude and CBZ induced less than 10% inhibition of the current. Interestingly, while 100µM CBZ induced a consistent 30Hz frequency-dependent facilitation of block (remaining mean peak current % at 30th pulse: control, 44% ± 6% (mean ± SD); CBZ, 32% ± 8%; n=7), BRV only produced a weak effect on this parameter (remaining mean peak current % at 30th pulse: control, 45% ± 5%; BRV, 40% ± 7%; n=7). Conclusions: BRV appears to interact preferentially on the inactivated state of the Na⁺ channel and induces a hyperpolarizing shift of fast inactivation, similar to CBZ. In contrast to CBZ, BRV only demonstrates a weak frequency-dependent facilitation of block. According to the Na⁺ current properties investigated in this study, BRV perfused at therapeutic concentrations demonstrates effects on Na⁺ currents comparable to those of CBZ but of a lower magnitude. In addition to its interaction with SV2A, the effects of BRV on Na⁺ currents may contribute to its antiepileptic properties.