Characterizing the effects of Eugenol on neuronal ionic currents and hyperexcitability

Rationale

Eugenol (EUG, 4-allyl-2-methoxyphenol), the main component of essential oil extracted from cloves, has various uses in medicine because of its potential to modulate neuronal excitability. However, its effects on the ionic mechanisms remains incompletely understood.

Objectives

We aimed to investigate EUG’s effects on neuronal ionic currents and excitability, especially on voltage-gated ion currents, and to verify the effects on a hyperexcitability-temporal lobe seizure model.

Methods

With the aid of patch-clamp technology, we first investigated the effects of EUG on ionic currents in NG108-15 neuronal cells differentiated with cyclic AMP. We then used modified Pinsky–Rinzel simulation modeling to evaluate its effects on spontaneous action potentials (APs). Finally, we investigated its effects on pilocarpine-induced seizures in rats.

Results

EUG depressed the transient and late components of I _Na in the neurons. It not only increased the degree of I _Na inactivation, but specifically suppressed the non-inactivating I _Na (I _Na(NI)). Its inhibition of I _Na(NI) was reversed by tefluthrin. In addition, EUG diminished L-type Ca²⁺ current and delayed rectifier K⁺ current only at higher concentrations. EUG’s effects on APs frequency reduction was verified by the simulation modeling. In pilocarpine-induced seizures, the EUG-treated rats showed no shorter seizure latency but a lower seizure severity and mortality than the control rats. The EUG’s effect on seizure severity was occluded by the I _Na(NI) antagonist riluzole.

Conclusion

The synergistic blocking effects of I _Na and I _Na(NI) contributes to the main mechanism through which EUG affects the firing of neuronal APs and modulate neuronal hyperexcitability such as pilocarpine-induced temporal lobe seizures.