Natural product incarvillateine aggravates epileptic seizures by inhibiting GABAA currents

A natural monoterpene alkaloid incarvillateine isolated from the plant Incarvillea sinensis is known to relieve inflammatory and neuropathic pain. However, the molecular target for the action of incarvillateine remains elusive. Here, we report that incarvillateine exacerbates epileptic seizures by inhibiting subtypes of γ-Aminobutyric acid type A (GABAA) receptors. Two-electrode voltage clamp recordings of α1β3γ2, α2β3γ2, α3β3γ2 and α5β3γ2 subtypes expressed in Xenopus oocytes revealed that incarvillateine inhibited the GABAA currents with IC50 of 25.1 μM, 43.1 μM, 105.1 μM and 93.7 μM, respectively. Whole-cell patch clamp recordings of hippocampal slices confirmed that incarvillateine inhibited spontaneous inhibitory postsynaptic currents (IPSCs), and miniature IPSCs and tonic currents. Moreover, inhibition of GABAA currents and spontaneous IPSCs by incarvillateine persisted even in the presence of blockers of adenosine receptors. In addition, incarvillateine enhanced epileptic discharges induced by Mg2+-free artificial cerebrospinal fluid (ACSF) in hippocampal slices. Furthermore, intracerebral ventricular injections of incarvillateine increased the severity of seizures induced by kainic acid in a dose-dependent manner. Taken together, our data demonstrate that incarvillateine aggravates seizures by inhibition of GABAA currents and GABAergic synaptic transmissions.