Abstracts

Rationale: Cannabidiol (CBD) is a nonpsychotropic component of the cannabis plant (Cannabis Sativa) that, while possessing negligible affinity and functional activity at the cannabinoid receptor type 1, engages multiple targets involved in the modulation of neuronal excitability. The transient receptor potential vanilloid 1 (TRPV1) receptor is a nonselective cation channel with high Ca2+ permeability, and its expression is increased in rodent models of epilepsy (Exp Neurol 2010;223:529-536) and in patients with temporal lobe epilepsy (J Mol Neurosci 2013;49:182-193). CBD acts as a TRPV1 agonist that rapidly desensitizes TRPV1 in a concentration and calcium-dependent fashion (ACS Chemical Neurosci 2014:19;5:1131-1141). A series of randomized placebo-controlled clinical trials have shown CBD oral solution (CBD-OS) to be significantly superior to placebo in reducing seizure frequency in patients with Lennox-Gastaut and Dravet Syndromes. Here, the effect of CBD upon seizure threshold in the maximal electroshock seizure threshold test in the mouse, a model of generalized seizure, was evaluated in wild-type (WT) and TRPV1 knockout (KO) animals. Methods: In two separate studies, TRPV1 -/- (homozygous TRPV1 B6.129X1-TRPV1tm1Jul/J Jackson Laboratory US) and WT +/+ mice (male, C57BI6 Charles River UK) were treated with either intraperitoneal CBD (GW Research; 10, 25, 50, 100, and 200 mg/kg), a CBD vehicle (ethanol:kolliphorEL:saline, 1:1:18 ratio) 60 minutes before testing, the TRPV1 antagonist, capsazepine (10 mg/kg in 2% DMSO and saline), or diazepam (2.5 mg/kg in saline) 30 minutes before testing, n=12/group. A constant current stimulus (1-300 mA; 0.1 s duration) was then delivered via corneal electrodes and mice individually assessed for exhibition of tonic hind limb extension indicative of acute generalized seizures. Stimulus intensity was varied by an “up and down” method of shock titration and the current required to produce maximal seizures in 50% of animals tested (CC50) ± SEM values calculated (Radiation Res 1957:7:1-12). Statistical analysis was performed according to Litchfield and Wilcoxon (J Pharmacol Exp Ther 1949;96:99-113). Brain and plasma concentrations of CBD were assessed by liquid chromatography/tandem mass spectrometry. Results: No significant difference was seen in CC50 values between vehicle treated WT and TRPV1 KO mice (P>.05); both diazepam and capsazepine were effective in WT and KO animals (P < .001 compared to vehicle). CBD (25-200 mg/kg) dose-dependently increased CC50 in WT mice compared to vehicle (P.05). Conclusions: CBD dose-dependently increased seizure threshold in WT mice. This effect was markedly reduced in TRPV1 KO mice. Brain exposure for CBD was consistent with concentrations required for TRPV1 activation and desensitization. These data suggest that the anticonvulsant effects of CBD in acute, murine generalized seizures are in part mediated via TRPV1 receptor interaction. Funding: Funded by GW Research Ltd