Abstracts

Rationale: Cannabidiol (CBD) is a component derived from the cannabis plant (Cannabis Sativa L.). In three separate randomized placebo-controlled clinical trials, purified CBD (GW Pharmaceuticals) was shown to be significantly superior to placebo in reducing seizure frequency in Lennox-Gastaut and Dravet syndromes (AES Ann Meeting; 2016; abst; 1.377; N Engl J Med; 2017; 376; 2011-20). 7-hydroxy CBD (7-OH-CBD) and 7-carboxy CBD (7-COOH-CBD) are two major metabolites produced after oral administration of CBD in humans (Cannabis Cannabinoid Res; 2016; 1; 90-101). However, neither central nervous system exposure nor contributions to the anticonvulsant effects of CBD of these metabolites have been assessed. We determined the potential for CNS exposure of these metabolites and examined their effects in the maximal electroshock seizure threshold test in the mouse; a model of generalized seizure. Methods: Each metabolite was investigated in a separate study. In the case of 7-OH-CBD, male NMRI mice (12 animals/group; 26.8 ± 0.2 g; Janvier Labs, France) were treated intraperitoneally (IP) with either 7-OH-CBD (150 & 200 mg/kg; GW Research) CBD (200 mg/kg; GW Research) or cannabinoid vehicle (ethanol:KolliphorEL:0.9% saline; 1:1:18) 60 minutes before testing, diazepam (2 mg/kg; Coopération Pharmaceutique Française, France) or diazepam vehicle (0.2% hydroxypropylmethylcellulose in 0.9% saline) 30 minutes before testing. In the case of 7-COOH-CBD, male NMRI mice (12 animals/group; 24.4 ± 0.2 g; Janvier Labs, France) were treated IP with either vehicle (ethanol:KolliphorEL:0.9% saline 1:1:18 ratio), 7-COOH-CBD (50, 100, 150 & 200 mg/kg; GW Research), CBD (200 mg/kg; GW Research) 60 minutes before testing or diazepam (2 mg/kg; Coopération Pharmaceutique Française, France) 30 minutes before testing. In both studies, seizure threshold was assessed via a stimulus (50 mA, 0.6 ms pulse, 0.4s duration, 50Hz) delivered using a constant current generator (Ugo Basile 57800) via corneal electrodes. Mice were assessed for exhibition of tonic convulsions (hind limb extension; J Pharmacol Exp Ther; 1952; 106; 319-330). Statistical analysis was performed by comparison of drug treated groups with respective vehicle group using Fisher’s Exact Probability Tests.  Results: 7-OH-CBD (P<0.001 for both doses), CBD (P<0.001) and diazepam (P<0.05) significantly reduced incidence of tonic convulsions when compared with the relevant vehicle-dosed groups. In the second study, while CBD (P<0.001) and diazepam (P<0.05) significantly reduced incidence of tonic convulsions, 7-COOH-CBD (P>0.05) had no effect at any dose examined when compared with the vehicle group. Conclusions: The present study determined that the two major human metabolites of CBD (7-OH-CBD and 7-COOH-CBD) are brain penetrant but only 7-OH-CBD exerts significant anticonvulsant effects in the MEST test in mice. As such, 7-OH-CBD but not 7-COOH-CBD may contribute towards the overall, independent anticonvulsant effect of CBD following systemic exposure. Funding: Funded by GW Research Ltd