Abstracts

Rationale: Cannabidiol (CBD), a non-psychotropic constituent of Cannabis sativa, has garnered significant interest as a "multi-target" antiseizure drug (ASD). Recent isobolographic studies in our laboratory evaluated CBD's effects alone and in fixed ratio combinations with various ASDs in the 6Hz model using CF#1 mice. These studies identified a synergistic interaction in only one of the combinations tested, 1:1 CBD and levetiracetam (LEV) (Smith MD et al., AES Abstract #1.215, 2015). The goal of the present study was to quantify CBD's efficacy in C57Bl6/J mice in the maximal electroshock (MES) and 6Hz acute seizure models and in a model of viral-induced epilepsy. Theiler's murine encephalomyelitis virus (TMEV)-infected C57BL/6J mice exhibit behavioral seizures from 3-7 days post-infection (dpi) and pathophysiological changes (i.e., hippocampal gliosis, neurodegeneration in CA1, hyperexcitability in CA3, increased oxidative stress biomarkers, increased expression of multiple inflammatory cytokines (i.e., TNF alpha, IL-6, IFN gamma, and IL-1 beta) as well as behavioral comorbidities (i.e., cognitive deficits and anxiety-like behavior). Thus, the TMEV model is an important tool to study mechanism(s) underlying epileptogenesis and disease modification by novel ASDs, such as CBD. Methods: For acute models, the median effective dose (ED50) of CBD was quantified in adult male C57BL6/J mice or Sprague Dawley rats (n=8/group) at the time of peak effect (TPE) determined for CBD following i.p. administration. CBD doses were varied to produce at least 4 doses resulting in 0-100% of animals tested being protected in each acute seizure model. ED50s were calculated using Probit analysis. For the TMEV model, naﶥ C57BL6/J mice were randomly assigned into 5 groups (n=10/group) and infected with TMEV (2x105 PFU/mouse) at day 0. Mice were monitored for handling-induced seizures twice daily, separated by >3 hours from 3-7 dpi. Vehicle-treated mice received 1:1:18 EtOH:Kolliphor:0.9% saline. Remaining groups received CBD doses ranging from 22.5-180.72 mg/kg (10 ml/kg, i.p., q 12 hr from 3-7 dpi). Seizure intensity was scored using a modified Racine scale (Stage 3 ?" forelimb clonus, Stage 4 ?" Stage 3+ rearing; Stage 5 ?" stage 4 + falling, few jumps; Stage 6 ?" Stage 5+ jumping, severe hind limb clonus). Cumulative seizure burden and seizure frequency were calculated and compared to the vehicle-treated group. All behavioral scoring was performed by trained staff blinded to treatment group. Results: The 6Hz (32mA) ED50 (95% confidence interval) in C57BL6/J mice was 42.75 (25.24 ?" 61.63) mg/kg at a 2 hour TPE. Vehicle-treated TMEV infected mice experienced seizures from 3-7 dpi. To date, only the 180.72 mg/kg (i.p.) dose of CBD significantly reduced seizure frequency as well as burden in TMEV-infected mice. Conclusions: CBD's efficacy in these focal and generalized acute seizure models, as well as, in an etiologically-relevant model of viral-induced epilepsy at doses devoid of minimal motor impairment support the therapeutic potential of CBD. Future studies will test if the synergistic combination of 1:1 CBD: LEV offers superior efficacy compared to CBD or LEV alone in terms of seizure burden, viral-induced inflammatory cytokine expression, and behavioral outcomes in the TMEV-infected mice. Funding: Epilepsy Foundation Targeted Research Initiative for Research Regarding CBD in Epilepsy