Abstracts

Rationale: About a quarter of patients with mitochondrial disease develop a severe form of epilepsy called mitochondrial epilepsy¹. Clinically, this form of epilepsy has a severe prognosis and tends to be resistant towards application of conventional antiepileptic agents². Phytocannabinoids have emerged as having therapeutic benefit in patients with drug resistant epilepsy³. We have used a novel in vitro model of mitochondrial epilepsy to examine the efficacy of cannabidiols for this condition. Methods: We developed a novel in vitro brain slice model of mitochondrial epilepsy by targeting two distinct cellular compartments, the astrocytic and the neuronal compartments. This manipulation produces continuous inter-ictal epileptiform discharges in the hippocampus CA3 of acutely prepared rat brain slices (450 mM) which were recorded as extracellular local field potential recordings in the CA3 subfield. Slices were acutely exposed to cumulative application of the phytocannabinoids (30 minutes for each concentration) across the concentration range (0.1 - 100µM). The frequency of epileptiform discharges was quantified and compared against DMSO vehicle application. Results: The bath application of purified cannabidiol (CBD) exhibited minimal inhibitory effect upon the frequency of epileptiform discharges. A statistically significant difference (p<0.05) was seen only at a concentration of 10µM. There was a reduction in the frequency of the epileptiform discharges by 13.12 ± 6.60 %, 28.71 ± 4.48 %, 33.03 ± 9.46 %, and 31.44 ± 10.22 % by application of CBD at the concentration of 0.1, 1, 10, and 100µM, respectively. The acute application of cannabidiolic acid (CBDA) elicited significant inhibitory effect (p<0.05) at concentrations of 10 and 100µM. This reduction was observed to be 14.03 ± 4.34 %, 36.07 ± 8.61 %, 45.09 ± 8.83 %, and 59.76 ± 7.8 % for concentrations of 0.1, 1, 10, and 100µM CBDA, respectively. This inhibitory effect was dose-dependent and the IC₅₀ of CBDA was 18.49µM. The application of cannabidivarin (CBDV) also elicited a significant inhibitory effect on pathological activity (p<0.05) at the 10 and 100µM concentrations. The reduction in the frequency of the epileptiform activity was found to be by 2.81 ± 6.95 %, 17.25 ± 6.65 %, 39.07 ± 11.13 %, and 49.81 ± 12.93 % at concentration of 0.1, 1, 10, and 100µM of CBDV, respectively. CBDV’s inhibitory effect was also dose-dependent with an IC₅₀ of 69.21µM. . Conclusions: Using an in vitro model of mitochondrial epilepsy, we have observed that all three phytocannabinoids tested, exercise a significant anti-epileptiform effect. Future work aims to examine the mechanism(s) by which cannabidiols are efficacious in this particular model.References(1) Whittaker RG et al. Annals of Neurology. 78(6):949-957.(2) Bindoff LA, Engelsen BA. Epilepsia. 53:92-97.(3) Devinsky O et al. Lancet Neurology. 15(3):270-278. Funding: Funded by GW Pharma.