Anti-epileptic effect of cannabidiol mediated by modulation of mitochondrial function

Background and objectives: Cannabidiol (CBD) is a non-psychoactive phytocannabinoid which exerts anti-convulsant effects in both rodents and humans. Although CBD appears to target a wide range of non-mitochondrial and mitochondrial proteins, the molecular mechanism underlying its anti-epileptic effect remains undetermined. In 2013, Rimmerman et al. demonstrated that CBD binds and inhibits the conductance of voltage-dependent anion-selective channel (VDAC) reconstituted in an artificial bilayer membrane. In the mitochondrion, VDAC is essentially expressed in the outer-membrane. Taken together, this led to the hypothesis that CBD may exert its anti-convulsant effect by altering mitochondrial function in a manner which is consistent with that of other VDAC inhibitors. To test this hypothesis, I assessed the effect of CBD on oxidative phosphorylation, Ca2+-induced mitochondrial swelling and cytochrome C release of non-synaptic mitochondria isolated from hippocampi of healthy rats and of rats that have been rendered epileptic following status epilepticus induced chemically with lithium-pilocarpine. Furthermore, the effect of CBD on mitochondrial function was compared to that of a VDAC blocker (namely S18 randomer). Finally, I investigated the effect of CBD on the electrophysiological proprieties of HEK293 cells overexpressing an isoform of VDAC (namely VDAC2). Results: CBD (10 μM) increased mitochondrial swelling and state 4 respiration in non-synaptic mitochondria from epileptic rats, while it exhibited no effect in non-synaptic mitochondria from healthy rats. I showed that CBD does not target complexes II, III and IV or the ATP4- 2 synthase. The direct effect of CBD on mitochondrial swelling and oxidative phosphorylation differed from that of S18 randomer. While S18 randomer dramatically increased Ca2+-induced cytochrome C release, CBD did not exhibit any effect on the latter. Conclusion: CBD induces weak uncoupling and increases Ca2+-induced mitochondrial swelling in non-synaptic mitochondria, suggesting that CBD may activate H+ uptake in these mitochondria. As the effects of CBD were inconsistent with that of S18 randomer, it is very likely that the mechanism of action of CBD is independent from VDAC