Abstracts

Rationale: Cannabidiol (CBD), the major non-psychoactive constituent of cannabis sativa, has received much attention for its therapeutic potential in neurologic disorders, especially epilepsy. The main pharmacological effects of the CBD appear neuromodulatory in nature, specifically with respect to cognition, emotional responses, and cellular homeostasis. However, the underlying mechanisms and both short- and long-term side effects of CBD remain unclear. Previously, (PMID: 15964987), chronic marijuana administration was shown to alter brain neurochemistry, morphology and physiology in a manner that could impair cognition and behavior, especially during brain maturation.  Given emerging evidence for cannabinoid interactions with mitochondria, we hypothesized that CBD might exert such changes through impairment of mitochondrial bioenergetics. Methods: The present study employed mitochondrial isolation and protein assays (PMID: 12783416 and PMID: 19477175), spectrofluorophotometer assays for mPT (mitochondrial permeability transition) (PMID: 16517608), and bioenergetics profiling using a Seahorse XFe24 extracellular flux analyzer (PMID: 25011527). Wistar rats (~P35 male, n=3 per group) were used for the most of experiments reported herein. Results: We found that CBD impairs respiration in acutely isolated brain mitochondria and lowers the threshold for calcium-induced activation of mPT. To assess whether these effects could be mediated through mitochondrial cannabinoid receptors, we repeated mPT threshold testing in brain mitochondria isolated from CB1 receptor knockout (CB1KO) mice. CBD (at concentrations >3.75µM) decreased the threshold for calcium-induced mPT threshold in acutely isolated brain mitochondria from CB1KO mice (reductions of 41% and 70% with 3.75µM and 7.5µM CBD, respectively), similar to that observed in normal Wistar rat brain. This strongly supports our contention that the observed mitochondrial effects of CBD are not mediated through mitochondrial CB1 receptors. Further, it has recently been reported that CBD acts on GPR55 receptors to exert anti-seizure activity in a mouse model of Dravet syndrome (PMID: 28973916). We found that the GPR55 receptor agonist LPI (lysophosphatidylinositol) had no effect on calcium-induced mPT threshold at concentrations ranging from 0.1µM to 10µM. Conclusions: While CBD has been used in various formulations to treat epilepsy for several decades, there remains a dearth of information regarding both short-term and long-term side-effects. Based on emerging experimental data linking cannabinoids to cellular metabolism, our data indicate that CBD can impair several measures of mitochondrial function through a mechanism unrelated to CB1 or GPR55 receptors. Funding: Alberta Children’s Hospital Research Institute and Alberta Children’s Hospital Foundation