Effects of Cannabidiol on Human Nav Channels

Abstract

Cannabis sativa contains many related compounds known as phytocannabinoids. The main psychoactive and non-psychoactive compounds are ∆9-tetrahydrocannabidiol (THC) and cannabidiol (CBD), respectively. Unlike THC, CBD has a low affinity for Cannabinoid receptors. Cannabis products are receiving attention as potential therapeutics for neurological conditions including epilepsy. Much of the evidence for clinical efficacy has been from case reports or smaller surveys until a recent phase III trial of CBD treatment for Dravet syndrome demonstrated efficacy. The mechanisms for the anticonvulsant effects of CBD are unclear and likely involve both cannabinoid and non-cannabinoid receptor pathways. CBD is reported to modulate several ion channels, including: TRP, T-type calcium, and sodium channels (Nav). Evaluating therapeutic mechanisms and safety of CBD demands a richer understanding of its interactions with CNS targets. We used the Qube-384, a high-throughput automated patch-clamp platform, to characterize the functional effects of CBD on Nav's. Our results show that CBD non-selectively inhibits Nav1.1-1.7, with 1.9-3.8 µM potency, suggesting that CBD-Nav interactions occur at physiologically relevant concentrations (in vivo brain exposures ∼10 µM). Cooperative block is indicated by a steep Hill slope of ∼3, suggesting multiple interaction sites. CBD exhibits resting-state block (IC50∼12 µM, −100 mV), and becomes more potent at depolarized potentials (IC50∼2 µM, −45 mV). This state-dependence has similarities to classic pore-blocking local anesthetics (LAs); CBD also slows recovery from slow and fast inactivation, supporting that binding preferentially stabilizes inactivated states. To examine whether CBD interacted with the canonical LA binding site we made a point mutation in the Nav1.1 pore, F1763A, which only mildly decreased potency (∼2-fold) suggesting that the CBD mechanism of inhibition involves more delocalized pore interactions than LAs. Lastly, the CBD block of Nav's is temperature-dependent, as its potency increases at lower temperatures.