Inhibitory effects of cannabidiol on voltage-dependent sodium currents

Mohammad-Reza Ghovanloo,Noah Gregory Shuart,Janette Mezeyova,Richard A Dean,Peter C Ruben,Samuel J Goodchild

doi:10.1074/jbc.ra118.004929

Mohammad-Reza Ghovanloo, Noah Gregory Shuart + Show 4 more

Open Access

https://doi.org/10.1074/jbc.ra118.004929

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Abstract

Cannabis sativa contains many related compounds known as phytocannabinoids. The main psychoactive and nonpsychoactive compounds are Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), respectively. Much of the evidence for clinical efficacy of CBD-mediated antiepileptic effects has been from case reports or smaller surveys. The mechanisms for CBD's anticonvulsant effects are unclear and likely involve noncannabinoid receptor pathways. CBD is reported to modulate several ion channels, including sodium channels (Nav). Evaluating the therapeutic mechanisms and safety of CBD demands a richer understanding of its interactions with central nervous system targets. Here, we used voltage-clamp electrophysiology of HEK-293 cells and iPSC neurons to characterize the effects of CBD on Nav channels. Our results show that CBD inhibits hNav1.1–1.7 currents, with an IC50 of 1.9–3.8 μm, suggesting that this inhibition could occur at therapeutically relevant concentrations. A steep Hill slope of ∼3 suggested multiple interactions of CBD with Nav channels. CBD exhibited resting-state blockade, became more potent at depolarized potentials, and also slowed recovery from inactivation, supporting the idea that CBD binding preferentially stabilizes inactivated Nav channel states. We also found that CBD inhibits other voltage-dependent currents from diverse channels, including bacterial homomeric Nav channel (NaChBac) and voltage-gated potassium channel subunit Kv2.1. Lastly, the CBD block of Nav was temperature-dependent, with potency increasing at lower temperatures. We conclude that CBD's mode of action likely involves 1) compound partitioning in lipid membranes, which alters membrane fluidity affecting gating, and 2) undetermined direct interactions with sodium and potassium channels, whose combined effects are loss of channel excitability.

Highlights

Cannabis sativa contains many related compounds known as phytocannabinoids
Because CBD has a lower affinity for the endocannabinoid receptors than THC [4], several studies suggest that the anticonvulsant effects of THC and CBD in maximal electroshock (ED50 ϳ120 mg/kg, brain concentration ϭ ϳ22 ␮M) and pilocarpine models occur via different mechanisms [5, 6]
Our results demonstrate that CBD inhibits the sodium current from both rest and inactivated states; the potency of CBD is ϳ10-fold greater for inhibiting inactivated compared with resting states (Fig. 3C)

Summary

Introduction

Cannabis sativa contains many related compounds known as phytocannabinoids. The main psychoactive and nonpsychoactive compounds are ⌬9-tetrahydrocannabinol (THC) and cannabidiol (CBD), respectively. The cannabis plant is composed of over 100 compounds known as phytocannabinoids [1] Among these phytocannabinoids, CBD, is of great interest because of its lack of potency on CB1 and CB2 receptors that are thought to mediate psychotropic activity. CBD, is of great interest because of its lack of potency on CB1 and CB2 receptors that are thought to mediate psychotropic activity Interactions with these receptors by yet another cannabinoid, THC, at submicromolar concentrations cause the well known cannabis effects [2]. CBD inhibits heterologously expressed Cav3.1, Cav3.2, and native neuronal T-type voltage-gated calcium channels [10] These low-voltage activated channels can be blocked by other antiepileptic drugs such as zonisamide [11]. CBD inhibition of Nav currents the EC50 of CBD is within the 1– 4 ␮M range while causing neurotoxicity at 33 ␮M [14]

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