Mechanism and effects of the skeletal muscle Nav1.4 inhibition by cannabidiol

Abstract

ABSTRACTCannabis sativa contains active constituents called phytocannabinoids. Some phytocannabinoids are psychotropic and others are not. The primary non-psychotropic phytocannabinoid is cannabidiol (CBD), which is proposed to be therapeutic against many conditions, including muscle spasms. Mechanisms have been proposed for the action of CBD on different systems, involving multiple targets, including the voltage-gated sodium channel (Nav) family, which are heavily implicated in many of the conditions CBD has been reported to relieve. In this study, we investigated the modulatory mechanism of CBD on Nav1.4. Based on previous results, we tested the hypothesis that CBD mechanism of action involves: 1) modulation of membrane elasticity, which indirectly contributes to Nav inhibition; and 2) physical block of the Nav pore. We first performed molecular dynamic (MD) simulations to visualize CBD effects and localization inside the membrane, and then performed NMR to verify the MD results, showing CBD localizes below membrane headgroups. Then, we performed a gramicidin-based fluorescence (GFA) assay that showed CBD alters membrane elasticity. Next, we used site-directed mutagenesis in (F1586A) and around (WWWW) the Nav1.4 pore. Removing the local anesthetic binding site with F1586A reduced CBD block of INa. Occluding the fenestrations with WWWW blocked CBD access from the membrane into the Nav1.4 pore. However, stabilization of inactivation, via CBD-induced changes in membrane elasticity persisted, in WWWW. To investigate the potential therapeutic value of CBD against some Nav1.4 channelopathies, we used a pathogenic variant of Nav1.4, P1158S, known to cause myotonia and periodic paralysis. We found CBD reduces excitability in both wild-type and the mixed myotonia/periodic paralysis variant. Our in-vitro/in-silico results suggest that CBD may have therapeutic value against myotonia. Because Nav1.4 is crucial to skeletal muscle contraction, we used rat diaphragm myography and found the presence of saturating levels of CBD reduces skeletal muscle contraction.SUMMARYWe used multidisciplinary approaches to show the mechanism and pathway by which CBD inhibits the skeletal muscle, Nav1.4. Our results suggest CBD modulates membrane elasticity and directly interacts with Nav1.4 within its pore.