TRPV2 Is Activated by Cannabidiol and Mediates CGRP Release in Cultured Rat Dorsal Root Ganglion Neurons

Abstract

Transient receptor potential V2 (TRPV2) has been proposed to be a high-threshold thermosensor. However, further elucidation of the channel properties and physiological role of TRPV2 have been hindered by the lack of selective pharmacological tools as well as by the species-dependent differences in the activation of this channel. In the present study, we have used cell-based calcium mobilization and electrophysiological assays to identify and characterize several novel cannabinoid TRPV2 agonists. Among these, cannabidiol was found to be the most robust and potent (EC 50 ϭ 3.7 M), followed by ⌬ 9 -tetrahydrocannabinol (EC 50 ϭ 14 M) and cannabinol (EC 50 ϭ 77.7 M). We also demonstrated that cannabidiol evoked a concentration-dependent release of calcitonin gene-related peptide (CGRP) from cultured rat dorsal root ganglion neurons in a cannabinoid receptor-and TRPV1-independent manner. Moreover, the cannabidiolevoked CGRP release depended on extracellular calcium and was blocked by the nonselective TRP channel blocker, ruthenium red. We further provide evidence through the use of small interfering RNA knockdown and repetitive stimulation studies, to show that cannabidiol-evoked CGRP release is mediated, at least in part, by TRPV2. Together, these data suggest not only that TRPV2 may comprise a mechanism whereby cannabidiol exerts its clinically beneficial effects in vivo, but also that TRPV2 may constitute a viable, new drug target.

Molecular Targets of Cannabidiol in Neurological Disorders

“…In contrast to the above studies, comparable fluorescencebased Ca 2+ imaging in HEK293 cells expressing rat TRPV1 receptors revealed that CBD (100 μM) produced a response that was only 21% of that produced by the positive control, capsaicin (500 nM), which was insufficient to determine reliably an EC 50 value [96]. Furthermore, a recent study used patch clamp techniques to assess the effect of CBD (3-30 μM) on the bidirectional current recorded in HEK293 cells overexpressing rat TRPV1 receptors that can be evoked by application of the TRPV1 agonist, capsaicin (1-10 μM) [98].…”

“…In addition to reports of TRPV1 receptor agonism, CBD has also been reported to interact with the TRPV2 receptor. In the first study reporting such effects [96], CBD agonized human TRPV2 receptors overexpressed in HEK293 cells when assessed using a fluorescence-based assay, a finding subsequently confirmed using patch clamp electrophysiology and extended to reveal similar effects upon rat TRPV2 overexpressed in the same cell line, although with markedly different potency [EC 50 = 3.7 μM (human) vs 31.7 μM (rat)] (Table 3). CBD effects upon rat TRPV2 receptors were also separately investigated in the same expression system and using patch clamp electrophysiology [98].…”

“…Although a complete concentration-response relationship for CBD was not determined, detectable currents were evoked by 10 and 30 μM CBD but not by 3 μM. While species-specific differences in TRPV1 responsiveness could account for efficacy and potency differences in the preceding studies, the use of rat TRPV1 here and by Qin et al [96] justifies the target's consideration. It is notable that the highest CBD concentration (30 μM) studied by Iannotti et al [98] elicited a peak response of~30% of that produced by capsaicin (c.f., 21%).…”

“…A first report stated that CBD acts as a potent and efficacious agonist at rat TRPA1 receptors overexpressed in HEK293 cells (Table 3), as assessed using a fluorescencebased assay, but went on to report that high concentrations (≥100 μM) of CBD failed to elicit [Ca 2+ ] i increases in mustard oil-sensitive dorsal root ganglion neurons [97]. Thereafter, CBD was reported to activate fully rat TRPA1 expressed in HEK293 cells when assessed in a similar fluorescence-based assay, but with much lower potency (EC 50 = 81.4 μM; Table 3) [96]. Subsequently, the first report was recapitulated by the same group and reported similar effects of CBD at rat TRPA1 in HEK293 cells but extended the study to show that CBD can also act as a potent desensitizer (IC 50 = 0.16 μM) of this receptor [97].…”

Cannabinoids, the Heart of the Matter

“…TRPV1 ion channels have important functions as cellular sensors, and are involved in nociception, taste perception, thermosensation, mechano‐ and osmolarity sensing, and regulation of signal transmission 15, 55, 56. In addition to ECS and physicochemical activators,15, 33, 55, 56, 57, 58 TRPV1 is activated by tetrahydrocannabinol, cannabinol, cannabigerol and some propyl homologs of THC and cannabigerol 59, 60, 61, 62, 63, 64, 65, 66, 67. Cannabichromene (CBC), cannabidiol, and cannabinol are strong TRPA1 agonists and desensitizers, and THCV (from a botanical extract) is a potent regulator of TRPA1 62…”