Nonpsychotropic Plant Cannabinoids, Cannabidivarin (CBDV) and Cannabidiol (CBD), Activate and Desensitize Transient Receptor Potential Vanilloid 1 (TRPV1) Channels in Vitro: Potential for the Treatment of Neuronal Hyperexcitability

Abstract

Epilepsy is the most common neurological disorder, with over 50 million people worldwide affected. Recent evidence suggests that the transient receptor potential cation channel subfamily V member 1 (TRPV1) may contribute to the onset and progression of some forms of epilepsy. Since the two nonpsychotropic cannabinoids cannabidivarin (CBDV) and cannabidiol (CBD) exert anticonvulsant activity in vivo and produce TRPV1-mediated intracellular calcium elevation in vitro, we evaluated the effects of these two compounds on TRPV1 channel activation and desensitization and in an in vitro model of epileptiform activity. Patch clamp analysis in transfected HEK293 cells demonstrated that CBD and CBDV dose-dependently activate and rapidly desensitize TRPV1, as well as TRP channels of subfamily V type 2 (TRPV2) and subfamily A type 1 (TRPA1). TRPV1 and TRPV2 transcripts were shown to be expressed in rat hippocampal tissue. When tested on epileptiform neuronal spike activity in hippocampal brain slices exposed to a Mg(2+)-free solution using multielectrode arrays (MEAs), CBDV reduced both epileptiform burst amplitude and duration. The prototypical TRPV1 agonist, capsaicin, produced similar, although not identical effects. Capsaicin, but not CBDV, effects on burst amplitude were reversed by IRTX, a selective TRPV1 antagonist. These data suggest that CBDV antiepileptiform effects in the Mg(2+)-free model are not uniquely mediated via activation of TRPV1. However, TRPV1 was strongly phosphorylated (and hence likely sensitized) in Mg(2+)-free solution-treated hippocampal tissue, and both capsaicin and CBDV caused TRPV1 dephosphorylation, consistent with TRPV1 desensitization. We propose that CBDV effects on TRP channels should be studied further in different in vitro and in vivo models of epilepsy.

Cannabis in epilepsy: From clinical practice to basic research focusing on the possible role of cannabidivarin

“…Notably, we can clearly state that CBDV and LEV did not act in a synergistic fashion on rundown improvement. In addition, this effect was not mediated by TRPV channels activity,9 but it was modulated by a kinase or a PKC isoform other than the PKC α, β1,δ, ζ 13…”

“…Interestingly, CBDV effect was not blocked by selective PKC antagonist GF 109203X 1 μ m 12 (I% = 60.5% ± 9.0, 19 oocytes; 4 patients) and by transient receptor potential vanilloid (TRPV) channel antagonist capsazepine 10 μ m 9 (see Table S1), but it was blocked by broad spectrum kinase inhibitor staurosporine13 (from I% = 42 ± 13 to I% = 44 ± 11, 10 oocytes, 2 TLE patients; see Table S1).…”

“…The potential mechanisms underlying CBDV clinical effects are several and only partially known 6, 9. Considering some recent data emphasizing the possible role of GABA‐mediated action of cannabis, we decided to test CBDV effect on GABAergic transmission in human tissue 10, 11.…”

“…Membrane and oocyte preparation/injection procedures were performed as previously detailed 8, 10. GABA current rundown (I%) was defined as the decrease, calculated in percentage, of the current peak amplitude after six 10‐s applications of 500 μ m GABA at 40‐s intervals;9 the percentage of the original current amplitude remains. Oocytes were incubated with CBDV (50 n m ) for 120–150 min after the control rundown protocol.…”

Molecular Targets of Cannabidiol in Neurological Disorders

“…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]. 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.…”