Evidence that Δ9-tetrahydrocannabivarin can reduce inflammation in mice by activating cannabinoid CB2 receptors

Daniele Bolognini1, Barbara Costa2, Maria Grazia Cascio1, Roger G Pertwee1. 1University of Aberdeen, Aberdeen, United Kingdom, 2University of Milano-Bicocca, Milano, Italy.

We have reported previously that Δ9-tetrahydrocannabivarin (THCV), opposes the ability of the cannabinoid receptor agonist, CP55940, to stimulate [35S]GTPγS binding to CB2 CHO (Chinese hamster ovary) cell membranes (Thomas et al., 2005). By itself, THCV behaves in this bioassay as a very low-efficacy partial agonist. The present investigation was directed at exploring further the ability of THCV to activate CB2 receptors both in vitro using a more sensitive bioassay, and in vivo.

In vitro experiments were performed with CHO cells transfected with human CB1 or CB2 receptors or untransfected, the measured response being inhibition of cyclic AMP production stimulated by 5 (CB1) or 10 μM (CB2) forskolin (Pertwee et al., 2000). The cannabinoid vehicle was dimethyl sulphoxide. In vivo experiments were conducted with adult male C57BL/6J mice. Acute inflammation was induced in the right hind paw by intraplantar injection of λ-carrageenan and paw oedema assessed 2 h later (Comelli et al., 2007). THCV or its vehicle, ethanol:cremophor:saline 1:1:18, were injected 30 min before λ-carrageenan. Data are expressed as means and variability as SEM or 95% confidence intervals. EC50 and Emax values were calculated using GraphPad Prism 5. In vivo values have been compared by one-way analysis of variance followed by Tukey’s post-hoc test for multiple comparison. P<0.05 was considered significant.

THCV inhibited cyclic AMP production by CB2 CHO cells (n = 4), its EC50 and Emax values with confidence intervals shown in parentheses being 38 nM (12 - 124 nM) and 40% (32 - 48%) respectively. Corresponding values for CP55940 (n = 4) were 6.9 nM (3.5 - 13 nM) and 55% (50 - 60%). At concentrations up to 10 μM, no such inhibition was induced by THCV in CB1 CHO cells or by THCV or CP55940 in untransfected CHO cells or in CB2 CHO cells that had been preincubated overnight with pertussis toxin (100 ng ml-1) to eliminate Gi/o-mediated signalling (n = 4 or 5). Paw oedema was reduced by THCV (0.3 mg kg-1 i.p.), though not by its vehicle, as indicated by a volume decrease of λ-carrageenan-injected hind paws from 124±8.5 μl to 80±1.5 μl (n = 9; P<0.01). This reduction was attenuated significantly (P<0.05) by the CB2-selective antagonist, SR144528 (1 mg kg-1 i.p.) but not the CB1-selective antagonist, rimonabant (0.5 mg kg-1 i.p.), injected 15 min before THCV. Paw volumes in these experiments were 122±7.3 μl (n = 8) and 73±6.7 μl (n = 8) respectively.

Hence, THCV behaves as a reasonably potent CB2 receptor partial agonist in vitro and displays anti-oedema activity in a model of acute inflammation. This anti-inflammatory effect seems to be CB2 rather than CB1 receptor-mediated. These findings suggest that THCV can activate CB2 receptors in vivo as well as in vitro and that it may have therapeutic potential as an anti-inflammatory agent.

Comelli F et al. (2007) Br J Pharmacol 152, 787-794.
Pertwee RG et al. (2000) Br J Pharmacol 129, 1577-1584.
Thomas A et al. (2005) Br J Pharmacol 146, 917-926.

Funded by GW Pharmaceuticals and NIH (DA-03672).