Molecular targets for cannabidiol and its synthetic analogues: effect on vanilloid VR1 receptors and on the cellular uptake and enzymatic hydrolysis of anandamide

1 (-)-Cannabidiol (CBD) is a non-psychotropic component of Cannabis with po ssible therapeutic use as an anti-inflammatory drug. Little is known on the possible molecular targets of this compound. We investigated whether CBD a nd some of its derivatives interact with vanilloid receptor type 1 (VR1), t he receptor for capsaicin, or with proteins that inactivate the endogenous cannabinoid, anandamide (AEA). 2 CBD and its enantiomer, (+)-CBD, together with seven analogues, obtained by exchanging the C-7 methyl group of CBD wi th a hydroxy-methyl or a carboxyl function and/or the C-5 ' pentyl group wi th a di-methyl-heptyl (DMH) group, were tested on: (a) VRI-mediated increas e in cytosolic Ca2+ concentrations in cells over-expressing human VR1; (b) [C-14]-AEA uptake by RBL-2H3 cells, which is facilitated by a selective mem brane transporter; and (c) [C-14]-AEA hydrolysis by rat brain membranes, wh ich is catalysed by the fatty acid amide hydrolase. 3 Both CBD and (+)-CBD, but not the other analogues, stimulated VR1 with EC50=3.2-3.5 mum, and wit h a maximal effect similar in efficacy to that of capsaicin, i.e. 67-70% of the effect obtained with ionomycin (4 mum). CBD (10 mum) desensitized VR1 to the action of capsaicin. The effects of maximal doses of the two compoun ds were not additive. 4 (+)-5 ' -DMH-CBD and (+)-7-hydroxy-5 ' -DMH-CBD inh ibited [C-14]-AEA uptake (IC50=10.0 and 7.0 mum); the (-)-enantiomers were slightly less active (IC50=14.0 and 12.5 muM). CBD and (+)-CBD were also ac tive (IC50=22.0 and 17.0 mum). 5 CBD (IC50=27.5 mum), (+)-CBD (IC50=63.5 mu M) and (-)-7-hydroxy-CBD (IC50=34 mum), but not the other analogues (IC50 > 100 um), weakly inhibited [C-14]-AEA hydrolysis. 6 Only the (+)-isomers ex hibited high affinity for CB1 and/or CB2 cannabinoid receptors. 7 These fin dings suggest that VR1 receptors, or increased levels of endogenous AEA, mi ght mediate some of the pharmacological effects of CBD and its analogues. I n view of the facile high yield synthesis, and the weak affinity for CB1 an d CB2 receptors, (-)-5 ' -DMH-CBD represents a valuable candidate for furth er investigation as inhibitor of AEA uptake and a possible new therapeutic agent.