Peripheral endocannabinoid overactivity might explain why CB(1) blockers cause weight-loss independent reduction of lipogenesis, of hypoadiponectinemia, and of hyperinsulinemia in obese animals and humans.

BACKGROUND AND PURPOSE Cannabidiol (CBD) and Δ9‐tetrahydrocannabinol (THC) interact with transient receptor potential (TRP) channels and enzymes of the endocannabinoid system. EXPERIMENTAL APPROACH The effects of 11 pure cannabinoids and botanical extracts [botanical drug substance (BDS)] from Cannabis varieties selected to contain a more abundant cannabinoid, on TRPV1, TRPV2, TRPM8, TRPA1, human recombinant diacylglycerol lipase α (DAGLα), rat brain fatty acid amide hydrolase (FAAH), COS cell monoacylglycerol lipase (MAGL), human recombinant N‐acylethanolamine acid amide hydrolase (NAAA) and anandamide cellular uptake (ACU) by RBL‐2H3 cells, were studied using fluorescence‐based calcium assays in transfected cells and radiolabelled substrate‐based enzymatic assays. Cannabinol (CBN), cannabichromene (CBC), the acids (CBDA, CBGA, THCA) and propyl homologues (CBDV, CBGV, THCV) of CBD, cannabigerol (CBG) and THC, and tetrahydrocannabivarin acid (THCVA) were also tested. KEY RESULTS CBD, CBG, CBGV and THCV stimulated and desensitized human TRPV1. CBC, CBD and CBN were potent rat TRPA1 agonists and desensitizers, but THCV‐BDS was the most potent compound at this target. CBG‐BDS and THCV‐BDS were the most potent rat TRPM8 antagonists. All non‐acid cannabinoids, except CBC and CBN, potently activated and desensitized rat TRPV2. CBDV and all the acids inhibited DAGLα. Some BDS, but not the pure compounds, inhibited MAGL. CBD was the only compound to inhibit FAAH, whereas the BDS of CBC > CBG > CBGV inhibited NAAA. CBC = CBG > CBD inhibited ACU, as did the BDS of THCVA, CBGV, CBDA and THCA, but the latter extracts were more potent inhibitors. CONCLUSIONS AND IMPLICATIONS These results are relevant to the analgesic, anti‐inflammatory and anti‐cancer effects of cannabinoids and Cannabis extracts. LINKED ARTICLES This article is part of a themed issue on Cannabinoids in Biology and Medicine. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2011.163.issue-7

1 (7)-Cannabidiol (CBD) is a non-psychotropic component of Cannabis with possible therapeutic use as an anti-in¯ammatory drug. Little is known on the possible molecular targets of this compound. We investigated whether CBD and some of its derivatives interact with vanilloid receptor type 1 (VR1), the 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 with a hydroxy-methyl or a carboxyl function and/or the C-5' pentyl group with a di-methyl-heptyl (DMH) group, were tested on: (a) VR1-mediated increase in cytosolic Ca 2+ concentrations in cells over-expressing human VR1; (b) [ 14 C]-AEA uptake by RBL-2H3 cells, which is facilitated by a selective membrane transporter; and (c) [ 14 C]-AEA hydrolysis by rat brain membranes, which is catalysed by the fatty acid amide hydrolase. 3 Both CBD and (+)-CBD, but not the other analogues, stimulated VR1 with EC 50 =3.2 ± 3.5 mM, and with a maximal e ect similar in e cacy to that of capsaicin, i.e. 67 ± 70% of the e ect obtained with ionomycin (4 mM). CBD (10 mM) desensitized VR1 to the action of capsaicin. The e ects of maximal doses of the two compounds were not additive. 4 (+)-5'-DMH-CBD and (+)-7-hydroxy-5'-DMH-CBD inhibited [ 14 C]-AEA uptake (IC 50 =10.0 and 7.0 mM); the (7)-enantiomers were slightly less active (IC 50 =14.0 and 12.5 mM). CBD and (+)-CBD were also active (IC 50 =22.0 and 17.0 mM). 5 CBD (IC 50 =27.5 mM), (+)-CBD (IC 50 =63.5 mM) and (7)-7-hydroxy-CBD (IC 50 =34 mM), but not the other analogues (IC 50 4100 mM), weakly inhibited [ 14 C]-AEA hydrolysis. 6 Only the (+)-isomers exhibited high a nity for CB 1 and/or CB 2 cannabinoid receptors. 7 These ®ndings suggest that VR1 receptors, or increased levels of endogenous AEA, might mediate some of the pharmacological e ects of CBD and its analogues. In view of the facile high yield synthesis, and the weak a nity for CB 1 and CB 2 receptors, (7)-5'-DMH-CBD represents a valuable candidate for further investigation as inhibitor of AEA uptake and a possible new therapeutic agent.

The term 'endocannabinoid' - originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands - now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.

The vanilloid receptor VR1 is a nonselective cation channel that is most abundant in peripheral sensory fibers but also is found in several brain nuclei. VR1 is gated by protons, heat, and the pungent ingredient of ''hot'' chili peppers, capsaicin. To date, no endogenous compound with potency at this receptor comparable to that of capsaicin has been identified. Here we examined the hypothesis, based on previous structure-activity relationship studies and the availability of biosynthetic precursors, that N-arachidonoyl-dopamine (NADA) is an endogenous ''capsaicin-like'' substance in mammalian nervous tissues. We found that NADA occurs in nervous tissues, with the highest concentrations being found in the striatum, hippocampus, and cerebellum and the lowest concentrations in the dorsal root ganglion. We also gained evidence for the existence of two possible routes for NADA biosynthesis and mechanisms for its inactivation in rat brain. NADA activates both human and rat VR1 overexpressed in human embryonic kidney (HEK)293 cells, with potency (EC50 Ϸ 50 nM) and efficacy similar to those of capsaicin. Furthermore, NADA potently activates native vanilloid receptors in neurons from rat dorsal root ganglion and hippocampus, thereby inducing the release of substance P and calcitonin gene-related peptide (CGRP) from dorsal spinal cord slices and enhancing hippocampal paired-pulse depression, respectively. Intradermal NADA also induces VR1-mediated thermal hyperalgesia (EC50 ‫؍‬ 1.5 ؎ 0.3 g). Our data demonstrate the existence of a brain substance similar to capsaicin not only with respect to its chemical structure but also to its potency at VR1 receptors. V anilloid receptors of type 1 (VR1) are nonselective cation channels, expressed in peripheral sensory C and A␦ fibers and gated by nociceptive stimuli such as low pH, heat, and some plant toxins, of which capsaicin, the pungent principle of chili peppers, is the best known example (1-4). Evidence obtained by several laboratories and using different techniques (5-10) showed that VR1 is present also in the central nervous system, where it is unlikely to be the target of noxious heat and low pH, thus suggesting the existence of brain endogenous agonists for this receptor (11). Indeed, lipid mediators previously known to serve other functions in the brain, i.e., the endocannabinoid anandamide and some lipoxygenase derivatives, activate VR1, albeit with a potency considerably lower than that of capsaicin (12)(13)(14). The antinociceptive effects of VR1 blockers in two models of inflammatory hyperalgesia (15, 16) suggest that ''endovanilloids'' might be produced also by peripheral tissues and act in concert with locally enhanced temperature and acidity during inflammation.If an endovanilloid did exist, what would be the structural prerequisites that would allow for an optimal interaction with vanilloid receptors? Structure-activity relationship studies for vanilloid receptors have indicated that both the vanillyl-amine moiety and a long, unsaturated acyl chain are necessary to...