The Pharmacological Profile of Plant-Derived Cannabinoids In Vitro.

2012 cannabinoid themed section

The cannabinoid system in the brain is targetted in the use and abuse of preparations from theCannabisplant. This system is composed of synthetic enzymes for the endogenous lipid‐derived ligands, the cannabinoid receptors they activate and the enzymes which transform them. These endocannabinoids are amides, such as anandamide, or esters, such as 2‐arachidonoylglycerol, whose primary target in the central nervous system is the CB1cannabinoid receptor, a G protein‐coupled receptor expressed to unusually high levels. Δ9‐Tetrahydrocannabinol (THC) appears to be the sole psychoactive entity present inCannabisplant, which elicits the characteristic responses in man and animals. The pharmacology and biochemistry of the endocannabinoid system has been thoroughly investigated since the identification of CB1cannabinoid receptors. As yet, however, the translation of this knowledge into a clinical setting has been of limited success.Key Concepts:Δ9‐Tetrahydrocannabinol appears to be the major psychoactive agent present in theCannabisplant.Δ9‐Tetrahydrocannabinol acts as a partial agonist at the CB1cannabinoid receptor.CB1cannabinoid receptors appear to be the most densely expressed G protein‐coupled receptors in the brain.CB1cannabinoid receptors couple functionally to an inhibition of transmitter release.CB2cannabinoid receptors are primarily associated with the immune system, but may also be found in the CNS.Endogenous cannabinoids, termed endocannabinoids, are fatty acid derivatives.Endocannabinoids are not stored in vesicles, but rather are made on demand.Endocannabinoid production is involved in two neurophysiological phenomena, termed depolarisation‐evoked suppression of excitation (DSE) and depolarisation‐evoked suppression of inhibition (DSI).Endocannabinoids may also act at particular ligand‐gated ion channels (notably the TRPV1 vanilloid receptor) and nuclear hormone receptors (notably peroxisome proliferator‐activated receptors).

GENERAL COMMENTARY article Front. Behav. Neurosci., 13 October 2011Sec. Learning and Memory volume 5 - 2011 | https://doi.org/10.3389/fnbeh.2011.00067

Novel selective antagonist of the cannabinoid CB1 receptor, MJ15, with prominent anti-obesity effect in rodent models

It is intriguing that during human cultural evolution man has detected plant natural products that appear to target key protein receptors of important physiological systems rather selectively. Plants containing such secondary metabolites usually belong to unique chemotaxa, induce potent pharmacological effects and have typically been used for recreational and medicinal purposes or as poisons. Cannabis sativa L. has a long history as a medicinal plant and was fundamental in the discovery of the endocannabinoid system. The major psychoactive Cannabis constituent Delta(9)-tetrahydrocannabinol (Delta(9)-THC) potently activates the G-protein-coupled cannabinoid receptor CB(1) and also modulates the cannabinoid receptor CB(2). In the last few years, several other non-cannabinoid plant constituents have been reported to bind to and functionally interact with CB receptors. Moreover, certain plant natural products, from both Cannabis and other plants, also target other proteins of the endocannabinoid system, such as hydrolytic enzymes that control endocannabinoid levels. In this commentary we summarize and critically discuss recent findings.

The human mu opioid receptor was expressed stably in Flp-In T-REx HEK293 cells. Occupancy by the agonist DAMGO (Tyr-d-Ala-Gly-N-methyl-Phe-Gly-ol) resulted in phosphorylation of the ERK1/2 MAP kinases, which was blocked by the opioid antagonist naloxone but not the cannabinoid CB1 receptor inverse agonist SR141716A. Expression of the human cannabinoid CB1 receptor in these cells from the inducible Flp-In T-REx locus did not alter expression levels of the mu opioid receptor. This allowed the cannabinoid CB1 agonist WIN55212-2 to stimulate ERK1/2 phosphorylation but resulted in a large reduction in the capacity of DAMGO to activate these kinases. Although lacking affinity for the mu opioid receptor, co-addition of SR141716A caused recovery of the effectiveness of DAMGO. In contrast co-addition of the CB1 receptor neutral antagonist O-2050 did not. Induction of the CB1 receptor also resulted in an increase of basal [(35)S]guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) binding and thereby a greatly reduced capacity of DAMGO to further stimulate [(35)S]GTPgammaS binding. CB1 inverse agonists attenuated basal [(35)S]GTPgammaS binding and restored the capacity of DAMGO to stimulate. Flp-In T-REx HEK293 cells were generated, which express the human mu opioid receptor constitutively and harbor a modified D163N cannabinoid CB1 receptor that lacks constitutive activity. Induction of expression of the modified cannabinoid CB1 receptor did not limit DAMGO-mediated ERK1/2 MAP kinase phosphorylation and did not allow SR141716A to enhance the function of DAMGO. These data indicate that it is the constitutive activity inherent in the cannabinoid CB1 receptor that reduces the capacity of co-expressed mu opioid receptor to function.

Alterations in Gene and Protein Expression of Cannabinoid CB2 and GPR55 Receptors in the Dorsolateral Prefrontal Cortex of Suicide Victims.

Cannabis sativa is possibly the plant with the longest history of cultivation by man (Russo, 2007). It has long been exploited for its fibre; as a biomass converter, it has exceptional utility. For most people, however, there is the association of cannabis with ‘recreational drugs’, which has lead to the profusion of names associated with the plant and extracts thereof (marijuana, hashish, bhang, weed, grass, etc.). The ‘modern’ scientific era of cannabis research was prompted by the discovery of the major psychoactive ingredient in cannabis extracts (Gaoni and Mechoulam, 1964). This was, of course, Δ9-tetrahydrocannabinol or THC. Raphael Mechoulam has numerous publications, filled with seminal observations, including the identification of the two ‘best’ candidates for endogenous cannabinoid molecules: anandamide (Devane et al., 1992) and 2-arachidonoylglycerol (Mechoulam et al., 1995). He has become something of an icon in the cannabis field, with this issue of BJP containing a series of original articles prompted by a symposium held in Jerusalem in November 2010 to celebrate his 80th birthday. The first issue, entitled ‘Cannabinoids in Biology and Medicine’, containing primarily reviews, was published in August 2011 (http://onlinelibrary.wiley.com/doi/10.1111/bph.2011.163.issue-7/issuetoc). Current research in cannabinoid-related areas is vibrant, with the added focus of TRPV1 ion channels, PPAR nuclear receptors and the ‘orphan’ G-protein coupled receptors, GPR18, GPR55 and GPR119, as molecular targets of cannabinoids and cannabinoid-like molecules. Furthermore, the identification of endogenous agonists at cannabinoid receptors which lead to the demonstration of multiple routes for synthesis and transformation of these endocannabinoids has added to the molecular targets available for potential exploitation. The involvement of ‘big pharma’ in cannabinoid research has been intermittent, with Pfizer and Sterling-Winthrop providing the very useful synthetic compounds CP55940 and WIN55212-2 in the 1970s and 1980s, respectively, without being able to translate these pharmacological successes into therapeutic solutions. The limiting factor for these compounds appears to have been the psychoactivity evoked through activation of CNS CB1 cannabinoid receptors. In the 2000s, Sanofi-Aventis achieved a measure of success with the CB1 cannabinoid receptor antagonist/inverse agonist rimonabant (Acomplia®, SR141716A; Sanofi-Aventis, Paris, France) as one of the few pharmacotherapeutic alternatives for obesity. This success was short lived, however (approval was for 2006–2009 in Europe, not approved in the US), through adverse CNS effects in a significant minority of patients. In the clinical setting, therefore, cannabinoids are currently represented by THC itself (dronabinol, Marinol®; Solvay Pharmaceuticals, Brussels, Belgium), a THC analogue (nabilone, Cesamet®; Valeant Pharmaceuticals International, Mississauga, Canada) and THC in combination with other cannabinoids derived from the cannabis plant, notably cannabidiol (Sativex®; GW Pharmaceuticals, London, UK). So where is cannabinoid research likely to go in the 2010s? The answer, as with many other fields of pharmacological/therapeutic interest, lies in the symposia and meetings focused on cannabinoids.

To clarify possible interaction between the ventral hippocampal cannabinoid CB2 receptors and the cholinergic system in control of the memory process, the effects of cannabinoid and acetylcholine receptor agents on memory consolidation have been investigated in mice. Animals implanted with bilateral cannulas at the CA3 region of the ventral hippocampus and microinjected with scopolamine and cannabinergic agents. These animals were tested using a one-trial step-down inhibitory avoidance task. The results indicated impairment of memory consolidation by posttraining intra-CA3 microinjection of scopolamine (1 and 2 µg/mouse). Nevertheless, coinjection of various doses of scopolamine (0.01, 1 and 2 µg/mouse) with an ineffective dose of AM630 (1 µg/mouse) or GP1a (1 µg/mouse) did not show any significant effect on deficiency of memory consolidation produced by scopolamine. Posttraining application of cannabinoid CB2 receptor antagonist, AM630 (1, 10 and 100 µg/mouse; intra-CA3) alone had no significant influence on memory performance, but its coinjection with significant dose of scopolamine (1 µg/mouse) decreased memory consolidation. Moreover, posttraining injection of GP1a, cannabinoid CB2 receptor agonist, (10 and 100 µg/mouse; intra-CA3) decreased memory consolidation. Posttraining coadministration of diverse doses of GP1a (1, 10 and 100 µg/mouse; intra-CA3) with an effective dose of scopolamine (1 µg/mouse) meaningfully increased deficiency of memory consolidation produced by GP1a (100 µg/mouse). In addition, all drugs had no significant effect on locomotion. Consequently, these results propose that a probable interaction between the CA3 cannabinoid CB2 receptors and muscarinic acetylcholine receptors (mAChR) modulates memory consolidation process in mice.

Identification and biochemical analyses of selective CB2 agonists

Genetic or pharmacological depletion of cannabinoid CB1 receptor protects against dopaminergic neurotoxicity induced by methamphetamine in mice

Activation of spinal cannabinoid CB2 receptors inhibits neuropathic pain in streptozotocin-induced diabetic mice

Endocannabinoids and neurodegenerative diseases

Activation of cannabinoid CB1 receptors (CB1R) by agonists induces analgesia but also induces cognitive impairment through the heteromer formed between CB1R and the serotonin 5HT2A receptor (5HT2AR). This side effect poses a serious drawback in the therapeutic use of cannabis for pain alleviation. Peptides designed from the transmembrane helices of CB1R, which are predicted to bind 5HT2AR and alter the stability of the CB1R-5HT2AR heteromer, have been shown to avert CB1R agonist-induced cognitive impairment while preserving analgesia. Using these peptides as templates, we have now designed nonpeptidic small molecules that prevent CB1R-5HT2AR heteromerization in bimolecular fluorescence complementation assays and the heteromerization-dependent allosteric modulations in cell signaling experiments. These results provide proof-of-principle for the design of optimized ligand-based disruptors of the CB1R-5HT2AR heteromer, opening new perspectives for in vivo studies.

Role of the σRs for Development of Medications.