Evidence That the Cannabinoid CB1 Receptor Is a 2-Arachidonoylglycerol Receptor

Abstract

An endogenous cannabimimetic molecule, 2-arachidonoylglycerol, induces a rapid, transient increase in intracellular free Ca 2؉ concentrations in NG108 -15 cells through a cannabinoid CB1 receptor-dependent mechanism. We examined the activities of 24 relevant compounds (2-arachidonoylglycerol, its structural analogues, and several synthetic cannabinoids). We found that 2-arachidonoylglycerol is the most potent compound examined so far: its activity was detectable from as low as 0.3 nM, and the maximal response induced by 2-arachidonoylglycerol exceeded the responses induced by others. Activities of HU-210 and CP55940, potent cannabinoid receptor agonists, were also detectable from as low as 0.3 nM, whereas the maximal responses induced by these compounds were low compared with 2-arachidonoylglycerol. Anandamide was also found to act as a partial agonist in this assay system. We confirmed that free arachidonic acid failed to elicit a response. Furthermore, we found that a metabolically stable ether-linked analogue of 2-arachidonoylglycerol possesses appreciable agonistic activity, although its activity was apparently lower than that of 2-arachidonoylglycerol. We also confirmed that pretreating cells with various cannabinoid receptor agonists nullified the response induced by 2-arachidonoylglycerol, whereas pretreating cells with other neurotransmitters or neuromodulators did not affect the response. These results strongly suggested that the cannabinoid CB1 receptor is originally a 2-arachidonoylglycerol receptor, and 2-arachidonoylglycerol is the intrinsic physiological ligand for the cannabinoid CB1 receptor.It is well known that ⌬ 9 -tetrahydrocannabinol (⌬ 9 -THC), 1 a psychoactive ingredient of marijuana, possesses a variety of pharmacological activities in vitro and in vivo (1), although, until recently, the mechanism of the action of ⌬ 9 -THC had long been unelucidated. In 1988, Devane et al. (2) provided evidence that a specific binding site(s) for cannabinoids is present in the brain. Soon after, Matsuda et al. (3) cloned a cDNA encoding a cannabinoid receptor (CB1) from a rat brain cDNA library. These findings raised the possibility that at least part of the action of ⌬ 9 -THC is mediated through such a specific receptor and prompted the search for endogenous cannabinoid receptor ligands in mammalian tissues.In 1992, Devane et al. (4) isolated N-arachidonoylethanolamine (anandamide) from porcine brain as the first endogenous cannabinoid receptor ligand. They demonstrated that anandamide exhibits several cannabimimetic activities in vitro and in vivo (4, 5). So far, a number of studies have been carried out on anandamide, and it has been assumed that anandamide is one of the important lipid mediators in the nervous system as well as in other systems (5). However, we (6, 7) and others (8 -11) have found that the levels of anandamide are very low in several mammalian tissues. In addition, the biosynthetic pathways for anandamide, either the N-acylphosphatidylethanolamine pathway (6,7,(11)(12)(13)(14) or t...

2-Arachidonyl glyceryl ether, an endogenous agonist of the cannabinoid CB 1 receptor

“…1) and had initiated an evaluation of its biological properties before the completion of the work described now (14,15). Independently, Sugiura et al had prepared this compound also (16) and Suhara et al had examined its effects on Ca 2ϩ levels in cells (17). The availability of synthetic noladin ether made possible a direct comparison with the natural product.…”

15-Lipoxygenase Metabolism of 2-Arachidonylglycerol

“…Subsequently, 2-AG was shown to be present in vivo at levels several orders of magnitude higher than the other known endocannabinoid, AEA (2)(3)(4). Accumulating evidence supports assertions that 2-AG serves as a physiologically relevant cannabinoid receptor ligand, occupying a central role within the endogenous cannabinoid system (5,6). Therefore, the identification and characterization of enzymes capable of metabolizing this lipid mediator should aid in the elucidation of mechanisms by which cannabinoid tone is modulated in vivo.…”

2-Arachidonoylglycerol Enhances the Phagocytosis of Opsonized Zymosan by HL-60 Cells Differentiated into Macrophage-Like Cells

“…[9][10][11] 2-AG elicits a variety of biological responses in various nervous tissues and cells. 15) For example, 2-AG induced a Ca 2ϩ transient in NG108-15 cells, 9,10) the inhibition of longterm potentiation 16) and the inhibition of synaptic transmission 17) in rat hippocampal slices, and the inhibition of voltage-gated Ca 2ϩ channels and the activation of inwardly rectifying K ϩ channels in rat sympathetic neurons 18) via CB1 receptor-dependent mechanisms. On the other hand, not much information is available concerning the effects of 2-AG on inflammatory cells and immune-competent cells which express the CB2 receptor.…”

“…7,8) Previously, we investigated in detail the structure-activity relationship of cannabinoid receptor ligands and found that 2-AG is the most efficacious agonist among the various structural analogs and homologs thus far examined. [9][10][11] Importantly, 2-AG acted as a full agonist toward these cannabinoid receptors in various assay systems, [9][10][11][12][13][14] whereas anandamide often acted as a partial agonist. Based on these experimental results, we proposed that 2-AG, rather than anandamide, is the true natural ligand for the cannabinoid receptors.…”