The antinociceptive triterpene β-amyrin inhibits 2-arachidonoylglycerol (2-AG) hydrolysis without directly targeting cannabinoid receptors.
OBJECTIVE
Pharmacological activation of cannabinoid CB(1) and CB(2) receptors is a therapeutic strategy to treat chronic and inflammatory pain. It was recently reported that a mixture of natural triterpenes α- and β-amyrin bound selectively to CB(1) receptors with a subnanomolar K(i) value (133 pM). Orally administered α/β-amyrin inhibited inflammatory and persistent neuropathic pain in mice through both CB(1) and CB(2) receptors. Here, we investigated effects of amyrins on the major components of the endocannabinoid system.


METHODS
We measured CB receptor binding interactions of α- and β-amyrin in validated binding assays using hCB(1) and hCB(2) transfected CHO-K1 cells. Effects on endocannabinoid transport in U937 cells and breakdown using homogenates of BV2 cells and pig brain, as well as purified enzymes, were also studied.


RESULTS
There was no binding of either α- or β-amyrin to hCB receptors in our assays (K(i) > 10 µM). The triterpene β-amyrin potently inhibited 2-arachidonoyl glycerol (2-AG) hydrolysis in pig brain homogenates, but not that of anandamide. Although β-amyrin only weakly inhibited purified human monoacylglycerol lipase (MAGL), it also inhibited α,β-hydrolases and more potently inhibited 2-AG breakdown than α-amyrin and the MAGL inhibitor pristimerin in BV2 cell and pig brain homogenates.


CONCLUSIONS
We propose that β-amyrin exerts its analgesic and anti-inflammatory pharmacological effects via indirect cannabimimetic mechanisms by inhibiting the degradation of the endocannabinoid 2-AG without interacting directly with CB receptors. Triterpenoids appear to offer a very broad and largely unexplored scaffold for inhibitors of the enzymic degradation of 2-AG.


BACKGROUND
This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.
Institute of Biochemistry and Molecular Medicine, National Centre of Competence in Research NCCR TransCure, University of Bern, Bern, Switzerland.
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Chicca
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Marazzi
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Gertsch
D000581:Amidohydrolases / Q000378:metabolism; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D063388:Endocannabinoids / Q000378:metabolism*; D005989:Glycerides / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D008994:Monoacylglycerol Lipases / Q000378:metabolism; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000378:metabolism; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism; D043885:Receptor, Cannabinoid, CB2 / Q000378:metabolism; D013552:Swine; D020298:U937 Cells; D000099252:Fatty Acid Amide Hydrolases
D000581:Amidohydrolases; D000700:Analgesics; D001095:Arachidonic Acids; D063388:Endocannabinoids; D005989:Glycerides; D008994:Monoacylglycerol Lipases; D009828:Oleanolic Acid; D053284:Polyunsaturated Alkamides; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; D000099252:Fatty Acid Amide Hydrolases; C094503:glyceryl 2-arachidonate; C505247:2-oleoylglycerol; C036380:beta-amyrin; C078814:anandamide