Biosynthesis of 2-Arachidonoyl-Glycerol, a Novel Cannabimimetic Eicosanoid, in Mouse Neuroblastoma Cells

Abstract

Following the original isolation from porcine brain of the first endogenous ligand of cannabinoid receptors, anandamide (arachidonoyl-ethanolamide)¹, another arachidonic acid (AA)-derived metabolite, 2-arachidonoyl-glycerol (2-AG), was found in canine gut² and reported to share with anandamide and plant cannabinoids several pharmacological actions. 2-AG binds to either brain (CB1) or spleen (CB2) cannabinoid receptor subtypes with Ki values in the high nmolar-low μmolar range and inhibits forskolin-induced adenylate cyclase activation; in vivo, 2-AG reproduces the typical cannabimimetic effects of hypothermy, hypomotility and analgesia². Moreover, 2-AG inhibits cell proliferation in lymphocytes that do not express the CB1 receptor subtype³, and, due to the inability of anandamide to functionally activate CB2 receptors⁴, has been suggested to act as the possible endogenous cannabinoid agonist in the immune system³, also on the basis of its recent finding in the spleen⁵. The isolation of mono-arachidonoyl-glycerol isomers from rat brain in levels 50–100 fold higher than those of anandamide⁶ and the recent report of a CB1 receptor-mediated stimulatory action by 2-AG on intracellular free Ca²⁺ in neuroblastoma x glioma hybrid cells⁷, however, raised the possibility that the monoglyceride might function as a possible ‘endocannabinoid’ also in the CNS. In this study we provide biochemical grounds to the hypothesis that 2-AG may be a neuronal mediator by describing: a) its Ca²⁺-dependent biosynthesis in mouse neuroblastoma N18TG2 cells, and b) the occurrence in the same cells of enzymatic activities responsible for 2-AG formation from diacylglycerols and (lyso)phosphatidylcholine.