Biosynthesis and inactivation of the endocannabinoid 2-arachidonoylglycerol in circulating and tumoral macrophages.

The stimulus-induced biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG) in intact mouse J774 macrophages and the inactivation of 2-AG by the same cells or by rat circulating macrophages was studied. By using gas chromatography-mass spectrometry, we found that ionomycin (5 mu M) and lipopolysaccharide (LPS, 200 mu g.mL(-1)) cause a 24-fold and 2.5-fold stimulation of 2-AG levels in J774 cells, respectively, thus providing unprecedented evidence that this cannabimimetic metabolite can be synthesized by macrophages. In J774 cells, LPS also induced a 7.8-fold increase of the levels of the other endocannabinoid, anandamide, and, in rat circulating macrophages, an almost twofold increase of 2-AG levels. Extracellular [H-3]2-AG was cleared from the medium of intact 5774 macrophages (t(1/2) = 19-38 min) and esterified to phospholipids, diacylglycerols and triglycerides or hydrolyzed to [H-3]arachidonic acid and glycerol. These catabolic processes were attenuated differentially by various enzyme inhibitors. Rat circulating macrophages were shown to contain enzymatic activities ibr the hydrolysis of 2-AG. including: (a) fatty acid amide hydrolase (FAAH), the enzyme responsible for anandamide breakdown and previously shown to catalyse also 2-AG hydrolysis, and (b) a 2-AG hydrolase activity different from FAAH and down-regulated by LPS. High levels of FAAH mRNA were found in circulating macrophages but not platelets, which, however, contain a 2-AG hydrolase. Both platelets and macrophages were shown to express the mRNA for the CB1 cannabinoid receptor. A macrophage 2-AG hydrolase with apparent K-m = 110 mu M and V-max = 7.9 nmol.min(-1)(mg protein)(-1) was partially characterized in 5774 cells and found to exhibit an optimal pH of 6-7 and little or no sensitivity to typical FAAH inhibitors. These findings demonstrate for the first time that macrophages participate in the homeostasis of the hypotensive and immunomodulatory endocannabinoid 2-AG through metabolic mechanisms that are subject to regulation.