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The endocannabinoids anandamide and 2-arachidonoylglycerol, and the anandamide-congener, palmitoylethanolamide, are all substrates for the enzyme fatty acid amide hydrolase, and are endowed with anti-inflammatory actions exerted via cannabinoid receptors or, in the case of palmitoylethanolamide, also via other targets. We investigated the role of the endocannabinoid system during granuloma formation, a model of chronic inflammation sustained by neoangiogenesis, in rats. Granuloma was induced by subcutaneous lambda-carrageenin-soaked sponge implants on the back of male Wistar rats. After 96h, granulomas were detached and tissue formation was evaluated as wet weight; the endocannabinoid system was evaluated by the measurement of endocannabinoid levels, by LC-MS, and of cannabinoid receptor expression, by western blot analysis. Moreover, angiogenesis was evaluated by the measurement of both hemoglobin content and CD31 protein expression. Arachidonoylserotonin (AA-5-HT, 12.5-50mug/ml), an inhibitor of FAAH, and palmitoylethanolamide (PEA, 200-800mug/ml) were given locally only once at the time of implantation. Granuloma formation was accompanied by a significant decrease in endocannabinoid and palmitoylethanolamide levels paralleled by increased levels of the fatty acid amide hydrolase, responsible for their breakdown. Moreover, an increase of cannabinoid receptor expression was also observed. Pharmacological elevation of endocannabinoids and palmitoylethanolamide, obtained separately by arachidonoylserotonin and exogenous palmitoylethanolamide treatment, dose-dependently reduced inflammatory hallmarks including tumor necrosis factor-alpha as well as granuloma-dependent angiogenesis. The effect of arachidonoylserotonin was accompanied by near-normalization of 2-arachidonoylglycerol and palmitoylethanolamide levels in the tissue. These findings suggest that chronic inflammation might develop also because of endocannabinoid and palmitoylethanolamide tissue concentration impairment, the correction of which might be exploited to develop new anti-inflammatory drugs.
Copyright 2009 Elsevier Ltd. All rights reserved.