The role of CB1 in intestinal permeability and inflammation

The endocannabinoid system has previously been shown to play a role in the permeability and inflammatory response of the human gut. The goal of our study was to determine the effects of endogenous anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) on the permeability and inflammatory response of intestinal epithelium under normal, inflammatory, and hypoxic conditions. Human intestinal mucosa was modeled using Caco-2 cells. Human tissue was collected from planned colorectal resections. Accumulation of AEA and 2-AG was achieved by inhibiting their metabolizing enzymes URB597 (a fatty acid amide hydrolase inhibitor) and JZL184 (a monoacylglycerol lipase inhibitor). Inflammation and ischemia were simulated with TNF-alpha and IFN-gamma and oxygen deprivation. Permeability changes were measured by transepithelial electrical resistance. The role of the CB1 receptor was explored using CB1-knockdown (CB(1)Kd) intestinal epithelial cells. Endocannabinoid levels were measured using liquid chromatography-mass spectrometry. Cytokine secretion was measured using multiplex and ELISA. URB597 and JZL184 caused a concentration-dependent increase in permeability via CB1 (P < 0.0001) and decreased cytokine production. Basolateral application of JZL184 decreased permeability via CB1 (P < 0.0001). URB597 and JZL184 increased the enhanced (worsened) permeability caused by inflammation and hypoxia (P < 0.0001 and P<0.05). CB(1)Kd cells showed reduced permeability response to inflammation (P<0.01) but not hypoxia. 2-AG levels were increased in response to inflammation and hypoxia in Caco-2 cells. In human mucosal tissue, inflammation increased the secretion of granulocyte macrophage-colony stimulating factor, IL-12, -13, and -15, which was prevented with ex vivo treatment with URB597 and JZL184, and was inhibited by a CB1 antagonist. The results of this study show that endogenous AEA and 2-AG production and CB1 activation play a key modulatory roles in normal intestinal mucosa permeability and in inflammatory and hypoxic conditions.