Does the hydrolysis of 2-arachidonoylglycerol regulate its cellular uptake?

Abstract

Very little is known about the processes regulating the cellular uptake of the endogenous cannabinoid 2-arachidonoylglycerol (2-AG). In the present study, we investigated whether inhibition of 2-AG hydrolysis reduced its uptake, i.e. whether this compound behaves in a manner analogous to the related endocannabinoid anandamide. The selective fatty acid amide hydrolase inhibitor URB597 (3′-(aminocarbamoyl)[1,1′-biphenyl]-3-yl)-cyclohexylcarbamate) completely blocked the hydrolysis of anandamide and reduced its uptake by about half in RBL2H3 basophilic leukaemia cells. In contrast, in these cells, in PC3 and R3327AT-1 prostate cancer cells and in Neuro-2a neuroblastoma cells, the compound had more modest effects upon the hydrolysis of 2-AG and did not affect its cellular uptake at all, indicating that in these cells fatty acid amide hydrolase does not regulate the uptake of 2-AG. The serine hydrolase inhibitor methylarachidonoyl fluoronophosphonate behaved like URB597 with respect to anandamide uptake by RBL2H3 and Neuro-2a cells, and inhibited the hydrolysis of 2-AG with IC 50 values of 0.014, 0.052, 0.41 and ∼1 μM for RBL2H3, PC3, AT-1 and Neuro-2a cells, respectively. MAFP (1 μM) did not significantly reduce the uptake of 2-AG by RBL2H3, PC3 and AT-1 cells but did reduce the uptake of this endocannabinoid by Neuro-2a cells. Arachidonoyl trifluoromethyl ketone and URB602 ([1,1′-biphenyl]-3-yl-carbamic acid, cyclohexyl ester) reduced the uptake of 2-AG by both RBL2H3 and Neuro-2a cells, but at the high concentrations needed, the compound also blocked the retention of these ligands by wells. It is concluded that unlike the situation for anandamide, hydrolysis of 2-AG does not regulate its cellular uptake in RBL2H3, AT-1 and PC3 cells, but may gate the uptake in Neuro-2a cells.