Oleamide is a selective endogenous agonist of rat and human CB1 cannabinoid receptors

1 The ability of the endogenous fatty acid amide, cis-oleamide (ODA), to bind to and activate cannabinoid CB1 and CB2 receptors was investigated. 2 ODA competitively inhibited binding of the nonselective cannabinoid agonist [H-3]CP55,940 and the selective CB1 antagonist [H-3]SR141716A to rat whole-brain membranes with K-i values of 1.14 muM (0.52-2.53 muM, Hill slope = 0.80, n = 6) and 2.63 muM (0.62-11.20 muM, Hill slope = 0.92, n = 4), respectively. AEA inhibited [H-3]CP55,940 binding in rat whole-brain membranes with a K-i of 428 nm (346-510 nM, Hill slope = -1.33, n = 3). 3 ODA competitively inhibited [H-3]CP55,940 binding in human CB1 (hCB(1)) cell membranes with a K-i value of 8.13 muM (4.97-13.32 muM, n = 2). In human CB2 transfected (hCB(2)) HEK-293T cell membranes, 100 muM ODA produced only a partial (42.5 +/- 7%) inhibition of [H-3]CP55,940 binding. 4 ODA stimulated [S-35]GTPgammaS binding in a concentration-dependent manner (EC50 = 1.64 muM (0.29-9.32 muM), R-2 = 0.99, n = 4-9), with maximal stimulation of 188 +/- 9% of basal at 100 muM. AEA stimulated [S-35]GTPgammaS binding with an EC50 of 10.43 muM (4.45-24.42 muM, R-2 = 1.00, n = 3, 195 +/- 4% of basal at 300 muM). Traps-oleamide (trans-ODA) failed to significantly stimulate [S-35]GTPgammaS binding at concentrations up to 100 muM. 5 ODA (10 muM)-stimulated [S-35]GTPgammaS binding was reversed by the selective CB1 antagonist SR141716A (IC50 = 2.11 nM (0.32-13.77 nm), R-2 =1.00, n = 6). 6 The anatomical distribution of ODA-stimulated [S-35]GTPgammaS binding in rat brain sections was indistinguishable from that of HU210. Increases of similar magnitude were observed due to both agonists in the striatum, cortex, hippocampus and cerebellum. 7 ODA (10 muM) significantly inhibited forskolin-stimulated cyclic AMP (CAMP) accumulation in mouse neuroblastoma N1E 115 cells (P = 0.02, n = 11). ODA-mediated inhibition was completely reversed by 1 muM SR141716A (P < 0.001, n = 11) and was also reversed by pretreatment with 300 ng ml(-1) pertussis toxin (P < 0.001, n = 6). 8 These data demonstrate that ODA is a full cannabinoid CB1 receptor agonist. Therefore, in addition to allosteric modulation of other receptors and possible entourage effects due to fatty acid amide hydrolase inhibition, the effects of ODA may be mediated directly via the CB1 receptor.