Biased signaling of lipids and allosteric actions of synthetic molecules for GPR119

GPR119 is a G alpha s-coupled lipid-sensor in the gut, where it mediates release of incretin hormones from the enteroendocrine cells and in pancreatic alpha-cells, where it releases insulin. Naturally occurring lipids such as monoacylglycerols (MAGs) and N-acylethanolamines (NAEs), like oleoylethanolamide (OEA), activate GPR119, and multiple synthetic ligands have been described. Here, we extend the GPR119 signaling profile to G alpha q and G alpha i in addition to beta-arrestin recruitment and the downstream transcription factors CRE (CAMP response element), SRE (serum response element) and NFAT (nuclear factor of activated T cells). The endogenous OEA and the synthetic AR231453 were full agonists in all pathways except for NFAT, where no ligand-modulation was observed. The potency of AR231453 varied <16-fold (EC50 from 6 to 95 nM) across the different signaling pathways, whereas that of OEA varied >175-fold (from 85 nM to 15 mu M) indicating a biased signaling for CEA. The degree of constitutive activity was 1-10%, 10-30% and 30-70% of OEA-induced E-max in G alpha i, G alpha q and G alpha s-driven pathways, respectively. This coincided with the lowest and highest OEA potency observed in G alpha i and G alpha s-driven pathways, respectively. Incubation for 2 h with the 2-MAG-lipase inhibitor JZL84 doubled the constitutive activity, indicating that endogenous lipids contribute to the apparent constitutive activity. Finally, besides being an agonist, AR231453 acted as a positive allosteric modulator of OEA and increased its potency by 54-fold at 100 nM AR231453. Our studies uncovering broad and biased signaling, masked constitutive activity by endogenous MAGs, and ago-allosteric properties of synthetic ligands may explain why many GPR119 drug-discovery programs have failed so far. (C) 2016 The Author(s). Published by Elsevier Inc.