Acknowledgments We would like to thank Dr Greg Morriello

Acknowledgments We would like to thank Dr. Greg Morriello, Mr. Lehua Chang, Mr. Chris Moyes and Mr. Nam Fung Kar for intermediate 3 syntheses. Cheng Zhu would like to thank Dr. Milana Maletic, Mr. Kake Zhao and Mrs. Wanying Sun for helpful discussions.
Introduction Glucagon-like peptide-1 (GLP-1) has multiple anti-diabetic effects, most notably enhancing insulin secretion, suppressing glucagon release and slowing gastric emptying [1]. Current incretin-based therapies focus on preventing the breakdown of GLP-1 by dipeptidyl peptidase-IV or administrating GLP-1 mimetics [2]. The benefits of increasing endogenous GLP-1 secretion are currently under evaluation, supported by evidence that gastric bypass surgery improves glucose tolerance, at least in part by increased GLP-1 secretion [3]. GPR119 is one of a number of candidate G-protein coupled receptors currently under investigation as a potential target for elevating GLP-1 and insulin release. GLP-1 is secreted from enteroendocrine L-cells in the intestinal epithelium, which express a variety of receptors and transporters capable of detecting ingested nutrients, including carbohydrates, lipids and proteins [4]. GPR119 is a Gαs-coupled receptor, linked to the elevation of intracellular cAMP concentrations [5], [6], [7], [8], [9], [10], [11]. Physiological GPR119 ligands include oleoylethanolamide (OEA) [6], produced locally within tissues [12], [13], [14], and 2-oleoyl glycerol (2-OG) [15] generated by luminal triacylglycerol Compstatin [16]. OEA as well as small molecule GPR119 agonists, increase GLP-1 and insulin release in rodent models [9], [17], [18], [19]. Indeed, GPR119 agonists were developed for human studies and taken into clinical trials in patients with type 2 diabetes, but were not found to improve metabolic control [20]. The reasons for the poor translatability remain uncertain, and the physiological roles and therapeutic potential of GPR119 are still under investigation.
Methods
Results
Discussion Following the de-orphanization of GPR119, small molecules targeting this receptor were developed as potential new treatments for diabetes that would increase secretion from intestinal L-cells [25]. Although subsequent trials have not yet demonstrated that metabolic improvements can be brought about by the use of GPR119 agonists in humans with type 2 diabetes [20], there is still a high level of academic and commercial interest in GPR119 as a potential drug target [26], [27]. Our results show that L-cell GPR119 is a critical component of the sensing mechanism responsible for GLP-1 responses to ingested lipid, and that L-cells in the distal intestine respond to GPR119 agonists with elevated cAMP and GLP-1 secretion. We show here that GPR119 ligands increase GLP-1 release from primary cultured ileal and colonic L-cells in a GPR119-dependent manner. Of the three GPR119 agonists tested, OEA and AR231453 were more effective than 2-OG. The magnitude of the secretory response triggered by the different GPR119 ligands increased progressively from the upper small intestine to the colon. Indeed, L-cell knockout of Gpr119 largely abolished responses to OEA, 2-OG and AR231453 in the colon. In the ileum, where the secretory response was smaller, only OEA and AR231453 raised secretion in WT tissues above that found in the Gpr119-KO, and in the duodenum/jejunum, none of the ligands had a greater effect in WT than KO cultures. While our results suggest that the small response to OEA in the duodenum/jejunum of WT tissue is independent of GPR119, we cannot exclude the possibility that the proportion of L-cells undergoing Cre-dependent GPR119 excision differed between tissues and that more residual L-cells expressed GPR119 in the upper intestine. Arguing against this idea, however, AR231453 had little effect on GLP-1 secretion in the WT duodenum/jejunum, and OEA has been reported to activate other pathways such as PPARα that might influence GLP-1 secretion even in the absence of Gpr119 [28].