Selective release of gastrointestinal hormones induced by an orally active GPR39 agonist

OBJECTIVES: Obesity is a complex disease associated with a high risk of co-morbidities. Gastric bypass surgery, an invasive procedure with low patient eligibility, is currently the most effective intervention that achieves sustained weight loss. This beneficial effect is attributed to alterations in gut hormone signaling. An attractive alternative is to pharmacologically mimic the effects of bariatric surgery by targeting several gut hormonal axes. The G protein-coupled receptor 39 (GPR39) expressed in the gastrointestinal tract has been shown to mediate ghrelin signaling and control appetite, food intake and energy homeostasis, but the broader effect on gut hormones is largely unknown. A potent and efficaous GPR39 agonist (Cpd1324) was recently discovered, but the in vivo function was not addressed. Here we studied the efficacy of the GPR39 agonist, Cpd1324, on metabolism and gut hormone secretion.

METHODS: Body weight, food intake and energy expenditure in GPR39 agonist-treated mice and GPR39 KO mice were studied in calorimetric cages. Plasma ghrelin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) levels were measured. Organoids generated from murine and human small intestine and mouse colon were used to study GLP-1 and PYY release. Upon GPR39 agonist administration, the dynamic changes in intracellular GLP-1 content was studied by means of immunostaining and changes in ion transport across colonic mucosa was monitored in Ussing chambers. The G protein activation underlying GPR39-mediated selective release of gut hormones was studied using bioluminescence resonance energy transfer biosensors.

RESULTS: GPR39 KO mice displayed a significantly increased food intake without corresponding increases in respiratory exchange ratio or energy expenditure. Oral administration of a GPR39 agonist induced an acute decrease in food intake and subsequent weightloss in high-fat diet (HFD)-fed mice without affecting energy expenditure. The tool compound, Cpd1324, increased GLP-1 secretion in mice as well as in mouse and human intestinal organoids, but not in GPR39 KO mouse organoids. In contrast, the GPR39 agonist had no effect on PYY or GIP secretion. Transepithelial ion transport was acutely affected by GPR39 agonism in a GLP-1- and calcitonin gene-related peptide (CGRP)-dependent manner. Analysis of Cpd1324 signaling properties showed activation of Gαq and Gα i/o signaling pathways in L cells, and not Gαs signaling.

CONCLUSIONS: The GPR39 agonist described in this study can potentially be used by oral administration as a weight-lowering agent due to its stimulatory effect on GLP-1 secretion, which is most likely mediated through a unique activation of Gα subunits. Thus, GPR39 agonism may represent a novel approach to effectively treat obesity through a selective modulation of gastrointestinal hormonal axes.