We recently showed that activation of G protein-coupled receptor 119 (GPR119) (also termed glucose dependent insulinotropic receptor) improves glucose homeostasis via direct cAMP-mediated enhancement of glucose-dependent insulin release in pancreatic beta-cells. Here we show that GPR119 also stimulates incretin hormone release and thus may regulate glucose homeostasis by this additional mechanism. GPR119 mRNA was found to be expressed at significant levels in intestinal subregions that produce glucose-dependent insulinotropic peptide and glucagon-like peptide (GLP)-1. Furthermore, in situ hybridization studies indicated that most GLP-1-producing cells coexpress GPR119 mRNA. In GLUTag cells, a well-established model of intestinal L-cell function, the potent GPR119 agonist AR231453 stimulated cAMP accumulation and GLP-1 release. When administered in mice, AR231453 increased active GLP-1 levels within 2 min after oral glucose delivery and substantially enhanced total glucose-dependent insulinotropic peptide levels. Blockade of GLP-1 receptor signaling with exendin(9-39) reduced the ability of AR231453 to improve glucose tolerance in mice. Conversely, combined administration of AR231453 and the DPP-4 inhibitor sitagliptin to wild-type mice significantly amplified both plasma GLP-1 levels and oral glucose tolerance, relative to either agent alone. In mice lacking GPR119, no such enhancement was seen. Thus, GPR119 regulates glucose tolerance by acting on intestinal endocrine cells as well as pancreatic beta-cells. These data also suggest that combined stimulation of incretin hormone release and protection against incretin hormone degradation may be an effective antidiabetic strategy.

Pancreatic ␤-cell dysfunction is a hallmark event in the pathogenesis of type 2 diabetes. Injectable peptide agonists of the glucagon-like peptide 1 (GLP-1) receptor have shown significant promise as antidiabetic agents by virtue of their ability to amplify glucose-dependent insulin release and preserve pancreatic ␤-cell mass. These effects are mediated via stimulation of cAMP through ␤-cell GLP-1 receptors. We report that the G␣ s -coupled receptor GPR119 is largely restricted to insulin-producing ␤-cells of pancreatic islets. Additionally, we show here that GPR119 functions as a glucose-dependent insulinotropic receptor. Unlike receptors for GLP-1 and other peptides that mediate enhanced glucose-dependent insulin release, GPR119 was suitable for the development of potent, orally active, small-molecule agonists. The GPR119-specific agonist AR231453 significantly increased cAMP accumulation and insulin release in both HIT-T15 cells and rodent islets. In both cases, loss of GPR119 rendered AR231453 inactive. AR231453 also enhanced glucose-dependent insulin release in vivo and improved oral glucose tolerance in wild-type mice but not in GPR119-deficient mice. Diabetic KK/A y mice were also highly responsive to AR231453. Orally active GPR119 agonists may offer significant promise as novel antihyperglycemic agents acting in a glucose-dependent fashion. (Endocrinology

5-Hydroxytryptamine (5-HT) 2C receptor agonists hold promise for the treatment of obesity. In this study, we describe the in vitro and in vivo characteristics of lorcaserin [(1R)-8-chloro-2,3,4,5-tetrahydro-1-methyl-1H-3 benzazepine], a selective, high affinity 5-HT 2C full agonist. Lorcaserin bound to human and rat 5-HT 2C receptors with high affinity (K i ϭ 15 Ϯ 1 nM, 29 Ϯ 7 nM, respectively), and it was a full agonist for the human 5-HT 2C receptor in a functional inositol phosphate accumulation assay, with 18-and 104-fold selectivity over 5-HT 2A and 5-HT 2B receptors, respectively. Lorcaserin was also highly selective for human 5-HT 2C over other human 5-HT receptors (5-HT 1A , 5-HT 3 , 5-HT 4C , 5-HT5 5A , 5-HT 6 , and 5-HT 7 ), in addition to a panel of 67 other G protein-coupled receptors and ion channels. Lorcaserin did not compete for binding of ligands to serotonin, dopamine, and norepinephrine transporters, and it did not alter their function in vitro. Behavioral observations indicated that unlike the 5-HT 2A agonist (Ϯ)-1-(2,5-dimethoxy-4-phenyl)-2-aminopropane, lorcaserin did not induce behavioral changes indicative of functional 5-HT 2A agonist activity. Acutely, lorcaserin reduced food intake in rats, an effect that was reversed by pretreatment with the 5-HT 2C -selective antagonist 6-chloro-5-methyl-1-[6-(2-methylpyridin-3-yloxy)pyridin-3-yl-carbamoyl]indoline (SB242,084) but not the 5-HT 2A antagonist (R)-(ϩ)-␣-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol (MDL 100,907), demonstrating mediation by the 5-HT 2C receptor. Chronic daily treatment with lorcaserin to rats maintained on a high fat diet produced dose-dependent reductions in food intake and body weight gain that were maintained during the 4-week study. Upon discontinuation, body weight returned to control levels. These data demonstrate lorcaserin to be a potent, selective, and efficacious agonist of the 5-HT 2C receptor, with potential for the treatment of obesity.Serotonin mediates its physiological effects through at least 14 different receptors. The serotonin 5-HT 2 receptor subfamily contains three distinct receptor subtypes, 5-HT 2A , 5-HT 2B , and 5-HT 2C , all of which share considerable sequence homology (Ͼ80% in transmembrane spanning regions) and activate common signaling pathways, including G q ␣-mediated stimulation of phospholipase-C␤, elevation of intracellular inositol phosphates, and elevation of intracellular calcium (Roth et al., 1998). Human 5-HT 2C receptors are predominately expressed in the CNS, and they are highly enriched in choroid plexus, prefrontal cortex, hippocampus, basal ganglia, and other brain regions associated with the control of mood, cognition, and appetite (Roth et al., 1998). Thus, 5-HT 2C receptors have been proposed as a therapeutic target for the treatment of CNS disorders, including epilepsy, obsessive compulsive disorder, Parkinson's disease, schizophrenia, depression and anxiety, sleep disorders, and drug abuse (Tecott et al

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In recent studies to clone and characterize genes coding for the corticotropin-releasing factor-binding protein (CRF-BP), analysis of the tissue distribution of the CRF-BP gene indicated a high level of expression in the rat brain. We have now characterized by immunohistochemical and hybridization histochemical means the cellular localization of CRF-BP protein and mRNA expression, respectively. Results from both approaches converged to indicate that CRF-BP is expressed predominantly in the cerebral cortex, including all major archi-, paleo-, and neocortical fields. Other prominent sites of mRNA and protein expression include subcortical limbic system structures (amygdala, bed nucleus of the stria terminalis), sensory relays associated with the auditory, olfactory, vestibular, and trigeminal systems, several raphe nuclei, and a number of cell groups in the brainstem reticular core. Expression in the hypothalamus appears largely limited to the ventral premammillary and dorsomedial nuclei; only isolated CRF-BP-stained cells are apparent in neurosecretory cell groups. Dual immunstaining for CRF and CRF-BP revealed a partial colocalization in some of these regions. In addition, prominent CRF-BP-stained terminal fields have been identified in association with CRF-expressing cell groups in circumscribed hypothalamic and limbic structures. In the anterior pituitary, CRF-BP mRNA and immunoreactivity were colocalized with corticotropin-immunoreactivity in a majority of corticotropes. Thus, CRF-BP could serve to modify the actions of CRF by intra-and intercellular mechanisms, in CRF-related pathways in the central nervous system and pituitary.