Endogenous and synthetic agonists of GPR119 differ in signalling pathways and their effects on insulin secretion in MIN6c4 insulinoma cells

GPCRs involved in metabolic diseases: pharmacotherapeutic development updates

G protein-coupled receptors (GPCRs) are expressed in a variety of cell types and tissues, and activation of GPCRs is involved in enormous metabolic pathways, including nutrient synthesis, transportation, storage or insulin sensitivity, etc. This review intends to summarize the regulation of metabolic homeostasis and mechanisms by a series of GPCRs, such as GPR91, GPR55, GPR119, GPR109a, GPR142, GPR40, GPR41, GPR43 and GPR120. With deep understanding of GPCR's structure and signaling pathways, it is attempting to uncover the role of GPCRs in major metabolic diseases, including metabolic syndrome, diabetes, dyslipidemia and nonalcoholic steatohepatitis, for which the global prevalence has risen during last two decades. An extensive list of agonists and antagonists with their chemical structures in a nature of small molecular compounds for above-mentioned GPCRs is provided as pharmacologic candidates, and their preliminary data of preclinical studies are discussed. Moreover, their beneficial effects in correcting abnormalities of metabolic syndrome, diabetes and dyslipidemia are summarized when clinical trials have been undertaken. Thus, accumulating data suggest that these agonists or antagonists might become as new pharmacotherapeutic candidates for the treatment of metabolic diseases.

The Role of G Protein-Coupled Receptors and Receptor Kinases in Pancreatic β-Cell Function and Diabetes

Type 2 diabetes (T2D) mellitus has emerged as a major global health concern that has accelerated in recent years due to poor diet and lifestyle. Afflicted individuals have high blood glucose levels that stem from the inability of the pancreas to make enough insulin to meet demand. Although medication can help to maintain normal blood glucose levels in individuals with chronic disease, many of these medicines are outdated, have severe side effects, and often become less efficacious over time, necessitating the need for insulin therapy. G protein-coupled receptors (GPCRs) regulate many physiologic processes, including blood glucose levels. In pancreatic β cells, GPCRs regulate β-cell growth, apoptosis, and insulin secretion, which are all critical in maintaining sufficient β-cell mass and insulin output to ensure euglycemia. In recent years, new insights into the signaling of incretin receptors and other GPCRs have underscored the potential of these receptors as desirable targets in the treatment of diabetes. The signaling of these receptors is modulated by GPCR kinases (GRKs) that phosphorylate agonist-activated GPCRs, marking the receptor for arrestin binding and internalization. Interestingly, genome-wide association studies using diabetic patient cohorts link the GRKs and arrestins with T2D. Moreover, recent reports show that GRKs and arrestins expressed in the β cell serve a critical role in the regulation of β-cell function, including β-cell growth and insulin secretion in both GPCR-dependent and -independent pathways. In this review, we describe recent insights into GPCR signaling and the importance of GRK function in modulating β-cell physiology. SIGNIFICANCE STATEMENT: Pancreatic β cells contain a diverse array of G protein-coupled receptors (GPCRs) that have been shown to improve β-cell function and survival, yet only a handful have been successfully targeted in the treatment of diabetes. This review discusses recent advances in our understanding of β-cell GPCR pharmacology and regulation by GPCR kinases while also highlighting the necessity of investigating islet-enriched GPCRs that have largely been unexplored to unveil novel treatment strategies.

Lysophosphatidylcholines Enriched with cis and trans Palmitoleic Acid Regulate Insulin Secretion via GPR119 Receptor

Among lipids, lysophosphatidylcholines (LPCs) with various fatty acyl chains have been identified as potential agonists of G protein-coupled receptors (GPCRs). Recently, targeting GPCRs has been switched to diabetes and obesity. Concomitantly, our last findings indicate the insulin secretagogue properties of cis and trans palmitoleic acid (16:1, n-7) resulting from GPCR activation, however, associated with different signaling pathways. We here report the synthesis of LPCs bearing two geometrical isomers of palmitoleic acids and investigation of their impact on human pancreatic β cells viability, insulin secretion, and activation of four GPCRs previously demonstrated to be targeted by free fatty acids and LPCs. Moreover, molecular modeling was exploited to investigate the probable binding sites of tested ligands and calculate their affinity toward GPR40, GPR55, GPR119, and GPR120 receptors.

Identifying target ion channel-related genes to construct a diagnosis model for insulinoma

Background: Insulinoma is the most common functional pancreatic neuroendocrine tumor (PNET) with abnormal insulin hypersecretion. The etiopathogenesis of insulinoma remains indefinable. Based on multiple bioinformatics methods and machine learning algorithms, this study proposed exploring the molecular mechanism from ion channel-related genes to establish a genetic diagnosis model for insulinoma. Methods: The mRNA expression profile dataset of GSE73338 was applied to the analysis, which contains 17 insulinoma samples, 63 nonfunctional PNET (NFPNET) samples, and four normal islet samples. Differently expressed ion channel-related genes (DEICRGs) enrichment analyses were performed. We utilized the protein-protein interaction (PPI) analysis and machine learning of LASSO and support vector machine-recursive feature elimination (SVM-RFE) to identify the target genes. Based on these target genes, a nomogram diagnostic model was constructed and verified by a receiver operating characteristic (ROC) curve. Moreover, immune infiltration analysis, single-gene gene set enrichment analysis (GSEA), and gene set variation analysis (GSVA) were executed. Finally, a drug-gene interaction network was constructed. Results: We identified 29 DEICRGs, and enrichment analyses indicated they were primarily enriched in ion transport, cellular ion homeostasis, pancreatic secretion, and lysosome. Moreover, the PPI network and machine learning recognized three target genes (MCOLN1, ATP6V0E1, and ATP4A). Based on these target genes, we constructed an efficiently predictable diagnosis model for identifying insulinomas with a nomogram and validated it with the ROC curve (AUC = 0.801, 95% CI 0.674-0.898). Then, single-gene GSEA analysis revealed that these target genes had a significantly positive correlation with insulin secretion and lysosome. In contrast, the TGF-beta signaling pathway was negatively associated with them. Furthermore, statistically significant discrepancies in immune infiltration were revealed. Conclusion: We identified three ion channel-related genes and constructed an efficiently predictable diagnosis model to offer a novel approach for diagnosing insulinoma.

DA-1241, a Novel GPR119 Agonist, Improves Hyperglycaemia by Inhibiting Hepatic Gluconeogenesis and Enhancing Insulin Secretion in Diabetic Mice

BACKGROUND

We investigated the antidiabetic effects of DA-1241, a novel G protein-coupled receptor (GPR) 119 agonist, in vitro and in vivo.

METHODS

DA-1241 was administrated to high-fat diet (HFD)-fed C57BL/6J mice for 12 weeks after hyperglycaemia developed. Oral/intraperitoneal glucose tolerance test and insulin tolerance test were performed. Serum insulin and glucagon-like peptide-1 (GLP-1) levels were measured during oral glucose tolerance test. Insulinoma cell line (INS-1E) cells and mouse islets were used to find whether DA-1241 directly stimulate insulin secretion in beta cell. HepG2 cells were used to evaluate the gluconeogenesis and autophagic process. Autophagic flux was evaluated by transfecting microtubule-associated protein 1 light chain 3-fused to green fluorescent protein and monomeric red fluorescent (mRFP-GFP-LC3) expression vector to HepG2 cells.

RESULTS

Although DA-1241 treatment did not affect body weight gain and amount of food intake, fasting blood glucose level decreased along with increase in GLP-1 level. DA-1241 improved only oral glucose tolerance test and showed no effect in intraperitoneal glucose tolerance test. No significant effect was observed in insulin tolerance test. DA-1241 did not increase insulin secretion in INS-1E cell and mouse islets. DA-1241 reduced triglyceride content in the liver thereby improved fatty liver. Additionally, DA-1241 reduced gluconeogenic enzyme expression in HepG2 cells and mouse liver. DA-1241 reduced autophagic flow in HepG2 cells.

CONCLUSION

These findings suggested that DA-1241 augmented glucose-dependent insulin release via stimulation of GLP-1 secretion, and reduced hepatic gluconeogenesis, which might be associated with autophagic blockage, leading to improved glycaemic control.

GPR55 and GPR119 Receptors Contribute to the Processing of Neuropathic Pain in Rats

Orphan G-protein-coupled receptors (GPCR) comprise a large number of receptors which are widely distributed in the nervous system and represent an opportunity to identify new molecular targets in pain medicine. GPR55 and GPR119 are two orphan GPCR receptors whose physiological function is unclear. The aim was to explore the participation of spinal GPR55 and GPR119 in the processing of neuropathic pain in rats. Mechanical allodynia was evaluated using von Frey filaments. Protein localization and modulation were measured by immunohistochemistry and western blotting, respectively. Intrathecal administration of CID16020046 (selective GPR55 antagonist) or AS1269574 (selective GPR119 agonist) produced a dose-dependent antiallodynic effect, whereas O1062 (GPR55 agonist) and G-protein antagonist peptide dose-dependently prevented the antiallodynic effect of CID16020046 and AS1269574, respectively. Both GPR55 and GPR119 receptors were expressed in spinal cord, dorsal root ganglia and sciatic nerve, but only GPR119 was downregulated after 14 days of spinal nerve ligation. Data suggest that GPR55 and GPR119 participate in the processing of neuropathic pain and could be useful targets to manage neuropathic pain disorders.

Selective measurement of NAPE-PLD activity via a PLA1/2-resistant fluorogenic N-acyl-phosphatidylethanolamine analog

N-acyl-phosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD) is a zinc metallohydrolase enzyme that converts NAPEs to bioactive N-acyl-ethanolamides. Altered NAPE-PLD activity may contribute to pathogenesis of obesity, diabetes, atherosclerosis, and neurological diseases. Selective measurement of NAPE-PLD activity is challenging, however, because of alternative phospholipase pathways for NAPE hydrolysis. Previous methods to measure NAPE-PLD activity involved addition of exogenous NAPE followed by TLC or LC/MS/MS, which are time and resource intensive. Recently, NAPE-PLD activity in cells has been assayed using the fluorogenic NAPE analogs PED-A1 and PED6, but these substrates also detect the activity of serine hydrolase-type lipases PLA1 and PLA2. To create a fluorescence assay that selectively measured cellular NAPE-PLD activity, we synthesized an analog of PED-A1 (flame-NAPE) where the sn-1 ester bond was replaced with an N-methyl amide to create resistance to PLA1 hydrolysis. Recombinant NAPE-PLD produced fluorescence when incubated with either PED-A1 or flame-NAPE, whereas PLA1 only produced fluorescence when incubated with PED-A1. Furthermore, fluorescence in HepG2 cells using PED-A1 could be partially blocked by either biothionol (a selective NAPE-PLD inhibitor) or tetrahydrolipstatin (an inhibitor of a broad spectrum of serine hydrolase-type lipases). In contrast, fluorescence assayed in HepG2 cells using flame-NAPE could only be blocked by biothionol. In multiple cell types, the phospholipase activity detected using flame-NAPE was significantly more sensitive to biothionol inhibition than that detected using PED-A1. Thus, using flame-NAPE to measure phospholipase activity provides a rapid and selective method to measure NAPE-PLD activity in cells and tissues.

Targeting the GPR119/incretin axis: a promising new therapy for metabolic-associated fatty liver disease

In the past decade, G protein-coupled receptors have emerged as drug targets, and their physiological and pathological effects have been extensively studied. Among these receptors, GPR119 is expressed in multiple organs, including the liver. It can be activated by a variety of endogenous and exogenous ligands. After GPR119 is activated, the cell secretes a variety of incretins, including glucagon-like peptide-1 and glucagon-like peptide-2, which may attenuate the metabolic dysfunction associated with fatty liver disease, including improving glucose and lipid metabolism, inhibiting inflammation, reducing appetite, and regulating the intestinal microbial system. GPR119 has been a potential therapeutic target for diabetes mellitus type 2 for many years, but its role in metabolic dysfunction associated fatty liver disease deserves further attention. In this review, we discuss relevant research and current progress in the physiology and pharmacology of the GPR119/incretin axis and speculate on the potential therapeutic role of this axis in metabolic dysfunction associated with fatty liver disease, which provides guidance for transforming experimental research into clinical applications.

GPR119 agonists: Novel therapeutic agents for type 2 diabetes mellitus

Diabetes mellitus type 2 (T2D) is a group of genetically heterogeneous metabolic disorders whose frequency has gradually risen worldwide. Diabetes mellitus Type 2 (T2D) has started to achieve a pandemic level, and it is estimated that within the next decade, cases of diabetes might get double due to increase in aging population. Diabetes is rightly called the 'silent killer' because it has emerged to be one of the major causes, leading to renal failure, loss of vision; besides cardiac arrest in India. Thus, a clinical requirement for the oral drug molecules monitoring glucose homeostasis appears to be unmet. GPR119 agonist, a family of G-protein coupled receptors, usually noticed in β-cells of pancreatic as well as intestinal L cells, drew considerable interest for type 2 diabetes mellitus (T2D). GPR119 monitors physiological mechanisms that enhance homeostasis of glucose, such as glucose-like peptide-1, gastrointestinal incretin hormone levels, pancreatic beta cell-dependent insulin secretion and glucose-dependent insulinotropic peptide (GIP). In this manuscript, we have reviewed the work done in the last five years (2015-2020) which gives an approach to design, synthesize, evaluate and study the structural activity relationship of novel GPR119 agonist-based lead compounds. Our article would help the researchers and guide their endeavours in the direction of strategy and development of innovative, effective GPR119 agonist-based compounds for the management of diabetes mellitus type 2.

GPCRs get fatty: the role of G protein-coupled receptor signaling in the development and progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), characterized by the abnormal deposition of lipids within the liver not due to alcohol consumption, is a growing epidemic affecting over 30% of the United States population. Both simple fatty liver and its more severe counterpart, nonalcoholic steatohepatitis, represent one of the most common forms of liver disease. Recently, several G protein-coupled receptors have emerged as targets for therapeutic intervention for these disorders. These include those with known hepatic function as well as those involved in global metabolic regulation. In this review, we highlight these emerging therapeutic targets, focusing on several common themes including their activation by microbial metabolites, stimulatory effect on insulin and incretin secretion, and contribution to glucose tolerance. The overlap in ligands, localization, and downstream effects of activation indicate the interdependent nature of these receptors and highlight the importance of this signaling family in the development and prevention of NAFLD.

GPR119 and GPR55 as Receptors for Fatty Acid Ethanolamides, Oleoylethanolamide and Palmitoylethanolamide

Oleoylethanolamide and palmitoylethanolamide are members of the fatty acid ethanolamide family, also known as acylethanolamides. Their physiological effects, including glucose homeostasis, anti-inflammation, anti-anaphylactic, analgesia, and hypophagia, have been reported. They have affinity for different receptor proteins, including nuclear receptors such as PPARα, channels such as TRPV1, and membrane receptors such as GPR119 and GPR55. In the present review, the pathophysiological functions of fatty acid ethanolamides have been discussed from the perspective of receptor pharmacology and drug discovery.

Metabolic Functions of G Protein-Coupled Receptors and β-Arrestin-Mediated Signaling Pathways in the Pathophysiology of Type 2 Diabetes and Obesity

Seven transmembrane receptors (7TMRs), often termed G protein-coupled receptors (GPCRs), are the most common target of therapeutic drugs used today. Many studies suggest that distinct members of the GPCR superfamily represent potential targets for the treatment of various metabolic disorders including obesity and type 2 diabetes (T2D). GPCRs typically activate different classes of heterotrimeric G proteins, which can be subgrouped into four major functional types: G_αs, G_αi, G_αq/11, and G_12/13, in response to agonist binding. Accumulating evidence suggests that GPCRs can also initiate β-arrestin-dependent, G protein-independent signaling. Thus, the physiological outcome of activating a certain GPCR in a particular tissue may also be modulated by β-arrestin-dependent, but G protein-independent signaling pathways. In this review, we will focus on the role of G protein- and β-arrestin-dependent signaling pathways in the development of obesity and T2D-related metabolic disorders.

Lysophosphatidylcholine Containing Anisic Acid Is Able to Stimulate Insulin Secretion Targeting G Protein Coupled Receptors

Diabetes mellitus is a worldwide health problem with high rates of mortality and morbidity. Management of diabetes mellitus by dietary components is achievable especially at the initial stage of the disease. Several studies confirmed the antidiabetic activities of simple phenolic acids and lysophosphatidylcholine (LPC). The main goal of this study was to identify new potential insulin secretion modulators obtained by combining the structures of two natural compounds, namely O-methyl derivatives of phenolic acids and phospholipids. LPC and phosphatidylcholine bearing methoxylated aromatic carboxylic acids were tested as potential agents able to improve glucose-stimulated insulin secretion (GSIS) and intracellular calcium mobilization in MIN6 β pancreatic cell line. Our results show that LPC with covalently bonded molecule of p-anisic acid at the sn-1 position was able to induce GSIS and intracellular calcium flux. Notably, 1-anisoyl-2-hydroxy-sn-glycero-3-phosphocholine did not affect the viability of MIN6 cells, suggesting its potential safe use. Furthermore, we have shown that three G protein coupled receptors, namely GPR40, GPR55, and GPR119, are targeted by this LPC derivative.

Identification of Novel, Structurally Diverse, Small Molecule Modulators of GPR119

GPR119 drug discovery efforts in the pharmaceutical industry for the treatment of type 2 diabetes mellitus (T2DM) and obesity, were initiated based on its restricted distribution in pancreas and GI tract, and its possible role in glucose homeostasis. While a number of lead series have emerged, the pharmacological endpoints they provide have not been clear. In particular, many lead series have demonstrated loss of efficacy and significant toxic side effects. Thus, we sought to identify novel, potent, positive modulators of GPR119. In this study, we have successfully developed and optimized a high-throughput screening strategy to identify GPR119 modulators using a live cell assay format that utilizes a cyclic nucleotide-gated channel as a biosensor for cAMP production. Our high-throughput screening (HTS) approach is unique to that of previous HTS approaches targeting this receptor, as changes in cAMP were measured both in the presence and absence of an EC₁₀ of the endogenous ligand, oleoylethanolamide, enabling detection of both agonists and potential allosteric modulators in a single assay. From these efforts, we have identified positive modulators of GPR119 with similar as well as unique scaffolds compared to existing compounds and similar as well as unique signaling properties. Our compounds will not only serve as novel molecular probes to better understand GPR119 pleiotropic signaling and the underlying physiological consequences of receptor activation, but are also well-suited for translation as potential therapeutic agents.

Targeting GPCRs Activated by Fatty Acid-Derived Lipids in Type 2 Diabetes

G protein-coupled receptors (GPCRs) are the most intensively studied drug targets, because of their diversity, cell-specific expression, and druggable sites accessible at the cell surface. Preclinical and clinical studies suggest that targeting GPCRs activated by fatty acid-derived lipids may have potential to improve glucose homeostasis and reduce complications in patients with type 2 diabetes (T2D). Despite the discontinued development of fasiglifam (TAK-875), the first FFA1 agonist to reach late-stage clinical trials, lipid-sensing receptors remain a viable target, albeit with a need for further characterization of their binding mode, intracellular signaling, and toxicity. Herein, we analyze general discovery trends, various signaling pathways, as well as possible challenges following activation of GPCRs that have been validated clinically to control blood glucose levels.

Endocannabinoid System in Hepatic Glucose Metabolism, Fatty Liver Disease, and Cirrhosis

There is growing evidence that glucose metabolism in the liver is in part under the control of the endocannabinoid system (ECS) which is also supported by its presence in this organ. The ECS consists of its cannabinoid receptors (CBRs) and enzymes that are responsible for endocannabinoid production and metabolism. ECS is known to be differentially influenced by the hepatic glucose metabolism and insulin resistance, e.g., cannabinoid receptor type 1(CB₁) antagonist can improve the glucose tolerance and insulin resistance. Interestingly, our own study shows that expression patterns of CBRs are influenced by the light/dark cycle, which is of significant physiological and clinical interest. The ECS system is highly upregulated during chronic liver disease and a growing number of studies suggest a mechanistic and therapeutic impact of ECS on the development of liver fibrosis, especially putting its receptors into focus. An opposing effect of the CBRs was exerted via the CB₁ or CB₂ receptor stimulation. An activation of CB₁ promoted fibrogenesis, while CB₂ activation improved antifibrogenic responses. However, underlying mechanisms are not yet clear. In the context of liver diseases, the ECS is considered as a possible mediator, which seems to be involved in the synthesis of fibrotic tissue, increase of intrahepatic vascular resistance and subsequently development of portal hypertension. Portal hypertension is the main event that leads to complications of the disease. The main complication is the development of variceal bleeding and ascites, which have prognostic relevance for the patients. The present review summarizes the current understanding and impact of the ECS on glucose metabolism in the liver, in association with the development of liver cirrhosis and hemodynamics in cirrhosis and its complication, to give perspectives for development of new therapeutic strategies.

Discovery and biological evaluation of novel G protein-coupled receptor 119 agonists for type 2 diabetes

G protein-coupled receptor 119 (GPR119) is a member of the GPCR family promising to be the target for type 2 diabetes mellitus (T2DM) treatment. In this work, 30 novel compounds were designed, synthesized, and evaluated by in vitro cAMP activation assay, where compounds II-14 and II-18 showed the best potency with EC₅₀ values of 69 and 99 nM, respectively. In the oral glucose tolerance test, compound II-18 showed even more efficacious activity in lowering blood excursions than MBX-2982 at a fixed dose of 30 mg/kg. Here, we report that compound II-18 with its excellent agonistic activity and its orally effective activity in decreasing blood glucose deviations may serve as a potent GPR119 agonist for the treatment of T2DM.

Lysophosphatidylcholine and its phosphorothioate analogues potentiate insulin secretion via GPR40 (FFAR1), GPR55 and GPR119 receptors in a different manner

Lysophosphatidylcholine (LPC) is an endogenous ligand for GPR119 receptor, mediating glucose-stimulated insulin secretion (GSIS). We demonstrate that LPC facilitates GSIS in MIN6 pancreatic β-cell line and murine islets of Langerhans by recognizing not only GPR119 but also GPR40 (free fatty acid receptor 1) and GPR55 activated by lysophosphatidylinositol. Natural LPCs are unstable when administered in vivo limiting their therapeutic value and therefore, we present phosphorothioate LPC analogues with increased stability. All the modified LPCs under study (12:0, 14:0, 16:0, 18:0, and 18:1) significantly enhanced GSIS. The 16:0 sulfur analogue was the most potent, evoking 2-fold accentuated GSIS compared to the native counterpart. Interestingly, LPC analogues evoked GPR40-, GPR55-and GPR119-dependent [Ca²⁺]_i signaling, but did not stimulate cAMP accumulation as in the case of unmodified molecules. Thus, introduction of a phosphorothioate function not only increases LPC stability but also modulates affinity towards receptor targets and evokes different signaling pathways.

Oleoyl-lysophosphatidylinositol enhances glucagon-like peptide-1 secretion from enteroendocrine L-cells through GPR119

The gastrointestinal tract is increasingly viewed as critical in controlling glucose metabolism, because of its role in secreting multiple glucoregulatory hormones, such as glucagon like peptide-1 (GLP-1). Here we investigate the molecular pathways behind the GLP-1- and insulin-secreting capabilities of a novel GPR119 agonist, Oleoyl-lysophosphatidylinositol (Oleoyl-LPI). Oleoyl-LPI is the only LPI species able to potently stimulate the release of GLP-1 in vitro, from murine and human L-cells, and ex-vivo from murine colonic primary cell preparations. Here we show that Oleoyl-LPI mediates GLP-1 secretion through GPR119 as this activity is ablated in cells lacking GPR119 and in colonic primary cell preparation from GPR119^-/- mice. Similarly, Oleoyl-LPI-mediated insulin secretion is impaired in islets isolated from GPR119^-/- mice. On the other hand, GLP-1 secretion is not impaired in cells lacking GPR55 in vitro or in colonic primary cell preparation from GPR55^-/- mice. We therefore conclude that GPR119 is the Oleoyl-LPI receptor, upstream of ERK1/2 and cAMP/PKA/CREB pathways, where primarily ERK1/2 is required for GLP-1 secretion, while CREB activation appears dispensable.

Structure and biological activity of endogenous and synthetic agonists of GPR119

A G-protein-coupled receptor, GPR119, is a promising pharmacological target for a new class of hypoglycaemic drugs with an original mechanism of action, namely, increase in the glucose-dependent incretin and insulin secretion. In 2005, the first ligands were found and in the subsequent years, a large number of GPR119 agonists were synthesized in laboratories in various countries; the safest and most promising agonists have entered phase I and II clinical trials as agents for the treatment of type 2 diabetes mellitus and obesity. The review describes the major endogenous GPR119 agonists and the main trends in the design and modification of synthetic structures for increasing the hypoglycaemic activity. The data on synthetic agonists are arranged according to the type of the central core of the molecules.

The bibliography includes 104 references.

Therapeutic application of GPR119 ligands in metabolic disorders

GPR119 belongs to the G protein-coupled receptor family and exhibits dual modes of action upon ligand-dependent activation: pancreatic secretion of insulin in a glucose-dependent manner and intestinal secretion of incretins. Hence, GPR119 has emerged as a promising target for treating type 2 diabetes mellitus without causing hypoglycaemia. However, despite continuous efforts by many major pharmaceutical companies, no synthetic GPR119 ligand has been approved as a new class of anti-diabetic agents thus far, nor has any passed beyond phase II clinical studies. Herein, we summarize recent advances in research concerning the physiological/pharmacological effects of GPR119 and its synthetic ligands on the regulation of energy metabolism, and we speculate on future applications of GPR119 ligands for the treatment of metabolic diseases, focusing on non-alcoholic fatty liver disease.

Chemistry and Hypoglycemic Activity of GPR119 Agonist ZB-16

This article is to highlight the chemical properties and primary pharmacology of novel GPR119 agonist ZB-16 and its analogs, which were rejected during the screening. Experiments were performed in vitro (specific activity, metabolism and cell toxicity) and in vivo (hypoglycemic activity and pharmacokinetics). ZB-16 exhibits nanomolar activity (EC50 = 7.3-9.7 nM) on target receptor GPR119 in vitro associated with hypoglycemic activity in vivo. In animals with streptozotocin-nicotinamide induced type 2 diabetes mellitus (STZ-NA T2D) daily oral dose of ZB-16 (1 mg/kg) or sitagliptin (10 mg/kg) for 28 days resulted in the reduction of blood glucose levels. The effects of ZB-16 were comparable to the hypoglycemic action of sitagliptin. ZB-16 demonstrated relatively low plasma exposition, high distribution volume, mild clearance and a prolonged half-life (more than 12 h). The present study demonstrates that the targeted search for selective GPR119 receptor agonists is a well-founded approach for developing novel drugs for the therapy of T2D. Based on the combination of high in vitro activity (compared to competitor standards), a useful ADME profile, distinct hypoglycemic activity which is comparable to the efficacy of sitagliptin in rats with experimental T2D, and the acceptable pharmacokinetic profile, we recommend the ZB-16 compound for further research.

Cannabinoids Modulate Neuronal Activity and Cancer by CB1 and CB2 Receptor-Independent Mechanisms

Cannabinoids include the active constituents of Cannabis or are molecules that mimic the structure and/or function of these Cannabis-derived molecules. Cannabinoids produce many of their cellular and organ system effects by interacting with the well-characterized CB1 and CB2 receptors. However, it has become clear that not all effects of cannabinoid drugs are attributable to their interaction with CB1 and CB2 receptors. Evidence now demonstrates that cannabinoid agents produce effects by modulating activity of the entire array of cellular macromolecules targeted by other drug classes, including: other receptor types; ion channels; transporters; enzymes, and protein- and non-protein cellular structures. This review summarizes evidence for these interactions in the CNS and in cancer, and is organized according to the cellular targets involved. The CNS represents a well-studied area and cancer is emerging in terms of understanding mechanisms by which cannabinoids modulate their activity. Considering the CNS and cancer together allow identification of non-cannabinoid receptor targets that are shared and divergent in both systems. This comparative approach allows the identified targets to be compared and contrasted, suggesting potential new areas of investigation. It also provides insight into the diverse sources of efficacy employed by this interesting class of drugs. Obtaining a comprehensive understanding of the diverse mechanisms of cannabinoid action may lead to the design and development of therapeutic agents with greater efficacy and specificity for their cellular targets.

A GPR119 Signaling System in the Murine Eye Regulates Intraocular Pressure in a Sex-Dependent Manner

Purpose

GPR119 is a G protein–coupled receptor that may be the endogenous target for 2-oleoylglycerol (2-OG), a lipid related to the endocannabinoid family of neuromodulators. Interest in GPR119 has centered on its role in regulating insulin secretion; however, the role of GPR119 has not been examined in the eye. The purpose of this study was to explore a potential GPR119-based signaling system in the murine eye.

Methods

We used a combination of RT-PCR, immunohistochemistry, lipid measurement, and IOP measurement in a normotensive mouse model, with GPR119 knockout mice as controls.

Results

We detected GPR119 mRNA and protein in the anterior eye of the mouse and cow, with GPR119 mRNA levels elevated in female relative to male mice. GPR119 protein expression is most prominent in structures near the angle, including trabecular meshwork, as well as iris and corneal epithelium. We detected 2-OG in the anterior eye and detected alterations in lipid levels in GPR119 knockout versus wild type and also by sex. Last, we found that 2-OG preferentially reduces IOP in female mice in a normotensive model.

Conclusions

In summary, we offer evidence for a GPR119-based signaling system in the mammalian eye, with receptors, ligands, and function in the form of a reduction in IOP. Notably this reduction in pressure is restricted to female mice.

Update on the treatment of type 2 diabetes mellitus

To achieve good metabolic control in diabetes and keep long term, a combination of changes in lifestyle and pharmacological treatment is necessary. Achieving near-normal glycated hemoglobin significantly, decreases risk of macrovascular and microvascular complications. At present there are different treatments, both oral and injectable, available for the treatment of type 2 diabetes mellitus (T2DM). Treatment algorithms designed to reduce the development or progression of the complications of diabetes emphasizes the need for good glycaemic control. The aim of this review is to perform an update on the benefits and limitations of different drugs, both current and future, for the treatment of T2DM. Initial intervention should focus on lifestyle changes. Moreover, changes in lifestyle have proven to be beneficial, but for many patients is a complication keep long term. Physicians should be familiar with the different types of existing drugs for the treatment of diabetes and select the most effective, safe and better tolerated by patients. Metformin remains the first choice of treatment for most patients. Other alternative or second-line treatment options should be individualized depending on the characteristics of each patient. This article reviews the treatments available for patients with T2DM, with an emphasis on agents introduced within the last decade.

G protein-coupled receptors: signalling and regulation by lipid agonists for improved glucose homoeostasis

G protein-coupled receptors (GPCRs) play a pivotal role in cell signalling, controlling many processes such as immunity, growth, cellular differentiation, neurological pathways and hormone secretions. Fatty acid agonists are increasingly recognised as having a key role in the regulation of glucose homoeostasis via stimulation of islet and gastrointestinal GPCRs. Downstream cell signalling results in modulation of the biosynthesis, secretion, proliferation and anti-apoptotic pathways of islet and enteroendocrine cells. GPR40 and GPR120 are activated by long-chain fatty acids (>C12) with both receptors coupling to the Gαq subunit that activates the Ca(2+)-dependent pathway. GPR41 and GPR43 are stimulated by short-chain fatty acids (C2-C5), and activation results in binding to Gαi that inhibits the adenylyl cyclase pathway attenuating cAMP production. In addition, GPR43 also couples to the Gαq subunit augmenting intracellular Ca(2+) and activating phospholipase C. GPR55 is specific for cannabinoid endogenous agonists (endocannabinoids) and non-cannabinoid fatty acids, which couples to Gα12/13 and Gαq proteins, leading to enhancing intracellular Ca(2+), extracellular signal-regulated kinase 1/2 (ERK) phosphorylation and Rho kinase. GPR119 is activated by fatty acid ethanolamides and binds to Gαs utilising the adenylate cyclase pathway, which is dependent upon protein kinase A. Current research indicates that GPCR therapies may be approved for clinical use in the near future. This review focuses on the recent advances in preclinical diabetes research in the signalling and regulation of GPCRs on islet and enteroendocrine cells involved in glucose homoeostasis.

Lipid derivatives activate GPR119 and trigger GLP-1 secretion in primary murine L-cells

AIMS/HYPOTHESIS

Glucagon-like peptide-1 (GLP-1) is an incretin hormone derived from proglucagon, which is released from intestinal L-cells and increases insulin secretion in a glucose dependent manner. GPR119 is a lipid derivative receptor present in L-cells, believed to play a role in the detection of dietary fat. This study aimed to characterize the responses of primary murine L-cells to GPR119 agonism and assess the importance of GPR119 for the detection of ingested lipid.

METHODS

GLP-1 secretion was measured from murine primary cell cultures stimulated with a panel of GPR119 ligands. Plasma GLP-1 levels were measured in mice lacking GPR119 in proglucagon-expressing cells and controls after lipid gavage. Intracellular cAMP responses to GPR119 agonists were measured in single primary L-cells using transgenic mice expressing a cAMP FRET sensor driven by the proglucagon promoter.

RESULTS

L-cell specific knockout of GPR119 dramatically decreased plasma GLP-1 levels after a lipid gavage. GPR119 ligands triggered GLP-1 secretion in a GPR119 dependent manner in primary epithelial cultures from the colon, but were less effective in the upper small intestine. GPR119 agonists elevated cAMP in ∼70% of colonic L-cells and 50% of small intestinal L-cells.

CONCLUSIONS/INTERPRETATION

GPR119 ligands strongly enhanced GLP-1 release from colonic cultures, reflecting the high proportion of colonic L-cells that exhibited cAMP responses to GPR119 agonists. Less GPR119-dependence could be demonstrated in the upper small intestine. In vivo, GPR119 in L-cells plays a key role in oral lipid-triggered GLP-1 secretion.

Simvastatin Impairs Insulin Secretion by Multiple Mechanisms in MIN6 Cells

Statins are widely used in the treatment of hypercholesterolemia and are efficient in the prevention of cardiovascular disease. Molecular mechanisms explaining statin-induced impairment in insulin secretion remain largely unknown. In the current study, we show that simvastatin decreased glucose-stimulated insulin secretion in mouse pancreatic MIN6 β-cells by 59% and 79% (p<0.01) at glucose concentration of 5.5 mmol/l and 16.7 mmol/l, respectively, compared to control, whereas pravastatin did not impair insulin secretion. Simvastatin induced decrease in insulin secretion occurred through multiple targets. In addition to its established effects on ATP-sensitive potassium channels (p = 0.004) and voltage-gated calcium channels (p = 0.004), simvastatin suppressed insulin secretion stimulated by muscarinic M3 or GPR40 receptor agonists (Tak875 by 33%, p = 0.002; GW9508 by 77%, p = 0.01) at glucose level of 5.5 mmol/l, and inhibited calcium release from the endoplasmic reticulum. Impaired insulin secretion caused by simvastatin treatment were efficiently restored by GPR119 or GLP-1 receptor stimulation and by direct activation of cAMP-dependent signaling pathways with forskolin. The effects of simvastatin treatment on insulin secretion were not affected by the presence of hyperglycemia. Our observation of the opposite effects of simvastatin and pravastatin on glucose-stimulated insulin secretion is in agreement with previous reports showing that simvastatin, but not pravastatin, was associated with increased risk of incident diabetes.

Functional metagenomic discovery of bacterial effectors in the human microbiome and isolation of commendamide, a GPCR G2A/132 agonist

The trillions of bacteria that make up the human microbiome are believed to encode functions that are important to human health; however, little is known about the specific effectors that commensal bacteria use to interact with the human host. Functional metagenomics provides a systematic means of surveying commensal DNA for genes that encode effector functions. Here, we examine 3,000 Mb of metagenomic DNA cloned from three phenotypically distinct patients for effectors that activate NF-κB, a transcription factor known to play a central role in mediating responses to environmental stimuli. This screen led to the identification of 26 unique commensal bacteria effector genes (Cbegs) that are predicted to encode proteins with diverse catabolic, anabolic, and ligand-binding functions and most frequently interact with either glycans or lipids. Detailed analysis of one effector gene family (Cbeg12) recovered from all three patient libraries found that it encodes for the production of N-acyl-3-hydroxypalmitoyl-glycine (commendamide). This metabolite was also found in culture broth from the commensal bacterium Bacteroides vulgatus, which harbors a gene highly similar to Cbeg12. Commendamide resembles long-chain N-acyl-amides that function as mammalian signaling molecules through activation of G-protein-coupled receptors (GPCRs), which led us to the observation that commendamide activates the GPCR G2A/GPR132. G2A has been implicated in disease models of autoimmunity and atherosclerosis. This study shows the utility of functional metagenomics for identifying potential mechanisms used by commensal bacteria for host interactions and outlines a functional metagenomics-based pipeline for the systematic identification of diverse commensal bacteria effectors that impact host cellular functions.

Structural basis for constitutive activity and agonist-induced activation of the enteroendocrine fat sensor GPR119

BACKGROUND AND PURPOSE

GPR119 is a Gαs-coupled 7TM receptor activated by endogenous lipids such as oleoylethanolamide (OEA) and by the dietary triglyceride metabolite 2-monoacylglycerol. GPR119 stimulates enteroendocrine hormone and insulin secretion. But despite massive drug discovery efforts in the field, very little is known about the basic molecular pharmacology of GPR119.

EXPERIMENTAL APPROACH

GPR119 receptor signalling was studied in transfected cells. Mutational mapping (30 mutations in 23 positions) was performed on residues required for ligand-independent and agonist-induced GPR119 activation (AR231453 and OEA). Novel Rosetta-based receptor modelling was applied, using a composite template approach with segments from different X-ray structures and fully flexible ligand docking.

KEY RESULTS

The increased signalling induced by increasing the cell surface expression of GPR119 in the absence of agonist and the inhibitory effect of two synthetic inverse agonists demonstrated that GRP119 signals with a high degree of constitutive activity through the Gαs pathway. The mutational maps for AR231453 and OEA were very similar and, surprisingly, also similar to the mutational map for residues affecting the constitutive signalling - albeit with key differences. Surprisingly, almost all residues in extracellular loop-2b were important for the constitutive activity. The molecular modelling and docking demonstrated that AR231453 binds in a 'vertical' pocket in between mutational hits reaching from the centre of the receptor out to extracellular loop-2b.

CONCLUSIONS AND IMPLICATIONS

The high constitutive activity of GPR119 should be taken into account in future drug discovery efforts, which can now be guided by the detailed knowledge of the physiochemical properties of the extended ligand-binding pocket.

Endogenous Ligand for GPR120, Docosahexaenoic Acid, Exerts Benign Metabolic Effects on the Skeletal Muscles via AMP-activated Protein Kinase Pathway

Docosahexaenoic acid (DHA) is an endogenous ligand of G protein-coupled receptor 120 (GPR120). However, the mechanisms underlying DHA action are poorly understood. In this study, DHA stimulated glucose uptake in the skeletal muscles in an AMP-activated protein kinase (AMPK)-dependent manner. GPR120-mediated increase in intracellular Ca(2+) was critical for DHA-mediated AMPK phosphorylation and glucose uptake. In addition, DHA stimulated GLUT4 translocation AMPK-dependently. Inhibition of AMPK and Ca(2+)/calmodulin-dependent protein kinase kinase blocked DHA-induced glucose uptake. DHA and GW9508, a GPR120 agonist, increased GPR120 expression. DHA-mediated glucose uptake was not observed in GPR120 knockdown conditions. DHA increased AMPK phosphorylation, glucose uptake, and intracellular Ca(2+) concentration in primary cultured myoblasts. Taken together, these results indicated that the beneficial metabolic role of DHA was attributed to its ability to regulate glucose via the GPR120-mediated AMPK pathway in the skeletal muscles.

Modulation of Glucagon-like Peptide-1 (GLP-1) Potency by Endocannabinoid-like Lipids Represents a Novel Mode of Regulating GLP-1 Receptor Signaling

Glucagon-like peptide-1 (GLP-1) analogs are approved for treatment of type 2 diabetes and are in clinical trials for disorders including neurodegenerative diseases. GLP-1 receptor (GLP-1R) is expressed in many peripheral and neuronal tissues and is activated by circulating GLP-1. Other than food intake, little is known about factors regulating GLP-1 secretion. Given a normally basal circulating level of GLP-1, knowledge of mechanisms regulating GLP-1R signaling, which has diverse functions in extrapancreatic tissues, remains elusive. In this study, we found that the potency of GLP-1, not exendin 4, is specifically enhanced by the endocannabinoid-like lipids oleoylethanolamide (OEA) and 2-oleoylglycerol but not by stearoylethanolamide (SEA) or palmitoylethanolamide. 9.2 μM OEA enhances the potency of GLP-1 in stimulating cAMP production by 10-fold but does not affect its receptor binding affinity. OEA and 2-oleoylglycerol, but not SEA, bind to GLP-1 in a dose-dependent and saturable manner. OEA but not SEA promoted GLP-1(7-36) amide to trypsin inactivation in a dose-dependent and saturable manner. Susceptibility of GLP-1(7-36) amide to trypsin inactivation is increased 40-fold upon binding to OEA but not to SEA. Our findings indicate that OEA binds to GLP-1(7-36) amide and enhances the potency that may result from a conformational change of the peptide. In conclusion, modulating potency of GLP-1 by physiologically regulated endocannabinoid-like lipids allows GLP-1R signaling to be regulated spatiotemporally at a constant basal GLP-1 level.

Activation of GPR119 by fatty acid agonists augments insulin release from clonal β-cells and isolated pancreatic islets and improves glucose tolerance in mice

G-protein coupled receptor 119 (GPR119) is emerging as a potential target for the treatment of type 2 diabetes with beneficial effects on glucose homeostasis. This study assessed the insulin-secreting properties of various GPR119 agonists and the distribution of GPR119 in pancreatic islets. Endogenous ligands [oleoylethanolamide (OEA), palmitoylethanolamine (PEA)] and chemically synthetic analogues (AS-1269574, PSN-375963) were investigated in clonal BRIN-BD11 cells and mouse pancreatic islets. Secondary messenger assays such as intracellular Ca²⁺ and cAMP in response to agonists at normoglycaemic and hyperglycaemic conditions were assessed. Cytotoxicity was assessed by LDH release. AS-1269574 was the most potent and selective agonist tested in isolated islets, with an EC₅₀ value of 9.7×10⁻⁷ mol/l, enhancing insulin release maximally by 63.2%. Stimulation was also observed with GPR119 ligands; OEA (3.0×10⁻⁶ mol/l; 37.5%), PSN-375963 (2.4×10⁻⁶ mol/l; 28.7%) and PEA (1.2×10⁻⁶ mol/l; 22.2%). Results were corroborated by studies using BRIN-BD11 cells, which revealed augmentation of intracellular Ca²⁺ and cAMP. Both OEA and AS-1269574 enhanced insulin release and improved glucose tolerance in vivo in NIH Swiss mice. These results demonstrate the cellular localisation of GPR119 on islet cells (β and pancreatic polypeptide cells), its activation of the β-cell stimulus-secretion coupling pathway and glucose lowering effects in vivo.

Direct activation of the proposed anti-diabetic receptor, GPR119 in cardiomyoblasts decreases markers of muscle metabolic activity

GPR119 agonists are emerging rapidly as a pharmaceutical treatment of diabetes. Diabetes is a known risk factor for cardiovascular disease yet the cardiac-specific consequences of GPR119 activation are unknown. This study demonstrated that GPR119 agonism in cardiac myoblasts reduces metabolic activity in high and low concentrations of fatty acids, with high concentrations of palmitate largely attenuating the effects of the GPR119 agonist, PSN632408. The effects of GPR119 activation on gene and protein markers of metabolism were dependent on fatty acid exposure. Activating GPR119 did not affect cell hypertrophy of lipid accumulation regardless of lipid exposure. These results suggest that the pathways activated in response to GPR119 modulation in cardiac muscle cells differ between healthy and metabolically dysregulated states. However regardless of the pathway activated by GPR119, these effects may cause detrimental reductions to oxidative/metabolic capacity under both conditions. Thus further development of GPR119 agonists for treating metabolic diseases is warranted.

GPR55: from orphan to metabolic regulator?

GPR55 belongs to the class A family of G-protein coupled receptor (GPCRs) and its activity is regulated by a range of synthetic and endogenous cannabinoids, and by lipid-derived ligands. Cannabinoids are known to be important in controlling appetite and metabolic balance, and it is now emerging that GPR55 may have a role to play in energy homeostasis through the regulation of food intake, fuel storage in adipocytes, gut motility and insulin secretion. This review summarises our current knowledge of expression and function of GPR55 in tissues involved in metabolic regulation, the signalling cascades through which GPR55 is reported to act to exert its effects, and it comments on the difficulties in reaching firm conclusions when using GPR55 ligands of poor specificity. Understanding the role of GPR55 in energy homeostasis may provide a novel target for therapeutic intervention in obesity and type 2 diabetes mellitus.

Evaluation of the insulin releasing and antihyperglycaemic activities of GPR55 lipid agonists using clonal beta-cells, isolated pancreatic islets and mice

BACKGROUND AND PURPOSE

G-protein coupled receptor (GPR)55 is a novel lipid sensing receptor activated by both cannabinoid endogenous ligands (endocannabinoids) and other non-cannabinoid lipid transmitters. This study assessed the effects of various GPR55 agonists on glucose homeostasis.

EXPERIMENTAL APPROACH

Insulin secretion and changes in intracellular Ca(2) (+) and cAMP in response to glucose and a range of GPR55 agonists [endogenous ligands (OEA, PEA), chemically synthetic cannabidiol (CBD) analogues (Abn-CBD, 0-1602), an analogue of rimonabant (AM-251) and antagonist (CBD)] were investigated in clonal BRIN-BD11 cells and mouse pancreatic islets. Cytotoxicity was assessed by LDH release, cellular localization by double-staining immunohistochemistry and in vivo effects assessed in mice.

KEY RESULTS

The most potent and selective GPR55 agonist was the synthetic CBD analogue, Abn-CBD (pEC50 10.33), maximum stimulation of 67% at 10(-4)  mol·L(-1) (P < 0.001) in BRIN-BD11 cells. AM-251 (pEC50 7.0), OEA (pEC50 7.0), 0-1602 (pEC50 7.3) and PEA (pEC50 6.0) stimulated insulin secretion. Results were corroborated by islet studies, with no cytotoxic effects. Concentration-dependent insulin secretion by GPR55 agonists was glucose-sensitive and accompanied by elevations of [Ca(2) (+) ]i (P < 0.01-P < 0.001) and cAMP (P < 0.05-P < 0.01). GPR55 agonists exhibited insulinotropic and glucose lowering activity in vivo. GPR55 was expressed on BRIN-BD11 cells and confined to islet beta cells with no distribution on alpha cells.

CONCLUSION AND IMPLICATIONS

These results demonstrate GPR55 is distributed in pancreatic beta cells and is a strong activator of insulin secretion, with glucose-lowering effects in vivo. Development of agents agonizing the GPR55 receptor may have therapeutic potential in the treatment of type 2 diabetes.

G protein-coupled receptors in energy homeostasis

G-protein coupled receptors (GPCRs) compromise the largest membrane protein superfamily which play vital roles in physiological and pathophysiological processes including energy homeostasis. Moreover, they also represent the up-to-date most successful drug target. The gut hormone GPCRs, such as glucagon receptor and GLP-1 receptor, have been intensively studied for their roles in metabolism and respective drugs have developed for the treatment of metabolic diseases such as type 2 diabetes (T2D). Along with the advances of biomedical research, more GPCRs have been found to play important roles in the regulation of energy homeostasis from nutrient sensing, appetite control to glucose and fatty acid metabolism with various mechanisms. The investigation of their biological functions will not only improve our understanding of how our body keeps the balance of energy intake and expenditure, but also highlight the possible drug targets for the treatment of metabolic diseases. The present review summarizes GPCRs involved in the energy control with special emphasis on their pathophysiological roles in metabolic diseases and hopefully triggers more intensive and systematic investigations in the field so that a comprehensive network control of energy homeostasis will be revealed, and better drugs will be developed in the foreseeable future.

Discovery and characterization of novel small molecule agonists of G protein-coupled receptor 119

AIM

GPR119 is a G protein-coupled receptor (GPCR) that is highly expressed in pancreatic β-cells and intestinal L-cells and facilitates glucose-stimulated insulin secretion (GSIS). GPR119 may represent a novel target for the treatment of metabolic disorders. Here, we sought to identify novel small-molecule GPR119 agonists.

METHODS

A cell-based high-throughput screening assay was established using HEK293 cells stably expressing GPR119 and pCRE-luc reporter plasmid (HEK293/GPR119/pCRE-luc). A compound library composed of 1440 compounds was screened. Mouse β-cell line MIN-6 and isolated mouse islets were used to evaluate the effects of candidate compounds on GSIS in vitro.

RESULTS

Three compounds with novel structures (ZSY-04, -06, and -13) were found to activate GPR119-mediated signaling and to induce GPR119 desensitization. The EC50 values of ZSY-04, -06, and -13 in stimulating intracellular cAMP accumulation in HEK293/GPR119 cells were 2.758, 3.046, and 0.778 μmol/L, respectively. Furthermore, all three compounds displayed high selectivity for GPR119, and did not activate other 9 GPCRs tested. Moreover, all three compounds significantly increased GSIS in both MIN-6 mouse β-cells and isolated mouse islets at concentration of 10 μmol/L.

CONCLUSION

Three novel small-molecule GPR119 agonists (ZSY-04, -06, and -13) with high receptor selectivity and capacity to induce GSIS in vitro were discovered. These compounds are potential candidates to be structurally optimized into drugs for the treatment of type 2 diabetes.

Elevation of endogenous anandamide impairs LTP, learning, and memory through CB1 receptor signaling in mice

In rodents, many exogenous and endogenous cannabinoids, such as anandamide (AEA) and 2-arachidonyl glycerol (2-AG), have been shown to play an important role in certain hippocampal memory processes. However, the mechanisms by which endogenous AEA regulate this processes are not well understood. Here the effects of AEA on long-term potentiation (LTP), hippocampal-dependent learning and memory tasks, pERK1/2, pCaMKIV, and pCREB signaling events in both cannabinoid receptor type 1 (CB1R) wild-type (WT) and knockout (KO) mice were assessed following administration of URB597, an inhibitor of the fatty acid amide hydrolase (FAAH). Acute administration of URB597 enhanced AEA levels without affecting the levels of 2-AG or CB1R in the hippocampus and neocortex as compared to vehicle. In hippocampal slices, URB597 impaired LTP in CB1R WT but not in KO littermates. URB597 impaired object recognition, spontaneous alternation and spatial memory in the Y-maze test in CB1R WT mice but not in KO mice. Furthermore, URB597 enhanced ERK phosphorylation in WT without affecting total ERK levels in WT or KO mice. URB597 impaired CaMKIV and CREB phosphorylation in WT but not in KO mice. CB1R KO mice have a lower pCaMKIV/CaMKIV ratio and higher pCREB/CREB ratio as compared to WT littermates. Our results indicate that pharmacologically elevated AEA impair LTP, learning and memory and inhibit CaMKIV and CREB phosphorylation, via the activation of CB1Rs. Collectively, these findings also suggest that pharmacological elevation of AEA beyond normal concentrations is also detrimental for the underlying physiological responses.

A lincRNA-DYNLRB2-2/GPR119/GLP-1R/ABCA1-dependent signal transduction pathway is essential for the regulation of cholesterol homeostasis

Accumulated evidence shows that G protein-coupled receptor 119 (GPR119) plays a key role in glucose and lipid metabolism. Here, we explored the effect of GPR119 on cholesterol metabolism and inflammation in THP-1 macrophages and atherosclerotic plaque progression in apoE(-/-) mice. We found that oxidized LDL (Ox-LDL) significantly induced long intervening noncoding RNA (lincRNA)-DYNLRB2-2 expression, resulting in the upregulation of GPR119 and ABCA1 expression through the glucagon-like peptide 1 receptor signaling pathway. GPR119 significantly decreased cellular cholesterol content and increased apoA-I-mediated cholesterol efflux in THP-1 macrophage-derived foam cells. In vivo, apoE(-/-) mice were randomly divided into two groups and infected with lentivirus (LV)-Mock or LV-GPR119 for 8 weeks. GPR119-treated mice showed decreased liver lipid content and plasma TG, interleukin (IL)-1β, IL-6, and TNF-α levels, whereas plasma levels of apoA-I were significantly increased. Consistent with this, atherosclerotic lesion development was significantly inhibited by infection of apoE(-/-) mice with LV-GPR119. Our findings clearly indicate that, Ox-LDL significantly induced lincRNA-DYNLRB2-2 expression, which promoted ABCA1-mediated cholesterol efflux and inhibited inflammation through GPR119 in THP-1 macrophage-derived foam cells. Moreover, GPR119 decreased lipid and serum inflammatory cytokine levels, decreasing atherosclerosis in apoE(-/-) mice. These suggest that GPR119 may be a promising candidate as a therapeutic agent.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

International Union of Basic and Clinical Pharmacology. LXXXVIII. G protein-coupled receptor list: recommendations for new pairings with cognate ligands

In 2005, the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) published a catalog of all of the human gene sequences known or predicted to encode G protein-coupled receptors (GPCRs), excluding sensory receptors. This review updates the list of orphan GPCRs and describes the criteria used by NC-IUPHAR to recommend the pairing of an orphan receptor with its cognate ligand(s). The following recommendations are made for new receptor names based on 11 pairings for class A GPCRs: hydroxycarboxylic acid receptors [HCA₁ (GPR81) with lactate, HCA₂ (GPR109A) with 3-hydroxybutyric acid, HCA₃ (GPR109B) with 3-hydroxyoctanoic acid]; lysophosphatidic acid receptors [LPA₄ (GPR23), LPA₅ (GPR92), LPA₆ (P2Y5)]; free fatty acid receptors [FFA4 (GPR120) with omega-3 fatty acids]; chemerin receptor (CMKLR1; ChemR23) with chemerin; CXCR7 (CMKOR1) with chemokines CXCL12 (SDF-1) and CXCL11 (ITAC); succinate receptor (SUCNR1) with succinate; and oxoglutarate receptor [OXGR1 with 2-oxoglutarate]. Pairings are highlighted for an additional 30 receptors in class A where further input is needed from the scientific community to validate these findings. Fifty-seven human class A receptors (excluding pseudogenes) are still considered orphans; information has been provided where there is a significant phenotype in genetically modified animals. In class B, six pairings have been reported by a single publication, with 28 (excluding pseudogenes) still classified as orphans. Seven orphan receptors remain in class C, with one pairing described by a single paper. The objective is to stimulate research into confirming pairings of orphan receptors where there is currently limited information and to identify cognate ligands for the remaining GPCRs. Further information can be found on the IUPHAR Database website (http://www.iuphar-db.org).

Gustducin couples fatty acid receptors to GLP-1 release in colon

Sweet taste receptor subunits and α-gustducin found in enteroendocrine cells of the small intestine have been implicated in release of the incretin hormones glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) in response to glucose and noncaloric sweeteners. α-Gustducin has also been found in colon, although its function there is unclear. We examined expression of α-gustducin, GLP-1, and GIP throughout the intestine. The number of α-gustducin-expressing cells and those coexpressing α-gustducin together with GLP-1 and/or GIP increased from small intestine to colon. α-Gustducin also was coexpressed with fatty acid G protein-coupled receptor (GPR) 40, GPR41, GPR43, GPR119, GPR120, and bile acid G protein-coupled receptor TGR5 in enteroendocrine cells of the colon. In colon, GPR43 was coexpressed with GPR119 and GPR120, but not with TGR5. Treatment of colonic mucosa isolated from wild-type mice with acetate, butyrate, oleic acid, oleoylethanolamide, or lithocholic acid stimulated GLP-1 secretion. However, GLP-1 release in response to these fatty acids was impaired in colonic tissue from α-gustducin knockout mice.