Peptide dual agonists toward both glucagon-like peptide 1 receptor (GLP-1R) and glucagon receptor (GCGR) are emerging as novel therapeutics for the treatment of type 2 diabetes mellitus (T2DM) patients with obesity. Our previous work identified a Xenopus GLP-1-based dual GLP-1R/GCGR agonist termed xGLP/GCG-13, which showed decent hypoglycemic and body weight lowering activity. However, the clinical utility of xGLP/GCG-13 is limited due to its short in vivo half-life. Inspired by the fact that O-GlcNAcylation of intracellular proteins leads to increased stability of secreted proteins, we rationally designed a panel of O-GlcNAcylated xGLP/GCG-13 analogs as potential long-acting GLP-1R/ GCGR dual agonists. One of the synthesized glycopeptides 1f was found to be equipotent to xGLP/GCG-13 in cell-based receptor activation assays. As expected, O-GlcNAcylation effectively improved the stability of xGLP/GCG-13 in vivo. Importantly, chronic administration of 1f potently induced body weight loss and hypoglycemic effects, improved glucose tolerance, and normalized lipid metabolism and adiposity in both db/db and diet induced obesity (DIO) mice models. These results supported the hypothesis that glycosylation is a useful strategy for improving the in vivo stability of GLP-1-based peptides and promoted the development of dual GLP-1R/GCGR agonists as antidiabetic/antiobesity drugs.
Mice ; Animals ; Glucagon-Like Peptide 1/metabolism* ; Receptors, Glucagon/therapeutic use* ; Xenopus laevis/metabolism* ; Diabetes Mellitus, Type 2/drug therapy* ; Glycopeptides/therapeutic use* ; Obesity/drug therapy* ; Hypoglycemic Agents/pharmacology* ; Peptides/pharmacology*

IL-18 is a crucial pro-inflammatory cytokine that mediates chronic intestinal inflammation. Metformin, an anti-diabetic drug, was reported to have ameliorative effects on inflammatory bowel disease. Recently, the mechanism of action of metformin was explained as a modulation of gut microbiota. In this study, fecal microbiota transplantation (FMT) using fecal material from metformin-treated mice was found to upregulate the expression of GLP-1 and pattern-recognition receptors TLR1 and TLR4 for the improvement in hyperglycemia caused by a high-fat diet. Further, FMT downregulated the expression of the inflammatory cytokine IL-18. Within the genera Akkermansia, Bacteroides, and Butyricimonas, which were promoted by metformin therapy, Butyricimonas was found to be consistently abundant following FMT. Our findings suggest that modulation of gut microbiota is a key factor for the anti-inflammatory effects of metformin which is used for the treatment of hyperglycemia.
Animals ; Bacteroides ; Diet, High-Fat ; Down-Regulation ; Fecal Microbiota Transplantation ; Gastrointestinal Microbiome ; Glucagon-Like Peptide 1 ; Hyperglycemia ; Inflammation ; Inflammatory Bowel Diseases ; Interleukin-18 ; Metformin ; Mice ; Toll-Like Receptors

Type 2 diabetes (T2D) has been known as 'bi-hormonal disorder' since decades ago, the role of glucagon from alpha-cell has languished whereas beta-cell taking center stage. Recently, numerous findings indicate that the defects of glucagon secretion get involve with development and exacerbation of hyperglycemia in T2D. Aberrant alpha-cell responses exhibit both fasting and postprandial states: hyperglucagonemia contributes to fasting hyperglycemia caused by inappropriate hepatic glucose production, and to postprandial hyperglycemia owing to blunted alpha-cell suppression. During hypoglycemia, insufficient counter-regulation response is also observed in advanced T2D. Though many debates still remained for exact mechanisms behind the dysregulation of alpha-cell in T2D, it is clear that the blockade of glucagon receptor or suppression of glucagon secretion from alpha-cell would be novel therapeutic targets for control of hyperglycemia. Whereas there have not been remarkable advances in developing new class of drugs, currently available glucagon-like peptide-1 and dipeptidyl peptidase-IV inhibitors could be options for treatment of hyperglucagonemia. In this review, we focus on alpha-cell dysfunction and therapeutic potentials of targeting alpha-cell in T2D.
Diabetes Mellitus, Type 2 ; Fasting ; Glucagon ; Glucagon-Like Peptide 1 ; Glucagon-Secreting Cells ; Glucose ; Hyperglycemia ; Hypoglycemia ; Insulin ; Insulin-Secreting Cells ; Receptors, Glucagon

OBJECTIVETo investigate the effects of activation of the GLP-1 receptor on the p38MAPK signaling pathway in hepatic stellate cells (HSCs).

METHODSHSCs were isolated and identified according to morphological features; the levels of GLP-1R protein were determined by western blotting.The HSCs were randomly divided into a control grouP (normal saline treatment) and experimental grouP(liraglutide treatment); after 120 hours, the expression of p38MAPK mRNA was examined by RT-PCR and of phosphorylated (p)-p38MAPK protein was detected by western blotting.

RESULTSGLP-1R proteins were detected in the HSCs. Compared with the control group, the experimental group showed significantly decreased p38MAPK mRNA and p-p38MAPK protein (both P < 0.01).

CONCLUSIONThe p38MAPK signaling pathway could be down-regulated when GLP-1R is activated in HSCs.

Cells, Cultured ; Glucagon-Like Peptide 1 ; analogs & derivatives ; pharmacology ; Glucagon-Like Peptide-1 Receptor ; Hepatic Stellate Cells ; metabolism ; Humans ; Liraglutide ; MAP Kinase Signaling System ; RNA, Messenger ; Receptors, Glucagon ; metabolism ; p38 Mitogen-Activated Protein Kinases ; metabolism

Type 2 diabetes has been identified as a risk factor for Alzheimer's disease (AD) and Parkinson's disease (PD). In the brains of patients with AD and PD, insulin signaling is impaired. This finding has motivated new research that showed good effects using drugs that initially had been developed to treat diabetes. Preclinical studies showed good neuroprotective effects applying insulin or long lasting analogues of incretin peptides. In transgenic animal models of AD or PD, analogues of the incretin GLP-1 prevented neurodegenerative processes and improved neuronal and synaptic functionality and reduced the symptoms of the diseases. Amyloid plaque load and synaptic loss as well as cognitive impairment had been prevented in transgenic AD mouse models, and dopaminergic loss of transmission and motor function has been reversed in animal models of PD. On the basis of these promising findings, several clinical trials are being conducted with the first encouraging clinical results already published. In several pilot studies in AD patients, the nasal application of insulin showed encouraging effects on cognition and biomarkers. A pilot study in PD patients testing a GLP-1 receptor agonist that is currently on the market as a treatment for type 2 diabetes (exendin-4, Byetta) also showed encouraging effects. Several other clinical trials are currently ongoing in AD patients, testing another GLP-1 analogue that is on the market (liraglutide, Victoza). Recently, a third GLP-1 receptor agonist has been brought to the market in Europe (Lixisenatide, Lyxumia), which also shows very promising neuroprotective effects. This review will summarise the range of these protective effects that those drugs have demonstrated. GLP-1 analogues show promise in providing novel treatments that may be protective or even regenerative in AD and PD, something that no current drug does.
Alzheimer Disease ; drug therapy ; Animals ; Diabetes Mellitus, Type 2 ; drug therapy ; Disease Models, Animal ; Glucagon-Like Peptide 1 ; analogs & derivatives ; pharmacology ; Glucagon-Like Peptide-1 Receptor ; Humans ; Liraglutide ; Mice ; Mice, Transgenic ; Neuroprotective Agents ; pharmacology ; Parkinson Disease ; drug therapy ; Peptides ; pharmacology ; Receptors, Glucagon ; agonists ; Venoms ; pharmacology

AIM: To identify the glucose lowering ability and chronic treatment effects of a novel coumarin-glucagon-like peptide-1 (GLP-1) conjugate HJ07. METHOD: A receptor activation experiment was performed in HEK 293 cells and the glucose lowering ability was evaluated with hypoglycemic duration and glucose stabilizing tests. Chronic treatment was performed by daily injection of exendin-4, saline, and HJ07. Body weight and HbA1c were measured every week, and an intraperitoneal glucose tolerance test was performed before treatment and after treatment. RESULTS: HJ07 showed well-preserved receptor activation efficacy. The hypoglycemic duration test showed that HJ07 possessed a long-acting, glucose-lowering effect and the glucose stabilizing test showed that the antihyperglycemic activity of HJ07 was still evident at a predetermined time (12 h) prior to the glucose challenge (0 h). The long time glucose-lowering effect of HJ07 was better than native GLP-1 and exendin-4. Furthermore, once daily injection of HJ07 to db/db mice achieved long-term beneficial effects on HbA1c lowering and glucose tolerance. CONCLUSION The biological activity results of HJ07 suggest that HJ07 is a potential long-acting agent for the treatment of type 2 diabetes.
Animals ; Blood Glucose ; metabolism ; Coumarins ; pharmacology ; Diabetes Mellitus ; blood ; drug therapy ; Diabetes Mellitus, Type 2 ; drug therapy ; Exenatide ; Glucagon-Like Peptide 1 ; analogs & derivatives ; pharmacology ; therapeutic use ; Glucagon-Like Peptide-1 Receptor ; Glucose Tolerance Test ; Glycated Hemoglobin A ; metabolism ; HEK293 Cells ; Humans ; Hypoglycemic Agents ; pharmacology ; therapeutic use ; Male ; Mice, Inbred C57BL ; Mice, Knockout ; Peptides ; pharmacology ; Receptors, Glucagon ; metabolism ; Venoms ; pharmacology

Metformin has been reported to increase the expression of the glucagon-like peptide-1 (GLP-1) receptor in pancreatic beta cells in a peroxisome proliferator-activated receptor (PPAR)-alpha-dependent manner. We investigated whether a PPARalpha agonist, fenofibrate, exhibits an additive or synergistic effect on glucose metabolism, independent of its lipid-lowering effect, when added to metformin. Non-obese diabetic Goto-Kakizaki (GK) rats were divided into four groups and treated for 28 days with metformin, fenofibrate, metformin plus fenofibrate or vehicle. The random blood glucose levels, body weights, food intake and serum lipid profiles were not significantly different among the groups. After 4 weeks, metformin, but not fenofibrate, markedly reduced the blood glucose levels during oral glucose tolerance tests, and this effect was attenuated by adding fenofibrate. Metformin increased the expression of the GLP-1 receptor in pancreatic islets, whereas fenofibrate did not. During the intraperitoneal glucose tolerance tests with the injection of a GLP-1 analog, metformin and/or fenofibrate did not alter the insulin secretory responses. In conclusion, fenofibrate did not confer any beneficial effect on glucose homeostasis but reduced metformin's glucose-lowering activity in GK rats, thus discouraging the addition of fenofibrate to metformin to improve glycemic control.
Animals ; Blood Glucose/metabolism ; Body Weight/drug effects ; Diabetes Mellitus, Experimental/*drug therapy/*metabolism ; Drug Therapy, Combination ; Feeding Behavior/drug effects ; Fenofibrate/*pharmacology/therapeutic use ; Glucagon-Like Peptide 1/agonists/metabolism ; Glucose/*metabolism ; Glucose Tolerance Test ; Homeostasis/*drug effects ; Immunohistochemistry ; Injections, Intraperitoneal ; Insulin-Secreting Cells/drug effects/metabolism/pathology ; Lipid Metabolism/drug effects ; Male ; Metformin/*pharmacology/therapeutic use ; Peptides/administration & dosage/pharmacology ; Rats ; Receptors, Glucagon/metabolism ; Venoms/administration & dosage/pharmacology

At present, surgery has become one of the treatments for type 2 diabetes, but it is still unclear about the therapeutic mechanism. Many experiments has proved that the anatomical and physiological structure has been altered leading to significant changes related to the secretion of gastrointestinal hormones and neuropeptides. These molecular are related to the metabolism of glucose, functions of islet cells and sensitivity of insulin. Intensive studies of glucagon-like peptide-1 (GLP-1) play an important role in the surgical treatment of diabetes and now it has gained increasing recognition. However, GLP-1 must be combined with GLP-1 receptor (GLP-1R) to execute its function. In this paper we reviewed the role of GLP-1 and its receptor in the mechanism of metabolic surgery.
Diabetes Mellitus, Type 2 ; surgery ; Glucagon-Like Peptide 1 ; Glucagon-Like Peptide-1 Receptor ; Humans ; Receptors, Glucagon

Through phage display, we tried to find out whether the N-terminal fragment of glucogan-like peptide 1 receptor (nGLP-1R) still had binding activity to Exendin-4 after missing one or two gene segments. By error-prone PCR, We constructed a randomly mutated phage display peptide library with different length of the N-terminal (21-145 residues) extracellular domain of glucogan-like peptide 1 receptor (GLP-1R) from rat lung. A mutant named EP16 without binding activity was found by ELISA. Through sequence alignment we found that EP16 missed the first 20 and last 10 amino acids and the 52nd tryptophan was mutated to arginine. In order to determine why Ep16 did not show its binding ability to Exendin-4, a wild type EP16 without the first 20 and last 10 amino acids and nGLP-1R(W52R) was constructed in which the 52nd tryptophan was mutated to arginine. The contrastive analysis showed that the substitution of W52R led to a markedly reduced binding ability of EP16. The mutation of the conserved W52 could change the biologic activity of the protein. The lack of the first 20 and last 10 amino acids had no effect on its biologic activity. Therefore, the mutation of a single amino acid residue of the key sequence could change the biologic activity of the nGLP-1R.
Amino Acid Sequence ; Amino Acid Substitution ; Animals ; Binding Sites ; Glucagon-Like Peptide-1 Receptor ; Molecular Sequence Data ; Mutagenesis, Site-Directed ; Mutation ; Peptide Fragments ; chemistry ; genetics ; metabolism ; Peptides ; metabolism ; Protein Binding ; Rats ; Receptors, Glucagon ; chemistry ; genetics ; metabolism ; Venoms ; metabolism

The incretin hormones glucagon like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) have recently received much attention for their roles in type 2 diabetes therapy. GLP-1 stimulated insulin secretion in a glucose-dependent manner and is secreted by intestinal L cells. It also regulates blood glucose concentration, stomach motility, appetite, and body weight. These actions are mediated through G-protein-coupled receptors highly expressed on pancreatic beta cells and also exert indirect metabolic actions. Activation of GLP-1 receptors also produces nonglycemic effects in various tissues. The pleiotropic effects of GLP-1 have been recently reported. The mechanisms identified in preclinical studies have potential translational relevance for the treatment of disease. Here, the nonglycemic effects of GLP-1, especially those on the liver, central nervous system, and bone, were reviewed.
Appetite ; Blood Glucose ; Body Weight ; Central Nervous System ; Enteroendocrine Cells ; Glucagon ; Glucagon-Like Peptide 1 ; Incretins ; Insulin ; Insulin-Secreting Cells ; Liver ; Receptors, G-Protein-Coupled ; Stomach