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

There is a close correlation between type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) in the course of pathophysiological processes. The neuroprotective action of glucagon-like peptide 1 (GLP-1), a latest drug for clinical treatment of T2DM, is being more deeply investigated at present, and a novel therapeutic strategy for AD with GLP-1 has been proposed boldly. This review mainly discussed the correlation of pathogenesis between T2DM and AD, the synthesis and secretion of GLP-1, the distribution and physiological effects of GLP-1 receptor in the brain, and the progresses on the study of GLP-1 in the treatment of AD.
Alzheimer Disease ; drug therapy ; physiopathology ; Amyloid beta-Peptides ; drug effects ; metabolism ; Animals ; Brain ; metabolism ; Diabetes Mellitus, Type 2 ; physiopathology ; Glucagon-Like Peptide 1 ; pharmacology ; therapeutic use ; Glucagon-Like Peptide-1 Receptor ; Humans ; Neuroprotective Agents ; pharmacology ; therapeutic use ; Receptors, Glucagon ; 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

New therapeutics for type 2 diabetes using incretin hormone were introduced recently. Incretin-based therapies consist of two types: GLP-1 agonists mainly acting on the GLP-1 receptor and dipeptidyl peptidase 4 inhibitors (DPP-4 inhibitors). The former is resistant to DPP-4 and injectable. The latter is oral medications raising endogenous GLP-1 by inhibiting the degrading enzyme DPP-4. The incretin based therapies are promising and more commonly used due to their action and safety profile. Stimulation of insulin secretion by these drugs occurs in a glucose-dependent manner. Incretin based therapies have low risk for hypoglycemia. The subsequent review outlines evidence from selected clinical trials of the currently available GLP-1 agonists, exenatide and liraglutide, and DPP-4 inhibitors, sitagliptin and vildagliptin.
Adamantane ; Dipeptidyl-Peptidase IV Inhibitors ; Glucagon-Like Peptide 1 ; Hypoglycemia ; Incretins ; Insulin ; Nitriles ; Peptides ; Pyrazines ; Pyrrolidines ; Receptors, Glucagon ; Triazoles ; Venoms ; Glucagon-Like Peptide-1 Receptor ; Liraglutide ; Sitagliptin Phosphate

<b>BACKGROUNDb>A number of studies have shown that oxidative stress and mitochondrial involvement are major triggering factors in the development of neurodegenerative diseases. Cobalt chloride (CoCl(2))-induced cell death in PC12 cells may serve a simple and convenient in vitro model of hypoxia-induced neuronal cytotoxicity. To explore the effect of geniposide on CoCl(2) which induced cytotoxicity and mitochondrial function in rat pheochromocytoma PC12 cells, we analyzed the influence of geniposide on the expression of apoptosis-related proteins.

<b>METHODSb>PC12 cells and RNAi PC12 cells were treated with 0, 12.5, 25, 50, 100 micromol/L geniposide for 12 hours and then exposure to 400 micromol/L CoCl(2) for 12 hours. Cell viability, cell morphology, and expression of Bcl-2, Bax, P53 and caspase-9 were determined using Western blotting.

<b>RESULTSb>Pretreatment with geniposide markedly improved the cells viability and morphology, decreased the expression of Bax, P53 and caspase-9, and increased the expression of Bcl-2 in PC12 cells challenged by CoCl(2)2. However, in the RNAi PC12 cells, geniposide had no significant effect on the expression of these proteins.

<b>CONCLUSIONb>Geniposide protects PC12 cells from CoCl(2) involved in mitochondrial mediated apoptosis, and GLP-1R might play a critical role in the neuroprotection of geniposide in PC12 cells.

Animals ; Apoptosis ; drug effects ; Cobalt ; toxicity ; Glucagon-Like Peptide-1 Receptor ; Iridoids ; pharmacology ; Mitochondria ; physiology ; Neuroprotective Agents ; pharmacology ; PC12 Cells ; Proto-Oncogene Proteins c-bcl-2 ; physiology ; Rats ; Receptors, Glucagon ; drug effects ; physiology ; Signal Transduction ; bcl-2-Associated X Protein ; physiology

BACKGROUND: Insulin receptor substrate 2 (IRS-2) is a key regulator of beta cell proliferation and apoptosis. This study was aimed to investigate effect of the glucolipotoxicity on apoptosis in INS-1 cell, and the effect of Exendin-4, a GLP-1 receptor agonist, on IRS-2 expression in the glucolipotoxicity induced INS-1 cell. The goal was to discover the new action mechanism and function of Exendin-4 in beta cell apoptosis. METHOD: INS-1 cells were cultured in glucolipotoxic condition for 2, 4 or 6 days and were categorized as G groups. Another group in which 50 nM Exendin-4 was added to INS-1 cells, cultured in glucolipotoxic condition, were named as Ex-4 groups. We investigated the expression of IRS-2 by RT-PCR, phosphorylated IRS-2 and phosphorylated Akt protein levels by western blot. We measured the apoptosis ratio of INS-1 cell in glucolipotoxic condition by TUNEL staining in both groups. RESULT: IRS-2 expression of INS-1 cells decreased with correlation to the time of exposure to glucolipotoxic condition. pIRS-2 and pAkt protein levels decreased in the similar pattern in glucolipotoxicity group. However, this effect of glucolipotoxicity on INS-1 cell was inhibited by the Exendin-4 treatment. In the Ex-4 groups, IRS-2 expression, pIRS-2 and pAkt protein levels remained at the similar level to low glucose condition state. Also, apoptosis induced by glucolipotoxicity was suppressed by Exendin-4 treatment significantly. CONCLUSION: We showed that the long-term treatment of Exendin-4 inhibited the apoptosis of beta cells significantly in glucolipotoxic condition and that this effect of Exendin-4 was related with IRS-2 and Akt among the beta cell's intracellular signal transduction pathway.
Apoptosis ; Blotting, Western ; Cell Proliferation ; Cells, Cultured ; Glucagon-Like Peptide 1 ; Glucagon-Like Peptide-1 Receptor ; Glucose ; In Situ Nick-End Labeling ; Insulin Receptor Substrate Proteins ; Peptides ; Phosphorylation ; Receptors, Glucagon ; Signal Transduction ; Venoms

<b>OBJECTIVEb>To investigate the effects of activation of the GLP-1 receptor on the p38MAPK signaling pathway in hepatic stellate cells (HSCs).

<b>METHODSb>HSCs 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.

<b>RESULTSb>GLP-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).

<b>CONCLUSIONb>The 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

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

BACKGROUND: The characteristic feature of pancreatic beta cells is highly developed endoplasmic reticulum (ER) due to a heavy engagement in insulin secretion. The ER serves several important function, including post-translational modification, folding, and assembly of newly synthesized secretory proteins, and its proper function is essential to cell survival. Various stress conditions can interfere with ER function. Pancreatic beta cells may be particularly vulnerable to ER stress that causes to impair insulin biosynthesis and beta cell survival through apoptosis. Glucagon like peptide-1 (GLP-1) is a new drug for treatment of type 2 diabetes and has effects on stimulation of insulin secretion and beta cell preservation. Also, it may have an antiapoptotic effect on beta cells, but detailed mechanisms are not proven. Therefore, we investigated the protective mechanism of GLP-1 in beta cells through ER stress response induced by 2-deoxy-D-glucose (2DG). METHODS: For induction of the ER stress, HIT-T15 cells (hamster beta cell line) were treated with 2DG (10 mM). Apoptosis was evaluated with MTT assay, hoechst 33342 staining and Annexin/PI flow cytometry. Expression of ER stress-related molecules was determined by real-time PCR or western blot. For blocking ER stress, we pretreated HIT-T15 cells with exendin-4 (Ex-4; GLP-1 receptor agonist) for 1 hour before stress induction. RESULTS: After induction with ER stress (2DG), beta cells were lost by apoptosis. We found that Ex-4 had a protective effect through ER stress related molecules (GRP78, GRP94, XBP-1, eIF2alpha, CHOP) modulation. Also, Ex-4 recovered the expression of insulin2 mRNA in beta cells. CONCLUSION: These results suggest that GLP-1 may protect beta cells apoptosis through ER stress modulation.
Apoptosis ; Benzimidazoles ; Blotting, Western ; Cell Survival ; Deoxyglucose ; Endoplasmic Reticulum ; Flow Cytometry ; Glucagon ; Glucagon-Like Peptide 1 ; Glucagon-Like Peptide-1 Receptor ; HSP70 Heat-Shock Proteins ; Insulin ; Insulin-Secreting Cells ; Membrane Proteins ; Peptides ; Protein Processing, Post-Translational ; Proteins ; Real-Time Polymerase Chain Reaction ; Receptors, Glucagon ; RNA, Messenger ; Venoms