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

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

Glucagon-like peptide-1 (GLP-1) expression is shared by both intestinal cells and neurons of brainstem, which plays anorexigenic role on food intake. However, the exact source of physiological GLP-1 influencing food intake and pertinent mechanism of GLP-1 receptor agonists (GLP-1RA) remain unelucidated. In this study, the immediate early gene product c-Fos was chosen as the specific antigen for immunohistochemistry to show the certain areas of central nervous system (CNS) activation by the GLP-1RA. Thirty normal SD rats were randomly assigned to 3 groups, which were single intraperitoneally injected with Liraglutide (200 μg/kg), Exenatide (10 μg/kg) and saline, respectively. After injection, the amount of food intake and acute glycemic variation were assessed for comparison. The results showed that acute pharmacological dosage of GLP-1RA (Liraglutide or Exenatide) could significantly influence food intake. However, glycemic change indicated that the anorexic effect was dissociated with change in blood glucose in normal rats. Moreover, c-Fos was expressed significantly higher in major critical nuclei related to food intake in GLP-1RA groups when compared with the control group, and its expression was also found in spinal cord. The results suggested that acute administration of pharmacological doses of GLP-1 influences CNS via circulation and vagal pathways, especially on the arcuate nucleus (ARC) and the nucleus of solitary tract (NTS), and GLP-1 modulates autonomic nervous activities.
Animals ; Eating ; drug effects ; Exenatide ; pharmacology ; Glucagon-Like Peptide-1 Receptor ; agonists ; Liraglutide ; pharmacology ; Random Allocation ; Rats ; Rats, Sprague-Dawley

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

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

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*

Dipeptidyl peptidase-4 (DPP-4) inhibitors are a new class of oral antidiabetic agent for the treatment of type 2 diabetes mellitus. They increase endogenous levels of incretin hormones, which stimulate glucose-dependent insulin secretion, decrease glucagon secretion, and contribute to reducing postprandial hyperglycemia. Although DPP-4 inhibitors have similar benefits, they can be differentiated in terms of their chemical structure, pharmacology, efficacy and safety profiles, and clinical considerations. Gemigliptin (brand name: Zemiglo), developed by LG Life Sciences, is a potent, selective, competitive, and long acting DPP-4 inhibitor. Various studies have shown that gemigliptin is an optimized DPP-4 inhibitor in terms of efficacy, safety, and patient compliance for treatment of type 2 diabetes mellitus. In this review, we summarize the characteristics of gemigliptin and discuss its potential benefits in clinical practice.
Biological Science Disciplines ; Diabetes Mellitus, Type 2* ; Dipeptidyl-Peptidase IV Inhibitors ; Glucagon ; Hyperglycemia ; Incretins ; Insulin ; Patient Compliance ; Pharmacology

GLP-1 has a variety of anti-diabetic effects. However, native GLP-1 is not suitable for treatment of diabetes due to its short half-life (t½, 2-5 min). Exendin-4 is a polypeptide isolated from lizard saliva, which can bind to GLP-1 receptor, produce physiological effects similar to GLP-1, t½ up to 2.5 h, therefore, we developed a long-lasting GLP-1 receptor agonists and GLP-1-exendin-4 fusion IgG4 Fc [GLP-1-exendin-4/ IgG4(Fc)]. We constructed the eukaryotic expression vector of human GLP-1-exendin-4/IgG4(Fc)-pOptiVEC- TOPO by gene recombination technique and expressed the fusion protein human GLP-1-IgG4 (Fc) in CHO/DG44 cells. The fusion protein stimulated the INS-1 cells secretion of insulin, GLP-1, exendin-4 and fusion protein in CD1 mice pharmacokinetic experiments, as well as GLP-1, exendin-4 and fusion protein did anti-diabetic effect on streptozotocin induced mice. Results demonstrated that the GLP-1-exendin-4/IgG4(Fc) positive CHO/DG44 clones were chosen and the media from these positive clones. Western blotting showed that one protein band was found to match well with the predicted relative molecular mass of human GLP-1-exendin-4/IgG4(Fc). Insulin RIA showed that GLP-1-exendin-4/IgG4(Fc) dose-dependently stimulated insulin secretion from INS-1 cells. Pharmacokinetic studies in CD1 mice showed that with intraperitoneal injection (ip), the fusion protein peaked at 30 min in circulation and maintained a plateau for 200 h. Natural biological half-life of exendin-4 was (1.39 ± 0.28) h, GLP-1 in vivo t½ 4 min, indicating that fusion protein has long-lasting effects on the modulation of glucose homeostasis. GLP-1-exendin-4/IgG4(Fc) was found to be effective in reducing the incidence of diabetes in multiple-low-dose streptozotocin-induced diabetes in mice, longer duration of the biological activity of the fusion protein. The biological activity was significantly higher than that of GLP-1 and exendin-4. GLP-1-exendin-4/IgG4(Fc) has good anti-diabetic activity. It can be used as a long-acting GLP-1 agonists.
Animals ; CHO Cells ; Cricetinae ; Cricetulus ; Diabetes Mellitus, Experimental ; drug therapy ; Glucagon-Like Peptide 1 ; pharmacology ; Glucagon-Like Peptide-1 Receptor ; agonists ; Half-Life ; Humans ; Hypoglycemic Agents ; pharmacology ; Immunoglobulin G ; pharmacology ; Insulin ; secretion ; Mice ; Peptides ; pharmacology ; Recombinant Fusion Proteins ; pharmacology ; Venoms ; pharmacology

Animals ; Animals, Newborn ; Cells, Cultured ; Cyclic AMP ; metabolism ; Glucagon-Like Peptide 1 ; pharmacology ; Insulin ; secretion ; Islets of Langerhans ; drug effects ; secretion ; Peptide Fragments ; pharmacology ; RNA, Messenger ; genetics ; Rats

BACKGROUNDThe pathophysiology of type 2 diabetes is progressive pancreatic beta cell failure with consequential reduced insulin secretion. Glucotoxicity results in the reduction of beta cell mass in type 2 diabetes by inducing apoptosis. Autophagy is essential for the maintenance of normal islet architecture and plays a crucial role in maintaining the intracellular insulin content by accelerating the insulin degradation rate in beta cells. Recently more attention has been paid to the effect of autophagy in type 2 diabetes. The regulatory pathway of autophagy in controlling pancreatic beta cells is still not clear. The aim of our study was to evaluate whether liraglutide can inhibit apoptosis and modulate autophagy in vitro in insulinoma cells (INS-1 cells).

METHODSINS-1 cells were incubated for 24 hours in the presence or absence of high levels of glucose, liraglutide (a long-acting human glucagon-like peptide-1 analogue), or 3-methyadenine (3-MA). Cell viability was measured using the Cell Counting Kit-8 (CCK8) viability assay. Autophagy of INS-1 cells was tested by monodansylcadaverine (MDC) staining, an autophagy fluorescent compound used for the labeling of autophagic vacuoles, and by Western blotting of microtubule-associated protein I light chain 3 (LC3), a biochemical markers of autophagic initiation.

RESULTSThe viability of INS-1 cells was reduced after treatment with high levels of glucose. The viability of INS-1 cells was reduced and apoptosis was increased when autophagy was inhibited. The viability of INS-1 cells was significantly increased by adding liraglutide to supplement high glucose level medium compared with the cells treated with high glucose levels alone.

CONCLUSIONSApoptosis and autophagy were increased in rat INS-1 cells when treated with high level of glucose, and the viability of INS-1 cells was significantly reduced by inhibiting autophagy. Liraglutide protected INS-1 cells from high glucose level-induced apoptosis that is accompanied by a significant increase of autophagy, suggesting that liraglutide plays a role in beta cell apoptosis by targeting autophagy. Thus, autophagy may be a new target for the prevention or treatment of diabetes.

Animals ; Apoptosis ; drug effects ; Autophagy ; drug effects ; Cell Line, Tumor ; Cell Survival ; drug effects ; Glucagon-Like Peptide 1 ; analogs & derivatives ; pharmacology ; Glucose ; pharmacology ; Insulinoma ; pathology ; Liraglutide ; Rats