Non-alcoholic fatty liver disease (NAFLD) is a common liver disease and it represents the hepatic manifestation of metabolic syndrome, which includes type 2 diabetes mellitus (T2DM), dyslipidemia, central obesity and hypertension. Glucagon-like peptide-1 (GLP-1) analogues and dipeptidyl peptidase-4 (DPP-4) inhibitors were widely used to treat T2DM. These agents improve glycemic control, promote weight loss and improve lipid metabolism. Recent studies have demonstrated that the GLP-1 receptor (GLP-1R) is present and functional in human and rat hepatocytes. In this review, we present data from animal researches and human clinical studies that showed GLP-1 analogues and DPP-4 inhibitors can decrease hepatic triglyceride (TG) content and improve hepatic steatosis, although some effects could be a result of improvements in metabolic parameters. Multiple hepatocyte signal transduction pathways and mRNA from key enzymes in fatty acid metabolism appear to be activated by GLP-1 and its analogues. Thus, the data support the need for more rigorous prospective clinical trials to further investigate the potential of incretin therapies to treat patients with NAFLD.
Animals ; Clinical Trials as Topic ; Dipeptidyl-Peptidase IV Inhibitors ; pharmacology ; therapeutic use ; Glucagon-Like Peptide 1 ; agonists ; Humans ; Hypoglycemic Agents ; pharmacology ; therapeutic use ; Lipid Metabolism ; drug effects ; Non-alcoholic Fatty Liver Disease ; drug therapy ; metabolism ; Triglycerides ; metabolism

To explore the effect of glucagon-like peptide-1 receptor agonist--Exendin-4 (Ex-4) on murine MIN6 pancreatic beta-cells apoptosis induced by oxidative stress, the morphological changes of cell damage were evaluated by epifluorescence microscopy after staining with AO-EB. The percentage of cell apoptosis was determined by flow cytometric assay after Annexin-V-FITC-PI staining. Nitric oxide level was measured by Griess reagent assay. Inducible nitric oxide synthase (iNOS) protein and NF-kappaBp65 fragment were detected by Western blotting. Ex-4 inhibited the increase of nitrite level and percentage of apoptosis induced by t-BHP in MIN6 cells. Furthermore, Ex-4 partly reduced the expression of iNOS protein and the ratio of NF-kappaBp65 protein in nucleus:cytosol induced by t-BHP. These results suggest that Ex4 protects MIN6 pancreatic kappa-cells from oxidative stress-induced apoptosis via down-regulation of NF-kappaB-iNOS-nitric oxide pathway.
Animals ; Apoptosis ; drug effects ; Down-Regulation ; Glucagon-Like Peptide-1 Receptor ; Hypoglycemic Agents ; pharmacology ; Incretins ; agonists ; Insulin-Secreting Cells ; cytology ; metabolism ; Lizards ; Mice ; Nitric Oxide ; metabolism ; Nitric Oxide Synthase Type II ; metabolism ; Oxidative Stress ; drug effects ; Peptides ; pharmacology ; Receptors, Glucagon ; agonists ; Signal Transduction ; Transcription Factor RelA ; metabolism ; Venoms ; pharmacology ; tert-Butylhydroperoxide ; pharmacology

Oxidative stress induced by chronic hyperglycemia in type 2 diabetes plays a crucial role in progressive loss of beta-cell mass through beta-cell apoptosis. Glucagon like peptide-1 (GLP-1) has effects on preservation of beta-cell mass and its insulin secretory function. GLP-1 possibly increases islet cell mass through stimulated proliferation from beta-cell and differentiation to beta-cell from progenitor cells. Also, it probably has an antiapoptotic effect on beta-cell, but detailed mechanisms are not proven. Therefore, we examined the protective mechanism of GLP-1 in beta-cell after induction of oxidative stress. The cell apoptosis decreased to ~50% when cells were treated with 100 microM H2O2 for up to 2 hr. After pretreatment of Ex-4, GLP-1 receptor agonist, flow cytometric analysis shows 41.7% reduction of beta-cell apoptosis. This data suggested that pretreatment of Ex-4 protect from oxidative stress-induced apoptosis. Also, Ex-4 treatment decreased GSK3beta activation, JNK phosphorylation and caspase-9, -3 activation and recovered the expression of insulin2 mRNA in beta-cell lines and secretion of insulin in human islet. These results suggest that Ex-4 may protect beta-cell apoptosis by blocking the JNK and GSK3beta mediated apoptotic pathway.
Animals ; *Apoptosis ; Caspase 3/metabolism ; Caspase 9/metabolism ; Cells, Cultured ; Cricetinae ; Flow Cytometry ; Glucagon-Like Peptide 1/pharmacology ; Glycogen Synthase Kinase 3/*metabolism ; Humans ; Hydrogen Peroxide/toxicity ; Insulin/genetics/metabolism ; Insulin-Secreting Cells/drug effects/*enzymology/metabolism ; JNK Mitogen-Activated Protein Kinases/*metabolism ; *Oxidative Stress ; Peptides/*pharmacology ; Phosphorylation ; Receptors, Glucagon/agonists/metabolism ; Signal Transduction ; Venoms/*pharmacology

The aim of this project is to establish a GLP-1 signaling pathway targeted cell model, for screening the new class of GLP-1 receptor agonists as anti-diabetic candidates. Firstly construct a recombined plasmid with multi-copied specific response element (RIP-CRE) regulated by GLP-1 signaling pathway and E-GFP reporter gene. Transient transfect this recombined plasmid into islet cell NIT-1, then detect the responsibility of transfected cell to GLP-1 analogue, Exendin 4. For secondly, use stable transfection and monocloning cell culture to obtain a GLP-1 signaling-specific cell line. It indicates that this cell model can response to Exendin 4, which response can be completely inhibited by GLP-1 receptor antagonist, Exendin 9-39, further showing GLP-1 receptor specific activity with a cAMP-PKA-independently mechanism. Establishment of this novel cell model can be used in high-throughput drug screening of peptides or small molecular GLP-1 analogues.
Animals ; Cell Line ; Cyclic AMP Response Element Modulator ; pharmacology ; Cyclic AMP-Dependent Protein Kinases ; antagonists & inhibitors ; Drug Delivery Systems ; Drug Evaluation, Preclinical ; Genes, Reporter ; Glucagon-Like Peptide-1 Receptor ; Green Fluorescent Proteins ; metabolism ; Hypoglycemic Agents ; agonists ; antagonists & inhibitors ; metabolism ; Islets of Langerhans ; cytology ; drug effects ; metabolism ; Isoquinolines ; pharmacology ; Peptide Fragments ; pharmacology ; Peptides ; antagonists & inhibitors ; pharmacology ; Plasmids ; Rats ; Receptors, Glucagon ; agonists ; antagonists & inhibitors ; genetics ; metabolism ; Recombinant Proteins ; genetics ; metabolism ; Signal Transduction ; Sulfonamides ; pharmacology ; Transfection ; 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