exendin-(9-39) and Inflammation

Inflammation and hyperglycaemia are associated with a prothrombotic state. Cell-derived microparticles (MPs) are the conveyors of active procoagulant tissue factor (TF) and circulate at high concentration in diabetic patients. Liraglutide, a glucagon-like peptide (GLP)-1 analogue, is known to promote insulin secretion and β-cell preservation. In this in vitro study, we examined the link between insulin impairment, procoagulant activity and plasma membrane remodelling, under inflammatory conditions. Rin-m5f β-cell function, TF activity mediated by MPs and their modulation by 1 μM liraglutide were examined in a cell cross-talk model. Methyl-β-cyclodextrine (MCD), a cholesterol depletor, was used to evaluate the involvement of raft on TF activity, MP shedding and insulin secretion as well as Soluble N-éthylmaleimide-sensitive-factor Attachment protein Receptor (SNARE)-dependent exocytosis. Cytokines induced a two-fold increase in TF activity at MP surface that was counteracted by liraglutide. Microparticles prompted TF activity on the target cells and a two-fold decrease in insulin secretion via protein kinase A (PKA) and p38 signalling, that was also abolished by liraglutide. Large lipid raft clusters were formed in response to cytokines and liraglutide or MCD-treated cells showed similar patterns. Cells pre-treated by saturating concentration of the GLP-1r antagonist exendin (9-39), showed a partial abolishment of the liraglutide-driven insulin secretion and liraglutide-decreased TF activity. Measurement of caspase 3 cleavage and MP shedding confirmed the contribution of GLP-1r-dependent and -independent pathways. Our results confirm an integrative β-cell response to GLP-1 that targets receptor-mediated signalling and membrane remodelling pointing at the coupling of insulin secretion and inflammation-driven procoagulant events.

Topics: Animals; Caspase 3; Cell Membrane; Cell-Derived Microparticles; Cells, Cultured; Cyclic AMP-Dependent Protein Kinases; Exocytosis; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Hyperglycemia; Inflammation; Insulin; Insulin-Secreting Cells; Liraglutide; MAP Kinase Signaling System; Peptide Fragments; Rats; SNARE Proteins; Thromboplastin

The number of pro-α cells is known to increase in response to β cell injury and these cells then generate glucagon-like peptide-1 (GLP-1), thus attenuating the development of diabetes. The aim of the present study was to further examine the role and the mechanisms responsible for intra-islet GLP-1 production as a self-protective response against lipotoxicity. The levels of the key enzyme, prohormone convertase 1/3 (PC1/3), as well as the synthesis and release of GLP-1 in models of lipotoxicity were measured. Furthermore, islet viability, apoptosis, oxidative stress and inflammation, as well as islet structure were assessed after altering GLP-1 receptor signaling. Both prolonged exposure to palmitate and a high-fat diet facilitated PC1/3 expression, as well as the synthesis and release of GLP-1 induced by β cell injury and the generation of pro-α cells. Prolonged exposure to palmitate increased reactive oxygen species (ROS) production, and the antioxidant, N-acetylcysteine (NAC), partially prevented the detrimental effects induced by palmitate on β cells, resulting in decreased GLP-1 levels. Furthermore, the inhibition of GLP-1 receptor (GLP-1R) signaling by treatment with exendin‑(9-39) further decreased cell viability, increased cell apoptosis and caused a stronger inhibition of the β cell-specific transcription factor, pancreatic duodenal homeobox 1 (PDX1). Moreover, treatment with the GLP-1R agonist, liraglutide, normalized islet structure and function, resulting in a decrease in cell death and in the amelioration of β cell marker expression. Importantly, liraglutide maintained the oxidative balance and decreased inflammatory factor and p65 expression. Overall, our data demonstrate that an increase in the number of pro-α cells and the activation of the intra-islet GLP-1 system comprise a self-defense mechanism for enhancing β cell survival to combat lipid overload, which is in part mediated by oxidative stress and inflammation.

Topics: Acetylcysteine; Animals; Apoptosis; Cell Survival; Cells, Cultured; Diet, High-Fat; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucagon-Secreting Cells; Homeodomain Proteins; Inflammation; Insulin-Secreting Cells; Liraglutide; Male; Mice; Mice, Inbred C57BL; Oxidative Stress; Palmitates; Peptide Fragments; Proprotein Convertase 1; Reactive Oxygen Species; Signal Transduction; Trans-Activators; Transcription Factor RelA

High mobility group box 1 protein (HMGB1) plays an important role in myocardial ischemia and reperfusion (I/R) injury. Preconditioning of exendin-4 (Ex), a glucagon-like peptide-1 receptor agonist, has been reported to attenuate myocardial I/R injury. The current study investigated whether Ex postconditioning also attenuated myocardial I/R injury and the potential mechanisms. Anesthetized male rats were subjected to ischemia for 30 min and treated with Ex (5 μg/kg, i.v.) 5 min before reperfusion, in the absence and/or presence of exendin (9-39) (an antagonist of glucagon-like peptide-1 receptor, 5 μg/kg, i.v.), followed by reperfusion for 4 h. Lactate dehydrogenase (LDH), creatine kinase (CK), tumor necrosis factor-α, interleukin-6, and infarct size were measured. HMGB1 expression was assessed by immunoblotting. Postconditioning with Ex significantly decreased infarct size and levels of LDH and CK after 4 h reperfusion (all p < 0.05). Ex also significantly inhibited the increase in malondialdehyde level and decreased the level of superoxide dismutase (both p < 0.05). In addition, the increase in HMGB1 expression induced by I/R was significantly attenuated by Ex postconditioning. Administration of exendin (9-39) abolished the protective effect of Ex postconditioning (all p < 0.05). The present study suggests that Ex postconditioning may attenuate myocardial I/R injury, which may in turn be associated with inhibiting inflammation.

Topics: Animals; Creatine Kinase; Exenatide; Gene Expression Regulation; Glucagon-Like Peptide-1 Receptor; HMGB1 Protein; Humans; Inflammation; Interleukin-6; L-Lactate Dehydrogenase; Myocardial Reperfusion Injury; Peptide Fragments; Peptides; Rats; Receptors, Glucagon; Tumor Necrosis Factor-alpha; Venoms

Hypoglycemia and hyperglycemia are both predictors for adverse outcome in critically ill patients. Hyperinsulinemia is induced by inflammatory stimuli as a relevant mechanism for glucose lowering in the critically ill. The incretine hormone GLP-1 was currently found to be induced by endotoxin, leading to insulin secretion and glucose lowering under inflammatory conditions in mice. Here, we describe GLP-1 secretion to be increased by a variety of inflammatory stimuli, including endotoxin, interleukin-1β (IL-1β), and IL-6. Although abrogation of IL-1 signaling proved insufficient to prevent endotoxin-dependent GLP-1 induction, this was abolished in the absence of IL-6 in respective knockout animals. Hence, we found endotoxin-dependent GLP-1 secretion to be mediated by an inflammatory cascade, with IL-6 being necessary and sufficient for GLP-1 induction. Functionally, augmentation of the GLP-1 system by pharmacological inhibition of DPP-4 caused hyperinsulinemia, suppression of glucagon release, and glucose lowering under endotoxic conditions, whereas inhibition of the GLP-1 receptor led to the opposite effect. Furthermore, total GLP-1 plasma levels were profoundly increased in 155 critically ill patients presenting to the intensive care unit (ICU) in comparison with 134 healthy control subjects. In the ICU cohort, GLP-1 plasma levels correlated with markers of inflammation and disease severity. Consequently, GLP-1 provides a novel link between the immune system and the gut with strong relevance for metabolic regulation in context of inflammation.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Animals; Blood Glucose; Female; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Humans; Hyperinsulinism; Inflammation; Interleukin-1beta; Interleukin-6; Lipopolysaccharides; Male; Mice, Knockout; Middle Aged; Peptide Fragments; Receptors, Glucagon; Young Adult

Glucagon-like peptide-1 (GLP-1) is a proglucagon-derived hormone with cellular protective actions. We hypothesized that GLP-1 would protect the endothelium from injury during inflammation. Our aims were to determine the: (1) effect of GLP-1 on basal microvascular permeability, (2) effect of GLP-1 on increased microvascular permeability induced by lipopolysaccaride (LPS), (3) involvement of the GLP-1 receptor in GLP-1 activity, and (4) involvement of the cAMP/PKA pathway in GLP-1 activity. Microvascular permeability (L(p)) of rat mesenteric post-capillary venules was measured in vivo. First, the effect of GLP-1 on basal L(p) was measured. Second, after systemic LPS injection, L(p) was measured after subsequent perfusion with GLP-1. Thirdly, L(p) was measured after LPS injection and perfusion with GLP-1+GLP-1 receptor antagonist. Lastly, L(p) was measured after LPS injection and perfusion with GLP-1+inhibitors of the cAMP/PKA pathway. Results are presented as mean area under the curve (AUC)+/-SEM. GLP-1 had no effect on L(p) (AUC: baseline=27+/-1.4, GLP-1=1+/-0.4, p=0.08). LPS increased L(p) two-fold (AUC: LPS=54+/-1.7, p<0.0001). GLP-1 reduced the LPS increase in L(p) by 75% (AUC: LPS+GLP-1=34+/-1.5, p<0.0001). GLP-1 antagonism reduced the effects of GLP-1 by 60% (AUC: LPS+GLP-1+antagonist=46+/-2.0, p<0.001). The cAMP synthesis inhibitor reduced the effects of GLP-1 by 60% (AUC: LPS+GLP-1+cAMP inhibitor=46+/-1.5, p<0.0001). The PKA inhibitor reduced the effects of GLP-1 by 100% (AUC: LPS+GLP-1+PKA inhibitor=56+/-1.5, p<0.0001). GLP-1 attenuates the increase in microvascular permeability induced by LPS. GLP-1 may protect the endothelium during inflammation, thus decreasing third-space fluid loss.

Topics: Animals; Capillary Permeability; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dideoxyadenosine; Endothelium, Vascular; Enzyme Inhibitors; Female; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Inflammation; Isoquinolines; Lipopolysaccharides; Mesentery; Peptide Fragments; Perfusion; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Receptors, Glucagon; Rolipram; Sulfonamides; Venules