incretins and exendin-(9-39)

The actions of both endogenous incretin hormones during a meal have not previously been characterized.. Using specific receptor antagonists, we investigated the individual and combined contributions of endogenous glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) to postprandial glucose metabolism, energy expenditure, and gallbladder motility.. Randomized, double-blinded, placebo-controlled, crossover design.. On four separate days, four liquid mixed meal tests (1894 kJ) over 270 minutes (min).. Twelve healthy male volunteers.. Infusions of the GIP receptor antagonist GIP(3-30)NH2 (800 pmol/kg/min), the GLP-1 receptor antagonist exendin(9-39)NH2 (0-20 min: 1000 pmol/kg/min; 20-270 min: 450 pmol/kg/min), GIP(3-30)NH2+exendin(9-39)NH2, or placebo/saline.. Baseline-subtracted area under the curve (bsAUC) of C-peptide.. Infusion of GIP(3-30)NH2+exendin(9-39)NH2 significantly increased plasma glucose excursions (bsAUC: 261 ± 142 mmol/L × min) during the liquid mixed meals compared with GIP(3-30)NH2 (180 ± 141 mmol/L × min; P = 0.048), exendin(9-39)NH2 (171 ± 114 mmol/L × min; P = 0.046), and placebo (116 ± 154 mmol/L × min; P = 0.015). Correspondingly, C-peptide:glucose ratios during GIP(3-30)NH2+exendin(9-39)NH2 infusion were significantly lower than during GIP(3-30)NH2 (P = 0.0057), exendin(9-39)NH2 (P = 0.0038), and placebo infusion (P = 0.014). GIP(3-30)NH2 resulted in significantly lower AUCs for glucagon than exendin(9-39)NH2 (P = 0.0417). Gallbladder ejection fraction was higher during GIP(3-30)NH2 compared with placebo (P = 0.004). For all interventions, energy expenditure and respiratory quotient were similar.. Endogenous GIP and GLP-1 lower postprandial plasma glucose excursions and stimulate insulin secretion but only endogenous GIP affects gallbladder motility. The two incretin hormones potentiate each other's effects in the control of postprandial glycemia in healthy men.

Topics: Adult; Aged; Blood Glucose; Cross-Over Studies; Double-Blind Method; Energy Metabolism; Gallbladder; Gastric Inhibitory Polypeptide; Gastrointestinal Motility; Glucagon-Like Peptide-1 Receptor; Healthy Volunteers; Humans; Incretins; Male; Meals; Middle Aged; Peptide Fragments; Postprandial Period; Receptors, Gastrointestinal Hormone; Young Adult

Glucagon-like peptide 1 (GLP-1) has incretin effects that are well-documented, but the independent role of GLP-1 action in human satiety perception is debated. We hypothesized that blockade of GLP-1 receptors would suppress postprandial satiety and increase voluntary food intake. After an overnight fast, eight normal weight participants (seven men, BMI 19-24.7 kg/m(2), age 19-29 year) were enrolled in a double-blind, placebo-controlled, randomized crossover study of the GLP-1 antagonist Exendin-[9-39] (Ex-9) to determine if the satiating effects of a meal are dependent on GLP-1 signaling in humans. Following a fasting blood draw, iv infusion of Ex-9 (600-750 pmol/kg/min) or saline began. Thirty minutes later, subjects consumed a standardized breakfast followed 90 min later (at the predicted time of maximal endogenous circulating GLP-1) by an ad libitum buffet meal to objectively measure satiety. Infusions ended once the buffet meal was complete. Visual analog scale ratings of hunger and fullness and serial assessments of plasma glucose, insulin, and GLP-1 concentrations were done throughout the experiment. Contrary to the hypothesis, during Ex-9 infusion subjects reported a greater decrease in hunger due to consumption of the breakfast (Ex-9 -62 ± 5; placebo -41 ± 9; P=0.01) than during placebo. There were no differences in ad libitum caloric intake between Ex-9 and placebo. Ex-9 increased glucose, insulin, and endogenous GLP-1, which may have counteracted any effects of Ex-9 infusion to block satiety signaling. Blockade of GLP-1 receptors failed to suppress subjective satiety following a standardized meal or increase voluntary food intake in healthy, normal-weight subjects.

Topics: Adult; Blood Glucose; Body Mass Index; Cross-Over Studies; Double-Blind Method; Eating; Energy Intake; Female; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Humans; Hunger; Incretins; Insulin; Male; Peptide Fragments; Postprandial Period; Receptors, Glucagon; Satiation; Signal Transduction; Young Adult

In order to quantify the role of incretins in first- and second-phase insulin secretion (ISR) in type 2 diabetes mellitus (T2DM), a double-blind, randomized study with 12 T2DM subjects and 12 healthy subjects (HS) was conducted using the hyperglycemic clamp technique together with duodenal nutrition perfusion and intravenous infusion of the glucagon-like peptide 1 (GLP-1) receptor antagonist exendin(9-39). Intravenous glucose alone resulted in a significantly greater first- and second-phase ISR in HS compared with T2DM subjects. Duodenal nutrition perfusion augmented both first- and second-phase ISR but first-phase ISR more in T2DM subjects (approximately eight- vs. twofold). Glucose-related stimulation of ISR contributed only 20% to overall ISR. Infusion with exendin(9-39) significantly reduced first- and second-phase ISR in both HS and T2DM subjects. Thus, both GLP-1 and non-GLP-1 incretins contribute to the incretin effect. In conclusion, both phases of ISR are impaired in T2DM. In particular, the responsiveness to glucose in first-phase ISR is blunted. GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) secretions are unaltered. The absolute incretin effect is reduced in T2DM; its relative importance, however, appears to be increased, highlighting its role as an important amplifier of first-phase ISR in T2DM.

Topics: Adult; Aged; Blood Glucose; Diabetes Mellitus, Type 2; Double-Blind Method; Female; Gastric Inhibitory Polypeptide; Glucagon; Glucagon-Like Peptide-1 Receptor; Glucose; Glucose Clamp Technique; Humans; Incretins; Insulin; Insulin Secretion; Male; Middle Aged; Peptide Fragments; Receptors, Glucagon

Stroke remains one of the most common causes of death and disability worldwide. Several preclinical studies demonstrated that the brain can be effectively protected against ischaemic stroke by two seemingly distinct treatments: remote ischaemic conditioning (RIC), involving cycles of ischaemia/reperfusion applied to a peripheral organ or tissue, or by systemic administration of glucagon-like-peptide-1 (GLP-1) receptor (GLP-1R) agonists. The mechanisms underlying RIC- and GLP-1-induced neuroprotection are not completely understood. In this study, we tested the hypothesis that GLP-1 mediates neuroprotection induced by RIC and investigated the effect of GLP-1R activation on cerebral blood vessels, as a potential mechanism of GLP-1-induced protection against ischaemic stroke. A rat model of ischaemic stroke (90 min of middle cerebral artery occlusion followed by 24-h reperfusion) was used. RIC was induced by 4 cycles of 5 min left hind limb ischaemia interleaved with 5-min reperfusion periods. RIC markedly (by ~ 80%) reduced the cerebral infarct size and improved the neurological score. The neuroprotection established by RIC was abolished by systemic blockade of GLP-1R with a specific antagonist Exendin(9-39). In the cerebral cortex of GLP-1R reporter mice, ~ 70% of cortical arterioles displayed GLP-1R expression. In acute brain slices of the rat cerebral cortex, activation of GLP-1R with an agonist Exendin-4 had a strong dilatory effect on cortical arterioles and effectively reversed arteriolar constrictions induced by metabolite lactate or oxygen and glucose deprivation, as an ex vivo model of ischaemic stroke. In anaesthetised rats, Exendin-4 induced lasting increases in brain tissue PO

Topics: Animals; Arterioles; Cerebrovascular Circulation; Disease Models, Animal; Glucagon-Like Peptide-1 Receptor; Hindlimb; Incretins; Infarction, Middle Cerebral Artery; Ischemic Preconditioning; Ischemic Stroke; Male; Neuroprotective Agents; Peptide Fragments; Rats, Sprague-Dawley; Regional Blood Flow; Vasodilation; Vasodilator Agents

Glucagon-like peptide-1 (GLP-1) is a neuroendocrine hormone secreted by the intestine. Its receptor (GLP-1R) is expressed in various organs, including the heart. However, the dynamics and function of the GLP-1 signal in heart failure remains unclear. We investigated the impact of the cardio-intestinal association on hypertensive heart failure using miglitol, an α-glucosidase inhibitor known to stimulate intestinal GLP-1 production.. Dahl salt-sensitive (DS) rats fed a high-salt diet were assigned to miglitol, exendin (9-39) (GLP-1R blocker) and untreated control groups and treated for 11 weeks. Control DS rats showed marked hypertension and cardiac dysfunction with left ventricular dilatation accompanied by elevated plasma GLP-1 levels and increased cardiac GLP-1R expression as compared with age-matched Dahl salt-resistant (DR) rats. Miglitol further increased plasma GLP-1 levels, suppressed adverse cardiac remodelling, and mitigated cardiac dysfunction. In cardiomyocytes from miglitol-treated DS hearts, mitochondrial size was significantly larger with denser cristae than in cardiomyocytes from control DS hearts. The change in mitochondrial morphology reflected enhanced mitochondrial fusion mediated by protein kinase A activation leading to phosphorylation of dynamin-related protein 1, expression of mitofusin-1 and OPA-1, and increased myocardial adenosine triphosphate (ATP) content. GLP-1R blockade with exendin (9-39) exacerbated cardiac dysfunction and led to fragmented mitochondria with disarrayed cristae in cardiomyocytes and reduction of myocardial ATP content. In cultured cardiomyocytes, GLP-1 increased expression of mitochondrial fusion-related proteins and ATP content. When GLP-1 and exendin (9-39) were administered together, their effects cancelled out.. Increased intestinal GLP-1 secretion is an adaptive response to heart failure that is enhanced by miglitol. This could be an effective strategy for treating heart failure through regulation of mitochondrial dynamics.

Topics: 1-Deoxynojirimycin; Animals; Cells, Cultured; Cyclic AMP-Dependent Protein Kinases; Disease Models, Animal; Dynamins; Enteroendocrine Cells; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glycoside Hydrolase Inhibitors; GTP Phosphohydrolases; Heart Failure; Ileum; Incretins; Male; Membrane Proteins; Mitochondria, Heart; Mitochondrial Dynamics; Mitochondrial Proteins; Myocytes, Cardiac; Paracrine Communication; Peptide Fragments; Rats, Inbred Dahl; Rats, Sprague-Dawley; Signal Transduction; Sodium Chloride, Dietary; Ventricular Function, Left

Abnormal cannabidiol (Abn-CBD) and AS-1269574 are potent selective agonists for GPR55 and GPR119, respectively. The present study evaluated the actions and ability of these small-molecule agonists to counteract experimental diabetes in mice.. Diabetes was induced in NIH Swiss mice by five consecutive daily intraperitoneal injections of 40 mg/(kg body weight) streptozotocin. Diabetic mice received daily oral administration of Abn-CBD or AS-1269574 (0.1 μmol/kg) or saline vehicle (0.9% wt/vol. NaCl) over 28 days. Body weight, food intake, fluid intake, plasma glucose, insulin, glucose tolerance, insulin release, lipid profile and pancreatic morphology were examined. Mechanism of action of agonists was assessed in acute studies using incretin-receptor-knockout mice.. Abn-CBD and AS-1269574 decreased plasma glucose (20-26%, p < 0.05) and increased circulating insulin (47-48%, p < 0.05) by 10-28 days, compared with saline-treated diabetic controls. Food intake and polydipsia were reduced by both agonists (21-23%, p < 0.05 and 33-35%, p < 0.01, respectively). After 28 days of treatment, plasma glucagon concentrations were reduced (p < 0.01) and glucose tolerance was enhanced by 19-44% by Abn-CBD (p < 0.05 or p < 0.001) and AS-1269574 (p < 0.05 to p < 0.001). Plasma insulin responses were improved (p < 0.01) and insulin resistance was decreased (p < 0.05 or p < 0.01) in both Abn-CBD- and AS-1269574-treated groups. Triacylglycerols were decreased by 19% with Abn-CBD (p < 0.05) and 32% with AS-1269574 (p < 0.01) while total cholesterol was reduced by 17% (p < 0.01) and 15% (p < 0.05), respectively. Both agonists enhanced beta cell proliferation (p < 0.001) although islet area was unchanged. Acute studies in Gipr- and Glp1r-knockout mice revealed an important role for the glucagon-like peptide 1 (GLP-1) receptor in the actions of both agonists, with the glucose-lowering effects of Abn-CBD also partly mediated through the glucose-dependent insulinotropic peptide (GIP) receptor.. These data highlight the potential for fatty acid G-protein-coupled receptor-based therapies as novel insulinotropic and glucose-lowering agents acting partly through the activation of incretin receptors.

Topics: Animals; Diabetes Mellitus, Experimental; Eating; Ethanolamines; Incretins; Insulin Resistance; Insulin-Secreting Cells; Male; Mice; Mice, Knockout; Peptide Fragments; Pyrimidines; Receptors, Cannabinoid; Receptors, G-Protein-Coupled; Resorcinols; Streptozocin

Experimental evidence suggested that Exendin-4 (Exe4), an agonist at glucagon like receptor-1 (GLP-1R), promoted tissue regeneration. We aimed to verify the effect of Exe4, in the absence or in the presence of Exendin-4(9-39), an antagonist at GLP-1R, on the healing of abraded skin. Two wounds (approximately 1.1×1.1 cm(2); namely "upper" and "lower" in respect of the head) were produced by abrasion on the back of 12 mice, which were then randomly assigned to receive an intradermal injection (20 μl) of Group 1: saline (NT) or Exe4 (62 ng) in the upper and lower wound respectively; Group 2: Exendin-4(9-39) (70 ng) in the upper and Exendin-4(9-39) (70 ng) and, after 15 min, Exe4 (62 ng) in the lower wound. Wounds were measured at the time of abrasion (T0) and 144 h (T3) afterward taking pictures with a ruler and by using a software. The inflammatory cell infiltrate, fibroblasts/myofibroblasts, endothelial cells and GLP-1R expression, were each labeled by immunofluorescence in each wound, pERK1/2 was evaluated by Western-blot in wound lysates. At T3, the percentage of healing surface was 53% and 92% for NT and Exe4 wounds respectively and 68% and 79% for those treated with Exendin-4(9-39) and Exendin-4(9-39)+Exe4 respectively. Exe4, but not Exendin-4(9-39) induced quantitative increase in fibroblasts/myofibroblasts and vessel density when compared to NT wounds. This increase was not evident in wounds treated with Exendin-4(9-39)+Exe4. Exe4 promotes wound healing opening to the possible dermatological use of this incretin analogue.

Topics: Animals; Cell Proliferation; Cell Transdifferentiation; Dermatologic Agents; Disease Models, Animal; Endothelial Cells; Enzyme Activation; Exenatide; Fibroblasts; Glucagon-Like Peptide-1 Receptor; Incretins; Male; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Myofibroblasts; Peptide Fragments; Peptides; Phosphorylation; Skin; Time Factors; Venoms; Wound Healing; Wounds and Injuries

Circadian clocks in peripheral tissues are powerfully entrained by feeding. The mechanisms underlying this food entrainment remain unclear, although various humoral and neural factors have been reported to affect peripheral clocks. Because glucagon-like peptide-1 (GLP-1), which is rapidly secreted in response to food ingestion, influences multiple humoral and neural signaling pathways, we suggest that GLP-1 plays a role in the food entrainment of peripheral clocks. To test this, we compared the effects of exendin-4, a GLP-1 receptor agonist, on mRNA expression of the clock genes (Clock, Bmal1, Nr1d1, Per1, Per2, and Cry1) with those of refeeding. In addition, we investigated whether exendin-4 could affect the rhythms of the peripheral clocks. In male C57BL/6J mice, although refeeding rapidly (within 2 h) altered mRNA levels of Per1 and Per2 in the liver and that of Per1 in adipose tissue, a single i.p. injection of exendin-4 did not cause such changes. However, unlike the GLP-1 receptor antagonist exendin-(9-39), exendin-4 significantly influenced Per1 mRNA levels in the liver at 12 h after injection. Moreover, pretreatment with exendin-4 affected the rapid-feeding-induced change in Per1 not only in the liver, but also in adipose tissue, without effect on food intake. Furthermore, during light-phase restricted feeding, repeated dosing of exendin-4 at the beginning of the dark phase profoundly influenced both the food intake and daily rhythms of clock gene expression in peripheral tissues. Thus, these results suggest that exendin-4 modulates peripheral clocks via multiple mechanisms different from those of refeeding.

Topics: Adipose Tissue; Animals; Circadian Clocks; Circadian Rhythm; CLOCK Proteins; Eating; Exenatide; Gene Expression Regulation; Glucagon-Like Peptide 1; Incretins; Liver; Male; Mice; Mice, Inbred C57BL; Peptide Fragments; Peptides; RNA, Messenger; Signal Transduction; Venoms

Glucagon-like peptide-1 (GLP-1) circulates at low levels and acts as an incretin hormone, potentiating glucose-dependent insulin secretion from islet β cells. GLP-1 also modulates gastric emptying and engages neural circuits in the portal region and CNS that contribute to GLP-1 receptor-dependent (GLP-1R-dependent) regulation of glucose homeostasis. To elucidate the importance of pancreatic GLP-1R signaling for glucose homeostasis, we generated transgenic mice that expressed the human GLP-1R in islets and pancreatic ductal cells (Pdx1-hGLP1R:Glp1r-/- mice). Transgene expression restored GLP-1R-dependent stimulation of cAMP and Akt phosphorylation in isolated islets, conferred GLP-1R-dependent stimulation of β cell proliferation, and was sufficient for restoration of GLP-1-stimulated insulin secretion in perifused islets. Systemic GLP-1R activation with the GLP-1R agonist exendin-4 had no effect on food intake, hindbrain c-fos expression, or gastric emptying but improved glucose tolerance and stimulated insulin secretion in Pdx1-hGLP1R:Glp1r-/- mice. i.c.v. GLP-1R blockade with the antagonist exendin(9-39) impaired glucose tolerance in WT mice but had no effect in Pdx1-hGLP1R:Glp1r-/- mice. Nevertheless, transgenic expression of the pancreatic GLP-1R was sufficient to normalize both oral and i.p. glucose tolerance in Glp1r-/- mice. These findings illustrate that low levels of endogenous GLP-1 secreted from gut endocrine cells are capable of augmenting glucoregulatory activity via pancreatic GLP-1Rs independent of communication with neural pathways.

Topics: Animals; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucose; Glucose Tolerance Test; Homeostasis; Humans; Incretins; Insulin; Insulin Secretion; Insulin-Secreting Cells; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Neurosecretory Systems; Pancreas; Peptide Fragments; Receptors, Glucagon; Recombinant Proteins; Signal Transduction

Topics: Diabetes Mellitus, Type 2; Female; Glucose; Humans; Incretins; Insulin; Insulin Secretion; Male; Peptide Fragments

Several lines of evidence suggest that incretin-based therapies suppress the development of cardiovascular disease in type 2 diabetes. We investigated the possibility that glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) can prevent the development of atherosclerosis in Apoe (-/-) mice.. Apoe (-/-) mice (17 weeks old) were administered GLP-1(7-36)amide, GLP-1(9-36)amide, GIP(1-42) or GIP(3-42) for 4 weeks. Aortic atherosclerosis, oxidised LDL-induced foam cell formation and related gene expression in exudate peritoneal macrophages were determined.. Administration of GLP-1(7-36)amide or GIP(1-42) significantly suppressed atherosclerotic lesions and macrophage infiltration in the aortic wall, compared with vehicle controls. These effects were cancelled by co-infusion with specific antagonists for GLP-1 and GIP receptors, namely exendin(9-39) or Pro(3)(GIP). The anti-atherosclerotic effects of GLP-1(7-36)amide and GIP(1-42) were associated with significant decreases in foam cell formation and downregulation of CD36 and acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) in macrophages. GLP-1 and GIP receptors were both detected in Apoe (-/-) mouse macrophages. Ex vivo incubation of macrophages with GLP-1(7-36)amide or GIP(1-42) for 48 h significantly suppressed foam cell formation. This effect was wholly abolished in macrophages pretreated with exendin(9-39) or (Pro(3))GIP, or with an adenylate cyclase inhibitor, MDL12,330A, and was mimicked by incubation with an adenylate cyclase activator, forskolin. The inactive forms, GLP-1(9-36)amide and GIP(3-42), had no effects on atherosclerosis and macrophage foam cell formation.. Our study is the first to demonstrate that active forms of GLP-1 and GIP exert anti-atherogenic effects by suppressing macrophage foam cell formation via their own receptors, followed by cAMP activation. Molecular mechanisms underlying these effects are associated with the downregulation of CD36 and ACAT-1 by incretins.

Topics: Acetyl-CoA C-Acetyltransferase; Animals; Apolipoproteins E; Atherosclerosis; Blotting, Western; CD36 Antigens; Cell Line; Cells, Cultured; Foam Cells; Gastric Inhibitory Polypeptide; Glucagon-Like Peptide 1; Humans; Incretins; Male; Mice; Mice, Knockout; Microscopy, Confocal; Peptide Fragments; Peptides; Real-Time Polymerase Chain Reaction

Intracerebroventricular (i.c.v.) glucagon-like peptide-1 (GLP-1) has been shown to prevent gastric mucosal lesions induced by reserpine and ethanol. Here, we aimed to investigate the effects of i.c.v. GLP-1 on stress-induced gastric mucosal lesions and the mechanisms which may mediate these effects.. Rats were equipped with intravenous and i.c.v. cannulas under ether anesthesia. To induce cold-restraint stress, rats were kept individually in wire cages, specifically prepared according to their sizes, at 7-9 degrees C for 5 hours. They were then decapitated, and their stomachs were removed and scored for mucosal damage. GLP-1 (1, 10, 100, 1000 ng/10 microl; i.c.v.) was injected 5 min before cold-restraint stress induction. Rats were pretreated with exendin-(9-39) (2.5 ng/10 microl; i.c.v. and 250 ng/kg; intraperitoneal [i.p.]), calcitonin gene-related peptide (CGRP)-(8-37) (10 microg/kg; i.p.), N(G)-nitro-L-arginine methyl ester (L-NAME) (3 mg/kg; i.v.), indomethacin (5 mg/kg; i.p.) and atropine (1 mg/kg; i.p.) to investigate mechanisms which may mediate the gastroprotective effect of GLP-1.. GLP-1 (1000 ng/10 microl; i.c.v.) significantly prevented gastric mucosal lesions induced by cold-restraint stress (p<0.01). Intracerebroventricular (i.c.v.), but not i.p., injection of exendin-(9-39) significantly blocked the gastroprotective effect of the peptide (p<0.05). Pretreatment with CGRP-(8-37), L-NAME and indomethacin also prevented the gastroprotective effect of i.c.v. GLP-1 (p<0.05, p<0.05 and p<0.01, respectively), while pretreatment with atropine did not prevent the gastroprotective effect of the peptide.. We conclude that i.c.v GLP-1 inhibits the gastric mucosal damage induced by cold-restraint stress via the activation of its specific receptors, and CGRP, nitric oxide and prostaglandins, but not cholinergic muscarinic receptors, mediate this effect.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Atropine; Calcitonin Gene-Related Peptide; Cold Temperature; Enzyme Inhibitors; Gastric Mucosa; Glucagon-Like Peptide 1; Incretins; Indomethacin; Injections; Male; NG-Nitroarginine Methyl Ester; Parasympatholytics; Peptide Fragments; Rats; Rats, Wistar; Restraint, Physical; Stress, Physiological