exendin-(9-39) and Obesity

GLP-1 secretion in response to meals is dramatically increased after gastric bypass operations. GLP-1 is a powerful insulinotropic and anorectic hormone, and analogs of GLP-1 are widely used for the treatment of diabetes and recently approved also for obesity treatment. It is, therefore, reasonable to assume that the exaggerated GLP-1 secretion contributes to the antidiabetic and anorectic effects of gastric bypass. Indeed, human experiments with the GLP-1 receptor antagonist, Exendin 9-39, have shown that the improved insulin secretion, which is responsible for part of the antidiabetic effect of the operation, is reduced and or abolished after GLP-1 receptor blockade. Also the postoperative improvement of glucose tolerance is eliminated and or reduced by the antagonist, pointing to a key role for the exaggerated GLP-1 secretion. Indeed, there is evidence that the exaggerated GLP-1 secretion is also responsible for postprandial hypoglycemia sometimes observed after bypass. Other operations (biliopancreatic-diversion and or sleeve gastrectomy) appear to involve different and/or additional mechanisms, and so does experimental bariatric surgery in rodents. However, unlike bypass surgery in humans, the rodent operations are generally associated with increased energy metabolism pointing to an entirely different mechanism of action in the animals.

Topics: Animals; Bile Acids and Salts; Diabetes Mellitus, Type 2; Disease Models, Animal; Gastric Bypass; Gastrointestinal Hormones; Glucagon-Like Peptide 1; Glucagon-Like Peptide 2; Humans; Insulin; Insulin Secretion; Intestinal Absorption; Mice; Obesity; Peptide Fragments; Remission Induction

Bariatric surgery is widely used to treat obesity and improves type 2 diabetes beyond expectations from the degree of weight loss. Elevated post-prandial concentrations of glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and insulin are widely reported, but the importance of GLP-1 in post-bariatric physiology remains debated. Here, we show that GLP-1 is a major driver of insulin secretion after bariatric surgery, as demonstrated by blocking GLP-1 receptors (GLP1Rs) post-gastrectomy in lean humans using Exendin-9 or in mice using an anti-GLP1R antibody. Transcriptomics and peptidomics analyses revealed that human and mouse enteroendocrine cells were unaltered post-surgery; instead, we found that elevated plasma GLP-1 and PYY correlated with increased nutrient delivery to the distal gut in mice. We conclude that increased GLP-1 secretion after bariatric surgery arises from rapid nutrient delivery to the distal gut and is a key driver of enhanced insulin secretion.

Topics: Adult; Animals; Bariatric Surgery; Enteroendocrine Cells; Female; Glucagon-Like Peptide 1; Glucose; Homeostasis; Humans; Hypoglycemic Agents; Insulin Secretion; Intestinal Mucosa; Male; Mice; Mice, Inbred C57BL; Middle Aged; Obesity; Peptide Fragments; Peptide YY; Postoperative Period; Transcriptome

Exaggerated secretion of glucagon-like peptide 1 (GLP-1) is important for postprandial glucose tolerance after Roux-en-Y gastric bypass (RYGB), whereas the role of glucose-dependent insulinotropic polypeptide (GIP) remains to be resolved. We aimed to explore the relative importance of endogenously secreted GLP-1 and GIP on glucose tolerance and β-cell function after RYGB. We used DPP-4 inhibition to enhance concentrations of intact GIP and GLP-1 and the GLP-1 receptor antagonist exendin-(9-39) (Ex-9) for specific blockage of GLP-1 actions. Twelve glucose-tolerant patients were studied after RYGB in a randomized, placebo-controlled, 4-day crossover study with standard mixed-meal tests and concurrent administration of placebo, oral sitagliptin, Ex-9 infusion, or combined Ex-9-sitagliptin. GLP-1 receptor antagonism increased glucose excursions, clearly attenuated β-cell function, and aggravated postprandial hyperglucagonemia compared with placebo, whereas sitagliptin had no effect despite two- to threefold increased concentrations of intact GLP-1 and GIP. Similarly, sitagliptin did not affect glucose tolerance or β-cell function during GLP-1R blockage. This study confirms the importance of GLP-1 for glucose tolerance after RYGB via increased insulin and attenuated glucagon secretion in the postprandial state, whereas amplification of the GIP signal (or other DPP-4-sensitive glucose-lowering mechanisms) did not appear to contribute to the improved glucose tolerance seen after RYGB.

Topics: Adult; Blood Glucose; C-Peptide; Cross-Over Studies; Enzyme-Linked Immunosorbent Assay; Female; Gastric Bypass; Gastric Inhibitory Polypeptide; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucose Tolerance Test; Humans; Hypoglycemic Agents; Linear Models; Male; Obesity; Peptide Fragments; Postprandial Period; Single-Blind Method; Sitagliptin Phosphate

To test the hypothesis that food intake reduction after glucagon-like peptide-1 (GLP-1) receptor activation is mediated through brain areas regulating anticipatory and consummatory food reward.. As part of a larger study, we determined the effects of GLP-1 receptor activation on brain responses to anticipation and receipt of chocolate milk versus a tasteless solution, using functional MRI (fMRI). Obese subjects with type 2 diabetes, and obese and lean subjects with normoglycaemia (n = 48) underwent three fMRI sessions at separate visits with intravenous infusion of the GLP-1 receptor agonist exenatide, exenatide with prior GLP-1 receptor blockade by exendin-9-39 or placebo, during somatostatin pituitary-pancreatic clamps.. Body mass index negatively correlated with brain responses to receipt of chocolate milk and positively correlated with anticipation of receipt of chocolate milk in brain areas regulating reward, appetite and motivation. Exenatide increased brain responses to receipt of chocolate milk and decreased anticipation of receipt of chocolate milk compared with placebo, paralleled by reductions in food intake. Exendin-9-39 largely prevented these effects.. Our findings show that GLP-1 receptor activation decreases anticipatory food reward, which may reduce cravings for food and increases consummatory food reward, which may prevent overeating.

Topics: Adult; Aged; Animals; Anticipation, Psychological; Appetite; Brain; Cacao; Diabetes Mellitus, Type 2; Exenatide; Feeding Behavior; Female; Glucagon-Like Peptide-1 Receptor; Humans; Hypoglycemic Agents; Magnetic Resonance Imaging; Male; Middle Aged; Milk; Motivation; Obesity; Peptide Fragments; Peptides; Reward; Venoms

Gut-derived hormones, such as GLP-1, have been proposed to relay information to the brain to regulate appetite. GLP-1 receptor agonists, currently used for the treatment of type 2 diabetes (T2DM), improve glycemic control and stimulate satiety, leading to decreases in food intake and body weight. We hypothesized that food intake reduction after GLP-1 receptor activation is mediated through appetite- and reward-related brain areas. Obese T2DM patients and normoglycemic obese and lean individuals (n = 48) were studied in a randomized, crossover, placebo-controlled trial. Using functional MRI, we determined the acute effects of intravenous administration of the GLP-1 receptor agonist exenatide, with or without prior GLP-1 receptor blockade using exendin 9-39, on brain responses to food pictures during a somatostatin pancreatic-pituitary clamp. Obese T2DM patients and normoglycemic obese versus lean subjects showed increased brain responses to food pictures in appetite- and reward-related brain regions (insula and amygdala). Exenatide versus placebo decreased food intake and food-related brain responses in T2DM patients and obese subjects (in insula, amygdala, putamen, and orbitofrontal cortex). These effects were largely blocked by prior GLP-1 receptor blockade using exendin 9-39. Our findings provide novel insights into the mechanisms by which GLP-1 regulates food intake and how GLP-1 receptor agonists cause weight loss.

Topics: Adult; Aged; Amygdala; Appetite; Brain; Case-Control Studies; Cerebral Cortex; Cross-Over Studies; Diabetes Mellitus, Type 2; Exenatide; Feeding Behavior; Female; Functional Neuroimaging; Glucagon-Like Peptide-1 Receptor; Humans; Hypoglycemic Agents; Magnetic Resonance Imaging; Male; Middle Aged; Obesity; Peptide Fragments; Peptides; Photic Stimulation; Prefrontal Cortex; Putamen; Receptors, Glucagon; Reward; Venoms

Topics: Adult; Bariatric Surgery; Body Composition; Case-Control Studies; Female; Gastrectomy; Gastric Bypass; Gastric Emptying; Gastrointestinal Hormones; Glucagon-Like Peptide-1 Receptor; Humans; Insulin; Male; Middle Aged; Obesity; Peptide Fragments; Pilot Projects; Postprandial Period; Weight Loss

Glucagon-like peptide-1 (GLP1) affects appetite, supposedly mediated via the central nervous system (CNS). In this study, we investigate whether modulation of CNS responses to palatable food consumption may be a mechanism by which GLP1 contributes to the central regulation of feeding. Using functional MRI, we determined the effects of endogenous GLP1 and treatment with the GLP1 analogue liraglutide on CNS activation to chocolate milk receipt. Study 1 included 20 healthy lean individuals and 20 obese patients with type 2 diabetes (T2DM). Scans were performed on two occasions: during infusion of the GLP1 receptor antagonist exendin 9-39 (blocking actions of endogenous GLP1) and during placebo infusion. Study 2 was a randomised, cross-over intervention study carried out in 20 T2DM patients, comparing treatment with liraglutide to insulin, after 10 days and 12 weeks. Compared with lean individuals, T2DM patients showed reduced activation to chocolate milk in right insula (P = 0.04). In lean individuals, blockade of endogenous GLP1 effects inhibited activation in bilateral insula (P ≤ 0.03). Treatment in T2DM with liraglutide, vs insulin, increased activation to chocolate milk in right insula and caudate nucleus after 10 days (P ≤ 0.03); however, these effects ceased to be significant after 12 weeks. Our findings in healthy lean individuals indicate that endogenous GLP1 is involved in the central regulation of feeding by affecting central responsiveness to palatable food consumption. In obese T2DM, treatment with liraglutide may improve the observed deficit in responsiveness to palatable food, which may contribute to the induction of weight loss observed during treatment. However, no long-term effects of liraglutide were observed.

Topics: Appetite; Blood Glucose; Case-Control Studies; Central Nervous System; Diabetes Mellitus, Type 2; Eating; Female; Glucagon-Like Peptide 1; Humans; Liraglutide; Magnetic Resonance Imaging; Male; Middle Aged; Obesity; Peptide Fragments

Roux-en-Y gastric bypass (RYGB) causes profound weight loss and remission of diabetes by influencing metabolic physiology, yet the mechanisms behind these clinical improvements remain undefined. After RYGB, levels of glucagon-like peptide-1 (GLP-1), a hormone that enhances insulin secretion and promotes satiation, are substantially elevated. Because GLP-1 signals in both the periphery and the brain to influence energy balance and glucose regulation, we aimed to determine the relative requirements of these systems to weight loss and improved glucose tolerance following RYGB surgery in mice. By pharmacologically blocking peripheral or central GLP-1R signaling, we examined whether GLP-1 action is necessary for the metabolic improvements observed after RYGB. Diet-induced obese mice underwent RYGB or sham operation and were implanted with osmotic pumps delivering the GLP-1R antagonist exendin-(9-39) (2 pmol·kg(-1)·min(-1) peripherally; 0.5 pmol·kg(-1)·min(-1) centrally) for up to 10 wk. Blockade of peripheral GLP-1R signaling partially reversed the improvement in glucose tolerance after RYGB. In contrast, fasting glucose and insulin sensitivity, as well as body weight, were unaffected by GLP-1R antagonism. Central GLP-1R signaling did not appear to be required for any of the metabolic improvements seen after this operation. Collectively, these results suggest a detectable but only modest role for GLP-1 in mediating the effects of RYGB and that this role is limited to its well-described action on glucose regulation.

Topics: Animals; Blood Glucose; Body Weight; Diet, High-Fat; Energy Metabolism; Gastric Bypass; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucose Tolerance Test; Insulin; Insulin Resistance; Male; Mice; Obesity; Peptide Fragments; Signal Transduction

Glucose homeostasis depends on the coordinated secretion of glucagon, insulin, and Glucagon-like peptide (GLP)-1 by pancreas and intestine. Obesity, which is associated with an increased risk of developing insulin resistance and type 2 diabetes, affects the function of these organs. Here, we investigate the functional and molecular adaptations of proglucagon-producing cells in obese mice to better define their involvement in type 2 diabetes development. We used GLU-Venus transgenic male mice specifically expressing Venus fluorochrome in proglucagon-producing cells. Mice were subjected to 16 weeks of low-fat diet or high-fat diet (HFD) and then subdivided by measuring glycated hemoglobin (HbA1c) in 3 groups: low-fat diet mice and I-HFD (glucose-intolerant) mice with similar HbA1c and H-HFD (hyperglycemic) mice, which exhibited higher HbA1c. At 16 weeks, both HFD groups exhibited similar weight gain, hyperinsulinemia, and insulin resistance. However, I-HFD mice exhibited better glucose tolerance compared with H-HFD mice. I-HFD mice displayed functional and molecular adaptations of enteroendocrine L-cells resulting in increased intestinal GLP-1 biosynthesis and release as well as maintained pancreatic α- and β-cell functions. By contrast, H-HFD mice exhibited dysfunctional L, α- and β-cells with increased β- and L-cell numbers. Administration of the GLP-1R antagonist Exendin9-39 in I-HFD mice led to hyperglycemia and alterations of glucagon secretion without changes in insulin secretion. Our results highlight the cross-talk between islet and intestine endocrine cells and indicate that a compensatory adaptation of L-cell function in obesity plays an important role in preserving glucose homeostasis through the control of pancreatic α-cell functions.

Topics: Animals; Diabetes Mellitus, Type 2; Diet, High-Fat; Enteroendocrine Cells; Glucagon; Glucagon-Like Peptide 1; Glucagon-Secreting Cells; Hyperglycemia; Insulin-Secreting Cells; Male; Mice, Inbred C57BL; Mice, Transgenic; Obesity; Peptide Fragments; Phenotype

The central nervous system (CNS) is a major player in the regulation of food intake. The gut hormone glucagon-like peptide-1 (GLP-1) has been proposed to have an important role in this regulation by relaying information about nutritional status to the CNS. We hypothesised that endogenous GLP-1 has effects on CNS reward and satiety circuits.. This was a randomised, crossover, placebo-controlled intervention study, performed in a university medical centre in the Netherlands. We included patients with type 2 diabetes and healthy lean control subjects. Individuals were eligible if they were 40-65 years. Inclusion criteria for the healthy lean individuals included a BMI <25 kg/m(2) and normoglycaemia. Inclusion criteria for the patients with type 2 diabetes included BMI >26 kg/m(2), HbA1c levels between 42 and 69 mmol/mol (6.0-8.5%) and treatment for diabetes with only oral glucose-lowering agents. We assessed CNS activation, defined as blood oxygen level dependent (BOLD) signal, in response to food pictures in obese patients with type 2 diabetes (n = 20) and healthy lean individuals (n = 20) using functional magnetic resonance imaging (fMRI). fMRI was performed in the fasted state and after meal intake on two occasions, once during infusion of the GLP-1 receptor antagonist exendin 9-39, which was administered to block actions of endogenous GLP-1, and on the other occasion during saline (placebo) infusion. Participants were blinded for the type of infusion. The order of infusion was determined by block randomisation. The primary outcome was the difference in BOLD signal, i.e. in CNS activation, in predefined regions in the CNS in response to viewing food pictures.. All patients were included in the analyses. Patients with type 2 diabetes showed increased CNS activation in CNS areas involved in the regulation of feeding (insula, amygdala and orbitofrontal cortex) in response to food pictures compared with lean individuals (p ≤ 0.04). Meal intake reduced activation in the insula in response to food pictures in both groups (p ≤ 0.05), but this was more pronounced in patients with type 2 diabetes. Blocking actions of endogenous GLP-1 significantly prevented meal-induced reductions in bilateral insula activation in response to food pictures in patients with type 2 diabetes (p ≤ 0.03).. Our findings support the hypothesis that endogenous GLP-1 is involved in postprandial satiating effects in the CNS of obese patients with type 2 diabetes.. ClinicalTrials.gov NCT 01363609. Funding The study was funded in part by a grant from Novo Nordisk.

Topics: Adult; Aged; Cross-Over Studies; Diabetes Mellitus, Type 2; Female; Food; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glycated Hemoglobin; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Obesity; Oxygen; Peptide Fragments; Photic Stimulation; Postprandial Period; Reward; Satiety Response

Exaggerated GLP-1 and PYY secretion is thought to be a major mechanism in the reduced food intake and body weight after Roux-en-Y gastric bypass surgery. Here, we use complementary pharmacological and genetic loss-of-function approaches to test the role of increased signaling by these gut hormones in high-fat diet-induced obese rodents. Chronic brain infusion of a supramaximal dose of the selective GLP-1 receptor antagonist exendin-9-39 into the lateral cerebral ventricle significantly increased food intake and body weight in both RYGB and sham-operated rats, suggesting that, while contributing to the physiological control of food intake and body weight, central GLP-1 receptor signaling tone is not the critical mechanism uniquely responsible for the body weight-lowering effects of RYGB. Central infusion of the selective Y2R-antagonist BIIE0246 had no effect in either group, suggesting that it is not critical for the effects of RYGB on body weight under the conditions tested. In a recently established mouse model of RYGB that closely mimics surgery and weight loss dynamics in humans, obese GLP-1R-deficient mice lost the same amount of body weight and fat mass and maintained similarly lower body weight compared with wild-type mice. Together, the results surprisingly provide no support for important individual roles of either gut hormone in the specific mechanisms by which RYGB rats settle at a lower body weight. It is likely that the beneficial effects of bariatric surgeries are expressed through complex mechanisms that require combination approaches for their identification.

Topics: Animals; Arginine; Benzazepines; Body Composition; Body Weight; Dietary Fats; Eating; Energy Metabolism; Gastric Bypass; Glucagon-Like Peptide-1 Receptor; Male; Mice; Mice, Knockout; Motor Activity; Obesity; Oxygen Consumption; Peptide Fragments; Rats; Rats, Sprague-Dawley; Receptors, Glucagon; Weight Loss

We investigated the potential anorectic action of peripherally administered glucagon-like peptide 2 (GLP2) in lean and diet-induced obese (DIO) mice. Mice, fasted for 16 h, were injected i.p. with native GLP2 or [Gly2]GLP2, stable analog of GLP2, before or after GLP2 (3-33), a GLP2 receptor (GLP2R) antagonist, or exendin (9-39), a GLP1R antagonist. Food intake was measured at intervals 1, 2, 4, 8, and 24 h postinjection. In addition, we tested in lean mice the influence of [Gly2]GLP2 on gastric emptying and the effects of GLP1 alone or in combination with [Gly2]GLP2 on food intake. [Gly2]GLP2 dose dependently and significantly inhibited food intake in lean and DIO mice. The reduction of food intake occurred in the first hour postinjection and it was sustained until 4 h postinjection in lean mice while it was sustained until 2 h postinjection in DIO mice. GLP2 significantly inhibited food intake in both lean and DIO mice but only in the first hour postinjection. The efficiency of [Gly2]GLP2 or GLP2 in suppressing food intake was significantly weaker in DIO mice compared with lean animals. The [Gly2]GLP2 anorectic actions were blocked by the GLP2R antagonist GLP2 (3-33) or by the GLP1R antagonist exendin (9-39). The coadministration of [Gly2]GLP2 and GLP1 did not cause additive effects. [Gly2]GLP2 decreased the gastric emptying rate. Results suggest that GLP2 can reduce food intake in mice in the short term, likely acting at a peripheral level. DIO mice are less sensitive to the anorectic effect of the peptide.

Topics: Animals; Appetite Depressants; Diet, High-Fat; Dose-Response Relationship, Drug; Eating; Gastric Emptying; Glucagon-Like Peptide 1; Glucagon-Like Peptide 2; Glucagon-Like Peptide-1 Receptor; Glucagon-Like Peptide-2 Receptor; Male; Mice; Mice, Inbred C57BL; Obesity; Peptide Fragments; Receptor Cross-Talk; Receptors, Glucagon; Time Factors

Central administration of glucagon-like peptide-1 (GLP-1) causes a dose-dependent reduction in food intake, but the role of endogenous CNS GLP-1 in the regulation of energy balance remains unclear. Here, we tested the hypothesis that CNS GLP-1 activity is required for normal energy balance by using two independent methods to achieve chronic CNS GLP-1 loss of function in rats. Specifically, lentiviral-mediated expression of RNA interference was used to knock down nucleus of the solitary tract (NTS) preproglucagon (PPG), and chronic intracerebroventricular (ICV) infusion of the GLP-1 receptor (GLP-1r) antagonist exendin (9-39) (Ex9) was used to block CNS GLP-1r. NTS PPG knockdown caused hyperphagia and exacerbated high-fat diet (HFD)-induced fat accumulation and glucose intolerance. Moreover, in control virus-treated rats fed the HFD, NTS PPG expression levels correlated positively with fat mass. Chronic ICV Ex9 also caused hyperphagia; however, increased fat accumulation and glucose intolerance occurred regardless of diet. Collectively, these data provide the strongest evidence to date that CNS GLP-1 plays a physiologic role in the long-term regulation of energy balance. Moreover, they suggest that this role is distinct from that of circulating GLP-1 as a short-term satiation signal. Therefore, it may be possible to tailor GLP-1-based therapies for the prevention and/or treatment of obesity.

Topics: Adiposity; Analysis of Variance; Animals; Dietary Fats; Energy Metabolism; Feeding Behavior; Fluorescent Antibody Technique; Glucagon-Like Peptide 1; Glucose Intolerance; Hyperphagia; In Situ Hybridization; Injections, Intraventricular; Islets of Langerhans; Male; Motor Activity; Obesity; Peptide Fragments; Proglucagon; Rats; Rats, Long-Evans; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; RNA, Messenger; Tissue Culture Techniques

Glucagon-like peptide-1 (GLP-1) (7-36) amide is a glucoregulatory hormone with insulinotropic and insulinomimetic actions. We determined whether the insulinomimetic effects of GLP-1 are mediated through its principal metabolite, GLP-1 (9-36) amide (GLP-1m).. Glucose turnover during two, 2-h, euglycemic clamps was measured in 12 lean and 12 obese (BMI <25 or >30 kg/m(2)) male and female subject volunteers with normal oral glucose tolerance test. Saline or GLP-1m were infused from 0 to 60 min in each study. Additionally, seven lean and six obese subjects underwent a third clamp in which the GLP-1 receptor (GLP-1R) antagonist, exendin (9-39) amide was infused from -60 to 60 min with GLP-1m from 0 to 60 min.. No glucose infusion was required in lean subjects to sustain euglycemia (glucose clamp) during saline or GLP-1m infusions. However, in obese subjects glucose infusion was necessary during GLP-1m infusion alone in order to compensate for a marked (>50%) inhibition of hepatic glucose production (HGP). Plasma insulin levels remained constant in lean subjects but rose significantly in obese subjects after termination of the peptide infusions. During GLP-1R blockade, infusion of glucose was immediately required upon starting GLP-1m infusions in all subjects due to a more dramatic reduction in HGP, as well as a delayed and modest insulinotropic response.. We conclude that GLP-1m potently inhibits HGP and is a weak insulinotropic agent. These properties are particularly apparent and pronounced in obese but only become apparent in lean subjects during GLP-1 (7-36) receptor blockade. These previously unrecognized antidiabetogenic actions of GLP-1m may have therapeutic usefulness.

Topics: Adult; Blood Glucose; Female; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucose Clamp Technique; Glucose Tolerance Test; Humans; Hypoglycemic Agents; Infusions, Parenteral; Insulin; Liver; Male; Middle Aged; Obesity; Peptide Fragments; Peptides; Receptors, Glucagon; Time Factors

Effects of chemical ablation of the GIP and GLP-1 receptors on metabolic aspects of obesity-diabetes were investigated using the stable receptor antagonists (Pro3)GIP and exendin(9-39)amide. Ob/ob mice received a daily i.p. injection of saline vehicle, (Pro3)GIP, exendin(9-39)amide or a combination of both peptides over a 14-day period. Non-fasting plasma glucose levels were significantly (p<0.05) lower in (Pro3)GIP-treated mice compared to control mice after just 9 days of treatment. (Pro3)GIP-treated mice also displayed significantly lower plasma glucose concentrations in response to feeding and intraperitoneal administration of either glucose or insulin (p<0.05 to p<0.001). The (Pro3)GIP-treated group also exhibited significantly (p<0.05) reduced pancreatic insulin content. Acute administration of exendin(9-39)amide immediately prior to re-feeding completely annulled the beneficial effects of sub-chronic (Pro3)GIP treatment, but non-fasting concentrations of active GLP-1 were unchanged. Combined sub-chronic administration of (Pro3GIP) with exendin(9-39)amide revealed no beneficial effects. Similarly, daily administration of exendin(9-39)amide alone had no significant effects on any of the metabolic parameters measured. These studies highlight an important role for GIP in obesity-related forms of diabetes, suggesting the possible involvement of GLP-1 in the beneficial actions of GIP receptor antagonism.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Disease Models, Animal; Dose-Response Relationship, Drug; Gastric Inhibitory Polypeptide; Glucagon-Like Peptide-1 Receptor; Injections, Intraperitoneal; Insulin; Mice; Mice, Obese; Obesity; Peptide Fragments; Receptors, Gastrointestinal Hormone; Receptors, Glucagon; Structure-Activity Relationship; Time Factors

Type 2 diabetes is characterized by reduced insulin secretion from the pancreas and overproduction of glucose by the liver. Glucagon-like peptide-1 (GLP-1) promotes glucose-dependent insulin secretion from the pancreas, while glucagon promotes glucose output from the liver. Taking advantage of the homology between GLP-1 and glucagon, a GLP-1/glucagon hybrid peptide, dual-acting peptide for diabetes (DAPD), was identified with combined GLP-1 receptor agonist and glucagon receptor antagonist activity. To overcome its short plasma half-life DAPD was PEGylated, resulting in dramatically prolonged activity in vivo. PEGylated DAPD (PEG-DAPD) increases insulin and decreases glucose in a glucose tolerance test, evidence of GLP-1 receptor agonism. It also reduces blood glucose following a glucagon challenge and elevates fasting glucagon levels in mice, evidence of glucagon receptor antagonism. The PEG-DAPD effects on glucose tolerance are also observed in the presence of the GLP-1 antagonist peptide, exendin(9-39). An antidiabetic effect of PEG-DAPD is observed in db/db mice. Furthermore, PEGylation of DAPD eliminates the inhibition of gastrointestinal motility observed with GLP-1 and its analogues. Thus, PEG-DAPD has the potential to be developed as a novel dual-acting peptide to treat type 2 diabetes, with prolonged in vivo activity, and without the GI side-effects.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Female; Gastrointestinal Motility; Glucagon; Glucagon-Like Peptide-1 Receptor; Glucose Tolerance Test; Insulin; Intercellular Signaling Peptides and Proteins; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Mutant Strains; Obesity; Peptide Fragments; Peptides; Polyethylene Glycols; Rats; Rats, Wistar; Receptors, Glucagon

Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic hormone proposed to play a role in both the pathophysiology and treatment of type 2 diabetes. This study has employed the GLP-1 receptor antagonist, exendin-4(9-39)amide (Ex(9-39)) to evaluate the role of endogenous GLP-1 in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob and normal mice. Acute in vivo antagonistic potency of Ex(9-39) was confirmed in ob/ob mice by blockade of the insulin-releasing and anti-hyperglycaemic actions of intraperitoneal GLP-1. In longer term studies, ob/ob mice were given once daily injections of Ex(9-39) or vehicle for 11 days. Feeding activity, body weight, and both basal and glucose-stimulated insulin secretion were not significantly affected by chronic Ex(9-39) treatment. However, significantly elevated basal glucose concentrations and impaired glucose tolerance were evident at 11 days. These disturbances in glucose homeostasis were independent of changes of insulin sensitivity and reversed by discontinuation of the Ex(9-39) for 9 days. Similar treatment of normal mice did not affect any of the parameters measured. These findings illustrate the physiological extrapancreatic glucose-lowering actions of GLP-1 in ob/ob mice and suggest that the endogenous hormone plays a minor role in the metabolic abnormalities associated with obesity-related diabetes.

Topics: Animals; Blood Glucose; Diabetes Mellitus, Type 2; Female; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucose Tolerance Test; Insulin; Male; Mice; Mice, Obese; Obesity; Peptide Fragments; Protein Precursors; Receptors, Glucagon; Time Factors

This study examined the biological effects of the GIP receptor antagonist, (Pro3)GIP and the GLP-1 receptor antagonist, exendin(9-39)amide.. Cyclic AMP production was assessed in Chinese hamster lung fibroblasts transfected with human GIP or GLP-1 receptors, respectively. In vitro insulin release studies were assessed in BRIN-BD11 cells while in vivo insulinotropic and glycaemic responses were measured in obese diabetic ( ob/ ob) mice.. In GIP receptor-transfected fibroblasts, (Pro(3))GIP or exendin(9-39)amide inhibited GIP-stimulated cyclic AMP production with maximal inhibition of 70.0+/-3.5% and 73.5+/-3.2% at 10(-6) mol/l, respectively. In GLP-1 receptor-transfected fibroblasts, exendin(9-39)amide inhibited GLP-1-stimulated cyclic AMP production with maximal inhibition of 60+/-0.7% at 10(-6) mol/l, whereas (Pro(3))GIP had no effect. (Pro(3))GIP specifically inhibited GIP-stimulated insulin release (86%; p<0.001) from clonal BRIN-BD11 cells, but had no effect on GLP-1-stimulated insulin release. In contrast, exendin(9-39)amide inhibited both GIP and GLP-1-stimulated insulin release (57% and 44%, respectively; p<0.001). Administration of (Pro(3))GIP, exendin(9-39)amide or a combination of both peptides (25 nmol/kg body weight, i.p.) to fasted (ob/ob) mice decreased the plasma insulin responses by 42%, 54% and 49%, respectively (p<0.01 to p<0.001). The hyperinsulinaemia of non-fasted (ob/ob) mice was decreased by 19%, 27% and 18% (p<0.05 to p<0.01) by injection of (Pro3)GIP, exendin(9-39)amide or combined peptides but accompanying changes of plasma glucose were small.. These data show that (Pro(3))GIP is a specific GIP receptor antagonist. Furthermore, feeding studies in one commonly used animal model of obesity and diabetes, (ob/ob) mice, suggest that GIP is the major physiological component of the enteroinsular axis, contributing approximately 80% to incretin-induced insulin release.

Topics: Animals; Cells, Cultured; Cricetinae; Cricetulus; Cyclic AMP; Diabetes Mellitus; Gastric Inhibitory Polypeptide; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptides; Humans; Hyperinsulinism; Insulin; Insulin Secretion; Mice; Obesity; Peptide Fragments; Postprandial Period; Protein Precursors; Spectrometry, Mass, Electrospray Ionization