Intact Glucagon-like Peptide-1 Research Articles

The effect of DPP‐4 inhibition with sitagliptin on incretin secretion and on fasting and postprandial glucose turnover in subjects with impaired fasting glucose

Low glucagon-like peptide-1 (GLP-1) concentrations have been observed in impaired fasting glucose (IFG). It is uncertain whether these abnormalities contribute directly to the pathogenesis of IFG and impaired glucose tolerance. Dipeptidyl peptidase-4 (DPP-4) inhibitors raise incretin hormone concentrations enabling an examination of their effects on glucose turnover in IFG. We studied 22 subjects with IFG using a double-blinded, placebo-controlled, parallel-group design. At the time of enrollment, subjects ate a standardized meal labelled with [1-(13)C]-glucose. Infused [6-(3)H] glucose enabled measurement of systemic meal appearance (MRa). Infused [6,6-(2)H(2)] glucose enabled measurement of endogenous glucose production (EGP) and glucose disappearance (Rd). Subsequently, subjects were randomized to 100 mg of sitagliptin daily or placebo. After an 8-week treatment period, the mixed meal was repeated. As expected, subjects with IFG who received placebo did not experience any change in glucose concentrations. Despite raising intact GLP-1 concentrations, treatment with sitagliptin did not alter either fasting or postprandial glucose, insulin or C-peptide concentrations. Postprandial EGP (18.1 +/- 0.7 vs 17.6 +/- 0.8 micromol/kg per min, P = 0.53), Rd (55.6 +/- 4.3 vs 58.9 +/- 3.3 micromol/kg per min, P = 0.47) and MRa (6639 +/- 377 vs 6581 +/- 316 micromol/kg per 6 h, P = 0.85) were unchanged. Sitagliptin was associated with decreased total GLP-1 implying decreased incretin secretion. DPP-4 inhibition did not alter fasting or postprandial glucose turnover in people with IFG. Low incretin concentrations are unlikely to be involved in the pathogenesis of IFG.

Expression of mRNA for proglucagon and glucagon-like peptide-2 (GLP-2) receptor in the ruminant gastrointestinal tract and the influence of energy intake

Glucagon-like peptide-2 (GLP-2) is a potent trophic gut hormone, yet its function in ruminants is relatively unknown. Experiment 1 was conducted as a pilot study to establish the presence of GLP-2 in ruminants and to ascertain whether it was responsive to increased nutrition, as in non-ruminants. Concentrations of intact GLP-2 in the blood and gut epithelial mRNA expression of proglucagon ( GCG) and the GLP-2 receptor ( GLP2R) were measured in 4 ruminally, duodenally, and ileally cannulated steers. Steers were fed to meet 0.75 × NE M for 21 d, and then increased to 1.75 × NE M requirement for another 29 d. Blood samples and ruminal, duodenal, and ileal epithelium biopsies were collected at low intake (Days −6 and −3), acute high intake (Days 1 and 3), and chronic high intake (Days 7 and 29) periods. Experiment 2 investigated the mRNA expression pattern of GCG and GLP2R in epithelial tissue obtained from the forestomachs (rumen, omasum, and abomasum) and intestines (duodenum, jejunum, ileum, and colon) of 18 forage-fed Angus steers (260 kg BW). In Experiments 1 and 2, real-time polymerase chain reaction showed that expression of GCG and GLP2R mRNA was detectable in forestomach tissues, but expression was greater ( P < 0.001) in small intestinal and colon tissue. High energy intake tended ( P = 0.07) to increase plasma GLP-2 during the acute period and was paralleled by a 78% increase ( P = 0.07) in ileal GCG mRNA expression. After this initial adaptation, duodenal GCG mRNA expression increased ( P = 0.08) during the chronic high intake period. Duodenal GLP2R mRNA expression was not affected by energy intake, but ileal GLP2R expression was increased after 29 d of high energy intake compared to both the low and acute high intake periods ( P = 0.001 and P = 0.01, respectively). These data demonstrate that cattle express GCG and GLP2R mRNA primarily in small intestinal and colon tissues. Increased nutrient intake increases ileal GCG mRNA and plasma GLP-2, suggesting that GLP-2 may play a role in the trophic response of the ruminant gastrointestinal tract to increased feed intake.

Twelve weeks treatment with the DPP‐4 inhibitor, sitagliptin, prevents degradation of peptide YY and improves glucose and non‐glucose induced insulin secretion in patients with type 2 diabetes mellitus

To examine the effects of 12 weeks of treatment with the DPP-4 inhibitor, sitagliptin, on gastrointestinal hormone responses to a standardized mixed meal and beta cell secretory capacity, measured as glucose and non-glucose induced insulin secretion during a hyperglycaemic clamp, in patients with type 2 diabetes. A double-blinded, placebo-controlled study over 12 weeks in which 24 patients with T2DM were randomized to receive either sitagliptin (Januvia) 100 mg qd or placebo as an add-on therapy to metformin. In week 0, 1 and 12 patients underwent a meal test and a 90-min 20 mM hyperglycaemic clamp with 5 g of l-arginine infusion. Main outcome measure was postprandial total glucagon-like peptide 1 (GLP-1) concentration. Additional measures were insulin and C-peptide, glycaemic control, intact and total peptide YY (PYY) and glucose-dependent insulinotropic polypeptide (GIP), and intact glucagon-like peptide 2 (GLP-2) and GLP-1. All patients [sitagliptin n = 12, age: 59.5 (39-64) years, HbA1c: 8.0 (7.3-10.0)%, BMI: 33.2 (29.3-39.4); placebo n = 12, age: 60 (31-72) years, HbA1c: 7.7 (7.1-9.8)%, BMI: 30.7 (25.7-40.5)] [median (range)] completed the trial. Sitagliptin treatment improved glycaemic control, had no effect on total GLP-1, GIP or intact GLP-2, but reduced total PYY and PYY(3- 36), and increased PYY(1- 36) and intact incretin hormones. Sitagliptin improved first and second phases of beta cell secretion and maximal secretory capacity. All effects were achieved after 1 week. No significant changes occurred in the placebo group. The postprandial responses of total GLP-1 and GIP and intact GLP-2 were unaltered. PYY degradation was prevented. Glucose and non-glucose induced beta cell secretion was improved. There was no difference in responses to sitagliptin between 1 and 12 weeks of treatment.

Intact Glucagon-like Peptide-1 Levels are not Decreased in Japanese Patients with Type 2 Diabetes

Impaired secretion of glucagon-like peptide 1 (GLP-1) has been suggested to contribute to the deficient incretin effect in patients with type 2 diabetes mellitus (T2DM). Recent studies, however, have not always supported this notion. Since Japanese patients with T2DM usually have severe impairment in the earlyphase of insulin secretion, the measurement of incretin secretions in Japanese T2DM patients would be useful for assessing the association between incretin levels and insulin secretion. We conducted an oral glucose tolerance test (75 g) (OGTT) and meal tolerance test (480 kcal) (MTT) for subjects with normal glucose tolerance (NGT, n=12), subjects with impaired glucose tolerance (IGT, n=7), and T2DM patients (n=21). The tests were carried out over 120-min study periods on separate occasions. Intact GLP-1, GIP, and dipeptidyl peptidase (DPP)-IV were measured by ELISA. T2DM exhibited an impaired early phase of insulin secretion and a reduction in glucagon suppression. There were no significant differences in GLP-1 or GIP levels at each sampling time among NGT, IGT, and T2DM after the ingestions; hence the incremental areas under the curve (IAUC) for the three groups were quite similar. The levels of DPP-IV, a limiting enzyme for the degradation of incretins, were comparable among the three groups. The GLP-1-IAUC was not correlated with IAUCs of insulin, C-peptide, or glucagon determined by the OGTT or the MTT. We concluded that intact GLP-1 levels are comparable between non-diabetics and T2DM, suggesting that impaired insulin secretion in Japanese T2DM is not attributable to defect in GLP-1 secretion.

Molecular Basis of Glucagon-like Peptide 1 Docking to Its Intact Receptor Studied with Carboxyl-terminal Photolabile Probes

The glucagon-like peptide 1 (GLP1) receptor is a member of Family B G protein-coupled receptors and represents an important drug target for type 2 diabetes. Despite recent solution of the structure of the amino-terminal domain of this receptor and that of several close family members, understanding of the molecular basis of natural ligand GLP1 binding to its intact receptor remains limited. The goal of this study was to explore spatial approximations between specific receptor residues within the carboxyl terminus of GLP1 and its receptor as normally docked. Therefore, we developed and characterized two high affinity, full-agonist photolabile GLP1 probes having sites for covalent attachment in positions 24 and 35. Both probes labeled the receptor specifically and saturably. Subsequent peptide mapping using chemical and proteinase cleavages of purified wild-type and mutant GLP1 receptor identified that the Arg(131)-Lys(136) segment at the juxtamembrane region of the receptor amino terminus contained the site of labeling for the position 24 probe, and the specific receptor residue labeled by this probe was identified as Glu(133) by radiochemical sequencing. Similarly, nearby residue Glu(125) within the same region of the receptor amino-terminal domain was identified as the site of labeling by the position 35 probe. These data represent the first direct demonstration of spatial approximation between GLP1 and its intact receptor as docked, providing two important constraints for the modeling of this interaction. This should expand our understanding of the molecular basis of natural agonist ligand binding to the GLP1 receptor and may be relevant to other family members.

No increased risk of hypoglycaemic episodes during 48 h of subcutaneous glucagon‐like‐peptide‐1 administration in fasting healthy subjects

It is uncertain whether the ability to avoid hypoglycaemia during fasting is preserved, and the risk of reactive hypoglycaemia after an oral glucose stimulus following a prolonged fasting period is increased at augmented glucagon-like peptide-1 (GLP-1) levels. A randomized, double-blind placebo-controlled cross-over study in eight healthy men to assess the safety, in terms of hypoglycaemia, of a continuously infused pharmacological dose of native GLP-1 during long-term fasting. After an overnight fast the fasting period continued for 48 h and was followed by a 3-h oral glucose tolerance test (OGTT). GLP-1(7-36 amide) or placebo was continuously infused subcutaneously and titrated to a dose of 4.8 pmol/kg per min. Two subjects in the GLP-1 group and one subject in the placebo group were withdrawn due to protocol specified plasma glucose (PG) < or = 2.8 mm and neuroglycopaenic symptoms. The infusion of GLP-1 resulted in pharmacological levels of intact GLP-1. During the fasting period PG, insulin and C-peptide levels declined and glucagon, GH and free fatty acid (FFA) levels increased with no differences between GLP-1 and placebo. During OGTT circulating levels of insulin and C-peptide were higher with GLP-1 infusion. However, PG was similar during GLP-1 vs. placebo infusions. GLP-1 infusion increased norepinephrine and cortisol levels during OGTT. The counter-regulatory response during 48 h of subcutaneous GLP-1 infusion was preserved despite long-term fasting with no apparent increased risk of hypoglycaemic episodes. No reactive hypoglycaemia was observed when the fast was followed by an OGTT. Thus use of long-acting GLP-1 analogues may not increase the risk of hypoglycaemia.

Mechanisms of Glucose Homeostasis After Roux-en-Y Gastric Bypass Surgery in the Obese, Insulin-Resistant Zucker Rat

Obesity-related diabetes is caused by insulin resistance and beta-cell dysfunction. The current study examines changes in food intake, weight loss, body fat depots, oxygen consumption, insulin sensitivity, and incretin levels as potential mechanisms for improved glucose tolerance after Roux-en-Y gastric bypass (RYGB). Three groups of genetically obese Zucker rats were studied: RYGB, sham surgery pair-fed (PF), and sham surgery ad libitum (AL) fed rats. Changes in body weight, visceral and subcutaneous fat depots, oral glucose tolerance, insulin sensitivity, and the plasma concentrations of insulin, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide, and peptide YY (PYY) were measured. Body weight and subcutaneous fat were decreased after RYGB, compared with the PF and AL groups. The reduction in visceral fat after RYGB appeared largely because of food restriction. Glucose tolerance and insulin sensitivity were significantly improved in only the RYGB group (P < 0.05 vs. AL, PF). Euglycemic, hyperinsulinemic clamp studies indicated RYGB improved the ability of insulin to stimulate peripheral (eg, skeletal muscle) glucose uptake. Fasting total GLP-1, glucose-dependent insulinotropic peptide, and PYY levels were similar between the groups, whereas postprandial plasma levels of intact GLP-1 (7-36) amide, total GLP-1, and PYY were increased in the RYGB group compared with PF and AL controls. Glucose homeostasis after RYGB is associated with decreased subcutaneous fat, increased postprandial PYY, GLP-1, and insulin, as well as improved insulin sensitivity/action. Changes in food intake and visceral fat do not seem to explain improvements in insulin action after RYGB in the Zucker rat model.

Increased Glucagon-Like Peptide-1 Secretion and Postprandial Hypoglycemia in Children after Nissen Fundoplication

Postprandial hypoglycemia (PPH) is a frequent complication of Nissen fundoplication in children. The mechanism responsible for the PPH is poorly understood, but involves an exaggerated insulin response to a meal and subsequent hypoglycemia. We hypothesize that increased glucagon-like peptide-1 (GLP-1) secretion contributes to the exaggerated insulin surge and plays a role in the pathophysiology of this disorder. The aim of the study was to characterize glucose, insulin, and GLP-1 response to an oral glucose load in children with symptoms of PPH after Nissen fundoplication. Ten patients with suspected PPH and a history of Nissen fundoplication and eight control subjects underwent a standard oral glucose tolerance test at The Children's Hospital of Philadelphia. Blood glucose (BG), insulin, and intact GLP-1 levels were obtained at various time points. Children ages 4 months to 13 years old were studied. Change scores for glucose, insulin, and intact GLP-1 were recorded after an oral glucose tolerance test. All cases had hypoglycemia after the glucose load. Mean BG at nadir (+/- sd) was 46.7 +/- 11 mg/dl for cases (vs. 85.9 +/- 21.3 mg/dl; P < 0.0005). Mean change in BG from baseline to peak (+/- sd) was 179.3 +/- 87.4 mg/dl for cases (vs. 57.8 +/- 39.5 mg/dl; P = 0.003). Mean change in BG (+/- sd) from peak to nadir was 214.4 +/- 85.9 mg/dl for cases (vs. 55.9 +/- 41.1 mg/dl, P < 0.0005). Mean change in insulin (+/- sd) from baseline to peak was 224.3 +/- 313.7 microIU/ml for cases (vs. 35.5 +/- 22.2 microIU/ml; P = 0.012). Mean change in GLP-1 (+/- sd) from baseline to peak was 31.2 +/- 24 pm (vs. 6.2 +/- 9.5 pm; P = 0.014). Children with PPH after Nissen fundoplication have abnormally exaggerated secretion of GLP-1, which may contribute to the exaggerated insulin surge and resultant hypoglycemia.

Paying the Price for Eating Ice Cream: Is Excessive GLP-1 Signaling in the Brain the Culprit?

Paying the Price for Eating Ice Cream: Is Excessive GLP-1 Signaling in the Brain the Culprit?

Incretin and islet hormonal responses to fat and protein ingestion in healthy men

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) regulate islet function after carbohydrate ingestion. Whether incretin hormones are of importance for islet function after ingestion of noncarbohydrate macronutrients is not known. This study therefore examined integrated incretin and islet hormone responses to ingestion of pure fat (oleic acid; 0.88 g/kg) or protein (milk and egg protein; 2 g/kg) over 5 h in healthy men, aged 20-25 yr (n=12); plain water ingestion served as control. Both intact (active) and total GLP-1 and GIP levels were determined as was plasma activity of dipeptidyl peptidase-4 (DPP-4). Following water ingestion, glucose, insulin, glucagon, GLP-1, and GIP levels and DPP-4 activity were stable during the 5-h study period. Both fat and protein ingestion increased insulin, glucagon, GIP, and GLP-1 levels without affecting glucose levels or DPP-4 activity. The GLP-1 responses were similar after protein and fat, whereas the early (30 min) GIP response was higher after protein than after fat ingestion (P<0.001). This was associated with sevenfold higher insulin and glucagon responses compared with fat ingestion (both P<0.001). After protein, the early GIP, but not GLP-1, responses correlated to insulin (r(2)=0.86; P=0.0001) but not glucagon responses. In contrast, after fat ingestion, GLP-1 and GIP did not correlate to islet hormones. We conclude that, whereas protein and fat release both incretin and islet hormones, the early GIP secretion after protein ingestion may be of primary importance to islet hormone secretion.

The dipeptidyl peptidase‐4 inhibitor PHX1149 improves blood glucose control in patients with type 2 diabetes mellitus

To determine the efficacy and tolerability of PHX1149, a novel dipeptidyl peptidase-4 (DPP4) inhibitor, in patients with type 2 diabetes. This is a multicentre, randomized, double-blind, placebo-controlled, 4-week study in patients with type 2 diabetes with suboptimal metabolic control. Patients with a baseline haemoglobin A(1c) (HbA(1c)) of 7.3 to 11.0% were randomized 1 : 1 : 1 : 1 to receive once-daily oral therapy with either PHX1149 (100, 200 or 400 mg) or placebo; patients were on a constant background therapy of either metformin alone or metformin plus a glitazone. Treatment with 100, 200 or 400 mg of PHX1149 significantly decreased postprandial glucose area under the curve AUC(0-2 h) by approximately 20% (+0.11 +/- 0.50, -2.08 +/- 0.51, -1.73 +/- 0.49 and -1.88 +/- 0.48 mmol/l x h, respectively, for placebo and 100, 200 and 400 mg (p = 0.002, 0.008 and 0.004 vs. placebo). Postprandial AUC(0-2 h) of intact glucagon-like peptide-1, the principal mediator of the biological effects of DPP4 inhibitors, was increased by 3.90 +/- 2.83, 11.63 +/- 2.86, 16.42 +/- 2.72 and 15.75 +/- 2.71 pmol/l x h, respectively, for placebo and 100, 200 and 400 mg (p = 0.053, 0.001 and 0.002 vs. placebo). Mean HbA(1c) was lower in all dose groups; the placebo-corrected change in the groups receiving 400 mg PHX1149 was -0.28% (p = 0.02). DPP4 inhibition on day 28 was 53, 73 and 78% at 24 h postdose in the groups receiving 100, 200 and 400 mg PHX1149, respectively. There were no differences in adverse events between PHX1149-treated and placebo subjects. Addition of the DPP4 inhibitor PHX1149 to a stable regimen of metformin or metformin plus a glitazone in patients with type 2 diabetes was well tolerated and improved blood glucose control.

Response to Comment on: Knop et al. (2007) Reduced Incretin Effect in Type 2 Diabetes: Cause or Consequence of the Diabetic State? Diabetes 56:1951–1959

We thank Choukem and Gautier (1) for their comment, in which constructive criticism relating to the evaluation of glucagon-like peptide-1 (GLP-1) secretion is raised, concerning our study (2). Secretion of hormones following different stimuli are difficult to estimate from peripheral levels of hormone concentrations. Therefore, hormone responses as measured by concentration changes in the peripheral circulation are often used as indicators of the actual amount of secretion. Choukem and Gautier are right that when the computation of the incremental area under curve (AUC) is based on the difference between the first and the subsequent measures, a possible error of that first measurement will accumulate (3). Therefore, in our studies, we use the average of three baseline values (time points −15, −10, and 0 min) when computing incremental AUCs to minimize the risk of errors at baseline. The incremental AUC values were chosen as a result of the relatively small intact GLP-1 responses observed. We anticipated that less pronounced differences between the responses to the two stimuli (50-g oral glucose tolerance test [OGTT] vs. isoglycemic intravenous glucose infusion) would be easier to detect using the incremental values. In the study in question, we measured both total GLP-1 concentrations (intact and active peptide plus the inactive metabolite) and intact levels (active peptide only) of GLP-1. The intact …

Comment on: Knop et al. (2007) Reduced Incretin Effect in Type 2 Diabetes: Cause or Consequence of the Diabetic State? Diabetes 56:1951–1959

In the excellent article by Knop et al. (1), the authors use an interesting design to show that the decreased incretin effect observed in patients with type 2 diabetes is a consequence of the diabetic state rather than a causal factor. However, analyses concerning glucagon-like peptide-1 (GLP-1) concentrations seem a bit disturbing. Looking at Fig. 3 in their article, it is obvious that a 50-g glucose ingestion induces a peak of intact GLP-1 concentrations in patients …

Effects of the Dipeptidyl Peptidase-IV Inhibitor Vildagliptin on Incretin Hormones, Islet Function, and Postprandial Glycemia in Subjects With Impaired Glucose Tolerance

This study was conducted to determine the effects of vildagliptin on incretin hormone levels, islet function, and postprandial glucose control in subjects with impaired glucose tolerance (IGT). A 12-week, double-blind, randomized, parallel-group study comparing vildagliptin (50 mg q.d.) and placebo was conducted in 179 subjects with IGT (2-h glucose 9.1 mmol/l, A1C 5.9%). Plasma levels of intact glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP), glucose, insulin, C-peptide, and glucagon were measured during standard meal tests performed at baseline and at week 12. Insulin secretory rate (ISR) was estimated by C-peptide deconvolution. The between-group differences (vildagliptin - placebo) in the adjusted mean changes from baseline to end point in the total and incremental (Delta) area under the curve (AUC)(0-2 h) for these analytes were assessed by ANCOVA; glucose AUC(0-2 h) was the primary outcome variable. Relative to placebo, vildagliptin increased GLP-1 (DeltaAUC, +6.0 +/- 1.2 pmol x l(-1) x h(-1), P < 0.001) and GIP (DeltaAUC, +46.8 +/- 5.4 pmol . l(-1) x h(-1), P < 0.001) and decreased glucagon (DeltaAUC, -3.0 +/- 1.0 pmol x l(-1) x h(-1), P = 0.003). Although postprandial insulin levels were unaffected (DeltaAUC, +20.8 +/- 35.7 pmol x l(-1) x h(-1), P = 0.561), prandial glucose excursions were reduced (DeltaAUC, -1.0 +/- 0.3 mmol x l(-1) x h(-1), P < 0.001), representing an approximately 30% decrease relative to placebo. Beta-cell function as assessed by the ISR AUC(0-2 h)/glucose AUC(0-2 h) was significantly increased (+6.4 +/- 2.0 pmol x min(-1) x m(-2) x mmol x l(-1), P = 0.002). Adverse event profiles were similar in the two treatment groups, and no hypoglycemia was reported. The known effects of vildagliptin on incretin levels and islet function in type 2 diabetes were reproduced in subjects with IGT, with a 32% reduction in postprandial glucose excursions and no evidence of hypoglycemia or weight gain.

Incretin‐based treatment of type 2 diabetes: glucagon‐like peptide‐1 receptor agonists and dipeptidyl peptidase‐4 inhibitors*

Incretins are gut peptides that potentiate nutrient-stimulated insulin secretion following meal ingestion. Activities of the dominant incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide, include glucose-dependent stimulation of insulin secretion and, in preclinical models, improvement in islet beta-cell mass. GLP-1 additionally reduces glucagon secretion, inhibits gastric emptying and promotes satiety. Patients with type 2 diabetes mellitus (T2DM) exhibit reduced total and intact GLP-1 levels, and exogenous administration of the hormone via continuous infusion results in glucose profiles similar to those in non-diabetic subjects. Incretins are rapidly degraded by dipeptidyl peptidase-4 (DPP-4). Thus, strategies to enhance incretin activity have included development of GLP-1 receptor agonists resistant to the action of DPP-4 (e.g. exenatide and liraglutide) and DPP-4 inhibitors that act to increase concentrations of endogenous intact incretins (e.g. sitagliptin and vildagliptin). Clinical trials of these incretin-based therapies have shown them to be effective in improving glycaemic control in patients with T2DM.

How the hindgut can cure type 2 diabetes. Ileal transposition improves glucose metabolism and beta-cell function in Goto-kakizaki rats through an enhanced Proglucagon gene expression and L-cell number

It has been hypothesized that glucagon-like peptide-1 (GLP-1), secreted by ileal L cells, plays a key-role in the resolution of type 2 diabetes after bariatric operations whose common feature is an expedite nutrient delivery to the hindgut. Ileal transposition (IT), an operation that permits L-cell stimulation by undigested food, was employed to verify this theory. IT was carried out in Goto-Kakizaki (GK) type 2 diabetic rats and in euglycemic Sprague-Dawley (SD) rats. Glucose tolerance, insulin resistance, food-intake, body weight, pancreas morphology, and function were evaluated to track the effects of IT on diabetes. Intact GLP-1 secretion and gene expression pattern of the transposed ileum were investigated to verify the molecular bases of the hindgut action. In GK rats, IT significantly improved glucose tolerance, insulin sensitivity, and acute insulin response without affecting body weight and food intake. Immunohistochemistry revealed remodeled islets strictly resembling that of euglycemic rats and signs of beta-cell neogenesis starting with exocrine structures. GLP-1 secretion in GK transposed rats was characterized by a more sustained response to oral glucose compared with nontreated rats. Gene expression of Proglucagon, Proconvertase 1/3 (PC1/3), and Chromogranin A in the transposed ileum significantly enhanced. Effects on glucose metabolism and pancreas morphology were not observed in the euglycemic rats as a consequence of the glucose-dependent action of GLP-1. This study gives strong evidences for the crucial role of the hindgut in the resolution of diabetes after Roux-en-Y gastric bypass (GBP) and biliopancreatic diversion (BPD). Moreover, these findings confirm at the preclinical level that IT is a surgical procedure of possible relevance in the therapy of type 2 diabetes in non-overweight and mildly obese patients.

Myocardial Ischaemia-reperfusion Injury is Attenuated by Intact Glucagon Like Peptide-1 (GLP-1) in the In Vitro Rat Heart and may Involve the p70s6K Pathway

Glucagon Like Peptide-1 (GLP-1), one of the most potent incretin hormones, has potential beneficial actions on the ischaemic and failing heart. This study sought to further identify the mechanisms of action of GLP-1 on the ischaemic heart using an in vitro isolated perfused rat heart model of ischaemic-reperfusion injury (measuring infarct size to area of risk (%)) subjected to 35 min regional ischaemia and 2 h reperfusion. To examine the effect of intact GLP-1 we used an inhibitor of GLP-1 breakdown, Valine pyrrolidide (VP). The downstream target of phosphatidylinositol 3-kinase includes the mTOR/p70s6 kinase pathway which was pharmacologically inhibited by rapamycin. GLP-1 alone did not decrease myocardial infarction (54.4 +/- 3.1%). VP alone did not decrease myocardial infarction (52.5 +/- 4%). GLP-1 in the presence of VP produced significant reduction in myocardial infarction compared to control hearts (28.4 +/- 2.7% vs. 56.4 +/- 3.9% vs. P < 0.05). Inhibiting p70s6 Kinase with rapamycin completely abolished GLP-1 induced protection (57.1 +/- 4.9% vs. 28.4 +/- 2.7% P < 0.05). There was no detectable increase in the phosphorylated p70s6k after either 5 or 10 min of treatment with GLP-1/VP or with VP alone in comparison to control blots. In conclusion we show for the first time that the protective effects of GLP-1 are mediated by intact GLP-1 and can be inhibited by blocking the p70s6 kinase.

DPP-4 inhibition improves glucose tolerance and increases insulin and GLP-1 responses to gastric glucose in association with normalized islet topography in mice with β-cell-specific overexpression of human islet amyloid polypeptide

Inhibition of dipeptidyl peptidase-4 (DPP-4) is currently explored as a novel therapy of type 2 diabetes. The strategy has been shown to improve glycemia in most, but not all, rodent forms of glucose intolerance. In this study, we explored the effects of DPP-4 inhibition in mice with β-cell overexpression of human islet amyloid polypeptide (IAPP). We therefore administered the orally active and highly selective DPP-4 inhibitor, vildagliptin (3 μmol/mouse daily) to female mice with β-cell overexpression of human IAPP. Controls were given plain water, and a series of untreated wildtype mice was also included. After five weeks, an intravenous glucose tolerance test showed improved glucose disposal and a markedly enhanced insulin response in mice treated with vildagliptin. After eight weeks, a gastric tolerance test showed that vildagliptin improved glucose tolerance and markedly (approximately ten-fold) augmented the insulin response in association with augmented (approximately five-fold) levels of intact glucagon-like peptide-1 (GLP-1). Furthermore, after nine weeks, islets were isolated. Islets from vildagliptin-treated mice showed augmented glucose-stimulated insulin response and a normalization of the islet insulin content, which was reduced by approximately 50% in transgenic controls versus wildtype animals. Double immunostaining of pancreatic islets for insulin and glucagon revealed that transgenic islets displayed severely disturbed intra-islet topography with frequently observed centrally located α-cells. Treatment with vildagliptin restored the islet topography. We therefore conclude that DPP-4 inhibition improves islet function and islet topography in mice with β-cell specific transgenic overexpression of human IAPP.

Dipeptidyl Peptidase-4 Inhibition and the Treatment of Type 2 Diabetes

Dipeptidyl peptidase (DPP)-4 is a complex enzyme that exists as a membrane-anchored cell surface peptidase that transmits intracellular signals via a short intracellular tail and as a second smaller soluble form present in the circulation. DPP-4 cleaves a large number of chemokines and peptide hormones in vitro, but comparatively fewer peptides have been identified as endogenous physiological substrates for DPP-4 in vivo. Both glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are endogenous physiological substrates for DPP-4, and chemical inhibition of DPP-4 activity, or genetic inactivation of DPP-4 in rodents, results in increased levels of intact bioactive GIP and GLP-1. Furthermore, mice and rats with genetic inactivation or inhibition of DPP-4 exhibit improved glucose tolerance, elevated levels of GLP-1 and GIP, and resistance to diet-induced obesity and hyperglycemia. Sustained DPP-4 inhibition lowers blood glucose via stimulation of insulin and inhibition of glucagon secretion and is associated with preservation of β-cell mass in preclinical studies. Although DPP-4 cleaves dozens of regulatory peptides and chemokines in vitro, studies of mice with genetic inactivation of incretin receptors demonstrate that GIP and GLP-1 receptor–dependent pathways represent the dominant mechanisms transducing the glucoregulatory actions of DPP-4 inhibitors in vivo. The available preclinical data suggests that highly selective DPP-4 inhibition represents an effective and safe strategy for the therapy of type 2 diabetes. DPP-4 is a widely expressed cell surface peptidase that exhibits a complex biology encompassing cell membrane–associated activation of intracellular signal transduction pathways, cell-cell interaction, and enzymatic activity exhibited by both the membrane-anchored and soluble forms of the enzyme (1). DPP-4, also originally known as the lymphocyte cell surface marker CD26, or as the adenosine deaminase (ADA)-binding protein, is a 766–amino acid serine protease that preferentially cleaves peptide hormones containing a position two alanine or proline. The human gene encoding DPP has been localized …

Metabolism of glucagon-like peptide-2 in pigs: Role of dipeptidyl peptidase IV

Little is known about the metabolism of the intestinotropic factor glucagon-like peptide-2 (GLP-2); except that it is a substrate for dipeptidyl peptidase IV (DPP-IV) and that it appears to be eliminated by the kidneys. We, therefore, investigated GLP-2 metabolism in six multicatheterized pigs receiving intravenous GLP-2 infusions (2 pmol/kg/min) before and after administration of valine-pyrrolidide (300 μmol/kg; a well characterized DPP-IV inhibitor). Plasma samples were analyzed by radioimmunoassays allowing determination of intact, biologically active GLP-2 and the DPP-IV metabolite GLP-2 (3–33). During infusion of GLP-2 alone, 30.9 ± 1.7% of the infused peptide was degraded to GLP-2 (3–33). After valine-pyrrolidide, there was no significant formation of the metabolite. Significant extraction of intact GLP-2 was observed across the kidneys, the extremities (represented by a leg), and the splanchnic bed, resulting in a metabolic clearance rate (MCR) of 6.80 ± 0.47 ml/kg/min and a plasma half-life of 6.8 ± 0.8 min. Hepatic extraction was not detected. Valine-pyrrolidide addition did not affect extraction ratios significantly, but decreased ( p = 0.003) MCR to 4.18 ± 0.27 ml/kg/min and increased ( p = 0.052) plasma half-life to 9.9 ± 0.8 min. The metabolite was eliminated with a half-life of 22.1 ± 2.6 min and a clearance of 2.07 ± 0.11 ml/kg/min. In conclusion, intact GLP-2 is eliminated in the peripheral tissues, the splanchnic bed and the kidneys, but not in the liver, by mechanisms unrelated to DPP-IV. However, DPP-IV is involved in the overall GLP-2 metabolism and seems to be the sole enzyme responsible for N-terminal degradation of GLP-2.