The therapeutic potential of glucagon-like peptide-1 (GLP-1) in improving glycaemic control in diabetes has been widely studied, but the potential beneficial effects of glucose-dependent insulinotropic polypeptide (GIP) have until recently been almost overlooked. One of the major problems, however, in exploiting either GIP or GLP-1 as potential therapeutic agents is their short duration of action, due to enzymatic degradation in vivo by dipeptidylpeptidase IV (DPP IV). Therefore, this study examined the plasma stability, biological activity and antidiabetic potential of two novel NH2-terminal Ala2-substituted analogues of GIP, containing glycine (Gly) or serine (Ser). Following incubation in plasma, (Ser2)GIP had a reduced hydrolysis rate compared with native GIP, while (Gly2)GIP was completely stable. In Chinese hamster lung fibroblasts stably transfected with the human GIP receptor, GIP, (Gly2)GIP and (Ser2)GIP stimulated cAMP production with EC(50) values of 18.2, 14.9 and 15.0 nM respectively. In the pancreatic BRIN-BD11 beta-cell line, (Gly2)GIP and (Ser2)GIP (10(-8) M) evoked significant increases (1.2- and 1.5-fold respectively; P<0.01 to P<0.001) in insulinotropic activity compared with GIP. In obese diabetic ob/ob mice, both analogues significantly lowered (P<0.001) the glycaemic excursion in response to i.p. glucose. This enhanced glucose-lowering ability was coupled to a significantly raised (P<0.01) and more protracted insulin response compared with GIP. These data indicate that substitution of the penultimate Ala2 in GIP by Gly or Ser confers resistance to plasma DPP IV degradation, resulting in enhanced biological activity, therefore raising the possibility of their use in the treatment of type 2 diabetes.
VA Gault, PR Flatt, P Harriott, MH Mooney, CJ Bailey and FP O'Harte
I Navarro and T W Moon
We have characterized the specific binding of glucagon in hepatocytes isolated from two teleost species, the American eel (Anguilla rostrata) and the brown bullhead (Ictalurus nebulosus). Specific glucagon binding was 9·3 and 10·7% in bullhead and eel hepatocytes respectively, after a 2-h incubation at 12 °C. Curvilinear Scatchard plots suggest the presence of two classes of binding sites with apparent dissociation constants (K d) of 1·97 nm (high affinity) and 17·3 nm (low affinity) for bullhead and 2·68 and 22·9 nm for eel cells. The number of high-affinity binding sites per cell was significantly higher in the eel (10 413) than in the bullhead (3811). The number of high-affinity insulin-binding sites was approximately two times higher than that for glucagon in bullheads and the opposite in the eel hepatocytes. In competition experiments, insulin did not displace 125I-labelled glucagon binding in the hepatocytes of either species, while glucagon-like peptide-1(7–37) (GLP-1) displaced glucagon but only at high concentrations, suggesting separate glucagon- and GLP-1-binding sites. The rate of dissociation of hepatocyte-bound 125I-labelled glucagon was similar for both species. Preincubation of hepatocytes in 100 nm glucagon decreased the number of high-affinity glucagon-binding sites by approximately 55% in both species, while the K d values remained unchanged. Glucagon bound to the cell surface is internalized by fish hepatocytes. These properties indicate that the glucagon binding to hepatocytes of these two teleost species is similar to that reported for mammalian hepatocytes.
Journal of Endocrinology (1994) 140, 217–227
stimulate insulin secretion from pancreatic β-cells and reduce excessive secretion of glucagon by pancreatic α-cells, thus improving two important defects of T2DM ( Holst et al . 2008 ). Of the two currently known incretins, glucagon-like peptide 1 (GLP1
Sara Baldassano, Antonella Amato, Francesco Cappello, Francesca Rappa and Flavia Mulè
, including the proglucagon-derived peptides, glucagon-like peptide-1 (GLP1), and GLP2, and there is evidence for a link among GLP2, intestinal growth, and increased energy intake ( Xiao et al . 1999 , Shin et al . 2005 , Nelson et al . 2008 ). GLP2 is a
B Messenger, MN Clifford and LM Morgan
Gastrointestinal peptides, including insulin, glucagon and glucose-dependent insulinotropic polypeptide (GIP) have previously been reported in salivary glands. Recent evidence has suggested they might influence postprandial macronutrient metabolism. This study therefore investigated and compared postprandial hormone concentrations in saliva and plasma to determine whether their secretion was influenced by oral food stimuli. In a within-subject randomised cross-over comparison of hormone concentrations in plasma and saliva following a mixed meal, 12 subjects were given two 1708 kJ mixed meals. On one occasion the meal was chewed and swallowed (swallowed meal), on the other it was chewed and expectorated (sham-fed meal). Salivary and plasma levels of immunoreactive insulin, GIP and glucagon-like peptide-1 (GLP-1), total protein, alpha-amylase, glucose and non-esterified fatty acid were measured before and for 90 min following the meals. Saliva total protein and alpha-amylase rose following both meals, indicating that the stimulus for salivary protein release is related to the presence of food in the mouth. GLP-1 was not detected in saliva. Fasting salivary insulin levels were lower in saliva than plasma (28+/-6 vs 40+/-25 pmol/l respectively). Both increased following the swallowed meal but the rise in saliva was slower and less marked than in plasma (peak levels 96+/-18 and 270+/-66 pmol/l for saliva and plasma respectively, P<0.01). Both were unchanged following the sham-fed meal. GIP was detected in saliva. Fasting GIP levels were significantly higher in saliva than plasma (183+/-23 compared with 20+/-7 pmol/l, P<0.01). They decreased in saliva following both swallowed and sham-fed meals to nadirs of 117+/-17 and 71+/-12 pmol/l respectively, but rose following the swallowed meal to peak levels of 268+/-66 pmol/l. These findings are consistent with insulin in saliva being an ultrafiltrate of that circulating in blood, but GIP in saliva being the product of local salivary gland synthesis, whose secretion is influenced, directly or indirectly, by oral stimuli. The function of salivary GIP is unknown, but we speculate that it may play a role in the regulation of gastric acid secretion in the fasting state.
S J Brandt, M Kleinert, M H Tschöp and T D Müller
). For example, following Roux-en-Y gastric bypass, gastric banding or sleeve gastronomy, there is an increase in the secretion of glucagon-like peptide 1 (GLP-1) ( Laferrere 2016 , Meek et al. 2016 , Clemmensen et al. 2017 ), which is known not
Paige V Bauer and Frank A Duca
. 2015 , Buse et al . 2016 ). Interestingly, this is not the only evidence for a therapeutic role of the gut in diabetes treatment. Over the past decade, incretin-based therapies including glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl
Jacob Jelsing, Niels Vrang, Søren B van Witteloostuijn, Michael Mark and Thomas Klein
Introduction The incretin hormone glucagon-like peptide 1 (GLP1) is a gut peptide that is secreted in response to nutrient ingestion. It enhances the glucose-dependent stimulation of insulin secretion and also controls blood glucose (BG) via
Bethany P Cummings, Andrew A Bremer, Timothy J Kieffer, David D'Alessio and Peter J Havel
hypothesized that dexamethasone may enhance postprandial insulin secretion by increasing meal-stimulated incretin hormone secretion and/or by increasing parasympathetic input to the pancreas. The incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose
Shin Tsunekawa, Naoki Yamamoto, Katsura Tsukamoto, Yuji Itoh, Yukiko Kaneko, Toshihide Kimura, Yoh Ariyoshi, Yoshitaka Miura, Yutaka Oiso and Ichiro Niki
Introduction The beneficial effects of glucagon-like peptide 1 (GLP-1) and its related substances such as inhibitors of dipeptidyl peptidase IV, its degrading enzyme, on the pancreatic β-cells have been reported; these agents enhance