Liver cirrhosis is often accompanied by a disturbed carbohydrate metabolism similar to type 2 diabetes. To investigate the severity of the defect in insulin secretion in this form of diabetes, we measured insulin release from isolated pancreatic islets of rats with CCl(4)-phenobarbital-induced liver cirrhosis. Cirrhosis was confirmed by clinical signs, elevated liver enzymes and histology. Fasting venous plasma glucose concentrations were equal in rats with liver cirrhosis and in controls. Plasma insulin and glucagon concentrations were significantly greater (P<0.01) in cirrhotic rats than in control animals. Glucose (16.7 mM)-induced stimulation of insulin release from pancreatic islets revealed a twofold increase in control and cirrhotic rats. Basal and stimulated insulin secretion, however, were significantly lower in cirrhotic animals. The incretin hormone, glucagon-like peptide-1 (GLP-1), has therapeutic potential for the treatment of type 2 diabetes. Therefore, islets from control and cirrhotic animals were incubated with GLP-1 in concentrations from 10(-)(11) to 10(-)(6) M. GLP-1 stimulated insulin release in a concentration-dependent manner. In islets from cirrhotic rats, basal and stimulated insulin secretion was blunted compared with controls. These data show that the hyperinsulinemia observed in liver cirrhosis is not due to an increase of insulin secretion from islets, but could be explained by decreased hepatic clearance of insulin. GLP-1 may ameliorate diabetes in patients with liver cirrhosis.
EG Siegel, A Seidenstucker, B Gallwitz, F Schmitz, A Reinecke-Luthge, G Kloppel, UR Folsch and WE Schmidt
JM Conlon, JB Kim, A Johansson and S Kikuyama
Electrospray mass spectrometry coupled with reverse-phase HPLC was used to identify peptides in the molecular mass range 3000-6000 Da in extracts of the pancreata of the clawed frog Xenopus laevis (Anura: Pipidae) and the red-bellied newt Cynops pyrrhogaster (Caudata: Salamandridae). Amino acid sequences of insulins, peptides derived from the post-translational processing of proglucagons and pancreatic polypeptide were determined by automated Edman degradation. Three molecular forms of insulin were isolated from the tetraploid organism X. laevis that represent insulin-1 and insulin-2, as deduced from the nucleotide sequences of previously characterized cDNAs, and a third form which differed from insulin-2 by the single amino acid substitution Asp(21)-->Glu in the B-chain. The amino acid sequence of Xenopus preproglucagons (genes 1 and 2 ) may be deduced from the nucleotide sequences of cDNAs but the pathways of post-translation processing of the precursors are not known. Two molecular forms of glucagon with 36 amino acids, derived from genes 1 and 2 and representing glucagon-29 extended from its C terminus by different heptapeptides, and five molecular forms of glucagon-like peptide 1 (GLP-1) were isolated. The GLPs represent proglucagon-(77-113), -(122-158) and -(160-191) from gene 1, and proglucagon-(77-113) and -(160-191) from gene 2. A single molecular form of insulin, glucagon-36, a C-terminally alpha-amidated GLP-1 with 30 amino acid residues, a 33 amino acid residue GLP-2 and pancreatic polypeptide were isolated from the pancreatic extract of the diploid organism C. pyrrhogaster. This study has illustrated the power of electrospray mass spectrometry for the rapid and reliable identification of peptides in chromatographic fractions without the need to use radioimmunoassay, radioreceptor assay or bioassay.
L Friis-Hansen, KA Lacourse, LC Samuelson and JJ Holst
The maturation of many peptide hormones is attenuated in carboxypeptidase E (CPE)-deficient fat/fat mice, leading to a slowly developing, adult-onset obesity with mild diabetes. To determine the contribution of the hormones generated from the proglucagon precursor to this phenotype, we studied the tissue-specific processing of glucagon and glucagon-like peptide-1 (GLP-1) in these mice. In all tissues examined there was a great reduction in mature amidated GLP-1. Furthermore, a lack of CPE attenuates prohormone convertase processing of proglucagon in both the pancreas and the intestine. These findings suggest that defects in proglucagon processing together with other endocrine malfunctions could contribute to the diabetic and obesity phenotype in fat/fat mice.
L Morgan, J Arendt, D Owens, S Folkard, S Hampton, S Deacon, J English, D Ribeiro and K Taylor
This study was undertaken to determine whether the internal clock contributes to the hormone and metabolic responses following food, in an experiment designed to dissociate internal clock effects from other factors. Nine female subjects participated. They lived indoors for 31 days with normal time cues, including the natural light: darkness cycle. For 7 days they retired to bed from 0000 h to 0800 h. They then underwent a 26-h 'constant routine' (CR) starting at 0800 h, being seated awake in dim light with hourly 88 Kcal drinks. They then lived on an imposed 27-h day (18 h of wakefulness, 9 h allowed for sleep), for a total of 27 days. A second 26-h CR, starting at 2200 h, was completed. During each CR salivary melatonin and plasma glucose, triacylglycerol (TAG), non-essential fatty acids (NEFA), insulin, gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured hourly. Melatonin and body temperature data indicated no shift in the endogenous clock during the 27-h imposed schedule. Postprandial NEFA, GIP and GLP-1 showed no consistent effects. Glucose, TAG and insulin increased during the night in the first CR. There was a significant effect of both the endogenous clock and sleep for glucose and TAG, but not for insulin. These findings may be relevant to the known increased risk of cardiovascular disease amongst shift workers.
Antonella Amato, Sara Baldassano and Flavia Mulè
the gastrointestinal tract and in the brain, resulting in glucagon-like peptide-1 (GLP1), GLP2, intervening peptide-2, oxynthomodulin and glicentin ( Ugleholdt et al . 2004 ). The studies on proglucagon-derived peptides have supplied two classes of
VA Gault, PR Flatt, P Harriott, MH Mooney, CJ Bailey and FP O'Harte
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.
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