Glycation of glucagon-like peptide-1(7-36)amide: characterization and impaired action on rat insulin secreting cells

Abstract

It has long been recognised that gut hormones have an important role in the regulation of endocrine pancreatic function [1]. Postprandial release of incretins from the intestine, including gastric inhibitory polypeptide (GIP) and glucagon-like-peptide-1(7±36) amide (truncated GLP-1, tGLP-1), stimulates insulin secretion through the enteroinsular axis [2]. This pathway has been estimated to contribute up to 50 % of the insulin released after ingestion of glucose [2].The incretin, tGLP-1, is a product of the preproglucagon gene [proglucagon (78±107)amide] and is secreted by L-cells in the intestine after ingestion of carbohydrate, fat or protein [3,4]. It is an extremely potent stimulator of insulin secretion as well as somatostatin release but is an inhibitor of glucagon secretion [4,5]. In humans, insulin secretion was considerably increased after intravenous infusion of tGLP-1 with glucose [4] and increased twofold when tGLP-1 was given alone [3]. Glucose clearance was also strongly increased by tGLP-1, suggesting that this peptide has an important impact on glucose turnover in humans [6]. Other studies have suggested that part of this action is attributable to direct effects of Diabetologia (1998) Summary Glucagon-likepeptide-1(7±36)amide(truncated GLP-1, tGLP-1) is a potent insulin releasing hormone of the enteroinsular axis. This study has examined glycation of tGLP-1 and effects of such structural modification on insulin secretion. Monoglycated tGLP-1 (M r 3463.8, determined by plasma desorption mass spectrometry) was prepared by incubation with glucose under reducing conditions and purified by reversed-phase high performance liquid chromatography. Automated Edman degradation indicated that tGLP-1 was specifically glycated at the amino terminal His 7 site. In extracts from mouse small intestine, glycated tGLP-1 represented approximately 14 % of the total tGLP-1 content. Effects of glycated and non-glycated tGLP-1 on insulin secretion were examined using glucose-responsive clonal BRIN-BD11 cells. In acute (20 min) incubations, 10 ±9 mol/l tGLP-1 enhanced insulin release by 2.2-fold and 1.5-fold at 5.6 and 11.1 mmol/l glucose, respectively. In contrast, 10 ±9 mol/l glycated tGLP-1 failed to stimulate secretion and insulin output was decreased by 34±73 % following glycation. At 5.6 mmol/l glucose, non-glycated tGLP-1 (3´10 ±10 mol/l±10 ±8 mol/l) exerted a 2.3-fold to 3.2-fold increase in insulin secretion compared with controls. The effect of glycated tGLP-1 at 10 ±9 mol/l and 3´10 ±9 mol/l was reduced by 51±55 % compared with non-glycated peptide, and its insulinotropic action was effectively abolished. These data indicate that when tGLP-1 is glycated at the amino terminal His

Function of a long‐term, GLP‐1‐treated, insulin‐secreting cell line is improved by preventing DPP IV‐mediated degradation of GLP‐1

“…The present investigation has several interesting observations regarding prolonged GLP-1 treatment on an insulin-secreting cell line, particularly when degradation by DPP IV (present in the media) is inhibited/prevented (using either a specific inhibitor, DPA) or a previously characterized DPP IV resistant analogue of GLP-1 with preserved biological activities, N-acetyl-GLP-1 [14,21,28]. First, we have confirmed the previously observed concentration-dependent effects of GLP-1 and N-acetyl-GLP-1 on insulin secretion from an insulin-secreting cell line [14,29]. N-terminal acetylation of GLP-1 did not significantly affect insulinotropic action, contrasting it with the enhanced action observed following acetylation of the sister incretin hormone, GIP [30].…”

Physiological and pharmacological regulation of insulin release: insights offered through exploitation of insulin‐secreting cell lines

“…As shown in Fig. 3(B), GIP, GLP‐1(7–36) amide and CCK‐8 stimulate insulin secretion from BRIN‐BD11 cells in the presence of a moderate concentration (5.6 mmol/l) of glucose[80–82]. Consistent with studies on normal β cells[16], the acetylcholine analogue carbachol stimulated insulin secretion while the inhibitory catecholamines, adrenaline and noradrenaline both inhibited glucose‐induced insulin release ( Fig.…”

Insulin Releasing Properties of the Temporin Family of Antimicrobial Peptides

“…The increase in insulin output produced by this peptide is comparable to that produced by the well-characterized incretins, glucagon-like peptide-1 [24] (Table 1) and gastric inhibitory polypeptide [25] under the same experimental conditions. The data provide further confirmation that peptides present in the skin secretions of several species of frogs have the potential for development into therapeuti-cally valuable agents for the treatment of diabetes.…”