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

Summary Glucagon-like peptide-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 His⁷ 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 His⁷, this modification substantially reduces the glucose-dependent insulinotropic action of the peptide. [Diabetologia (1998) 41: 1187–1193] Received: 6 April 1998 and in revised form: 12 June 1998