Biological Activities of Glucagon-Like Peptide-1 Analogues in Vitro and in Vivo

Abstract

Studies support a role for glucagon-like peptide 1 (GLP-1) as a potential treatment for diabetes. However, since GLP-1 is rapidly degraded in the circulation by cleavage at Ala(2), its clinical application is limited. Hence, understanding the structure-activity of GLP-1 may lead to the development of more stable and potent analogues. In this study, we investigated GLP-1 analogues including those with N-, C-, and midchain modifications and a series of secretin-class chimeric peptides. Peptides were analyzed in CHO cells expressing the hGLP-1 receptor (R7 cells), and in vivo oral glucose tolerance tests (OGTTs) were performed after injection of the peptides in normal and diabetic (db/db) mice. [D-Ala(2)]GLP-1 and [Gly(2)]GLP-1 showed normal or relatively lower receptor binding and cAMP activation but exerted markedly enhanced abilities to reduce the glycemic response to an OGTT in vivo. Improved biological effectiveness of [D-Ala(2)]GLP-1 was also observed in diabetic db/db mice. Similarly, improved biological activity of acetyl- and hexenoic-His(1)-GLP-1, glucagon((1-5)-, glucagon((1-10))-, PACAP(1-5)-, VIP(1-5)-, and secretin((1-10))-GLP-1 was observed, despite normal or lower receptor binding and activation in vitro. [Ala(8/11/12/16)] substitutions also increased biological activity in vivo over wtGLP-1, while C-terminal truncation of 4-12 amino acids abolished receptor binding and biological activity. All other modified peptides examined showed normal or decreased activity in vitro and in vivo. These results indicate that specific N- and midchain modifications to GLP-1 can increase its potency in vivo. Specifically, linkage of acyl-chains to the alpha-amino group of His(1) and replacement of Ala(2) result in significantly increased biological effects of GLP-1 in vivo, likely due to decreased degradation rather than enhanced receptor interactions. Replacement of certain residues in the midchain of GLP-1 also augment biological activity.

Glucagon-like peptide-1 regulates proliferation and apoptosis via activation of protein kinase B in pancreatic INS-1 beta cells

“…GLP-1 stimulates insulin secretion through modulation of the cAMP-PKA pathway [5,42], and in keeping with these findings, wortmannin treatment did not affect GLP-1-stimulated insulin secretion by the INS-1 cells. However, there is growing evidence that a number of hormones that signal through GPCRs can also activate cell growth and survival pathways, including GLP-1 (present study), GIP, the GLP-1-related intestinal hormone GLP-2 and parathyroid hormone-related protein (PTHrP).…”

Membrane-tethered ligands are effective probes for exploring class B1 G protein-coupled receptor function

“…The residues that confer activity to soluble versus tethered ligands appear to share significant overlap (19). A previously published alanine scan of soluble GLP-1 demonstrated that H 1 and T 7 were among the important determinants of ligand function (20).…”

Glucagon-Like Peptide-1 Synthetic Analogs: New Therapeutic Agents for Use in the Treatment of Diabetes Mellitus

“…This compound stimulated cAMP production, insulin secretion, and lowered blood glucose concentration in Zucker fa/fa rats. Finally, it has been reported that substitution of L-alanine with D-alanine at position 8 of GLP-1 generates a DPP IV resistant peptide with insulinotropic and blood glucose lowering activities in db/db mice [139].Midchain modifications of GLP-1 have also been investigated with the expectation that such substitutions might improve the duration of action, potency, or efficacy. These expectations are based on the belief that the overall conformation of the GLP-1 peptide is strongly influenced by the midchain tertiary structure.…”