GLP-1 C-terminal structures affect its blood glucose lowering-function

Abstract

Glucagon-like peptide-1 (GLP-1), which is an endogenous insulinotropic peptide that can stimulate islet cells to secret insulin, is a promising new drug candidate for the treatment of type 2 diabetes. However, due to the very short half-life of this peptide, the clinical value of GLP-1 is restricted. A GLP-1 peptide analog that had been altered by deletion of five amino acids from the C-terminus (sGLP-1) was selected and investigated in vivo for the therapeutic effect on GK rats with type II DM (T2DM). The results revealed that sGLP-1 exhibited decreased blood glucose-lowering ability compared to GLP-1 in the first week, as measured after once-daily administration. However, after drug administration for 2 weeks, the blood glucose-lowering effect of sGLP-1 became superior to that of GLP-1. sGLP-1 reduced apoptosis of the old islets, enhanced insulin production, and promoted new islets replication. sGLP-1 is a shorter but more efficient GLP-1 analog for type 2 diabetes management. Because sGLP-1 prolonged the proliferation and recovery of islet cells, the ability to maintain blood glucose (BG) within a normal range was still present 2 weeks after drug withdrawal. These results confirmed the importance of the C-terminus of GLP-1 molecule, and further demonstrated that GLP-1 (7-37) can be truncated till the 32nd amino acid to have a better long-term BG lowing function. This result may imply for the presence of glucagon family clearance receptors in vivo and demonstrates that the C-terminus participates in GLP-1 clearance.