Glucagon like peptide-1 gene therapy for the treatment of type 2 diabetes

Abstract

Glucagon like peptide-1 (GLP-1) is a potent insulinotrophic hormone, which makes GLP-1 an attractive candidate for the treatment of type 2 diabetes. It was reported that the continuous infusion of GLP-1 normalized the blood glucose level in type 2 diabetes animal model. However, the short half-life of GLP-1 has limited its application to clinical settings and prompted us to develop a GLP-1 gene therapy system. In this study, we evaluated the effect of GLP-1 gene delivery both in vitro and in vivo using a new plasmid constructed with a modified GLP-1 (7-37) cDNA. This cDNA contains a furin cleavage site between the start codon and the GLP-1 coding region. After translation, methionine encoded by the start codon was eliminated by furin in Golgi, producing active form of GLP-1. In the GLP-1 expression plasmids, the expression of the GLP-1 gene was driven by the chicken β-actin promoter (p -GLP1) or SV40 promoter (pSV-GLP1-NF B). The in vitro results showed a dose dependent expression of GLP-1. Co-culture assay of the GLP-1 plasmid transfected cells with isolated rat islet cells demonstrated that GLP-1 increased insulin secretion by two-fold, compared to controls during a hyperglycemic challenge. In addition, the more efficient GLP-1 expression system was developed using two-step transcription amplification (TSTA). To evaluate the TSTA system, p -Gal4-p65 and pUAS-GLP-1 were constructed. In TSTA system, a transcription factor Gal4-p65, which was expressed by p -Gal4-p65, bound to cis-regulatory element of pUAS-GLP-1 and activated the GLP-1 transcription. The pUAS-GLP-1/p -Gal4-p65 system showed higher mRNA level than p -GLP-1. Also, the level of GLP-1 by the pUAS-GLP-1/p -Gal4-p65 system was more than 4 times higher than p -GLP-1. In the in vivo evaluation, a single injection of polyethylenimine (PEI)/GLP1 plasmid complex into animal model resulted in increasing insulin secretion and decreasing blood glucose level that was maintained for 2 weeks. The GLP-1 gene delivery system may provide an effective and safe treatment modality for type 2 diabetes.