Glucagon-like peptide (GLP-1) encoding dual plasmid (pDNA) system (TSTA (SP-GLP-1)) which is composed of pβ-Gal4-p65 and pUAS-SP-GLP-1 was constructed to improve the production and secretion of expressed GLP-1 by combining the advantages of signal peptide (SP) and two-step transcription amplification (TSTA) system. Its potential for GLP-1 gene delivery system was investigated with employment of arginine-grafted bioreducible polymer (ABP) as a gene carrier. Their polyplexes have about 140nm-sizes and 20mV Zeta-potential values. ABP showed no cytotoxicity contrary to PEI25k. It was found in RT-PCR experiments that TSTA-SP pDNA systems showed increased GLP-1 gene transcription level in comparison with mono pDNA system (pβ-GLP-1). It was also observed in GLP-1 ELISA that GLP-1 secretion level of TSTA (SP-GLP-1) pDNA system was 2.7-3.4 times higher than those of pβ-GLP-1 and 1.5-1.7 times than TSTA (GLP-1). Additionally, 2.5-3.5 folds increased level of GLP-1 secretion was found in ABP gene carrier system in comparison with PEI25k. When transfection medium containing secreted GLP-1 was transferred to NIT-1 insulinoma cells, the highest secretion level of insulin was induced in ABP/TSTA (SP-GLP-1) polyplex medium-treated cells. Therefore, this novel system could be utilized as a safe and efficient GLP-1 gene delivery system for type 2 diabetes therapy.
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