非病毒性載體作為口服基因投遞系統，可攜帶基因片段至細胞以表達具療效之蛋白分子，被視為具有治療慢性病的應用潛力，然而如何提升其低轉染效率一直是尚待努力的課題。本研究以小分子的分枝狀聚乙烯亞胺 (Polyethylenimine)高接枝度地接於幾丁聚醣 (Chitosan)合成出一帶強正電共聚物 (CS-grafted-branched PEI, CS-g-bPEI)。在與帶負電的基因 (Plasmid DNA)片段混合後可形成一奈米微粒，作為非病毒型之口服基因載體。在腸胃道環境下，此奈米微粒可保護DNA不受胃酸破壞以及腸道內的酵素降解，並且有效穿越小腸上皮細胞，達到血液循環中使得口服基因轉染 (Gene transfection)不在局限於腸胃道細胞。在動物實驗中，單次口服攜有胰島素基因之奈米微粒可以使動物在肝臟表現胰島素長達十天，同時穩定的控制糖尿病小鼠之空腹血糖。另外，連續多次的口服投遞此奈米微粒均可穩定且有效的表現胰島素、控制血糖。最後，在長時間的觀察下，動物的血液檢測和病理切片皆沒有發現任何肝臟毒性。本研究證實，CS-g-bPEI奈米微粒為一高效率且安全的口服基因投遞系統，對於需要長時間投藥的慢性疾病有很高的應用潛力。

Oral gene delivery to target systemic cell transfection is an appealing method for treating chronic diseases. In this investigation, a copolymer with a high degree of substitution of branched polyethylenimine on chitosan (CS-g-bPEI) is synthesized as a non-viral vector for the oral delivery of a human insulin plasmid. The as-synthesized CS-g-bPEI copolymer can form nanoparticles (NPs) with plasmids and effectively protects them from gastric acidic denaturation and degradation by intestinal enzyme, mediating the transcytosis of NPs across the epithelial cells, eventually achieving systemic cell transfection. A single dose of orally administered insulin plasmid NPs can result in sustained therapeutic gene expression in diabetic mice over a period of ten days, and the level of expression of insulin suffices to ameliorate their hyperglycemia. Efficient expressions of genes in liver tissues in diabetic mice following the repeated oral administration of test NPs is confirmed, while no evidence of significant hepatotoxicity in test animals is detected, revealing that the repeated oral administration of CS-g-bPEI NPs is an effective strategy for treating a chronic disease such as diabetes mellitus.

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