Regeneration of Pancreatic Islets in Vivo by Ultrasound-Targeted Gene Therapy

The present study uses a novel approach to gene therapy in which plasmid DNA is targeted to the pancreas in vivo using ultrasound targeted microbubble destruction (UTMD) to achieve islet regeneration. Intravenous microbubbles carrying plasmids are destroyed within the pancreatic microcirculation by ultrasound, achieving local gene expression that is further targeted to beta-cells by a modified rat insulin promoter (RIP3.1). A series of genes implicated in endocrine development were delivered to rats 2 days after streptozotocin-induced diabetes. The genes PAX4, Nkx2.2, Nkx6.1, Ngn3, and Mafa produced alpha cell hyperplasia, but no significant improvement in beta cell mass or blood glucose 30 days after UTMD. In contrast, RIP3.1-NeuroD1 promoted islet regeneration from surviving beta-cells, with normalization of glucose, insulin, and C-peptide at 30 days. In a longer-term experiment, 4 of 6 rats had return of diabetes at 90 days, accompanied by beta cell apoptosis on Tunel staining. Pre-treatment with the JNK inhibitor SP600125 successfully blocked beta-cell apoptosis and resulted in restoration of beta cell mass and normalization of blood glucose for up to 90 days. This technique allows in vivo islet regeneration, restoration of beta cell mass, and normalization of blood sugar, insulin, and C-peptide in rats without viruses.