Safety and efficacy of adeno-associated viral vector-mediated insulin gene transfer via portal vein to the livers of streptozotocin-induced diabetic Sprague-Dawley rats

BACKGROUND: Previous studies demonstrating the efficacy of insulin gene therapy have mostly involved use of adenoviral vectors or naked DNA to deliver the insulin gene. However, this procedure may not guarantee long-term insulin production. To improve the performance, we prepared recombinant adeno-associated viral vectors (rAAV) harboring the gene encoding a furin-modified human insulin under the cytomegalovirus (CMV) promoter rAAV-hPPI(F12)]. METHODS: Streptozotocin (STZ)-induced diabetic Sprague-Dawley rats were used as a diabetic animal model. The levels of blood glucose, insulin, and HbA1c were measured to test the effect. An intraperitoneal glucose tolerance test was performed to test the capability of blood glucose disposal. Immunohistochemical staining and Northern blot analyses were performed to survey the expression pattern of the therapeutic insulin gene. RESULTS: STZ-induced diabetic Sprague-Dawley rats infused via the portal vein with rAAV-hPPI(F12) produced human insulin and after a 6-h fast were normoglycemic for over 90 days post-treatment, whereas diabetic rats treated with recombinant adenoviral vector harboring the hPPI(F12) gene rAV-hPPI(F12)] were normoglycemic only for days 3 to 13 post-treatment. Insulin mRNA was detected mainly in the liver of the rAAV-hPPI(F12)-treated diabetic rats. The glucose tolerance capability of the rAAV-hPPI(F12)-treated diabetic rats was comparable to that of non-diabetic rats, even without injection of recombinant insulin. Furthermore, blood HbA1c concentrations in rAAV-hPPI(F12)-treated diabetic rats were reduced to almost the normal level. Importantly, studies of rAV or rAAV vector-dependent side effects on the targeted liver strongly suggested that only rAAV treatment caused no side effects. CONCLUSIONS: These results demonstrate that our rAAV-mediated in vivo insulin gene therapy provides safer maintenance of the insulin gene expression required for long-term and thus more effective blood glycemic control.