Proinsulin gene therapy in diabetic rats——Comparison of the effects on blood glucose by intraportal infusion and intramuscular injection

Objective To compare the effects of rat proinsulin gene therapy via intraportal infusion and intramuscular injection blood glucose level in streptozotocin-induced diabetic rots. Methods (1) Recombinant eukaryotic cell expression plasmid of rat proinsulin gene pCMV/proiusulin was transferred into streptozotocin-induced diabetic rats by intraportal infusion and intramuscular injection to observe the effect of rat proiusulin gene therapy in diabetic rats. The treatment group by intraportal infusion (group A) and the group by intramuscular injection (group C) were given pCMV/proinsulin naked plasmid DNA 100 μg, while the control groups by intraportal infusion (group B) or by intramuscular injection (group D) were treated with similar amount of pCMV DNA. Normal group and diabetes mellitus group were also observed at the same time. (2) Blood glucose level was tested and serum insulin was determined by radioimmunoassay. RT-PCR and immunohistochemistry were used to detemine proinsulin mRNA and protein expressions in liver and skeletal muscle and protein. Results (1) The blood glucose levels in two treated groups were both decreased. In group A, levels of blood sugar decreased about 7 mmol/L and glycemie control was maintained for 3-4 weeks. Serum insulin levels step up significantly after pCMV/proinsulin gene therapy. The blood glucose level in group A was significantly lower than those of group B and DM group (P<0.05), while the serum insulin level was higher than those of two groups (P<0.05). In group C, blood glucose levels decreased about 4 mmol/L and glycemic control was maintained for 1-2 weeks. Meanwhile, the concentrations of insulin increased markedly after gene therapy. The blood glucose in group C was significantly lower than those of group D and DM group (P<0.05), while the serum insulin level was higher than those of two groups (P<0.05). (2) Proinsulin mRNA and protein expressions could be detected in either hepatic cell of group A or skeletal muscle cell of group C, not in group B and group D. Conclusion Proiusulin genetherapy via intraportal infusion or intramuscular injection lowers significantly blood glucose in diabetic rats, and thus offers a potential approach to treatment of diabetes. Key words: Diabetes mellitus;  Gene therapy;  Proinsulin gene;  Intraportal infusion;  Intramuscular injection