Intramuscular injection of naked plasmid DNA encoding human preproinsulin gene in streptozotocin-diabetes mice results in a significant reduction of blood glucose level.

The insulin complement with gene therapy has been used as an experimental treatment for insulin dependent diabetes (IDDM). In the present study, we constructed naked plasmid DNA vector encoding recombinant human preproinsulin gene (pCMV-IN), and injected the plasmids (100 microg/mouse) intramuscularly combined with electroporation, to achieve the in vivo transfer of insulin gene in streptozotocin (STZ)-induced diabetic C57 mice. The expression of vector-derived insulin mRNA was detected with RT-PCR in transfected local skeletal muscles. The plasma insulin was elevated significantly in pCMV-IN injected diabetic C57 mice, which was complemented to the level similar to the intact normal control. The protein expression lasted for at least 35 days after the plasmid injection. Gene therapy with pCMV-IN plasmids considerably decreased the blood glucose level in STZ-induced diabetic mice from d 7 to d 35 by about 6 mmol/L. The gene therapy also reduced the mortality of severe diabetic mice significantly from 100% to 37% at the 6th week. Our results indicate that the direct intramuscular injection of naked plasmids encoding human preproinsulin gene achieves the effective expression of insulin. The restoration of insulin decreases blood glucose and increases the survival in severe diabetic mice. The gene therapy might be provided as a practical therapeutic approach to IDDM.