Plasmid DNA Delivery into the Skin via Electroporation with a Depot-Type Electrode

Objectives: Non-viral mediated plasmid DNA transfection by electroporation (EP) is an established method for gene transfection. In this study, the usefulness of direct EP at an intradermal (i.d.) site (D_EP) with implanted electrodes to achieve a high protein expression level was investigated. In addition, D_EP application with various intervals with a low application voltage was also evaluated to confirm its effect on protein expression. Methods: Green fluorescent protein (GFP)- and luciferase-encoding DNA were administrated, and GFP and luciferase were evaluated. Results: A higher protein expression level was observed after green fluorescent protein (GFP)- and luciferase-encoding DNA were delivered by i.d. injection followed by D_EP application. When luciferase expression was observed with an in vivo imaging system, continuous expression was confirmed over 21 days after i.d. injection followed by D_EP at 100 V. This approach provided increased gene expression levels compared with conventional EP methods via the stratum corneum layer. In addition, the effect of application voltage on luciferase expression was investigated; two-time applications (repeated D_EP) at 20 V with 5 min intervals showed similar luciferase expression level to single D_EP application with 100 V. Histological observations showed the skin became thicker after a single D_EP at 100 V, whereas no apparent thickness changes were confirmed after repeated D_EP at 20 V with 5 min intervals. Conclusions: This study revealed that direct i.d. voltage application achieved high protein expression levels even at low voltages. Skin is a promising administration site for DNA vaccines, so this approach may be effective for DNA vaccine delivery into skin tissue.