Intra-articular administration of naked plasmid DNA with a guide-equipe jet injector in rat knee joints

Previous studies showed that intradermal delivery of naked plasmid DNA using the needle-free pyro-drive jet injector, Actranza™, significantly enhanced gene expression compared to needle-syringe injections in animals. Here, we targeted intra-articular (IA) tissues, including cartilage in the rat knee joint. In order to accurately deliver the DNA solution to the joint cavity, the Actranza prototype attaching a 30G needle as a guide was used (30G-Acranza). The injection powers are controllable adjusting the amounts of ignition powder (IP) and smokeless powder (SP). Preliminary tests determined an optimal injection site (5 mm depth from the skin surface into the anterior joint cavity with the knee flexed) and injection volume (30 µL). Initial trials with 30G-Actranza-25/40 (IP/SP = 25 mg/40 mg) showed luciferase plasmid (pLuc) expression levels (relative luminescence units, RLU) that were approximately 40 times higher than manual syringe injections 24 h after the administration. Additional Green Fluorescent Protein plasmid (pGFP) experiments detected fluorescence in chondrocytes and cruciate ligament fibroblasts. The higher-powered 30G-Actranza-35/40 further increased pLuc expression compared to syringe injections (∼ 100 times). The expression remained detectable 10 days post-injection, though reduced from day one. Speed-controlled tests indicated that pLuc expression levels increased with injection speed, reaching saturation at 693 µL/s of 30G-Actranza-35/40. Reference data showed transdermal needle-free jet injection favored skin and proximal tissues over IA sites. In conclusion, needle-equipped jet injection effectively transfects naked plasmid DNA into IA tissues like cartilage, synovium, ligaments, and tendons with potential applications for encapsulated tissues such as tumors, broadening prospects for gene therapy, gene editing, and regenerative medicine.