Mechanism of naked DNA clearance after intravenous injection

BACKGROUND: Injection of naked DNA has been viewed as a safer alternative to current gene delivery systems; however, the rate of clearance from the circulation has been a constant barrier in developing these methods. Naked DNA after intravenous (i.v.) injection will be taken up by the liver and depredated by serum nucleases. MATERIALS AND METHODS: Our study examines the mechanisms involved in clearance of naked DNA by each compartment, the blood and the liver, in an in vivo mouse model. Confocal microscopy and transmission electron microscopy were employed to identify the type of cells taking up DNA and the barrier to DNA access to hepatocytes, respectively. RESULTS: Our data showed the liver could take up over 50% of 5 microg perfused pDNA, with a maximum 25 microg of pDNA during a single pass, and a slower clearance rate compared to that of liver uptake. It was demonstrated that naked DNA is primarily taken up by the liver endothelial cells and this endothelial barrier to transfection could be overcome by manually massaging the liver, which enlarges the fenestrae. CONCLUSIONS: This study clarifies the mechanism by which naked DNA is eliminated from the circulation after i.v. injection, focusing on the role of both the liver and blood compartments in vivo (i.e. mouse). With this knowledge, we can more clearly understand the mechanism of naked DNA clearance and develop more efficient strategies for DNA transfer in vivo.