Nonviral gene delivery to the rat kidney with polyethylenimine

The aim of this study was to establish a nonviral method for gene delivery to the rat kidney. To this purpose, a panel of reagents was tested, including a monocationic lipid, DOTAP, a polycationic lipid, DOGS (or Transfectam), and three different forms of the cationic polymer polyethylenimine (PEI). A comparison among these compounds was performed in vivo, using luciferase as reporter gene. Complexes containing 10 microg of DNA were injected into the left renal artery of rats and allowed to remain in contact with the kidney for 10 min. Forty-eight hours later, luciferase expression levels in kidney extracts were measured. Kidneys injected with DNA complexed to the branched, 25-kD PEI polymer (PEI 25k) yielded activity levels significantly higher than control, sham-operated kidneys (2.7 x 10(4) vs. 5.2 x 10(3) RLU/kidney, respectively), whereas the other transfecting agents did not yield significant activity over controls. PEI 25k was therefore chosen for further optimization of transfection conditions. Dose-dependent luciferase expression was shown for 10, 50, and 100 microg of PEI-complexed DNA, reaching maximal levels of 2.4 x 10(5) RLU/kidney at 100 microg DNA. The optimal PEI nitrogen/DNA phosphate molar ratio was 10 equivalents. Luciferase activity peaked at 2 days, was still significantly higher than controls at 7 days, and was undetectable at 14 days post-injection. Using beta-galactosidase (beta-Gal) as a reporter, transgene expression was localized almost exclusively in proximal tubular cells.