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 polyethyleninine (PEI). A comparison among these compounds was performed in vivo, using luciferase as reporter gene. Complexes containing 10 mu g 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 mu g of PEI-complexed DNA, reaching maximal levels of 2.4 X 10(5) RLU/kidney at 100 mu g 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.