Improved transfection efficiency of an aliphatic lipid substituted 2 kDa polyethylenimine is attributed to enhanced nuclear association and uptake in rat bone marrow stromal cell.

BACKGROUND: Lipid substitutions of cationic polymers are actively explored to enhance the efficiency of nonviral gene carriers. We recently took this approach to develop a novel gene carrier by grafting linoleic acid (LA) to relatively biocompatible 2 kDa polyethylenimine (PEI2). The resulting polymer (PEI2LA) displayed improved transfection efficiency over the unmodified PEI2. The intracellular kinetics and distribution of the respective polyplexes were investigated in the present study to gain a better understanding of the role of lipid modification in intracellular trafficking of gene carriers.
METHODS: A Cy5-labeled plasmid DNA (pDNA) expressing the green fluorescent protein (GFP) was complexed with PEI2, PEI2LA, and 25 kDa polyethylenimine (PEI25) to transfect rat bone marrow stromal cells (BMSC). Subcellular fractionation was performed to measure the amount of nuclear associated pDNA. pDNA uptake, GFP-expression and nuclear-associated pDNA were measured by both flow cytometry and confocal laser scanning microscopy.
RESULTS: PEI2LA mediated higher transgene expression and percentages of transfected cells than PEI25 and PEI2, respectively. There was a strong correlation between nuclear associated pDNA and transgene expression. PEI2LA polyplexes were significantly larger in size than PEI25. The amounts of pDNA associated with the nuclei were greater in PEI2LA than PEI25 polyplexes. The perinuclear pDNA distribution between GFP-expressing and nonGFP-expressing indicated that GFP-positive cells had a higher amount of pDNA associated with their nuclei.
CONCLUSIONS: Improved transfection efficiency of PEI2LA was attributed to enhanced association with the nucleus, which may be a result of hydrophobic interaction between the lipid moieties on the modified lipopolymer and the nuclear membrane.