Transfection efficiency influenced by aggregation of DNA/polyethylenimine max/magnetic nanoparticle complexes

Gene delivery using magnetic nanoparticles (MNPs) is known as magnetofection and is an efficient non-viral gene delivery system. γ-Fe2O3 nanoparticles (primary diameter = 29 nm) and Fe3O4 nanoparticles (primary diameter = 20–30 nm) coated with deacylated linear polyethylenimine (PEI max) were prepared and conjugated with DNA. The dependency of transfection efficiency on the weight of MNPs, viability of HeLa cells, and size of DNA/PEI max/MNP complexes was evaluated. Transfection efficiency initially increased with the weight of the complexes; however, it decreased with further increase in weight. In contrast, cell viability increased with further increase in weight. Cytotoxicity assay showed that the decline in transfection efficiency at higher weights was not attributable to cytotoxicity of DNA/PEI max/MNP complexes. The DNA/PEI max/MNP complexes aggregated because of DNA binding and pH interaction with the medium. Aggregation depending on the weight of MNPs was confirmed. The number of complexes was estimated from the size distribution. In addition, the dependency of the transfection efficiency on aggregation was assessed with respect to cellular endocytic pathways using the complexes. The complexes were internalized through clathrin-dependent endocytosis, which was a size-dependent pathway. This study reveals that decreased transfection efficiency was associated with the extent of aggregation, which was induced by high weight of MNPs.