The role of PEI structure and size in the PEI/liposome-mediated synergism of gene transfection.

Polyethylenimines (PEIs) and cationic liposomes are widely used for nonviral gene delivery. When PEIs have been used alone, the transfection efficiency has been higher for larger or linear than smaller or branched PEIs. We have reported previously that a combination of small PEIs and liposomes results in a potentiation of transfection efficiency in vitro. Here, the role of PEI size and structure in this synergism has been clarified further. Therefore, two structurally different high MW PEIs, i.e. the linear PEI22K and branched PEI25K, were studied in the SMC cells. We found that both linear PEI22K and branched PEI25K resulted in a similar synergism and comparable transfection efficiencies. However, the potentiation for larger PEIs found in the present study was weaker than that for smaller PEIs obtained in our previous studies. In conclusion, our present and previous results demonstrate that the increment of PEI/liposome-mediated gene transfection by different types of PEIs in vitro is a common attribute that is rather associated with their size than the structure. Interestingly, the effect of PEI size seems to be opposite when combined with liposome or given alone, i.e. the small PEIs are more effective when combined and less effective when alone than the larger ones.