Preparation of a low molecular weight polyethylenimine for efficient cell transfection

Polyethylenimines (PEIs) of a molecular weight between 25 and about 800 kDa have successfully been used for in vitro and in vivo gene delivery approaches. Recent publications indicated that PEI molecules of lower molecular weight and a small molecular weight range are also efficient transfection reagents with a much lower cytotoxicity compared to high molecular weight PEIs. Here, we describe the application of a molecular sieve chromatography to fractionate a commercially available 25-kDa PEI. We generated three pools of PEIs with molecular weight ranges of 70-360 (I), 10-70 (II), and 0.5-10 kDa (III), respectively. We show that, in comparison with the 25-kDa PEI, pool III increased the expression of luciferase up to 100-fold and the number of transfected cells 2-3 fold. In addition, the kinetics of reporter gene expression was also much faster in pool III, compared with the 25-kDa PEI or with pools I or II. Finally, pool III showed the lowest cytotoxicity in comparison with the other PEI preparations. Thus, we provide a one-step processing of a 25-kDa PEI, resulting in a more effective and also less cytotoxic transfection reagent.