Chitosan-mediated non-viral gene delivery with improved serum stability and reduced cytotoxicity

Polyethyleneimine (PEI) has been widely used in gene delivery systems because of its outstanding ability to promote DNA condensation and endosome escape. However, its use for the introduction of foreign DNA into host cells is compromised by high cytotoxicity and serum reactivity. In this study we examined the possibility of improving the PEI-mediated gene delivery using the serum-stable and biodegradable polymer, chitosan. Among chitosans of different molecular weights, the 45 kD form exhibited significantly higher gene delivery efficiency than the 15 and 100 kD forms. Using the 45 kDa form of chitosan, we formulated composite PEI/DNA/chitosan (PDC) complexes consisting of the core part where DNA chains were tightly condensed by PEI and the outer layer lined with chitosan, and found that an optimal PDC complex exhibits a significantly higher transfection efficiency in a high serum condition and a lower toxicity than monolithic PEI/DNA (PD) complex. Moreover, addition of chitosan to PEI/DNA complex reduced nonspecific interactions with erythrocytes, which may eventually contribute to improved transfection efficiency in high serum concentrations. These results demonstrate that chitosan coating of PD complex might increase the efficiency of PEI-mediated gene delivery in vivo as well as in vitro.