Abstract

Polyplexes, which are formed spontaneously between cationic polymer and negatively charged nucleic acids, are commonly used for gene and oligonucleotide delivery in vitroand in vivo. Many kinds of cationic polymers have been used to condense DNA by electrostatic interaction into small particles (Polyplexes), for protecting the DNA from degradation and enhancing its uptake via endocytosis. Polyethylenimine (PEI) appears to be one of the most advanced delivery materials that can condense DNA efficiently forming PEI/DNA complexes. The PEI/DNA interaction was evaluated by measuring zeta potential and DNA secondary structures using Fourier-transform infrared (FTIR) technique. IR results show that the antisymmetric PO^2- vibration of DNA (at 1236 cm^-1) shifts toward lower frequencies when complexed with PEI. The secondary conformation of DNA in aqueous solution clearly remains in B-form. Thermal behaviors of plasmid DNA, polymer and their formed complexes were recorded to give insights into their conformational changes when temperature was raised. DSC results showed a disappearance of the main DNA transition band at 94°C at all examined N/P (0.3 to 5) ratios of PEI/DNA complexes. These findings could be useful for the developing polymer-based gene delivery systems with better in vitro and in vivo performance.

Key words: Polyethylenimine, DNA, Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), zeta potential.