Studies on the condensation of depolymerized chitosans with DNA for preparing chitosan-DNA nanoparticles for gene...

High molecular weight chitosan (CS) was depolymerized by oxidative degradation with NaNO(2) at room temperature to get 11 samples of CS derivatives of varying molecular weights with a view to assessing their effective molecular weight range for gene delivery applications. Viscosity studies indicated that the molecular weight of the depolymerized CS was proportional to the CS/NaNO(2) ratio. The condensation behavior of DNA/CS complexes at various charge ratios was studied using UV spectroscopy, FTIR, CD, SEM, and AFM. The results indicated that CSs having very low molecular weights and high charge density exhibited strong binding affinity to DNA compared to high molecular weight CSs. However, the very low molecular weight (1.9-7.7 kDa) CSs were found to form aggregates easily even at very low charge ratios. On the other hand, CSs having medium molecular weight (49-51 kDa) and high degree of deacetylation (DD) gave stable uniform-sized nanoparticles. Biological studies carried out with the spherical nano-sized polyplexes formed between CS of 50 kDa (DD of 94%) and pEGFP plasmid DNA at N/P ratio of 5.0 showed excellent gene transfection efficiency at pH 6.5 in HeLa cells without cytotoxicity indicating their potential as gene delivery carriers.