Chitosan–DNA complexes: Effect of molecular parameters on the efficiency of delivery

In the last few decades, there has been a growing interest towards the use of delivery systems for a more effective treatment of various diseases and the research increasingly focused on designing innovative solutions based on intra-cellular vectors. Among them, biocompatible DNA–polyelectrolyte complexes appear as a promising strategy for in vivo delivery of biologically active macromolecules. One of the most largely employed cationic polymer is Chitosan, which is special for its biological properties such as biodegradability, biocompatibility, mucoadhesivity, and permeability enhancer capacity. Due to this, complexes formed by condensation of DNA by Chitosan have been largely investigated for their potential use in gene therapy. Nevertheless the extensive efforts, the correlation between the physicochemical properties of the Chitosan–DNA polyplexes with their transfection efficiency still remains a central challenge. Moreover, the criteria and strategies for the design of efficient Chitosan-based gene delivery systems remain inconclusive. In a recent paper, we studied the aggregation behavior of Chitosan–DNA complexes and compared it with the predictions of existing models for the complexation of oppositely charged polyelectrolytes, showing that these models can serve as useful guide for the optimization of the complexes. Here, in order to understand the relation between physicochemical and transfection properties of Chitosan–DNA complexes, we study the efficiency of Chitosan–pDNA aggregates obtained in different conditions as vectors for DNA transfection. Small, globular and positively charged aggregates formed at large Chitosan excess, which can be obtained independently of the length of the Chitosan employed, appear to be the more effective for transfection, the more stable aggregates resulting the ones formed with longer chains.