Comparison of chitosan/siRNA and trimethylchitosan/siRNA complexes behaviour in vitro

Chitosan and trimethylchitosan (TMC)-siRNA nanoparticles were produced by simple complexation technique or by ionic gelation using tripolyphosphate (TPP). The obtained complexes were characterized in terms of physicochemical properties such as size, zeta potential, complexation efficiency and stability. Furthermore, cytotoxicity, cell uptake and transfection efficiency of polyplexes were evaluated in vitro. Under pH condition of cell culture medium, a strong decrease in siRNA condensation efficiency was observed with chitosan nanoparticles. This characteristic resulted in low transfection efficiencies in HEK293 cell line. Formulation of chitosan polyplexes with TPP led to improvement of polyplexes stability but no significant increase in transfection efficiency was observed compared to simple chitosan complexes. By contrast, TMC complexes did not have pH dependency on siRNA complexation. TMC-siRNA nanoparticles were stable in physiological condition. Accordingly, cellular uptake was increased compared to chitosan polyplexes. However, improvement of transfection efficiency was low regarding to cellular uptake of these complexes. Chitosan and TMC complexes present some characteristics favourable for siRNA delivery, such as ability to integrate siRNA into small discrete particles or low toxicity of the complexes. This study also highlights the importance of complexes stability in physiological environment for siRNA transfection purposes.