Delphine Castagne

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.

Spectroscopic studies and molecular modeling for understanding the interactions between cholesterol and cyclodextrins.

PURPOSE Cholesterol is a major lipid constituent of biological membranes which could be included in cyclodextrin (CD) cavities. Solubilization and cell extraction of cholesterol have been previously performed in order to study its interaction with beta-CD and methylated beta-derivatives notably. The present work aims at confirming the formation of inclusion complexes between these CDs and cholesterol in order to understand their solubilization and cell extraction capacities. METHODS In this context, liquid-state NMR spectroscopy (1H NMR studies and ROESY experiments) as well as theoretical studies (molecular modeling) have been performed. RESULTS Rather than preferential conformations, the spectroscopic studies showed us the possible interactions between cholesterol and dimethyl-beta-CD, trimethyl-beta-CD, randomly methylated beta-CD or Crysmeb®. Weak interactions were detected using the latter one, confirming the advantage of the low substitution to decrease membrane loss of integrity and cytotoxicity. Molecular modeling studies should be used to determine which stoichiometry and conformations are energetically more favorable. The semi-empirical AM1 level was used to investigate both 1:1 and 1:2 complexes whereas 1:1 complexes were also studied using minimal or double ζ basis sets. Four conformations for each 1:2 complexes have been envisaged and studied for the methylated CDs. CONCLUSIONS These studies allowed us to confirm the interactions between cholesterol and beta-CDs especially the methylated derivatives.