Methylated N-(4-N,N-dimethylaminobenzyl) chitosan as effective gene carriers: Effect of degree of substitution

The objective of this study was to investigate the transfection efficiency of quaternized N-(4-N,N-dimethylaminobenzyl) chitosan; TM-Bz-CS, using the plasmid DNA encoding green fluorescent protein (pEGFP-C2) on human hepatoma cell lines (Huh7 cells). The factors affecting the transfection efficiency e.g. degree of quaternization (DQ), the degree of dimethylaminobenzyl substitution (DS) and polymer/DNA weight ratio, have been evaluated. The results revealed that all TM-Bz-CS derivatives were able to condense with DNA. Illustrated by agarose gel electrophoresis, complete complexes of TM₅₇-Bz₄₂-CS/DNA were formed at weight ratio of above 0.5, whereas those of TM₄₇-Bz₄₂-CS/DNA and TM₅₇- Bz₁₇-CS/DNA were above 1. The rank of transfection efficiency of the chitosan derivatives were TM₅₇-Bz₄₂-CS > TM₄₇-Bz₄₂-CS > TM₅₇-Bz₁₈-CS. The pH of culture medium did not affect the transfection efficiency of TM₅₇-Bz₄₂-CS/DNA complex, whereas it affected the transfection efficiency of chitosan/DNA complex. The results indicated that the improved gene transfection was due to the hydrophobic group (N,N-dimethylaminobenzyl) substitution on chitosan which promoted the interaction and condensation with DNA as well as N-quaternization which increased chitosan water solubility and enhance gene expression. For cytotoxicity studies, TM-Bz-CS was safe at the concentration of the highest transfection. In conclusion, this novel chitosan derivative, TM₅₇-Bz₄₂-CS showed elevated potential as gene carrier by efficient DNA condensation and mediated highest level of gene transfection with negligible cytotoxicity in Huh7 cells.