title: Transfection efficiency of chitosan and thiolated chitosan in retinal pigment epithelium cells: A comparative study.
abstract: OBJECTIVE
  Gene therapy relies on efficient vector for a therapeutic effect. Efficient non-viral vectors are sought as an alternative to viral vectors. Chitosan, a cationic polymer, has been studied for its gene delivery potential. In this work, disulfide bond containing groups were covalently added to chitosan to improve the transfection efficiency. These bonds can be cleaved by cytoplasmic glutathione, thus, releasing the DNA load more efficiently.
  
  
  METHODS
  Chitosan and thiolated chitosan nanoparticles (NPs) were prepared in order to obtain a NH3(+):PO(4) (-) ratio of 5:1 and characterized for plasmid DNA complexation and release efficiency. Cytotoxicity and gene delivery studies were carried out on retinal pigment epithelial cells.
  
  
  RESULTS
  In this work, we show that chitosan was effectively modified to incorporate a disulfide bond. The transfection efficiency of chitosan and thiolated chitosan varied according to the cell line used, however, thiolation did not seem to significantly improve transfection efficiency.
  
  
  CONCLUSIONS
  The apparent lack of improvement in transfection efficiency of the thiolated chitosan NPs is most likely due to its size increase and charge inversion relatively to chitosan. Therefore, for retinal cells, thiolated chitosan does not seem to constitute an efficient strategy for gene delivery.
authors.affiliation: Centre for Molecular and Structural Biomedicine (CBME/IBB, LA), University of Algarve, Faro, 8005-139, Portugal ; PhD Program in Biomedical Sciences, University of Algarve, Faro, 8005-139, Portugal ; Department of Biomedical Sciences and Medicine, University of Algarve, Faro, 8005-139, Portugal.
authors.forename: Ana V
authors.initials: AV
authors.lastname: Oliveira
authors.forename: Andreia P
authors.initials: AP
authors.lastname: Silva
authors.forename: Diogo B
authors.initials: DB
authors.lastname: Bitoque
authors.forename: Gabriela A
authors.initials: GA
authors.lastname: Silva
authors.forename: Ana M
authors.initials: AM
authors.lastname: Rosa da Costa
keywords: Chitosan; gene therapy; non-viral vectors; thiolation; transfection efficiency