title: Influence of chitosan structure on the formation and stability of DNA-chitosan polyelectrolyte complexes.
abstract: The interactions between DNA and chitosans varying in fractional content of acetylated units (FA), degree of polymerization (DP), and degree of ionization were investigated by several techniques, including an ethidium bromide (EtBr) fluorescence assay, gel retardation, atomic force microscopy, and dynamic and electrophoretic light scattering. The charge density of the chitosan and the number of charges per chain were found to be the dominating factors for the structure and stability of DNA-chitosan complexes. All high molecular weight chitosans condensed DNA into physically stable polyplexes; however, the properties of the complexes were strongly dependent on FA, and thereby the charge density of chitosan. By employing fully charged oligomers of constant charge density, it was shown that the complexation of DNA and stability of the polyplexes is governed by the number of cationic residues per chain. A minimum of 6-9 positive charges appeared necessary to provide interaction strength comparable to that of polycations. In contrast, further increase in the number of charges above 9 did not increase the apparent binding affinity as judged from the EtBr displacement assay. The chitosan oligomers exhibited a pH-dependent interaction with DNA, reflecting the number of ionized amino groups. The complexation of DNA and the stability of oligomer-based polyplexes became reduced above pH 7.4. Such pH-dependent dissociation of polyplexes around the physiological pH is highly relevant in gene delivery applications and might be one of the reasons for the high transfection activity of oligomer-based polyplexes observed.
authors.affiliation: NOBIPOL, Department of Biotechnology, and Biophysics and Medical Technology, The Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway. sabina.strand@biotech.ntnu.no
authors.forename: Sabina P
authors.initials: SP
authors.lastname: Strand
authors.forename: Signe
authors.initials: S
authors.lastname: Danielsen
authors.forename: Bjørn E
authors.initials: BE
authors.lastname: Christensen
authors.forename: Kjell M
authors.initials: KM
authors.lastname: Vårum
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D002412:Cations; D002417:Cattle; D048271:Chitosan / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry*; D004586:Electrophoresis; D004996:Ethidium / Q000737:chemistry / Q000494:pharmacology; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D006863:Hydrogen-Ion Concentration; D007364:Intercalating Agents; D007477:Ions; D008027:Light; D046911:Macromolecular Substances / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D011094:Polyethyleneimine; D011107:Polylysine; D011108:Polymers / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D012542:Scattering, Radiation; D055672:Static Electricity; D013950:Thymus Gland / Q000378:metabolism; D013997:Time Factors
chemical_list: D001672:Biocompatible Materials; D002412:Cations; D004573:Electrolytes; D007364:Intercalating Agents; D007477:Ions; D046911:Macromolecular Substances; D011108:Polymers; D011107:Polylysine; D011094:Polyethyleneimine; D004247:DNA; D048271:Chitosan; D004996:Ethidium