title: Chitosan-DNA complexes: charge inversion and DNA condensation.
abstract: The design of biocompatible polyelectrolyte complexes is a promising strategy for in vivo delivery of biologically active macromolecules. Particularly, the condensation of DNA by polycations received considerable attention for its potential in gene delivery applications, where the development of safe and effective non-viral vectors remains a central challenge. Among polymeric polycations, Chitosan has recently emerged as a very interesting material for these applications. In this study, we compare the observed aggregation behavior of Chitosan-DNA complexes with the predictions of existing models for the complexation of oppositely charged polyelectrolytes. By using different and complementary microscopy approaches (AFM, FESEM and TEM), light scattering and electrophoretic mobility techniques, we characterized the structures of the complexes formed at different charge ratios and Chitosan molecular weight. In good agreement with theoretical predictions, a reentrant condensation, accompanied by charge inversion, is clearly observed as the polycation/DNA charge ratio is increased. In fact, the aggregates reach their maximum size in correspondence of a value of the charge ratio where their measured net charge inverts its sign. This value does not correspond to the stoichiometric 1:1 charge ratio, but is inversely correlated with the polycation length. Distinctive "tadpole-like" aggregates are observed in excess polycation, while only globular aggregates are found in excess DNA. Close to the isoelectric point, elongated fiber-like structures appear. Within the framework of the models discussed, different apparently uncorrelated observations reported in the literature find a systematic interpretation. These results suggest that these models are useful tools to guide the design of new and more efficient polycation-based vectors for a more effective delivery of genetic material.
authors.affiliation: Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Amaduzzi
authors.affiliation: Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Bomboi
authors.affiliation: Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy.
authors.forename: Adalberto
authors.initials: A
authors.lastname: Bonincontro
authors.affiliation: Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy; CNR-IPCF UOS Roma, c/o Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy. Electronic address: federico.bordi@roma1.infn.it.
authors.forename: Federico
authors.initials: F
authors.lastname: Bordi
authors.affiliation: Dipartimento di Igiene del Lavoro, ISPESL, 00040 Monte Porzio Catone, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Casciardi
authors.affiliation: Dipartimento di Chimica, Sapienza Università di Roma, P.zzle A. Moro, 5, 00185 Roma, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Chronopoulou
authors.affiliation: Dipartimento di Tecnologie e Salute, Istituto Superiore di Sanità, V.le Regina Elena 299, 00161 Roma, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Diociaiuti
authors.affiliation: Dipartimento di Scienze di Base Applicate all'Ingegneria, Sapienza Università di Roma, Via A. Scarpa, 14, 00183 Roma, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Mura
authors.affiliation: Dipartimento di Chimica, Sapienza Università di Roma, P.zzle A. Moro, 5, 00185 Roma, Italy.
authors.forename: Cleofe
authors.initials: C
authors.lastname: Palocci
authors.affiliation: Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy; CNR-IPCF UOS Roma, c/o Dipartimento di Fisica, Sapienza Università di Roma, P.zzle A. Moro, 2, 00185 Roma, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Sennato
mesh_terms: D000818:Animals; D002417:Cattle; D048271:Chitosan / Q000737:chemistry*; D004247:DNA / Q000737:chemistry* / Q000648:ultrastructure; D057446:Hydrodynamics; D007526:Isoelectric Point; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D010316:Particle Size; D055672:Static Electricity
chemical_list: D004247:DNA; D048271:Chitosan; C427203:calf thymus DNA
keywords: Charge inversion; Chitosan; DNA; Gene-therapy; Polyelectrolytes; Polyplexes