Journal of Colloid and Interface Science 312 (2007) 87–97 www.elsevier.com/locate/jcis DNA encapsulation by biocompatible catanionic vesicles ✩ Mónica Rosa a,b,∗ , Maria da Graça Miguel a , Björn Lindman a,b a Chemistry Department, Coimbra University, 3004-535 Coimbra, Portugal b Physical Chemistry 1, Lund University, P.O. Box 124, 22100 Lund, Sweden Received 16 May 2006; accepted 29 July 2006 Available online 9 August 2006 Abstract The encapsulation of DNA by catanionic vesicles has been investigated; the vesicles are composed of one cationic surfactant, in excess, and one anionic. Since cationic systems are often toxic, we introduced a novel divalent cationic amino-acid-based amphiphile, which may enhance transfection and appears to be nontoxic, in our catanionic vesicle mixtures. The cationic amphiphile is arginine–N -lauroyl amide dihydrochloride (ALA), while the anionic one is sodium cetylsulfate (SCS). Vesicles formed spontaneously in aqueous mixtures of the two surfactants and were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM); the vesicles are markedly polydisperse. The results are compared with a study of an analogous system based on a short-chained anionic surfactant, sodium octylsulfate (SOS). Addition of DNA to catanionic vesicles resulted in associative phase separation at very low DNA concentrations; there is a separation into a precipitate and a supernatant solution; the latter is first bluish but becomes clearer as more DNA is added. From studies using cryo-TEM and small angle X-ray scattering (SAXS) it is demonstrated that there is a lamellar structure with DNA arranged between the amphiphile bilayers. Comparing the SOS containing DNA–vesicle complexes with the SCS ones, an increase in the repeat distance is perceived for SCS. Regarding the phase-separating DNA–amphiphile particles, cryo-TEM demonstrates a large and nonmonotonic variation of particle size as the DNA–amphiphile ratio is varied, with the largest particles obtained in the vicinity of overall charge neutrality. No major differences in phase behavior were noticed for the systems here presented as compared with those based on classical cationic surfactants. However, the prospect of using these systems in real biological applications offers a great advantage. © 2006 Elsevier Inc. All rights reserved. Keywords: Catanionic vesicles; DNA 1. Introduction The research activity involving gene therapy with either viral or synthetic vectors is extensive and unique. Synthetic vectors have generally been considered to be less efficient than their viral counterparts but have clear advantages [1,2]: ease and variability of preparation; lack of immune response; and unlim- ited DNA-carrying capacity (allows delivery of human artificial chromosomes [3]). Recent problems in clinical trials with vi- ral vectors, namely a fatality induced by a severe inflammatory ✩ This work is submitted to honor the memory of the great chemist Professor Kunieda, with whom the senior authors had many fruitful contacts and collab- orations during a long sequence of years. * Corresponding author. E-mail address: acinom@ci.uc.pt (M. Rosa). response [4] and insertional mutagenesis caused by retroviral vectors [5], have further encouraged the study and development of new efficient nonviral vectors. Furthermore, a recent study on nonviral systems suggested that the anti-tumor activity of some cationic entities together with their transfection capabil- ity can be explored to successfully improve gene therapy [6]. This study by Dufes et al. [6] could potentially revitalize the advancement of nonviral vectors not only with the purpose of improving the cellular delivery of genetic material, but also to exploit the vector’s intrinsic biological activities for additive or synergistic therapeutic effects. Usually, vesicular transport systems are the vehicles of choice within nonviral gene therapy, liposome-based systems being the most popular ones so far [7]. Due to the growing need for novel engineered vehicles, we present in this study catan- ionic vesicle systems as DNA carriers. By catanionic systems 0021-9797/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2006.07.084