International Journal of Pharmaceutics 420 (2011) 341–349 Contents lists available at SciVerse ScienceDirect International Journal of Pharmaceutics jo ur nal homep a ge: www.elsevier.com/locate/ijpharm Pharmaceutical Nanotechnology Cationic solid lipid nanoparticles (cSLN): Structure, stability and DNA binding capacity correlation studies S. Doktorovova a,b , R. Shegokar b , E. Rakovsky c , E. Gonzalez-Mira d , C.M. Lopes a,e , A.M. Silva f , P. Martins-Lopes a , R.H. Muller b , E.B. Souto a,e,∗ a Institute of Biotechnology and Bioengineering, Centre of Genomics and Biotechnology, University of Trás-os-Montes and Alto Douro (IBB/CGB-UTAD), Vila-Real, Portugal b Institute of Pharmacy, Department of Pharmaceutics, Biopharmaceutics & NutriCosmetics, Freie Universität Berlin, Berlin, Germany c Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia d Department of Physical Chemistry, Faculty of Pharmacy, University of Barcelona, Barcelona, Spain e Faculty of Health Sciences, Fernando Pessoa University, Porto, Portugal f Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (CITAB-UTAD), Vila-Real, Portugal a r t i c l e i n f o Article history: Received 5 July 2011 Received in revised form 24 August 2011 Accepted 26 August 2011 Available online 2 September 2011 Keywords: Solid lipid nanoparticles Gene delivery Differential scanning calorimetry Wide angle X-ray scattering Stability studies a b s t r a c t Cationic solid lipid nanoparticles (cSLN) are promising lipid nanocarriers for intracellular gene deliv- ery based on well-known and widely accepted materials. cSLN containing single-chained cationic lipid cetyltrimethylammonium bromide were produced by high pressure homogenization and characterized in terms of (a) particle size distribution by photon correlation spectroscopy (PCS) and laser diffractometry (LD), (b) thermal behaviour using differential scanning calorimetry (DSC) and (c) the presence of vari- ous polymorphic phases was confirmed by X-ray diffraction (WAXD). SLN composed of Imwitor 900P TM (IMW) showed different pDNA stability and binding capacity in comparison to those of Compritol 888 ATO TM (COM). IMW-SLN, having z-ave = 138–157 nm and d(0.5) = 0.15–0.158 m could maintain this size for 14 days at room temperature. COM-SLN had z-ave = 334 nm and d(0.5) = 0.42 m on the day of produc- tion and could maintain similar size during 90 days. IMW-SLN revealed improved pDNA binding capacity. We attempted to explain these differences by different interactions between the solid lipid and the tested cationic lipid. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Solid lipid nanoparticles (SLN) are versatile colloidal carriers being currently explored for administration routes (e.g. parenteral, oral, topical, dermal and transderaml) (Souto and Müller, 2007). Their advantage over colloidal carriers composed of polymers or inorganic material is the use of biocompatible lipids with well- established use in pharmaceuticals, e.g. glycerols with fatty acids, free fatty acids, fatty alcohols or waxes. This makes these systems closer to real-life use (Souto et al., 2011). Distinct advantage of SLN over polymeric nanoparticles is that SLN can be produced without Abbreviations: CMC, critical micelle concentration; COM, Compritol 888 ATO; CTAB, cetyltrimethylammonium bromide; HLB, hydrophilic–lipophilic balance; IMW, Imwitor 900; LD, laser diffraction; MIR, Miranol Ultra C-32; PCS, photon cor- relation spectroscopy; Polox, Poloxamer 188; SLN, solid lipid nanoparticles; Tm, melting temperature; z-ave, z-average (intensity weighed diameter); ZP, zeta poten- tial. ∗ Corresponding author at: Faculty of Health Sciences of Fernando Pessoa Univer- sity, Rua Carlos da Maia, 296, P-4200-150 Porto, Portugal. Tel.: +351 22 507 4630; fax: +351 22 550 4637. E-mail addresses: eliana@ufp.edu.pt, souto.eliana@gmail.com (E.B. Souto). use of organic solvents, using high pressure homogenization (HPH) method that is already successfully implemented in pharmaceuti- cal industry. Cationic SLN (cSLN), i.e. SLN containing at least one cationic lipid, have been proposed as non-viral vectors for gene delivery (Bondi and Craparo, 2010). The use of cSLN in this application is already quite well proven – it has been shown that cSLN can effectively bind nucleic acids, protect them from DNAase I degradation and deliver them into living cells (Bondi et al., 2007; Vighi et al., 2007; Xue and Wong, 2011). First proof of in vivo efficiency of SLN has also been reported (del Pozo-Rodríguez et al., 2010). A review of materials, production methods and in vitro testing has been reviewed by Bondi and Craparo (2010). Although efficacy in DNA/RNA delivery into living cells has been satisfactorily proven (Bondi and Craparo, 2010; del Pozo-Rodríguez et al., 2010), there are still many features that need to be explained. Hardly predictable stability and polymorphic transformations of SLN have been related to their solid state (Bunjes, 2010). These fea- tures may have an impact on their use in future medicines. The same holds true for cSLN. In this study, we focused on cSLN containing one cationic lipid with a single hydrocarbon chain. We attempted to correlate physicochemical characteristics of the developed 0378-5173/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpharm.2011.08.042