Spontaneous Formation of Cationic Vesicles in Aqueous DDAB-Lecithin Mixtures for Efficient Plasmid DNA Complexation and Gene Transfection.

Cationic liposomes have become an attractive tool to deliver genes and interfering RNA into cells. Herein, we report the application of spontaneously formed cationic vesicles in mixtures of lecithin and cationic amphiphiles for efficient transfection of plasmid DNA and siRNA into cells. The average hydrodynamic diameter of the phospholipid vesicles was modulated by changing the ratio of dihexadecyldimethylammonium bromide (DDAB) to phospholipid in the vesicles. The vesicles were characterized by dynamic light scattering, ζ potential, and small-angle X-ray scattering. Depending on the ratio of DDAB to phospholipid, the average size of the vesicles can be varied in the range of 150-300 nm with a ζ potential of +40 mV. The ability of these cationic vesicles to form lipoplexes upon binding with pDNA is demonstrated by ζ potential, isothermal titration calorimetry, gel retardation, and DNase I digestion assay. The enthalpy of binding between pDNA and cationic liposome was found to be -5.7 (±0.8) kJ/mol. The cellular uptake studies of lipoplexes observed by fluorescence microscopy confirmed good transfection efficiency of DDAB liposomes in MCF-7 and HeLa cells. The fluorescent imaging analysis showed effective gene delivery and expression of green fluorescent protein. In addition, the formulation has demonstrated an ability to deliver small interfering RNA (siBRD4) for efficient gene silencing as seen by a significant decrease in BRD4 protein level in siBRD4-treated cells. Comparison of the transfection efficiency of different formulations suggests that DDAB-rich mixed phospholipid vesicles with size <200 nm are better than large size vesicles for improved endocytosis and gene expression.

Discerning the Structure Factor of Charged Micelles in Water and Supercooled Solvent by Contrast Variation X-ray Scattering.

Sodium dodecyl sulfate (SDS) is a well-known anionic surfactant that forms micelles in various solvents including supercooled sugar-urea melt. Here, we explore the application of contrast variation small-angle X-ray scattering (SAXS) in discerning the structure and interactions of SDS micelles in aqueous solution and in a room-temperature supercooled solvent. The SAXS patterns can be analyzed in terms of a core-shell ellipsoid model. For aqueous SDS micelles, at low volume fractions, the features due to intermicellar interaction, S(q), in the SAXS pattern are poorly resolved because of the prominent contribution from shell scattering. Increasing the electron density of the solvent by the addition of the urea or fructose-urea mixture (at a weight ratio of 6:4) permits the systematic variation of shell scattering without influencing the structure drastically. For a 10% solution of SDS in water, the contribution from the shell can be completely masked by the addition of 40% urea or fructose-urea mixture. The fructose-urea mixture is a preferred additive as it can vary the scattering length density over a wide range and serves as a matrix to form supercooled micelles. The structural parameters of micelles in supercooled fructose-urea melt are obtained from contrast variation SAXS, small-angle neutron scattering, and high-resolution transmission electron microscopy.