Controlled embedment and release of DNA from lipidic reverse columnar hexagonal mesophases

DNA-lipid interactions have important implications for biological functions, gene therapy and biotechnology. In the present work, we exploit hydrogen bonding and ionic interactions between lipids and DNA to control the entrapment, the binding and the release properties of DNA confined within the water channels of reverse hexagonal columnar phases. Two lipid formulations were considered, consisting of glycerol monooleate/tricaprylin and glycerol monooleate/oleyl amine/tricaprylin, yielding the nonionic and cationic-based systems, respectively. In the presence of water, or water-DNA dilute solutions, both formulations led to the formation of reverse hexagonal columnar mesophases. To study the confinement of DNA in the reverse hexagonal mesophases, and to understand its interactions with the nonionic and cationic lipid formulations, we relied on small-angle X-ray scattering (SAXS) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The release of the DNA from these hosting systems in excess water was monitored by UV spectrophotometry and single molecule atomic force microscopy (AFM). In the case of the nonionic columnar system, DNA confined within the water cylinders, was stabilized by hydrogen bonding with the lipid polar heads, as revealed by the dehydration of the glycerol monooleate polar headgroups and a decrease in the water channel diameter. The diffusion of DNA out of the mesophase water channels was found to occur in three steps correlated with the different contour lengths of the DNA fragments generated enzymatically from the same pristine DNA macromolecule. In contrast, the presence of a low dose of cationic surfactants in the formulation enabled strong electrostatic interactions with the DNA molecules, swelling the water cylinders and entirely suppressing the release of DNA. These results show that lipidic mesophases constitute an appealing, fully biocompatible carrier, allowing a fine control on the encapsulation and delivery of DNA in excess water environment.