Coprecipitation of DNA-lipid complexes with apatite and comparison with superficial adsorption for gene transfer applications

Apatite can mediate gene transfer into cells by serving as a safe and biocompatible immobilization matrix for DNA and transfection reagents. Recently, an apatite layer that immobilized DNA-lipid complexes was prepared by a coprecipitation process in a supersaturated calcium phosphate solution. This composite layer (DNA–lipid–apatite layer) showed a higher gene transfer capability than an apatite layer with superficially adsorbed DNA-lipid complexes (DNA-lipid-adsorbed apatite layer). In this study, the DNA–lipid–apatite layer and the DNA-lipid-adsorbed apatite layer were compared for their physicochemical properties and gene transfer capabilities. The higher gene transfer capability of the DNA–lipid–apatite layer compared with that of the DNA-lipid-adsorbed apatite layer was reconfirmed by a luciferase assay using epithelial-like CHO-K1 cells. Physicochemical structure analyses showed that the DNA–lipid–apatite layer possessed a larger capacity for DNA-lipid complexes than the DNA-lipid-adsorbed apatite layer. The DNA–lipid–apatite layer released DNA-lipid complexes in a slow and sustained manner, whereas the DNA-lipid-adsorbed apatite layer released them in short bursts. Consequently, the release of DNA-lipid complexes from the DNA–lipid–apatite layer was larger in amount and longer in duration than release from the DNA-lipid-adsorbed apatite layer. This difference in release profiles may be responsible for the higher gene transfer capability of the DNA–lipid–apatite layer compared with that of the DNA-lipid-adsorbed apatite layer. The coprecipitation process and the resulting DNA–lipid–apatite layer have many applications in tissue engineering.