Calcium Effect on Anionic Bicelle-DNA Complexes

Different from The liposome-DNA complexes, which were well-known to be used as nonviral vectors for improving the transfection efficiency of gene delivery, we demonstrate a novel type of anionic lipid-DNA (AB-DNA) complexes based on using typical disk-shaped bicelles. Having the advantage of lower cytotoxicity, the approach was proposed to induce anionic DPPG doped bicelles for forming the lamellar stacked structure with negatively charged DNA in the presence of sufficient calcium ions. Without the help of calcium ions or less ([Ca 2+ ] = 1 mM), anionic bicelles and DNA can’t complex together spontaneously. When [Ca 2+ ] was above threshold concentration of 10 mM, AB-DNA complex was found and had a bicelleCa 2+ -DNA alternating lamellar structure with a periodicity of 79.5 Å which composes by a bilayer and a DNA/Ca 2+ layer of 55 Å and 24.5 Å , respectively. Once AB-DNA complexes were formed, the spacing is independent of [Ca 2+ ]. Over a critical calcium ions concentration of 60 mM, the other lamellar phase of DPPG-containing multilamellar vesicles with Ca 2+ showed a decreasing spacing with increasing [Ca 2+ ] and coexists with AB-DNA complex. An excess of calcium ions facilitates more 2D DNA condensation in between bicelles so that extra lipids were repelled to form lamellar complexes with Ca 2+ . The data suggest an existence of critical calcium concentration under a certain component of anionic lipids in bicelles accompanied with constant DNA. This ion-mediated phase behavior may be helpful to the improvement on nonviral vector for gene therapy and delivery applications.