EFFECT OF PH ON THE STRUCTURE OF LIPOPLEXES

Recently, it has been postulated that a primary importance of the pH is for accomplishing efficient lipid-mediated translocation of nucleic acids across the endosomal membrane into the cytosol for transport to the nucleus. With the aim of providing insight into the postulated correlation between transfection efficiency, phase evolution of lipoplexes upon acidification, and DNA release, we investigated the pH dependence of the structure of low efficiency 1,2-di- oleoyl-3-trimethylammonium-propane-dioleoylphosphocholine/DNA and high efficiency 3B-[N- (N',N'-dimethylaminoethane)-carbamoyl]-cholesterol-dioleoylphosphatidylethanolamine/DNAlipo- plexes by high-resolution synchrotron small-angle x-ray diffraction, while the extent of DNA release was estimated by means of electrophoresis on agarose gels. Here we show that upon acidification from physiological to acidic values (as those characteristic of endosomes), (i) the lamellar structure of lipoplexes was preserved with a decrease in the one-dimensional DNA packing density, reflecting a pH-induced contraction of interfacial area of lipid head groups and (ii) DNA was not released from lipoplexes. Distinct levels of transfection between lipoplexes were interpreted in terms of the different DNA-binding capacities of cationic liposomes