Structure and Interfacial Aspects of Self-Assembled Cationic Lipid−DNA Gene Carrier Complexes

Abstract

Cationic lipid−DNA (CL−DNA) complexes were recently found to exhibit a novel multilamellar structure composed of alternating lipid bilayer and DNA monolayer with distinct interhelical DNA spacings (Rädler et al. Science 1997, 275, 810). We report on the aggregation behavior, morphology, and interfacial properties related to the solution structure of DOPC/DOTAP−DNA complexes. Using optical microscopy and synchrotron X-ray diffraction, we found two discrete regimes for the complex size and surface charge as a function of the lipid-to-DNA mass ratio. The regimes correspond to the coexistence of complexes with either excess DNA or excess liposomes, characterized by a negative and positive surface potential of the complexes, respectively. The internal structure in these cases exhibited different but constant DNA packing distances of 35 and 46 Å, respectively. The regimes are separated by a transition region around the isoelectric point, where the number of cationic lipids equals the number of DNA phosphate groups. At the isoelectric point the average complex size diverged and the DNA packing spacing is described by a simple volume fraction calculation. The complex formation occurred on three time scales: rapid condensation, a slower colloidal aggregation, and finally, a long term reorganization or compaction. Complexes with positive surface charge were shown to adhere to negatively charged giant liposomes.

DNA and surfactants in bulk and at interfaces

“…These systems have been extensively studied and even though the mechanism of formation is still far from understood, the structure of the complexes is believed to be a short ranged lamellar, composed of amphiphile bilayers with DNA molecules ordered and packed between the lipid stacks. This type of structure has been observed for systems with different lipid components [55][56][57][58].…”

The association of DNA and stable catanionic amino acid-based vesicles

“…As DNA is added to the vesicle solution, small complexes start to form at low concentrations; at slightly higher DNA concentrations they begin to aggregate forming larger clusters, as noted from the maximum in x c>300 nm × 300 nm for R = 1. Cluster formation at electroneutrality has been seen previously in systems of hydrophobically modified polyelectrolytes/oppositely charged surfactants [53], on DNA/cationic liposomes [8,44,55,56] as well as in Monte Carlo simulations of polyelectrolyte-macroion solutions [54]. Above this isoelectric point, the clusters start to become smaller and the complexes begin drifting apart from each other, due to electrostatic repulsions generated by the excess of negative charges in the structures.…”

“…The formation of this kind of structure has previously been reported in the literature for lipidic and amphiphilic-based systems and DNA [8,[40][41][42]. Furthermore, we believe that the fact that the DNA-DNA spacing decreases for R values above 1 is characteristic of catanionic-based systems, and that it represents an advantage from a transfection point of view [43] since it allows further compaction of DNA compared with liposome-based systems, where, after reaching the charge stoichiometry between cationic lipid and DNA, further addition of DNA does not result in a decrease in the DNA-DNA spacing within the complex [44].…”

“…Above this isoelectric point, the clusters start to become smaller and the complexes begin drifting apart from each other, due to electrostatic repulsions generated by the excess of negative charges in the structures. Rädler et al have also described this decrease in aggregation and related it with the charge reversal of the complexes due to excess of DNA [44]. From this point on, the fraction of smaller complexes increases considerably and the amount of complexes visualized decreases.…”

Synthesis and study of the complex formation of a cationic alkyl-chain bola amino alcohol with DNA: in vitro transfection efficiency

“…In a lipid membrane, the bolaamphiphile can extend completely across the membrane or form a U-shape conformation in a single membrane leaflet, depending on the length and flexibility of the hydrophobic chain. The bolaamphiphile considered here can in principle adopt both conformations: Either fully extended in a DOTAP bilayer with a thickness of approximately 3.7 nm [46] (the monomolecular layer of long alkyl monofunctional silanes (docosyl C22) has an average thicknesses of 3.5 nm [47]) or U-shape, as single-chain bolaamphiphiles form U-shapes at the air−water interface [35]. The mixed system BA:DOTAP formed stable complexes with DNA and the transfection efficiencies were similar or better than those of the pure DOTAP system.…”