Stabilisation Studies of Nucleic Acid Transfection Complexes
The transfection efficacy of DNA into cells is improved when DNA can form a complex with cationic lipids. However, one of the limitations of cationic lipid-DNA complexes is their instability in in-vivo systems. Several analytical techniques such as atomic force microscopy, transmission electro microscopy and dynamic light scattering were used to measure the size, shape and structure of these complexes. The complexes consist of spherical primary particles of approximately 60 nm in diameter connected to each other by DNA strands to form small clusters of approximately 70-200 nm in diameter. At low lipid concentrations, DNA strands protrude from the core of the complexes providing a strong negative charge for electrostatic repulsion between the complexes. At high lipid concentrations, these free DNA strands have disappeared, and the complexes are more compact and positively charged. These charged complexes are very stable at low salt concentrations, however they rapidly form large aggregates (micron size) in high salt concentrations or when the complex is electrically neutral, which may reduce their transfection efficacy of DNA into cells. The aggregation of the complexes was studied as a function of time, and the effect of stabilising compounds, such as pegylated lipids, on the complex stability and structure was also monitored.