Characterization of calcium phosphate as a gene carrier (II): Zeta potential and DNA transfection

The pH of the transfection medium has been shown to be crucial for the calcium phosphate (CaPi)-mediated DNA transfection. This study was undertaken in an attempt to examine several physicochemical properties associated with the pH change as related to DNA transfection efficiency. The zeta potential, flocculation coefficient, and adsorption kinetics of [(3)H]DNA-CaPi complexes onto FR3T3 cells were experimentally examined as a function of pH of the Hepes-buffered saline (HBS) in which the coprecipitates were formed, which were then correlated with the DNA transfection efficiency. (3)H-labeled plasmid DNA was found to be adsorbed on the flocculated CaPi particles for the HBS pH greater than 6.16. Adsorption of CaPi-DNA complexes onto the cell surfaces renders the cell surface charge less negative. Both zeta potentials and the flocculation coefficients of the CaPi-DNA coprecipitates were shown to vary with pH of the system, but no significant difference in the kinetics of adsorption was observed for the CaPi-DNA coprecipitates prepared at various pH. Zeta potentials of the CaPi-DNA coprecipitates lying between 11 and 21 mV were determined to be efficient for the CaPi-DNA complexes to be effectively internalized by the cells. The pH appears to be a determinant factor in the properties studied. The physicochemical properties of the CaPi-DNA complexes play important roles in the interaction between CaPi-DNA complexes and cells, which consequently affect the cell transformation efficiency.