Evaluation of different buffers on plasmid DNA encapsulation into PLGA microparticles

Double emulsion solvent evaporation is a widely used method to prepare poly(dl-lactide-co-glycolide) (PLGA) microparticles encapsulating plasmid DNA. There are inherent problems associated with preparing plasmid DNA in this form, in particular the DNA is liable to degrade during manufacture and the resulting powder has low encapsulation efficiencies. This study compares the use of two buffers, 0.1 M NaHCO3 and 0.07 M Na2HPO4 and the effect these have on the encapsulation efficiency and other critical parameters associated with these encapsulated DNA materials. Both buffers preserved the conformation of the original plasmid DNA during the homogenization process, but those made with 0.07 M Na2HPO4 had higher encapsulation efficiencies, as well as smaller diameters, compared with those made with 0.1 M NaHCO3 (encapsulation efficiencies of 40.72–45.65%, and mean volume diameters of 2.96–4.45 μm). Buffers with a range of pH from 5 to 12 were investigated, and it was demonstrated that pH 9 was the point at which the highest amount of supercoiled DNA was balanced with the highest encapsulation efficiency. To simulate in vitro release, it was shown that microparticles made with 0.07 M Na2HPO4 had lower DNA release rates than those made with 0.1 M NaHCO3. These results demonstrate that the use of different buffers can aid in retaining the conformation of plasmid DNA, and can also modulate the amount of DNA encapsulated and the release profiles of microparticles.