Encapsulation of protamine sulphate compacted DNA in polylactide and polylactide-co-glycolide microparticles

This paper details the development and characterisation of a DNA-loaded microsphere system for gene delivery purposes. Encapsulation of DNA in microspheres was carried out by precondensation of the DNA with protamine sulphate, followed by encapsulation in a polymeric microsphere using a water-oil-water (w/o/w) solvent evaporation-emulsion process. The polymers used were polylactide and polylactide-co-glycolide. The amount of DNA encapsulated in the microsphere formulation was dependent on the weight ratio of protamine sulphate: DNA, with higher ratios (0.87:1 or 2:1) giving better encapsulation efficiencies (> or =62%). Additionally, compared to non-compacted DNA, the encapsulation of a protamine sulphate:DNA complex increased protection of the DNA against nuclease and decreased shear effects during processing. The release profile of DNA was shown to be dependent on the polymer type and polymer molecular weight. DNA was released relatively quickly from the microspheres and the released DNA primarily existed in a relaxed state. However, in vitro transfection experiments indicated that the DNA was still active upon release from the microspheres.