Submicron cationic emulsions as a new delivery system for oligonucleotides.

Abstract

The main purpose of the present study was to investigate submicron emulsions as potential oligonucleotide (ON) delivery system. Submicron emulsions containing various concentrations of stearylamine (SA) were prepared by microfluidization. After association with model oligothymidylates, these emulsions were characterized in terms of particle size, zeta-potential, association efficiency and release upon dilution. The interactions between ON and SA were investigated by partitioning studies between water and oily phases, with ON of three different lengths (pdT16, pdT30, pdT50). The stability of pdT16 in the presence of nucleases was evaluated by incubation in cell culture medium supplemented with 10% of foetal calf serum. The ON association efficiency was much higher with emulsions containing SA (E(SA)) than with control emulsions (E0), whatever the ON length. In addition, E(SA) was shown to protect ON against degradation for up to 3 hours in culture medium. ON and SA were able to form ion-pairs and the resulting complex was found to be insoluble both in water and in oil. Zeta potential was maintained constant when increasing the ON concentration, until flocculation occurred (up to 250 microM in the case of pdT16 for example). This has been explained by the presence of SA in excess, soluble in the oily core of droplets, able to migrate towards the interface and replacing SA neutralized in ion-pairs. ESA appears to be a valuable system for delivery of ON and might even be improved by selecting an oily phase in which the SA/ON complex would be soluble.