Development of an osmoprotective microemulsion as a therapeutic platform for ocular surface protection

Abstract

Self-emulsified osmoprotective ophthalmic microemulsions (O/A) were prepared by combining betaine/leucine, clusterin/oleanolic acid, and hyaluronic acid or Dextran. The microemulsions contained an internal oily phase (1.2%), an external aqueous phase (96.3%), cosolvents (1%), and surfactants (1.5%). Physicochemical characterization and in vivo and in vitro tolerance were analyzed. The formulations’ osmoprotective in vitro activity was assayed in a hyperosmolar model in human corneal cells. Average internal phase sizes were 16–26 nm for the microemulsions including Dextran. Addition of hyaluronic acid increased the size range (25–39 nm). Addition of osmoprotectants did not change nanodroplet size. The formulations were isotonic (280–290 mOsm/L) with neutral pH (≈7) and zeta potential (−10 to 0 mV), low surface tension (≈35–40mN·m−1), and low viscosity (≈1 mPa·s), except for the microemulsions containing hyaluronic acid (≈4–5 mPa·s). SEM and cryo-TEM showed that all formulations exhibited sphere-shaped morphology with good cell tolerance (≈100%) and were stable at 8 °C for 9 months. Osmoprotective formulations were well tolerated in vitro and in vivo, protecting cells from hypertonic stress. We therefore developed stable microemulsions compatible with the ocular surface that could constitute a novel tool for treatment of ophthalmic diseases.