New trends towards glaucoma treatment: Topical osmoprotective microemulsions loaded with latanoprost.

The chronic use of hypotensive agents eventually leads to ocular surface damage and poor patient compliance during glaucoma management. Thus, new sustained drug delivery systems are needed. This work aimed to develop osmoprotective latanoprost-loaded microemulsion formulations as new potential glaucoma treatments with ocular surface protective properties. The microemulsions were characterized and latanoprost encapsulation efficacy determined. In-vitro tolerance, osmoprotective efficacy, cell internalization as well as cell-microemulsion interactions and distribution were performed. In vivo hypotensive activity was conducted in rabbits to assess intraocular pressure reduction and relative ocular bioavailability. Physicochemical characterization showed nanodroplet sizes within 20-30 nm, being in vitro tolerance within 80 and 100% viability in corneal and conjunctival cells. Besides, microemulsions exhibited higher protection under hypertonic conditions than untreated cells. Cell fluorescence lasted for 11 days after short exposure to coumarin-loaded microemulsions (5 min) showing extensive internalization in different cell compartments by electronic microscopy. In vivo studies exhibited that a single instillation of latanoprost-loaded microemulsions reduced the intraocular pressure for several days (4-6 days without polymer and 9-13 days with polymers). Relative ocular bioavailability was 4.5 and 19 times higher than the marketed formulation. These findings suggest the use of these microemulsions as potential combined strategies for extended surface protection and glaucoma treatment.

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

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.

Novel Water-Soluble Mucoadhesive Carbosilane Dendrimers for Ocular Administration.

The purpose of this research was to determine the potential use of water-soluble anionic and cationic carbosilane dendrimers (generations 1-3) as mucoadhesive polymers in eyedrop formulations. Cationic carbosilane dendrimers decorated with ammonium -NH3(+) groups were prepared by hydrosylilation of Boc-protected allylamine and followed by deprotection with HCl. Anionic carbosilane dendrimers with terminal carboxylate groups were also employed in this study. In vitro and in vivo tolerance studies were performed in human ocular epithelial cell lines and rabbit eyes respectively. The interaction of dendrimers with transmembrane ocular mucins was evaluated with a surface biosensor. As proof of concept, the hypotensive effect of a carbosilane dendrimer eyedrop formulation containing acetazolamide (ACZ), a poorly water-soluble drug with limited ocular penetration, was tested after instillation in normotensive rabbits. The methodology used to synthesize cationic dendrimers avoids the difficulty of obtaining neutral -NH2 dendrimers that require harsher reaction conditions and also present high aggregation tendency. Tolerance studies demonstrated that both prototypes of water-soluble anionic and cationic carbosilane dendrimers were well tolerated in a range of concentrations between 5 and 10 µM. Permanent interactions between cationic carbosilane dendrimers and ocular mucins were observed using biosensor assays, predominantly for the generation-three (G3) dendrimer. An eyedrop formulation containing G3 cationic carbosilane dendrimers (5 µM) and ACZ (0.07%) (289.4 mOsm; 5.6 pH; 41.7 mN/m) induced a rapid (onset time 1 h) and extended (up to 7 h) hypotensive effect, and led to a significant increment in the efficacy determined by AUC0(8h) and maximal intraocular pressure reduction. This work takes advantage of the high-affinity interaction between cationic carbosilane dendrimers and ocular transmembrane mucins, as well as the tensioactive behavior observed for these polymers. Our results indicate that low amounts of cationic carbosilane dendrimers are well tolerated and able to improve the hypotensive effect of an acetazolamide solution. Our results suggest that carbosilane dendrimers can be used in a safe range of concentrations to enhance the bioavailability of drugs topically administered in the eye.