Abstract
Glaucoma is one of the leading causes of blindness worldwide and is characterized by progressive retinal ganglion cell degeneration and optic nerve damage. Current therapies primarily target to reduce intraocular pressure (IOP), they remain unsuccessful in preventing neurodegeneration associated with glaucoma progression. Therefore, there is a need of a better treatment that can target both - reducing IOP and providing retinal neuroprotection. Hydrogen sulfide (H2S), an endogenous gasotransmitter, has shown therapeutic potential in glaucoma because of its dual action in lowering IOP and providing neuroprotection. However, the clinical application of H2S is challenging because of its gaseous nature, instability, rapid oxidation, short half-life, toxicity, and difficulty in achieving controlled delivery. Therefore, the present study focused on the development of a sustained-release polymeric microparticle system for ocular delivery of H2S donor compounds.Polycaprolactone (PCL)-based microparticles loaded with sodium sulfide nonahydrate (Na2S·9H2O) (a model H2S donor) and GYY4137 were prepared using a non-aqueous coacervation method. Initial preparation attempts using coacervation solvent-evaporation resulted in overheating, uncontrolled solvent evaporation, polymer aggregation, and poor reproducibility. To overcome these limitations, a coacervation solvent-extraction method using a closed apparatus system was successfully developed. The stability window for coacervate formation in the PCL–dichloromethane–silicone oil system was determined using ternary phase behavior studies, and formulation parameters including silicone oil concentration, surfactant type, and surfactant concentration were optimized.
The optimized formulations were characterized for particle size, span value, morphology, encapsulation efficiency, and in vitro H2S release. H2S release was quantified using an ISO-H2S-100 amperometric microsensor electrode. GYY4137-loaded microparticles showed comparatively higher encapsulation efficiency (12.29%), whereas Na2S·9H2O-loaded microparticles exhibited lower encapsulation efficiency (0.32%). In vitro release studies demonstrated sustained H2S release from both GYY4137 solution (0.23-0.6%) and microparticle formulations (below 0.25%) for up to 72 hours under physiological conditions. Preliminary cytotoxicity studies in ARPE-19 cells indicated acceptable cytocompatibility of GYY4137 loaded (≥ 87.62%) and blank microparticles (≥ 76.6%) within the tested concentration range. Overall, this study demonstrates the potential of PCL-based microparticles as a sustained ocular delivery platform for H2S donor compounds in glaucoma therapy. Future studies should target enhancing encapsulation efficiency and extending sustained release period.