Sustained-Release Delivery System of a Slow Hydrogen Sulfide Donor, GYY 4137, for Potential Application in Glaucoma.

Hydrogen sulfide (HS) targets both underlying factors in glaucoma pathogenesis by reducing elevated intraocular pressure (IOP) and providing retinal neuroprotection, whereas the current clinical approaches targets only reducing IOP. Therefore, HS could be a potential superior candidate for glaucoma pharmacotherapy. However, HS could be toxic in a concentration greater than 200 μM and its donors are unstable in water. Therefore, this study investigated the preparation and characterization of a non-aqueous in situ gelling sustained-release delivery system for HS donors. The delivery system was prepared by dissolving GYY 4137, a HS donor, in poly lactide-co-glycolide polymer (PLGA) (Resomer® RG 502H) solution prepared by dissolving polymer in a mixture of benzyl alcohol and benzyl benzoate in a ratio of 7:3, respectively. The GYY 4137 formulation was characterized for syringeability/injectability, change in pH and tonicity, moisture content, GYY 4137 degradation, and toxicity using rheometer, pH and osmometer, Karl Fisher titrimeter, NMR spectrometer, and Y79 retinoblastoma cells, respectively. The formulation was easily syringeable and injectable as evidenced by rheological data (plastic flow pattern with 43.89 ± 3.21 cP viscosity and 1.12 ± 0.15 Pa yield value). The pH, tonicity, and moisture content values were within acceptable range. NMR spectroscopy indicated presence of 4-methoxyphenylphosphonic acid (GYY 4137 degradation product). The GYY 4137 formulation did not show any significant (p < 0.05) toxicity except the solvent mixture. A sustained release of HS was observed up to 72 h. The in situ gel forming PLGA-based system can be manipulated to achieve sustained release of HS from its donor GYY 4137.