Abstract
Glaucoma is an ocular neurodegenerative condition that leads to progressive irreversible blindness due to loss of retinal ganglion cells (RGCs) and optic nerve head (ONH) damage. Currently, glaucoma affects 80 million people globally and the burden of this disease is expected to increase to over 100 million people by 2040. Primary Open Angle Glaucoma (POAG) is the most prevalent type of glaucoma, and its pathophysiology is multifactorial. The main modifiable risk factor in POAG is elevated intraocular pressure (IOP). Most FDA-approved drugs for POAG target this IOP elevation to provide symptomatic relief. There is a growing recognition of the need for neuroprotective strategies to preserve vision in glaucoma patients. The lack of neuroprotective agents can be potentially fulfilled by the use of hydrogen sulfide (H2S)-producing compounds. H2S, is the third endogenous gaseous transmitter with physiological and pharmacological implications in mammalian cells. Multiple studies have reported its cytoprotective, anti-inflammatory, anti-apoptotic, and vasodilatory effects. In the context of glaucoma, studies have revealed its antioxidant effects can potentially preserve RGCs and the ONH from injury in glaucoma. Furthermore, H2S-producing compounds have been reported to lower to IOP by modulating aqueous humor (AH) dynamics in different animal models of glaucoma. These promising findings need to be fully harnessed by addressing the challenges associated with the development of H2S-producing compounds as therapeutic agents for glaucoma. Issues such as limited bioavailability and stability of H2S present hurdles in developing effective treatment strategies. Optimal dosing regimens and delivery systems must be refined to ensure sustained release of the gas while minimizing adverse reactions. This study aims to address these challenges because they will be instrumental in advancing H2S-based therapies as a viable strategy for lowering IOP and preserving vision in glaucoma patients. First, we assessed the hypotensive effects of H2S-producing compounds, DATTS and GYY4137 in female normotensive rabbits. Furthermore, we tested the ocular hypotensive effects of these H2S-producing compounds in an in vivo glaucoma model that we developed in male and female New Zealand albino rabbits by administering a bilateral intracameral injection of carbomer (100 µL; 0.3 w./v %) into eyes of these animals. Injection of carbomer resulted in ocular hypertension (OHT) in the rabbits and increased IOP by over 100% for up to 30 days in both male and female rabbits. This glaucoma model was also used to assess the neuroprotective effects of DATTS and GYY4137 using H&E and TUNEL assays, in vivo. Finally, a microparticle formulation of H2S-producing compound (Na2S) was formulated and optimized using Quality by design (QbD). Main Effects screening (MES) and a Response Surface design (RSD)-based design of experiments (DOE) were used to optimize Critical Quality Attributes (CQAs) and Critical Process Parameters (CPPs) associated with microparticle formulation. In conclusion, pharmacological data from our studies affirm both an IOP-lowering and neuroprotective action of H2S-producing compounds in an animal model of glaucoma. Our formulation data supports the development of a microparticle formulation of a H2S-producing compound that may have utility in the treatment of glaucoma.