Neuroprotective Effects of DHED Eyedrops Protects Visual Function Despite Elevated IOP in an Ocular Hypertension Animal Model

Purpose: Glaucoma remains the second leading cause of irreversible blindness and is often associated with chronically elevated intraocular pressure (IOP) leading to ocular hypertension (OHT). All of the currently accepted therapies attempt to reduce the elevated IOP. However, despite intervention, studies show progressive neuronal damage continues in the retina and may extend to the rest of the visual system, leading to additional neuropathologies. Interest in utilizing 17β-estradiol (E2) for its neuroprotective effects has become increasingly recognized; however, due to its side effects, such as cancer risk and feminization in males, its application as a therapy is limited. Our lab has developed the estrogen prodrug, 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED), which remains inactive until its CNS-specific metabolism via short-chain reductase into the active compound E2. This study aims to elucidate the pleiotropic effects of E2 derived from DHED as a potential therapy for preserving the visual system under OHT. We hypothesize that topical application of DHED will prevent the neurodegenerative effects of chronic OHT on the retina and maintain visual function. Methods: OHT was induced in 8 to 10-month-old male Brown Norway rats via hypertonic saline injection into an episcleral vein. IOP was measured via a tonometer (Tonolab) to confirm sustained elevated IOP post-surgery and throughout the treatment period. DHED was topically delivered through eyedrops (20% 2-hydroxylpropyl-beta-cyclodextrin, 0.1% DHED, and saline) once per day. Visual acuity (VA) and contrast sensitivity (CS) were measured using the OptoMotry system with the OptoMotry 1.7 software (Cerebral Mechanics Inc). VA and CS were assessed using the "Rat" preset, and gratings were adjusted using a simple staircase progression. A fixed frequency of 0.272 c/D was chosen for the CS based on prior studies. Observers for the OptoMotry tests were blinded. The eyes and optic nerves were collected and fixed for RGC and axon counts, respectively. Seminal vesicles were collected and weighed to assess peripheral estrogenic effects. Results: The IOP was elevated by 53 % ± 15% and was sustained in both vehicle and DHED-treated groups with no differences between treatment groups. The vehicle-treated group gradually lost visual function, retaining only 60% ± 5% and 30% ± 4% of their VA and CS, respectively, by the end of the treatment period. However, the DHED-treated group maintained significantly better visual performance, retaining 91% ± 3% and 75% ± 7% of their VA and CS compared to the baseline. No differences in the mass of the seminal vesicles between treatment groups. Comparison of RGC and axon counts in the optic nerve are ongoing. Conclusion: This study demonstrates the neuroprotective effects of DHED-derived E2 on the visual system without peripheral side effects. Despite sustained OHT, the VA and CS of the topically administered DHED reduced the impact of injury compared to the vehicle control group. Future studies will investigate DHED administration's impact on the retina and visual cortex proteome.