Enhanced Protection of Retinal Ganglion Cells against Ischemia/Reperfusion Injury and Neurotrophic Factor Deprivation with Compound SA-10

Purpose: Glaucoma is one of the leading causes of irreversible blindness worldwide. In glaucoma, the retinal ganglion cells (RGCs), which transmit visual signals to the brain, undergo neurodegeneration, leading to a gradual loss of vision. Oxidative stress is the imbalance between antioxidant activity and free radical production, which has been shown to be associated with glaucomatous RGC degeneration. In this study, we investigated the potential of SA-10, a hybrid nitric oxide donating and sulfone reactive oxygen species (ROS) scavenging molecule, to promote the survival of RGCs against glaucomatous damage. We investigated its neuroprotective effects following retinal ischemia/reperfusion (I/R) injury in mice and ex vivo following neurotrophic factor (NF) deprivation in human retinal explants (HREs).

Methods: Acute I/R injury was induced in C57BL/6J mice (n=2-3 mice/group/sex) through intracameral pressure elevation to 120 mmHg for 1 hour. The mice were pre-treated topically with a PLGA nanosuspension of SA-10 (1% SA-10-NPs) and treated for 14 days (7 doses) after I/R injury. The obtained retinal sections were stained with anti-heme oxygenase-1 antibody (Hmox1, a marker of protective response to oxidative stress) to quantify its expression levels. H&E sections were used to measure retinal thickness.

In another set of experiments, biopsy punches from HREs (n=3 donors) were isolated and treated with either SA-10 [10 µM] or vehicle and maintained without NF for 7 days ex vivo (DEV). Four control punches were collected on day 0 (0 DEV). After 7 days, HREs were immunostained with RBPMS (RGC-specific marker), and cell survival was analyzed. Analysis of Variance (ANOVA) was performed for all experiments.

Results: In the nerve fiber and ganglion cell layers (ganglion cell complex, GCC), I/R injury caused a significant reduction in Hmox1 expression in female (79.8%, p<0.05) and male (54.5%, p<0.05) mice, compared to the sham control. Additionally, I/R injury led to a decline in GCC thickness by 27.5% (p=0.23) in females and 32.7% (n=2) in males. However, treatment with SA-10-NPs increased Hmox1 expression by 4.2-fold (p<0.05) in females and by 0.5-fold (p=0.43) in males. SA-10-NPs also preserved GCC thickness by 17.6% (p=0.68) in females and 27.1% in males. In human retinal explants, the 7 DEV vehicle-treated group had a significant loss in RGCs by 45.2% (p<0.01) compared to 0 DEV. In contrast, SA-10 treatment enhanced RGC survival at 7 days with an 83.1% (p<0.01) higher RGC counts than the vehicle group.

Conclusions: SA-10 and its nanosuspension exhibited significant neuroprotective effects by enhancing Hmox1 expression, preserving retinal thickness, and promoting RGC survival, highlighting its potential as a therapeutic candidate for glaucoma and ischemic stroke.