Neuroprotective Actions of Hydrogen Sulfide-Releasing Compounds in Isolated Bovine Retinae

Background: We have evidence that hydrogen sulfide (H₂S)-releasing compounds can reduce intraocular pressure in normotensive and glaucomatous rabbits by increasing the aqueous humor (AH) outflow through the trabecular meshwork. Since H₂S has been reported to possess neuroprotective actions, the prevention of retinal ganglion cell loss is an important strategy in the pharmacotherapy of glaucoma. Consequently, the present study aimed to investigate the neuroprotective actions of H₂S-releasing compounds against hydrogen peroxide (H₂O₂)-induced oxidative stress in an isolated bovine retina. Materials and Methods: The isolated neural retinae were pretreated with a substrate for H₂S biosynthesis called L-cysteine, with the fast H₂S-releasing compound sodium hydrosulfide, and with a mitochondrial-targeting H₂S-releasing compound, AP123, for thirty minutes before a 30-min oxidative insult with H₂O₂ (100 µM). Lipid peroxidation was assessed via an enzyme immunoassay by measuring the stable oxidative stress marker, 8-epi PGF2α (8-isoprostane), levels in the retinal tissues. To determine the role of endogenous H₂S, studies were performed using the following biosynthesis enzyme inhibitors: aminooxyacetic acid (AOAA, 30 µM); a cystathione-β-synthase/cystathionine-γ-lyase (CBS/CSE) inhibitor, α-ketobutyric acid (KBA, 1 mM); and a 3-mercaptopyruvate-s-sulfurtransferase (3-MST) inhibitor, in the absence and presence of H₂S-releasing compounds. Results: Exposure of the isolated retinas to H₂O₂ produced a time-dependent (10-40 min) and concentration-dependent (30-300 µM) increase in the 8-isoprostane levels when compared to the untreated tissues. L-cysteine (10 nM-1 µM) and NaHS (30 -100 µM) significantly (p < 0.001; n = 12) prevented H₂O₂-induced oxidative damage in a concentration-dependent manner. Furthermore, AP123 (100 nM-1 µM) attenuated oxidative H₂O₂ damage resulted in an approximated 60% reduction in 8-isoprostane levels compared to the tissues treated with H₂O₂ alone. While AOAA (30 µM) and KBA (1 mM) did not affect the L-cysteine evoked attenuation of H₂O₂-induced oxidative stress, KBA reversed the antioxidant responses caused by AP123. Conclusions: In conclusion, various forms of H₂S-releasing compounds and the substrate, L-cysteine, can prevent H₂O₂-induced lipid peroxidation in an isolated bovine retina.