Nitrite-induced photo-oxidation of thiol and its implications in smog toxicity to the eye: prevention by ascorbate.

Studies have been conducted on nitrite-induced oxidation of corneal thiols and reduced glutathione (GSH). Oxidation of GSH in the presence of nitrite (NaNO2) was minimal in the dark. Exposure of GSH to UV (365 nm) in the presence of nitrite substantially accelerated this oxidation; only < 10% of the original GSH remained at the end of 20 minutes. A similar Thiol depletion was observed in the case of corneal epithelial extracts irradiated with UV in the presence of the nitrite. Nitrite is therefore considered to be a potent phototoxicant with possible pathophysiological implications to the external eye tissues. Ascorbate was found to be effective in preventing thiol oxidation, suggesting the possibility of preventing nitrogen oxide-based smog irritation to the eye by this physiologically compatible antioxidant.