Ergothioneine: Evaluation of a Novel Antioxidant for Targeting Ocular Oxidative Stress

Purpose To evaluate ergothioneine (EGT), a naturally occurring amino acid and endogenous antioxidant, as a novel therapeutic agent for oxidative stress-related ocular diseases. This evaluation specifically aimed to address the challenge of targeted ocular delivery by assessing EGT’s antioxidant potency, stability, ocular tolerance, and crucially, its ability to reach the posterior segment (fundus) via topical administration.Methods This study evaluated EGT as a novel ocular antioxidant by examining its radical scavenging capacity (DPPH assay compared to glutathione, astaxanthin, and coenzyme Q10), stability (at 40 °C/75% relative humidity for six months using HPLC), ocular tolerance (using a New Zealand rabbit model), and fundus delivery efficiency (topical D9-EGT eye drops quantified by LC-MS/MS).Results EGT demonstrated significantly superior radical scavenging activity, exhibiting 6.4-fold and 46-fold higher rates than glutathione and coenzyme Q10, respectively, at 50 ppm. It also showed excellent stability, retaining over 97% of its initial concentration after six months, and caused no ocular irritation at any tested concentration (score 0). Importantly, topical administration of EGT resulted in effective fundus delivery, with peak concentrations reached at 0.5 h post-application (1181 ± 56 ng/g), confirming successful penetration through corneal and scleral barriers. These findings establish EGT as a potent, multi-mechanistic antioxidant characterized by high stability, ocular safety, and exceptional posterior segment penetrance via noninvasive eye drops.Conclusion These findings establish EGT as a potent, multi-mechanistic antioxidant characterized by high stability, ocular safety, and exceptional posterior segment penetrance via noninvasive eye drops. By overcoming key delivery limitations, EGT presents a promising therapeutic strategy for oxidative stress-related ocular diseases such as age-related macular degeneration and diabetic retinopathy. Further studies are warranted to evaluate its long-term efficacy and clinical translation potential.