Redox homeostasis is a delicate balancing act of maintaining appropriate levels of antioxidant defense mechanisms and reactive oxidizing oxygen and nitrogen species. Any disruption of this balance leads to oxidative stress, which is a key pathogenic factor in several ocular diseases. In this review, we present the current evidence for oxidative stress and mitochondrial dysfunction in conditions affecting both the anterior segment (e.g., dry eye disease, keratoconus, cataract) and posterior segment (age-related macular degeneration, proliferative vitreoretinopathy, diabetic retinopathy, glaucoma) of the human eye. We posit that further development of therapeutic interventions to promote pro-regenerative responses and maintenance of the redox balance may delay or prevent the progression of these major ocular pathologies. Continued efforts in this field will not only yield a better understanding of the molecular mechanisms underlying the pathogenesis of ocular diseases but also enable the identification of novel druggable redox targets and antioxidant therapies.

Geographic atrophy or late-stage dry age-related macular degeneration (AMD) is characterized by drusen deposition and progressive retinal pigment epithelium (RPE) degeneration, leading to irreversible vision loss. The formation of drusen leads to dyshomeostasis, oxidative stress, and irreversible damage to the RPE. In this study, we used an in vitro model of oxidized low-density lipoprotein (ox-LDL)-induced human RPE damage/death to investigate the mechanism through which a sterically hindered phenol antioxidant compound, PMC (2,2,5,7,8-pentamethyl-6-chromanol), protects the RPE against ox-LDL-induced damage. We show that PMC exerts its protective effect by preventing the upregulation of stress-responsive heme oxygenase-1 (HMOX1/HO-1) and NAD(P)H: quinone oxidoreductase (NQO1) at the mRNA and protein levels. This effect was due to PMC’s blockade of ROS generation, which in turn blocked nuclear translocation of the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor, ultimately preventing the upregulation of antioxidant response elements (AREs), including HMOX1 and NQO1. The key role of HO-1 was demonstrated when the protective effect of PMC was inhibited by the knockdown of HMOX1. Additionally, PMC treatment under different experimental conditions and at different time points revealed that the continuous presence of PMC is required for the optimal protection against ox-LDL-induced cytotoxicity, defining the cellular pharmacokinetics of this molecule. Our data demonstrate the involvement of a key antioxidant pathway through which PMC mitigates the oxidative stress induced by ox-LDL and provides a potential therapeutic strategy for suppressing RPE degeneration/damage during AMD progression.