Topical Ascorbic Acid Ameliorates Oxidative Stress-Induced Corneal Endothelial Damage via Suppression of Apoptosis and Autophagic Flux Blockage

Abstract

Compromised pumping function of the corneal endothelium, due to loss of endothelial cells, results in corneal edema and subsequent visual problems. Clinically and experimentally, oxidative stress may cause corneal endothelial decompensation after phacoemulsification. Additionally, in vitro and animal studies have demonstrated the protective effects of intraoperative infusion of ascorbic acid (AA). Here, we established a paraquat-induced cell damage model, in which paraquat induced reactive oxygen species (ROS) production and apoptosis in the B4G12 and ARPE-19 cell lines. We demonstrate that oxidative stress triggered autophagic flux blockage in corneal endothelial cells and that addition of AA ameliorated such oxidative damage. We also demonstrate the downregulation of Akt phosphorylation in response to oxidative stress. Pretreatment with ascorbic acid reduced the downregulation of Akt phosphorylation, while inhibition of the PI3K/Akt pathway attenuated the protective effects of AA. Further, we establish an in vivo rabbit model of corneal endothelial damage, in which an intracameral infusion of paraquat caused corneal opacity. Administration of AA via topical application increased its concentration in the corneal stroma and reduced oxidative stress in the corneal endothelium, thereby promoting corneal clarity. Our findings indicate a perioperative strategy of topical AA administration to prevent oxidative stress-induced damage, particularly for those with vulnerable corneal endothelia.

Analysis of aqueous humor total antioxidant capacity and its correlation with corneal endothelial health

“…18,19 In addition, several in vitro studies have also shown that antioxidants can promote CEC proliferation and prevent apoptosis. [20][21][22] Despite this body of knowledge, there have not been any clinical studies directly showing the relationship between ECD and aqueous humor antioxidants.…”

“…On the other hand, it has recently been reported that taking antioxidant supplements before or during the phacoemulsification process of cataract surgery can protect CEC from free radical damage 18,19 . In addition, several in vitro studies have also shown that antioxidants can promote CEC proliferation and prevent apoptosis 20‐22 . Despite this body of knowledge, there have not been any clinical studies directly showing the relationship between ECD and aqueous humor antioxidants.…”

The Pathomechanism, Antioxidant Biomarkers, and Treatment of Oxidative Stress-Related Eye Diseases

“…We observed that the prophylactical application of topical AA can improve phacoemulsification-induced oxidative stress and loss of human CECs [219]. Furthermore, it also has been shown that oxidative stress-induced cell autophagy and apoptosis can be reversed by AA pretreatment [26].…”

“…Lipidated microtubule-associated protein light chain 3 (LC3-II; an autophagosome membrane-bound protein) assists in autophagosome formation, and sequestosome 1 (p62/SQSTM1) binds to LC3-II to assist in autophagosome and lysosome fusion and the formation of autolysosomes to remove abnormal proteins and organelles; this process is called autophagic flux [24]. Severe oxidative stress damage can block autophagic flux, leading to the inability of autophagosomes to bind to lysosomes, resulting in p62 accumulation [25,26]. p62 accumulation induces apoptosis through the activation of caspase-8 [27].…”

“…Sulforaphane (an agonist of Nrf2) treatment can reduce the loss of FECD CECs by reducing apoptosis [74]. Oxidative stress triggers an autophagic flux blockade in CECs, resulting in p62 accumulation; the accumulation of p62 induces CEC apoptosis through the activation of caspase 8 [26,27]. Peroxiredoxin 1 (PRDX1) is a redox sensor that is involved in the regulation of lipid peroxidation.…”