Glaucoma causes redox imbalance in the primary visual cortex by modulating NADPH oxidase-4, iNOS, and Nrf2 pathway in...

The aim of this study was to elucidate the intracellular sources of oxidant species, the antioxidant response as well as the main signaling pathways involved in the regulation of the redox balance in the primary visual cortex of rats subjected to an experimental glaucoma model. 3-month female Wistar strain rats were operated under a microscope by cauterizing two of the episcleral veins in order to elevate the intraocular pressure (glaucoma group); the control group received a sham procedure. Seven days after surgery, the animals were sacrificed, the brains were carefully removed, and the primary visual cortex was dissected. NADPH oxidase (NOX) activity, as well as the inducible nitric oxide synthase (iNOS) expression, the enzymatic antioxidant defenses, the metabolism of glutathione, and the translocation of Nuclear factor-erythroid 2-related factor-2 (Nrf2) and Nuclear factor k-light-chain-enhancer of activated B cells (NF-κB) were assessed. Compared to control, glaucoma group displayed an increase in NOX activity (147%, p < 0.05), leading to a rise in the steady state concentration of oxidant species. Specifically, NOX4 expression was higher (90%, p < 0.05), suggesting that it could be a source of H₂O₂. In addition, iNOS expression was increased in glaucoma (47%, p < 0.05), as a source of NO in the brain, induced by NF-κB translocation to the nucleus (48%, p < 0.01). An increase in primary antioxidant enzymes superoxide dismutase (40%, p < 0.01) and glutathione peroxidase (55%, p < 0.05) was observed as an adaptive response to reactive oxygen species (ROS) production. However, an alteration in glutathione metabolism was shown in glaucoma due to a decrease in its recycling (40%, p < 0.05) as well as in its de novo synthesis (53%, p < 0.05), leading to a decreased in reduced/oxidized glutathione ratio (55%, p < 0.001). Moreover, a lower expression of Nfr2 was shown in glaucoma (40%, p < 0.05), suggesting that the cell signaling pathway that regulates the antioxidant capacity is compromised. In this context, redox imbalance takes place, resulting in oxidative damage to both lipids (70%, p < 0.001) and proteins (140%, p < 0.001). These results suggest that glaucoma damages not only eye structures but also brain visual targets such as the primary visual cortex. Redox imbalance takes place due to an enhancement in ROS and reactive nitrogen species production from different sources, such as NOX family and iNOS, respectively, in an onset where the antioxidant defenses are overwhelmed due to an impaired Nrf2 signaling, leading to oxidative damage to macromolecules.