Abstract
Age-related macular degeneration (AMD) involves the loss of retinal pigment epithelium (RPE) and photoreceptors and is one of the leading causes of blindness in the elderly. Oxidative damage to proteins, lipids, and DNA has been associated with RPE dysfunction and AMD. In this study, we evaluated oxidative stress in AMD and the efficacy of antioxidant, N-acetyl-L-cysteine (NAC), in protecting RPE from oxidative damage. To test this idea, primary cultures of RPE from human donors with AMD (n = 32) or without AMD (No AMD, n = 21) were examined for expression of NADPH oxidase (NOX) genes, a source of reactive oxygen species (ROS). Additionally, the cells were pretreated with NAC for 2 hours and then treated with either hydrogen peroxide (H2O2) or tert-butyl hydroperoxide (t-BHP) to induce cellular oxidation. Twenty-four hours after treatment, ROS production, cell survival, the content of glutathione (GSH) and adenosine triphosphate (ATP), and cellular bioenergetics were measured. We found increased expression of p22phox, a NOX regulator, in AMD cells compared to No AMD cells (p = 0.02). In both AMD and No AMD cells, NAC pretreatment reduced t-BHP-induced ROS production and protected from H2O2-induced cell death and ATP depletion. In the absence of oxidation, NAC treatment improved mitochondrial function in both groups (p < 0.01). Conversely, the protective response exhibited by NAC was disease-dependent for some parameters. In the absence of oxidation, NAC significantly reduced ROS production (p < 0.001) and increased GSH content (p = 0.02) only in RPE from AMD donors. Additionally, NAC-mediated protection from H2O2-induced GSH depletion (p = 0.04) and mitochondrial dysfunction (p < 0.05) was more pronounced in AMD cells compared with No AMD cells. These results demonstrate the therapeutic benefit of NAC by mitigating oxidative damage in RPE. Additionally, the favorable outcomes observed for AMD RPE support NAC's relevance and the potential therapeutic value in treating AMD.
Highlights
Age-related macular degeneration (AMD) is the leading cause of progressive and irreversible vision loss in the aging population [1]
Our results show that NAC protects against oxidative damage by preventing excessive reactive oxygen species (ROS) production, cell death, Glutathione H2O2 (GSH) and adenosine triphosphate (ATP) depletion, and impairment of mitochondrial oxidative phosphorylation
We found that treatment with NAC (500 μM) alone had no effect on ROS levels in No AMD cells (Figure 1(a)) but caused a significant decrease in basal ROS content (25%) in AMD (p = 0 0009) cells compared to no treatment controls (Figure 1(b))
Summary
Age-related macular degeneration (AMD) is the leading cause of progressive and irreversible vision loss in the aging population [1]. The macula, a small central area of the retina that deteriorates with AMD, is responsible for high acuity and color vision. 10% of the AMD patient population has the “wet” form of the disease, which manifests as abnormal growth of blood vessels into the retina from the choriocapillaris, a fenestrated blood vessel network outside the eye [2]. The majority of the AMD patient population has “dry” AMD, characterized by the loss of retinal pigment epithelium (RPE) and photoreceptors in the absence of abnormal blood vessel growth. The treatment of wet AMD has significantly improved with the introduction of anti-VEGF therapy [3].
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