A Novel Tool for the Assessment Oxidative Stress in Age-Related Macular Degeneration: Thiol/Disulfide Homeostasis Revisited

Purpose: To investigate thiol/disulfide status using a novel automated assay in patients with age-related macular degeneration (AMD) compared to age-matched healthy controls.Methods: A total of 64 AMD patients [51 (79%) non-exudative, 13 (21%) exudative AMD] and 21 age-matched healthy control subjects were enrolled in this study. Plasma total thiol, native thiol, disulfide levels were measured and native thiol/disulfide ratio (TDR) was calculated using a novel spectrophotometric assay.Results: Patients with AMD had significantly lower levels of total thiol (434.8 7.0 mol/L vs. 472.2 +/- 7.9 mol/L, p < 0.001), native thiol (393.6 +/- 6.5 mol/L vs. 437.5 +/- 7.1 mol/L, p = 0.004) compared to healthy controls. However, plasma disulfide levels were higher in AMD patients (20.6 +/- 0.9 mol/L vs. 17.3 +/- 1.3 mol/L, p = 0.113) compared to healthy controls. The TDR was not statistically different between the early AMD group and healthy controls (24.2 +/- 2.3 vs. 29.5 +/- 3.1, p = 0.345). However, intermediate and advanced stage AMD groups had significantly lower levels of TDR compared to healthy controls (21.6 +/- 2.6 vs. 29.5 +/- 3.1, p = 0.023 and 20.3 +/- 1.2 vs. 29.5 +/- 3.1, p = 0.005, respectively). Native TDR was significantly lower in patients with exudative and non-exudative AMD (19.9 +/- 2.3 vs. 29.5 +/- 3.1, p = 0.024 and 21.8 +/- 1.14 vs. 29.47 +/- 3.1 respectively, p = 0.011).Conclusion: A greater extent of thiol consumption occurred in AMD patients compared to age-matched healthy controls. However, despite the similar levels of total thiol levels between several grades of AMD, the plasma native TDR value was decreased in accordance with the severity of the disease, which reflected the disease grade better.