Figure 2. Protective effect of N-acetylcysteine against 6.25 μM hydrogen peroxide–induced proliferation of orbital fibroblasts from patients with Graves’ ophthalmopathy. After pretreatment of Graves’ ophthalmopathy (GO) orbital fibroblasts (n=7) with 100 μM or 200 μM N-acetylcysteine (NAC) for 1 h, followed by the addition of 6.25 μM hydrogen peroxide (H₂O₂) for 24 h, the cell proliferation rate was examined with the AlamarBlue assay. The data were normalized to each control that was not exposed to H₂O₂, and the mean values of cell proliferation are shown in the histogram. The pretreatment of NAC at 100 μM and 200 μM in GO orbital fibroblasts significantly abolished H₂O₂-induced cell proliferation. The data are presented as mean ± standard deviation of the results from three independent experiments. (p<0.001 and p<0.0001 represented significant decrease.)