Figure 1. Comparison of the effects of hydrogen peroxide at various concentrations on the viability of orbital fibroblasts between patients with Graves’ ophthalmopathy (GO) and normal controls. We treated orbital fibroblasts from patients with GO (n=7) and age-matched normal subjects (n=5) with various concentrations of hydrogen peroxide (H₂O₂) for 24 h. The cell proliferation rate was examined with the AlamarBlue assay as methods described and normalized to each control not exposed to H₂O₂. The mean values of cell proliferation in H₂O₂-treated orbital fibroblasts are shown in the histogram. Treatment with a low concentration of H₂O₂ (<25 μM) in GO orbital fibroblasts significantly induced the cell proliferation, but the effect was not observed in normal subjects. The cytotoxicity of H₂O₂ was observed in GO orbital fibroblasts above 50 μM and in normal subjects above 100 μM. The data are presented as mean ± standard deviation of the results from three independent experiments. (Significant increase when ** p<0.01 and *p<0.05; significant decrease when ##p<0.01 and #p<0.05.)