Figure 4. Protective effect of N-acetylcysteine and vitamin C against hydrogen peroxide–induced expression of intracellular levels of interleukin-1β and transforming growth factor, beta 1 in Graves’ ophthalmopathy orbital fibroblasts. After pretreatment of Graves’ ophthalmopathy (GO) orbital fibroblasts (n=7) with 200 μM N-acetylcysteine (NAC) or 500 μM vitamin C (VitC) for 1 h, followed by the addition of 6.25 μM hydrogen peroxide (H₂O₂) for 24 h, the release of the intracellular levels of interleukin-1β (IL-1β) and transforming growth factor, beta 1 (TGF-β1) was determined with an enzyme-linked immunosorbent assay kit. No H₂O₂ treatment in GO orbital fibroblasts was represented as the control (basal level). The mean values of IL-1β and TGF-β1 from the GO orbital fibroblasts are shown in the histogram (A and B, respectively). The H₂O₂-induced release of the IL-1β and TGF-β1 levels in the GO orbital fibroblasts was significantly abolished by pretreatment with 200 μM NAC or 500 μM VitC, respectively. The data are presented as mean ± standard deviation of the results from three independent experiments. (p<0.05, p<0.005, and p<0.001 represented significant decrease.)