FIGURE 2.

A heme oxygenase 1 (HO-1) inhibitor, zinc protoporphyrin (ZnPP), abrogated the inhibitory effect of α-lipoic acid (ALA) on production of reactive oxygen species (ROS). Orbital fibroblasts from patients with Graves ophthalmopathy (GO) were pretreated with ZnPP (10 μM) for 1 h followed by treatment with ALA (500 μM) for 24 h, and were then stimulated with 100 μM H₂O₂ for 30 min. ROS were quantified by flow cytometry with 5-(and 6)-carboxy-2′,7′-dichlorodihydrofluorescein diacetate (H₂DCFDA). The data are expressed as percentages of the no-treatment control values, mean ± SEM (n = 3). ^∗P < 0.05 compared with the untreated cells; ^§P < 0.05 compared with the cells stimulated with H₂O₂.