Fig. 1. Cyclosporin A (CsA) enhances hydrogen peroxide (H₂O₂) injury in human kidney proximal tubule epithelial cells. Human kidney proximal tubule epithelial HK-2 cells were cultured in RPMI 1640 until reaching 80% confluence. (A) HK-2 cells were treated with either CsA (1, 10, or 100 nM) or 1% dimethyl sulfoxide (vehicle) for 1 hour and then exposed to 1 mM H₂O₂ or distilled water (control) for 60 minutes. Cell viability was measured using MTT assay (n=9 wells from 3 experiments per condition). In box plots, whiskers represent the minimum and maximum; bases represent the interquartile range between the first and third quartiles; and midlines represent the median. (B) HK-2 cells were treated with either 10 nM CsA or vehicle for 60 minutes and then exposed to 1 mM H₂O₂ or control for 30, 60, or 120 minutes. Cell viability was measured using MTT assay (n=9 wells from 3 experiments per condition). (C, D) HK-2 cells were treated with either 10 nM CsA or vehicle for 60 minutes and then exposed to 1 mM H₂O₂ or control for 60 minutes. Cell death was analyzed by flow cytometry with an annexin V-FITC detection kit after treatment with FITC-conjugated annexin V and propidium iodide. The flow cytometry assay distinguishes among normal (lower left), early apoptosis (lower right), late apoptosis (upper right), and necrosis (upper left). Three experiments were performed to evaluate the cell death. In each experiment, three samples per experimental condition were included. ^a)P<0.05 vs. control. ^b)P<0.05 vs. vehicle. ^c)P<0.01 vs. 0 mol/l.