Effects of carnosic acid on cell viability. (A) Cell cytotoxicity assay. A549 cells were treated with increased concentration of carnosic acid for 24 hours and subjected to a MTT assay. Data represent means ± SD. (B) Viable cell count assay. A549 cells were treated with increased amount of carnosic acid for 24 hours or 48 hours. Cells were detached and mixed with trypan blue cell staining solution. Viable cells and dead cells were counted under microscope. All the experiments were performed in triplicate and data represent the percentage of viable cells (means ± SD). N.S.: not significant. * p < 0.01 versus Mock-treated (Mock). (C) Apoptosis assay. Apoptotic cell death of A549 cells incubated with or without carnosic acid (20 μg/ml) for 24 and 48 hours was analyzed by flow cytometry using Annexin V-FITC and propidium iodide.