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Oxidative stress is important in carcinogenesis and metastasis. Salidroside, a phenylpropanoid glycoside isolated from Rhodiola rosea L., shows potent antioxidant properties. The aim of the present study was to investigate the roles of salidroside in cell proliferation, the cell cycle, apoptosis, invasion and epithelial-mesenchymal transition (EMT) in A549 cells. The human alveolar adenocarcinoma cell line, A549, was incubated with various concentrations of salidroside (0, 1, 5, 10 and 20 µg/ml) and cell proliferation was detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Propidium iodide (PI) staining was used to determine the cell cycle by low cytometry. Cell apoptosis was detected by Annexin V-fluorescein isothiocyanate and PI double-staining, and tumor invasion was detected by Boyden chamber invasion assay. Western blot analysis was performed to detect the expression of EMT markers, Snail and phospho-p38. The results showed that salidroside significantly reduced the proliferation of A549 cells, inhibited cell cycle arrest in the G0/G1 phase and induced apoptosis. Salidroside inhibited transforming growth factor-ß-induced tumor invasion and suppressed the protein expression of Snail. As an antioxidant, salidroside inhibited the intracellular reactive oxygen species (ROS) formation in a dose-dependent manner in A549 cells, and depletion of intracellular ROS by vitamin C suppressed apoptosis by salidroside treatment. Salidroside was also found to inhibit the expression of phospho-p38 in A549 cells. In conclusion, salidroside inhibits cell proliferation, the cell cycle and metastasis and induces apoptosis, which may be due to its interference in the intracellular ROS generation, thereby, downregulating the ROS-phospho-p38 signaling pathway. [ABSTRACT FROM AUTHOR]