2.6. MTT assay
Cell viability was determined by the MTTassay. Cells were seeded at a density of 104 in 0.2 ml of medium into each well of 96-well plates. After 18 h of incubation, the cells were washed with PBS and cultured for 24 h with 200 ml of FBS-free DMEM, together with the indicated concentrations of A. radix extract. Then, the medium was removed and 100 ml of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] (1 mg/ml) (Sigma—Aldrich, St. Louis, MO) in PBS was added. At the end of 4 h incubation, the plates were centrifuged, and the untransformed MTT was removed. After 100 ml of absolute ethanol was added to each well, the plates were shaken for 5 min. The optical density at 570 nm was determined using an ELISA reader. The cell viability rates were calculated from the OD readings and are represented as percentages of the control value (untreated cells).