2.5. Cellular Toxicity MTT Assay

MTT (Sigma Chemical Co., St. Louis, MO, USA) assays were conducted as previously described [29] with some modifications. Briefly, cells were seeded into 96-well plates. The MTT stock solution of 5 mg/mL was prepared in PBS (pH 7.2) and filtered through 2 µm pore-size membrane. At the end of the treatment period with extracts (12, 24 or 48 h), 20 µL of MTT solution were added to each well and incubated for 4 h at 37 °C. Then, 100 µL of solubilizing buffer (prepared by dissolving of 10% sodium dodecyl sulfate SDS in 0.01 N HCl) were added to each well and incubated overnight. After that, the 96-well plate was read using an ELISA reader at 570 nm for absorbance density values. Viable cells produce a dark blue formazan product, whereas no such staining was formed in dead cells. The percentage of viable cells was calculated.