4.6. Cell Viability Assay

MTT assay was applied as previously described [47]. Briefly, HEK293 cells were plated in a 96-well plate, at a density of 1.5 × 10⁴ cells/well, for 24 h in DMEM medium (4.5 g/L glucose), supplemented with 10% FBS, 2 mM L-glutamine, and 100 units/mL pen/strep. The next day, cells were treated with leaves fractions, at a wide range of concentrations (5–100 μg/mL), diluted in DMSO, and incubated for 6 and 48 h. Then, the MTT reagent was added at a final concentration of 0.5 mg/mL for 3–4 h. Finally, formazan crystals were diluted with 100% isopropanol, and absorbance was measured at 570 nm using a multimode plate reader (EnSpire, PerkinElmer, Beaconsfield, UK). Background absorbance was also measured at 690 nm, as a reference.