Cell Viability Assay of Plant Extracts

Cell vitality was determined by MTT assay. A total of 2 × 10⁴ cells/well were plated in a 96-well plate and treated, in triplicates, with extract of WND, CWND, and CBND at different concentrations and times. Thiazolyl Blue Tetrazolium Bromide [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT; Sigma-Aldrich) solution was added at 0.5 mg/mL. After 4 h, for the adhesion cells HaCat and MCF-7, the supernatant was simply removed, whereas, for the suspension cells U-937 and HL-60, the plates were first centrifuged. The purple formazan crystals were dissolved in isopropanol (Carlo Erba Reagents, Cornaredo, Italy), and the absorbance was read at a wavelength of 570 nm with a TECAN M-200 reader (Tecan, Männedorf, Switzerland) [25 (link)].