2.3. Cell proliferation assay

Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide salt (MTT) kit (USB). Equal numbers of HUVECs (1 × 10⁴ cells/well) were seeded onto 96-well plates and incubated overnight. After the indicated time, cells were incubated with MTT solution (0.5 mg/mL) in assay medium for 4 h. Then the residual MTT was removed and the crystals were dissolved by incubation with DMSO solution for color development. The absorbance at wavelengths 450 nm and 690 nm (reference) were measured using a microplate reader (ELx800; Biotek, Winooski, VT, USA).