MTT assay for cell viability

The assessment of cell vitality was performed by MTT assay. Briefly, HUVECs were seeded into 96-well cell culture plates at an initial density of 1×10⁴ cells/well. Following a 24 h treatment of 4 ng/mL, 20 ng/mL, 0.1 μg/mL, 0.5 μg/mL and 5 μg/mL ISMN, 20 μL of a 5 mg/mL solution in PBS of the MTT substrate (Sigma-Aldrich, MO, USA) was added and incubated for up to 4 h. The resulting blue-brown formazan precipitate formed was solubilized by DMSO. A curve of cell vitality was constructed by measuring cell growth with a microplate reader at 490 nm.