2.2. MTT Assay

We incubated 1 × 10⁴/ml diluted H9C2 cells in 96-well plates at 37°C and 5% CO₂ in a humidified incubator. The culture solution was changed every day. After incubation for 24 h, 48 h, and 72 h, respectively, the culture solution was discarded, and the cells were washed with PBS [30]. Then, 20 μl of MTT solution was added to each well and incubated at 37°C for 4 h in the dark. After discarding the culture solution with MTT, we added 150 μl DMSO into each well [31]. The plate was constantly shaken for 10 min to fully dissolve the purple crystals. Then, the OD values were measured in an enzyme-linked immunosorbent detector at 490 nm wavelength [32, 33].