2.2 Cell viability and cytotoxicity assays
For the cell viability assay, MDCK cells were cultured on a 96-well
plate (2 × 104 cells/well) in Growth Medium. After
incubation for 16 h at 37 °C, the cells were infected with each
influenza virus at 103 50% tissue culture infectious
dose (TCID50)/well and were washed with
phosphate-buffered saline (PBS) at 1 h post-infection. Various
concentrations (10 to 200 nM, n = 3 per dose) of aprotinin diluted with
Infection Medium were added into each well to a final volume of 100
μl/well. After incubation for 72 h at 37 °C, cell viability was
determined using the EZ-Cytox kit (Daeillab service Co., South Korea)
according to the manufacturer’s instructions. Cell viability was
indicated by percentage values, compared to the negative control (cells
that were infected but not treated with aprotinin). Cytotoxicity of
aprotinin was measured similarly as described above, but without
infecting with the virus. Cytotoxicity was presented as a percentage
value, compared to the negative control (wells containing cells only).