Cells (1 × 104 cells/well) were added to wells of a 96-well culture plate. After 24 h, the fluid was replaced with complete medium containing EETC and incubation continued for 24 h. Cell viability was measured by the MTT assay, which is based on the ability of viable cells to convert soluble MTT into an insoluble dark blue formazan. MTT solution (5 mg/ml) was added to each well and the plate was incubated at 37 °C for 4 h. The purple formazan product was dissolved with 200 μl DMSO and the optical density at 570 nm was determined with a microplate reader (Bio-Rad, Hercules, CA).