2.4. Cell viability assay
Cell viability was determined colorimetrically using the 3-(4,5-dimethylthiazole-
2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reagent (Duchefa, Haarlem,
Netherlands). The procedures were as described previously (Park et al., 2012). Data
are expressed as percentage of viable cell when compared with control.