Effects of oleuropein aglycone on breast cancer apoptotic cell death. Quantification of apoptosis-related cell death in MCF-7, MCF-7/(pBABE)HER2 and SKBR3 cells treated with increasing concentrations of oleuropein aglycone was determined by Cell Death ELISA as described in "Material and methods". The enrichment of histone-DNA fragments in oleuropein aglycone-treated cells was expressed as fold-increase in absorbance by comparing with control (vehicle-treated) cells using the following formula: [A405 – A490]TREATED/[A405-A490]UNTREATED. Data are the mean (columns) and 95% confidence intervals (bars) of three independent experiments performed in duplicate. One-factor ANOVA was used to analyze differences in the percentage of apoptosis between the various treatment groups and the control group. * P < .01; ** P < .001; N.S.: Not statistically significant (one-factor analysis of variance). All statistical tests were two-sided.