In order to confirm the apoptotic induction effect of Thai
rat-tailed radish extract, the treated HCT116 cells were
stained with Annexin V FITC/propidium iodide (PI), which
was then analyzed using flow cytometry. Theoretically, viable
cells cannot be labeled by both Annexin V and PI (Annexin V
/PI ), while necrotic cells—which have lost their membrane
integrity—will permit PI to pass through the cell membrane
and intercalate with the nucleic acid (Annexin V /PI +). During
early-stage apoptosis, the loss of cell membrane asymmetry
leads to externalization of phosphatidylserine (PS) to the
cell surface; thereby allowing Annexin V to bond with PS (Annexin
V +/PI ). In late stage apoptosis, cells lose their membrane
integrity and are permeable to PI (Annexin V +/PI+)
(Zhang, Gurtu, Kain, & Yan, 1997); thus, the apoptotic death
mode can be distinguished from the undesirable necrosis
death mode.