Morphological change, loss of Δψm and activation of caspases upon apoptosis of colorectal adenocarcinoma induced by 5-FU

Apoptosis is clearly distinguished from necrosis, morphologically and chemically. Morphologically, apoptosis is characterized by a condensed nucleus and the disappearance of microvilli without disruption of the cytoplasm. In this report, we demonstrate that 5-fluorouracil (5-FU)-induced early apoptotic cells are characterized by (i) ultracondensed mitochondria, (ii) no change in the microvilli or nucleus, (iii) a high mitochondrial transmembrane potential (Δψm), and (iv) being annexin Vnegative. The early apoptotic cells also show the active forms of caspase 8 and caspase 9. They rapidly lose Δψm after further incubation. Therefore, we conclude that the ultracondensation of mitochondria precedes the loss of Δψm and the exposure of phosphatidylserine to the outer leaflet of the cell membrane.