Olive fruit extracts inhibit proliferation and induce apoptosis in HT-29 human colon cancer cells

Olives and their derivatives represent an important component of the Mediterranean diet that has been considered to be protective against cancer. We investigated the effect on cell proliferation and apoptosis in HT-29 cells of an extract from the skin of olives composed of pentacyclic triterpenes with the main components maslinic acid (73.25%) and oleanolic acid (25.75%). Studies of the dose-dependent effects showed antiproliferative activity at an EC50 value of 73.96 +/- 3.19 mu mol/L of maslinic acid and 26.56 +/- 2.55 mu mol/L of oleanolic acid without displaying necrosis. Apoptosis was confirmed by the microscopic observation of changes in membrane permeability in 40.9 +/- 3.9% and detection of DNA fragmentation in 24.5 +/- 1.5% of HT-29 cells incubated for 24 h with olive fruit extract containing 150 and 55.5 mu mol/L of maslinic and oleanolic acids, respectively. Caspase-3 was activated in a dose-dependent manner after incubation for 24 h. The extract containing 200 mu mol/L maslinic acid and 74 mu mol/L oleanolic acid increased caspase-3-like activity to 6-fold that of control cells. Programmed cell death was induced by the intrinsic pathway, as evidenced by the production of superoxide anions in the mitochondria of cells treated with olive fruit extracts containing 150 and 55.5 mu mol/L of maslinic and oleanolic acids, respectively. Our results report for the first time, to our knowledge, the inhibition of cell proliferation without cytotoxicity and the restoration of apoptosis in colon cancer cells by maslinic and oleanolic acids present in olive fruit extracts.