Cancer chemoprevention by hydroxytyrosol isolated from virgin olive oil through G1 cell cycle arrest and apoptosis

Recent epidemiological evidence and animal studies suggest a relationship between the intake of olive oil and a reduced risk of several malignancies. The present study assesses the effect of hydroxytyrosol, a major antioxidant compound of virgin olive oil, on proliferation, apoptosis and cell cycle of tumour cells. Hydroxytyrosol inhibited proliferation of both human promyelocytic leukaemia cells HL60 and colon adenocarcinoma cells HT29 and HT29 clone 19A. The concentrations of hydroxytyrosol which inhibited 50% of cell proliferation were similar to50 and similar to750 mumol/l for HL60 and both HT29 and HT29 clone 19A cells, respectively. At concentrations ranging from 50 to 100 mumol/l, hydroxytyrosol induced an appreciable apoptosis in HL60 cells after 24 h of incubation as evidenced by flow cytometry, fluorescence microscopy and internucleosomal DNA fragmentation. Interestingly, no effect on apoptosis was observed after similar treatment of freshly isolated human lymphocytes and polymorphonuclear cells. The DNA cell cycle analysis, quantified by flow cytometry, showed that the treatment of HL60 cells with hydroxytyrosol 50-100 mumol/l arrested the cells in the G(0)/G(1) phase with a concomitant decrease in the cell percentage in the S and G(2)/M phases. These results support the hypothesis that hydroxytyrosol may exert a protective activity against cancer by arresting the cell cycle and inducing apoptosis in tumour cells, and suggest that hydroxytyrosol, an important component of virgin olive oil, may be responsible for its anticancer activity. (C) 2002 Lippincott Williams Wilkins.