Effect of virgin olive oil phenols on proliferation, cell cycle and apoptosis of tumour cell lines.

Epidemiological evidences and animal studies suggest a relationship between the intake of olive oil and a reduced risk of several malignancies. Recently, this protective activity has been ascribed, at least in part, to the high content of antioxidant phenols present in the olive oil. Aim The aim of the present study was to assess the effect of pure hydroxytyrosol (a major antioxidant compound of virgin olive oil) and of a methanol extract of olive oil phenols, on proliferation, apoptosis and cell cycle of tumour cells. Methods Apoptosis was quantified by flow cytometry, fluorescence microscopy and internucleosomal DNA fragmentation. The DNA cell cycle analysis was carried out by flow cytometry. Results Hydroxytyrosol inhibited proliferation of both human promyelocytic leukemia cells HL60 and colon adenocarcinoma cells HT29 and HT29 clone 19A. The concentrations of hydroxytyrosol which inhibited 50% of cell proliferation were ∼50 and ∼750 μM for HL60 and both HT29 and HT29 clone 19A cells, respectively. Hydroxytyrosol (50 and 100 μM) induced an appreciable apoptosis in HL60 cells after 24h of incubation while no effect was observed after similar treatment of freshly isolated human lymphocytes and polymorphonuclear cells. The DNA cell cycle analysis showed that the treatment of HL60 cells with hydroxytyrosol (50 and 100 μM) arrested the cells in the G0/G1 phase with a concomitant decrease in the cell percentage in the S and G2/M phases. Similar effects were observed with a methanol extract of olive oil containing different phenols including hydroxytyrosol, tyrosol and their derived compounds. In this case the inhibition of proliferation, the cell cycle arrest and the induction of apoptosis was evident in a range of concentrations of phenols (expressed as μM of hydroxytyrosol containing compounds) about 10 times lower than that of hydroxytyrosol suggesting that the phenol mixture may potentiate the effect of hydroxytyrosol. Conclusions These results support the hypothesis that olive oil phenols may exert a protective activity against cancer by arresting the cell cycle and inducing apoptosis in tumour cells, and suggest that they may be responsible for the olive oil anti-cancer activity.