Virgin Olive Oil Phenols Inhibit Proliferation of Human Promyelocytic Leukemia Cells (HL60) by Inducing Apoptosis and Differentiation

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ABSTRACT

Although epidemiologic evidence and animal studies suggest that olive oil may prevent the onset of cancer, the components responsible for such an effect and their mechanisms of action remain largely unknown. In the present study, we investigated the effect of a virgin olive oil phenol extract (PE) on proliferation, the cell cycle distribution profile, apoptosis, and differentiation of the human promyelocytic cell line HL60. PE inhibited HL60 cell proliferation in a time- and concentration-dependent manner, as demonstrated by the viable cell count and 3-[4,5-dimethyl(thiazol-2-yl)]-3,5-diphenyltetrazolium bromide (MTT) metabolism. Cell growth was completely blocked at a PE concentration of 13.5 mg/L; apoptosis was also induced as detected by fluorescence microscopy and flow cytometry. Determination of the cell cycle distribution by flow cytometry revealed an accumulation of cells in the G0/G1 phase. Two compounds isolated from PE, the dialdehydic forms of elenoic acid linked to hydroxytyrosol (3,4-DHPEA-EDA) and to tyrosol (pHPEA-EDA), were shown to possess properties similar to those of PE; they account for a part of the powerful effects exerted by the complex mixture of compounds present in PE. The concentrations of the different compounds in PE were determined by HPLC, and the purity of 3,4-DHPEA-EDA and pHPEA-EDA was ascertained by NMR. Treatment with PE induced a differentiation in HL60 cells, which subsequently acquired the ability to produce superoxide ions and reduce nitroblue tetrazolium to formazan. These results support the hypothesis that polyphenols play a critical role in the anticancer activity of olive oil.

KEY WORDS

olive oil
phenols
apoptosis
differentiation
chemoprevention

Abbreviations

ATRA
all-trans retinoic acid
Cdk
cyclin-dependent kinase
3,4-DHPEA
3,4-dihydroxyphenyl-ethanol or hydroxytyrosol
3,4-DHPEA-EDA
dialdehydic form of elenoic acid linked to hydroxytyrosol
3,4-DHPEA-EA
oleuropein aglycon
DMSO
dimethyl sulfoxide
MTT
(3-[4,5-dimethyl(thiazol-2-yl)]-3,5-diphenyltetrazolium bromide)
NBT
nitroblue tetrazolium
PE
phenol extract
pHPEA
p-hydroxyphenyl-ethanol or tyrosol
pHPEA-EDA
dialdehydic form of elenoic acid linked to tyrosol
PI
propidium iodide
PMA
phorbol 12-myristate 13-acetate

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