Background and aim: Extra virgin olive oil has been associated with a reduced incidence of risk factors for coronary heart disease also owing to the presence of antioxidant biophenols. This study compared the protective effects of tyrosol and hydroxytyrosol, two biophenols greatly different in antioxidant power, on J774 A.1-mediated oxidation of LDL.
Methods and results: Cell-mediated oxidation of LDL was evaluated by TBARS formation, and relative electrophoretic mobility increase. Redox imbalance was studied by: (i) cytofluorimetric determination of intracellular ROS and GSH, and (ii) evaluation of GSH-related enzyme activities and gene expressions by colorimetric and RT-PCR analyses, respectively. The cellular uptake of the biophenols was evaluated by HPLC. Both biophenols inhibited cell-mediated oxidation of LDL but to a different extent (100% hydroxytyrosol vs 40% tyrosol), and counteracted the impairment of antioxidant cellular defence, i.e., GSH and related enzymes. Tyrosol was effective in inhibiting about 30% of ROS production only at later time-points (12h for superoxide, 24h for hydrogen peroxides). Interestingly, both biophenols were effective when added to the cells for 2h and removed before LDL treatment. This was probably related to cell-biophenol interactions: hydroxytyrosol was rapidly found inside the cells (1.12+/-0.05ng/mg cell protein) and disappeared within 18h, while tyrosol accumulated intracellularly with time (0.68+/-0.09 vs 1.72+/-0.13ng/mg cell protein at minute 5 and hour 18, respectively).
Conclusions: In spite of its weak antioxidant activity, tyrosol was effective in preserving cellular antioxidant defences, probably by intracellular accumulation. These findings give further evidence in favour of olive oil consumption to counteract cardiovascular diseases.