Supplementation of Plasma with Olive Oil Phenols and Extracts:  Influence on LDL Oxidation

Abstract

Phenols present in olive oil may contribute to the health effects of the Mediterranean lifestyle. Olive oil antioxidants increase the resistance of low-density lipoproteins (LDL) against oxidation in vitro, but human intervention studies have failed to demonstrate similar consistent effects. To better mimic the in vivo situation, plasma was incubated with either individual olive oil phenols or olive oil extracts with different phenolic compositions, and LDL was subsequently isolated and challenged for its resistance to oxidation. The results show that the ortho-dihydroxy phenols (hydroxytyrosol and oleuropein-aglycone) are more efficient than their mono-hydroxy counterparts (tyrosol and ligstroside-aglycone) in increasing the resistance of LDL to oxidation. However, the concentration of antioxidants required to inhibit LDL oxidation when added to whole plasma was substantially higher as compared to previous data where antioxidants are directly added to isolated LDL. In conclusion, this study supports the hypothesis that extra virgin olive oil phenols protect LDL in plasma against oxidation. The explanation that in vitro studies show protective effects in contrast to the lack of effect in the majority of human studies may be that the dose of the phenols and thus their plasma concentration in humans was too low to influence ex vivo LDL oxidizability. Further studies are required to gain a better understanding of the potential health benefits that extra virgin olive oil may provide.

Phenolic Molecules in Virgin Olive Oils: a Survey of Their Sensory Properties, Health Effects, Antioxidant Activity and Analytical Methods. An Overview of the Last Decade Alessandra

“…In the context of the Mediterranean diet and coronary heart diseases, it has also been shown that VOO rich in phenols increases the resistance of LDL to oxidation, both in vitro and ex vivo [67][68][69]. The study carried out by Bogani et al [70] confirmed the anti-thrombotic and anti-inflammatory effects of VOO phenolic components, in a postprandial setting; in fact, the results showed significant reductions in serum concentration of inflammatory markers (TXB 2 and LTB 4 ) at 2 and 6 h after consumption of VOO, but not after consumption of either olive oil or corn oil.…”

Bioavailability and antioxidant effects of olive oil phenols in humans: a review

“…However, this does not yet represent the total amount of effective olive oil phenols. Part of the phenols in olive oil are ligstrosideaglycones and tyrosol, which are mono-phenols (Figure 1) with little or no antioxidant capacity (Rice-Evans et al, 1996;Leenen et al, 2002). Of the six analysed Greek olive oils, the mean percentage of diphenols was 44 mol% (range 39-51 mol%).…”

“…The daily intake, bioavailability, and the amount of hydroxyl groups per molecule, and thus the antioxidant potential (Rice-Evans et al, 1996;Leenen et al, 2002), differ among various types of phenols. Therefore, it is difficult to compare the antioxidant effect of olive oil phenols in vivo with that of phenols from other foods, like wine, coffee, tea, onions, or apples.…”

“…Phenols are compounds with an aromatic ring structure with one or more hydroxyl groups. Phenols with two or more hydroxyl groups show antioxidant capacity in vitro, whereas phenols with one hydroxyl group have little or none (Rice-Evans et al, 1996;Leenen et al, 2002). Extra virgin olive oil contains phenols with either one or two hydroxyl groups (Figure 1).…”

Olive oil exhibits osteoprotection in ovariectomized rats without estrogenic effects

“…A diet rich in unsaturated fatty acids from olive oil reduces waist girth, a significant indicator of metabolic disease, in addition to reducing body mass index (40). In addition, a study supports the hypothesis that extra virgin olive oil phenols protect low density lipoproteins in the plasma against oxidation (41).…”