Protective effect of oleuropein, an olive oil biophenol, on low density lipoprotein oxidizability in rabbits

Abstract

On the basis of the results obtained with pilot studies conducted in vitro on human low density lipoprotein (LDL) and on cell cultures (Caco-2), which had indicated the ability of certain molecules present in olive oil to inhibit prooxidative processes, an in vivo study was made of laboratory rabbits fed special diets. Three different diets were prepared: a standard diet for rabbits (diet A), a standard diet for rabbits modified by the addition of 10% (w/w) extra virgin olive oil (diet B), a modified standard diet for rabbits (diet C) differing from diet B only in the addition of 7 mg kg(-1) of oleuropein. A series of biochemical parameters was therefore identified, both in the rabbit plasma and the related isolated LDL, before and after Cu-induced oxidation. The following, in particular, were selected: (i) biophenols, vitamins E and C, uric acid, and total, free, and ester cholesterol in the plasma; (ii) proteins, triglycerides, phospholipids, and total, free, and ester cholesterol in the native LDL (for the latter, the dimensions were also measured); (iii) lipid hydroperoxides, aldehydes, conjugated dienes, and relative electrophoretic mobility (REM) in the oxidized LDL (ox-LDL). In an attempt to summarize the results obtained, it can be said that this investigation has not only verified the antioxidant efficacy of extra virgin olive oil biophenols and, in particular, of oleuropein, but has also revealed a series of thus far unknown effects of the latter on the plasmatic lipid situation. In fact, the addition of oleuropein in diet C increased the ability of LDL to resist oxidation (less conjugated diene formation) and, at the same time, reduced the plasmatic levels of total, free, and ester cholesterol (-15, -12, and -17%, respectively), giving rise to a redistribution of the lipidic components of LDL (greater phospholipid and cholesterol amounts) with an indirect effect on their dimensions (bigger by about 12%).

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

“…We found 13 publications that addressed absorption, metabolism, or urinary excretion of olive oil phenols: five animal (Bai et al, 1998;Coni et al, 2000;D'Angelo et al, 2001;Tuck et al, 2001;Visioli et al, 2001), six human studies (Bonanome et al, 2000;Visioli et al, 2000a, b;Miro-Casas et al, 2001a, b;Vissers et al, 2002), and two studies that addressed characterisation of the metabolites of hydroxytyrosol in urine from two of the above-mentioned studies Tuck et al, 2002). One study by our group showed that apparent in vivo absorption of the ingested olive oil phenols was more than 55-66 mol% in humans.…”

“…However, Bai et al analysed hydroxytyrosol without prior deconjugation, which may cause underestimation of total hydroxytyrosol in plasma. Likewise, Coni et al (2000) also analysed olive oil phenols without deconjugation in plasma of rabbits that consumed extra virgin olive oil for 6 weeks. Thus, reliable data on plasma concentration of olive oil phenols are scarce.…”

Effect of ingestion of virgin olive oil on human low-density lipoprotein composition

“…Recent studies have shown the bioavailability of some phenols from wine or onions (Lapidot et al, 1998;Manach et al, 1998;Bell et al, 2000) but data on olive oil are scarce. Moreover, most of these studies have been done with rats or rabbits (Wiseman et al, 1996;Coni et al, 2000), but few with humans (Paganga & Rice-Evans, 1997;Miró -Casas et al, 2001). …”

Understanding the Characteristics of Oleuropein for Table Olive Processing

“…Antioxidant activity of oleuropein is mainly due to the hydroxytyrosol moiety in its structure [11]. Also oleuropein contributes to the prevention of atherosclerosis by inhibiting the oxidation of LDL and by scavenging several species that react with oxygen in the vascular wall [12,13].…”