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

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 inh ibit prooxidative processes,an in vivo study was made of laboratory rabbits fed special diets. Three different diets were prepared: a standard diet fo r 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 ra bbits (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, b oth in the rabbit plasma and the related isolated LDL, before and after Cu- induced oxidation. The following, in particular, were selected: ii) biophen ols, 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 wer e also measured); (iii) lipid hydroperoxides, aldehydes, conjugated dienes, and relative electrophoretic mobility (REM) in the oxidized LDL (ox-LDL). In an attempt;tp summarize the results obtained, it can be said that this i nvestigation has not only verified the antioxidant efficacy of extra virgin olive oil biophenols and, in particular, of oleuropein, but has also revea led a series of thus far unknown effects of the latter on the plasmatic lip id situation. In fact, the addition of oleuropein in diet C increased the a bility of LDL to resist oxidation (less conjugated diene formation) and, at the same time, reduced the plasmatic levels of total, free, and ester chol esterol (-15, -12, and -17%, respectively), giving rise to a redistribution of the lipidic components of LDL (greater phospholipid and cholesterol amo unts) with an indirect effect on their dimensions (bigger by about 12%).