New insights into controversies on the antioxidant potential of the olive oil antioxidant hydroxytyrosol

In the present study, the antioxidant profile of olive oil antioxidants was investigated. Hydroxytyrosol and oleuropein are potent scavengers of hydroxyl radicals (OH*), peroxynitrite (ONOOH), and superoxide radicals (O(2)*(-)). Homovanillic alcohol, one of the main metabolites of hydroxytyrosol, and tyrosol are less potent scavengers of these reactive species. None of the olive oil antioxidants are good hypochlorous acid (HOCl) or hydrogen peroxide (H(2)O(2)) scavengers. Hydroxytyrosol efficiently protects against LDL oxidation in vitro and in vivo. However, no protective effect of hydroxytyrosol is usually demonstrated ex vivo against the oxidation of LDL isolated from humans after hydroxytyrosol consumption. The present study shows that this controversy is due to the isolation of LDL, which greatly reduces the protective effect of hydroxytyrosol against LDL oxidation. Hydroxytyrosol is an efficient scavenger of several free radicals. The physiological relevance of the high intrinsic antioxidant activity of hydroxytyrosol is illustrated by its protection against LDL oxidation.