Comparison of Radical Scavenging Effect, Inhibition of Microsomal Oxygen Free Radical Generation, and Serum Lipoprotein Oxidation of Several Natural Antioxidants

Typical components of the Mediterranean diet, such as olive oil and red wine, contain high concentrations of complex phenols, which have been suggested to have an important antioxidant role. The aim of the present work was to determine the inhibitory potency of compounds such as oleuropein, hydroxytyrosol, and other structurally related compounds, such as gallic acid, toward reactive oxygen species generation and free radical scavenging ability. The potency of these compounds was also examined with respect to protecting in vitro low-density lipoprotein oxidation. These studies indicate that complex phenols, such as hydroxytyrosol, and gallic acid both inhibit free radical generation and act as free radical scavengers. The use of three different approaches to determine antioxidant potency demonstrates that activity in one test does not necessarily correlate with activity in another. It was also demonstrated that the presence of two phenolic groups is not always associated with antioxidant activity. Keywords: Hydroxytyrosol; oleuropein; gallic acid; CYP3A; low-density lipoprotein; 2‘,7‘-dichlorofluorescin diacetate; 2,2-diphenyl-1-picrylhydrazyl radical