Olive oils rich in natural catecholic phenols decrease isoprostane excretion in humans

This study was undertaken to evaluate, in humans, the antioxidant activity of olive oil phenolics, namely hydroxytyrosol and oleuropein aglycone that share an orthodiphenolic (catecholic) structure. Human volunteers were admi nistered olive oil samples containing increasing amounts of an olive oil ph enolic extract that was characterized by gas-chromatography/mass spectromet ry, The administration of phenol-rich oils was dose-dependently associated with a decreased urinary excretion of 8-iso-PGF(2 alpha), a biomarker of ox idative stress. Also, a statistically significant negative correlation betw een homovanillyl alcohol (HValc, hydroxytyrosol's major metabolite, formed through the COMT system) and F-2-isoprostanes excretion was found. Thus, th e administration of oil samples with increasing, albeit low, concentrations of orthodiphenolic compounds, namely hydroxytyrosol and oleuropein aglycon e, results in a dose-dependent reduction in the urinary excretion of 8-iso- PGF(2 alpha). The statistically significant negative correlation between 8- iso-PGF(2 alpha) and HValc urinary concentrations suggests that this metabo lite better reflects the in vivo activities of hydroxytyrosol, (C) 2000 Aca demic Press.