title: Radical-scavenging Activity and Antioxidative Effects of Olive Leaf Components Oleuropein and Hydroxytyrosol in Comparison with Homovanillic Alcohol.
abstract: Olive leaf has great potential as a natural antioxidant, and one of its major phenolic components is oleuropein. In this study, the antioxidant activity of oleuropein against oxygen-centered radicals was measured by examining its sparing effects on the peroxyl radical-induced decay of fluorescein and pyrogallol red, in comparison with related compounds. The antioxidant capacity of oleuropein against lipid peroxidation was also assessed through its effect on the free radical-induced oxidation of methyl linoleate in a micelle system. On a molar basis, oleuropein and hydroxytyrosol inhibited the decay of fluorescein for longer than both homovanillic alcohol and the vitamin-E mimic 2-carboxy-2,5,7,8-tetramethyl-6-chromanol (Trolox), but did not suppress pyrogallol red decay in a concentration-dependent manner. Measurement of the fluorescein decay period revealed that the stoichiometric number of oleuropein and hydroxytyrosol against peroxyl radicals was twice that of Trolox, which is substantially higher than expectations based on chemical structure. Oleuropein and hydroxytyrosol were also more effective than Trolox and homovanillic alcohol at suppressing the oxidation of methyl linoleate in the micelle system. Thus, both oleuropein and hydroxytyrosol exhibit high antioxidative activity against lipid peroxidation induced by oxygen-centered radicals, but the high reactivity of phenolic/catecholic radicals makes their mechanism of action complex.
authors.affiliation: Health Research Institute, National Institute of Advanced Industrial Science and Technology (AIST).
authors.forename: Aya
authors.initials: A
authors.lastname: Umeno
authors.forename: Mizuki
authors.initials: M
authors.lastname: Takashima
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Murotomi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Taisuke
authors.initials: T
authors.lastname: Koike
authors.forename: Toshiki
authors.initials: T
authors.lastname: Matsuo
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Yoshida
mesh_terms: D000975:Antioxidants; D002839:Chromans / Q000494:pharmacology; D016166:Free Radical Scavengers; D006719:Homovanillic Acid / Q000494:pharmacology*; D057888:Iridoid Glucosides; D039823:Iridoids / Q000494:pharmacology*; D008041:Linoleic Acids; D015227:Lipid Peroxidation / Q000187:drug effects*; D008823:Micelles; D031658:Olea / Q000737:chemistry*; D010084:Oxidation-Reduction / Q000187:drug effects; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives* / Q000494:pharmacology; D018515:Plant Leaves / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D002839:Chromans; D016166:Free Radical Scavengers; D057888:Iridoid Glucosides; D039823:Iridoids; D008041:Linoleic Acids; D008823:Micelles; C532664:homovanillic alcohol; C005975:3,4-dihydroxyphenylethanol; C005575:methyl linoleate; C002769:oleuropein; D010626:Phenylethyl Alcohol; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D006719:Homovanillic Acid