title: Versatile redox chemistry complicates antioxidant capacity assessment: flavonoids as milieu-dependent anti- and pro-oxidants.
abstract: Some antioxidants have been shown to possess additional pro-oxidant effects. Diverse methodologies exist for studying redox properties of synthetic and natural chemicals. The latter are substantial components of our diet. Exploration of their contribution to life-extending or -compromising effects is mandatory. Among reactive oxygen species (ROS), hydroxyl radical (•OH) is the most damaging species. Due to its short half-life, the assay has to contain a specific generation system. Plants synthesize flavonoids, phenolic compounds recognized as counter-agents to coronary heart disease. Their antioxidant activities are affected by their hydroxylation patterns. Moreover, in the plant, they mainly occur as glycosides. We chose three derivatives, quercetin, luteolin, and rutin, in attempts to explore their redox chemistry in contrasting hydrogen peroxide environments. Initial addition of hydrogen peroxide in high concentration or gradual development constituted a main factor affecting their redox chemical properties, especially in case of quercetin. Our study exemplifies that a combination of a chemical assay (deoxyribose degradation) with an electrochemical method (square-wave voltammetry) provides insightful data. The ambiguity of the tested flavonoids to act either as anti- or pro-oxidant may complicate categorization, but probably contributed to their evolution as components of a successful metabolic system that benefits both producer and consumer.
authors.affiliation: Department of Molecular Systems Biology, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria. vladimir.chobot@univie.ac.at.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Chobot
authors.forename: Lenka
authors.initials: L
authors.lastname: Kubicova
authors.forename: Gert
authors.initials: G
authors.lastname: Bachmann
authors.forename: Franz
authors.initials: F
authors.lastname: Hadacek
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D001205:Ascorbic Acid / Q000737:chemistry; D055664:Electrochemical Techniques; D005419:Flavonoids / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D047311:Luteolin / Q000737:chemistry; D016877:Oxidants / Q000737:chemistry*; D010084:Oxidation-Reduction; D011794:Quercetin / Q000737:chemistry; D012431:Rutin / Q000737:chemistry; D017392:Thiobarbituric Acid Reactive Substances
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D016877:Oxidants; D017392:Thiobarbituric Acid Reactive Substances; D012431:Rutin; D011794:Quercetin; D006861:Hydrogen Peroxide; D007501:Iron; D047311:Luteolin; D001205:Ascorbic Acid