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.

Effects of Selected Dietary Secondary Metabolites on Reactive Oxygen Species Production Caused by Iron(II) Autoxidation

“…By contrast, rutin behaved as an antioxidant in both pHs ( Figure 2 B), the o -dihydroxyl group arrangement of ring B being most probably responsible. This points to the contribution of the non-substituted 3-hydroxyl group on ring C to the pro-oxidant activity of quercetin [ 42 , 43 , 44 ]. The pro-oxidant properties of quercetin at pH 7.4 depend on ability of quercetin and its semiquinone to reduce molecular oxygen to superoxide anion radical and hydrogen peroxide [ 38 , 45 ].…”

Photoperiod Extension Enhances Sexual Megaspore Formation and Triggers Metabolic Reprogramming in Facultative Apomictic Ranunculus auricomus

“…A lot of attention is paid to flavonoid and other phenols due to their diversity, ubiquity and documented in vitro bioactivity ( Buer et al, 2010 ) in assumptions that the activity is mainly antioxidant ( Nakabayashi and Saito, 2015 ). Other studies, however, point to the fact that anti- and pro-oxidant activities depend both on electron availability and metal catalysts of these electron transfers and are thus highly locally milieu-dependent ( Chobot et al, 2013 ). Substantial experimental evidence points to the fact that the cellular redox signaling hub interacts complexly with the hormone signaling network at multiple levels, which synergistically not only controls plant growth and development but also modulates response to environmental stress ( Considine and Foyer, 2014 ).…”

Multiple functional roles of anthocyanins in plant-environment interactions

“…It has been speculated that once cells evolved mechanisms to deal with supernumerary ROS, they began to utilize ROS for efficient intra/intercellular signalling processes (Mittler et al, 2011;Chobot et al, 2013). The ROS signalling network is complex in plants, but the dynamic nature of ROS production and scavenging represents a rapid and efficient mechanism to sense and respond to environmental cues (Halliwell and Gutteridge, 1989;Mittler, 2002;Foyer and Noctor, 2005).…”