Concentration Dependence of Anti- and Pro-Oxidant Activity of Polyphenols as Evaluated with a Light-Emitting Fe2+-Egta-H2O2 System

Abstract

Hydroxyl radical (•OH) scavenging and the regeneration of Fe2+ may inhibit or enhance peroxidative damage induced by a Fenton system, respectively. Plant polyphenols reveal the afore-mentioned activities, and their cumulative net effect may determine anti- or pro-oxidant actions. We investigated the influence of 17 phenolics on ultra-weak photon emission (UPE) from a modified Fenton system (92.6 µmol/L Fe2+, 185.2 µmol/L EGTA (ethylene glycol-bis(β-aminoethyl-ether)-N,N,N′,N,-tetraacetic acid) and 2.6 mmol/L H2O2 pH = 7.4). A total of 8 compounds inhibited (antioxidant effect), and 5 enhanced (pro-oxidant effect) UPE at all studied concentrations (5 to 50 µmol/L). A total of 4 compounds altered their activity from pro- to antioxidant (or vice versa) along with increasing concentrations. A total of 3 the most active of those (ferulic acid, chlorogenic acid and cyanidin 3-O-glucoside; mean UPE enhancement by 63%, 5% and 445% at 5 µmol/L; mean UPE inhibition by 28%, 94% and 24% at 50 µmol/L, respectively) contained catechol or methoxyphenol structures that are associated with effective •OH scavenging and Fe2+ regeneration. Most likely, these structures can determine the bidirectional, concentration-dependent activity of some phenolics under stable in vitro conditions. This is because the concentrations of the studied compounds are close to those occurring in human fluids, and this phenomenon should be considered in the case of dietary supplementation with isolated phenolics.

Possible Side Effects of Polyphenols and Their Interactions with Medicines

“…There have been many studies demonstrating the prooxidant activity and the associated destructive potential of various polyphenolic compounds, including resveratrol [ 370 ], kaempferol [ 371 ], curcumin [ 372 , 373 ], caffeic acid [ 374 , 375 ], p -coumaric acid [ 376 ], ferulic acid [ 377 ], gallic acid [ 378 ], salicylic, syringic, vanillic, p -, m - and o -coumaric acids, p - and m -hydroxybenzoic acids [ 379 ], catechin [ 380 ], epicatechin and epigallocatechin [ 381 ], ellagic acid, phloroglucinol, pelargonidin, pelargonidin-3- O -rutinoside [ 382 ], quercetin [ 383 , 384 ], and metal complexes of quercetin such as quercetin copper(II) complex [ 385 ], quercetin nickel(II) complex [ 386 ], quercetin zinc(II) complex [ 387 ], and quercetin manganese(II) complexes [ 388 ]. Moreover, it is not only pure polyphenols which can act as prooxidants.…”

Neuro-Nutraceutical Polyphenols: How Far Are We?

“…This is in line with polyphenols being able to stabilize Fe(III) more than Fe(II), the binding of polyphenols to Fe(II) reduces the reduction potential of iron, and Fe(II)-polyphenol complexes can be rapidly oxidized to Fe(III)-polyphenolic complexes [ 146 ]. Through a Fenton’s-reaction-based system, releasing ultra-weak chemiluminescence, composed by Fe 2+ , ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′,-tetraacetic acid (EGTA), and hydrogen peroxide, the anti- and pro-oxidant activities of different polyphenols (5–50 µM) were investigated, and chemical features such as the presence of catechol or methoxyphenol appeared to be able to effectively scavenge hydroxyl radicals, thus exerting antioxidant activity, and to regenerate, acting as a pro-oxidant, Fe(II), by the reduction of Fe(III) [ 147 ]. Iron dyshomeostasis is associated with cell senescence in age-related disorders; thus, compounds that are able to counteract iron-dependent oxidation could be protective against the unrelenting cell death [ 148 ].…”

Relation between Strawberry Fruit Redness and Bioactivity: Deciphering the Role of Anthocyanins as Health Promoting Compounds

“…Application of most of the concentrations of white and red receptacles or achen the cells decreased ROS values close to the control baseline, showing no significan ference in their ROS level compared to untreated cells, supporting the position that concentrations were not cytotoxic, as previously demonstrated by MTT (Figu However, the red receptacle at 25 µg/mL showed significantly higher values with re to the control, but its ROS values were not as high as when AAPH was applied, w can be considered an elevated concentration but not harmful to the cell. This could b to the fact that it has been described that a high concentration of antioxidants could to pro-oxidation [58], and therefore to an increase in cellular ROS.…”

“…However, the red receptacle at 25 µg/mL showed significantly higher values with respect to the control, but its ROS values were not as high as when AAPH was applied, which can be considered an elevated concentration but not harmful to the cell. This could be due to the fact that it has been described that a high concentration of antioxidants could lead to pro-oxidation [58], and therefore to an increase in cellular ROS. However, when receptacle extracts were applied before incubation with AAPH, in most cases they did not cause a reduction in ROS level compared to untreated cells.…”