title: Protection of cells against oxidative stress by nanomolar levels of hydroxyflavones indicates a new type of intracellular antioxidant mechanism.
abstract: Natural polyphenol compounds are often good antioxidants, but they also cause damage to cells through more or less specific interactions with proteins. To distinguish antioxidant activity from cytotoxic effects we have tested four structurally related hydroxyflavones (baicalein, mosloflavone, negletein, and 5,6-dihydroxyflavone) at very low and physiologically relevant levels, using two different cell lines, L-6 myoblasts and THP-1 monocytes. Measurements using intracellular fluorescent probes and electron paramagnetic resonance spectroscopy in combination with cytotoxicity assays showed strong antioxidant activities for baicalein and 5,6-dihydroxyflavone at picomolar concentrations, while 10 nM partially protected monocytes against the strong oxidative stress induced by 200 µM cumene hydroperoxide. Wide range dose-dependence curves were introduced to characterize and distinguish the mechanism and targets of different flavone antioxidants, and identify cytotoxic effects which only became detectable at micromolar concentrations. Analysis of these dose-dependence curves made it possible to exclude a protein-mediated antioxidant response, as well as a mechanism based on the simple stoichiometric scavenging of radicals. The results demonstrate that these flavones do not act on the same radicals as the flavonol quercetin. Considering the normal concentrations of all the endogenous antioxidants in cells, the addition of picomolar or nanomolar levels of these flavones should not be expected to produce any detectable increase in the total cellular antioxidant capacity. The significant intracellular antioxidant activity observed with 1 pM baicalein means that it must be scavenging radicals that for some reason are not eliminated by the endogenous antioxidants. The strong antioxidant effects found suggest these flavones, as well as quercetin and similar polyphenolic antioxidants, at physiologically relevant concentrations act as redox mediators to enable endogenous antioxidants to reach and scavenge different pools of otherwise inaccessible radicals.
authors: Department of Sciences, University Roma Tre, Rome, Italy.
authors: Emanuele
authors: E
authors: Lombardo
authors: Cristian
authors: C
authors: Sabellico
authors: Jan
authors: J
authors: Hájek
authors: Veronika
authors: V
authors: Staňková
authors: Tomáš
authors: T
authors: Filipský
authors: Valentina
authors: V
authors: Balducci
authors: Paolo
authors: P
authors: De Vito
authors: Stefano
authors: S
authors: Leone
authors: Eugenia I
authors: EI
authors: Bavavea
authors: Ilaria Proietti
authors: IP
authors: Silvestri
authors: Giuliana
authors: G
authors: Righi
authors: Paolo
authors: P
authors: Luly
authors: Luciano
authors: L
authors: Saso
authors: Paolo
authors: P
authors: Bovicelli
authors: Jens Z
authors: JZ
authors: Pedersen
authors: Sandra
authors: S
authors: Incerpi
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D044950:Flavanones / Q000494:pharmacology*; D047309:Flavones / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D009000:Monocytes / Q000187:drug effects; D032446:Myoblasts / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats
chemical_list: D000975:Antioxidants; D044950:Flavanones; D047309:Flavones; D016166:Free Radical Scavengers; C507557:negletein; C006680:baicalein
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