Interactions of Flavonoids with Iron and Copper Ions: A Mechanism for their Antioxidant Activity

Abstract

The metal chelating properties of flavonoids suggest that they may play a role in metal-overload diseases and in all oxidative stress conditions involving a transition metal ion. A detailed study has been made of the ability of flavonoids to chelate iron (including Fe3+) and copper ions and its dependence of structure and pH. The acid medium may be important in some pathological conditions. In addition, the ability of flavonoids to reduce iron and copper ions and their activity-structure relationships were also investigated. To fulfill these objectives, flavones (apigenin, luteolin, kaempferol, quercetin, myricetin and rutin), isoflavones (daidzein and genistein), flavanones (taxifolin, naringenin and naringin) and a flavanol (catechin) were investigated. All flavonoids studied show higher reducing capacity for copper ions than for iron ions. The flavonoids with better Fe3+ reducing activity are those with a 2,3-double bond and possessing both the catechol group in the B-ring and the 3-hydroxyl group. The copper reducing activity seems to depend largely on the number of hydroxyl groups. The chelation studies were carried out by means of ultraviolet spectroscopy and electrospray ionisation mass spectrometry. Only flavones and the flavanol catechin interact with metal ions. At pH 7.4 and pH 5.5 all flavones studied appear to chelate Cu2+ at the same site, probably between the 5-hydroxyl and the 4-oxo groups. Myricetin and quercetin, however, at pH 7.4, appear to chelate Cu2+ additionally at the ortho-catechol group, the chelating site for catechin with Cu2+ at pH 7.4. Chelation studies of Fe3+ to flavonoids were investigated only at pH 5.5. Only myricetin and quercetin interact strongly with Fe3+, complexation probably occurring again between the 5-hydroxyl and the 4-oxo groups. Their behaviour can be explained by their ability to reduce Fe3+ at pH 5.5, suggesting that flavonoids reduce Fe3+ to Fe2+ before association.

Effects of astaxanthin on oxidative stress induced by Cu2+ in prostate cells

“…Some results showed that AST protected neuronal cells against oxidative damage, and thus it has been a potent candidate for brain food (Liu and Osawa, 2009), and additionally could protect PC12 cells against glucose toxicity (Zhang et al, 2015). On the other hand, Cu 2+ could lead to various cell injuries by inducing oxidative stress and mitochondrial dysfunction (Murphy and Taiz, 1997;Mira et al, 2002;Ma et al, 2014). Cu 2+ -induced production of hydrogen peroxide and hydroxyl radicals has been directly correlated with the damage to proteins and lipids .…”

Fenton Reaction Driven by Iron Ligands

“…According to way (I), organic ligands at higher pH values can chelate iron completely (60)(61)(62) , changing the redox potential of Fe 2+ /Fe 3+ pair (E°=+0.771 V) (63) . Considering the way (II) and highlighting that the first transition period are labile, following a dissociative mechanisms (S N 1) (64) .…”

Piper Betel Leaf: A Reservoir of Potential Xenohormetic Nutraceuticals with Cancer-Fighting Properties

“…Furthermore, the orthohydroxyphenoxy radical produced from the oxidation of a catechol/pyrogallol moiety can also react with a second freeradical species, including 3 O 2 , to afford oxidizing orthoquinones and O 2 À. (59). Because of these reactions, the catecholic betel phenolic compounds like hydroxychavicol and ChA (Fig.…”