The effect of flavonoids on the reduction of cupric ions, the copper-driven Fenton reaction and copper-triggered haemolysis

Flavonoids are considered beneficial, but they may exhibit pro-oxidative effects likely due to metal reducing properties. For the first time, 24 structurally related flavonoids were compared for copper reduction, and modulation of the copper-triggered Fenton reaction and lysis of erythrocytes. The vast majority of flavonoids reduced cupric ions; their behaviour ranged from progressive gradual reduction through bell-shaped, neutral, to a blockade of spontaneous reduction. Similarly, different behaviours were observed with the Fenton reaction. Flavone was the only flavonoid that potentiated copper-triggered haemolysis (155 +/- 81 % at twice the amount of Cu2+), while 18 flavonoids were at least partly protective in some concentrations. Only 5-hydroxyflavone did not reduce Cu2+ and behaved as an antioxidant in both assays (reduction of 60 +/- 10 % and 88 +/- 1%, respectively, at an equimolar ratio with Cu2+). In conclusion, relatively subtle structural differences resulted in very different anti/prooxidant behaviour depending on the model.

Automated summary

Structural differences in flavonoids can result in different effects on copper reduction, Fenton reaction, and erythrocyte lysis, showing varied antioxidant or prooxidant behavior depending on the model.