Orange flavonoid hesperetin modulates cardiac hERG potassium channel via binding to amino acid F656

Back-ground and aims: Hesperetin belongs to the flavonoid subgroup classified as citrus flavonoids and is the main flavonoid in oranges. A high dietary intake of flavonoids has been associated with a significant reduction in cardiovascular mortality. HERG potassium channels play a major rote in cardiac repolarisation and represent the most important pharmacologic target of both antiarrhythmic and proarrhythmic drugs. Methods and results: We used the two-microelectrode vottage-clamp technique to analyse inhibitory effects of hesperetin on hERG potassium channels heterologously expressed in Xenopus oocytes. Hesperetin blocked hERG potassium channels in a concentration dependent manner. Onset of block was fast and completely reversible upon wash-out. There was no significant effect of hesperetin on channel kinetics. Affinity of hesperetin to mutant F656A hERG channel was significantly decreased compared to WT hERG, indicating a binding site in the channel pore cavity. In contrast, affinity of hesperetin to Y652A hERG was not different from the affinity to WT hERG. Conclusion: We found an antagonist of cardiac hERG channels that modulates hERG currents by accessing the aromatic pore binding site, particularly amino acid phe-656. Regarding high hesperetin concentrations found in oranges and the increasing consumption of oranges and orange juice in Europe, potential effects of hesperetin on cardiac electrophysiology in vivo deserve further investigation. (c) 2006 Elsevier B.V. All rights reserved.