Proceedings of The Physiological Society

University College Dublin (2009) Proc Physiol Soc 15, C129

Oral Communications

The Importance of Flavonone B-Ring Catechol in Suppression of Intracellular Fenton Reactions.

R. J. Naftalin1, E. Vlachodimitropoulou1, P. Sharp2

1. Physiology, King's College London, London, United Kingdom. 2. Nutrition, King's College London, London, United Kingdom.

Quercetin, like dehydroascorbate (DHA) is transported into cells via the passive glucose transporters, GLUTs 1 and 4(1). We have demonstrated that quercetin, like ascorbate, acts as an electron donor to the erythrocyte transmembrane oxidoreductase, DcytB(3;4). Ascorbate also interacts with Fe2+/Fe3+ and H2O2 to produce very reactive OH. radicals. In contrast to ascorbate, quercetin is a known suppressant of the Fenton reaction (2). We have compared the iron chelating efficacy of several flavonones to determine which hydroxyl groups suppress intracellular free OH. radical formation. Following overnight loading of Madin Darby canine kidney cells with 20μM ferrous sulphate, the cells were washed free of adherent extracellular Fe2+ with 300μM desferrioximine, an impermeant iron chelator which suppresses extracellular Fenton reactions, then exposed to varying concentrations of permeable polyphenols, 100μM H2O2 and the luminescent OH. radical sensor L-012. The intracellular luminescence was assayed in a 96 well luminescence plate reader. The I.C.50 of quercetin and luteolin-induced inhibitions of intracellular iron-dependent luminescence was 3.4±0.9 and 3.7±0.8 μM respectively and with 3,5-dihydroxyflavone and chrysin was 9.4±1.5 μM and 18.1±14 μM (S.E.M, 2 experiments, with each compound, 6 concentrations and 3 replicates). The differences between the efficacies of the flavonone suppression of the Fenton reaction shows the key importance of the 3’-4’ dihydroxylated B ring as an Fe2+ chelator, present in both quercetin and luteolin. Since human ingestion of the natural product quercetin, even in large quantities, is non-toxic (5), it may be a useful therapeutic agent against oxidative stress induced by iron overload, as in thallasemia and pre-eclampsia.

Where applicable, experiments conform with Society ethical requirements