The predictive value of the antioxidant capacity of structurally related flavonoids using the Trolox equivalent antioxidant capacity (TEAC) assay

The antioxidant capacity of a series of structurally related flavonoids is quantified by the amount of ABTS [2,2'-azinobis-(3-ethylbenzthiazoline-6-su lfonate)] radical anions (ABTS(.-)) that is able to react with the flavonoi d and expressed as the Trolox equivalent antioxidant capacity (TEAC). To ev aluate the predictive value of the TEAC, the antioxidant activity of this s eries of flavonoids was also assessed in other in vitro assays, measuring t he effect on hydroxyl scavenging, lipid peroxidation and doxorubicin-induce d toxicity as typical scavenging or damage assays. The flavonoids tested we re mono HER, di HER, tri HER, tetra HER and tri HEQ, differing in the numbe r of aromatic hydroxyl groups. It was found that these compounds showed bot h a fast and slow scavenging effect in the TEAC assay and therefore the TEA C at 10 s ('fast' TEAC) and 6 min ('total' TEAC) was determined. Both this 'total' and 'fast' TEAC are negatively correlated with hydroxyl radical sca venging. The 'total' TEAC showed a better correlation than the 'fast' TEAC with the inhibition of lipid peroxidation and the protection against doxoru bicin-induced toxicity. This indicates that beside the fast reaction of sca vengers with the ABTS radical, also the slow reaction should be taken into consideration. It is concluded that the antioxidant capacity, assessed with the modified TEAC assay, can be useful to predict the in vivo antioxidant effect in a series of structurally related compounds. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.