Flavonoid structure affects the inhibition of lipid peroxidation in Caco-2 intestinal cells at physiological concentrations.

The antioxidant activity of flavonoids in cell-free systems has been studied extensively. We compared flavonoids with different structural features on their abilities to protect live Caco-2 intestinal cells from lipid peroxidation due to hydrogen peroxide and Fe(2+) treatment. Flavonoids with o-dihydroxyl or vicinal-trihydroxyl groups, including quercetin, myricetin (flavonol), luteolin (flavone) and (-)-epigallocatechin gallate (EGCG; flavanol), when co-incubated with a mixture of 30 micro mol/L H(2)O(2) and 30 micro mol/L FeSO(4), prevented the formation of malondialdehyde (MDA) at 1 or 10 micro mol/L in at least one of two separate experiments. In experiments in which flavonoids were preincubated with cells but removed before the 30 micro mol/L H(2)O(2) and Fe(2+) treatment, quercetin at 0.1 micro mol/L, EGCG at 1 micro mol/L and luteolin at 10 micro mol/L exerted protective effects in at least one of two experiments. Kaempferol (flavonol) and the isoflavones, genistein and daidzein, did not prevent lipid peroxidation at 0.1-10 micro mol/L in either co- or preincubation experiments. None of the flavonoids tested at 0.1-10 micro mol/L increased H(2)O(2) and Fe(2+)-induced lipid peroxidation after co- or preincubation. In summary, these observations support the importance of plant-based food items such as vegetables, fruits and teas in the diet.