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 Fe²⁺ treatment. Flavonoids with o-dihydroxyl or vicinal-trihydroxyl groups, including quercetin, myricetin (flavonol), luteolin (flavone) and (-)-epigallocatechin gallate (EGCG; flavanol), when coincubated with a mixture of 30/μmol/L H₂O₂ and 30 μmol/L FeSO₄, prevented the formation of malondialdehyde (MDA) at 1 or 10 μmol/L in at least one of two separate experiments. In experiments in which flavonoids were preincubated with cells but removed before the 30 μmol/L H₂O₂ and Fe²⁺ treatment, quercetin at 0.1 μmol/L, EGCG at 1 μmol/L and luteolin at 10 μmol/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 μmol/L in either co- or preincubation experiments. None of the flavonoids tested at 0.1-10 μmol/L increased H₂O₂ and Fe²⁺-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.