Flavonoids are ubiquitous substances in fruits and vegetables. A main subgroup of the flavonoids are the flavonols, of which quercetin and kaempferol are the major representatives in foods. They are used in food supplements at high doses, because of their preventive effects on degenerative diseases. The aim of this study was to determine the combined and separate effects of kaempferol and quercetin on oxidative stress in cow pulmonary artery endothelium (CPAE) cells over a broad concentration range. The results demonstrate that cell viability was greatly increased in kaempferol and quercetin treated cells whether H2O2-treated or not. Cell viability also increased when treated with flavonols in the absence of oxidative stress. Both preincubation and simultaneous incubation with kaempferol and quercetin protected against the loss of cell viability induced by 1mM H2O2(5h). Protective effects of flavonols against oxidative stress were shown to depend on the treated flavonol concentrations. No protective effect was shown under low concentration treatment and cell viability increased 1.6 times at 200 μMrelative to the control group. At the highest flavonol concentration of 300 μM, the increased cell viability by flavonol treatment was decreased to almost half of the maximum values. Combined treatments with kaempferol and quercetin showed more protective effects against oxidative stress by H2O2 than the separate effects of each flavonol. In conclusion, the protective effect of kaempferol and quercetin against oxidative stress was very pronounced but high concentrations of flavonols can also induce cell cytotoxicity.
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