Evaluation of antioxidative and antimutagenic effects of quercetin in humans, in vitro and ex vivo

Abstract

Antioxidants play a vital role in the cellular protection against oxidative damage. Quercetin is a well-investigated antioxidant and known to be able to protect against cellular oxidative DNA damage. In this study, we tried to relate the protection by quercetin pre-treatment against oxidative DNA damage in human lymphocytes in vitro to the interaction of quercetin in solution with hydroxyl and superoxide anion radicals as measured by ESR (Electron Spin Resonance) spectrometry, using DMPO as a spin trap. Further, scavenging capacity of quercetin-treated lymphocytes in vitro was evaluated by ESR spectrometry. Quercetin appears capable of protecting human lymphocytes against oxidative DNA damage caused by hydrogen peroxide in a dosedependent manner. The protection of lymphocytes against superoxides is ambiguous. Incubation concentrations of quercetin (1, 10, and 50 μM) reduced levels of superoxide-induced oxidative DNA damage, while at 100 μM the amount of damage was increased. These results are supported by ESR-findings on quercetin in solution, also showing a prooxidant effect at 100 μM. ESR spectrometry showed rate constant values for the reaction kinetics of quercetin in lowering iron-dependent hydroxyl radical formation and NADH-dependent superoxide anion formation of respectively 3.2 x 10 M s and 1.1 x 10 M s. This shows that quercetin is a more potent inhibitor of hydroxyl radical formation than a scavenger of superoxide anions. Hydroxyl and superoxide anion radicals | 29