Does quercetin protect human red blood cell membranes against γ-irradiation?

Radioprotective potential of quercetin, a powerful free radical scavenger, was investigated in human red blood cells (RBCs) and in isolated RBC membranes exposed to γ-irradiation-induced oxidative stress.

RBCs and RBC membrane suspensions were irradiated (50 Gy) in the presence of quercetin (2-50 µM). Oxidative damage of the membranes was analysed by protein carbonyl measurement (enzyme-linked immunosorbent assay). In RBCs, the concentration of glutathione (GSH) was determined. Lipid peroxidation in RBCs, and for comparison in plasma and peripheral lymphocytes, was quantified by the amount of thiobarbituric acid-reactive substances (TBARS). Radiation-induced damage of the RBC membrane integrity was evaluated by the degree of haemolysis.

Quercetin (50 µM) brought back the level of carbonyls to normal in γ-irradiated RBC membrane proteins and inhibited radiation-induced lipid peroxidation in plasma and lymphocytes, by 75 and 96%, respectively. However, it moderately decreased reduced/oxidized glutathione (GSH/GSSG) ratio and significantly increased TBARS concentrations, by 60 and 28% in irradiated and non-irradiated RBCs, respectively. Haemolysis rate was much higher in RBCs irradiated in the presence of quercetin vs. non antioxidant.

In non-cellular systems (RBC membranes or plasma) and in lymphocytes, quercetin shows antioxidative/radioprotective activity but in whole RBCs it acts as a pro-oxidant and a cytotoxic substance. The possible mechanisms of such action are discussed.