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Heterogeneous effect of flavonoids on K+ loss and lipid peroxidation induced by oxygen-free radicals in human red cells.

Treatment of fresh erythrocytes with phenazine methosulfate, an intracellular generator of oxygen-free radicals, and diethyldithiocarbamate an inhibitor of superoxide dismutase results in membrane damage consisting in lipid peroxidation and increase in passive K+ permeability. Various flavonoids which have previously been reported to act as oxygen-free radical scavengers were tested on this erythrocyte model. Surprisingly, flavonoids did not exhibit the same effect on the oxygen free radical-stimulated K+ permeability. It was possible to classify these agents into four groups: protective (those decreasing the oxygen-free radical-stimulated K+ permeability): kaempferol, naringenin, apigenin, naringin; toxic (those increasing the deleterious effect of oxygen-free radicals): myricetin, delphinidin, quercetin; biphasic effective (characterized by opposite effects depending on the concentration): phloretin, cyanin, catechin, morin and inactive: rutin, phloridzin. In addition, a similar classification was observed when membrane lipid peroxidation was examined, i.e. kaempferol decreased lipid peroxide formation whereas myricetin enhanced it, morin exhibited a biphasic effect and rutin has no effect. The previously reported metal chelating effect of flavonoids could not totally explain the protective effect of kaempferol as was demonstrated by the partial protective effect exhibited by desferrioxamine. Moreover, this study suggests that a generation of oxygen-free radicals in red cells induced a K+ loss which probably results from membrane lipid peroxidation.