Protective effect of quercetin and rutin on photosensitized lysis of human erythrocytes in the presence of hematoporphyrin.

Photosensitized hemolysis of human erythrocytes by hematoporphyrin was suppressed by flavonols such as quercetin and rutin at submillimolar concentrations. The suppression of photohemolysis was accompanied by inhibition of lipid peroxidation by the reagents. Quercetin and rutin were photooxidized in the presence of hematoporphyrin and the photooxidation was partially suppressed by 1 mM NaN3, a quencher of singlet molecular oxygen. Flavonols were also oxidized by radicals formed during degradation of lauroyl peroxide. These results indicate that flavonols can function as antioxidants in biological systems by terminating radical chain reactions and removing singlet molecular oxygen. A pharmacological function of flavonols, decrease of the increased permeability and fragility of capillary, was discussed in relation to their antioxidative functions.