INHIBITION OF PHTHALOCYANINE-SENSITIZED PHOTOHEMOLYSIS OF HUMAN ERYTHROCYTES BY QUERCETIN

Photohemolysis of erythrocytes in the presence of aluminum phthalocyan ine tetrasulfonate as a sensitizer is inhibited by quercetin. D2O (98. 5%) stimulated photohemolysis regardless of quercetin presence, sugges ting the participation of singlet oxygen in the process. Since it has been shown that this flavonoid reacts with singlet oxygen, the protect ive effect might be attributed, at least partially, to its competitive reaction with singlet oxygen. At the molecular level, the alterations of membrane proteins that escort the process of photohemolysis, such as cross-linking of spectrin monomers and of other membrane proteins, were selectively inhibited by quercetin. This effect was qualitatively similar to that induced by NaF, suggesting that quercetin may, like N aF, also inhibit type I photooxidations, which contribute to hemolysis . The lipophilicity of quercetin seems to be an essential factor in th e inhibition process; rutin, a water-soluble 3-rutinoside of quercetin , had only a negligible protective effect on photohemolysis.