PPIX induced photohemolysis of erythrocytes partially-depleted of cholesterol.

The protoporphyrin IX (PPIX)-sensitized hemolysis of erythrocytes depleted of cholesterol was investigated. From 20% to 30% of the total membrane cholesterol was removed from cells by incubation with old autologous plasma or by means of interaction with L-alpha-phosphatidylcholine dipalmitoyl (DPPC) liposomes. As expected, after this treatment, the cells show an overall increase in membrane fluidity revealed by means of specific fluorescent probes. The same cells are more susceptible to the photohemolysis induced by PPIX excited by visible light, but gave no lysis in the absence of the sensitizer. As a consequence, the primary oxidative damage which is produced during irradiation can be possibly assigned to the phospholipidic and/or proteic moiety instead of the steroidal moiety.