Photodynamic effects of protoporphyrin on cholesterol and unsaturated fatty acids in erythrocyte membranes in protoporphyria and in normal red blood cells.

The protoporphyrin-induced photodynamic damage of erythrocytes is caused by photooxidation of a cellular target, localized in the red cell membrane. In model experiments it appeared that some amino acid residues of membrane proteins, unsaturated fatty acid side chains of phospholipids and cholesterol are sensitive to photooxidation, induced by protoporphyrin. In previous studies it has been shown that the membrane damage cannot be attributed to photooxidation of unsaturated fatty acid side chains. Photosensitized peroxidation of cholesterol was studied in model systems, in red cell ghosts and in intact cells. Although cholesterol appeared to be sensitive to protoporphyrin-induced photooxidation in model systems and in red cell ghosts, it could be shown that photohemolysis of red blood cells of patients with erythropoietic protoporphyria cannot be rationalized on the basis of a cholesterol peroxidation.