Mechanisms of porphyrin-mediated photohemolysis of erythrocytes

Abstract

The photoinduced hemolysis of erythrocytes mediated by porphyrin photosensitizers – the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4), cationic 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP), and their respective zinc (II) complexes (ZnTPPS₄ and ZnTMPyP) - was evaluated spectrophotometrically by monitoring hemoglobin release and malondialdehyde (MDA) formation. Erythrocyte ghosts (EG) were used as a model to evaluate the photohemolysis, which proved to be caused by photodecomposition of erythrocyte membrane due to lipid peroxidation. The photohemolytic efficiency of the porphyrins increases in the sequence TPPS4 < ZnTPPS4 < TMPyP < ZnTMPyP which coincides with the porphyrin affinity to the erythrocyte membrane, determined by fluorescence spectroscopy methods. Using the EPR spin trap method, it was shown that lipid peroxidation of EG is performed through the generation of both radical reactive oxygen species (ROS) (Type I mechanism) and singlet oxygen (Type II mechanism); however, it should be noted that the detected ROS predominantly originate in the surrounding solution rather than exclusively at the membrane interface, although they contribute to membrane lipid peroxidation. The highest photodynamic activity of ZnTMPyP is due to both its highest affinity for EG membranes and highest quantum yield of the excited triplet state formation, which is responsible for the efficient production of both singlet oxygen and radical ROS species.