Plasma membrane properties involved in the photodynamic efficacy of merocyanine 540 and tetrasulfonated aluminum phthalocyanine

Merocyanine 540 (MC540)-mediated photodynamic damage to erythrocytes was st rongly reduced when illumination was performed at pH 8.5 as compared to pH 7.4. This could be explained by high pa-mediated hyperpolarization of the e rythrocyte membrane, resulting in decreased MC540 binding at pH 8.5, In acc ordance, the MC540-mediated photooxidation of open ghosts was not inhibited at pH 8.5, Photoinactivation of vesicular stomatitis virus (VSV) was not i nhibited at pH 8.5, This suggests that illumination at increased pH could b e an approach to protect red blood cells selectively against MC540-mediated virucidal phototreatment, With tetrasulfonated aluminum phthalocyanine (Al PcS4) as photosensitizer, damage to erythrocytes, open ghosts and VSV was d ecreased when illuminated at pH 8.5. A decreased singlet oxygen yield at hi gh pH could be excluded. The AlPcS4-mediated photooxidation of fixed erythr ocytes was strongly dependent on the cation concentration in the buffer, in dicating that the surface potential may affect the efficacy of this photose nsitizer, This study showed that altering the environment of the target cou ld increase both the efficacy and the specificity of a photodynamic treatme nt.