The Effect of Fluoride on Photodynamic-induced Fluorescence Changes of Aluminium Phthalocyanine in Chinese Hamster Cells

Abstract

Fluence-dependent changes in the fluorescence of aluminium phthalocyanine (AlPc) were measured in Chinese hamster ovary (CHO) cells using digital fluorescence microscopy of single cells and spectrofluorimetry of cell suspensions. During illumination the fluorescence initially increased and later progressively decreased. In the presence of fluoride, which protects against phototoxicity of AlPc by forming a fluoroaluminium complex, there was no initial increase in fluorescence: it decreased about 10 times faster than in the absence of fluoride. Qualitatively similar results were observed using single-cell fluorescence microscopy, which also showed the dye to be mostly localized in cytoplasmic organelles and membranes. The pattern of localization did not change during illumination. Concomitant assays of dye extracted from cells revealed little photodegradation that could not account for the fluorescence changes. The absorption spectra of AlPc-loaded cells showed some aggregation of the dye prior to light exposure. During illumination the dye was initially monomerized and subsequently progressively reaggregated. In the presence of fluoride no monomerization was seen, and the aggregation proceeded at a much faster rate. It is concluded that the fluorescence changes are not due to major relocalization of AlPc in the cells, but to light-induced monomerization followed by reaggregation. The protective effect of fluoride may be due to the enhanced aggregation rate, because aggregated dye molecules are photochemically inactive. Because D₂0 affects neither the initial enhanced fluorescence in the absence of fluoride nor the rapid decrease in its presence it appears that ¹O₂ is not involved in the photodynamic reactions leading to these changes.