Distribution and retention of rose bengal and disulphonated aluminium phthalocyanine: a comparative study in unicellular eukaryote.

Enhanced video-fluorescence microscopy and microspectrofluorometry were used to characterize the internalization, distribution and retention of two photosensitizers, rose bengal--a xanthene dye--and disulphonated aluminium phthalocyanine in eukaryote Paramecium aurelia. Rose bengal, because of its anionic nature, cannot diffuse across the cell membrane and accumulates there preferentially. In a drug-free medium the membrane fluorescence disappears after a few minutes. Complexation of rose bengal with low density lipoproteins gives rise to a different fluorescence pattern, where, in addition to membrane localization and diffuse cytoplasmic fluorescence, highly fluorescent endosomes are observed, which persisted for at least 1 h after drug treatment. Disulphonated aluminium phthalocyanine, on the contrary, seems to be directly internalized through an endocytotic process leading to the appearance of fluorescent endosomes, exhibiting a long persistence, together with cytoplasmic diffuse fluorescence. The presence of low density lipoproteins does not modify the internalization of the drug significantly, because of the very low yield of the complexation reaction. The potential of rose bengal as a photosensitizer for photodynamic therapy is discussed.