INTRACELLULAR TARGET FOR α‐TERTHIENYL PHOTOSENSITIZATION: INVOLVEMENT OF LYSOSOMAL MEMBRANE DAMAGE

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Abstract
Abstract—Intracellular targets for the photosensitizer α‐terthienyl (αT) were examined by fluorescence microscopy and microfluorospectrometry using human nonkeratinized buccal cells. Intracellular distribution of αT was observed as fluorescent patches widely dispersed in the cytoplasm. The distribution of the fluorescent patches was compared with that of acid phosphatase activity visualized as an azo dye produced by the fast garnet 2‐methyl‐4‐[(2‐methyl‐phenyl)azo]benzenediasonium sulfate reaction. Because both the distribution sites coincided, lysosomes were the likely sites of intracellular affinity of αT. However, because acid phosphatase is not a specific lysosomal marker, we tried to detect another lysosomal enzyme, β‐galactosidase, to confirm if the fluorescent patches were lysosomes, using fluorescein‐di‐(β‐D‐galactopyranoside) (FDG) as a fluorogenic substrate. Without UV‐A (320–400 nm) irradiation of the cells after uptake of αT and FDG, no significant fluorescence was observed. In contrast, with prior UV‐A irradiation in the presence of αT and FDG, the bright yellow fluorescence of fluorescein, which is the digested product of FDG, was clearly detected in the cells by fluorescence microscopy. This observation implied that inflow of external FDG into the lysosomes is caused by lysosomal membrane damage on αT photosensitization. The present results indicated that lysosomes are the primary photosensitization site of αT.