Phototoxic process after rapid photosensitive membrane damage of 5,5 ''-bis(aminomethyl)-2,2 ': 5 ',2 ''-terthiophene dihydrochloride

We report a new aspect of rapid (< 30 s) light-induced cell membrane damage photosensitized by 5,5 " -bis(aminomethyl)-2,2 ' :5 ' ,2 " -terthiophene d ihydrochloride (BAT), which is a water-soluble alpha -terthienyl analogue, using a high-power laser (Light intensity 1.6 W cm(-2)). In this paper, we will discuss the relationship between the exposure time of the cells to the photosensitizer and the phototoxic process, Three toxic processes can be i dentified: first, a non-light-mediated toxicity dependent on BAT-cell incub ation; second, a phototoxicity independent of BAT exposure time when the BA T concentration is in the 2-10-muM range; third, a phototoxicity dependent on BAT exposure time when BAT concentration becomes 20 muM. The cytotoxicit y decreases when alpha -tocopherol, an antioxidant, is added to a cell memb rane. This pattern of phototoxicity is the typical of a phospholipid peroxi dation chain reaction and oxidative damage of membrane proteins triggered b y a reactive oxygen species generated by a triplet state of BAT. The BAT ex posure time is clearly correlated with the partition of the photosensitizer in the cell membrane and inside the cell. (C) 2001 Elsevier Science B.V. A ll rights reserved.