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 dihydrochloride (BAT), which is a water-soluble α-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 identified: first, a non-light-mediated toxicity dependent on BAT-cell incubation; second, a phototoxicity independent of BAT exposure time when the BAT concentration is in the 2-10-μM range; third, a phototoxicity dependent on BAT exposure time when BAT concentration becomes 20 μM. The cytotoxicity decreases when α-tocopherol, an antioxidant, is added to a cell membrane. This pattern of phototoxicity is the typical of a phospholipid peroxidation chain reaction and oxidative damage of membrane proteins triggered by a reactive oxygen species generated by a triplet state of BAT. The BAT exposure time is clearly correlated with the partition of the photosensitizer in the cell membrane and inside the cell.