Laser-induced release of liposome-encapsulated dye to monitor tissue temperature: study of different liposome compositions

摘要

This study aimed to evaluate the interest of several liposome compositions (DPPC, DSPC, DPPA) to control specific ranges of temperature and to assess the possible use of temperature sensitive liposomes in an established model such as the liver as a new approach to monitor tissue temperature under laser irradiation. Temperature sensitive liposomes (DPPC or DSPC or DPPA) loaded with carboxy-fluorescein were injected to Wistar rats. The liver was exposed and irradiated with a 100 W Nd:YAG laser (single pulse mode, pulses ranging from 100 to 260 ms, spot diameter: 4 mm) to avoid direct absorption by the dye entrapped in the liposomes. The temperature was measured with an infrared camera during laser irradiation. The animals were then sacrificed and the liver was surgically removed. Immediately after, the fluorescence was measured - ex vivo - with a fluorescent imaging system. We were not able to prepare stable high transition temperature liposomes (DPPE). Concerning DPPC, the mechanism of dye release at the basal temperature led to a complete leakage of the dye in less than 5 minutes. Only background fluorescence was observed but no specific response due to laser irradiation. Nevertheless the results obtained using DSPC liposomes meet to a large extent our requirements since a useful monitoring of temperature is feasible from 42$DGR@C to 62$DGR@C. In fact the critical temperature of most tissues varies from 53$DGR@C to 58$DGR@C.