In vitro study on methemoglobin formation in erythrocytes following hexyl-aminolevulinate induced photodynamic therapy

摘要

Photodynamic therapy (PDT) is a treatment modality which has been shown to be effective for both malignant and non-malignant diseases. New photosensitizers such as hexyl-aminolevulinate (HAL) may increase the efficiency of PDT. HAL penetrates into the cell where the photosensitizer protoporphyrin IX (PPIX) is produced endogenously. In a previous study on HAL based PDT treatment of rat bladder cancer (AY-27 transitional cell carcinoma), a depression of the optical reflectance spectra after treatment was observed in some of the animals. This depression of the spectra was caused by metHemoglobin (metHb). MetHb is an indication of oxidative stress, and can be formed as a result of for instance UV-radiation and heating of blood. The aim of this study was to identify if metHb can be formed in vitro as a result of oxidative stress caused by singlet oxygen and ROS produced during PDT. Methemoglobin formed during PDT might thus be used as an indirect measure of the photochemical processes. This may help predict the PDT treatment outcome. Red blood cells mixed with AY-27 cells exposed to HAL, or PPIX received light treatment, and the changes in the absorption spectra were measured spectrophotometrically. The methemoglobin absorbance spectrum was also studied, and found to be strongly dependant on pH. Hemolysis of erythrocytes by PDT was found, however no metHb was formed in vitro.