Merocyanine 540 induces specific base oxidation in human lymphocyte DNA

We studied the mechanism of action of the photosensitising fluorescent dye Merocyanine (MC 540) at membrane and DNA levels. The spectrofluorimetric me thod was used to characterise MC 540 binding to the cell membrane. Human ly mphocytes from 6 healthy subjects were exposed to MC 540 in PBS and excitat ion spectra from 400 to 575 nm (emission wavelength 585 nm) were measured i n the dark and after 1 min and 5 min of exposure to white light. At the sam e time strand breaks and oxidised bases were measured in nuclei by the come t assay modified with lesion-specific enzymes. We found that irradiation in combination with MC 540 caused oxidation of purines and to a lesser extent pyrimidines in lymphocyte DNA, with only limited DNA strand breakage; the dye was able to enter the cell plasma membrane. These results suggest that MC 540 could be a promising dye for the study of mechanisms of oxidative da mage in model conditions.