Photodynamic effect of methionine-riboflavin mixture on rabbit red blood cells

The photodynamic effect of methionine-riboflavin mixture (MR) on membranous system of living cells was examined using rabbit red blood cells (RBCs) as an assay system. Evident increases of thiobarbituric acid (TBA) reactive substances, which reflected presumably the production of malondialdehyde (MDA) and the peroxidation of membrane lipid, were detected from tested MR-RBCs system shortly after light exposure. Moreover, there was a paralleled increase of leakage of hemoglobin and other cellular proteins from the treated cells which indicated the substantial damages on the membrane function. At pHs ranged from 4.0 to 8.0, the rate of MDA production of RBCs in MR appeared to increase with the decrease of pH. By polyacrylamide gel electrophoresis, it was also noted that the extent of protein leakage from MR-treated RBCs and the associated protein degredation were both greatest at pH around 4.0-5.0. This strongly supported our previous view on the participation of Haber-Weiss reaction and hydroxyl radicals in the biological damages of the studied MR reaction system. The lethal effect of MR on living cells was clearly shown by evidence obtained from scanning electron microscopy which indicated that tested RBCs in MR were severely deformed very shortly after illumination. It seemed apparent that the strong biocidal activity of MR was due in great part to the peroxidation of membrane lipid and the destruction of cellular protein molecules.