HUMAN CELL-MEMBRANE OXIDATIVE DAMAGE-INDUCED BY SINGLE AND FRACTIONATED DOSES OF IONIZING-RADIATION - A FLUORESCENCE SPECTROSCOPY STUDY

Purpose: To investigate the production and repair of lipid oxidative d amage in two human cell lines exposed to acute and fractionated dose o f ionizing radiation. Radiation dose was in the range from 0.1 to 44 G y. Materials and Methods: K562 and HL60 human cell lines have been use d, 24 and 96 h after seeding. Membrane lipid oxidative damage has been detected by the measurement of the fluorescence decay of 1,6-diphenyl -1,3,5-hexatriene (DPH), its polarization value and the conjugated die nes concentration. The modification of DPH decay has been previously r eported to be directly related to the lipid hydroperoxide concentratio n. Results: A modification of the DPH decay has been observed as a lin ear function of the logarithm of the radiation dose and only when the irradiation was performed in the presence of oxygen. The amount of the damage is related to the time after the cell medium change. By exposi ng the cells to fractionated radiation doses for several days (10 cGy day(-1)), the oxidative damage has been found to be cumulative. After a single acute dose, evidence of repair of the lipid oxidative damage was not obtained. Conclusions: Following a previously developed method , the membrane damage was attributed to the production of hydroperoxid e residues in the lipid acyl chains with the consequence of water pene tration into the external portion of the bilayer, from the aqueous env ironment to the position of hydroperoxides. This damage is not repaire d. The results obtained by measuring the DPH fluorescence decay have b een compared with those obtained using other current optical and bioch emical methods. None of these techniques could detect membrane oxidati ve damage at doses <10Gy. Finally, the different sensitivity of 'young ' and 'old' cells to the oxidative damage can be related to different cholesterol concentrations.