The role of biological membranes as a target in biological radiation damage remains unclear. The present study investigates how the biochemical and biophysical properties of a simple biological model, i.e. human erythrocyte membranes, are altered after exposure to relatively low doses of (60)Co gamma rays. Lipid peroxidation increased in the hours after radiation exposure, based on measurements of MDA and on the lipid peroxidation index after parinaric acid incorporation. Protein carbonyl content also increased rapidly after radiation exposure. An imbalance between the radiation-mediated oxidative damages and the antioxidant capacity of the erythrocytes was observed in the hours after radiation exposure. Antioxidant enzyme activities, mainly catalase and glutathione peroxidase, were found to decrease after irradiation. The development of a radiation-induced oxidative stress probably explains the reorganization of the fatty acid pattern 72 h after radiation exposure. The phosphatidylethanolamine (PE) fatty acids of the (n-3) and (n-6) series decreased, while the PE saturated fatty acid content increased. All these modifications may be involved in the variation of the biophysical properties of the membranes that we noted after radiation exposure. Specifically, we observed that the lipid compartment of the membrane became more fluid while the lipid-protein membrane interface became more rigid. Taken together, these findings reinforce our understanding that the cell membrane is a significant biological target of radiation. Thus the role of the biological membrane in the expression and course of cell damage after radiation exposure must be considered.

BACKGROUND Modifications of intracellular transfer, resulting from a loss of membrane integrity may contribute toward setting the cell onto the pathway of apoptosis. METHODS We have developed an original technique of measuring simultaneously, with flow cytometry, changes in membrane fluidity and cell death status. Our aim was to assess the extent to which radio‐induced cell death and membrane alterations are linked. Investigations were performed on lymphocytes 24 h after whole human blood γ‐irradiation. RESULTS Our results confirmed the expected increase in the percentage of apoptotic cells as a function of dose, but revealed that the percentage of necrotic cells appeared stable after irradiation. At the same time, the fluorescence anisotropy of the living lymphocyte subpopulation decreased significantly and dose dependently as measured 24 h post‐irradiation. With TMA‐DPH, the anisotropy index of apoptotic lymphocytes was always lower than that of the viable lymphocyte subpopulation. On the other hand, 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) anisotropy was similar in apoptotic and viable cells after irradiation. These findings suggest that apoptotic lymphocytes are characterised by a membrane fluidisation that mainly occurs on the cell membrane surface. CONCLUSION Our study made technical advances in using cytometric fluorescence anisotropy measurement as an early biological indicator of apoptosis after cellular exposure to ionising radiation. Cytometry 39:151–157, 2000 © 2000 Wiley‐Liss, Inc.

These findings suggest the utility of structural membrane modification measurements as an early bio-indicator of ionizing radiation exposure.

The aim of this study was to detect membrane fluidity modifications in blood lymphocytes that had been exposed to gamma-radiation, at a graded series of depths from the surface to the centre of the membrane bilayer and as a function of cell viability. A time course was performed to verify the contribution of the membrane to radiation-induced apoptosis. In comparison with spectrofluorimetry, flow cytometry proved to be a reliable method for measuring radiation-induced membrane alterations. Late apoptotic lymphocytes were characterised by a significant decrease of the 3-SA, 6-SA and 9-SA fluorescence anisotropy values, compared to viable lymphocytes. Moreover, a highly significant difference was observed in the early apoptotic lymphocyte subpopulation between the fluorescence anisotropy values measured 24 h (radiation-induced apoptosis) and those measured 1 h (spontaneous apoptosis) after irradiation. The simultaneous assessment of cellular viability and membrane fluidity using n-(9-anthroyloxy) fatty acid probes, may be relevant for the investigation of interactions which may exist between membrane modifications and the apoptotic process. Our observations support the specificity of radiation-induced apoptosis compared to spontaneous apoptosis in terms of biophysical modifications of membrane properties.