M.H. GABER*, N.A. ABD EL HALIM**, W.A. KHALIL**

*Department of Biophysics, Faculty of Science, Cairo University, Giza, Egypt
**Central Lab for NMR, Faculty of Science, Cairo University, Giza, Egypt

Abstract. Ionizing radiation induced damage of cellular membrane is known to alter many structural and physiological processes leading to the loss of the normal cellular function including cell death. The present study was designed to determine the changes in bilayer permeability in egg lecithin multilamellar vesicles after exposure to gamma-radiation at doses of 500 Gy and 1 kGy. Liposomal changes in permeability were monitored by measuring the leakage of pre-encapsulated 6-carboxyfluorescein (CF). The changes in permeability in the bilayer were found to be dependent on radiation dose. The presence of hydrophilic antioxidant ascorbic acid (0.1 mM) in the aqueous medium drastically increased the leakage of carboxyfluorescein from liposomes. IR and NMR studies which have been employed to reveal structural alterations in irradiated vesicles showed an increased damage upon exposure to radiation in the presence of ascorbic acid. The proton nuclear magnetic resonance (1H NMR) spectrum of the irradiated lipid vesicles (in the presence of ascorbic acid) showed a preponderance of signals attributable to new compounds formed as a consequence of the degradation process. The obtained results contribute to our understanding of the mechanism of radiation oxidative damage and its modification by radical scavenging and/or organizational modulation, which emphasize the importance of structure and composition of antioxidant in developing new strategies to reduce the damaging effects of ionizing radiation.

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