GAMMA-IRRADIATION DAMAGE TO LIPOSOMES DIFFERING IN COMPOSITION AND THEIR PROTECTION BY NITROXIDES

The present study aims to determine the effect of bilayer composition on oxidative damage and the protection against it in lipid multicompon ent membranes. Irradiation damage in 200-nm liposomes and the protecti on provided by the nitroxide radicals, 2,2,6,6-tetramethylpiperidine-1 -oxyl (Tempo) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Temp ol) were assessed by monitoring several chemical and physical paramete rs. Liposomes were prepared in four different lipid compositions (mole ratios), DPPC:DPPG 10:1; DPPC:DPPG:cholesterol 10:1:4; EPC:EPG 10:1; and EPC:EPG:cholesterol 10:1:4, and gamma-irradiated with a dose of 32 kGy. Lipid degradation was determined by HPLC and CC analyses, wherea s size and differential scanning calorimetry measurements were used to monitor physical changes in the liposomal dispersions. The results in dicate that: (1) addition of 5 mM Tempo or Tempol, or freezing of the sample inhibited radiation-induced lipid degradation; (2) Tempo and Te mpol caused neither physical nor chemical changes in the liposomal dis persions; and(3) both nitro?tides prevented or reduced some of the rad iation-induced changes in thermotropic characteristics of the liposome s, preventing a shift in the temperature of the maximum of the main ph ase transition (T-m). (C) 1997 Elsevier Science Inc.