Structural modification of human erythrocyte membranes following gamma-irradiation

Structural damage to isolated erythrocyte membranes ('ghosts') has been studied following gamma-irradiation under a variety of conditions. For this two fluorescent probes were used; one 1-anilino-8-naphthalene sulphonate probes the lipid-aqueous interface, the other, diphenylhexatriene, was used to probe the membrane fluidity. Irradiation of the membranes caused a decrease in fluorescent intensity of the added probes, and changes in polarization of fluorescence. Oxygen was found to enhance the radiation damage, and scavenger experiments showed the hydroxyl radical was the major radical species involved. The structural modifications are therefore interpreted in terms of preliminary chemical damage involving peroxidation of unsaturated lipids. In addition sensitization and protection was observed in the presence of known dose-modifying chemicals.

Radiosensitization of cultured mammalian cells by 5-iodouridine

Radiosensitization of cultured mammalian cells was studied with halogenated pyrimidines, such as 5-iodouridine or 6-chloropurine, which have been shown to promote bacterial cell lethality when combined with gamma-irradiation. When Chinese hamster cells were exposed to gamma-rays to acidic pH values and the number of colonies was scored after 6 to 11 days of incubation, many more cells were inactivated in the presence of the drug than in its absence. This may be due to radiation-induced cytotoxic iodine radicals from the reagent in the case of 5-iodouridine, because the cells were inactivated efficiently only be contact with the previously-irradiated drug solution. The toxicity of the irradiated drug solution increased remarkably when the pH shifted to acidic side. The radiosensitization and the cytotoxic effects of gamma-irradiated drug solution were not found with 6-chloropurine. This may be the first observation on the lethal effect of chemical radicals on mammalian cells, and it is concluded that radiosensitization with 5-iodouridine does not require the drug incorporation into cellular DNA, at least under the conditions adopted in the present studies.