THE EFFECT OF DIMETHYL-SULFOXIDE ON THE INDUCTION OF DNA DOUBLE-STRAND BREAKS IN V79-4 MAMMALIAN-CELLS BY ALPHA-PARTICLES

The present study was undertaken to assess the protective effect of dimethyl sulfoxide (DMSO) against the induction and rejoining of DNA double-strand breaks (DSBs) and inactivation of V79-4 Chinese hamster cells by both high- and low-linear energy transfer (LET) radiations. The cells were exposed under aerobic conditions as monolayers to either low-LET photons (Co-60 gamma rays) or high-LET alpha particles (Pu-238) at 277 K. The initial yield of DSBs, determined by elution under nondenaturing conditions, is linearly dependent on dose. When the irradiation was carried out in the presence of DMSO (0-0.6 mol dm(-3)), the initial yields of DSBs induced by both gamma and alpha-particle irradiation decrease. With gamma irradiation at [DMSO] >0.6 mol dm(-3), a further decrease in the yield of DSBs occurs. DMSO (0.5 mol dm(-3)) reduces the initial yield of DSBs by 50 +/- 5% and 32 +/- 4% for photons and alpha particles, respectively. DMSO protects more effectively against cellular inactivation and DSB induction at low LET compared with alpha-particle irradiation with protection factors of 1.7 and 1.4, respectively, for survival and 2.0 and 1.5, respectively, for DSBs. After incubation of the irradiated cells for 3 h at 310 K after high-LET irradiation, the residual yield of DSBs is reduced by <13% when the irradiations were carried out in the presence of 0.5 mol dm(-3) DMSO. With gamma irradiation in the presence of 0.5 mol dm(-3) DMSO, 90% of the DSBs are rejoined by 3 h incubation at 310 K. Therefore, the nonscavengeable DSBs induced by alpha particles are not significantly rejoined within 3 h, in contrast to rejoining of the majority of the nonscavengeable DSBs induced by gamma irradiation. From comparison of the data on DSBs and survival for alpha-particle irradiation, it is inferred that the severity of damage is reduced by DMSO through minimizing the formation of OH-induced sugar/base modifications in the vicinity of nonscavengeable DSBs. (C) 1995 by Radiation Research Society