Relationships Between Cell Killing, Mutation Induction and DNA Damage in X-irradiated V79 Cells: The Influence of Oxygen and DMSO

Abstract

The relationships between cell killing, mutation induction and DNA double (dsb) and single (ssb) strand breaks have been studied in V79 cells irradiated with X-rays under oxic and anoxic conditions in the presence and in the absence of dimethylsulphoxide (DMSO). Curvilinear relationships were found between all pairs of endpoints, except for dsb versus ssb. Statistical analysis of experimental data has shown that in the absence of DMSO there is evidence of good correlations between cell killing, mutation induction and dsb in oxic and anoxic conditions. However, when DMSO was present, no significant correlation was found. In the presence of oxygen DMSO always exerts a protective effect while in anoxia it is generally much less protective and induces a strong sensitization with respect to mutation induction. Possibly DMSO acts not only as a radical scavenger but also as an agent inducing chromatin relaxation and/or under anoxia, forming highly mutagenic short-term radicals. The present data suggest that lethal and mutational events are at least partially independent and not proportional to the initial number of DNA breaks. This may imply that either other kinds of lesions are involved in cell lethality and mutability, or dose-dependent repair mechanisms of dsb have to be considered.

OH Radicals from the Indirect Actions of X-Rays Induce Cell Lethality and Mediate the Majority of the Oxygen Enhancement Effect

“…Previous studies found that the contributions of indirect action on cell killing using high concentrations of radical scavengers (2-4 M) were about 55% under oxic conditions and about 20% under hypoxic conditions (7,(11)(12)(13)20). Our data had higher values than previous reports, although the general trend of our data agrees with previous results.…”

“…Similarly, the contributions of indirect action in CHO (50%) and AA8 (47%) cells under hypoxic conditions in this study concurred with our previous report (5). However, the values we determined in this study were higher than those published by others (9-30%) (7,(11)(12)(13). The higher values found in our study are likely due to a different method to assess the maximum values obtained by extrapolation to the infinite concentration of DMSO.…”

“…Several investigations in E. coli and mammalian cells have found that the indirect actions contribute only about 20% to cell killing under hypoxic conditions (7,(11)(12)(13). Modest concentrations of 2.0-4.0 Molar (M) dimethyl sulfoxide (DMSO), which scavenge the OH radicals, have been used to study the indirect action of radical-mediated damage under hypoxic conditions.…”

DNA double strand breaks induced by the indirect effect of radiation are more efficiently repaired by non-homologous end joining compared to homologous recombination repair

“…The free radical scavenging effect of 2 M DMSO has been shown to reduce induction of DSBs in Chinese hamster V79 cells after irradiation to X-rays by a factor of 1.8 and in normal human fibroblasts after irradiation to ␥-rays, He 2+ or N 6+ ions by a factor of 4.0, 3.6, 4.5 or 1.4, respectively [38,41]. Studies on the repair of DSBs after low-or high-LET irradiation revealed that rejoining of DSBs consists of a fast and a slow component and that DMSO reduces mainly the fast component of DSB-repair [5,[42][43][44], while slow repair is related to repair of complex DSBs, particularly by HRR [45,46].…”

“…DMSO is a potent radical scavenger but may also influence membrane and protein structure with possible effects other than the action as a radical scavenger [37,38]. Toxicity of 2 M DMSO was determined as described elsewhere [21] and for the treatment times used in this study no significant effects were observed on cell growth.…”