Abstract
The mechanism of radioprotective effect by DMSO is believed that hydroxyradical are scavenged and DNA strand breaks are suppressed immediately after irradiation. However, this theory is not completely confirmed by experiments. Here, we examined the mechanisms of radioprotective effect by 0.5% DMSO treated CHO cells. First of all, significant reduction of micronuclei formations by X-irradiation was observed in 0.5% DMSO treated cells. Cell killing effect was also suppressed by this DMSO treatment. Interestingly, this suppressive effect of DMSO on micronuclei induction was not observed in Ku80 deficient xrs5 cells and DNA-PKcs deficient Scid cells. These results imply that there is a relationship between radioprotective effects of DMSO and non-homologous end joining pathway (NHEJ). We next examined the kinetics for disappearance of 53BP1 foci after X-irradiation. In the case of 15 min after irradiation, the number of foci were not different between DMSO treated cells and non-treated cells. However, the number of foci at 1 hr and 2 hr after irradiation were reduced in time dependent manner, and faster disappearance of foci was observed in DMSO treated cells. It is suggested that the repair kinetics for DNA double strand breaks are faster in DMSO treated cells. We believe that radioprotective effect by DMSO is not caused by suppression of initial DNA damage level, but caused by effective clearance of DNA double strand breaks through the enhanced NHEJ repair.
