Dose-Rate Effectiveness for Unstable-Type Chromosome Aberrations Detected in Mice after Continuous Irradiation with Low-Dose-Rate γ Rays

Abstract

Chronological changes in the chromosome aberration rates of splenocytes from specific-pathogen-free (SPF) mice after continuous and long-term exposure to low-dose-rate gamma rays were studied. Incidences of dicentrics plus centric rings (Dic+Rc), detected by conventional Giemsa staining, and dicentric chromosomes, detected by fluorescence in situ hybridization (Dic by FISH) using a centromere probe, showed an essentially linear increase up to a total accumulated dose of 8000 mGy after irradiation for about 400 days at a low dose rate of 20 mGy/day. For comparison, acute high-dose-rate and medium-dose-rate irradiation were performed. The values of the alpha coefficients in the linear regression lines for these unstable-type aberrations decreased as the dose rates were lowered from medium dose rates (200 and 400 mGy/day) to low dose rates (1 and 20 mGy/day). The dose and dose-rate effectiveness factor (DDREF), estimated by the ratio of calculated incidences using the best-fit regression lines at a high dose rate (890 mGy/min) and low dose rate (20 mGy/day), was 4.5 for Dic by FISH and 5.2 for Dic+Rc, respectively, at the same dose of 100 mGy, while different DDREFs were obtained for different accumulated doses. This is the first study to provide information regarding the effects of long-term exposure to low-dose-rate radiation on chromosomes.

Changes in the Number of Double-Strand DNA Breaks in Chinese Hamster V79 Cells Exposed to γ-Radiation with Different Dose Rates

“…As shown earlier in TERT-immortalized human fibroblast, the cytogenetic lesions frequency as well as an elimination of cells irradiated at a low dose rate (0.3 mGy/min) were significantly lower than those in cells irradiated at a high dose rate (2000 mGy/min) [21]. Similar effects were observed in the animal model experiments [22–24]. …”

Chromosomal Aberrations in Wild Mice Captured in Areas Differentially Contaminated by the Fukushima Dai-Ichi Nuclear Power Plant Accident

“…XXXX, XXX, XXX−XXX even in mice captured in this heavily contaminated area, the frequency of chromosomal aberrations might have increased to a large extent. Thus, our results showing a 2-to 3-fold increase in the frequency of dicentric chromosomes in mice captured in the moderately and heavily contaminated areas (Figure 2) is consistent with the data of laboratory mice reported by Tanaka et al 23 Potential Variation in Cell-Cycling of Splenic Lymphocytes of Wild Mice. Chromosomal aberrations induced in vivo as a biomarker of the effect of radiation should preferentially be observed in M1 metaphase cells after the cells are forced to enter the cell cycle in vitro, since over multiple cell cycle progressions, unstable chromosomal aberrations formed in vivo might dilute out or disappear, while additional, derivative aberrations might appear due to in vitro culturing conditions.…”

Unstable Chromosome Aberrations Do Not Accumulate in Normal Human Fibroblast after Fractionated X-Irradiation

“…reported that, with a low-dose-rate of 0.02 Gy/day, the number of dicentric chromosome in spleen cells increases almost linearly as the total accumulated IR dose increased up to the highest dose of 8 Gy; however, such an increase is not evident with a dose-rate of 0.001 Gy/day [25]. Although the dose-rate was not similar to our study, we are able to assume that mis-joining of DSBs on two different chromosome might have spatial as well as temporal limitations, and this is the reason why accumulation of dicentric chromosome was not observed following fractionated irradiation with prolonged fraction intervals with 5 minutes or more.…”