Change in centromeric and acentromeric micronucleus frequencies in human populations after chronic radiation exposure

Acute radiation exposure of humans was observed to induce various forms of cytogenetic damage, including increased frequencies of micronuclei and chromosomal aberrations. However, the cytogenetic effects of chronic low dose radiation exposure in vivo needs further characterization. Sixteen subjects with chronic low dose rates of γ-radiation exposure from ⁶⁰Co-contaminated steel in radioactive buildings were compared with seven non-exposed reference subjects for micronucleus frequencies after they relocated. By in situ hybridization using a digoxigenin-labeled anti-α all human centromere probe, the exposed subjects were shown to have a significant increase in cytochalasin B-modulated micronucleus (CBMN) frequencies, as well as a significant increase in centromere-positive (C+) CBMN, centromere-negative (C-) CBMN, total C+ signals, single C+ MN signals and multiple C+ signals/1000 binucleated cells (BN). However, decreases in the ratios C+ MN/C- MN and C+ MN/total CBMN (%) were also noted in the exposed subjects. By mixed effects analysis, considering individuals from the same families, the C- MN and single C+ MN/1000 BN were both positively and moderately associated with previous cumulative exposure. When the time period of relocation post-exposure (relocation time or RT) was considered, total C+ MN and multiple C+ MN/1000 BN were negatively and significantly associated with RT. Moreover, the C+ MN, C- MN, CS MN/C- MN ratio and single C+ MN/1000 BN were all negatively and moderately associated with RT, but not with exposure dose. This suggested that acentromeric and single or multiple centromeric CBMN cytogenetic damage seems to disappear differentially in human subjects post chronic low dose radiation exposure.