mBAND analysis of chromosome aberrations in human epithelial cells induced by γ-rays and secondary neutrons of low dose rate

Human risks from chronic exposures to both low- and high-LET radiation are of intensive research interest in recent years. In the present study, human epithelial cells were exposed in vitro to γ-rays at a dose rate of 17 mGy/h or secondary neutrons of 25 mGy/h. The secondary neutrons have a broad energy spectrum that simulates the Earth's atmosphere at high altitude, as well as the environment inside spacecrafts like the Russian MIR station and the International Space Station (ISS). Chromosome aberrations in the exposed cells were analyzed using the multicolor banding in situ hybridization (mBAND) technique with chromosome 3 painted in 23 colored bands that allows identification of both inter- and intrachromosome exchanges including inversions. Comparison of present dose responses between γ-rays and neutron irradiations for the fraction of cells with damaged chromosome 3 yielded a relative biological effectiveness (RBE) value of 26 ± 4 for the secondary neutrons. Our results also revealed that secondary neutrons of low dose rate induced a higher fraction of intrachromosome exchanges than γ-rays, but the fractions of inversions observed between these two radiation types were indistinguishable. Similar to the previous findings after acute radiation exposures, most of the inversions observed in the present study were accompanied by other aberrations. The fractions of complex type aberrations and of unrejoined chromosomal breakages were also found to be higher in the neutron-exposed cells than after γ-rays. We further analyzed the location of the breaks involved in chromosome aberrations along chromosome 3, and observed hot spots after γ-ray, but not neutron, exposures.