The Lowest Radiation Dose Having Molecular Changes in the Living Body

Abstract

We herein attempted to identify the lowest radiation dose causing molecular changes in the living body. We investigated the effects of radiation in human cells, animals, and humans. DNA double-strand breaks (DSBs) formed in cells at γ- or X-ray irradiation doses between 1 mGy and 0.5 Gy; however, the extent of DSB formation differed depending on the cell species. The formation of micronuclei (MNs) and nucleoplasmic bridges (NPBs) was noted at radiation doses between 0.1 and 0.2 Gy. Stress-responsive genes were upregulated by lower radiation doses than those that induced DNA DSBs or MN and NPBs. These γ- or X-ray radiation doses ranged between approximately 10 and 50 mGy. In animals, chromosomal aberrations were detected between 50 mGy and 0.1 Gy of low linear energy transfer radiation, 0.1 Gy of metal ion beams, and 9 mGy of fast neutrons. In humans, DNA damage has been observed in children who underwent computed tomography scans with an estimated blood radiation dose as low as 0.15 mGy shortly after examination. The frequencies of chromosomal translocations were lower in residents of high background areas than in those of control areas. In humans, systemic adaptive responses may have been prominently expressed at these radiation doses.

Keywords: DNA damage; chromosomal aberrations; genomic instability; lowest radiation dose; molecular changes.

Figure 1.

The estimated smallest dose causing DNA DSBs, MN, NPBs, and chromosomal aberrations reported by several researchers. The doses are the smallest that were tried by each report. The cells examined were MRC-5, AG01552, HFL III, GM15036, GM15510, GM15268, GM15526, peripheral blood lymphocytes, and HMEC. DSBs indicates double-strand breaks; MN, micronucleus; NPBs, nucleoplasmic bridges; HMEC, human mammary epithelial cell.

Figure 2.

The estimated smallest dose causing the upregulation of stress-response genes or proteins that reported by several researchers. The doses are the smallest that were tried by each report. The cells examined were HUVECs, ATM-deficient cells, CD4+ T lymphocytes, ML-1, normal human fibroblast cells, and hESCs. HUVECs indicates human umbilical vein endothelial cells; ATM, ataxia telangiectasia, mutated; hESCs, human embryonic stem cells.

Figure 3.

The estimated smallest dose causing abnormalities in fetuses, chromosomal inversions, genomic instability, chromosomal breaks, and MN in mice reported by several researchers. The doses are the smallest that were tried by each report. MN indicates micronucleus.

Figure 4.

A conceptual diagram of the relationship between the chromosomal inversion frequency in the spleen of pKZ1 mice and radiation doses. The arrow shows the endogenous inversion level. Radiation doses between 1 and 10 µGy revealed a lower inversion level than those of other radiation doses. This figure was made from the findings of Hooker et al.

Figure 5.

The estimated smallest dose causing molecular changes by high-LET radiation. Spleen cells, HSPCs, and lung and testicular tissues of CBA/CaJ mice were used for the detection of chromosomal deletions, chromosome aberrations, and DNA methylation, respectively. Wister rat PBMCs and leukocytes were used for the detection of DNA breaks and chromatin fragmentation. The doses are the smallest that were tried by each report. LET indicates linear energy transfer; HSPCs, hematopoietic stem/progenitor cells; PBMCs, peripheral blood mononuclear cells.