[en] We exposed ICR mice to low-dose (0.2 Gy) and low-dose-rate (0.7 mGy/h) -radiation (¹³⁷Cs) in the Low-dose-rate Irradiation Facility at the Radiation Health Research Institute to evaluate systemic effects of low-dose radiation. We compared the body and organ weights, number of blood cells (white and red blood cells and platelets), levels of biochemical markers in serum, and frequency of micronuclei in polychromatic erythrocytes between low-dose irradiated and nonirradiated control mice. The ICR mice irradiated with total doses of 0.2 and 2 Gy showed no changes in body and organ weights, number of blood cells (white and red blood cells), or frequency of micronuclei in the polychromatic erythrocytes of peripheral blood. However, the number of platelets (P = 0.002) and the liver weight (P < 0.01) were significantly increased in mice exposed to 0.2 and 2 Gy, respectively. These results suggest that a low-dose-rate of 0.7 mGy/h does not induce systemic damage. This dose promotes hematopoiesis in the bone marrow microenvironment and the proliferation of liver cells. In the future, the molecular biological effects of lower doses and dose rates need to be evaluated

[en] This study evaluated the effects of low dose radiation on spermatogenic cells using the morphological characteristics of sperm in the caudal epididymis of ICR mice. In this study, six abnormal sperm shapes (amorphous heads, blunt hooks, excessive hooks, two heads and tails, folded tails and short tails) were observed at eight days after γ-irradiation (¹³⁷Cs, 0, 0.2, 0.5, 1, 2 or 4 Gy) with both a high-dose-rate (0.8 Gy/min) and a low-dose-rate (0.7 mGy/hr). Fewer abnormal forms of sperm were observed in low-dose-rate irradiated mice than in mice that received a high-dose-rate irradiation (P=0.002). The ratio of the dose rate effect among low-dose-rate irradiated mice to high-dose-rate irradiated mice was approximately 0.6. In addition, sperm with blunt hooks and two heads and tails significantly increased in number after irradiation, potentially providing an endpoint marker for estimating the effects of radiation. This study suggests that low-dose-rate (0.7 mGy/hr) radiation does not damage stem spermatogonia and probably stimulates repair in damaged spermatogonial stem cells in male mice. (author)

[en] The harmful effects of high-dose radiation on living organisms, including humans and animals, have been well-demonstrated through the findings of epidemiological studies of the effects of the atomic bombings in Hiroshima and Nagasaki and the Chemobyl nuclear accident Currently, a large number of studies are being conducted on the systemic effects of low-dose radiation these studies have been performed using both in-vivo and vitro systems. However, there have been few studies on the effects of low-dose (≤200 mGy) and low-dose-rate (LDR, ≤6 mGy/h) irradiation on spermiogenesis in small experimental animals. The effects of radiation on humans and animals are manifested in form of miscarriages, stillbirths, congenital malformations, and cancers: these effects occur as a result of genetic defects in paternal germ cells, It is well-known that genome instabilities in parental germ cells are spontaneously transferred to the next generation. However, it is difficult to precisely identify their response to radiation by using currently reported endpoint markers (apoptosis, gene mutation, repair capabilities, and chromosome aberrations of spermatogonia), since the testicles contain developmental stages of germ cells. Recently, we have conducted studies on the abnormalities of sperms in the caudal epididymis to investigate whether the genetic damage in the spermatogonial stem cells induced by LDR irradiation are transmitted to the next generation. Interestingly, our previous data showed that LDR (0.7 mGy/h) radiation does not damage spermatogonial stem cells and instead stimulates repair in these damaged cells in ICR mice. However, the relationships between the frequency of sperm abnormalities and the total accumulated dose with continuous LDR irradiation have not been investigated in Korean dark-striped field mice, A. a. coreae. In this study, we analyzed the frequency of sperm abnormalities in low- (0.7 mGy/h) and high-dose-rate (HDR, 0.8 Gy/min) irradiated Korean dark-striped field mice, A. a. coreae. We also determined the ratio of the dose-rate effect on the LDR γ-irradiated mice to that in the HDR γ-irradiated mice. This is the first report of the effects of radiation on spermatogenic cells in Korean dark-striped field mice, A. a. coreae

[en] To determine the biological effects of low-dose-rate radiation (¹³⁷Cs, 2.95 mGy/h) on EL4 lymphoma cells during 24 h, we investigated the expression of genes related to apoptosis, cell cycle arrest, DNA repair, iron transport, and ribonucleotide reductase. EL4 cells were continuously exposed to low-dose-rate radiation (total dose: 70.8 mGy) for 24 h. We analyzed cell proliferation and apoptosis by trypan blue exclusion and flow cytometry, gene expression by real-time PCR, and protein levels with the apoptosis ELISA kit. Apoptosis increased in the Low-dose-rate irradiated cells, but cell number did not differ between non- (Non-IR) and Low-dose-rate irradiated (LDR-IR) cells. In concordance with apoptotic rate, the transcriptional activity of ATM, p53, p21, and Parp was upregulated in the LDR-IR cells. Similarly, Phospho-p53 (Ser15), cleaved caspase 3 (Asp175), and cleaved Parp (Asp214) expression was upregulated in the LDR-IR cells. No difference was observed in the mRNA expression of DNA repair-related genes (Msh2, Msh3, Wrn, Lig4, Neil3, ERCC8, and ERCC6) between Non-IR and LDR-IR cells. Interestingly, the mRNA of Trfc was upregulated in the LDR-IR cells. Therefore, we suggest that short-term Low-dose-rate radiation activates apoptosis in EL4 lymphoma cells.

[en] While high-dose ionizing radiation results in long term cellular cytotoxicity, chronic low-dose (<0.2 Gy) of X- or -ray irradiation can be beneficial to living organisms by inducing radiation hormesis, stimulating immune function, and adaptive responses. During chronic low-dose-rate radiation (LDR) exposure, whole body of mice is exposed to radiation, however, it remains unclear if LDR causes changes in gene expression of the whole brain. Therefore, we aim to investigate expressed genes (EGs) and signaling pathways specifically regulated by LDR-irradiation (¹³⁷Cs, a cumulative dose of 1.7 Gy for total 100 days) in the whole brain. Using micro array analysis of whole brain RNA extracts harvested from ICR and AKR/J mice after LDR-irradiation, we discovered that two mice strains displayed distinct gene regulation patterns upon LDR-irradiation. In ICR mice, genes involved in ion transport, transition metal ion transport, and developmental cell growth were turned on while, in AKR/J mice, genes involved in sensory perception, cognition, olfactory transduction, G-protein coupled receptor pathways, inflammatory response, proteolysis, and base excision repair were found to be affected by LDR. We validated LDR-sensitive EGs by qPCR and confirmed specific upregulation of S100a7a, Olfr624, and Gm4868 genes in AKR/J mice whole brain. Therefore, our data provide the first report of genetic changes regulated by LDR in the mouse whole brain, which may affect several aspects of brain function

[en] While a high-dose of ionizing radiation is generally harmful and causes damage to living organisms, a low-dose of radiation has been shown to be beneficial in a variety of animal models. To understand the basis for the effect of low-dose radiation in vivo, we examined the cellular and immunological changes evoked in mice exposed to low-dose radiation at very low (0.7 mGy/h) and low (3.95 mGy/h) dose rate for the total dose of 0.2 and 2 Gy, respectively. Mice exposed to low-dose radiation, either at very low- or low-dose rate, demonstrated normal range of body weight and complete blood counts. Likewise, the number and percentage of peripheral lymphocyte populations, CD4⁺ T, CD8⁺ T, B, or NK cells, stayed unchanged following irradiation. Nonetheless, the sera from these mice exhibited elevated levels of IL-3, IL-4, leptin, MCP-1, MCP-5, MIP-1α, thrombopoietin, and VEGF along with slight reduction of IL-12p70, IL-13, IL-17, and IFN-γ. This pattern of cytokine release suggests the stimulation of innate immunity facilitating myeloid differentiation and activation while suppressing pro-inflammatory responses and promoting differentiation of naive T cells into T-helper 2, not T-helper 1, types. Collectively, our data highlight the subtle changes of cytokine milieu by chronic low-dose γ-radiation, which may be associated with the functional benefits observed in various experimental models.