Natural background ionizing radiation is present on the earth's surface; however, the biological role of this chronic low-dose-rate exposure remains unknown. The Researching the Effects of the Presence and Absence of Ionizing Radiation (REPAIR) project is examining the impacts of sub-natural background radiation exposure through experiments conducted 2 km underground in SNOLAB. The rock overburden combined with experiment-specific shielding provides a background radiation dose rate 30 times lower than on the surface. We hypothesize that natural background radiation is essential for life and maintains genomic stability and that prolonged exposure to sub-background environments will be detrimental to biological systems. To evaluate this, human hybrid CGL1 cells were continuously cultured in SNOLAB and our surface control laboratory for 16 weeks. Cells were assayed every 4 weeks for growth rate, alkaline phosphatase (ALP) activity (a marker of cellular transformation in the CGL1 system), and the expression of genes related to DNA damage and cell cycle regulation. A subset of cells was also exposed to a challenge radiation dose (0.1 to 8 Gy of X rays) and assayed for clonogenic survival and DNA double-strand break induction to examine if prolonged sub-background exposure alters the cellular response to high-dose irradiation. At each 4-week time point, sub-background radiation exposure did not significantly alter cell growth rates, survival, DNA damage, or gene expression. However, cells cultured in SNOLAB showed significantly higher ALP activity, a marker of carcinogenesis in these cells, which increased with longer exposure to the sub-background environment, indicative of neoplastic progression. Overall, these data suggest that sub-background radiation exposure does not impact growth, survival, or DNA damage in CGL1 cells but may lead to increased rates of neoplastic transformation, highlighting a potentially important role for natural background radiation in maintaining normal cellular function and genomic stability.

The present paper provides an overview of the methods and summarizes the results of estimating radiation doses and their uncertainties for Ukrainian-American epidemiological studies among the Chernobyl (Chornobyl) cleanup workers. After the Chernobyl accident occurred on April 26, 1986, more than 300,000 Ukrainian cleanup workers took part between 1986 and 1990 in decontamination and recovery activities at the site of the Chernobyl Nuclear Power Plant. The U.S. National Cancer Institute in collaboration with the Ukrainian National Research Center for Radiation Medicine conducted several epidemiological studies in this population. An important part of these studies was the reconstruction of the study participants' radiation doses and the assessment of uncertainties in doses. A method called realistic analytical dose reconstruction with uncertainty estimation (RADRUE) was used to calculate the doses from external irradiation during cleanup missions, which was the main exposure pathway for most study participants. At the initial phase of the accident during the atmospheric releases of radioactivity from the destroyed reactor, the cleanup workers also received doses from inhalation of radionuclides. In addition, study participants received doses at their places of residence, especially those who lived in highly contaminated areas. The radiation doses estimated for 2,048 male cleanup workers included in the Ukrainian-American epidemiological studies varied widely: (i) bone-marrow doses from external irradiation in the case-control study of leukemia of 1,000 cleanup workers ranged from 3.7 × 102⁵ mGy to 3.3 Gy (mean = 92 mGy); (ii) thyroid doses in the case-control study of thyroid cancer in 607 persons from all exposure pathways combined were from 0.15 mGy to 9.0 Gy (mean = 199 mGy); (iii) gonadal doses in 183 cleanup workers from all exposure pathways combined in the study of germline mutations in the offspring after parental irradiation (trio study) ranged from 0.58 mGy to 4.1 Gy (mean = 392 mGy); (iv) thyroid doses in the human factor uncertainties study among 47 persons were from 20 mGy to 2.1 Gy (mean = 295 mGy); and (v) lung doses in the study of germline genetic variants associated with host susceptibility to COVID-19 estimated for 211 cleanup workers were from 0.024 mGy to 2.5 Gy (mean = 249 mGy). Doses of female cleanup workers were much lower than those of male cleanup workers: the mean doses for female cleanup workers were 27 mGy for 34 women included in the trio study and 56 mGy for 48 women participated in the study of germline genetic variants associated with host susceptibility to COVID-19. Uncertainties in dose estimates included two components: (i) inherent uncertainties arising from the stochastic random variability of the parameters used in exposure assessment and from a lack of knowledge about the true values of the parameters; and (ii) human factor uncertainties due to poor memory recall resulting in incomplete, inaccurate, or missing responses during personal interviews with cleanup workers conducted long after exposure. This paper also discusses possible developments and improvements in the methods to assess the radiation doses and associated uncertainties for cleanup workers.

The rationale of this study stems from the concern of a radiation-induced accident or terrorist-mediated nuclear attack resulting in large populations of people exposed to nonlethal radiation doses or after a course of definitive radiation therapy which could substantially increase the risk for cancer induction after exposure. Currently, there are no safe and effective interventions to reduce this increased cancer risk to humans. We have tested the hypothesis that the mTOR inhibitor, rapamycin, administered in the diet of mice would reduce or delay radiation-induced cancer when given after radiation exposure. A total-body irradiation (TBI) of 3 Gy was administered to female C3H/Hen mice. Immediately after TBI, along with untreated control groups, animals were placed on chow containing different concentrations of encapsulated rapamycin (14, 40, 140 mg/kg chow). Animals remained on the respective control or rapamycin diets and were followed for their entire lifespan (total of 795 mice). The endpoint for the study was tumor formation (not to exceed 1 cm) or until the animal reached a humane endpoint at which time the animal was euthanized and evaluated for the presence of tumors (pathology evaluated on all animals). Kaplan-Meier survival curves revealed that all three concentrations of rapamycin afforded a significant survival advantage by delaying the time at which tumors appeared and reduction of the incidence of certain tumor types such as hepatocellular carcinomas. The survival advantage was dependent on the rapamycin concentration used. Further, there was a survival advantage when delaying the rapamycin chow by 1 month after TBI. Rapamycin is FDA-approved for human use and could be considered for use in individuals exposed to nonlethal TBI from a nuclear accident or attack or after significant therapeutic doses for cancer treatment.

High-dose radiation has been widely recognized as a risk factor for circulatory diseases. There is increasing evidence for risk of circulatory diseases in response to low and moderate radiation doses in recent years, but the results are not always consistent. We aimed to evaluate the associations between low-dose radiation exposure (<0.1 Gy) and the incidence of circulatory disease in a large cohort of Korean radiation workers. We collected data from a cohort of 187,001 radiation workers monitored for personal radiation dose since 1984 and linked with the National Health Insurance Service data from 2002 to 2021. Excess relative risks (ERRs) per 100 mGy were calculated to quantify the radiation dose-response relationship. The mean duration of follow-up was 13.3 years. A total of 12,705 cases of cerebrovascular disease (CeVD) and 19,647 cases of ischemic heart disease (IHD) were diagnosed during the follow-up period (2002–2021). The average cumulative heart dose was 4.10 mGy, ranging from 0 to 992.62 mGy. The ERR per 100 mGy with 10-year lagged cumulative heart doses was estimated at –0.094 (95% CI –0.248, 0.070) for CeVD and –0.173 (95% CI –0.299, –0.041) for IHD. The ERRs were not significantly changed after adjusting for confounding factors such as smoking, income, blood pressure, body mass index, and blood glucose level. A linear quadratic model was found to provide a better fit for the ERR of CeVD and IHD than a linear model (P = 0.009 and 0.030, respectively). There were no statistically significant variations in ERR/100 mGy estimates for either CeVD or IHD in terms of sex, attained age, and duration of employment; however, heterogeneity in the ERR/100 mGy estimates for CeVD among occupations was observed (P = 0.001). Our study did not find conclusive evidence supporting the association between occupational low-dose radiation and an increased risk of circulatory diseases. The significant negative ERR estimates for IHD need further investigation with a more extended follow-up period.

The search for single or combined radiation countermeasures that mitigate the development of Acute Radiation Syndrome (ARS) after radiation exposure remains a prominent goal of the U.S. government. This study was undertaken to determine whether PrC-210 and G-CSF, when administered 24-48 h postirradiation, would confer an additive or synergistic survival benefit and mitigate ARS in mice that had received an otherwise 96% lethal radiation dose. Our results show that optimum systemic doses of PrC-210 and G-CSF, when administered 24 h or later after a 96% lethal dose of whole-body irradiation, conferred: 1. strong individual survival benefits (PrC-210 44%, P = 0.003), (G-CSF 48%, P = 0.0002), 2. a profound combined 85% survival benefit (P < 0.0001) when administered together, and on day 14 postirradiation, 3. peripheral white blood cell/lymphocyte counts equal to unirradiated controls, 4. dense bone marrow cell density (>65% of unirradiated controls), 5. jejunal villi density that equaled 90% of unirradiated controls, and 6. spleen weights that equaled 93% of unirradiated controls. Our results show that PrC-210 and G-CSF given together 24 h after irradiation confer strong additive efficacy by protecting the immune system, and enabling recovery of the bone marrow, and they work synergistically to enable recovery of peripheral white blood cells in circulating blood.

Radiotherapy is a common therapeutic strategy for various solid tumors, with vascular endothelial injury being a common side effect. The study aimed to examine the effect of long non-coding RNA PVT1 on radiation-induced vascular endothelial cell injury, and explore the possible underlying mechanism. Human umbilical vein endothelial cells (HUVECs) were exposed to different doses of X ray to mimic radiation. LncRNA and miRNA levels were detected via qRT-PCR. Interaction between lncRNA and miRNAs was determined through dual-luciferase reporter assay. Statistical processing was conducted using student's t test between two groups and one-way ANOVA among multiple groups, and P < 0.05 means a significant difference. GO and KEGG were performed for the function and pathway enrichment analysis. LncRNA PVT1 elevated along with the increase of radiation dose in HUVECs. Poorly expressed lncRNA PVT1 promotes cell viability and inhibits oxidative stress. PVT1 serves as a competitive endogenous RNA (ceRNA) of miR-9-5p. miR-9-5p inhibitor inverted the influence of PVT1 knockdown on radiation-stimulated cell apoptosis and oxidative stress in HUVECs. KEGG analysis identified significant enrichment of the MAPK signaling pathway among overlapping target genes of miR-9-5p. LncRNA PVT1 knockdown alleviated radiation-induced vascular endothelial injury via sponging miR-9-5p. The underlying mechanism might be probably MAPK signaling-related.

The radiosensitivity of mice differs between postnatal days 10 (P10) and 21(P21); these days mark different stages of brain development. In the present study, Ki67 and doublecotin (DCX) immunostaining and hematoxylin staining was performed, which showed that acute radiation exposure at postnatal day 10 induced higher cell apoptosis and loss in the hilus of the dentate gyrus at day 1 postirradiation than postnatal day 21. MicroRNA (miRNA) sequencing and real-time quantitative reverse transcription PCR (qRT-PCR) analysis indicated the upregulation of miRNA-34a-5p at days 1 and 7 after irradiation at postnatal day 10, but not at postnatal day 21. Down-regulation of T-cell intracytoplasmic antigen-1 pathway (Tia1) was indicated by qRT-PCR at day 1 day but not day 7 after irradiation at postnatal day 10. Neurobehavioral testing in mature mice irradiated at postnatal day 10 demonstrated the impairment of short-term memory in novel object recognition and spatial memory, compared to those irradiated at postnatal day 21. Combined with our previous luciferase assay showing the direct interaction of miRNA34a-5p and Tia1, these findings suggest that radiation-induced abnormal miR-34a-5p/Tial interaction at day 1 after irradiation at postnatal day 10 may be involved in apoptosis of the dentate gyrus hilar, impairment of neurogenesis and subsequent short-term memory loss as observed in the novel object recognition and Barnes maze tests.

The relative biological effectiveness (RBE) of densely ionizing radiation can depend on the biological context. From a radiological perspective, age is an important factor affecting health risks of radiation exposure, but little is known about the modifying impact of age on the effects of densely ionizing radiation. Herein, we addressed the influence of age on leukemogenesis induced by accelerator-generated fast neutrons (mean energy, ∼2 MeV). Male C3H/HeNrs mice were exposed to ¹³⁷Cs c rays (0.2–3.0 Gy) or neutrons (0.0485–0.97 Gy, c ray contamination 0.0105–0.21 Gy) at 1, 3, 8, or 35 weeks of age and observed over their lifetimes under specific pathogen-free conditions. Leukemia and lymphoma were diagnosed pathologically. Hazard ratio (HR) and RBE for myeloid leukemia mortality as well as the age dependence of these two parameters were modeled and analyzed using Cox regression. Neutron exposure increased HR concordant with a linear dose response. The increase of HR per dose depended on age at exposure, with no significant dose dependence at age 1 or 3 weeks but a significant increase in HR of 5.5 per Gy (c rays) and 16 per Gy (neutrons) at 8 weeks and 5.8 per Gy (c rays) and 9 per Gy (neutrons) at 35 weeks. The RBE of neutrons was 2.1 (95% confidence interval, 1.1–3.7), with no dependence on age. The development of lymphoid neoplasms was not related to radiation exposure. The observed increasing trend of radiation-associated mortality of myeloid leukemia with age at exposure supports previous epidemiological and experimental findings. The results also suggest that exposure at the susceptible age of 8 or 35 weeks does not significantly influence the RBE value for neutrons for induction of leukemia, unlike what has been documented for breast and brain tumors.

In future mass casualty medical management scenarios involving radiation injury, medical diagnostics to both identify those who have been exposed and the level of exposure will be needed. As almost all exposures in the field are heterogeneous, determination of degree of exposure and which vital organs have been exposed will be essential for effective medical management. In the current study we sought to characterize novel proteomic biomarkers of radiation exposure and develop exposure and dose prediction algorithms for a variety of exposure paradigms to include uniform total-body exposures, and organ-specific partial-body exposures to only the brain, only the gut and only the lung. C57BL6 female mice received a single total-body irradiation (TBI) of 2, 4 or 8 Gy, 2 and 8 Gy for lung or gut exposures, and 2, 8 or 16 Gy for exposure to only the brain. Plasma was then screened using the SomaScan v4.1 assay for ∼7,000 protein analytes. A subset panel of protein biomarkers demonstrating significant (FDR<0.05 and |logFC|>0.2) changes in expression after radiation exposure was characterized. All proteins were used for feature selection to build 7 different predictive models of radiation exposure using different sample cohort combinations. These models were structured according to practical field considerations to differentiate level of exposure, in addition to identification of organ-specific exposures. Each model algorithm built using a unique sample cohort was validated with a training set of samples and tested with a separate new sample series. The overall predictive accuracy for all models was 100% at the model training level. When tested with reserved samples Model 1 which compared an exposure group inclusive of all TBI and organ-specific partial-body exposures in the study vs. control, and Model 2 which differentiated between control, TBI and partials (all organ-specific partial-body exposures) the resulting prediction accuracy was 92.3% and 95.4%, respectively. For identification of organ-specific exposures vs. control, Model 3 (only brain), Model 4 (only gut) and Model 5 (only lung) were developed with predictive accuracies of 78.3%, 88.9% and 94.4%, respectively. Finally, for Models 6 and 7, which differentiated between TBI and separate organ-specific partial-body cohorts, the testing predictive accuracy was 83.1% and 92.3%, respectively. These models represent novel predictive panels of radiation responsive proteomic biomarkers and illustrate the feasibility of development of biodosimetry algorithms with utility for simultaneous classification of total-body, partial-body and organ-specific radiation exposures.

Total-body irradiation (TBI) with gamma rays can damage organisms in various unexpected ways and trigger several organ dysfunction syndromes, such as acute radiation syndrome (ARS). Hematopoietic cells and enterocytes are particularly sensitive to radiation due to their self-renewal ability and rapid division, which leads to hematopoietic ARS (H-ARS) and gastrointestinal ARS (GI-ARS). We previously showed that a lipid-based small molecule, 1-palmitoyl-2-linoleoyl-3-acetyl-rac-glycerol (PLAG), improved 30-day survival and alleviated H-ARS symptoms in BALB/c mice after a lethal dose (LD_70/30) of gamma-ray TBI. In this study, we investigated the mitigating effects of PLAG on radiation-induced GI damage that occurs under the same conditions as H-ARS in BALB/c mice. Our study showed that PLAG facilitated the structural restoration of intestinal tissues by increasing villus height, crypt depth, crypt number, mucin-producing goblet cells, and proliferating cell nuclear antigen (PCNA)-positive crypt cells. PLAG significantly improved intestinal absorptive capacity and reduced intestinal injury-induced bacterial translocation. In addition, PLAG effectively inhibited radiation-induced necroptosis signaling activation in the intestinal crypt cells, which was responsible for sustained tissue damage and the release of high mobility group box 1 (HMGB1), a typical damage-associated molecular pattern. Overall, our findings support the radiation-mitigating potential of PLAG against GI-ARS after accidental radiation exposure.

Centrosomes are important organelles for cell division and genome stability. Ionizing radiation exposure efficiently induces centrosome overduplication via the disconnection of the cell and centrosome duplication cycles. Over duplicated centrosomes cause mitotic catastrophe or chromosome aberrations, leading to cell death or tumorigenesis. Pluripotent stem cells, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), can differentiate into all organs. To maintain pluripotency, PSCs show specific cellular dynamics, such as a short G₁ phase and silenced cell-cycle checkpoints for high cellular proliferation. However, how exogenous DNA damage affects cell cycle-dependent centrosome number regulation in PSCs remains unknown. This study used human iPSCs (hiPSCs) derived from primary skin fibroblasts as a PSC model to address this question. hiPSCs derived from somatic cells could be a useful tool for addressing the radiation response in cell lineage differentiation. After radiation exposure, the hiPSCs showed a higher frequency of centrosome overduplication and multipolar cell division than the differentiated cells. To suppress the indirect effect of radiation exposure, we used the radical scavenger dimethyl sulfoxide (DMSO). Combined treatment with radiation and DMSO efficiently suppressed DNA damage and centrosome overduplication in hiPSCs. Our results will contribute to the understanding of the dynamics of stem cells and the assessment of the risk of genome instability for regenerative medicine.