Dose-dependence, sex- and tissue-specificity, and persistence of radiation-induced genomic DNA methylation changes

Application of a mathematical model to clarify the statistical characteristics of a pan-tissue DNA methylation clock

DNA methylation clocks estimate biological age based on DNA methylation profiles. This study developed a mathematical model to describe DNA methylation aging and the establishment of a pan-tissue DNA methylation clock. The model simulates the aging dynamics of DNA methylation profiles based on passive demethylation as well as the process of cross-sectional bulk data acquisition. As a result, this study identified two conditions under which the pan-tissue DNA methylation clock can successfully predict biological age: one condition is that the target tissues are sufficiently well represented in the training dataset, and the other condition is that the target sample contains cell subsets that are common among different tissues. When either of these conditions is met, the clock performs well. It is also suggested that the epigenetic age of all samples in the target tissue tends to be either over or underestimated when biological age prediction fails. The model can reveal the statistical characteristics of DNA methylation clocks.

Time- and sex-dependent delayed effects of acute radiation exposure manifest via miRNA dysregulation

The detrimental effects of high-dose ionizing radiation on human health are well-known, but the influence of sex differences on the delayed effects of acute radiation exposure (DEARE) remains unclear. Here, we conducted six-month animal experiments using escalating radiation doses (7-9 Gy) on male and female C57BL/6 mice. The results show that female mice exhibited greater resistance to radiation, showing increased survival at six months post-total body irradiation. LD50/30 (lethal dose expected to cause 50% lethality in 30 days) for female mice is 8.08 Gy, while for male mice it is 7.76 Gy. DEARE causes time- and sex-dependent dysregulation of microRNA expression, processing enzymes, and the HOTAIR regulatory pathway. Differential regulation of molecular patterns associated with growth, development, apoptosis, and cancer is also observed in male and female mice. These findings shed light on the molecular basis of age and sex differences in DEARE response and emphasize the importance of personalized medicine for mitigating radiation-induced injuries and diseases.

Identification of DNA methylation biomarkers for evaluating cardiovascular disease risk from epigenome profiles altered by low-dose ionizing radiation

BACKGROUND

Environmental exposure, medical diagnostic and therapeutic applications, and industrial utilization of radionuclides have prompted a growing focus on the risks associated with low-dose radiation (< 100 mGy). Current evidence suggests that such radiation can induce epigenetic changes. Nevertheless, whether exposure to low-dose radiation can disrupt endothelial cell function at the molecular level is unclear. Because endothelial cells play crucial roles in cardiovascular health and disease, we aimed to investigate whether low-dose radiation could lead to differential DNA methylation patterns at the genomic level in endothelial cell (EC) lines.

METHODS

We screened for changes in DNA methylation patterns in primary human aortic (HAECs) and coronary artery endothelial cells following exposure to low-dose ionizing radiation. Using a subset of genes altered via DNA methylation by low-dose irradiation, we performed gene ontology (GO) analysis to predict the possible biological network mediating the effect of low-dose radiation. In addition, we performed comprehensive validation using methylation and gene expression analyses, and ChIP assay to identify useful biomarkers among candidate genes for use in detecting low-dose radiation exposure in human primary normal ECs.

RESULTS

Low-dose radiation is sufficient to induce global DNA methylation alterations in normal EC lines. GO analysis demonstrated that these hyper- or hypo-methylated genes were linked to diverse biological pathways. Our findings indicated a robust correlation between promoter hypermethylation and transcriptional downregulation of four genes (PGRMC1, UNC119B, RERE, and FNDC3B) in response to low-dose ionizing radiation in HAECs.

CONCLUSIONS

Based on these findings, the identified genes can serve as potential DNA methylation biomarkers for the assessment of cardiovascular risk upon exposure to low-dose radiation.

Genome-wide study reveals novel roles for formin-2 in axon regeneration as a microtubule dynamics regulator and therapeutic target for nerve repair

Peripheral nerves regenerate successfully; however, clinical outcome after injury is poor. We demonstrated that low-dose ionizing radiation (LDIR) promoted axon regeneration and function recovery after peripheral nerve injury (PNI). Genome-wide CpG methylation profiling identified LDIR-induced hypermethylation of the Fmn2 promoter, exhibiting injury-induced Fmn2 downregulation in dorsal root ganglia (DRGs). Constitutive knockout or neuronal Fmn2 knockdown accelerated nerve repair and function recovery. Mechanistically, increased microtubule dynamics at growth cones was observed in time-lapse imaging of Fmn2-deficient DRG neurons. Increased HDAC5 phosphorylation and rapid tubulin deacetylation were found in regenerating axons of neuronal Fmn2-knockdown mice after injury. Growth-promoting effect of neuronal Fmn2 knockdown was eliminated by pharmaceutical blockade of HDAC5 or neuronal Hdac5 knockdown, suggesting that Fmn2deletion promotes axon regeneration via microtubule post-translational modification. In silico screening of FDA-approved drugs identified metaxalone, administered either immediately or 24-h post-injury, accelerating function recovery. This work uncovers a novel axon regeneration function of Fmn2 and a small-molecule strategy for PNI.

Histological assessment of intestinal injury by ionizing radiation

Given the potential risk of radiological terrorism and disasters, it is essential to develop plans to prepare for such events. In these hazardous scenarios, radiation-induced gastrointestinal (GI) syndrome is one of the many manifestations that may happen after the organism is exposed to a lethal dose of ionizing radiation. Therefore, it is critical to better understand how the intestinal tissues initiate and orchestrate regeneration following severe radiation injury. In this chapter, we aimed to provide several key considerations for researchers who utilize histological assessment to study radiation-induced intestinal injury. Rigor and reproducibility are critical in experimental design and can be achieved by maintaining proper radiation administration, maintaining consistency in sample collection, and selecting and using appropriate controls. We also provided technical details of histological preparation of the intestines with tips on dissecting, cleaning, fixing, and preserving. Step-by-step descriptions of both bundling and Swiss rolling are provided with discussion on how to choose between the two approaches. In the following section, we detailed several histological assessment methods and then provided suggestions on how to use histological assessment to study cellular dynamics in the small intestines. Finally, we touched on some non-histological assessments. We hope that the information provided in this chapter will contribute to the research society of radiation-induced intestinal injury with an ultimate goal of promoting the development of radiation countermeasures against the GI acute radiation syndrome.

Differences in radiation-induced heart dysfunction in male versus female rats

PURPOSE

Radiation therapy remains part of the standard of care for breast, lung, and esophageal cancers. While radiotherapy improves local control and survival, radiation-induced heart dysfunction is a common side effect of thoracic radiotherapy. Cardiovascular dysfunction can also result from non-therapeutic total body radiation exposures. Numerous studies have evaluated the relationship between radiation dose to the heart and cardiotoxicity, but relatively little is known about whether there are differences based on biological sex in radiation-induced heart dysfunction (RIHD).

MATERIALS AND METHODS

We evaluated whether male and female inbred Dahl SS rats display differences in RIHD following delivery of 24 Gy in a single fraction to the whole heart using a 1.5 cm beam size (collimater). We also compared the 2.0 cm vs. 1.5 cm collimator in males. Pleural and pericardial effusions and normalized heart weights were measured, and echocardiograms were performed.

RESULTS

Female SS rats displayed more severe RIHD relative to age-matched SS male rats. Normalized heart weight was significantly increased in females, but not in males. A total of 94% (15/16) of males and 55% (6/11) of females survived 5 months after completion of radiotherapy (p < .01). Among surviving rats, 100% of females and 14% of males developed moderate-to-severe pericardial effusions at 5 months. Females demonstrated increased pleural effusions, with the mean normalized pleural fluid volume for females and males being 56.6 mL/kg ± 12.1 and 10.96 mL/kg ± 6.4 in males (p = .001), respectively. Echocardiogram findings showed evidence of heart failure, which was more pronounced in females. Because age-matched female rats have smaller lungs, a higher percentage of the total lung was treated with radiation in females than males using the same beam size. After using a larger 2 cm beam in males which results in higher lung exposure, there was not a significant difference between males and females in terms of the development of moderate-to-severe pericardial effusions or pleural effusions. Treatment of males with a 2 cm beam resulted in comparable increases in LV mass and reductions in stroke volume to female rats treated with a 1.5 cm beam.

CONCLUSION

Together, these results illustrate that there are differences in radiation-induced cardiotoxicity between male and female SS rats and add to the data that lung radiation doses, in addition to other factors, may play an important role in cardiac dysfunction following heart radiation exposure. These factors may be important to factor into future mitigation studies of radiation-induced cardiotoxicity.

Insights into radiation carcinogenesis based on dose-rate effects in tissue stem cells

PURPOSE

Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the 'dose-rate effect,' where the biological effect of low dose-rate radiation is lower than that of the same dose at a high dose-rate. This effect has been reported in epidemiological studies and experimental biology, although the underlying biological mechanisms are not completely understood. In this review, we aim to propose a suitable model for radiation carcinogenesis based on the dose-rate effect in tissue stem cells.

METHODS

We surveyed and summarized the latest studies on the mechanisms of carcinogenesis. Next, we summarized the radiosensitivity of intestinal stem cells and the role of dose-rate in the modulation of stem-cell dynamics after irradiation.

RESULTS

Consistently, driver mutations can be detected in most cancers from past to present, supporting the hypothesis that cancer progression is initiated by the accumulation of driver mutations. Recent reports demonstrated that driver mutations can be observed even in normal tissues, which suggests that the accumulation of mutations is a necessary condition for cancer progression. In addition, driver mutations in tissue stem cells can cause tumors, whereas they are not sufficient when they occur in non-stem cells. For non-stem cells, tissue remodeling induced by marked inflammation after the loss of tissue cells is important in addition to the accumulation of mutations. Therefore, the mechanism of carcinogenesis differs according to the cell type and magnitude of stress. In addition, our results indicated that non-irradiated stem cells tend to be eliminated from three-dimensional cultures of intestinal stem cells (organoids) composed of irradiated and non-irradiated stem cells, supporting the stem-cell competition.

CONCLUSIONS

We propose a unique scheme in which the dose-rate dependent response of intestinal stem cells incorporates the concept of the threshold of stem-cell competition and context-dependent target shift from stem cells to whole tissue. The concept highlights four key issues that should be considered in radiation carcinogenesis: i.e. accumulation of mutations; tissue reconstitution; stem-cell competition; and environmental factors like epigenetic modifications.

Considerations of Medical Preparedness to Assess and Treat Various Populations During a Radiation Public Health Emergency

During a radiological or nuclear public health emergency, given the heterogeneity of civilian populations, it is incumbent on medical response planners to understand and prepare for a potentially high degree of interindividual variability in the biological effects of radiation exposure. A part of advanced planning should include a comprehensive approach, in which the range of possible human responses in relation to the type of radiation expected from an incident has been thoughtfully considered. Although there are several reports addressing the radiation response for special populations (as compared to the standard 18-45-year-old male), the current review surveys published literature to assess the level of consideration given to differences in acute radiation responses in certain sub-groups. The authors attempt to bring clarity to the complex nature of human biology in the context of radiation to facilitate a path forward for radiation medical countermeasure (MCM) development that may be appropriate and effective in special populations. Consequently, the focus is on the medical (as opposed to logistical) aspects of preparedness and response. Populations identified for consideration include obstetric, pediatric, geriatric, males, females, individuals of different race/ethnicity, and people with comorbidities. Relevant animal models, biomarkers of radiation injury, and MCMs are highlighted, in addition to underscoring gaps in knowledge and the need for consistent and early inclusion of these populations in research. The inclusion of special populations in preclinical and clinical studies is essential to address shortcomings and is an important consideration for radiation public health emergency response planning. Pursuing this goal will benefit the population at large by considering those at greatest risk of health consequences after a radiological or nuclear mass casualty incident.

Electromagnetic fields exposure on fetal and childhood abnormalities: Systematic review and meta-analysis

Today, in the modern world, people are often exposed to electromagnetic waves, which can have undesirable effects on cell components that lead to differentiation and abnormalities in cell proliferation, deoxyribonucleic acid (DNA) damage, chromosomal abnormalities, cancers, and birth defects. This study aimed to investigate the effect of electromagnetic waves on fetal and childhood abnormalities. PubMed, Scopus, Web of Science, ProQuest, Cochrane Library, and Google Scholar were searched on 1 January 2023. The Cochran's Q-test and I ² statistics were applied to assess heterogeneity, a random-effects model was used to estimate the pooled odds ratio (OR), standardized mean difference (SMD), and mean difference for different outcomes, and a meta-regression method was utilized to investigate the factors affecting heterogeneity between studies. A total of 14 studies were included in the analysis, and the outcomes investigated were: change in gene expression, oxidant parameters, antioxidant parameters, and DNA damage parameters in the umbilical cord blood of the fetus and fetal developmental disorders, cancers, and childhood development disorders. Totally, the events of fetal and childhood abnormalities were more common in parents who have been exposed to EMFs compared to those who have not (SMD and 95% confidence interval [CI], 0.25 [0.15-0.35]; I ², 91%). Moreover, fetal developmental disorders (OR, 1.34; CI, 1.17-1.52; I ², 0%); cancer (OR, 1.14; CI, 1.05-1.23; I ², 60.1%); childhood development disorders (OR, 2.10; CI, 1.00-3.21; I ², 0%); changes in gene expression (mean difference [MD], 1.02; CI, 0.67-1.37; I ², 93%); oxidant parameters (MD, 0.94; CI, 0.70-1.18; I ², 61.3%); and DNA damage parameters (MD, 1.01; CI, 0.17-1.86; I ², 91.6%) in parents who have been exposed to EMFs were more than those in parents who have not. According to meta-regression, publication year has a significant effect on heterogeneity (coefficient: 0.033; 0.009-0.057). Maternal exposure to electromagnetic fields, especially in the first trimester of pregnancy, due to the high level of stem cells and their high sensitivity to this radiation, the biochemical parameters of the umbilical cord blood examined was shown increased oxidative stress reactions, changes in protein gene expression, DNA damage, and increased embryonic abnormalities. In addition, parental exposure to ionizing and non-ionizing radiation can lead to the enhancement of different cell-based cancers and developmental disorders such as speech problems in childhood.

Radioresistance in rhabdomyosarcomas: Much more than a question of dose

Management of rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, frequently accounting the genitourinary tract is complex and requires a multimodal therapy. In particular, as a consequence of the advancement in dose conformity technology, radiation therapy (RT) has now become the standard therapeutic option for patients with RMS. In the clinical practice, dose and timing of RT are adjusted on the basis of patients' risk stratification to reduce late toxicity and side effects on normal tissues. However, despite the substantial improvement in cure rates, local failure and recurrence frequently occur. In this review, we summarize the general principles of the treatment of RMS, focusing on RT, and the main molecular pathways and specific proteins involved into radioresistance in RMS tumors. Specifically, we focused on DNA damage/repair, reactive oxygen species, cancer stem cells, and epigenetic modifications that have been reported in the context of RMS neoplasia in both in vitro and in vivo studies. The precise elucidation of the radioresistance-related molecular mechanisms is of pivotal importance to set up new more effective and tolerable combined therapeutic approaches that can radiosensitize cancer cells to finally ameliorate the overall survival of patients with RMS, especially for the most aggressive subtypes.

Evaluating the Influences of Confounding Variables on Benchmark Dose using a Case Study in the Field of Ionizing Radiation

Purpose A vast amount of data regarding the effects of radiation stressors on transcriptional changes has been produced over the past few decades. These data have shown remarkable consistency across platforms and experimental design, enabling increased understanding of early molecular effects of radiation exposure. However, the value of transcriptomic data in the context of risk assessment is not clear and represents a gap that is worthy of further consideration. Recently, benchmark dose (BMD) modeling has shown promise in correlating a transcriptional point of departure (POD) to that derived using phenotypic outcomes relevant to human health risk assessment. Although frequently applied in chemical toxicity evaluation, our group has recently demonstrated application within the field of radiation research. This approach allows the possibility to quantitatively compare radiation-induced gene and pathway alterations across various datasets using BMD values and derive meaningful biological effects. However, before BMD modeling can confidently be used, an understanding of the impact of confounding variables on BMD outputs is needed. Methods: To this end, BMD modeling was applied to a publicly available microarray dataset (Gene Expression Omnibus #GSE23515) that used peripheral blood ex-vivo gamma-irradiated at 0.82 Gy/min, at doses of 0, 0.1, 0.5 or 2 Gy, and assessed 6 hours post-exposure. The dataset comprised six female smokers (F-S), six female non-smokers (F-NS), six male smokers (M-S), and six male non-smokers (M-NS). Results: A combined total of 412 genes were fit to models and the BMD distribution was noted to be bi-modal across the four groups. A total of 74, 41, 62 and 62 genes were unique to the F-NS, M-NS, F-S and M-S groups. Sixty-two BMD modeled genes and nine pathways were common across all four groups. There were no differential sensitivity of responses in the robust common genes and pathways. Conclusion: For radiation-responsive genes and pathways common across the study groups, the BMD distribution of transcriptional activity was unaltered by sex and smoking status. Although further validation of the data is needed, these initial findings suggest BMD values for radiation relevant genes and pathways are robust and could be explored further in future studies.

Detecting Blood Methylation Signatures in Response to Childhood Cancer Radiotherapy via Machine Learning Methods

Radiotherapy is a helpful treatment for cancer, but it can also potentially cause changes in many molecules, resulting in adverse effects. Among these changes, the occurrence of abnormal DNA methylation patterns has alarmed scientists. To explore the influence of region-specific radiotherapy on blood DNA methylation, we designed a computational workflow by using machine learning methods that can identify crucial methylation alterations related to treatment exposure. Irrelevant methylation features from the DNA methylation profiles of 2052 childhood cancer survivors were excluded via the Boruta method, and the remaining features were ranked using the minimum redundancy maximum relevance method to generate feature lists. These feature lists were then fed into the incremental feature selection method, which uses a combination of deep forest, k-nearest neighbor, random forest, and decision tree to find the most important methylation signatures and build the best classifiers and classification rules. Several methylation signatures and rules have been discovered and confirmed, allowing for a better understanding of methylation patterns in response to different treatment exposures.

Differential molecular response in mice and human thymocytes exposed to a combined-dose radiation regime

In the quest for more effective radiation treatment options that can improve both cell killing and healthy tissue recovery, combined radiation therapies are lately in the spotlight. The molecular response to a combined radiation regime where exposure to an initial low dose (priming dose) of ionizing radiation is administered prior to a subsequent higher radiation dose (challenging dose) after a given latency period have not been thoroughly explored. In this study we report on the differential response to either a combined radiation regime or a single challenging dose both in mouse in vivo and in human ex vivo thymocytes. A differential cell cycle response including an increase in the subG1 fraction on cells exposed to the combined regime was found. Together with this, a differential protein expression profiling in several pathways including cell cycle control (ATM, TP53, p21^CDKN1A), damage response (γH2AX) and cell death pathways such as apoptosis (Cleaved Caspase-3, PARP1, PKCδ and H3T45ph) and ferroptosis (xCT/GPX4) was demonstrated. This study also shows the epigenetic regulation following a combined regime that alters the expression of chromatin modifiers such as DNMTs (DNMT1, DNMT2, DNMT3A, DNMT3B, DNMT3L) and glycosylases (MBD4 and TDG). Furthermore, a study of the underlying cellular status six hours after the priming dose alone showed evidence of retained modifications on the molecular and epigenetic pathways suggesting that the priming dose infers a “radiation awareness phenotype” to the thymocytes, a sensitization key to the differential response seen after the second hit with the challenging dose. These data suggest that combined-dose radiation regimes could be more efficient at making cells respond to radiation and it would be interesting to further investigate how can these schemes be of use to potential new radiation therapies.

Radiobiological features in offspring of natural populations of Drosophila melanogaster after Chernobyl accident

In their natural habitats, populations of organisms are faced with different levels of chronic low-intensity radiation, causing a wide range of radiobiological effects (from radiosensitivity to radioadaptive response and hormesis). In this study, specimens of Drosophila melanogaster were selected from territories of the Chernobyl nuclear power plant with different levels of radioactive contamination. The isogenic stocks derived from these specimens represent the genetic systems of current populations and make it possible to study radioresistance and its mechanisms in future generations under controlled laboratory conditions. Previous studies have shown that transgenerational radiation effects at the level of lethal mutations and survival rate are unstable and depend not only on the level of chronic low-intensity irradiation, but also on other factors. A single acute irradiation exposure of offspring whose parents inhabited a site with a higher level of chronic irradiation made it possible to reveal pronounced radioresistant features in the offspring. And the offspring whose parents were exposed to radiation levels close to the natural radiation background, on the contrary, acquired radiosensitive features. Their response to acute exposure includes a high-frequency of lethal mutations and a short lifespan. The differential response to different levels of chronic parental exposure is caused by differences in the activities of certain transposons that destabilize the genome. Our data contribute to the understanding of genetic and epigenetic mechanisms (via transposon activity) of the effect of parental radiation exposure on the health and adaptive potential of populations affected by the technogenically increased radiation background.

Stress Responses as Master Keys to Epigenomic Changes in Transcriptome and Metabolome for Cancer Etiology and Therapeutics

From initiation through progression, cancer cells are subjected to a magnitude of endogenous and exogenous stresses, which aid in their neoplastic transformation. Exposure to these classes of stress induces imbalance in cellular homeostasis and, in response, cancer cells employ informative adaptive mechanisms to rebalance biochemical processes that facilitate survival and maintain their existence. Different kinds of stress stimuli trigger epigenetic alterations in cancer cells, which leads to changes in their transcriptome and metabolome, ultimately resulting in suppression of growth inhibition or induction of apoptosis. Whether cancer cells show a protective response to stress or succumb to cell death depends on the type of stress and duration of exposure. A thorough understanding of epigenetic and molecular architecture of cancer cell stress response pathways can unveil a plethora of information required to develop novel anticancer therapeutics. The present view highlights current knowledge about alterations in epigenome and transcriptome of cancer cells as a consequence of exposure to different physicochemical stressful stimuli such as reactive oxygen species (ROS), hypoxia, radiation, hyperthermia, genotoxic agents, and nutrient deprivation. Currently, an anticancer treatment scenario involving the imposition of stress to target cancer cells is gaining traction to augment or even replace conventional therapeutic regimens. Therefore, a comprehensive understanding of stress response pathways is crucial for devising and implementing novel therapeutic strategies.

Evaluation of Global DNA Methylation and Gene Expression of Izumo1 and Izumo1r in Gonads after High- and Low-Dose Radiation in Neonatal Mice

The intergenerational effects from chronic low-dose exposure are matters of concern. It is thus important to elucidate the radiation-induced effects of germ cell maturation, fertilization and embryonic development. It is well known that DNA methylation levels in CpG sites in gametes are reprogrammed in stages during their maturity. Furthermore, the binding of Izumo on the surface of sperm and Juno on the surface of oocytes is essential for fertilization. Thus, there is a possibility that these genes are useful indicators to evaluate fertility in mice after irradiation exposure. Therefore, in this study, we analyzed global DNA methylation patterns in the testes and gene expression of Izumo1 and Izumo1r (Juno) in the gonads of mice after neonatal acute high-dose ionizing radiation (HDR) and chronic low-dose ionizing radiation (LDR). One-week-old male and female mice were irradiated with a total dose of 4 Gy, with acute HDR at 7 days at a dose rate of 30 Gy/h and LDR continuously at a dose rate of 6 mGy/h from 7 to 35 days. Their gonads were subsequently analyzed. The results of global DNA methylation patterns in the testes showed that methylation level increased with age in the control group, the LDR group maintained its DNA methylation level, and the HDR group showed decreased DNA methylation levels with age. In the control group, the gene expression level of Izumo1 in the testis did not show age-related changes, although there was high expression at 100 days of age. However, in the LDR group, the expression level recovered after the end of irradiation, while it remained low regardless of age in the HDR group. Conversely, gene expression of Izumo1r (Izumo1 receptor) in the ovary decreased with age in the control group. Although the gene expression of Izumo1r decreased with age in the LDR group, it remained low in the HDR group. Our results indicate that LDR can induce different DNA methylation patterns, and both high- and low-dose radiation before sexual maturity might affect gametogenesis and fertility.

Impact of medical imaging on the epigenome - low-dose exposure in the course of computed tomography does not induce detectable changes of DNA-methylation profiles in peripheral blood cells

BACKGROUND

Computed tomography (CT) is a main contributor to artificial low-dose exposure. Understanding the biological effects induced by CT exposure and their dependency on the characteristics of photon spectra is essential for knowledge-driven risk assessment. In a previous gene expression study, we have identified upregulation of AEN, BAX, DDB2, EDA2R and FDXR after ex vivo exposure with single-energy CT and dual-energy CT (DECT). In this study, we focused on CT-induced changes of DNA methylation. This epigenetic modification of DNA is a central regulator of gene expression and instrumental in preserving genome integrity. Previous studies reported focal hypermethylation and global hypomethylation after exposure with doses above 100 mSv, however, the effect of low dose exposure on DNA methylation is hardly explored.

MATERIALS AND METHODS

DNA was isolated from peripheral blood of three healthy individuals 6 h after ex vivo exposition to single-energy (80 kV and 150 kV) and DECT (80 kV/Sn150 kV) with a calculated effective dose of 7.0 ± 0.08 mSv. The experimental setting was identical to the one used in our previous gene expression study enabling a direct comparison of gene expression results with changes of DNA methylation identified in this study. DNA methylation was analyzed by high-throughput sequencing of bisulfite-treated DNA targeted methylation sequencing.

RESULTS

Unsupervised hierarchical clustering based on DNA methylation profiles of all samples created three distinct clusters. Formation of these three clusters was solely determined by the origin of samples, indicating the absence of prominent irradiation-associated changes of DNA methylation. In line with this observation, inter-individual comparison of non-irradiated samples revealed 1163, 1224 and 4550 significant differentially methylated regions (DMRs), respectively, whereas the pairwise comparison of irradiated and non-irradiated samples failed to identify irradiation-induced DMRs in any of the three probands. This even applied to the genomic regions harboring AEN, BAX, DDB2, EDA2R and FDXR, the five genes known to be upregulated by CT exposure.

CONCLUSIONS

CT exposure with various photon spectra did not result in detectable changes of DNA methylation. However, minor effects in a subpopulation of irradiated cells cannot be ruled out. Thus, future studies with extended observation intervals are needed to investigate DNA methylation changes that are induced by indirect effects at later points of time or become detectable by clonal expansion of affected cells. Moreover, our data suggest that DNA methylation analysis is less sensitive in detecting immediate effects of low-dose irradiation when compared to gene expression analysis.

Global DNA methylation profile at LINE-1 repeats and promoter methylation of genes involved in DNA damage response and repair pathways in human peripheral blood mononuclear cells in response to γ-radiation

DNA methylation is an epigenetic mechanism, which plays an important role in gene regulation. The present study evaluated DNA methylation profile of LINE1 repeats and promoter methylation of DNA damage response (DDR) and DNA repair (DR) genes (PARP1, ATM, BRCA1, MLH1, XPC, RAD23B, APC, TNFα, DNMT3A, MRE11A, MGMT, CDKN2A, MTHFR) in human peripheral blood mononuclear cells (PBMCs) of healthy donors in response to γ-radiation. Methylation level was correlated with gene expression profile of selected DDR and DR genes (APC, MLH1, PARP1, MRE11A, TNFα, MGMT) to understand their role in gene regulation. Blood samples were collected from 15 random healthy donors, PBMCs were isolated, exposed to 0.1 Gy (low) and 2.0 Gy (high) doses of γ-radiation and proliferated for 48 h and 72 h. Genomic DNA and total RNA were isolated from irradiated PBMCs along with un-irradiated control. Methylation profile was determined from bisulphite converted DNA and amplified by methylation sensitive high resolution melting (MS-HRM) method. Total RNA was converted to cDNA and relative expression was analysed using real time quantitative-PCR. Our results revealed that at 0.1 Gy, MRE11A and TNFα showed significant (P < 0.05) increase in methylation at 72 h. At 2.0 Gy, significant increase (P < 0.05) in methylation profile was observed at LINE1, MRE11A, PARP1, BRCA1, DNMT3A and RAD23B at 48 h and 72 h. PARP1 showed significant positive correlation of methylation status with gene expression. In conclusion, low and high doses of γ-radiation have significant influence on DNA methylation status of LINE1, DDR and DR genes suggesting their potential role as epigenetic signatures in human PBMCs, which can be further explored in human populations.

DNA repair- and nucleotide metabolism-related genes exhibit differential CHG methylation patterns in natural and synthetic polyploids (Brassica napus L.)

Polyploidization plays a crucial role in the evolution of angiosperm species. Almost all newly formed polyploids encounter genetic or epigenetic instabilities. However, the molecular mechanisms contributing to genomic instability in synthetic polyploids have not been clearly elucidated. Here, we performed a comprehensive transcriptomic and methylomic analysis of natural and synthetic polyploid rapeseeds (Brassica napus). Our results showed that the CHG methylation levels of synthetic rapeseed in different genomic contexts (genes, transposon regions, and repeat regions) were significantly lower than those of natural rapeseed. The total number and length of CHG-DMRs between natural and synthetic polyploids were much greater than those of CG-DMRs and CHH-DMRs, and the genes overlapping with these CHG-DMRs were significantly enriched in DNA damage repair and nucleotide metabolism pathways. These results indicated that CHG methylation may be more sensitive than CG and CHH methylation in regulating the stability of the polyploid genome of B. napus. In addition, many genes involved in DNA damage repair, nucleotide metabolism, and cell cycle control were significantly differentially expressed between natural and synthetic rapeseeds. Our results highlight that the genes related to DNA repair and nucleotide metabolism display differential CHG methylation patterns between natural and synthetic polyploids and reveal the potential connection between the genomic instability of polyploid plants with DNA methylation defects and dysregulation of the DNA repair system. In addition, it was found that the maintenance of CHG methylation in B. napus might be partially regulated by MET1. Our study provides novel insights into the establishment and evolution of polyploid plants and offers a potential idea for improving the genomic stability of newly formed Brassica polyploids.

Methylation of PAX1 gene promoter in the prediction of concurrent chemo-radiotherapy efficacy in cervical cancer

Objectives: Cervical cancer is the fourth leading cause of cancer death among women worldwide. In currently, aberrant methylation of PAX1 is found in variety of solid tumors, including cervical cancer. In addition, the role of PAX1 gene methylation in cervical cancer and precancerous lesions screening has been confirmed in previous study. Here, we evaluated the predictive value of PAX1 methylation in concurrent chemo-radiotherapy (CCRT) outcomes in cervical cancer.

Methods: This study enrolled 82 cervical cancer patients from August 2018 to August 2020. We compared the clinical results between different PAX1 methylation status. Hyper-methylation patients were subjects to MRI and quantitative methylation-specific PCR (QMSP) for PAX1 before, in the middle, immediately after, 1 month and 3 months after CCRT. The changes in PAX1 methylation during CCRT were analyzed.

Results: The lower PAX1 methylation status were related to a poor tumor response. Based on the MRI findings three months post-treatment, the hypermethylated patients were classified into the complete response (CR; n=50) and partial remission (PR; n=18) groups. The average PAX1 △Cp value of CR and PR groups before radiotherapy was 5.08±1.98 and 4.32±2.00 respectively, and after concurrent chemo-radiotherapy was significantly increased to 17.35±4.96 and 16.99±6.17, respectively (P<0.05). Furthermore, the PAX1 △Cp value between CR and PR groups were significantly different at mid-treatment and performed well in predicting short-term efficacy (AUC 0.84) in this period, and its sensitivity and specificity for predicting PR were 0.72 and 0.88, respectively.

Conclusion: The PAX1 methylation level may predict the sensitivity and efficacy of CCRT in cervical cancer.

Lasting Effects of Low to Non-Lethal Radiation Exposure during Late Gestation on Offspring's Cardiac Metabolism and Oxidative Stress

Ionizing radiation (IR) is known to cause fetal programming, but the physiological effects of low-dose IR are not fully understood. This study examined the effect of low (50 mGy) to non-lethal (300 and 1000 mGy) radiation exposure during late gestation on cardiac metabolism and oxidative stress in adult offspring. Pregnant C57BL/6J mice were exposed to 50, 300, or 1000 mGy of gamma radiation or Sham irradiation on gestational day 15. Sixteen weeks after birth, ¹⁸F-Fluorodeoxyglucose (FDG) uptake was examined in the offspring using Positron Emission Tomography imaging. Western blot was used to determine changes in oxidative stress, antioxidants, and insulin signaling related proteins. Male and female offspring from irradiated dams had lower body weights when compared to the Sham. 1000 mGy female offspring demonstrated a significant increase in ¹⁸F-FDG uptake, glycogen content, and oxidative stress. 300 and 1000 mGy female mice exhibited increased superoxide dismutase activity, decreased glutathione peroxidase activity, and decreased reduced/oxidized glutathione ratio. We conclude that non-lethal radiation during late gestation can alter glucose uptake and increase oxidative stress in female offspring. These data provide evidence that low doses of IR during the third trimester are not harmful but higher, non-lethal doses can alter cardiac metabolism later in life and sex may have a role in fetal programming.

A Perspective of Epigenetic Regulation in Radiotherapy

Radiation therapy (RT) has been employed as a tumoricidal modality for more than 100 years and on 470,000 patients each year in the United States. The ionizing radiation causes genetic changes and results in cell death. However, since the biological mechanism of radiation remains unclear, there is a pressing need to understand this mechanism to improve the killing effect on tumors and reduce the side effects on normal cells. DNA break and epigenetic remodeling can be induced by radiotherapy. Hence the modulation of histone modification enzymes may tune the radiosensitivity of cancer cells. For instance, histone deacetylase (HDAC) inhibitors sensitize irradiated cancer cells by amplifying the DNA damage signaling and inhibiting double-strand DNA break repair to influence the irradiated cells’ survival. However, the combination of epigenetic drugs and radiotherapy has only been evaluated in several ongoing clinical trials for limited cancer types, partly due to a lack of knowledge on the potential mechanisms on how radiation induces epigenetic regulation and chromatin remodeling. Here, we review recent advances of radiotherapy and radiotherapy-induced epigenetic remodeling and introduce related technologies for epigenetic monitoring. Particularly, we exploit the application of fluorescence resonance energy transfer (FRET) biosensors to visualize dynamic epigenetic regulations in single living cells and tissue upon radiotherapy and drug treatment. We aim to bridge FRET biosensor, epigenetics, and radiotherapy, providing a perspective of using FRET to assess epigenetics and provide guidance for radiotherapy to improve cancer treatment. In the end, we discuss the feasibility of a combination of epigenetic drugs and radiotherapy as new approaches for cancer therapeutics.

Role of epigenetic mechanisms in propagating off-targeted effects following radiation based therapies - A review

Despite being an important diagnostic and treatment modality, ionizing radiation (IR) is also known to cause genotoxicity and multiple side effects leading to secondary carcinogenesis. While modern cancer radiation therapy has improved patient recovery and enhanced survival rates, the risk of radiation-related adverse effects has become a growing challenge. It is now well-accepted that IR-induced side effects are not exclusively restricted to exposed cells but also spread to distant 'bystander' cells and even to the unexposed progeny of the irradiated cells. These 'off-targeted' effects involve a plethora of molecular events depending on the type of radiation and tumor tissue background. While the mechanisms by which off-targeted effects arise remain obscure, emerging evidence based on the non-mendelian inheritance of various manifestations of them as well as their persistence for longer periods supports a contribution of epigenetic factors. This review focuses on the major epigenetic phenomena including DNA methylation, histone modifications, and small RNA mediated silencing and their versatile role in the manifestation of IR induced off-targeted effects. As short- and long-range communication vehicles respectively, the role of gap junctions and exosomes in spreading these epigenetic-alteration driven off-targeted effects is also discussed. Furthermore, this review emphasizes the possible therapeutic potentials of these epigenetic mechanisms and how beneficial outcomes could potentially be achieved by targeting various signaling molecules involved in these mechanisms.

Dose-dependent genomic DNA hypermethylation and mitochondrial DNA damage in Japanese tree frogs sampled in the Fukushima Daiichi area

The long-term consequences of the nuclear disaster at the Fukushima Daiichi Nuclear Power Plant (FDNPP) that occurred on March 2011, have been scarcely studied on wildlife. We sampled Japanese tree frogs (Dryophytes japonicus), in a 50 -km area around the FDNPP to test for an increase of DNA damages and variation of DNA methylation level. The ambient dose rate ranged between 0.4 and 2.8 μGy h^-1 and the total estimated dose rate absorbed by frogs ranged between 0.3 and 7.7 μGy h^-1. Frogs from contaminated sites exhibited a dose-dependent increase of global genomic DNA methylation level (5-mdC and 5-hmdC) and of mitochondrial DNA damages. Such DNA damages may indicate a genomic instability, which may induce physiological adaptations governed by DNA methylation changes. This study stresses the need for biological data combining targeted molecular methods and classic ecotoxicology, in order to better understand the impacts on wildlife of long term exposure to low ionizing radiation levels.

Genome-Wide Sex and Gender Differences in Cancer

Despite their known importance in clinical medicine, differences based on sex and gender are among the least studied factors affecting cancer susceptibility, progression, survival, and therapeutic response. In particular, the molecular mechanisms driving sex differences are poorly understood and so most approaches to precision medicine use mutational or other genomic data to assign therapy without considering how the sex of the individual might influence therapeutic efficacy. The mandate by the National Institutes of Health that research studies include sex as a biological variable has begun to expand our understanding on its importance. Sex differences in cancer may arise due to a combination of environmental, genetic, and epigenetic factors, as well as differences in gene regulation, and expression. Extensive sex differences occur genome-wide, and ultimately influence cancer biology and outcomes. In this review, we summarize the current state of knowledge about sex-specific genetic and genome-wide influences in cancer, describe how differences in response to environmental exposures and genetic and epigenetic alterations alter the trajectory of the disease, and provide insights into the importance of integrative analyses in understanding the interplay of sex and genomics in cancer. In particular, we will explore some of the emerging analytical approaches, such as the use of network methods, that are providing a deeper understanding of the drivers of differences based on sex and gender. Better understanding these complex factors and their interactions will improve cancer prevention, treatment, and outcomes for all individuals.

Generalizability of "GWAS Hits" in Clinical Populations: Lessons from Childhood Cancer Survivors

With mounting interest in translating genome-wide association study (GWAS) hits from large meta-analyses (meta-GWAS) in diverse clinical settings, evaluating their generalizability in target populations is crucial. Here, we consider long-term survivors of childhood cancers from the St. Jude Lifetime Cohort Study, and we show the limited generalizability of 1,376 robust SNP associations reported in the general population across 12 complex anthropometric and cardiometabolic phenotypes (n = 2,231; observed-to-expected replication ratio = 0.70, p = 6.2 × 10^-8). An examination of five comparable phenotypes in a second independent cohort of survivors from the Childhood Cancer Survivor Study corroborated the overall limited generalizability of meta-GWAS hits to survivors (n = 4,212; observed-to-expected replication ratio = 0.55, p = 5.6 × 10^-15). Finally, in direct comparisons of survivor samples against independent equivalently powered general population samples from the UK Biobank, we consistently observed lower meta-GWAS hit replication rates and poorer polygenic risk score predictive performance in survivor samples for multiple phenotypes. As a possible explanation, we found that meta-GWAS hits were less likely to be replicated in survivors who had been exposed to cancer therapies that are associated with phenotype risk. Examination of complementary DNA methylation data in a subset of survivors revealed that treatment-related methylation patterns at genomic sites linked to meta-GWAS hits may disrupt established genetic signals in survivors.

Study logistics that can impact medical countermeasure efficacy testing in mouse models of radiation injury

PURPOSE

To address confounding issues that have been noted in planning and conducting studies to identify biomarkers of radiation injury, develop animal models to simulate these injuries, and test potential medical countermeasures to mitigate/treat damage caused by radiation exposure.

METHODS

The authors completed an intensive literature search to address several key areas that should be considered before embarking on studies to assess efficacy of medical countermeasure approaches in mouse models of radiation injury. These considerations include: (1) study variables; (2) animal selection criteria; (3) animal husbandry; (4) medical management; and (5) radiation attributes.

RESULTS

It is important to select mouse strains that are capable of responding to the selected radiation exposure (e.g. genetic predispositions might influence radiation sensitivity and proclivity to certain phenotypes of radiation injury), and that also react in a manner similar to humans. Gender, vendor, age, weight, and even seasonal variations are all important factors to consider. In addition, the housing and husbandry of the animals (i.e. feed, environment, handling, time of day of irradiation and animal restraint), as well as the medical management provided (e.g. use of acidified water, antibiotics, routes of administration of drugs, consideration of animal numbers, and euthanasia criteria) should all be addressed. Finally, the radiation exposure itself should be tightly controlled, by ensuring a full understanding and reporting of the radiation source, dose and dose rate, shielding and geometry of exposure, while also providing accurate dosimetry. It is important to understand how all the above factors contribute to the development of radiation dose response curves for a given animal facility with a well-defined murine model.

CONCLUSIONS

Many potential confounders that could impact the outcomes of studies to assess efficacy of a medical countermeasure for radiation-induced injuries are addressed, and recommendations are made to assist investigators in carrying out research that is robust, reproducible, and accurate.

Epigenetic Age Acceleration and Chronic Health Conditions Among Adult Survivors of Childhood Cancer

BACKGROUND

Mounting evidence supports the occurrence of accelerating aging among long-term survivors of childhood cancer. We aimed to investigate epigenetic age acceleration (EAA) in survivors and evaluate associations between EAA, treatment exposures, health behaviors, and chronic health conditions (CHCs).

METHODS

Genome-wide methylation data were generated with Infinium EPIC BeadChip on blood-derived DNA from 2139 survivors and 282 frequency matched controls from the St Jude Lifetime Cohort Study. EAAs were estimated as residuals from a linear regression of epigenetic age (Levine's clock) against chronological age. Adjusted least square mean (ALSM) of EAA was calculated and compared between survivors and controls, across treatment exposures and health behaviors. Associations of EAA with 20 clinically assessed CHCs were evaluated with multivariable piecewise-exponential models. All statistical tests for P values below were 2-sided.

RESULTS

EAA was statistically significantly higher in survivors than controls (ALSM = 0.63, 95% confidence interval [CI] = 0.26 to 1.01 vs -3.61, 95% CI = -4.43 to 2.80). In a multivariable model among survivors, statistically significantly higher EAA (P < .05) was observed in those exposed to chest radiotherapy, abdomen or pelvic radiotherapy, alkylating agents, glucocorticoids, or epipodophyllotoxins. Compared with survivors with favorable health behaviors (ALSM = 0.26, 95% CI=-0.36 to 0.87), EAA was statistically significantly higher among survivors with intermediate (ALSM = 1.07, 95% CI = 0.59 to 1.54) or unfavorable health behaviors (ALSM = 1.45, 95% CI = 0.60 to 2.30). In time-to-event analyses, statistically significant associations were identified between EAA tertiles and incidence of 7 CHCs: hypertension (3rd vs 1st tertile, relative rate [RR] = 1.83, 95% CI = 1.17 to 2.83), myocardial infarction (RR = 2.91, 95% CI = 1.27 to 7.21), obesity (RR = 1.39, 95% CI = 1.17 to 1.66), obstructive pulmonary deficit (RR = 1.86, 95% CI = 0.95 to 3.77), peripheral motor neuropathy (RR = 2.89, 95% CI = 1.24 to 6.97), peripheral sensory neuropathy (RR = 2.04, 95% CI = 0.99 to 4.26), and pulmonary diffusion deficits (RR = 2.75, 95% CI = 0.95 to 7.63).

CONCLUSIONS

EAA is statistically significantly higher in survivors of childhood cancer than in noncancer controls and is associated with specific treatment exposures, unfavorable health behaviors, and presence of specific CHCs.

Ionizing Radiation-Induced Epigenetic Modifications and Their Relevance to Radiation Protection

The present system of radiation protection assumes that exposure at low doses and/or low dose-rates leads to health risks linearly related to the dose. They are evaluated by a combination of epidemiological data and radiobiological models. The latter imply that radiation induces deleterious effects via genetic mutation caused by DNA damage with a linear dose-dependence. This picture is challenged by the observation of radiation-induced epigenetic effects (changes in gene expression without altering the DNA sequence) and of non-linear responses, such as non-targeted and adaptive responses, that in turn can be controlled by gene expression networks. Here, we review important aspects of the biological response to ionizing radiation in which epigenetic mechanisms are, or could be, involved, focusing on the possible implications to the low dose issue in radiation protection. We examine in particular radiation-induced cancer, non-cancer diseases and transgenerational (hereditary) effects. We conclude that more realistic models of radiation-induced cancer should include epigenetic contribution, particularly in the initiation and progression phases, while the impact on hereditary risk evaluation is expected to be low. Epigenetic effects are also relevant in the dispute about possible "beneficial" effects at low dose and/or low dose-rate exposures, including those given by the natural background radiation.

Precision radiotherapy for non-small cell lung cancer

Precision medicine is becoming the standard of care in anti-cancer treatment. The personalized precision management of cancer patients highly relies on the improvement of new technology in next generation sequencing and high-throughput big data processing for biological and radiographic information.

Systemic precision cancer therapy has been developed for years. However, the role of precision medicine in radiotherapy has not yet been fully implemented. Emerging evidence has shown that precision radiotherapy for cancer patients is possible with recent advances in new radiotherapy technologies, panomics, radiomics and dosiomics.

This review focused on the role of precision radiotherapy in non-small cell lung cancer and demonstrated the current landscape.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Gender-dependent radiotherapy: The next step in personalised medicine?

Individuals do not react to radiation in a homogeneous manner. Recent radiogenomic research has proven that individual polymorphisms can correlate with treatment response most likely due to variation in the ability to recognise and repair DNA breaks. The difference in radiosensitivity between genders has been well documented, yet most radiotherapeutic guidelines are based solely on population averages rather than demographic subgroups such as age, race and gender. This paper is a review of the burgeoning literature available on the differences in efficacy and outcome of radiotherapy between genders. The work examines the effect of radiation on gender both from a tumour control as well as normal tissue toxicity perspective. While the literature reporting such findings is limited, the results show a small but significant difference in response to radiotherapy between sexes. Prospective and retrospective studies for evaluating these gender-specific differences are encouraged as a next step in personalised medicine.

Time-Dependent Measurement of Nrf2-Regulated Antioxidant Response to Ionizing Radiation Toward Identifying Potential Protein Biomarkers for Acute Radiation Injury

PURPOSE

Potential acute exposure to ionizing radiation in nuclear or radiological accidents presents complex mass casualty scenarios that demand prompt triage and treatment decisions. Due to delayed symptoms and varied response of radiation victims, there is an urgent need to develop robust biomarkers to assess the extent of injuries in individuals.

EXPERIMENTAL DESIGN

The transcription factor Nrf2 is the master of redox homeostasis and there is transcriptional evidence of Nrf2-dependent antioxidant response activation upon radiation. The biomarker potential of Nrf2-dependent downstream target enzymes is investigated by measuring their response in bone marrow extracted from C57Bl/6 and C3H mice of both genders for up to 4 days following 6 Gy total body irradiation using targeted MS.

RESULTS

Overall, C57Bl/6 mice have a stronger proteomic response than C3H mice. In both strains, male mice have more occurrences of upregulation in antioxidant enzymes than female mice. For C57Bl/6 male mice, three proteins show elevated abundances after radiation exposure: catalase, superoxide dismutase 1, and heme oxygenase 1. Across both strains and genders, glutathione S-transferase Mu 1 is consistently decreased.

CONCLUSIONS AND CLINICAL RELEVANCE

This study provides the basis for future development of organ-specific protein biomarkers used in diagnostic blood test for radiation injury.

Exposure to environmental radionuclides is associated with altered metabolic and immunity pathways in a wild rodent

Wildlife inhabiting environments contaminated by radionuclides face putative detrimental effects of exposure to ionizing radiation, with biomarkers such as an increase in DNA damage and/or oxidative stress commonly associated with radiation exposure. To examine the effects of exposure to radiation on gene expression in wildlife, we conducted a de novo RNA sequencing study of liver and spleen tissues from a rodent, the bank vole Myodes glareolus. Bank voles were collected from the Chernobyl Exclusion Zone (CEZ), where animals were exposed to elevated levels of radionuclides, and from uncontaminated areas near Kyiv, Ukraine. Counter to expectations, we did not observe a strong DNA damage response in animals exposed to radionuclides, although some signs of oxidative stress were identified. Rather, exposure to environmental radionuclides was associated with upregulation of genes involved in lipid metabolism and fatty acid oxidation in the livers - an apparent shift in energy metabolism. Moreover, using stable isotope analysis, we identified that fur from bank voles inhabiting the CEZ had enriched isotope values of nitrogen: such an increase is consistent with increased fatty acid metabolism, but also could arise from a difference in diet or habitat between the CEZ and elsewhere. In livers and spleens, voles inhabiting the CEZ were characterized by immunosuppression, such as impaired antigen processing, and activation of leucocytes involved in inflammatory responses. In conclusion, exposure to low dose environmental radiation impacts pathways associated with immunity and lipid metabolism, potentially as a stress-induced coping mechanism.

Sex Difference of Radiation Response in Occupational and Accidental Exposure

Ionizing radiation is a well-established cause of deleterious effects on human health. Understanding the risks of radiation exposure is important for the development of protective measures and guidelines. Demographic factors such as age, sex, genetic susceptibility, comorbidities, and various other lifestyle factors influence the radiosensitivity of different subpopulations. Amongst these factors, the influence of sex differences on radiation sensitivity has been given very less attention. In fact, the International Commission on Radiological Protection (ICRP) has based its recommendations on a population average, rather than the data on the radiosensitivity of distinct subpopulations. In this study, we reviewed major human studies on the health risks of radiation exposure and showed that sex-related factors may potentially influence the long-term response to radiation exposure. Available data suggest that long-term radiosensitivity in women is higher than that in men who receive a comparable dose of radiation. The report on the biological effects of ionizing radiation (BEIR VII) published in 2006 by the National Academy of Sciences, United States emphasized that women may be at significantly greater risk of suffering and dying from radiation-induced cancer than men exposed to the same dose of radiation. We show that radiation effects are sex-specific, and long-term radiosensitivity in females is higher than that in males. We also discuss the radiation effects as a function of age. In the future, more systematic studies are needed to elucidate the sex differences in radiation responses across the life continuum - from preconception through childhood, adulthood, and old age - to ensure that boys and girls and men and women are equally protected across ages.

Adaptive responses to low doses of radiation or chemicals: their cellular and molecular mechanisms

This article reviews the current knowledge on the mechanisms of adaptive response to low doses of ionizing radiation or chemical exposure. A better knowledge of these mechanisms is needed to improve our understanding of health risks at low levels of environmental or occupational exposure and their involvement in cancer or non-cancer diseases. This response is orchestrated through a multifaceted cellular program involving the concerted action of diverse stress response pathways. These evolutionary highly conserved defense mechanisms determine the cellular response to chemical and physical aggression. They include DNA damage repair (p53, ATM, PARP pathways), antioxidant response (Nrf2 pathway), immune/inflammatory response (NF-κB pathway), cell survival/death pathway (apoptosis), endoplasmic response to stress (UPR response), and other cytoprotective processes including autophagy, cell cycle regulation, and the unfolded protein response. The coordinated action of these processes induced by low-dose radiation or chemicals produces biological effects that are currently estimated with the linear non-threshold model. These effects are controversial. They are difficult to detect because of their low magnitude, the scarcity of events in humans, and the difficulty of corroborating associations over the long term. Improving our understanding of these biological consequences should help humans and their environment by enabling better risk estimates, the revision of radiation protection standards, and possible therapeutic advances.

Persistent DNA methylation changes in zebrafish following graphene quantum dots exposure in surface chemistry-dependent manner

Modified nano-graphene quantum dots (M-GQDs) are widely used in bioimaging, drug delivery, and chemical engineering. Because M-GQDs could induce reactive oxygen species and DNA damage, we hypothesized that M-GQDs modulate DNA methylation. To test this hypothesis, zebrafish were exposed to reduced, hydroxylated, or aminated GQDs (graphene quantum dots) at different concentrations for 7 days; global DNA methylation in liver, gill, and intestine was then studied. M-GQDs induced global DNA hypermethylation in various tissues in a dose-dependent manner. The global DNA methylation of reduced and aminated GQDs exposure showed a significant increase in intestines even at low concentrations (2 mg/L), suggesting that intestines are the main target for these two M-GQDs. The effects of global DNA methylation were evaluated 14 days after exposure had ceased. DNA methylation in the livers of exposure groups was significantly higher than in control zebrafish. Global DNA methylation increased in livers of zebrafish even after exposure to aminated GQDs (2 mg/L) had ceased, indicating a more complex mechanism of DNA methylation deregulation. The present results showed that chemical groups in the surface of GQDs are a critical factor for modulating DNA methylation.

LINE-1 hypomethylation is associated with radiation-induced genomic instability in industrial radiographers

Global DNA hypomethylation is proposed as a potential biomarker for cancer risk associated with genomic instability, which is an important factor in radiation-induced cancer. However, the associations among radiation exposure, changes in DNA methylation, and carcinogenesis are unclear. The aims of this study were (1) to examine whether low-level occupational radiation exposure induces genomic DNA hypomethylation; and (2) to determine the relationships between radiation exposure, genomic DNA hypomethylation and radiation-induced genomic instability (RIGI) in industrial radiographers. Genomic DNA methylation levels were measured in blood DNA from 40 radiographers and 28 controls using the LINE-1 pyrosequencing assay and the luminometric methylation assay. Further, the micronucleus-centromere assay was performed to measure aneuploidy of chromosomes 1 and 4 as a marker of delayed RIGI. Genomic DNA methylation levels were significantly lower in radiographers than those in controls. LINE-1 hypomethylation was not significantly correlated with recent 1-year, recent 3-year, or total cumulative radiation doses in radiographers; however, LINE-1 hypomethylation significantly correlated with the cumulative radiation dose without recent 3-year exposure data (D3dose, r = -0.39, P < 0.05). In addition, LINE-1 hypomethylation was a significant contributor to aneuploidy frequency by D3dose (F (2, 34) = 13.85, P < 0.001), in which a total of 45% of the variance in aneuploidy frequency was explained. Our results provide suggestive evidence regarding the delayed effects of low-dose occupational radiation exposure in radiographers and its association with LINE-1 hypomethylation; however, additional studies using more subjects are needed to fully understand the relationship between genomic DNA hypomethylation and RIGI. Environ. Mol. Mutagen. 60: 174-184, 2019. © 2018 Wiley Periodicals, Inc.

Sex-specific differences in genotoxic and epigenetic effects of 1,3-butadiene among mouse tissues

Exposure to environmental chemicals has been shown to have an impact on the epigenome. One example is a known human carcinogen 1,3-butadiene which acts primarily by a genotoxic mechanism, but also disrupts the chromatin structure by altering patterns of cytosine DNA methylation and histone modifications. Sex-specific differences in 1,3-butadiene-induced genotoxicity and carcinogenicity are well established; however, it remains unknown whether 1,3-butadiene-associated epigenetic alterations are also sex dependent. Therefore, we tested the hypothesis that inhalational exposure to 1,3-butadiene will result in sex-specific epigenetic alterations. DNA damage and epigenetic effects of 1,3-butadiene were evaluated in liver, lung, and kidney tissues of male and female mice of two inbred strains (C57BL/6J and CAST/EiJ). Mice were exposed to 0 or 425 ppm of 1,3-butadiene by inhalation (6 h/day, 5 days/week) for 2 weeks. Strain- and tissue-specific differences in 1,3-butadiene-induced DNA adducts and crosslinks were detected in the liver, lung and kidney; however, significant sex-specific differences in DNA damage were observed in the lung of C57BL/6J mice only. In addition, we assessed expression of the DNA repair genes and observed a marked upregulation of Mgmt in the kidney in female C57BL/6J mice. Sex-specific epigenetic effects of 1,3-butadiene exposure were evident in alterations of cytosine DNA methylation and histone modifications in the liver and lung in both strains. Specifically, we observed a loss of cytosine DNA methylation in the liver and lung of male and female 1,3-butadiene-exposed C57BL/6J mice, whereas hypermethylation was found in the liver and lung in 1,3-butadiene-exposed female CAST/EiJ mice. Our findings suggest that strain- and sex-specific effects of 1,3-butadiene on the epigenome may contribute to the known differences in cancer susceptibility.

Molecular and epigenetic regulatory mechanisms of normal stem cell radiosensitivity

Ionizing radiation (IR) therapy is a major cancer treatment modality and an indispensable auxiliary treatment for primary and metastatic cancers, but invariably results in debilitating organ dysfunctions. IR-induced depletion of neural stem/progenitor cells in the subgranular zone of the dentate gyrus in the hippocampus where neurogenesis occurs is considered largely responsible for deficiencies such as learning, memory, and spatial information processing in patients subjected to cranial irradiation. Similarly, IR therapy-induced intestinal injuries such as diarrhea and malabsorption are common side effects in patients with gastrointestinal tumors and are believed to be caused by intestinal stem cell drop out. Hematopoietic stem cell transplantation is currently used to reinstate blood production in leukemia patients and pre-clinical treatments show promising results in other organs such as the skin and kidney, but ethical issues and logistic problems make this route difficult to follow. An alternative way to restore the injured tissue is to preserve the stem cell pool located in that specific tissue/organ niche, but stem cell response to ionizing radiation is inadequately understood at the molecular mechanistic level. Although embryonic and fetal hypersensity to IR has been very well known for many decades, research on embryonic stem cell models in culture concerning molecular mechanisms have been largely inconclusive and often in contradiction of the in vivo observations. This review will summarize the latest discoveries on stem cell radiosensitivity, highlighting the possible molecular and epigenetic mechanism(s) involved in DNA damage response and programmed cell death after ionizing radiation therapy specific to normal stem cells. Finally, we will analyze the possible contribution of stem cell-specific chromatin's epigenetic constitution in promoting normal stem cell radiosensitivity.

X-ray irradiation induced Disabled-2 gene promoter de-methylation enhances radiosensitivity of non-small-cell lung carcinoma cells

BACKGROUND

Disabled-2 (Dab2) is known as a tumor suppressor as well as a Wnt pathway inhibitor. We previously reported that Dab2 was down-regulated due to gene promoter hypermethylation in lung cancer. Here, we aim to study if X-ray irradiation can induce de-methylation of the Dab2 gene and subsequently up-regulate its expression, and also to attempt to suppress the malignant biological behavior of and enhance the radiosensitivity in lung cancer cells with hypermethylation of the Dab2 gene.

METHODS

Immunostaining was performed to investigate the relationship between Dab2 expression and lung cancer clinicopathological characteristics. Bisulfite sequencing PCR (BSP) was used to evaluate the methylation status of lung cancer cells with or without X-ray treatment. Real-time PCR and western Blot were performed to investigate the expression of Dab2, Wnt pathway factors, DNMTs and methyl CpG binding protein 2 (MeCP2). Colony Formation, matrigel invasion and xenograft experiment were performed to evaluate the malignant biological behavior of lung cancer cells with irradiation.

RESULTS

The result of immunostaining of Dab2 in lung cancer tissues showed that decreased Dab2 expression was positively correlated with poor differentiation, lymph node metastasis, advanced TNM stage and poor prognosis. X-ray treatment significantly up-regulated Dab2 expression and inhibited Wnt factors in LK2 cells (with hypermethylation of the Dab2 gene promoter, P < 0.05), but not in SPC-A-1 cells (with hypomethylation of the Dab2 gene promoter); however, the effect could be reversed by Dab2 or Axin knockdown (P < 0.05). Decreased expression of DNMT1, DNMT3b and MeCP2 could be detected in both LK2 and SPC-A-1 cells compared to non-irradiated cells (P < 0.05). Both in vitro studies and in vivo xenograft tumor growth demonstrated that X-ray could significantly inhibit the proliferation and invasion of LK2 but not SPC-A-1 cells (P < 0.05).

CONCLUSION

In general, X-ray-induced up-regulation of Dab2 and inhibition of the Wnt pathway may be mediated by de-methylation of a hypermethylated Dab2 gene promoter. X-ray treatment significantly inhibits proliferation and invasion of lung cancer cells with hypermethylation of the Dab2 gene promoter, but is less effective in lung cancer cells with hypomethylation of the Dab2 gene promoter. These results indicate that the methylation status of the Dab2 gene promoter might be a potential predictor of the radiosensitivity of lung cancer cells.

Genome-wide DNA methylation changes in two Brassicaceae species sampled alongside a radiation gradient in Chernobyl and Fukushima

The long-term radiological impact to the environment of the nuclear accidents in Chernobyl and Fukushima is still under discussion. In the course of spring of 2016 we sampled two Brassicacea plants, Arabidopsis thaliana and Capsella bursa-pastoris native to Ukraine and Japan, respectively, alongside a gradient of radiation within the exclusion and difficult to return zones of Chernobyl (CEZ) and Fukushima (FEZ). Ambient dose rates were similar for both sampling gradients ranging from 0.5 to 80 μGy/h at plant height. The hypothesis was tested whether a history of several generations of plants growing in enhanced radiation exposure conditions would have led to changes in genome-wide DNA methylation. However, no differences were found in the global percentage of 5-methylated cytosines in Capsella bursa pastoris plants sampled in FEZ. On the other hand a significant decrease in whole genome methylation percentage in Arabidopsis thaliana plants was found in CEZ mainly governed by the highest exposed plants. These data support a link between exposure to changed environmental conditions and changes genome methylation. In addition to methylation the activity concentration of different radionuclides, ¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am and Pu-238,239,240 for CEZ and ^{137, 134}Cs for FEZ, was analysed in both soil and plant samples. The ratio of 5.6 between ¹³⁷Cs compared to ¹³⁴Cs was as expected five years after the FEZ accident. For CEZ ¹³⁷Cs is the most abundant polluting radionuclide in soil followed by ⁹⁰Sr. Whereas ²⁴¹Am and Pu-isotopes are only marginally present. In the plant tissue, however, higher levels of Sr than Cs were retrieved due to a high uptake of ⁹⁰Sr in the plants. The ⁹⁰Sr transfer factors ranged in CEZ from 5 to 20 (kg/kg) depending on the locality. Based on the activity concentrations of the different radionuclides the ERICA tool was used to estimate the total dose rates to the plants. It was found that for FEZ the doses was mainly contributable to the external Cs-isotopes and as such estimated total dose rates (0.13-38 μGy/h) were in the same range as the ambient measured dose rates. In strong contrast this was not true for CEZ where the total dose rate was mainly due to high uptake of the ⁹⁰Sr leading to dose rates ranging from 1 to 370 μGy/h. Hence our data clearly indicate that not taking into account the internal contamination in CEZ will lead to considerable underestimation of the doses to the plants. Additionally they show that it is hard to compare the two nuclear accidental sites and one of the main reasons is the difference in contamination profile.

Ionizing radiation induces transgenerational effects of DNA methylation in zebrafish

Ionizing radiation is known to cause DNA damage, yet the mechanisms underlying potential transgenerational effects of exposure have been scarcely studied. Previously, we observed effects in offspring of zebrafish exposed to gamma radiation during gametogenesis. Here, we hypothesize that these effects are accompanied by changes of DNA methylation possibly inherited by subsequent generations. We assessed DNA methylation in F1 embryos (5.5 hours post fertilization) with whole genome bisulfite sequencing following parental exposure to 8.7 mGy/h for 27 days and found 5658 differentially methylated regions (DMRs). DMRs were predominantly located at known regulatory regions, such as gene promoters and enhancers. Pathway analysis indicated the involvement of DMRs related to similar pathways found with gene expression analysis, such as development, apoptosis and cancers, which could be linked to previous observed developmental defects and genomic instability in the offspring. Follow up of 19 F1 DMRs in F2 and F3 embryos revealed persistent effects up to the F3 generation at 5 regions. These results indicate that ionizing radiation related effects in offspring can be linked to DNA methylation changes that partly can persist over generations. Monitoring DNA methylation could serve as a biomarker to provide an indication of ancestral exposures to ionizing radiation.

Influence of diet and metabolism on hematopoietic stem cells and leukemia development following ionizing radiation exposure

PURPOSE

The review aims to discuss the prominence of dietary and metabolic regulators in maintaining hematopoietic stem cell (HSC) function, long-term self-renewal, and differentiation.

RESULTS

Most adult stem cells are preserved in a quiescent, nonmotile state in vivo which acts as a "protective state" for stem cells to reduce endogenous stress provoked by DNA replication and cellular respiration as well as exogenous environmental stress. The dynamic balance between quiescence, self-renewal and differentiation is critical for supporting a functional blood system throughout life of an organism. Stress-conditions, for example ionizing radiation exposure can trigger the blood forming HSCs to proliferate and migrate through extramedullary tissues to expand the number of HSCs and increase hematopoiesis. In addition, a wealth of investigation validated that deregulation of this balance plays a critical pathogenic role in various different hematopoietic diseases including the leukemia development.

CONCLUSION

The review summarizes the current knowledge on how alterations in dietary and metabolic factors could alter the risk of leukemia development following ionizing radiation exposure by inhibiting or even reversing the leukemic progression. Understanding the influence of diet, metabolism, and epigenetics on radiation-induced leukemogenesis may lead to the development of practical interventions to reduce the risk in exposed populations.

Ionizing Radiation and Human Health: Reviewing Models of Exposure and Mechanisms of Cellular Damage. An Epigenetic Perspective

We reviewed available evidence in medical literature concerning experimental models of exposure to ionizing radiations (IR) and their mechanisms of producing damages on living organisms. The traditional model is based on the theory of “stochastic breakage” of one or both strands of the DNA double helix. According to this model, high doses may cause the breaks, potentially lethal to the cell by damaging both DNA strands, while low doses of IR would cause essentially single strands breaks, easily repairable, resulting in no permanent damages. The available evidence makes this classical model increasingly less acceptable, because the exposure to low doses of IR seems to have carcinogenic effects, even after years or decades, both in the exposed individuals and in subsequent generations. In addition, the cells that survived the exposure to low doses, despite being apparently normal, accumulate damages that become evident in their progeny, such as nonclonal chromosomal aberrations, which can be found even in cells not directly irradiated due to the exchange of molecular signals and complex tissue reactions involving neighboring or distant cells. For all these reasons, a paradigm shift is needed, based on evidence and epigenetics.

Galactic Cosmic Radiation Induces Persistent Epigenome Alterations Relevant to Human Lung Cancer

Human deep space and planetary travel is limited by uncertainties regarding the health risks associated with exposure to galactic cosmic radiation (GCR), and in particular the high linear energy transfer (LET), heavy ion component. Here we assessed the impact of two high-LET ions ⁵⁶Fe and ²⁸Si, and low-LET X rays on genome-wide methylation patterns in human bronchial epithelial cells. We found that all three radiation types induced rapid and stable changes in DNA methylation but at distinct subsets of CpG sites affecting different chromatin compartments. The ⁵⁶Fe ions induced mostly hypermethylation, and primarily affected sites in open chromatin regions including enhancers, promoters and the edges ("shores") of CpG islands. The ²⁸Si ion-exposure had mixed effects, inducing both hyper and hypomethylation and affecting sites in more repressed heterochromatic environments, whereas X rays induced mostly hypomethylation, primarily at sites in gene bodies and intergenic regions. Significantly, the methylation status of ⁵⁶Fe ion sensitive sites, but not those affected by X ray or ²⁸Si ions, discriminated tumor from normal tissue for human lung adenocarcinomas and squamous cell carcinomas. Thus, high-LET radiation exposure leaves a lasting imprint on the epigenome, and affects sites relevant to human lung cancer. These methylation signatures may prove useful in monitoring the cumulative biological impact and associated cancer risks encountered by astronauts in deep space.