Radio-adaptive response to environmental exposures at Chernobyl

Fundamentals of wildlife dosimetry and lessons learned from a decade of measuring external dose rates in the field

Methods for determining the radiation dose received by exposed biota require major improvements to reduce uncertainties and increase precision. We share our experiences in attempting to quantify external dose rates to free-ranging wildlife using GPS-coupled dosimetry methods. The manuscript is a primer on fundamental concepts in wildlife dosimetry in which the complexities of quantifying dose rates are highlighted, and lessons learned are presented based on research with wild boar and snakes at Fukushima, wolves at Chornobyl, and reindeer in Norway. GPS-coupled dosimeters produced empirical data to which numerical simulations of external dose using computer software were compared. Our data did not support a standing paradigm in risk analyses: Using averaged soil contaminant levels to model external dose rates conservatively overestimate the dose to individuals within a population. Following this paradigm will likely lead to misguided recommendations for risk management. The GPS-dosimetry data also demonstrated the critical importance of how modeled external dose rates are impacted by the scale at which contaminants are mapped. When contaminant mapping scales are coarse even detailed knowledge about each animal's home range was inadequate to accurately predict external dose rates. Importantly, modeled external dose rates based on a single measurement at a trap site did not correlate to actual dose rates measured on free ranging animals. These findings provide empirical data to support published concerns about inadequate dosimetry in much of the published Chernobyl and Fukushima dose-effects research. Our data indicate that a huge portion of that literature should be challenged, and that improper dosimetry remains a significant source of controversy in radiation dose-effect research.

Evolutionary approach for pollution study: The case of ionizing radiation

Estimating the consequences of environmental changes, specifically in a global change context, is essential for conservation issues. In the case of pollutants, the interest in using an evolutionary approach to investigate their consequences has been emphasized since the 2000s, but these studies remain rare compared to the characterization of direct effects on individual features. We focused on the study case of anthropogenic ionizing radiation because, despite its potential strong impact on evolution, the scarcity of evolutionary approaches to study the biological consequences of this stressor is particularly true. In this study, by investigating some particular features of the biological effects of this stressor, and by reviewing existing studies on evolution under ionizing radiation, we suggest that evolutionary approach may help provide an integrative view on the biological consequences of ionizing radiation. We focused on three topics: (i) the mutagenic properties of ionizing radiation and its disruption of evolutionary processes, (ii) exposures at different time scales, leading to an interaction between past and contemporary evolution, and (iii) the special features of contaminated areas called exclusion zones and how evolution could match field and laboratory observed effects. This approach can contribute to answering several key issues in radioecology: to explain species differences in the sensitivity to ionizing radiation, to improve our estimation of the impacts of ionizing radiation on populations, and to help identify the environmental features impacting organisms (e.g., interaction with other pollution, migration of populations, anthropogenic environmental changes). Evolutionary approach would benefit from being integrated to the ecological risk assessment process.

Comparative Analysis of Driver Mutations and Transcriptomes in Papillary Thyroid Cancer by Region of Residence in South Korea

BACKGRUOUND

Radiation exposure is a well-known risk factor for papillary thyroid cancer (PTC). South Korea has 24 nuclear reactors in operation; however, no molecular biological analysis has been performed on patients with PTC living near nuclear power plants.

METHODS

We retrospectively included patients with PTC (n=512) divided into three groups according to their place of residence at the time of operation: inland areas (n=300), coastal areas far from nuclear power plants (n=134), and nuclear power plant areas (n=78). After propensity score matching (1:1:1) by age, sex, and surgical procedure, the frequency of representative driver mutations and gene expression profiles were compared (n=50 per group). Epithelial-mesenchymal transition (EMT), BRAF, thyroid differentiation, and radiation scores were calculated and compared.

RESULTS

No significant difference was observed in clinicopathological characteristics, including radiation exposure history and the frequency of incidentally discovered thyroid cancer, among the three groups. BRAFV600E mutation was most frequently detected in the groups, with no difference among the three groups. Furthermore, gene expression profiles showed no statistically significant difference. EMT and BRAF scores were higher in our cohort than in cohorts from Chernobyl tissue bank and The Cancer Genome Atlas Thyroid Cancer; however, there was no difference according to the place of residence. Radiation scores were highest in the Chernobyl tissue bank but exhibited no difference according to the place of residence.

CONCLUSION

Differences in clinicopathological characteristics, frequency of representative driver mutations, and gene expression profiles were not observed according to patients' region of residence in South Korea.

Unlaid Eggs: Ovarian Damage after Low-Dose Radiation

The total body irradiation of lymphomas and co-irradiation in the treatment of adjacent solid tumors can lead to a reduced ovarian function, premature ovarian insufficiency, and menopause. A small number of studies has assessed the radiation-induced damage of primordial follicles in animal models and humans. Studies are emerging that evaluate radiation-induced damage to the surrounding ovarian tissue including stromal and immune cells. We reviewed basic laboratory work to assess the current state of knowledge and to establish an experimental setting for further studies in animals and humans. The experimental approaches were mostly performed using mouse models. Most studies relied on single doses as high as 1 Gy, which is considered to cause severe damage to the ovary. Changes in the ovarian reserve were related to the primordial follicle count, providing reproducible evidence that radiation with 1 Gy leads to a significant depletion. Radiation with 0.1 Gy mostly did not show an effect on the primordial follicles. Fewer data exist on the effects of radiation on the ovarian microenvironment including theca-interstitial, immune, endothelial, and smooth muscle cells. We concluded that a mouse model would provide the most reliable model to study the effects of low-dose radiation. Furthermore, both immunohistochemistry and fluorescence-activated cell sorting (FACS) analyses were valuable to analyze not only the germ cells but also the ovarian microenvironment.

Integration of ecosystem science into radioecology: A consensus perspective

In the Fall of 2016 a workshop was held which brought together over 50 scientists from the ecological and radiological fields to discuss feasibility and challenges of reintegrating ecosystem science into radioecology. There is a growing desire to incorporate attributes of ecosystem science into radiological risk assessment and radioecological research more generally, fueled by recent advances in quantification of emergent ecosystem attributes and the desire to accurately reflect impacts of radiological stressors upon ecosystem function. This paper is a synthesis of the discussions and consensus of the workshop participant's responses to three primary questions, which were: 1) How can ecosystem science support radiological risk assessment? 2) What ecosystem level endpoints potentially could be used for radiological risk assessment? and 3) What inference strategies and associated methods would be most appropriate to assess the effects of radionuclides on ecosystem structure and function? The consensus of the participants was that ecosystem science can and should support radiological risk assessment through the incorporation of quantitative metrics that reflect ecosystem functions which are sensitive to radiological contaminants. The participants also agreed that many such endpoints exit or are thought to exit and while many are used in ecological risk assessment currently, additional data need to be collected that link the causal mechanisms of radiological exposure to these endpoints. Finally, the participants agreed that radiological risk assessments must be designed and informed by rigorous statistical frameworks capable of revealing the causal inference tying radiological exposure to the endpoints selected for measurement.

Adaptation to ionizing radiation of higher plants: From environmental radioactivity to chernobyl disaster

The purpose of this work is to highlight the effects of ionizing radiation on the genetic material in higher plants by assessing both adaptive processes as well as the evolution of plant species. The effects that the ionizing radiation has on greenery following a nuclear accident, was examined by taking the Chernobyl Nuclear Power Plant disaster as a case study. The genetic and evolutionary effects that ionizing radiation had on plants after the Chernobyl accident were highlighted. The response of biota to Chernobyl irradiation was a complex interaction among radiation dose, dose rate, temporal and spatial variation, varying radiation sensitivities of the different plants' species, and indirect effects from other events. Ionizing radiation causes water radiolysis, generating highly reactive oxygen species (ROS). ROS induce the rapid activation of detoxifying enzymes. DeoxyriboNucleic Acid (DNA) is the object of an attack by both, the hydroxyl ions and the radiation itself, thus triggering a mechanism both direct and indirect. The effects on DNA are harmful to the organism and the long-term development of the species. Dose-dependent aberrations in chromosomes are often observed after irradiation. Although multiple DNA repair mechanisms exist, double-strand breaks (DSBs or DNA-DSBs) are often subject to errors. Plants DSBs repair mechanisms mainly involve homologous and non-homologous dependent systems, the latter especially causing a loss of genetic information. Repeated ionizing radiation (acute or chronic) ensures that plants adapt, demonstrating radioresistance. An adaptive response has been suggested for this phenomenon. As a result, ionizing radiation influences the genetic structure, especially during chronic irradiation, reducing genetic variability. This reduction may be associated with the fact that particular plant species are more subject to chronic stress, confirming the adaptive theory. Therefore, the genomic effects of ionizing radiation demonstrate their likely involvement in the evolution of plant species.

The role of radiation induced oxidative stress as a regulator of radio-adaptive responses

Purpose: Various sources of radiation including radiofrequency, electromagnetic radiation (EMR), low- dose X-radiation, low-level microwave radiation and ionizing radiation (IR) are indispensable parts of modern life. In the current review, we discussed the adaptive responses of biological systems to radiation with a focus on the impacts of radiation-induced oxidative stress (RIOS) and its molecular downstream signaling pathways.Materials and methods: A comprehensive search was conducted in Web of Sciences, PubMed, Scopus, Google Scholar, Embase, and Cochrane Library. Keywords included Mesh terms of "radiation," "electromagnetic radiation," "adaptive immunity," "oxidative stress," and "immune checkpoints." Manuscripts published up until December 2019 were included.Results: RIOS induces various molecular adaptors connected with adaptive responses in radiation exposed cells. One of these adaptors includes p53 which promotes various cellular signaling pathways. RIOS also activates the intrinsic apoptotic pathway by depolarization of the mitochondrial membrane potential and activating the caspase apoptotic cascade. RIOS is also involved in radiation-induced proliferative responses through interaction with mitogen-activated protein kinases (MAPks) including p38 MAPK, ERK, and c-Jun N-terminal kinase (JNK). Protein kinase B (Akt)/phosphoinositide 3-kinase (PI3K) signaling pathway has also been reported to be involved in RIOS-induced proliferative responses. Furthermore, RIOS promotes genetic instability by introducing DNA structural and epigenetic alterations, as well as attenuating DNA repair mechanisms. Inflammatory transcription factors including macrophage migration inhibitory factor (MIF), nuclear factor κB (NF-κB), and signal transducer and activator of transcription-3 (STAT-3) paly major role in RIOS-induced inflammation.Conclusion: In conclusion, RIOS considerably contributes to radiation induced adaptive responses. Other possible molecular adaptors modulating RIOS-induced responses are yet to be divulged in future studies.

Differential radio-adaptive responses in BALB/c and C57BL/6 mice: pivotal role of calcium and nitric oxide signalling

Purpose: Our earlier studies demonstrated that transient radio-adaptive responses (RAR) in BALB/c mice were due to MAPK hyperactivation. The objective of this study was to determine the time duration of this low dose induced MAPK activation in BALB/c mice and to find out if similar adaptive responses are observed in C57BL/6 mice. Materials and methods: Mice were irradiated with 0.1 Gy priming dose (PD), 2 Gy challenge dose (CD) with an interval of 4 h (P + CD) and radiation induced immunosuppression in splenic lymphocytes was monitored as the endpoint for RAR. Results: Time kinetics following 0.1 Gy demonstrated persistence of MAPK hyperactivation till 48 h. Similar experiments in C57BL/6 mice indicated absence of RAR at 24 h following CD, in spite of MAPK activation which was also confirmed by time kinetics. Therefore, upstream activators of MAPK, viz., reactive oxygen and nitrogen species (ROS, RNS) and calcium levels were estimated. There was increased intracellular calcium (Ca²⁺) and nitric oxide (NO) in BALB/c and an increase in intracellular ROS in C57BL/6 mice 24 h after PD. Inhibition of NO and calcium chelation abrogated RAR in BALB/c mice. In vitro treatment of spleen cells with combination of NO donor and Ca²⁺ ionophore mimicked the effect of PD and induced adaptive response after 2 Gy not only in BALB/c but also in C57BL/6 mice confirming their crucial role in RAR. Conclusions: These results suggest that low dose induced differential induction of Ca²⁺ and NO signaling along with MAPK was responsible for contrasting RAR with respect to immune system of BALB/c and C57BL/6 mice. Abbreviations [³H]-TdR: ³H-methyl-thymidine; BAPTA: 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; CD: Challenge Dose; CFSE: Carboxy Fluorescein Succinamidyl Ester; on A: Concanavalin A; DAF-FM: 4-amino-5-methylamino-2',7'-difluorescein; DCF-DA: 2',7'-dichlorofluorescein diacetate; DSB: Double Strand Break; ELISA: Enzyme Linked ImmunoSorbent Assay; ERK: Extracellular signal-Regulated protein Kinase; FBS: Fetal Bovine Serum; HIF-1A: Hypoxia-Inducible Factor 1-alpha; LDR: Low Dose Radiation; MAPK: Mitogen Activated Protein Kinase; MAPKK/MKK: MAPK Kinase; MAPKKK: MAPK Kinase Kinase; NO: Nitric Oxide; NOS: Nitric Oxide Synthase; P + CD: Priming + Challenge dose; PBS: Phosphate Buffered Saline; PBST: Phosphate Buffered Saline-Tween 20; PD: Priming Dose; PI3K: Phosphatidyl Inositol 3-Kinase; PKC: Protein Kinase C; RAR: Radio Adaptive Response; RNS: Reactive Nitrogen Species; ROS: Reactive Oxygen Species; RPMI-1640: Roswell Park Memorial Institute-1640 medium; SAPK/JNK: Stress-Activated Protein Kinase/ c-Jun NH2-terminal Kinase; SEM: Standard Error of Mean; SNAP: S-nitro amino penicillamine; TP53: Tumor Protein 53; γ-H2AX: Gamma- H2A histone family member X; Th1: Type 1 helper T cell responses; Th2: Type 2 helper T cell responses.

Chronic radiation exposure as an ecological factor: Hypermethylation and genetic differentiation in irradiated Scots pine populations

Genetic and epigenetic changes were investigated in chronically irradiated Scots pine (Pinus sylvestris L.) populations from territories that were heavily contaminated by radionuclides as result of the Chernobyl Nuclear Power Plant accident. In comparison to the reference site, the genetic diversity revealed by electrophoretic mobility of AFLPs was found to be significantly higher at the radioactively contaminated areas. In addition, the genome of pine trees was significantly hypermethylated at 4 of the 7 affected sites.

Radio-adaptive response in peripheral blood lymphocytes of individuals residing in high-level natural radiation areas of Kerala in the southwest coast of India

The present study investigates whether the chronic low-dose radiation exposure induces an in vivo radio-adaptive response in individuals from high-level natural radiation areas (HLNRA) of the Kerala coast. Peripheral blood samples from 54 adult male individuals aged between 26 and 65 years were collected for the study with written informed consent. Each of the whole blood sample was divided into three, one was sham irradiated, second and third was exposed to challenging doses of 1.0 and 2.0 Gy gamma radiation, respectively. Cytokinesis-block micronucleus (CBMN) assay was employed to study the radio-adaptive response. Seventeen individuals were from normal-level natural radiation area (NLNRA ≤1.5 mGy/year) and 37 from HLNRA (> 1.5 mGy/year). Based on the annual dose received, individuals from HLNRA were further classified into low-dose group (LDG, 1.51-5.0 mGy/year, N = 19) and high-dose group (HDG >5.0 mGy/year, N = 18). Basal frequency of micronucleus (MN) was comparable across the three dose groups (NLNRA, LDG and HDG, P = 0.64). Age of the individuals showed a significant effect on the frequency of MN after challenging dose exposures. The mean frequency of MN was significantly lower in elder (>40 years) individuals from HDG of HLNRA as compared to the young (≤40 years) individuals after 1.0 Gy (P < 0.001) and 2.0 Gy (P = 0.002) of challenging doses. However, young and elder individuals within NLNRA and LDG of HLNRA showed similar frequency of MN after the challenging dose exposures. Thus, increased level of chronic low-dose radiation (>5.0 mGy/year) seems to act as a priming dose resulting in the induction of an in vivo radio-adaptive response in elder individuals of the Kerala coast.

Dose assessment in environmental radiological protection: State of the art and perspectives

Exposure to radiation is a potential hazard to humans and the environment. The Fukushima accident reminded the world of the importance of a reliable risk management system that incorporates the dose received from radiation exposures. The dose to humans from exposure to radiation can be quantified using a well-defined system; its environmental equivalent, however, is still in a developmental state. Additionally, the results of several papers published over the last decade have been criticized because of poor dosimetry. Therefore, a workshop on environmental dosimetry was organized by the STAR (Strategy for Allied Radioecology) Network of Excellence to review the state of the art in environmental dosimetry and prioritize areas of methodological and guidance development. Herein, we report the key findings from that international workshop, summarise parameters that affect the dose animals and plants receive when exposed to radiation, and identify further research needs. Current dosimetry practices for determining environmental protection are based on simple screening dose assessments using knowledge of fundamental radiation physics, source-target geometry relationships, the influence of organism shape and size, and knowledge of how radionuclide distributions in the body and in the soil profile alter dose. In screening model calculations that estimate whole-body dose to biota the shapes of organisms are simply represented as ellipsoids, while recently developed complex voxel phantom models allow organ-specific dose estimates. We identified several research and guidance development priorities for dosimetry. For external exposures, the uncertainty in dose estimates due to spatially heterogeneous distributions of radionuclide contamination is currently being evaluated. Guidance is needed on the level of dosimetry that is required when screening benchmarks are exceeded and how to report exposure in dose-effect studies, including quantification of uncertainties. Further research is needed to establish whether and how dosimetry should account for differences in tissue physiology, organism life stages, seasonal variability (in ecology, physiology and radiation field), species life span, and the proportion of a population that is actually exposed. We contend that, although major advances have recently been made in environmental radiation protection, substantive improvements are required to reduce uncertainties and increase the reliability of environmental dosimetry.

Radioactively contaminated areas: Bioindicator species and biomarkers of effect in an early warning scheme for a preliminary risk assessment

Concerns about the impacts on public health and on the natural environment have been raised regarding the full range of operational activities related to uranium mining and the rest of the nuclear fuel cycle (including nuclear accidents), nuclear tests and depleted uranium from military ammunitions. However, the environmental impacts of such activities, as well as their ecotoxicological/toxicological profile, are still poorly studied. Herein, it is discussed if organisms can be used as bioindicators of human health effects, posed by lifetime exposure to radioactively contaminated areas. To do so, information was gathered from several studies performed on vertebrates, invertebrate species and humans, living in these contaminated areas. The retrieved information was compared, to determine which are the most used bioindicators and biomarkers and also the similarities between human and non-human biota responses. The data evaluated are used to support the proposal for an early warning scheme, based on bioindicator species and on the most sensitive and commonly shared biomarkers, to perform a screening evaluation of radioactively contaminated sites. This scheme could be used to support decision-making for a deeper evaluation of risks to human health, making it possible to screen a large number of areas, without disturbing and alarming local populations.

Gamma radiation at a human relevant low dose rate is genotoxic in mice

Even today, 70 years after Hiroshima and accidents like in Chernobyl and Fukushima, we still have limited knowledge about the health effects of low dose rate (LDR) radiation. Despite their human relevance after occupational and accidental exposure, only few animal studies on the genotoxic effects of chronic LDR radiation have been performed. Selenium (Se) is involved in oxidative stress defence, protecting DNA and other biomolecules from reactive oxygen species (ROS). It is hypothesised that Se deficiency, as it occurs in several parts of the world, may aggravate harmful effects of ROS-inducing stressors such as ionising radiation. We performed a study in the newly established LDR-facility Figaro on the combined effects of Se deprivation and LDR γ exposure in DNA repair knockout mice (Ogg1^−/−) and control animals (Ogg1^+/−). Genotoxic effects were seen after continuous radiation (1.4 mGy/h) for 45 days. Chromosomal damage (micronucleus), phenotypic mutations (Pig-a gene mutation of RBC^CD24−) and DNA lesions (single strand breaks/alkali labile sites) were significantly increased in blood cells of irradiated animals, covering three types of genotoxic activity. This study demonstrates that chronic LDR γ radiation is genotoxic in an exposure scenario realistic for humans, supporting the hypothesis that even LDR γ radiation may induce cancer.

Effects of different gamma exposure regimes on reproduction in the earthworm Eisenia fetida (Oligochaeta)

Ecological risk assessment of ionising radiation requires knowledge about the responses of individuals and populations to chronic exposures, including situations when exposure levels change over time. The present study investigated processes such as recovery and the adaptive response with respect to reproduction endpoints in the earthworm Eisenia fetida exposed to (60)Co γ-radiation. Furthermore, a crossed experiment was performed to investigate the influence of F0 parental and F1 embryonic irradiation history on the response of irradiated or non-irradiated F1 offspring. Recovery: The sterility induced by sub-chronic exposure at 17 m Gy/h (accumulated dose: 25 Gy) was temporary, and 8 weeks after irradiation the worms had regained their reproductive capacity (number of viable offspring produced per adult per week). Adaptive response: Adult worms were continuously exposed at a low priming dose rate of 0.14 mGy/h for 12 weeks (accumulated dose: 0.24 Gy), followed by 14 weeks exposure at a challenge dose rate of 11 mGy/h. The results suggest a lack of adaptive response, since there were no significant differences in the effects on reproduction capacity between the primed and the unprimed groups after challenge doses ranging from 7.6 to 27 Gy. Crossed experiment: The effects of exposure at 11 mGy/h for 21 weeks on growth, sexual maturation and reproduction of offspring, derived either from parent worms and cocoons both exposed at 11 mGy/h, or from non-irradiated parents and cocoons (total accumulated dose 44 and 38 Gy, respectively) were compared. There were no significant differences between the two exposed offspring groups for any of the endpoints. The reproduction capacity was very low for both groups compared to the controls, but the reproduction seemed to be maintained at the reduced level, which could indicate acclimatisation or stabilisation. Finally, parental and embryonic exposures at 11 mGy/h did not affect reproduction in the F1 offspring as adults.

The effects of environmental low-dose irradiation on tolerance to chemotherapeutic agents

The nuclear disaster at Chernobyl, Ukraine, in April of 1986 continues to impact the environment on many different levels. Studies of epidemiological, environmental, and genetic impacts have been prolific since the accident, revealing interesting results concerning the effects of radiation. The long-tailed field mouse, Apodemus flavicollis, was collected from distinct localities near the Chernobyl site and evaluated based on in vivo responses to the current clinically employed chemotherapeutic agents bleomycin (BLM) and vinblastine (VBL), as well as the immune modulator lipopolysaccharide (LPS). Maximum tolerable doses of three different cancer drugs were administered to the rodents from three different lifestyles: native mice living and reproducing in a radioactive environment, native mice living and reproducing in an uncontaminated region, and laboratory-reared mice (Mus musculus BALB/c) with a known sensitivity to the chemical agents tested. The endpoints employed include micronucleus formation, immune cell induction, differential gene expression, and chemotherapeutic side effects such as lethargy and weight loss. In accordance with the well-studied phenomenon termed radio-adaptation, we observed varied tolerance to chemotherapeutic treatment dependent on history of ionizing radiation exposure. The results of the present study demonstrate a differential response to chemotherapeutic treatment with respect to previous levels of radiation exposure, suggesting a potential benefit associated with low-dose radiation exposure. Data reported herein could have a profound impact on the development of novel cancer treatments involving low-dose ionizing radiation.

Radiation worker protection by exposure scheduling

The discovery of the protective adaptive response of cells to a low dose of radiation suggests applications to radiation worker/first responder protection. Its use in cancer radiotherapy has been discussed in a separate publication. This paper describes simple changes in scheduling that can make use of these beneficial adaptive effects for protection. No increase in total exposure is necessary, only a simple change in the timing of radiation exposure. A low dose of radiation at a sufficient dose rate will trigger the adaptive response. This in turn will offer a considerable protection against the damage from a subsequent high dose. A simple scenario is discussed as well as a brief review of the experimental basis of the adaptive response.

Low-dose pretreatment for radiation therapy

In radiotherapy, a large radiation dose must be applied to both cancer and neighboring healthy cells. Recent experiments have shown that a low dose of ionizing radiation turns on certain protective mechanisms that allow a cell to better survive a subsequent high dose of radiation. This adaptive response can have important and positive consequences for radiotherapy. This paper describes a simple change in treatment procedures to make use of these beneficial effects. A low dose applied only to the healthy cells will probably produce some damage. However, it will also start the adaptive response which will yield increased protection when the large therapeutic dose is applied. The resultant immediate damage will be thereby reduced as well as the probability that the high dose therapy itself will induce a subsequent secondary cancer. After a brief historical review, the effects of a low radiation dose on a canine cancer cell line will be discussed as well as trials of the suggested pre-dose therapy on canine cancer patients undergoing standard radiation therapy.