Exposure to Low Doses of Ionizing Radiation: Is the Linear No-Threshold Model Valid?

2014 ◽  
Author(s):  
Luca Giannoni ◽  
Marino Mazzini
Keyword(s):  
Risk Assessment ◽  
Ionizing Radiation ◽  
Low Dose ◽  
Threshold Dose ◽  
High Dose ◽  
Low Doses ◽  
Repair Capacity ◽  
Nobel Lecture ◽  
Starting Point ◽  
Lnt Model

The risk assessment for population’s exposures to low doses and low dose-rates of ionizing radiation is still subject to clear uncertainties. The issue has outstanding societal importance in relation to radiologic occupational safety, medical applications of radiation, effects of the natural background radioactivity and the future of nuclear power, due to its particular influence on the public acceptance of this form of energy. This review article analyzes, in a critical, historical and bibliographical manner, the worldwide accepted hypothesis of linearity without a threshold dose (LNT model). As well known, it rejects, from its first proposal in 1946 by American geneticist and Nobel laureate Hermann J. Muller, the concept of zero-risk for exposures to any dose level of ionizing radiation. The starting point is the dose-effects relationship provided by this model and related risk’s excess graphic curve. The biological and physical motivations for the linearity assumption are argued and challenged by the explanation of human body’s natural defense mechanisms and its repair capacity of the radiation damage. Furthermore, the historical and political truthfulness of the LNT model is also contested by the review of a recent investigation by Prof. Edward Calabrese, regarding the lack of scientific sources behind Muller’s Nobel Prize Lecture. Calabrese’s inquiry demonstrates that Muller, at the moment of his declaration on LNT model’s validity, had experimental proofs contradicting his conclusions about the unacceptability of a threshold dose. This finding is of historical importance since Muller’s Nobel Lecture is a turning point in the acceptance of the linearity model in risk assessment by the major regulatory agencies till today. Finally, the results of many epidemiological and statistical studies are shown specifically. They give further evidences concerning the inapplicability of the LNT model and its overestimation of the risk for various cases of exposures to low doses of ionizing radiation in different fields. By that, hormesis model is also discussed, with its assumption of possible benefits for the organism following low dose exposures: a dose-response model characterized by low-dose stimulation and high-dose inhibition, which has been frequently observed in the aforementioned studies. The argumentations and the experimental evidences provided here challenge the validity of the LNT model. We contest the fact that its establishment is principally based on a cautionary philosophy on nuclear public safety, rather than on actual scientific comprehension of the phenomenon. As such, it implies an exaggerated conception of the radiological hazard. In particular, this article calls attention to the need for a deeper understanding of the biological impact of low doses of ionizing radiation and the development of further specific and exhaustive researches.

scholarly journals Biodosimetry of Low Dose Ionizing Radiation Using DNA Repair Foci in Human Lymphocytes

Genes ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 58 ◽  
Author(s):  
Lukáš Jakl ◽  
Eva Marková ◽  
Lucia Koláriková ◽  
Igor Belyaev
Keyword(s):  
Dna Repair ◽  
Ionizing Radiation ◽  
Low Dose ◽  
Time Window ◽  
Human Lymphocytes ◽  
High Dose ◽  
Low Doses ◽  
Significant Difference ◽  
Kinetics Of ◽  
Higher Doses

Purpose: Ionizing radiation induced foci (IRIF) known also as DNA repair foci represent most sensitive endpoint for assessing DNA double strand breaks (DSB). IRIF are usually visualized and enumerated with the aid of fluorescence microscopy using antibodies to γH2AX and 53BP1. This study analyzed effect of low dose ionizing radiation on residual IRIF in human lymphocytes to the aim of potential biodosimetry and possible extrapolation of high-dose γH2AX/53BP1 effects to low doses and compared kinetics of DSB and IRIF. We also analyzed whether DNaseI, which is used for reducing of clumps, affects the IRIF level. Materials and Methods: The cryopreserved human lymphocytes from umbilical cord blood (UCB) were thawed with/without DNaseI, γ-irradiated at doses of 0, 5, 10, and 50 cGy and γH2AX/53BP1 foci were analyzed 30 min, 2 h, and 22 h post-irradiation using appropriate antibodies. We also analyzed kinetics of DSB using PFGE. Results: No significant difference was observed between data obtained by γH2AX foci evaluation in cells that were irradiated by low doses and data obtained by extrapolation from higher doses. Residual 53BP1 foci induced by low doses significantly outreached the data extrapolated from irradiation by higher doses. 53BP1 foci induced by low dose-radiation remain longer at DSB loci than foci induced by higher doses. There was no significant effect of DNaseI on DNA repair foci. Conclusions: Primary γH2AX, 53BP1 foci and their co-localization represent valuable markers for biodosimetry of low doses, but their usefulness is limited by short time window. Residual γH2AX and 53BP1 foci are more useful markers for biodosimetry in vitro. Effects of low doses can be extrapolated from high dose using γH2AX residual foci while γH2AX/53BP1 foci are valuable markers for evaluation of initial DSB induced by ionizing radiation. Residual IRIF induced by low doses persist longer time than those induced by higher doses.

scholarly journals Until There Is a Resolution of the Pro-LNT/Anti-LNT Debate, We Should Head Toward a More Sensible Graded Approach for Protection From Low-Dose Ionizing Radiation

Dose-Response ◽  
2020 ◽  
Vol 18 (2) ◽  
pp. 155932582092165 ◽  
Author(s):  
Pamela J. Sykes
Keyword(s):  
Ionizing Radiation ◽  
Animal Studies ◽  
Low Dose ◽  
The Other ◽  
Low Doses ◽  
Current Regulation ◽  
The Public ◽  
Small Risk ◽  
Public Workers ◽  
Lnt Model

Current regulation of ionizing radiation is based on the linear no-threshold (LNT) model where any radiation dose increases cancer risk and is independent of dose rate, resulting in large amounts of time and money being spent protecting from extremely small radiation exposures and hence extremely small risk. There are animal studies which demonstrate that LNT is incorrect at low doses, supporting a threshold or hormesis model and thus indicating that there is no need to protect from very low doses. This has led to a sometimes bitter debate between pro-LNT and anti-LNT camps, and the debate has been at a stalemate for some time. This commentary is not aimed at taking either side of the debate. It is likely that the public, workers, and the environment are adequately protected under current regulation, which is the most important outcome. Until those on one side of the debate can convince the other, it would be sensible to move forward toward a graded (risk-based) approach to regulation, where the stringency of control is commensurate with the risk, resulting hopefully in more sensible practical thresholds. This approach is gradually being put forward by international radiation protection advisory bodies.

Hormesis, resveratrol and plant-derived polyphenols: some comments

2011 ◽  
Vol 30 (12) ◽  
pp. 2027-2030 ◽  
Author(s):  
Salvatore Chirumbolo
Keyword(s):  
Risk Assessment ◽  
Dose Response ◽  
Adaptive Response ◽  
Low Dose ◽  
High Dose ◽  
Low Doses ◽  
General Behaviour

Hormesis is a dose–response phenomenon, usually present in plants and animals, characterized by a low-dose stimulation and high-dose inhibition, often resulting in typical U-shaped or J-shaped curves. Hormesis has become an interesting model for toxicology and risk assessment, as it has been described for several nature-derived phytochemicals but also because this adaptive response to stressors might hide an underlying more general behaviour of cell towards low doses.

scholarly journals Ripk3 Signaling Regulates Hematopoietic Stem Cell Number and Function during Stress

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 3714-3714
Author(s):  
Lei Zhang ◽  
Huacheng Luo ◽  
Jing Li ◽  
Hong-Min Ni ◽  
Mark Sellin ◽  
...  
Keyword(s):  
Inflammatory Cytokines ◽  
Low Dose ◽  
Conflicts Of Interest ◽  
Lymphoblastic Leukemia ◽  
High Dose ◽  
Low Doses ◽  
Hematopoietic Stem ◽  
Increased Risk ◽  
Leukemia Development ◽  
Serial Transplantation

Background: Among all tissues, bone marrow (BM) is the most sensitive tissue to ionizing radiation (IR)-induced acute tissue damage (ATD) and chronic long-term residual damage (LT-RD). BM failure and a significant reduction in blood cells (pancytopenia) often occurs within days after exposure to IR due to the massive death of proliferative hematopoietic progenitor cells (HPCs). However, due to their quiescent cell cycle status and reduced fidelity of DNA repair feature, many hematopoietic stem cells (HSCs) cannot fully eliminate such damage and enter senescence; this results in LT-RD. Abnormal dysplastic hematopoiesis is the most common LT-RD in most victims of IR, followed by an increased risk of leukemia/lymphoma development. Thus IR exposure is an established cause of BM failure and leukemia. A significant increase in the production of inflammatory cytokines is induced by IR which contributes to the pathogenesis of both ATD and LT-RD. Such inflammatory cytokines induce the activation of Ripk3-Mlkl-mediated necroptotic signaling in HSCs. However, the role of Ripk3-Mlkl signaling in IR-induced damage has not studied. Experimental procedures: The self-renewal capacity of HSCs among Ripk3-/-, Mlkl-/- and WT mice were examined and compared by serial transplantation assay. The phenotypes of ATD and LT-RD induced by different dosages of IR were compared among Ripk3-/-, Mlkl-/- and WT mice. The mechanism by which Ripk3 signaling prevents IR-induced leukemia development was studied. Results: Ripk3-Mlkl signaling is not required for hematopoiesis during homeostatic condition. However, during serial transplantation, inactivation of such signaling prevents stress-induced loss of HSCs. Interestingly, Ripk3 signaling also induces an Mlkl-independent ROS-p38-p16-mediated senescence in HSCs. Thus Ripk3-/- HSCs showed better competitive hematopoietic ability compared to Mlkl-/- and WT HSCs during serial transplantation. A sub-lethal dosage of IR (6Gy) induces Ripk3-dependent NF-κB activation and pro-survival gene expression in HSCs, which is necessary for the survival of damaged HSCs. After 6Gy IR, although DNA damage is repaired in most HSCs within 2 days, a proportion of HSCs in WT and Mlkl-/- mice fail to fully repair the damage and undergo p53-p21-dependent senescence. However such cells in Ripk3-/- mice die from apoptosis. Thus the remaining HSCs in Ripk3-/- mice should be functionally normal, while a proportion of the remaining HSCs in Mlkl-/- and WT mice remain damaged but senescent, all as demonstrated by competitive hematopoietic reconstitution assay. Multiple low-doses of IR (1.75Gy once week × 4) induce HSC exhaustion in WT mice but not in Ripk3-/- and Mlkl-/- mice. Interestingly, almost all Ripk3-/- mice develop acute lymphoblastic leukemia within 200 days after such low dose IR, while 45% of WT and 60% of Mlkl-/- mice develop thymomas within 360 days (see Figure). Mechanistically, such low-dose IR stimulates chronic inflammatory cytokine production. Such cytokines induce Ripk3-Mlkl-mediated necroptosis in response to HSC exhaustion observed in WT mice. These cytokines also induce Ripk3-ROS-p38-p16-mediated senescence in response to impaired HSC functioning observed in both WT and Mlkl-/- mice. In Ripk3-/- mice, due to the lack of both necroptotic and senescent signaling, mutant HSCs accumulate and leukemia development is accelerated. Conclusion: Ripk3 signaling plays distinct roles in HSCs in response to different doses of IR. High-dose IR induces Ripk3-dependent NF-κB/survival signaling, which is required for the survival of HSCs which fail to repair the damage. Thus temporal inhibition of Ripk3-NF-κB signaling might help to remove the damaged HSCs thus preventing the occurrence of LT-RD. However multiple low-doses of IR induces Ripk3 activation in HSCs which represses leukemia development by inducing both ROS-p38-p16-mediated senescence and Ripk3-Mlkl-mediated necroptosis. Induced activation of Mlkl-necroptosis might help to repress leukemia development by removing damaged HSCs. Disclosures No relevant conflicts of interest to declare.

scholarly journals Phosphoprotein profiles of candidate markers for early cellular responses to low-dose γ-radiation in normal human fibroblast cells

2017 ◽  
Vol 58 (3) ◽  
pp. 329-340 ◽  
Author(s):  
Ji-Hye Yim ◽  
Jung Mi Yun ◽  
Ji Young Kim ◽  
In Kyung Lee ◽  
Seon Young Nam ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Human Fibroblast ◽  
Low Dose ◽  
High Dose ◽  
Normal Human Fibroblast ◽  
Low Dose Radiation ◽  
Γ Radiation ◽  
Normal Human ◽  
Dose Radiation ◽  
In Cells

Abstract Ionizing radiation causes biological damage that leads to severe health effects. However, the effects and subsequent health implications caused by exposure to low-dose radiation are unclear. The objective of this study was to determine phosphoprotein profiles in normal human fibroblast cell lines in response to low-dose and high-dose γ-radiation. We examined the cellular response in MRC-5 cells 0.5 h after exposure to 0.05 or 2 Gy. Using 1318 antibodies by antibody array, we observed ≥1.3-fold increases in a number of identified phosphoproteins in cells subjected to low-dose (0.05 Gy) and high-dose (2 Gy) radiation, suggesting that both radiation levels stimulate distinct signaling pathways. Low-dose radiation induced nucleic acid–binding transcription factor activity, developmental processes, and multicellular organismal processes. By contrast, high-dose radiation stimulated apoptotic processes, cell adhesion and regulation, and cellular organization and biogenesis. We found that phospho-BTK (Tyr550) and phospho-Gab2 (Tyr643) protein levels at 0.5 h after treatment were higher in cells subjected to low-dose radiation than in cells treated with high-dose radiation. We also determined that the phosphorylation of BTK and Gab2 in response to ionizing radiation was regulated in a dose-dependent manner in MRC-5 and NHDF cells. Our study provides new insights into the biological responses to low-dose γ-radiation and identifies potential candidate markers for monitoring exposure to low-dose ionizing radiation.

Abstract 528: Dose- And Salt-dependency Of Angiogenesis Inhibition-induced Blood Pressure Rise And Renal Toxicity

Hypertension ◽  
2014 ◽  
Vol 64 (suppl_1) ◽  
Author(s):  
Stephanie Lankhorst ◽  
Mariëtte H Kappers ◽  
Stefan Sleijfer ◽  
A H Danser ◽  
Anton H van den Meiracker
Keyword(s):  
Low Dose ◽  
Renal Toxicity ◽  
Pressure Rise ◽  
High Salt ◽  
High Dose ◽  
Low Doses ◽  
High Salt Diet ◽  
Salt Diet ◽  
Angiogenesis Inhibition ◽  
Cystatine C

Angiogenesis inhibition with the VEGF inhibitor sunitinib is an established anti-cancer therapy, inducing hypertension and nephrotoxicity. We explored the dose- and salt-dependency of these side effects. In male WKY rats, mean arterial pressure (MAP) was monitored telemetrically during oral treatment with a high (27.5 mg/kg.day, n=14), an intermediate (14 mg/kg.day, n=6) and low dose (7 mg/kg.day, n=6) of sunitinib or vehicle (n=8) after normal salt diet for 2 weeks. The low dose-model was also combined with a high salt diet (8% NaCl and saline water). Eight days after administration rats were sacrificed and blood and 24h urine samples collected for biochemical measurements. With the high dose of sunitinib, MAP increased from 94.7±0.9 mmHg to 125.8±1.5 mmHg (Δ31.1±0.9 mmHg, p<0.001). The intermediate and low doses induced MAP rises of 24.3±2.7 mmHg (p<0.001) and 13.4±3.3 mmHg (p<0.001), respectively. The low dose of sunitinib with high salt, induced a MAP rise of 43.5±2.2 mmHg (p<0.001 compared to normal salt). With the high dose, circulating ET-1 increased from 0.6±0.1 pg/ml to 1.6±0.2 pg/ml (p<0.01) and serum cystatine-C from 4.5±0.1 mg/L to 6.6±0.3 mg/L (p<0.001). Comparable increases in circulating ET-1 were seen with the intermediate and low doses, whereas serum cystatine-C did increase with the intermediate dose (to 6.3±0.1 mg/L, p0.05). Serum cystatine-C levels with low and high salt were identical. With the high dose of sunitinib, proteinuria increased from 7.5±1.3 to 33.3±4.8 mg/day (p<0.05). The rise in proteinuria was attenuated with the intermediate (16.2±2.1 mg/day, p<0.01) and low dose (19.9±3.3 mg/day, p<0.01), but increased to 40.4±30.1 mg/day (p>0.05) with high salt. Angiogenesis inhibition-induced hypertension and nephrotoxicity are dose-dependent with a lower threshold for the rise in BP than for renal toxicity. The BP rise observed with the low dose of sunitinib observed in normotensive rats is comparable to the sunitinib-induced BP rise observed in patients and clearly is salt-sensitive. Since cystatine-C levels during normal and high salt diet were comparable, the BP rise during high salt seems independent of renal dysfunction.

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