A comparative study on the dose-effect of low-dose radiation based on microdosimetric analysis and single-cell sequencing technology

The biological mechanisms triggered by low-dose exposure still need to be explored in depth. In this study, the potential mechanisms of low-dose radiation when irradiating the BEAS-2B cell lines with a Cs-137 gamma-ray source were investigated through simulations and experiments. Monolayer cell population models were constructed for simulating and analyzing distributions of nucleus-specific energy within cell populations combined with the Monte Carlo method and microdosimetric analysis. Furthermore, the 10 × Genomics single-cell sequencing technology was employed to capture the heterogeneity of individual cell responses to low-dose radiation in the same irradiated sample. The numerical uncertainties can be found both in the specific energy distribution in microdosimetry and in differential gene expressions in radiation cytogenetics. Subsequently, the distribution of nucleus-specific energy was compared with the distribution of differential gene expressions to guide the selection of differential genes bioinformatics analysis. Dose inhomogeneity is pronounced at low doses, where an increase in dose corresponds to a decrease in the dispersion of cellular-specific energy distribution. Multiple screening of differential genes by microdosimetric features and statistical analysis indicate a number of potential pathways induced by low-dose exposure. It also provides a novel perspective on the selection of sensitive biomarkers that respond to low-dose radiation.

Role of TLR4 signaling pathway in the mitigation of damaged lung by low-dose gamma irradiation

Organisms frequently suffer negative effects from large doses of ionizing radiation. However, radiation is not as hazardous at lower doses as was once believed. The current study aims to evaluate the possible radio-adaptive effect induced by low-dose radiation (LDR) in modulating high-dose radiation (HDR) and N-nitrosodiethylamine (NDEA)-induced lung injury in male albino rats. Sixty-four male rats were randomly divided into four groups: Group 1 (control): normal rats; Group 2 (D): rats given NDEA in drinking water; Group 3 (DR): rats administered with NDEA then exposed to fractionated HDR; and Group 4 (DRL): rats administered with NDEA then exposed to LDR + HDR. In the next stage, malondialdehyde (MDA), glutathione reduced (GSH), catalase (CAT), and superoxide dismutase (SOD) levels in the lung tissues were measured. Furthermore, the enzyme-linked immunoassay analysis technique was performed to assess the Toll-like receptor 4 (TLR4), interleukin-1 receptor-associated kinase 4 (IRAK4), and mitogen-activated protein kinases (MAPK) expression levels. Histopathological and DNA fragmentation analyses in lung tissue, in addition to hematological and apoptosis analyses of the blood samples, were also conducted. Results demonstrated a significant increase in antioxidant defense and a reduction in MDA levels were observed in LDR-treated animals compared to the D and DR groups. Additionally, exposure to LDR decreased TLR4, IRAK4, and MAPK levels, decreased apoptosis, and restored all the alterations in the histopathological, hematological parameters, and DNA fragmentation, indicating its protective effects on the lung when compared with untreated rats. Taken together, LDR shows protective action against the negative effects of subsequent HDR and NDEA. This impact may be attributable to the adaptive response induced by LDR, which decreases DNA damage in lung tissue and activates the antioxidative, antiapoptotic, and anti-inflammatory systems in the affected animals, enabling them to withstand the following HDR exposure.

Chrysin Encapsulated Copper Nanoparticles with Low Dose of Gamma Radiation Elicit Tumor Cell Death Through p38 MAPK/NF-κB Pathways

Improving radiation effect on tumor cells using radiosensitizers is gaining traction for improving chemoradiotherapy. This study aimed to evaluate copper nanoparticles (CuNPs) synthesized using chrysin as radiosensitizer with γ-radiation on biochemical and histopathological approaches in mice bearing Ehrlich solid tumor. CuNPs were characterized with irregular round sharp shape with size range of 21.19-70.79 nm and plasmon absorption at 273 nm. In vitro study on MCF-7 cells detected cytotoxic effect of CuNPs with IC50 of 57.2 ± 3.1 μg. In vivo study was performed on mice transplanted with Ehrlich solid tumor (EC). Mice were injected with CuNPs (0.67 mg/kg body weight) and/or exposed to low dose of gamma radiation (0.5 Gy). EC mice exposed to combined treatment of CuNPs and radiation showed a marked reduction in tumor volume, ALT and CAT, creatinine, calcium, and GSH, along with elevation in MDA, caspase-3 in parallel with inhibition of NF-κB, p38 MAPK, and cyclin D1 gene expression. Comparing histopathological findings of treatment groups ends that combined treatment was of higher efficacy, showing tumor tissue regression and increase in apoptotic cells. In conclusion, CuNPs with a low dose of gamma radiation showed more powerful ability for tumor suppression via promoting oxidative state, stimulating apoptosis, and inhibiting proliferation pathway through p38MAPK/NF-κB and cyclinD1.

Accelerated subsequent lung cancer after post-operative radiotherapy for breast cancer

BACKGROUND

Post-operative whole breast radiotherapy for breast cancer (BC) may increase the risk of subsequent lung cancer (LC). The impact of radiotherapy intensification (boost) has not been specifically explored in this context. We investigated the role of radiation modalities on the development of subsequent LC among our patients treated by radiotherapy for localized BC.

METHODS

All patients with a diagnosis of LC between 2000 and 2020 with a history of prior localized BC treated by surgery and post-operative radiotherapy were retrospectively reviewed. Primary endpoint was time to first diagnosis of LC after BC treatment with radiotherapy (RT).

RESULTS

From 98 patients who developed subsequent LC after primary BC treated with post-operative RT, 38% of patients (n = 37) received an additional RT boost, and 46% (n = 45) received hormonal treatment post radiation. A total of 61% (n = 60) were smokers. With regards to LC characteristics, adenocarcinoma was the most frequent histology (68%, n = 66); 36% (n = 35) harbored at least 1 molecular alteration, 57% (n = 20) of them being amenable to targeted therapy. Median time to first diagnosis of LC was 6 years [1.7-28.4 yrs] in the whole cohort. In the subgroup of patients treated with boost this time was reduced to 4 years [1.8-20.8 years] compared to 8 years for patients without boost [1.7-28.4 yrs] (p = 0.007). Boost, smoking usage, endocrine therapy, and age <50 yrs old at BC radiation remained independent factors associated with shorter time to first diagnosis of LC after BC treatment.

DISCUSSION

We report for the first time the potential impact of boost -part of BC radiation treatment- for BC on the risk of subsequent LC. The impact of low dose radiation on lung parenchyma could explain this phenomenon, but the underlying physiopathology is still under investigation. This work highlights the need for clinicians to identify patients at risk of developing faster subsequent thoracic malignancy after BC radiation, for implementing personalized surveillance.

Concerted regulation of OPG/RANKL/ NF‑κB/MMP-13 trajectories contribute to ameliorative capability of prodigiosin and/or low dose γ-radiation against adjuvant- induced arthritis in rats

BACKGROUND

Prodigiosin (PDG) is a microbial red dye with antioxidant and anti-inflammatory properties, although its effect on rheumatoid arthritis (RA) remains uncertain. Also, multiple doses of low dose γ- radiation (LDR) have been observed to be as a successful intervention for RA. Thus, the purpose of this study was to investigate the ameliorative potential of PDG and/or LDR on adjuvant-induced arthritis (AIA) in rats.

METHODS

The anti-inflammatory and anti-arthritic effects of PDG and/or LDR were examined in vitro and in vivo, respectively. In the AIA model, the arthritic indexes, paw swelling degrees, body weight gain, and histopathological assessment in AIA rats were assayed. The impact of PDG (200 µg/kg; p.o) and/or LDR (0.5 Gy) on the levels of pro- and anti-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-18, IL-17A, and IL-10) as well as the regulation of osteoprotegrin (OPG)/ receptor activator of nuclear factor κB ligand (RANKL)/ nuclear factor-κB (NF-κB)/MMP-13 pathways was determined. Methotrexate (MTX; 0.05 mg/kg; twice/week, i.p) was administered concurrently as a standard anti-arthritic drug.

RESULTS

PDG and/or LDR markedly diminished the arthritic indexes, paw edema, weigh loss in AIA rats, alleviated the pathological alterations in joints, reduced the levels of pro-inflammatory cytokines IL-1β, TNF-α, IL-6, IL-18, IL-17A, and RANKL in serum and synovial tissues, while increasing anti-inflammatory cytokines IL-10 and OPG levels. Moreover, PDG and/or LDR down-regulated the expression of RANKL, NF-κBp65, MMP13, caspase-3, and decreased the RANKL/OPG ratio, whereas OPG and collagen II were enhanced in synovial tissues.

CONCLUSION

PDG and/or LDR exhibited obvious anti-RA activity on AIA.

Biological and cellular responses of humans to high-level natural radiation: A clarion call for a fresh perspective on the linear no-threshold paradigm

There remains considerable uncertainty in obtaining risk estimates of adverse health outcomes of chronic low-dose radiation. In the absence of reliable direct data, extrapolation through the linear no-threshold (LNT) hypothesis forms the cardinal tenet of all risk assessments for low doses (≤ 100 mGy) and for the radiation protection principle of As Low As Reasonably Achievable (ALARA). However, as recent evidences demonstrate, LNT assumptions do not appropriately reflect the biology of the cell at the low-dose end of the dose-response curve. In this regard, human populations living in high-level natural radiation areas (HLNRA) of the world can provide valuable insights into the biological and cellular effects of chronic radiation to facilitate improved precision of the dose-response relationship at low doses. Here, data obtained over decades of epidemiological and radiobiological studies on HLNRA populations is summarized. These studies do not show any evidence of unfavourable health effects or adverse cellular effects that can be correlated with high-level natural radiation. Contrary to the assumptions of LNT, no excess cancer risks or untoward pregnancy outcomes have been found to be associated with cumulative radiation dose or in-utero exposures. Molecular biology-driven studies demonstrate that chronic low-dose activates several cellular defence mechanisms that help cells to sense, recover, survive, and adapt to radiation stress. These mechanisms include stress-response signaling, DNA repair, immune alterations and most importantly, the radiation-induced adaptive response. The HLNRA data is consistent with the new evolving paradigms of low-dose radiobiology and can help develop the theoretical framework of an alternate dose-response model. A rational integration of radiobiology with epidemiology data is imperative to reduce uncertainties in predicting the potential health risks of chronic low doses of radiation.

Low and high doses of ionizing radiation evoke discrete global (phospho)proteome responses

BACKGROUND

Although cancer risk is assumed to be linear with ionizing radiation (IR) dose, it is unclear to what extent low doses (LD) of IR from medical and occupational exposures pose a cancer risk for humans. Improved mechanistic understanding of the signaling responses to LD may help to clarify this uncertainty. Here, we performed quantitative mass spectrometry-based proteomics and phosphoproteomics experiments, using mouse embryonic stem cells, at 0.5 h and 4 h after exposure to LD (0.1 Gy) and high doses (HD; 1 Gy) of IR.

RESULTS

The proteome remained relatively stable (29; 0.5% proteins responded), whereas the phosphoproteome changed dynamically (819; 7% phosphosites changed) upon irradiation. Dose-dependent alterations of 25 IR-responsive proteins were identified, with only four in common between LD and HD. Mitochondrial metabolic proteins and pathways responded to LD, whereas transporter proteins and mitochondrial uncoupling pathways responded to HD. Congruently, mitochondrial respiration increased after LD exposure but decreased after HD exposure. While the bulk of the phosphoproteome response to LD (76%) occurred already at 0.5 h, an equivalent proportion of the phosphosites responded to HD at both time points. Motif, kinome/phosphatome, kinase-substrate, and pathway analyses revealed a robust DNA damage response (DDR) activation after HD exposure but not after LD exposure. Instead, LD-irradiation induced (de)phosphorylation of kinases, kinase-substrates and phosphatases that predominantly respond to reactive oxygen species (ROS) production.

CONCLUSION

Our analyses identify discrete global proteome and phosphoproteome responses after LD and HD, uncovering novel proteins and protein (de)phosphorylation events involved in the dose-dependent ionizing radiation responses.

Low dose radiation therapy attenuates ACE2 depression and inflammatory cytokines induction by COVID-19 viral spike protein in human bronchial epithelial cells

Purpose: Low-dose radiation therapy (LDRT) is an evidence-based anti-inflammatory treatment. In anti-COVID-19, our study suggests that low to moderate dose radiation of < 1.5 Gy can inhibit the induction of inflammatory cytokine and attenuate the ACE2 depression induced by spike protein in human bronchial epithelial cells in COVID-19 infection. Our study provided further mechanistic evidence to support LDRT as a cost-effective treatment for COVID-19 to relieve the severe inflammatory reaction and lung injury. Methods and materials: A cellular model was created by treating human bronchial epithelial cells (BEP2D) with SARS-CoV-2 spike protein. We used the qRT-PCR and ELISA analysis to identify the production of inflammatory cytokines. The BEP2D control cells and the spike-treated cells were irradiated using a single low to moderate dose radiation of 0.5 Gy, 1 Gy, and 1.5 Gy. The inflammatory cytokines and ACE2 expression were detected at different time points. Results: The soluble SARS-CoV-2 spike protein stimulated the formation of inflammatory cytokines IL-6 and TNF-α while reducing the ACE2 protein expression in human bronchial epithelial cells. A single low to moderate dose exposure of 0.5 Gy, 1 Gy, and 1.5 Gy could attenuate the IL-6 and TNF-α induction and rescue the depression of ACE2 by spike protein. Moreover, the spike protein increased the proteolytic degradation of ACE2 protein by promoting NEDD4-mediated ubiquitination of ACE2. Conclusions: The low-dose radiation can attenuate ACE2 depression and inflammatory response produced in the targeted human bronchial epithelial cells by spike protein. This coordinating effect of LDRT may relieve the severe inflammatory reaction and lung injury in COVID-19 patients.

Low dose radiation mechanisms: The certainty of uncertainty

This paper reviews the current understanding of low dose radiobiology, and how it has evolved from classical target theory. It highlights the uncertainty around low dose effects, which is due in part to the complexity of "context" surrounding the ultimate expression of biological effects following low dose exposure. The paper makes special reference to low dose non-targeted effects which, are currently ignored in radiation protection and population level risk assessment, because it is unclear what they mean for risk. The view of the authors is that this "lack of clarity" about what the effects mean is precisely the point. It indicates the uncertainty of outcomes after a given exposure. The uncertainty stems from multiple outcome options resulting from the intrinsic uncertainty of the stochastic interaction of low dose radiation with matter. This uncertainty should be embraced rather than eschewed. The impacts of the uncertainties identified in this paper is explored and an approach to quantifying mutation probability in relation to dose is presented.

Oral administration of inorganic nitrate alleviated biological damage induced by cone-beam computed tomography examination in Wistar rats

OBJECTIVES

To explore whether the inorganic nitrate has a protective effect on biological damage induced by cone-beam computed tomography (CBCT) and compare it with Vitamin C.

MATERIALS AND METHODS

Sixty Wistar rats were randomly separated into 6 groups: control group, irradiation (IR) group, NaNO₃ group, IR + NaNO₃ group, Vitamin C group, and IR + Vitamin C group. Rats were whole-body irradiated with CBCT four times. The absorbed dose of the skin surface was measured using thermoluminescent dosemeter chips and the mean whole-body absorbed dose was calculated. Peripheral blood was collected at 0.5h and 24h after irradiation. Bodyweight and organ index of rats before and after irradiation were analyzed. The bone marrow was taken for micronucleus test. Lymphocytes were isolated from peripheral blood for γ-H2AX immunofluorescence assay, apoptosis and reactive oxygen species (ROS) analysis. Total antioxidant capacity (TAC), malondialdehyde (MDA) and superoxide dismutase (SOD) in serum were detected.

RESULTS

The mean absorbed dose of four whole-body CBCT scans for rats was 73.04 mGy. Bodyweight and organ index before and after irradiation with X-ray had no significant differences. The micronuclei frequency of IR + NaNO3 and IR + Vitamin C groups showed a significant decrease than that in the IR group, which was not significantly different from that of the control group. The γ-H2AX foci rates in the IR + NaNO3 group and the IR + Vitamin C group were significantly lower than that in the IR group. In addition, the foci rate of the IR + NaNO3 group returned to the baseline level of the control group 24h after CBCT scanning. The apoptosis of lymphocytes in rats did not increase. The IR + NaNO3 group (P < 0.001) or IR + Vitamin C group (P < 0.001) showed a significant increase in ROS positive cells rate with the control group, while were significantly lower than those in the IR group (P < 0.01). In addition, the ROS-positive cell rate in the IR + NaNO3 group was significantly lower than that in the IR + Vitamin C group. The MDA in the serum of rats increased significantly, while SOD and TAC decreased significantly at 0.5h after irradiation.

CONCLUSIONS

Compared with Vitamin C, inorganic nitrate had better preventive effects on biological damage induced by CBCT scans in rats.

Effects of low dose ionizing radiation on the brain- a functional, cellular, and molecular perspective

Over the years, the advancement of radio diagnostic imaging tools and techniques has radically improved the diagnosis of different pathophysiological conditions, accompanied by increased exposure to low-dose ionizing radiation. Though the consequences of high dose radiation exposure on humans are very well comprehended, the more publicly relevant effects of low dose radiation (LDR) (≤100 mGy) exposure on the biological system remain ambiguous. The central nervous system, predominantly the developing brain with more neuronal precursor cells, is exceptionally radiosensitive and thus more liable to neurological insult even at low doses, as shown through several rodent studies. Further molecular studies have unraveled the various inflammatory and signaling mechanisms involved in cellular damage and repair that drive these physiological alterations that lead to functional alterations. Interestingly, few studies also claim that LDR exerts therapeutic effects on the brain by initiating an adaptive response. The present review summarizes the current understanding of the effects of low dose radiation at functional, cellular, and molecular levels and the various risks and benefits associated with it based on the evidence available from in vitro, in vivo, and clinical studies. Although the consensus indicates minimum consequences, the overall evidence suggests that LDR can bring about considerable neurological effects in the exposed individual, and hence a re-evaluation of the LDR usage levels and frequency of exposure is required.

COVID-19 and low-dose radiation therapy

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pathogen of the coronavirus disease 2019 (COVID-19), has caused more than 179 million infections and 3.8 million deaths worldwide. Global health authorities working on the COVID-19 outbreak continue to explore methods to reduce the rate of its transmission to healthy individuals. Treatment protocols thus far have focused on social distancing and masking, treatment with antivirals early in infection, and steroids to reduce the inflammatory response. An alternative approach is therapy with low dose radiation (LDR), which has several advantages compared to the current drugs and medicines. To date more than 10 case reports and pilot clinical trial preliminary outcome are available from different countries. These reports cover a wide range of patient conditions and LDR treatment strategies. Although one report showed the failure to observe the improvement of COVID-19 patients after LDR therapy, the majority showed some clinical improvement, and demonstrated the safety of LDR for COVID-19 patients, particularly with 0.5 Gy. This review aims to summarize the potential rationales and mechanisms of LDR therapy for COVID-19 patients, and its current clinical status and potential use.

Immunotherapy combined with high- and low-dose radiation to all sites leads to complete clearance of disease in a patient with metastatic vaginal melanoma

A 73-year-old woman with metastatic vaginal mucosal melanoma that had progressed on ipilimumab and nivolumab experienced clinical and radiographic complete response to dual checkpoint inhibitor immunotherapy given in combination with high-dose plus low-dose radiation. General characteristics and treatment options in this disease are highlighted.

Concerted outcome of metformin and low dose of radiation in modulation of cisplatin induced uremic encephalopathy via renal and neural preservation

AIM

The therapeutic expediency of cisplatin was limited due to its nephrotoxic side effects, so this study planned to assess the nephrotic and neuroprotective impact of metformin (MET) and low-dose radiation (LDR) in cisplatin-prompted kidney injury and uremic encephalopathy (UE).

METHODS

The effect of the 10-day MET treatment (200 mg/kg, orally) and/or fractionated LDR (0.25 Gy, of the total dose of 0.5 Gy, 1st and 7th day, respectively) on (5 mg/kg, intraperitoneally) cisplatin as a single dose was administered at the 5th day. Serum urea, creatinine and renal kidney injury molecule-1 were measured for the assessment of kidney function. Furthermore, the antioxidant potential in the renal and brain tissues was evaluated through, malondialdehyde and reduced glutathione estimation. Moreover, renal apoptotic markers: AMP-activated protein kinase, lipocalin, B-cell lymphoma 2 associated X protein, B-cell lymphoma 2, P53 and beclin 1 were estimated. UE was evaluated through the determination of serum inflammatory markers: nuclear factor kappa B, tumor-necrosis factor-α and interleukin 1 beta likewise, the cognitive deficits were assessed via forced swimming test, gamma-aminobutyric acid, n-methyl-d-aspartate and neuronal nitric oxide synthases besides AMP-activated protein kinase, light chain 3 and caspase3 levels in rats' cerebella.

KEY FINDINGS

The obtained results revealed a noticeable improvement in the previously mentioned biochemical factors and behavioral tasks that was reinforced by histopathological examination when using the present remedy.

SIGNIFICANCE

metformin and low doses of radiation afforded renoprotection and neuroprotection against cisplatin-induced acute uremic encephalopathy.

Isolation of the effects of alpha-related components from total effects of radium at low doses

PURPOSE

Radium is the most common source of alpha radiation exposure to humans and non-human species in the environment but the dosimetry is complicated by the decay chain which involves gamma exposure due to radon daughters. This paper seeks to determine the separate contributions of alpha and gamma doses to the total dose and total direct and non-targeted effect in a fish and a human cell line.

MATERIALS AND METHODS

This study aimed to isolate the effect of alpha particles following exposure to low doses of radium in cells, and their progeny which received no further exposure. This was initially done by comparing the survival values of a human keratinocyte cell line (HaCaT) and an embryonic Chinook salmon cell line (CHSE-214) exposed to gamma radiation, from survival of the same cell lines exposed to mixed alpha and gamma radiation through exposure to Ra-226 and its decay products. A Monte Carlo simulation was later performed to determine the contributions of radium decay products including radon daughters.

RESULTS

The human cell line showed increased radioresistance when exposed to low doses of alpha particles. In contrast the fish cell line, which demonstrated radioresistance to low dose gamma radiation, showed increased lethality when exposed to low doses of alpha particles. Significant and complex levels of non-targeted effects were induced in progeny of irradiated cells. The simulation showed that gamma and beta decay products did not contribute significant dose and the highest beta dose was below the threshold for inducing non-targeted effects.

CONCLUSIONS

The results confirm the need to consider the dose-response relationship when developing radiation weighting factors for low dose exposures, as well as the need to be aware of possible cell line and species differences.

Association between low doses of ionizing radiation, administered acutely or chronically, and time to onset of stroke in a rat model

Exposure to high-doses of ionizing radiation has been reported to be associated with the risk of stroke. However, risks associated with lower dose exposures remain unclear, and there is little information available for the risk modification according to the dose-rate. There are few studies using animal models which might be able to provide complementary information on this association. In this study, the male stroke-prone spontaneously hypertensive rat (SHRSP) was used as a model animal. The rats were acutely irradiated with doses between 0 and 1.0 Gy or chronically irradiated with a cumulative dose of 0.5 or 1.0 Gy (at a dose rate of 0.05 or 0.1 Gy/day, respectively). The onset time of stroke related symptoms in SHRSP was used as an endpoint for evaluating the effects of low dose and the low dose-rate gamma-ray exposures. With respect to acute exposure, the time to the onset of stroke in the irradiated rats suggested the presence of a threshold around 0.1 Gy. For the low dose-rate chronically exposed, no significant increase in stroke symptom was observed. These findings are novel and demonstrate that the SHRSP system can be used to determine the association between the risk of stroke and radiation exposure with high sensitivity. Moreover, these studies provide important information regarding the association between the low dose and low dose-rate radiation exposure and circulatory diseases, especially stroke.

Investigating the expression level of NF-KB and HIF1A genes among the inhabitants of two different background radiation areas in Ramsar, Iran

This study investigated the fluctuation of NF-KB and HIF-1a gene expression between inhabitants of a high-level background radiation area (HBRA) and a normal-level background radiation area (NBRA) of Ramsar, Iran. Sixty participants with the mean age of 48 ± 15 years were selected and divided into two groups. The group receiving a dose of ≤1.5 mGy/year (NBRA) was considered the control group and the target group (HBRA) received a dose of >1.5 mGy/year. These two groups were from neighbor regions to minimize socioeconomic differences between the participants. Blood samples were collected from each group and NF-KB and HIF-1a expression levels were compared using quantitative real-time PCR (qPCR) based on the stem loop method. The effects of residency duration in the respective areas and gender on the expression of NF-KB and HIF-1a was also examined. The HIF-1a expression level was statistically lower in the HLBRA region (P < 0.0002), while NF-KB expression was upregulated (P < 0.0001). Although the under-expression of HIF-1a in response to dose rate was significant in females (P < 0.0004), it was not different in males (P = 0.74), indicating a significant difference between sexes (P = 0.0047). The upregulation of NF-KB expression related to dose level was also significant for the female group (P < 0.0001), whereas it was not for the male group (P = 0.72). Notably and as expected, there was a significant relation between longer residency in the HBRA and HIF-1A under-expression (P < 0.026), while there was no effect of increasing residency time for NF-KB over-expression level (P = 0.29). The dwellers of the HBRA those noted that despite receiving an elevated radiation level were seemingly good in general health, showed some alterations in their molecular mechanisms, specifically HIF-1a and NF-KB expression levels. It is not clear if this is indicative of a beneficial adaptive response and more research is recommended.

Prolonged effect associated with inflammatory response observed after exposure to low dose of tritium β-rays

Background: The value of relative biological effectiveness of tritium increases at low dose domain, which results in the suspicion of weighting factor of 1 for tritium after low dose exposure. Thus, present study was carried out to analyze the differences in the cellular responses at early and late period between low dose of tritium β-rays and γ-rays radiation.Methods: MCF-10A cells were exposed to low dose of tritium β-rays or γ-rays, then cellular behaviors, such as DNA double strand breaks (DSBs), apoptosis, reactive oxygen species (ROS) level and inflammatory relevant gene expression were analyzed at early and late period post-irradiation.Results: At early period the elimination of DSB foci produced by HTO is longer than γ-rays. High ROS level and a continual change of cell cycle distribution are observed in HTO radiation group. Based on the results of RNA sequencing, Ingenuity Pathway Analysis (IPA) indicates TNFR1 signaling and production of nitric oxide and ROS are activated as an acute response at 24 h post radiation. Moreover, it also shows a disturbance in cholesterol biosynthesis. The results of 30 days point that there is a lasting active inflammatory response, accompanying with a persistent high expression of relevant cytokines, such as TNF and IL1R.Conclusion: Compared to an acute response induced by γ-rays, a persistent inflammatory response exists in HTO-irradiated cells when cultured for 30 days, which might be related to accumulation of tritium in the form of organically bound tritium (OBT) in cellular DNA or lipids.

Amelioration of adjuvant-induced arthritis by exposure to low dose gamma radiation and resveratrol administration in rats

Purpose: Low dose radiation has been reported as an effective treatment for rheumatoid arthritis via multiple dose exposures. The present study was designed to increase the therapeutic efficacy of low dose radiation with the minimum exposure level in arthritic rats by concurrent administration of resveratrol (RSV) as an adjunctive therapy with anti-inflammatory properties.Materials and methods: Rats were rendered arthritic by sub-plantar injection of Freund's complete adjuvant (FCA) and exposed to low dose radiation at a total exposure level of 0.5 Gy (2 × 0.25). During the exposure course, RSV (50 mg/kg) was orally administered once daily for two weeks. Diclofenac (3 mg/kg) was administered as a standard anti-inflammatory drug. Paw volume was measured every 4 days. After 28 days of induction, rats were sacrificed and serum was collected for estimation of tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), thiobarbituric acid reactive substances (TBARS), and total nitrate/nitrite (NO_x). Furthermore, paws were dissected for histopathological examinations and immuno-histochemical estimation of nuclear factor-kappa B p65 (NF-κB p65) expression.Results: Administration of RSV during the low dose radiation exposure course produced a significant decrease in the paw swelling and a potentiated inhibition in the serum levels of TNF-α, IL-1β, TBARs, and NO_x. The dual treatment strategy alleviated the histopathological damage to a greater extent than that produced by each treatment. Moreover, a pronounced suppression of NF-κB p65 expression in the synovial tissue was observed in the combination group. The combination treatment showed a nearly similar potency to that observed in the diclofenac treated group.Conclusion: Administration of RSV augmented the modulatory activity of low dose radiation with minimum exposure level on the disease progression.

Low-Dose radiation therapy for benign pathologies

Radiotherapy (RT) has always been a mainstay for malignant tumors therapy, but it is also used for benign pathology. The application of low or intermediate doses of RT has been widely studied. This topic was presented and discussed in the last XX GOCO (Grup Oncològic Català-Occità) meeting. The aim of this article is to review the indications of low dose irradiation (LD-RT), total dose and different fractionations, the public to whom it can be directed, and to offer an analysis about secondary effects. We believe it can be useful not only for radiation oncologists, but for other physicians to consider this option for future patients.

The expression of MLH1 and MSH2 genes among inhabitants of high background radiation area of Ramsar, Iran

Previous studies evidenced the critical role of the mismatch repair system in DNA damage recognition, cell cycle arrest, apoptosis and DNA repair. MLH1 and MSH2 genes belong to repairing complexes of mismatch repair system. The side effects of ionizing radiation on the human health were proved, but researches on the inhabitants of high background radiation areas, with extra-ordinary radiation exposure, showed that the prevalence of cancer or radiation-related diseases is not significantly higher than normal background areas. The city of Ramsar, in northern Iran, has the highest level of natural background radiation in the world and in this study, we aimed to evaluate the expression of MLH1 and MSH2 genes among the inhabitants of high background radiation areas of Ramsar compared to normal background radiation areas. In the present study, 60 blood sample from high and normal background inhabitants were collected and we MLH1, and MSH2 genes expressions in residents of high background radiation area compared with normal background radiation area were evaluated by Quantitative Real-Time PCR. Our results showed a significant upregulation of MLH1 in residents of high background radiation area. Also, there is a significant association between MLH1 and MSH2 gene expression in both sexes. Also, the increased expression of MLH1 in HBRA is notable. There is an increased expression of MLH1 in age above 50 and a decreased expression of MSH2 in ages under 50 years (P < 0.0001). These findings are suggesting the triggering of Mismatch Repair system in response to high-level of natural background radiation.

Re-evaluation of the linear no-threshold (LNT) model using new paradigms and modern molecular studies

The linear no-threshold (LNT) model is currently used to estimate low dose radiation (LDR) induced health risks. This model lacks safety thresholds and postulates that health risks caused by ionizing radiation is directly proportional to dose. Therefore even the smallest radiation dose has the potential to cause an increase in cancer risk. Advances in LDR biology and cell molecular techniques demonstrate that the LNT model does not appropriately reflect the biology or the health effects at the low dose range. The main pitfall of the LNT model is due to the extrapolation of mutation and DNA damage studies that were conducted at high radiation doses delivered at a high dose-rate. These studies formed the basis of several outdated paradigms that are either incorrect or do not hold for LDR doses. Thus, the goal of this review is to summarize the modern cellular and molecular literature in LDR biology and provide new paradigms that better represent the biological effects in the low dose range. We demonstrate that LDR activates a variety of cellular defense mechanisms including DNA repair systems, programmed cell death (apoptosis), cell cycle arrest, senescence, adaptive memory, bystander effects, epigenetics, immune stimulation, and tumor suppression. The evidence presented in this review reveals that there are minimal health risks (cancer) with LDR exposure, and that a dose higher than some threshold value is necessary to achieve the harmful effects classically observed with high doses of radiation. Knowledge gained from this review can help the radiation protection community in making informed decisions regarding radiation policy and limits.

Distinct response of adult neural stem cells to low versus high dose ionising radiation

Radiosusceptibility is the sensitivity of a biological organism to ionising radiation (IR)-induced carcinogenesis, an outcome of IR exposure relevant following low doses. The tissue response is strongly influenced by the DNA damage response (DDR) activated in stem and progenitor cells. We previously reported that in vivo exposure to 2 Gy X-rays activates apoptosis, proliferation arrest and premature differentiation in neural progenitor cells (transit amplifying cells and neuroblasts) but not in neural stem cells (NSCs) of the largest neurogenic region of the adult brain, the subventricular zone (SVZ). These responses promote adult quiescent NSC (qNSC) activation after 2 Gy. In contrast, neonatal (P5) SVZ neural progenitors continue proliferating and do not activate qNSCs. Significantly, the human and mouse neonatal brain is radiosusceptible. Here, we examine the response of stem and progenitor cells in the SVZ to low IR doses (50-500 mGy). We observe a linear dose-response for apoptosis but, in contrast, proliferation arrest and neuroblast differentiation require a threshold dose of 200 or 500 mGy, respectively. Importantly, qNSCs were not activated at doses below 500 mGy. Thus, full DDR activation in the neural stem cell compartment in vivo necessitates a threshold dose, which can be considered of significance when evaluating IR-induced cancer risk and dose extrapolation.

Effects of low dose ionizing radiation on DNA damage-caused pathways by reverse-phase protein array and Bayesian networks

Ionizing radiation (IR) causing damages to Deoxyribonucleic acid (DNA) constitutes a broad range of base damage and double strand break, and thereby, it induces the operation of relevant signaling pathways such as DNA repair, cell cycle control, and cell apoptosis. The goal of this paper is to study how the exposure to low dose radiation affects the human body by observing the signaling pathway associated with Ataxia Telangiectasia mutated (ATM) using Reverse-Phase Protein Array (RPPA) and isogenic human Ataxia Telangiectasia (A-T) cells under different amounts and durations of IR exposure. In order to verify which proteins could be involved in a DNA damage-caused pathway, only proteins that highly interact with each other under IR are selected by using correlation coefficient. The pathway inference is derived from learning Bayesian networks in combination with prior knowledge such as Protein-Protein Interactions (PPIs) and signaling pathways from well-known databases. Learning Bayesian networks is based on a score and search scheme that provides the highest scored network structure given a score function, and the prior knowledge is included in the score function as a prior probability by using Dempster-Shafer theory (DST). In this way, the inferred network can be more likely to be similar to already discovered pathways and consistent with confirmed PPIs for more reliable inference. The experimental results show which proteins are involved in signaling pathways under IR, how the inferred pathways are different under low and high doses of IR, and how the selected proteins regulate each other in the inferred pathways. As our main contribution, overall results confirm that low dose IR could cause DNA damage and thereby induce and affect related signaling pathways such as apoptosis, cell cycle, and DNA repair.

Evolving paradigms for the biological response to low dose ionizing radiation; the role of epigenetics

PURPOSE

In the late 1990s, it had become clear that the long-standing paradigm for the action of radiation on living cells and organisms did not have sufficient power to explain the observed effects of low dose ionizing radiation. The purpose of this commentary is to examine the experiments that lead up to the modification of the classic paradigm consequent on these observations, their historical precedents, and the development of our understanding of the role of epigenetics in low dose radiation effects.

RESULTS AND CONCLUSIONS

We discuss how parallel advances in epigenetics from developmental biology and cancer studies, and the discovery of epigenetic modifications of chromatin, such as DNA methylation, impacted on the development of an epigenetic paradigm for low dose effects. We also assess the impact of technology development in supporting the paradigm shift. We then examine recent accumulated data on epigenetic modification in response to irradiation since that shift took place, and identify areas where bringing together data from developmental biology and cancer might answer some of the paradoxes and contradictions in this data. We predict that further paradigm shifts are imminent.

Low dose radiation risks for women surviving the a-bombs in Japan: generalized additive model

BACKGROUND

Analyses of cancer mortality and incidence in Japanese A-bomb survivors have been used to estimate radiation risks, which are generally higher for women. Relative Risk (RR) is usually modelled as a linear function of dose. Extrapolation from data including high doses predicts small risks at low doses. Generalized Additive Models (GAMs) are flexible methods for modelling non-linear behaviour.

METHODS

GAMs are applied to cancer incidence in female low dose subcohorts, using anonymous public data for the 1958 - 1998 Life Span Study, to test for linearity, explore interactions, adjust for the skewed dose distribution, examine significance below 100 mGy, and estimate risks at 10 mGy.

RESULTS

For all solid cancer incidence, RR estimated from 0 - 100 mGy and 0 - 20 mGy subcohorts is significantly raised. The response tapers above 150 mGy. At low doses, RR increases with age-at-exposure and decreases with time-since-exposure, the preferred covariate. Using the empirical cumulative distribution of dose improves model fit, and capacity to detect non-linear responses. RR is elevated over wide ranges of covariate values. Results are stable under simulation, or when removing exceptional data cells, or adjusting neutron RBE. Estimates of Excess RR at 10 mGy using the cumulative dose distribution are 10 - 45 times higher than extrapolations from a linear model fitted to the full cohort. Below 100 mGy, quasipoisson models find significant effects for all solid, squamous, uterus, corpus, and thyroid cancers, and for respiratory cancers when age-at-exposure > 35 yrs. Results for the thyroid are compatible with studies of children treated for tinea capitis, and Chernobyl survivors. Results for the uterus are compatible with studies of UK nuclear workers and the Techa River cohort.

CONCLUSION

Non-linear models find large, significant cancer risks for Japanese women exposed to low dose radiation from the atomic bombings. The risks should be reflected in protection standards.

Anti-apoptotic and antioxidant effects of low dose gamma irradiation against diabetes-induced brain injury in rats

The current study aimed to investigate the effect of different low doses of gamma irradiation on hyperglycemia-induced brain injury. The aim was further extended to investigate the sub-chronic effect of low dose radiation on the neuronal damage induced by diabetes. To induce diabetes, male albino rats were injected with dexamethasone (10 mg/kg/day, for 9 successive days, subcutaneously). Different diabetic groups were irradiated with 0.1, 0.25 and 0.5 Gy. The effect of low dose gamma irradiation on the hyperglycemia-induced brain damage based was analyzed at two levels: oxidative stress and apoptosis. The brain contents of glutathione, malondialdhyde and total nitrate/nitrite were measured to assess the oxidative stress. In order to evaluate the extent of the apoptotic changes in brain, tissue caspase-3 expression was detected using immunohistochemistry and the degree of DNA fragmentation was estimated. Moreover, brain tissues were examined using light microscopy to evaluate the histological changes in different groups and serum lactate dehydrogenase activity was determined as an indicator for the brain tissue damage. Results indicated that exposure to 0.5 Gy ameliorated the hyperglycemia and subsequently inhibited oxidative stress and apoptosis. Radiation exposure at this dose level also increased the survival rate of diabetic animals.

Low dose X-irradiation mitigates diazepam induced depression in rat brain

Depression is considered as one of the most prevalent health ailments. Various anti-depressant drugs have been used to provide succour to this ailment, but with little success and rather have resulted in many side effects. On the other hand, low dose of ionizing radiations are reported to exhibit many beneficial effects on human body by stimulating various biological processes. The present study was conducted to investigate the beneficial effects of low doses of X-rays, if any, during diazepam induced depression in rats. Female Sprague Dawley rats were segregated into four different groups viz: Normal control, Diazepam treated, X-irradiated and Diazepam + X-irradiated. Depression model was created in rats by subjecting them to diazepam treatment at a dosage of 2 mg/kg b.wt./day for 3 weeks. The skulls of animals belonging to X-irradiated and Diazepam + X-irradiated rats were X-irradiated with a single fraction of 0.5 Gy, given twice a day for 3 days, thereby delivered dose of 3 Gy. Diazepam treated animals showed significant alterations in the neurobehavior and neuro-histoarchitecture, which were improved after X-irradiation. Further, diazepam exposure significantly decreased the levels of neurotransmitters and acetylcholinesterase activity, but increased the monoamine oxidase activity in brain. Interestingly, X-rays exposure to diazepam treated rats increased the levels of neurotransmitters, acetylcholinesterase activity and decreased the monoamine oxidase activity. Further, depressed rats also showed increased oxidative stress with altered antioxidant parameters, which were normalized on X-rays exposure. The present study, suggests that low dose of ionizing radiations, shall prove to be an effective intervention and a novel therapy in controlling depression and possibly other brain related disorders.

Overview of ICRP Committee 1: radiation effects

This paper does not necessarily reflect the views of the International Commission on Radiological Protection. The author passed away on 13 November 2015.Committee 1 of the International Commission on Radiological Protection (ICRP) addresses issues pertinent to tissue reactions, risks of cancer and heritable diseases, radiation dose responses, effects of dose rate, and radiation quality. In addition, it reviews data on the effects of radiation on the embryo/fetus, genetic factors in radiation response, and uncertainties in providing judgements on radiation-induced health effects. Committee 1 advises the Main Commission on the biological basis of radiation-induced health effects, and how epidemiological, experimental, and theoretical data can be combined to make quantitative judgements on health risks to humans. The emphasis is on low radiation doses, in the form of detriment-adjusted nominal risk coefficients, where there are considerable uncertainties in terms of the biology and the epidemiology. Furthermore, Committee 1 reviews data from radiation epidemiology studies and publications on the molecular and cellular effects of ionising radiation relevant to updating the basis of the 2007 Recommendations published in ICRP Publication 103 This paper will provide an overview of the activities of Committee 1, the updated work of the Task Groups and Working Parties, and the future activities being pursued.

Low Radiation Dose Calcium Scoring: Evidence and Techniques

Coronary computed tomography (CT) allows for the acquisition of thin slices of the heart and coronary arteries, which can be used to detect and quantify coronary artery calcium (CAC), a marker of atherosclerotic cardiovascular disease. Despite the proven clinical value in cardiac risk prognostication, there remain concerns regarding radiation exposure from CAC CT scans. There have been several recent technical advancements that allow for significant radiation dose reduction in CAC scoring. This paper reviews the clinical utility and recent literature in low radiation dose CAC scoring.

Low dose radiation adaptive protection to control neurodegenerative diseases

Concerns have been expressed recently regarding the observed increased DNA damage from activities such as thinking and exercise. Such concerns have arisen from an incomplete accounting of the full effects of the increased oxidative damage. When the effects of the induced adaptive protective responses such as increased antioxidants and DNA repair enzymes are taken into consideration, there would be less endogenous DNA damage during the subsequent period of enhanced defenses, resulting in improved health from the thinking and exercise activities. Low dose radiation (LDR), which causes oxidative stress and increased DNA damage, upregulates adaptive protection systems that may decrease diseases in an analogous manner. Though there are ongoing debates regarding LDR's carcinogenicity, with two recent advisory committee reports coming to opposite conclusions, data published since the time of the reports have overwhelmingly ruled out its carcinogenicity, paving the way for consideration of its potential use for disease reduction. LDR adaptive protection is a promising approach to control neurodegenerative diseases, for which there are no methods of prevention or cure. Preparation of a compelling ethics case would pave the way for LDR clinical studies and progress in dealing with neurodegenerative diseases.

Effect of low dose radiation on differentiation of bone marrow cells into dendritic cells

Low dose radiation has been shown to be beneficial to living organisms using several biological systems, including immune and hematopoietic systems. Chronic low dose radiation was shown to stimulate immune systems, resulting in controlling the proliferation of cancer cells, maintain immune balance and induce hematopoietic hormesis. Since dendritic cells are differentiated from bone marrow cells and are key players in maintaining the balance between immune activation and tolerance, it may be important to further characterize whether low dose radiation can influence the capacity of bone marrow cells to differentiate into dendritic cells. We have shown that bone marrow cells from low dose-irradiated (γ-radiation, 0.2Gy, 15.44mGy/h) mice can differentiate into dendritic cells that have several different characteristics, such as expression of surface molecules, cytokine secretion and antigen uptake capacity, when compared to dentritic cells differentiated from the control bone marrow cells. These differences observed in the low dose radiation group can be beneficial to living organisms either by activation of immune responses to foreign antigens or tumors, or maintenance of self-tolerance. To the best of our knowledge, this is the first report showing that total-body low dose radiation can modulate the capacity of bone marrow cells to differentiate into dendritic cells.

Shifting the paradigm in radiation safety

The current radiation safety paradigm using the linear no-threshold (LNT) model is based on the premise that even the smallest amount of radiation may cause mutations increasing the risk of cancer. Autopsy studies have shown that the presence of cancer cells is not a decisive factor in the occurrence of clinical cancer. On the other hand, suppression of immune system more than doubles the cancer risk in organ transplant patients, indicating its key role in keeping occult cancers in check. Low dose radiation (LDR) elevates immune response, and so it may reduce rather than increase the risk of cancer. LNT model pays exclusive attention to DNA damage, which is not a decisive factor, and completely ignores immune system response, which is an important factor, and so is not scientifically justifiable. By not recognizing the importance of the immune system in cancer, and not exploring exercise intervention, the current paradigm may have missed an opportunity to reduce cancer deaths among atomic bomb survivors. Increased antioxidants from LDR may reduce aging-related non-cancer diseases since oxidative damage is implicated in these. A paradigm shift is warranted to reduce further casualties, reduce fear of LDR, and enable investigation of potential beneficial applications of LDR.

Stochastic thresholds: a novel explanation of nonlinear dose-response relationships for stochastic radiobiological effects

New research data for low-dose, low-linear energy transfer (LET) radiation-induced, stochastic effects (mutations and neoplastic transformations) are modeled using the recently published NEOTRANS(3) model. The model incorporates a protective, stochastic threshold (StoThresh) at low doses for activating cooperative protective processes considered to include presumptive p53-dependent, high-fidelity repair of nuclear DNA damage in competition with presumptive p53-dependent apoptosis and a novel presumptive p53-independent protective apoptosis mediated (PAM) process which selectively removes genomically compromised cells (mutants, neoplastic transformants, micronucleated cells, etc.). The protective StoThresh are considered to fall in a relatively narrow low-dose zone (Transition Zone A). Below Transition Zone A is the ultra-low-dose region where it is assumed that only low-fidelity DNA repair is activated along with presumably apoptosis. For this zone there is evidence for an increase in mutations with increases in dose. Just above Transition Zone A, a Zone of Maximal Protection (suppression of stochastic effects) arises and is attributed to maximal cooperation of high-fidelity, DNA repair/apoptosis and the PAM process. The width of the Zone of Maximal Protection depends on low-LET radiation dose rate and appears to depend on photon radiation energy. Just above the Zone of Maximal Protection is Transition Zone B, where deleterious StoThresh for preventing the PAM process fall. Just above Transition Zone B is a zone of moderate doses where complete inhibition of the PAM process appears to occur. However, for both Transition Zone B and the zone of complete inhibition of the PAM process, high-fidelity DNA repair/apoptosis are presumed to still operate. The indicated protective and deleterious StoThresh lead to nonlinear, hormetic-type dose-response relationships for low-LET radiation-induced mutations, neoplastic transformation and, presumably, also for cancer.