Effects of ionizing radiation on biological molecules--mechanisms of damage and emerging methods of detection

Radiation activates myeloperoxidase (MPO) to generate active chlorine species (ACS) via a dephosphorylation mechanism - inhibitory effect of LGM2605

BACKGROUND

Radiation exposure of tissues is associated with inflammatory cell influx. Myeloperoxidase (MPO) is an enzyme expressed in granulocytes, such as neutrophils (PMN) and macrophages, responsible for active chlorine species (ACS) generation. The present study aimed to: 1) determine whether exposure to γ-irradiation induces MPO-dependent ACS generation in murine PMN; 2) elucidate the mechanism of radiation-induced ACS generation; and 3) evaluate the effect of the synthetic lignan LGM2605, known for ACS scavenging properties.

METHODS

MPO-dependent ACS generation was determined by using hypochlorite-specific 3'-(p-aminophenyl) fluorescein (APF) and a highly potent MPO inhibitor, 4-aminobenzoic acid hydrazide (ABAH), and confirmed in PMN derived from MPO-/- mice. Radiation-induced MPO activation was determined by EPR spectroscopy and computational analysis identified tyrosine, serine, and threonine residues near MPO's active site.

RESULTS

γ-radiation increased MPO-dependent ACS generation dose-dependently in human MPO and in wild-type murine PMN, but not in PMN from MPO-/- mice. LGM2605 decreased radiation-induced, MPO-dependent ACS. Protein tyrosine phosphatase (PTP) and protein serine/threonine phosphatase (PSTP) inhibitors decreased the radiation-induced increase in ACS. Peroxidase cycle results demonstrate that tyrosine phosphorylation blocks MPO Compound I formation by preventing catalysis on H2O2 in the active site of MPO. EPR data demonstrate that γ-radiation increased tyrosyl radical species formation in a dose-dependent manner.

CONCLUSIONS

We demonstrate that γ-radiation induces MPO-dependent generation of ACS, which is dependent, at least in part, by protein tyrosine and Ser/Thr dephosphorylation and is reduced by LGM2605. This study identified for the first time a novel protein dephosphorylation-dependent mechanism of radiation-induced MPO activation.

Effect of Different Antioxidants on X-ray Induced DNA Double-strand Breaks Using γ-H2AX in Human Blood Lymphocytes

Ionizing radiation exposure produces direct or indirect biological effects on genomic DNA. The latter are ionizing radiation mediated by induction of free radicals and oxygen species (ROS). The study was conducted to evaluate the dose-effect/time-effect of antioxidant treatments in reducing the induction of double-strand breaks in human blood lymphocytes. Human peripheral blood samples of 2 mL each from healthy donors were irradiated with 10 mGy after pre-incubation with different antioxidants (β-carotene, vitamin E, vitamin C, N-acetyl L-cysteine). In order to assess their efficiency as prophylactic therapy for irradiation, various concentrations and combinations of antioxidants, as well as different incubation times, have been evaluated. To assess double-strand breaks induced by ionizing radiation, the phosphorylated histone γ-H2AX has been used. A significant reduction (p < 0.001) in double-strand breaks studied with a γ-H2AX assay was observed with N-acetyl L-cysteine with a 1-h incubation time, followed by vitamin C, vitamin E, and β-carotene. The use of antioxidants, especially N-acetyl L-cysteine before irradiation, significantly decreased the occurrence of double-strand breaks, demonstrating the potential radiological protection for exposure to ionizing radiation.

The Radioprotective Effect of Procaine and Procaine-Derived Product Gerovital H3 in Lymphocytes from Young and Aged Individuals

Ionizing radiation induces genomic instability in living organisms, and several studies reported an ageing-dependent radiosensitivity. Chemical compounds, such as scavengers, radioprotectors, and modifiers, contribute to reducing the radiation-associated toxicity. These compounds are often antioxidants, and therefore, in order to be effective, they must be present before or during exposure to radiation. However, not all antioxidants provide radioprotection. In this study, we investigated the effects of procaine and of a procaine-based product Gerovital H3 (GH3) on the formation of endogenous and X-ray-induced DNA strand breaks in peripheral blood mononuclear cells (PBMCs) isolated from young and elderly individuals. Interestingly, GH3 showed the strongest radioprotective effects in PBMCs from young subjects, while procaine reduced the endogenous amount of DNA strand breaks more pronounced in aged individuals. Both procaine and GH3 inhibited lipid peroxidation, but procaine was more effective in inhibiting mitochondria free radicals' generation, while GH3 showed a higher antioxidant action on macrophage-induced low-density lipoprotein oxidation. Our findings provide new insights into the mechanisms underlying the distinct effects of procaine and GH3 on DNA damage.

Identification of Plasma Lipidome Changes Associated with Low Dose Space-Type Radiation Exposure in a Murine Model

Long-term exposures to low dose space radiation may have adverse effects on human health during missions in deep space. Conventional dosimetry, monitoring of prodromal symptoms, and peripheral lymphocyte counts are of limited value as biomarkers of organ- and tissue-specific radiation injury, particularly of injuries that appear weeks or months after radiation exposure. To assess the feasibility of using plasma metabolic and lipidomic profiles as biomarkers of injury from space radiation, we used a mouse model of exposure to low doses of oxygen ions (¹⁶O) and protons (¹H). Plasma profiles were compared with those of mice exposed to γ-rays as a reference set. Our results demonstrate major changes in glycerophospholipid metabolism, amino acid metabolism, as well as fatty acid metabolism. We also observed dyslipidemia and lipid peroxidation, suggesting an inflammatory phenotype with possible long-term consequences to overall health upon exposure to low doses of high linear energy transfer (LET) radiation.

Gamma radiation in the mineral hot springs of Ardabil, Iran: Assessment of Environmental Dose Rate and health risk for swimmers

The main aim of this study was to evaluate gamma radiation level in the mineral hot springs of Ardabil province in Iran. In addition, the cancer risk of gamma radiation was assessed for swimmers. Natural gamma radiation was measured using Ion Chamber Survey Meter 451B in 22 springs throughout the province. Gamma was measured at 20 cm and 100 cm above the ground level in 15 locations of each spring. Excess lifetime cancer risk was calculated to investigate the risk of exposure to gamma radiation. The highest and lowest annual absorbed dose rate of gamma were found to be 1.17(10^-3) and 1.99(10^-3) Sv/y at the height of 20 cm above the ground level and 5.26(10^-4) and 1.52(10^-3) Sv/y at the height of 100 cm above the ground level, respectively. Excess lifetime cancer risk ranged from 4.57(10^-4) to 7.76(10^-4) at the height of 20 cm and from 2.06(10^-4) to 5.94(10^-4) at the height of 100 cm which are lower than global average of 1.45(10^-3) declared by the United Nations. Although the risk level in this study is lower than the global average, protective and preventive measures should be considered by individuals and authorities in these areas to reduce the effects of gamma radiation on the health of the swimmers.

Amelioration of Radiation-Induced Damages in Mice by Curcuminoids: The Role of Bioavailability

PURPOSE

The present study investigated the role of free curcuminoids bioavailability on the relative radioprotective efficacy of natural unformulated curcuminoids.

MATERIALS AND METHODS

A food-grade bioavailable formulation of curcuminoids as curcumagalactomannosides (CGM) and unformulated curcuminoids (UC) were employed for the study. Swiss albino mice were randomized into Normal control, Radiation control, Radiation + UC, and Radiation + CGM groups and irradiated with γ-radiation of 6, 8, 10 and 12 Gy. Survival rate, hematological and biochemical parameters, bone marrow cellularity, chromosomal aberrations and histopathology of intestine were followed as a measure of the relative efficacy.Results and Discussion: Oral administration with both UC and CGM at 100 mg/kg. b.wt. produced significant radioprotective effect over the untreated control group of animals. However, CGM treatment was found to provide better clastogenic and genotoxic potential as compared to UC. Further, the histopathology analysis of intestine confirmed the better protective effect of CGM over UC-treated animals.

CONCLUSION

The present study demonstrated the positive role of the bioavailability of curcuminoids in the amelioration of radiation-induced damages in mice since CGM treatment exerted better survival rate and radioprotective effect as compared with UC, despite the relatively low concentrations of curcuminoids in CGM (39% w/w).

Stimulation of cytoprotective autophagy and components of mitochondrial biogenesis / proteostasis in response to ionizing radiation as a credible pro-survival strategy

The present study illustrates mitochondria-mediated impact of ionizing radiation which is paralleled by activation of several pro-adaptive responses in normal human dermal fibroblast cells. Irradiation of cells with X-rays (5 Gy) led to an increase in fragmentation and mitochondrial mass. Distinct temporal changes in cytosolic and mitochondrial reactive oxygen species (ROS) were noted in response to radiation, which was associated with depletion in mitochondrial membrane potential followed by decrease in ATP levels. Long Amplicon-Polymerase Chain Reaction (LA-PCR) analysis showed time-dependent increase in mitochondrial DNA damage that preceded mitochondrial ROS generation. Irradiation of cells led to an initial G₂/M arrest at 8 h that persisted till 16 h, with subsequent block at G₀/G₁ measured at 48 and 72 h time points. Interestingly, cells activated autophagy as a countermeasure against radiation-mediated cellular insults and aided in removal of damaged mitochondria. Blocking autophagy using 3-methyladenine led to cell death via activation of enhanced ROS, PARP-1 and caspase 3 cleavage. Upregulation of mitochondrial biogenesis factors Nrf1/PGC-1α, following irradiation was observed. Irradiated cells exhibited an increase in the phosphorylation of GCN2, PERK and eIF2α that might be responsible for the up-regulation of ATF4 and CHOP thereby regulating autophagy and components of integrated stress response. Apart from this, we measured accumulation of mitochondrial chaperones (HSP60/HSP10) and ATF5 which is a major molecule involved in mitochondrial stress. Taken together, mitochondria are one of the major cytoplasmic targets for ionizing radiation and possibly act as an early indicator of cellular insult. The findings also show that stressed mitochondria might influence endoplasmic reticulum (ER)-related signalling leading to the activation of adaptive mechanisms like cytoprotective autophagy, and molecules responsible for mitochondrial biogenesis and protein quality control in order to replenish mitochondrial pool and maintain cellular homeostasis.

In vivo assessment of reactive oxygen species production and oxidative stress effects induced by chronic exposure to gamma radiation in Caenorhabditis elegans

In the current study, effects of chronic exposure to ionizing gamma radiation were assessed in the radioresistant nematode Caenorhabditis elegans in order to understand whether antioxidant defences (AODs) could ameliorate radical formation, or if increased ROS levels would cause oxidative damage. This analysis was accompanied by phenotypical as well as molecular investigations, via assessment of reproductive capacity, somatic growth and RNA-seq analysis. The use of a fluorescent reporter strain (sod1::gfp) and two ratiometric biosensors (HyPer and Grx1-roGFP2) demonstrated increased ROS production (H₂O₂) and activation of AODs (SOD1 and Grx) in vivo. The data showed that at dose-rates ≤10 mGy h^-1 defence mechanisms were able to prevent the manifestation of oxidative stress. In contrast, at dose-rates ≥40 mGy h^-1 the continuous formation of radicals caused a redox shift, which lead to oxidative stress transcriptomic responses, including changes in mitochondrial functions, protein degradation, lipid metabolism and collagen synthesis. Moreover, genotoxic effects were among the most over-represented functions affected by chronic gamma irradiation, as indicated by differential regulation of genes involved in DNA damage, DNA repair, cell-cycle checkpoints, chromosome segregation and chromatin remodelling. Ultimately, the exposure to gamma radiation caused reprotoxic effects, with >20% reduction in the number of offspring per adult hermaphrodite at dose-rates ≥40 mGy h^-1, accompanied by the down-regulation of more than 300 genes related to reproductive system, apoptosis, meiotic functions and gamete development and fertilization.

Assessment of function, histopathological changes, and oxidative stress in liver tissue due to ionizing and non-ionizing radiations

BACKGROUND

Compared to past decades, humans are exposed to rapidly increasing levels of radiofrequency electromagnetic radiations (RF-EMF). Despite numerous studies, the biological effects of human exposure to different levels of RF-EMF are not fully understood yet. This study aimed to evaluate the bioeffects of exposure to "900/1800 MHz" and "2.4 GHz" RF-EMFs, and x-rays alone as well as their potential interactions, i.e. inducing simple additive, adaptive, or synergistic effects.

METHODS

120 Wistar rats were randomly divided into ten groups of 12 each. The rats were exposed to RF-EMF, 10 cGy, and 8 Gy x-rays, a combination of these exposures, or only sham-exposed. The levels of liver enzymes were determined in serum samples by an auto-analyzer. Moreover, the histopathological changes, and the levels of malondialdehyde (MDA), nitric oxide, ferric reducing antioxidant power, total thiols, and protein carbonyl (PCO) were measured.

RESULTS

Among the markers of liver function, gamma-glutamyltransferase was not associated with irradiation but, aspartate transaminase, alanine transaminase, and alkaline phosphatase showed some levels of association. MDA and PCO levels after 8 Gy irradiation increased, but pre-exposure to RF-EMF could modulate their changes. At the cellular level, the frequency of lobular inflammation was associated with the type of intervention.

CONCLUSION

The exposure to both ionizing and non-ionizing radiations could alter some liver function tests. A short term pre-exposure to RF-EMF before exposure to an 8 Gy challenging dose of x-rays caused the alterations in oxidative stress markers and liver function tests, which indicate that oxidative stress is possibly involved in the adaptive response.

Chromosome aberration in typical biological systems under exposure to low- and high-intensity magnetic fields

The aim of this study was to investigate the response of chromosomes in typical human and plant cells under applied low-frequency magnetic fields at low and high intensities. Neuronal-like cells and roots of Allium sativum and Vicia faba were used to investigate chromosome's response to a static and 50 Hz magnetic fields at intensities ranging from 1 mT to 0.8 T, generated by two Helmholtz coils driven by direct current or alternate current voltage. Vertex spectrometer and Olympus microscope with camera were used. A significant decrease in intensity of the phosphate bands in the DNA infrared region was observed by FTIR spectroscopy analysis after exposure of neuronal-like cells to static and 50 Hz magnetic field at low intensity of 1 mT, which can be explained assuming that uncoiling and unpackaging of chromatin constituents occurred after exposure. This effect was directly observed by microscope in roots of Allium sativum and Vicia faba under exposure to a static magnetic field at high intensity of 0.8 T. These findings can be explained assuming that exposure to both low- and high-intensity magnetic fields of chromosomes in typical human and plant cells induces uncoiling and unpackaging of chromatin constituents, followed by chromosome alignment towards the direction of applied magnetic field, providing further demonstration that magnetic fields can induce the orientation of organic macromolecules even at low-intensity values.

Effect of Low-Level Laser on Some Metals Related to Redox State and Histological Alterations in the Liver and Kidney of Irradiated Rats

Low-level laser therapy (LLLT) is a type of medicine that uses laser light at low levels to activate the cellular chromophores and the initiation of cellular signaling. This study aimed to evaluate the photomodulation effect of LLL against ionizing radiation (IR)-induced metal disorders related to redox state in the liver and kidney of male rats. Rats were divided into 4 groups (control, LLLT, IR (7Gy), IR+LLLT). The results showed that LLLT 870 nm one time for 3 days post-irradiation revealed redistribution of iron (Fe), copper (Cu), zinc (Zn),calcium (Ca), magnesium (Mg), manganese (Mn), and selenium (Se) in the liver and kidney tissues. Moreover, LLLT attenuated the oxidative stress manifested by a marked reduction of hydrogen peroxide (H₂O₂), 4-hydroxynonenal (4-HNE), total oxidant state (TOS), and oxidative stress index (OSI) associated with a significant increase in total antioxidant status (TAS), glutathione (GSH) content, and glutathione peroxide (GPx), glutathione reductase (GRx), superoxide dismutase(SOD), and catalase (CAT) activities. Moreover, LLLT displayed an increase in glutathione-S-transferase (GSH-T) and ceruloplasmin activities and a decrease in the activity of gamma-glutamyl transferase (γ-GT). Besides, LLLT significantly attenuated the histological changes in the liver and kidney tissues, denoted by a reduction in the necrotic and degenerative changes of hepatocytes and an improvement in the corpuscles and tubules of the kidney. In conclusion, LLLT could be used as an adjuvant treatment post-exposure to radiation, while it is not beneficial to use it on the normal tissue.

Enhancement of membrane lipid peroxidation in lung cancer cells irradiated with monoenergetic X-rays at the K-shell resonance absorption peak of phosphorus

The aim of this study was to determine whether membrane lipid peroxidation in mammalian cells is enhanced by X-ray irradiation at the K-shell resonance absorption peak of phosphorus. A549 and wild-type p53-transfected H1299 (H1299/wtp53) cell lines derived from human lung carcinoma were irradiated with monoenergetic X-rays at 2.153 keV, the phosphorus K-shell resonance absorption peak, or those at 2.147 or 2.160 keV, which are off peaks. Immunofluorescence staining for 4-hydroxy-2-nonenal (HNE), a lipid peroxidation product, was used as marker for protein modification. In both cell lines, the HNE production was significantly enhanced after irradiation at 2.153 keV compared to sham-irradiation. The enhancement (E) was calculated as the ratio of the fluorescence intensity of irradiated cells to that of sham-irradiated cells. In both the cell lines, E2.153 was significantly larger than E2.147 and no significant difference between E2.147 and E2.160 was observed. The extra enhancement at 2.153 keV was possibly caused by energy transition within the phosphorus K-shell resonance absorption. Our results indicate that membrane lipid peroxidation in cells is enhanced by the Auger effect after irradiation at the K-shell resonance absorption peak of phosphorus rather than by the photoelectric effect of the constituent atoms in the membrane lipid at 2.147 keV.

Radiation induced apoptosis and pulmonary fibrosis: curcumin an effective intervention?

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by interstitial remodeling, leading to compromised lung function. Extra vascular fibrin deposition and abnormalities in the fibrinolysis are the major clinical manifestations of lung diseases such as acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS). ALI progresses to pulmonary fibrosis (PF) and makes patient's life miserable. Anti-fibrinolysis and apoptosis are involved in the progression of PF. Apoptotic markers are detectable within IPF lung tissue and senescent cell deletion can rejuvenate pulmonary health. Enhanced expression of p53 due to DNA damage is seen in irradiated lung tissue. The role of fibrinolytic components such as Urokinase Plasminogen activator (uPA), uPA receptor (uPAR) and Plasminogen activator inhibitor-1 (PAI-1) has been detailed in I. Curcumin is known to possess anti-inflammatory and anti-fibrotic effects. Radioprotective effect of curcumin enables it to attenuate radiation-induced inflammation and fibrosis. Understanding the mechanism of radioprotective effect of curcumin in radiation-induced PF and apoptosis can lead to the development of an effective therapeutic to combat acute lung injury and fibrosis.

Radon Biomonitoring and microRNA in Lung Cancer

Radon is the number one cause of lung cancer in non-smokers. microRNA expression in human bronchial epithelium cells is altered by radon, with particular reference to upregulation of miR-16, miR-15, miR-23, miR-19, miR-125, and downregulation of let-7, miR-194, miR-373, miR-124, miR-146, miR-369, and miR-652. These alterations alter cell cycle, oxidative stress, inflammation, oncogene suppression, and malignant transformation. Also DNA methylation is altered as a consequence of miR-29 modification induced by radon. Indeed miR-29 targets DNA methyltransferases causing inhibition of CpG sites methylation. Massive microRNA dysregulation occurs in the lung due to radon expose and is functionally related with the resulting lung damage. However, in humans this massive lung microRNA alterations only barely reflect onto blood microRNAs. Indeed, blood miR-19 was not found altered in radon-exposed subjects. Thus, microRNAs are massively dysregulated in experimental models of radon lung carcinogenesis. In humans these events are initially adaptive being aimed at inhibiting neoplastic transformation. Only in case of long-term exposure to radon, microRNA alterations lead towards cancer development. Accordingly, it is difficult in human to establish a microRNA signature reflecting radon exposure. Additional studies are required to understand the role of microRNAs in pathogenesis of radon-induced lung cancer.

Direct effects of low-energy electrons on including sulfur bonds in proteins: a second-order Møller-Plesset perturbation (MP2) theory approach

In an attempt to describe how low-energy electrons (LEEs) damage the polypeptide chain at disulfide bridges, ab initio electronic structure estimates on LEE interactions with cysteine-cysteine (Cys-Cys) disulfide bond model have been performed. Here, the fundamental mechanisms in LEE impression on S-S and C-S bond ruptures in the Cys-Cys model have been discussed. The electronic energy was calculated using the MP2 method with a Hartree-Fock exchange during the SCF and the Møller-Plesset correlation energy correction on the converged HF orbitals with 6-311++G(d,p) atomic orbital basis set. Further, six more sets of diffuse s and p functions with extra basis on the sulfur and relevant carbon atoms were used to describe the added electron to located away as much as possible from the nuclei in anions. The bonds rupture mechanisms involve the primary placement of LEEs to the π* orbital of the model to construct the shape-resonance state following by an adiabatic or nonadiabatic electron migration to either S-S or C-S bond σ* orbital. The formed radical anion undergoes S-S or C-S bonds cleavage by energy barriers of ca. 5.68 and 9.19 kcal/mol, respectively, to produce either (2-amino-2-carboxyethyl) sulfanyl (cysteine radical), aziridine-2-carboxylic acid or mercapto-L-cysteine lesions. In SMD solvent, calculations suggest electronically stable of the formed π* and σ* states by solvation, something that induces either S-S or C-S bond break even when the electron energy is near zero. The required barrier energy of only 0 to < 0.4 eV indicates a high kinetic favorable fragmentation for involved sulfur polypeptides with LEEs.Communicated by Ramaswamy H. Sarma.

Exposure to radioactive rocks from the Egyptian eastern desert attenuates the efficiency of the immune organs and induces apoptosis of blood lymphocytes in rat model

Exposure to ionizing radiation emitted from natural sources induces many health hazards. The response to ionizing radiation involves a number of mediators including inflammatory cytokines and free radicals which mediate immunosuppression. The present study aimed to monitor the impact of exposure to natural radioactive rocks from the Egyptian eastern desert on the primary immune organs. Therefore, three experimental groups (15 rats per group) were used: group I included the control non-irradiated rats; group II included rats that were exposed for 28 consecutive days to natural radioactive rocks from the Egyptian eastern desert (IR/R group); and group III (positive control group) included rats that were exposed to high dose of γ-rays (4 Gy/14 days for 28 days) (IR/γR group). We found that rats of both the IR/R and IR/γR groups exhibited pathological alterations in the architecture of the primary immune organs (bone marrow and thymus). Additionally, the levels of C-reactive protein (CRP), proinflammatory cytokines (IL-1β, IL-6 and TNF-α), and reactive oxygen species (ROS) were significantly increased in the IR/R and IR/γR groups compared to the control group. Furthermore, rats from the IR/R and IR/γR groups exhibited significant increase in the activity of caspase-3 and caspase-9 and subsequently exhibited a significant increase in the apoptosis of PBMCs compared with the control group. Most importantly, apoptosis induction in the PBMCs was associated with increased expression of cyclin B1 and decreased expression of cyclin D1 and survivin compared with the control non-irradiated group. Taken together, our data demonstrated that consecutive exposure to natural radioactive rocks from the Egyptian eastern desert could dampen the immune response through damaging the architectures of the immune system and mediating serious health problems to the population inhabiting this region.

Assessment of absorbed dose of gamma rays using the simultaneous determination of inactive hemoglobin derivatives as a biological dosimeter

Biological dosimetry based on sulfhemoglobin (SHb), methemoglobin (MetHb), and carboxyhemoglobin (HbCO) levels was evaluated. SHb, MetHb and HbCO levels were estimated in erythrocytes of mice irradiated by γ rays from a ⁶⁰Co source using the method of multi-component spectrophotometric analysis developed recently. In this method, absorption measurements of diluted aqueous Hb-solution were made at λ = 500, 569, 577 and 620 nm, and using the mathematical formulas based on multi-component spectrophotometric analysis and the mathematical Gaussian elimination method for matrix calculation, the concentrations of various Hb-derivatives and total Hb in mice blood were estimated. The dose range of γ rays was from 0.5 to 8 Gy and the dose rate was 0.5 Gy min^-1. Among all Hb-derivatives, MetHb, SHb and HbCO demonstrated an unambiguous dose-dependent response. For SHb and MetHb, the detection limits were about 0.5 Gy and 1 Gy, respectively. After irradiation, high levels of MetHb, SHb and HbCO persisted for at least 10 days, and the maximal increase of MetHb, SHb and HbCO occurred up to 24 h following γ irradiation. The use of this "MetHb + SHb + HbCO"-derivatives-based absorbed dose relationship showed a high accuracy. It is concluded that simultaneous determination of MetHb, SHb and HbCO, by multi-component spectrophotometry provides a quick, simple, sensitive, accurate, stable and inexpensive biological indicator for the early assessment of the absorbed dose in mice.

A Facile One-Pot Synthesis of Versatile PEGylated Platinum Nanoflowers and Their Application in Radiation Therapy

Nanomedicine has stepped into the spotlight of radiation therapy over the last two decades. Nanoparticles (NPs), especially metallic NPs, can potentiate radiotherapy by specific accumulation into tumors, thus enhancing the efficacy while alleviating the toxicity of radiotherapy. Water radiolysis is a simple, fast and environmentally-friendly method to prepare highly controllable metallic nanoparticles in large scale. In this study, we used this method to prepare biocompatible PEGylated (with Poly(Ethylene Glycol) diamine) platinum nanoflowers (Pt NFs). These nanoagents provide unique surface chemistry, which allows functionalization with various molecules such as fluorescent markers, drugs or radionuclides. The Pt NFs were produced with a controlled aggregation of small Pt subunits through a combination of grafted polymers and radiation-induced polymer cross-linking. Confocal microscopy and fluorescence lifetime imaging microscopy revealed that Pt NFs were localized in the cytoplasm of cervical cancer cells (HeLa) but not in the nucleus. Clonogenic assays revealed that Pt NFs amplify the gamma rays induced killing of HeLa cells with a sensitizing enhancement ratio (SER) of 23%, thus making them promising candidates for future cancer radiation therapy. Furthermore, the efficiency of Pt NFs to induce nanoscopic biomolecular damage by interacting with gamma rays, was evaluated using plasmids as molecular probe. These findings show that the Pt NFs are efficient nano-radio-enhancers. Finally, these NFs could be used to improve not only the performances of radiation therapy treatments but also drug delivery and/or diagnosis when functionalized with various molecules.

Developing polyphenolic acetates as radiation countermeasure agents: current status and future perspectives

Total-body exposure to ionizing radiation (TBI) results in life-threatening acute radiation syndrome (ARS), which encompasses hematopoietic and gastrointestinal (GI) injuries and results in dose-dependent morbidity and mortality. Management of ARS warrants the deployment of effective medical countermeasure agents (MCM) that protect against and/or mitigate lethal radiation injury. The polyphenolic acetate (PA) 7,8-diacetoxy-4-methylthiocoumarin (DAMTC) has been identified as a potential MCM against ARS by virtue of it mitigating the lethal effects of TBI in C57BL/6 mice. Herein, we describe current evidence, including mechanistic aspects, for the use of PAs as MCMs against ARS and provide perspectives for their further development as approved drugs for the mitigation of ARS.

NASA GeneLab Platform Utilized for Biological Response to Space Radiation in Animal Models

Background: Ionizing radiation from galactic cosmic rays (GCR) is one of the major risk factors that will impact the health of astronauts on extended missions outside the protective effects of the Earth's magnetic field. The NASA GeneLab project has detailed information on radiation exposure using animal models with curated dosimetry information for spaceflight experiments. Methods: We analyzed multiple GeneLab omics datasets associated with both ground-based and spaceflight radiation studies that included in vivo and in vitro approaches. A range of ions from protons to iron particles with doses from 0.1 to 1.0 Gy for ground studies, as well as samples flown in low Earth orbit (LEO) with total doses of 1.0 mGy to 30 mGy, were utilized. Results: From this analysis, we were able to identify distinct biological signatures associating specific ions with specific biological responses due to radiation exposure in space. For example, we discovered changes in mitochondrial function, ribosomal assembly, and immune pathways as a function of dose. Conclusions: We provided a summary of how the GeneLab's rich database of omics experiments with animal models can be used to generate novel hypotheses to better understand human health risks from GCR exposures.

Targeting DNA repair in cancer: current state and novel approaches

DNA damage response, DNA repair and genomic instability have been under study for their role in tumor initiation and progression for many years now. More recently, next-generation sequencing on cancer tissue from various patient cohorts have revealed mutations and epigenetic silencing of various genes encoding proteins with roles in these processes. These findings, together with the unequivocal role of DNA repair in therapeutic response, have fueled efforts toward the clinical exploitation of research findings. The successful example of PARP1/2 inhibitors has also supported these efforts and led to numerous preclinical and clinical trials with a large number of small molecules targeting various components involved in DNA repair singularly or in combination with other therapies. In this review, we focus on recent considerations related to DNA damage response and new DNA repair inhibition agents. We then discuss how immunotherapy can collaborate with these new drugs and how epigenetic drugs can rewire the activity of repair pathways and sensitize cancer cells to DNA repair inhibition therapies.

Post-translational modifications of protein in response to ionizing radiation

Based on central dogma of genetics, protein is the embodiment and executor of genetic function, post-translational modifications (PTMs) of protein are particularly important and involved in almost all aspects of cell biology and pathogenesis. Studies have shown that ionizing radiation (IR) alters gene expression much more profoundly and a broad variety of cell-process pathways, lots of proteins are modified and activated. Our understanding of the protein in response to ionizing radiation is steadily increasing. Among the various biological processes known to induce radioresistance, PTMs have attracted marked attention in recent years. The present review summarizes the latest knowledge about how PTMs response to ionizing radiation and pathway analysis were conducted. The data provided insights into biological effects of IR and contributing to the development of novel IR-based strategies.

"An End to a Means": How DNA-End Structure Shapes the Double-Strand Break Repair Process

Endogenously-arising DNA double-strand breaks (DSBs) rarely harbor canonical 5′-phosphate, 3′-hydroxyl moieties at the ends, which are, regardless of the pathway used, ultimately required for their repair. Cells are therefore endowed with a wide variety of enzymes that can deal with these chemical and structural variations and guarantee the formation of ligatable termini. An important distinction is whether the ends are directly “unblocked” by specific enzymatic activities without affecting the integrity of the DNA molecule and its sequence, or whether they are “processed” by unspecific nucleases that remove nucleotides from the termini. DNA end structure and configuration, therefore, shape the repair process, its requirements, and, importantly, its final outcome. Thus, the molecular mechanisms that coordinate and integrate the cellular response to blocked DSBs, although still largely unexplored, can be particularly relevant for maintaining genome integrity and avoiding malignant transformation and cancer.

The hunt for radiation biomarkers: current situation

Purpose: The possibility of a large-scale acute radiation exposure necessitates the development of new methods that could provide a rapid assessment of the doses received by individuals using high-throughput technologies. There is also a great interest in developing new biomarkers of dose exposure, which could be used in large molecular epidemiological studies in order to correlate estimated doses received and health effects. The goal of this review was to summarize current literature focused on biological dosimetry, namely radiation-responsive biomarkers.Methods: The studies involved in this review were thoroughly selected according to the determined criteria and PRISMA guidelines.Results: We described briefly recent advances in radiation genomics and metabolomics, giving particular emphasis to proteomic analysis. The majority of studies were performed on animal models (rats, mice, and non-human primates). They have provided much beneficial information, but the most relevant tests have been done on human (oncological) patients. By inspecting the radiaiton biodosimetry literate of the last 10 years, we identified a panel of candidate markers for each -omic approach involved.Conslusions: We reviewed different methodological approaches and various biological materials, which can be exploited for dose-effect prediction. The protein biomarkers from human plasma are ideal for this specific purpose. From a plethora of candidate markers, FDXR is a very promising transcriptomic candidate, and importantly this biomarker was also confirmed by some studies at protein level in humans.

The progeny of Chernobyl Arabidopsis thaliana plants does not exhibit changes in morphometric parameters and cellular antioxidant defence system of shoots

Morphometric parameters and functional state of the cellular antioxidant defence system of shoots were studied in the progeny of Arabidopsis thaliana (L.) Heynh. (A. thaliana) plants, previously and chronically exposed in the Chernobyl Exclusion Zone (ChEZ). Changes in cellular antioxidant enzyme activities in the progeny of exposed plants were assumed because antioxidant status of cell may be altered by inherited epigenetic changes, resulting in changes in antioxidant-response genes expression. These changes can be inferred as induced expression of CAT and SOD genes was found previously for A. thaliana plants by another group of scientists. It is well-known that ionizing radiation may induce changes in hormonal-signalling net-work, shifting balance in growth factors that may cause changes in morphometric parameters of plants. Seeds from A. thaliana plants were collected in the ChEZ at different levels of the external dose rate from 0.28 ± 0.01 to 12.93 ± 0.08 μGy/h. Internal dose rate for parent plants was calculated on the basis of the activity concentration of ⁹⁰Sr and ¹³⁷Cs in the plants, using dose conversion coefficients for wild grass. Total dose rate, absorbed by parent plants, was calculated as the sum of the external and internal dose rate and was in a range between 2.8 ± 0.2 and 99 ± 8 μGy/h. Seeds were then grown in the standard laboratory conditions (nutrient-agar, light-dark cycle and appropriate temperature) to analyse morphometric parameters of seedlings and final germination percentage. No significant changes in the morphometric parameters (root length and rosette diameter of shoots) of the seedlings were observed. Changes in the final germination percentage of the studied seeds were found, but low correlation was observed between found changes and the dose rate, absorbed by parent plants. In contrast to the results obtained in A. thaliana plants directly sampled in the field, no effect on the functional state of the cellular antioxidant defence system of shoots in the progeny of Chernobyl A. thaliana plants was observed.

Radiation-induced curcumin release from curcumin–chitosan polymer films

The probability of human exposure to damaging radiation is increased in activities associated with long-term space flight, medical radiation therapies, and responses to nuclear accidents. However, the development of responsive countermeasures to combat radiation damage to biological tissue is lagging behind rates of human exposure. Herein, we report a radiation-responsive drug delivery system that releases doses of curcumin from a chitosan polymer/film in response to low level gamma radiation exposure. As a fibrous chitosan–curcumin polymer, 1 Gy gamma irradiation (¹³⁷Cs) released 5 ± 1% of conjugated curcumin, while 6 Gy exposure releases 98 ± 1% of conjugated curcumin. The same polymer was formed into a film through solvent casting. The films showed similar, albeit attenuated behavior in water (100% released) and isopropyl alcohol (32% released) with statistically significant drug release following 2 Gy irradiation. ATR FT-IR studies confirmed glycosidic bond cleavage in the chitosan–curcumin polymer in response to gamma radiation exposure. Similar behavior was noted upon exposure of the polymer to 20 cGy (1 GeV amu⁻¹, at 20 cGy min⁻¹) high linear energy transfer (LET) ⁵⁶Fe radiation based on FTIR studies. Density Functional Theory calculations indicate homolytic bond scission as the primary mechanism for polymer disintegration upon radiation exposure. Films did not change in thickness during the course of radiation exposure. The successful demonstration of radiation-triggered drug release may lead to new classes of radio-protective platforms for developing countermeasures to biological damage from ionizing radiation.

The probability of human exposure to damaging radiation is increased in activities associated with long-term space flight, medical radiation therapies, and responses to nuclear accidents.

Mitochondrial DNA damage in the hair bulb: can it be used as a noninvasive biomarker of local exposure to low LET ionizing radiation?

Purpose: Our aim was to evaluate whether mitochondrial DNA (mtDNA) damage in hair bulbs could be a suitable biomarker for the detection of local exposure to ionizing radiation.Materials and methods: Mouse hair was collected 4 and 24 hours, 3 and 10 days after single whole-body exposure to 0, 0.1, and 2 Gy radiation. Pubic hair (treated area) and scalp hair (control area) were collected from 13 prostate cancer patients before and after fractioned radiotherapy with an average total dose of 2.7 Gy to follicles after five fractions. Unspecified lesion frequency of mtDNA was analyzed with long PCR, large mtDNA deletion levels were tested with real-time PCR.Results: Unspecified lesion frequency of mtDNA significantly increased in mouse hair 24 hours after irradiation with 2 Gy, but variance among samples was high. No increase in lesion frequency could be detected after 0.1 Gy irradiation. In prostate cancer patients, there was no significant change in either the unspecified lesion frequency or in the proportion of 4934-bp deleted mtDNA in pubic hair after radiotherapy. The proportions of murine 3860-bp common deletion, human 4977-bp common deletion and 7455-bp deleted mtDNA were too low to be analyzed reliably.Conclusions: Our results suggest that the unspecified lesion frequency and proportion of large deletions of mtDNA in hair bulbs are not suitable biomarkers of exposure to ionizing radiation.

Gamma radiation induces life stage-dependent reprotoxicity in Caenorhabditis elegans via impairment of spermatogenesis

The current study investigated life stage, tissue and cell dependent sensitivity to ionizing radiation of the nematode Caenorhabditis elegans. Results showed that irradiation of post mitotic L4 stage larvae induced no significant effects with respect to mortality, morbidity or reproduction at either acute dose ≤6 Gy (1500 mGy·h^-1) or chronic exposure ≤15 Gy (≤100 mGy·h^-1). In contrast, chronic exposure from the embryo to the L4-young adult stage caused a dose and dose-rate dependent reprotoxicity with 43% reduction in total brood size at 6.7 Gy (108 mGy·h^-1). Systematic irradiation of the different developmental stages showed that the most sensitive life stage was L1 to young L4. Exposure during these stages was associated with dose-rate dependent genotoxic effects, resulting in a 1.8 to 2 fold increase in germ cell apoptosis in larvae subjected to 40 or 100 mGy·h^-1, respectively. This was accompanied by a dose-rate dependent reduction in the number of spermatids, which was positively correlated to the reprotoxic effect (0.99, PCC). RNAseq analysis of nematodes irradiated from L1 to L4 stage revealed a significant enrichment of differentially expressed genes related to both male and hermaphrodite reproductive processes. Gene network analysis revealed effects related to down-regulation of genes required for spindle formation and sperm meiosis/maturation, including smz-1, smz-2 and htas-1. Furthermore, the expression of a subset of 28 set-17 regulated Major Sperm Proteins (MSP) required for spermatid production was correlated (R² 0.80) to the reduction in reproduction and the number of spermatids. Collectively these observations corroborate the impairment of spermatogenesis as the major cause of gamma radiation induced life-stage dependent reprotoxic effect. Furthermore, the progeny of irradiated nematodes showed significant embryonal DNA damage that was associated with persistent effect on somatic growth. Unexpectedly, these nematodes maintained much of their reproductive capacity in spite of the reduced growth.

Extracellular Vesicles in Modifying the Effects of Ionizing Radiation

Extracellular vesicles (EVs) are membrane-coated nanovesicles actively secreted by almost all cell types. EVs can travel long distances within the body, being finally taken up by the target cells, transferring information from one cell to another, thus influencing their behavior. The cargo of EVs comprises of nucleic acids, lipids, and proteins derived from the cell of origin, thereby it is cell-type specific; moreover, it differs between diseased and normal cells. Several studies have shown that EVs have a role in tumor formation and prognosis. It was also demonstrated that ionizing radiation can alter the cargo of EVs. EVs, in turn can modulate radiation responses and they play a role in radiation-induced bystander effects. Due to their biocompatibility and selective targeting, EVs are suitable nanocarrier candidates of drugs in various diseases, including cancer. Furthermore, the cargo of EVs can be engineered, and in this way they can be designed to carry certain genes or even drugs, similar to synthetic nanoparticles. In this review, we describe the biological characteristics of EVs, focusing on the recent efforts to use EVs as nanocarriers in oncology, the effects of EVs in radiation therapy, highlighting the possibilities to use EVs as nanocarriers to modulate radiation effects in clinical applications.

Comparative sensitivity to gamma radiation at the organismal, cell and DNA level in young plants of Norway spruce, Scots pine and Arabidopsis thaliana

Persistent DNA damage in gamma-exposed Norway spruce, Scots pine and Arabidopsis thaliana, but persistent adverse effects at the organismal and cellular level in the conifers only. Gamma radiation emitted from natural and anthropogenic sources may have strong negative impact on plants, especially at high dose rates. Although previous studies implied different sensitivity among species, information from comparative studies under standardized conditions is scarce. In this study, sensitivity to gamma radiation was compared in young seedlings of the conifers Scots pine and Norway spruce and the herbaceous Arabidopsis thaliana by exposure to ⁶⁰Co gamma dose rates of 1-540 mGy h^-1 for 144 h, as well as 360 h for A. thaliana. Consistent with slightly less prominent shoot apical meristem, in the conifers growth was significantly inhibited with increasing dose rate ≥ 40 mGy h^-1. Post-irradiation, the conifers showed dose-rate-dependent inhibition of needle and root development consistent with increasingly disorganized apical meristems with increasing dose rate, visible damage and mortality after exposure to ≥ 40 mGy h^-1. Regardless of gamma duration, A. thaliana showed no visible or histological damage or mortality, only delayed lateral root development after ≥ 100 mGy h^-1 and slightly, but transiently delayed post-irradiation reproductive development after ≥ 400 mGy h^-1. In all species dose-rate-dependent DNA damage occurred following ≥ 1-10 mGy h^-1 and was still at a similar level at day 44 post-irradiation. In conclusion, the persistent DNA damage (possible genomic instability) following gamma exposure in all species may suggest that DNA repair is not necessarily mobilized more extensively in A. thaliana than in Norway spruce and Scots pine, and the far higher sensitivity at the organismal and cellular level in the conifers indicates lower tolerance to DNA damage than in A. thaliana.

Bifunctional Au-Fe3O4 Nanoheterodimers Acting as X-ray Protector in Healthy Cells and as X-ray Enhancer in Tumor Cells

Bifunctional Au-Fe₃O₄ nanoheterodimers were synthesized by thermally decomposing Fe(III)oleate on gold nanoparticles followed by functionalizing with tiron, 2,3-dihydroxybenzoic acid, or caffeic acid. These catechol derivatives are antioxidative and thus are predicted to function as superoxide scavengers. In particular, caffeic acid lost its antioxidant capacity, although it was covalently linked through its carboxyl moiety to the Fe₃O₄ surface. Tiron was shown to bind via its catechol group to the Au-Fe₃O₄ nanoheterodimers, and 2,3-dihydroxybenzoic was just physisorbed between the oleic acid surface structures. Caffeic-acid stabilized Au-Fe₃O₄ nanoheterodimers turned out to act as X-ray protector in healthy cells but as X-ray enhancing agents in cancer cells. Furthermore, these functionalized Au-Fe₃O₄ nanoheterodimers were found to inhibit the migratory capacity of the cancer cells.

Effects of Simulated Space Radiations on the Tomato Root Proteome

Plant cultivation on spacecraft or planetary outposts is a promising and actual perspective both for food and bioactive molecules production. To this aim, plant response to ionizing radiations, as an important component of space radiation, must be assessed through on-ground experiments due to the potentially fatal effects on living systems. Hereby, we investigated the effects of X-rays and γ-rays exposure on tomato "hairy root" cultures (HRCs), which represent a solid platform for the production of pharmaceutically relevant molecules, including metabolites and recombinant proteins. In a space application perspective, we used an HRC system previously fortified through the accumulation of anthocyanins, which are known for their anti-oxidant properties. Roots were independently exposed to different photon radiations, namely X-rays (250 kV) and γ-rays (Co60, 1.25 MeV), both at the absorbed dose levels of 0.5, 5, and 10 Gy. Molecular changes induced in the proteome of HRCs were investigated by a comparative approach based on two-dimensional difference in-gel electrophoresis (2D-DIGE) technology, which allowed to highlight dynamic processes activated by these environmental stresses. Results revealed a comparable response to both photon treatments. In particular, the presence of differentially represented proteins were observed only when roots were exposed to 5 or 10 Gy of X-rays or γ-rays, while no variations were appreciated at 0.5 Gy of both radiations, when compared with unexposed control. Differentially represented proteins were identified by mass spectrometry procedures and their functional interactions were analyzed, revealing variations in the activation of stress response integrated mechanisms as well as in carbon/energy and protein metabolism. Specific results from above-mentioned procedures were validated by immunoblotting. Finally, a morphometric analysis verified the absence of significant alterations in the development of HRCs, allowing to ascribe the observed variations of protein expression to processes of acclimation to ionizing radiations. Overall results contribute to a meaningful risk evaluation for biological systems exposed to extra-terrestrial environments, in the perspective of manned interplanetary missions planned for the near future.

Reducing the ionizing radiation background does not significantly affect the evolution of Escherichia coli populations over 500 generations

Over millennia, life has been exposed to ionizing radiation from cosmic rays and natural radioisotopes. Biological experiments in underground laboratories have recently demonstrated that the contemporary terrestrial radiation background impacts the physiology of living organisms, yet the evolutionary consequences of this biological stress have not been investigated. Explaining the mechanisms that give rise to the results of underground biological experiments remains difficult, and it has been speculated that hereditary mechanisms may be involved. Here, we have used evolution experiments in standard and very low-radiation backgrounds to demonstrate that environmental ionizing radiation does not significantly impact the evolutionary trajectories of E. coli bacterial populations in a 500 generations evolution experiment.

The Screening of Renoprotective Agents by 99mTc-DMSA: A Review of Preclinical Studies

BACKGROUND

Nephrotoxicity is a prevalent consequence of cancer treatment using radiotherapy and chemotherapy or their combination. There are two methods; histological and biochemical, to assess the kidney damage caused by toxic agents in animal studies. Although these methods are used for the try-out of renoprotective factors, these methods are invasive and time-consuming, and also, lack the necessary sensitivity for primary diagnosis. Quantitative renal 99mTc-DMSA scintigraphy is a noninvasive, precise and sensitive radionuclide technique which is used to assess the extent of kidney damage, so that the extent of injury to the kidney will be indicated by the renal uptake rate of 99mTc-DMSA in the kidney. In addition, this scintigraphy evaluates the effect of the toxic agents by quantifying the alterations in the biodistribution of the radiopharmaceutical.

CONCLUSION

In this review, the recent findings about the renoprotective agents were evaluated and screened with respect to the use of 99mTc-DMSA , which is preclinically and clinically used for animal cases and cancer patients under the treatment by radiotherapy and chemotherapy.

Implementation of the Chick Chorioallantoic Membrane (CAM) Model in Radiation Biology and Experimental Radiation Oncology Research

Radiotherapy (RT) is part of standard cancer treatment. Innovations in treatment planning and increased precision in dose delivery have significantly improved the therapeutic gain of radiotherapy but are reaching their limits due to biologic constraints. Thus, a better understanding of the complex local and systemic responses to RT and of the biological mechanisms causing treatment success or failure is required if we aim to define novel targets for biological therapy optimization. Moreover, optimal treatment schedules and prognostic biomarkers have to be defined for assigning patients to the best treatment option. The complexity of the tumor environment and of the radiation response requires extensive in vivo experiments for the validation of such treatments. So far in vivo investigations have mostly been performed in time- and cost-intensive murine models. Here we propose the implementation of the chick chorioallantoic membrane (CAM) model as a fast, cost-efficient model for semi high-throughput preclinical in vivo screening of the modulation of the radiation effects by molecularly targeted drugs. This review provides a comprehensive overview on the application spectrum, advantages and limitations of the CAM assay and summarizes current knowledge of its applicability for cancer research with special focus on research in radiation biology and experimental radiation oncology.

Gut Microbiomics-A Solution to Unloose the Gordian Knot of Biological Effects of Ionizing Radiation

The Chernobyl and Fukushima nuclear accidents have called forth a growing body of research on their biological aftermaths. A variety of wild organisms, including primates, birds, fish, insects, and worms are being studied in the affected areas, with emerging morphological, physiological, and genetic aberrations ascribed to ionizing radiation. Despite the effort in surveying Chernobyl and Fukushima wildlife, little is known about the microorganisms associated with these radiation-contaminated animals. The microbiota, especially the gut commensal, plays an important role in shaping the metabolic reservoir and immune system of the host, and is sensitive to a wide array of environmental factors, including ionizing radiation. Humans and limited numbers of laboratory species have been the main subjects of microbiome studies, however, a more practical insight on host-gut microbiota dynamics under environmental impact should be explored in natural habitats. In this analysis, we introduced a working model explaining possible mechanisms of ionizing radiation on the gut microbiota, with an evaluation of the gut microbiota as a potential biomarker for exposure to ionizing radiation.

No evidence of a protective or cumulative negative effect of UV-B on growth inhibition induced by gamma radiation in Scots pine (Pinus sylvestris) seedlings

Exposure to ambient UV-B radiation may prime protective responses towards various stressors in plants, though information about interactive effects of UV-B and gamma radiation is scarce. Here, we aimed to test whether UV-B exposure could prime acclimatisation mechanisms contributing to tolerance to low-moderate gamma radiation levels in Scots pine seedlings, and concurrently whether simultaneous UV-B and gamma exposure may have an additive adverse effect on seedlings that had previously not encountered either of these stressors. Responses to simultaneous UV-B (0.35 W m-2) and gamma radiation (10.2-125 mGy h-1) for 6 days with or without UV-B pre-exposure (0.35 W m-2, 4 days) were studied across various levels of organisation, as compared to effects of either radiation type. In contrast to UV-B, and regardless of UV-B presence, gamma radiation at ≥42.9 mGy h-1 caused increased formation of reactive oxygen species and reduced shoot length, and reduced root length at 125 mGy h-1. In all experiments there was a gamma dose rate-dependent increase in DNA damage at ≥10.8 mGy h-1, generally with additional UV-B-induced damage. Gamma-induced growth inhibition and gamma- and UV-B-induced DNA damage were still visible 44 days post-irradiation, even at 20.7 mGy h-1, probably due to genomic instability, but this was reversed after 8 months. In conclusion, there was no evidence of a protective effect of UV-B on gamma-induced growth inhibition and DNA damage in Scots pine, and no additive adverse effect of gamma and UV-B radiation on growth in spite of the additional UV-B-induced DNA damage.

Exploring Radiation Response in Two Head and Neck Squamous Carcinoma Cell Lines Through Metabolic Profiling

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common form of cancer worldwide. Radiotherapy, with or without surgery, represents the major approach to curative treatment. However, not all tumors are equally sensitive to irradiation. It is therefore of interest to apply newer system biology approaches (e.g., metabolic profiling) in squamous cancer cells with different radiosensitivities in order to provide new insights on the mechanisms of radiation response. In this study, two cultured HNSCC cell lines from the same donor, UM-SCC-74A and UM-SCC-74B, were first genotyped using Short Tandem Repeat (STR), and assessed for radiation response by the means of clonogenic survival and growth inhibition assays. Thereafter, cells were cultured, irradiated and collected for subsequent metabolic profiling analyses using liquid chromatography-mass spectrometry (LC-MS). STR verified the similarity of UM-SCC-74A and UM-SCC-74B cells, and three independent assays proved UM-SCC-74B to be clearly more radioresistant than UM-SCC-74A. The LC-MS metabolic profiling demonstrated significant differences in the intracellular metabolome of the two cell lines before irradiation, as well as significant alterations after irradiation. The most important differences between the two cell lines before irradiation were connected to nicotinic acid and nicotinamide metabolism and purine metabolism. In the more radiosensitive UM-SCC-74A cells, the most significant alterations after irradiation were linked to tryptophan metabolism. In the more radioresistant UM-SCC-74B cells, the major alterations after irradiation were connected to nicotinic acid and nicotinamide metabolism, purine metabolism, the methionine cycle as well as the serine, and glycine metabolism. The data suggest that the more radioresistant cell line UM-SCC-74B altered the metabolism to control redox-status, manage DNA-repair, and change DNA methylation after irradiation. This provides new insights on the mechanisms of radiation response, which may aid future identification of biomarkers associated with radioresistance of cancer cells.

Laser-driven radiation: Biomarkers for molecular imaging of high dose-rate effects

Recently developed short‐pulsed laser sources garner high dose‐rate beams such as energetic ions and electrons, x rays, and gamma rays. The biological effects of laser‐generated ion beams observed in recent studies are different from those triggered by radiation generated using classical accelerators or sources, and this difference can be used to develop new strategies for cancer radiotherapy. High‐power lasers can now deliver particles in doses of up to several Gy within nanoseconds. The fast interaction of laser‐generated particles with cells alters cell viability via distinct molecular pathways compared to traditional, prolonged radiation exposure. The emerging consensus of recent literature is that the differences are due to the timescales on which reactive molecules are generated and persist, in various forms. Suitable molecular markers have to be adopted to monitor radiation effects, addressing relevant endogenous molecules that are accessible for investigation by noninvasive procedures and enable translation to clinical imaging. High sensitivity has to be attained for imaging molecular biomarkers in cells and in vivo to follow radiation‐induced functional changes. Signal‐enhanced MRI biomarkers enriched with stable magnetic nuclear isotopes can be used to monitor radiation effects, as demonstrated recently by the use of dynamic nuclear polarization (DNP) for biomolecular observations in vivo. In this context, nanoparticles can also be used as radiation enhancers or biomarker carriers. The radiobiology‐relevant features of high dose‐rate secondary radiation generated using high‐power lasers and the importance of noninvasive biomarkers for real‐time monitoring the biological effects of radiation early on during radiation pulse sequences are discussed.

Modes of action and adverse effects of gamma radiation in an aquatic macrophyte Lemna minor

High dose rates of ionizing radiation have been reported to cause adverse effects such as reduction in reproduction and growth, and damage to protein and lipids in primary producers. However, the relevant effects of ionizing radiation are still poorly understood in aquatic plants. This study was intended to characterize the biological effects and modes of action (MoAs) of ionizing radiation using gamma radiation as the prototypical stressor and duckweed Lemna minor as a model organism. Lemna minor was exposed to 1, 14, 24, 46, 70 mGy/h gamma radiation dose rates from a cobalt-60 source for 7 days following the testing principles of the OECD test guideline 221. A suite of bioassays was applied to assess the biological effects of gamma radiation at multiple levels of biological organization, including detection of reactive oxygen species (ROS), oxidative stress responses (total glutathione, tGSH; lipid peroxidation, LPO), DNA damage, mitochondrial dysfunctions (mitochondrial membrane potential, MMP), photosynthetic parameters (chlorophyll a, chl a; chlorophyll b, chl b; carotenoids; Photosystem II (PSII) performance; CO₂ uptake), intercellular signaling (Ca²⁺ release) and growth. Gamma radiation increased DNA damage, tGSH level and Ca²⁺ content together with reduction in chlorophyll content, maximal PSII efficiency and CO₂ uptake at dose rates between 1 and 14 mGy/h, whereas increases in cellular ROS and LPO, inhibition of MMP and growth were observed at higher dose rates (≥24 mGy/h). A network of toxicity pathways was proposed to portray the causal relationships between gamma radiation-induced physiological responses and adverse outcomes to support the development of Adverse Outcome Pathways (AOPs) for ionizing radiation-mediated effects in primary producers.

DNA Damage and Associated DNA Repair Defects in Disease and Premature Aging

Genetic information is constantly being attacked by intrinsic and extrinsic damaging agents, such as reactive oxygen species, atmospheric radiation, environmental chemicals, and chemotherapeutics. If DNA modifications persist, they can adversely affect the polymerization of DNA or RNA, leading to replication fork collapse or transcription arrest, or can serve as mutagenic templates during nucleic acid synthesis reactions. To combat the deleterious consequences of DNA damage, organisms have developed complex repair networks that remove chemical modifications or aberrant base arrangements and restore the genome to its original state. Not surprisingly, inherited or sporadic defects in DNA repair mechanisms can give rise to cellular outcomes that underlie disease and aging, such as transformation, apoptosis, and senescence. In the review here, we discuss several genetic disorders linked to DNA repair defects, attempting to draw correlations between the nature of the accumulating DNA damage and the pathological endpoints, namely cancer, neurological disease, and premature aging.

An investigation into neutron-induced bystander effects: How low can you go?

Neutron radiation is very harmful to both individual organisms and the environment. A n understanding of all aspects of both direct and indirect effects of radiation is necessary to accurately assess the risk of neutron radiation exposure. This review seeks to review current evidence in the literature for radiation-induced bystander effects and related effects attributable to neutron radiation. It also attempts to determine if the suggested evidence in the literature is sufficient to justify claims that neutron-based radiation can cause radiation-induced bystander effects. Lastly, the present paper suggests potential directions for future research concerning neutron radiation-induced bystander effects. Data was collected from studies investigating radiation-induced bystander effects and was used to mathematically generate pooled datasets and putative trends; this was done to potentially elucidate both the appearance of a conventional trend for radiation-induced bystander effects in studies using different types of radiation. Furthermore, literature review was used to compare studies utilizing similar tissue models to determine if neutron effects follow similar trends as those produced by electromagnetic radiation. We conclude that the current understanding of neutron-attributable radiation-induced bystander effects is incomplete. Various factors such as high gamma contamination during the irradiations, unestablished thresholds for gamma effects, different cell lines, energies, and different dose rates affected our ability to confirm a relationship between neutron irradiation and RIBE, particularly in low-dose regions below 100 mGy. It was determined through meta-analysis of the data that effects attributable to neutrons do seem to exist at higher doses, while gamma effects seem likely predominant at lower dose regions. Therefore, whether neutrons can induce bystander effects at lower doses remains unclear. Further research is required to confirm these findings and various recommendations are made to assist in this effort. With these recommendations, we hope that research conducted in the future will be better equipped to explore the indirect effects of neutron radiation as they pertain to biological and ecological phenomena.

An Effective Protocol for Proteome Analysis of Medaka (Oryzias latipes) after Acute Exposure to Ionizing Radiation

All terrestrial organisms are subject to evolutionary pressures associated with natural sources of ionizing radiation (IR). The legacy of human-induced IR associated with energy, weapons production, medicine, and research has changed the distribution and magnitude of these evolutionary pressures. To date, no study has systematically examined the effects of environmentally relevant doses of radiation exposure across an organismal proteome. This void in knowledge has been due, in part, to technological deficiencies that have hampered quantifiable environmentally relevant IR doses and sensitive detection of proteomic responses. Here, we describe a protocol that addresses both needs, combining quantifiable IR delivery with a reliable method to yield proteomic comparisons of control and irradiated Medaka fish. Exposures were conducted at the Savannah River Ecology Laboratory (SREL, in Aiken, SC), where fish were subsequently dissected into three tissue sets (carcasses, organs and intestines) and frozen until analysis. Tissue proteins were extracted, resolved by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE), and each sample lane was divided into ten equal portions. Following in-gel tryptic digestion, peptides released from each gel portion were identified and quantified by Liquid Chromatography-Mass Spectrometry (LC-MS/MS) to obtain the most complete, comparative study to date of proteomic responses to environmentally relevant doses of IR. This method provides a simple approach for use in ongoing epidemiologic studies of chronic exposure to environmentally relevant levels of IR and should also serve well in physiological, developmental, and toxicological studies.