Effects of ionizing radiation in targeted and nontargeted cells

Radiation-induced bystander effect on the brain after fractionated spinal cord irradiation of aging rats

We investigated the influence of the so-called bystander effect on metabolic and histopathological changes in the rat brain after fractionated spinal cord irradiation. The study was initiated with adult Wistar male rats (n = 20) at the age of 9 months. The group designated to irradiation (n = 10) and the age-matched control animals (n = 10) were subjected to an initial measurement using in vivo proton magnetic resonance spectroscopy (1H MRS) and magnetic resonance imaging (MRI). After allowing the animals to survive until 12 months, they received fractionated spinal cord irradiation with a total dose of 24 Gy administered in 3 fractions (8 Gy per fraction) once a week on the same day for 3 consecutive weeks. 1H MRS and MRI of brain metabolites were performed in the hippocampus, corpus striatum, and olfactory bulb (OB) before irradiation (9-month-old rats) and subsequently 48 h (12-month-old) and 2 months (14-month-old) after the completion of irradiation. After the animals were sacrificed at the age of 14 months, brain tissue changes were investigated in two neurogenic regions: the hippocampal dentate gyrus (DG) and the rostral migratory stream (RMS). By comparing the group of 9-month-old rats and individuals measured 48 h (at the age of 12 months) after irradiation, we found a significant decrease in the ratio of total N-acetyl aspartate to total creatine (tNAA/tCr) and gamma-aminobutyric acid to tCr (GABA/tCr) in OB and hippocampus. A significant increase in myoinositol to tCr (mIns/tCr) in the OB persisted up to 14 months of age. Proton nuclear magnetic resonance (1H NMR)-based plasma metabolomics showed a significant increase in keto acids and decreased tyrosine and tricarboxylic cycle enzymes. Morphometric analysis of neurogenic regions of 14-month-old rats showed well-preserved stem cells, neuroblasts, and increased neurodegeneration. The radiation-induced bystander effect more significantly affected metabolite concentration than the distribution of selected cell types.

Two distinct mechanisms lead to either oocyte or spermatocyte decrease in C. elegans after whole developmental exposure to γ-rays

Wildlife is subject to various sources of pollution, including ionizing radiation. Adverse effects can impact the survival, growth, or reproduction of organisms, later affecting population dynamics. In invertebrates, reproduction, which directly impacts population dynamics, has been found to be the most radiosensitive endpoint. Understanding the underlying molecular pathways inducing this reproduction decrease can help to comprehend species-specific differences in radiosensitivity. From our previous studies, we found that decrease in reproduction is life stage dependent in the roundworm Caenorhabditis elegans, possibly resulting from an accumulation of damages during germ cell development and gamete differentiation. To go further, we used the same experimental design to assess more precisely the molecular determinants of reproductive toxicity, primarily decreases in gamete number. As before, worms were chronically exposed to 50 mGy·h-1 external gamma ionizing radiation throughout different developmental periods (namely embryogenesis, gametogenesis, and full development). To enable cross species extrapolation, conserved molecular pathways across invertebrates and vertebrates were analysed: apoptosis and MAP kinase Ras/ERK (MPK-1), both involved in reproduction and stress responses. Our results showed that these pathways are life-stage dependent, resulting from an accumulation of damages upon chronic exposure to IR throughout the life development. The Ras/ERK pathway was activated in our conditions in the pachytene region of the gonad where it regulates cell fate including apoptosis, but not in the ovulation zone, where it controls oocyte maturation and ovulation. Additionally, assessment of germ cell proliferation via Ras/ERK pathway showed no effect. Finally, a functional analysis of apoptosis revealed that while the decrease of the ovulation rate is caused by DNA-damaged induced apoptosis, this process does not occur in spermatocytes. Thus, sperm decrease seems to be mediated via another mechanism, probably a decrease in germ cell proliferation speed that needs further investigation to better characterize sex-specific responses to IR exposure. These results are of main importance to describe radio-induced reprotoxic effects and contribute as weight of evidence for the AOP #396 "Deposition of ionizing energy leads to population decline via impaired meiosis".

Radiation-induced bystander effect and its clinical implications

For many years, targeted DNA damage caused by radiation has been considered the main cause of various biological effects. Based on this paradigm, any small amount of radiation is harmful to the organism. Epidemiological studies of Japanese atomic bomb survivors have proposed the linear-non-threshold model as the dominant standard in the field of radiation protection. However, there is increasing evidence that the linear-non-threshold model is not fully applicable to the biological effects caused by low dose radiation, and theories related to low dose radiation require further investigation. In addition to the cell damage caused by direct exposure, non-targeted effects, which are sometimes referred to as bystander effects, abscopal effects, genetic instability, etc., are another kind of significant effect related to low dose radiation. An understanding of this phenomenon is crucial for both basic biomedical research and clinical application. This article reviews recent studies on the bystander effect and summarizes the key findings in the field. Additionally, it offers a cross-sectional comparison of bystander effects caused by various radiation sources in different cell types, as well as an in-depth analysis of studies on the potential biological mechanisms of bystander effects. This review aims to present valuable information and provide new insights on the bystander effect to enlighten both radiobiologists and clinical radiologists searching for new ways to improve clinical treatments.

Short-term and bystander effects of radiation on murine submandibular glands

Many patients treated for head and neck cancers experience salivary gland hypofunction due to radiation damage. Understanding the mechanisms of cellular damage induced by radiation treatment is important in order to design methods of radioprotection. In addition, it is crucial to recognize the indirect effects of irradiation and the systemic responses that may alter saliva secretion. In this study, radiation was delivered to murine submandibular glands (SMGs) bilaterally, using a 137Cs gamma ray irradiator, or unilaterally, using a small-animal radiation research platform (SARRP). Analysis at 3, 24 and 48 h showed dynamic changes in mRNA and protein expression in SMGs irradiated bilaterally. Unilateral irradiation using the SARRP caused similar changes in the irradiated SMGs, as well as significant off-target, bystander effects in the non-irradiated contralateral SMGs.

Inhibitory effects of saeu-jeot extract on NLRP3 inflammasome activation and radiation-induced micronucleus formation

Purpose

Saeu‐jeot, or shrimp paste, is a traditional Korean high‐salt fermented seafood. This study elucidated the effects of saeu‐jeot extract (SJE) on NLRP3 inflammasome activation and radiation‐induced micronucleus formation.

Method

We treated lipopolysaccharide‐primed mouse bone marrow‐derived macrophages with the NLRP3 inflammasome activators ATP and nigericin. We also analyzed the acute effects of ionizing radiation on micronucleated polychromatic erythrocytes (MnPCEs) in whole‐body gamma‐irradiated male BALB/c and C57BL/6 mice after oral administration of SJE.

Results

SJE significantly inhibited NLRP3 inflammasome activation, reducing IL‐1β secretion in vitro. In addition, the frequency of MnPCEs was significantly lower in SJE‐treated mice.

Conclusions

SJE has anti‐inflammatory effects and reduces radiation‐induced chromosome damage.

Advance in knowledge: There are no reports concerning the effects of SJE on NLRP3 inflammasome activation or radioprotection. This experiment showed the radioprotective effects of saeu‐jeot.

Micro-RNA and Proteomic Profiles of Plasma-Derived Exosomes from Irradiated Mice Reveal Molecular Changes Preventing Apoptosis in Neonatal Cerebellum

Cell communication via exosomes is capable of influencing cell fate in stress situations such as exposure to ionizing radiation. In vitro and in vivo studies have shown that exosomes might play a role in out-of-target radiation effects by carrying molecular signaling mediators of radiation damage, as well as opposite protective functions resulting in resistance to radiotherapy. However, a global understanding of exosomes and their radiation-induced regulation, especially within the context of an intact mammalian organism, has been lacking. In this in vivo study, we demonstrate that, compared to sham-irradiated (SI) mice, a distinct pattern of proteins and miRNAs is found packaged into circulating plasma exosomes after whole-body and partial-body irradiation (WBI and PBI) with 2 Gy X-rays. A high number of deregulated proteins (59% of WBI and 67% of PBI) was found in the exosomes of irradiated mice. In total, 57 and 13 miRNAs were deregulated in WBI and PBI groups, respectively, suggesting that the miRNA cargo is influenced by the tissue volume exposed to radiation. In addition, five miRNAs (miR-99b-3p, miR-200a-3p, miR-200a, miR-182-5p, miR-182) were commonly overexpressed in the exosomes from the WBI and PBI groups. In this study, particular emphasis was also given to the determination of the in vivo effect of exosome transfer by intracranial injection in the highly radiosensitive neonatal cerebellum at postnatal day 3. In accordance with a major overall anti-apoptotic function of the commonly deregulated miRNAs, here, we report that exosomes from the plasma of irradiated mice, especially in the case of WBI, prevent radiation-induced apoptosis, thus holding promise for exosome-based future therapeutic applications against radiation injury.

Towards the characterization of neutron carcinogenesis through direct action simulations of clustered DNA damage

Neutron exposure poses a unique radiation protection concern because neutrons have a large, energy-dependent relative biological effectiveness (RBE) for stochastic effects. Recent computational studies on the microdosimetric properties of neutron dose deposition have implicated clustered DNA damage as a likely contributor to this marked energy dependence. So far, publications have focused solely on neutron RBE for inducing clusters of DNA damage containing two or more DNA double strand breaks (DSBs). In this study, we have conducted a novel assessment of neutron RBE for inducing all types of clustered DNA damage that contain two or more lesions, stratified by whether the clusters contain DSBs (complex DSB clusters) or not (non-DSB clusters). This assessment was conducted for eighteen initial neutron energies between 1 eV and 10 MeV as well as a reference radiation of 250 keV x-rays. We also examined the energy dependence of cluster length and cluster complexity because these factors are believed to impact the DNA repair process. To carry out our investigation, we developed a user-friendly TOPAS-nBio application that includes a custom nuclear DNA model and a novel algorithm for recording clustered DNA damage. We found that neutron RBE for inducing complex DSB clusters exhibited similar energy dependence to the canonical neutron RBE for stochastic radiobiological effects, at multiple depths in human tissue. Qualitatively similar results were obtained for non-DSB clusters, although the quantitative agreement was lower. Additionally we identified a significant neutron energy dependence in the average length and complexity of clustered lesions. These results support the idea that many types of clustered DNA damage contribute to the energy dependence of neutron RBE for stochastic radiobiological effects and imply that the size and constituent lesions of individual clusters should be taken into account when modeling DNA repair. Our results were qualitatively consistent for (i) multiple radiation doses (including a low-dose 0.1 Gy irradiation), (ii) variations in the maximal lesion separation distance used to define a cluster, and (iii) two distinct collections of physics models used to govern particle transport. Our complete TOPAS-nBio application has been released under an open-source license to enable others to independently validate our work and to expand upon it.

Deciphering Differential Life Stage Radioinduced Reproductive Decline in Caenorhabditis elegans through Lipid Analysis

Wildlife is chronically exposed to various sources of ionizing radiations, both environmental or anthropic, due to nuclear energy use, which can induce several defects in organisms. In invertebrates, reproduction, which directly impacts population dynamics, has been found to be the most radiosensitive endpoint. Understanding the underlying molecular pathways inducing this reproduction decrease can help in predicting the effects at larger scales (i.e., population). In this study, we used a life stage dependent approach in order to better understand the molecular determinants of reproduction decrease in the roundworm C. elegans. Worms were chronically exposed to 50 mGy·h⁻¹ external gamma ionizing radiations throughout different developmental periods (namely embryogenesis, gametogenesis, and full development). Then, in addition to reproduction parameters, we performed a wide analysis of lipids (different class and fatty acid via FAMES), which are both important signaling molecules for reproduction and molecular targets of oxidative stress. Our results showed that reproductive defects are life stage dependent, that lipids are differently misregulated according to the considered exposure (e.g., upon embryogenesis and full development) and do not fully explain radiation induced reproductive defects. Finally, our results enable us to propose a conceptual model of lipid signaling after radiation stress in which both the soma and the germline participate.

Radioprotective Effect of Flavonoids on Ionizing Radiation-Induced Brain Damage

Patients receiving brain radiotherapy may suffer acute or chronic side effects. Ionizing radiation induces the production of intracellular reactive oxygen species and pro-inflammatory cytokines in the central nervous system, leading to brain damage. Complementary Chinese herbal medicine therapy may reduce radiotherapy-induced side effects. Flavonoids are a class of natural products which can be extracted from Chinese herbal medicine and have been shown to have neuroprotective and radioprotective properties. Flavonoids are effective antioxidants and can also inhibit regulatory enzymes or transcription factors important for controlling inflammatory mediators, affect oxidative stress through interaction with DNA and enhance genomic stability. In this paper, radiation-induced brain damage and the relevant molecular mechanism were summarized. The radio-neuro-protective effect of flavonoids, i.e., antioxidant, anti-inflammatory and maintaining genomic stability, were then reviewed. We concluded that flavonoids treatment may be a promising complementary therapy to prevent radiotherapy-induced brain pathophysiological changes and cognitive impairment.

The influence of H/D kinetic isotope effect on radiation-induced transformations of hydroxyl-containing compounds in aqueous solutions

Vicinal diols and its derivatives can be exploited as model compounds for the investigation of radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as carbohydrates, phospholipids, ribonucleotides, amino acids, and peptides. In this paper, for the first time, the prospects of isotope reinforcement approach in inhibiting free-radical transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d₁ aqueous solutions. At an absorbed dose rate of 0.110 ± 0.003 Gy·s^-1 a profound kinetic isotope effect (KIE) is observed for the non-branched chain formation of acetone, which is a final dehydration product of predominant carbon-centred radicals CH₃·C(OH)CH₂OH. In 0.1 and 1 M deaerated solutions at pH 7.00 ± 0.01, the values of KIE are 8.9 ± 1.7 and 15.3 ± 3.1, respectively. A rationale for the fact that a strong KIE takes place only in the case of chain processes, which may occur during free-radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol and 2-propanol-2-d₁ indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d₂. This indicates that the type (primary, secondary) of the β-carbonyl radicals formed as a result of CH₃·C(OH)CH(OH)R (R = H, CH₃) dehydration determines the manifestation of the effect.

Reprint of: Deciphering and simulating models of radiation genotoxicity with CRISPR/Cas9 systems

This short review explores the utility and applications of CRISPR/Cas9 systems in radiobiology. Specifically, in the context of experimentally simulating genotoxic effects of Ionizing Radiation (IR) to determine the contributions from DNA targets and 'Complex Double-Stranded Breaks' (complex DSBs) to the IR response. To elucidate this objective, this review considers applications of CRISPR/Cas9 on nuclear DNA targets to recognize the respective 'nucleocentric' response. The article also highlights contributions from mitochondrial DNA (mtDNA) - an often under-recognized target in radiobiology. This objective requires accurate experimental simulation of IR-like effects and parameters with the CRISPR/Cas9 systems. Therefore, the role of anti-CRISPR proteins in modulating enzyme activity to simulate dose rate - an important factor in radiobiology experiments is an important topic of this review. The applications of auxiliary domains on the Cas9 nuclease to simulate oxidative base damage and multiple stressor experiments are also topics of discussion. Ultimately, incorporation of CRISPR/Cas9 experiments into computational parameters in radiobiology models of IR damage and shortcomings to the technology are discussed as well. Altogether, the simulation of IR parameters and lack of damage to non-DNA targets in the CRISPR/Cas9 system lends this rapidly emerging tool as an effective model of IR induced DNA damage. Therefore, this literature review ultimately considers the relevance of complex DSBs to radiobiology with respect to using the CRISPR/Cas9 system as an effective experimental tool in models of IR induced effects.

Deciphering and simulating models of radiation genotoxicity with CRISPR/Cas9 systems

This short review explores the utility and applications of CRISPR/Cas9 systems in radiobiology. Specifically, in the context of experimentally simulating genotoxic effects of Ionizing Radiation (IR) to determine the contributions from DNA targets and 'Complex Double-Stranded Breaks' (complex DSBs) to the IR response. To elucidate this objective, this review considers applications of CRISPR/Cas9 on nuclear DNA targets to recognize the respective 'nucleocentric' response. The article also highlights contributions from mitochondrial DNA (mtDNA) - an often under-recognized target in radiobiology. This objective requires accurate experimental simulation of IR-like effects and parameters with the CRISPR/Cas9 systems. Therefore, the role of anti-CRISPR proteins in modulating enzyme activity to simulate dose rate - an important factor in radiobiology experiments is an important topic of this review. The applications of auxiliary domains on the Cas9 nuclease to simulate oxidative base damage and multiple stressor experiments are also topics of discussion. Ultimately, incorporation of CRISPR/Cas9 experiments into computational parameters in radiobiology models of IR damage and shortcomings to the technology are discussed as well. Altogether, the simulation of IR parameters and lack of damage to non-DNA targets in the CRISPR/Cas9 system lends this rapidly emerging tool as an effective model of IR induced DNA damage. Therefore, this literature review ultimately considers the relevance of complex DSBs to radiobiology with respect to using the CRISPR/Cas9 system as an effective experimental tool in models of IR induced effects.

DNA damage in human skin and the capacities of natural compounds to modulate the bystander signalling

Human skin is a stratified organ frequently exposed to sun-generated ultraviolet radiation (UVR), which is considered one of the major factors responsible for DNA damage. Such damage can be direct, through interactions of DNA with UV photons, or indirect, mainly through enhanced production of reactive oxygen species that introduce oxidative changes to the DNA. Oxidative stress and DNA damage also associate with profound changes at the cellular and molecular level involving several cell cycle and signal transduction factors responsible for DNA repair or irreversible changes linked to ageing. Crucially, some of these factors constitute part of the signalling known for the induction of biological changes in non-irradiated, neighbouring cells and defined as the bystander effect. Network interactions with a number of natural compounds, based on their known activity towards these biomarkers in the skin, reveal the capacity to inhibit both the bystander signalling and cell cycle/DNA damage molecules while increasing expression of the anti-oxidant enzymes. Based on this information, we discuss the likely polypharmacology applications of the natural compounds and next-generation screening technologies in improving the anti-oxidant and DNA repair capacities of the skin.

Investigating the Sonodynamic-Radiosensitivity Effect of Gold Nanoparticles on HeLa Cervical Cancer Cells

BACKGROUND

In this article, we estimated the combined effect of radiotherapy (RT) with ultrasound (US) wave and the ability of gold nanoparticles (GNPs) to improve their combined therapeutic effects.

METHODS

At first, HeLa cells received the various treatment modalities: RT (6 MV; 0.5, 1, and 2 Gy), US irradiation (1 MHz; 0.5, 1, and 1.5 W/cm², 1 minute), and RT+US. Afterwards, the enhanced effect of US on RT was evaluated. Then, the effect of the synthesized GNPs at different concentrations (0.2, 1, and 5 μg/mL, 24 hours) was evaluated to assess the effect on HeLa cells combined with RT+US. Cell survival rates in the different treatment groups at 24, 48, and 72 hours post-treatment were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and trypan blue assays.

RESULTS

Our results show US irradiation could enhance the effect of RT at the same radiation dose and could be utilized as a sensitizer agent for RT. Moreover, our findings indicate RT+US in combination with different nanoparticle concentrations could enhance the effect of RT+US so that they can improve the treatment results up to 9.93 times and act as sonodynamic-radiosensitivity. These results also indicate that the combination of RT with US along with GNPs has synergistic effects compared to RT or US alone. Cell survival results show that combining the low US waves (1.5 W/cm²), GNPs (5 μ/mL), and X-rays (2 Gy) increase the cytotoxicity on HeLa cell up to 95.8%.

CONCLUSION

We concluded that GNPs could act as a good sensitizing agent in RT+US irradiation and could result in the synergistic effects.

Relevance of Non-Targeted Effects for Radiotherapy and Diagnostic Radiology; A Historical and Conceptual Analysis of Key Players

Non-targeted effects (NTE) such as bystander effects or genomic instability have been known for many years but their significance for radiotherapy or medical diagnostic radiology are far from clear. Central to the issue are reported differences in the response of normal and tumour tissues to signals from directly irradiated cells. This review will discuss possible mechanisms and implications of these different responses and will then discuss possible new therapeutic avenues suggested by the analysis. Finally, the importance of NTE for diagnostic radiology and nuclear medicine which stems from the dominance of NTE in the low-dose region of the dose–response curve will be presented. Areas such as second cancer induction and microenvironment plasticity will be discussed.

Protective effects of tea polyphenols and β-carotene against γ-radiation induced mutation and oxidative stress in Drosophila melanogaster

Background

The commonly consumed antioxidants β-carotene and tea polyphenols were used to assess their protective effects against γ-radiation induced sex-linked recessive lethal (SLRL) mutation and oxidative stress in Drosophila melanogaster. Third instar larvae and adult males of wild-type Oregon-K (ORK) were fed on test agents for 24 and 72 h respectively before exposure to 10Gy γ-irradiation. The treated/control flies were used to assess the induction of SLRLs. We also evaluated antioxidant properties of these phytochemicals in the third instar larvae.

Results

Different stages of spermatogenesis in adult males showed a decrease in γ-radiation induced SLRL frequencies upon co-treatment with test agents. A similar trend was observed in larvae. Furthermore, a significant increase in antioxidant enzymatic activities with a decrease in malondialdehyde content was observed.

Conclusion

β-carotene and tea polyphenols have exerted antigenotoxic and antioxidant effects in Drosophila. This study demonstrated the suitability of Drosophila as an alternative to mammalian testing for evaluating the antigenotoxic and antioxidant activity of natural products.

Bystander signaling via oxidative metabolism

The radiation-induced bystander effect (RIBE) is the initiation of biological end points in cells (bystander cells) that are not directly traversed by an incident-radiation track, but are in close proximity to cells that are receiving the radiation. RIBE has been indicted of causing DNA damage via oxidative stress, besides causing direct damage, inducing tumorigenesis, producing micronuclei, and causing apoptosis. RIBE is regulated by signaling proteins that are either endogenous or secreted by cells as a means of communication between cells, and can activate intracellular or intercellular oxidative metabolism that can further trigger signaling pathways of inflammation. Bystander signals can pass through gap junctions in attached cell lines, while the suspended cell lines transmit these signals via hormones and soluble proteins. This review provides the background information on how reactive oxygen species (ROS) act as bystander signals. Although ROS have a very short half-life and have a nanometer-scale sphere of influence, the wide variety of ROS produced via various sources can exert a cumulative effect, not only in forming DNA adducts but also setting up signaling pathways of inflammation, apoptosis, cell-cycle arrest, aging, and even tumorigenesis. This review outlines the sources of the bystander effect linked to ROS in a cell, and provides methods of investigation for researchers who would like to pursue this field of science.

Micronuclei Assessment of The Radioprotective Effects of Melatonin and Vitamin C in Human Lymphocytes

Objective

Critical macromolecules such as DNA maybe damaged by free radicals that are generated from the interaction of ionizing radiation with biological systems. Melatonin and vitamin C have been shown to be direct free radical scavengers. The aim of this study was to investigate the in vivo/in vitro radioprotective effects of melatonin and vitamin C separately and combined against genotoxicity induced by 6 MV x-ray irradiation in human cultured blood lymphocytes.

Materials and Methods

In this experimental study, fifteen volunteers were divided into three groups of melatonin, vitamin C and melatonin plus vitamin C treatment. Peripheral blood samples were collected from each group before, and 1, 2 and 3 hours after melatonin and vitamin C administration (separately and combined). The blood samples were then irradiated with 200 cGy of 6 MV x-ray. In order to characterize chromosomal aberrations, the lymphocyte samples were cultured with mitogenic stimulus on cytokinesisblocked binucleated cells.

Results

The samples collected 1hour after melatonin and vitamin C (separately and combined) ingestion exhibited a significant decrease in the incidence of micronuclei compared with their control group (P<0.05). The maximum synergic protection and reduction in frequency of micronuclei (57%) was observed 1 hour after vitamin C and melatonin administration combined.

Conclusion

We conclude that simultaneous administration of melatonin and vitamin C as radioprotector substances before irradiation may reduce genotoxicity caused by x-ray irradiation.

Key mechanisms involved in ionizing radiation-induced systemic effects. A current review

Organisms respond to physical, chemical and biological threats by a potent inflammatory response, aimed at preserving tissue integrity and restoring tissue homeostasis and function. Systemic effects in an organism refer to an effect or phenomenon which originates at a specific point and can spread throughout the body affecting a group of organs or tissues. Ionizing radiation (IR)-induced systemic effects arise usually from a local exposure of an organ or part of the body. This stress induces a variety of responses in the irradiated cells/tissues, initiated by the DNA damage response and DNA repair (DDR/R), apoptosis or immune response, including inflammation. Activation of this IR-response (IRR) system, especially at the organism level, consists of several subsystems and exerts a variety of targeted and non-targeted effects. Based on the above, we believe that in order to understand this complex response system better one should follow a 'holistic' approach including all possible mechanisms and at all organization levels. In this review, we describe the current status of knowledge on the topic, as well as the key molecules and main mechanisms involved in the 'spreading' of the message throughout the body or cells. Last but not least, we discuss the danger-signal mediated systemic immune effects of radiotherapy for the clinical setup.

Phenolic Compounds from Atriplex littoralis and Their Radiation-Mitigating Activity

From the aerial parts of Atriplex littoralis, three new flavonoid glycosides named atriplexins I-III (1-3), a known flavonoid glycoside, spinacetin 3-O-β-d-glucopyranoside (4), arbutin (5), and 4-hydroxybenzyl-β-d-glucopyranoside (6) were isolated. Their structures were elucidated on the basis of detailed spectroscopic analysis, including 1D and 2D NMR (COSY, NOESY, TOCSY, HSQC, HMBC) and HRESITOF MS data. The compounds were tested for in vitro protective effects on chromosome aberrations in peripheral human lymphocytes using a cytochalasin-B-blocked micronucleus (MN) assay in a concentration range of 0.8-7.4 μM of final culture solution. Chromosomal damage was induced by 2 Gy of γ-radiation on binucleated human lymphocytes, and the effects of the compounds were tested 2 to 19 h after irradiation. The frequency of micronuclei (MNi) was scored in binucleated cells, and the nuclear proliferation index was calculated. The highest prevention of in vitro biochemical and cytogenetic damage of human lymphocytes induced by γ-radiation was exhibited by 3 (reduction of MN frequency by 31%), followed by 4 and 6.

Oxidative DNA damage caused by inflammation may link to stress-induced non-targeted effects

A spectrum of radiation-induced non-targeted effects has been reported during the last two decades since Nagasawa and Little first described a phenomenon in cultured cells that was later called the "bystander effect". These non-targeted effects include radiotherapy-related abscopal effects, where changes in organs or tissues occur distant from the irradiated region. The spectrum of non-targeted effects continue to broaden over time and now embrace many types of exogenous and endogenous stressors that induce a systemic genotoxic response including a widely studied tumor microenvironment. Here we discuss processes and factors leading to DNA damage induction in non-targeted cells and tissues and highlight similarities in the regulation of systemic effects caused by different stressors.

Bystander signalling: exploring clinical relevance through new approaches and new models

Classical radiation biology research has centred on nuclear DNA as the main target of radiation-induced damage. Over the past two decades, this has been challenged by a significant amount of scientific evidence clearly showing radiation-induced cell signalling effects to have important roles in mediating overall radiobiological response. These effects, generally termed radiation-induced bystander effects (RIBEs) have challenged the traditional DNA targeted theory in radiation biology and highlighted an important role for cells not directly traversed by radiation. The multiplicity of experimental systems and exposure conditions in which RIBEs have been observed has hindered precise definitions of these effects. However, RIBEs have recently been classified for different relevant human radiation exposure scenarios in an attempt to clarify their role in vivo. Despite significant research efforts in this area, there is little direct evidence for their role in clinically relevant exposure scenarios. In this review, we explore the clinical relevance of RIBEs from classical experimental approaches through to novel models that have been used to further determine their potential implications in the clinic.

Molecular characterization of TP53 gene in human populations exposed to low-dose ionizing radiation

Ionizing radiation, such as that emitted by uranium, may cause mutations and consequently lead to neoplasia in human cells. The TP53 gene acts to maintain genomic integrity and constitutes an important biomarker of susceptibility. The present study investigated the main alterations observed in exons 4, 5, 6, 7, and 8 of the TP53 gene and adjacent introns in Amazonian populations exposed to radioactivity. Samples were collected from 163 individuals. Occurrence of the following alterations was observed: (i) a missense exchange in exon 4 (Arg72Pro); (ii) 2 synonymous exchanges, 1 in exon 5 (His179His), and another in exon 6 (Arg213Arg); (iii) 4 intronic exchanges, 3 in intron 7 (C → T at position 13.436; C → T at position 13.491; T → G at position 13.511) and 1 in intron 8 (T → G at position 13.958). Alteration of codon 72 was found to be an important risk factor for cancer development (P = 0.024; OR = 6.48; CI: 1.29–32.64) when adjusted for age and smoking. Thus, TP53 gene may be an important biomarker for carcinogenesis susceptibility in human populations exposed to ionizing radiation.

Biological complexities in radiation carcinogenesis and cancer radiotherapy: impact of new biological paradigms

Although radiation carcinogenesis has been shown both experimentally and epidemiologically, the use of ionizing radiation is also one of the major modalities in cancer treatment. Various known cellular and molecular events are involved in carcinogenesis. Apart from the known phenomena, there could be implications for carcinogenesis and cancer prevention due to other biological processes such as the bystander effect, the abscopal effect, intrinsic radiosensitivity and radioadaptation. Bystander effects have consequences for mutation initiated cancer paradigms of radiation carcinogenesis, which provide the mechanistic justification for low-dose risk estimates. The abscopal effect is potentially important for tumor control and is mediated through cytokines and/or the immune system (mainly cell-mediated immunity). It results from loss of growth and stimulatory and/or immunosuppressive factors from the tumor. Intrinsic radiosensitivity is a feature of some cancer prone chromosomal breakage syndromes such as ataxia telangectiasia. Radiosensitivity is manifested as higher chromosomal aberrations and DNA repair impairment is now known as a good biomarker for breast cancer screening and prediction of prognosis. However, it is not yet known whether this effect is good or bad for those receiving radiation or radiomimetic agents for treatment. Radiation hormesis is another major concern for carcinogenesis. This process which protects cells from higher doses of radiation or radio mimic chemicals, may lead to the escape of cells from mitotic death or apoptosis and put cells with a lower amount of damage into the process of cancer induction. Therefore, any of these biological phenomena could have impact on another process giving rise to genome instability of cells which are not in the field of radiation but still receiving a lower amount of radiation. For prevention of radiation induced carcinogenesis or risk assessment as well as for successful radiation therapy, all these phenomena should be taken into account.

Modulation of gamma ray-induced genotoxic effect by thymol, a monoterpene phenol derivative of cymene

The radioprotective effect of thymol (TOH), a monoterpene phenol, on radiation-induced DNA damage was analyzed in vitro. Chinese hamster lung fibroblast cells (V79) were treated with different concentrations of TOH (0-100 µg/mL) for 1 hour before exposure to 3 Gy gamma irradiation, and then cytokinesis-blocked micronucleus and single-cell gel electrophoresis (comet assay) assays were used to evaluate the radiation-induced cytogenetic damage and genotoxic effects. Furthermore, the modulating effect of TOH on radiation-induced cell death was assessed by apoptotic and necrotic cell detection by staining with ethidium bromide/acridine orange using fluorescence microscopy. To understand the mechanism of TOH-imparted cytoprotection, mitochondrial membrane potential (MMP) was detected by flow cytometry after staining the cells with Rhodamine 123. Pretreatment of V79 cells with various concentrations of TOH (0-100 µg/mL) for 1 hour reduced the radiation-induced micronuclei as well as percent tail DNA and mean Olive tail moment with a maximum protective effect observed at TOH (25 µg/mL). Apoptosis by microscopic, MMP measurements indicated that the V79 cells exposed to gamma radiation alone showed a maximal increase in the number of early and late apoptotic and necrotic cell death associated with a significant loss of the MMP. Pretreatment with TOH (25 µg/mL) showed a significant (P < .01) decrease in the level of apoptotic fraction as well as necrotic cells and suppressed the radiation-induced collapse of MMP when compared with the radiation alone group. These results suggest that TOH suppresses radiation-induced genotoxicity, apoptosis, and necrosis primarily by the free radical scavenging and modulation of oxidative stress.

Dendro[C(60)]fullerene DF-1 provides radioprotection to radiosensitive mammalian cells

In this study, the ability of the C(60) fullerene derivative DF-1 to protect radiosensitive cells from the effects of high doses of gamma irradiation was examined. Earlier reports of DF-1's lack of toxicity in these cells were confirmed, and DF-1 was also observed to protect both human lymphocytes and rat intestinal crypt cells against radiation-induced cell death. We determined that DF-1 protected both cell types against radiation-induced DNA damage, as measured by inhibition of micronucleus formation. DF-1 also reduced the levels of reactive oxygen species in the crypt cells, a unique capability of fullerenes because of their enhanced reactivity toward electron-rich species. The ability of DF-1 to protect against the cytotoxic effects of radiation was comparable to that of amifostine, another ROS-scavenging radioprotector. Interestingly, localization of fluorescently labeled DF-1 in fibroblast was observed throughout the cell. Taken together, these results suggest that DF-1 provides powerful protection against several deleterious cellular consequences of irradiation in mammalian systems including oxidative stress, DNA damage, and cell death.

Irradiated Blm-deficient mice are a highly tumor prone model for analysis of a broad spectrum of hematologic malignancies

Mutations in the BLM gene cause human Bloom syndrome (BS), an autosomal recessive disorder of growth retardation, immunodeficiency and cancer predisposition. Homozygous null Blm(m3/m3) mice are cancer prone with a 5-fold increased risk of cancer compared with Blm(m3/+) and Blm(+/+) mice. Irradiation of Blm(m3/m3) mice increased the risk to 28-fold. Tumors occurred mainly in the hematopoietic system and were similar to those in BS based on detailed histologic and immunohistochemical analyses. Irradiated Blm-deficient mice thus provide a novel model for understanding accelerated malignancies in BS and a new platform for investigating the molecular basis for a wide range of hematopoietic neoplasms.

A computational model for radiation-induced cellular transformation to in vitro irradiation of cells by acute doses of X-rays

This research incorporates new biological concepts to improve the predictive ability of a state-vector model with respect to dose-response data on in vitro oncogenic transformation, including mechanisms of DNA damage, DNA repair, cell death, cell proliferation and intercellular communication. Experimentally recognized biological processes, including background transformation, compensatory proliferation and bystander cell-killing effect were formulated mathematically and included as model parameters. These were then adjusted with an optimization method to reproduce in vitro transformation frequency data from C3H10T1/2 mouse cells exposed to acute doses of X-rays. A plateau observed in the data at low doses is reproduced well and a dose-dependent increase above 1 Gy is predicted almost precisely. Extension of the model predictions to the dose range 0-100 mGy indicates that transformation frequencies are practically constant over this low dose region. Results suggest a protective, rather than detrimental, bystander cell-killing effect. Further analysis of model sensitivity to this bystander parameter, though, revealed uncertainties with respect to its biological plausibility in the model.

Long-term mutagenic effects of ionising radiation on mice which vary in their p53 status

The tumor suppressor gene p53 plays a major role in the maintenance of genomic integrity. The impact that variations in cellular turnover rates and sensitivity to DNA damage will have on the effectiveness of p53 in this role was examined by following the induction and persistence of mutations in the brain and small intestine of mice after exposure to ionising radiation (IR). The examination of mutagenesis was carried out using the pUR288 LacZ plasmid-based mouse model-consisting of mice containing a target gene for mutation analysis integrated into every cell. In addition the mice varied in their p53 status. The tissues were compared at post-irradiation time-points from 24h to 3 months. The mutation frequencies (MFs) in the p53 wildtype and heterozygous brains peaked at 24h post-irradiation, and then returned to background or close to background levels, respectively. The p53 nullizygous brain showed a more fluctuating MF pattern, but returned to background levels by 3 months, indicating that the effect of the loss of p53 did not result in lasting differences in the response to mutation induction in the brain. In the intestine, there was a different pattern; in the wildtype and heterozygous animals, the MFs increased from 24h to a peak at 4 weeks post-irradiation, before decreasing towards background levels at 3 months. The MFs in the intestine from the nullizygous animals did not decrease significantly between 4 weeks and 3 months, illustrating that the loss of p53 had a greater impact in this tissue than the brain. The variation in mutation frequencies and the type of mutations generated after DNA damage suggests that while p53 plays a significant role in the maintenance of genomic integrity, other mechanisms, such as the drive to replicate in progenitor cells, can reduce its effectiveness as the "guardian of the genome".

Bystander response in human lymphoblastoid TK6 cells

The mechanisms of the medium-mediated bystander response induced by gamma-rays in non-irradiated TK6 cells were investigated. Cell cultures were irradiated and the culture medium discarded immediately after irradiation and replaced with a fresh one. In cells incubated with conditioned medium from irradiated cells (CM), a significant decrease in cell viability and cloning efficiency was observed, together with a significant increase in apoptosis, also in directly irradiated cells. To examine whether bystander apoptosis involved the extrinsic pathway, an inhibitor of caspase-8 was added to CM cultures, which significantly decreased apoptosis to control levels. The addition to CM of ROS scavengers, Cu-Zn superoxide dismutase and N-acetylcysteine did not affect the induction of apoptosis. To assess whether CM treatment activates a DNA damage response, also the formation of gamma-H2AX foci, as markers of double-strand breaks and their colocalisation with 53-binding protein 1 (53BP1) and the protein mutated in the Nijmegen breakage syndrome 1 (NBS1) was analysed. In cultures treated for 2h with CM, 9-11% of cells showed gamma-H2AX foci, which partially or totally lacked colocalisation with 53BP1 and NBS1 foci. About 85% of irradiated cells were positive for gamma-H2AX foci, which colocalised with 53BP1 and NBS1 proteins. At 24h from irradiation, very few irradiated cells retained foci, fitting DNA repair kinetics. The number of foci-positive bystander cells also decreased to background values 24h after CM incubation. Our results suggest that irradiated TK6 cells release into the medium some soluble factors, not ROS, which are responsible for the cytotoxic effects induced in bystander cells. In our experimental system, the role of ROS appeared to be of minor importance in inducing cell mortality, but probably critical in activating the DNA damage response in the responsive fraction of bystander cells.

Effects of low and high LET radiations on bystander human lung fibroblast cell survival

PURPOSE

This investigation is aimed to determine the role of low LET (linear energy transfer, gamma-rays) and high LET (alpha-particles) radiations on bystander effect of using the same type of cells and its implications on colony-forming efficiency from a single cell.

MATERIALS AND METHODS

Normal human fetal lung (MRC-5), immortalized repair deficient ataxia telangiectasia mutated (ATM) (GM5,849C) and normal (GM637H) fibroblast cells were used. Colony-forming efficiency in bystander cells (GM637H) was studied using the medium transfer technique from the two donor (MRC-5 and GM5,849C) cells and the procedure followed for bystander treatment is presented schematically in Figure 1. Evidence of change in colony formation in bystander cells, was assessed by scavenging nitric oxide (NO).

RESULTS

Enhancement of 10 - 30% in colony-forming efficiency was observed in bystander GM637H cells treated with irradiated conditioned medium (ICM) from MRC-5 cells collected 1 h after different doses of either gamma-rays (1, 2.5, 5 and 10 Gy) or alpha particles (0.25, 0.5, 1 and 2.5 Gy) irradiation. Similar results were obtained when ICM derived from the ATM (GM5,849C) cells. However, the stimulation was not dose dependent. Furthermore, we also show that the increase in dilutions of ICM (1:1, 1:5 and 1:10) showed an inverse correlation with cloning efficiency. Treatment of MRC-5 cells with PTIO (2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide) a NO scavenger, 1 h prior to irradiation reduced the enhancement of ICM mediated cell survival.

CONCLUSIONS

In the present study, though both the low and high LET radiations enhanced the clonogenic potential of the bystander recipient cells, medium from the ATM defective (GM5,849C) cells after gamma-irradiation showed less stimulating effect than the medium from the normal (MRC-5) cells. However, after alpha-irradiation an inverse effect was seen. NO may play an important role in enhancing the growth potential in these bystander cells.

[Alpha-radioimmunotherapy: a review of recent developments]

The use of heavy particles in the treatment of cancer is increasing remarkably, whether with external radiation or using a vector such as an antibody in radioimmunotherapy. Recent pre-clinical and clinical developments of alpha-radioimmunotherapy have provided more interesting information in parallel of the use of high Linear Energy Transfer (LET) external irradiation. This review aims at presenting recent advances of this therapeutic approach, and at detailing the biological specificities of this kind of radiation.

Challenges and progress in predicting biological responses to incorporated radioactivity

Prediction of risks and therapeutic outcome in nuclear medicine largely rely on calculation of the absorbed dose. Absorbed dose specification is complex due to the wide variety of radiations emitted, non-uniform activity distribution, biokinetics, etc. Conventional organ absorbed dose estimates assumed that radioactivity is distributed uniformly throughout the organ. However, there have been dramatic improvements in dosimetry models that reflect the substructure of organs as well as tissue elements within them. These models rely on improved nuclear medicine imaging capabilities that facilitate determination of activity within voxels that represent tissue elements of approximately 0.2-1 cm(3). However, even these improved approaches assume that all cells within the tissue element receive the same dose. The tissue element may be comprised of a variety of cells having different radiosensitivities and different incorporated radioactivity. Furthermore, the extent to which non-uniform distributions of radioactivity within a small tissue element impact the absorbed dose distribution is strongly dependent on the number, type, and energy of the radiations emitted by the radionuclide. It is also necessary to know whether the dose to a given cell arises from radioactive decays within itself (self-dose) or decays in surrounding cells (cross-dose). Cellular response to self-dose can be considerably different than its response to cross-dose from the same radiopharmaceutical. Bystander effects can also play a role in the response. Evidence shows that even under conditions of 'uniform' distribution of radioactivity, a combination of organ dosimetry, voxel dosimetry and dosimetry at the cellular and multicellular levels can be required to predict response.

Cell-cell interactions in spheroids maintained in suspension

We have developed a system of mixed aggregates of cultured cells, to model in situ cell interactions. This three-dimensional (3D) system of floating cell aggregates, termed spheroids for their round shape, enables one to monitor their growth in both size and number of constituent clonogens and to measure survival curves for cells having 3D cell-cell interactions. This system was used to measure the three-dimensional cell-cell interactions on growth, and clonogenicity of either AG1522 fibroblasts, or HeLa cervical cancer cells (pure spheroids, or if both feeder and test cells are the same type, pseudohybrid spheroids), and/or of mixtures of both (hybrid spheroids). By following the increase or decrease in size of, or number of clonogens per, spheroid over time, one obtains growth or inhibition curves. By relating these clonogen numbers, one obtains, after a suitable growth period, relative survival. The system allows one to score the effects of irradiation and of other treatments, as well as the effect of interaction of the constituent cells on their survival. Floating pure, or pseudohybrid (composed of 10% live fibroblasts and 90% supralethally irradiated fibroblast feeder cells) spheroids, shrank to about 10-20% of their volume in three days and then remained at that size for up to six days. In contrast, pure spheroids composed of live HeLa cells increased their volume by an order of magnitude over the same period. Survival of cells in spheroids was measured by the ability of individual spheroids to grow beyond a size implying a ten-fold increase. A caveat to be observed is to correct survival for cellular multiplicity, i.e. reduce survival values to compensate for more than one colony former at the time of irradiation. The system of spheroids floating and growing in nutrient medium provides a selective system for evaluating growth of HeLa, and by implication, other neoplastic cells, without interference from (overgrowth by) normal fibroblasts. Thus it is possible to discriminate between normal and neoplastic cells by virtue of whether or not cells grow in suspension. Such a system seems ideal for testing novel strategies (radiation in combination with chemicals), in an in vivo-like environment.

Bystander effect: biological endpoints and microarray analysis

In cell populations exposed to ionizing radiation, the biological effects occur in a much larger proportion of cells than are estimated to be traversed by radiation. It has been suggested that irradiated cells are capable of providing signals to the neighboring unirradiated cells resulting in damage to these cells. This phenomenon is termed the bystander effect. The bystander effect induces persistent, long-term, transmissible changes that result in delayed death and neoplastic transformation. Because the bystander effect is relevant to carcinogenesis, it could have significant implications for risk estimation for radiation exposure. The nature of the bystander effect signal and how it impacts the unirradiated cells remains to be elucidated. Examination of the changes in gene expression could provide clues to understanding the bystander effect and could define the signaling pathways involved in sustaining damage to these cells. The microarray technology serves as a tool to gain insight into the molecular pathways leading to bystander effect. Using medium from irradiated normal human diploid lung fibroblasts as a model system we examined gene expression alterations in bystander cells. The microarray data revealed that the radiation-induced gene expression profile in irradiated cells is different from unirradiated bystander cells suggesting that the pathways leading to biological effects in the bystander cells are different from the directly irradiated cells. The genes known to be responsive to ionizing radiation were observed in irradiated cells. Several genes were upregulated in cells receiving media from irradiated cells. Surprisingly no genes were found to be downregulated in these cells. A number of genes belonging to extracellular signaling, growth factors and several receptors were identified in bystander cells. Interestingly 15 genes involved in the cell communication processes were found to be upregulated. The induction of receptors and the cell communication processes in bystander cells receiving media from irradiated cells supports the active involvement of these processes in inducing bystander effect.

A comprehensive stochastic model of irradiated cell populations in culture

A comprehensive entirely mechanistic model of the kinetics of cell population in vitro exposed to continuous irradiation is formulated and analysed. The model provides a stochastic description of the processes of formation and repair of radiation-induced lesions, as well as of cell cycling, cell proliferation, and cell death. Unobservable kinetic parameters of the model are estimated from experimental data on the sizes of clones formed in synchronized cultures of S3 HeLa cells exposed to continuous irradiation by gamma-rays at various dose rates. The effects of dose rate on cell cycle duration and damage repair kinetics are studied. Continuous and acute exposures with the same total dose are compared in terms of their impact on cell survival.

Bystander effects in unicellular organisms

Radiation-induced bystander effects have been seen in mammalian cells from diverse origins. These effects can be transmitted through the medium to cells not present at the time of irradiation. We have developed an assay for detecting bystander effects in the unicellular eukaryote, the fission yeast Schizosaccharomyces pombe. This assay allows maximal exposure of unirradiated cells to cells that have received electron beam irradiation. S. pombe cells were irradiated with 16-18 MeV electrons from a pulsed electron LINAC. When survival of the irradiated cells decreased to approximately 50%, forward-mutation to 2-deoxy-d-glucose resistance increased in the unirradiated bystander cells. Further increase in dose had no additional effect on this increase. In order to detect this response, it was necessary for the irradiated cell/unirradiated cell ratio to be high. Other cellular stresses, such as heat treatment, UV irradiation, and bleomycin exposure, also caused a detectable response in untreated cells grown with the treated cells. We discuss evolutionary implications of these results.

Cell cycle arrest and apoptosis inCaenorhabditis elegansgermline cells following heavy-ion microbeam irradiation

PURPOSE

To investigate positional effects of radiation with an energetic heavy-ion microbeam on germline cells using an experimental model metazoan Caenorhabditis elegans.

MATERIALS AND METHODS

The germline cells were irradiated with raster-scanned broad beam or collimated microbeam of 220 MeV 12C5+ particles delivered from the azimuthally varying field (AVF) cyclotron, and subsequently observed for cell cycle arrest and apoptosis.

RESULTS

Whole-body irradiation with the broad beam at the L4 larval stage arrested germ cell proliferation. When the tip region of the gonad arm was irradiated locally with the microbeam at the L4 stage, the same arrest was observed. When the microbeams were used to irradiate the pachytene region of the gonad arm, at a young gravid stage, radiation-induced apoptosis occurred in the gonad. In contrast, arrest and apoptosis were not induced in the non-irradiated neighboring region or the opposite gonad. Similar results were confirmed in the c-abl-1 (mammalian ortholog of cellular counterpart of Abelson murine leukemia virus) mutant that is hypersensitive to radiation-induced apoptosis.

CONCLUSION

These results indicate that the microbeam irradiation is useful in characterizing tissue-specific, local biological response to radiation in organisms. DNA damage-induced cell cycle arrest and apoptosis were observed in locally irradiated regions, but there was little, if any, 'bystander effect' in the nematode.

Experimental techniques for studying bystander effects in vitro by high and low-LET ionising radiation

Ionising radiation can induce responses within non-exposed neighbouring (bystander) cells which potentially have important implications on the estimates of risk from low dose or low dose rate exposures of ionising radiations. A range of strategies have been developed for investigating bystander effects in vitro for both high-LET alpha particles or low-LET ultrasoft X rays using either partial shielding (grids, half-shields and slits) or by using a co-culture system where two physically separated populations of cells can be cultured together, allowing one population of cells to be irradiated while the second population remains unirradiated. The techniques described provide a useful tool to study bystander effects and complement microbeam studies. Studies using these systems show significant increases in the unirradiated bystander cells for various end points including the induction of chromosomal instability in haemopoetic stem cells and transformation in CGL1 cells.

Radiation responses of perfused tracheal tissue

We are using a novel perfusion system to examine the effects of radiation on a model respiratory tissue. Tracheas taken from young adult male Fischer 344 rats are embedded in a growth factor-enriched agarose matrix that is mounted in a special apparatus designed to allow growth medium to periodically wash the epithelial surface of the lumen. A comparison of the microarray expression profiles of freshly harvested tracheas and tracheas maintained in perfusion culture for 24 h shows no significant difference except for an increase in expression of a few metabolism- and surfactant-related genes. Perfusion culture samples exposed to 4 Gy of X rays show a lower than expected increase in expression for some cell cycle- and repair-related genes.

Production and validation of CR-39-based dishes for alpha-particle radiobiological experiments

The study of radiobiological effects induced in vitro by low fluences of alpha particles would be significantly enhanced if the precise localization of each particle track in the cell monolayer was known. From this perspective, we developed a new method based on tailor-made UV-radiation-cured CR-39, the production of which is described. Its validation both as a petri dish and as solid-state nuclear track detectors is demonstrated. With respect to the demands on solid-state nuclear track detectors in such experiments, these biologically compatible detectors have a controlled micrometric thickness that allows them to be crossed by the alpha particles. In this study, we present a method for obtaining 10-mum-thick CR-39, its chemical characterization, and its properties as a solid-state nuclear track detector under the environmental conditions of radiobiological experiments. The experimental studies performed with 3.5 MeV alpha particles show that their transmitted energy is sufficient enough to cross the entire cellular volume. Under optimal conditions, etched tracks are clearly defined 2 h after etching. Moreover, the UV-radiation-cured CR-39 represents an essentially zero background that is due to the short time between the production and use of the polymer. Under a confocal microscope, this thin solid-state nuclear track detector allows the precise localization of the impact parameter at the subcellular level.

Bound PCNA in nuclei of primary rat tracheal epithelial cells after exposure to very low doses of plutonium-238 alpha particles

Bystander effects from ionizing radiation have been detailed for a number of cell systems and a number of end points. We wished to use a cell culture/ex vivo rat model of respiratory tissue to determine whether a bystander effect detected in culture could also be shown in a tissue. Examination by immunofluorescence techniques of tracheal cell cultures after exposure to very low doses of alpha particles revealed a large proportion of cells with proliferating cell nuclear antigen (PCNA) bound in their nuclei. PCNA was selected as an end point because it is involved in both DNA repair and the changes in cell cycle that are typical of many reported bystander effects. Maximum response can be detected in up to 28% of the cells in sub-confluent cultures with a dose of only 2 mGy. At this dose less than 2% of the cell nuclei have experienced a particle traversal and less than 6% of the cells have experienced an alpha-particle traversal through either their nucleus or some part of their cytoplasm. The hypothesis that this bystander response in nontargeted cells is mediated through secreted factor(s) is presented, and supporting evidence was found using partial irradiation and co-culture experiments. Examination of the effect with excised pieces of trachea demonstrated a response similar to that seen in culture.