Radiation-induced Non-targeted Effects Research Articles

Effect of radiotherapy on the DNA cargo and cellular uptake mechanisms of extracellular vesicles.

In the past decades, plenty of evidence has gathered pointing to the role of extracellular vesicles (EVs) secreted by irradiated cells in the development of radiation-induced non-targeted effects. EVs are complex natural structures composed of aphospholipid bilayer which are secreted by virtually all cells and carry bioactive molecules. They can travel certain distances in the body before being taken up by recipient cells. In this review we discuss the role and fate of EVs in tumor cells and highlight the importance of DNA specimens in EVs cargo in the context of radiotherapy. The effect of EVs depends on their cargo, which reflects physiological and pathological conditions of donor cell types, but also depends on the mode of EV uptake and mechanisms involved in the route of EV internalization. While the secretion and cargo of EVs from irradiated cells has been extensively studied in recent years, their uptake is much less understood. In this review, we will focus on recent knowledge regarding the EV uptake of cancer cells and the effect of radiation in this process.

The Footprint of Exosomes in the Radiation-Induced Bystander Effects.

Radiation therapy is widely used as the primary treatment option for several cancer types. However, radiation therapy is a nonspecific method and associated with significant challenges such as radioresistance and non-targeted effects. The radiation-induced non-targeted effects on nonirradiated cells nearby are known as bystander effects, while effects far from the ionising radiation-exposed cells are known as abscopal effects. These effects are presented as a consequence of intercellular communications. Therefore, a better understanding of the involved intercellular signals may bring promising new strategies for radiation risk assessment and potential targets for developing novel radiotherapy strategies. Recent studies indicate that radiation-derived extracellular vesicles, particularly exosomes, play a vital role in intercellular communications and may result in radioresistance and non-targeted effects. This review describes exosome biology, intercellular interactions, and response to different environmental stressors and diseases, and focuses on their role as functional mediators in inducing radiation-induced bystander effect (RIBE).

Some Aspects Related to Transmission of Radiation-Induced Alterations due to the Bystander Effect

This paper presents the first results of research and observations within the framework of the Integrated Project for the assessment of radiation-induced nontargeted effects. The remote bystander effect, related to nontargeted effects, is one of the least studied phenomena in terms of manifestations and mechanisms. The international laboratory practice with respect to this phenomenon commenced with demonstration of the bystander effect in fish and other aquacultures. Our studies have revealed changes similar to radiation-induced pathologies in nonirradiated mice kept for three months in contact with the irradiated species (exposed to a 3 Gy γ-ray dose). Changes in behavioral responses, a statistically significant trend for decreasing spleen weight (r = –0.416; p = 0.048), an expanding area of alopecia (r = –0.631; p = 0.001), and other anomalies are noted. Discussions on possible mechanisms of the phenomena refer to both A.M. Kuzin’s theory of radiotoxins (1966) and the interpretation of the hypotheses investigated by C. Mothersill (2010–2019). An assumption is made on the important role of derivatives of lipid peroxides in the formation of this effect. The results of these studies indicate the need for further investigation of the radiation-induced bystander effect by using the molecular and cellular methodological approaches.

Evaluation of the role of mitochondria in the non-targeted effects of ionizing radiation using cybrid cellular models

Radiobiology is moving towards a better understanding of the intercellular signaling that occurs upon radiation and how its effects relate to the dose applied. The mitochondrial role in orchestrating this biological response needs to be further explored. Cybrids (cytoplasmic hybrids) are useful cell models for studying the involvement of mitochondria in cellular processes. In the present study we used cybrid cell lines to investigate the role of mitochondria in the response to radiation exposure. Cybrid cell lines, derived from the osteosarcoma human cell line 143B, harboring, either wild-type mitochondrial DNA (Cy143Bwt), cells with mitochondria with mutated DNA that causes mitochondrial dysfunction (Cy143Bmut), as well as cells without mitochondrial DNA (mtDNA) (143B-Rho0), were irradiated with 0.2 Gy and 2.0 Gy. Evaluation of the non-targeted (or bystander) effects in non-irradiated cells were assessed by using conditioned media from the irradiated cells. DNA double stranded breaks were assessed with the γH2AX assay. Both directly irradiated cells and cells treated with the conditioned media, showed increased DNA damage. The effect of the irradiated cells media was different according to the cell line it derived from: from Cy143Bwt cells irradiated with 0.2 Gy (low dose) and from Cy143Bmut irradiated with 2.0 Gy (high dose) induced highest DNA damage. Notably, media obtained from cells without mtDNA, the143B-Rho0 cell line, produced no effect in DNA damage. These results point to a possible role of mitochondria in the radiation-induced non-targeted effects. Furthermore, it indicates that cybrid models are valuable tools for radiobiological studies.

One-Decade-Spanning transgenerational effects of historic radiation dose in wild populations of bank voles exposed to radioactive contamination following the chernobyl nuclear disaster

The concept of historic radiation doses associated with accidental radioactive releases and their role in leading to radiation-induced non-targeted effects on affected wild animals are currently being evaluated. Previous research studying Fukushima butterfly, Chernobyl bird and fruit fly populations shows that the effects are transgenerational, underlined by the principles of genomic instability, and varied from one species to another. To further expand on the responses of and their sensitivity in different taxonomically distinct groups, the present study sought to reconstruct historic radiation doses and delineate their effects on bank voles (Clethrionomys glareolus) found within a 400-km radius of the Chernobyl Nuclear Power Plant meltdown site. Historic dose reconstruction from the whole-body dose rates for the bank vole samples for their parental generation at the time of radioactive release was performed. Relationships between the historic doses and cytogenetic aberrations and embryonic lethality were examined via graphical presentations. Results suggest that genomic instability develops at the historic dose range of 20–51 mGy while a radioadaptive response develops at the historic dose range of 51–356 mGy. The Linear No-Threshold (LNT) relationship was absent at historic doses of lower than 356 mGy at all generations. However, LNT was apparent when the very high historic dose of 10.28 Gy in one sampling year was factored into the dose response curve for the bank vole generation 21–22. It is worth being reminded that natural mutation accumulation and other environmental stressors outside the realm of dose effects could contribute to the observed effects in a multiple-stressor environment. Nevertheless, the consistent development of genomic instability and radio-adaptive response across generations and sampling sites unearths the utmost fundamental radiobiological principle of transgenerational non-targeted effects. As a result, it calls for better attention and regulation from global governing bodies of environmental health protection.

Epithelial-mesenchymal transition in non-targeted lung tissues of Kunming mice exposed to X-rays is suppressed by celecoxib.

Lung cancer is one of the highest health risks caused by ionizing radiation, which induces both direct effects and non-targeted effects. However, whether radiation-induced non-targeted effects result in epithelial–mesenchymal transition, a critical process during tumorigenesis, in non-targeted lung tissues remains unknown. In the present study, Kunming mice were subjected to whole-body, cranial or local abdominal irradiation of single-dose or fractionated 4 Gy X-rays, and the expressions of epithelial–mesenchymal transition markers in non-targeted lung tissues were assessed by both qRT-PCR and immunofluorescent staining. It was found that the epithelial marker was downregulated while the mesenchymal markers were upregulated significantly in non-targeted lung tissues of the irradiated mice. Local abdominal irradiation was more efficient in inducing epithelial–mesenchymal transition than whole-body or cranial irradiation when the fractionated irradiation method was adopted. In addition, the intraperitoneal administration of celecoxib suppressed epithelial–mesenchymal transition in the non-targeted lung tissues. In conclusion, our findings suggest that epithelial–mesenchymal transition is induced in non-targeted lung tissues, but can be suppressed by inhibition of cyclooxygenase-2 by celecoxib.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Localized Synchrotron Irradiation of Mouse Skin Induces Persistent Systemic Genotoxic and Immune Responses.

The importance of nontargeted (systemic) effects of ionizing radiation is attracting increasing attention. Exploiting synchrotron radiation generated by the Imaging and Medical Beamline at the Australian Synchrotron, we studied radiation-induced nontargeted effects in C57BL/6 mice. Mice were locally irradiated with a synchrotron X-ray broad beam and a multiplanar microbeam radiotherapy beam. To assess the influence of the beam configurations and variations in peak dose and irradiated area in the response of normal tissues outside the irradiated field at 1 and 4 days after irradiation, we monitored oxidatively induced clustered DNA lesions (OCDL), DNA double-strand breaks (DSB), apoptosis, and the local and systemic immune responses. All radiation settings induced pronounced persistent systemic effects in mice, which resulted from even short exposures of a small irradiated area. OCDLs were elevated in a wide variety of unirradiated normal tissues. In out-of-field duodenum, there was a trend for elevated apoptotic cell death under most irradiation conditions; however, DSBs were elevated only after exposure to lower doses. These genotoxic events were accompanied by changes in plasma concentrations of macrophage-derived cytokine, eotaxin, IL10, TIMP1, VEGF, TGFβ1, and TGFβ2, along with changes in tissues in frequencies of macrophages, neutrophils, and T lymphocytes. Overall, our findings have implications for the planning of therapeutic and diagnostic radiation treatments to reduce the risk of radiation-related adverse systemic effects. Cancer Res; 77(22); 6389-99. ©2017 AACR.

Localized Irradiation of Cell Membrane by Auger Electrons Is Cytotoxic Through Oxidative Stress-Mediated Nontargeted Effects.

Aims: We investigated whether radiation-induced nontargeted effects are involved in the cytotoxic effects of anticell surface monoclonal antibodies labeled with Auger electron emitters, such as iodine 125 (monoclonal antibodies labeled with 125I [125I-mAbs]). Results: We showed that the cytotoxicity of 125I-mAbs targeting the cell membrane of p53+/+ HCT116 colon cancer cells is mainly due to nontargeted effects. Targeted and nontargeted cytotoxicities were inhibited in vitro following lipid raft disruption with Methyl-β-cyclodextrin (MBCD) or filipin or use of radical oxygen species scavengers. 125I-mAb efficacy was associated with acid sphingomyelinase activation and modulated through activation of the AKT, extracellular signal-related kinase ½ (ERK1/2), p38 kinase, c-Jun N-terminal kinase (JNK) signaling pathways, and also of phospholipase C-γ (PLC-γ), proline-rich tyrosine kinase 2 (PYK-2), and paxillin, involved in Ca2+ fluxes. Moreover, the nontargeted response induced by directing 5-[(125)I]iodo-2′-deoxyuridine to the nucleus was comparable to that of 125I-mAb against cell surface receptors. In vivo, we found that the statistical significance of tumor growth delay induced by 125I-mAb was removed after MBCD treatment and observed oxidative DNA damage beyond the expected Auger electron range. These results suggest the involvement of nontargeted effects in vivo also. Innovation: Low-energy Auger electrons, such as those emitted by 125I, have a short tissue range and are usually targeted to the nucleus to maximize their cytotoxicity. In this study, we show that targeting the cancer cell surface with 125I-mAbs produces a lipid raft-mediated nontargeted response that compensates for the inferior efficacy of non-nuclear targeting. Conclusion: Our findings describe the mechanisms involved in the efficacy of 125I-mAbs targeting the cancer cell surface. Antioxid. Redox Signal. 25, 467–484.

Assessing patient characteristics and radiation-induced non-targeted effects in vivo for high dose-rate (HDR) brachytherapy

Purpose: To test whether blood, urine, and tissue based colony-forming assays are a useful clinical detection tool for assessing fractionated treatment responses and non-targeted radiation effects in bystander cells.Materials and methods: To assess patients’ responses to radiation treatments, blood serum, urine, and an esophagus explant-based in vivo colony-forming assay were used from oesophageal carcinoma patients. These patients underwent three fractions of high dose rate (HDR) intraluminal brachytherapy (ILBT).Results: Human keratinocyte reporters exposed to blood sera taken after the third fraction of brachytherapy had a significant increase in cloning efficiency compared to baseline samples (p < 0.001). Such results may suggest an induced radioresistance response in bystander cells. The data also revealed a clear inverse dose-rate effect during late treatment fractions for the blood sera data only. Patient characteristics such as gender had no statistically significant effect (p > 0.05). Large variability was observed among the patients’ tissue samples, these colony-forming assays showed no significant changes throughout fractionated brachytherapy (p > 0.05).Conclusion: Large inter-patient variability was found in the urine and tissue based assays, so these techniques were discontinued. However, the simple blood-based assay had much less variability. This technique may have future applications as a biological dosimeter to predict treatment outcome and assess non-targeted radiation effects.

Radiation-induced non-targeted effects: some open questions.

The existence of non-targeted effects (NTEs) of radiation (genomic instability and bystander effects) has been generally accepted for >20 y; however, there is research, which was largely ignored going back to 1915 reporting these effects. Despite today's general acceptance of the phenomenon of NTE, there is little agreement about the mechanisms involved and the implications in radiation biology and radiation protection. The aim of this review was to consider some of the odd data, which have been published in the field with a view to obtaining insights or stimulating new ways of thinking about this field. By highlighting some key challenges and controversies, concerning the mechanisms and more importantly, the reason these effects exist, current ideas about the wider implications of NTEs in evolution and biology are also discussed.

Particle Radiation-Induced Nontargeted Effects in Bone-Marrow-Derived Endothelial Progenitor Cells

Bone-marrow- (BM-) derived endothelial progenitor cells (EPCs) are critical for endothelial cell maintenance and repair. During future space exploration missions astronauts will be exposed to space irradiation (IR) composed of a spectrum of low-fluence protons (1H) and high charge and energy (HZE) nuclei (e.g., iron-56Fe) for extended time. How the space-type IR affects BM-EPCs is limited. In media transfer experiments in vitro we studied nontargeted effects induced by 1H- and 56Fe-IR conditioned medium (CM), which showed significant increase in the number of p-H2AX foci in nonirradiated EPCs between 2 and 24 h. A 2–15-fold increase in the levels of various cytokines and chemokines was observed in both types of IR-CM at 24 h. Ex vivo analysis of BM-EPCs from single, low-dose, full-body 1H- and 56Fe-IR mice demonstrated a cyclical (early 5–24 h and delayed 28 days) increase in apoptosis. This early increase in BM-EPC apoptosis may be the effect of direct IR exposure, whereas late increase in apoptosis could be a result of nontargeted effects (NTE) in the cells that were not traversed by IR directly. Identifying the role of specific cytokines responsible for IR-induced NTE and inhibiting such NTE may prevent long-term and cyclical loss of stem and progenitors cells in the BM milieu.

The non-targeted effects of radiation are perpetuated by exosomes

Exosomes contain cargo material from endosomes, cytosol, plasma membrane and microRNA molecules, they are released by a number of non-cancer and cancer cells into both the extracellular microenvironment and body fluids such as blood plasma.Recently we demonstrated radiation-induced non-targeted effects [NTE: genomic instability (GI) and bystander effects (BE)] are partially mediated by exosomes, particularly the RNA content. However the mechanistic role of exosomes in NTE is yet to be fully understood.The present study used MCF7 cells to characterise the longevity of exosome-induced activity in the progeny of irradiated and unirradiated bystander cells. Exosomes extracted from conditioned media of irradiated and bystander progeny were added to unirradiated cells. Analysis was carried out at 1 and 20/24 population doublings following medium/exosome transfer for DNA/chromosomal damage. Results confirmed exosomes play a significant role in mediating NTE of ionising radiation (IR). This effect was remarkably persistent, observed >20 doublings post-irradiation in the progeny of bystander cells. Additionally, cell progeny undergoing a BE were themselves capable of inducing BE in other cells via exosomes they released. Furthermore we investigated the role of exosome cargo. Culture media from cells exposed to 2Gy X-rays was subjected to ultracentrifugation and four inoculants prepared, (a) supernatants with exosomes removed, and pellets with (b) exosome proteins denatured, (c) RNA degraded, and (d) a combination of protein–RNA inactivation. These were added to separate populations of unirradiated cells. The BE was partially inhibited when either exosome protein or exosome RNA were inactivated separately, whilst combined RNA–protein inhibition significantly reduced or eliminated the BE. These results demonstrate that exosomes are associated with long-lived signalling of the NTE of IR. Both RNA and protein molecules of exosomes work in a synergistic manner to initiate NTE, spread these effects to naïve cells, and perpetuate GI in the affected cells.

Connexins and cyclooxygenase-2 crosstalk in the expression of radiation-induced bystander effects.

Background:Signalling events mediated by connexins and cyclooxygenase-2 (COX-2) have important roles in bystander effects induced by ionising radiation. However, whether these proteins mediate bystander effects independently or cooperatively has not been investigated.Methods:Bystander normal human fibroblasts were cocultured with irradiated adenocarcinoma HeLa cells in which specific connexins (Cx) are expressed in the absence of endogenous Cx, before and after COX-2 knockdown, to investigate DNA damage in bystander cells and their progeny.Results:Inducible expression of gap junctions composed of connexin26 (Cx26) in irradiated HeLa cells enhanced the induction of micronuclei in bystander cells (P<0.01) and reduced the coculture time necessary for manifestation of the effect. In contrast, expression of connexin32 (Cx32) conferred protective effects. COX-2 knockdown in irradiated HeLa Cx26 cells attenuated the bystander response due to connexin expression. However, COX-2 knockdown resulted in enhanced micronucleus formation in the progeny of the bystander cells (P<0.001). COX-2 knockdown delayed junctional communication in HeLa Cx26 cells, and reduced, in the plasma membrane, the physical interaction of Cx26 with MAPKKK, a controller of the MAPK pathway that regulates COX-2 and connexin.Conclusions:Junctional communication and COX-2 cooperatively mediate the propagation of radiation-induced non-targeted effects. Characterising the mediating events affected by both mechanisms may lead to new approaches that mitigate secondary debilitating effects of cancer radiotherapy.

Research and development of focused proton microbeam irradiation system, SPICE for radio-biological studies.

There is continuing interest for the use of microbeam irradiation systems designed to deliver a defined number of charged particles on a single cell with a resolution of a few micrometers. Irradiation of an exact number of charged particles on a single cell means that the limitations of the Poisson distribution of the number of charged particles can be overcome. Moreover, microbeams are particularly useful for the field of radiation-induced non-targeted effects, so-called bystander effects that are considered to be one of the major effects in the low-dose region. Thus, microbeam technique is one of the powerful tools for investigating studies related to radiation effect and risk of low dose in space radiation for astronauts and cosmonauts.Our microbeam irradiation system, the Single-Particle Irradiation system to CEll (SPICE) provides a 3.4 MeV proton microbeam focused with a quadrupole magnetic lens on an upward vertical beam line. SPICE was severely damaged by the Tohoku-oki Earthquake on 11 March 2011, and was out of operation for about a year and a half. We have successfully reconstructed the facility, and it is now operational with system refinements. At present, SPICE is the only proton microbeam facility in Japan at which a single-ion single-cell irradiation can be performed on mammalian cells with stability and high throughput using an upward vertical beam of below 2-μm diameter, focused with a magnetic quadrupole triplet lens [ 1]. A variety of irradiation modes have been established for radiation-induced bystander effects, cytoplasm irradiation etc. An example of cells targeted with a multi-position targeting mode is shown in Fig. 1, which cells were targeted with five different positions in the nucleus with 50 protons per position. SPICE has been administrated as a ‘Joint-use facility for Collaborative Research’, and thus researchers outside NIRS can apply for beam time of SPICE after their research proposals are approved.Fig. 1.(A) Nuclei of HCT116 cells were targeted with five different positions (3-µm apart), and 50 protons were delivered to each position. (B) Cells were incubated for 1 h and then fixed for immunostaining against γ-H2AX.

TNF- and IL-1 but not MCP-1 and Rantes increase significantly the formation of p-H2AX foci in naive BM-derived TNFR1/p55KO EPCs

Background: Tumor necrosis factor-α (TNF) binds two receptors TNFR1/p55 and TNFR2/p75 and activates several signaling cascades. Ionizing radiation (IR) increases tissue levels of TNF. TNF signaling regulates numerous cytokines and chemokines that are known to mediate radiation-induced non-targeted effects (NTEs), a phenomenon where cells that are not directly ‘hit’ by IR exhibit IR effects as a result of signals received from nearby or distant IR cells. Little is known about the role of p55 or p75 in regulating NTE in bone marrow (BM) cells, specifically in BM-derived endothelial progenitor cells (EPCs). In media transfer experiments, we have previously shown that compared with WT EPCs, early NTEs (within 1–5 h) are inhibited in p55KO and p75KO EPCs, whereas delayed NTEs (within 3–5 days) are amplified in p55KO and to a lesser degree in p75KO EPCs, suggesting significant role of TNFR/p75 signaling (the remaining active receptor in p55KO EPCs) in mediating delayed NTEs. We hypothesized that signaling through TNFR2/p75 may alter radiation-induced TNF-mediated inflammatory response increasing tissue levels of various cytokines, chemokines and growth factors that could then induce NTE, possibly, via activation of NFkB and other stress response transcription factors.Methods: To test our hypothesis ex vivo, expanded p55KO EPCs were irradiated with 1 Gy of γ-IR, then IR-conditioned medium (CM) was collected at 1, 5, 24 h, and 3, 5 days post-IR. CM from IR p55KO EPCs were processed for multiplex ELISA (12 proteins). After determining concentrations of each of 12 proteins in control and IR-CM media of p55KO EPCs over 5 days, we treated naïve p55KO EPCs with various concentrations of four mouse recombinant (rm) proteins that were steadily increased in IR-CM between Days 3–5. After 24 h incubation, naïve p55KO EPCs were stained with anti-p-H2AX antibodies and the formation of p-H2AX foci was visualized at ×100 magnification using laser scanning confocal microscopy. The p-H2AX foci were quantified manually by a single investigator blindfolded to the treatment conditions and were confirmed using computer-assisted algorithm.Results: ELISA profiling of 12 proteins in IR-CM over 5 days post-IR showed 200–1600% increases (P < 0.02, at least, p55KO vs WT, Days 3–5) in cumulative levels of TNF, IFNr, IL1α, IL1β, IL6, EGF, MIP-1α, MCP-1, GCSF, GM-CSF, Rantes and Leptin. The steadiest and the highest increases between Days 3 and 5 were observed in IL-1α, MCP-1 and Rantes.Naïve p55KO EPCs were then treated ex vivo with concentrations determined in the ELISA: IL-1α (290, 580 pg/ml), MCP-1 (580, 1160, 2900 pg/ml), Rantes (600, 1500 pg/ml) and TNF (100 pg/ml, 1, 40 ng/ml). After 24 h incubation with rm proteins, p55KO EPCs were stained with anti-p-H2AX antibodies. The cells were imaged and the quantification of the p-H2AX foci was performed as described above.Results showed that the mean p-H2AX foci count of MCP-1 and Rantes was not significantly different from control which had a mean of 0.98 p-H2AX foci/cell count, with the exception of MCP-1 at 1160 pg/ml (P < 0.03, mean foci count of 1.9). TNF-treated naïve p55KO EPCs showed a significant increase in the mean p-H2AX foci/cell count at all concentration compared with the control, MCP-1 and Rantes (P < 0.0001 with the mean p-H2AX foci ranging from 2.8 to 3.9).IL1α-treated p55KO EPCs showed the greatest increase in p-H2AX foci with the mean foci count of 7.1 at 290 pg/ml and 9.3 at 580 pg/ml, and was significantly different from all tested mouse recombinant proteins. Analysis of p-H2AX foci distribution of EPCs with one or more foci showed that in control p55KO EPCs, <1% of cells had a maximum of 4–9 p-H2AX foci/cell. Whereas in TNF- and IL-1α-treated p55KO EPCs, >2% and >4% of cells had 9–18 foci/cell, respectively. Remarkably, 1% of cells had as many as 18–31 foci/cell for TNF-treated cells and as many as 19–51 foci/cell for IL-1α-treated p55KO EPCs.We conclude that TNF-TNFR2/p75 axis may induce NTEs in naïve BM-EPCs and suggest that blocking/neutralizing TNFR2/p75 signaling could represent a mitigating measure for prevention of delayed NTEs, specifically, in BM-derived EPCs and, conceivably, in BM milieu in general.

Heavy ion-related bystander effects

Space radiation is composed of high-energy protons and heavier charged particles, which is distinct from common terrestrial forms of radiation. These particles can damage both shielding materials and biological systems. Although the fluence of space radiation is typically low, the effects are cumulative and may pose great risk during human exploration beyond low Earth orbit. In recent years, radiation-induced non-targeted effects, in which extranuclear and extracellular events may also contribute to the biological consequences of exposure to low doses of radiation, have been demonstrated to increase the detrimental effects caused by radiation in some in vitro and in vivo systems. Here, studies on non-targeted effects caused by radiation are summarized, with special emphasis on heavy ion-related bystander effects and cytoplasmic irradiation-induced effects.

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.

Abstract 184: TNF-TNFR1/p55 or TNFR2/p75 Receptor-Ligand Interactions Inhibit Early and Increase Delayed Radio-Biological Bystander Responses in BM-Derived EPCs

TNF-α (TNF) binds two receptors TNFR1-p55 and TNFR2-p75. Ionizing radiation (IR) increases tissue TNF levels. TNF signaling regulates numerous cyto- and chemokines, known to mediate radiation-induced non-targeted effects (NTE), a phenomenon where cells that are not directly “hit” by IR exhibit IR effects as a result of signals received from nearby or distant IR cells. Little is known about the role of p55 or p75 in regulating NTEs in bone marrow (BM)-derived EPCs. We hypothesized that inhibition of TNF signaling either via p55, or p75 may alter TNF-mediated inflammatory responses, inducing NTEs. Medium transfer experiments (MTE) were performed in WT, p55 knockout(KO) and p75KO BM-derived EPC ex-vivo, where one set of EPCs was irradiated with 1Gy of γ-IR, then IR-conditioned medium (CM) was collected from these dishes at 1, 5, 24h and 3, 5d post-IR. Filtered (0.22µm) IR-CM was transferred to naïve non-IR same genotype EPCs and 24h post-incubation naïve EPCs were processed for p-y-H2AX staining for presence and decay of double strand breaks (DSB). CM from IR EPCs were processed for ELISA profiling (16 genes) and IR EPCs were processed for transcriptional profiling. In WT EPC the peak of detectable mean p-y-H2AX foci/cell were at 24h, whereas in p55 and p75KOs p-y-H2AX were the lowest at 24h (9±0.8 vs 4.8±0.6 and 3.7±0.5, p&lt;0.01 and 0.001, WT vs p55 and p75KOs). This finding indicates that altered TNF signaling inhibits early NTEs (hours) in EPCs. Compared to WT, delayed (5 days) NTEs were amplified in naïve p55 and p75KO EPCs (3.8±0.4 vs 8.5±1 and 5.9±0.8, p&lt;0.02 and 0.01, WT vs p55 and p75KOs), suggesting significant role for TNF signaling in mediating delayed NTEs. ELISA profiling of 16 proteins in CM over 5 days post-IR showed 200-1600% increases (p&lt;0.002, p55KO vs WT) in cumulative levels of TNF, IFNr, IL6, EGF, MIP-1α, GM-SCF, Rantes, and 200-1000%, increases (p&lt;0.05, p75KO vs WT) in IL1α, IL1β, G -CSF, MCP-1, SCF. Transcriptional profiling of γ-IR EPC revealed 139 genes (&gt;2 fold) up or down regulated, clustered into 9 groups. Other aspects of gene array data are being considered. We conclude that TNF ligand-receptor axis regulates NTEs in naïve EPCs and suggest that restoring TNF signaling balance could be used to prevent delayed NTEs in distant from primary IR target tissues.

In Vivo Space Radiation-Induced Non-Targeted Responses: Late Effects on Molecular Signaling in Mitochondria

The lack of clear knowledge about space radiation-induced biological effects has been singled out as the most important factor limiting the prediction of radiation risk associated with human space exploration. The expression of space radiation-induced non-targeted effects is thought to impact our understanding of the health risks associated with exposure to low fluences of particulate radiation encountered by astronauts during prolonged space travel. Following a brief review of radiation-induced bystander effects and the growing literature for the involvement of oxidative metabolism in their expression, we show novel data on the induction of in vivo non-targeted effects following exposure to 1100 MeV/nucleon titanium ions. Analyses of proteins by two-dimensional gel electrophoresis in non-targeted liver of cranially-irradiated Sprague Dawley rats revealed that the levels of key proteins involved in mitochondrial fatty acid metabolism are decreased. In contrast, those of proteins involved in various cellular defense mechanisms, including antioxidation, were increased. These data contribute to our understanding of the mechanisms underlying the biological responses to space radiation, and support the involvement of mitochondrial processes in the expression of radiation induced non-targeted effects. Significantly, they reveal the cross-talk between propagated stressful effects and induced adaptive responses. Together, with the accumulating data in the field, our results may help reduce the uncertainty in the assessment of the health risks to astronauts. They further demonstrate that ‘network analyses’ is an effective tool towards characterizing the signaling pathways that mediate the long-term biological effects of space radiation. Keywords: High charge and high energy particles, ionizing radiation, liver, mitochondria, non-targeted responses, oxidative metabolism, space radiation, Mass spectrometry, Mitochondrial DNA, Reactive oxygen species