Ionizing radiation alters Fas antigen ligand at the cell surface and on exfoliated plasma membrane-derived vesicles: implications for apoptosis and intercellular signaling

Biology of Exfoliation of Plasma Membrane-Derived Vesicles and the Radiation Response: Historical Background, Applications in Biodosimetry and Cell-Free Therapeutics, and Quantal Mechanisms for Their Release and Function with Implications for Space Travel

This historical review of extracellular vesicles in the setting of exposure to ionizing radiation (IR) traces our understanding of how vesicles were initially examined and reported in the literature in the late 1970s (for secreted exosomes) and early 1980s (for plasma membrane-derived, exfoliated vesicles) to where we are now and where we may be headed in the next decade. An emphasis is placed on biophysical properties of extracellular vesicles, energy consumption and the role of vesiculation as an essential component of membrane turnover. The impact of intercellular signal trafficking by vesicle surface and intra-vesicular lipids, proteins, nucleic acids and metabolites is reviewed in the context of biomarkers for estimating individual radiation dose after exposure to radiation, pathogenesis of disease and development of cell-free therapeutics. Since vesicles express both growth stimulatory and inhibitory molecules, a hypothesis is proposed to consider superposition in a shared space and entanglement of molecules by energy sources that are external to human cells. Implications of this approach for travel in deep space are briefly discussed in the context of clinical disorders that have been observed after space travel.

Abscopal Effects, Clastogenic Effects and Bystander Effects: 70 Years of Non-Targeted Effects of Radiation

In vitro and in vivo observations accumulated over several decades have firmly shown that the biological effects of ionizing radiation can spread from irradiated cells/tissues to non-targeted cells/tissues. Redox-modulated intercellular communication mechanisms that include a role for secreted factors and gap junctions, can mediate these non-targeted effects. Clearly, the expression of such effects and their transmission to progeny cells has implications for issues related to radiation protection. Their elucidation is also relevant towards enhancing the efficacy of cancer radiotherapy and reducing its impact on the development of normal tissue toxicities. In addition, the study of non-targeted effects is pertinent to our basic understanding of intercellular communications under conditions of oxidative stress. This review will trace the history of non-targeted effects of radiation starting with early reports of abscopal effects which described radiation induced effects in tissues distant from the site of radiation exposure. A related effect involved the production of clastogenic factors in plasma following irradiation which can induce chromosome damage in unirradiated cells. Despite these early reports suggesting non-targeted effects of radiation, the classical paradigm that a direct deposition of energy in the nucleus was required still dominated. This paradigm was challenged by papers describing radiation induced bystander effects. This review will cover mechanisms of radiation-induced bystander effects and the potential impacts on radiation protection and radiation therapy.

Endothelial Cell Derived Extracellular Vesicles and Hematopoiesis

Extracellular vesicles (EVs) have been recognized as a novel way of cell-to-cell communication in the last several decades. It is believed that EVs exert their functions on nearby or distant cells through transfer of the cargo that they carry. In this review, we focus on EVs produced by endothelial cells, with emphasis on their role in hematopoiesis. We first describe how endothelial cells interact with hematopoietic stem/progenitor cells during development and in disease conditions. We then discuss EVs, ranging from their subtypes to isolation methods and analysis of EVs. With the above background information, we next review the literature related to endothelial cell derived EVs (ECEVs), including physiological functions and their clinical uses. In the last sections, we summarize the current results about the effect of ECEVs on hematopoiesis under physiological and stress conditions.

Ionizing radiation-induced cancer: perplexities of the bystander effect

Ionizing radiation (IR) is a carcinogen. This has been established beyond doubt from many years of studies such as those conducted among the survivors of the atomic bomb attacks on Hiroshima and Nagasaki and later from the Chernobyl accident. Despite immense progress in the field of carcinogenesis, complete understanding of the underlying mechanisms behind IR-induced cancer remains elusive. In particular, the long gestation period between exposure to IR and the onset of cancer, frequently unpredictable, and sometimes lasting for many years, remains poorly understood. The centrality of DNA damage and misrepair in carcinogenesis research has not entirely benefited IR-induced cancer research and the past decade has seen a shift in understanding radiation-driven cellular mechanisms beyond simplistic models of targeted DNA damage. This paper presents a viewpoint on the gaps in our knowledge of IR-induced cancer with a focus on the non-targeted bystander effect, the mechanisms underlying which may be key to radiotherapeutic advances.

Medical management of acute radiation syndrome

Acute radiation syndrome (ARS) is a clinical syndrome involving four organ systems, resulting in the hematopoietic syndrome (HS), gastrointestinal subsyndrome (GIS), neurovascular subsyndrome (NVS) and cutaneous subsyndrome (CS). Since few healthcare providers have seen an ARS case, evidence-based recommendations are needed to guide medical management in a mass casualty scenario. The authors reviewed recommendations from evidence-based and narrative reviews by expert consultants to the World Health Organisation (WHO), a subsequent review of published HS cases, and infectious disease guidelines for management of febrile neutropenia. The WHO Consultancy applied a rigorous grading system to evaluate treatment strategies described in published ARS cases as of 2009, strategies to manage HS in unirradiated persons, results of ARS studies in animal models of ARS, and recommendations of prior expert panels. Major findings for HS were (a) no randomised controlled studies have been performed, (b) data are restricted by the lack of comparator groups, and (c) reports of countermeasures for management of injury to non-hematopoietic organs are often incomplete. Strength of recommendations ranged from strong to weak. Countermeasures of potential benefit include cytokines and for a subgroup of HS patients, hematopoietic stem cell transplantation. These recommendations did not change in a subsequent analysis of HS cases. Recommendations also included fluoroquinolones, bowel decontamination, serotonin receptor antagonists, loperamide and enteral nutrition for GIS; supportive care for NVS; and topical steroids, antihistamines and antibiotics, and surgical excision/grafting for CS. Also reviewed are critical care management guidelines, the role of mesenchymal stem cells for CS, the potential of a platelet-stimulating cytokine for HS, and the author's approach to clinical management of microbial infections associated with ARS based on published guidelines of infectious disease experts. Today's management of HS is supported by evidence-based guidelines. Management of non-HS subsyndromes is supported by a narrative review of the literature and recommendations of infectious disease societies.

Extracellular Vesicles Derived from Bone Marrow in an Early Stage of Ionizing Radiation Damage Are Able to Induce Bystander Responses in the Bone Marrow

Ionizing radiation (IR)-induced bystander effects contribute to biological responses to radiation, and extracellular vesicles (EVs) play important roles in mediating these effects. In this study we investigated the role of bone marrow (BM)-derived EVs in the bystander transfer of radiation damage. Mice were irradiated with 0.1Gy, 0.25Gy and 2Gy, EVs were extracted from the BM supernatant 24 h or 3 months after irradiation and injected into bystander mice. Acute effects on directly irradiated or EV-treated mice were investigated after 4 and 24 h, while late effects were investigated 3 months after treatment. The acute effects of EVs on the hematopoietic stem and progenitor cell pools were similar to direct irradiation effects and persisted for up to 3 months, with the hematopoietic stem cells showing the strongest bystander responses. EVs isolated 3 months after irradiation elicited no bystander responses. The level of seven microRNAs (miR-33a-3p, miR-140-3p, miR-152-3p, miR-199a-5p, miR-200c-5p, miR-375-3p and miR-669o-5p) was altered in the EVs isolated 24 hour but not 3 months after irradiation. They regulated pathways highly relevant for the cellular response to IR, indicating their role in EV-mediated bystander responses. In conclusion, we showed that only EVs from an early stage of radiation damage could transmit IR-induced bystander effects.

The Role of the CREB Protein Family Members and the Related Transcription Factors in Radioresistance Mechanisms

In the framework of space flight, the risk of radiation carcinogenesis is considered a "red" risk due to the high likelihood of occurrence as well as the high potential impact on the quality of life in terms of disease-free survival after space missions. The cyclic AMP response element-binding protein (CREB) is overexpressed both in haematological malignancies and solid tumours and its expression and function are modulated following irradiation. The CREB protein is a transcription factor and member of the CREB/activating transcription factor (ATF) family. As such, it has an essential role in a wide range of cell processes, including cell survival, proliferation, and differentiation. Among the CREB-related nuclear transcription factors, NF-κB and p53 have a relevant role in cell response to ionising radiation. Their expression and function can decide the fate of the cell by choosing between death or survival. The aim of this review was to define the role of the CREB/ATF family members and the related transcription factors in the response to ionising radiation of human haematological malignancies and solid tumours.

MSC-Derived Extracellular Vesicles: New Emergency Treatment to Limit the Development of Radiation-Induced Hematopoietic Syndrome?

Nuclear accidents or acts of terrorism involving radioactive sources might lead to mass casualties irradiation. The hematopoietic system is one of the most critical and radiation-sensitive tissues because the limited life span of blood cells requires the continuous division of hematopoietic stem cells (HSCs) into the bone marrow. The radiation-induced hematopoietic syndrome, RI-HS, is an impairment of the hematopoiesis that will result in pancytopenia of various degrees. In fact, treatment with granulocyte-colony stimulating factor (G-CSF) is considered as a valuable adjunct to treatment controls in some irradiated patients. Nevertheless, these overexposed patients with bone marrow suppression have minimal medullary territories that do not allow complete recovery of hematopoiesis but lead to significant immunoreactivity following allogeneic hematopoietic stem cell transplantation (HSCT). The high morbidity and mortality of these overexposed patients is a reminder of the lack of effective treatment for hematopoietic syndrome. During the last 20 y, a therapeutic approach for mesenchymal stem cells (MSC) has been proposed for the management of accidentally irradiated victims. Many preclinical animal studies have shown that MSC, mainly by their secretory activity, in particular extracellular vesicles (EVs), contribute to the control of inflammation and promote regeneration of tissues by accelerating angiogenesis and re-epithelialization processes. Therefore, we investigated the potential effect of EVs on the reduction of early bone marrow ionization toxicity, early anti-apoptotic therapy, and vascular protection in the RI-HS model. The main purpose is to propose an innovative treatment of non-patient-specific RI-HS emergency treatment in order to limit allogeneic HSC.

Exosomes in Cancer Radioresistance

Radiation is a mainstay of cancer therapy. Radioresistance is a significant challenge in the treatment of locally advanced, recurrent and metastatic cancers. The mechanisms of radioresistance are complicated and still not completely understood. Exosomes are 40–150 nm vesicles released by cancer cells that contain pathogenic components, such as proteins, mRNAs, DNA fragments, non-coding RNAs, and lipids. Exosomes play a critical role in cancer progression, including cell-cell communication, tumor-stromal interactions, activation of signaling pathways, and immunomodulation. Emerging data indicate that radiation-derived exosomes increase tumor burden, decrease survival, cause radiation-induced bystander effects and promote radioresistance. In addition, radiation can change the contents of exosomes, which allows exosomes to be used as a prognostic and predictive biomarker to monitor radiation response. Therefore, understanding the roles and mechanisms of exosomes in radiation response may shed light on how exosomes play a role in radioresistance and open a new way in radiotherapy and translational medicine. In this review, we discuss recent advances in radiation-induced exosome changes in components, focus on the roles of exosome in radiation-induced bystander effect in cancer and emphasize the importance of exosomes in cancer progression and radioresistance for developing novel therapy.

Radiation-Induced Bystander Effect is Mediated by Mitochondrial DNA in Exosome-Like Vesicles

Exosome-like vesicles (ELV) are involved in mediating radiation-induced bystander effect (RIBE). Here, we used ELV from control cell conditioned medium (CCCM) and from 4 Gy of X-ray irradiated cell conditioned medium (ICCM), which has been used to culture normal human fibroblast cells to examine the possibility of ELV mediating RIBE signals. We investigated whether ELV from 4 Gy irradiated mouse serum mediate RIBE signals. Induction of DNA damage was observed in cells that were treated with ICCM ELV and ELV from 4 Gy irradiated mouse serum. In addition, we treated CCCM ELV and ICCM ELV with RNases, DNases, and proteinases to determine which component of ELV is responsible for RIBE. Induction of DNA damage by ICCM ELV was not observed after treatment with DNases. After treatment, DNA damages were not induced in CCCM ELV or ICCM ELV from mitochondria depleted (ρ0) normal human fibroblast cells. Further, we found significant increase in mitochondrial DNA (mtDNA) in ICCM ELV and ELV from 4 Gy irradiated mouse serum. ELV carrying amplified mtDNA (ND1, ND5) induced DNA damage in treated cells. These data suggest that the secretion of mtDNA through exosomes is involved in mediating RIBE signals.

Changes in gene expression as one of the key mechanisms involved in radiation-induced bystander effect

The radiation-induced bystander effect (RIBE) refers to the manifestation of responses by non-targeted/non-hit cells or tissues situated in proximity to cells and tissues directly exposed to ionizing radiation (IR). The RIBE is elicited by agents and factors released by IR-hit cells. The growing body of data suggests that the underlying mechanisms of the RIBE are multifaceted depending both on the biological (characteristics of directly IR-exposed cells, bystander cells, intercellular milieu) and the physical (dose, rate and type of IR, time after exposure) factors/parameters. Although the exact identity of bystander signal(s) is yet to be identified, the published data indicate changes in gene expression for multiple types of RNA (mRNA, microRNA, mitochondrial RNA, long non-coding RNA, small nucleolar RNA) as being one of the major responses of cells and tissues in the context of the RIBE. Gene expression profiles demonstrate a high degree of variability between distinct bystander cell and tissue types. These alterations could independently, or in a signaling cascade, result in the manifestation of readily observable endpoints, including changes in viability and genomic instability. Here, the relevant publications on the gene candidates and signaling pathways involved in the RIBE are reviewed, and a framework for future studies, both in vitro and in vivo, on the genetic aspect of the RIBE is provided.

Extracellular vesicles mediate low dose ionizing radiation-induced immune and inflammatory responses in the blood

PURPOSE

Radiation-induced bystander effects (RIBE) imply the involvement of complex signaling mechanisms, which can be mediated by extracellular vesicles (EVs). Using an in vivo model, we investigated EV-transmitted RIBE in blood plasma and radiation effects on plasma EV miRNA profiles.

MATERIALS AND METHODS

C57Bl/6 mice were total-body irradiated with 0.1 and 2 Gy, bone marrow-derived EVs were isolated, and injected systemically into naive, 'bystander' animals. Proteome profiler antibody array membranes were used to detect alterations in plasma, both in directly irradiated and bystander mice. MiRNA profile of plasma EVs was determined by PCR array.

RESULTS

M-CSF and pentraxin-3 levels were increased in the blood of directly irradiated and bystander mice both after low and high dose irradiations, CXCL16 and lipocalin-2 increased after 2 Gy in directly irradiated and bystander mice, CCL5 and CCL11 changed in bystander mice only. Substantial overlap was found in the cellular pathways regulated by those miRNAs whose level were altered in EVs isolated from the plasma of mice irradiated with 0.1 and 2 Gy. Several of these pathways have already been associated with bystander responses.

CONCLUSION

Low and high dose effects overlapped both in EV-mediated alterations in signaling pathways leading to RIBE and in their systemic manifestations.

In vivo validation of the bystander effect

The bystander effect post radionuclide decay describes the biologic response(s) of cells not directly targeted by the radiation insult. Recently, we demonstrated that the specific irradiation of human tumor cells in vivo leads to a bystander effect in subcutaneously growing tumors. These in vivo findings 1) call for the re-evaluation of approaches currently used for estimating the risks to individuals/populations inadvertently exposed internally to radioactivity (e.g., alpha particles) as well as to patients undergoing routine diagnostic nuclear medical procedures, and 2) impact significantly the current dogma for assessing the therapeutic potential of internally administered radionuclides.

Radiological and Nuclear Terrorism: The Oncologic Emergency Response

Public concern about the possibility of terrorism involving radiological materials has grown rapidly since the September 11, 2001 terrorist attacks on New York City, the Pentagon, and Pennsylvania. Such concern is driven by the widespread availability of radiological materials and the intentions of malfeasants and organizations around the world to do harm to others. In contrast to nuclear materials, radiological materials are ubiquitous and are found in most cities throughout the country at academic institutions, hospitals, and many businesses and industrial settings. In contrast, nuclear materials are difficult to access because of their rarity and the security of the settings in which they are found. A radiological or nuclear incident of any kind will require prompt assessment of the location and nature of the incident, activation of mass casualty response systems, followed by immediate consultation of hematology, health and medical physics, and nuclear medicine personnel. Radiation-induced injuries and illnesses are typically delayed. Successful assessment and management of individuals with acute radiation syndrome (ARS), including the hematopoietic subsyndrome (HS), is required to support management of injuries resulting from a high radiation dose, including injuries to the gastrointestinal and neurovascular systems. Administration of cytokines within 24 h of exposure shortens the period of granulocytopenia and is strongly recommended by subject matter experts in the management of the HS. Hematopoietic stem cell transplantation after failure of a 2–3 week trial of cytokines has been clearly documented and is weakly recommended in selected individuals with the HS. Administration of prophylactic and therapeutic broad-spectrum antimicrobials (including antibacterial, antiviral, and antifungal agents) is recommended and should be guided by recommendations of the Infectious Diseases Society of America for management of febrile neutropenia. This article provides an overview for clinicians who are called upon in a radiological and/or nuclear incident to manage individuals with ARS and other radiation-related illnesses.

Abscopal Effects: Case Report and Emerging Opportunities

The abscopal effect is a phenomenon observed in the treatment of metastatic cancer where localized irradiation of a particular tumor site causes a response in a site distant to the irradiated volume. The mechanisms of the abscopal effect are speculated to be of several origins, including distant effects on p53, elaboration of inflammatory agents including cytokines, and, most recently, secondary to immune mechanisms. In this case report, we present a rare report of a patient with hepatocellular carcinoma with lung metastases who, after receiving radiation treatment to the liver, had a treatment response in the liver and a complete response in the lung. Recent advances in the understanding of the primary role of immune-modulated cytotoxicity, especially with the success of immune checkpoint inhibitors, have the potential to turn the abscopal effect from a rare phenomenon into a tool to guide antineoplastic therapy and provide a new line of research.

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.

Radiation triggering immune response and inflammation

Radiation therapy (RT) is a well-established but still under optimization branch of Cancer Therapy (CT). RT uses electromagnetic waves or charged particles in order to kill malignant cells, by accumulating the energy onto these cells. The issue at stake for RT, as well as for any other Cancer Therapy technique, is always to kill only cancer cells, without affecting the surrounding healthy ones. This perspective of CT is usually described under the terms "specificity" and "selectivity". Specificity and selectivity are the ideal goal, but the ideal is never entirely achieved. Thus, in addition to killing healthy cells, changes and effects are observed in the immune system after irradiation. In this review, we mainly focus on the effects of ionizing radiation on the immune system and its components like bone marrow. Additionally, we are interested in the effects and benefits of low-dose ionizing radiation on the hematopoiesis and immune response. Low dose radiation has been shown to induce biological responses like inflammatory responses, innate immune system activation and DNA repair (adaptive response). This review reveals the fact that there are many unanswered questions regarding the role of radiation as either an immune-activating (low dose) or immunosuppressive (high dose) agent.

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 2 Gy 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.

Changing paradigms in radiobiology

The last 25 years have seen a major shift in emphasis in the field of radiobiology from a DNA-centric view of how radiation damage occurs to a much more biological view that appreciates the importance of macro-and micro-environments, hierarchical organization, underlying genetics, evolution, adaptation and signaling at all levels from atoms to ecosystems. The new view incorporates concepts of hormesis, nonlinear systems, bioenergy field theory, uncertainty and homeodynamics. While the mechanisms underlying these effects and responses are still far from clear, it is very apparent that their implications are much wider than the field of radiobiology. This reflection discusses the changing views and considers how they are influencing thought in environmental and medical science and systems biology.

Bystander effect induced changes in apoptosis related proteins and terminal differentiation in in vitro murine bladder cultures

PURPOSE

Radiation-induced bystander effects are now an established phenomenon seen in numerous cell and tissue culture models. The aim of this investigation was to examine the bystander signal and response in a multicellular primary tissue culture system in vitro.

METHODS AND MATERIALS

Murine bladder samples were explanted and directly exposed to gamma radiation, or treated with irradiated tissue conditioned medium (ITCM) generated from the directly irradiated cultures.

RESULTS

Results indicated that there was a strong bystander signal produced by the tissue that caused both dose-dependent and -independent changes in the ITCM treated tissue. Significantly increased B-cell lymphoma 2 (Bcl2) expression was noted after treatment with 0.5Gy and 5Gy ITCM (approximately 80%), while dose-dependent changes were observed in c-myelocytomatosis (cMyc) (39.48% at 0.5 Gy ITCM, 81.28% at 5 Gy ITCM) and the terminal differentiation marker uroplakin III (17.88% at 0.5 Gy). Nuclear fragmentation was also significantly increased at both doses of ITCM.

CONCLUSION

These data suggest that the bystander signal produced in a multicellular environment induces complex changes in the ITCM-treated culture, and that these changes are reflective of a coordinated response to maintain integrity throughout the tissue.

NASA Radiation Biomarker Workshop, September 27-28, 2007

A summary is provided of presentations and discussions at the NASA Radiation Biomarker Workshop held September 27-28, 2007 at NASA Ames Research Center in Mountain View, CA. Invited speakers were distinguished scientists representing key sectors of the radiation research community. Speakers addressed recent developments in the biomarker and biotechnology fields that may provide new opportunities for health-related assessment of radiation-exposed individuals, including those exposed during long-duration space travel. Topics discussed included the space radiation environment, biomarkers of radiation sensitivity and individual susceptibility, molecular signatures of low-dose responses, multivariate analysis of gene expression, biomarkers in biodefense, biomarkers in radiation oncology, biomarkers and triage after large-scale radiological incidents, integrated and multiple biomarker approaches, advances in whole-genome tiling arrays, advances in mass spectrometry proteomics, radiation biodosimetry for estimation of cancer risk in a rat skin model, and confounding factors. A summary of conclusions is provided at the end of the report.

Bystander effects of ionizing radiation can be modulated by signaling amines

Actual risk and risk management of exposure to ionizing radiation are among the most controversial areas in environmental health protection. Recent developments in radiobiology especially characterization of bystander effects have called into question established dogmas and are thought to cast doubt on the scientific basis of the risk assessment framework, leading to uncertainty for regulators and concern among affected populations. In this paper we test the hypothesis that small signaling molecules widely used throughout the animal kingdom for signaling stress or environmental change, such as 5-Hydroxytryptamine (5-HT, serotonin), l-DOPA, glycine or nicotine are involved in bystander signaling processes following ionizing radiation exposure. We report data which suggest that nano to micromolar concentrations of these agents can modulate bystander-induced cell death. Depletion of 5-HT present in tissue culture medium, occurred following irradiation of cells. This suggested that 5-HT might be bound by membrane receptors after irradiation. Expression of 5-HT type 3 receptors which are Ca(2+) ion channels was confirmed in the cells using immunocytochemistry and receptor expression could be increased using radiation or 5-HT exposure. Zofran and Kitryl, inhibitors of 5-HT type 3 receptors, and reserpine a generic serotonin antagonist block the bystander effect induced by radiation or by serotonin. The results may be important for the mechanistic understanding of how low doses of radiation interact with cells to produce biological effects.

Bystander killing of breast cancer MCF-7 cells by MDA-MB-231 cells exposed to 5-fluorouracil is mediated via Fas

The major drawback with cancer therapy is the development of resistant cells within tumors due to their heterogeneous nature and due to inadequate drug delivery during chemotherapy. Therefore, the propagation of injury ("bystander effect" (BE)) from directly damaged cells to other cells may have great implications in cancer chemotherapy. The general advantage of the bystander cell killing phenomenon is the large therapeutic index that can be achieved. Experiments suggest that this phenomenon is detected in radiation therapy as well as in gene therapy in conjunction with chemotherapy. In the present study, we developed an original in vitro model dedicated to the exploration of bystander cytotoxicity induced during breast carcinoma chemotherapy. In brief, we investigated this perpetuation of injury on untreated bystander MCF-7 breast cancer cells which were coplated with 5-fluorouracil (5-FU)-treated MDA-MB-231 breast cancer cells. To achieve this goal, a specific in vitro coculture model which involved mixing of aggressive MDA-MB-231 breast cancer cells with enhanced green fluorescent protein (EGFP) expressing stable clone of non-metastatic MCF-7 breast cancer cells (MCF-EGFP), was used. A bystander killing effect was observed in MCF-EGFP cells cocultured with MDA-MB-231 cells pretreated with 5-FU. The striking decrease in MCF-EGFP cells, as detected by assaying for total GFP intensity, is mediated by activation of Fas/FasL system. The implication of Fas in MCF-EGFP cell death was confirmed by using antagonistic anti-FasL antibody that reverses bystander cell death by blocking FasL on MDA-MB-231 cells. In addition, inhibition of CD95/Fas receptor on the cell surface of MCF-EGFP cells by treatment with Pifithrin-alpha, a p53 specific transactivation inhibitor, partially abrogated the sensitivity of bystander MCF-EGFP cells. Our data, therefore, demonstrates that the Fas/FasL system could be considered as a new determinant for chemotherapy-induced bystander cell death in breast cancers.

Multivariate analysis of low-dose radiation-associated changes in cytokine gene expression profiles using microarray technology

OBJECTIVE

The availability of microarray technology, which permits evaluation of the entire cellular transcriptome in a single experiment, has provided new insights on the function of the genome under normal and pathological conditions, as well as in response to genotoxic stimuli, including ionizing radiation. The aims of this study were to: 1) determine whether specific cytokine gene expression profiles can be delineated in individuals exposed to chronic, low-dose radiation; and 2) compare analyses from three multivariate analytic methodologies, hierarchical clustering analysis (HCA), principal component analysis (PCA), and projection pursuit (PP), in evaluating transcriptional responses in human mononuclear cells to low doses of ionizing radiation (IR), as determined by cDNA microarrays.

MATERIALS AND METHODS

Total RNA isolated from mononuclear cells of 19 apparently healthy adult individuals exposed to low doses of IR ranging from 0.18 mSv to 49 mSv over a period of 11 to 13 years, as a result of the Chernobyl Nuclear Power Plant catastrophe, was reverse transcribed in the presence of radioactive dATP to generate radiolabeled complementary cDNA. Target cDNA was hybridized to human cytokine and receptor arrays and mRNA transcriptional patterns were evaluated using HCA, PCA, and PP.

RESULTS

Statistical analyses of the data generated from 19 microarrays revealed distinct gene expression patterns in mononuclear cells of individuals exposed to radiation doses of greater than 10 mSv or less than 10 mSv. Genes encompassed within clusters discerned by HCA, PCA, and PP varied depending on the methodology used to analyze the microarray data. The most frequently expressed genes across all radiation doses were serine/threonine protein kinase receptor (11/19), transforming growth factor (TGF) receptor (11/19), EB13 (10/19), and CD40 ligand.

CONCLUSIONS

Although our findings suggest that it may be possible to assign gene expression profiles to low-dose-irradiated individuals, we show that gene expression profiles vary, depending on the statistical method used to analyze the data. Since there is, as of yet, no consensus regarding the best method to analyze a multivariate dataset, and since discarding the raw data and repeating the experiment at a later date constitutes an unwarranted expenditure, it is important to submit microarray data to public databases where these data can be reevaluated and interpreted by investigators holding expertise in various fields within the scientific community, including radiation biology, statistics, and bioinformatics.

Tissue-sparing effect of x-ray microplanar beams particularly in the CNS: is a bystander effect involved?

OBJECTIVE

Normal tissues, including the central nervous system, tolerate single exposures to narrow planes of synchrotron-generated x-rays (microplanar beams; microbeams) up to several hundred Gy. The repairs apparently involve the microvasculature and the glial system. We evaluate a hypothesis on the involvement of bystander effects in these repairs.

METHODS

Confluent cultures of bovine aortic endothelial cells were irradiated with three parallel 27-microm microbeams at 24 Gy. Rats' spinal cords were transaxially irradiated with a single microplanar beam, 270 microm thick, at 750 Gy; the dose distribution in tissue was calculated.

RESULTS

Within 6 hours following irradiation of the cell culture the hit cells died, apparently by apoptosis, were lost, and the confluency was maintained. The spinal cord study revealed a loss of oligodendrocytes, astrocytes, and myelin in 2 weeks, but by 3 months repopulation and remyelination was nearly complete. Monte Carlo simulations showed that the microbeam dose fell from the peak's 80% to 20% in 9 microm.

CONCLUSIONS

In both studies the repair processes could have involved "beneficial" bystander effects leading to tissue restoration, most likely through the release of growth factors, such as cytokines, and the initiation of cell-signaling cascades. In cell culture these events could have promoted fast disappearance of the hit cells and fast structural response of the surviving neighboring cells, while in the spinal cord study similar events could have been promoting angiogenesis to replace damaged capillary blood vessels, and proliferation, migration, and differentiation of the progenitor glial cells to produce new, mature, and functional glial cells.

Therapeutic Vaccines for Prostate Cancer

Prostate cancer is the most common, noncutaneous cancer for men in the U.S., leading to more than 30,000 deaths a year. Vaccines for prostate cancer, which for several years have been shown to generate immunologic responses, are beginning to show significant clinical promise. At present, numerous therapeutic options are being investigated, including autologous and allogeneic whole-tumor cell vaccines, dendritic cell vaccines, and poxvirus-based vaccines. Advances in basic immunology have translated into new, more complex therapeutic strategies. The findings from current trials and the demonstrated potential to combine vaccines with conventional therapies herald a promising future for the treatment of prostate cancer. This review highlights recent advances and clinical trials in immunotherapy for prostate cancer, along with current thoughts on immunologic and clinical monitoring of these trials.

Vascular Endothelial Cells Produce Soluble Factors That Mediate the Recovery of Human Hematopoietic Stem Cells after Radiation Injury

The risk of terrorism with nuclear or radiologic weapons is considered to be high over the coming decade. Ionizing radiation can cause a spectrum of hematologic toxicities, from mild myelosuppression to myeloablation and death. However, the potential regenerative capacity of human hematopoietic stem cells (HSCs) after radiation injury has not been well characterized. In this study, we sought to characterize the effects of ionizing radiation on human HSCs and to determine whether signals from vascular endothelial cells could promote the repair of irradiated HSCs. Exposure of human bone marrow CD34+ cells to 400 cGy caused a precipitous decline in hematopoietic progenitor cell content and primitive cells capable of repopulating nonobese diabetic/severe combined immunodeficient mice (SCID-repopulating cells), which was not retrievable via treatment with cytokines. Conversely, culture of 400 cGy-irradiated bone marrow CD34+ cells with endothelial cells under noncontact conditions supported the differential recovery of both viable progenitor cells and primitive SCID-repopulating cells. These data illustrate that vascular endothelial cells produce soluble factors that promote the repair and functional recovery of HSCs after radiation injury and suggest that novel factors with radiotherapeutic potential can be identified within this milieu.

Radiation-induced bystander effects and the DNA paradigm: an "out of field" perspective

Over the past 20 years there has been increasing evidence that cells and the progeny of cells surviving a very low dose of ionizing radiation [micro-mGy] can exhibit a wide range of non-monotonic effects such as adaptive responses, low dose hypersensitivity and other delayed effects. These effects are inconsistent with the expected dose-response, when based on extrapolation of high dose data and cast doubt on the reliability of extrapolating from high dose data to predict low dose effects. Recently the cause of many of these effects has been tentatively ascribed to so-called "bystander effects". These are effects that occur in cells not directly hit by an ionizing track but which are influenced by signals from irradiated cells and are thus highly relevant in situations where the dose is very low. Not all bystander effects may be deleterious although most endpoints measured involve cell damage or death. In this commentary, we consider how these effects impact the historical central dogma of radiobiology and radiation protection, which is that DNA double strand breaks are the primary radiation-induced lesion which can be quantifiably related to received dose and which determine the probability that a cancer will result from a radiation exposure. We explore the low dose issues and the evidence and conclude that in the very low dose region, the primary determinant of radiation exposure outcome is the genetic and epigenetic background of the individual and not solely the dose. What this does is to dissociate dose from effect as a quantitative relationship, but it does not necessarily mean that the effect is ultimately unrelated to DNA damage. The fundamental thesis we present is that at low doses fundamentally different mechanisms underlie radiation action and that at these doses, effect is not quantitatively related to dose.

Actions of radiation on living cells in the "post-bystander" era

Over the past 20 years there has been increasing evidence that cells and the progeny of cells surviving a dose of ionizing radiation can exhibit a wide range of effects inconsistent with the level of dose received. Recently, the cause of these delayed effects has been ascribed to so-called bystander effects, occurring in cells not directly hit by an ionizing track, but which are influenced by signals from irradiated cells. These effects are not necessarily deleterious, although most of the literature deals with adverse delayed effects. What is important to consider is what, if anything, these effects mean for what is still the central dogma of radiobiology and radiation protection, i.e., that DNA double-strand breaks are the primary radiation-induced lesion that can be quantifiably related to received dose, and which determine the probability that a cancer will result from a radiation exposure. In this chapter we review the history of radiation biology which led to the DNA paradigm. We explore the issues and the evidence which are now challenging the view that dose deposition in DNA is all important. We conclude that in the low-dose region, the primary determinant of radiation exposure outcome is the genetic and epigenetic background of the individual and not the dose. This effectively dissociates dose from effect as a quantitative relationship, but it does not necessarily mean that the effect is unrelated to DNA damage somewhere in the system.

Fast neutrons-induced apoptosis is Fas-independent in lymphoblastoid cells

We have previously shown that ionizing radiation-induced apoptosis in human lymphoblastoid cells differs according to their p53 status, and that caspase 8-mediated cleavage of BID is involved in the p53-dependent pathway. In the present study, we investigated the role of Fas signaling in caspase 8 activation induced by fast neutrons irradiation in these cells. Fas and FasL expression was assessed by flow cytometry and by immunoblot. We also measured Fas aggregation after irradiation by fluorescence microscopy. We found a decrease of Fas expression after irradiation, but no change in Fas ligand expression. We also showed that, in contrast to the stimulation of Fas by an agonistic antibody, Fas aggregation did not occur after irradiation. Altogether, our data strongly suggest that fast neutrons induced-apoptosis is Fas-independent, even in p53-dependent apoptosis.

Radiation-induced adaptive responses and bystander effects

A classical paradigm [correction of paradym] of radiation biology asserts that all radiation effects on cells, tissues and organisms are due to the direct action of radiation. However, there has been a recent growth of interest in the indirect actions of radiation including the radiation-induced adaptive response, the bystander effect, low-dose hypersensitivity, and genomic instability, which are specific modes of stress exhibited in response to low-dose/low-dose rate radiation. This review focuses on the radiation-induced bystander effect and the adaptive response, provides a description of the two phenomena, and discusses the contribution of the former to the latter.

Radiation-induced cell death and dendritic cells: potential for cancer immunotherapy?

Dendritic cells are key orchestrators of the immune system. There is considerable interest in their use for treating cancer. Whether they initiate an effective cytotoxic response against antigen-bearing cells, or produce tolerance, depends on the context in which those antigens are presented. Ionising radiation, and the cell death it causes, has several properties that may facilitate such an effective response. A range of in-vitro and in-vivo data supports this, although potential problems exist that may require concurrent strategies.

Radiobiology of radioimmunotherapy: targeting CD20 B-cell antigen in non-Hodgkin's lymphoma

The radiobiology of radioimmunotherapy is an important determinant of both the toxicity and the efficacy associated with the treatment of B-cell non-Hodgkin's lymphoma with radiolabeled anti-CD20 monoclonal antibodies. The properties of the target, CD20, and the mechanisms of action of both the monoclonal antibodies and the associated exponentially decreasing low-dose-rate radiotherapy are described. The radiation dose and dose-rate effects are discussed and related to both the tumor responses and normal organ toxicity. Finally, the use of either unlabeled or radiolabeled anti-CD20 monoclonal antibodies as a component of combined modality therapy (including the sequential or concurrent use of sensitizers) and future directions of the field are discussed.

Ex vivo culture rescues hematopoietic stem cells with long-term repopulating capacity following harvest from lethally irradiated mice

OBJECTIVE

High-dose ionizing radiation can cause lethal myeloablation in exposed individuals. We examined whether ex vivo culture could rescue hematopoietic stem cells with repopulating capacity following harvest from lethally irradiated animals.

METHODS

We exposed B6.SJL mice to 1050 cGy, harvested their irradiated bone marrow (BM), and examined whether ex vivo culture of the irradiated BM mononuclear cells (MNC) with porcine microvascular endothelial cells (PMVEC) or cytokines alone could rescue hematopoietic cells with in vitro colony-forming activity, in vivo radioprotective capacity, and long-term repopulating potential.

RESULTS

PMVEC coculture supported the recovery of fourfold and 80-fold greater numbers of total cells and colony-forming cells (CFC) compared to cyokines alone following 1050 cGy irradiation. All control mice irradiated with 1050 cGy died by day 30, as did mice transplanted with 1050 cGy-irradiated BM MNC. In contrast, transplantation of 1050 cGy-irradiated/PMVEC-cultured BM was fully radioprotective in 12 of 16 recipient mice (75%) exposed to 1050 cGy. Six of the 12 CD45.2+ mice (50%) transplanted with 1050 cGy-irradiated/PMVEC-cultured cells showed long-term (>6 months) multilineage repopulation derived from irradiated donor CD45.1+ cells. Surprisingly, transplantation of identical doses of 1050 cGy-irradiated/cytokine-cultured BM was also radioprotective in 50% of irradiated recipient mice and 50% of these mice demonstrated donor-derived repopulation.

CONCLUSIONS

Fully functional BM stem and progenitor cells can be rescued following harvest from lethally irradiated animals via ex vivo culture with PMVEC or cytokines alone. This method can serve as a model for the rapid ex vivo rescue and transplantation of autologous BM progenitors in the treatment of victims of radiation injury.

Cell proximity is a prerequisite for the proliferative response of bystander cells co-cultured with cells irradiated with ?-rays

BACKGROUND

In a recent study, we showed that unirradiated cells, when they are in the presence of cells irradiated with gamma-rays, are characterized by enhanced cell growth (Cytometry 2003;54A:1-7). However, the mechanisms and factors involved in the proliferative response of bystander cells are largely unknown. The aim of the current work was to investigate the possible role of spatial proximity of cells, including gap junctional intercellular communication (GJIC), in transmitting proliferation signals from cells irradiated with gamma-rays to unirradiated cells (bystander cells).

METHODS

Confluent monolayers of rat liver epithelial cells (WB-F344) were irradiated with 137Cs gamma-rays at doses ranging between 0.5 and 10 Gy. The impact of cell proximity on the proliferative response of bystander cells was determined by co-culturing different densities of irradiated and unirradiated cells (ratio 1:1) followed 24 h later by two-scheme flow cytometric analysis of their proliferation. To determine whether soluble extracellular factors play a role in this response, irradiated cells were plated together with unirradiated cells at the same ratio (1:1), but they were not allowed to directly contact unirradiated cells by using porous low-protein binding polyethylene terephthalate membranes. After 24 h, the numbers of unirradiated cells in the co-culture with irradiated cells were compared with the numbers of unirradiated cells in the control (unirradiated cells co-cultured with unirradiated cells). To investigate the possible involvement of GJIC in mediating the proliferative response in the bystander cells, the proliferation status of unirradiated GJIC-incompetent WB-aB1 cells was compared with that of unirradiated WB-F344 cells that were GJIC competent. In all of the protocols, the two populations of co-cultured cells were distinguished by labeling one population with fluorescent cell tracers, such as membrane-resident or CFDA SE (carboxy) fluorescein diacetate, succinimidyl ester that metabolizes intracellularly.

RESULTS

Unirradiated cells that were co-cultured with irradiated cells, but were not allowed to directly contact them, did not show any changes in the proliferation rate compared with that of unirradiated cells in the control. Unirradiated cells that were co-cultured as a mixture with irradiated cells showed enhanced and statistically significant proliferation, particularly when they were plated together more densely. The proliferation rate of bystander WB-aB1 cells was apparently higher than that of bystander WB-F344 cells; however, the difference was statistically insignificant.

CONCLUSIONS

In the present experimental model, the spatial proximity of cells is a crucial element for transmitting growth stimulation signals from irradiated cells to neighboring unirradiated cells. Direct cell-to-cell contact appears to be required for transmitting these signals. Neither functional GJIC nor soluble extracellular factors released by irradiated cells into the culture medium appear to play significant roles in this process under the present experimental conditions.

Irradiation of tumor cells up-regulates Fas and enhances CTL lytic activity and CTL adoptive immunotherapy

CD8(+) CTL play important roles against malignancy in both active and passive immunotherapy. Nonetheless, the success of antitumor CTL responses may be improved by additional therapeutic modalities. Radiotherapy, which has a long-standing use in treating neoplastic disease, has been found to induce unique biologic alterations in cancer cells affecting Fas gene expression, which, consequently, may influence the overall lytic efficiency of CTL. Here, in a mouse adenocarcinoma cell model, we examined whether exposure of these tumor cells to sublethal doses of irradiation 1) enhances Fas expression, leading to more efficient CTL killing via Fas-dependent mechanisms in vitro; and 2) improves antitumor activity in vivo by adoptive transfer of these Ag-specific CTL. Treatment of carcinoembryonic Ag-expressing MC38 adenocarcinoma cells with irradiation (20 Gy) in vitro enhanced Fas expression at molecular, phenotypic, and functional levels. Furthermore, irradiation sensitized these targets to Ag-specific CTL killing via the Fas/Fas ligand pathway. We examined the effect of localized irradiation of s.c. growing tumors on the efficiency of CTL adoptive immunotherapy. Irradiation caused up-regulation of Fas by these tumor cells in situ, based on immunohistochemistry. Moreover, localized irradiation of the tumor significantly potentiated tumor rejection by these carcinoembryonic Ag-specific CTL. Overall, these results showed for the first time that 1) regulation of the Fas pathway in tumor cells by irradiation plays an important role in their sensitization to Ag-specific CTL; and 2) a combination regimen of tumor-targeted irradiation and CTL promotes more effective antitumor responses in vivo, which may have implications for the combination of immunotherapy and radiation therapy.

Low-dose radiation effects: experimental hematology and the changing paradigm

This review looks at the emerging field of nontargeted radiation effects and their impact on low-dose radiation risk assessment and radiotherapy. It identifies the major role of experimental hematologists and cytogeneticists in changing the old view of radiation action on living things. It also considers the history of radiobiology, seeking to explain why it is only now that we are considering indirect or nontargeted effects of low doses even though the evidence was there, though buried, in the old literature. Effects receiving major attention worldwide now include genomic instability and bystander effects. The impact of these effects, both on radiotherapy used to treat cancer and on radiation induction of cancer, still need to be clarified. Techniques developed by experimental hematologists are central to these efforts and have been instrumental in causing radiobiologists to consider that a paradigm shift is necessary. Throughout, we make a plea to think "outside the box" since the very construction of a framework necessarily limits our thinking and our experimental design.

Modulation of intercellular communication mediated at the cell surface and on extracellular, plasma membrane-derived vesicles by ionizing radiation

The plasma membrane is a dynamic organelle whose function includes receptor-mediated signal transduction into the cell. Conversely, the plasma membrane is the origin of inter-cellular signaling. In addition to expressing and releasing growth factors in a soluble form(through exocytosis) and via proteolysis of cell surface components, membrane ligands may signal nearby cells through juxtacrine stimulation or by the exfoliation or shedding of plasma membrane-derived vesicles. Ionizing radiation (IR) has a profound effect on plasma membrane structure and function. IR-induced ultrastructural alterations are mediated via lipid interaction with water radiolysis products (e.g., hydroxyl radicals, hydrogen radicals, and hydrated electrons). Ionizing radicals act directly on lipid molecules to promote lipid hydro-peroxides and lipid hydroperoxide breakdown products (e.g., alpha, beta unsaturated aldehydes) that contribute to altered plasma membrane lipid composition. A change in lipid composition increases membrane lipid microviscosity and results in membrane fenestrations that enhance permeability to small molecules and ions. Reactive ionizing species also stimulate sphingomyelinase activity, leading to sphingomyelin hydrolysis and ceramide generation that further contributes to altered membrane lipid composition and cellular apoptosis. In addition, exposure to IR results in impaired rate of and cumulative shedding of plasma membrane-associated growth factors. Mechanisms of exfoliation are reviewed for normal cells and the impact of radiation on modulating signal transduction mediated by exfoliation is summarized.

The cell membrane as a biosensor of oxidative stress induced by radiation exposure: a multiparameter investigation

The role of biological membranes as a target in biological radiation damage remains unclear. The present study investigates how the biochemical and biophysical properties of a simple biological model, i.e. human erythrocyte membranes, are altered after exposure to relatively low doses of (60)Co gamma rays. Lipid peroxidation increased in the hours after radiation exposure, based on measurements of MDA and on the lipid peroxidation index after parinaric acid incorporation. Protein carbonyl content also increased rapidly after radiation exposure. An imbalance between the radiation-mediated oxidative damages and the antioxidant capacity of the erythrocytes was observed in the hours after radiation exposure. Antioxidant enzyme activities, mainly catalase and glutathione peroxidase, were found to decrease after irradiation. The development of a radiation-induced oxidative stress probably explains the reorganization of the fatty acid pattern 72 h after radiation exposure. The phosphatidylethanolamine (PE) fatty acids of the (n-3) and (n-6) series decreased, while the PE saturated fatty acid content increased. All these modifications may be involved in the variation of the biophysical properties of the membranes that we noted after radiation exposure. Specifically, we observed that the lipid compartment of the membrane became more fluid while the lipid-protein membrane interface became more rigid. Taken together, these findings reinforce our understanding that the cell membrane is a significant biological target of radiation. Thus the role of the biological membrane in the expression and course of cell damage after radiation exposure must be considered.

The hematologist and radiation casualties

Since the terrorist attack of September 11, 2001, preparation by the health care system for an act of terrorism has been mandated by leaders of governments. Scenarios for terrorist acts involving radioactive material have been identified, and approaches to management (based on past experience from atomic weapons detonations and radiation accidents) have been developed. Because of their experience in managing patients with profound cytopenia and/or marrow aplasia, hematologists will be asked to play a significant role in evaluating and treating victims of mass accidental or deliberate exposure to radiation. This review provides a framework for understanding how radiation levels are quantified, how radiation alters the function of hematopoietic (and nonhematopoietic) cells and tissues, and how victims receiving a significant radiation dose can be identified and managed. In Section I, Dr. Nicholas Dainiak reviews four components of the Acute Radiation Syndrome: the hematopoietic, neurovascular, gastrointestinal and cutaneous subsyndromes. Clinical signs and symptoms are discussed for exposed individuals at the time of initial presentation (the prodromal phase) and during their course of disease (the manifest illness). In Section II, he presents clinical and laboratory methods to assess radiation doses, including time to onset and severity of vomiting, rate of decline in absolute blood lymphocyte count and the appearance of chromosome aberrations such as dicentrics and ring forms. Potential scenarios of a radiation terrorist event are reviewed, and methods for initial clinical assessment, triage, and early management of the acute radiation syndrome and its component subsyndromes are summarized. In Section III, Dr. Jamie Waselenko reviews the hematopoietic syndrome, and presents guidelines for the use of cytokine therapy, antibiotics, and supportive care that have been developed by the Strategic National Pharmaceutical Stockpile Working Group. Results of preclinical and clinical growth factor therapy studies with G-CSF, GM-CSF, pegylated G-CSF, SCF, and IL-3 are summarized. When and how potassium iodide should be used after exposure to radioiodines is also reviewed. In Section IV, Dr. James Armitage describes a narrow "window" of 7 to 10 Gy where therapy with stem cell transplantation may be appropriate. Victims who are candidates for allotransplantation should not have major trauma or significant injury to other (nonhematopoietic) tissues. Rarely, victims may have an identical sibling or autologous stored marrow or blood stem cells, in which case the threshold for transplantation is 4 Gy. In Section V, Dr. Thomas MacVittie describes new directions for therapy, using cytokines such as IL-7, keratinocyte growth factor, and FLT-3. The potential for combinations of cytokines to enhance hematopoietic recovery is also reviewed.

Bystander effect produced by radiolabeled tumor cells in vivo

The bystander effect, originating from cells irradiated in vitro, describes the biologic response(s) of surrounding cells not directly targeted by a radiation insult. To overcome the limitations of in vitro tissue culture models and determine whether a bystander effect that is initiated by the in vivo decay of a radionuclide can be demonstrated in an animal, the ability of 5-[(125)I]iodo-2'-deoxyuridine ((125)IUdR)-labeled tumor cells to exert a damaging effect on neighboring unlabeled tumor cells growing s.c. in nude mice has been investigated. When mice are injected with a mixture of human colon LS174T adenocarcinoma cells and LS174T cells prelabeled with lethal doses of DNA-incorporated (125)I, a distinct inhibitory effect on the growth of s.c. tumor (derived from unlabeled cells) is observed. Because (i) the (125)I present within the cells is DNA-bound, (ii) approximately 99% of the electrons emitted by the decaying (125)I atoms have a subcellular range (<0.5 microm), and (iii) the overall radiation dose deposited by radiolabeled cells in the unlabeled cells within the growing tumor is <10 cGy, we conclude that the results obtained are a consequence of a bystander effect that is generated in vivo by factor(s) present within and/or released from the (125)IUdR-labeled cells. These in vivo findings significantly impact the current dogma for assessing the therapeutic potential of internally administered radionuclides. They also call for reevaluation of the approaches currently used for estimating the risks to individuals and populations inadvertently exposed internally to radioactivity as well as to patients undergoing routine diagnostic nuclear medical procedures.

Low dose, low-LET ionizing radiation-induced radioadaptation and associated early responses in unirradiated cells

Numerous investigators have reported that irradiation of cells with a low dose of ionizing radiation (IR) can induce a condition of enhanced radioresistance, i.e. a radioadaptive response. In this report, we investigated the hypothesis that a radioadaptive bystander effect may be induced in unirradiated cells by a transmissible factor(s) present in the supernatants of cells exposed to low dose gamma-rays. Normal human lung fibroblasts (HFL-1) were irradiated with a 1 cGy dose of gamma-rays and their supernatants were transferred to unirradiated HFL-1 as a bystander cell model. Compared with the directly irradiated cells, such treatment resulted in increased clonogenic survival following subsequent gamma-irradiation with 2 and 4 Gy. This radioadaptive bystander effect was found to be preceded by early decreases in cellular levels of TP53 protein, increase in intracellular ROS, and increase in the redox and DNA repair protein AP-endonuclease (APE). The demonstration that radioadaptation can occur in unirradiated cells via a fluid-phase, transferable factor(s) adds to the complexity of the current understanding of mechanisms by which radioadaptive responses can be induced by low dose, low-LET IR.

Hematologic consequences of exposure to ionizing radiation

From the early 1900s, it has been known that ionizing radiation (IR) impairs hematopoiesis through a variety of mechanisms. IR exposure directly damages hematopoietic stem cells and alters the capacity of bone marrow stromal elements to support and/or maintain hematopoiesis in vivo and in vitro. Exposure to IR induces dose-dependent declines in circulating hematopoietic cells not only through reduced bone marrow production, but also by redistribution and apoptosis of mature formed elements of the blood. Recently, the importance of using lymphocyte depletion kinetics to provide a "crude" dose estimate has been emphasized, particularly in rapid assessment of large numbers of individuals who may be exposed to IR through acts of terrorism or by accident. A practical strategy to estimate radiation dose and triage victims based upon clinical symptomatology is presented. An explosion of knowledge has occurred regarding molecular and cellular pathways that trigger and mediate hematologic responses to IR. In addition to damaging DNA, IR alters gene expression and transcription, and interferes with intracellular and intercellular signaling pathways. The clinical expression of these disturbances may be the development of leukemia, the most significant hematologic complication of IR exposure among survivors of the atomic bomb detonations over Japan. Those at greatest risk for leukemia are individuals exposed during childhood. The association of leukemia with chronic, low-dose-rate exposure from nuclear power plant accidents and/or nuclear device testing has been more difficult to establish, due in part to lack of precision and sensitivity of methods to assess doses that approach background radiation dose. Nevertheless, multiple myeloma may be associated with chronic exposure, particularly in those exposed at older ages.

Kinetics of apoptotic markers in exogeneously induced apoptosis of EL4 cells

We investigated the time-dependence of apoptotic events in EL4 cells by monitoring plasma membrane changes in correlation to DNA fragmentation and cell shrinkage. We applied three apoptosis inducers (staurosporine, tubericidine and X-rays) and we looked at various markers to follow the early-to-late apoptotic events: phospholipid translocation (identified through annexin V-fluorescein assay and propidium iodide), lipid package (via merocyanine assay), membrane fluidity and anisotropy (via fluorescent measurements), DNA fragmentation by the fluorescence-labeling test and cell size measurements. The different apoptotic inducers caused different reactions of the cells: staurosporine induced apoptosis most rapidly in a high number of cells, tubercidine triggered apoptosis only in the S phase cells, while X-rays caused a G2/M arrest and subsequently apoptosis. Loss of lipid asymmetry is promptly detectable after one hour of incubation time. The phosphatidylserine translocation, decrease of lipid package and anisotropy, and the increase of membrane fluidity appeared to be based on the same process of lipid asymmetry loss. Therefore, the DNA fragmentation and the cell shrinkage appear to be parallel and independent processes running on different time scales but which are kinetically inter-related. The results indicate different signal steps to apoptosis dependent on inducer characteristics but the kinetics of "early-to-late" apoptosis appears to be a fixed program.