NASA Radiation Biomarker Workshop, September 27-28, 2007

Transcriptomic Profiling and Pathway Analysis of Mesenchymal Stem Cells Following Low Dose-Rate Radiation Exposure

Low dose-rate radiation exposure can occur in medical imaging, as background from environmental or industrial radiation, and is a hazard of space travel. In contrast with high dose-rate radiation exposure that can induce acute life-threatening syndromes, chronic low-dose radiation is associated with Chronic Radiation Syndrome (CRS), which can alter environmental sensitivity. Secondary effects of chronic low dose-rate radiation exposure include circulatory, digestive, cardiovascular, and neurological diseases, as well as cancer. Here, we investigated 1-2 Gy, 0.66 cGy/h, ⁶⁰Co radiation effects on primary human mesenchymal stem cells (hMSC). There was no significant induction of apoptosis or DNA damage, and cells continued to proliferate. Gene ontology (GO) analysis of transcriptome changes revealed alterations in pathways related to cellular metabolism (cholesterol, fatty acid, and glucose metabolism), extracellular matrix modification and cell adhesion/migration, and regulation of vasoconstriction and inflammation. Interestingly, there was increased hypoxia signaling and increased activation of pathways regulated by iron deficiency, but Nrf2 and related genes were reduced. The data were validated in hMSC and human lung microvascular endothelial cells using targeted qPCR and Western blotting. Notably absent in the GO analysis were alteration pathways for DNA damage response, cell cycle inhibition, senescence, and pro-inflammatory response that we previously observed for high dose-rate radiation exposure. Our findings suggest that cellular gene transcription response to low dose-rate ionizing radiation is fundamentally different compared to high-dose-rate exposure. We hypothesize that cellular response to hypoxia and iron deficiency are driving processes, upstream of the other pathway regulation.

Impact of spaceflight stressors on behavior and cognition: A molecular, neurochemical, and neurobiological perspective

The response of the human body to multiple spaceflight stressors is complex, but mounting evidence implicate risks to CNS functionality as significant, able to threaten metrics of mission success and longer-term behavioral and neurocognitive health. Prolonged exposure to microgravity, sleep disruption, social isolation, fluid shifts, and ionizing radiation have been shown to disrupt mechanisms of homeostasis and neurobiological well-being. The overarching goal of this review is to document the existing evidence of how the major spaceflight stressors, including radiation, microgravity, isolation/confinement, and sleep deprivation, alone or in combination alter molecular, neurochemical, neurobiological, and plasma metabolite/lipid signatures that may be linked to operationally-relevant behavioral and cognitive performance. While certain brain region-specific and/or systemic alterations titrated in part with neurobiological outcome, variations across model systems, study design, and the conspicuous absence of targeted studies implementing combinations of spaceflight stressors, confounded the identification of specific signatures having direct relevance to human activities in space. Summaries are provided for formulating new research directives and more predictive readouts of portending change in neurobiological function.

Transcriptome of rhesus macaque (Macaca mulatta) exposed to total-body irradiation

The field of biodosimetry has seen a paradigm shift towards an increased use of molecular phenotyping technologies including omics and miRNA, in addition to conventional cytogenetic techniques. Here, we have used a nonhuman primate (NHP) model to study the impact of gamma-irradiation on alterations in blood-based gene expression. With a goal to delineate radiation induced changes in gene expression, we followed eight NHPs for 60 days after exposure to 6.5 Gy gamma-radiation for survival outcomes. Analysis of differential gene expression in response to radiation exposure yielded 26,944 dysregulated genes that were not significantly impacted by sex. Further analysis showed an increased association of several pathways including IL-3 signaling, ephrin receptor signaling, ErbB signaling, nitric oxide signaling in the cardiovascular system, Wnt/β-catenin signaling, and inflammasome pathway, which were associated with positive survival outcomes in NHPs after acute exposure to radiation. This study provides novel insights into major pathways and networks involved in radiation-induced injuries that may identify biomarkers for radiation injury.

A translatable predictor of human radiation exposure

Terrorism using radiological dirty bombs or improvised nuclear devices is recognized as a major threat to both public health and national security. In the event of a radiological or nuclear disaster, rapid and accurate biodosimetry of thousands of potentially affected individuals will be essential for effective medical management to occur. Currently, health care providers lack an accurate, high-throughput biodosimetric assay which is suitable for the triage of large numbers of radiation injury victims. Here, we describe the development of a biodosimetric assay based on the analysis of irradiated mice, ex vivo-irradiated human peripheral blood (PB) and humans treated with total body irradiation (TBI). Interestingly, a gene expression profile developed via analysis of murine PB radiation response alone was inaccurate in predicting human radiation injury. In contrast, generation of a gene expression profile which incorporated data from ex vivo irradiated human PB and human TBI patients yielded an 18-gene radiation classifier which was highly accurate at predicting human radiation status and discriminating medically relevant radiation dose levels in human samples. Although the patient population was relatively small, the accuracy of this classifier in discriminating radiation dose levels in human TBI patients was not substantially confounded by gender, diagnosis or prior exposure to chemotherapy. We have further incorporated genes from this human radiation signature into a rapid and high-throughput chemical ligation-dependent probe amplification assay (CLPA) which was able to discriminate radiation dose levels in a pilot study of ex vivo irradiated human blood and samples from human TBI patients. Our results illustrate the potential for translation of a human genetic signature for the diagnosis of human radiation exposure and suggest the basis for further testing of CLPA as a candidate biodosimetric assay.

Biodosimetry using radiation-induced micronuclei in skin fibroblasts

PURPOSE

We assessed micronuclei in dermal fibroblasts as a local biodosimeter for estimating accidental in vivo radiation exposure.

MATERIALS AND METHODS

Male and female C3H/HeJ and C57Bl6 mice of four age groups (∼11, 36, 60 and 99 weeks) received a single whole body dose of gamma radiation (0-10 Gy) and radiation-induced micronuclei per 1,000 binucleated cells were assessed in skin fibroblasts in their first division after isolation from biopsies taken on days 1 and 7 post irradiation. The method of generalized estimating equations was used for statistical analyses.

RESULTS

Total micronuclei were increased on day 1 in a dose-dependent manner in the range of 1-10 Gy, with no significant attenuation of response between day 1 and day 7 and no significant effect of gender. Between-strain differences were observed with C3H/HeJ mice showing lower background micronuclei and a slightly steeper dose response. Age affected only the background micronuclei (moderate increase with age). The model demonstrated that the assay yields 'unbiased' prediction of the dose between 0 and 7 Gy. Within this dose range, the predicted dose was found to be accurate within ±1.5-2 Gy. When the specificity is set to 95%, the assay can distinguish between unexposed and 2 Gy exposed mice with a sensitivity of around 60%. The sensitivity approached 100% when discriminating between unexposed mice and mice receiving doses equal to or greater than 4 Gy. The percentage of binucleated cells with micronuclei was shown to be useful as a simpler and slightly faster substitute for the total micronuclei count.

CONCLUSION

Micronuclei in dermal fibroblasts isolated up to 1 week after irradiation can be a useful biodosimeter for local dose after accidental radiation exposure.

Radiation injury treatment network (RITN): healthcare professionals preparing for a mass casualty radiological or nuclear incident

PURPOSE

To describe the history, composition, and activities of the Radiation Injury Treatment Network (RITN). The Radiation Injury Treatment Network® is a cooperative effort of the National Marrow Donor Program and the American Society for Blood and Marrow Transplantation. The goals of RITN are to educate hematologists, oncologists, and stem cell transplant practitioners about their potential involvement in the response to a radiation incident and provide treatment expertise. Injuries to the marrow system readily occur when a victim is exposed to ionising radiation. This focus therefore leverages the expertise of these specialists who are accustomed to providing the intensive supportive care required by patients with a suppressed marrow function. Following a radiological incident, RITN centres may be asked to: Accept patient transfers to their institutions; provide treatment expertise to practitioners caring for victims at other centres; travel to other centres to provide medical expertise; or provide data on victims treated at their centres. Moving forward, it is crucial that we develop a coordinated interdisciplinary approach in planning for and responding to radiological and nuclear incidents. The ongoing efforts of radiation biologists, radiation oncologists, and health physicists can and should complement the efforts of RITN and government agencies.

CONCLUSION

RITN serves as a vital partner in preparedness and response efforts for potential radiological and nuclear incidents.

Radiation victim management and the haematologist in the future: time to revisit therapeutic guidelines?

PURPOSE

The use of nuclear/radiation devices against the civilian population is now a realistic scenario. Haematopoietic syndrome is the primary therapeutic challenge in the case of whole body acute exposure over 2 Grays (Gy) whereas burns and combined injuries would be frequently observed in myelo-suppressed patients. Optimisation of scoring and treatments are important goals to achieve.

CONCLUSION

The European Response Category (RC) concept represents an attempt to integratively assess haematological/extrahematological radiation-induced lesions. Based on the frequently observed heterogeneity of bone marrow damage in accidental/intentional irradiations, the stimulation of residual stem cells using granulocyte Colony-stimulating factor remains the therapeutic standard after exposure to less than the lethal dose 50 % (Haematopoietic[H] score 3-H3). Allogeneic stem cell transplantation is indicated in case of medullary eradication (Haematopoietic score 4-H4) whereas extramedullary toxicity may determine the outcome. Especially in case of numerous casualties exhibiting acute radiation syndrome, the administration of survival factor combinations remains questionable, at least as a palliative treatment. In addition pleiotropic cytokines injection such as erythropoietin and keratinocyte growth factor and grafting multipotent mesenchymal stem cells - from underexposed bone marrow areas or fat tissues - could be proposed to prevent multiple organ failure syndrome development. Multi-disciplinary teams should be prepared to manage such patients.

The role of mass spectrometry-based metabolomics in medical countermeasures against radiation

Radiation metabolomics can be defined as the global profiling of biological fluids to uncover latent, endogenous small molecules whose concentrations change in a dose-response manner following exposure to ionizing radiation. In response to the potential threat of nuclear or radiological terrorism, the Center for High-Throughput Minimally Invasive Radiation Biodosimetry was established to develop field-deployable biodosimeters based, in part, on rapid analysis by mass spectrometry of readily and easily obtainable biofluids. In this review, we briefly summarize radiation biology and key events related to actual and potential nuclear disasters, discuss the important contributions the field of mass spectrometry has made to the field of radiation metabolomics, and summarize current discovery efforts to use mass spectrometry-based metabolomics to identify dose-responsive urinary constituents, and ultimately to build and deploy a noninvasive high-throughput biodosimeter.

Flow cytometric scoring of micronucleated reticulocytes as a possible high-throughput radiation biodosimeter

Micronucleated reticulocyte (MN-RET) scoring by flow cytometry (FCM) has been used in assessment of the clastogenic effects of chemicals. However, its dose-response to acute whole body irradiation (WBI) at moderate dose rates remains to be established. We show that FCM scoring of MN-RET in peripheral blood from male ICR mice exposed to WBI X-ray doses of 0.5-5 Gy at a dose rate of 0.488 Gy/min exhibits a linear dose-response relationship 24, 48, and 72 hr following WBI. Parallel microscopic counting of micronucleated polychromatic erythrocytes (MN-PCE) in bone marrow smears from the same animals showed similar linear dose-response patterns at the same time points. Indeed, MN-RET and MN-PCE were highly correlated at all doses and time points. In view of the speed and accuracy of this method, in addition to the small blood sample size needed for the assay, the flow cytometric protocol for MN-RET scoring may provide a minimally-invasive, high throughput radiation biodosimeter.

Dynamics of micronuclei in mouse skin fibroblasts after gamma irradiation

Micronuclei (MN) were assessed in dermal fibroblasts from C3H HeJ and C57 Bl6 mice (6-10 mo of age) irradiated in vivo as a potential method of biodosimetry. Radiation-induced MN [per 1,000 binucleated (BN) cells], assessed in fibroblasts obtained 1 d post-irradiation, increased in a dose-dependent manner in the range of 1 - 10 Gy per single dose. Analysis at 1 wk post irradiation showed some attenuation of MN response in C3H HeJ male mice, suggesting partial recovery of DNA damage. This was not observed in C57 Bl6 mice. Monomicronucleated cells predominated in unirradiated fibroblasts, whereas in irradiated fibroblasts multimicronucleated cells predominated at dose levels above about 5 Gy (more than 1,000 MN per 1,000 BN cells). Modeling of the data indicate that assaying total MN in dermal fibroblasts from samples of irradiated skin taken up to 1 wk after irradiation can provide biodosimetric information (with an accuracy of 1-2 Gy) for doses up to at least 6 Gy with lesser accuracy at higher doses. Percentage of multimicronucleated cells may be useful as a substitute of total MN at the higher doses, but total percentage of micronucleated cells is of limited value as a substitute.

Synopsis of partial-body radiation diagnostic biomarkers and medical management of radiation injury workshop

Radiation exposures from accidents, nuclear detonations or terrorist incidents are unlikely to be homogeneous; however, current biodosimetric approaches are developed and validated primarily in whole-body irradiation models. A workshop was held at the Armed Forces Radiobiology Research Institute in May 2008 to draw attention to the need for partial-body biodosimetry, to discuss current knowledge, and to identify the gaps to be filled. A panel of international experts and the workshop attendees discussed the requirements and concepts for a path forward. This report addresses eight key areas identified by the Workshop Program Committee for future focus: (1) improved cytogenetics, (2) clinical signs and symptoms, (3) cutaneous bioindicators, (4) organ-specific biomarkers, (5) biophysical markers of dose, (6) integrated diagnostic approaches, (7) confounding factors, and (8) requirements for post-event medical follow-up. For each area, the status, advantages and limitations of existing approaches and suggestions for new directions are presented.