Medical management of the acute radiation syndrome: recommendations of the Strategic National Stockpile Radiation Working Group

Physicians, hospitals, and other health care facilities will assume the responsibility for aiding individuals injured by a terrorist act involving radioactive material. Scenarios have been developed for such acts that include a range of exposures resulting in few to many casualties. This consensus document was developed by the Strategic National Stockpile Radiation Working Group to provide a framework for physicians in internal medicine and the medical subspecialties to evaluate and manage large-scale radiation injuries. Individual radiation dose is assessed by determining the time to onset and severity of nausea and vomiting, decline in absolute lymphocyte count over several hours or days after exposure, and appearance of chromosome aberrations (including dicentrics and ring forms) in peripheral blood lymphocytes. Documentation of clinical signs and symptoms (affecting the hematopoietic, gastrointestinal, cerebrovascular, and cutaneous systems) over time is essential for triage of victims, selection of therapy, and assignment of prognosis. Recommendations based on radiation dose and physiologic response are made for treatment of the hematopoietic syndrome. Therapy includes treatment with hematopoietic cytokines; blood transfusion; and, in selected cases, stem-cell transplantation. Additional medical management based on the evolution of clinical signs and symptoms includes the use of antimicrobial agents (quinolones, antiviral therapy, and antifungal agents), antiemetic agents, and analgesic agents. Because of the strong psychological impact of a possible radiation exposure, psychosocial support will be required for those exposed, regardless of the dose, as well as for family and friends. Treatment of pregnant women must account for risk to the fetus. For terrorist or accidental events involving exposure to radioiodines, prophylaxis against malignant disease of the thyroid is also recommended, particularly for children and adolescents.

Development and assessment of a quantitative reverse transcription-PCR assay for simultaneous measurement of four amplicons

BACKGROUND

High-throughput and forward-deployable biological dosimetry capabilities are required for tactical and medical decisions after radiologic events. We previously reported a quantitative reverse transcription (QRT)-PCR assay for human radiation-responsive gene targets using a whole-blood ex vivo irradiation model, but we needed a multitarget assay on a smaller, less costly, real-time PCR detection system.

METHODS

We developed a quadruplex QRT-PCR assay in a 96-well, closed-plate format suitable for use with RNA extracted from whole blood. Four cDNA targets were simultaneously amplified in a sealed tube by hybridization to exonuclease probes, each conjugated to distinct fluorogenic reporters. A novel primer-limited 18S rRNA reference target was validated from serial dilutions of human total RNA. To test assay precision, we incorporated a positive-control cDNA mimic into duplex and quadruplex PCR reactions. The master mixture was supplemented with more enzyme, MgCl(2), and deoxyribonucleotides. Simultaneous detection of four targets was evaluated in comparison with respective duplex QRT-PCR assays.

RESULTS

The simultaneous detection of three radiation-responsive genes by quadruplex QRT-PCR was quantitative, with gene expression changes similar to those observed with optimized duplex and triplex QRT-PCR assays. The 18S rRNA and GADD45 calibration curves (threshold cycle vs log(10) cDNA) were linear and reproducible and showed optimal PCR efficiencies as indicated by slopes statistically equivalent to the theoretical value of -3.322.

CONCLUSIONS

This is the first study of a quadruplex QRT-PCR assay. Our approach has diagnostic utility in the detection of biomarkers, biological and toxicologic agents, and genes of inherited diseases and cancer.

Molecular and cellular biology of moderate-dose (1-10 Gy) radiation and potential mechanisms of radiation protection: report of a workshop at Bethesda, Maryland, December 17-18, 2001

Exposures to doses of radiation of 1-10 Gy, defined in this workshop as moderate-dose radiation, may occur during the course of radiation therapy or as the result of radiation accidents or nuclear/radiological terrorism alone or in conjunction with bioterrorism. The resulting radiation injuries would be due to a series of molecular, cellular, tissue and whole-animal processes. To address the status of research on these issues, a broad-based workshop was convened. The specific recommendations were: (1) RESEARCH: Identify the key molecular, cellular and tissue pathways that lead from the initial molecular lesions to immediate and delayed injury. The latter is a chronic progressive process for which postexposure treatment may be possible. (2) Technology: Develop high-throughput technology for studying gene, protein and other biochemical expression after radiation exposure, and cytogenetic markers of radiation exposure employing rapid and accurate techniques for analyzing multiple samples. (3) Treatment strategies: Identify additional biological targets and develop effective treatments for radiation injury. (4) Ensuring sufficient expertise: Recruit and train investigators from such fields as radiation biology, cancer biology, molecular biology, cellular biology and wound healing, and encourage collaboration on interdisciplinary research on the mechanisms and treatment of radiation injury. Communicate knowledge of the effects of radiation exposure to the general public and to investigators, policy makers and agencies involved in response to nuclear accidents/events and protection/treatment of the general public.

Radiation biodosimetry: applications for spaceflight

The multiparametric dosimetry system that we are developing for medical radiological defense applications could be adapted for spaceflight environments. The system complements the internationally accepted personnel dosimeters and cytogenetic analysis of chromosome aberrations, considered the best means of documenting radiation doses for health records. Our system consists of a portable hematology analyzer, molecular biodosimetry using nucleic acid and antigen-based diagnostic equipment, and a dose assessment management software application. A dry-capillary tube reagent-based centrifuge blood cell counter (QBC Autoread Plus, Becton [correction of Beckon] Dickinson Bioscience) measures peripheral blood lymphocytes and monocytes, which could determine radiation dose based on the kinetics of blood cell depletion. Molecular biomarkers for ionizing radiation exposure (gene expression changes, blood proteins) can be measured in real time using such diagnostic detection technologies as miniaturized nucleic acid sequences and antigen-based biosensors, but they require validation of dose-dependent targets and development of optimized protocols and analysis systems. The Biodosimetry Assessment Tool, a software application, calculates radiation dose based on a patient's physical signs and symptoms and blood cell count analysis. It also annotates location of personnel dosimeters, displays a summary of a patient's dosimetric information to healthcare professionals, and archives the data for further use. These radiation assessment diagnostic technologies can have dual-use applications supporting general medical-related care.

Real-time quantitative RT-PCR assay of GADD45 gene expression changes as a biomarker for radiation biodosimetry

PURPOSE

To assess the efficacy of fluorescent-based quantitative reverse transcription-polymerase chain reaction (QRT-PCR) technology to measure gene expression changes (GEC) for rapid, point-of-care radiation dose assessment.

MATERIALS AND METHODS

A real-time QRT-PCR assay based on 5'-fluorogenic nuclease TaqMan(TM) methodology was developed, which employs both relative and absolute quantification of a candidate mRNA biomarker. Growth arrest and DNA damage gene 45 (GADD45), a cell-cycle regulation and DNA repair gene, served as the paradigm because of the reported linear dose-response relationship for mRNA induction in the human myeloid tumor cell line (ML-1) over the range of 2-50 cGy. Using an ex vivo whole-blood model, GEC was measured from total blood RNA at 24h and 48 h after (60)Co gamma-ray exposures (0-3 Gy; 0.1 Gy/min).

RESULTS

A linear and reproducible up-regulation representing a twofold to fourfold change in GADD45 relative and absolute GEC was confirmed in both intra- and inter-assay analyses.

CONCLUSIONS

Primer and probes to detect GADD45 targets using real-time PCR were developed. This is the first report using realtime QRT-PCR to measure radiation-induced GEC dose response. Real-time QRT-PCR using GEC as biomarkers offers rapidity, sensitivity, and reproducibility as a potential efficient biological dosimetry tool applicable in radiation therapy applications and early-response accident biodosimetry.

Overview of low-level radiation exposure assessment: biodosimetry

The capability to make diagnostic assessments of radiation exposure is needed to support triage of radiation casualties and medical treatment decisions in military operations. At the International Conference on Low-Level Radiation Injury and Medical Countermeasures session on biodosimetry in the military, participants reviewed the field of biomarkers, covering a wide range of biological endpoints. Participants evaluated early changes associated with exposure to ionizing radiation, including chromosomal and DNA damage, gene expression and associated proteins, and DNA mutations. The use and development of advanced monitoring and diagnostic technologies compatible with military operations was emphasized. Conventional radiation bioassays require a substantial amount of time between when the sample is taken and when the data can be provided for decision making. These "reach back" bioassays are evaluated in laboratories that are not in the field; these laboratories routinely measure exposures of 25 cGy (photon equivalent levels). Detection thresholds can be reduced approximately fivefold by the addition of significant and tiresome scoring efforts. Alternative real-time biomarkers that can be measured in field laboratories or with handheld detection devices show promise as screening and clinical diagnostic tools, but they require further development and validation studies.

Nucleic acid molecular biomarkers for diagnostic biodosimetry applications: use of the fluorogenic 5'-nuclease polymerase chain reaction assay

A reliable, relatively easy method for diagnostic assessment of radiation exposure is needed to support the triage of radiation casualties and medical treatment decisions in military defense operations. Our strategy is to identify radiation-responsive DNA mutations and gene expression targets that can be analyzed using polymerase chain reaction (PCR) assays and an existing fluorescence-based nucleic acid analysis system designed for forward-deployable laboratory applications. Using an in vitro model system of human peripheral blood lymphocytes, we identified a candidate nucleic acid biomarker (i.e., gene expression target) that is responsive to ionizing radiation. In this report, we describe our preliminary Haras gene expression findings. A dose-dependent elevation in Haras gene expression levels was demonstrated using Northern-blot analysis 17 hours after exposure to a 250-kVp dose of X-rays (25-100 cGy, 1 Gy/minute); c-Haras expression levels at 100 cGy were ninefold higher than those of controls. An alternative protocol to quantify the Haras cDNA target, using the rapid, real-time reverse transcriptase fluorogenic 5'-nuclease PCR assay, is described, along with a preliminary characterization of the dynamic range for detection. Our research shows that the analysis of multitarget nucleic acid biomarkers, using the multiplex fluorogenic 5'-nuclease PCR assay, has beneficial applications in radiation epidemiology, radiation therapy, and biodosimetry.

Biological dosimetry using human interphase peripheral blood lymphocytes

Conventional metaphase-spread chromosome-aberration-based biodosimetry techniques for radiation dose assessment, although robust, are laborious and time consuming. The molecular cytogenetic laboratory of the Armed Forces Radiobiology Research Institute is developing simple and rapid interphase-based cytological assays that will be applicable to a broad range of radiation exposure scenarios. These assays include analysis of chromosome aberrations (premature chromosome condensation-fluorescence in situ hybridization assay) and mitochondrial DNA mutations (mtDNA4977 deletion assay) using resting human peripheral blood lymphocytes. The dose-effect relationship for radiation-induced aberrations involving chromosome 1 after 24 hours of repair at 37 degrees C in resting human peripheral blood lymphocytes was studied using fluorescence in situ hybridization after chemical induction of premature chromosome condensation as previously explained. In the present study, we examined whether gamma irradiation in the range of 0 to 7.5 Gy induces a dose-dependent increase in aberrations manifested as "excess spots." The number of excess spots per cell, reflecting aberrations involving chromosome 1, increased from 0.035 at 0.5 Gy to 0.236 at 7.5 Gy. This observed dose-effect relationship was fit with a nonlinear power model. This technique may be extended to the study of radiation-induced translocations in interphase cells for retrospective dose reconstruction. With a recently developed in situ polymerase chain reaction method to detect and quantify mtDNA deletion in interphase cells after radiation exposure in cultured human peripheral blood lymphocytes, 90% to 95% of cells are analyzable. We discuss the potential use of the mtDNA deletion assay in biological dosimetry applications. Interphase-based cytological assays may eliminate some inherent problems associated with metaphase-spread-based assays. These problems involve (1) the limited number of analyzable cells containing chromosome aberrations, which is due to various factors including radiation-induced cell death and delay in cell cycle progression into mitosis, and (2) the requirements for radiation cytogenetics expertise and tedious labor to manually score chromosome aberrations.

Proto-oncogene expression: a predictive assay for radiation biodosimetry applications

Using a model system of in vitro human peripheral blood lymphocytes, the effect of low-dose (0.25 to 1.50 Gy) 250-kVp X ray radiation (1 Gy.min-1) on the expression of several proto-oncogenes was examined (c-Haras, c-src, c-met, c-jun, c-fos, and c-myc) and beta-actin from 0.25 to 17 h post-radiation. RNA was extracted from cells harvested at various times after exposure and examined for levels of particular mRNAs by northern blot hybridisation. A progressive time- and dose-dependent increase in mRNA levels was observed for c-Haras mRNA, while the other proto-oncogenes (c-src, c-met, c-fos, c-jun and c-myc) examined were variable during the same time period. beta-actin levels were initially decreased but at 17 h post-radiation had returned to control levels. A comparison of the rate of c-Haras transcription at 5 and 17 h post-irradiation revealed that c-Haras transcription was higher at 5 h than at 17 h. These findings suggest that the level of specific proto-oncogene expression, particularly c-Haras, may be useful early diagnostic molecular biomarkers for biodosimetry applications. The use of real-time PCR technologies to quantify gene expression changes will also be discussed.

Biodosimety Assessment Tool: a post-exposure software application for management of radiation accidents

The Biodosimetry Assessment Tool software application under development will equip health care providers with diagnostic information (clinical signs and symptoms, physical dosimetry, etc.) germane to the management of human radiation casualties. Designed primarily for prompt use after a radiation incident, the user-friendly program facilitates collection, integration, and archiving of data obtained from exposed persons. Data collected in templates are compared with established radiation dose responses obtained from the literature to provide multiparameter dose assessments. The program archives clinical information (e.g., extent of contamination, wounds, infection, etc.) useful for casualty management, displays relevant diagnostic information in a concise format, and can be used to manage both military and civilian radiation accidents. In addition, monitoring of diagnostic information of individuals using this program could potentially minimize the severity of psychological casualties by making a marked impact on the way that both radiation casualties and the worried well view their exposure, dose, and future risk for the development of disease.

Radiation exposure assessment using cytological and molecular biomarkers

Chromosome aberration analysis is the conventional means of assessing radiation exposure. The Armed Forces Radiobiology Research Institute recently established an alternative method to measure radiation-induced chromosome aberrations in interphase cells. The method uses commercially available chemical agents to induce premature chromosome condensation in resting' G0 human peripheral blood lymphocytes. Then specific whole-chromosome DNA probes are used with fluorescence in situ hybridisation to detect aberrant cells rapidly over a broad dose range. In new research, the real-time fluorogenic 5'-nuclease, or TaqMan, polymerase chain reaction assay is being used to identify radiation-responsive molecular biomarkers, including gene expression targets and DNA mutations. The goal is to establish rapid, precise, high-throughput assay systems that are practical in a variety of radiation exposure scenarios. The new methodologies that have a number of other applications, together with diagnostic software now in development, could improve the United States military's emergency response capability and medical readiness.

Quantitative plasmid mixture analysis using the fluorogenic 5'-nuclease polymerase chain reaction assay

The fluorogenic 5'-nuclease polymerase chain reaction (PCR) assay has been shown to be useful for quantifying a given DNA target in a sample. Here we show how an existing PCR protocol can be amended for quantification by incorporating distinctive dual-labeled, sequence-specific oligonucleotide probes and resulting in a two- to threefold broader and more reliable dynamic range than that of conventional end-point analysis of PCR products. Moreover, we show a multiplex situation in which two targets, one normal and one mutated, can be amplified and quantified simultaneously and in the same reaction tube. Use of this novel approach for quantitative PCR applications eliminates the need for post-PCR processing and has clinical- and research-based diagnostic applications, particularly for measuring levels of mutations in a mixture.

Induction of premature chromosome condensation by a phosphatase inhibitor and a protein kinase in unstimulated human peripheral blood lymphocytes: a simple and rapid technique to study chromosome aberrations using specific whole-chromosome DNA hybridization probes for biological dosimetry

We developed a simple and rapid method to study chromosome aberrations involving specific chromosomes using unstimulated human peripheral blood lymphocytes (HPBL). Premature chromosome condensation (PCC) was induced by incubating unstimulated HPBL in the presence of okadaic acid (OA, a phosphatase inhibitor), adenosine triphosphate (ATP), and p34(cdc2)/cyclin B kinase [an essential component of mitosis-promoting factor (MPF)], which eliminated the need for fusion with mitotic cells. OA concentration and duration of incubation for PCC induction was optimized using mitogen-stimulated HPBL; a final concentration of 0.75 microM incubated for 3 h was optimum, resulting in approximately 20% PCC yield. In unstimulated HPBL, PCC was induced by the addition of p34(cdc2)/cyclin B kinase at concentrations as low as 5 units/ml to a cell culture medium containing OA. Increases in the concentration of p34(cdc2)/cyclin B kinase from 5 to 50 units/ml resulted in a concentration-dependent increase in PCC yield (30% to 42%). We demonstrate that this technique of inducing PCC in unstimulated HPBL is suitable for studying radiation-induced aberrations involving a specific chromosome (chromosome 1) after 24 h repair using a whole-chromosome in situ hybridization probe and chromosome painting. Cells with aberrant chromosome number 1 are characterized with more than two chromosome spots. The frequency of cells with aberrant chromosome 1 increased with 60Co gamma-radiation doses in the region 0-7.5 Gy. The observed dose-effect relationship for the percentage of cells with aberrant chromosome 1 (Y) was explained by using both a linear [Y=(2.77+/-0.230)D+0.90+/-0.431, r(2)=0.966] and a nonlinear power [Y=(5.70+/-0.46)D((0.61+/-0.05)), r(2)=0.9901) model. This technique can be applied to biological dosimetry of radiation exposures involving uniform whole-body low linear energy transfer (LET) exposures.

In situ detection of a PCR-synthesized human pancentromeric DNA hybridization probe by color pigment immunostaining: application for dicentric assay automation

We report a low cost and efficient method for synthesizing a human pancentromeric DNA probe by the polymerase chain reaction (PRC) and an optimized protocol for in situ detection using color pigment immunostaining. The DNA template used in the PCR was a 2.4 kb insert containing human alphoid repeated sequences of pancentromeric DNA subcloned into pUC9 (Miller et al. 1988) and the primers hybridized to internal sequences of the 172 bp consensus tandem repeat associated with human centromeres. PCR was performed in the presence of biotin-11-dUTP, and the product was used for in situ hybridization to detect the pancentromeric region of human chromosomes in metaphase spreads. Detection of pancentromeric probe was achieved by immunoenzymatic color pigment painting to yield a permanent image detected at high resolution by bright field microscopy. The ability to synthesize the centromeric probe rapidly and to detect it with color pigment immunostaining will lead to enhanced identification and eventually to automation of various chromosome aberration assays.

Fast-in situ hybridization and immunoenzymatic color pigment detection of mouse bone marrow micronucleus

The development of a whole mouse genomic DNA probe coupled to color pigment painting detection methodology can accurately verify mouse micronuclei induced by chemicals or drugs leading to a lower probability of potential artifacts. Using color pigment painting detection of probes in conjunction with Wright's Giemsa counterstain instead of the current fluorescence detection technology ensures low cost, high resolution permanent documentation of slides for a particular test compound. The permanent color pigment-detected micronuclei and adjoining counterstain allows slides to be stored for future analysis without enhancing the signal or adding antifading agents that are associated with fluorescence detection. Combining innovative technology such as fast-in situ hybridization of DNA probes with immunoenzymatic color pigment detection provides rapid verification of true micronuclei (DNA containing) within 2-3 hr.

Quantitative assessment of the contribution of clustered damage to DNA double-strand breaks induced by 60Co gamma rays and fission neutrons

The induction of DNA strand breaks by fission neutrons was studied in aqueous plasmid (pBR322) DNA under aerobic conditions for a wide range of hydroxyl radical (*OH) scavenger concentrations and was compared to the induction of strand breaks by 6OCo gamma rays. Strand breaks were measured using agarose gel electrophoresis coupled with sensitive 32P-based phosphor imaging. Yields are reported for DNA single-strand breaks (SSBs) and double-strand breaks formed linearly with dose (alphaDSBs). The fraction of alphaDSBs that were dependent on the multiply damaged site (MDS) or clustered damage mechanism was also calculated using a model. G values for SSBs and alphaDSBs declined with increasing *OH scavenging capacity. However, with increasing *OH scavenging capacities, the decrease in yields of strand breaks for fission neutrons was not as pronounced as for gamma rays. The percentage of alphaDSBs for gamma rays was dependent on *OH scavenging capacity, appearing negligible at low scavenging capacities but increasing at higher scavenging capacities. In contrast, fission neutrons induced high percentages of alphaDSBs that were approximately independent of *OH scavenging capacity. The levels of alphaDSBs formed by the MDS mechanism after exposure to fission neutrons are consistent with the expected distinctive features of high-LET energy deposition events and track structure. The results also confirm observations made by others that even for low-LET radiation, the MDS mechanism contributes significantly to DNA damage at cell-like scavenging conditions.

Transformation of human osteoblast cells to the tumorigenic phenotype by depleted uranium-uranyl chloride

Depleted uranium (DU) is a dense heavy metal used primarily in military applications. Although the health effects of occupational uranium exposure are well known, limited data exist regarding the long-term health effects of internalized DU in humans. We established an in vitro cellular model to study DU exposure. Microdosimetric assessment, determined using a Monte Carlo computer simulation based on measured intracellular and extracellular uranium levels, showed that few (0.0014%) cell nuclei were hit by alpha particles. We report the ability of DU-uranyl chloride to transform immortalized human osteoblastic cells (HOS) to the tumorigenic phenotype. DU-uranyl chloride-transformants are characterized by anchorage-independent growth, tumor formation in nude mice, expression of high levels of the k-ras oncogene, reduced production of the Rb tumor-suppressor protein, and elevated levels of sister chromatid exchanges per cell. DU-uranyl chloride treatment resulted in a 9.6 (+/- 2.8)-fold increase in transformation frequency compared to untreated cells. In comparison, nickel sulfate resulted in a 7.1 (+/- 2.1)-fold increase in transformation frequency. This is the first report showing that a DU compound caused human cell transformation to the neoplastic phenotype. Although additional studies are needed to determine if protracted DU exposure produces tumors in vivo, the implication from these in vitro results is that the risk of cancer induction from internalized DU exposure may be comparable to other biologically reactive and carcinogenic heavy-metal compounds (e.g., nickel).

Premature chromosome condensation assay for biodosimetry: studies with fission-neutrons

Characterization of the premature chromosome condensation assay for radiation quality is needed. To that end, human lymphocytes were exposed in vitro to various doses of 250-kVp x rays (Y(D) = 4 keV microm(-1), Y(D) is the dose-mean lineal energy of the absorbed dose distribution, D(y), where y is defined as the energy deposited in a volume by a single event divided by the mean chord length of the volume) and to fission neutrons (Y(D) = 65 keV microm(-1)). The distribution of prematurely condensed chromosome and fragments following exposure to x rays or to neutrons were non-Poisson after repair at 37 degrees C for 24 h. Dose-response curves were constructed for the yield of excess prematurely condensed chromosome fragments as necessary for biodosimetry applications. The curves were fitted to a weighted linear model by the least-squares regression method. The neutron relative biological effectiveness (RBE) value was estimated to be 2.4 +/- 0.39.