The Pseudo-Pelger HuËt Cell-A New Permanent Radiation Biomarker

Estimate of the Deterministic Neutron RBE for Radiation-induced Pseudo-Pelger Huët Cell Formation

ABSTRACT

Using archival peripheral blood slides from radiation accident patients, we have recently described the pseudo-Pelger Huët anomaly (PPHA) in neutrophils as a new radiation-induced biomarker, useful for dosimetry not only immediately after a radiation incident but also potentially helpful as a tool in retrospective dosimetry. In conjunction with the Radiation Accident Registry at the Radiation Emergency Assistance Center/Training Site (REAC/TS), the frequency of PPHA cells has been compared from selected patients in the Y-12 criticality accident in Oak Ridge, TN, in 1958 and from the patient in the 1971 60Co accident at the USAEC Comparative Animal Research Laboratory (CARL), also in Oak Ridge. Patients A, C, and D in the Y-12 accident are described as having an average dose of 2.53 ± 0.14 Gy gamma + 0.90 ± 0.05 Gy neutron, while the patient in the CARL event had 2.6 Gy gamma dose from event reconstruction. Since the average gamma energies are almost identical in these two cohorts, it is possible to estimate the deterministic neutron relative biological effectiveness (RBEd) for PPHA formation in a criticality event. The neutron RBEd calculated in this way is an average value over the neutron fission energy spectrum and is found to be 3.4 ± 0.6, in good agreement with the currently recommended value of 3 for acute neutron dose to red marrow.

Early-response multiple-parameter biodosimetry and dosimetry: risk predictions

The accepted generic multiple-parameter and early-response biodosimetry and dosimetry assessment approach for suspected high-dose radiation (i.e. life-threatening) exposure includes measuring radioactivity associated with the exposed individual (if appropriate); observing and recording prodromal signs/symptoms; obtaining serial complete blood counts with white-blood-cell differential; sampling blood for the chromosome-aberration cytogenetic bioassay using the 'gold standard' dicentric assay (premature chromosome condensation assay for exposures >5 Gy photon acute doses equivalent), measurement of proteomic biomarkers and gene expression assays for dose assessment; bioassay sampling, if appropriate, to determine radioactive internal contamination; physical dose reconstruction, and using other available opportunistic dosimetry approaches. Biodosimetry and dosimetry resources are identified and should be setup in advance along with agreements to access additional national, regional, and international resources. This multifaceted capability needs to be integrated into a biodosimetry/dosimetry 'concept of operations' for use in a radiological emergency. The combined use of traditional biological-, clinical-, and physical-dosimetry should be use in an integrated approach to provide: (a) early-phase diagnostics to guide the development of initial medical-management strategy, and (b) intermediate and definitive assessment of radiation dose and injury. Use of early-phase (a) clinical signs and symptoms, (b) blood chemistry biomarkers, and (c) triage cytogenetics shows diagnostic utility to predict acute radiation injury severity.

Cytogenetic follow-up studies on humans with internal and external exposure to ionizing radiation

Cells exposed to ionizing radiation have a wide spectrum of DNA lesions that include DNA single-strand breaks, DNA double-strand breaks (DSBs), oxidative base damage and DNA-protein crosslinks. Among them, DSB is the most critical lesion, which when mis-repaired leads to unstable and stable chromosome aberrations. Currently, chromosome aberration analysis is the preferred method for biological monitoring of radiation-exposed humans. Stable chromosome aberrations, such as inversions and balanced translocations, persist in the peripheral blood lymphocytes of radiation-exposed humans for several years and, therefore, are potentially useful tools to prognosticate the health risks of radiation exposure, particularly in the hematopoietic system. In this review, we summarize the cytogenetic follow-up studies performed by REAC/TS (Radiation Emergency Assistance Center/Training site, Oak Ridge, USA) on humans exposed to internal and external radiation. In the light of our observations as well as the data existing in the literature, this review attempts to highlight the importance of follow-up studies for predicting the extent of genomic instability and its impact on delayed health risks in radiation-exposed victims.

Pseudo Pelger-Huët anomalies as potential biomarkers for acute exposure radiation dose in rhesus macaques (Macaca mulatta)

PURPOSE

The potential for malicious use of radiation, or radiation accidents could potentially lead to acute, high radiation doses to the public. Following acute accidental exposure to high doses of radiation, medical intervention is pivotal to the survivability of the patient, and the sooner the appropriate measures are taken the better the odds for survival. Early estimates of acute accidental radiation doses can be determined via biomarkers such as dicentric chromosome analysis or scenario reconstruction using computer software. However, both take valuable time and can be expensive. Increased frequencies of abnormal neutrophils in peripheral blood, referred to as pseudo Pelger-Huët anomalies (PPHAs), have been shown to be potential biomarkers of radiation exposure in several scenarios, including the 1958 Y-12 criticality accident and the radium dial painters. PPHAs are potentially a faster and cheaper quantitative biomarker for radiation exposure, and here they were evaluated in acutely exposed rhesus macaques.

METHODS AND MATERIALS

Peripheral blood smears from acutely exposed rhesus macaques were evaluated for the percentage of neutrophils that displayed the PPHA morphology using light microscopy. Irradiated animals received 0 to 8.5 Gy total body radiation using one of two strategies: (1) linear accelerator-produced 6 MV photons delivered at 80 cGy/minute; or (2) Cobalt 60-produced gamma irradiation delivered at 60 cGy/min. Zero dose animals were used to determine a baseline percentage of PPHAs, and blood smears taken periodically throughout the lifetime of exposed animals post-irradiation were used to determine the persistence and biokinetics of PPHAs.

RESULTS

The baseline prevalence of the PPHA in rhesus macaques was determined to be 0.58 ± 0.46%. The dose-response curve with doses ranging from 0 Gy to 8.5 Gy (LD90/30) displayed a strong positive correlation between PPHA percentage and acute radiation dose (R² of 0.88 p =  3.62 × 10^-22). Statistically significant differences were found when animals were separated into dose cohorts of 0, 4, 6.4-6.5, and 8-8.5 Gy. The biokinetics model utilized only 4 Gy exposures and blood smears taken periodically over 3.1 years post-irradiation. PPHA morphology increases quickly following irradiation and appears stable over 3.1 years post-irradiation.

CONCLUSION

PPHA morphology was confirmed to be present in rhesus macaques, a dose-response relationship was constructed, and it is stable over 3 years post-irradiation. This study demonstrates that PPHA analysis can be a fast and cheap method of biodosimetry. Future studies will work to determine the accuracy of dose determination and lower limits of detection.

Radium dial workers: back to the future

PURPOSE

This paper reviews the history of the radium dial workers in the United States, summarizes the scientific progress made since the last evaluation in the early 1990s, and discusses current progress in updating the epidemiologic cohort and applying new dosimetric models for radiation risk assessment.

BACKGROUND

The discoveries of radiation and radioactivity led quickly to medical and commercial applications at the turn of the 20th century, including the development of radioluminescent paint, made by combining radium with phosphorescent material and adhesive. Workers involved with the painting of dials and instruments included painters, handlers, ancillary workers, and chemists who fabricated the paint. Dial painters were primarily women and, prior to the mid to late 1920s, would use their lips to give the brush a fine point, resulting in high intakes of radium. The tragic experience of the dial painters had a significant impact on industrial safety standards, including protection measures taken during the Manhattan Project. The dial workers study has formed the basis for radiation protection standards for intakes of radionuclides by workers and the public.

EPIDEMIOLOGIC APPROACH

The mortality experience of 3,276 radium dial painters and handlers employed between 1913 and 1949 is being determined through 2019. The last epidemiologic follow-up was 30 years ago when most of these workers were still alive. Nearly 65% were born before 1920, 37.5% were teenagers when first hired, and nearly 50% were hired before 1930 when the habit of placing brushes in mouths essentially stopped. Comprehensive dose reconstruction techniques are being applied to estimate organ doses for each worker related to the intake of 226Ra, 228Ra, and associated photon exposures. Time dependent dose-response analyses will estimate lifetime risks for specific causes of death.

DISCUSSION

The study of radium dial workers is part of the Million Person Study of low-dose health effects that is designed to evaluate radiation risks among healthy American workers and veterans. Despite being one of the most important and influential radiation effects studies ever conducted, shifting programmatic responsibilities and declining funding led to the termination of the radium program of studies in the early 1990s. Renewed interest and opportunity have arisen. With scientific progress made in dosimetric methodology and models, the ability to perform a study over the entire life span, and the potential applicability to other scenarios such as medicine, environmental contamination and space exploration, the radium dial workers have once again come to the forefront.

The Pseudo-Pelger huët Cell as a Retrospective Dosimeter: Analysis of a Radium Dial Painter Cohort

Recently, the pseudo-Pelger Huët anomaly in peripheral blood neutrophils has been described as a new radiation-induced, stable biomarker. In this study, pseudo-Pelger Huët anomaly was examined in peripheral blood slides from a cohort of 166 former radium dial painters and ancillary personnel in the radium dial industry, 35 of whom had a marrow dose of zero above background. Members of the radium dial painter cohort ingested Ra and Ra at an early age (average age 20.6 ± 5.4 y; range 13-40 y) during the years 1914-1955. Exposure duration ranged from 1-1,820 wk with marrow dose 1.5-6,750 mGy. Pseudo-Pelger Huët anomaly expressed as a percentage of total neutrophils in this cohort rises in a sigmoidal fashion over five decades of red marrow dose. Six subjects in this cohort eventually developed malignancies: five osteosarcomas and one mastoid cell neoplasm. The pseudo-Pelger Huët anomaly percentage in these cases of neoplasm increases with marrow dose and is best fit with a sigmoid function, suggestive of a threshold effect. No sarcomas are seen for a marrow dose under 2 Gy. These results indicate that pseudo-Pelger Huët anomaly in peripheral blood is a reasonable surrogate for the estimation of alpha dose to bone marrow in historic radiation cases. Hypotheses are discussed to explain late (months to years), early (hours to days), and intermediate (weeks to months) effects of ionizing radiation, respectively, on the expression of genes encoding inner nuclear membrane proteins and their receptors, on the structure and function of nuclear membrane proteins and lipids, and on cytokinesis through chromatin bridge formation.

Delineating the Effects of Ionizing Radiation on Erythropoietic Lineage-Implications for Radiation Biodosimetry

The overall lethality/morbidity of ionizing radiation exposure involves multiple forms of inhibitory or cytotoxic effects that may manifest in different tissues with a varying dose and time response. One of the major systemic effects leading to lethality of radiation includes its suppressive effect on hematopoiesis, which could be observed even at doses as low as 1-2 Gy, whereas effects on gastrointestinal and nervous systems appear at relatively higher doses in the same order. This article reviews the effects of radiation on the three distinct stages of erythropoiesis-formation of erythroid progenitor cells, differentiation of erythroid precursor cells, and terminal maturation. During these stepwise developmental processes, erythroid progenitor cells undergo rapid expansion to form terminally differentiated red blood cells that are continuously replenished from bone marrow into the circulating peripheral blood stream. Cellular radiation response depends upon many factors such as cell lineage, rate of proliferation, and differentiation status. Therefore, we discuss radiation-induced alterations during the progenitor, precursor, and terminal maturation stages and the implications thereof. Since biomarkers of ionizing radiation exposure in human populations are of great interest for assessing normal tissue injury as well as for biodosimetry in the event of accidental or incidental radiation exposures, we also highlight blood-based biomarkers that have potential utility for medical management.