RESUMEN
Archival data of leukocyte count and the differentials obtained from control and irradiated Rhesus Macaques (Macaca mulatta) were statistically analyzed to understand the long-term effect of ionizing radiation exposure. Nine animals received total-body irradiation (TBI) of 7.2-8.4 Gy at 3-4 years old. Twelve animals served as age-matched controls with no radiation exposure. The complete blood cell count dataset was obtained during regular health exams every 2-6 months for 8 years from their age of 8 to 17 years old. Linear mixed models for leukocyte, neutrophil, lymphocyte, and monocyte counts and their percentages were successfully developed. Estimated marginal means calculated based on the models revealed statistically significant elevations in leukocyte and neutrophil counts and neutrophil percentages in irradiated animals compared to the controls. Lymphocyte percentage was significantly lower in irradiated animals. Longitudinal trends for both control and irradiated animals were consistent with expected trends of aging in hematopoiesis, which is skewed towards production of myeloid lineage cells such as neutrophils and monocytes rather than lymphoid cells. Longitudinal trends from irradiated animals suggested the age-related increase in neutrophils and decrease in lymphocytes were stronger than in the controls, although the difference did not reach statistical significance. The mechanism of the long-term effects in the hematopoietic system were not investigated. However, the results suggest ionizing radiation causes long-term effects on some of the factors implicated in hematopoietic aging, possibly inducing early-onset or accelerated aging in the hematopoietic system. Extended analysis with observations including before and after the follow-up period in this study will be beneficial to understand the timeline and features of the long-term response.
RESUMEN
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.
