The Hematopoietic Syndrome of the Acute Radiation Syndrome in Rhesus Macaques: A Systematic Review of the Lethal Dose Response Relationship

Whole thorax irradiation of non-human primates induces persistent nuclear damage and gene expression changes in peripheral blood cells

We investigated the cytogenetic and gene expression responses of peripheral blood cells of non-human primates (NHP, Macaca mulatta) that were whole-thorax irradiated with a single dose of 10 Gy. In this model, partial irradiation of NHPs in the thoracic region (Whole Thorax Lung Irradiation, WTLI) allows the study of late radiation-induced lung injury, while avoiding acute radiation syndromes related to hematopoietic and gastrointestinal injury. A transient drop in circulating lymphocytes and platelets was seen by 9 days, followed by elevations in respiratory rate, circulating neutrophils, lymphocytes, and monocytes at 60-100 days, corresponding to computed tomography (CT) and histologic evidence of pneumonitis, and elective euthanasia of four animals. To evaluate long-term DNA damage in NHP peripheral blood lymphocytes after 10 Gy WTLI, we used the cytokinesis-block micronucleus (CBMN) assay to measure chromosomal aberrations as post-mitotic micronuclei in blood samples collected up to 8 months after irradiation. Regression analysis showed significant induction of micronuclei in NHP blood cells that persisted with a gradual decline over the 8-month study period, suggesting long-term DNA damage in blood lymphocytes after WTLI. We also report transcriptomic changes in blood up to 30 days after WTLI. We isolated total RNA from peripheral blood at 3 days before and then at 2, 5 and 30 days after irradiation. We identified 1187 transcripts that were significantly changed across the 30-day time course. From changes in gene expression, we identified biological processes related to immune responses, which persisted across the 30-day study. Response to oxygen-containing compounds and bacteria were implicated by gene-expression changes at the earliest day 2 and latest, day 30 time-points. Gene expression changes suggest a persistent altered state of the immune system, specifically response to infection, for at least a month after WTLI.

Organ Doses Associated with Partial-Body Irradiation with 2.5% Bone Marrow Sparing of the Non-Human Primate: A Retrospective Study

A partial-body irradiation model with approximately 2.5% bone marrow sparing (PBI/BM2.5) was established to determine the radiation dose-response relationships for the prolonged and delayed multi-organ effects of acute radiation exposure. Historically, doses reported to the entire body were assumed to be equal to the prescribed dose at some defined calculation point, and the dose-response relationship for multi-organ injury has been defined relative to the prescribed dose being delivered at this point, e.g., to a point at mid-depth at the level of the xiphoid of the non-human primate (NHP). In this retrospective-dose study, the true distribution of dose within the major organs of the NHP was evaluated, and these doses were related to that at the traditional dose-prescription point. Male rhesus macaques were exposed using the PBI/BM2.5 protocol to a prescribed dose of 10 Gy using 6-MV linear accelerator photons at a rate of 0.80 Gy/min. Point and organ doses were calculated for each NHP from computed tomography (CT) scans using heterogeneous density data. The prescribed dose of 10.0 Gy to a point at midline tissue assuming homogeneous media resulted in 10.28 Gy delivered to the prescription point when calculated using the heterogeneous CT volume of the NHP. Respective mean organ doses to the volumes of nine organs, including the heart, lung, bowel and kidney, were computed. With modern treatment planning systems, utilizing a three-dimensional reconstruction of the NHP's CT images to account for the variations in body shape and size, and using density corrections for each of the tissue types, bone, water, muscle and air, accurate determination of the differences in dose to the NHP can be achieved. Dose and volume statistics can be ascertained for any body structure or organ that has been defined using contouring tools in the planning system. Analysis of the dose delivered to critical organs relative to the total-body target dose will permit a more definitive analysis of organ-specific effects and their respective influence in multiple organ injury.

Targeted Metabolomics Identifies Pharmacodynamic Biomarkers for BIO 300 Mitigation of Radiation-Induced Lung Injury

PURPOSE

Biomarkers serve a number of purposes during drug development including defining the natural history of injury/disease, serving as a secondary endpoint or trigger for intervention, and/or aiding in the selection of an effective dose in humans. BIO 300 is a patent-protected pharmaceutical formulation of nanoparticles of synthetic genistein being developed by Humanetics Corporation. The primary goal of this metabolomic discovery experiment was to identify biomarkers that correlate with radiation-induced lung injury and BIO 300 efficacy for mitigating tissue damage based upon the primary endpoint of survival.

METHODS

High-throughput targeted metabolomics of lung tissue from male C57L/J mice exposed to 12.5 Gy whole thorax lung irradiation, treated daily with 400 mg/kg BIO 300 for either 2 weeks or 6 weeks starting 24 h post radiation exposure, were assayed at 180 d post-radiation to identify potential biomarkers.

RESULTS

A panel of lung metabolites that are responsive to radiation and able to distinguish an efficacious treatment schedule of BIO 300 from a non-efficacious treatment schedule in terms of 180 d survival were identified.

CONCLUSIONS

These metabolites represent potential biomarkers that could be further validated for use in drug development of BIO 300 and in the translation of dose from animal to human.

Succinate ester derivative of δ-tocopherol enhances the protective effects against 60Co γ-ray-induced hematopoietic injury through granulocyte colony-stimulating factor induction in mice

α-tocopherol succinate (α-TOS), γ-tocotrienol (GT3) and δ-tocotrienol (DT3) have drawn large attention due to their efficacy as radioprotective agents. α-TOS has been shown to act superior to α-tocopherol (α-TOH) in mice by reducing lethality following total body irradiation (TBI). Because α-TOS has been shown to act superior to α-tocopherol (α-TOH) in mice by reducing lethality following total body irradiation (TBI), we hypothesized succinate may be contribute to the radioprotection of α-TOS. To study the contributions of succinate and to identify stronger radioprotective agents, we synthesized α-, γ- and δ-TOS. Then, we evaluated their radioprotective effects and researched further mechanism of δ-TOS on hematological recovery post-irradiation. Our results demonstrated that the chemical group of succinate enhanced the effects of α-, γ- and δ-TOS upon radioprotection and granulocyte colony-stimulating factor (G-CSF) induction, and found δ-TOS a higher radioprotective efficacy at a lower dosage. We further found that treatment with δ-TOS ameliorated radiation-induced pancytopenia, augmenting cellular recovery in bone marrow and the colony forming ability of bone marrow cells in sublethal irradiated mice, thus promoting hematopoietic stem and progenitor cell recovery following irradiation exposure. δ-TOS appears to be an attractive radiation countermeasure without known toxicity, but further exploratory efficacy studies are still required.

The Evolving Mcart Multimodal Imaging Core: Establishing a Protocol for Computed Tomography and Echocardiography in the Rhesus Macaque to Perform Longitudinal Analysis of Radiation-Induced Organ Injury

Computed Tomography (CT) and Echocardiography (EC) are two imaging modalities that produce critical longitudinal data that can be analyzed for radiation-induced organ-specific injury to the lung and heart. The Medical Countermeasures Against Radiological Threats (MCART) consortium has a well established animal model research platform that includes nonhuman primate (NHP) models of the acute radiation syndrome and the delayed effects of acute radiation exposure. These models call for a definition of the latency, incidence, severity, duration, and resolution of different organ-specific radiation-induced subsyndromes. The pulmonary subsyndromes and cardiac effects are a pair of interdependent syndromes impacted by exposure to potentially lethal doses of radiation. Establishing a connection between these will reveal important information about their interaction and progression of injury and recovery. Herein, the authors demonstrate the use of CT and EC data in the rhesus macaque models to define delayed organ injury, thereby establishing: a) consistent and reliable methodology to assess radiation-induced damage to the lung and heart; b) an extensive database in normal age-matched NHP for key primary and secondary endpoints; c) identified problematic variables in imaging techniques and proposed solutions to maintain data integrity; and d) initiated longitudinal analysis of potentially lethal radiation-induced damage to the lung and heart.