Low doses of oxygen ion irradiation cause long-term damage to bone marrow hematopoietic progenitor and stem cells in mice

Protection of the hematopoietic system against radiation-induced damage: drugs, mechanisms, and developments

Sometimes, people can be exposed to moderate or high doses of radiation accidentally or through the environment. Radiation can cause great harm to several systems within organisms, especially the hematopoietic system. Several types of drugs protect the hematopoietic system against radiation damage in different ways. They can be classified as "synthetic drugs" and "natural compounds." Their cellular mechanisms to protect organisms from radiation damage include free radical-scavenging, anti-oxidation, reducing genotoxicity and apoptosis, and alleviating suppression of the bone marrow. These topics have been reviewed to provide new ideas for the development and research of drugs alleviating radiation-induced damage to the hematopoietic system.

Total body proton and heavy-ion irradiation causes cellular senescence and promotes pro-osteoclastogenic activity in mouse bone marrow

Low-LET photon radiation-induced persistent alterations in bone marrow (BM) cells are well documented in total-body irradiated (TBI) rodents and also among radiotherapy patients. However, the late effects of protons and high-LET heavy-ion radiation on BM cells and its implications in osteoclastogenesis are not fully understood. Therefore, C57BL6/J female mice (8 weeks; n = 10/group) were irradiated to sham, and 1 Gy of the proton (0.22 keV/μm), or high-LET ⁵⁶Fe-ions (148 keV/μm) and at 60 d post-exposure, mice were sacrificed and femur sections were obtained for histological, cellular and molecular analysis. Cell proliferation (PCNA), cell death (active caspase-3), senescence (p16), osteoclast (RANK), osteoblast (OPG), osteoblast progenitor (c-Kit), and osteoclastogenesis-associated secretory factors (like RANKL) were assessed using immunostaining. While no change in cell proliferation and apoptosis between control and irradiated groups was noted, the number of BM megakaryocytes was significantly reduced in irradiated mice at 60 d post-exposure. A remarkable increase in p16 positive cells indicated a persistent increase in cell senescence, whereas increased RANKL/OPG ratio, reductions in the number of osteoblast progenitor cells, and osteocalcin provided clear evidence that exposure to both proton and ⁵⁶Fe-ions promotes pro-osteoclastogenic activity in BM. Among irradiated groups, ⁵⁶Fe-induced alterations in the BM cellularity and osteoclastogenesis were significantly greater than the protons that demonstrated a radiation quality-dependent effect. This study has implications in understanding the role of IR-induced late changes in the BM cells and its involvement in bone degeneration among deep-space astronauts, and also in patients undergoing proton or heavy-ion radiotherapy.

The Particle Radiobiology of Multipotent Mesenchymal Stromal Cells: A Key to Mitigating Radiation-Induced Tissue Toxicities in Cancer Treatment and Beyond?

Mesenchymal stromal cells (MSCs) comprise a heterogeneous population of multipotent stromal cells that have gained attention for the treatment of irradiation-induced normal tissue toxicities due to their regenerative abilities. As the vast majority of studies focused on the effects of MSCs for photon irradiation-induced toxicities, little is known about the regenerative abilities of MSCs for particle irradiation-induced tissue damage or the effects of particle irradiation on the stem cell characteristics of MSCs themselves. MSC-based therapies may help treat particle irradiation-related tissue lesions in the context of cancer radiotherapy. As the number of clinical proton therapy centers is increasing, there is a need to decidedly investigate MSC-based treatments for particle irradiation-induced sequelae. Furthermore, therapies with MSCs or MSC-derived exosomes may also become a useful tool for manned space exploration or after radiation accidents and nuclear terrorism. However, such treatments require an in-depth knowledge about the effects of particle radiation on MSCs and the effects of MSCs on particle radiation-injured tissues. Here, the existing body of evidence regarding the particle radiobiology of MSCs as well as regarding MSC-based treatments for some typical particle irradiation-induced toxicities is presented and critically discussed.

Changes in one-carbon metabolism and DNA methylation in the hearts of mice exposed to space environment-relevant doses of oxygen ions (16O)

Cardiovascular disease constitutes an important threat to humans after space missions beyond the Earth's magnetosphere. Epigenetic alterations have an important role in the etiology and pathogenesis of cardiovascular disease. Previous research in animal models has shown that protons and ⁵⁶Fe ions cause long-term changes in DNA methylation and expression of repetitive elements in the heart. However, astronauts will be exposed to a variety of ions, including the smaller fragmented products of heavy ions after they interact with the walls of the space craft. Here, we investigated the effects of ¹⁶O on the cardiac methylome and one-carbon metabolism in male C57BL/6 J mice. Left ventricles were examined 14 and 90 days after exposure to space-relevant doses of 0.1, 0.25, or 1 Gy of ¹⁶O (600 MeV/n). At 14 days, the two higher radiation doses elicited global DNA hypomethylation in the 5'-UTR of Long Interspersed Nuclear Elements 1 (LINE-1) compared to unirradiated, sham-treated mice, whereas specific LINE-1 elements exhibited hypermethylation at day 90. The pericentromeric major satellites were affected both at the DNA methylation and expression levels at the lowest radiation dose. DNA methylation was elevated, particularly after 90 days, while expression showed first a decrease followed by an increase in transcript abundance. Metabolomics analysis revealed that metabolites involved in homocysteine remethylation, central to DNA methylation, were unaffected by radiation, but the transsulfuration pathway was impacted after 90 days, with a large increase in cystathione levels at the lowest dose. In summary, we observed dynamic changes in the cardiac epigenome and metabolome three months after exposure to a single low dose of oxygen ions.

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.

Effects of low-dose oxygen ions and protons on cardiac function and structure in male C57BL/6J mice

PURPOSE

Astronauts traveling beyond low-Earth orbit will be exposed to high linear-energy transfer charged particles. Because there is concern about the adverse effects of space radiation on the cardiovascular system, this study assessed cardiac function and structure and immune cell infiltration in a mouse model of charged-particle irradiation.

MATERIALS AND METHODS

Male C57BL/6 J mice were exposed to oxygen ions (¹⁶O, 600 MeV/n at 0.25-0.26 Gy/min to a total dose of 0, 0.05, 0.1, 0.25, or 1 Gy), protons (150 MeV, 0.35-0.55 Gy/min to 0, 0.5, or 1 Gy), or protons (150 MeV, 0.5 Gy) followed by ¹⁶O (600 MeV/n, 0.1 Gy). Separate groups of mice received ¹³⁷Cs γ-rays (1 Gy/min to 0, 0.5, 1, or 3 Gy) as a reference. Cardiac function and blood velocity were measured with ultrasonography at 3, 5, 7, and 9 months after irradiation. At 2 weeks, 3 months, and 9 months, cardiac tissue was collected to assess apoptosis, tissue remodeling, and markers of immune cells.

RESULTS

Ejection fraction and fractional shortening decreased at 3 and 7 months after ¹⁶O. These parameters did not change in mice exposed to γ-rays, protons, or protons followed by ¹⁶O. Each of the radiation exposures caused only small increases in cleaved caspase-3 and numbers of apoptotic nuclei. Changes in the levels of α-smooth muscle cell actin and a 75-kDa peptide of collagen type III in the left ventricle suggested tissue remodeling, but there was no significant change in total collagen deposition at 2 weeks, 3 months, and 9 months. Increases in protein amounts of cluster of differentiation (CD)2, CD68, and CD45 as measured with immunoblots at 2 weeks, 3 months, and 9 months after exposure to protons or ¹⁶O alone suggested immune cell infiltration. For type III collagen, CD2 and CD68, the efficacy in inducing protein abundance of CD2, CD68, and CD45 was ¹⁶O > protons > γ-rays > protons followed by ¹⁶O.

CONCLUSIONS

Low-dose, high-energy charged-particle irradiation caused mild changes in cardiac function and tissue remodeling in the mouse.

Combined Effects of Low-Dose Proton Radiation and Simulated Microgravity on the Mouse Retina and the Hematopoietic System

The purpose of the current study was to characterize the effects of simulated microgravity and radiation-induced changes in retina and retinal vasculature, and to assess the accompanying early changes in immune cells and hematological parameters. To better understand the effects of spaceflight, we used a combination of treatments designed to simulate both the radiation and low-gravity aspects of space conditions. To simulate the broad energy spectrum of a large solar particle event (SPE) and galactic cosmic ray (GCR) radiation, male C57BL/6J mice were exposed to whole-body irradiation using fully modulated beams of 150-MeV protons containing particles of energy from 0 to 150 MeV and a uniform dose-vs.-depth profile. The mice were also hindlimb-unloaded (HLU) by tail suspension. Mice were unloaded for 7 days, exposed to 50 cGy, unloaded for an additional 7 days and then sacrificed for tissue isolation at days 4 and 30 after the combined treatments. Increases in the number of apoptotic cells were observed in the endothelial cells of mice that received radiation alone or with HLU compared to controls at both days 4 and 30 (P < 0.05). Endothelial nitric oxide synthase (eNOS) levels were significantly elevated in the retina after irradiation only or combined with HLU compared to controls at the 30-day time point (P < 0.05). The most robust changes were observed in the combination group, suggesting a synergistic response to radiation and unloading. For hematopoietic parameters, our analysis indicated the main effects for time and radiation at day 4 after treatments (day 11 postirradiation) (P < 0.05), but a smaller influence of HLU for both white blood cell and lymphocyte counts. The group treated with both radiation and HLU showed greater than 50% reduction in lymphocyte counts compared to controls. Radiation-dependent differences were also noted in specific lymphocyte subpopulations (T, B, natural killer cells). This study shows indications of an early effect of low-dose radiation and spaceflight conditions on retina and immune populations.

Increased Hematopoietic Stem Cells/Hematopoietic Progenitor Cells Measured as Endogenous Spleen Colonies in Radiation-Induced Adaptive Response in Mice (Yonezawa Effect)

The existence of radiation-induced adaptive response (AR) was reported in varied biosystems. In mice, the first in vivo AR model was established using X-rays as both the priming and the challenge doses and rescue of bone marrow death as the end point. The underlying mechanism was due to the priming radiation-induced resistance in the blood-forming tissues. In a series of investigations, we further demonstrated the existence of AR using different types of ionizing radiation (IR) including low linear energy transfer (LET) X-rays and high LET heavy ion. In this article, we validated hematopoietic stem cells/hematopoietic progenitor cells (HSCs/HPCs) measured as endogenous colony-forming units-spleen (CFU-S) under AR inducible and uninducible conditions using combination of different types of IR. We confirmed the consistency of increased CFU-S number change with the AR inducible condition. These findings suggest that AR in mice induced by different types of IR would share at least in part a common underlying mechanism, the priming IR-induced resistance in the blood-forming tissues, which would lead to a protective effect on the HSCs/HPCs and play an important role in rescuing the animals from bone marrow death. These findings provide a new insight into the mechanistic study on AR in vivo.

Exposure to galactic cosmic radiation compromises DNA repair and increases the potential for oncogenic chromosomal rearrangement in bronchial epithelial cells

Participants in deep space missions face protracted exposure to galactic cosmic radiation (GCR). In this setting, lung cancer is a significant component of the overall risk of radiation-exposure induced death. Here we investigate persistent effects of GCR exposure on DNA repair capacity in lung-derived epithelial cells, using an enzyme-stimulated chromosomal rearrangement as an endpoint. Replicate cell cultures were irradiated with energetic ⁴⁸Ti ions (a GCR component) or reference γ-rays. After a six-day recovery, they were challenged by expression of a Cas9/sgRNA pair that creates double-strand breaks simultaneously in the EML4 and ALK loci, misjoining of which creates an EML4-ALK fusion oncogene. Misjoining was significantly elevated in ⁴⁸Ti-irradiated populations, relative to the baseline rate in mock-irradiated controls. The effect was not seen in γ-ray irradiated populations exposed to equal or higher radiation doses. Sequence analysis of the EML4-ALK joints from ⁴⁸Ti-irradiated cultures showed that they were far more likely to contain deletions, sometimes flanked by short microhomologies, than equivalent samples from mock-irradiated cultures, consistent with a shift toward error-prone alternative nonhomologous end joining repair. Results suggest a potential mechanism by which a persistent physiological effect of GCR exposure may increase lung cancer risk.