Ferroptosis, Inflammation, and Microbiome Alterations in the Intestine in the Göttingen Minipig Model of Hematopoietic-Acute Radiation Syndrome.

Hematopoietic acute radiation syndrome (H-ARS) involves injury to multiple organ systems following total body irradiation (TBI). Our laboratory demonstrated that captopril, an angiotensin-converting enzyme inhibitor, mitigates H-ARS in Göttingen minipigs, with improved survival and hematopoietic recovery, as well as the suppression of acute inflammation. However, the effects of captopril on the gastrointestinal (GI) system after TBI are not well known. We used a Göttingen minipig H-ARS model to investigate captopril's effects on the GI following TBI (60Co 1.79 or 1.80 Gy, 0.42-0.48 Gy/min), with endpoints at 6 or 35 days. The vehicle or captopril (0.96 mg/kg) was administered orally twice daily for 12 days, starting 4 h post-irradiation. Ilea were harvested for histological, protein, and RNA analyses. TBI increased congestion and mucosa erosion and hemorrhage, which were modulated by captopril. GPX-4 and SLC7A11 were downregulated post-irradiation, consistent with ferroptosis at 6 and 35 days post-irradiation in all groups. Interestingly, p21/waf1 increased at 6 days in vehicle-treated but not captopril-treated animals. An RT-qPCR analysis showed that radiation increased the gene expression of inflammatory cytokines IL1B, TNFA, CCL2, IL18, and CXCL8, and the inflammasome component NLRP3. Captopril suppressed radiation-induced IL1B and TNFA. Rectal microbiome analysis showed that 1 day of captopril treatment with radiation decreased overall diversity, with increased Proteobacteria phyla and Escherichia genera. By 6 days, captopril increased the relative abundance of Enterococcus, previously associated with improved H-ARS survival in mice. Our data suggest that captopril mitigates senescence, some inflammation, and microbiome alterations, but not ferroptosis markers in the intestine following TBI.

Iron Deposition in the Bone Marrow and Spleen of Nonhuman Primates with Acute Radiation Syndrome.

The risk of exposure to high levels of ionizing radiation from nuclear weapons or radiological accidents is an increasing world concern. Partial- or total-body exposure to high doses of radiation is potentially lethal through the induction of acute radiation syndrome (ARS). Hematopoietic cells are sensitive to radiation exposure; white blood cells primarily undergo apoptosis while red blood cells (RBCs) undergo hemolysis. Several laboratories demonstrated that the rapid hemolysis of RBCs results in the release of acellular iron into the blood. We recently demonstrated using a murine model of ARS after total-body irradiation (TBI) and the loss of RBCs, iron accumulated in the bone marrow and spleen, notably between 4-21 days postirradiation. Here, we investigated iron accumulation in the bone marrow and spleens from TBI nonhuman primates (NHPs) using histological stains. We observed trends in increased intracellular and extracellular brown pigmentation in the bone marrow after various doses of radiation, especially after 4-15 days postirradiation, but these differences did not reach significance. We observed a significant increase in Prussian blue-staining intracellular iron deposition in the spleen 13-15 days after 5.8-8.5 Gy of TBI. We observed trends of increased iron in the spleen after 30-60 days postirradiation, with varying doses of radiation, but these differences did not reach significance. The NHP model of ARS confirms our earlier findings in the murine model, showing iron deposition in the bone marrow and spleen after TBI.

Transcriptomic Profiling and Pathway Analysis of Mesenchymal Stem Cells Following Low Dose-Rate Radiation Exposure.

Low dose-rate radiation exposure can occur in medical imaging, as background from environmental or industrial radiation, and is a hazard of space travel. In contrast with high dose-rate radiation exposure that can induce acute life-threatening syndromes, chronic low-dose radiation is associated with Chronic Radiation Syndrome (CRS), which can alter environmental sensitivity. Secondary effects of chronic low dose-rate radiation exposure include circulatory, digestive, cardiovascular, and neurological diseases, as well as cancer. Here, we investigated 1-2 Gy, 0.66 cGy/h, 60Co radiation effects on primary human mesenchymal stem cells (hMSC). There was no significant induction of apoptosis or DNA damage, and cells continued to proliferate. Gene ontology (GO) analysis of transcriptome changes revealed alterations in pathways related to cellular metabolism (cholesterol, fatty acid, and glucose metabolism), extracellular matrix modification and cell adhesion/migration, and regulation of vasoconstriction and inflammation. Interestingly, there was increased hypoxia signaling and increased activation of pathways regulated by iron deficiency, but Nrf2 and related genes were reduced. The data were validated in hMSC and human lung microvascular endothelial cells using targeted qPCR and Western blotting. Notably absent in the GO analysis were alteration pathways for DNA damage response, cell cycle inhibition, senescence, and pro-inflammatory response that we previously observed for high dose-rate radiation exposure. Our findings suggest that cellular gene transcription response to low dose-rate ionizing radiation is fundamentally different compared to high-dose-rate exposure. We hypothesize that cellular response to hypoxia and iron deficiency are driving processes, upstream of the other pathway regulation.

Comparison of the Medical Uses and Cellular Effects of High and Low Linear Energy Transfer Radiation.

Exposure to ionizing radiation can occur during medical treatments, from naturally occurring sources in the environment, or as the result of a nuclear accident or thermonuclear war. The severity of cellular damage from ionizing radiation exposure is dependent upon a number of factors including the absorbed radiation dose of the exposure (energy absorbed per unit mass of the exposure), dose rate, area and volume of tissue exposed, type of radiation (e.g., X-rays, high-energy gamma rays, protons, or neutrons) and linear energy transfer. While the dose, the dose rate, and dose distribution in tissue are aspects of a radiation exposure that can be varied experimentally or in medical treatments, the LET and eV are inherent characteristics of the type of radiation. High-LET radiation deposits a higher concentration of energy in a shorter distance when traversing tissue compared with low-LET radiation. The different biological effects of high and low LET with similar energies have been documented in vivo in animal models and in cultured cells. High-LET results in intense macromolecular damage and more cell death. Findings indicate that while both low- and high-LET radiation activate non-homologous end-joining DNA repair activity, efficient repair of high-LET radiation requires the homologous recombination repair pathway. Low- and high-LET radiation activate p53 transcription factor activity in most cells, but high LET activates NF-kB transcription factor at lower radiation doses than low-LET radiation. Here we review the development, uses, and current understanding of the cellular effects of low- and high-LET radiation exposure.

Iron Deposition and Ferroptosis in the Spleen in a Murine Model of Acute Radiation Syndrome.

Total body irradiation (TBI) can result in death associated with hematopoietic insufficiency. Although radiation causes apoptosis of white blood cells, red blood cells (RBC) undergo hemolysis due to hemoglobin denaturation. RBC lysis post-irradiation results in the release of iron into the plasma, producing a secondary toxic event. We investigated radiation-induced iron in the spleens of mice following TBI and the effects of the radiation mitigator captopril. RBC and hematocrit were reduced ~7 days (nadir ~14 days) post-TBI. Prussian blue staining revealed increased splenic Fe3+ and altered expression of iron binding and transport proteins, determined by qPCR, western blotting, and immunohistochemistry. Captopril did not affect iron deposition in the spleen or modulate iron-binding proteins. Caspase-3 was activated after ~7-14 days, indicating apoptosis had occurred. We also identified markers of iron-dependent apoptosis known as ferroptosis. The p21/Waf1 accelerated senescence marker was not upregulated. Macrophage inflammation is an effect of TBI. We investigated the effects of radiation and Fe3+ on the J774A.1 murine macrophage cell line. Radiation induced p21/Waf1 and ferritin, but not caspase-3, after ~24 h. Radiation ± iron upregulated several markers of pro-inflammatory M1 polarization; radiation with iron also upregulated a marker of anti-inflammatory M2 polarization. Our data indicate that following TBI, iron accumulates in the spleen where it regulates iron-binding proteins and triggers apoptosis and possible ferroptosis.

Transcriptomic profiling and pathway analysis of cultured human lung microvascular endothelial cells following ionizing radiation exposure.

The vascular system is sensitive to radiation injury, and vascular damage is believed to play a key role in delayed tissue injury such as pulmonary fibrosis. However, the response of endothelial cells to radiation is not completely understood. We examined the response of primary human lung microvascular endothelial cells (HLMVEC) to 10 Gy (1.15 Gy/min) X-irradiation. HLMVEC underwent senescence (80-85%) with no significant necrosis or apoptosis. Targeted RT-qPCR showed increased expression of genes CDKN1A and MDM2 (10-120 min). Western blotting showed upregulation of p2/waf1, MDM2, ATM, and Akt phosphorylation (15 min-72 h). Low levels of apoptosis at 24-72 h were identified using nuclear morphology. To identify novel pathway regulation, RNA-seq was performed on mRNA using time points from 2 to 24 h post-irradiation. Gene ontology and pathway analysis revealed increased cell cycle inhibition, DNA damage response, pro- and anti- apoptosis, and pro-senescence gene expression. Based on published literature on inflammation and endothelial-to-mesenchymal transition (EndMT) pathway genes, we identified increased expression of pro-inflammatory genes and EndMT-associated genes by 24 h. Together our data reveal a time course of integrated gene expression and protein activation leading from early DNA damage response and cell cycle arrest to senescence, pro-inflammatory gene expression, and endothelial-to-mesenchymal transition.

Effects of captopril against radiation injuries in the Göttingen minipig model of hematopoietic-acute radiation syndrome.

Our laboratory has demonstrated that captopril, an angiotensin converting enzyme inhibitor, mitigates hematopoietic injury following total body irradiation in mice. Improved survival in mice is correlated with improved recovery of mature blood cells and bone marrow, reduction of radiation-induced inflammation, and suppression of radiation coagulopathy. Here we investigated the effects of captopril treatment against radiation injuries in the Göttingen mini pig model of Hematopoietic-Acute Radiation Syndrome (H-ARS). Minipigs were given captopril orally (0.96 mg/kg) twice daily for 12 days following total body irradiation (60Co 1.79 Gy, 0.42-0.48 Gy/min). Blood was drawn over a time course following irradiation, and tissue samples were collected at euthanasia (32-35 days post-irradiation). We observed improved survival with captopril treatment, with survival rates of 62.5% in vehicle treated and 87.5% in captopril treated group. Additionally, captopril significantly improved recovery of peripheral blood mononuclear cells, and a trend toward improvement in recovery of red blood cells and platelets. Captopril significantly reduced radiation-induced expression of cytokines erythropoietin and granulocyte-macrophage colony-stimulating factor and suppressed radiation-induced acute-phase inflammatory response cytokine serum amyloid protein A. Using quantitative-RT-PCR to monitor bone marrow recovery, we observed significant suppression of radiation-induced expression of redox stress genes and improved hematopoietic cytokine expression. Our findings suggest that captopril activities in the Göttingen minipig model of hematopoietic-acute radiation syndrome reflect findings in the murine model.

Deposition of Iron in the Bone Marrow of a Murine Model of Hematopoietic Acute Radiation Syndrome.

Exposure to high-dose total body irradiation (TBI) can result in hematopoietic acute radiation syndrome (H-ARS), characterized by leukopenia, anemia, and coagulopathy. Death from H-ARS occurs from hematopoietic insufficiency and opportunistic infections. Following radiation exposure, red blood cells (RBCs) undergo hemolysis from radiation-induced hemoglobin denaturation, causing the release of iron. Free iron can have multiple detrimental biological effects, including suppression of hematopoiesis. We investigated the impact of radiation-induced iron release on the bone marrow following TBI and the potential impact of the ACE inhibitor captopril, which improves survival from H-ARS. C57BL/6J mice were exposed to 7.9 Gy, 60Co irradiation, 0.6 Gy/min (LD70-90/30). RBCs and reticulocytes were significantly reduced within 7 days of TBI, with the RBC nadir at 14-21 days. Iron accumulation in the bone marrow correlated with the time course of RBC hemolysis, with an ∼10-fold increase in bone marrow iron at 14-21 days post-irradiation, primarily within the cytoplasm of macrophages. Iron accumulation in the bone marrow was associated with increased expression of genes for iron binding and transport proteins, including transferrin, transferrin receptor 1, ferroportin, and integrin αMß2. Expression of the gene encoding Nrf2, a transcription factor activated by oxidative stress, also increased at 21 days post-irradiation. Captopril did not alter iron accumulation in the bone marrow or expression of iron storage genes, but did suppress Nrf2 expression. Our study suggests that following TBI, iron is deposited in tissues not normally associated with iron storage, which may be a secondary mechanism of radiation-induced tissue injury.