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.

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.

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.

Captopril reduces lung inflammation and accelerated senescence in response to thoracic radiation in mice.

The lung is sensitive to radiation and exhibits several phases of injury, with an initial phase of radiation-induced pneumonitis followed by delayed and irreversible fibrosis. The angiotensin-converting enzyme inhibitor captopril has been demonstrated to mitigate radiation lung injury and to improve survival in animal models of thoracic irradiation, but the mechanism remains poorly understood. Here we investigated the effect of captopril on early inflammatory events in the lung in female CBA/J mice exposed to thoracic X-ray irradiation of 17-17.9 Gy (0.5-0.745 Gy min-1). For whole-body + thoracic irradiation, mice were exposed to 7.5 Gy (0.6 Gy min-1) total-body 60Co irradiation and 9.5 Gy thoracic irradiation. Captopril was administered orally (110 mg kg-1 day-1) in the drinking water, initiated 4 h through to150 days post-irradiation. Captopril treatment increased survival from thoracic irradiation to 75% at 150 days compared with 0% survival in vehicle-treated animals. Survival was characterized by a significant decrease in radiation-induced pneumonitis and fibrosis. Investigation of early inflammatory events showed that captopril significantly attenuated macrophage accumulation and decreased the synthesis of radiation-induced interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) pro-inflammatory cytokines in the lungs of irradiated mice. Suppression of IL-1ß and TNF-α correlated with an increase of the anti-inflammatory cytokine IL-10 in the spleen with captopril treatment. We also found that captopril decreased markers for radiation-induced accelerated senescence in the lung tissue. Our data suggest that suppression of inflammation and senescence markers, combined with an increase of anti-inflammatory factors, are a part of the mechanism for captopril-induced survival in thoracic irradiated mice.

Comparison of the effects of osmotic pump implantation with subcutaneous injection for administration of drugs after total body irradiation in mice.

The increasing potential for radiation exposure from nuclear accidents or terrorist activities has intensified the need to develop pharmacologic countermeasures against injury from total body irradiation (TBI). Many initial experiments to develop and test these countermeasures utilize murine irradiation models. Yet, the route of drug administration can alter the response to irradiation injury. Studies have demonstrated that cutaneous injuries can exacerbate damage from radiation, and thus surgical implantation of osmotic pumps for drug delivery could adversely affect the survival of mice following TBI. However, daily handling and injections to administer drugs could also have negative consequences. This study compared the effects of subcutaneous needlesticks with surgical implantation of osmotic pumps on morbidity and mortality in a murine model of hematopoietic acute radiation syndrome (H-ARS). C57BL/6 mice were sham irradiated or exposed to a single dose of 7.7 Gy 60Co TBI. Mice were implanted with osmotic pumps containing sterile saline seven days prior to irradiation or received needlesticks for 14 days following irradiation or received no treatment. All irradiated groups exhibited weight loss. Fewer mice with osmotic pumps survived to 30 days post irradiation (37.5%) than mice receiving needlesticks or no treatment (70% and 80%, respectively), although this difference was not statistically significant. However, mice implanted with the pump lost significantly more weight than mice that received needlesticks or no treatment. These data suggest that surgical implantation of a drug-delivery device can adversely affect the outcome in a murine model of H-ARS.

Effect of 3,3'-Diindolylmethane on Pulmonary Injury Following Thoracic Irradiation in CBA Mice.

The molecule 3,3'-diindolylmethane (DIM) is small, a major bioactive metabolite of indole-3 carbinol (13C), and a phytochemical compound from cruciferous vegetables released upon exposure to the gut acid environment. DIM is a proposed anti-cancer agent and was previously demonstrated to prevent radiation damage in the bone marrow and the gastrointestinal tract. Here we investigated the effect of DIM on radiation-induced injury to the lung in a murine model through untargeted metabolomics and gene expression studies of select genes. CBA mice were exposed to thoracic irradiation (17.5 Gy). Mice were treated with vehicle or DIM (250 mg kg, subcutaneous injection) on days -1 pre-irradiation through +14 post-irradiation. DIM induced a significant improvement in survival by day 150 post-irradiation. Fibrosis-related gene expression and metabolomics were examined using lung tissue from days 15, 45, 60, 90, and 120 post-irradiation. Our qRT-PCR experiments showed that DIM treatment reduced radiation-induced late expression of collagen Iα and the cell cycle checkpoint proteins p21/waf1 (CDKN1A) and p16ink (CDKN2A). Metabolomic studies of lung tissue demonstrated a significant dampening of radiation-induced changes following DIM treatment. Metabolites associated with pro-inflammatory responses and increased oxidative stress, such as fatty acids, were suppressed by DIM treatment compared to irradiated samples. Together these data suggest that DIM reduces radiation-induced sequelae in the lung.

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.

Delayed Captopril Administration Mitigates Hematopoietic Injury in a Murine Model of Total Body Irradiation.

The increasing potential for accidental radiation exposure from either nuclear accidents or terrorist activities has escalated the need for radiation countermeasure development. We previously showed that a 30-day course of high-dose captopril, an ACE inhibitor, initiated 1-4 h after total body irradiation (TBI), improved Hematopoietic Acute Radiation Syndrome (H-ARS) and increased survival in mice. However, because of the time likely required for the deployment of a stockpiled radiation countermeasure to a radiation mass casualty site, there is a need for therapies that can be administered 24-48 hours after initial exposure. Using C57BL/6 mice exposed to an LD50-80/30 of 60Co TBI (7.75-7.9 Gy, 0.615 Gy/min), we show that low-dose captopril administration, initiated as late as 48 h post-TBI and continued for 14 days, significantly enhanced overall survival similarly to high-dose, rapid administration. Captopril treatment did not affect radiation-induced cell cycle arrest genes or the immediate loss of hematopoietic precursors. Reduced mortality was associated with the recovery of bone marrow cellularity and mature blood cell recovery at 21-30 days post-irradiation. Captopril reduced radiation-induced cytokines EPO, G-CSF, and SAA in the plasma. Finally, delayed captopril administration mitigated brain micro-hemorrhage at 21 days post-irradiation. These data indicate that low dose captopril administered as late as 48 h post-TBI for only two weeks improves survival that is associated with hematopoietic recovery and reduced inflammatory response. These data suggest that captopril may be an ideal countermeasure to mitigate H-ARS following accidental radiation exposure.

Dynorphin up-regulation in the dentate granule cell mossy fiber pathway following chronic inhibition of GluN2B-containing NMDAR is associated with increased CREB (Ser 133) phosphorylation, but is independent of BDNF/TrkB signaling pathways.

Emerging evidence suggests that neuronal responses to N-methyl-d-aspartate (NMDAR) activation/inactivation are influenced by subunit composition. For example, activation of synaptic NMDAR (comprised of GluN2A>GluN2B) phosphorylates cAMP-response-element-binding protein (CREB) at Ser 133, induces BDNF expression and promotes neuronal survival. Activation of extrasynaptic NMDAR (comprised of GluN2B>GluN2) dephosphorylates CREB (Ser 133), reduces BDNF expression and triggers neuronal death. These results led us to hypothesize that chronic inhibition of GluN2B-containing NMDAR would increase CREB (Ser 133) phosphorylation, increase BDNF levels and subsequently alter downstream dynorphin (DYN) and neuropeptide Y (NPY) expression. We focused on DYN and NPY because these neuropeptides can decrease excitatory neurotransmission and seizure occurrence and we reported previously that seizure-like events are reduced following chronic treatment with GluN2B antagonists. Consistent with our hypothesis, chronic treatment (17-21days) of hippocampal slice cultures with the GluN2B-selective antagonists ifenprodil or Ro25,6981 increased both CREB (Ser 133) phosphorylation and granule cell mossy fiber pathway DYN expression. Similar treatment with the non-subtype-selective NMDAR antagonists d-APV or memantine had no significant effect on either CREB (Ser 133) phosphorylation or DYN expression. In contrast to our hypothesis, BDNF levels were decreased following chronic treatment with Ro25,6981, but not ifenprodil, d-APV or memantine. Blockade of BDNF actions and TrkB activation did not significantly augment hilar DYN expression in vehicle-treated cultures and had no effect in Ro25,6981 treated cultures. These findings suggest that chronic exposure to GluN2B-selective NMDAR antagonists increased DYN expression through a putatively pCREB-dependent, but BDNF/TrkB-independent mechanism.

Increased Kv1 channel expression may contribute to decreased sIPSC frequency following chronic inhibition of NR2B-containing NMDAR.

Numerous studies have documented the effects of chronic N-methyl-D-aspartate receptor (NMDAR) blockade on excitatory circuits, but the effects on inhibitory circuitry are not well studied. NR2A- and NR2B-containing NMDARs play differential roles in physiological processes, but the consequences of chronic NR2A- or NR2B-containing NMDAR inhibition on glutamatergic and GABAergic neurotransmission are unknown. We investigated altered GABAergic neurotransmission in dentate granule cells and interneurons following chronic treatment with the NR2B-selective antagonist, Ro25,6981, the NR2A-prefering antagonist, NVP-AAM077, or the non-subunit-selective NMDAR antagonist, D-APV, in organotypic hippocampal slice cultures. Electrophysiological recordings revealed large reductions in spontaneous inhibitory postsynaptic current (sIPSC) frequency in both granule cells and interneurons following chronic Ro25,6981 treatment, which was associated with minimally altered sIPSC amplitude, miniature inhibitory postsynaptic current (mIPSC) frequency, and mIPSC amplitude, suggesting diminished action potential-dependent GABA release. Chronic NVP-AAM077 or D-APV treatment had little effect on these measures. Reduced sIPSC frequency did not arise from downregulated GABA(A)R, altered excitatory or inhibitory drive to interneurons, altered interneuron membrane properties, increased failure rate, decreased action potential-dependent release probability, or mGluR/GABA(B) receptor modulation of GABA release. However, chronic Ro25,6981-mediated reductions in sIPSC frequency were occluded by the K+ channel blockers, dendrotoxin, margatoxin, and agitoxin, but not dendrotoxin-K or XE991. Immunohistochemistry also showed increased Kv1.2, Kv1.3, and Kv1.6 in the dentate molecular layer following chronic Ro25,6981 treatment. Our findings suggest that increased Kv1 channel expression/function contributed to diminished action potential-dependent GABA release following chronic NR2B-containing NMDAR inhibition and that these Kv1 channels may be heteromeric complexes containing Kv1.2, Kv1.3, and Kv1.6.