Sensitization of Vascular Endothelial Cells to Ionizing Radiation Promotes the Development of Delayed Intestinal Injury in Mice

Enteric α-Defensin Contributes to Recovery of Radiation-Induced Intestinal Injury by Modulating Gut Microbiota and Fecal Metabolites

The effect of ionizing radiation on the gastrointestinal tract is a common complication of abdominal and pelvic radiotherapy. However, the pathological features of radiation enteropathy and its effective medical intervention regimen is still a global challenge. Here, we explored the role and mechanism of enteric alpha-defensins (EαDs) in protecting against radiation enteropathy. To address this, we utilized EαDs-deficiency mice, in which the matrix metallopeptidase 7 to activate Paneth cell α-defensins was knockout (KO) mice, and the complementary wild-type (WT) control mice for this study. Remarkably, the KO mice were more susceptible to 5.0 Gy total-body irradiation, resulting in worse clinic scores and lower survival rate, compared with the wild-type mice. Histological examination indicated that the KO mice were subjected to slow recovery of intestinal villus and mucosa function, characterized by the reduced expression of TFF3, Glut1 and Muc2. In addition, compared with the wild-type controls, the KO mice experienced serious inflammation response in intestinal tissue, indicated by the remarkably increased expression level of IL-1β, IL-6 and IL-12. Using high-throughput sequencing analysis, we found that the intestinal bacterial community of the KO mice was more prone to dysbiosis than that of the WT mice, with significantly increased abundance of opportunistic pathogenic bacteria, such as Streptococcus sp. and Escherichia-Shigella sp., whereas remarkably decreased probiotics harboring Lactobacillus sp., Desulfovibrio sp. etc. Fecal metabolomics analysis indicated that the relative abundance of 31 metabolites arose significantly different between WT and KO mice on day 10 after radiation exposure. A subset of differential metabolites to regulate host metabolism and immunity, such as acetic acid, acetate, butanoic acid, was negatively correlated with the alteration of gut microbiota in the irradiated KO mice. This study provides new insight into EαDs contribution to the recovery of radiation-induced intestinal damage, and suggests a potential novel target to prevent the adverse effects of radiotherapy.

Temporary Knockdown of p53 During Focal Limb Irradiation Increases the Development of Sarcomas

Approximately half of patients with cancer receive radiotherapy and, as cancer survivorship increases, the low rate of radiation-associated sarcomas is rising. Pharmacologic inhibition of p53 has been proposed as an approach to ameliorate acute injury of normal tissues from genotoxic therapies, but how this might impact the risk of therapy-induced cancer and normal tissue injuries remains unclear. We utilized mice that express a doxycycline (dox)-inducible p53 short hairpin RNA to reduce Trp53 expression temporarily during irradiation. Mice were placed on a dox diet 10 days prior to receiving 30 or 40 Gy hind limb irradiation in a single fraction and then returned to normal chow. Mice were examined weekly for sarcoma development and scored for radiation-induced normal tissue injuries. Radiation-induced sarcomas were subjected to RNA sequencing. Following single high-dose irradiation, 21% of animals with temporary p53 knockdown during irradiation developed a sarcoma in the radiation field compared with 2% of control animals. Following high-dose irradiation, p53 knockdown preserves muscle stem cells, and increases sarcoma development. Mice with severe acute radiation-induced injuries exhibit an increased risk of developing late persistent wounds, which were associated with sarcomagenesis. RNA sequencing revealed radiation-induced sarcomas upregulate genes related to translation, epithelial-mesenchymal transition (EMT), inflammation, and the cell cycle. Comparison of the transcriptomes of human and mouse sarcomas that arose in irradiated tissues revealed regulation of common gene programs, including elevated EMT pathway gene expression. These results suggest that blocking p53 during radiotherapy could minimize acute toxicity while exacerbating late effects including second cancers.

SIGNIFICANCE

Strategies to prevent or mitigate acute radiation toxicities include pharmacologic inhibition of p53 and other cell death pathways. Our data show that temporarily reducing p53 during irradiation increases late effects including sarcomagenesis.

Immediate effects of acute Mars mission equivalent doses of SEP and GCR radiation on the murine gastrointestinal system-protective effects of curcumin-loaded nanolipoprotein particles (cNLPs)

Introduction

Missions beyond low Earth orbit (LEO) will expose astronauts to ionizing radiation (IR) in the form of solar energetic particles (SEP) and galactic cosmic rays (GCR) including high atomic number and energy (HZE) nuclei. The gastrointestinal (GI) system is documented to be highly radiosensitive with even relatively low dose IR exposures capable of inducing mucosal lesions and disrupting epithelial barrier function. IR is also an established risk factor for colorectal cancer (CRC) with several studies examining long-term GI effects of SEP/GCR exposure using tumor-prone APC mouse models. Studies of acute short-term effects of modeled space radiation exposures in wildtype mouse models are more limited and necessary to better define charged particle-induced GI pathologies and test novel medical countermeasures (MCMs) to promote astronaut safety.

Methods

In this study, we performed ground-based studies where male and female C57BL/6J mice were exposed to γ-rays, 50 MeV protons, or 1 GeV/n Fe-56 ions at the NASA Space Radiation Laboratory (NSRL) with histology and immunohistochemistry endpoints measured in the first 24 h post-irradiation to define immediate SEP/GCR-induced GI alterations.

Results

Our data show that unlike matched γ-ray controls, acute exposures to protons and iron ions disrupts intestinal function and induces mucosal lesions, vascular congestion, epithelial barrier breakdown, and marked enlargement of mucosa-associated lymphoid tissue. We also measured kinetics of DNA double-strand break (DSB) repair using gamma-H2AX- specific antibodies and apoptosis via TUNEL labeling, noting the induction and disappearance of extranuclear cytoplasmic DNA marked by gamma-H2AX only in the charged particle-irradiated samples. We show that 18 h pre-treatment with curcumin-loaded nanolipoprotein particles (cNLPs) delivered via IV injection reduces DSB-associated foci levels and apoptosis and restore crypt villi lengths.

Discussion

These data improve our understanding of physiological alterations in the GI tract immediately following exposures to modeled space radiations and demonstrates effectiveness of a promising space radiation MCM.

Potential role of gut microbiota and its metabolites in radiation-induced intestinal damage

Radiation-induced intestinal damage (RIID) is a serious disease with limited effective treatment. Nuclear explosion, nuclear release, nuclear application and especially radiation therapy are all highly likely to cause radioactive intestinal damage. The intestinal microecology is an organic whole with a symbiotic relationship formed by the interaction between a relatively stable microbial community living in the intestinal tract and the host. Imbalance and disorders of intestinal microecology are related to the occurrence and development of multiple systemic diseases, especially intestinal diseases. Increasing evidence indicates that the gut microbiota and its metabolites play an important role in the pathogenesis and prevention of RIID. Radiation leads to gut microbiota imbalance, including a decrease in the number of beneficial bacteria and an increase in the number of harmful bacteria that cause RIID. In this review, we describe the pathological mechanisms of RIID, the changes in intestinal microbiota, the metabolites induced by radiation, and their mechanism in RIID. Finally, the mechanisms of various methods for regulating the microbiota in the treatment of RIID are summarized.

Organ-Specific Endothelial Dysfunction Following Total Body Irradiation Exposure

As the single cell lining of the heart and all blood vessels, the vascular endothelium serves a critical role in maintaining homeostasis via control of vascular tone, immune cell recruitment, and macromolecular transit. For victims of acute high-dose radiation exposure, damage to the vascular endothelium may exacerbate the pathogenesis of acute and delayed multi-organ radiation toxicities. While commonalities exist between radiation-induced endothelial dysfunction in radiosensitive organs, the vascular endothelium is known to be highly heterogeneous as it is required to serve tissue and organ specific roles. In keeping with its organ and tissue specific functionality, the molecular and cellular response of the endothelium to radiation injury varies by organ. Therefore, in the development of medical countermeasures for multi-organ injury, it is necessary to consider organ and tissue-specific endothelial responses to both injury and candidate mitigators. The purpose of this review is to summarize the pathogenesis of endothelial dysfunction following total or near total body irradiation exposure at the level of individual radiosensitive organs.

Centella asiatica-Derived Endothelial Paracrine Restores Epithelial Barrier Dysfunction in Radiation-Induced Enteritis

Radiation-induced enteritis is frequently observed following radiotherapy for cancer or occurs due to radiation exposure in a nuclear accident. The loss of the epithelial integrity leads to ‘leaky gut’, so recovery of damaged epithelium is an important strategy in therapeutic trials. Centella asiatica (CA), a traditional herbal medicine, is widely used for wound healing by protecting against endothelial damage. In this study, we investigated the radio-mitigating effect of CA, focusing on the crosstalk between endothelial and epithelial cells. CA treatment relieved radiation-induced endothelial dysfunction and mitigated radiation-induced enteritis. In particular, treatment of the conditioned media from CA-treated irradiated endothelial cells recovered radiation-induced epithelial barrier damage. We also determined that epidermal growth factor (EGF) is a critical factor secreted by CA-treated irradiated endothelial cells. Treatment with EGF effectively improved the radiation-induced epithelial barrier dysfunction. We also identified the therapeutic effects of CA-induced endothelial paracrine in a radiation-induced enteritis mouse model with epithelial barrier restoration. Otherwise, CA treatment did not show radioprotective effects on colorectal tumors in vivo. We showed therapeutic effects of CA on radiation-induced enteritis, with the recovery of endothelial and epithelial dysfunction. Thus, our findings suggest that CA is an effective radio-mitigator against radiation-induced enteritis.

First demonstration of the FLASH effect with ultrahigh dose rate high-energy X-rays

PURPOSE

This study aimed to evaluate whether high-energy X-rays (HEXs) of the PARTER (platform for advanced radiotherapy research) platform built on CTFEL (Chengdu THz Free Electron Laser facility) can produce ultrahigh dose rate (FLASH) X-rays and trigger the FLASH effect.

MATERIALS AND METHODS

EBT3 radiochromic film and fast current transformer (FCT) devices were used to measure absolute dose and pulsed beam current of HEXs. Subcutaneous tumor-bearing mice and healthy mice were treated with sham, FLASH, and conventional dose rate radiotherapy (CONV), respectively to observe the tumor control efficiency and normal tissue damage.

RESULTS

The maximum dose rate of HEXs of PARTER was up to over 1000 Gy/s. Tumor-bearing mice experiment showed a good result on tumor control (p < 0.0001) and significant difference in survival curves (p < 0.005) among the three groups. In the thorax-irradiated healthy mice experiment, there was a significant difference (p = 0.038) in survival among the three groups, with the risk of death decreased by 81% in the FLASH group compared to that in the CONV group. The survival time of healthy mice irradiated in the abdomen in the FLASH group was undoubtedly higher (62.5% of mice were still alive when we stopped observation) than that in the CONV group (7 days).

CONCLUSION

This study confirmed that HEXs of the PARTER system can produce ultrahigh dose rate X-rays and trigger a FLASH effect, which provides a basis for future scientific research and clinical application of HEX in FLASH radiotherapy.

Sensitization of Endothelial Cells to Ionizing Radiation Exacerbates Delayed Radiation Myelopathy in Mice

Delayed radiation myelopathy is a rare, but significant late side effect from radiation therapy that can lead to paralysis. The cellular and molecular mechanisms leading to delayed radiation myelopathy are not completely understood but may be a consequence of damage to oligodendrocyte progenitor cells and vascular endothelial cells. Here, we aimed to determine the contribution of endothelial cell damage to the development of radiation-induced spinal cord injury using a genetically defined mouse model in which endothelial cells are sensitized to radiation due to loss of the tumor suppressor p53. Tie2Cre; p53FL/+ and Tie2Cre; p53FL/- mice, which lack one and both alleles of p53 in endothelial cells, respectively, were treated with focal irradiation that specifically targeted the lumbosacral region of the spinal cord. The development of hindlimb paralysis was followed for up to 18 weeks after either a 26.7 Gy or 28.4 Gy dose of radiation. During 18 weeks of follow-up, 83% and 100% of Tie2Cre; p53FL/- mice developed hindlimb paralysis after 26.7 and 28.4 Gy, respectively. In contrast, during this period only 8% of Tie2Cre; p53FL/+ mice exhibited paralysis after 28.4 Gy. In addition, 8 weeks after 28.4 Gy the irradiated spinal cord from Tie2Cre; p53FL/- mice showed a significantly higher fractional area positive for the neurological injury marker glial fibrillary acidic protein (GFAP) compared with the irradiated spinal cord from Tie2Cre; p53FL/+ mice. Together, our findings show that deletion of p53 in endothelial cells sensitizes mice to the development of delayed radiation myelopathy indicating that endothelial cells are a critical cellular target of radiation that regulates myelopathy.

Evaluation of sodium orthovanadate as a radioprotective agent under total-body irradiation and partial-body irradiation conditions in mice

PURPOSE

Our previous study indicated that sodium orthovanadate (vanadate), a strong inhibitor of p53, effectively suppressed the lethality from the hematopoietic (HP) and gastrointestinal (GI) syndromes after 12 Gy total-body irradiation (TBI) in mice. This conclusion, however, was inconsistent with the fact that p53 plays a radioprotective role in the intestinal epithelium. The death after TBI of around 12 Gy was attributed to a combined effect of HP and GI syndromes. To verify the effect from prophylactic administration of p53 inhibitor on protection of HP and GI syndromes, in this study, the radioprotective effects from vanadate were investigated in TBI and lower half-body irradiation (partial-body irradiation: PBI) mouse models.

METHODS

Female ICR mice were given a single injection of vanadate or vehicle, followed by a lethal dose of TBI or PBI. Radioprotective effects of vanadate against the irradiations were evaluated by analyzing survival rate, body weight, hematopoietic parameters, and histological changes in the bone marrow and intestinal epithelium.

RESULTS

TBI-induced HP syndrome was effectively suppressed by vanadate treatment. After TBI, the vanadate-treated mice retained better bone marrow cellularity and showed markedly higher survival rate compared to the vehicle-treated animals. In contrast, vanadate did not relieve loss of intestinal crypts and failed to rescue mice from GI death after PBI.

CONCLUSION

Vanadate is a p53 inhibitor that has been shown to be beneficial as a radiation protective agent against HP but was not effective in protecting against acute GI radiation injury.

The effects of myeloablative or non-myeloablative total body irradiations on intestinal tract in mice

Acute radiation injury caused by high-dose radiation exposure severely impedes the application of radiotherapy in cancer management. To deeply understand the side effects of radiation on intestinal tract, an irradiation murine model was applied and evaluated. C57BL/6 mice were given 4 Gy non-myeloablative irradiation, 8 Gy myeloablative irradiation and non-irradiation (control), respectively. Results demonstrated that the 8 Gy myeloablative irradiations significantly damaged the gut barrier along with decreasing MECA32 and ZO-1. However, a slight increase in MECA32 and ZO-1 was detected in the 4 Gy non-myeloablative irradiations treatment from day 5 to day 10. Further, the irradiations affected the expression of P38 and JNK mitogen-activated protein kinase (MAPK) but not ERK1/2 MAPK signal pathway. Moreover, irradiation had adverse effects on hematopoietic system, altered the numbers and percentages of intestinal inflammatory cells. The IL-17/AhR had big increase in the gut of 4 Gy irradiation mice at day 10 compared with other groups. Both 8 Gy myeloablative and 4 Gy non-myeloablative irradiation disturbed the levels of short-chain fatty acids (SCFAs) in intestine. Meanwhile, high dosage of irradiation decreased the intestinal bacterial diversity and altered the community composition. Importantly, the fatty acids generating bacteria Bacteroidaceae and Ruminococcaceae played key roles in community distribution and SCFAs metabolism after irradiation. Collectively, the irradiation induced gut barrier damage with dosages dependent that led to the decreased p38 MAPK and increased JNK MAPK, unbalanced the mononuclear cells (MNCs) of gut, disturbed intestinal bacterial community and SCFAs level.

Protective Effects of p53 Regulatory Agents Against High-LET Radiation-Induced Injury in Mice

Radiation damage to normal tissues is one of the most serious concerns in radiation therapy, and the tolerance dose of the normal tissues limits the therapeutic dose to the patients. p53 is well known as a transcription factor closely associated with radiation-induced cell death. We recently demonstrated the protective effects of several p53 regulatory agents against low-LET X- or γ-ray-induced damage. Although it was reported that high-LET heavy ion radiation (>85 keV/μm) could cause p53-independent cell death in some cancer cell lines, whether there is any radioprotective effect of the p53 regulatory agents against the high-LET radiation injury in vivo is still unclear. In the present study, we verified the efficacy of these agents on bone marrow and intestinal damages induced by high-LET heavy-ion irradiation in mice. We used a carbon-beam (14 keV/μm) that was shown to induce a p53-dependent effect and an iron-beam (189 keV/μm) that was shown to induce a p53-independent effect in a previous study. Vanadate significantly improved 60-day survival rate in mice treated with total-body carbon-ion (p < 0.0001) or iron-ion (p < 0.05) irradiation, indicating its effective protection of the hematopoietic system from radiation injury after high-LET irradiation over 85 keV/μm. 5CHQ also significantly increased the survival rate after abdominal carbon-ion (p < 0.02), but not iron-ion irradiation, suggesting the moderate relief of the intestinal damage. These results demonstrated the effectiveness of p53 regulators on acute radiation syndrome induced by high-LET radiation.