TLR9 agonist protects mice from radiation-induced gastrointestinal syndrome

Anti-ceramide Single-Chain Variable Fragment Mitigates Gastrointestinal-Acute Radiation Syndrome and Improves Marrow Reconstitution, Rendering Near-Normal 90-Day Autopsies

PURPOSE

After September 11, 2001, nuclear threat prompted government agencies to develop medical countermeasures to mitigate two syndromes, the hematopoietic-acute radiation syndrome (H-ARS) and the higher-dose gastrointestinal-acute radiation syndrome (GI-ARS), both lethal within weeks. While repurposing leukemia drugs that enhance bone marrow repopulation successfully treats H-ARS, no mitigator potentially deliverable under mass casualty conditions preserves the GI tract. We recently reported that anti-ceramide single-chain variable fragment (scFv) mitigates GI-ARS lethality, abrogating ongoing small intestinal endothelial apoptosis to rescue Lgr5+ stem cells. Here, we examine long-term consequences of prevention of acute GI-ARS lethality.

METHODS AND MATERIALS

For these studies, C57BL/6J male mice were treated with 15 Gy whole body irradiation, the 90% GI-ARS lethal dose for this mouse strain.

RESULTS

Mice irradiated with 15 Gy alone or with 15 Gy + bone marrow transplantation (BMT) or anti-ceramide scFv, succumb to an ARS within 8 to 10 days. Autopsies reveal only mice receiving anti-ceramide scFv at 24 hours post-whole body irradiation display small intestinal rescue. No marrow reconstitution occurs in any group with attendant undetectable circulating blood elements. Mice receiving 15 Gy + BMT + scFv, however, normalize blood counts by day 12, suggesting that scFv also improves marrow reconstitution, a concept for which we provide experimental support. We show that at 14 Gy, the upper limit dose for H-ARS lethality before transition to GI-ARS lethality, anti-ceramide scFv markedly improves marrow take, reducing the quantity of marrow-conferring survival by more than 3-fold. Consistent with these findings, mice receiving 15 Gy + BMT + scFv exhibit prolonged survival. At day 90, before sacrifice, they display normal appearance, behavior, and serum biochemistries, and surprisingly, at full autopsy, near-normal physiology in all 42 tissues examined.

CONCLUSIONS

Anti-ceramide scFv mitigates GI-ARS lethality and improves marrow reconstitution rendering prolonged survival with near normal autopsies.

Modulation of β-Catenin is important to promote WNT expression in macrophages and mitigate intestinal injury

Macrophages are the major source of WNT ligands. Macrophage-derived WNT is one of the most potent regenerative signals to mitigate intestinal injury. However, regulation of WNT expression in macrophages has not been studied. In the present study, we discovered that activation of canonical β-Catenin suppresses WNT expression in macrophages. Our CHIP-seq and validation study demonstrated the involvement of β-Catenin in the transcriptional regulation of WNT expression. Genetic and pharmacological approaches to de-stabilize/inactivate β-Catenin induce WNT expression in macrophages. Extracellular vesicles (EVs) are a major career of WNT ligands. Transfusion of EVs from pre-conditioned WNT-enriched macrophages demonstrated significant regenerative benefit over native macrophage-derived EVs to mitigate radiation-induced intestinal injury. Transfusion of WNT-enriched EVs also reduces DSS-induced colitis. Our study provides substantial evidence to consider that macrophage-targeted modulation of canonical WNT signaling to induce WNT expression followed by treatment with WNT-enriched EVs can be a lead therapy against intestinal injury..

SUMMARY

Activation of β-Catenin suppresses WNT expression in macrophages. Macrophage-targeted pharmacological modulation of canonical WNT signaling followed by adoptive transfer mitigate radiation injury in intestine. EVs from these preconditioned macrophages mitigate chemical or radiation induced intestinal injury.

Gastrointestinal Acute Radiation Syndrome: Mechanisms, Models, Markers, and Medical Countermeasures

There have been a number of reported human exposures to high dose radiation, resulting from accidents at nuclear power plants (e.g., Chernobyl), atomic bombings (Hiroshima and Nagasaki), and mishaps in industrial and medical settings. If absorbed radiation doses are high enough, evolution of acute radiation syndromes (ARS) will likely impact both the bone marrow as well as the gastrointestinal (GI) tract. Damage incurred in the latter can lead to nutrient malabsorption, dehydration, electrolyte imbalance, altered microbiome and metabolites, and impaired barrier function, which can lead to septicemia and death. To prepare for a medical response should such an incident arise, the National Institute of Allergy and Infectious Diseases (NIAID) funds basic and translational research to address radiation-induced GI-ARS, which remains a critical and prioritized unmet need. Areas of interest include identification of targets for damage and mitigation, animal model development, and testing of medical countermeasures (MCMs) to address GI complications resulting from radiation exposure. To appropriately model expected human responses, it is helpful to study analogous disease states in the clinic that resemble GI-ARS, to inform on best practices for diagnosis and treatment, and translate them back to inform nonclinical drug efficacy models. For these reasons, the NIAID partnered with two other U.S. government agencies (the Biomedical Advanced Research and Development Authority, and the Food and Drug Administration), to explore models, biomarkers, and diagnostics to improve understanding of the complexities of GI-ARS and investigate promising treatment approaches. A two-day workshop was convened in August 2022 that comprised presentations from academia, industry, healthcare, and government, and highlighted talks from 26 subject matter experts across five scientific sessions. This report provides an overview of information that was presented during the conference, and important discussions surrounding a broad range of topics that are critical for the research, development, licensure, and use of MCMs for GI-ARS.

Radiation enteropathy-related depression: A neglectable course of disease by gut bacterial dysbiosis

Radiation enteropathy (RE) is common in patients treated with radiotherapy for pelvic-abdominal cancers. Accumulating data indicate that gut commensal bacteria determine intestinal radiosensitivity. Radiotherapy can result in gut bacterial dysbiosis. Gut bacterial dysbiosis contributes to the pathogenesis of RE. Mild to moderate depressive symptoms can be observed in patients with RE in clinical settings; however, the rate of these symptoms has not been reported. Studies have demonstrated that gut bacterial dysbiosis induces depression. In the state of comorbidity, RE and depression may be understood as local and abscopal manifestations of gut bacterial disorders. The ability of comorbid depression to worsen inflammatory bowel disease (IBD) has long been demonstrated and is associated with dysfunction of cholinergic neural anti-inflammatory pathways. There is a lack of direct evidence for RE comorbid with depression. It is widely accepted that RE shares similar pathophysiologic mechanisms with IBD. Therefore, we may be able to draw on the findings of the relationship between IBD and depression. This review will explore the relationship between gut bacteria, RE, and depression in light of the available evidence and indicate a method for investigating the mechanisms of RE combined with depression. We will also describe new developments in the treatment of RE with probiotics, prebiotics, and fecal microbial transplantation.

Radioprotective countermeasures for radiation injury (Review)

A series of physiological and pathological changes occur after radiotherapy and accidental exposure to ionizing radiation (IR). These changes cause serious damage to human tissues and can lead to death. Radioprotective countermeasures are radioprotective agents that prevent and reduce IR injury or have therapeutic effects. Based on a good understanding of radiobiology, a number of protective agents have achieved positive results in early clinical trials. The present review grouped known radioprotective agents according to biochemical categories and potential clinical use, and reviewed radiation countermeasures, i.e., radioprotectors, radiation mitigators and radiotherapeutic agents, with an emphasis on their current status and research progress. The aim of the present review is to facilitate the selection and application of suitable radioprotectors for clinicians and researchers, to prevent or reduce IR injury.

Radiotherapy/Chemotherapy-Immunotherapy for Cancer Management: From Mechanisms to Clinical Implications

Cancer immunotherapy has drawn much attention because it can restart the recognition and killing function of the immune system to normalize the antitumor immune response. However, the role of radiotherapy and chemotherapy in cancer treatment cannot be ignored. Due to cancer heterogeneity, combined therapy has become a new trend, and its efficacy has been confirmed in many studies. This review discussed the clinical implications and the underlying mechanisms of cancer immunotherapy in combination with radiotherapy or chemotherapy, offering an outline for clinicians as well as inspiration for future research.

Combined Administration of Pravastatin and Metformin Attenuates Acute Radiation-Induced Intestinal Injury in Mouse and Minipig Models

Radiation-induced gastrointestinal (GI) damage is one of the critical factors that serve as basis for the lethality of nuclear accidents or terrorism. Further, there are no Food and Drug Administration-approved agents available to mitigate radiation-induced intestinal injury. Although pravastatin (PS) has been shown to exhibit anti-inflammatory and epithelial reconstructive effects following radiation exposure using mouse and minipig models, the treatment failed to improve the survival rate of high-dose irradiated intestinal injury. Moreover, we previously found that metformin (MF), a common drug used for treating type 2 diabetes mellitus, has a mitigating effect on radiation-induced enteropathy by promoting stem cell properties. In this study, we investigated whether the combined administration of PS and MF could achieve therapeutic effects on acute radiation-induced intestinal injury in mouse and minipig models. We found that the combined treatment markedly increased the survival rate and attenuated histological damage in a radiation-induced intestinal injury mouse model, in addition to epithelial barrier recovery, anti-inflammatory effects, and improved epithelial proliferation with stem cell properties. Furthermore, in minipig models, combined treatment with PS and MF ameliorates gross pathological damage in abdominal organs and attenuated radiation-induced intestinal histological damage. Therefore, the combination of PS and MF effectively alleviated radiation-induced intestinal injury in the mouse and minipig models. We believe that the combined use of PS and MF is a promising therapeutic approach for treating radiation-induced intestinal injury.

The Role of the Human Gut Microbiome in Inflammatory Bowel Disease and Radiation Enteropathy

The human gut microbiome plays a key role in regulating host physiology. In a stable state, both the microbiota and the gut work synergistically. The overall homeostasis of the intestinal flora can be affected by multiple factors, including disease states and the treatments given for those diseases. In this review, we examine the relatively well-characterised abnormalities that develop in the microbiome in idiopathic inflammatory bowel disease, and compare and contrast them to those that are found in radiation enteropathy. We discuss how these changes may exert their effects at a molecular level, and the possible role of manipulating the microbiome through the use of a variety of therapies to reduce the severity of the underlying condition.

Metformin Protects the Intestinal Barrier by Activating Goblet Cell Maturation and Epithelial Proliferation in Radiation-Induced Enteropathy

Radiotherapy or accidental exposure to high-dose radiation can cause severe damage to healthy organs. The gastrointestinal (GI) tract is a radiation-sensitive organ of the body. The intestinal barrier is the first line of defense in the GI tract, and consists of mucus secreted by goblet cells and a monolayer of epithelium. Intestinal stem cells (ISCs) help in barrier maintenance and intestinal function after injury by regulating efficient regeneration of the epithelium. The Wnt/β-catenin pathway plays a critical role in maintaining the intestinal epithelium and regulates ISC self-renewal. Metformin is the most widely used antidiabetic drug in clinical practice, and its anti-inflammatory, antioxidative, and antiapoptotic effects have also been widely studied. In this study, we investigated whether metformin alleviated radiation-induced enteropathy by focusing on its role in protecting the epithelial barrier. We found that metformin alleviated radiation-induced enteropathy, with increased villi length and crypt numbers, and restored the intestinal barrier function in the irradiated intestine. In a radiation-induced enteropathy mouse model, metformin treatment increased tight-junction expression in the epithelium and inhibited bacterial translocation to mesenteric lymph nodes. Metformin increased the number of ISCs from radiation toxicity and enhanced epithelial repair by activating Wnt/β-catenin signaling. These data suggested that metformin may be a potential therapeutic agent for radiation-induced enteropathy.

Micro-RNA and Proteomic Profiles of Plasma-Derived Exosomes from Irradiated Mice Reveal Molecular Changes Preventing Apoptosis in Neonatal Cerebellum

Cell communication via exosomes is capable of influencing cell fate in stress situations such as exposure to ionizing radiation. In vitro and in vivo studies have shown that exosomes might play a role in out-of-target radiation effects by carrying molecular signaling mediators of radiation damage, as well as opposite protective functions resulting in resistance to radiotherapy. However, a global understanding of exosomes and their radiation-induced regulation, especially within the context of an intact mammalian organism, has been lacking. In this in vivo study, we demonstrate that, compared to sham-irradiated (SI) mice, a distinct pattern of proteins and miRNAs is found packaged into circulating plasma exosomes after whole-body and partial-body irradiation (WBI and PBI) with 2 Gy X-rays. A high number of deregulated proteins (59% of WBI and 67% of PBI) was found in the exosomes of irradiated mice. In total, 57 and 13 miRNAs were deregulated in WBI and PBI groups, respectively, suggesting that the miRNA cargo is influenced by the tissue volume exposed to radiation. In addition, five miRNAs (miR-99b-3p, miR-200a-3p, miR-200a, miR-182-5p, miR-182) were commonly overexpressed in the exosomes from the WBI and PBI groups. In this study, particular emphasis was also given to the determination of the in vivo effect of exosome transfer by intracranial injection in the highly radiosensitive neonatal cerebellum at postnatal day 3. In accordance with a major overall anti-apoptotic function of the commonly deregulated miRNAs, here, we report that exosomes from the plasma of irradiated mice, especially in the case of WBI, prevent radiation-induced apoptosis, thus holding promise for exosome-based future therapeutic applications against radiation injury.

Mitochondrial DNA as a Possible Ligand for TLR9 in Irinotecan-induced Small Intestinal Mucositis

Cancer chemotherapy and radiotherapy may result in mucositis characterized by stem cell damage and inflammation in the gastrointestinal tract. The molecular mechanisms underlying this pathology remain unknown. Based on the assumption that mitochondrial CPG-DNA (mtDNA) released and sensed by TLR9 could underlie mucositis pathology, we analyzed the mtDNA levels in sera as well as inflammatory and disease parameters in the small intestine from wild-type (WT) and TLR9-deficient mice (TLR9-/-) in an experimental model of intestinal mucositis induced by irinotecan. Additionally, we verified the ability of WT and TLR9-/- macrophages to respond to CpG-DNA in vitro. WT mice injected with irinotecan presented a progressive increase in mtDNA in the serum along with increased hematocrit, shortening of small intestine length, reduction of intestinal villus:crypt ratio and increased influx of neutrophils, which were followed by higher expression of Nlrp3 and Casp1 mRNA and increased IL-1β levels in the ileum when compared to vehicle-injected mice. TLR9-deficient mice were protected in all these parameters when compared to WT mice. Furthermore, TLR9 was required for the production of IL-1β and NO after macrophage stimulation with CpG-DNA. Overall, our findings show that the amount of circulating free CpG-DNA is increased upon chemotherapy and that TLR9 activation is important for NLRP3 inflammasome transcription and further IL-1β release, playing a central role in the development of irinotecan-induced intestinal mucositis. We suggest that TLR9 antagonism may be a new therapeutic strategy for limiting irinotecan-induced intestinal inflammation.

Development of nanotechnology-mediated precision radiotherapy for anti-metastasis and radioprotection

Radiotherapy (RT), including external beam RT and internal radiation therapy, uses high-energy ionizing radiation to kill tumor cells.

Effects of radiation and chemotherapy on adipose stem cells: Implications for use in fat grafting in cancer patients

Autologous fat transplantation is a versatile tool in reconstructive surgery. Adipose-derived stem cells (ASCs) increase survival of fat grafts and thus are increasingly used for breast reconstruction in breast cancer patients. However, radiation and/or chemotherapy have been proposed to inhibit soft tissue regeneration in wound healing thus suggesting alteration in stem cell pathways. Therefore, elucidating effects of radiation and chemotherapy on ASCs is critical if one desires to enhance the survival of fat grafts in patients. This review outlines our work evaluating the function and recoverability of ASCs from radiation or chemotherapy patients, focusing specifically on their availability as a source of autologous stem cells for fat grafting and breast reconstruction in cancer patients. Even though evidence suggests radiation and chemotherapy negatively influence ASCs at the cellular level, the efficiency of the isolation and differentiation capacity did not appear influenced in patients after receiving chemotherapy treatment, although fat from radiated patients exhibited significantly altered ASC differentiation into endothelial-like cells. Further, the in vitro growth rates of patient’s ASCs do not differ significantly before or after treatment. Taken together, these studies suggest ASCs as an important new tool for grafting and reconstruction even when radiation and chemotherapy treatment are involved.

Immunohistochemical Analysis of Toll-Like Receptors, MyD88, and TRIF in Human Papillary Thyroid Carcinoma and Anaplastic Thyroid Carcinoma

Purpose

We hypothesized that innate immune response pathways might be involved in thyroid carcinogenesis. To investigate this hypothesis, we aimed at analyzing the expression of several receptors and molecules in the innate immune system in papillary thyroid carcinoma (PTC) and anaplastic thyroid carcinoma (ATC) tissues.

Methods

Of the surgically resected specimens, 11 ATC tissues, 25 PTC tissues, and 8 nodular hyperplasia (NH) tissues were selected and examined for the expression of toll-like receptor (TLR) 2, TLR3, TLR4, TLR5, TLR7, TLR9, the myeloid differentiation primary response gene 88 (MyD88), and toll-interleukin-1 receptor domain-containing adaptor inducing INF-β (TRIF) by immunohistochemistry (IHC).

Results

Several TLRs were expressed in each tissue. TLR3 was strongly expressed in all tissues. In contrast, TLR4 was not detected in any tissues. While TLR5 was moderately expressed in NH but significantly reduced in PTC and ATC, TLR9 was absent in NH tissue but moderately expressed in both PTC and ATC. On MyD88 expression, no significant difference was found between PTC and ATC. TRIF was significantly upregulated in PTC and ATC compared to NH. Surprisingly, PTC and ATC tissues exhibited similar expression patterns of TLRs, MyD88, and TRIF.

Conclusion

These data suggest the involvement of the innate immune system in both PTC and ATC. Specifically, TLR3-mediated TRIF activation was confirmed in PTC and ATC. This provides new insight into thyroid carcinogenesis.

Genistein From Fructus sophorae Protects Mice From Radiation-Induced Intestinal Injury

The development of an effective pharmacological countermeasure is needed to reduce the morbidity and mortality in high-dose ionizing radiation-induced acute damage. Genistein has shown bioactivity in alleviating radiation damage and is currently synthesized by chemosynthetic methods. Due to concerns about chemical residues and high costs, the clinical application of genistein is still a major challenge. In this study, we aimed to establish an efficient method for the extraction of genistein from Fructus sophorae. The effects of extracted genistein (FSGen) on preventing intestinal injury from radiation were further investigated in this study. C57/BL mice were exposed to 7.5 Gy whole body irradiation with and without FSGen treatments. Histological analysis demonstrated significant structural and functional restitution of the intestine and bone marrow in FSGen-pretreated cohorts after irradiation. Through mRNA expression, protein expression, and small interfering RNA analyses, we demonstrated that FSGen protects IEC-6 cells against radiation damage by upregulating the Rassf1a and Ercc1 genes to effectively attenuate DNA irradiation damage. Together, our data established an effective method to extract genistein from the Fructus sophorae plant with high purity, and validated the beneficial roles of the FSGen in protecting the radiation damage. These results promise the future applications of Fructus sophorae extracted genistein in the protection of radiation related damages.

Ionizing radiation and toll like receptors: A systematic review article

Ionizing radiation, including X and gamma rays, are used for various purposes such as; medicine, nuclear power, research, manufacturing, food preservation and construction. Furthermore, people are also exposed to ionizing radiation from their workplace or the environment. Apart from DNA fragmentation resulting in apoptosis, several additional mechanisms have been proposed to describe how radiation can alter human cell functions. Ionizing radiation may alter immune responses, which are the main cause of human disorders. Toll like receptors (TLRs) are important human innate immunity receptors which participate in several immune and non-immune cell functions including, induction of appropriate immune responses and immune related disorders. Based on the role played by ionizing radiation on human cell systems, it has been hypothesized that radiation may affect immune responses. Therefore, the main aim of this review article is to discuss recent information regarding the effects of ionizing radiation on TLRs and their related disorders.

Exogenous activation of toll-like receptor 5 signaling mitigates acetaminophen-induced hepatotoxicity in mice

Acetaminophen (APAP) poisoning is the most common cause of drug-induced acute liver injury (ALI). Our results showed that toll-like receptor 5 (TLR5) was abundantly expressed in hepatocytes and dramatically downregulated in the toxic mouse livers. Hence, we herein investigated the role of TLR5 signaling after APAP overdose. Mice were intraperitoneally (i.p.) injected with APAP to induce ALI, and then injected with flagellin at one hour after APAP administration. Flagellin attenuated APAP-induced ALI based on decreased histopathologic lesions, serum biochemical, oxidative stress, and inflammation. Furthermore, the protective effects of flagellin were abolished by TH1020 (a TLR5 antagonist) treatment. These results suggest that flagellin exerted protective effects on ALI via TLR5 activation. Mechanistically, flagellin injection promoted the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) to the nucleus in hepatocytes. Consistent with the in vivo results, flagellin increased the activation of Nrf2 in hepatocytes, resulting in decreased APAP toxicity. ML385, a selective inhibitor of Nrf2, abolished the flagellin-mediated hepatoprotective effects in damaged livers and hepatocytes. Additionally, the flagellin-induced Nrf2 translocation was dependent upon the activation of TLR5-JNK/p38 pathways. These findings suggest that TLR5 signaling-induced Nrf2 activation, at least partially, contributed to the protection against APAP-induced ALI by flagellin treatment.

Furazolidone Increases Survival of Mice Exposed to Lethal Total Body Irradiation through the Antiapoptosis and Antiautophagy Mechanism

Exposure to total body irradiation (TBI) causes dose- and tissue-specific lethality. However, there are few effective and nontoxic radiation countermeasures for the radiation injury. In the current study, mice were pretreated with a traditional antimicrobial agent, FZD, before TBI; the protective effects of FZD on radiation injury were evaluated by using parameters such as the spleen index and thymus index, immunohistochemical staining of intestinal tissue, and frequency of micronuclei in polychromatophilic erythrocytes of bone marrow. The intestinal epithelial cell line IEC-6 was used to investigate the underlying mechanisms. Our results indicated that FZD administration significantly improved the survival of lethal dose-irradiated mice, decreased the number of micronuclei, upregulated the number of leukocytes and immune organ indices, and restored intestinal integrity in mice after TBI. TUNEL and western blot showed that FZD protected intestinal tissue by downregulating radiation-induced apoptosis and autophagy. Meanwhile, FZD protected IEC-6 cells from radiation-induced cell death by inhibiting apoptosis and autophagy. To sum up, FZD protected against radiation-induced cell death both in vitro and in vivo through antiapoptosis and antiautophagy mechanisms.

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.

A Minireview on Gastrointestinal Microbiota and Radiosusceptibility

Gastrointestinal (GI) microbiota maintains a symbiotic relationship with the host and plays a key role in modulating many important biological processes and functions of the host, such as metabolism, inflammation, immune and stress response. It is becoming increasingly apparent that GI microbiota is susceptible to a wide range of environmental factors and insults, for examples, geographic location of birth, diet, use of antibiotics, and exposure to radiation. Alterations in GI microbiota link to various diseases, including radiation-induced disorders. In addition, GI microbiota composition could be used as a biomarker to estimate radiosusceptibility and radiation health risk in the host. In this minireview, we summarized the documented studies on radiation-induced alterations in GI microbiota and the relationship between GI microbiota and radiosusceptibility of the host, and mainly discussed the possible mechanisms underlying GI microbiota influencing the outcome of radiation response in humans and animal models. Furthermore, we proposed that GI microbiota manipulation may be used to reduce radiation injury and improve the health of the host.

Targets for protection and mitigation of radiation injury

Protection of normal tissues against toxic effects of ionizing radiation is a critical issue in clinical and environmental radiobiology. Investigations in recent decades have suggested potential targets that are involved in the protection against radiation-induced damages to normal tissues and can be proposed for mitigation of radiation injury. Emerging evidences have been shown to be in contrast to an old dogma in radiation biology; a major amount of reactive oxygen species (ROS) production and cell toxicity occur during some hours to years after exposure to ionizing radiation. This can be attributed to upregulation of inflammatory and fibrosis mediators, epigenetic changes and disruption of the normal metabolism of oxygen. In the current review, we explain the cellular and molecular changes following exposure of normal tissues to ionizing radiation. Furthermore, we review potential targets that can be proposed for protection and mitigation of radiation toxicity.

Citrulline, A Potential Biomarker of Radiation-Induced Small Intestine Damage

Radiation damage assessment of the small intestine is important in nuclear accidents or routine radiotherapy of abdominal tumors. This article reviews the clinical symptoms and molecular mechanisms of radiation-induced small intestinal damage and summarizes recent research on biomarkers of such damage. Citrulline is the most promising biomarker for the evaluation of radiation-induced small intestinal damage caused by radiotherapy and nuclear accidents. This article also summarizes the factors influencing plasma citrulline measurement investigated in the latest research, as well as new findings on the concentration of citrulline in saliva and urine after different types of radiation.

Monophosphoryl lipid A alleviated radiation-induced testicular injury through TLR4-dependent exosomes

Radiation protection on male testis is an important task for ionizing radiation-related workers or people who receive radiotherapy for tumours near the testicle. In recent years, Toll-like receptors (TLRs), especially TLR4, have been widely studied as a radiation protection target. In this study, we detected that a low-toxicity TLR4 agonist monophosphoryl lipid A (MPLA) produced obvious radiation protection effects on mice testis. We found that MPLA effectively alleviated testis structure damage and cell apoptosis induced by ionizing radiation (IR). However, as the expression abundance differs a lot in distinct cells and tissues, MPLA seemed not to directly activate TLR4 singling pathway in mice testis. Here, we demonstrated a brand new mechanism for MPLA producing radiation protection effects on testis. We observed a significant activation of TLR4 pathway in macrophages after MPLA stimulation and identified significant changes in macrophage-derived exosomes protein expression. We proved that after MPLA treatment, macrophage-derived exosomes played an important role in testis radiation protection, and specially, G-CSF and MIP-2 in exosomes are the core molecules in this protection effect.

Toll-like receptor 4 protects against irradiation-induced hematopoietic injury by promoting granulopoiesis and alleviating marrow adipogenesis

Irradiation induces severe damage in the hematopoietic system, which leads to bone marrow hyperplasia, pancytopenia, and aggravated tissue formation in bone marrow. Studies have shown that Toll-like receptor 4 (TLR4) has a protective effect against irradiation, but the underlying mechanism remains unclear. In this study, we used a TLR4 knockout (TLR4^-/-) mouse irradiation model and found that the white blood cell and platelet counts in the peripheral blood of TLR4^-/- mice recovered slowly after irradiation, with bone marrow hyperplasia and increased mortality. Additionally, we found that the proportion of CD11b⁺Gr1⁺ granulocytes in the peripheral blood and bone marrow of TLR4^-/- mice was lower than that of wild-type mice after irradiation. Further, we found that the expression of NADPH Oxidases (NOXs) in the bone marrow was down-regulated after irradiation of TLR4^-/- mice, and administration of the NOXs inhibitor VAS2870 reduced the proportion of CD11b⁺Gr1⁺ cells in the bone marrow and peripheral blood of wild-type mice after irradiation. Irradiation induced severe marrow adipocytes accumulation in TLR4^-/- mice, TLR4 ligand lipopolysaccharide promoted proliferation and inhibited adipogenic differentiation of mesenchymal stromal cells. In summary, our data suggest that TLR4 promotes myeloid hyperplasia by up-regulating the expression of NOXs after irradiation, prohibits marrow adipogensis and increases the tolerance of mice to irradiation.

Intratumoural immunotherapy: activation of nucleic acid sensing pattern recognition receptors

Recently, it has become clear that the tumour microenvironment (TME) is important in cancer immunotherapy. While immune checkpoint inhibitors are effective for some patients, the heterogeneous nature and status of the TME (‘cold’ tumours) play a critical role in suppressing antitumour immunity in non-responding patients. Converting ‘cold’ to ‘hot’ tumours through modulation of the TME may enable expansion of the therapeutic efficacy of immunotherapy to a broader patient population. This paper describes advances in intratumoural immunotherapy, specifically activation of nucleic acid sensing pattern recognition receptors to modulate the TME.

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Intratumoural immunotherapy to modulate the tumour microenvironment.

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Use of novel immunostimulatory agents which activate nucleic acid sensing pattern recognition receptors.

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Harnessing innate and adaptive immunity induced by receptor-mediated immune cascade.

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Intratumoural therapy leads to local and anenestic tumour responses.

Mitigation of radiation-induced gastro-intestinal injury by the polyphenolic acetate 7, 8-diacetoxy-4-methylthiocoumarin in mice

Radiation-induced intestinal injury (RIII) constitutes a crucial clinical element of acute radiation syndrome with life-threatening implications posing challenges in devising effective medical countermeasures. Herein, we report the potential of 7, 8-diacetoxy-4-methylthiocoumarin (DAMTC) to mitigate RIII following total-body irradiation (TBI) in C57BL/6 mice and underlying mechanisms. Administration of DAMTC 24 hours post TBI facilitated structural reconstitution and restoration of functional absorption linked to alleviation of radiation-induced apoptotic death of intestinal crypt progenitor/stem (ICPS) and villus stromal cells through induction of Bcl-2 family-mediated anti-apoptotic signalling. Reduction in TBI-induced DNA damage accumulation coupled with inhibition of cell cycle arrest through stimulation of anti-p53- and anti-p21-dependent synergistic signalling protected ICPS cells from radiation injury. Enhanced proliferation of crypt stem cells, induction of anti-oxidant defence, subjugation of TBI-induced lipid peroxidation and phenotypic polarization of intestinal macrophages to anti-inflammatory M2 class underlie amelioration of RIII. Stimulation of multiple mitigative signalling processes by DAMTC appeared to be associated with enhanced protein acetylation, an important regulator of cellular responses to radiation damage. Our findings establish the mitigative potential of DAMTC against RIII by hyper-acetylation-mediated epigenetic regulation, which triggers axes of anti-apoptotic and pro-survival pathways, enabling proliferation and maintenance of ICPS cells leading to epithelial regeneration.

An adenosine derivative (IFC-305) reduced the risk of radiation-induced intestinal toxicity in the treatment of colon cancer by suppressing the methylation of PPAR-r promoter

BACKGROUND

IFC-305, an adenosine derivative, has been proved to exert a therapeutic effect on radiation-induced intestinal toxicity in colon cancer (CC). The aim of the present study was to investigate the underlying molecular mechanism of protective role of IFC-305 in CC by modifying the methylation of peroxisome proliferator-activated receptor (PPAR)-r promoter.

METHOD

Peripheral blood and cancerous tissues samples were collected from the CC patients. Irradiation (IR) mice models were established in comparison with control mice accordingly. Bisulfite sequencing, real-time PCR, Western-blot analysis, immunohistochemistry (IHC) and hematoxylin eosin (HE) staining were performed upon both human and animal samples.

RESULT

The results upon the human CC samples demonstrated that the level of methylation of PPAR-r promoter in methylated patients was increased, while the risk of radiation-induced intestinal toxicity in methylated patients was also increased compared with unmethylated patients. Also, the PPAR-r mRNA/protein expression was lower in methylated patients compared with unmethylated patients, thus indicating the presence of PPAR-r promoter methylation repressed PPAR-r expression in vivo. Moreover, in the mice models, IFC-305 treatment partially alleviated radiation-induced toxicity in the columnar epithelia and tubular glands of IR mice, and villus height and the number/circumference of crypts were also increased while the relative number of inflammatory cells was decreased in IR + IFC-305 mice group compared with the control mice. Compared with the control group, the levels of PPAR-r mRNA/protein expression were significantly decreased in IR mice, while the presence of IFC-305 exerted therapeutic effect upon IR rats via elevating the PPAR-r mRNA/protein expression to a certain extent.

CONCLUSION

In this study, we demonstrated the relationship between PPAR-r promoter methylation and the risk of radiation-induced intestinal toxicity via studying the clinical samples collected from CC patients. And the study upon mice models suggested that the administration of IFC-305 could alleviate radiation-induced intestinal toxicity through decreasing the methylation of PPAR-r promoter and enhancing the expression of PPAR-r in IR mice.

The pathogenesis of mucositis: updated perspectives and emerging targets

Mucositis research and treatment are a rapidly evolving field providing constant new avenues of research and potential therapies. The MASCC/ISOO Mucositis Study Group regularly assesses available literature relating to pathogenesis, mechanisms, and novel therapeutic approaches and distils this to summary perspectives and recommendations. Reviewers assessed 164 articles published between January 2011 and June 2016 to identify progress made since the last review and highlight new targets for further investigation. Findings were organized into sections including established and emerging mediators of toxicity, potential insights from technological advances in mucositis research, and perspective. Research momentum is accelerating for mucositis pathogenesis, and with this has come utilization of new models and interventions that target specific mechanisms of injury. Technological advances have the potential to revolutionize the field of mucositis research, although focused effort is needed to move rationally targeted interventions to the clinical setting.

The Microbiome and Radiation Induced-Bowel Injury: Evidence for Potential Mechanistic Role in Disease Pathogenesis

Radiotherapy has played a major role in both the curative and palliative treatment of cancer patients for decades. However, its toxic effect to the surrounding normal healthy tissue remains a major drawback. In cases of intra-abdominal and/or pelvic malignancy, healthy bowel is inevitably included in the radiation field, causing undesirable consequences that subsequently manifest as radiation-induced bowel injury, which is associated with significant morbidity and mortality. The pathophysiology of radiation-induced bowel injury is poorly understood, although we now know that it derives from a complex interplay of epithelial injury and alterations in the enteric immune, nervous, and vascular systems in genetically predisposed individuals. Furthermore, evidence supporting a pivotal role for the gut microbiota in the development of radiation-induced bowel injury has been growing. In this review, we aim to appraise our current understanding of radiation-induced bowel injury and the role of the microbiome in its pathogenesis as well as prevention and treatment. Greater understanding of the relationship between the disease mechanism of radiation-induced bowel injury and gut microbiome might shed light on potential future prevention and treatment strategies through the modification of a patient's gut microbiome.

In vitro photoacoustic spectroscopy of pulsatile blood flow: Probing the interrelationship between red blood cell aggregation and oxygen saturation

We investigate the optical wavelength dependence in quantitative photoacoustic (QPA) assessment of red blood cell (RBC) aggregation and oxygen saturation (sO₂ ) during pulsatile blood flow. Experimentally, the pulsatile flow was imaged with a 700 to 900 nm laser using the VevoLAZR. Theoretically, the photoacoustic (PA) signals were computed based on a Green's function integrated with a Monte Carlo simulation of radiant fluence. The pulsatile flow created periodic conditions of RBC aggregation/nonaggregation, altering the aggregate size, and, in turn, the sO₂ . The dynamic range, DR (a metric of change in PA power) from 700 to 900 nm for nonaggregated RBCs, was 5 dB for both experiment and theory. A significant difference in the DR for aggregated RBCs was 1.5 dB between experiment and theory. Comparing the DR at different wavelengths, the DR from nonaggregated to aggregated RBCs at 700 nm was significantly smaller than that at 900 nm for both experiment (4.0 dB < 7.1 dB) and theory (5.3 dB < 9.0 dB). These results demonstrate that RBC aggregation simultaneously affects the absorber size and the absorption coefficient in photoacoustic imaging (PAI) of pulsatile blood flow. This investigation elucidates how QPA spectroscopy can be used for probing hemodynamics and oxygen transport by PAI of blood flow.

Differential effects of peptidoglycan on colorectal tumors and intestinal tissue post-pelvic radiotherapy

Immediate medical intervention is required after pelvic tumor radiotherapy to protect the radiosensitive intestine and also to mitigate tumor growth. Toll-like receptors (TLRs) have been shown to promote tissue repair processes. Here, we analyzed the effect observed upon combining the TLR2 agonist, peptidoglycan (PGN), with radiation therapy on tumors as well as intestinal tissue, both in vitro and in vivo. In contrast to radiotherapy alone, PGN when combined with ionizing radiation (IR) elicited enhanced antitumor effects and also reduced the IR-induced intestinal damage. Mechanistic studies showed that PGN first induced an IL13 response in the irradiated intestine, but was decreased in tumor cell models screened by Th1/Th2 FlowCytomix assay and validated by the application of IL13 and anti-IL13 neutralizing antibodies. Next, PGN stimulated Akt3, but not Akt1/2, as was verified by AKT1/2/3 plasmid transfection assay and in AKT1/2/3 knockout mice in vivo. Akt3 expression was inhibited in 20 μg/mL PGN-treated tumor cells and in 1.5 mg/kg PGN-treated mouse tumor models. However, Akt3 was raised via IL13 in the irradiated intestine and human intestinal cell line after the same treatment. Finally, PGN activated mTOR via IL13/AKT3 in the intestine and restored intestinal structure and function. As an adjuvant to radiotherapy, PGN inhibited tumorigenesis by suppression of mTOR activity. To summarize, the IL13/AKT3/mTOR pathway was lessened in PGN-treated irradiated tumors but was raised in the normal intestine tissue. This distinct effect of PGN on normal and tumor tissues during pelvic radiotherapy suggests that PGN may be a promising adjuvant therapy to radiation.

BCN057 induces intestinal stem cell repair and mitigates radiation-induced intestinal injury

BACKGROUND

Radiation-induced gastrointestinal syndrome (RIGS) results from the acute loss of intestinal stem cells (ISC), impaired epithelial regeneration, and subsequent loss of the mucosal barrier, resulting in electrolyte imbalance, diarrhea, weight loss, sepsis, and mortality. The high radiosensitivity of the intestinal epithelium limits effective radiotherapy against abdominal malignancies and limits the survival of victims of nuclear accidents or terrorism. Currently, there is no approved therapy to mitigate radiation toxicity in the intestine. Here we demonstrate that BCN057, an anti-neoplastic small molecular agent, induces ISC proliferation and promotes intestinal epithelial repair against radiation injury.

METHODS

BCN057 (90 mg/kg body weight, subcutaneously) was injected into C57Bl6 male mice (JAX) at 24 h following abdominal irradiation (AIR) and was continued for 8 days post-irradiation. BCN057-mediated rescue of Lgr5-positive ISC was validated in Lgr5-EGFP-Cre-ERT2 mice exposed to AIR. The regenerative response of Lgr5-positive ISC was examined by lineage tracing assay using Lgr5-EGFP-ires-CreERT2-TdT mice with tamoxifen administration to activate Cre recombinase and thereby marking the ISC and their respective progeny. Ex vivo three-dimensional organoid cultures were developed from surgical specimens of human colon or from mice jejunum and were used to examine the radio-mitigating role of BCN057 on ISC ex vivo. Organoid growth was determined by quantifying the budding crypt/total crypt ratio. Statistical analysis was performed using Log-rank (Mantel-Cox) test and paired two-tail t test.

RESULTS

Treatment with BCN057 24 h after a lethal dose of AIR rescues ISC, promotes regeneration of the intestinal epithelium, and thereby mitigates RIGS. Irradiated mice without BCN057 treatment suffered from RIGS, resulting in 100% mortality within 15 days post-radiation. Intestinal organoids developed from mice jejunum or human colon demonstrated a regenerative response with BCN057 treatment and mitigated radiation toxicity. However, BCN057 did not deliver radio-protection to mouse or human colon tumor tissue.

CONCLUSION

BCN057 is a potential mitigator against RIGS and may be useful for improving the therapeutic ratio of abdominal radiotherapy. This is the first report demonstrating that a small molecular agent mitigates radiation-induced intestinal injury by inducing ISC self-renewal and proliferation.

The GS-nitroxide JP4-039 improves intestinal barrier and stem cell recovery in irradiated mice

Total body irradiation (TBI) leads to dose- and tissue-specific lethality. In the current study, we demonstrate that a mitochondrion-targeted nitroxide JP4-039 given once 24 hours after 9–10 Gy TBI significantly improves mouse survival, and the recovery of intestinal barrier, differentiation and stem cell functions. The GI-protective effects are associated with rapid and selective induction of tight junction proteins and cytokines including TGF-β, IL-10, IL-17a, IL-22 and Notch signaling long before bone marrow depletion. However, no change was observed in crypt death or the expression of prototypic pro-inflammatory cytokines such as TNF-α, IL-6 or IL-1β. Surprisingly, bone marrow transplantation (BMT) performed 24 hours after TBI improves intestinal barrier and stem cell recovery with induction of IL-10, IL-17a, IL-22, and Notch signaling. Further, BMT-rescued TBI survivors display increased intestinal permeability, impaired ISC function and proliferation, but not obvious intestinal inflammation or increased epithelial death. These findings identify intestinal epithelium as a novel target of radiation mitigation, and potential strategies to enhance ISC recovery and regeneration after accidental or medical exposures.

Bowel Radiation Injury: Complexity of the Pathophysiology and Promises of Cell and Tissue Engineering

Ionizing radiation is effective to treat malignant pelvic cancers, but the toxicity to surrounding healthy tissue remains a substantial limitation. Early and late side effects not only limit the escalation of the radiation dose to the tumor but may also be life-threatening in some patients. Numerous preclinical studies determined specific mechanisms induced after irradiation in different compartments of the intestine. This review outlines the complexity of the pathogenesis, highlighting the roles of the epithelial barrier in the vascular network, and the inflammatory microenvironment, which together lead to chronic fibrosis. Despite the large number of pharmacological molecules available, the studies presented in this review provide encouraging proof of concept regarding the use of mesenchymal stromal cell (MSC) therapy to treat radiation-induced intestinal damage. The therapeutic efficacy of MSCs has been demonstrated in animal models and in patients, but an enormous number of cells and multiple injections are needed due to their poor engraftment capacity. Moreover, it has been observed that although MSCs have pleiotropic effects, some intestinal compartments are less restored after a high dose of irradiation. Future research should seek to optimize the efficacy of the injected cells, particularly with regard to extending their life span in the irradiated tissue. Moreover, improving the host microenvironment, combining MSCs with other specific regenerative cells, or introducing new tissue engineering strategies could be tested as methods to treat the severe side effects of pelvic radiotherapy.

Biodistribution and tolerance of intravenous iodine-131-labelled hypericin in healthy dogs

Hypericin (Hyp) is a necrosis-avid compound that can be efficiently labelled with radioiodine for both diagnostic and therapeutic purposes. Before ¹³¹ I-Hyp can be considered as a clinically useful drug in a combination therapy for canine cancer patients, evaluation of its toxicity is necessary. The aim of this study was to investigate the biodistribution and tolerance of a single dose administration of ¹³¹ I-Hyp. Three healthy dogs were included. ¹³¹ I-Hyp at a dose of 0.2 mg/kg and an activity of 185 MBq was intravenously injected. The effects on physical, haematological and biochemical parameters were characterized and the biodistribution and elimination pattern, the effective half-life and dose rate were assessed. Drug-related adverse events were limited to mild gastrointestinal signs, resolving within 48 hours. No significant differences were found in blood haematology and serum biochemistry before and after treatment. Following administration, highest percentage of injected dose (%ID ± SD) was found in the liver (5.5 ± 0.33), the lungs (4.17 ± 0.14) and the heart (3.11 ± 0.78). After 24 hours, highest %ID was found in colon (4.25 ± 1.45) and liver (3.45 ± 0.60). Clearance from all organs was effective within 7 days. Effective half-life was established at 80 hours, and the dose rate fell below <20 μSv/h at 1 m within 1 day. The current study reveals that single dose treatment with ¹³¹ I-Hyp at the described dose is well tolerated by healthy dogs and supports the use of radioiodinated hypericin in a combination therapy for canine cancer patients.

A Chemical Modulator of p53 Transactivation that Acts as a Radioprotective Agonist

Inhibiting p53-dependent apoptosis by inhibitors of p53 is an effective strategy for preventing radiation-induced damage in hematopoietic lineages, while p53 and p21 also play radioprotective roles in the gastrointestinal epithelium. We previously identified some zinc(II) chelators, including 8-quinolinol derivatives, that suppress apoptosis in attempts to discover compounds that target the zinc-binding site in p53. We found that 5-chloro-8-quinolinol (5CHQ) has a unique p53-modulating activity that shifts its transactivation from proapoptotic to protective responses, including enhancing p21 induction and suppressing PUMA induction. This p53-modulating activity also influenced p53 and p53-target gene expression in unirradiated cells without inducing DNA damage. The specificity of 5CHQ for p53 and p21 was demonstrated by silencing the expression of each protein. These effects seem to be attributable to the sequence-specific alteration of p53 DNA-binding, as evaluated by chromatin immunoprecipitation and electrophoretic mobility shift assays. In addition, 5-chloro-8-methoxyquinoline itself had no antiapoptotic activity, indicating that the hydroxyl group at the 8-position is required for its antiapoptotic activity. We applied this remarkable agonistic activity to protecting the hematopoietic and gastrointestinal system in mouse irradiation models. The dose reduction factors of 5CHQ in total-body and abdominally irradiated mice were about 1.2 and 1.3, respectively. 5CHQ effectively protected mouse epithelial stem cells from a lethal dose of abdominal irradiation. Furthermore, the specificity of 5CHQ for p53 in reducing the lethality induced by abdominal irradiation was revealed in Trp53-KO mice. These results indicate that the pharmacologic upregulation of radioprotective p53 target genes is an effective strategy for addressing the gastrointestinal syndrome. Mol Cancer Ther; 17(2); 432-42. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Involvement of reactive oxygen species in ionizing radiation-induced upregulation of cell surface Toll-like receptor 2 and 4 expression in human monocytic cells

Toll-like receptors (TLRs) are pattern recognition receptors that recognize pathogen-associated molecular patterns and are indispensable for antibacterial and antiviral immunity. Our previous report showed that ionizing radiation increases the cell surface expressions of TLR2 and TLR4 and enhances their responses to agonists in human monocytic THP1 cells. The present study investigated how ionizing radiation increases the cell surface expressions of TLR2 and TLR4 in THP1 cells. The THP1 cells treated or not treated with pharmaceutical agents such as cycloheximide and N-acetyl-L-cysteine (NAC) were exposed to X-ray irradiation, following which the expressions of TLRs and mitogen-activated protein kinase were analyzed. X-ray irradiation increased the mRNA expressions of TLR2 and TLR4, and treatment with a protein synthesis inhibitor cycloheximide abolished the radiation-induced upregulation of their cell surface expressions. These results indicate that radiation increased those receptors through de novo protein synthesis. Furthermore, treatment with an antioxidant NAC suppressed not only the radiation-induced upregulation of cell surface expressions of TLR2 and TLR4, but also the radiation-induced activation of the c-Jun N-terminal kinase (JNK) pathway. Since it has been shown that the inhibitor for JNK can suppress the radiation-induced upregulation of TLR expression, the present results suggest that ionizing radiation increased the cell surface expressions of TLR2 and TLR4 through reactive oxygen species-mediated JNK activation.

Differences in sustained alterations in protein expression between livers of mice exposed to high-dose-rate and low-dose-rate radiation

Molecular mechanisms of radiation dose-rate effects are not well understood. Among many possibilities, long-lasting sustained alterations in protein levels would provide critical information. To evaluate sustained effects after acute and chronic radiation exposure, we analyzed alterations in protein expression in the livers of mice. Acute exposure consisted of a lethal dose of 8 Gy and a sublethal dose of 4 Gy, with analysis conducted 6 days and 3 months after irradiation, respectively. Chronic irradiation consisted of a total dose of 8 Gy delivered over 400 days (20 mGy/day). Analyses following chronic irradiation were done immediately and at 3 months after the end of the exposure. Based on antibody arrays of protein expression following both acute lethal and sublethal dose exposures, common alterations in the expression of two proteins were detected. In the sublethal dose exposure, the expression of additional proteins was altered 3 months after irradiation. Immunohistochemical analysis showed that the increase in one of the two commonly altered proteins, MyD88, was observed around blood vessels in the liver. The alterations in protein expression after chronic radiation exposure were different from those caused by acute radiation exposures. Alterations in the expression of proteins related to inflammation and apoptosis, such as caspase 12, were observed even at 3 months after the end of the chronic radiation exposure. The alterations in protein expression depended on the dose, the dose rate, and the passage of time after irradiation. These changes could be involved in long-term effects of radiation in the liver.

Antioxidant Supplementation: A Linchpin in Radiation-Induced Enteritis

Radiation enteritis is one of the most feared complications of abdominal and pelvic regions. Thus, radiation to abdominal or pelvic malignancies unavoidably injures the intestine. Because of rapid cell turnover, the intestine is highly sensitive to radiation injury, which is the limiting factor in the permissible dosage of irradiation. Bowel injuries such as fistulas, strictures, and chronic malabsorption are potentially life-threatening complications and have an impact on patient quality of life. The incidence of radiation enteritis is increasing because of the current trend of combined chemotherapy and radiation. The consequences of radiation damage to the intestine may result in considerable morbidity and even mortality. The observed effects of ionizing radiation are mediated mainly by oxygen-free radicals that are generated by its action on water and are involved in several steps of signal transduction cascade, leading to apoptosis. The oxyradicals also induce DNA strand breaks and protein oxidation. An important line of defense against free radical damage is the presence of antioxidants. Therefore, administration of antioxidants may ameliorate the radiation-induced damage to the intestine.

Macrophage-derived extracellular vesicle-packaged WNTs rescue intestinal stem cells and enhance survival after radiation injury

WNT/β-catenin signalling is crucial for intestinal homoeostasis. The intestinal epithelium and stroma are the major source of WNT ligands but their origin and role in intestinal stem cell (ISC) and epithelial repair remains unknown. Macrophages are a major constituent of the intestinal stroma. Here, we analyse the role of macrophage-derived WNT in intestinal repair in mice by inhibiting their release using a macrophage-restricted ablation of Porcupine, a gene essential for WNT synthesis. Such Porcn-depleted mice have normal intestinal morphology but are hypersensitive to radiation injury in the intestine compared with wild-type (WT) littermates. Porcn-null mice are rescued from radiation lethality by treatment with WT but not Porcn-null bone marrow macrophage-conditioned medium (CM). Depletion of extracellular vesicles (EV) from the macrophage CM removes WNT function and its ability to rescue ISCs from radiation lethality. Therefore macrophage-derived EV-packaged WNTs are essential for regenerative response of intestine against radiation.

The intestinal stroma secretes WNT ligands but the role of WNT in intestinal repair is unclear. Here, the authors show that when WNT synthesis is ablated from stromal macrophages, the intestine morphology is normal but hypersensitive to radiation injury, implicating macrophage-derived WNT in intestinal repair.

The potential role of some phytochemicals in recognition of mitochondrial damage-associated molecular patterns

Mitochondria are the source of damage-associated molecular patterns (DAMPs). DAMPs modulate responses to stress and trauma in animals, influencing the onset of many diseases. Dietary phytochemicals, which target various cellular molecules, are potential modulators of immunological status. In this review the existence of the possible impact of some plant-derived compounds with proven anti-cancer and anti-inflammatory properties (isothiocyanates and curcumin) on DAMPs recognition is highlighted. Special consideration is given to the mtDNA recognizing Toll-like receptor 9 and formyl peptide receptors. In the context of the phytochemicals action, the role of these receptors in epithelial homeostasis is also discussed.

Amifostine alleviates radiation-induced lethal small bowel damage via promotion of 14-3-3σ-mediated nuclear p53 accumulation

Amifostine (AM) is a radioprotector that scavenges free radicals and is used in patients undergoing radiotherapy. p53 has long been implicated in cell cycle arrest for cellular repair after radiation exposure. We therefore investigated the protective p53-dependent mechanism of AM on small bowel damage after lethal whole-abdominal irradiation (WAI). AM increased both the survival rate of rats and crypt survival following lethal 18 Gy WAI. The p53 inhibitor PFT-α compromised AM-mediated effects when administered prior to AM administration. AM significantly increased clonogenic survival in IEC-6 cells expressing wild type p53 but not in p53 knockdown cells. AM significantly increased p53 nuclear accumulation and p53 tetramer expression before irradiation through the inhibition of p53 degradation. AM inhibited p53 interactions with MDM2 but enhanced p53 interactions with 14-3-3σ. Knockdown of 14-3-3σ also compromised the effect of AM on clonogenic survival and p53 nuclear accumulation in IEC-6 cells. For the first time, our data reveal that AM alleviates lethal small bowel damage through the induction of 14-3-3σ and subsequent accumulation of p53. Enhancement of the p53/14-3-3σ interaction results in p53 tetramerization in the nucleus that rescues lethal small bowel damage.

Radiation takes its Toll

The ability to recognize and respond to universal molecular patterns on invading microorganisms allows our immune system to stay on high alert, sensing danger to our self-integrity. Our own damaged cells and tissues in pathological situations activate similar warning systems as microbes. In this way, the body is able to mount a response that is appropriate to the danger. Toll-like receptors are at the heart of this pattern recognition system that initiates innate pro-oxidant, pro-inflammatory signaling cascades and ultimately bridges recognition of danger to adaptive immunity. The acute inflammatory lesions that are formed segue into resolution of inflammation, repair and healing or, more dysfunctionally, into chronic inflammation, autoimmunity, excessive tissue damage and carcinogenesis. Redox is at the nexus of this decision making process and is the point at which ionizing radiation initially intercepts to trigger similar responses to self-damage. In this review we discuss our current understanding of how radiation-damaged cells interact with Toll-like receptors and how the immune systems interprets these radiation-induced danger signals in the context of whole-body exposures and during local tumor irradiation.

Mitigation of the hematopoietic and gastrointestinal acute radiation syndrome by octadecenyl thiophosphate, a small molecule mimic of lysophosphatidic acid

We have previously demonstrated that the small molecule octadecenyl thiophosphate (OTP), a synthetic mimic of the growth factor-like mediator lysophosphatidic acid (LPA), showed radioprotective activity in a mouse model of total-body irradiation (TBI) when given orally or intraperitoneally 30 min before exposure to 9 Gy γ radiation. In the current study, we evaluated the effects of OTP, delivered subcutaneously, for radioprotection or radiomitigation from -24 h before to up to +72 h postirradiation using a mouse TBI model with therapeutic doses at around 1 mg/kg. OTP was injected at 10 mg/kg without observable toxic side effects in mice, providing a comfortable safety margin. Treatment of C57BL/6 mice with a single dose of OTP over the time period from -12 h before to +26 h after a lethal dose of TBI reduced mortality by 50%. When administered at +48 h to +72 h postirradiation (LD50/30 to LD100/30), OTP reduced mortality by ≥34%. OTP administered at +24 h postirradiation significantly elevated peripheral white blood cell and platelet counts, increased crypt survival in the jejunum, enhanced intestinal glucose absorption and reduced endotoxin seepage into the blood. In the 6.4-8.6 Gy TBI range using LD50/10 as the end point, OTP yielded a dose modification factor of 1.2. The current data indicate that OTP is a potent radioprotector and radiomitigator ameliorating the mortality and tissue injury of acute hematopoietic as well as acute gastrointestinal radiation syndrome.

The many interactions between the innate immune system and the response to radiation

The role of the immune system in the protection of the organism against biological aggressions is long established and well-studied. A new role emerged more recently in the protection from - and the response to - physical trauma such as exposure to ionizing radiation. A pre-existing inflammation, induced by administration of an inflammatory cytokine or of a Toll-like receptor agonist, is indeed able to mitigate the toxic effects of acute radiation exposure. Conversely, it appears that the innate immune system can be activated during the course of the cellular response to radiation. Activation of different sensors and pattern recognition receptors by intra-cellular molecules such as HMGB1 or DNA released in the extra-cellular milieu or in the cytosol by irradiated cells induces the production of inflammatory and anti-viral cytokines. In addition, in human monocytes and macrophages, the expression of inflammatory cytokine genes can be directly induced by p53- and ATM-dependent mechanisms. This last finding establishes a direct link between radiation-induced DNA damage response and radiation-induced inflammation.

Gastrointestinal acute radiation syndrome in Göttingen minipigs (Sus scrofa domestica)

In the absence of supportive care, exposing Göttingen minipigs to γ-radiation doses of less than 2 Gy achieves lethality due to hematopoietic acute radiation syndrome. Doses of 2 to 5 Gy are associated with an accelerated hematopoietic syndrome, characterized by villus blunting and fusion, the beginning of sepsis, and a mild transient reduction in plasma citrulline concentration. We exposed male Göttingen minipigs (age, 5 mo; weight, 9 to 11 kg) to γ-radiation doses of 5 to 12 Gy (total body; (60)Co, 0.6 Gy/min) to test whether these animals exhibit classic gastrointestinal acute radiation syndrome (GI-ARS). After exposure, the minipigs were monitored for 10 d by using clinical signs, CBC counts, and parameters associated with the development of the gastrointestinal syndrome. Göttingen minipigs exposed to γ radiation of 5 to 12 Gy demonstrate a dose-dependent occurrence of all parameters classically associated with acute GI-ARS. These results suggest that Göttingen minipigs may be a suitable model for studying GI-ARS after total body irradiation, but the use of supportive care to extend survival beyond 10 d is recommended. This study is the first step toward determining the feasibility of using Göttingen minipigs in testing the efficacy of candidate drugs for the treatment of GI-ARS after total body irradiation.

Radiation protection of the gastrointestinal tract and growth inhibition of prostate cancer xenografts by a single compound

Normal tissue toxicity markedly reduces the therapeutic index of genotoxic anticancer agents, including ionizing radiation. Countermeasures against tissue damage caused by radiation are limited by their potential to also protect malignant cells and tissues. Here, we tested a panel of signal transduction modifiers for selective radioprotection of normal but not tumor tissues. These included three inhibitors of GSK3 (LiCl, SB216763, and SB415286) and two inhibitors of NF-κB (ethyl pyruvate and RTA 408). Among these, the thiol-reactive triterpenoid RTA 408 emerged as a robust and effective protector of multiple organ systems (gastrointestinal, skin, and hemopoietic) against lethal doses of radiation. RTA 408 preserved survival and proliferation of intestinal crypt cells in lethally irradiated mice while reducing apoptosis incidence in crypts and villi. In contrast, RTA 408 uniformly inhibited growth of established CWR22Rv1, LNCaP/C4-2B, PC3, and DU145 xenografts either alone or combined with radiation. Antitumor effects in vivo were associated with reduced proliferation and intratumoral apoptosis and with inhibition of NF-κB-dependent transcription in PC3 cells. Selective protection of normal tissue compartments by RTA 408 critically depended on tissue context and could not be replicated in vitro. Collectively, these data highlight the potential of RTA 408 as a cytoprotective agent that may be safely used in chemoradiation approaches.