Bax and Bak do not exhibit functional redundancy in mediating radiation-induced endothelial apoptosis in the intestinal mucosa

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.

[Radiation-induced retinopathy: actual knowledge and new concepts]

Radiation retinopathy is an occlusive vascular pathology following radiotherapy, generally targeted on the eye or peri-ocular structures. Despite increasingly precise techniques (stereotactic radiosurgery, proton therapy, etc.), the inclusion of the retina in the radiation field is sometimes unavoidable. This can lead to a severe pathology, which can ultimately cause blindness or even the anatomical loss of the eye when neovascular glaucoma occurs, due to the abnormal proliferation of neovessels. Radiation retinopathy have been described for more than a century, but it has recently seen great advances in both diagnosis and treatment. The advances of efficient and less invasive examinations in our clinical practice, such as OCT-angiography, allows for easier screening and diagnosis at earlier stages. Thus a new approach to the pathology is necessary, first of all through new definitions and classifications including previously undetected minimal forms. Furthermore, the recent appearance of intravitreal therapies by injection of anti-VEGF or dexamethasone implants has drastically changed the visual prognosis of these patients, who were previously treated only by retinal photocoagulation of the ischaemic areas. Recent studies have even shown the effectiveness of these new molecules in preventing the development of radiation retinopathy. This review of the literature provides an update on this disease and details how these recent diagnostic and therapeutic developments may play a role in the management of this complication.

Intestinal Radiation Protection and Mitigation by Second-Generation Probiotic Lactobacillus-reuteri Engineered to Deliver Interleukin-22

(1) Background: The systemic administration of therapeutic agents to the intestine including cytokines, such as Interleukin-22 (IL-22), is compromised by damage to the microvasculature 24 hrs after total body irradiation (TBI). At that time, there is significant death of intestinal microvascular endothelial cells and destruction of the lamina propria, which limits drug delivery through the circulation, thus reducing the capacity of therapeutics to stabilize the numbers of Lgr5+ intestinal crypt stem cells and their progeny, and improve survival. By its direct action on intestinal stem cells and their villus regeneration capacity, IL-22 is both an ionizing irradiation protector and mitigator. (2) Methods: To improve delivery of IL-22 to the irradiated intestine, we gavaged Lactobacillus-reuteri as a platform for the second-generation probiotic Lactobacillus-reuteri-Interleukin-22 (LR-IL-22). (3) Results: There was effective radiation mitigation by gavage of LR-IL-22 at 24 h after intestinal irradiation. Multiple biomarkers of radiation damage to the intestine, immune system and bone marrow were improved by LR-IL-22 compared to the gavage of control LR or intraperitoneal injection of IL-22 protein. (4) Conclusions: Oral administration of LR-IL-22 is an effective protector and mitigator of intestinal irradiation damage.

A novel human colon signet-ring cell carcinoma organoid line: establishment, characterization and application

Colon signet-ring cell carcinoma (SRCC) is a rare type of malignant dedifferentiated adenocarcinomas, and is associated with poor survival. However, an in-depth study of the biological features of SRCC is hindered by the lack of a reliable in vitro model of colon SRCC. Thus, the establishment of cell cultures from SRCC has become the most challenging task. Here, by harnessing the power of the organoid culture system, we describe the establishment of a human colon SRCC organoid line from a surgical sample from one patient with colon SRCC. The colon SRCC organoid line, YQ-173, was characterized for morphology, histology, ultrastructure and chromosome stability levels, showing that it resembles the histological and growth characteristics of the original tumor cells; xenografts were used to show that it also has a high tumor formation rate. RNA sequencing of YQ-173 compared with the normal tissue verified its mucinous nature. Capture-based targeted DNA sequencing combined with drug screening based on a bespoke 88 compound library identified that JAK2 might be a treatment target. An in vitro drug screening found that AT9283 and Pacritinib could be effective JAK2 inhibitors, which was consistent with the in vivo xenograft response. We report, for the first time, the establishment of an SRCC organoid line allowing in-depth study of SRCC biology, as well as a strategy to assess in vitro drug testing in a personalized fashion.

Secretion of Acid Sphingomyelinase and Ceramide by Endothelial Cells Contributes to Radiation-Induced Intestinal Toxicity

Ceramide-induced endothelial cell apoptosis boosts intestinal stem cell radiosensitivity. However, the molecular connection between these two cellular compartments has not been clearly elucidated. Here we report that ceramide and its related enzyme acid sphingomyelinase (ASM) are secreted by irradiated endothelial cells and act as bystander factors to enhance the radiotoxicity of intestinal epithelium. Ceramide and the two isoforms of ASM were acutely secreted in the blood serum of wild-type mice after 15 Gy radiation dose, inducing a gastrointestinal syndrome. Interestingly, serum ceramide was not enhanced in irradiated ASMKO mice, which are unable to develop intestinal failure injury. Because ASM/ceramide were secreted by primary endothelial cells, their contribution was studied in intestinal epithelium dysfunction using coculture of primary endothelial cells and intestinal T84 cells. Adding exogenous ASM or ceramide enhanced epithelial cell growth arrest and death. Conversely, blocking their secretion by endothelial cells using genetic, pharmacologic, or immunologic approaches abolished intestinal T84 cell radiosensitivity. Use of enteroid models revealed ASM and ceramide-mediated deleterious mode-of-action: when ceramide reduced the number of intestinal crypt-forming enteroids without affecting their structure, ASM induced a significant decrease of enteroid growth without affecting their number. Identification of specific and different roles for ceramide and ASM secreted by irradiated endothelial cells opens new perspectives in the understanding of intestinal epithelial dysfunction after radiation and defines a new class of potential therapeutic radiomitigators. SIGNIFICANCE: This study identifies secreted ASM and ceramide as paracrine factors enhancing intestinal epithelial dysfunction, revealing a previously unknown class of mediators of radiosensitivity.

Organoids Reveal That Inherent Radiosensitivity of Small and Large Intestinal Stem Cells Determines Organ Sensitivity

Tissue survival responses to ionizing radiation are nonlinear with dose, rather yielding tissue-specific descending curves that impede straightforward analysis of biologic effects. Apoptotic cell death often occurs at low doses, while at clinically relevant intermediate doses, double-strand break misrepair yields mitotic death that determines outcome. As researchers frequently use a single low dose for experimentation, such strategies may inaccurately depict inherent tissue responses. Cutting edge radiobiology has adopted full dose survival profiling and devised mathematical algorithms to fit curves to observed data to generate highly reproducible numerical data that accurately define clinically relevant inherent radiosensitivities. Here, we established a protocol for irradiating organoids that delivers radiation profiles simulating the organ of origin. This technique yielded highly similar dose-survival curves of small and large intestinal crypts in vivo and their cognate organoids analyzed by the single-hit multi-target (SHMT) algorithm, outcomes reflecting the inherent radiation profile of their respective Lgr5⁺ stem cell populations. As this technological advance is quantitative, it will be useful for accurate evaluation of intestinal (patho)physiology and drug screening. SIGNIFICANCE: These findings establish standards for irradiating organoids that deliver radiation profiles that phenocopy the organ of origin.See related commentary by Muschel et al., p. 927.

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.

Protective effect of polydatin on radiation-induced injury of intestinal epithelial and endothelial cells

This study aimed to examine the radioprotective effect of polydatin (PD) on crypt and endothelial cells of the small intestines of C57BL/6 mice that received abdominal irradiation (IR). Mice were treated with 6 MV X-ray (20 Gy) abdominal IR at a dose rate of 200 cGy/min. Thirty minutes before or after IR, mice were intraperitoneally injected with PD. The rate of survival of the mice at 30 days after IR was determined. The duodenum (upper small intestine), jejunum (middle small intestine), and ileum (lower small intestine) were collected and subjected to hematoxylin and eosin staining. Tissue sample sections were analyzed through light microscopy, and the lengths of at least 20 intestinal villi were measured in each group; the average number of crypts was obtained from 10 intestinal samples in each group. Microvessel density was assessed using CD31-positive (brown) vascular endothelial cells/cell clusters. FHs74Int cell proliferation was measured using the CCK-8 assay. PD administration (25 mg/kg) before IR was the most effective in prolonging the survival of C57BL/6 mice. PD reduced radiation-induced injury of intestinal villi, prevented loss of crypts, increased intestinal crypt growth, protected against IR-induced intestinal injury, and enhanced the proliferative potential and reduced the apoptosis of FHs74Int cells after IR. Moreover, PD increased small intestinal MVD and reduced the apoptosis of intestinal microvascular endothelial cells in mice after IR. Therefore, PD was found to be able to protect the two types of cells from radiation damage and to thus alleviate radiation-induced injury of small intestine.

Distinct Levels of Radioresistance in Lgr5+ Colonic Epithelial Stem Cells versus Lgr5+ Small Intestinal Stem Cells

Although small and large intestines possess seemingly similar Wnt-driven leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)⁺ adult epithelial stem cells, we report here that the two organs exhibit distinct mechanisms of tissue response to ionizing radiation. Employing Lgr5-lacZ transgenic mice and Lgr5 in situ hybridization, we found colonic epithelial stem cells (CESC) markedly more radioresistant in vivo than small intestinal crypt base columnar stem cells (CBC; D₀ = 6.0 ± 0.3 Gy vs. 1.3 ± 0.1, respectively; P < 0.01). Accordingly, CESCs survived 30 Gy exposure, while CBCs were completely depleted after 15 Gy. EdU incorporation studies indicated that after 19 Gy, CBCs exited growth arrest at 12 hours, resuming normal mitotic activity despite 60% of this population displaying residual γH2AX foci, indicative of persistent unrepaired DNA damage. Checkpoint recovery before complete double-strand break (DSB) repair represents the sine qua non of a newly defined potentially lethal pathophysiology termed checkpoint adaptation. In the small intestinal mucosa, checkpoint adaptation resulted in CBCs succumbing to an 8-fold increase in the incidence of highly lethal chromosomal aberrations and mitotic catastrophe by 48 hours postradiation. In contrast, Lgr5⁺ CESCs displayed delayed checkpoint recovery at 48 hours post-19 Gy, coordinated with complete DSB repair and regeneration of colonic mucosa originating, at least in part, from surviving CESCs. The discovery that small intestinal CBCs succumb to checkpoint adaptation is the first demonstration that this aberrant cell-cycle response may drive mammalian tissue radiosensitivity. Cancer Res; 77(8); 2124-33. ©2017 AACR.

The role of gene mutations and gene products in intestinal tissue reactions from ionising radiation

The response of the intestine to (low linear-energy-transfer) ionising radiation is reviewed regarding the cellular basis to the reactions, the regenerative processes which restore the tissue, and external agents which aid its recovery. In the steady-state, it is generally considered that the crypt cell lineages in both small and large intestine are maintained by a small number of stem cells, but there are differences for example in the composition of their niche residence and in the numbers of transit cell generations. Various cell surface markers are now available to indentify particular lineage cell types. Radiation doses up to 1Gy cause apoptotic stem-cell death in particular locations, at higher doses to >6Gy Lgr5⁺ stem cells are required for normal intestinal recovery, and at >8Gy some crypts are sterilised and the probability of animal death from intestinal injury increases with higher doses. Mutations in repair genes, tumour suppressor genes, and survival genes cause various degrees of stem cell and clonogenic cell radiosensitisation. Recent evidence is suggesting much plasticity in the crypt cell lineage, potentially contributing to flexibility in the hierarchical lineage, clonogen number variations and the sensitisation differences. Knockout mice for many different genes have been used to detect their role in both steady state and in irradiated conditions, expected to lead to further insight to the damage and restorative processes. Many different external agents have been used to ameliorate intestinal reactions, including prostaglandins, interleukins, angiogenic and epithelial growth factors, other cytokines, and intraluminal factors.

The Effects of ASMase Mediated Endothelial Cell Apoptosis in Multiple Hypofractionated Irradiations in CT26 Tumor Bearing Mice

BACKGROUND

To investigate the effects of ASMase mediated endothelial cell apoptosis in multiple hypofractionated irradiations in CT26 tumor bearing mice.

MATERIALS AND METHODS

Thirty-five CT26 tumor bearing mice were subjected to single ionizing radiation (IR) of 0, 3, 6, 9, 12, 15, 18 Gy. Eight hours after IR, the mice were sacrificed and tumor tissues were used for CD31 immunohistochemistry staining, TUNEL and CD31 double staining, ASMase activity assay. Then 6 and 12 Gy were chosen for multiple hypofractionated IR experiments according to the above results. Each time after IR, 5 mice were sacrificed and assayed as above.

RESULTS

The ASMase activities were increased significantly after a single IR of 12 Gy or higher which was accompanied with remarkable increased endothelial cell apoptosis and decreased MVD. For 6 Gy which was not high enough to trigger ASMase activation, after 2 or more times of IR, the ASMase activities were significantly increased accompanied with remarkable increased endothelial cell apoptosis and decreased MVD. While for 12 Gy, after 2 or more times of IR, the ASMase activities and endothelial cell apoptosis rates were maintained without remarkable increase; however, the MVD was significantly decreased. What's more, the cancer cell apoptosis rates were significantly increased after multiple IR for both 6 Gy and 12 Gy.

CONCLUSIONS

ASMase mediated endothelial cell apoptosis may play an important role in the process of multiple hypofractionated IR for CT26 colorectal carcinoma.

Silencing Egr1 Attenuates Radiation-Induced Apoptosis in Normal Tissues while Killing Cancer Cells and Delaying Tumor Growth

Normal tissue toxicity reduces the therapeutic index of radiotherapy and decreases the quality of life for cancer survivors. Apoptosis is a key element of the radiation response in normal tissues like the hippocampus and small intestine, resulting in neurocognitive disorders and intestinal malabsorption. The Early Growth Response 1 (Egr1) transcription factor mediates radiation-induced apoptosis by activating the transcription of proapoptosis genes in response to ionizing radiation (IR). Therefore, we hypothesized that the genetic abrogation of Egr1 and the pharmacologic inhibition of its transcriptional activity could attenuate radiation-induced apoptosis in normal tissues. We demonstrated that Egr1-null mice had less apoptosis in the hippocampus and intestine following irradiation as compared with their wild-type littermates. A similar result was achieved using Mithramycin A (MMA) to prevent binding of Egr1 to target promoters in the mouse intestine. Abolishing Egr1 expression using shRNA dampened apoptosis and enhanced the clonogenic survival of irradiated HT22 hippocampal neuronal cells and IEC6 intestinal epithelial cells. Mechanistically, these events involved an abrogation of p53 induction by IR and an increase in the ratio of Bcl-2/Bax expression. In contrast, targeted silencing of Egr1 in two cancer cell lines (GL261 glioma cells and HCT116 colorectal cancer cells) was not radioprotective, since it reduced their growth while also sensitizing them to radiation-induced death. Further, Egr1 depletion delayed the growth of heterotopically implanted GL261 and HCT116 tumors. These results support the potential of silencing Egr1 in order to minimize the normal tissue complications associated with radiotherapy while enhancing tumor control.

Radioprotective effect of kupffer cell depletion on hepatic sinusoidal endothelial cells

Radiation-induced liver injury remains a clinical problem and data suggest that sinusoidal endothelial cells (SECs) are an important target. The purpose of this study was to determine whether the inhibition of Kupffer cells before exposure would protect SECs from radiation-induced injury. Sprague-Dawley rats were intravenously injected 24 h before irradiation with Kupffer cell inhibitor gadolinium chloride (GdCl3) (10 mg/kg body weight). Three groups of animals were treated: 1. control group (saline and sham irradiation); 2. GdCl3 + 30 Gy radiation group and 3. 30 Gy radiation only group. Specimens were collected at 2, 6, 12, 24 and 48 h after completion of each treatment. Liver tissue was assessed for inflammatory cytokine expression and radiation-induced SEC injury based on serum hyaluronic acid (HA) level, apoptosis and ultrastructural and histological analyses. The results showed that radiation exposure caused apoptosis of SECs, but not hepatocytes. Inflammatory cytokine expression, including tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) expression, was significantly attenuated in the GdCl3 + 30 Gy radiation group, compared with the 30 Gy radiation-only group (P < 0.05). The GdCl3 + radiation-treated rats exhibited significantly lower levels of HA and SEC apoptosis than the radiation-treated only rats at early time points, and radiation-induced liver injury was also attenuated. In conclusion, we hypothesize that selective Kupffer cell inhibition by gadolinium chloride was shown to reduce apoptosis in SECs caused by irradiation of the live and protected the liver against radiation-induced injury.

Endothelial perturbations and therapeutic strategies in normal tissue radiation damage

Most cancer patients are treated with radiotherapy, but the treatment can also damage the surrounding normal tissue. Radiotherapy side-effects diminish patients’ quality of life, yet effective biological interventions for normal tissue damage are lacking. Protecting microvascular endothelial cells from the effects of irradiation is emerging as a targeted damage-reduction strategy. We illustrate the concept of the microvasculature as a mediator of overall normal tissue radiation toxicity through cell death, vascular inflammation (hemodynamic and molecular changes) and a change in functional capacity. Endothelial cell targeted therapies that protect against such endothelial cell perturbations and the development of acute normal tissue damage are mostly under preclinical development. Since acute radiation toxicity is a common clinical problem in cutaneous, gastrointestinal and mucosal tissues, we also focus on damage in these tissues.

Application of human bone marrow-derived mesenchymal stem cells in the treatment of radiation-induced Gastrointestinal syndrome

Nuclear accidents and terrorism present a serious threat for mass casualty. Accidental or intended radiation exposure leads to radiation-induced gastrointestinal (GI) syndrome. However, currently there are no approved medical countermeasures for GI syndrome. Thus, developing novel treatments for GI syndrome is urgent. Mesenchymal stem cells (MSCs) derived from bone marrow are a subset of multipotent adult somatic stem cells that have the ability to undergo self-renewal, proliferation and pluripotent differentiation. MSCs have advantages over other stem cells; they can be easily isolated from patients or donors, readily expanded ex vivo, and they possess reparative and immunomodulatory properties. Moreover, MSCs have been shown to be powerful tools in gene therapy and can be effectively transduced with vectors containing therapeutic genes. Therefore, the therapeutic potential of MSCs has been brought into the spotlight for the clinical treatment of GI syndrome. In this review, we discuss the possible role of MSCs in radiation-induced GI syndrome.

Bioactive lipids and the control of Bax pro-apoptotic activity

Lipids are key regulators of cell physiology through the control of many aspects of cellular life and survival. In particular, lipids have been implicated at different levels and through many different mechanisms in the cell death program called apoptosis. Here, we discuss the action of lipids in the regulation of the activation and the integration of Bax into the mitochondrial outer membrane, a key pro-apoptotic member of the BCL-2 family. We describe how, during apoptosis, lipids can act simultaneously or in parallel as receptors or ligands for Bax to stimulate or inhibit its pro-death activity.

Ceramide signaling in mammalian epidermis

Ceramide, the backbone structure of all sphingolipids, as well as a minor component of cellular membranes, has a unique role in the skin, by forming the epidermal permeability barrier at the extracellular domains of the outermost layer of the skin, the stratum corneum, which is required for terrestrial mammalian survival. In contrast to the role of ceramide in forming the permeability barrier, the signaling roles of ceramide and its metabolites have not yet been recognized. Ceramide and/or its metabolites regulate proliferation, differentiation, and apoptosis in epidermal keratinocytes. Recent studies have further demonstrated that a ceramide metabolite, sphingosine-1-phosphate, modulates innate immune function. Ceramide has already been applied to therapeutic approaches for treatment of eczema associated with attenuated epidermal permeability barrier function. Pharmacological modulation of ceramide and its metabolites' signaling can also be applied to cutaneous disease prevention and therapy. The author here describes the signaling roles of ceramide and its metabolites in mammalian cells and tissues, including the epidermis. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Adenoviral transduction of human acid sphingomyelinase into neo-angiogenic endothelium radiosensitizes tumor cure

These studies define a new mechanism-based approach to radiosensitize tumor cure by single dose radiotherapy (SDRT). Published evidence indicates that SDRT induces acute microvascular endothelial apoptosis initiated via acid sphingomyelinase (ASMase) translocation to the external plasma membrane. Ensuing microvascular damage regulates radiation lethality of tumor stem cell clonogens to effect tumor cure. Based on this biology, we engineered an ASMase-producing vector consisting of a modified pre-proendothelin-1 promoter, PPE1(3x), and a hypoxia-inducible dual-binding HIF-2α-Ets-1 enhancer element upstream of the asmase gene, inserted into a replication-deficient adenovirus yielding the vector Ad5H2E-PPE1(3x)-ASMase. This vector confers ASMase over-expression in cycling angiogenic endothelium in vitro and within tumors in vivo, with no detectable enhancement in endothelium of normal tissues that exhibit a minute fraction of cycling cells or in non-endothelial tumor or normal tissue cells. Intravenous pretreatment with Ad5H2E-PPE1(3x)-ASMase markedly increases SDRT cure of inherently radiosensitive MCA/129 fibrosarcomas, and converts radiation-incurable B16 melanomas into biopsy-proven tumor cures. In contrast, Ad5H2E-PPE1(3x)-ASMase treatment did not impact radiation damage to small intestinal crypts as non-dividing small intestinal microvessels did not overexpress ASMase and were not radiosensitized. We posit that combination of genetic up-regulation of tumor microvascular ASMase and SDRT provides therapeutic options for currently radiation-incurable human tumors.

Tie2(+) bone marrow endothelial cells regulate hematopoietic stem cell regeneration following radiation injury

Hematopoietic stem cells (HSCs) reside in proximity to bone marrow endothelial cells (BM ECs) and maintenance of the HSC pool is dependent upon EC-mediated c-kit signaling. Here, we used genetic models to determine whether radioprotection of BM ECs could facilitate hematopoietic regeneration following radiation-induced myelosuppression. We developed mice bearing deletion of the proapoptotic proteins, BAK and BAX, in Tie2(+) ECs and HSCs (Tie2Bak/Bax(Fl/-) mice) and compared their hematopoietic recovery following total body irradiation (TBI) with mice which retained Bax in Tie2(+) cells. Mice bearing deletion of Bak and Bax in Tie2(+) cells demonstrated protection of BM HSCs, preserved BM vasculature, and 100% survival following lethal dose TBI. In contrast, mice that retained Bax expression in Tie2(+) cells demonstrated depletion of BM HSCs, disrupted BM vasculature, and 10% survival post-TBI. In a complementary study, VEcadherinBak/Bax(Fl/-) mice, which lack Bak and Bax in VEcadherin(+) ECs, also demonstrated increased recovery of BM stem/progenitor cells following TBI compared to mice which retained Bax in VEcadherin(+) ECs. Importantly, chimeric mice that lacked Bak and Bax in HSCs but retained Bak and Bax in BM ECs displayed significantly decreased HSC content and survival following TBI compared to mice lacking Bak and Bax in both HSCs and BM ECs. These data suggest that the hematopoietic response to ionizing radiation is dependent upon HSC-autonomous responses but is regulated by BM EC-mediated mechanisms. Therefore, BM ECs may be therapeutically targeted as a means to augment hematopoietic reconstitution following myelosuppression.

A novel radioprotective function for the mitochondrial tumor suppressor protein Fus1

FUS1/TUSC2 is a mitochondrial tumor suppressor with activity to regulate cellular oxidative stress by maintaining balanced ROS production and mitochondrial homeostasis. Fus1 expression is inhibited by ROS, suggesting that individuals with a high level of ROS may have lower Fus1 in normal tissues and, thus, may be more prone to oxidative stress-induced side effects of cancer treatment, including radiotherapy. As the role of Fus1 in the modulation of cellular radiosensitivity is unknown, we set out to determine molecular mechanisms of Fus1 involvement in the IR response in normal tissues. Mouse whole-body irradiation methodology was employed to determine the role for Fus1 in the radiation response and explore underlying molecular mechanisms. Fus1(-/-) mice were more susceptible to radiation compared with Fus1(+/+) mice, exhibiting increased mortality and accelerated apoptosis of the GI crypt epithelial cells. Following untimely reentrance into the cell cycle, the Fus1(-/-) GI crypt cells died at accelerated rate via mitotic catastrophe that resulted in diminished and/or delayed crypt regeneration after irradiation. At the molecular level, dysregulated dynamics of activation of main IR response proteins (p53, NFκB, and GSK-3β), as well as key signaling pathways involved in oxidative stress response (SOD2, PRDX1, and cytochrome c), apoptosis (BAX and PARP1), cell cycle (Cyclins B1 and D1), and DNA repair (γH2AX) were found in Fus1(-/-) cells after irradiation. Increased radiosensitivity of other tissues, such as immune cells and hair follicles was also detected in Fus1(-/-) mice. Our findings demonstrate a previously unknown radioprotective function of the mitochondrial tumor suppressor Fus1 in normal tissues and suggest new individualized therapeutic approaches based on Fus1 expression.

Crypt base columnar stem cells in small intestines of mice are radioresistant

BACKGROUND & AIMS

Adult stem cells have been proposed to be quiescent and radiation resistant, repairing DNA double-strand breaks by nonhomologous end joining. However, the population of putative small intestinal stem cells (ISCs) at position +4 from the crypt base contradicts this model, in that they are highly radiosensitive. Cycling crypt base columnar cells (CBCs) at crypt positions +1-3 recently were defined as an alternative population of ISCs. Little is known about the sensitivity of this stem cell population to radiation.

METHODS

Radiation-induced lethality of CBCs was quantified kinetically in Lgr5-lacZ transgenic mice. γ-H2AX, BRCA1, RAD51, and DNA-PKcs foci were used as DNA repair surrogates to investigate the inherent ability of CBCs to recognize and repair double-strand breaks. 5-ethynyl-2'-deoxyuridine and 5-bromo-2'-deoxyuridine incorporation assays were used to study patterns of CBC growth arrest and re-initiation of cell cycling. Apoptosis was evaluated by caspase-3 staining.

RESULTS

CBCs are relatively radioresistant, repairing DNA by homologous recombination significantly more efficiently than transit amplifying progenitors or villus cells. CBCs undergo apoptosis less than 24 hours after irradiation (32% ± 2% of total lethality) or mitotic death at 24-48 hours. Survival of CBCs at 2 days predicts crypt regeneration at 3.5 days and lethality from gastrointestinal syndrome. Crypt repopulation originates from CBCs that survive irradiation.

CONCLUSIONS

Adult ISCs in mice can cycle rapidly yet still be radioresistant. Importantly, homologous recombination can protect adult stem cell populations from genotoxic stress. These findings broaden and refine concepts of the phenotype of adult stem cells.

Vascular Strategies for Enhancing Tumour Response to Radiation Therapy

Radiation therapy is prescribed to more than 50% of patients diagnosed with cancer. Although mechanisms of interaction between radiation and tumour cells are well understood on a molecular level, much remains uncertain concerning the interaction of radiation with the tumour as a whole. Recent studies have demonstrated that single large doses of radiation (8–20 Gy) may primarily target tumour endothelial cells, leading to secondary tumour clonogenic cell death. These studies suggest that blood vessels play an important role in radiation response. As a result, various strategies have been proposed to effectively combine radiation with vascular targeting agents. While most proposed schemes focus on methods to disrupt tumour blood vessels, recent evidence supporting that some anti-angiogenic agents may “normalize” tumour blood vessels, in turn enhancing tumour oxygenation and radiosensitivity, indicates that there may be more efficient strategies. Furthermore, vascular targeting agents have recently been demonstrated to enhance radiation therapy by targeting endothelial cells. When combined with radiation, these agents are believed to cause even more localized vascular destruction followed by tumour clonogenic cell death. Taken together, it is now crucial to elucidate the role of tumour blood vessels in radiation therapy response, in order to make use of this knowledge in developing therapeutic strategies that target tumour vasculature above and beyond classic clonogenic tumour cell death. In this report, we review some major developments in understanding the importance of tumour blood vessels during radiation therapy. A discussion of current imaging modalities used for studying vascular response to treatments will also be presented.

PAI-1-dependent endothelial cell death determines severity of radiation-induced intestinal injury

Normal tissue toxicity still remains a dose-limiting factor in clinical radiation therapy. Recently, plasminogen activator inhibitor type 1 (SERPINE1/PAI-1) was reported as an essential mediator of late radiation-induced intestinal injury. However, it is not clear whether PAI-1 plays a role in acute radiation-induced intestinal damage and we hypothesized that PAI-1 may play a role in the endothelium radiosensitivity. In vivo, in a model of radiation enteropathy in PAI-1 −/− mice, apoptosis of radiosensitive compartments, epithelial and microvascular endothelium was quantified. In vitro, the role of PAI-1 in the radiation-induced endothelial cells (ECs) death was investigated. The level of apoptotic ECs is lower in PAI-1 −/− compared with Wt mice after irradiation. This is associated with a conserved microvascular density and consequently with a better mucosal integrity in PAI-1 −/− mice. In vitro, irradiation rapidly stimulates PAI-1 expression in ECs and radiation sensitivity is increased in ECs that stably overexpress PAI-1, whereas PAI-1 knockdown increases EC survival after irradiation. Moreover, ECs prepared from PAI-1 −/− mice are more resistant to radiation-induced cell death than Wt ECs and this is associated with activation of the Akt pathway. This study demonstrates that PAI-1 plays a key role in radiation-induced EC death in the intestine and suggests that this contributes strongly to the progression of radiation-induced intestinal injury.

Anti-ceramide antibody prevents the radiation gastrointestinal syndrome in mice

Radiation gastrointestinal (GI) syndrome is a major lethal toxicity that may occur after a radiation/nuclear incident. Currently, there are no prophylactic countermeasures against radiation GI syndrome lethality for first responders, military personnel, or remediation workers entering a contaminated area. The pathophysiology of this syndrome requires depletion of stem cell clonogens (SCCs) within the crypts of Lieberkühn, which are a subset of cells necessary for postinjury regeneration of gut epithelium. Recent evidence indicates that SCC depletion is not exclusively a result of DNA damage but is critically coupled to ceramide-induced endothelial cell apoptosis within the mucosal microvascular network. Here we show that ceramide generated on the surface of endothelium coalesces to form ceramide-rich platforms that transmit an apoptotic signal. Moreover, we report the generation of 2A2, an anti-ceramide monoclonal antibody that binds to ceramide to prevent platform formation on the surface of irradiated endothelial cells of the murine GI tract. Consequently, we found that 2A2 protected against endothelial apoptosis in the small intestinal lamina propria and facilitated recovery of crypt SCCs, preventing the death of mice from radiation GI syndrome after high radiation doses. As such, we suggest that 2A2 represents a prototype of a new class of anti-ceramide therapeutics and an effective countermeasure against radiation GI syndrome mortality.

ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs--threshold doses for tissue reactions in a radiation protection context

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It was instigated following a recommendation in Publication 103 (ICRP, 2007), and it provides updated estimates of 'practical' threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the haematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40-50years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. A variety of biological response modifiers have been used to help reduce late reactions in many tissues. These include antioxidants, radical scavengers, inhibitors of apoptosis, anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, growth factors, and cytokines. In many cases, these give dose modification factors of 1.1-1.2, and in a few cases 1.5-2, indicating the potential for increasing threshold doses in known exposure cases. In contrast, there are agents that enhance radiation responses, notably other cytotoxic agents such as antimetabolites, alkylating agents, anti-angiogenic drugs, and antibiotics, as well as genetic and comorbidity factors. Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events. For these two tissues, a threshold dose of 0.5Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgement further.

TLR9 agonist protects mice from radiation-induced gastrointestinal syndrome

Purpose

Radiation-induced gastrointestinal syndrome (RIGS) is due to the clonogenic loss of crypt cells and villi depopulation, resulting in disruption of mucosal barrier, bacterial invasion, inflammation and sepsis. Intestinal macrophages could recognize invading bacterial DNA via TLR9 receptors and transmit regenerative signals to the neighboring crypt. We therefore investigated whether systemic administration of designer TLR9 agonist could ameliorate RIGS by activating TLR9.

Methods and Materials

Male C57Bl6 mice were distributed in four experimental cohorts, whole body irradiation (WBI) (8.4–10.4 Gy), TLR9 agonist (1 mg/kg s.c.), 1 h pre- or post-WBI and TLR9 agonist+WBI+iMyd88 (pretreatment with inhibitory peptide against Myd88). Animals were observed for survival and intestine was harvested for histological analysis. BALB/c mice with CT26 colon tumors in abdominal wall were irradiated with 14 Gy single dose of whole abdominal irradiation (AIR) for tumor growth study.

Results

Mice receiving pre-WBI TLR9 agonist demonstrated improvement of survival after 10.4 Gy (p<0.03), 9.4 Gy (p<0.008) and 8.4 Gy (p<0.002) of WBI, compared to untreated or iMyd88-treated controls. Post-WBI TLR9 agonist mitigates up to 8.4 Gy WBI (p<0.01). Histological analysis and xylose absorption test demonstrated significant structural and functional restitution of the intestine in WBI+TLR9 agonist cohorts. Although, AIR reduced tumor growth, all animals died within 12 days from RIGS. TLR9 agonist improved the survival of mice beyond 28 days post-AIR (p<0.008) with significant reduction of tumor growth (p<0.0001).

Conclusions

TLR9 agonist treatment could serve both as a prophylactic or mitigating agent against acute radiation syndrome and also as an adjuvant therapy to increase the therapeutic ratio of abdominal Radiation Therapy for Gastro Intestinal malignancies.

Radiation-induced damage in different segments of the rat intestine after external beam irradiation of the liver

INTRODUCTION

The out-of-field effects on the intestine, caused by radiation treatment of a parenchymatous organ, have not previously been studied.

METHODS

A single dose of 25Gy was administered percutaneously to the liver of male Wistar rats after a planning CT-scan. Sham-irradiated animals served as controls. At 1, 6, 24, 96h, 1.5 and 3months the duodenum, jejunum, ileum and distal colon were removed, washed and deep-frozen or prepared for paraffin staining.

RESULTS

All animals survived the treatment. Epithelial cell damage occurred in all small-intestinal segments. However, prolonged denudation of the villi together with destruction of the crypt lining was only observed in the ileum, resulting in deficient regeneration. In the colon, changes were minor. Radiation mucositis with granulocyte (MP0+) infiltration was seen from 1 to 24h in the duodenum and jejunum, when ED1+ macrophages, CD3+ T-lymphocytes, and CD34+ hematopoietic precursor cells were recruited, accompanied by an increase in the chemokines MCP-1, MIP-1α, MIP3α and Il-8. In the ileum, early granulocyte infiltration was delayed but continuous. Recruitment of macrophages and lymphocytes was deficient and induction of chemokines as of the adhesion molecules PECAM-1, ICAM-1 was lacking.

CONCLUSION

Post-irradiation damage to the ileum was delayed and followed by an altered repair process with structural changes of the villi. The observed changes might result from a higher sensitivity to oxidative stress mechanisms with subsequent damage of the regenerative capacity of the crypt-villus axis, accompanied by a sustained "inflammatory response" and vascular damage with a lack of regeneratory cell recruitment.

Tumor control outcomes after hypofractionated and single-dose stereotactic image-guided intensity-modulated radiotherapy for extracranial metastases from renal cell carcinoma

PURPOSE

To report tumor local progression-free outcomes after treatment with single-dose, image-guided, intensity-modulated radiotherapy and hypofractionated regimens for extracranial metastases from renal cell primary tumors.

PATIENTS AND METHODS

Between 2004 and 2010, 105 lesions from renal cell carcinoma were treated with either single-dose, image-guided, intensity-modulated radiotherapy to a prescription dose of 18-24 Gy (median, 24) or hypofractionation (three or five fractions) with a prescription dose of 20-30 Gy. The median follow-up was 12 months (range, 1-48).

RESULTS

The overall 3-year actuarial local progression-free survival for all lesions was 44%. The 3-year local progression-free survival for those who received a high single-dose (24 Gy; n = 45), a low single-dose (<24 Gy; n = 14), or hypofractionation regimens (n = 46) was 88%, 21%, and 17%, respectively (high single dose vs. low single dose, p = .001; high single dose vs. hypofractionation, p < .001). Multivariate analysis revealed the following variables were significant predictors of improved local progression-free survival: 24 Gy dose compared with a lower dose (p = .009) and a single dose vs. hypofractionation (p = .008).

CONCLUSION

High single-dose, image-guided, intensity-modulated radiotherapy is a noninvasive procedure resulting in high probability of local tumor control for metastatic renal cell cancer generally considered radioresistant according to the classic radiobiologic ranking.

Sphingosine-1-phosphate activates the AKT pathway to protect small intestines from radiation-induced endothelial apoptosis

A previous in vitro study showed that sphingosine-1-phosphate (S1P), a ceramide antagonist, preserved endothelial cells in culture from radiation-induced apoptosis. We proposed to validate the role of S1P in tissue radioprotection by inhibiting acute gastrointestinal (GI) syndrome induced by endothelial cell apoptosis after high dose of radiation. Retro-orbital S1P was injected in mice exposed to 15 Gy, a dose-inducing GI syndrome within 10 days. Overall survival and apoptosis on intestines sections were studied. Intestinal cell type targeted by S1P and early molecular survival pathways were researched using irradiated in vitro cell models and in vivo mouse models. We showed that retro-orbital S1P injection before irradiation prevented GI syndrome by inhibiting endothelium collapse. We defined endothelium as a specific therapeutic target because only these cells and not intestinal epithelial cells, or B and T lymphocytes, were protected. Pharmacologic approaches using AKT inhibitor and pertussis toxin established that S1P affords endothelial cell protection in vitro and in vivo through a mechanism involving AKT and 7-pass transmembrane receptors coupled to Gi proteins. Our results provide strong pharmacologic and mechanistic proofs that S1P protects endothelial cells against acute radiation enteropathy.

Endothelial membrane remodeling is obligate for anti-angiogenic radiosensitization during tumor radiosurgery

Background

While there is significant interest in combining anti-angiogenesis therapy with conventional anti-cancer treatment, clinical trials have as of yet yielded limited therapeutic gain, mainly because mechanisms of anti-angiogenic therapy remain to a large extent unknown. Currently, anti-angiogenic tumor therapy is conceptualized to either “normalize” dysfunctional tumor vasculature, or to prevent recruitment of circulating endothelial precursors into the tumor. An alternative biology, restricted to delivery of anti-angiogenics immediately prior to single dose radiotherapy (radiosurgery), is provided in the present study.

Methodology/Principal Findings

Genetic data indicate an acute wave of ceramide-mediated endothelial apoptosis, initiated by acid sphingomyelinase (ASMase), regulates tumor stem cell response to single dose radiotherapy, obligatory for tumor cure. Here we show VEGF prevented radiation-induced ASMase activation in cultured endothelium, occurring within minutes after radiation exposure, consequently repressing apoptosis, an event reversible with exogenous C₁₆-ceramide. Anti-VEGFR2 acts conversely, enhancing ceramide generation and apoptosis. In vivo, MCA/129 fibrosarcoma tumors were implanted in asmase^+/+ mice or asmase^−/− littermates and irradiated in the presence or absence of anti-VEGFR2 DC101 or anti-VEGF G6-31 antibodies. These anti-angiogenic agents, only if delivered immediately prior to single dose radiotherapy, de-repressed radiation-induced ASMase activation, synergistically increasing the endothelial apoptotic component of tumor response and tumor cure. Anti-angiogenic radiosensitization was abrogated in tumors implanted in asmase^−/− mice that provide apoptosis-resistant vasculature, or in wild-type littermates pre-treated with anti-ceramide antibody, indicating that ceramide is necessary for this effect.

Conclusions/Significance

These studies show that angiogenic factors fail to suppress apoptosis if ceramide remains elevated while anti-angiogenic therapies fail without ceramide elevation, defining a ceramide rheostat that determines outcome of single dose radiotherapy. Understanding the temporal sequencing of anti-angiogenic drugs and radiation enables optimized radiosensitization and design of innovative radiosurgery clinical trials.

Bone marrow transplantation in mice as a tool for studying the role of hematopoietic cells in metabolic and cardiovascular diseases

Hematopoietic cells have been established as major players in cardiovascular disease, with an important role in the etiology of atherosclerotic plaque. In addition, hematopoietic cells, and in particular the cells of monocyte and macrophage lineages, have recently been unmasked as one of the main causes of metabolic abnormalities leading to insulin resistance and type 2 diabetes. With the availability of transgenic mouse models that reproduce many aspects of these diseases, research in these areas has been able to make exceptional progress. Much of the work exploring the role of hematopoietic cells has been carried out on chimeric mice made by the recipient disease model mice being given donor bone marrow cells from transgenic mice harboring a genetic alteration in a relevant pathway. Here, we will describe the potential of the bone marrow transplantation approach and discuss recent developments, including the use of virally transduced cells. We will explain some of the caveats, their effect on the experimental outcomes, and some possible solutions. Taken as a whole, this technology offers great advantages in efficiency and cost-effectiveness, and it is expected to continue to be a crucial technique in cardiovascular research work.

A new class of molecular targeted radioprotectors: GSK-3beta inhibitors

PURPOSE

Development of new treatments is critical to effective protection against radiation-induced injury. We investigate the potential of developing small-molecule inhibitors of glycogen synthase kinase 3beta (GSK-3beta)-SB216763 or SB415286-as radioprotective agents to attenuate intestinal injury.

METHODS AND MATERIALS

A survival study was done by use of C57BL/6J mice to evaluate the radioprotective effect of GSK-3beta inhibitors. Terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay and immunohistochemical staining for Bax and Bcl-2 were used to assess apoptosis in the small intestines of the treated mice. A clonogenic survival study, apoptosis assays (staining with annexin V or 4',6-diamidino-2-phenylindole), and immunoblot analysis of beta-catenin, Bcl-2, Bax, and caspase 3 were done by use of Rat intestinal epithelial cell line IEC-6 cells.

RESULTS

Pretreatment with SB415286 significantly improved survival of mice irradiated with 8 and 12 Gy. Mice pretreated with SB216763 or SB415286 showed a significant reduction in TUNEL- and Bax-positive cells and an increase in Bcl-2-positive cells in intestinal crypts at 4 and/or 12 h after radiation with 4 and/or 8 Gy compared with radiation alone. Pretreatment of irradiated IEC-6 cells with GSK-3beta inhibitors significantly increased clonogenic survival compared with cells treated with radiation alone. This increase was due to the attenuation of radiation-induced apoptosis, as shown by annexin V and 4',6-diamidino-2-phenylindole assays, as well as immunoblot analysis of Bcl-2, Bax, and caspase 3.

CONCLUSIONS

Glycogen synthase kinase 3beta small-molecule inhibitors protect mouse intestine from radiation-induced damage in cell culture and in vivo and improve survival of mice. Molecular mechanisms of this protection involve attenuated radiation-induced apoptosis regulated by Bcl-2, Bax, and caspase 3. Therefore GSK-3beta inhibitors reduce deleterious consequences of intestinal irradiation and thereby improve quality of life during radiation therapy.

p53 controls radiation-induced gastrointestinal syndrome in mice independent of apoptosis

Acute exposure to ionizing radiation can cause lethal damage to the gastrointestinal (GI) tract, a condition called the GI syndrome. Whether the target cells affected by radiation to cause the GI syndrome are derived from the epithelium or endothelium and whether the target cells die by apoptosis or other mechanisms are controversial issues. Studying mouse models, we found that selective deletion of the proapoptotic genes Bak1 and Bax from the GI epithelium or from endothelial cells did not protect mice from developing the GI syndrome after sub-total-body gamma irradiation. In contrast, selective deletion of p53 from the GI epithelium, but not from endothelial cells, sensitized irradiated mice to the GI syndrome. Transgenic mice overexpressing p53 in all tissues were protected from the GI syndrome after irradiation. These results suggest that the GI syndrome is caused by the death of GI epithelial cells and that these epithelial cells die by a mechanism that is regulated by p53 but independent of apoptosis.

Regulation of ceramide synthase-mediated crypt epithelium apoptosis by DNA damage repair enzymes

Acute endothelial cell apoptosis and microvascular compromise couple gastrointestinal tract irradiation to reproductive death of intestinal crypt stem cell clonogens (SCCs) following high-dose radiation. Genetic or pharmacologic inhibition of endothelial apoptosis prevents intestinal damage, but as the radiation dose is escalated, SCCs become directly susceptible to an alternate cell death mechanism, mediated via ceramide synthase (CS)-stimulated de novo synthesis of the proapoptotic sphingolipid ceramide, and p53-independent apoptosis of crypt SCCs. We previously reported that ataxia-telangiectasia mutated deficiency resets the primary radiation lethal pathway, allowing CS-mediated apoptosis at the low-dose range of radiation. The mechanism for this event, termed target reordering, remains unknown. Here, we show that inactivation of DNA damage repair pathways signals CS-mediated apoptosis in crypt SCCs, presumably via persistent unrepaired DNA double-strand breaks (DSBs). Genetic loss of function of sensors and transducers of DNA DSB repair confers the CS-mediated lethal pathway in intestines of sv129/B6Mre11(ATLD1/ATLD1) and C57BL/6(Prkdc/SCID) (severe combined immunodeficient) mice exposed to low-dose radiation. In contrast, CS-mediated SCC lethality was mitigated in irradiated gain-of-function Rad50(s/s) mice, and epistasis studies order Rad50 upstream of Mre11. These studies suggest unrepaired DNA DSBs as causative in target reordering in intestinal SCCs. As such, we provide an in vivo model of DNA damage repair that is standardized, can be exploited to understand allele-specific regulation in intact tissue, and is pharmacologically tractable.

Cytolytic T cells induce ceramide-rich platforms in target cell membranes to initiate graft-versus-host disease

Alloreactive donor cytolytic T lymphocytes play a critical role in pathophysiology of acute graft-versus-host disease (GVHD). As GVHD progression involves tumor necrosis factor superfamily receptor activation, and as apoptotic signaling for some tumor necrosis factor superfamily receptors might involve acid sphingomyelinase (ASMase)-mediated ceramide generation, we hypothesized that ASMase deletion would ameliorate GVHD. Using clinically relevant mouse models of acute GVHD in which allogeneic bone marrow and T cells were transplanted into asmase+/+ and asmase(-/-) hosts, we identify host ASMase as critical for full-blown GVHD. Lack of host ASMase reduced the acute inflammatory phase of GVHD, attenuating cytokine storm, CD8+ T-cell proliferation/activation, and apoptosis of relevant graft-versus-host target cells (hepatocytes, intestinal, and skin cells). Organ injury was diminished in asmase(-/-) hosts, and morbidity and mortality improved at 90 days after transplantation. Resistance to cytolytic T lymphocyte-induced apoptosis was found at the target cell membrane if hepatocytes lack ASMase, as hepatocyte apoptosis required target cell ceramide generation for formation of ceramide-rich macrodomains, sites concentrating proapoptotic Fas. These studies indicate a requirement for target cell ASMase in evolution of GVHD in liver, small intestines, and skin and provide potential new targets for disease management.

The somatostatin analog SOM230 (pasireotide) ameliorates injury of the intestinal mucosa and increases survival after total-body irradiation by inhibiting exocrine pancreatic secretion

Somatostatin analogs ameliorate intestinal injury after localized irradiation. This study investigated whether SOM230, a novel, metabolically stable analog with broad receptor affinity, reduces intestinal injury and lethality in mice exposed to total-body irradiation (TBI). Male CD2F1 mice were exposed to 7-15 Gy TBI. Twice-daily administration of SOM230 (1, 4 or 10 mg/kg per day) or vehicle was started either 2 days before or 4 h after TBI and continued for either 14 or 21 days. Parameters of intestinal and hematopoietic radiation injury, bacterial translocation, and circulating cytokine levels were assessed. Animal survival was monitored for up to 30 days. SOM230 increased survival (P < 0.001) and prolonged survival time (P < 0.001) whether administration was initiated before or after TBI. There was no benefit from administration for 21 compared to 14 days. The survival benefit of SOM230 was completely reversed by co-administration of pancreatic enzymes (P = 0.009). Consistent with the presumed non-cytoprotective mechanism of action, SOM230 did not influence hematopoietic injury or intestinal crypt lethality. However, SOM230 preserved mucosal surface area (P < 0.001) and reduced bacterial translocation in a dose-dependent manner (P < 0.001). Circulating IL-12 levels were reduced in SOM230-treated mice (P = 0.007). No toxicity from SOM230 was observed. SOM230 enhances animal survival whether administration begins before or after TBI; i.e., it is effective both as a protector and as a mitigator. The mechanism likely involves reduction of intraluminal pancreatic enzymes. Because of its efficacy and favorable safety profile, SOM230 is a promising countermeasure against radiation and should undergo further development.

gamma-Tocotrienol ameliorates intestinal radiation injury and reduces vascular oxidative stress after total-body irradiation by an HMG-CoA reductase-dependent mechanism

Analogs of vitamin E (tocols) are under development as radioprophylactic agents because of their high efficacy and lack of toxicity. Gamma-tocotrienol (GT3) is of particular interest because, in addition to being an antioxidant, it also inhibits 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and accumulates to greater extent in endothelial cells than other tocols. We addressed in vivo whether HMG-CoA reductase inhibition contributes to the radioprotection conferred by GT3. Groups of mice were treated with vehicle, mevalonate (the product of the reaction catalyzed by HMG-CoA reductase), GT3 alone or GT3 in combination with mevalonate. Lethality and standard parameters of injury to the hematopoietic, intestinal and vascular/endothelial systems were assessed after exposure to total-body irradiation. GT3 improved postirradiation survival and decreased radiation-induced vascular oxidative stress, an effect that was reversible by mevalonate. GT3 also enhanced hematopoietic recovery, reduced intestinal radiation injury, and accelerated the recovery of soluble markers of endothelial function. These parameters were not reversed by mevalonate co-administration. Our data confirm GT3's radioprophylactic properties against hematopoietic injury and, for the first time, demonstrate benefits in terms of protection against gastrointestinal and vascular injury. The radioprotective efficacy of GT3 against vascular injury is related to its properties as an HMG-CoA reductase inhibitor.

Suppression of apoptosis, crypt hyperplasia, and altered differentiation in the colonic epithelia of bak-null mice

BACKGROUND & AIMS

Members of the bcl-2 family of proteins are important determinants of cell fate. Bcl-2 and bcl-w have previously been identified as antiapoptotic members of this family that promote gastrointestinal epithelial cell survival. However, a proapoptotic family member that exerts important effects in the gastrointestinal tract has not yet been identified. We have therefore investigated intestinal epithelial apoptosis in bak-null mice.

METHODS

Apoptosis, mitosis, differentiated cell composition, and cell number were assessed on a cell positional basis in the small intestinal and colonic epithelia of bak-null mice and their C57BL/6 wild-type counterparts. Apoptosis was induced by 1-Gy gamma-irradiation or 10mg/kg azoxymethane (AOM). Aberrant crypt foci were induced by 3 weekly injections of 10mg/kg AOM.

RESULTS

The amount of spontaneous apoptosis in the colonic intercrypt table was reduced, and colonic crypt cell number and mitotic index were elevated in bak-null mice relative to C57BL/6 wild-type mice. Bak-null colonic crypts contained more goblet cells and fewer endocrine cells than those from C57BL/6 mice. Fewer colonic epithelial apoptotic cells were observed after gamma-radiation and AOM in bak-null mice, and these mice also displayed greater numbers of colonic AOM-induced aberrant crypt foci. None of these parameters differed in the small intestinal epithelium of bak-null mice compared with C57BL/6.

CONCLUSIONS

Bak prevents colonic crypt hyperplasia by regulating spontaneous apoptosis at the colonic intercrypt table region and also regulates damage-induced apoptosis in the colonic crypt. Deletion of bak in vivo results in altered colonic proliferation and differentiation, and causes increased susceptibility to colonic carcinogenesis.