Role of mast cells in early and delayed radiation injury in rat intestine

Radiation-Induced Intestinal Injury: Injury Mechanism and Potential Treatment Strategies

Radiation-induced intestinal injury (RIII) is one of the most common intestinal complications caused by radiotherapy for pelvic and abdominal tumors and it seriously affects the quality of life of patients. However, the treatment of acute RIII is essentially symptomatic and nutritional support treatment and an ideal means of prevention and treatment is lacking. Researchers have conducted studies at the cellular and animal levels and found that some chemical or biological agents have good therapeutic effects on RIII and may be used as potential candidates for clinical treatment. This article reviews the injury mechanism and potential treatment strategies based on cellular and animal experiments to provide new ideas for the diagnosis and treatment of RIII in clinical settings.

The effects of radiation on myeloid lineage immune cells within the rodent urinary bladder: a systematic review

PURPOSE

Radiotherapy is a prominent therapy for many malignant and non-malignant disorders, though it can cause side effects such as radiation-induced cystitis. Current research has highlighted a role for mast cells and macrophages in the prognosis of such radiation-induced toxicities. However, the prognostic value of these immune cells in the pathophysiology of radiation-induced cystitis is not clear. As such, a systematic review was conducted to assess myeloid-lineage immune cells for their prognostic value in radiation-induced cystitis to address this gap in literature.

METHODS

The protocol was registered in PROSPERO, and searches were performed in PubMed, Embase and Web of Science databases for pre-clinical rodent studies on radiation-induced cystitis.

RESULTS

After de-duplication, 153 articles were screened for relevancy by title and abstract. Title and abstract screening deemed 64 studies irrelevant. The remaining 85 studies were full-text screened, yielding seven unique articles for data extraction. Most included studies had an unclear risk of bias. The findings of this systematic review suggest that the prognostic value of myeloid-lineage immune cells in radiation-induced cystitis is still unclear, indicating a need for further research in this field.

CONCLUSION

Although the studies reviewed provide some insight into the role of these immune cells in disease pathology, the limited number of studies and unclear risk of bias further highlights a need for additional, high-quality research in this area. In summary, this systematic review highlights a need to understand the involvement of immune cells in radiation-induced cystitis pathophysiology and lay the groundwork for further research in this area.

TRIAL REGISTRATION

PROSPERO registration: CRD42022345960.

Prostate Cancer Radiotherapy: Increased Biochemical Control and Late Toxicity in Men With Medication Allergies

Background

Given similarities in the mediators of medication allergy (MA) and tissue response to radiotherapy, we assessed whether outcomes following prostate radiotherapy differ in patients with MAs.

Methods

A total 587 men with known MA history and nonmetastatic prostate cancer underwent radiotherapy from 1989 to 2006. Clinicopathologic and treatment variables were analyzed for association with freedom from biochemical failure (FFBF) and late treatment–related, physician-defined Radiation Therapy Oncology Group gastrointestinal (GI) and genitourinary (GU) toxicity. Covariates identified on univariate analysis for toxicity and disease control were examined on multivariable analysis. All statistical tests were 2-sided, and a P less than .05 was considered statistically significant.

Results

A total of 155 of 587 men (26.4%) had 1 or more MAs, most commonly to penicillin (n = 71), sulfa (n = 35), and aspirin or nonsteroidal antiinflammatory drugs (n = 28). On univariate analysis, men with MAs had superior 10-y FFBF (71.5% vs 63.5%, P = .02) and higher incidence of late GI grade 2 or higher (G2+; 20.6% vs 13.2%, P = .04) and grade 3 or higher (G3+; 7.5% vs 3.9%, P = .08) as well as late GU G2+ (42.5% vs 33.2%, P = .04) and G3+ (7.5% vs 3.0%, P = .02) toxicity than men without MAs. On multivariable analysis, MA history remained a statistically significant predictor of FFBF (hazard ratio [HR] = 0.64, 95% confidence interval [CI] = 0.43 to 0.93, P = .02), late G2+ GI (HR = 1.76, 95% CI = 1.06 to 2.90, P=.03), and G3+ GU (HR = 2.69, 95% CI = 1.16 to 6.27, P = .02) toxicity after controlling for corresponding covariates in each model.

Conclusions

Men with MAs had improved FFBF and increased treatment-related toxicity following radiotherapy for prostate cancer. MA history could be a relevant consideration in the management of men with localized prostate cancer.

NZO/HlLtJ as a novel model for the studies on the role of metabolic syndrome in acute radiation toxicity

Purpose: Growing rates of metabolic syndrome and associated obesity warrant the development of appropriate animal models for better understanding of how those conditions may affect sensitivity to IR exposure.Materials and methods: We subjected male NZO/HlLtJ mice, a strain prone to spontaneous obesity and diabetes, to 0, 5.5, 6.37, 7.4 or 8.5 Gy (137Cs) of total body irradiation (TBI). Mice were monitored for 30 days, after which proximal jejunum and colon tissues were collected for further histological and molecular analysis.Results: Obese NZO/HlLtJ male mice are characterized by their lower sensitivity to IR at doses of 6.37 Gy and under, compared to other strains. Further escalation of the dose, however, results in a steep survival curve, reaching LD100/30 values at a dose of 8.5 Gy. Alterations in the expression of various tight junction-related proteins coupled with activation of inflammatory responses and cell death were the main contributors to the gastrointestinal syndrome.Conclusions: We demonstrate that metabolic syndrome with exhibited hyperglycemia but without alterations to the microvasculature is not a pre-requisite of the increased sensitivity to TBI at high doses. Our studies indicate the potential of NZO/HlLtJ mice for the studies on the role of metabolic syndrome in acute radiation toxicity.

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

Exposure of the gastrointestinal (GI) tract to ionizing radiation can cause acute and delayed injury. However, critical cellular targets that regulate the development of radiation-induced GI injury remain incompletely understood. Here, we investigated the role of vascular endothelial cells in controlling acute and delayed GI injury after total-abdominal irradiation (TAI). To address this, we used genetically engineered mice in which endothelial cells are sensitized to radiation due to the deletion of the tumor suppressor p53. Remarkably, we found that VE-cadherin-Cre; p53^FL/FL mice, in which both alleles of p53 are deleted in endothelial cells, were not sensitized to the acute GI radiation syndrome, but these mice were highly susceptible to delayed radiation enteropathy. Histological examination indicated that VE-cadherin-Cre; p53^FL/FL mice that developed delayed radiation enteropathy had severe vascular injury in the small intestine, which was manifested by hemorrhage, loss of microvessels and tissue hypoxia. In addition, using dual-energy CT imaging, we showed that VE-cadherin-Cre; p53^FL/FL mice had a significant increase in vascular permeability of the small intestine in vivo 28 days after TAI. Together, these findings demonstrate that while sensitization of endothelial cells to radiation does not exacerbate the acute GI radiation syndrome, it is sufficient to promote the development of late radiation enteropathy.

Histopathological Features of the Development of Intestine and Mesenteric Lymph Node Injury in a Nonhuman Primate Model of Partial-body Irradiation with Minimal Bone Marrow Sparing

Male rhesus macaques were subjected to partial-body irradiation at 10, 11, or 12 Gy with 5% bone marrow protection. Animals were euthanized when dictated by prospectively determined clinical parameters or at approximately 180 d following irradiation. Histological sections of jejunum, colon, and mesenteric lymph node were stained with hematoxylin and eosin as well as a battery of histochemical and immunohistochemical stains. The immediate postirradiation histopathological alterations in the jejunum and colon were based primarily on injury to rapidly proliferating crypt epithelial cells, though there was evidence of additional radiation-induced fibrogenic responses. There was substantial resolution of the radiation-related mucosal injury through the observation period, but microscopically visible defects in mucosal structure persisted to the end of the observation period. In the later stages of the observation period, the jejunum and colon had overt fibrosis that was most commonly located in the submucosa and serosa, with less microscopically discernible involvement of the mucosa. Mesenteric lymph nodes had an immediate postirradiation reduction in cellularity due to the known effects of irradiation on lymphoid cell populations. In later stages of the observation period the lymph nodes also developed fibrotic changes, possibly related to transmigration of immunomodulatory cells and/or signaling molecules from the radiation-damaged intestine.

Interleukin 6 Signaling Blockade Exacerbates Acute and Late Injury From Focal Intestinal Irradiation

PURPOSE

To evaluate the acute changes in leukocyte populations after focal irradiation and to assess the role of interleukin 6 (IL-6) in acute and late radiation injury.

METHODS AND MATERIALS

Mice were surgically implanted with a radiopaque marker on the surface of the small intestine. Mice were then imaged with cone beam computed tomography to locate the marker and irradiated with 18 Gy of 5 × 5 mm collimated x-rays onto the marked intestine using the Small Animal Radiation Research Platform. Intestinal sections and blood were harvested 1, 3.5, 7, and 14 days and 2 months postirradiation (post-IR) for histology and complete blood count, respectively. Immune cell populations were assessed by immunofluorescence in the acute phase. Collagen deposition was assessed 2 months post-IR. IL-6^-/- intestinal sections were assessed post-IR for morphology, EdU, Ki67, and TUNEL in comparison to IL-6^+/+ mice. Furthermore, a set of IL-6^+/+ mice were treated with anti-IL-6R to assess the role of IL-6 in late intestinal injury.

RESULTS

Intestinal radiation damage peaked 14 days post-IR, and fibrosis had developed by 60 days post-IR. There was a marked infiltration of immune cells into the irradiated intestine, with increased neutrophils, macrophages, B-cells, and CD4⁺ T cells maintained from 3.5 to 14 days post-IR. CD8⁺ T cells were decreased from days 7 to 14 post-IR. Systemically, leukocytes were increased in the peripheral blood 14 days post-IR with anemia being maintained from 14 days to 2 months. IL-6 was significantly increased in the serum post-IR. IL-6^-/- mice demonstrated worsened intestinal injury acutely post-IR. Moreover, anti-IL-6R-treated mice presented with worsened intestinal fibrosis 2 months post-IR.

CONCLUSIONS

Focal irradiation of the intestine produced a significant increase in immune cells in the irradiated area and systemic inflammation and anemia. Blockade of IL-6 signaling was found to exacerbate acute intestinal injury and late intestinal injury after focal irradiation.

Utility of polaprezinc in reducing toxicities during radiotherapy: a literature review

Chemoradiotherapy is important for treating malignancies. However, radiation-induced toxicities develop as chemoradiotherapy-related complications. Various agents reduce or prevent toxicities, but there are no standard treatments. Polaprezinc (PZ), a chelating compound used for gastric ulcers, has antioxidant and free radical scavenging effects. Although few studies have evaluated PZ and radiation-induced normal tissue damage, several clinical studies have shown the efficacy of PZ for oral mucositis, esophagitis, proctitis and taste alterations during and after radiotherapy. Moreover, preclinical data support the clinical data, indicating good potential of testing PZ in future trials. However, as there are only few well-documented review articles on PZ use in cancer treatment, we conducted this literature review. PZ reduced several radiation-induced toxicities and improved the quality of life.

Radiation-induced pulmonary gene expression changes are attenuated by the CTGF antibody Pamrevlumab

BACKGROUND

Fibrosis is a delayed side effect of radiation therapy (RT). Connective tissue growth factor (CTGF) promotes the development of fibrosis in multiple settings, including pulmonary radiation injury.

METHODS

To better understand the cellular interactions involved in RT-induced lung injury and the role of CTGF in these responses, microarray expression profiling was performed on lungs of irradiated and non-irradiated mice, including mice treated with the anti-CTGF antibody pamrevlumab (FG-3019). Between group comparisons (Welch's t-tests) and principal components analyses were performed in Genespring.

RESULTS

At the mRNA level, the ability of pamrevlumab to prolong survival and ameliorate RT-induced radiologic, histologic and functional lung deficits was correlated with the reversal of a clear enrichment in mast cell, macrophage, dendritic cell and mesenchymal gene signatures. Cytokine, growth factor and matrix remodeling genes that are likely to contribute to RT pneumonitis and fibrosis were elevated by RT and attenuated by pamrevlumab, and likely contribute to the cross-talk between enriched cell-types in injured lung.

CONCLUSIONS

CTGF inhibition had a normalizing effect on select cell-types, including immune cells not typically regarded as being regulated by CTGF. These results suggest that interactions between RT-recruited cell-types are critical to maintaining the injured state; that CTGF plays a key role in this process; and that pamrevlumab can ameliorate RT-induced lung injury in mice and may provide therapeutic benefit in other immune and fibrotic disorders.

Silibinin attenuates radiation-induced intestinal fibrosis and reverses epithelial-to-mesenchymal transition

Radiotherapy is a common treatment for cancer patients, but its use is often restricted by the tolerance of normal tissue. As cancer patients live longer, delayed radiation effects on normal tissue have become a concern. Radiation-induced enteropathy, including inflammatory bowel disease and fibrosis, are major issues for long-term cancer survivors. To investigate whether silibinin attenuates delayed radiation-induced intestinal injury in mice, we focused on intestinal fibrotic changes. Silibinin improved delayed radiation injuries in mice in association with decreased collagen deposition within the intestines and deceased transforming growth factor (TGF)-β1 levels in the intestine and plasma. Treating mice bearing CT26 mouse colon cancer tumors with both silibinin and radiation stimulated tumor regression more than radiation alone. We also investigated the effect of silibinin on the radiation-induced epithelial-to-mesenchymal transition (EMT), the primary mechanism of fibrosis. We assessed changes in E-cadherin, N-cadherin, and α-smooth muscle actin expression, and demonstrated that silibinin attenuates radiation-induced EMT. Irradiating intestinal epithelial cells increased TGF-β1 levels, but silibinin suppressed TGF-β1 expression by inhibiting Smad2/3 phosphorylation. These results suggest silibinin has the potential to serve as a useful therapeutic agent in patients with radiation-induced intestinal fibrosis.

Hesperidin as Radioprotector against Radiation-induced Lung Damage in Rat: A Histopathological Study

Reactive oxygen species (ROS) are generated by ionizing radiation, and one of the organs commonly affected by ROS is the lung. Radiation-induced lung injury including pneumonia and lung fibrosis is a dose-limiting factor in radiotherapy (RT) of patients with thorax irradiation. Administration of antioxidants has been proved to protect against ROS. The present study was aimed to assess the protective effect of hesperidin (HES) against radiation-induced lung injury of male rats. Fifty rats were divided into three groups. G1: Received no HES and radiation (sham). G2: Underwent γ-irradiation to the thorax. G3: Received HES and underwent γ-irradiation. The rats were exposed to a single dose of 18 Gy using cobalt-60 unit and were administered HES (100 mg/kg) for 7 days before irradiation. Histopathological analysis was performed 24 h and 8 weeks after RT. Histopathological results in 24 h showed radiation-induced inflammation and presence of more inflammatory cells as compared to G1 (P < 0.05). Administration of HES significantly decreased such an effect when compared to G2 (P < 0.05). Histopathological evaluation in 8 weeks showed a significant increase in mast cells, inflammation, inflammatory cells, alveolar thickness, vascular thickness, pulmonary edema, and fibrosis in G2 when compared to G1 (P < 0.05). HES significantly decreased inflammatory response, fibrosis, and mast cells when compared to G2 (P < 0.05). Administration of HES resulted in decreased radiation pneumonitis and radiation fibrosis in the lung tissue. Thus, the present study showed HES to be an efficient radioprotector against radiation-induced damage in the lung of tissue rats.

Modeling of chronic radiation-induced cystitis in mice

Purpose

Radiation cystitis (RC), a severe inflammatory bladder condition, develops as a side effect of pelvic radiation therapy in cancer patients. There are currently no effective therapies to treat RC, in part from the lack of preclinical model systems. In this study, we developed a mouse model for RC and used a Small Animal Radiation Research Platform to simulate the targeted delivery of radiation as used with human patients.

Methods and materials

To induce RC, C3H mice received a single radiation dose of 20 Gy delivered through 2 beams. Mice were subjected to weekly micturition measurements to assess changes in urinary frequency. At the end of the study, bladder tissues were processed for histology.

Results

Radiation was well-tolerated; no change in weight was observed in the weeks after treatment, and there was no hair loss at the irradiation sites. Starting at 17 weeks after treatment, micturition frequency was significantly higher in irradiated mice versus control animals. Pathological changes include fibrosis, inflammation, urothelial thinning, and necrosis. At a site of severe insult, we observed telangiectasia, absence of uroplakin-3 and E-cadherin relocalization.

Conclusions

We developed an RC model that mimics the human pathology and functional changes. Furthermore, radiation exposure attenuates the urothelial integrity long-term, allowing for potential continuous irritability of the bladder wall from exposure to urine. Future studies will focus on the underlying molecular changes associated with this condition and investigate novel treatment strategies.

Palmitoylethanolamide regulates development of intestinal radiation injury in a mast cell-dependent manner

BACKGROUND

Mast cells and neuroimmune interactions regulate the severity of intestinal radiation mucositis, a dose-limiting toxicity during radiation therapy of abdominal malignancies.

AIM

Because endocannabinoids (eCB) regulate intestinal inflammation, we investigated the effect of the cannabimimetic, palmitoylethanolamide (PEA), in a mast competent (+/+) and mast cell-deficient (Ws/Ws) rat model.

METHODS

Rats underwent localized, fractionated intestinal irradiation, and received daily injections with vehicle or PEA from 1 day before until 2 weeks after radiation. Intestinal injury was assessed noninvasively by luminol bioluminescence, and, at 2 weeks, by histology, morphometry, and immunohistochemical analysis, gene expression analysis, and pathway analysis.

RESULTS

Compared with +/+ rats, Ws/Ws rats sustained more intestinal structural injury (p = 0.01), mucosal damage (p = 0.02), neutrophil infiltration (p = 0.0003), and collagen deposition (p = 0.004). PEA reduced structural radiation injury (p = 0.02), intestinal wall thickness (p = 0.03), collagen deposition (p = 0.03), and intestinal inflammation (p = 0.02) in Ws/Ws rats, but not in +/+ rats. PEA inhibited mast cell-derived cellular immune response and anti-inflammatory IL-6 and IL-10 signaling and activated the prothrombin pathway in +/+ rats. In contrast, while PEA suppressed nonmast cell-derived immune responses, it increased anti-inflammatory IL-10 and IL-6 signaling and decreased activation of the prothrombin pathway in Ws/Ws rats.

CONCLUSIONS

These data demonstrate that the absence of mast cells exacerbate radiation enteropathy by mechanisms that likely involve the coagulation system, anti-inflammatory cytokine signaling, and the innate immune system; and that these mechanisms are regulated by PEA in a mast cell-dependent manner. The eCB system should be explored as target for mitigating intestinal radiation injury.

Radiation enteropathy--pathogenesis, treatment and prevention

Changes in cancer incidence and mortality have been modest during the past several decades, but the number of cancer survivors has almost tripled during the same period. With an increasing cohort of cancer survivors, efforts to prevent, diagnose and manage adverse effects of cancer therapy, in general, and those of radiation therapy specifically, have intensified. Many cancer survivors have undergone radiation therapy of tumours in the pelvis or abdomen, thus rendering the bowel at risk of injury. In fact, the current prevalence of patients who have long-term radiation-induced intestinal adverse effects exceeds that of IBD. Considerable progress towards reducing toxicity of radiation therapy has been made by the introduction of so-called dose-sculpting treatment techniques, which enable precise delivery of the radiation beam. Moreover, new insights into the underlying pathophysiology have resulted in an improved understanding of mechanisms of radiation-induced bowel toxicity and in development of new diagnostic strategies and management opportunities. This Review discusses the pathogenesis of early and delayed radiation-induced bowel toxicity, presents current management options and outlines priorities for future research. By adding insight into molecular and cellular mechanisms of related bowel disorders, gastroenterologists can substantially strengthen these efforts.

Inflammation and immunity in radiation damage to the gut mucosa

Erythema was observed on the skin of the first patients treated with radiation therapy. It is in particular to reduce this erythema, one feature of tissue inflammation, that prescribed dose to the tumor site started to be fractionated. It is now well known that radiation exposure of normal tissues generates a sustained and apparently uncontrolled inflammatory process. Radiation-induced inflammation is always observed, often described, sometimes partly explained, but still today far from being completely understood. The thing with the gut and especially the gut mucosa is that it is at the frontier between the external milieu and the organism, is in contact with a plethora of commensal and foreign antigens, possesses a dense-associated lymphoid tissue, and is particularly radiation sensitive because of a high mucosal turnover rate. All these characteristics make the gut mucosa a strong responsive organ in terms of radiation-induced immunoinflammation. This paper will focus on what has been observed in the normal gut and what remains to be done concerning the immunoinflammatory response following localized radiation exposure.

Mast cells and ionizing radiation induce a synergistic expression of inflammatory genes in endothelial cells by a mechanism involving p38α MAP kinase and (p65) NF-κB activation

Vascular endothelium is a key compartment involved in the development of normal tissue toxicity associated with cancer radiation therapy, i.e., acute inflammation and late fibrosis. Radiation-induced endothelial cell activation has been extensively studied, and activated endothelial cells are characterized by increased expression of inflammatory mediators and adhesion molecules, and activation of the coagulation and thrombosis pathways. However, little is known about the role of vascular endothelium interaction with resident immune cells, such as mast cells on its response to irradiation. Here, we report that endothelial exposure to mast cell conditioned medium and irradiation induces a synergistic expression of many inflammatory genes including interleukin-6 and interleukin-8, CXCL2 and E-selectin. This synergy is blocked by the histamine H1 receptor antagonist mepyramine and partially mimicked by exogenous histamine addition before irradiation. Using pharmacological and molecular inhibition approaches, we show the p38α MAP kinase and p65 (NF-κB) dependence of the synergy. Moreover, our data show a link between both pathways, with p65 (NF-κB) being downstream of p38. These data highlight the possible exacerbation of the radiation-induced endothelial inflammatory response by its interactions with immune cells. It also suggest that p38α MAP kinase and p65 (NF-κB) inhibition in vascular endothelium may limit excessive tissue inflammation induced by radiation therapy, and thereby limit the associated acute and late tissue damage.

Animal models of intestinal fibrosis: new tools for the understanding of pathogenesis and therapy of human disease

Fibrosis is a serious condition complicating chronic inflammatory processes affecting the intestinal tract. Advances in this field that rely on human studies have been slow and seriously restricted by practical and logistic reasons. As a consequence, well-characterized animal models of intestinal fibrosis have emerged as logical and essential systems to better define and understand the pathophysiology of fibrosis. In point of fact, animal models allow the execution of mechanistic studies as well as the implementation of clinical trials with novel, pathophysiology-based therapeutic approaches. This review provides an overview of the currently available animal models of intestinal fibrosis, taking into consideration the methods of induction, key characteristics of each model, and underlying mechanisms. Currently available models will be classified into seven categories: spontaneous, gene-targeted, chemical-, immune-, bacteria-, and radiation-induced as well as postoperative fibrosis. Each model will be discussed in regard to its potential to create research opportunities to gain insights into the mechanisms of intestinal fibrosis and stricture formation and assist in the development of effective and specific antifibrotic therapies.

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.

Mast cells are an essential component of human radiation proctitis and contribute to experimental colorectal damage in mice

Radiation proctitis is characterized by mucosal inflammation followed by adverse chronic tissue remodeling and is associated with substantial morbidity and mortality. Mast cell hyperplasia has been associated with diseases characterized by pathological tissue remodeling and fibrosis. Rectal tissue from patients treated with radiotherapy shows mast cell hyperplasia and activation, suggesting that these cells play a role in the development of radiation-induced sequelae. To investigate the role of mast cells in radiation damage, experimental radiation proctitis was induced in a mast cell-deficient (W(sh)/W(sh)) mouse model. The colon and rectum of W(sh)/W(sh) and wild-type mice were exposed to 27-Gy single-dose irradiation and studied after 2 and 14 weeks. Irradiated rodent rectum showed mast cell hyperplasia. W(sh)/W(sh) mice developed less acute and chronic rectal radiation damage than their control littermates. Tissue protection was associated with increased tissue neutrophil influx and expression of several inflammatory mediators immediately after radiation exposure. It was further demonstrated that mast cell chymase, tryptase, and histamine could change human muscularis propria smooth muscle cells into a migrating/proliferating and proinflammatory phenotype. These data show that mast cells have deleterious effects on both acute and chronic radiation proctitis, possibly by limiting acute tissue neutrophil influx and by favoring phenotypic orientation of smooth muscle cells, thus making them active participants in the radiation-induced inflammatory process and dystrophy of the rectal wall.

Activation of protease activated receptor 2 by exogenous agonist exacerbates early radiation injury in rat intestine

PURPOSE

Protease-activated receptor-2 (PAR(2)) is highly expressed throughout the gut and regulates the inflammatory, mitogenic, fibroproliferative, and nociceptive responses to injury. PAR(2) is strikingly upregulated and exhibits increased activation in response to intestinal irradiation. We examined the mechanistic significance of radiation enteropathy development by assessing the effect of exogenous PAR(2) activation.

METHODS AND MATERIALS

Rat small bowel was exposed to localized single-dose radiation (16.5 Gy). The PAR(2) agonist (2-furoyl-LIGRLO-NH(2)) or vehicle was injected intraperitoneally daily for 3 days before irradiation (before), for 7 days after irradiation (after), or both 3 days before and 7 days after irradiation (before-after). Early and delayed radiation enteropathy was assessed at 2 and 26 weeks after irradiation using quantitative histologic examination, morphometry, and immunohistochemical analysis.

RESULTS

The PAR(2) agonist did not elicit changes in the unirradiated (shielded) intestine. In contrast, in the irradiated intestine procured 2 weeks after irradiation, administration of the PAR(2) agonist was associated with more severe mucosal injury and increased intestinal wall thickness in all three treatment groups (p <.05) compared with the vehicle-treated controls. The PAR(2) agonist also exacerbated the radiation injury score, serosal thickening, and mucosal inflammation (p <.05) in the before and before-after groups. The short-term exogenous activation of PAR(2) did not affect radiation-induced intestinal injury at 26 weeks.

CONCLUSION

The results of the present study support a role for PAR(2) activation in the pathogenesis of early radiation-induced intestinal injury. Pharmacologic PAR(2) antagonists might have the potential to reduce the intestinal side effects of radiotherapy and/or as countermeasures in radiologic accidents or terrorism scenarios.

Genome-wide transcriptomic profiling of microdissected human breast tissue reveals differential expression of KIT (c-Kit, CD117) and oestrogen receptor-alpha (ERalpha) in response to therapeutic radiation

The pathogenesis of late normal tissue fibrosis after high-dose ionizing radiation involves multiple cell types and signalling pathways but is not well understood. To identify the molecular changes occurring after radiotherapy, paired normal tissue samples were collected from the non-irradiated breast and from the treated breast of women who had undergone curative radiotherapy for early breast cancer months or years previously. As radiation may induce distinct transcriptional changes in the different components of the breast, laser capture microdissection and gene expression microarray profiling were performed separately for epithelial and stromal components and selected genes were validated using immunohistochemistry. In the epithelial compartment, a reduction of KIT (c-Kit; CD117) and a reciprocal increase in ESR1 (oestrogen receptor-alpha, ERalpha) mRNA and protein levels were seen in irradiated compared to non-irradiated samples. In the stromal compartment, extracellular matrix genes including FN1 (fibronectin 1) and CTGF (connective tissue growth factor; CCN2) were increased. Further investigation revealed that c-Kit and ERalpha were expressed in distinct subpopulations of luminal epithelial cells. Interlobular c-Kit-positive mast cells were also increased in irradiated cases not showing features of post-radiation atrophy. Pathway analysis revealed 'cancer, reproductive system disease and tumour morphology' as the most significantly enriched network in the epithelial compartment, whereas in the stromal component, a significant enrichment for 'connective tissue disorders, dermatological diseases and conditions, genetic disorder' and 'cancer, tumour morphology, infection mechanism' networks was observed. These data identify previously unreported changes in the epithelial compartment and show altered expression of genes implicated in late normal tissue injury in the stromal compartment of normal breast tissue. The findings are relevant to both fibrosis and atrophy occurring after radiotherapy for early breast cancer.

Ionizing radiation induces degranulation of human mast cells and release of tryptase

PURPOSE

Skin fibrosis is a hallmark of ionizing radiation-induced tissue injury and we hypothesized that mast cells via their products (especially tryptase) are involved in this event. We therefore investigated whether: (i) irradiation with 5 Gray (Gy) is able to induce the release of the typical mast cell mediator tryptase from human mast cells (HMC-1) in vitro, (ii) this effect can be influenced by application of clinically relevant mast cell blockers, and (iii) irradiation leads to mast cell degranulation in ex vivo skin culture models.

MATERIALS AND METHODS

The human mast cell line (HMC)-1, as well as ex vivo skin tissue served as experimental models. Fluorescence activated cell sorting (FACS), Enzyme linked immunosorbent assays (ELISA), mast cell degranulation assays and immunohistochemistry were applied.

RESULTS

Ionizing radiation induces a time-dependent, statistically significant increase in the release of tryptase by HMC-1 cultured in vitro. Mast cell degranulation and secretion of tryptase was partially, but not significantly, inhibited by pre-incubation with the histamine-1 receptor (H1) blocker cetirizine. Mast cell degranulation was also clearly evident after irradiation using an ex vivo skin culture model of mastocytoma tissue.

CONCLUSIONS

We propose that ionizing radiation leads to a degranulation of dermal mast cells, an event which is accompanied by the release of tryptase.

Specific signals involved in the long-term maintenance of radiation-induced fibrogenic differentiation: a role for CCN2 and low concentration of TGF-beta1

The fibrogenic differentiation of resident mesenchymal cells is a key parameter in the pathogenesis of radiation fibrosis and is triggered by the profibrotic growth factors transforming growth factor (TGF)-beta1 and CCN2. TGF-beta1 is considered the primary inducer of fibrogenic differentiation and is thought to control its long-term maintenance, whereas CCN2 is considered secondary effector of TGF-beta1. Yet, in long-term established fibrosis like that associated with delayed radiation enteropathy, in situ TGF-beta1 deposition is low, whereas CCN2 expression is high. To explore this apparent paradox, cell response to increasing doses of TGF-beta1 was investigated in cells modeling initiation and maintenance of fibrosis, i.e., normal and fibrosis-derived smooth muscle cells, respectively. Activation of cell-specific signaling pathways by low TGF-beta1 doses was demonstrated with a main activation of the Rho/ROCK pathway in fibrosis-derived cells, whereas the Smad pathway was mainly activated in normal cells. This leads to subsequent and cell-specific regulation of the CCN2 gene. These results suggested a specific profibrotic role of CCN2 in fibrosis-initiated cells. Furthermore, the modulation of CCN2 expression by itself and the combination of TGF-beta1 and CCN2 was investigated in fibrosis-derived cells. In fibrosis-initiated cells CCN2 triggered its autoinduction; furthermore, low concentration of TGF-beta1-potentiated CCN2 autoinduction. Our findings showed a differential requirement and action of TGF-beta1 in the fibrogenic response of normal vs. fibrosis-derived cells. This study defines a novel Rho/ROCK but Smad3-independent mode of TGF-beta signaling that may operate during the chronic stages of fibrosis and provides evidence of both specific and combinatorial roles of low TGF-beta1 dose and CCN2.

Pravastatin Inhibits the Rho/CCN2/extracellular matrix cascade in human fibrosis explants and improves radiation-induced intestinal fibrosis in rats

PURPOSES

Intestinal complications after radiotherapy are caused by transmural fibrosis and impair the quality of life of cancer survivors. Radiation fibrosis was considered permanent and irreversible, but recently, its dynamic nature was shown, providing new opportunities for the development of antifibrotic therapies. Among these new targets, we identified the Rho/ROCK pathway and thought to investigate whether pravastatin treatment inhibits Rho pathway activation and elicits an antifibrotic action.

EXPERIMENTAL DESIGN

Rho and ROCK activities were monitored in human explants presenting radiation fibrosis remodeling after incubation with pravastatin. Subsequent modulation of CCN2, type I collagen, and fibronectin expression were assessed ex vivo and in intestinal smooth muscle cells derived from radiation enteropathy. Then, the therapeutic relevance of the antifibrotic action of pravastatin was explored in vivo in a rat model of chronic radiation fibrosis (19 Gy X-rays) treated with 30 mg/kg/d pravastatin in the drinking water.

RESULTS

The results obtained with human explants show that pravastatin specifically inhibits Rho activity in submucosal mesenchymal cells. Pravastatin also elicits ROCK inhibition, and subsequent CCN2 production in human explants and smooth muscle cells isolated from radiation enteropathy. Inhibition of type I collagen and fibronectin does occur, showing that pravastatin modulates the secretory phenotype of mesenchymal cells. Lastly, curative pravastatin administration improves radiation enteropathy in rats. This structural improvement is associated with decreased deposition of CCN2 and subsequent decreased extracellular matrix deposition.

CONCLUSION

Targeting established fibrosis with pravastatin is an efficient and safe antifibrotic strategy in radiation-induced enteropathy, and is easily transferable into the clinic.

Calcitonin gene-related peptide and substance P regulate the intestinal radiation response

PURPOSE

Intestinal toxicity is important in the therapeutic use of radiation as well as in nontherapeutic radiation exposure scenarios. Enteric sensory nerves are critical for mucosal homeostasis and for an appropriate response to injury. This study assessed the role of the two major neuropeptides released by sensory nerves, calcitonin gene-related peptide (CGRP) and substance P, in the intestinal radiation response.

EXPERIMENTAL DESIGN

Male rats received full-length CGRP, CGRP antagonist (CGRP(8-37)), a modified substance P peptide (GR73632), a small-molecule substance P receptor antagonist (neurokinin-1 receptor antagonist, SR140333), or vehicle for 2 weeks after localized X irradiation of a 4-cm loop of small bowel. Structural, cellular, and molecular aspects of the intestinal radiation response were assessed.

RESULTS

Intestinal CGRP and substance P transcript levels increased after irradiation. Multivariate analysis showed that CGRP and SR140333 ameliorated and CGRP(8-37) and GR73632 exacerbated intestinal radiation injury. Univariate analysis revealed increased radiation injury score, bowel wall thickening, and collagen III deposition after treatment with CGRP(8-37), whereas SR140333 ameliorated radiation injury score, loss of mucosal surface area, collagen III deposition, and mucosal inflammation.

CONCLUSIONS

The two major neuropeptides released by sensory neurons, CGRP and substance P, are overexpressed after irradiation and have opposing effects during development of intestinal radiation injury. Systematic studies to assess CGRP agonists and/or neurokinin-1 receptor blockers as protectors against intestinal toxicity during radiation therapy and after nontherapeutic radiation exposure are warranted.

Local administration of interleukin-11 ameliorates intestinal radiation injury in rats

Intestinal radiation injury is dose limiting during abdominal and pelvic radiotherapy and critical for the outcome after accidental whole-body radiation exposure. The multifunctional cytokine, interleukin-11 (IL-11), ameliorates the intestinal radiation response, but its clinical use is hampered by severe toxicity after systemic administration. This study addressed whether protection against intestinal radiation injury can be achieved by intraluminal administration of IL-11. Male rats underwent surgical transposition of a 4-cm small bowel loop to the scrotum. For repeated intraluminal drug administration, an ileostomy, proximal to the bowel loop in the scrotum, was created. The transposed intestinal loop was exposed to 5 Gy fractions on 9 consecutive days. Recombinant human IL-11 (rhIL-11; 2 mg/kg/d) or vehicle was given through the ileostomy from 2 days before until 2 weeks after irradiation. At 2 weeks, structural, cellular, and molecular aspects of intestinal radiation injury were assessed. rhIL-11 ameliorated structural manifestations of radiation enteropathy, including radiation injury score (6.5 +/- 0.6 in the vehicle group versus 4.0 +/- 0.3 in the IL-11 group; P = 0.001), mucosal surface area loss (0.2 +/- 0.1 versus 0.5 +/- 0.03; P < 0.0001), and intestinal wall thickening (842 +/- 66 microm versus 643 +/- 54 microm; P = 0.02), reduced postradiation transforming growth factor-beta overexpression, and reduced numbers of ED2-positive cells. Postirradiation mucosal mast cell numbers were partially restored by rhIL-11. These data show that local administration of rhIL-11 ameliorates early intestinal radiation injury and support further development of rhIL-11 to reduce manifestations of intestinal radiation injury in the clinic.

Neuroimmune interactions: potential target for mitigating or treating intestinal radiation injury

Intestinal radiation injury is characterized by breakdown of the epithelial barrier and mucosal inflammation. In addition to replicative and apoptotic cell death, radiation also induces changes in cellular function, as well as alterations secondary to tissue injury. The recognition of these "non-cytocidal" radiation effects has enhanced the understanding of normal tissue radiation toxicity, thus allowing an integrated systems biology-based approach to modulating radiation responses and providing a mechanistic rationale for interventions to mitigate or treat radiation injuries. The enteric nervous system regulates intestinal motility, blood flow and enterocyte function. The enteric nervous system also plays a central role in maintaining the physiological state of the intestinal mucosa and in coordinating inflammatory and fibroproliferative processes. The afferent component of the enteric nervous system, in addition to relaying sensory information, also exerts important effector functions and contributes critically to preserving mucosal integrity. Interactions between afferent nerves, mast cells as well as other cells of the resident mucosal immune system serve to maintain mucosal homeostasis and to ensure an appropriate response to injury. Notably, enteric sensory neurons regulate the activation threshold of mast cells by secreting substance P, calcitonin gene-related peptide and other neuropeptides, whereas mast cells signal to enteric nerves by the release of histamine, nerve growth factor and other mediators. This article reviews how enteric neurons interact with mast cells and other immune cells to regulate the intestinal radiation response and how these interactions may be modified to mitigate intestinal radiation toxicity. These data are not only applicable to radiation therapy, but also to intestinal injury in a radiological terrorism scenario.

Simvastatin ameliorates radiation enteropathy development after localized, fractionated irradiation by a protein C-independent mechanism

PURPOSE

Microvascular injury plays a key role in normal tissue radiation responses. Statins, in addition to their lipid-lowering effects, have vasculoprotective properties that may counteract some effects of radiation on normal tissues. We examined whether administration of simvastatin ameliorates intestinal radiation injury, and whether the effect depends on protein C activation.

METHODS AND MATERIALS

Rats received localized, fractionated small bowel irradiation. The animals were fed either regular chow or chow containing simvastatin from 2 weeks before irradiation until termination of the experiment. Groups of rats were euthanized at 2 weeks and 26 weeks for assessment of early and delayed radiation injury by quantitative histology, morphometry, and quantitative immunohistochemistry. Dependency on protein C activation was examined in thrombomodulin (TM) mutant mice with deficient ability to activate protein C.

RESULTS

Simvastatin administration was associated with lower radiation injury scores (p < 0.0001), improved mucosal preservation (p = 0.0009), and reduced thickening of the intestinal wall and subserosa (p = 0.008 and p = 0.004), neutrophil infiltration (p = 0.04), and accumulation of collagen I (p = 0.0003). The effect of simvastatin was consistently more pronounced for delayed than for early injury. Surprisingly, simvastatin reduced intestinal radiation injury in TM mutant mice, indicating that the enteroprotective effect of simvastatin after localized irradiation is unrelated to protein C activation.

CONCLUSIONS

Simvastatin ameliorates the intestinal radiation response. The radioprotective effect of simvastatin after localized small bowel irradiation does not appear to be related to protein C activation. Statins should undergo clinical testing as a strategy to minimize side effects of radiation on the intestine and other normal tissues.

Maintenance of radiation-induced intestinal fibrosis: cellular and molecular features

Recent advances in cell and molecular radiobiology clearly showed that tissue response to radiation injury cannot be restricted to a simple cell-killing process, but depends upon continuous and integrated pathogenic processes, involving cell differentiation and crosstalk between the various cellular components of the tissue within the extracellular matrix. Thus, the prior concept of primary cell target in which a single-cell type (whatever it's epithelial or endothelial cells) dictates the whole tissue response to radiation injury has to be replaced by the occurrence of coordinated multicellular response that may either lead to tissue recovery or to sequel development. In this context, the present review will focus on the maintenance of the radiation-induced wound healing and fibrogenic signals triggered by and through the microenvironment toward the mesenchymal cell compartment, and will highlight how sequential and sustained modifications in cell phenotypes will in cascade modify cell-to-cell interactions and tissue composition.

Influence of mast cells on outcome after heterotopic cardiac transplantation in rats

Correlative data suggest that mast cells adversely affect cardiac transplantation. This study uses a mast cell-deficient rat model to directly address the role of mast cells in cardiac allotransplantation. Standardized cardiac heterotopic transplantation with cyclosporine immunosuppression was performed in mast cell-deficient and mast cell-competent rats. Rejection, ischemia, fibrosis, fibrin deposition, numbers of T-cell receptor alpha/beta positive cells, expression of transforming growth factor-beta (TGF-beta), and of endothelin-1 (ET-1) and its receptors ETA and ETB were assessed. Differences in baseline cardiac gene expression were quantified by real-time PCR in a separate group of untransplanted animals. Baseline cardiac gene expression levels of all investigated growth factors, cytokines, ET-1, ETA, and ETB were similar in mast cell-deficient and mast cell-competent rats. Surprisingly, upon heterotopic transplantation, donor heart survival was significantly reduced in mast cell-deficient rats. Moreover, in mast cell-deficient donor hearts rejection was more severe, although nonsignificant, and extracellular matrix associated TGF-beta immunoreactivity was significantly lower than in mast cell-competent donor hearts. Fibrin immunoreactive area, on the other hand, was only increased in mast cell-deficient donor hearts, but not in mast cell-competent donor hearts. Histopathological changes in all donor hearts were accompanied by increased immunoreactivity for ET-1. In conclusion, this study shows that mast cells play a protective role after cardiac transplantation.

Orazipone, a locally acting immunomodulator, ameliorates intestinal radiation injury: a preclinical study in a novel rat model

PURPOSE

Intestinal radiation injury (radiation enteropathy) is relevant to cancer treatment, as well as to radiation accidents and radiation terrorism scenarios. This study assessed the protective efficacy of orazipone, a locally-acting small molecule immunomodulator.

METHODS AND MATERIALS

Male rats were orchiectomized, a 4-cm segment of small bowel was sutured to the inside of the scrotum, a proximal anteperistaltic ileostomy was created for intraluminal drug administration, and intestinal continuity was re-established by end-to-side anastomosis. After three weeks postoperative recovery, the intestine in the "scrotal hernia" was exposed locally to single-dose or fractionated X-radiation. Orazipone (30 mg/kg/day) or vehicle was administered daily through the ileostomy, either during and after irradiation, or only after irradiation. Structural, cellular, and molecular aspects of intestinal radiation toxicity were assessed two weeks after irradiation.

RESULTS

Orazipone significantly ameliorated histologic injury and transforming growth factor-beta immunoreactivity levels, both after single-dose and fractionated irradiation. Intestinal wall thickness was significantly reduced after single-dose and nonsignificantly after fractionated irradiation. Mucosal surface area and numbers of mast cells were partially restored by orazipone after single-dose irradiation.

CONCLUSIONS

This work (1) demonstrates the utility of the ileostomy rat model for intraluminal administration of response modifiers in single-dose and fractionated radiation studies; (2) shows that mucosal immunomodulation during and/or after irradiation ameliorates intestinal toxicity; and (3) highlights important differences between single-dose and fractionated radiation regimens.

Radiotherapy and wound healing

Radiotherapy is an invaluable weapon when treating cancer. However, the deleterious effects of radiation, both immediate and long-term, may have a significant effect on local tissues. Problematic wound healing in radiation-damaged tissue constitutes a major problem that is frequently overlooked during the management of patients who require radiotherapy, or have had radiotherapy in the past. Poor wound healing may lead to chronic ulceration, pain, secondary infection and psychological distress and compromise the outcome of general or reconstructive surgery. We discuss the pathophysiology of poor wound healing following radiotherapy, specific problems for radiation-damaged tissue and potential treatments to improve wound healing of irradiated tissues.

Regulation of early and delayed radiation responses in rat small intestine by capsaicin-sensitive nerves

PURPOSE

Mast cells protect against the early manifestations of intestinal radiation toxicity, but promote chronic intestinal wall fibrosis. Intestinal sensory nerves are closely associated with mast cells, both anatomically and functionally, and serve an important role in the regulation of mucosal homeostasis. This study examined the effect of sensory nerve ablation on the intestinal radiation response in an established rat model.

METHODS AND MATERIALS

Rats underwent sensory nerve ablation with capsaicin or sham ablation. Two weeks later, a localized segment of ileum was X-irradiated or sham irradiated. Structural, cellular, and molecular changes were examined 2 weeks (early injury) and 26 weeks (chronic injury) after irradiation. The mast cell dependence of the effect of sensory nerve ablation on intestinal radiation injury was assessed using c-kit mutant (Ws/Ws) mast cell-deficient rats.

RESULTS

Capsaicin treatment caused a baseline reduction in mucosal mast cell density, crypt cell proliferation, and expression of substance P and calcitonin gene-related peptide, two neuropeptides released by sensory neurons. Sensory nerve ablation strikingly exacerbated early intestinal radiation toxicity (loss of mucosal surface area, inflammation, intestinal wall thickening), but attenuated the development of chronic intestinal radiation fibrosis (collagen I accumulation and transforming growth factor beta immunoreactivity). In mast cell-deficient rats, capsaicin treatment exacerbated postradiation epithelial injury (loss of mucosal surface area), but none of the other aspects of radiation injury were affected by capsaicin treatment.

CONCLUSIONS

Ablation of capsaicin-sensitive enteric neurons exacerbates early intestinal radiation toxicity, but attenuates development of chronic fibroproliferative changes. The effect of capsaicin treatment on the intestinal radiation response is partly mast cell dependent.

Influence of Mast Cells on Structural and Functional Manifestations of Radiation-Induced Heart Disease

Radiation-induced heart disease (RIHD), characterized by accelerated atherosclerosis and adverse tissue remodeling, is a serious sequelae after radiotherapy of thoracic and chest wall tumors. Adverse cardiac remodeling in RIHD and other cardiac disorders is frequently accompanied by mast cell hyperplasia, suggesting that mast cells may affect the development of cardiac fibrosis. This study used a mast cell-deficient rat model to define the role of mast cells in RIHD. Mast cell-deficient rats (Ws/Ws) and mast cell-competent littermate controls (+/+) were exposed to 18 Gy localized single-dose irradiation of the heart. Six months after irradiation, cardiac function was examined by echocardiography and Langendorff-perfused isolated heart preparation, whereas structural changes were assessed using quantitative histology and immunohistochemical analysis. Mast cell-deficient rats exhibited more severe postradiation changes than mast cell-competent littermates. Hence, mast cell-deficient rats exhibited a greater upward/leftward shift in the left ventricular (LV) diastolic pressure-volume relationship (P = 0.001), a greater reduction in in vivo LV diastolic area (from 0.50 +/- 0.024 cm in age-matched controls to 0.24 +/- 0.032 cm after irradiation; P = 0.006), and a greater increase in LV posterior wall thickness (from 0.13 +/- 0.003 cm in age-matched controls to 0.15 +/- 0.003 cm after irradiation; P = 0.04). Structural analysis revealed more pronounced postradiation accumulation of interstitial collagen III but less myocardial degeneration in hearts from mast cell-deficient rats. These data show that the absence of mast cells accelerates the development of functional changes in the irradiated heart, particularly diastolic dysfunction, and suggest that, in contrast to what has been the prevailing assumption, the role of mast cells in RIHD is predominantly protective.

Perspectives on cancer therapy-induced mucosal injury: pathogenesis, measurement, epidemiology, and consequences for patients

BACKGROUND

A frequent complication of anticancer treatment, oral and gastrointestinal (GI) mucositis, threatens the effectiveness of therapy because it leads to dose reductions, increases healthcare costs, and impairs patients' quality of life. The Multinational Association of Supportive Care in Cancer and the International Society for Oral Oncology assembled an international multidisciplinary panel of experts to create clinical practice guidelines for the prevention, evaluation, and treatment of mucositis.

METHODS

The panelists examined medical literature published from January 1966 through May 2002, presented their findings at two separate conferences, and then created a writing committee that produced two articles: the current study and another that codifies the clinical implications of the panel's findings in practice guidelines.

RESULTS

New evidence supports the view that oral mucositis is a complex process involving all the tissues and cellular elements of the mucosa. Other findings suggest that some aspects of mucositis risk may be determined genetically. GI proapoptotic and antiapoptotic gene levels change along the GI tract, perhaps explaining differences in the frequency with which mucositis occurs at different sites. Studies of mucositis incidence in clinical trials by quality and using meta-analysis techniques produced estimates of incidence that are presented herein for what to our knowledge may be a broader range of cancers than ever presented before.

CONCLUSIONS

Understanding the pathobiology of mucositis, its incidence, and scoring are essential for progress in research and care directed at this common side-effect of anticancer therapies.

Up-regulation and activation of proteinase-activated receptor 2 in early and delayed radiation injury in the rat intestine: influence of biological activators of proteinase-activated receptor 2

Proteinase-activated receptor 2 (Par2, F2rl1, also designated PAR-2 or PAR2) is prominently expressed in the intestine and has been suggested as a mediator of inflammatory, mitogenic and fibrogenic responses to injury. Mast cell proteinases and pancreatic trypsin, both of which have been shown to affect the intestinal radiation response, are the major biological activators of Par2. Conventional Sprague-Dawley rats, mast cell-deficient rats, and rats in which pancreatic exocrine secretion was blocked pharmacologically by octreotide underwent localized irradiation of a 4-cm loop of small bowel. Radiation injury was assessed 2 weeks after irradiation (early, inflammatory phase) and 26 weeks after irradiation (chronic, fibrotic phase). Par2 expression and activation were assessed by in situ hybridization and immunohistochemistry, using antibodies that distinguished between total (preactivated and activated) Par2 and preactivated Par2. Compared to unirradiated intestine, irradiated intestine exhibited increased Par2 expression, particularly in areas of myofibroblast proliferation and collagen accumulation, after both single-dose and fractionated irradiation. The majority of Par2 expressed in fibrotic areas was activated. Postirradiation Par2 overexpression was greatly attenuated in both mast cell-deficient and octreotide-treated rats. The severity of acute mucosal injury did not affect postirradiation Par2 expression. Mast cells and pancreatic proteinases may exert their fibro-proliferative effects partly through activation of Par2. Par2 may be a potential target for modulating the intestinal radiation response, particularly delayed intestinal wall fibrosis.

Fibrogenic signals in patients with radiation enteritis are associated with increased connective tissue growth factor expression

PURPOSE

To investigate the expression of a new fibrogenic cytokine the connective tissue growth factor (CTGF) in intestinal radiation fibrosis and to characterize the mesenchymal cell subtypes involved in CTGF synthesis and collagen deposition.

METHODS AND MATERIALS

Sixteen patients with radiation enteritis that occurred after radiotherapy for pelvic malignancies and 6 with histologically normal bowel entered the study. Immunohistochemistry, Western blot analysis, and real-time reverse transcriptase-polymerase chain reaction were performed to study CTGF expression, along with other known markers of radiation fibrosis: the pro-fibrogenic cytokine transforming growth factor (TGF)-beta1 and phenotypic markers of the fibroblast differentiation the alpha-sm actin (A), vimentin (V), and desmin (D). Finally, the collagen accumulation was measured by Sirius red staining and colorimetric assay.

RESULTS

Radiation enteritis was characterized by increased collagen content within the intestinal wall. CTGF immunoreactivity, protein, and mRNA level were increased in radiation enteritis compared with the healthy bowel. On the contrary, no increase of the TGF-beta1 mRNA level was observed in radiation enteritis compared with healthy bowel, and the level of TGF-beta protein was slightly increased in radiation enteritis. A co-localization of CTGF immunoreactivity and collagen deposition was found in the extracellular matrix and subtypes of activated mesenchymal cells with a fibroblast phenotype (V(+)/D(-)/A(-)) and myofibroblast phenotype (V(+)/D(-/+)/A(+)).

CONCLUSION

The increased level of CTGF protein and mRNA associated with the accumulation of fibroblasts/myofibroblasts and collagen deposition were parts of the fibrogenic signals involved in the persistence of late intestinal radiation fibrosis.

Intestinal barrier function

Intestinal barrier function regulates transport and host defense mechanisms at the mucosal interface with the outside world. Transcellular and paracellular fluxes are tightly controlled by membrane pumps, ion channels and tight junctions, adapting permeability to physiological needs. Food and microbial antigens are under constant surveillance of the mucosal immune system. Tolerance against commensals and immunity against pathogens require intact antigen uptake, recognition, processing and response mechanisms. Disturbance at any level, but particularly bacterial translocation due to increased permeability and breakdown of oral tolerance due to compromised epithelial and T cell interaction, can result in inflammation and tissue damage. New therapeutic approaches including probiotics and peptides to restore disrupted barrier function are evolving.

The radiotherapeutic injury--a complex 'wound'

Radiotherapeutic normal tissue injury can be viewed as two simultaneously ongoing and interacting processes. The first has many features in common with the healing of traumatic wounds. The second is a set of transient or permanent alterations of cellular and extracellular components within the irradiated volume. In contrast to physical trauma, fractionated radiation therapy produces a series of repeated insults to tissues that undergo significant changes during the course of radiotherapy. Normal tissue responses are also influenced by rate of dose accumulation and other factors that relate to the radiation therapy schedule. This article reviews the principles of organised normal tissue responses during and after radiation therapy, the effect of radiation therapy on these responses, as well as some of the mechanisms underlying the development of recognisable injury. Important clinical implications relevant to these processes are also discussed.

The recovery of the neurally evoked secretory response of rat colonic mucosa after irradiation is independent of mast cells

The ability of the enteric submucosal plexus to influence the transport of water and electrolytes in the colon was investigated in rats for 1 week after acute whole-body gamma irradiation. The involvement of neuroimmune links in the epithelial responses to nerve stimulation was confirmed by the sensitivity of the tissue to tetrodotoxin, mepyramine and doxantrazole. At 1 and 3 days after irradiation, colon tissues were hyporesponsive to nerve stimulation. This was associated with a drastic diminution of mucosal mast cell numbers, tissue histamine levels, and rat mast cell protease II (RMCP II) levels, and by a decreased maximal epithelial response to exogenously added histamine. The responses to electric-field stimulation were insensitive to both mepyramine and doxantrazole. At 7 days, neurally evoked responses recovered, despite the virtual absence of mast cells, tissue histamine and RMCP II, and the continuing decreased response to histamine. The responses were insensitive to doxantrazole but were decreased by mepyramine. This study showed that the establishment of a normal epithelial response to neural stimulation can occur despite the radiation-induced depletion of mucosal mast cells. The recovery of the epithelial response, which was sensitive to mepyramine, may be ascribed to the reappearance of an unknown histaminergic pathway, which probably has indirect effects on epithelial transport but is independent of nerve-mast cell connections.

Effects of radiation damage on intestinal morphology

The current flow of papers on intestinal structure, radiation science, and intestinal radiation response is reflected in the contents of this review. Multiparameter findings and changes in compartments, cells, or subcellular structure all contribute to the overall profile of the response. The well-recognized changes in proliferation, vessels, and fibrogenesis are accompanied by alterations in other compartments, such as neuroendocrine or immune components of the intestinal wall. The responses at the molecular level, such as in levels of hormones, cytokines, or neurotransmitters, are of fundamental importance. The intestine responds to localized radiation, or to changes in other organs that influence its structure or function: some structural parameters respond differently to different radiation schedules. Apart from radiation conditions, factors affecting the outcome include the pathophysiology of the irradiated subject and accompanying treatment or intervention. More progress in understanding the overall responses is expected in the next few years.

Consequential late effects in normal tissues

Unconventional, more aggressive irradiation protocols are usually associated with aggravation of acute reactions. In recent clinical studies, this has resulted in modulation of late effects in the same organ. This phenomenon has been termed consequential late effect (CLE). Correlations between acute and late effects have been reported in a number of tissues. Moreover, some radiobiological parameters may be used to differentiate between consequential and generic late effects: Dose fractionation and overall treatment time have a similar effect on acute and consequential responses, but opposing effects on generic late effects. Modulation of acute effects will affect the consequential component of late sequelae. Similarly, it will be influenced by the irradiated volume if a volume effect exists for the acute response. Moreover, markers for the acute response should be predictive for consequential effects. The present review gives preclinical and clinical evidence for CLE. These are predominantly found in organ systems where the acute response (of the epithelial lining) is associated with an impairment of the barrier against mechanical or chemical stress, which may cause additional trauma to the underlying tissues. Therefore, CLE are mainly found in the urinary and intestinal system, in mucosa and, to some extent, in skin. In these tissues with a consequential component of the late sequelae, amelioration of the acute response to irradiation may be a useful approach to minimize late side effects of effective radiation therapy.