Relationship between intestinal fibrosis and histopathologic and morphometric changes in consequential and late radiation enteropathy

Association between fibrosis around the tumor and postoperative infectious complication in patients with esophageal cancer who underwent preoperative therapy

BACKGROUND

Multidisciplinary treatment combining chemotherapy, chemo radiation therapy (CRT), and surgery has been utilized for advanced esophageal cancer. However, preoperative treatment could cause postoperative inflammation and complications. We hypothesized that fibrosis surrounding tumor tissue caused by preoperative treatment could induce postoperative systemic inflammation and influence postoperative complications.

METHODS

Surgical specimens from patients with thoracic esophageal cancer who underwent preoperative CRT (38 cases) or chemotherapy (77 cases) and those who received no preoperative treatment (49 cases) were evaluated to measure the fibrotic area adjacent to the tumor (10 mm from the tumor edge) by applying Azan staining. Pleural effusion and peripheral blood serum interleukin-6 levels were analyzed to evaluate local and systemic postoperative inflammation in 37 patients.

RESULTS

The fibrotic areas around the tumors were significantly larger in patients who underwent preoperative CRT than in patients who underwent chemotherapy (p < 0.001) or who had received no preoperative therapy (p < 0.001). Infectious complications were higher in patients who underwent preoperative CRT than chemotherapy (p = 0.047) or surgery alone (p < 0.001). The patients with larger fibrotic areas had more infectious complications (p = 0.028). Multivariate analysis showed that both a large fibrotic area and preoperative CRT were correlated with infectious complications, but not significantly. Pleural effusion interleukin-6 was significantly higher in patients who underwent preoperative CRT than in patients who received no preoperative therapy (p = 0.013).

CONCLUSIONS

A large fibrotic peritumoral esophageal tissue area after preoperative treatment could cause postoperative inflammatory response and infectious complications.

Fecal bacteria-free filtrate transplantation is proved as an effective way for the recovery of radiation-induced individuals in mice

Background

Ionizing radiation can cause intestinal microecological dysbiosis, resulting in changes in the composition and function of gut microbiota. Altered gut microbiota is closely related to the development and progression of radiation-induced intestinal damage. Although microbiota-oriented therapeutic options such as fecal microbiota transplantation (FMT) have shown some efficacy in treating radiation toxicity, safety concerns endure. Therefore, fecal bacteria-free filtrate transplantation (FFT), which has the potential to become a possible alternative therapy, is well worth investigating. Herein, we performed FFT in a mouse model of radiation exposure and monitored its effects on radiation damage phenotypes, gut microbiota, and metabolomic profiles to assess the effectiveness of FFT as an alternative therapy to FMT safety concerns.

Results

FFT treatment conferred radioprotection against radiation-induced toxicity, representing as better intestinal integrity, robust proinflammatory and anti-inflammatory cytokines homeostasis, and accompanied by significant shifts in gut microbiome. The bacterial compartment of recipients following FFT was characterized by an enrichment of radioprotective microorganisms (members of family Lachnospiraceae). Furthermore, metabolome data revealed increased levels of microbially generated short-chain fatty acids (SCFAs) in the feces of FFT mice.

Conclusions

FFT improves radiation-induced intestinal microecological dysbiosis by reshaping intestinal mucosal barrier function, gut microbiota configurations, and host metabolic profiles, highlighting FFT regimen as a promising safe alternative therapy for FMT is effective in the treatment of radiation intestinal injury.

Effects of Gamma-Tocotrienol on Partial-Body Irradiation-Induced Intestinal Injury in a Nonhuman Primate Model

Exposure to high doses of radiation, accidental or therapeutic, often results in gastrointestinal (GI) injury. To date, there are no therapies available to mitigate GI injury after radiation exposure. Gamma-tocotrienol (GT3) is a promising radioprotector under investigation in nonhuman primates (NHP). We have shown that GT3 has radioprotective function in intestinal epithelial and crypt cells in NHPs exposed to 12 Gy total-body irradiation (TBI). Here, we determined GT3 potential in accelerating the GI recovery in partial-body irradiated (PBI) NHPs using X-rays, sparing 5% bone marrow. Sixteen rhesus macaques were treated with either vehicle or GT3 24 h prior to 12 Gy PBI. Structural injuries and crypt survival were examined in proximal jejunum on days 4 and 7. Plasma citrulline was assessed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Crypt cell proliferation and apoptotic cell death were evaluated using Ki-67 and TUNEL staining. PBI significantly decreased mucosal surface area and reduced villous height. Interestingly, GT3 increased crypt survival and enhanced stem cell proliferation at day 4; however, the effects seemed to be minimized by day 7. GT3 did not ameliorate a radiation-induced decrease in citrulline levels. These data suggest that X-rays induce severe intestinal injury post-PBI and that GT3 has minimal radioprotective effect in this novel model.

Effects of Gamma-Tocotrienol on Intestinal Injury in a GI-Specific Acute Radiation Syndrome Model in Nonhuman Primate

The gastrointestinal (GI) system is highly susceptible to irradiation. Currently, there is no Food and Drug Administration (FDA)-approved medical countermeasures for GI radiation injury. The vitamin E analog gamma-tocotrienol (GT3) is a promising radioprotector in mice and nonhuman primates (NHP). We evaluated GT3-mediated GI recovery in total-body irradiated (TBI) NHPs. Sixteen rhesus macaques were divided into two groups; eight received vehicle and eight GT3 24 h prior to 12 Gy TBI. Proximal jejunum was assessed for structural injuries and crypt survival on day 4 and 7. Apoptotic cell death and crypt cell proliferation were assessed with TUNEL and Ki-67 immunostaining. Irradiation induced significant shortening of the villi and reduced mucosal surface area. GT3 induced an increase in crypt depth at day 7, suggesting that more stem cells survived and proliferated after irradiation. GT3 did not influence crypt survival after irradiation. GT3 treatment caused a significant decline in TUNEL-positive cells at both day 4 (p < 0.03) and 7 (p < 0.0003). Importantly, GT3 induced a significant increase in Ki-67-positive cells at day 7 (p < 0.05). These data suggest that GT3 has radioprotective function in intestinal epithelial and crypt cells. GT3 should be further explored as a prophylactic medical countermeasure for radiation-induced GI injury.

Contribution of the Gut Microbiota to Intestinal Fibrosis in Crohn's Disease

In Crohn's disease (CD), intestinal fibrosis is a critical determinant of a patient's prognosis. Although inflammation may be a prerequisite for the initiation of intestinal fibrosis, research shows that the progression or continuation of intestinal fibrosis can occur independently of inflammation. Thus, once initiated, intestinal fibrosis may persist even if medical treatment controls inflammation. Clearly, an understanding of the pathophysiological mechanisms of intestinal fibrosis is required to diminish its occurrence. Accumulating evidence suggests that the gut microbiota contributes to the pathogenesis of intestinal fibrosis. For example, the presence of antibodies against gut microbes can predict which CD patients will have intestinal complications. In addition, microbial ligands can activate intestinal fibroblasts, thereby inducing the production of extracellular matrix. Moreover, in various animal models, bacterial infection can lead to the development of intestinal fibrosis. In this review, we summarize the current knowledge of the link between intestinal fibrosis in CD and the gut microbiota. We highlight basic science and clinical evidence that the gut microbiota can be causative for intestinal fibrosis in CD and provide valuable information about the animal models used to investigate intestinal fibrosis.

Platelet glycoprotein Ibα provides radiation protection

BACKGROUND AND PURPOSE

Platelet membrane glycoprotein Ibα (GPIbα), the major ligand-binding subunit of the GPIb-IX-V complex, binds to a number of ligands contributing to hemostasis, thrombosis, and inflammation. Binding to von Willebrand factor (VWF) initiates the process of hemostasis/thrombosis, while binding to the leukocyte receptor Macrophage-1 antigen (Mac-1) has been implicated in modulating the inflammatory response. Thus as GPIbα resides at the nexus of thrombosis and inflammation, we investigated the impact of GPIbα on radiation injury outcomes as this injury triggers both the thrombotic and inflammatory pathways.

MATERIALS AND METHODS

We used wild-type (WT) C57BL/6J mice and a dysfunctional GPIbα mouse model, in which endogenous GPIbα is replaced with a non-functional α-subunit (hIL-4R/Ibα), to determine whether the impairment of platelet GPIbα alters radiation response. Following exposure to 8.5 Gy total body irradiation (TBI), a series of parameters including radiation lethality, platelet-neutrophil/monocyte interactions, neutrophil/monocyte activation, serum cytokine levels and intestinal injury, were compared between the strains.

RESULTS

The lack of functional GPIbα resulted in higher radiation lethality, greater monocyte activation, increased levels of serum pro-inflammatory cytokines, heightened intestinal damage, and a reduction of intestinal neutrophil recovery.

CONCLUSION

These data suggest that loss of platelet GPIbα enhances radiation toxicity and that GPIbα-mediated interactions may play a crucial role in limiting radiation damage. Thus, a mechanistic understanding of the biological impact of GPIbα following TBI could provide crucial insights for improving the safety of radiotherapy and minimizing the deleterious effects of accidental or occupational exposure to high-dose radiation.

Coenzyme Q10 attenuates inflammation and fibrosis implicated in radiation enteropathy through suppression of NF-kB/TGF-β/MMP-9 pathways

Radiation enteropathy is one the most common clinical issue for patients receiving radiotherapy for abdominal/pelvic tumors which severely affect the quality of life of cancer patients due to dysplastic lesions (ischemia, ulcer, or fibrosis) that aggravate the radiation damage. Herein, this study demonstrated the prophylactic role of coenzyme Q10 (CoQ10), a powerful antioxidant, against radiotherapy-induced gastrointestinal injury. Male Sprague Dawley rats were divided into four groups: group 1 was defined as control, and group 2 was the irradiated group. Group 3 and 4 were CoQ10 control and radiation plus CoQ10 groups, respectively. CoQ10 (10 mg/kg) was orally administered for 10 days before 10 Gy whole-body radiation and was continued for 4 days post-irradiation. CoQ10 administration protected rats delivered a lethal dose of ϒ-radiation from changes in crypt-villus structures and promoted regeneration of the intestinal epithelium. CoQ10 attenuated radiation-induced oxidative stress by decreasing lipid peroxidation and increasing the antioxidant enzyme catalase activity and reduced glutathione level. CoQ10 also counteracts inflammatory response mediated after radiation exposure through downregulating intestinal NF-ĸB expression which subsequently decreased the level of inflammatory cytokine IL-6 and the expression of COX-2. Radiation-induced intestinal fibrosis confirmed via Masson's trichrome staining occurred through upregulating transforming growth factor (TGF)-β1 and matrix metalloproteinase (MMP)-9 expression, while CoQ10 administration significantly diminishes these effects which further confirmed the anti-fibrotic property of CoQ10. Therefore, CoQ10 is a promising radioprotector that could prevent intestinal complications and enhance the therapeutic ratio of radiotherapy in patients with pelvic tumors through suppressing the NF-kB/TGF-β1/MMP-9 signaling pathway.

Methionine dietary supplementation potentiates ionizing radiation-induced gastrointestinal syndrome

Methionine is an essential amino acid needed for a variety of processes in living organisms. Ionizing radiation depletes tissue methionine concentrations and leads to the loss of DNA methylation and decreased synthesis of glutathione. In this study, we aimed to investigate the effects of methionine dietary supplementation in CBA/CaJ mice after exposure to doses ranging from 3 to 8.5 Gy of ¹³⁷Cs of total body irradiation. We report that mice fed a methionine-supplemented diet (MSD; 19.5 vs. 6.5 mg/kg in a methionine-adequate diet, MAD) developed acute radiation toxicity at doses as low as 3 Gy. Partial body irradiation performed with hindlimb shielding resulted in a 50% mortality rate in MSD-fed mice exposed to 8.5 Gy, suggesting prevalence of radiation-induced gastrointestinal syndrome in the development of acute radiation toxicity. Analysis of the intestinal microbiome demonstrated shifts in the gut ecology, observed along with the development of leaky gut syndrome and bacterial translocation into the liver. Normal gut physiology impairment was facilitated by alterations in the one-carbon metabolism pathway and was exhibited as decreases in circulating citrulline levels mirrored by decreased intestinal mucosal surface area and the number of surviving crypts. In conclusion, we demonstrate that a relevant excess of methionine dietary intake exacerbates the detrimental effects of exposure to ionizing radiation in the small intestine.NEW & NOTEWORTHY Methionine supplementation, instead of an anticipated health-promoting effect, sensitizes mice to gastrointestinal radiation syndrome. Mechanistically, excess of methionine negatively affects intestinal ecology, leading to a cascade of physiological, biochemical, and molecular alterations that impair normal gut response to a clinically relevant genotoxic stressor. These findings speak toward increasing the role of registered dietitians during cancer therapy and the necessity of a solid scientific background behind the sales of dietary supplements and claims regarding their benefits.

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.

Pancreatic radiation effect in apoptosis-related rectal radiation toxicity

Pancreatic radiation effect (PRE) can be a component of gastrointestinal tract (GIT) radiotoxicity. This inter-organ correlation between the GIT and the pancreas was assessed through a rat model. Separate local irradiation to the abdomen and the pelvis was applied concurrently for 8-week-old male Sprague Dawley rats. Abdominal irradiation was categorized into pancreatic shield (PS) and non-pancreatic shield (NPS) irradiation. After 5 Gy and 15 Gy irradiation, the rectal mucosa was analyzed at the first week (early phase, Ep) and the 14th week (late phase, Lp). A slow gain in body weight was observed initially, particularly in the NPS group receiving a 15 Gy dose (P < 0.001). The large number of apoptotic bodies after 15 Gy at Ep decreased at Lp. At Ep for the 5-Gy group, the NPS group revealed more fibrotic change than the PS group (P = 0.002). Cleaved caspase-3 (CCP3) expression was greater at Lp, and the Ep-Lp increase was prominent in the NPS-15-Gy group (P = 0.010). At Lp, for 15 Gy irradiation, CCP3 was expressed more in the NPS group than in the PS group (P = 0.032). Despite no direct toxicity difference between the PS and NPS groups, small changes in parameters such as fibrosis or CCP3 expression suggest that pancreatic shielding does have an effect on the radiation response in the rectal mucosa, which suggests a need for a multi-organ effect-based approach in GIT radiotoxicity assessment.

Short-term dietary methionine supplementation affects one-carbon metabolism and DNA methylation in the mouse gut and leads to altered microbiome profiles, barrier function, gene expression and histomorphology

BACKGROUND

Methionine, a central molecule in one-carbon metabolism, is an essential amino acid required for normal growth and development. Despite its importance to biological systems, methionine is toxic when administered at supra-physiological levels. The aim of this study was to investigate the effects of short-term methionine dietary modulation on the proximal jejunum, the section of the gut specifically responsible for amino acid absorption, in a mouse model. Eight-week-old CBA/J male mice were fed methionine-adequate (MAD; 6.5 g/kg) or methionine-supplemented (MSD; 19.5 g/kg) diets for 3.5 or 6 days (average food intake 100 g/kg body weight). The study design was developed in order to address the short-term effects of the methionine supplementation that corresponds to methionine dietary intake in Western populations. Biochemical indices in the blood as well as metabolic, epigenetic, transcriptomic, metagenomic, and histomorphological parameters in the gut were evaluated.

RESULTS

By day 6, feeding mice with MSD (protein intake <10% different from MAD) resulted in increased plasma (2.3-fold; p < 0.054), but decreased proximal jejunum methionine concentrations (2.2-fold; p < 0.05) independently of the expression of neutral amino acid transporters. MSD has also caused small bowel bacteria colonization, increased the abundance of pathogenic bacterial species Burkholderiales and decreased the gene expression of the intestinal transmembrane proteins-Cldn8 (0.18-fold, p < 0.05), Cldn9 (0.24-fold, p < 0.01) and Cldn10 (0.05-fold, p < 0.05). Feeding MSD led to substantial histomorphological alterations in the proximal jejunum exhibited as a trend towards decreased plasma citrulline concentrations (1.8-fold, p < 0.07), as well as loss of crypt depth (by 28%, p < 0.05) and mucosal surface (by 20%, p < 0.001).

CONCLUSIONS

Together, these changes indicate that short-term feeding of MSD substantially alters the normal gut physiology. These effects may contribute to the pathogenesis of intestinal inflammatory diseases and/or sensitize the gut to exposure to other stressors.

Recombinant Thrombomodulin (Solulin) Ameliorates Early Intestinal Radiation Toxicity in a Preclinical Rat Model

Intestinal radiation toxicity occurs during and after abdominopelvic radiotherapy. Endothelial cells play a significant role in modulating radiation-induced intestinal damage. We demonstrated that the endothelial cell surface receptor thrombomodulin (TM), a protein with anticoagulant, anti-inflammatory and antioxidant properties, mitigates radiation-induced lethality in mice. The goal of this study was to determine whether recombinant TM (Solulin) can protect the intestine from toxicity in a clinically relevant rat model. A 4 cm loop of rat small bowel was exposed to fractionated 5 Gy X radiation for 9 consecutive days. The animals were randomly assigned to receive daily subcutaneous injections of vehicle or Solulin (3 mg/kg/day or 10 mg/kg/day) for 27 days starting 4 days before irradiation. Early intestinal injury was assessed two weeks after irradiation by quantitative histology, morphometry, immunohistochemistry and luminol bioluminescence imaging. Solulin treatment significantly ameliorated intestinal radiation injury, made evident by a decrease in myeloperoxidase (MPO) activity, transforming growth factor beta (TGF-β) immunoreactivity, collagen-I deposition, radiation injury score (RIS) and intestinal serosal thickening. These findings indicate the need for further development of Solulin as a prophylactic and/or therapeutic agent to mitigate radiation-induced intestinal damage.

The Delayed Effects of Acute Radiation Syndrome: Evidence of Long-Term Functional Changes in the Clonogenic Cells of the Small Intestine

Long term or residual damage post-irradiation has been described for many tissues. In hematopoietic stem cells (HSC), this is only revealed when the HSC are stressed and required to regenerate and repopulate a myeloablated host. Such an assay cannot be used to assess the recovery potential of previously irradiated intestinal stem cells (ISC) due to their incompatibility with transplantation. The best approximation to the HSC assay is the crypt microcolony assay, also based on clonogen survival. In the current study, the regenerative capacity of intestinal clonogenic cells in mice that had survived 13 Gy irradiation (with 5% bone marrow shielding to allow survival through the hematopoietic syndrome) and were then aged for 200 d was compared to previously unirradiated age-matched controls. Interestingly, at 200 d following 13 Gy, there remained a statistically significant reduction in crypts present in the various small intestinal regions (illustrating that the gastrointestinal epithelium had not fully recovered despite the 200-d interval). However, upon re-irradiation on day 196, those mice previously irradiated had improved crypt survival and regeneration compared to the age-matched controls. This was evident in all regions of the small intestine following 11-13 Gy re-exposure. Thus, there were either more clonogens per crypt within those previously irradiated and/or those that were present were more radioresistant (possibly because a subpopulation was more quiescent). This is contrary to the popular belief that previously irradiated animals may have an impaired/delayed regenerative response and be more radiosensitive.

The potential of mesenchymal stem cells in the management of radiation enteropathy

Although radiotherapy is effective in managing abdominal and pelvic malignant tumors, radiation enteropathy is still unavoidable. This disease severely affects the quality of life of cancer patients due to some refractory lesions, such as intestinal ischemia, mucositis, ulcer, necrosis or even perforation. Current drugs or prevailing therapies are committed to alleviating the symptoms induced by above lesions. But the efficacies achieved by these interventions are still not satisfactory, because the milieus for tissue regeneration are not distinctly improved. In recent years, regenerative therapy for radiation enteropathy by using mesenchymal stem cells is of public interests. Relevant results of preclinical and clinical studies suggest that this regenerative therapy will become an attractive tool in managing radiation enteropathy, because mesenchymal stem cells exhibit their pro-regenerative potentials for healing the injuries in both epithelium and endothelium, minimizing inflammation and protecting irradiated intestine against fibrogenesis through activating intrinsic repair actions. In spite of these encouraging results, whether mesenchymal stem cells promote tumor growth is still an issue of debate. On this basis, we will discuss the advances in anticancer therapy by using mesenchymal stem cells in this review after analyzing the pathogenesis of radiation enteropathy, introducing the advances in managing radiation enteropathy using regenerative therapy and exploring the putative actions by which mesenchymal stem cells repair intestinal injuries. At last, insights gained from the potential risks of mesenchymal stem cell-based therapy for radiation enteropathy patients may provide clinicians with an improved awareness in carrying out their studies.

Caffeic acid phenethyl ester attenuates ionize radiation-induced intestinal injury through modulation of oxidative stress, apoptosis and p38MAPK in rats

Caffeic acid phenyl ester (CAPE) is a potent anti-inflammatory agent and it can eliminate the free radicals. This study aimed to investigate the radioprotective effects of CAPE on X-ray irradiation induced intestinal injury in rats. Rats were intragastrically administered with 10 μmol/kg/d CAPE for 7 consecutive days before exposing them to a single dose of X-ray irradiation (9Gy) to abdomen. Rats were sacrificed 72 h after exposure to radiation. We found that pretreatment with CAPE effectively attenuated intestinal pathology changes, apoptosis, oxidative stress, bacterial translocation, the content of nitric oxide and myeloperoxidase as well as the concentration of plasma tumor necrosis factor-α. Pretreatment with CAPE also reversed the activation of p38MAPK and the increased expression of intercellular cell adhesion molecule-1 induced by radiation in intestinal mucosa. Taken together, these results suggest that pretreatment with CAPE could be a promising candidate for treating radiation-induced intestinal injury.

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 lethality potentiation in total body irradiated mice by a commonly prescribed proton pump inhibitor, Pantoprazole sodium

PURPOSE

Pantoprazole sodium (Protonix) is a proton pump inhibitor (PPI) widely used to treat peptic ulcer and gastroesophageal reflux due to its ability to inhibit gastric acid secretion. Therefore, a large group of the population exposed to total body irradiation (TBI) in the event of a nuclear disaster would be on this or similar medications. We investigated the effect of pantoprazole on TBI-induced lethality in mice.

METHODS AND MATERIALS

Male CD2F1 mice were exposed to various doses of uniform TBI using a (137)Cs irradiator. Pantoprazole was administered by twice daily subcutaneous injection in saline from 4 days before to 5 days after irradiation. Effects on gastric pH, and gastrointestinal (GI) and hematopoietic toxicity were evaluated.

RESULTS

Pantoprazole administration significantly exacerbated 30 day lethality and gastrointestinal toxicity. Median survival after 9.0 Gy TBI was reduced from 22 days to 12 days (p = 0.006). Pantoprazole adversely effected intestinal crypt survival and mucosal surface area. In contrast, equivalent doses of a histamine type-2(H2) receptor blocker (cimetidine) did not alter TBI-induced lethality.

CONCLUSION

The adverse effect of pantoprazole on TBI-induced lethality is highly important because of the widespread use of PPI in the general population, as well as use of these drugs for acid suppression in individuals exposed to radiation. Further studies of the mechanisms underlying the adverse effect of PPI after exposure to TBI are clearly warranted. Until results from such studies are available, other acid-suppressing strategies should be preferred in the context of radiation exposure.

Bone marrow transplantation helps restore the intestinal mucosal barrier after total body irradiation in mice

Bone marrow transplantation (BMT) substantially improves 10-day survival after total body irradiation (TBI), consistent with an effect on intestinal radiation death. Total body irradiation, in addition to injuring the intestinal epithelium, also perturbs the mucosal immune system, the largest immune system in the body. This study focused on how transplanted bone marrow cells (BMCs) help restore mucosal immune cell populations after sublethal TBI (8.0 Gy). We further evaluated whether transplanted BMCs: (a) home to sites of radiation injury using green fluorescent protein labeled bone marrow; and (b) contribute to restoring the mucosal barrier in vivo. As expected, BMT accelerated recovery of peripheral blood (PB) cells. In the intestine, BMT was associated with significant early recovery of mucosal granulocytes (P = 0.005). Bone marrow transplantation did not affect mucosal macrophages or lymphocyte populations at early time points, but enhanced the recovery of these cells from day 14 onward (P = 0.03). Bone marrow transplantation also attenuated radiation-induced increase of intestinal CXCL1 and restored IL-10 levels (P = 0.001). Most importantly, BMT inhibited the post-radiation increase in intestinal permeability after 10 Gy TBI (P = 0.02) and modulated the expression of tight junction proteins (P = 0.01-0.05). Green fluorescent protein-positive leukocytes were observed both in intestinal tissue and in PB. These findings strongly suggest that BMT, in addition to enhancing general hematopoietic and immune system recovery, helps restore the intestinal immune system and enhances intestinal mucosal barrier function. These findings may be important in the development and understanding of strategies to alleviate or treat intestinal radiation toxicity.

Oral interleukin 11 as a countermeasure to lethal total-body irradiation in a murine model

Countermeasures against radiation are critically needed. Ideally, these measures would be easy to store, easy to administer and have minimal toxicity. We used oral delivery of interleukin 11 (IL11) in mice exposed to lethal doses of total-body irradiation (TBI). Animals were given IL11 by gavage at various daily doses beginning 24 h after TBI, which continued for 5 days. At a TBI of 9.0 Gy, mice treated with IL11 had a 70% survival at 30 days compared with control group survival of 25% (P = 0.035). At 10.0 Gy, treated animals had 50% survival at 30 days compared with no survivors in the control group. Treated animals had significant improvement in intestinal mucosal surface area and crypt survival. In addition bacterial translocation of coliform bacteria was significantly less in the treated animals. Systemic absorption of IL11 was low in treated animals and effects on the hematopoietic cells were not seen. Serum citrulline levels rebounded significantly faster after irradiation in the IL11 treated animals, indicating quicker recovery of small intestine health. These data suggest that IL11 given orally protects the intestinal mucosa from radiation damage and that this compound is beneficial as a mitigating agent even when started 24 h after radiation exposure.

Pharmacological induction of transforming growth factor-beta1 in rat models enhances radiation injury in the intestine and the heart

Radiation therapy in the treatment of cancer is dose limited by radiation injury in normal tissues such as the intestine and the heart. To identify the mechanistic involvement of transforming growth factor-beta 1 (TGF-β1) in intestinal and cardiac radiation injury, we studied the influence of pharmacological induction of TGF-β1 with xaliproden (SR 57746A) in rat models of radiation enteropathy and radiation-induced heart disease (RIHD). Because it was uncertain to what extent TGF-β induction may enhance radiation injury in heart and intestine, animals were exposed to irradiation schedules that cause mild to moderate (acute) radiation injury. In the radiation enteropathy model, male Sprague-Dawley rats received local irradiation of a 4-cm loop of rat ileum with 7 once-daily fractions of 5.6 Gy, and intestinal injury was assessed at 2 weeks and 12 weeks after irradiation. In the RIHD model, male Sprague-Dawley rats received local heart irradiation with a single dose of 18 Gy and were followed for 6 months after irradiation. Rats were treated orally with xaliproden starting 3 days before irradiation until the end of the experiments. Treatment with xaliproden increased circulating TGF-β1 levels by 300% and significantly induced expression of TGF-β1 and TGF-β1 target genes in the irradiated intestine and heart. Various radiation-induced structural changes in the intestine at 2 and 12 weeks were significantly enhanced with TGF-β1 induction. Similarly, in the RIHD model induction of TGF-β1 augmented radiation-induced changes in cardiac function and myocardial fibrosis. These results lend further support for the direct involvement of TGF-β1 in biological mechanisms of radiation-induced adverse remodeling in the intestine and the heart.

Multi-therapeutic effects of human adipose-derived mesenchymal stem cells on radiation-induced intestinal injury

Radiation-induced intestinal injuries (RIII) commonly occur in patients who suffer from pelvic or abdominal cancer. However, current management of these injuries is ineffective. Recently, mesenchymal stem cells (MSCs) have been extensively used in regenerative medicine and have achieved a high level of efficacy. In the present study, we hypothesised that human adipose-derived mesenchymal stem cells (hAd-MSCs) could be used as potential tools to heal RIII. We observed that adult Sprague-Dawley rats that received whole-abdominal irradiation benefitted from hAd-MSC injection. hAd-MSCs had RIII-healing effects, including anti-inflammation, neovascularisation and maintenance of epithelium homeostasis, as indicated by elevated serum IL-10, upregulation of vascular endothelial growth factor, basic fibroblast growth factor and epidermal growth factor in irradiated intestine, mobilisation of CD31-positive haematopoietic stem cells or haematopoietic progenitor cells, and the prolonged presence of Bmi1-positive cells within crypts. Consequently, after hAd-MSC treatment, irradiated rats survived longer than non-treated animals. These results suggest that hAd-MSCs have therapeutic potential for RIII management.

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.

Evidence of delayed gastrointestinal syndrome in high-dose irradiated mice

The acute effects of irradiation on the gastrointestinal (GI) system are well documented, but the longer-term effects are less well known. Increased incidence of adenocarcinoma has been noted, but apart from descriptions of fibrosis, the development of other pathologies specific to survivors of acute radiation is poorly understood. Samples were taken from C57BL/6 mice irradiated with partial-body irradiation where the thorax, head, and forelimbs were shielded (i.e., sparing 40% of the bone marrow). Tissue from age-matched controls was also collected. There were clear pathological changes in the intestine associated with DEARE (Delayed Effects of Acute Radiation Exposure) at doses greater than 12 Gy, with a dose-related increase in observed pathologies. Mice maintained on the synthetic antibiotic ciprofloxacin during the acute phase (days 4 to 20), however, had a lower or delayed incidence of symptoms. After 20 d, mice developed structures similar to early adenomas. Abnormally high levels of apoptotic and mitotic cells were present in some crypts, along with the early adenomas, suggesting tissue regeneration and areas of deregulated cell turnover. Over time, there was inhibited crypt cell proliferation in animals with advanced symptoms, a blunting of the crypts and villi, and an enlargement of villus girth, with an increasingly acellular and fibrotic extracellular matrix (a characteristic that has been demonstrated previously in aging mice). Together these changes may lead to a reduced functional surface area and less motile intestine. These observations are similar to those seen in geriatric animals, suggesting a premature aging of the GI tract.

Inhibition of protease-activated receptor 1 ameliorates intestinal radiation mucositis in a preclinical rat model

PURPOSE

To determine, using a specific small-molecule inhibitor of protease-activated receptor 1 (PAR1) signaling, whether the beneficial effect of thrombin inhibition on radiation enteropathy development is due to inhibition of blood clotting or to cellular (PAR1-mediated) thrombin effects.

METHODS AND MATERIALS

Rats underwent fractionated X-irradiation (5 Gy×9) of a 4-cm small-bowel segment. Early radiation toxicity was evaluated in rats receiving PAR1 inhibitor (SCH602539, 0, 10, or 15 mg/kg/d) from 1 day before to 2 weeks after the end of irradiation. The effect of PAR1 inhibition on development of chronic intestinal radiation fibrosis was evaluated in animals receiving SCH602539 (0, 15, or 30 mg/kg/d) until 2 weeks after irradiation, or continuously until termination of the experiment 26 weeks after irradiation.

RESULTS

Blockade of PAR1 ameliorated early intestinal toxicity, with reduced overall intestinal radiation injury (P=.002), number of myeloperoxidase-positive (P=.03) and proliferating cell nuclear antigen-positive (P=.04) cells, and collagen III accumulation (P=.005). In contrast, there was no difference in delayed radiation enteropathy in either the 2- or 26-week administration groups.

CONCLUSION

Pharmacological blockade of PAR1 seems to reduce early radiation mucositis but does not affect the level of delayed intestinal radiation fibrosis. Early radiation enteropathy is related to activation of cellular thrombin receptors, whereas platelet activation or fibrin formation may play a greater role in the development of delayed toxicity. Because of the favorable side-effect profile, PAR1 blockade should be further explored as a method to ameliorate acute intestinal radiation toxicity in patients undergoing radiotherapy for cancer and to protect first responders and rescue personnel in radiologic/nuclear emergencies.

Pentoxifylline enhances the radioprotective properties of γ-tocotrienol: differential effects on the hematopoietic, gastrointestinal and vascular systems

The vitamin E analog γ-tocotrienol (GT3) is a potent radioprotector and mitigator. This study was performed to (a) determine whether the efficacy of GT3 can be enhanced by the addition of the phosphodiesterase inhibitor pentoxifylline (PTX) and (b) to obtain information about the mechanism of action. Mice were injected subcutaneously with vehicle, GT3 [400 mg/kg 24 h before total-body irradiation (TBI)], PTX (200 mg/kg 30 min before TBI), or GT3+PTX before being exposed to 8.5-13 Gy TBI. Overall lethality, survival time and intestinal, hematopoietic and vascular injury were assessed. Cytokine levels in the bone marrow microenvironment were measured, and the requirement for endothelial nitric oxide synthase (eNOS) was studied in eNOS-deficient mice. GT3+PTX significantly improved survival compared to GT3 alone and provided full protection against lethality even after exposure to 12.5 Gy. GT3+PTX improved bone marrow CFUs, spleen colony counts and platelet recovery compared to GT3 alone. GT3 and GT3+PTX increased bone marrow plasma G-CSF levels as well as the availability of IL-1α, IL-6 and IL-9 in the early postirradiation phase. GT3 and GT3+PTX were equally effective in ameliorating intestinal injury and vascular peroxynitrite production. Survival studies in eNOS-deficient mice and appropriate controls revealed that eNOS was not required for protection against lethality after TBI. Combined treatment with GT3 and PTX increased postirradiation survival over that with GT3 alone by a mechanism that may depend on induction of hematopoietic stimuli. GT3+PTX did not reduce GI toxicity or vascular oxidative stress compared to GT3 alone. The radioprotective effect of either drug alone or both drugs in combination does not require the presence of eNOS.

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.

A murine model for the study of molecular pathogenesis of radiation proctitis

PURPOSE

To establish a novel mouse brachytherapy model with which to study the role of inflammation in the pathogenesis of radiation proctitis.

METHODS AND MATERIALS

The distal rectums of BALB/c and C57BL/6 mice were irradiated with three to five fractions of 5.5 to 8 Gy. Tissues were harvested and evaluated for histopathology, using the radiation injury score (RIS). Cytokine mRNA expression was assessed using real-time PCR.

RESULTS

Fifty percent of the mice treated with 22 Gy delivered in four fractions of 5.5 Gy died as a result of anorectal stenosis and distal bowel obstruction prior to the time of scheduled sacrifice, with a latency period of 4 to 10 weeks for the BALB/c and 3 to 4 weeks for the C57BL/6 mice. The RISs were 7, 12, and 8 at 2, 6, and 11 weeks, respectively, in the BALB/c mice and was 8.7 in the C57BL/6 mice on week 6. A 100- to 300-fold increase in interleukin-1beta (IL-1beta) (p = 0.04) and IL-6 mRNA (p = 0.07) and a 5- to 6-fold increase in transforming growth factor (TGF) and tumor necrosis factor-alpha mRNA expression levels (p < 0.001 and p = 0.01) were observed at 2 to 6 weeks after radiation. Cytokine mRNA tissue expression correlated positively with radiation dose (p < 0.0001). The RIS correlated well with IL-1beta and IL-6 mRNA levels in the BALB/c mice and with IL-1beta, IL-6, and TGF mRNA levels in C57BL/6 mice. Analysis of receiver operating characteristic curve showed that IL-1beta and IL-6 have the largest area under the curve and therefore are good markers of radiation proctitis (p < 0.001).

CONCLUSIONS

Radiation-induced proctitis was associated with a dose-dependent, characteristic proinflammatory cytokine response pattern in a novel mouse model suitable for interventional studies.

Oral PEG 15-20 protects the intestine against radiation: role of lipid rafts

Intestinal injury following abdominal radiation therapy or accidental exposure remains a significant clinical problem that can result in varying degrees of mucosal destruction such as ulceration, vascular sclerosis, intestinal wall fibrosis, loss of barrier function, and even lethal gut-derived sepsis. We determined the ability of a high-molecular-weight polyethylene glycol-based copolymer, PEG 15-20, to protect the intestine against the early and late effects of radiation in mice and rats and to determine its mechanism of action by examining cultured rat intestinal epithelia. Rats were exposed to fractionated radiation in an established model of intestinal injury, whereby an intestinal segment is surgically placed into the scrotum and radiated daily. Radiation injury score was decreased in a dose-dependent manner in rats gavaged with 0.5 or 2.0 g/kg per day of PEG 15-20 (n = 9-13/group, P < 0.005). Complementary studies were performed in a novel mouse model of abdominal radiation followed by intestinal inoculation with Pseudomonas aeruginosa (P. aeruginosa), a common pathogen that causes lethal gut-derived sepsis following radiation. Mice mortality was decreased by 40% in mice drinking 1% PEG 15-20 (n = 10/group, P < 0.001). Parallel studies were performed in cultured rat intestinal epithelial cells treated with PEG 15-20 before radiation. Results demonstrated that PEG 15-20 prevented radiation-induced intestinal injury in rats, prevented apoptosis and lethal sepsis attributable to P. aeruginosa in mice, and protected cultured intestinal epithelial cells from apoptosis and microbial adherence and possible invasion. PEG 15-20 appeared to exert its protective effect via its binding to lipid rafts by preventing their coalescence, a hallmark feature in intestinal epithelial cells exposed to radiation.

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.

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.

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.

Acute and late genitourinary toxicity of conformal radiotherapy for prostate cancer

PURPOSE

The aim of this study was to identify predictive factors for genitourinary (GU) toxicity in prostate cancer patients who underwent conformal radiotherapy (CRT).

MATERIALS AND METHODS

In this study we analyzed 154 cases of T1-3N0M0 prostate adenocarcinoma and evaluated the occurrence rate of acute and late GU toxicity and the duration of acute toxicity according to clinical parameters: age, transurethral resection of the prostate prior to CRT, hormone therapy, CRT dose, length of planning target volume (PTV).

RESULTS

Altogether, 41% of the patients developed grade 2 or higher acute GU toxicity. Longer PTV was significantly associated with a higher incidence of acute GU toxicity (>7 cm, 53%; <or=7 cm, 31%; P = 0.003), and hormone therapy prolonged the duration of the toxicity (P = 0.007). Grade 1 or higher late GU toxicity developed in 23% of the patients, and the 2-year late GU toxicity-free survival rate was 79%. Acute GU toxicity was significantly associated with the late GU toxicity-free survival rate (grade 0-1, 88.7%; grade 2-4, 73.2%; P = 0.0007).

CONCLUSION

The length of PTV and hormone therapy were predictive factors for acute GU toxicity. Furthermore, acute GU toxicity was the most important predictive factor for late GU toxicity.

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.

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.

Effect of long-term hyperhomocysteinemia on myocardial structure and function in hypertensive rats

BACKGROUND

Postulated mechanisms of hyperhomocysteinemia (Hhe) overlap with proposed mechanisms of adverse cardiac remodeling such as altered collagen metabolism and oxidant stress. Hence we examined the hypothesis that Hhe would promote myocardial fibrosis and systolic dysfunction.

METHODS

Three-month-old spontaneously hypertensive rats (SHRs) were divided into three groups: (1) control, given amino-acid defined diet for 20 weeks; (2) Hhe group, given Hhe-inducing diet for 20 weeks; and (3) combined diet group, which were given Hhe-inducing diet for 10 weeks (which leads to myocardial fibrosis and diastolic dysfunction as shown in our prior studies) and subsequently returned to amino acid-defined diet for 10 more weeks. At the end of the treatment period, plasma homocysteine (Hcy) levels and blood pressure were measured, and hearts were isolated for histomorphometric and biochemical assessment of cardiac remodeling and myocardial oxidative stress, and for in vitro cardiac function studies.

RESULTS

The Hhe animals demonstrated a significant increase in the ratio of collagenous to noncollagenous protein due to reactive interstitial fibrosis, and increased myocardial oxidant stress, compared to the control group. Systolic function was significantly depressed in the Hhe animals compared to the control group. These changes were partially prevented by return to control diet at 10 weeks.

CONCLUSIONS

Our results demonstrate that clinically relevant levels of Hhe accelerate progression of hypertensive heart disease to systolic dysfunction and that increased myocardial oxidant stress may play a role in this process. Considering the high prevalence of hypertension and Hhe in the general population, our findings may have great clinical significance.

Protective role of mast cells in homocysteine-induced cardiac remodeling

Recent reports including those from our laboratories indicate that hyperhomocysteinemia (Hhe) is an independent risk factor for cardiac dysfunction and clinical heart failure. Mast cell accumulation is a prominent feature in our model of Hhe-induced cardiac dysfunction. Because mast cell-derived mediators can potentially attenuate cardiac remodeling, we investigated the possible protective role of mast cells in Hhe-induced cardiac remodeling using a mast cell-deficient rat model that in our recent report did not demonstrate any adverse cardiac function at younger age (6 mo) than mast cell-competent control animals. Mast cell-deficient ( Ws/Ws) rats and mast cell-competent (+/+) littermate control animals (3 mo of age) were treated with a Hhe-inducing diet for 10 wk. Cardiac remodeling was assessed structurally utilizing histomorphometric methods and functionally using an isolated Langendorff-perfused heart preparation. The Hhe-inducing diet caused similar elevations of homocysteine levels in the two groups. Compared with Hhe +/+ rats, the Hhe Ws/Ws rats demonstrated strikingly exacerbated adverse cardiac remodeling and myocardial fibrosis. Cardiac function measurement showed worsened diastolic function in Hhe Ws/Ws rats compared with Hhe +/+ rats. The absence of mast cells strikingly exacerbates Hhe-induced adverse cardiac remodeling and diastolic dysfunction. These findings indicate a potential dual rather than sole deleterious role for mast cells in cardiac injury.

Hirudin ameliorates intestinal radiation toxicity in the rat: support for thrombin inhibition as strategy to minimize side-effects after radiation therapy and as countermeasure against radiation exposure

BACKGROUND

The small bowel is a dose-limiting normal tissue in radiation therapy of malignancies in the abdomen and pelvis, as well as an important determinant of survival after non-therapeutic radiation exposure. Irradiation of normal tissues, including intestine, causes loss of vascular thromboresistance and upregulation of thrombin receptors. Radiation-induced endothelial dysfunction is thought to be involved in both early and delayed radiation responses. Hence, thrombin may be a potential target for ameliorating normal tissue radiation toxicity.

OBJECTIVE

To assess direct thrombin inhibition as a protective strategy against small bowel radiation toxicity.

METHODS

Rat small intestine was exposed to localized orthovoltage X-radiation. Recombinant hirudin, a direct thrombin inhibitor, or vehicle was infused from 2 days before irradiation to 14 days after irradiation. Structural, cellular, and molecular aspects of intestinal radiation injury were assessed at 2 weeks (early toxicity) and 26 weeks (chronic toxicity) after irradiation.

RESULTS

Compared with unirradiated intestine, irradiated intestine showed increased expression of tissue factor, increased immunoreactivity for enzymatically active thrombin, and increased extravascular fibrin(ogen) deposition. Hirudin treatment significantly attenuated radiation-induced mucosal damage (P = 0.04), reactive intestinal wall thickening (P = 0.02), transforming growth factor-beta immunoreactivity levels (P = 0.0002), and collagen III deposition (P = 0.003). The differences between hirudin-treated and control rats were more pronounced at 2 weeks than at 26 weeks after irradiation. Hirudin treatment did not affect postradiation granulocyte infiltration.

CONCLUSIONS

Short-term thrombin inhibition attenuates important aspects of intestinal radiation toxicity. Thrombin is a promising target for minimizing normal tissue injury after radiation therapy of cancer, as well as for protecting normal tissues from the adverse effects of non-therapeutic radiation exposure.

Gene expression profile in human late radiation enteritis obtained by high-density cDNA array hybridization

Late radiation enteritis is a sequela of radiation therapy to the abdomen. The pathogenic process is poorly understood at the molecular level. cDNA array analysis was used to provide new insights into the pathogenesis of this disorder. Gene profiles of six samples of fibrotic bowel tissue from patients with radiation enteritis and six healthy bowel tissue samples from patients without radiation enteritis were compared using membrane-based arrays containing 1314 cDNAs. Results were confirmed with real-time RT-PCR and Western blot analysis. Array analysis identified many differentially expressed genes involved in fibrosis, stress response, inflammation, cell adhesion, intracellular and nuclear signaling, and metabolic pathways. Increased expression of genes coding for proteins involved in the composition and remodeling of the extracellular matrix, along with altered expression of genes involved in cell- to-cell and cell-to-matrix interactions, were observed mainly in radiation enteritis samples. Stress, inflammatory responses, and antioxidant metabolism were altered in radiation enteritis as were genes coding for recruitment of lymphocytes and macrophages. The Rho/HSP27 (HSPB1)/zyxin pathway, involved in tissue contraction and myofibroblast transdifferentiation, was also altered in radiation enteritis, suggesting that this pathway could be related to the fibrogenic process. Our results provide a global and integrated view of the alteration of gene expression associated with radiation enteritis. They suggest that radiation enteritis is a dynamic process involving constant remodeling of each structural component of the intestinal tissue, i.e. the mucosa, the mesenchyme, and blood vessels. Functional studies will be necessary to validate the present results.

Clinical effects in a cohort of cancer patients overexposed during external beam pelvic radiotherapy

PURPOSE

To evaluate the clinical outcome of 28 overexposed cancer patients in a cohort of 153 treated with pelvic irradiation and to correlate the outcome with the doses received.

METHODS AND MATERIALS

Between August 2000 and March 2001, 153 patients were treated at the Instituto Oncológico Nacional of Panama with radiotherapy for cancers of the cervix, uterus, endometrium, prostate, and rectum using conventional techniques. In 56 patients, irradiated with partially blocked teletherapy fields, the treatment times were determined using a treatment planning system that generated isodose distributions. The absorbed doses received by the patients were calculated and the biologically effective doses (BEDs) and 2-Gy equivalent doses derived. The clinical outcome was evaluated using the Radiation Therapy Oncology Group (RTOG) and late effects on normal tissues-subjective, objective, management, analytic scales (LENT/SOMA). The relationships between clinical outcome and dose were investigated and compared with published data.

RESULTS

Of the 56 patients for whom treatment times were generated with the treatment planning system, 28 received some doses per fraction approximately double those prescribed. Using an alpha/beta = 10 Gy, the tumor BED(10) values ranged from 77 to 225 Gy. The rest of the patients received doses within 10% of the prescribed values. Seventeen of the 28 overexposed patients died 35 days to 21 months after treatment; 13 of the fatalities were caused by rectal complications. Survival was longer in those patients who had undergone colostomy. Bladder complications were less enhanced. The nonoverexposed patients with cervical cancer exhibited a greater incidence of treatment failures than generally reported in other centers.

CONCLUSION

This study provides the clinical outcome after high doses of pelvic radiotherapy in a range not previously well documented. For cervical cancer patients receiving both tele- and brachytherapy, some deaths in this overexposure cohort occurred from assumed consequential rectal injury within 2 years, when the BED(10) values exceeded 70-80 Gy. The incidence was asymptotic to 100% fatalities at >150 Gy. This confirmed and extended other data in the literature.

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.

Hyperhomocysteinemia leads to pathological ventricular hypertrophy in normotensive rats

A recent report indicated that hyperhomocysteinemia (Hhe), in addition to its atherothrombotic effects, exacerbates the adverse cardiac remodeling seen in response to hypertension, a powerful stimulus for pathological ventricular hypertrophy. The present study was undertaken to determine whether Hhe has a direct effect on ventricular remodeling and function in the absence of other hypertrophic stimuli. Male Wistar-Kyoto rats were fed either an amino acid-defined control diet or an intermediate Hhe-inducing diet. After 10 wk of dietary treatment, rats were subjected to echocardiographic assessment of left ventricular (LV) dimensions and systolic function. Subsequently, blood was collected for plasma homocysteine measurements, and the rats were killed for histomorphometric and biochemical assessment of cardiac remodeling and for in vitro cardiac function studies. Significant LV hypertrophy was detected by echocardiographic measurements, and in vitro results showed hypertrophy with significantly increased myocyte size in the LV and right ventricle (RV). LV and RV remodeling was characterized by a disproportionate increase in perivascular and interstitial collagen, coronary arteriolar wall thickening, and myocardial mast cell infiltration. In vitro study of LV function demonstrated abnormal diastolic function secondary to decreased compliance because the rate of relaxation did not differ between groups. LV systolic function did not vary between groups in vitro. In summary, in the absence of other hypertrophic stimuli short-term intermediate Hhe caused pathological hypertrophy and remodeling of both ventricles with diastolic dysfunction of the LV. These results demonstrate that Hhe has direct adverse effects on cardiac structure and function, which may represent a novel direct link between Hhe and cardiovascular morbidity and mortality, independent of other risk factors.

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.

Radiation-induced rectal complications are not influenced by age: a dose fractionation study in the rat

Radiation-induced complications of the rectum are an important dose-limiting factor in radiotherapy of pelvic malignancies. In general, animal studies demonstrated no differences in acute and late normal tissue toxicity with age, but little is known about rectal complications in relation to age. For this purpose, an extensive histological and dose fractionation study was carried out on the rectum of young (12 weeks) and older (77-80 weeks) rats. In this paper, the results of dose fractionation are presented in relation to age at the time of irradiation. Young and older animals were irradiated with single and fractionated doses. After irradiation, rectal complications could lead to occlusion and stenosis, eventually resulting in the clinical symptoms of a megacolon and a possible fistula. For each dose group, cumulative survival rates were obtained with Kaplan-Meier analysis, from which dose-effect curves and the associated LD(50) values for a megacolon/fistula were calculated. The majority of responders died between 8 and 24 weeks after irradiation, irrespective of age. For both age groups, only the fractionation data showed a reduction in the mean latency with increasing dose. In the older age group, 39% of the responders developed a fistula compared to 26% for the younger animals. The LD(50) values increased from around 30 Gy after single doses to nearly 65 Gy after 10 fractions. The increases in LD(50) values with the number of fractions were independent of the age of the rats. For each of the dose fractionation schedules, log-rank testing indicated no significant differences in cumulative survival rates between younger and older animals (P > 0.10). The high alpha/beta ratios obtained for both the young and older animals strongly suggested that the late rectal complications were a consequence of early epithelial injury. Associated histological findings indicated that blood vessel damage, which was already evident at a high incidence at 4 weeks after irradiation, could also play a significant role in the occurrence of consequential late injuries. In conclusion, data obtained for the latent period of rectal occlusion, for the dose-effect curves, for the log-rank testing of cumulative survival rates, and for the alpha/beta ratios strongly support the hypothesis that the incidence of radiation-induced rectal complications is independent of age. Late rectal complications could be a consequence of radiation-induced acute injury.

Deficiency of microvascular thrombomodulin and up-regulation of protease-activated receptor-1 in irradiated rat intestine: possible link between endothelial dysfunction and chronic radiation fibrosis

Microvascular injury is believed to be mechanistically involved in radiation fibrosis, but direct molecular links between endothelial dysfunction and radiation fibrosis have not been established in vivo. We examined radiation-induced changes in endothelial thrombomodulin (TM) and protease-activated receptor-1 (PAR-1) in irradiated intestine, and their relationship to structural, cellular, and molecular aspects of radiation injury. Rat small intestine was locally exposed to fractionated X-radiation. Structural injury was assessed 24 hours and 2, 6, and 26 weeks after the last radiation fraction using quantitative histology and morphometry. TM, neutrophils, transforming growth factor-beta, and collagens I and III were assessed by quantitative immunohistochemistry. PAR-1 protein was localized immunohistochemically, and cells expressing TM or PAR-1 transcript were identified by in situ hybridization. Steady-state PAR-1 mRNA levels in intestinal smooth muscle were determined using laser capture microdissection and competitive reverse transcriptase-polymerase chain reaction. Radiation caused a sustained, dose-dependent decrease in microvascular TM. The number of TM-positive vessels correlated with all parameters of radiation enteropathy and, after adjusting for radiation dose and observation time in a statistical model, remained independently associated with neutrophil infiltration, intestinal wall thickening, and collagen I accumulation. PAR-1 immunoreactivity and transcript increased in vascular and intestinal smooth muscle cells in irradiated intestine. PAR-1 mRNA increased twofold in irradiated intestinal smooth muscle. Intestinal irradiation up-regulates PAR-1 and causes a dose-dependent, sustained deficiency of microvascular TM that is independently associated with the severity of radiation toxicity. Interventions aimed at preserving or restoring endothelial TM or blocking PAR-1 should be explored as strategies to increase the therapeutic ratio in clinical radiation therapy.

Morphological aspects of ionizing radiation response of small intestine

Knowledge of the acute and late ionizing radiation exposure damage to the gastrointestinal tract, particularly injury of the small intestine, is of great significance in radiotherapy, as is management of accidental radiation exposure. Irradiation (X-ray, neutron, cobalt gamma) induces a series of events in this rapidly renewing tissue resulting in the well-known symptoms of the gastrointestinal (GI) radiation syndrome, such as GI haemorrhage, endotoxemia, bacterial infection, anorexia, nausea, vomiting, diarrhoea, and loss of electrolytes and fluid. In spite of the significant advances that have occurred in research on underlying mechanisms over the last two decades, the overall etiology and pathogenesis of the GI-syndrome still remains unclear. Currently, to our knowledge, these symptoms are probably due to a rapid modification of the intestinal motility and to the structural alteration of the intestinal mucosa (cell loss and altered crypt integrity). Several evidences suggest that radiation-induced dysfunctions and structural changes of this organ (either changes in subcellular, cellular, and histological structure) are mediated by concerted and interrelated changes of a plethora of various extracellular mediators and their intracellular messengers. The aim of this review is to summarize our current knowledge about the pathomorphology and cell biology of the ionizing radiation response of the GI tract with a focus on the small intestine.

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.