The temporal and spatial changes in cell proliferation within the irradiated crypts of the murine small intestine

Epithelial argininosuccinate synthetase is dispensable for intestinal regeneration and tumorigenesis

The epithelial signaling pathways involved in damage and regeneration, and neoplastic transformation are known to be similar. We noted upregulation of argininosuccinate synthetase (ASS1) in hyperproliferative intestinal epithelium. Since ASS1 leads to de novo synthesis of arginine, an important amino acid for the growth of intestinal epithelial cells, its upregulation can contribute to epithelial proliferation necessary to be sustained during oncogenic transformation and regeneration. Here we investigated the function of ASS1 in the gut epithelium during tissue regeneration and tumorigenesis, using intestinal epithelial conditional Ass1 knockout mice and organoids, and tissue specimens from colorectal cancer patients. We demonstrate that ASS1 is strongly expressed in the regenerating and Apc-mutated intestinal epithelium. Furthermore, we observe an arrest in amino acid flux of the urea cycle, which leads to an accumulation of intracellular arginine. However, loss of epithelial Ass1 does not lead to a reduction in proliferation or increase in apoptosis in vivo, also in mice fed an arginine-free diet. Epithelial loss of Ass1 seems to be compensated by altered arginine metabolism in other cell types and the liver.

New insight into the significance of KLF4 PARylation in genome stability, carcinogenesis, and therapy

KLF4 plays a critical role in determining cell fate responding to various stresses or oncogenic signaling. Here, we demonstrated that KLF4 is tightly regulated by poly(ADP‐ribosyl)ation (PARylation). We revealed the subcellular compartmentation for KLF4 is orchestrated by PARP1‐mediated PARylation. We identified that PARylation of KLF4 is critical to govern KLF4 transcriptional activity through recruiting KLF4 from soluble nucleus to the chromatin. We mapped molecular motifs on KLF4 and PARP1 that facilitate their interaction and unveiled the pivotal role of the PBZ domain YYR motif (Y430, Y451 and R452) on KLF4 in enabling PARP1‐mediated PARylation of KLF4. Disruption of KLF4 PARylation results in failure in DNA damage response. Depletion of KLF4 by RNA interference or interference with PARP1 function by KLF4^YYR/AAA (a PARylation‐deficient mutant) significantly sensitizes breast cancer cells to PARP inhibitors. We further demonstrated the role of KLF4 in modulating homologous recombination through regulating BRCA1 transcription. Our work points to the synergism between KLF4 and PARP1 in tumorigenesis and cancer therapy, which provides a potential new therapeutic strategy for killing BRCA1‐proficient triple‐negative breast cancer cells.

β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation

Gastrointestinal toxicity limits the clinical application of abdominal and pelvic radiotherapy and currently has no effective treatment. Intestinal leucine-rich-repeat-containing GPCR 5 (Lgr5)-positive stem cell depletion and loss of proliferative ability due to radiation may be the primary factors causing intestinal injury following radiation. Here, we report the critical role of β-arrestin1 (βarr1) in radiation-induced intestinal injury. Intestinal βarr1 was highly expressed in radiation enteritis and in a radiation model. βarr1 knockout (KO) or knockdown mice exhibited increased proliferation in intestinal Lgr5+ stem cell, crypt reproduction, and survival following radiation. Unexpectedly, the beneficial effects of βarr1 deficiency on intestinal stem cells in response to radiation were compromised when the endoplasmic reticulum stress-related protein kinase RNA-like ER kinase (PERK)/eukaryotic initiation factor-2α (eIF2α) pathway was inhibited, and this result was further supported in vitro. Furthermore, we found that βarr1 knockdown with small interfering RNA significantly enhanced intestinal Lgr5⁺ stem cell proliferation after radiation via directly targeting PERK. βarr1 offers a promising target for mitigating radiation-induced intestinal injury.-Liu, Z., Jiang, J., He, Q., Liu, Z., Yang, Z., Xu, J., Huang, Z., Wu, B. β-Arrestin1-mediated decrease in endoplasmic reticulum stress impairs intestinal stem cell proliferation following radiation.

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

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

Antioxidant Supplementation: A Linchpin in Radiation-Induced Enteritis

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

An Evaluation of the Common Mechanism Approach to the Food Quality Protection Act: Captan and Four Related Fungicides, a Practical Example

Under the Food Quality Protection Act (FQPA) of 1996 (Act), the United States Environmental Protection Agency (EPA) is mandated to conduct cumulative risk assessment on pesticides that act through a common mechanism of toxicity. Incumbent on the Agency is the development of sound scientific principles upon which to evaluate compounds for the presence of a common mechanism. Using the currently available draft guidance criteria, this paper employs five fungicides of the same general class, typified by captan, to evaluate both the criteria and the available scientific data.

Captan and folpet are two chloroalkylthio fungicides currently registered with EPA under Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) for agricultural use. As such, these compounds are subject to the provisions of FQPA. Three additional fungicidal compounds—dichlofluanid, tolylfluanid, and captafol—are not registered for use in the United States; however, these five compounds have chemical structure and biological toxicity similarities and differences that permit their utility as test cases to determine what the EPA would conclude, with regard to common mechanism, if these draft guidelines were applied to these compounds.

The results of the analyses are consistent and support the conclusion that captan and folpet share a common mode of toxicity for mouse duodenal tumors as defined in the Act. This common mode of toxicity is not shared by dichlofluanid, tolylfluanid, or captafol.

The basis for concluding a common mechanism exists between captan and folpet. They include 1. Structural Similarity—The compounds are structural analogs having the identical biologically active moiety (i.e., the-SCCl3side chain). 2. Mechanisms of Pesticidal Action—The compounds have the same mechanism of action. The overwhelming body of evidence suggests they are active because of their reactions with thiols. Both compounds, in reacting with thiols, produce similar degradates. Differences in rates of reaction are attributable to physical-chemical properties of the two compounds. 3. General Mechanisms of Mammalian Toxicity—The compounds induce mammalian toxicity through the same mechanism that is responsible for their pesticidal action, reactions with thiols. Another, albeit less likely, mechanism (for both compounds) is cross-Unking of proteins with DNA, although the extremely short half-lives of these compounds (seconds) argues against this possibility. 4. Sites of Action—Both compounds express their primary toxicity as local rather than systemic effects. 5. Common Toxic Endpoint—These two compounds induce gastrointestinal tumors (in mice only). 6. Mode of Action—Both compounds express their common toxic endpoint through a nongenotoxic, compensatory proliferation mechanism. 7. Specificity of Action—For both compounds, the majority of tumors appear in the duodenum. Furthermore, these tumors are induced only in mice. Repeated carcinogenicity testing suggests that rats are refractive to the effects of captan and folpet. The significantly faster hydrolytic rate for folpet at the lower pH values (e.g., increased 8-fold at pH 5) encountered in the stomach is believed to account for the tumors of the stomach observed with folpet and not captan. 8. Other Toxic Endpoints—For other toxic endpoints where comparative data are available, captan and folpet show similar patterns of toxicity (e.g., mutagenicity, skin sensitization, and acute toxicity).

Phosphorylations of Serines 21/9 in Glycogen Synthase Kinase 3α/β Are Not Required for Cell Lineage Commitment or WNT Signaling in the Normal Mouse Intestine

The WNT signalling pathway controls many developmental processes and plays a key role in maintenance of intestine renewal and homeostasis. Glycogen Synthase Kinase 3 (GSK3) is an important component of the WNT pathway and is involved in regulating β-catenin stability and expression of WNT target genes. The mechanisms underpinning GSK3 regulation in this context are not completely understood, with some evidence suggesting this occurs through inhibitory N-terminal serine phosphorylation in a similar way to GSK3 inactivation in insulin signaling. To investigate this in a physiologically relevant context, we have analysed the intestinal phenotype of GSK3 knockin mice in which N-terminal serines 21/9 of GSK3α/β have been mutated to non-phosphorylatable alanine residues. We show that these knockin mutations have very little effect on overall intestinal integrity, cell lineage commitment, β-catenin localization or WNT target gene expression although a small increase in apoptosis at villi tips is observed. Our results provide in vivo evidence that GSK3 is regulated through mechanisms independent of N-terminal serine phosphorylation in order for β-catenin to be stabilised.

Growth Hormone Protects the Intestine Preserving Radiotherapy Efficacy on Tumors: A Short-Term Study

The efficacy of radiotherapy on tumors is hampered by its devastating adverse effects on healthy tissue, particularly that of the gastrointestinal tract. These effects cause acute symptoms that are so disruptive to patients that they can lead to interruption of the radiotherapy program. These adverse effects could limit the intensity of radiation received by the patient, resulting in a sublethal dose to the tumor, thus increasing the risk of tumor resistance. The lack of an effective treatment to protect the bowel during radiation therapy to allow higher radiation doses that are lethal to the tumor has become a barrier to implementing effective therapy. In this study, we present a comparative analysis of both intestinal and tumor tissue in regard to the efficacy and the preventive impact of a short-term growth hormone (GH) treatment in tumor-bearing rats as a protective agent during radiotherapy. Our data show that the exogenous administration of GH improved intestinal recovery after radiation treatment while preserving the therapeutic effect against the tumor. GH significantly increased proliferation in the irradiated intestine but not in the irradiated tumors, as assessed by Positron Emission Tomography and the proliferative markers Ki67, cyclin D3, and Proliferating Cell Nuclear Antigen. This proliferative effect was consistent with a significant increase in irradiated intestinal villi and crypt length. Furthermore, GH significantly decreased caspase-3 activity in the intestine, whereas GH did not produce this effect in the irradiated tumors. In conclusion, short-term GH treatment protects the bowel, inducing proliferation while reducing apoptosis in healthy intestinal tissue and preserving radiotherapy efficacy on tumors.

bak deletion stimulates gastric epithelial proliferation and enhances Helicobacter felis-induced gastric atrophy and dysplasia in mice

Helicobacter infection causes a chronic superficial gastritis that in some cases progresses via atrophic gastritis to adenocarcinoma. Proapoptotic bak has been shown to regulate radiation-induced apoptosis in the stomach and colon and also susceptibility to colorectal carcinogenesis in vivo. Therefore we investigated the gastric mucosal pathology following H. felis infection in bak-null mice at 6 or 48 wk postinfection. Primary gastric gland culture from bak-null mice was also used to assess the effects of bak deletion on IFN-γ-, TNF-α-, or IL-1β-induced apoptosis. bak-null gastric corpus glands were longer, had increased epithelial Ki-67 expression, and contained fewer parietal and enteroendocrine cells compared with the wild type (wt). In wt mice, bak was expressed at the luminal surface of gastric corpus glands, and this increased 2 wk post-H. felis infection. Apoptotic cell numbers were decreased in bak-null corpus 6 and 48 wk following infection and in primary gland cultures following cytokine administration. Increased gastric epithelial Ki-67 labeling index was observed in C57BL/6 mice after H. felis infection, whereas no such increase was detected in bak-null mice. More severe gastric atrophy was observed in bak-null compared with C57BL/6 mice 6 and 48 wk postinfection, and 76% of bak-null compared with 25% of C57BL/6 mice showed evidence of gastric dysplasia following long-term infection. Collectively, bak therefore regulates gastric epithelial cell apoptosis, proliferation, differentiation, mucosal thickness, and susceptibility to gastric atrophy and dysplasia following H. felis infection.

Radioprotective effect of kupffer cell depletion on hepatic sinusoidal endothelial cells

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

Pharmacologically blocking p53-dependent apoptosis protects intestinal stem cells and mice from radiation

Exposure to high levels of ionizing radiation (IR) leads to debilitating and dose-limiting gastrointestinal (GI) toxicity. Using three-dimensional mouse crypt culture, we demonstrated that p53 target PUMA mediates radiation-induced apoptosis via a cell-intrinsic mechanism, and identified the GSK-3 inhibitor CHIR99021 as a potent radioprotector. CHIR99021 treatment improved Lgr5+ cell survival and crypt regeneration after radiation in culture and mice. CHIR99021 treatment specifically blocked apoptosis and PUMA induction and K120 acetylation of p53 mediated by acetyl-transferase Tip60, while it had no effect on p53 stabilization, phosphorylation or p21 induction. CHIR99021 also protected human intestinal cultures from radiation by PUMA but not p21 suppression. These results demonstrate that p53 posttranslational modifications play a key role in the pathological and apoptotic response of the intestinal stem cells to radiation and can be targeted pharmacologically.

Krüppel-like factor 4 is a radioprotective factor for the intestine following γ-radiation-induced gut injury in mice

Gut radiation-induced injury is a concern during treatment of patients with cancer. Krüppel-like factor 4 (KLF4) is expressed in differentiated villous epithelial cells of the small intestine. We previously showed that KLF4 protects cells from apoptosis following γ-irradiation in vitro. We sought to determine whether KLF4 mediates the small intestinal response to γ-irradiation in vivo. Mice with intestinal epithelium-specific deletion of Klf4 (Klf4(ΔIS)) and control (Klf4(fl/fl)) mice were irradiated with total-body γ-radiation. Following irradiation, the Klf4(ΔIS) mice had significantly increased mortality compared with irradiated Klf4(fl/fl) mice. Immunohistochemistry and immunofluorescence staining were used to assess the morphological changes, levels of proliferation, and apoptosis in the intestinal epithelium. At 96 h following irradiation, there was a regenerative response manifested by an expansion of the proliferative zone in both mouse groups, with the control mice having a higher proliferative activity than the Klf4(ΔIS) group. In addition, there was a significant increase in the number of Klf4/Ki67-copositive cells in the irradiated control mice compared with unirradiated mice. Also, the irradiated Klf4(ΔIS) mice had a significantly higher number of crypt cells positive for apoptosis, p53, and p21 compared with irradiated Klf4(fl/fl) mice. Taken together, our data suggest that Klf4 may function as a radioprotective factor against gastrointestinal syndrome in mice following γ-irradiation by inhibiting apoptosis in the acute response to irradiation and contributing to crypt regeneration.

Stem cell therapies for the treatment of radiation-induced normal tissue side effects

SIGNIFICANCE

Targeted irradiation is an effective cancer therapy but damage inflicted to normal tissues surrounding the tumor may cause severe complications. While certain pharmacologic strategies can temper the adverse effects of irradiation, stem cell therapies provide unique opportunities for restoring functionality to the irradiated tissue bed.

RECENT ADVANCES

Preclinical studies presented in this review provide encouraging proof of concept regarding the therapeutic potential of stem cells for treating the adverse side effects associated with radiotherapy in different organs. Early-stage clinical data for radiation-induced lung, bone, and skin complications are promising and highlight the importance of selecting the appropriate stem cell type to stimulate tissue regeneration.

CRITICAL ISSUES

While therapeutic efficacy has been demonstrated in a variety of animal models and human trials, a range of additional concerns regarding stem cell transplantation for ameliorating radiation-induced normal tissue sequelae remain. Safety issues regarding teratoma formation, disease progression, and genomic stability along with technical issues impacting disease targeting, immunorejection, and clinical scale-up are factors bearing on the eventual translation of stem cell therapies into routine clinical practice.

FUTURE DIRECTIONS

Follow-up studies will need to identify the best possible stem cell types for the treatment of early and late radiation-induced normal tissue injury. Additional work should seek to optimize cellular dosing regimes, identify the best routes of administration, elucidate optimal transplantation windows for introducing cells into more receptive host tissues, and improve immune tolerance for longer-term engrafted cell survival into the irradiated microenvironment.

Use of mesenchymal stem cells (MSC) in chronic inflammatory fistulizing and fibrotic diseases: a comprehensive review

Mesenchymal stem cells (MSC), multipotent adult stem cells, feature the potential to regenerate tissue damage and, in parallel, inhibit inflammation and fibrosis. MSC can be safely transplanted in autologous and allogeneic ways as they are non-immunogenic, and consequently represent a therapeutic option for refractory connective tissue diseases, fibrosing diseases like scleroderma and fistulizing colitis like in Crohn's disease. Actually, there are more than 200 registered clinical trial sites for evaluating MSC therapy, and 22 are on autoimmune diseases. In irradiation-induced colitis, MSC accelerate functional recovery of the intestine and dampen the systemic inflammatory response. In order to provide rescue therapy for accidentally over-irradiated prostate cancer patients who underwent radiotherapy, allogeneic bone marrow-derived MSC from family donors were intravenously infused to three patients with refractory and fistulizing colitis resembling fistulizing Crohn's disease. Systemic MSC therapy of refractory irradiation-induced colitis was safe and effective on pain, diarrhoea, hemorrhage, inflammation and fistulization accompanied by modulation of the lymphocyte subsets towards an increase of T regulatory cells and a decrease of activated effector T cells. The current data indicate that MSC represent a promising alternative strategy in the treatment of various immune-mediated diseases. Encouraging results have already been obtained from clinical trials in Crohn's disease and SLE as well as from case series in systemic sclerosis. MSC represent a safe therapeutic measure for patients who suffer from chronic and fistulizing colitis. These findings are instructional for the management of refractory inflammatory bowel diseases that are characterized by similar clinical and immunopathological features.

Gastro-intestinal autoimmunity: preclinical experiences and successful therapy of fistulizing bowel diseases and gut Graft versus host disease by mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are multipotent adult stem cells with the potential to regenerate tissue damage and inhibit inflammation and fibrosis in parallel. As they are non-immunogenic, MSC can be safely auto- and allotransplanted and consequently represent a therapeutic option for refractory connective tissue diseases and fistulizing colitis like Crohn's disease. Actually, there are more than 200 registered clinical trial sites for evaluating MSC therapy, 22 are on autoimmune diseases and 27 are actually recruiting bowel disease' patients. More than 1,500 patients with bowel diseases like Crohn's disease were treated in clinical trials by local as well as systemic MSC therapy. Phase I and II trials on fistula documented the feasibility and safety of MSC therapy, and a significant superiority compared to fibrin glue in fistulizing bowel diseases was demonstrated. Autologous as well as allogeneic use of Bone marrow as well as of adipose tissue-derived MSC are feasible. In refractory Graft versus host disease, especially in refractory gut Graft versus host diseases, encouraging results were reported using MSC. Systemic MSC therapy of refractory irradiation-induced colitis was safe and effective on pain, diarrhea, hemorrhage, inflammation and fistulization accompanied by modulation of the lymphocyte subsets toward an increase in T regulatory cells and a decrease in activated effector T cells. Mesenchymal stem cells represent a safe therapy for patients with refractory inflammatory bowel diseases.

Computational models reveal a passive mechanism for cell migration in the crypt

Cell migration in the intestinal crypt is essential for the regular renewal of the epithelium, and the continued upward movement of cells is a key characteristic of healthy crypt dynamics. However, the driving force behind this migration is unknown. Possibilities include mitotic pressure, active movement driven by motility cues, or negative pressure arising from cell loss at the crypt collar. It is possible that a combination of factors together coordinate migration. Here, three different computational models are used to provide insight into the mechanisms that underpin cell movement in the crypt, by examining the consequence of eliminating cell division on cell movement. Computational simulations agree with existing experimental results, confirming that migration can continue in the absence of mitosis. Importantly, however, simulations allow us to infer mechanisms that are sufficient to generate cell movement, which is not possible through experimental observation alone. The results produced by the three models agree and suggest that cell loss due to apoptosis and extrusion at the crypt collar relieves cell compression below, allowing cells to expand and move upwards. This finding suggests that future experiments should focus on the role of apoptosis and cell extrusion in controlling cell migration in the crypt.

Progastrin-induced secretion of insulin-like growth factor 2 from colonic myofibroblasts stimulates colonic epithelial proliferation in mice

BACKGROUND & AIMS

Many colon cancers produce the hormone progastrin, which signals via autocrine and paracrine pathways to promote tumor growth. Transgenic mice that produce high circulating levels of progastrin (hGAS) have increased proliferation of colonic epithelial cells and are more susceptible to colon carcinogenesis than control mice. We investigated whether progastrin affects signaling between colonic epithelial and myofibroblast compartments to regulate tissue homeostasis and cancer susceptibility.

METHODS

Colonic myofibroblast numbers were assessed in hGAS and C57BL/6 mice by immunohistochemistry. Human CCD18Co myofibroblasts were incubated with recombinant human progastrin (rhPG)(1-80) for 18 hours, and proliferation was assessed in the presence of pharmacologic inhibitors. The proliferation of human HT29 colonic epithelial cells was assessed after addition of conditioned media from CCD18Co cells incubated with progastrin. The effects of the insulin-like growth factor (IGF)-I receptor antagonist AG1024 were investigated in cultured HT29 cells and on the colonic epithelium of hGAS mice compared with mice that did not express transgenic progastrin (controls).

RESULTS

The colonic mucosa of hGAS mice contained greater numbers of myofibroblasts that expressed α-smooth muscle actin and vimentin than controls. Incubation of CCD18Co myofibroblasts with 0.1 nmol/L rhPG(1-80) increased their proliferation, which required activation of protein kinase C and phosphatidylinositol-3 kinase. CCD18Co cells secreted IGF-II in response to rhPG(1-80), and conditioned media from CCD18Co cells that had been incubated with rhPG(1-80) increased the proliferation of HT29 cells. The colonic epithelial phenotype of hGAS mice (crypt hyperplasia, increased proliferation, and altered proportions of goblet and enteroendocrine cells) was inhibited by AG1024.

CONCLUSIONS

Progastrin stimulates colonic myofibroblasts to release IGF-II, which increases proliferation of colonic epithelial cells. Progastrin might therefore alter colonic epithelial cells via indirect mechanisms to promote neoplasia.

Patterns of proliferative activity in the colonic crypt determine crypt stability and rates of somatic evolution

Epithelial cells in the colon are arranged in cylindrical structures called crypts in which cellular proliferation and migration are tightly regulated. We hypothesized that the proliferation patterns of cells may determine the stability of crypts as well as the rates of somatic evolution towards colorectal tumorigenesis. Here, we propose a linear process model of colonic epithelial cells that explicitly takes into account the proliferation kinetics of cells as a function of cell position within the crypt. Our results indicate that proliferation kinetics has significant influence on the speed of cell movement, kinetics of mutation propagation, and sensitivity of the system to selective effects of mutated cells. We found that, of all proliferation curves tested, those with mitotic activities concentrated near the stem cell, including the actual proliferation kinetics determined in in vivo labeling experiments, have a greater ability of delaying the rate of mutation accumulation in colonic stem cells compared to hypothetical proliferation curves with mitotic activities focused near the top of the crypt column. Our model can be used to investigate the dynamics of proliferation and mutation accumulation in spatially arranged tissues.

Mathematical and computational models have a long and rich history in enhancing our understanding of intestinal epithelial cells. A plethora of models have been proposed to describe different aspects of cellular behavior, including cell proliferation, migration, differentiation, and mutation accumulation. Here, we present a novel approach to examine the effects of proliferation kinetics on the rate of somatic evolution in a spatially arranged model of the colon. Based on our simulation results, we demonstrate that spatially determined proliferation kinetics has the ability to delay the rate of somatic evolution, and changes in proliferation patterns can significantly affect the speed of mutation accumulation. Our work highlights the importance of considering proliferation kinetics as well as the spatial organization of tissues when investigating the dynamics of cancer initiation.

Protection by L-carnitine against radiation-induced ileal mucosal injury in the rat: pattern of oxidative stress, apoptosis and cytokines

PURPOSE

In this study, we tested the effects of L-carnitine (LC) on radiation-induced ileal mucosal damage.

MATERIALS AND METHODS

Thirty Wistar albino rats were divided into five groups. The control group received physiological saline intraperitoneally (i.p.). Radiation-1 and radiation-2 groups received whole-body X-irradiation of 8.3 Gy as a single dose. These groups were sacrificed at the 6th hour and 4th day after irradiation, respectively. The Radiation-1 + LC and the radiation-2 + LC groups received the same dose irradiation plus a daily dose of 200 mg/kg LC. LC was applied one day before and for four days after irradiation.

RESULTS

The levels of serum monocyte chemotactic protein-1 (MCP-1) and interferon gamma (IFN-γ) were significantly higher in the radiation groups when compared with the control. Treatment with LC decreased the serum MCP-1 and IFN-γ levels considerably. In the radiations groups, the Chiu score was significantly elevated compared with that of the control group. However, LC administered prior to the irradiation reduced the severity of mucosal damage. The number of apoptotic cells of the ileal crypt in the irradiated rats increased from the 6th hour after irradiation and then decreased at 4th day.

CONCLUSIONS

Our data demonstrated that LC may be beneficial to radiation enteritis.

Ciprofloxacin modulates cytokine/chemokine profile in serum, improves bone marrow repopulation, and limits apoptosis and autophagy in ileum after whole body ionizing irradiation combined with skin-wound trauma

Radiation combined injury (CI) is a radiation injury (RI) combined with other types of injury, which generally leads to greater mortality than RI alone. A spectrum of specific, time-dependent pathophysiological changes is associated with CI. Of these changes, the massive release of pro-inflammatory cytokines, severe hematopoietic and gastrointestinal losses and bacterial sepsis are important treatment targets to improve survival. Ciprofloxacin (CIP) is known to have immunomodulatory effect besides the antimicrobial activity. The present study reports that CIP ameliorated pathophysiological changes unique to CI that later led to major mortality. B6D2F1/J mice received CI on day 0, by RI followed by wound trauma, and were treated with CIP (90 mg/kg p.o., q.d. within 2 h after CI through day 10). At day 10, CIP treatment not only significantly reduced pro-inflammatory cytokine and chemokine concentrations, including interleukin-6 (IL-6) and KC (i.e., IL-8 in human), but it also enhanced IL-3 production compared to vehicle-treated controls. Mice treated with CIP displayed a greater repopulation of bone marrow cells. CIP also limited CI-induced apoptosis and autophagy in ileal villi, systemic bacterial infection, and IgA production. CIP treatment led to LD_0/10 compared to LD_20/10 for vehicle-treated group after CI. Given the multiple beneficial activities of CIP shown in our experiments, CIP may prove to be a useful therapeutic drug for CI.

Use of mesenchymal stem cells (MSC) in chronic inflammatory fistulizing and fibrotic diseases: a comprehensive review

Mesenchymal stem cells (MSC), multipotent adult stem cells, feature the potential to regenerate tissue damage and, in parallel, inhibit inflammation and fibrosis. MSC can be safely transplanted in autologous and allogeneic ways as they are non-immunogenic, and consequently represent a therapeutic option for refractory connective tissue diseases, fibrosing diseases like scleroderma and fistulizing colitis like in Crohn's disease. Actually, there are more than 200 registered clinical trial sites for evaluating MSC therapy, and 22 are on autoimmune diseases. In irradiation-induced colitis, MSC accelerate functional recovery of the intestine and dampen the systemic inflammatory response. In order to provide rescue therapy for accidentally over-irradiated prostate cancer patients who underwent radiotherapy, allogeneic bone marrow-derived MSC from family donors were intravenously infused to three patients with refractory and fistulizing colitis resembling fistulizing Crohn's disease. Systemic MSC therapy of refractory irradiation-induced colitis was safe and effective on pain, diarrhoea, hemorrhage, inflammation and fistulization accompanied by modulation of the lymphocyte subsets towards an increase of T regulatory cells and a decrease of activated effector T cells. The current data indicate that MSC represent a promising alternative strategy in the treatment of various immune-mediated diseases. Encouraging results have already been obtained from clinical trials in Crohn's disease and SLE as well as from case series in systemic sclerosis. MSC represent a safe therapeutic measure for patients who suffer from chronic and fistulizing colitis. These findings are instructional for the management of refractory inflammatory bowel diseases that are characterized by similar clinical and immunopathological features.

CD24 is expressed in gastric parietal cells and regulates apoptosis and the response to Helicobacter felis infection in the murine stomach

CD24 is expressed in the putative stem cells within several tissues and is overexpressed in gastric and colonic adenocarcinomas. Perturbed CD24 expression may therefore alter the response of gastrointestinal epithelia to damage-inducing stimuli that induce cancer. We have investigated the effects of CD24 deletion on gastric responses to Helicobacter felis infection and γ-irradiation using CD24-null mice. Gastric CD24 expression was determined by immunohistochemistry in C57BL/6 mice. Female CD24-null and C57BL/6 mice were infected with H. felis for 6 wk, and inflammation, proliferation, apoptosis, and parietal cell numbers were assessed in gastric tissue sections. Apoptosis and proliferation were analyzed on a cell-positional basis in stomach, small intestine, and colon of CD24-null and C57BL/6 mice following γ-irradiation. Apoptosis was also assessed in HT29 cells following CD24 siRNA transfection. Of CD24-positive cells in the gastric corpus, 98% were H(+)-K(+)-ATPase-expressing parietal cells. CD24-null mice showed more prominent gastric H. felis colonization than C57BL/6 mice but displayed a marked reduction in corpus inflammation, reduced Ki67 labeling, and less gastric atrophy 6 wk following infection. Corpus apoptosis was elevated in CD24-null mice, but this did not increase further with H. felis infection as observed in C57BL/6 mice. More apoptotic cells were found following γ-irradiation in the stomach, small intestine, and colon of CD24-null mice and following CD24 knockdown in vitro. In conclusion, CD24 is expressed in gastric parietal cells, where it modulates gastric responses to H. felis and γ-radiation. CD24 also regulates susceptibility to apoptosis in the distal murine gastrointestinal tract.

Wnt signaling, stem cells, and cancer of the gastrointestinal tract

The Wnt signaling pathway was originally uncovered as one of the prototype developmental signaling cascades in invertebrates as well as in vertebrates. The first indication that Wnt signaling also plays a role in the adult animal came from the study of the intestine of Tcf-4 (Tcf7L2) knockout mice. The gastrointestinal epithelium continuously self-renews over the lifetime of an organism and is, in fact, the most rapidly self-renewing tissue of the mammalian body. Recent studies indicate that Wnt signaling plays a central role in the biology of gastrointestinal stem cells. Furthermore, mutational activation of the Wnt cascade is the principle cause of colon cancer.

Origin and maintenance of the intestinal cancer stem cell

Colorectal cancer is one of the most common cancers in the western world and its incidence is steadily increasing. Understanding the basic biology of both the normal intestine and of intestinal tumorigenesis is vital for developing appropriate and effective cancer therapies. However, relatively little is known about the normal intestinal stem cell or the hypothetical intestinal cancer stem cell, and there is much debate surrounding these areas. This review briefly describes our current understanding of the properties of both the intestinal stem cell and the intestinal cancer stem cell. We also discuss recent theories regarding the origin of the intestinal cancer stem cell, and the signals required for its maintenance and proliferation. Finally, we place the relevance of cancer stem cell research into context by discussing potential clinical applications of targeting the intestinal cancer stem cell.

Redistribution of the tight junction protein ZO-1 during physiological shedding of mouse intestinal epithelial cells

We questioned how tight junctions contribute to intestinal barrier function during the cell shedding that is part of physiological cell renewal. Intravital confocal microscopy studied the jejunal villus epithelium of mice expressing a fluorescent zonula occludens 1 (ZO-1) fusion protein. Vital staining also visualized the cell nucleus (Hoechst staining) or local permeability to luminal constituents (Lucifer Yellow; LY). In a cell fated to be shed, ZO-1 redistributes from the tight junction toward the apical and then basolateral cell region. ZO-1 rearrangement occurs 15 ± 6 min (n = 28) before movement of the cell nucleus from the epithelial layer. During cell extrusion, permeation of luminal LY extends along the lateral intercellular spaces of the shedding cell only as far as the location of ZO-1. Within 3 min after detachment from the epithelial layer, nuclear chromatin condenses. After cell loss, a residual patch of ZO-1 remains in the space previously occupied by the departed cell, and the size of the patch shrinks to 14 ± 2% (n = 15) of the original cell space over 20 min. The duration of cell shedding measured by nucleus movement (14 ± 1 min) is much less than the total duration of ZO-1 redistribution at the same sites (45 ± 2 min). In about 15% of cell shedding cases, neighboring epithelial cells also undergo extrusion with a delay of 5-10 min. With the use of normal mice, ZO-1 immunofluorescent staining of fixed tissue confirmed ZO-1 redistribution and the presence of ZO-1 patches beneath shedding cells. Immunostaining also showed that redistribution of ZO-1 occurred without corresponding mixing of apical and basolateral membrane domains as marked by ezrin or E-cadherin. ZO-1 redistribution is the earliest cellular event yet identified as a herald of physiological cell shedding, and redistribution of tight junction function along the lateral plasma membrane sustains epithelial barrier during cell shedding.

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

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

Circadian regulation of cell cycle: Molecular connections between aging and the circadian clock

The circadian clock generates oscillations in physiology and behavior, known as circadian rhythms. Links between the circadian clock genes Periods, Bmal1, and Cryptochromes and aging and cancer are emerging. Circadian clock gene expression is changed in human pathologies, and transgenic mice with mutations in clock genes develop cancer and premature aging. Control of genome integrity and cell proliferation play key roles in the development of age-associated pathologies and carcinogenesis. Here, we review recent data on the connection between the circadian clock and control of the cell cycle. The circadian clock regulates the activity and expression of several critical cell cycle and cell cycle check-point-related proteins, and in turn cell cycle-associated proteins regulate circadian clock proteins. DNA damage can reset the circadian clock, which provides a molecular mechanism for reciprocal regulation between the circadian clock and the cell cycle. This circadian clock-dependent control of cell proliferation, together with other known physiological functions of the circadian clock such as the control of metabolism, oxidative and genotoxic stress response, and DNA repair, opens new horizons for understanding the mechanisms behind aging and carcinogenesis.

Fishing for intestinal cancer models: unraveling gastrointestinal homeostasis and tumorigenesis in zebrafish

Zebrafish has proven to be a highly versatile model for comprehensive studies of gene function in development. Given that the molecular pathways involved in epithelial carcinogenesis appear to be conserved across vertebrates, zebrafish is now considered as a valid model to study tumor biology. Development and homeostasis in multicellular organisms are dependent on a complex interplay between cell proliferation, migration, differentiation, and cell death. The Wnt signaling pathway is a major signaling pathway during embryonic development and is the key regulator of self-renewal homeostasis in several adult tissues. A large body of knowledge on adult stem-cell biology has arisen from the study of the intestinal epithelium over the past 20 years. The Wnt pathway has appeared as its principal regulator of homeostatic self-renewal. Moreover, most cancers of the intestine are caused by activating mutations in the Wnt pathway. Recently, zebrafish models have been developed to study Wnt pathway-induced cancer. An appealing avenue for cancer research in zebrafish is large-scale screens to identify chemotherapeutic and chemopreventive agents in conjunction with the in vivo imaging approaches that zebrafish affords.

Shorter exposures to harder X-rays trigger early apoptotic events in Xenopus laevis embryos

Background

A long-standing conventional view of radiation-induced apoptosis is that increased exposure results in augmented apoptosis in a biological system, with a threshold below which radiation doses do not cause any significant increase in cell death. The consequences of this belief impact the extent to which malignant diseases and non-malignant conditions are therapeutically treated and how radiation is used in combination with other therapies. Our research challenges the current dogma of dose-dependent induction of apoptosis and establishes a new parallel paradigm to the photoelectric effect in biological systems.

Methodology/Principal Findings

We explored how the energy of individual X-ray photons and exposure time, both factors that determine the total dose, influence the occurrence of cell death in early Xenopus embryo. Three different experimental scenarios were analyzed and morphological and biochemical hallmarks of apoptosis were evaluated. Initially, we examined cell death events in embryos exposed to increasing incident energies when the exposure time was preset. Then, we evaluated the embryo's response when the exposure time was augmented while the energy value remained constant. Lastly, we studied the incidence of apoptosis in embryos exposed to an equal total dose of radiation that resulted from increasing the incoming energy while lowering the exposure time.

Conclusions/Significance

Overall, our data establish that the energy of the incident photon is a major contributor to the outcome of the biological system. In particular, for embryos exposed under identical conditions and delivered the same absorbed dose of radiation, the response is significantly increased when shorter bursts of more energetic photons are used. These results suggest that biological organisms display properties similar to the photoelectric effect in physical systems and provide new insights into how radiation-mediated apoptosis should be understood and utilized for therapeutic purposes.

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

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

Protective effect of Biophytum sensitivum (L.) DC on radiation-induced damage in mice

The radioprotective effect of Biophytum sensitivum methanol extract was studied using in vivo mice model . Animals were exposed to whole body gamma irradiation (6 Gy/animal) after treatment with B. sensitivum (50mg/kg b.wt.) followed by estimation of cytosolic enzymes, level of antioxidants, hematological parameters, bone marrow cellular progenitors, serum cytokine levels and spleen hematopoietic colonies. Administration of B. sensitivum could reduce the enhanced level of ALP, GPT and LPO levels in irradiated animals. B. sensitivum could significantly enhance the glutathione (GSH) content in liver and intestinal mucosa of irradiated animals. B. sensitivum treatment could enhance the Total WBC count, cellularity of bone marrow, alpha-esterase positive cells, and relative organ weight of spleen as well as thymus. The number of hematopoietic colonies on the surface of the spleen was found to be enhanced after B. sensitivum treatment. B. sensitivum treatment could also stimulate the production of cytokines such as IL-1beta, IFN-gamma and GM-CSF in animals exposed to whole body gamma irradiation. The present investigation suggests that the protective effect of Biophytum sensitivum on Radiation-Induced hemopoietic damage is mediated through immunomodulation as well as sequential induction of IL-1beta, GM-CSF and IFN-gamma.

Efficacy of CR3294, a new benzamidine derivative, in the prevention of 5-fluorouracil-induced gastrointestinal mucositis and diarrhea in mice

PURPOSE

Gastrointestinal mucositis, commonly associated with diarrhea, is a dose-limiting toxicity of chemotherapy. The new benzamidine derivative CR3294 reduces tissue damage in animal models of intestinal inflammation. Thus, we tested whether CR3294 had the potential to prevent chemotherapy-induced mucositis.

METHODS

In tests on isolated cells, reactive oxygen species (ROS) formation and cytokine release were measured by chemiluminescence and immunoassays, respectively. In studies in vivo, BDF1 mice were given oral CR3294 (2.5-20 mg/kg) for 3 days before receiving 5-fluorouracil. Intestinal crypt survival, cell apoptosis and proliferation, and diarrhea score were assessed. Additionally, nude mice bearing tumor xenografts were treated with CR3294 and/or 5-fluorouracil, and tumor growth was monitored.

RESULTS

CR3294 significantly inhibited cytokine release from stimulated leukocytes at concentrations similar to the IC(50) (2.9 +/- 0.2 muM) for ROS production by these cells. Consistent with these molecular findings, CR3294 dose-dependently protected the intestinal mucosa against 5-fluorouracil-induced toxicity in a mouse model of mucositis. The number of surviving crypts per cross-section in mice receiving 20 mg/kg CR3294 was 2.8-fold that in vehicle-treated animals (18.1 +/- 1.9 vs. 6.5 +/- 0.9, P < 0.001). Moreover, CR3294 decreased the cumulative diarrhea score by 50%, reduced by nearly 70% the incidence of severe episodes, and increased by 3-fold the number of mice without diarrhea. CR3294 neither affected the growth of tumor xenografts nor protected tumors from the cytotoxic activity of 5-fluorouracil.

CONCLUSIONS

This study demonstrates that CR3294 acts on key molecular targets to reduce the signs of mucositis and the occurrence of diarrhea in mice exposed to the chemotherapy drug 5-fluorouracil.

The stem cells of small intestinal crypts: where are they?

Recently, there has been resurgence of interest in the question of small intestinal stem cells, their precise location and numbers in the crypts. In this article, we attempt to re-assess the data, including historical information often omitted in recent studies on the subject. The conclusion we draw is that the evidence supports the concept that active murine small intestinal stem cells in steady state are few in number and are proliferative. There are two evolving, but divergent views on their location (which may be more related to scope of capability and reversibility than to location) several lineage labelling and stem cell self-renewing studies (based on Lgr5 expression) suggest a location intercalated between the Paneth cells (crypt base columnar cells (CBCCs)), or classical cell kinetic, label-retention and radiobiological evidence plus other recent studies, pointing to a location four cell positions luminally from the base of the crypt The latter is supported by recent lineage labelling of Bmi-1-expressing cells and by studies on expression of Wip-1 phosphatase. The situation in the human small intestine remains unclear, but recent mtDNA mutation studies suggest that the stem cells in humans are also located above the Paneth cell zone. There could be a distinct and as yet undiscovered relationship between these observed traits, with stem cell properties both in cells of the crypt base and those at cell position 4.

Inflammation and proliferation act together to mediate intestinal cell fusion

Cell fusion between circulating bone marrow-derived cells (BMDCs) and non-hematopoietic cells is well documented in various tissues and has recently been suggested to occur in response to injury. Here we illustrate that inflammation within the intestine enhanced the level of BMDC fusion with intestinal progenitors. To identify important microenvironmental factors mediating intestinal epithelial cell fusion, we performed bone marrow transplantation into mouse models of inflammation and stimulated epithelial proliferation. Interestingly, in a non-injury model or in instances where inflammation was suppressed, an appreciable baseline level of fusion persisted. This suggests that additional mediators of cell fusion exist. A rigorous temporal analysis of early post-transplantation cellular dynamics revealed that GFP-expressing donor cells first trafficked to the intestine coincident with a striking increase in epithelial proliferation, advocating for a required fusogenic state of the host partner. Directly supporting this hypothesis, induction of augmented epithelial proliferation resulted in a significant increase in intestinal cell fusion. Here we report that intestinal inflammation and epithelial proliferation act together to promote cell fusion. While the physiologic impact of cell fusion is not yet known, the increased incidence in an inflammatory and proliferative microenvironment suggests a potential role for cell fusion in mediating the progression of intestinal inflammatory diseases and cancer.

Effects of pharmacological inhibition and genetic deficiency of plasminogen activator inhibitor-1 in radiation-induced intestinal injury

PURPOSE

To investigate effects of plasminogen activator inhibitor 1 (PAI-1) genetic deficiency and pharmacological PAI-1 inhibition with PAI-039 in a mouse model of radiation-induced enteropathy.

METHODS AND MATERIALS

Wild-type (Wt) and PAI-1(-/-) knockout mice received a single dose of 19 Gy to an exteriorized localized intestinal segment. Sham and irradiated Wt mice were treated orally with 1 mg/g of PAI-039. Histological modifications were quantified using a radiation injury score. Moreover, intestinal gene expression was monitored by real-time PCR.

RESULTS

At 3 days after irradiation, PAI-039 abolished the radiation-induced increase in the plasma active form of PAI-1 and limited the radiation-induced gene expression of transforming growth factor beta1 (TGF-beta1), CTGF, PAI-1, and COL1A2. Moreover, PAI-039 conferred temporary protection against early lethality. PAI-039 treatment limited the radiation-induced increase of CTGF and PAI-1 at 2 weeks after irradiation but had no effect at 6 weeks. Radiation injuries were less severe in PAI-1(-/-) mice than in Wt mice, and despite the beneficial effect, 3 days after irradiation, PAI-039 had no effects on microscopic radiation injuries compared to untreated Wt mice.

CONCLUSIONS

A genetic deficiency of PAI-1 is associated with amelioration of late radiation enteropathy. Pharmacological inhibition of PAI-1 by PAI-039 positively impacts the early, acute phase increase in plasma PAI-1 and the associated radiation-induced gene expression of inflammatory/extracellular matrix proteins. Since PAI-039 has been shown to inhibit the active form of PAI-1, as opposed to the complete loss of PAI-1 in the knockout animals, these data suggest that a PAI-1 inhibitor could be beneficial in treating radiation-induced tissue injury in acute settings where PAI-1 is elevated.

Aminoguanidine alleviates radiation-induced small-bowel damage through its antioxidant effect

PURPOSE

To evaluate the effect and its mechanism of aminoguanidine (AG) on small-bowel protection after whole-abdominal irradiation (WAI) in rats.

METHODS AND MATERIALS

Male Sprague-Dawley rats (300-400 g) subjected to 12 Gy WAI were used for the study. Aminoguanidine at a dose of 50-800 mg/kg was administered by the gavage route 2 h before WAI. Mucosal damage of small bowel was evaluated by the grade of diarrhea and crypt survival; oxidative stress was determined by the level of 8-hydroxy 2'-deoxyguanosine (8-OHdG) with immunohistochemistry (IHC). Nitrosative stress was evaluated by the expression of inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (3-NT) with IHC, and systemic and portal vein NOx (nitrite + nitrate) levels were measured and compared with and without AG treatment after WAI.

RESULTS

Aminoguanidine showed a dose-dependent effect against WAI-induced diarrhea. Aminoguanidine at a dose of 400 mg/kg had the best protective effect, from 92% to 17% (p = 0.002). Aminoguanidine increased crypt survival from 23% to 46% (p = 0.003). It also significantly attenuated 8-OHdG expression but not 3-NT and iNOS expression at both 4 and 8 h after 12-Gy WAI. Aminoguanidine did not alter the portal vein NOx levels 4 and 8 h after 12-Gy WAI.

CONCLUSION

Aminoguanidine has a radioprotective effect against radiation-induced small-bowel damage due to its antioxidant effect but not inhibition of nitric oxide production. Dietary AG may have a potentially protective effect on the small intestine of patients subjected to pelvic and abdominal radiotherapies.

[Radiotherapy: what therapeutic orientations against the digestive aftereffects?]

Despite constant progress in radiotherapy techniques such as tumour imaging and cartography, techniques of radiation delivery or fractionation schedules, damage to normal gastro-intestinal tissues is inevitably associated with radiation therapy of pelvic tumours. Acute radiation enteritis concerns 80% of patients. It is related to stem cell loss, default in epithelial regenerating capacity and inflammation-induced mucosal dystrophy and ulceration. Chronic injury may develop in 5 to 10% of patients and is characterized by intestinal wall fibrosis resulting from an exaggerated scarring process, chronic inflammation and tissue necrosis. Research in mechanistic processes of normal tissue damage paved the way for new therapeutic approaches to emerge. These new targets include mucosal regeneration, reduction of vascular activation, inflammation and thrombosis, and fight against mesenchymal cells sustained activation. Effective strategies are multiple on preclinical models, but numerous efforts have to be made to achieve the complicated goal of protection of normal tissues from the side effects of radiation therapy.

Epithelial stem cell-related alterations in Trichinella spiralis-infected small intestine

OBJECTIVES

Infection of mice with the parasite Trichinella spiralis leads to small intestinal inflammation, characterized by changes in mucosal architecture and subpopulations of epithelial cells. This model has been used to explore changes in the epithelial proliferative cell population and expression of transforming growth factor-beta (TGF-beta).

MATERIALS AND METHODS

Histochemical and immunohistochemical studies were undertaken in duodenal samples. Location and number of Ki-67-positive cells were assessed using Score and Wincrypts program. Changes in mRNA transcripts were studied by real-time RT-PCR.

RESULTS

T. spiralis infection induced an increase in total number of proliferative (Ki-67-positive) cells per half crypt on day 2 post-infection. Transcription of Math1, a transcription factor required for secretory cell differentiation in the intestine, was up-regulated on days 6-18 post-infection. At these time points, numbers of Paneth cells at the crypt base were also increased and the epithelial proliferative zone was shifted up the crypt-villus axis. Transcription of TGF-beta isoforms within the small intestine was up-regulated on days 6 and 12 post-infection, but anti-TGF-beta antibody treatment had no effect on T. spiralis-induced changes in mucosal architecture or increase in Paneth/intermediate cells.

CONCLUSIONS

T. spiralis infection promotes an initial increase in small intestinal epithelial proliferation and subsequent cell differentiation along the secretory cell lineage. The resulting increase in numbers of Paneth cells at the crypt base causes the proliferative zone to move up the crypt-villus axis. Further studies are required to determine the significance of an increase in the expression of TGF-beta transcripts.

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

KLF4 gene expression is inhibited by the notch signaling pathway that controls goblet cell differentiation in mouse gastrointestinal tract

In Kruppel-like factor (KLF)-4-deficient mice, colonic goblet cell numbers are significantly reduced. Goblet cell development is regulated by the Notch signaling pathway. The aim of this study was to examine whether Notch represses KLF4 expression to regulate goblet cell differentiation. We first detected that KLF4 gene expression was upregulated in a human progastrin-overexpressing mouse model where goblet cell hyperplasia has been observed. We then found that mice treated with a gamma-secretase inhibitor (compound E, 10 micromol/kg) for 24 h, which inhibits the Notch signaling pathway, had significantly increased KLF4 mRNA levels in small intestine and colon, accompanied by an increased number of KLF4-expressing cells at the bottom of crypts in small intestine and colon. In a colon cancer cell line (HCT116 cells), KLF4 promoter activity was inhibited by a constitutively active form of Notch1 (ICN1) by transient cotransfection assays. This inhibition was significantly compromised by a dominant-negative RBPjk, a repressive mediator of the Notch signaling pathway. An ICN1-responsive element was then mapped in the human KLF4 promoter between -151 and -122 nucleotides upstream of the transcriptional start site. It was also found that an intact ICN1-responsive element is required for ICN1 to inhibit KLF4 promoter activity by transient cotransfection assays. Our findings thus reveal a possible mechanism by which KLF4 is inhibited by Notch, which controls goblet cell differentiation in mouse gastrointestinal tract.

Colonic and colorectal cancer stem cells: progress in the search for putative biomarkers

The maintenance of healthy colonic crypts is dependent on the integrity of the adult epithelial stem cells located within them. Perturbations in stem cell dynamics are generally believed to represent the first step towards colorectal tumorigenesis. Experimental manipulation of intestinal stem cells has greatly increased our understanding of them, but further progress has been slowed due to the absence of a reliable stem cell biomarker. In this review we discuss the candidate colonic stem cell biomarkers which have been proposed. Furthermore, we investigate the putative biomarkers for so-called colorectal cancer stem cells, a highly aggressive subpopulation of cells considered to drive tumour development.