Role of impaired regeneration of the mucosal epithelium in the pathogenesis of acute ulcers of the stomach and small intestine

The method of modelling of acute gastric and small intestinal ulcers by intraperitoneal administration of vincristine at a dose of 0.15-0.30 mg/kg body weight is suggested. The method is based on the property of vincristine to stop mitotic cell division at the stage of metaphase, thus impairing regeneration of the epithelium in the stomach and small intestine. The experiments on 20 dogs have shown that single vincristine administration caused the accumulation of cells with nuclei at the stage of metaphase in the generative areas. Mucosa defects formed at these sites acquired all the features of acute ulcers by the third day. The model demonstrates the pathogenetic role of impaired mucous epithelium regeneration and permits the studies of pathogenesis of acute ulcer formation.     

Simulation modelling of the postradiation restoration of the crypt-villus system

Basic principles have been developed for a discrete stochastic simulation model of an elementary proliferative unit of the intestinal epithelium, a "crypt-villus" system. The analysis of the results obtained after a single exposure of the animal's abdomen to 3 and 6 Gy radiation has demonstrated that the dynamics of the number of cells that synthesize DNA in a small intestine crypt of exposed mice depends on the rate of radiation damage repair (50 to 100 h following irradiation). The rate of repair after 6 Gy irradiation is 1.5 times lower that after 3 Gy. The changes in the shape of the labeled mitoses curve, followed up during the postirradiation recovery of the intestinal epithelium, may occur with the time parameters of the cell mitotic cycle being invariable.     

Radiobiology of stem cells in intestinal epithelium. Effect of single and multiple preliminary sublethal irradiation of mice on the dose dependence of the survival of stem cells in small intestine epithelium

After a single or three-fold whole body irradiation of mice with a dose of 4 Gy and the time interval for the proliferation to be restored (5 days or 3 weeks) the survival curve for stem cells of small intestine epithelium with regard to radiation dose was the same as that for non-preirradiated mice. This indicated that the proliferative potential of stem cells in these experimental conditions was not reduced.     

Hypophysectomy-induced inhibition of augmented acetylcholine responses of the rat bowel following adrenalectomy and/or whole body irradiation

Summary Functional changes in the intestinal responsiveness to a fixed. dose of acetylcholine were studied in muscle strips removed from young adult male rats previously exposed to whole body gamma radiation. In the irradiated rat the responsiveness to a fixed dose of acetylcholine was found to be augmented in the small intestine but not in the colon. Similar motor patterns for the small intestine were found when muscle strips from adrenalectomized rats were studied. Preradiation adrenalectomy further exaggerated the post-radiation sensitivity of the rat small intestine to acetylcholine. Hypophysectomy prior to either adrenalectomy and/or whole body radiation was associated with an absence of augmented small intestinal motor activity following administration of acetylcholine. The response of the large bowel to acetylcholine, however, was not modified by adrenalectomy and/or hypophysectomy. These observations suggest an endocrine component to the acute 3–5 day intestinal radiation syndrome.This work was presented at the 25th Annual Meeting of the Radiation Research Society, San Juan, Puerto Rico, May 1977     

Mathematical modeling of the dynamics of the intestinal epithelium in non-irradiated and irradiated mammals]

A mathematical model has been developed to describe the dynamics of the crypt-villus system of the small intestine epithelium in nonirradiated and chronically irradiated mammals. The model involves the chalone mechanism of regulation of crypt cell reproduction and represents a system of nonlinear differentiation equations. The model presents the dynamics of the small intestine epithelium in nonirradiated animals, including stable fluctuations of the concentrations of crypt and villus cells (the limited cycle), and simulates quantitatively the impairment of the intestinal epithelium in small laboratory animals subjected to long-term irradiation.     

Gut commensal bacteria,Paneth cells and their relations to radiation enteropathy

In steady state, the intestinal epithelium forms an important part of the gut barrier to defend against luminal bacterial attack. However, the intestinal epithelium is compromised by ionizing irradiation due to its inherent self-renewing capacity. In this process, small intestinal bacterial overgrowth is a critical event that reciprocally alters the immune milieu. In other words, intestinal bacterial dysbiosis induces inflammation in response to intestinal injuries, thus influencing the repair process of irradiated lesions. In fact, it is accepted that commensal bacteria can generally enhance the host radiation sensitivity. To address the determination of radiation sensitivity, we hypothesize that Paneth cells press a critical “button” because these cells are central to intestinal health and disease by using their peptides, which are responsible for controlling stem cell development in the small intestine and luminal bacterial diversity. Herein, the most important question is whether Paneth cells alter their secretion profiles in the situation of ionizing irradiation. On this basis, the tolerance of Paneth cells to ionizing radiation and related mechanisms by which radiation affects Paneth cell survival and death will be discussed in this review. We hope that the relevant results will be helpful in developing new approaches against radiation enteropathy.     

Expression of apolipoprotein B-100 in isolated human small intestine epithelium.

Apolipoprotein B-48 (apoB48) is synthesized in the small intestine and becomes a component of chylomicrons (CM). Apolipoprotein B-100 (apoB100) is synthesized in liver and becomes a component of both very low density lipoprotein (VLDL) and low density lipoprotein (LDL). To evaluate whether apoB100 is present in the human small intestine, we performed immunohistochemical staining using anti-apoB100 monoclonal antibody (mAb). Jejunal samples stained positive and the granular staining was noted in the supranuclear region of epithelial cells. We also identified apoB100 expression in the epithelial cells by immunoblotting and dot-blotting of PCR-amplified cDNA. In order to exclude submucosal stroma contaminated with blood, we used isolated epithelium from human small intestine obtained by a crypt isolation technique. The results indicate that not only apoB48, but also apoB100 are expressed in human small intestine epithelium. The expression of apoB100 suggests that the dietary VLDL may be synthesized in human small intestine epithelium and converted into LDL, which might play an important role in atherosclerosis.     

Prenatal and postnatal development of the small intestine in the insectivore Suncus murinus

The development of the small intestine in the insectivore Suncus murinus was noted during the period from 21 days' gestation to 20 days after birth. At 21 days of gestation, the proximal small intestine exhibited the beginning of villus formation, whereas the distal small intestine preserved the stratified epithelium. Stratified epithelium in the distal small intestine changed into a single layer by 24 days' gestation. At 26 days' gestation, each epithelial cell was immature; but by 28 days mature-looking epithelial cells were found. The shape of the villi changed from cuboid to columnar during the same period. The connective-tissue cores of the villi began to develop at 7 days after birth in the proximal small intestine and at 15 days after birth in the distal small intestine. Crypts appeared at 15 days after birth. Endocytosis of epithelial cells took place at 28 days of gestation. In the proximal small intestine, supranuclear vesicle clusters were observed first at birth; they began to decrease both in number and size at 10 days' gestation and then disappeared completely by 20 days after birth. In the distal small intestine, large supranuclear vacuoles were observed first at 28 days of gestation. Although these vacuoles invariably were found up to 15 days after birth, they also disappeared completely by 20 days. Epithelial cells showed a structure similar to those of the adult after weaning.     

(−)-Epicatechin mitigates radiation-induced intestinal injury and promotes intestinal regeneration via suppressing oxidative stress

Abstract

The high radiosensitivity of the intestinal epithelium limits the survival of victims by nuclear accidents or terrorism and limits effective radiotherapy against abdominal malignancies. Recently, we reported that (?)-epicatechin (EC) modulates oxidative stress and exerts neuroprotection. Here, we investigate the protective effects of EC against intestinal damage induced by radiation. The established model is acute moderate but reversible intestinal injury damage. We also set up the injured model of “minigut” ex vivo, which mimic the process of intestinal regeneration in vivo. We found that EC can repress oxidative stress by regulating SOD and MDA levels in serum and intestine tissue. Correspondingly, EC can decrease apoptosis of crypt cells in Lgr5-EGFP-IRES-creERT2 mice after radiation. Further studies demonstrated that EC can promote Nrf2 translocation from cytoplasm to nuclear and then activate the expression of HO1 and NQO1. Interestingly, EC can enhance the activity of intestine stem cells labelled by Lgr5 and promote intestinal epithelium regeneration determined by HE and immunofluorescence staining in vivo and in vitro. We also found that EC can activate the Wnt/β-catenin signal pathway confirmed by TCF/LEF luciferase reporter assay. Together, EC can provide the protective effect on intestine and promote intestinal regeneration after radiation through Nrf2 and Wnt/β-catenin signal pathway.     

The problem of sugar resorption in the small intestine: histochemical studies by means of the Gomori method]

The role of alkaline phosphatase during active absorption of sugars is experimented with Gomori's histochemical method. Experiments on empty intestine show that the surgical intervention does not alter the phosphate content of the wall of the small intestine. Absorption experiments with 10% and 5,4% (isotonic) glucose solutions demonstrate a marked decrease in the alkaline phosphatase content of the wall of the small intestine. In half of the cases only, absorption experiments with a 10% mannitol solution determine a small decrease in the alkaline phosphatase of the wall of the small intestine. In 90% of the cases, there are lesions of the intestinal epithelium.     

Hyaluronic acid is radioprotective in the intestine through a TLR4 and COX-2-mediated mechanism

The intestinal epithelium is sensitive to radiation injury. Damage to the intestinal epithelium is dose limiting in radiation therapy of abdominal cancers. There is a need for agents that can be given before radiation therapy to protect the intestinal epithelium. C57BL6 mice were subjected to 12 Gy of total body radiation. Some mice received intraperitoneal hyaluronic acid (HA) before radiation. Mice were killed 6 h after radiation to assess radiation-induced apoptosis in the intestine; other mice were killed at 84 h to assess crypt survival. Total body radiation (12 Gy) resulted in increased expression of HA synthases and HA in the intestine and increased plasma HA (5-fold). Intraperitoneal injection of HA (30 mg/kg) before radiation resulted in a 1.8-fold increase in intestinal crypt survival and a decrease in radiation-induced apoptosis. The radioprotective effects of HA were not seen in Toll-like receptor 4 (TLR4)- or cyclooxygenase-2 (COX-2)-deficient mice. Intraperitoneal injection of HA induced a 1.5-fold increase in intestinal COX-2 expression, a 1.5-fold increase in intestinal PGE?, and the migration of COX-2-expressing mesenchymal stem cells from the lamina propria in the villi to the lamina propria near the crypt. We conclude that 1) radiation induces increased HA expression through inducing HA synthases, 2) intraperitoneal HA given before radiation reduces radiation-induced apoptosis and increases crypt survival, and 3) these radioprotective effects are mediated through TLR4, COX-2, and the migration of COX-2-expressing mesenchymal stem cells.     

Dosimetric criteria for the intestinal form of acute radiation injury in man. An empirical model

On the basis of the results of radiobiological studies on acute nonuniform irradiation of the animal's abdomen a dose dependence has been found for the duration of the injury to barrier properties of the small intestine epithelium, T(D). With relative coordinates x = D/LD50 and y = T (D)/T(LD50), this dependence may be represented by a single function for various animal species.     

Pathologies Associated with the p53 Response

Although p53 is a major cancer preventive factor, under certain extreme stress conditions it may induce severe pathologies. Analyses of animal models indicate that p53 is largely responsible for the toxicity of ionizing radiation or DNA damaging drugs contributing to hematopoietic component of acute radiation syndrome and largely determining severe adverse effects of cancer treatment. p53-mediated damage is strictly tissue specific and occurs in tissues prone to p53-dependent apoptosis (e.g., hematopoietic system and hair follicles); on the contrary, p53 can serve as a survival factor in tissues that respond to p53 activation by cell cycle arrest (e.g., endothelium of small intestine). There are multiple experimental indications that p53 contributes to pathogenicity of acute ischemic diseases. Temporary reversible suppression of p53 by small molecules can be an effective and safe approach to reduce severity of p53-associated pathologies.     

Role of intestinal lymphatics in interstitial volume regulation and transmucosal water transport

Two of the principal functions of intestinal lymphatics are to assist in the maintenance of interstitial volume within relatively normal limits during alterations in capillary filtration (e.g., acute portal hypertension) and the removal of absorbed water and chylomicrons. The contribution of lymphatics to the prevention of interstitial overhydration or dehydration during alterations in transcapillary filtration is similar in the small intestine and colon. While the lymphatics of the small intestine contribute substantially to the removal of absorbed water (particularly at low and moderate absorption rates), the contribution of colonic lymphatics to the removal of the fluid absorbate is negligible. This difference is attributed to the relative caliber and location of lymphatics in the mucosal layer of the small and large intestines. In the small intestine, large lacteals lie in close proximity to transporting epithelium, while colonic lymph vessels are rather sparse and confined to the basal portion of the mucosa. In the small intestine, the lymphatics assume a more important role in removing absorbed water during lipid absorption than during glucose absorption.     

Radiation-induced gastric epithelial apoptosis occurs in the proliferative zone and is regulated by p53, bak, bax, and bcl-2

Unlike the small intestine and colon where gamma-radiation-induced apoptosis has previously been well characterized, the response of murine gastric epithelium to gamma-radiation has not been investigated in detail. Apoptosis was therefore assessed on a cell positional basis in gastric antral and corpus glands from adult male mice following gamma-radiation. Maximum numbers of apoptotic cells were observed in both antrum and corpus at 48 h and at radiation doses greater than 12 Gy. However, the number of apoptotic cells observed in the gastric epithelium was much lower than observed in the small intestine or colon after similar doses of radiation. Hematoxylin and eosin, caspase 3 immunohistochemistry, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling detected similar numbers and cell positional distributions of apoptotic cells, hence hematoxylin and eosin was used for subsequent studies. The highest numbers of apoptotic cells were observed at cell positions 5-6 in the antrum and cell positions 15-18 in the corpus. These distributions coincided with the distributions of PCNA-labeled proliferating cells, but not with the distributions of H(+)-K(+)-ATPase-labeled parietal cells or TFF2-labeled mucous neck cells. Decreased numbers of apoptotic gastric epithelial cells were observed in p53-null, bak-null, and bax-null mice compared with wild-type counterparts 6 and 48 h after 12 Gy gamma-radiation. Significantly increased numbers of apoptotic gastric epithelial cells were observed in bcl-2-null mice compared with wild-type littermates 6 h after 12 Gy gamma-radiation. Radiation therefore induces apoptosis in the proliferative zone of mouse gastric epithelium. This response is regulated by the expression of p53, bak, bax, and bcl-2.     

Differentiation of endocrinocytes in the small-intestinal epithelium of albino rats in ontogenesis]

By means of the light microscopy method differentiation and dynamics on contents of endocrinocytes have been studied in epithelium of the initial part of the jejunum, of the caudal part of the ileum and of the middle part between them during pre- and postnatal periods of development. Formation of the endocrine apparatus of the mucous membrane epithelium in the small intestine takes place simultaneously with tissue differentiation of the epithelial layer. The population density of endotheliocytes of the mucous membrane is maximal in the initial part of the jejunum and decreases gradually in the caudal direction. By the 15th day of the postnatal development endocrinocytes in composition of the epithelium in the small intestine reach a high level of the specific differentiation and their amount increases by 1.3 times in comparison with that in newborn animals.     

Inductive action of epithelium on differentiation of intestinal connective tissue of Xenopus laevis tadpoles during metamorphosis in vitro

The action of the epithelium on differentiation of connective tissue cells of Xenopus small intestine during metamorphosis was investigated by using culture and morphological techniques. Connective tissue fragments isolated from the small intestine at stage 57 were cultivated in the presence or absence of homologous epithelium. In the presence of the epithelium, metamorphic changes in the connective tissue were fully induced by hormones including thyroid hormone (T₃), as during spontaneous metamorphosis, whereas they were partially induced in the absence of the epithelium. Macrophage-like cells showing non-specific esterase activity in the connective tissue were much fewer in the absence of the epithelium than in the presence of it, and aggregates of fibroblasts possessing well-developed rough endoplasmic reticulum developed only in the presence of the epithelium. Just before the aggregation of the fibroblasts, the connective tissue close to the epithelium became intensely stained with concanavalin A (ConA) and wheat germ agglutinin (WGA). The present results indicate that the epithelium plays important roles in the differentiation of intestinal connective tissue cells, which in turn affect the epithelial transformation from larval to adult form during anuran metamorphosis. Thus, the tissue interaction between the epithelium and the connective tissue in the anuran small intestine is truly bidirectional.     

The cell cycle in the small intestine transplanted beneath the kidney capsule in syngenic mice

Summary Transplantation of a small fragment of the ileum beneath the kidney capsule in syngenic mice results in the formation of a cyst lined with proliferating intestinal epithelium. The duration of the cell cycle in this epithelium was determined (using tritiated thymidine and the FLM method) as 14.5 h, as compared with 11.5 h in the intestinal epithelium in situ. We conclude that the intestinal content has little effect on the cell cycle of epithelial cells of the small intestine.     

Localized Intestinal Radiation and Liquid Diet Enhance Survival and Permit Evaluation of Long-Term Intestinal Responses to High Dose Radiation in Mice

Background

In vivo studies of high dose radiation-induced crypt and intestinal stem cell (ISC) loss and subsequent regeneration are typically restricted to 5–8 days after radiation due to high mortality and immune failure. This study aimed to develop murine radiation models of complete crypt loss that permit longer-term studies of ISC and crypt regeneration, repair and normalization of the intestinal epithelium.

Methods

In C57Bl/6J mice, a predetermined small intestinal segment was exteriorized and exposed to 14Gy-radiation, while a lead shield protected the rest of the body from radiation. Sham controls had segment exteriorization but no radiation. Results were compared to C57Bl/6J mice given 14 Gy-abdominal radiation. Effects of elemental liquid diet feeding from the day prior to radiation until day 7 post-radiation were assessed in both models. Body weight and a custom-developed health score was assessed every day until day 21 post-radiation. Intestine was assessed histologically.

Results

At day 3 after segment radiation, complete loss of crypts occurred in the targeted segment, while adjacent and remaining intestine in segment-radiated mice, and entire intestine of sham controls, showed no detectable epithelial damage. Liquid diet feeding was required for survival of mice after segment radiation. Liquid diet significantly improved survival, body weight recovery and normalization of intestinal epithelium after abdominal radiation. Mice given segment radiation combined with liquid diet feeding showed minimal body weight loss, increased food intake and enhanced health score.

Conclusions

The segment radiation method provides a useful model to study ISC/crypt loss and long-term crypt regeneration and epithelial repair, and may be valuable for future application to ISC transplantation or to genetic mutants that would not otherwise survive radiation doses that lead to complete crypt loss. Liquid diet is a simple intervention that improves survival and facilitates long-term studies of intestine in mice after high dose abdominal or segment radiation.     

Late effects in the mouse small intestine after a clinically relevant multifractionated radiation treatment

Late radiation effects were investigated in the mouse small intestine after a daily fractionated radiation treatment. Mice were given 14 X 3 Gy in 2 weeks over a partial abdominal irradiation field. There was evidence for late injury in the intestinal epithelium, the submucosa, and the subserosa. Late damage in the epithelium was shown histologically by a reduced crypt number and villus atrophy at 3 and 6 months but not at 24 h after the end of treatment. The reduction in crypt number was significant in the ileum at 3 and 6 months after irradiation: 100 +/- 4 and 98 +/- 5 (SEM) per circumference, respectively, versus 132 +/- 3 and 146 +/- 6 in age-matched controls (P less than 0.01, t test). The mitotic activity in the crypts of the irradiated animals was significantly increased at all investigated times, suggesting a prolonged but insufficient compensatory response to maintain the mucosal integrity. The repercussion on intestinal epithelial function was, at least in part, reflected by a progressively reduced body weight gain up to 5 g at 3 months after treatment. The ability of the surviving crypt stem cells to form microcolonies after irradiation, however, was not impaired. Evidence for injury in the submucosa was provided from macroscopic and histological examination. Macroscopically, at 6 months after treatment, narrowed and rigid bowel segments surrounded by fibrotic adhesions were observed, causing partial intestinal obstruction. In addition, sometimes focal areas of hemorrhage and infarction in small bowel segments were present. Histologically, diffuse and pronounced submucosal edema without increased fibrosis was seen, together with markedly dilated small blood vessels in focal areas of macroscopic intestinal infarction. The intestinal perfusion, as assessed by 86Rb extraction, was significantly but transiently reduced at 3 months after irradiation. These data suggest mainly late effects in the small intestine after this daily fractionated irradiation treatment. The reduced number of epithelial cells and the submucosal edema are possibly mediated by radiation injury in the intestinal microvasculature.