肠屏障功能障碍与新生儿坏死性小肠结肠炎

坏死性小肠结肠炎( necrotizing enterocolitis,NEC)是严重危及新生儿生命的消化系统疾病,是导致新生儿,尤其是早产儿死亡的重要病因之一。新生儿,尤其是早产儿维持肠屏障功能的作用元件发育不成熟,极易受损,不能有效形成上皮细胞间的紧密连接,无法早期形成正常肠道蠕动以及分泌型IgA的减少,因此各种致病因素极易诱发肠屏障功能障碍,导致菌群移位和败血症,造成严重的肠道损害甚至并发症。缺氧缺血、炎症反应、病原体感染均可造成肠机械屏障损害,微生态屏障建立延迟、免疫屏障发育的不成熟以及病理情况下的肠微循环障碍均参与NEC的发生。此外,miRNA在肠上皮细胞的分化、结构和屏障功能调控中也发挥重要作用。 NEC的组织病理改变是肠屏障功能障碍的结果,而肠屏障功能的损害则加重NEC的病理改变。因此,认识肠屏障功能障碍在 NEC发病过程中的作用,对于防治NEC意义重大。     

肠道微生态和新生儿坏死性小肠结肠炎

肠道微生态是由体内有益菌及有害菌共同构成的生态环境,是人体最大、最复杂的微生态系统.研究表明,适当的肠道微生物定植过程有助于肠道结构和功能发育以及免疫系统成熟,它决定了之后肠道发生疾病的风险.肠道微生态或益生菌与新生儿坏死性小肠结肠炎（neonatal necrotizing enterocolitis,NEC）的关系已越来越受到关注.该文就新生儿肠道微生态的构成及作用、肠道微生态在NEC发生中的作用及机制、益生菌对NEC的防治作用等研究进展作一综述.     

Intestinal obstruction following necrotizing enterocolitis (author's transl)

The increase in survival from necrotizing enterocolitis results in an increased rate of late sequelae. We would like to take the opportunity to emphasize these new complications by a review of our patient material. 11 (23.9%) patients from a total number of 46 showed signs and symptoms of intestinal obstruction at different points in the course of the disease. In two surviving patients out of this group of 11, a resection of postinflammatory gut stenosis had to be performed within the first year. In the 9 children who died, particular emphasis is being paid in the autopsy reports to obstructive lesions in the gastrointestinal tract. Due to this rather frequent event (23.9%) of postinflammatory formation of strictures and stenoses in the recovery from NEC a functional radiographic study of the intestinal patency seems mandatory before discharge of any patient with NEC with operative or conservative treatment.     

Intestinal atresia and necrotizing enterocolitis: Embryology and anatomy

The primitive gut originates at week 3 of gestation from the endoderm, with posterior incorporation of the remaining embryo layers. Wnt, Notch and TLR4 pathways have been shown to play central roles in the correct development of the intestine. The classical hypothesis for intestinal atresia development consists of failure in bowel recanalization or a vascular accident with secondary bowel reabsorption. These have been challenged due to the high frequency of associated malformations, and furthermore, with the discovery of molecular pathways and genes involved in bowel formation and correlated defects producing atresia.Necrotizing enterocolitis (NEC) has a multifactorial pathogenesis with prematurity being the most important risk factor; therefore, bowel immaturity plays a central role in NEC. Some of the same molecular pathways involved in gut maturation have been found to correlate with the predisposition of the immature bowel to develop the pathological findings seen in NEC.     

Intestinal epithelial apoptosis initiates gross bowel necrosis in an experimental rat model of neonatal necrotizing enterocolitis

The histopathology of necrotizing enterocolitis (NEC) is characterized by destruction of the mucosal layer in initial stages and by transmural necrosis of the intestinal wall in advanced stages of the disease. To test the hypothesis that enhanced epithelial apoptosis is an initial event underlying the gross histologic changes, we analyzed epithelial apoptosis and tissue morphology in an animal model of NEC and evaluated the effect of caspase inhibition on the incidence of experimental NEC in this model. Apoptosis was analyzed with terminal deoxynucleotidyltransferase-mediated dUTP-FITC nick end labeling (TUNEL) staining in intestinal sections and by measuring caspase 3 activity from intestinal lysates of neonatal rats subjected to formula feeding and cold/asphyxia stress (FFCAS) and from mother-fed (MF) controls. Morphologic evaluation was based on hematoxylin and eosin staining of intestinal sections. FFCAS resulted in histologic changes consistent with NEC, which were absent from MF animals. FFCAS was also associated with a significantly increased rate of nuclear DNA fragmentation in the small intestinal epithelium compared with MF. Elevated tissue caspase 3 activity confirmed the presence of apoptosis in samples with increased DNA fragmentation. Analysis of the coincidence of morphologic damage and apoptosis in corresponding tissue sections indicated that apoptosis precedes gross morphologic changes in this model. Furthermore, supplementation of formula with 8 boc-aspartyl(OMe)-fluoromethylketone, a pan-caspase inhibitor, significantly reduced the incidences of apoptosis and experimental NEC. These findings indicate that in neonatal rats FFCAS induces epithelial apoptosis that serves as an underlying cause for subsequent gross tissue necrosis.     

Pathogenetic lessons from experimental models of necrotizing enterocolitis

The pathogenesis of necrotizing enterocolitis (NEC) is poorly understood. We have developed several experimental models of NEC in rats and mice, and produced pathological changes similar to human NEC by injecting the animal with various combinations of inflammatory mediators, i.e., platelet activating factor (PAF), tumor necrosis factor (TNF), and bacterial endotoxin (LPS). In this review, we discuss the mechanism of actions of LPS, PAF, and TNF in the pathogenesis of bowel injury and present evidence associating these mediators with human NEC. Correspondence to: W. Hsueh     

Beneficial effects of Etanercept on experimental necrotizing enterocolitis

Purpose

Tissue damage in necrotizing enterocolitis (NEC) of infants occurs as a result of an uncontrolled inflammatory response. The aim of this study was to investigate any potential anti-inflammatory effects that Etanercept may have on the inflammatory response in an experimental NEC model in newborn rats.

Methods

Newborn pups were randomized into three groups immediately after birth (Control, NEC + Placebo and NEC + Etanercept). Pups in the NEC + Placebo and NEC + Etanercept groups were subjected to an NEC-inducing protocol (hypercarbia, hypothermia and hyperoxia) twice a day for 3 days. Pups in the NEC + Etanercept group were given an intraperitoneal injection of Etanercept. Rats were harvested for biochemical and histopathological examinations.

Results

The histopathological injury score of rats in the NEC + Placebo group was significantly higher compared to the NEC + Etanercept and Control groups (p < 0.05 for both comparisons). Tissue levels of tumor necrosis factor-α, interleukin-1β, and malondialdehyde were higher in the placebo group compared to the Etanercept group.

Conclusion

Our results suggest that Etanercept attenuates intestinal tissue damage in NEC by reducing inflammation and blocking the production of free-oxygen radicals, while also reducing tissue levels of tumor necrosis factor-α and interleukin-1β.     

T-cell-mediated mucosal immunity is attenuated in experimental necrotizing enterocolitis

In premature infants with necrotizing enterocolitis (NEC) the gastrointestinal mucosal barrier is immature, but little is known about the immune response of immature bowel. The aim of this study was to evaluate the intestinal mucosal immune response in experimental NEC. In general anaesthesia, NEC was induced in six newborn piglets by injection of bovine casein into terminal ileum. Six controls received an equal amount of saline. Four hours later, samples were taken from the macroscopically most affected part of the treated loop and from the macroscopically healthy untreated intestine. Monoclonal antibodies to porcine CD1, CD2, CD4, CD8, CD45 and IgM were used for immunohistochemical staining. Casein-treated bowel showed typical macro- and microscopic findings of NEC. No changes were found in the saline-treated bowel. In both groups the bowel outside the treatment sector was normal. In casein-treated animals, treated samples showed significant decrease in density of CD4+ cells when compared with saline-treated controls. Similar trend was found in CD2+ and CD8+ cells but without statistical significance. Macroscopically healthy proximal untreated samples showed significant decrease in densities of CD2+, CD4+ and CD8+ lymphocytes in casein-treated group when compared with control samples. In casein-treated animals the density of CD45+ cells in the non-injected bowel was also decreased, but this did not reach statistical significance. Densities of CD1+ and IgM+ cells did not differ between casein-treated and saline-treated groups. A significant T-cell decrease was found in the present NEC model. Surprisingly, this was most prominent in the macroscopically healthy bowel outside the casein injection segment. The reason for T-cell decrease remains unclear, but bovine casein is known to contain peptide fractions that can modulate immune function. These findings may have implications in the design of neonatal milk formulas.     

Osmolality of enteral formula and severity of experimental necrotizing enterocolitis

Purpose

Administration of hyperosmolar formula is regarded as a risk factor for the development of necrotizing enterocolitis (NEC). However, there are limited number of reports about the relationship between formula osmolality and NEC. The aim of this study is to evaluate the effects of formula concentration in an experimental model of NEC.

Methods

We studied experimental NEC in C57BL/6 mice. NEC was induced by giving hypoxia, gavage administration of lipopolysaccharide and gavage formula feeding from postnatal day 5–9. We used two types of formula: (1) hyperosmolar formula (HF): 15 g Similac + 75 ml Esbilac (849 mOsm/kg); (2) diluted formula (DF): dilute hyperosmolar formula with an equal amount of water (325 mOsm/kg). Controls were fed by the mother. On postnatal day 9, the ileum was harvested and evaluated for severity of mucosal injury (hematoxylin/eosin staining) and inflammation (PCR for IL6 and TNFα mRNA expression).

Results

The incidence of NEC was same in both HF and DF (80%). The intestinal inflammatory response was similar between HF and DF (IL6: p = 0.26, TNFα: p = 0.69).

Conclusions

This study indicates the osmolality of enteral formula does not affect incidence of experimental NEC. This experimental study provides new insights into the relationship between formula feeding and NEC.

     

Disordered enterocyte signaling and intestinal barrier dysfunction in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in neonates, and is characterized by the development of diffuse intestinal necrosis in the stressed, pre-term infant. Systemic stress causes a breakdown in the intestinal mucosal barrier, which leads to translocation of bacteria and endotoxin and the initiation of a signaling response within the enterocyte. This review summarizes recent evidence defining a clear role that defective enterocyte signaling plays in the pathogenesis of NEC through the following mechanisms: 1) The localized production of nitric oxide by villus enterocytes results in an increase in enterocyte apoptosis and impaired proliferation; 2) The translocation of endotoxin results in a PI3K-dependent activation of RhoA-GTPase within the enterocyte leading to decreased enterocyte migration and impaired restitution; 3) Dysregulated sodium-proton exchange within the enterocyte by endotoxin renders the enterocyte monolayer more susceptible to damage in the face of the acidic microenvironment characteristic of systemic sepsis; and 4) Endotoxin causes a p38-dependent release of the pro-inflammatory molecule COX-2 by the enterocyte, which potentiates the systemic inflammatory response. An understanding of the mechanisms by which disordered enterocyte signaling contributes to the pathogenesis of barrier failure and NEC--through these and other mechanisms--may lead to the identification of novel therapeutic approaches for this devastating disease.     

Intestinal innate immunity: how does it relate to the pathogenesis of necrotizing enterocolitis

The pathogenesis of necrotizing enterocolitis (NEC) is poorly understood, but appears to be multifactorial and highly associated with immaturity of the gastrointestinal tract, colonization of the intestinal microbiota, and immature innate immune system. The goal of this review is to provide an overview of some of these risk factors and how they might lead to the genesis of NEC. A better understanding of these factors should help us prevent and treat this devastating disease.     

Intestinal microcirculation and necrotizing enterocolitis: The vascular endothelial growth factor system

Necrotizing enterocolitis (NEC), a leading cause of morbidity and mortality in preterm neonates, is a devastating disease characterized by intestinal tissue inflammation and necrosis. NEC pathogenesis is multifactorial but remains unclear. Translocation of bacteria and/or bacterial products across a weak intestinal barrier in the setting of impaired mucosal immunity leads to an exaggerated inflammatory response and secondary mucosal epithelial injury. In addition to prematurity, other risk factors for NEC include congenital heart disease, maternal pre-eclampsia with placental vascular insufficiency, severe anemia and blood transfusion – all conditions that predispose the intestine to ischemia. We recently found that maldevelopment of the intestinal microvasculature plays an important role in NEC pathogenesis. Here we review the evidence supporting a role for defective development of the intestinal mucosal microvasculature and perturbations of intestinal blood flow in NEC, emphasizing the importance of vascular endothelial growth factor (VEGF) and the VEGF receptor-2 signaling pathway.     

Epidermal growth factor reduces hepatic sequelae in experimental necrotizing enterocolitis

BACKGROUND AND AIM: Neonatal necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. We recently demonstrated that the gut/liver axis plays an important role in the pathophysiology of NEC through the release of inflammatory mediators into the intestinal lumen. We have also shown that supplementation of formula with epidermal growth factor (EGF) dramatically decreases ileal pathology associated with experimental NEC. In this study, we examined the effects of EGF on the liver portion of the gut/liver axis in the neonatal rat model of NEC. METHODS: Newborn rats were divided into three experimental groups, NEC, hand-fed with growth-factor free formula; NEC + EGF, hand-fed with formula supplemented with 500 ng/ml rat EGF; or DF, dam fed. All animals were exposed to asphyxia and cold stress twice daily for 4 days to develop NEC. RESULTS: EGF receptor expression was significantly (p 相似文献   

Epidemiology of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a worldwide problem that has emerged in the past 25 years as the most common gastrointestinal emergency in neonatal intensive care units (NICU). In the United States the incidence ranges from 1 to 7.7% of NICU admissions. Ninety percent of the patients are premature infants. Mucosal injury, bacterial colonization and formula feeding are the three major pathogenetic factors that have been documented in most infants who have developed NEC. However, NEC may develop only if a threshold of injury, imposed by the coincidence of at least two of three events (intestinal ischemia, pathogenic bacteria, and excess of protein substrate) is exceeded. Immunological immaturity of the gut in premature babies may represent the crucial risk factor.