肠道微生态与早产儿坏死性小肠结肠炎的研究进展

坏死性小肠结肠炎（NEC）是早产儿常见的严重胃肠道疾病,其发病率及病死率与早产儿胎龄及出生体重呈负相关,可引起多种胃肠道并发症,并可对患儿神经系统发育造成不良影响。近年来研究发现肠道微生态失调在NEC发病中起重要作用,探究肠道微生态改变与NEC的相关性有助于NEC早期诊断及严重程度的预测。益生菌在降低早产儿NEC发病率和病死率中的作用已受到业界广泛关注,但其在临床应用中的有效性和安全性仍存在较大争议。本文主要就新生儿肠道微生态发育及其与早产儿NEC之间的关系,以及益生菌对NEC的预防作用作一综述。     

Microecology, intestinal epithelial barrier and necrotizing enterocolitis

Soon after birth, the neonatal intestine is confronted with a massive antigenic challenge of microbial colonization. Microbial signals are required for maturation of several physiological, anatomical, and biochemical functions of intestinal epithelial barrier (IEB) after birth. Commensal bacteria regulate intestinal innate and adaptive immunity and provide stimuli for ongoing repair and restitution of IEB. Colonization by pathogenic bacteria and/or dysmature response to microbial stimuli can result in flagrant inflammatory response as seen in necrotizing enterocolitis (NEC). Characterized by inflammation and hemorrhagic–ischemic necrosis, NEC is a devastating complication of prematurity. Although there is evidence that both prematurity and presence of bacteria, are proven contributing factors to the pathogenesis of NEC, the molecular mechanisms involved in IEB dysfunction associated with NEC have begun to emerge only recently. The metagenomic advances in the field of intestinal microecology are providing insight into the factors that are required for establishment of commensal bacteria that appear to provide protection against intestinal inflammation and NEC. Perturbations in achieving colonization by commensal bacteria such as premature birth or hospitalization in intensive care nursery can result in dysfunction of IEB and NEC. In this article, microbial modulation of functions of IEB and its relationship with barrier dysfunction and NEC are described.     

Mechanisms of nitric oxide-mediated intestinal barrier failure in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading intestinal emergency in premature infants. The underlying etiology of NEC remains elusive, but hypoxic conditions and early enteral feeding are consistently implicated as the main risk factors in the pathogenesis of NEC. We postulate that nitric oxide (NO) plays a key role as a molecular signaling "hub" in the generation of gut barrier failure in NEC. Clinical studies suggest that inflammatory cytokines and excessive NO production may contribute to the pathogenesis of NEC. One of the major challenges in defining the critical signaling pathways that lead to the development of NEC is the lack of specific biochemical markers that consistently delineate the early stages of NEC. Intestinal pathology and molecular markers derived from late-stage NEC represent end-stage findings and thus provide little insight into the early events that led to intestinal inflammation. Such markers may not represent viable therapeutic targets for the treatment or prevention of NEC. Therefore, novel strategies are needed to identify the patients at risk for NEC and define the clinically relevant molecules that characterize the early stages of NEC. This review will examine the mechanisms of NO-mediated gut barrier failure and propose novel genetic-based approaches for elucidating the critical molecular pathways in 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.     

Neonatal necrotizing enterocolitis, a disease of the immature intestinal mucosal barrier

Necrotizing enterocolitis (NEC) is an enigmatic process in that one single etiologic factor has been sought and not found. Epidemiologic studies suggest that immaturity of the host plays a very important role. This article reviews the intestinal host defense system and its immature nature early in life in animal models and humans and suggests that it is this immaturity, along with other factors, which allows for the proliferation and invasion of antigens and organism, and the subsequent development of NEC. Data are presented which support the efficacy of pharmacologic maturation of the intestinal barrier with growth factors, either prenatally or postnatally, to decrease the incidence of NEC or, potentially, to provide a more benign course for the disease.     

Mechanisms of gut barrier failure in the pathogenesis of necrotizing enterocolitis: Toll-like receptors throw the switch

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal causes in premature infants, and its overall survival has not improved in the past three decades. While the precise cause of NEC remains incompletely understood, we and others have shown that a major predisposing factor in the development and propagation of NEC is a breakdown of the intestinal barrier which leads to bacterial translocation and systemic sepsis. In seeking to identify the causes involved, we and others have also determined that activation of the receptor for bacterial endotoxin, namely toll-like receptor 4 (TLR4), is required for the development of intestinal barrier failure leading to NEC. We have also shown that the premature infant is endowed with strategies that can either limit or promote the extent of TLR4 signaling within the gut, which together determine the relative propensity with which NEC develops. In this review, we highlight the evidence for TLR4 signaling in the pathogenesis of NEC through a survey of its effects on gut barrier failure. We identify how TLR4 regulation within the gut can explain the unique susceptibility of the premature infant to the development of NEC, and highlight how strategies to limit the degree of TLR4 signaling can serve as novel therapeutic approaches for this devastating disease.     

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。     

The role of the intestinal microcirculation in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) continues to be a devastating inflammatory disease of the newborn intestine. Despite advances in management, morbidity and mortality remain high. While it is clear that intestinal ischemia plays a large role in disease pathogenesis, attempts to link NEC to intestinal macrovascular derangement have been largely unsuccessful. More recently, there has been a concerted effort to characterize the pathologic changes of the intestinal microcirculation in response to intestinal injury, including NEC. This microcirculatory regulation is controlled by a balance of vasoconstrictor and vasodilator forces. Vasoconstriction is mediated primarily by endothelin-1 (ET-1), while vasodilation is mediated primarily by nitric oxide (NO). These chemical mediators have been implicated in many aspects of intestinal ischemic injury and NEC, with the balance shifting toward increased vasoconstriction associated with intestinal injury. With a proper understanding of these antagonistic forces, potential therapeutic avenues may result from improving this pathologic microcirculatory dysregulation.     

Preterm birth and necrotizing enterocolitis alter gut colonization in pigs

Necrotizing enterocolitis (NEC) in preterm neonates is dependent on bacterial colonization, but it remains unclear whether a particular microbiota or specific pathogens are involved. We hypothesized that gut colonization differs between preterm and term neonates and that overgrowth of Clostridium perfringens predisposes to NEC. By using terminal-RFLP and FISH, we characterized the gut microbiota of preterm, caesarean-delivered, formula-fed pigs (n = 44) with or without NEC and of formula- or colostrum-fed term, and vaginally born pigs (n = 13). A different microbiota with high C. perfringens abundance was observed in preterm pigs with NEC compared with healthy individuals. However, immunization against C. perfringens toxins did not prevent NEC, and C. perfringens inoculation (3.6 × 10 cfu/d) failed to induce NEC (n = 16), whereas prophylactic broad-spectrum antibiotics treatment prevented NEC (n = 24). Colonization in both groups of term pigs differed from preterm pigs and was dominated by Lactobacilli spp. In conclusion, gestational age (GA) and NEC influence neonatal gut colonization, whereas diet has minor effects. C. perfringens is more abundant in pigs with NEC but rather as a consequence than a cause of disease. The general bacterial load and underdeveloped gut immune responses in preterm neonates seem more important for NEC development than specific pathogens.     

A scoring system in predicting the risk of intestinal stricture in necrotizing enterocolitis

Of 46 infants with a diagnosis of necrotizing enterocolitis (NEC) admitted to the neonatal intensive care unit over the period 1981–1985, 40 have been followed from 2 to 6 years after the acute episode. A contrast enema (CE) to look for intestinal strictures (IS) was performed either during the first months in surgically managed patients, or between 2 and 6 years in asymptomatic patients. Clinical, laboratory and radiology parameters collected during the 7 days following NEC were used to establish a score which was correlated with radiological data obtained after CE. Of the 40 infants, 17 developed symptomatic or asymptomatic IS and 16 of these 17 infants has a score 7. Nineteen of the 23 patients without IS had a score <7. We conclude that the proposed score established on day 8 after onset of NEC helps to identify infants at higher risk of developing IS and for whom closer follow up appears necessary.     

The preterm gut microbiota: changes associated with necrotizing enterocolitis and infection

Aim: To describe gut colonization in preterm infants using standard culture and 16S gene rRNA profiling, exploring differences in healthy infants and those who developed NEC/late onset sepsis (LOS). Methods: Ninety‐nine stools from 38 infants of median 27‐week gestation were cultured; 44 stools from 27 infants had their microbial profiles determined by 16S. Ordination analyses explored effects of patient variables on gut communities. Results: Standard microbiological culture identified a mean of two organisms (range 0–7), DGGE 12 (range 3–18) per patient. Enterococcus faecalis and coagulase negative staphylococci (CONS) were most common by culture (40% and 39% of specimens). Meconium was not sterile. No fungi were cultured. Bacterial community structures in infants with NEC and LOS differed from healthy infants. Infants who developed NEC carried more CONS (45% vs 30%) and less Enterococcus faecalis (31% vs 57%). 16S identified Enterobacter and Staphylococcus presence associated with NEC/LOS, respectively. Conclusions: Important differences were found in the gut microbiota of preterm infants who develop NEC/LOS. The relationship of these changes to current practices in neonatal intensive care requires further exploration.     

The role of the intestinal microbiota in the pathogenesis of necrotizing enterocolitis

Development of necrotizing enterocolitis (NEC) requires a susceptible host, typically a premature infant or an infant with congenital heart disease, enteral feedings and bacterial colonization. Although there is little doubt that microbes are critically involved in the pathogenesis of NEC, the identity of specific causative pathogens remains elusive. Unlike established normal adult gut microbiota, which is quite complex, uniform, and stable, early postnatal bacterial populations are simple, diverse, and fluid. These properties complicate studies aimed at elucidating characteristics of the gut microbiome that may play a role in the pathogenesis of NEC. A broad variety of bacterial, viral, and fungal species have been implicated in both clinical and experimental NEC. Frequently, however, the same species have also been found in physiologically matched healthy individuals. Clustered outbreaks of NEC, in which the same strain of a suspected pathogen is detected in several patients suggest, but do not prove, a causative relationship between the specific pathogen and the disease. Studies in Cronobacter sakazakii, the best characterized NEC pathogen, have demonstrated that virulence is not a property of a bacterial species as a whole, but rather a characteristic of certain strains, which may explain why the same species can be pathogenic or non-pathogenic. The fact that a given microbe may be innocuous in a full-term, yet pathogenic in a pre-term infant has led to the idea of opportunistic pathogens in NEC. Progress in understanding the infectious nature of NEC may require identifying specific pathogenic strains and unambiguously establishing their virulence in animal models.     

Late intestinal strictures following successful treatment of necrotizing enterocolitis

Between 1975 and 1992, in 16 infants (14%) out of 113 neonates with previous necrotizing enterocolitis (NEC) a total of 25 intestinal strictures had to be treated. Four (16%) were found in the ileum and 21 (84%) in the colon, and in 50% multiple strictures were present. In these 16 patients initial treatment for acute NEC included conservative treatment in 5, primary resection and enterostomies in 6 and proximal diverting enterostomies in 5. Therefore, the incidence of late strictures was 11% after conservative therapy, 11% after primary resection and 55% after primary proximal diverting enterostomies. An average of 49 days elapses between the recovery from NEC and the diagnosis of late strictures in conservatively treated patients. After initial surgical treatment, late strictures were detected on contrast studies on an average of 80 days. In pathologic specimens, marked fibrosis in the submucosa was consistently present in all strictures, whereas inflammatory changes in the mucosa, disruption or hypertrophy of the muscle layers or absence of ganglion cells were seen less frequently. All strictures were resected and primary end-to-end anastomosis was performed. But despite the development of late intestinal strictures, bowel preservation was improved after initial restrictive surgical therapy and aggressive medical treatment.     

Comparative study between isolated intestinal perforation and necrotizing enterocolitis.

INTRODUCTION: Intestinal perforations in the neonatal period are usually related to necrotizing enterocolitis (NEC) or intestinal occlusion. Intestinal perforation in the absence of these conditions is called isolated perforation (IP). Several risk factors and pathogenic mechanisms have been suggested, and most of them are common to those classically attributed to NEC. AIM: To identify and compare the clinical and pathological features of IP and NEC. MATERIAL AND METHODS: We reviewed all cases of neonatal intestinal perforation and NEC in the last five years. Thirty-three patients were retrospectively classified into Group NEC: 24 cases, and Group IP: 9 cases. We collected multiple data as study variables: 1) General features; 2) Obstetric history; 3) Neonatal treatment; 4) Comorbidity; 5) Perforation features; 6) Treatment and outcome. RESULTS: Comparing the groups, we found statistical significant differences in isolated perforation cases with these risk factors: extreme prematurity, very low birth weight, abruptio placenta, intubation and neonatal mechanical ventilation, umbilical catheterization, precocious sepsis, and indomethacin therapy. A more precocious operation and a good prognosis also reached statistical significance. In the other hand, we found statistically significant differences in NEC with congenital cardiopathy (excluding isolated patent ductus arteriosus), with intestinal pneumatosis, with diffuse bowel involvement and a worse prognosis. Risk factors and pathologic findings seem to support an ischaemic pathogenesis in both diseases.     

Interdisciplinary treatment of necrotizing enterocolitis and spontaneous intestinal perforations in preterm infants

From January 1986 to December 1992, 13 patients with necrotizing enterocolitis (NEC) (Grade II-III; Bell) were treated. The incidence was highest in the very immature infants with birth weight < 1000 g: 6/148 (4%). From onset, NEC was associated with clinical symptoms such as abdominal distension, bloody stools, retained gastric contents and septicemia. Indications of inflammation were seen in only 6 out of 13 patients at the time of diagnosis. No complications were seen in 10 patients during the acute phase. Two infants developed a bowel perforation and another one a gangrene. Immediate surgery was performed. In three other infants, elective surgery was performed because of colonic strictures. Twelve (92%) patients survived NEC. Five other VLBW infants developed spontaneous perforations of the bowel. The clinical presentation, laboratory and radiological findings differed greatly from those with NEC. Four infants survived. A primarily conservative therapeutic regime with close cooperation between the surgeon and pediatrician may be an alternative to early surgical intervention in NEC.     

The impact of maternal stress on the development of necrotizing enterocolitis: A comprehensive review

Necrotizing Enterocolitis (NEC) is a devastating intestinal inflammatory disease with significant morbidity and mortality. Numerous predictors have been implicated in the development of NEC, with a relatively less emphasis on maternal factors. Pregnancy drives women into a new stage of life that increases their susceptibility to biological and psychological stress. Additionally, maternal stress during pregnancy has been linked to various complications that can negatively impact both the mother and the developing fetus. These detrimental effects are facilitated by various systemic modifications. Similarly, there is evidence from animal studies that suggest a relationship between maternal stress and the occurrence of NEC due to the alterations observed in neonates. In this review, we will (1) discuss the physiological and psychological burden of maternal stress and how it can be linked to NEC, (2) summarize various predictors and risk factors of NEC, and (3) discuss the most widely utilized animal models for assessing the effects of prenatal stress on offspring.     

早产极低出生体重儿肠道菌群变化与坏死性小肠结肠炎的相关性

目的:探讨早产极低出生体重儿（VLBWI）坏死性小肠结肠炎（NEC）发生前肠道菌群结构特征变化。方法:采用前瞻性巢式病例对照研究。将2018年4月20日至11月20日生后24 h内收住苏州大学附属儿童医院或苏州市立医院新生儿重症监护病房（NICU）且出生体重<1 500 g、出生胎龄<35周的46例早产VLBWI作为研...