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

Protonophore activity of short-chain fatty acids induces their intracellular accumulation and acidification

Short-chain fatty acids (SCFAs), produced by dietary fiber fermentation in the colon, play essential roles in cellular metabolism, with butyrate notably modulating immune responses and epigenetic regulation. Their production contributes to an acidic colonic environment where protonated SCFAs permeate membranes, leading to intracellular acidification and SCFA accumulation. Using our method to measure intracellular pH, we investigated how extracellular pH influences butyrate-induced acidification and immunomodulatory effects in human macrophages. Our data show that butyrate accumulates and acidifies cells at acidic extracellular pH due to the permeability of its protonated form. While inflammatory cytokine production was mildly influenced by extracellular pH, butyrate-induced histone acetylation exhibited a pH dependence, underscoring the importance of considering extracellular pH when assessing the SCFA's functions.

Infant and adult human intestinal enteroids are morphologically and functionally distinct

Human intestinal enteroids (HIEs) are gaining recognition as physiologically relevant models of the intestinal epithelium. While HIEs from adults are used extensively in biomedical research, few studies have used HIEs from infants. Considering the dramatic developmental changes that occur during infancy, it is important to establish models that represent infant intestinal characteristics and physiological responses. We established jejunal HIEs from infant surgical samples and performed comparisons to jejunal HIEs from adults using RNA sequencing (RNA-Seq) and morphologic analyses. We then validated differences in key pathways through functional studies and determined whether these cultures recapitulate known features of the infant intestinal epithelium. RNA-Seq analysis showed significant differences in the transcriptome of infant and adult HIEs, including differences in genes and pathways associated with cell differentiation and proliferation, tissue development, lipid metabolism, innate immunity, and biological adhesion. Validating these results, we observed a higher abundance of cells expressing specific enterocyte, goblet cell, and enteroendocrine cell markers in differentiated infant HIE monolayers, and greater numbers of proliferative cells in undifferentiated 3D cultures. Compared to adult HIEs, infant HIEs portray characteristics of an immature gastrointestinal epithelium including significantly shorter cell height, lower epithelial barrier integrity, and lower innate immune responses to infection with an oral poliovirus vaccine. HIEs established from infant intestinal tissues reflect characteristics of the infant gut and are distinct from adult cultures. Our data support the use of infant HIEs as an ex vivo model to advance studies of infant-specific diseases and drug discovery for this population.

IMPORTANCE

Tissue or biopsy stem cell-derived human intestinal enteroids are increasingly recognized as physiologically relevant models of the human gastrointestinal epithelium. While enteroids from adults and fetal tissues have been extensively used for studying many infectious and non-infectious diseases, there are few reports on enteroids from infants. We show that infant enteroids exhibit both transcriptomic and morphological differences compared to adult cultures. They also differ in functional responses to barrier disruption and innate immune responses to infection, suggesting that infant and adult enteroids are distinct model systems. Considering the dramatic changes in body composition and physiology that begin during infancy, tools that appropriately reflect intestinal development and diseases are critical. Infant enteroids exhibit key features of the infant gastrointestinal epithelium. This study is significant in establishing infant enteroids as age-appropriate models for infant intestinal physiology, infant-specific diseases, and responses to pathogens.

Selection of Fermentation Supernatant from Probiotic Strains Exhibiting Intestinal Epithelial Barrier Protective Ability and Evaluation of Their Effects on Colitis Mouse and Weaned Piglet Models

The intestinal epithelial barrier can prevent the invasion of pathogenic microorganisms and food antigens to maintain a consistent intestinal homeostasis. However, an imbalance in this barrier can result in various diseases, such as inflammatory bowel disease, malnutrition, and metabolic disease. Thus, the aim of this study was to select probiotic strains with epithelial barrier-enhancing ability in cell-based model and further investigate them for their improving effects on colitis mouse and weaned piglet models. The results showed that selected specific cell-free fermentation supernatants (CFSs) from Ligilactobacillus salivarius P1, Lactobacillus gasseri P12, and Limosilactobacillus reuteri G7 promoted intestinal epithelial cell growth and proliferation, strengthening the intestinal barrier in an intestinal epithelial cell line Caco-2 model. Further, the administration of CFSs of L. salivarius P1, L. gasseri P12, and L. reuteri G7 were found to ameliorate DSS-induced colitis in mice. Additionally, spray-dried powders of CFS from the three strains were examined in a weaned piglet model, only CFS powder of L. reuteri G7 could ameliorate the feed/gain ratio and serum levels of D-lactate and endotoxin. In conclusion, a new potential probiotic strain, L. reuteri G7, was selected and showed ameliorating effects in both colitis mouse and weaned piglet models.

Infant and Adult Human Intestinal Enteroids are Morphologically and Functionally Distinct

Background & Aims

Human intestinal enteroids (HIEs) are gaining recognition as physiologically relevant models of the intestinal epithelium. While HIEs from adults are used extensively in biomedical research, few studies have used HIEs from infants. Considering the dramatic developmental changes that occur during infancy, it is important to establish models that represent infant intestinal characteristics and physiological responses.

Methods

We established jejunal HIEs from infant surgical samples and performed comparisons to jejunal HIEs from adults using RNA sequencing (RNA-Seq) and morphologic analyses. We validated differences in key pathways through functional studies and determined if these cultures recapitulate known features of the infant intestinal epithelium.

Results

RNA-Seq analysis showed significant differences in the transcriptome of infant and adult HIEs, including differences in genes and pathways associated with cell differentiation and proliferation, tissue development, lipid metabolism, innate immunity, and biological adhesion. Validating these results, we observed a higher abundance of cells expressing specific enterocyte, goblet cell and enteroendocrine cell markers in differentiated infant HIE monolayers, and greater numbers of proliferative cells in undifferentiated 3D cultures. Compared to adult HIEs, infant HIEs portray characteristics of an immature gastrointestinal epithelium including significantly shorter cell height, lower epithelial barrier integrity, and lower innate immune responses to infection with an oral poliovirus vaccine.

Conclusions

HIEs established from infant intestinal tissues reflect characteristics of the infant gut and are distinct from adult cultures. Our data support the use of infant HIEs as an ex-vivo model to advance studies of infant-specific diseases and drug discovery for this population.

New insights into intestinal macrophages in necrotizing enterocolitis: the multi-functional role and promising therapeutic application

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disease that profoundly affects preterm infants. Currently, the pathogenesis of NEC remains controversial, resulting in limited treatment strategies. The preterm infants are thought to be susceptible to gut inflammatory disorders because of their immature immune system. In early life, intestinal macrophages (IMφs), crucial components of innate immunity, demonstrate functional plasticity and diversity in intestinal development, resistance to pathogens, maintenance of the intestinal barrier, and regulation of gut microbiota. When the stimulations of environmental, dietary, and bacterial factors interrupt the homeostatic processes of IMφs, they will lead to intestinal disease, such as NEC. This review focuses on the IMφs related pathogenesis in NEC, discusses the multi-functional roles and relevant molecular mechanisms of IMφs in preterm infants, and explores promising therapeutic application for NEC.

Programmed death of intestinal epithelial cells in neonatal necrotizing enterocolitis: a mini-review

Necrotizing enterocolitis (NEC) is one of the most fatal diseases in premature infants. Damage to the intestinal epithelial barrier (IEB) is an important event in the development of intestinal inflammation and the evolution of NEC. The intestinal epithelial monolayer formed by the tight arrangement of intestinal epithelial cells (IECs) constitutes the functional IEB between the organism and the extra-intestinal environment. Programmed death and regenerative repair of IECs are important physiological processes to maintain the integrity of IEB function in response to microbial invasion. However, excessive programmed death of IECs leads to increased intestinal permeability and IEB dysfunction. Therefore, one of the most fundamental questions in the field of NEC research is to reveal the pathological death process of IECs, which is essential to clarify the pathogenesis of NEC. This review focuses on the currently known death modes of IECs in NEC mainly including apoptosis, necroptosis, pyroptosis, ferroptosis, and abnormal autophagy. Furthermore, we elaborate on the prospect of targeting IECs death as a treatment for NEC based on exciting animal and clinical studies.

Microbiota from Preterm Infants Who Develop Necrotizing Enterocolitis Drives the Neurodevelopment Impairment in a Humanized Mouse Model

Necrotizing enterocolitis (NEC) is the leading basis for gastrointestinal morbidity and poses a significant risk for neurodevelopmental impairment (NDI) in preterm infants. Aberrant bacterial colonization preceding NEC contributes to the pathogenesis of NEC, and we have demonstrated that immature microbiota in preterm infants negatively impacts neurodevelopment and neurological outcomes. In this study, we tested the hypothesis that microbial communities before the onset of NEC drive NDI. Using our humanized gnotobiotic model in which human infant microbial samples were gavaged to pregnant germ-free C57BL/6J dams, we compared the effects of the microbiota from preterm infants who went on to develop NEC (MNEC) to the microbiota from healthy term infants (MTERM) on brain development and neurological outcomes in offspring mice. Immunohistochemical studies demonstrated that MNEC mice had significantly decreased occludin and ZO-1 expression compared to MTERM mice and increased ileal inflammation marked by the increased nuclear phospho-p65 of NFκB expression, revealing that microbial communities from patients who developed NEC had a negative effect on ileal barrier development and homeostasis. In open field and elevated plus maze tests, MNEC mice had worse mobility and were more anxious than MTERM mice. In cued fear conditioning tests, MNEC mice had worse contextual memory than MTERM mice. MRI revealed that MNEC mice had decreased myelination in major white and grey matter structures and lower fractional anisotropy values in white matter areas, demonstrating delayed brain maturation and organization. MNEC also altered the metabolic profiles, especially carnitine, phosphocholine, and bile acid analogs in the brain. Our data demonstrated numerous significant differences in gut maturity, brain metabolic profiles, brain maturation and organization, and behaviors between MTERM and MNEC mice. Our study suggests that the microbiome before the onset of NEC has negative impacts on brain development and neurological outcomes and can be a prospective target to improve long-term developmental outcomes.

Human Bone Marrow-Derived Mesenchymal Stromal Cells Reduce the Severity of Experimental Necrotizing Enterocolitis in a Concentration-Dependent Manner

Necrotizing enterocolitis (NEC) is a devastating gut disease in preterm neonates. In NEC animal models, mesenchymal stromal cells (MSCs) administration has reduced the incidence and severity of NEC. We developed and characterized a novel mouse model of NEC to evaluate the effect of human bone marrow-derived MSCs (hBM-MSCs) in tissue regeneration and epithelial gut repair. NEC was induced in C57BL/6 mouse pups at postnatal days (PND) 3-6 by (A) gavage feeding term infant formula, (B) hypoxia/hypothermia, and (C) lipopolysaccharide. Intraperitoneal injections of PBS or two hBM-MSCs doses (0.5 × 10⁶ or 1 × 10⁶) were given on PND2. At PND 6, we harvested intestine samples from all groups. The NEC group showed an incidence of NEC of 50% compared with controls (p < 0.001). Severity of bowel damage was reduced by hBM-MSCs compared to the PBS-treated NEC group in a concentration-dependent manner, with hBM-MSCs (1 × 10⁶) inducing a NEC incidence reduction of up to 0% (p < 0.001). We showed that hBM-MSCs enhanced intestinal cell survival, preserving intestinal barrier integrity and decreasing mucosal inflammation and apoptosis. In conclusion, we established a novel NEC animal model and demonstrated that hBM-MSCs administration reduced the NEC incidence and severity in a concentration-dependent manner, enhancing intestinal barrier integrity.

Probiotics to improve the gut microbiome in premature infants: are we there yet?

Gut microbiome maturation in infants born prematurely is uniquely influenced by the physiological, clinical, and environmental factors surrounding preterm birth and early life, leading to altered patterns of microbial succession relative to term infants during the first months of life. These differences in microbiome composition are implicated in acute clinical conditions that disproportionately affect preterm infants, including necrotizing enterocolitis (NEC) and late-onset sepsis (LOS). Probiotic supplementation initiated early in life is an effective prophylactic measure for preventing NEC, LOS, and other clinical concerns relevant to preterm infants. In parallel, reported benefits of probiotics on the preterm gut microbiome, metabolome, and immune function are beginning to emerge. This review summarizes the current literature on the influence of probiotics on the gut microbiome of preterm infants, outlines potential mechanisms by which these effects are exerted, and highlights important clinical considerations for determining the best practices for probiotic use in premature infants.

Asphyxia-Induced Bacterial Translocation in an Animal Experimental Model in Neonatal Piglets

BACKGROUND

The term "bacterial translocation" (BT) refers to the migration of bacteria or their products from the gastrointestinal tract to tissues located outside it, and may occur after intestinal ischemia-reperfusion injury. The term "endotoxin" is synonymous, and is used interchangeably with the term lipopolysaccharide (LPS). LPS, a component of Gram-negative gut bacteria, is a potent microbial virulence factor, that can trigger production of pro-inflammatory mediators, causing localized and systemic inflammation. The aim of this study is to investigate if neonatal asphyxia provokes BT and an increased concentration of LPS in an animal model of asphyxia in piglets.

METHODS

Twenty-one (21) newborn male Landrace/Large White piglets, 1-4 days old, were randomly allocated into three groups, Control (A), Asphyxia (B) and Asphyxia-Cardiopulmonary Resuscitation (CPR) (C). All animals were instrumented, anesthetized and underwent hemodynamic monitoring. In Group A, the animals were euthanized. In Group B, the endotracheal tube was occluded to cause asphyxia leading to cardiopulmonary arrest. In Group C, the animals were resuscitated after asphyxia and further monitored for 30'. Bacterial translocation was assessed by the measurement of endotoxin in blood from the portal vein and the aorta, and also by the measurement of endotoxin in mesenteric lymph nodes (MLNs) at euthanasia. The results are given as median (IQR) with LPS concentration in EU/mL.

RESULTS

BT was observed in all groups with minimum LPS concentration in the MLN and maximum concentration in the portal vein. LPS levels in the MLNs were higher in the Group B: 6.38 EU/mL (2.69-9.34) compared to the other groups (Group A: 2.1 EU/mL (1.08-2.52), Group C: 1.66 EU/mL (1.51-2.48), p = 0.012). The aorta to MLNs LPS difference (%) was lower in Group B: 0.13% (0.04-1.17), compared to Group A: 5.08% (2.2-10.7), and Group C: 3.42% (1.5-5.1)) (p = 0.042). The same was detected for portal to MLNs LPS difference (%) which was lower in Group B: 0.94% (0.5-3) compared to Group A: 4.9% (4-15), and Group C: 3.85% (1.5-5.1)) (p = 0.044).

CONCLUSIONS

Neonatal asphyxia can provoke ΒΤ and increased LPS concentration in blood and tissue located outside the gastrointestinal system.

Time to occurrence of necrotizing enterocolitis and its predictors among low birth weight neonates admitted at neonatal intensive care unit of felege hiwot compressive specialized hospital BahirDar, Ethiopia, 2021: A retrospective follow-up study

Background

Globally, the incidence of necrotizing enterocolitis (NEC) varies between 6 and 15% of all neonates admitted to the neonatal intensive care unit (NICU). Though necrotizing enterocolitis is a multifactorial and life-threatening disease, low birth prematurity is the single cause. Therefore, determining the time to presentation and its predictors of necrotizing enterocolitis were the main goals of this investigation.

Materials and methods

An institution-based retrospective follow-up study was conducted among 747 low birth weight (LBW) neonates admitted to the neonatal intensive care unit of Felege Hiwot comprehensive specialized Hospital from 1 January 2017 to 30 December 2019. The sample size was calculated by using the STATA package. Data were entered into Epi data version 3.1 and exported to STATA version 14 for analysis. The log-rank test and the Kaplan-Meier estimator were used to display the survival probability and differences between groups. At a significance threshold of 5%, Cox proportional hazard regression was performed to determine the net independent predictors of necrotizing enterocolitis.

Result

The overall incidence rate was 0.86 per 1,000 person-days (95% CI: 0.67, 1.14) with a 6.8% (95% i: 5.2, 8.9) proportion of necrotizing enterocolitis among low birth weight neonates. Preeclampsia [adjusted hazard ratio (AHR);1.92 (95% CI: 1.03-3.58)], premature rapture of membrane [AHR; 2.36 (95%, CI: 1.19-4.69)], perinatal asphyxia [AHR; 4.05 (95%, CI: 2.04-8.60)], gestational age between 28 and 32 weeks [AHR; 3.59 (95% CI: 1.01-8.83)], and birth weigh less than 1,000 g [AHR; 5.45 (95% CI: 3.84-9.12) were the independent predictors of necrotizing enterocolitis.

Conclusion

Within the first 1-7 days of a newborn's life, necrotizing enterocolitis was most common. It was discovered that preeclampsia, premature rupture of membrane, perinatal asphyxia, gestational age of 28-32 weeks, and birth weight less than 1,000 g were predictors of its occurrence.

Microbial Translocation and Perinatal Asphyxia/Hypoxia: A Systematic Review

The microbiome is vital for the proper function of the gastrointestinal tract (GIT) and the maintenance of overall wellbeing. Gut ischemia may lead to disruption of the intestinal mucosal barrier, resulting in bacterial translocation. In this systematic review, according to PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) guidelines, we constructed a search query using the PICOT (Patient, Intervention, Comparison, Outcome, Time) framework. Eligible studies reported in PubMed, up to April 2021 were selected, from which, 57 publications’ data were included. According to these, escape of intraluminal potentially harmful factors into the systemic circulation and their transmission to distant organs and tissues, in utero, at birth, or immediately after, can be caused by reduced blood oxygenation. Various factors are involved in this situation. The GIT is a target organ, with high sensitivity to ischemia–hypoxia, and even short periods of ischemia may cause significant local tissue damage. Fetal hypoxia and perinatal asphyxia reduce bowel motility, especially in preterm neonates. Despite the fact that microbiome arouse the interest of scientists in recent decades, the pathophysiologic patterns which mediate in perinatal hypoxia/asphyxia conditions and gut function have not yet been well understood.

Chlorothalonil induces the intestinal epithelial barrier dysfunction in Caco-2 cell-based in vitro monolayer model by activating MAPK pathway

The widespread use of chlorothalonil (CTL) has caused environmental residues and food contamination. Although the intestinal epithelial barrier (IEB) is directly involved in the metabolism and transportation of various exogenous compounds, there are few studies on the toxic effects of these compounds on the structure and function of IEB. The disassembly of tight junction (TJ) is a major cause of intestinal barrier dysfunction under exogenous compounds intake, but the precise mechanisms are not well understood. Here, we used Caco-2 cell monolayers as an in vitro model of human IEB to evaluate the toxicity of CTL exposure on the structure and function of IEB. Results showed that CTL exposure increased the paracellular permeability of the monolayers and downregulated mRNA levels of the TJ genes (ZO-1, OCLN, and CLDN1), polarity marker gene (SI), and anti-apoptosis gene (BCL-2) but upregulated the mRNA levels of apoptosis-related genes, including BAD, BAX, CASP3, and CASP8. Western blot analysis and immunofluorescence assay results showed the decreased levels and disrupted distribution of TJ protein network, including ZO-1 and CLDN1 in CTL-exposed IEB. In addition, the accumulation of intracellular reactive oxygen species, decreased mitochondrial membrane potential, and increased active CASP3 expression were observed in treated IEB. The result of TUNEL assay further confirmed the occurrence of cell apoptosis after CTL exposure. In addition, the phosphorylation of mitogen-activated protein kinases, including ERK, JNK and p38, was increased in CTL-exposed IEB. In summary, our results demonstrated that CTL exposure induced IEB dysfunction in Caco-2 cell monolayers by activating the mitogen-activated protein kinase pathway.

Proliferation in the developing intestine is regulated by the endosomal protein Endotubin

During postnatal intestinal development, the intestinal epithelium is highly proliferative, and this proliferation is regulated by signaling in the intervillous and crypt regions. This signaling is primarily mediated by Wnt, and requires membrane trafficking. However, the mechanisms by which membrane trafficking regulates signaling during this developmental phase are largely unknown. Endotubin (EDTB, MAMDC4) is an endosomal protein that is highly expressed in the apical endocytic complex (AEC) of villus enterocytes during fetal and postnatal development, and knockout of EDTB results in defective formation of the AEC and giant lysosome. Further, knockout of EDTB in cell lines results in decreased proliferation. However, the role of EDTB in proliferation during the development of the intestine is unknown. Using Villin-CreERT2 in EDTB^fl/fl mice, we deleted EDTB in the intestine in the early postnatal period, or in enteroids in vitro after isolation of intervillous cells. Loss of EDTB results in decreased proliferation in the developing intestinal epithelium and decreased ability to form enteroids. EDTB is present in cells that contain the stem cell markers LGR5 and OLFM4, indicating that it is expressed in the proliferative compartment. Further, using immunoblot analysis and TCF/LEF-GFP mice as a reporter of Wnt activity, we find that knockout of EDTB results in decreased Wnt signaling. Our results show that EDTB is essential for normal proliferation during the early stages of intestinal development and suggest that this effect is through modulation of Wnt signaling.

Causative role of mast cell and mast cell-regulatory function of disialyllacto-N-tetraose in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) remains a fatal gastrointestinal disorder in neonates. Disialyllacto-N-tetraose (DSLNT), a function-unclear human milk-derived hexasaccharide, shows anti-NEC potential in previous animal studies. This study is aimed to explore the role of mast cell (MC), a fundamental cell type of mucosal immune system and protective DSLNT in regulating pathological process of NEC. For this purpose, infantile intestinal-tissues were collected from NEC neonates for examination of MCs and its proteases-positive cells. MC accumulation and MC-specific proteases (chymase, tryptase and dipeptidyl peptidase I) were firstly found in lesioned area of NEC infants in-vivo. Subsequent in-situ experiments on neonatal ileum segments showed that purified MC-chymase induced a destructive epithelial layer shedding from basement and microvascular endothelium damage in infantile intestinal segments. Human foreskin MC-activation model was established and DSLNT were applied; MC products (histamine and MC-proteases) were used as MC activation/degranulation indicators. In this in-vitro model, DSLNT pretreatment suppressed release of histamine, chymase and tryptase by MC to the tissue supernatants during lipopolysaccharide or complement C5a stimulation. Newborn rats were formula-hand-fed with or without DSLNT supplement and exposed to hypoxia/cold-stress to induce experimental-NEC-model. In NEC rats, DSLNT supplementation reduced the incidence and pathological scores of NEC, inhibited local accumulation of MC and reduced cytokines (IL-1β, IL-6 and TNF-α) levels in the ileum of rats. In conclusion, MC was causally implicated in epithelium barrier failure in pathogenesis of NEC. DSLNT favorably modulated MC homeostasis by regulating MC degranulation/accumulation, contributing to attenuated NEC. This indicated novel pathomechanisms and potential targets of NEC.

Stress and corticotropin releasing factor (CRF) promote necrotizing enterocolitis in a formula-fed neonatal rat model

The etiology of necrotizing enterocolitis (NEC) is not known. Alterations in gut microbiome, mucosal barrier function, immune cell activation, and blood flow are characterized events in its development, with stress as a contributing factor. The hormone corticotropin-releasing factor (CRF) is a key mediator of stress responses and influences these aforementioned processes. CRF signaling is modulated by NEC's main risk factors of prematurity and formula feeding. Using an established neonatal rat model of NEC, we tested hypotheses that: (i) increased CRF levels-as seen during stress-promote NEC in formula-fed (FF) newborn rats, and (ii) antagonism of CRF action ameliorates NEC. Newborn pups were formula-fed to initiate gut inflammation and randomized to: no stress, no stress with subcutaneous CRF administration, stress (acute hypoxia followed by cold exposure-NEC model), or stress after pretreatment with the CRF peptide antagonist Astressin. Dam-fed unstressed and stressed littermates served as controls. NEC incidence and severity in the terminal ileum were determined using a histologic scoring system. Changes in CRF, CRF receptor (CRFRs), and toll-like receptor 4 (TLR4) expression levels were determined by immunofluorescence and immunoblotting, respectively. Stress exposure in FF neonates resulted in 40.0% NEC incidence, whereas exogenous CRF administration resulted in 51.7% NEC incidence compared to 8.7% in FF non-stressed neonates (p<0.001). Astressin prevented development of NEC in FF-stressed neonates (7.7% vs. 40.0%; p = 0.003). CRF and CRFR immunoreactivity increased in the ileum of neonates with NEC compared to dam-fed controls or FF unstressed pups. Immunoblotting confirmed increased TLR4 protein levels in FF stressed (NEC model) animals vs. controls, and Astressin treatment restored TLR4 to control levels. Peripheral CRF may serve as specific pharmacologic target for the prevention and treatment of NEC.

Sodium butyrate converts Caco-2 monolayers into a leaky but healthy intestinal barrier resembling that of a newborn infant

A simple and reliable in vitro model of the infant intestinal barrier is needed to study nutrient absorption and drug permeability specifically for this life stage. This study investigated the treatment of 20 day old differentiated Caco-2 monolayers with sodium butyrate at various concentrations (0-250 mM). Monolayer integrity, cytotoxicity, permeability and inflammatory response were tracked. An intestinal barrier model, with infant gut characteristics, was developed based on the treatment of mature monolayers with 125 mM sodium butyrate for 24 h. Such treatment was not cytotoxic but caused a stable transepithelial electrical resistance value of 408 ± 52 Ω cm2. The ratio of lactulose to mannitol transport across the intestinal barrier increased 1.79-fold. Redistribution of the tight junction proteins, occludin and ZO-1, in response to sodium butyrate treatment was visualized with immunofluorescence. Levels of the cytokines, TNF-α and IL-6, although modestly increased did not indicate an inflammatory response by Caco-2 to sodium butyrate. This intestinal barrier demonstrated physiologically relevant transport rates for dairy protein of 0.01-0.06%, suggesting it may be used to track permeability of proteins in infant nutritional products.

Effects of Taraxacum and Astragalus extracts combined with probiotic Bacillus subtilis and Lactobacillus on Escherichia coli-infected broiler chickens

Diarrhea caused by Escherichia coli (E. coli) is one of the most common diseases that affects the growth and development of poultry. This study was conducted to investigate the synergistic effects of traditional Chinese medicine (TCM) combined with probiotics against E. coli infection and its mechanism in broiler chickens. The optimal proportion formula TCM and probiotics was screened by orthogonal test and range analysis method; the in vitro antibacterial activity was based on the Oxford cup method. Isolated pathogenic E. coli was injected subcutaneously into the neck of the broilers to establish an E. coli-infected model. The broilers were administrated with drugs in drinking water daily for 7 d before and after E. coli infection. The diarrhea rate, mortality, body weight (BW) gain, feed intake, immune organ index, intestinal and hepatic histopathological changes were monitored. The expression of IL-2, IL-10, and TLR-4 mRNA in the intestinal tissues was measured by RT-PCR. Our results showed that the optimal proportion formula of Taraxacum extracts: total flavonoids of Astragalus: polysaccharides of Astragalus: probiotics was 5: 2: 2: 2; TCM combined with probiotics was highly sensitive to E. coli. TCM combined with probiotics synergistically increased BW gain, decreased the diarrhea rate and mortality of broilers, alleviated intestinal and hepatic pathological changes, accompanied by the increase of IL-2 and IL-10 mRNA expression and the inhibition of TLR-4 mRNA expression. It suggests that the combination of TCM and probiotics may produce a synergistic protective effect against E. coli infection by improving the indicators of diarrhea and regulating the expression of IL-2, IL-10, and TLR-4 mRNA in broiler chickens. The synergistic interactions between TCM and probiotics represent a promising strategy for the treatment of E. coli infection.

Necrotizing Enterocolitis: LPS/TLR4-Induced Crosstalk Between Canonical TGF-β/Wnt/β-Catenin Pathways and PPARγ

Necrotizing enterocolitis (NEC) represents one of the major causes of morbidity and mortality in premature infants. Several recent studies, however, have contributed to a better understanding of the pathophysiology of this dreadful disease. Numerous intracellular pathways play a key role in NEC, namely: bacterial lipopolysaccharide (LPS), LPS toll-like receptor 4 (TLR4), canonical Wnt/β-catenin signaling and PPARγ. In a large number of pathologies, canonical Wnt/β-catenin signaling and PPARγ operate in opposition to one another, so that when one of the two pathways is overexpressed the other is downregulated and vice-versa. In NEC, activation of TLR4 by LPS leads to downregulation of the canonical Wnt/β-catenin signaling and upregulation of PPARγ. This review aims to shed light on the complex intracellular mechanisms involved in this pathophysiological profile by examining additional pathways such as the GSK-3β, NF-κB, TGF-β/Smads, and PI3K-Akt pathways.

Site-specific contribution of Toll-like receptor 4 to intestinal homeostasis and inflammatory disease

Toll-like receptor 4 (TLR4) is a highly conserved protein of innate immunity, responsible for the regulation and maintenance of homeostasis, as well as immune recognition of external and internal ligands. TLR4 is expressed on a variety of cell types throughout the gastrointestinal tract, including on epithelial and immune cell populations. In a healthy state, epithelial cell expression of TLR4 greatly assists in homeostasis by shaping the host microbiome, promoting immunoglobulin A production, and regulating follicle-associated epithelium permeability. In contrast, immune cell expression of TLR4 in healthy states is primarily centred on the maturation of dendritic cells in response to stimuli, as well as adequately priming the adaptive immune system to fight infection and promote immune memory. Hence, in a healthy state, there is a clear distinction in the site-specific roles of TLR4 expression. Similarly, recent research has indicated the importance of site-specific TLR4 expression in inflammation and disease, particularly the impact of epithelial-specific TLR4 on disease progression. However, the majority of evidence still remains ambiguous for cell-specific observations, with many studies failing to provide the distinction of epithelial versus immune cell expression of TLR4, preventing specific mechanistic insight and greatly impacting the translation of results. The following review provides a critical overview of the current understanding of site-specific TLR4 activity and its contribution to intestinal/immune homeostasis and inflammatory diseases.

Hyaluronan 35 kDa enhances epithelial barrier function and protects against the development of murine necrotizing enterocolitis

BACKGROUND

Disruption of tight junctions (TJs) predisposes to bacterial translocation, intestinal inflammation, and necrotizing enterocolitis (NEC). Previously, studies showed that hyaluronan (HA), a glycosaminoglycan in human milk, maintains intestinal permeability, enhances intestinal immunity, and reduces intestinal infections. In this study, we investigated the effects of HA 35 kDa on a NEC-like murine model.

METHODS

Pups were divided into Sham, NEC, NEC+HA 35, and HA 35. Severity of intestinal injury was compared using a modified macroscopic gut scoring and histologic injury grading. The effect of HA 35 on intestinal permeability was determined by measuring FITC dextran and bacterial translocation. RNA and protein expression of TJ proteins (claudin-2, -3, -4, occludin, and ZO-1) were compared between the groups.

RESULTS

Pups in the NEC+HA 35 group had increased survival and lower intestinal injury compared to untreated NEC. In addition, HA 35 reduced intestinal permeability, bacterial translocation, and proinflammatory cytokine release. Ileal expression of claudin-2, -3, -4, occludin, and ZO-1 was upregulated in NEC+HA 35 and HA 35 compared to untreated NEC and shams.

CONCLUSION

These findings suggest that HA 35 protects against NEC partly by upregulating intestinal TJs and enhancing intestinal barrier function.

Human breast milk exosomes attenuate intestinal damage

BACKGROUND

Human breast milk (HBM), which contains an abundant supply of exosomes, is known to prevent necrotizing enterocolitis (NEC). Preterm infants are commonly given pasteurized donor milk when HBM is unavailable. However, pasteurization can disrupt its components. This study investigates the effects of both raw and pasteurized HBM-derived exosomes on intestinal inflammation.

METHODS

HBM exosomes were isolated and characterized by positive CD63 and negative calnexin markers from western blot, nanoparticle tracking analysis and transmission electron microscopy. Mouse intestine organoids were established and treated with exosomes from raw or pasteurized HBM in healthy and injury conditions. Following ethical approval (#44032), mice pups were randomly assigned to (1) breastfed control; (2) NEC; (3) NEC receiving raw HBM exosomes; (4) NEC receiving pasteurized HBM exosomes. NEC was induced by hypoxia, gavage feeding and lipopolysaccharide (LPS). Ileum was evaluated. Data were analyzed using one-way ANOVA with Bonferroni post-test.

RESULTS

Both raw and pasteurized HBM exosomes decreased inflammation in hypoxia and LPS-treated organoids compared to control. In vivo, NEC-induced mucosal injury, inflammation and mucous production were improved by raw and pasteurized HBM-derived exosomes.

CONCLUSIONS

Exosomes derived from raw and pasteurized HBM equally reduced intestinal damage. Exosome administration in clinical practice requires further investigation.

Elevated Coefficient of Variation in Total Fecal Bile Acids Precedes Diagnosis of Necrotizing Enterocolitis

Accumulation of bile acids (BAs) may mediate development of necrotizing enterocolitis (NEC). Serial fecal samples were collected from premature infants with birth weight (BW) ≤ 1800 g, estimated gestational age (EGA) ≤ 32 weeks, and <30 days old prior to initiation of enteral feeding. Nine infants that developed Bell’s Stage ≥ II NEC were matched with control infants based on BW, EGA, day of life (DOL) enteral feeding was initiated and DOL of the first sample. From each subject, five samples matched by DOL collected were analyzed for BA levels and composition. Fifteen individual BA species were measured via LC-MS/MS and total BA levels were measured using the Diazyme Total Bile Acid Assay kit. No statistically significant differences in composition were observed between control and NEC at the level of individual species (p = 0.1133) or grouped BAs (p = 0.0742). However, there was a statistically significant difference (p = 0.000012) in the mean coefficient of variation (CV) between the two groups with infants developing NEC having more than four-fold higher mean CV than controls. Importantly, these variations occurred prior to NEC diagnosis. These data suggest fluctuations in total fecal BA levels could provide the basis for the first predictive clinical test for NEC.

Intestinal dysbiosis and necrotizing enterocolitis: assessment for causality using Bradford Hill criteria

In recent years, several studies have shown that premature infants who develop NEC frequently display enteric dysbiosis with increased Gram-negative bacteria for several days to weeks prior to NEC onset. The importance of these findings, for the possibility of a causal role of these bacteria in NEC pathogenesis, and for potential value of gut dysbiosis as a biomarker of NEC, is well-recognized. In this review, we present current evidence supporting the association between NEC in premature infants and enteric dysbiosis, and its evaluation using the Bradford Hill criteria for causality. To provide an objective appraisal, we developed a novel scoring system for causal inference. Despite important methodological and statistical limitations, there is support for the association from several large studies and a meta-analysis. The association draws strength from strong biological plausibility of a role of Gram-negative bacteria in NEC and from evidence for temporality, that dysbiosis may antedate NEC onset. The weakness of the association is in the low level of consistency across studies, and the lack of specificity of effect. There is a need for an improved definition of dysbiosis, either based on a critical threshold of relative abundances or at higher levels of taxonomic resolution.

A Preterm Rat Model for Immunonutritional Studies

Neonates are born with an immature immune system, which develops during the first stages of life. This early immaturity is more acute in preterm newborns. The aim of the present study was to set up a preterm rat model, in which representative biomarkers of innate and adaptive immunity maturation that could be promoted by certain dietary interventions are established. Throughout the study, the body weight was registered. To evaluate the functionality of the intestinal epithelial barrier, in vivo permeability to dextrans was measured and a histomorphometric study was performed. Furthermore, the blood cell count, phagocytic activity of blood leukocytes and plasmatic immunoglobulins (Ig) were determined. Preterm rats showed lower erythrocyte and platelet concentration but a higher count of leukocytes than the term rats. Although there were no changes in the granulocytes’ ability to phagocytize, preterm monocytes had lower phagocytic activity. Moreover, lower plasma IgG and IgM concentrations were detected in preterm rats compared to full-term rats, without affecting IgA. Finally, the intestinal study revealed lower permeability in preterm rats and reduced goblet cell size. Here, we characterized a premature rat model, with differential immune system biomarkers, as a useful tool for immunonutritional studies aimed at boosting the development of the immune system.

Curcumin and Intestinal Inflammatory Diseases: Molecular Mechanisms of Protection

Intestinal inflammatory diseases, such as Crohn’s disease, ulcerative colitis, and necrotizing enterocolitis, are becoming increasingly prevalent. While knowledge of the pathogenesis of these related diseases is currently incomplete, each of these conditions is thought to involve a dysfunctional, or overstated, host immunological response to both bacteria and dietary antigens, resulting in unchecked intestinal inflammation and, often, alterations in the intestinal microbiome. This inflammation can result in an impaired intestinal barrier allowing for bacterial translocation, potentially resulting in systemic inflammation and, in severe cases, sepsis. Chronic inflammation of this nature, in the case of inflammatory bowel disease, can even spur cancer growth in the longer-term. Recent research has indicated certain natural products with anti-inflammatory properties, such as curcumin, can help tame the inflammation involved in intestinal inflammatory diseases, thus improving intestinal barrier function, and potentially, clinical outcomes. In this review, we explore the potential therapeutic properties of curcumin on intestinal inflammatory diseases, including its antimicrobial and immunomodulatory properties, as well as its potential to alter the intestinal microbiome. Curcumin may play a significant role in intestinal inflammatory disease treatment in the future, particularly as an adjuvant therapy.

Anemia induces gut inflammation and injury in an animal model of preterm infants

BACKGROUND

While very low birth weight (VLBW) infants often require multiple red blood cell transfusions, efforts to minimize transfusion-associated risks have resulted in more restrictive neonatal transfusion practices. However, whether restrictive transfusion strategies limit transfusions without increasing morbidity and mortality in this population remains unclear. Recent epidemiologic studies suggest that severe anemia may be an important risk factor for the development of necrotizing enterocolitis (NEC). However, the mechanism whereby anemia may lead to NEC remains unknown.

STUDY DESIGN AND METHODS

The potential impact of anemia on neonatal inflammation and intestinal barrier disruption, two well-characterized predisposing features of NEC, was defined by correlation of hemoglobin values to cytokine levels in premature infants and by direct evaluation of intestinal hypoxia, inflammation and gut barrier disruption using a pre-clinical neonatal murine model of phlebotomy-induced anemia (PIA).

RESULTS

Increasing severity of anemia in the preterm infant correlated with the level of IFN-gamma, a key pro-inflammatory cytokine that may predispose an infant to NEC. Gradual induction of PIA in a pre-clinical model resulted in significant hypoxia throughout the intestinal mucosa, including areas where intestinal macrophages reside. PIA-induced hypoxia significantly increased macrophage pro-inflammatory cytokine levels, while reducing tight junction protein ZO-1 expression and increasing intestinal barrier permeability. Macrophage depletion reversed the impact of anemia on intestinal ZO-1 expression and barrier function.

CONCLUSIONS

Taken together, these results suggest that anemia can increase intestinal inflammation and barrier disruption likely through altered macrophage function, leading to the type of predisposing intestinal injury that may increase the risk for NEC.

Blocking NF-κB Activation in Ly6c+ Monocytes Attenuates Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a devastating disease affecting premature infants with intestinal inflammation and necrosis. The neonatal intestinal inflammatory response is rich in macrophages, and blood monocyte count is low in human NEC. We previously found that NF-κB mediates the intestinal injury in experimental NEC. However, the role of NF-κB in myeloid cells during NEC remains unclear. Herein, inhibitor of kappaB kinase β (IKKβ), a critical kinase mediating NF-κB activation, was deleted in lysozyme M (Lysm)-expressing cells, which were found to be Cd11b+Ly6c+ monocytes but not Cd11b+Ly6c- macrophages in the dam-fed neonatal mouse intestine. NEC induced differentiation of monocytes into intestinal macrophages and up-regulation of monocyte recruitment genes (eg, L-selectin) in the macrophage compartment in wild-type mice, but not in pups with IKKβ deletion in Lysm+ cells. Thus, NF-κB is required for NEC-induced monocyte activation, recruitment, and differentiation in neonatal intestines. Furthermore, pups with Lysm-IKKβ deletion had improved survival and decreased incidence of severe NEC compared with littermate controls. Decreased NEC severity was not associated with an improved intestinal barrier. In contrast, NEC was unabated in mice with IKKβ deletion in intestinal epithelial cells. Together, these data suggest that recruitment of Ly6c+ monocytes into the intestine, NF-κB activation in these cells, and differentiation of Ly6c+ monocytes into macrophages are critical cellular and molecular events in NEC development to promote disease.

Regulation of ROS-NF-κB axis by tuna backbone derived peptide ameliorates inflammation in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common life-threatening gastrointestinal disease encountered in the premature infant. It has been shown that the intercellular reactive oxygen species (ROS) generation activated by lipopolysaccharide involved in the nuclear factor kappa B (NF-κB) activation and pathogenesis of NEC. Here, we report that an antioxidant peptide from tuna backbone protein (APTBP) reduces the inflammatory cytokines transcription and release. APTBP directly scavenges the free radical through 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) assay. In addition, APTBP reduces the intracellular ROS level, exhibiting an antioxidant activity within cells. Remarkably, gavage with APTBP attenuates the phenotype of NEC in the mice model. Mechanically, the NF-κB activation, together with the expression of inflammatory cytokines are decreased significantly when intracellular ROS are eliminated by APTBP. Therefore, our findings demonstrated that an antioxidant peptide, APTBP, ameliorates inflammation in NEC through attenuating ROS-NF-κB axis.

Innate and adaptive immunity in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most frequent and devastating gastrointestinal disease of premature infants. Although the precise mechanisms are not fully understood, NEC is thought to develop following a combination of prematurity, formula feeding, and adverse microbial colonization. Within the last decade, studies increasingly support an important role of a heightened mucosal immune response initiating a pro-inflammatory signaling cascade, which can lead to the disruption of the intestinal epithelium and translocation of pathogenic species. In this review, we first describe the cellular composition of the intestinal epithelium and its critical role in maintaining epithelial integrity. We then discuss cell signaling during NEC, specifically, toll-like receptors and nucleotide oligomerization domain-like receptors. We further review cytokines and cellular components that characterize the innate and adaptive immune systems and how they interact to support or modulate NEC development.

Intestinal tight junctions are severely altered in NEC preterm neonates

BACKGROUND & AIMS

Necrotizing Enterocolitis (NEC) is a severe inflammatory disorder of the intestine endangering the health and survival of preterm infants. It is well established that the gut barrier is severely damaged in NEC patients, nonetheless an in depth investigation of modifications at the transcriptional and translational levels of tight junction genes and proteins during NEC are still missing. The aim of this study was to investigate changes in the expression of tight junctions and other associated proteins during NEC and determine their correlation to the disease severity.

METHODS

We examined intestinal specimens from six NEC patients and compared them with six control specimens from patients that underwent surgeries for reasons other than NEC. The expression of genes was analyzed by real time PCR and protein expression by immunohistochemistry.

RESULTS

The tight junction genes ZO-1, occludin, cingulin and claudin-4 were significantly down regulated in NEC. Furthermore TLR4, BAX and SIRT1 genes were found to be significantly down regulated while HIF-1A showed a trend of up regulation in NEC patients. These changes were found to correlate with the severity of the disease. Additionally we demonstrated in an ex-vivo model that hypoxic conditions initiated a destructive process of the epithelial barrier. We also showed that the expression of the tight junction proteins ZO-1 and occludin were significantly down regulated in NEC specimens.

CONCLUSIONS

The expression of tight junction proteins and their encoding genes are significantly altered in NEC. We surmise that SIRT1 and HIF-1A may play a role in controlling these effects.

There is an association between disease location and gestational age at birth in newborns submitted to surgery due to necrotizing enterocolitis

OBJECTIVES

To evaluate if there are differences regarding disease location and mortality of necrotizing enterocolitis, according to the gestational age at birth, in newborns submitted to surgery due to enterocolite.

METHODS

A historical cohort study of 198 newborns submitted to surgery due to necrotizing enterecolitis in a tertiary hospital, from November 1991 to December 2012. The newborns were divided into different categories according to gestational age (<30 weeks, 30-33 weeks and 6 days, 34-36 weeks and 6 days, and ≥37 weeks), and were followed for 60 days after surgery. The inclusion criterion was the presence of histological findings of necrotizing enterocolitis in the pathology. Patients with single intestinal perforation were excluded.

RESULTS

The jejunum was the most commonly affected site in extremely premature infants (p=0.01), whereas the ileum was the most commonly affected site in premature infants (p=0.002), and the colon in infants born at term (p<0.001). With the increasing gestational age, it was observed that intestinal involvement decreased for the ileum and the jejunum (decreasing from 45% to 0% and from 5% to 0%, respectively), with a progressive increase in colon involvement (0% to 84%). Total mortality rate was 45.5%, and no statistical difference was observed in the mortality at different gestational ages (p=0.287).

CONCLUSIONS

In newborns submitted to surgery due to necrotizing enterocolitis, the disease in extremely preterm infants was more common in the jejunum, whereas in preterm infants, the most affected site was the ileum, and in newborns born close to term, it was the colon. No difference in mortality was observed according to the gestational age at birth.

Role of intestinal Hsp70 in barrier maintenance: contribution of milk to the induction of Hsp70.2

BACKGROUND

Necrotizing enterocolitis (NEC) is a gastrointestinal disease of complex etiology resulting in devastating systemic inflammation and often death in premature newborns. We previously demonstrated that formula feeding inhibits ileal expression of heat shock protein-70 (Hsp70), a critical stress protein within the intestine. Barrier function for the premature intestine is critical. We sought to determine whether reduced Hsp70 protein expression increases neonatal intestinal permeability.

METHODS

Young adult mouse colon cells (YAMC) were utilized to evaluate barrier function as well as intestine from Hsp70-/- pups (KO). Sections of intestine were analyzed by Western blot, immunohistochemistry, and real time PCR. YAMC cells were sub-lethally heated or treated with expressed milk (EM) to induce Hsp70.

RESULTS

Immunostaining demonstrates co-localized Hsp70 and tight junction protein zona occludens-1 (ZO-1), suggesting physical interaction to protect tight junction function. The permeability of YAMC monolayers increases following oxidant injury and is partially blocked by Hsp70 induction either by prior heat stress or EM. RT-PCR analysis demonstrated that the Hsp70 isoforms, 70.1 and 70.3, predominate in WT pup; however, Hsp70.2 predominates in the KO pups. While Hsp70 is present in WT milk, it is not present in KO EM. Hsp70 associates with ZO-1 to maintain epithelial barrier function.

CONCLUSION

Both induction of Hsp70 and exposure to EM prevent stress-induced increased permeability. Hsp70.2 is present in both WT and KO neonatal intestine, suggesting a crucial role in epithelial integrity. Induction of the Hsp70.2 isoform appears to be mediated by mother's milk. These results suggest that mother's milk feeding modulates Hsp70.2 expression and could attenuate injury leading to NEC.

LEVEL OF EVIDENCE

Level III.

The Endosomal Protein Endotubin Is Required for Enterocyte Differentiation

BACKGROUND & AIMS

During late embryonic development and through weaning, enterocytes of the ileum are highly endocytic. Defects in endocytosis and trafficking are implicated in neonatal disease, however, the mechanisms regulating trafficking during the developmental period are incompletely understood. The apical endosomal protein endotubin (EDTB) is highly expressed in the late embryonic and neonatal ileum. In epithelial cells in vitro, EDTB regulates both trafficking of tight junction proteins and proliferation through modulation of YAP activity. However, EDTB function during the endocytic stage of development of the intestine is unknown.

METHODS

By using Villin-CreERT2, we induced knockout of EDTB during late gestation and analyzed the impact on endocytic compartments and enterocyte structure in neonates using immunofluorescence, immunocytochemistry, and transmission electron microscopy.

RESULTS

Deletion of the apical endosomal protein EDTB in the small intestine during development impairs enterocyte morphogenesis, including loss of the apical endocytic complex, defective formation of the lysosomal compartment, and some cells had large microvillus-rich inclusions similar to those observed in microvillus inclusion disease. There also was a decrease in apical endocytosis and mislocalization of proteins involved in apical trafficking.

CONCLUSIONS

Our results show that EDTB-mediated trafficking within the epithelial cells of the developing ileum is important for maintenance of endocytic compartments and enterocyte integrity during early stages of gut development.

Protective effects of amniotic fluid in the setting of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common life threatening condition affecting preterm infants. NEC occurs in 1-5% of all neonatal intensive care admissions and 5-10% of very low birth weight infants. The protective role of human breast milk (BM) has been well established. It has also been shown that amniotic fluid (AF) and BM have many similarities in terms of presence of growth and other immune-modulatory factors. This finding led to the initial hypothesis that AF may exert similar protective effects against the development of NEC, as does BM. Multiple studies have elucidated the presence of growth factors in AF and the protective effect of AF against NEC. Studies have also described possible mechanisms how AF protects against NEC. At present, research in this particular area is extremely active and robust. This review summarizes the various studies looking at the protective effects of AF against the development of NEC. It also provides an insight into future directions, the vast potential of AF as a readily available biologic medium, and the ethical barriers that must be overcome before using AF.

The Role of Mucosal Immunity in the Pathogenesis of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is the most devastating gastrointestinal disease of prematurity. Although the precise cause is not well understood, the main risk factors thought to contribute to NEC include prematurity, formula feeding, and bacterial colonization. Recent evidence suggests that NEC develops as a consequence of intestinal hyper-responsiveness to microbial ligands upon bacterial colonization in the preterm infant, initiating a cascade of aberrant signaling events, and a robust pro-inflammatory mucosal immune response. We now have a greater understanding of important mechanisms of disease pathogenesis, such as the role of cytokines, immunoglobulins, and immune cells in NEC. In this review, we will provide an overview of the mucosal immunity of the intestine and the relationship between components of the mucosal immune system involved in the pathogenesis of NEC, while highlighting recent advances in the field that have promise as potential therapeutic targets. First, we will describe the cellular components of the intestinal epithelium and mucosal immune system and their relationship to NEC. We will then discuss the relationship between the gut microbiota and cell signaling that underpins disease pathogenesis. We will conclude our discussion by highlighting notable therapeutic advancements in NEC that target the intestinal mucosal immunity.

Inflammation and Apoptosis: Dual Mediator Role for Toll-like Receptor 4 in the Development of Necrotizing Enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is the leading cause of neonatal gastrointestinal mortality; effective interventions are lacking with limited understanding of the pathogenesis of NEC. The importance of Toll-like receptor 4 (TLR4) signaling in NEC is well documented; however, the potential mechanisms that regulate enterocyte inflammation and apoptosis remain unclear. The aim of this study was to characterize the role of TLR4-mediated inflammation and apoptosis in the development of NEC and to determine the major apoptotic pathways and regulators in the process.

METHODS

TLR4-deficient C57BL/10ScNJ mice and lentivirus-mediated stable TLR4-silent cell line (IEC-6) were used. NEC was induced by formula gavage, cold, hypoxia, combined with lipopolysaccharide in vivo or lipopolysaccharide stimulation in vitro. Enterocyte apoptosis was evaluated by TUNEL or Annexin analysis. The expression of TLR4, caspase3, caspase8, caspase9, Bip, Bax, Bcl-2, and RIP was detected by Western blot and immunofluorescence. Inflammatory factors such as tumor necrosis factor-α and interleukin-2 were examined by Luminex.

RESULTS

Defect of TLR4 led to suppressed enterocytes apoptosis both in vitro and in vivo; the expression of caspase3, caspase8, Bip, and Bax was decreased; and caspase9 and Bcl-2 were increased. NEC severity was attenuated in TLR4-deficient mice compared with wild-type counterparts, and enterocytes apoptosis was correlated with NEC severity. RIP and cytokine level of tumor necrosis factor-α and interleukin-2 were also decreased.

CONCLUSIONS

TLR4-induced inflammation and apoptosis play a critical role in the pathogenesis of NEC. TLR4 inhibition, combined with extrinsic (caspase8) and/or endoplasmic reticulum stress (Bip) apoptosis signaling blockade could serve as a potential effective treating strategy for NEC.

Necrotizing enterocolitis: new insights into pathogenesis and mechanisms

Necrotizing enterocolitis (NEC) is the most frequent and lethal disease of the gastrointestinal tract of preterm infants. At present, NEC is thought to develop in the premature host in the setting of bacterial colonization, often after administration of non-breast milk feeds, and disease onset is thought to be due in part to a baseline increased reactivity of the premature intestinal mucosa to microbial ligands as compared with the full-term intestinal mucosa. The increased reactivity leads to mucosal destruction and impaired mesenteric perfusion and partly reflects an increased expression of the bacterial receptor Toll-like receptor 4 (TLR4) in the premature gut, as well as other factors that predispose the intestine to a hyper-reactive state in response to colonizing microorganisms. The increased expression of TLR4 in the premature gut reflects a surprising role for this molecule in the regulation of normal intestinal development through its effects on the Notch signalling pathway. This Review will examine the current approach to the diagnosis and treatment of NEC, provide an overview of our current knowledge regarding its molecular underpinnings and highlight advances made within the past decade towards the development of specific preventive and treatment strategies for this devastating disease.

Protective Effects of Bifidobacterium on Intestinal Barrier Function in LPS-Induced Enterocyte Barrier Injury of Caco-2 Monolayers and in a Rat NEC Model

Zonulin protein is a newly discovered modulator which modulates the permeability of the intestinal epithelial barrier by disassembling intercellular tight junctions (TJ). Disruption of TJ is associated with neonatal necrotizing enterocolitis (NEC). It has been shown bifidobacterium could protect the intestinal barrier function and prophylactical administration of bifidobacterium has beneficial effects in NEC patients and animals. However, it is still unknown whether the zonulin is involved in the gut barrier dysfunction of NEC, and the protective mechanisms of bifidobacterium on intestinal barrier function are also not well understood. The present study aims to investigate the effects of bifidobacterium on intestinal barrier function, zonulin regulation, and TJ integrity both in LPS-induced enterocyte barrier injury of Caco-2 monolayers and in a rat NEC model. Our results showed bifidobacterium markedly attenuated the decrease in transepithelial electrical resistance and the increase in paracellular permeability in the Caco-2 monolayers treated with LPS (P < 0.01). Compared with the LPS group, bifidobacterium significantly decreased the production of IL-6 and TNF-α (P < 0.01) and suppressed zonulin release (P < 0.05). In addition, bifidobacterium pretreatment up-regulated occludin, claudin-3 and ZO-1 expression (P < 0.01) and also preserved these proteins localization at TJ compared with the LPS group. In the in vivo study, bifidobacterium decreased the incidence of NEC from 88 to 47% (P < 0.05) and reduced the severity in the NEC model. Increased levels of IL-6 and TNF-α in the ileum of NEC rats were normalized in bifidobacterium treated rats (P < 0.05). Moreover, administration of bifidobacterium attenuated the increase in intestinal permeability (P < 0.01), decreased the levels of serum zonulin (P < 0.05), normalized the expression and localization of TJ proteins in the ileum compared with animals with NEC. We concluded that bifidobacterium may protect against intestinal barrier dysfunction both in vitro and in NEC. This protective effect is associated with inhibition of proinflammatory cytokine secretion, suppression of zonulin protein release and improvement of intestinal TJ integrity.

Oropharyngeal administration of mother's colostrum, health outcomes of premature infants: study protocol for a randomized controlled trial

Background

Extremely premature (birth weight < 1250 g) infants are at high risk for acquiring late-onset sepsis and necrotizing enterocolitis, which are associated with significant mortality and morbidity. Own mother's milk contains protective (immune and trophic) biofactors which provide antimicrobial, anti-inflammatory, antioxidant, and immunomodulatory functions, enhance intestinal microbiota, and promote intestinal maturation. Many of these biofactors are most highly concentrated in the milk expressed by mothers of extremely premature infants. However, since extremely premature infants do not receive oral milk feeds until 32 weeks post-conceptional age, they lack the potential benefit provided by milk (biofactor) exposure to oropharyngeal immunocompetent cells, and this deficiency could contribute to late-onset sepsis and necrotizing enterocolitis. Therefore, oropharyngeal administration of own mother's milk may improve the health outcomes of these infants.

Objectives

To compare the effects of oropharyngeal administration of mother’s milk to a placebo, for important clinical outcomes, including (1A) reducing the incidence of late-onset sepsis (primary outcome) and (1B) necrotizing enterocolitis and death (secondary outcomes). To identify the biomechanisms responsible for the beneficial effects of oropharyngeal mother’s milk for extremely premature infants, including; (2A) enhancement of gastrointestinal (fecal) microbiota (2B) improvement in antioxidant defense maturation or reduction of pro-oxidant status, and (2C) maturation of immunostimulatory effects as measured by changes in urinary lactoferrin.

Methods/Design

A 5-year, multi-center, double-blind, randomized controlled trial designed to evaluate the safety and efficacy of oropharyngeal mother’s milk to reduce the incidence of (1A) late-onset sepsis and (1B) necrotizing enterocolitis and death in a large cohort of extremely premature infants (n = 622; total patients enrolled). Enrolled infants are randomly assigned to one of 2 groups: Group A infants receive 0.2 mL of own mother's milk, via oropharyngeal administration, every 2 hours for 48 hours, then every 3 hours until 32 weeks corrected-gestational age. Group B infants receive a placebo (0.2 mL sterile water) following the same protocol. Milk, urine, oral mucosal swab, and stool samples are collected at various time points, before, during and after the treatment periods. Health outcome and safety data are collected throughout the infant’s stay.

Trial registration

ClinicalTrials.gov identifier: NCT02116699 on 11 April 2014. Last updated: 26 May 2015

Pathogenesis of neonatal necrotizing enterocolitis

Although necrotizing enterocolitis (NEC) is the most lethal gastrointestinal disease in the neonatal population, its pathogenesis is poorly understood. Risk factors include prematurity, bacterial colonization, and formula feeding. This review examines how mucosal injury permits opportunistic pathogens to breach the gut barrier and incite an inflammatory response that leads to sustained overproduction of mediators such as nitric oxide and its potent adduct, peroxynitrite. These mediators not only exacerbate the initial mucosal injury, but they also suppress the intestinal repair mechanisms, which further compromises the gut barrier and culminates in bacterial translocation, sepsis, and full-blown NEC.

White and dark kidney beans reduce colonic mucosal damage and inflammation in response to dextran sodium sulfate

Common beans are a rich source of nondigestible fermentable components and phenolic compounds that have anti-inflammatory effects. We assessed the gut-health-promoting potential of kidney beans in healthy mice and their ability to attenuate colonic inflammation following dextran sodium sulphate (DSS) exposure (via drinking water, 2% DSS w/v, 7 days). C57BL/6 mice were fed one of three isocaloric diets: basal diet control (BD), or BD supplemented with 20% cooked white (WK) or dark red kidney (DK) bean flour for 3 weeks. In healthy mice, anti-inflammatory microbial-derived cecal short chain fatty acid (SCFA) levels (acetate, butyrate and propionate), colon crypt height and colonic Mucin 1 (MUC1) and Resistin-like Molecule beta (Relmβ) mRNA expression all increased in WK- and DK-fed mice compared to BD, indicative of enhanced microbial activity, gut barrier integrity and antimicrobial defense response. During colitis, both bean diets reduced (a) disease severity, (b) colonic histological damage and (c) increased mRNA expression of antimicrobial and barrier integrity-promoting genes (Toll-like Receptor 4 (TLR4), MUC1-3, Relmβ and Trefoil Factor 3 (TFF3)) and reduced proinflammatory mediator expression [interleukin (IL)-1β, IL-6, interferon (IFN)γ, tumor necrosis factor (TNF)α and monocyte chemoattractant protein-1], which correlated with reduced colon tissue protein levels. Further, bean diets exerted a systemic anti-inflammatory effect during colitis by reducing serum levels of IL-17A, IFNγ, TNFα, IL-1β and IL-6. In conclusion, both WK and DK bean-supplemented diets enhanced microbial-derived SCFA metabolite production, gut barrier integrity and the microbial defensive response in the healthy colon, which supported an anti-inflammatory phenotype during colitis. Collectively, these data demonstrate a beneficial colon-function priming effect of bean consumption that mitigates colitis severity.

Protective effects of transforming growth factor β2 in intestinal epithelial cells by regulation of proteins associated with stress and endotoxin responses

Transforming growth factor (TGF)-β2 is an important anti-inflammatory protein in milk and colostrum. TGF-β2 supplementation appears to reduce gut inflammatory diseases in early life, such as necrotizing enterocolitis (NEC) in young mice. However, the molecular mechanisms by which TGF-β2 protects immature intestinal epithelial cells (IECs) remain to be more clearly elucidated before interventions in infants can be considered. Porcine IECs PsIc1 were treated with TGF-β2 and/or lipopolysaccharide (LPS), and changes in the cellular proteome were subsequently analyzed using two-dimensional gel electrophoresis-MS and LC-MS-based proteomics. TGF-β2 alone induced the differential expression of 13 proteins and the majority of the identified proteins were associated with stress responses, TGF-β and Toll-like receptor 4 signaling cascades. In particular, a series of heat shock proteins had similar differential trends as previously shown in the intestine of NEC-resistant preterm pigs and young mice. Furthermore, LC-MS-based proteomics and Western blot analyses revealed 20 differentially expressed proteins following treatment with TGF-β2 in LPS-challenged IECs. Thirteen of these proteins were associated with stress response pathways, among which five proteins were altered by LPS and restored by TGF-β2, whereas six were differentially expressed only by TGF-β2 in LPS-challenged IECs. Based on previously reported biological functions, these patterns indicate the anti-stress and anti-inflammatory effects of TGF-β2 in IECs. We conclude that TGF-β2 of dietary or endogenous origin may regulate the IEC responses against LPS stimuli, thereby supporting cellular homeostasis and innate immunity in response to bacterial colonization, and the first enteral feeding in early life.

Dietary intake and bio-activation of nitrite and nitrate in newborn infants

Nitrate and nitrite are commonly thought of as inert end products of nitric oxide (NO) oxidation, possibly carcinogenic food additives, or well-water contaminants. However, recent studies have shown that nitrate and nitrite play an important role in cardiovascular and gastrointestinal homeostasis through conversion back into NO via a physiological system involving enterosalivary recirculation, bacterial nitrate reductases, and enzyme-catalyzed or acidic reduction of nitrite to NO. The diet is a key source of nitrate in adults; however, infants ingest significantly less nitrate due to low concentrations in breast milk. In the mouth, bacteria convert nitrate to nitrite, which has gastro-protective effects. However, these nitrate-reducing bacteria are relatively inactive in infants. Swallowed nitrite is reduced to NO by acid in the stomach, affecting gastric blood flow, mucus production, and the gastric microbiota. These effects are likely attenuated in the less acidic neonatal stomach. Systemically, nitrite acts as a reservoir of NO bioactivity that can protect against ischemic injury, yet plasma nitrite concentrations are markedly lower in infants than in adults. The physiological importance of the diminished nitrate→nitrite→NO axis in infants and its implications in the etiology and treatment of newborn diseases such as necrotizing enterocolitis and hypoxic/ischemic injury are yet to be determined.

Critical role of myeloid differentiation factor 88 in necrotizing enterocolitis

BACKGROUND

The importance of toll-like receptor 4 in necrotizing enterocolitis (NEC) has been intensively studied, but its downstream signaling and the potential regulatory mechanisms remain unidentified. Our study focused on the role of myeloid differentiation factor 88 (MyD88), the first downstream adaptor of toll-like receptor 4 inflammatory and apoptotic signaling in the pathogenesis of NEC.

METHODS

MyD88 knockout (MyD88(-/-)-Ko) mice and lentivirus-mediated stable MyD88-knockdown cell line (IEC-6) were used. NEC was induced by formula gavage, cold, hypoxia, combined with lipopolysaccharide (LPS) in vivo, or LPS stimulation in vitro. NEC was evaluated by histology and multiple inflammatory cytokines. Enterocyte apoptosis was evaluated by terminal-deoxynucleoitidyl transferase-mediated nick end labeling (TUNEL) or Annexin analysis. Inflammatory or apoptotic molecules including NF-κB, Toll/IL-1R domain-containing adaptor-inducing IFN-β, interferon regulatory factor 3, Bax, Bcl-2, and caspases were examined by quantitative real-time PCR (qRT-PCR).

RESULTS

In the MyD88-Ko group, NEC severity and intestinal enterocyte apoptosis rate were reduced, the expression of NF-κB, caspases, and Bax, were all downregulated, while Toll/IL-1R domain-containing adaptor-inducing IFN-β and were upregulated, and antiapoptotic gene Bcl-2 remained stable. Cytokine levels of interleukin (IL)-6, IL-1β, and tumor necrosis factor-α (TNF-α) were also all decreased.

CONCLUSION

MyD88-dependent signaling is the prevailing inflammatory and apoptotic signaling in toll-like receptor 4 downstream signaling; MyD88-Ko resulted in reduced inflammatory severity and apoptosis, though MyD88-independent signaling can also be activated, but is of less dominant for the development of NEC.

Antibiotics modulate intestinal immunity and prevent necrotizing enterocolitis in preterm neonatal piglets

Preterm birth, bacterial colonization, and formula feeding predispose to necrotizing enterocolitis (NEC). Antibiotics are commonly administered to prevent sepsis in preterm infants, but it is not known whether this affects intestinal immunity and NEC resistance. We hypothesized that broad-spectrum antibiotic treatment improves NEC resistance and intestinal structure, function, and immunity in neonates. Caesarean-delivered preterm pigs were fed 3 days of parenteral nutrition followed by 2 days of enteral formula. Immediately after birth, they were assigned to receive either antibiotics (oral and parenteral doses of gentamycin, ampicillin, and metronidazole, ANTI, n = 11) or saline in the control group (CON, n = 13), given twice daily. NEC lesions and intestinal structure, function, microbiology, and immunity markers were recorded. None of the ANTI but 85% of the CON pigs developed NEC lesions by day 5 (0/11 vs. 11/13, P < 0.05). ANTI pigs had higher intestinal villi (+60%), digestive enzyme activities (+53-73%), and goblet cell densities (+110%) and lower myeloperoxidase (-51%) and colonic microbial density (10(5) vs. 10(10) colony-forming units, all P < 0.05). Microarray transcriptomics showed strong downregulation of genes related to inflammation and innate immune response to microbiota and marked upregulation of genes related to amino acid metabolism, in particular threonine, glucose transport systems, and cell cycle in 5-day-old ANTI pigs. In a follow-up experiment, 5 days of antibiotics prevented NEC at least until day 10. Neonatal prophylactic antibiotics effectively reduced gut bacterial load, prevented NEC, intestinal atrophy, dysfunction, and inflammation and enhanced expression of genes related to gut metabolism and immunity in preterm pigs.

Toll-like receptor regulation of intestinal development and inflammation in the pathogenesis of necrotizing enterocolitis

Toll-like receptors (TLRs) are a structurally related family of molecules that respond to a wide variety of endogenous and exogenous ligands, and which serve as important components of the innate immune system. While TLRs have established roles in host defense, these molecules have also been shown to play important roles in the development of various disease states. A particularly important example of the role of TLRs in disease induction includes necrotizing enterocolitis (NEC), which is the most common gastrointestinal disease in preterm infants, and which is associated with extremely high morbidity and mortality rates. The development of NEC is thought to reflect an abnormal interaction between microorganisms and the immature intestinal epithelium, and emerging evidence has clearly placed the spotlight on an important and exciting role for TLRs, particularly TLR4, in NEC pathogenesis. In premature infants, TLR4 signaling within the small intestinal epithelium regulates apoptosis, proliferation and migration of enterocytes, affects the differentiation of goblet cells, and reduces microcirculatory perfusion, which in combination result in the development of NEC. This review will explore the signaling properties of TLRs on hematopoietic and non-hematopoietic cells, and will examine the role of TLR4 signaling in the development of NEC. In addition, the effects of dampening TLR4 signaling using synthetic and endogenous TLR4 inhibitors and active components from amniotic fluid and human milk on NEC severity will be reviewed. In so doing, we hope to present a balanced approach to the understanding of the role of TLRs in both immunity and disease pathogenesis, and to dissect the precise roles for TLR4 in both the cause and therapeutic intervention of necrotizing enterocolitis.