Heparin-binding epidermal growth factor-like growth factor overexpression in transgenic mice increases resistance to necrotizing enterocolitis

Prenatal administration of heparin-binding epidermal growth factor-like growth factor in an experimental model of necrotizing enterocolitis decreased both incidence and severity of the disease

Background

Necrotizing enterocolitis (NEC) is the leading gastrointestinal cause of death in premature infants and causes long-term disabilities. Previously, enteral heparin-binding epidermal growth factor-like growth factor (HB-EGF) administered after birth demonstrated decreased incidence and severity of NEC in a neonatal animal model of NEC. We investigated the potential prophylactic strategy of preventing NEC using prenatally administered HB-EGF.

Methods

An HB-EGF (800 µg/kg/dose) dose was injected into pregnant rats via tail vein or intraperitoneal route 2 hours prior to delivery. After cesarean section (C-section) at 21 days' gestation, the rat pups were subjected to the NEC protocol by inducing stressors: hypoxia, hypothermia, hypertonic feeds, and orogastric gavage of lipopolysaccharide (2 mg/kg). Postnatally, pups were monitored for 96 hours and assessed for the development of clinical and postmortem histological NEC.

Results

The experimental NEC incidence in untreated, stressed rat pups was 66%. Compared with untreated pups, the maternal administration of HB-EGF correlated with a significant NEC incidence and severity decrease in rat pups. The strongest decrease was seen when HB-EGF was administered via the intraperitoneal route 2 hours prior to C-section (66% vs 31%, *p<0.05). Prenatal HB-EGF administration significantly increased pups' survival after NEC protocol exposure, with the greatest benefit observed in the group that received HB-EGF intraperitoneally 2 hours before delivery.

Conclusions

Prenatal administration of HB-EGF decreases the incidence and severity of NEC, preserves gut barrier function and increases survival. This may represent a novel prophylactic clinical strategy for NEC offered to mothers at risk of delivering a premature infant.

Prenatal stress increases IgA coating of offspring microbiota and exacerbates necrotizing enterocolitis-like injury in a sex-dependent manner

Necrotizing enterocolitis (NEC) is an intestinal inflammatory disease with high morbidity and mortality that affects almost exclusively premature infants. Breast milk feeding is known to substantially lower NEC incidence, and specific components of breast milk, such as immunoglobulin (Ig) A, have been identified as mediating this protective effect. On the other hand, accumulating evidence suggests dysbiosis of the neonatal intestinal microbiome contributes to NEC pathogenesis. In mice, neonates can inherit a dysbiotic microbiome from dams that experience stress during pregnancy. Here we show that while prenatal stress lowers fecal IgA levels in pregnant mice, it does not result in lower levels of IgA in the breast milk. Nevertheless, coating of female, but not male, offspring microbiota by IgA is increased by prenatal stress. Accordingly, prenatal stress was found to alter the bacterial community composition in female neonates but not male neonates. Furthermore, female, but not male, offspring of prenatally stressed mothers exhibited more severe colonic tissue damage in a NEC-like injury model compared to offspring with non-stressed mothers. Our results point to prenatal stress as a possible novel risk factor for NEC and potentially reveal new avenues in NEC prevention and therapy.

Human Mesenchymal Stem Cell Hydrogen Sulfide Production Critically Impacts the Release of Other Paracrine Mediators After Injury

BACKGROUND

The use of mesenchymal stem cells (MSCs) for treatment during ischemia is novel. Hydrogen sulfide (H₂S) is an important paracrine mediator that is released from MSCs to facilitate angiogenesis and vasodilation. Three enzymes, cystathionine-beta-synthase (CBS), cystathionine-gamma-lyase (CSE), and 3-mercaptopyruvate-sulfurtransferase (MPST), are mainly responsible for H₂S production. However, it is unclear how these enzymes impact the production of other critical growth factors and chemokines. We hypothesized that the enzymes responsible for H₂S production in human MSCs would also critically regulate other growth factors and chemokines.

MATERIALS AND METHODS

Human MSCs were transfected with CBS, MPST, CSE, or negative control small interfering RNA. Knockdown of enzymes was confirmed by polymerase chain reaction. Cells were plated in 12-well plates at 100,000 cells per well and stimulated with tumor necrosis factor-α (TNF-α; 50 ng/mL), lipopolysaccharide (LPS; 200 ng/mL), or 5% hypoxia for 24 h. Supernatants were collected, and cytokines measured by multiplex beaded assay. Data were compared with the Mann-Whitney U-test, and P < 0.05 was significant.

RESULTS

TNF-α, LPS, and hypoxia effectively stimulated MSCs. Granulocyte colony-stimulating factor (GCSF), epidermal growth factor, fibroblast growth factor, granulocyte/monocyte colony-stimulating factor (GMCSF), vascular endothelial growth factor, and interferon gamma-inducible protein 10 were all significantly elevated when CSE was knocked down during TNF-α stimulation (P < 0.05). Knockdown of MPST during LPS stimulation more readily increased GCSF and epidermal growth factor but decreased GMCSF (P < 0.05). CBS knockdown decreased production of GCSF, fibroblast growth factor, GMCSF, and vascular endothelial growth factor (P < 0.05) after hypoxia.

CONCLUSIONS

The enzymes that produce H₂S in MSCs are also responsible for the production of other stem cell paracrine mediators under stressful stimuli. Therefore, reprogramming MSCs to endogenously produce more H₂S as a therapeutic intervention could also critically impact other paracrine mediators, which may alter the desired beneficial effects.

Saccharomyces boulardii modulates necrotizing enterocolitis in neonatal mice by regulating the sirtuin 1/NF‑κB pathway and the intestinal microbiota

Exaggerated inflammatory response and gut microbial dysbiosis play a crucial role in necrotizing enterocolitis (NEC). The probiotic Saccharomyces boulardii (SB) is a yeast that has a beneficial effect on NEC; however, the association between its protective effects and the regulation of the inflammation-related sirtuin 1 (SIRT1)/nuclear factor-κB (NF-κB) signaling pathway and gut microbiota in NEC is unknown. In the present study, the NEC model was established by artificial feeding and lipopolysaccharide (LPS), hypoxia and hypothermia stimulation. Mice were divided into normal, control (artificial feeding), NEC and NEC + SB groups. Hematoxylin and eosin staining demonstrated that SB improved the pathological damage of the intestine caused by NEC in neonatal mice. Furthermore, downregulation of SIRT1 and upregulation of NF-κB expression were confirmed by immunofluorescence staining, western blotting and reverse transcription-quantitative PCR (RT-qPCR) in NEC mice. SB treatment concurrently inhibited the NEC roles on the SIRT1 and NF-κB pathway at both the protein and mRNA levels. Deletion of SIRT1 [SIRT1 knockout (KO)] in the intestine abolished all the effects of SB in NEC mice, including protection of pathological damage and inhibition of the SIRT1/NF-κB pathway activation. The abundance of gut microbial composition, as determined by RT-qPCR, was significantly decreased in the control group compared with the normal group. A further decrease in microbiota abundance was observed in the NEC group, and SB administration significantly improved the enrichment of gut microbiota in neonatal mice with NEC. As anticipated, the increased abundance of gut microbiota modulated by SB was markedly reduced in SIRT1KO NEC mice. The present study revealed that the protective role of SB on NEC was associated with the SIRT1/NF-κB pathway and gut microbiota regulation.

Animal models of necrotizing enterocolitis

Background

Necrotizing enterocolitis (NEC) is one of the leading causes of death in premature infants. To determine the factors present in the disease that lead to increased morbidity and mortality, manipulation of variables that are shown to have a positive response has been tested using various animal models. Testing and manipulation of these variables are unwarranted in humans due to regulatory health standards.

Methods

The purpose of this review is to provide an update to previous summaries that determine the significance of animal models in studying the mechanisms of NEC. A large variety of animal models including rats, mice, rabbits, piglets, nonhuman primates, and quails have been described in literature. We reviewed the reported animal models of NEC and examined the pros and cons of the various models as well as the scientific question addressed.

Results

The animals used in these experiments were subject to gavage feeding, hypoxia, hypothermia, oxygen perfusion, and other methods to induce the disease state. Each of these models has been utilized to show the effects of NEC on the premature, undeveloped gut in animals to find a correlation to the disease state present in humans. We found specific advantages and disadvantages for each model.

Conclusions

Recent advances in our understanding of NEC and the ongoing therapeutic strategy developments underscore the importance of animal models for this disease.

Genetic predisposition to necrotizing enterocolitis in premature infants: Current knowledge, challenges, and future directions

The role of genetics in the pathogenesis of necrotizing enterocolitis (NEC) was initially informed by epidemiological data indicating differences in prevalence among different ethnic groups as well as concordance in twins. These early observations, together with major advances in genomic research, paved the way for studies that begin to reveal the contribution of genetics to NEC. Using the candidate gene or pathway approach, several potential pathogenic variants for NEC in premature infants have already been identified. More recently, genome-wide association studies and exome-sequencing based studies for NEC have been reported. These advances, however, are tempered by the lack of adequately powered replication cohorts to validate the accuracy of these discoveries. Despite many challenges, genetic research in NEC is expected to increase, providing new insights into its pathogenesis and bringing the promise of personalized care closer to reality. In this review we provide a summary of genetic studies in NEC along with defining the challenges and possible future approaches.

Evolving understanding of neonatal necrotizing enterocolitis

PURPOSE OF REVIEW

Necrotizing enterocolitis (NEC) is a devastating disease that predominately affects premature neonates. The pathogenesis of NEC is multifactorial and poorly understood. Risk factors include low birth weight, formula-feeding, hypoxic/ischemic insults, and microbial dysbiosis. This review focuses on our current understanding of the diagnosis, management, and pathogenesis of NEC.

RECENT FINDINGS

Recent findings identify specific mucosal cell types as potential therapeutic targets in NEC. Despite a broadly accepted view that bacterial colonization plays a key role in NEC, characteristics of bacterial populations associated with this disease remain elusive. The use of probiotics such as lactobacilli and bifidobacteria has been studied in numerous trials, but there is a lack of consensus regarding specific strains and dosing. Although growth factors found in breast milk such as epidermal growth factor and heparin-binding epidermal growth factor may be useful in disease prevention, developing new therapeutic interventions in NEC critically depends on better understanding of its pathogenesis.

SUMMARY

NEC is a leading cause of morbidity and mortality in premature neonates. Recent data confirm that growth factors and certain bacteria may offer protection against NEC. Further studies are needed to better understand the complex pathogenesis of NEC.

Association of Heparin-binding EGF-like Growth Factor Polymorphisms With Necrotizing Enterocolitis in Preterm Infants

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) protects the intestines from injury in experimental necrotizing enterocolitis (NEC). We hypothesized that polymorphisms in the HB-EGF gene lead to low HB-EGF production in peripheral blood and increased risk of NEC in the Chinese Han population. To test this hypothesis, 30 NEC patients and 80 control subjects were selected. Five HB-EGF single-nucleotide polymorphisms (SNPs) and its plasma levels were measured by genotyping and enzyme-linked immunosorbent assay, respectively. Only 1 out of the 5 SNPs showed a notable result. The notable SNP (rs4912711) was associated with NEC in its minor allele frequency and its "G/T" genotype distribution. In addition, plasma HB-EGF levels were reduced especially the "G/T" genotype in NEC patients. Our data suggest that if validated in larger studies screening for HB-EGF SNPs/genotypes and plasma levels may be useful as a risk factor for NEC in the future.

Heparin-binding EGF-like growth factor promotes neuronal nitric oxide synthase expression and protects the enteric nervous system after necrotizing enterocolitis

BackgroundNeonatal necrotizing enterocolitis (NEC) is associated with alterations of the enteric nervous system (ENS), with loss of neuronal nitric oxide synthase (nNOS)-expressing neurons in the intestine. The aim of this study was to investigate the roles of heparin-binding EGF-like growth factor (HB-EGF) in neural stem cell (NSC) differentiation, nNOS expression, and effects on ENS integrity during experimental NEC.MethodsThe effects of HB-EGF on NSC differentiation and nNOS production were determined using cultured enteric NSCs. Myenteric neuronal subpopulations were examined in HB-EGF knockout mice. Rat pups were exposed to experimental NEC, and the effects of HB-EGF treatment on nNOS production and intestinal neuronal apoptosis were determined.ResultsHB-EGF promotes NSC differentiation, with increased nNOS production in differentiated neurons and glial cells. Moreover, loss of nNOS-expressing neurons in the myenteric plexus and impaired neurite outgrowth were associated with absence of the HB-EGF gene. In addition, administration of HB-EGF preserves nNOS expression in the myenteric plexus and reduces enteric neuronal apoptosis during experimental NEC.ConclusionHB-EGF promotes the differentiation of enteric NSCs into neurons in a nitric oxide (NO)-dependent manner, and protects the ENS from NEC-induced injury, providing new insights into potential therapeutic strategies for the treatment of NEC in the future.

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.

Formula feeding and systemic hypoxia synergistically induce intestinal hypoxia in experimental necrotizing enterocolitis

PURPOSE

Feeding and systemic hypoxia are major stresses inducing necrotizing enterocolitis (NEC). This study aims to investigate the role of systemic hypoxia in NEC and its effect before and after feeding.

METHODS

Neonatal mice were studied in three groups. Control (N = 9): breast feeding; NEC A (N = 8), gavage feeding + lipopolysaccharide (LPS) + preprandial hypoxia; and NEC B (N = 9), feeding + LPS + postprandial hypoxia. Pimonidazole, a hypoxia marker, was injected intraperitoneally before ileum was harvested for histology and quantitative RT-PCR studies. Statistical analysis was done using the ANOVA and Chi-square test.

RESULTS

NEC incidence was 62.5% in NEC A and 88.9% in NEC B. The mortality in NEC B (55.6%) but not A (25%) is significantly higher than control (0%, p < 0.05). Pimonidazole staining elevated in both NEC A and B with higher pimonidazole grade in NEC B (p < 0.01). Both NEC groups had increased the expression of hypoxia-related genes: HIF-1α, GLUT-1, and PHD-3 with GLUT-1 expressed more in NEC B compared with NEC A (p < 0.01). The inflammation marker, IL6, was similarly raised in both NEC A and B.

CONCLUSION

Feeding and postprandial hypoxia synergistically induce intestinal hypoxia in NEC. As feeding increases intestinal oxygen demand, maintaining a balance between intestinal oxygen supply and demand is important to prevent NEC.

The viral dsRNA analogue poly (I:C) induces necrotizing enterocolitis in neonatal mice

BACKGROUND

Necrotizing enterocolitis (NEC) is a life-threatening gastrointestinal disease in premature infants with high mortality and morbidity with uncertain pathogenesis. Recent research focused on the role of intraluminal bacteria and lipopolysaccharide (LPS). However, an additional role of viral agents in the pathogenesis of NEC has recently been postulated. We assessed the role of polyinosinic:polycytidylic acid (pIC) mimicking viral dsRNA in contributing to the development of NEC in neonatal mice.

METHODS

Four-d-old C57BL/6J pups were stressed by asphyxia and hypothermia twice daily. Animals were either fed by formula only (FO), formula containing LPS or pIC. After 72 h, mice were euthanized, intestines harvested, and the severity of NEC was assessed.

RESULTS

Breastfed mice showed no evidence of NEC. Very mild NEC-like lesions were observed in mice fed by FO. Supplementation of LPS or pIC to the formula led to increased intestinal tissue damage and inflammation compared with FO in a similar manner.

CONCLUSION

Our study demonstrates the ability of viral factors to induce NEC in neonatal mice even in the absence of LPS. Furthermore, we present a new mouse model of pIC-induced NEC which may be used to obtain further mechanistic insights in the pathogenesis of this disease.

A spectrum of intestinal injury models in neonatal mice

PURPOSE

To compare the degree of necrotizing enterocolitis (NEC)-like damage under different stress conditions in neonatal mice.

METHODS

5-day-old C57BL/6 mice were assigned to: (A) breastfed and no stress factors; (B) breastfed+maternal separation (3 h daily); (C) breastfed+hypoxia+lipopolysaccharide (LPS-4 mg/kg/day); (D) hyperosmolar formula+hypoxia+LPS. Mice were killed at 9 days of life. Ileum and colon were stained for hematoxylin/eosin and blindly assessed. A scoring ≥2 was considered NEC. Data were compared using one-way ANOVA and reported as median (range).

RESULTS

Ileum-Mucosal injury was mild in group B (0.0-1). Hypoxia+LPS induced greater injury in group C (1.6, 1-2.5; p < 0.0001 to B) and D (2, 0.5-3.5; p < 0.0001 to B). There were no differences between group C and D (p = n.s.). There were no cases of NEC in group A or B, whereas NEC was present in 36 % group C and 68 % group D mice. Colon-a similar degree of mucosal injury was observed among group B (2, 1-3), C (1.7, 0-3) and D (1.5, 1-3; p = n.s.). NEC was present in 75 % of group B, 50 % of group C and 86 % of group D.

CONCLUSION

These models establish a spectrum of intestinal injury and are useful to investigate the variability of neonatal intestinal diseases, such as NEC.

Necrotizing enterocolitis in a mouse model leads to widespread renal inflammation, acute kidney injury, and disruption of renal tight junction proteins

BACKGROUND

Necrotizing enterocolitis (NEC) is a devastating condition affecting premature infants and leads to high mortality and chronic morbidity. Severe form of NEC is associated with acute renal failure, fluid imbalance, hyponatremia, and acidosis. We investigated the effect of NEC on tight junction (TJ) proteins in kidneys using a NEC mouse model to investigate the basis for the observed renal dysfunction.

METHODS

NEC was induced in C57BL/6 mice by formula feeding and subjecting them to periods of hypoxia and cold stress. NEC was confirmed by gross and histological examination. We studied various markers of inflammation in kidneys and investigated changes in expression of several TJ proteins and AQP2 using immunofluorecent staining and western blotting.

RESULTS

We found markedly increased expression of NFκB, TGFβ, and ERK1/2 along with claudin-1, -2, -3, -4, -8, and AQP-2 in NEC kidneys. The membrane localization of claudin-2 was altered in the NEC kidneys and its immunostaining signal at TJ was disrupted.

CONCLUSION

NEC led to a severe inflammatory response not only in the gut but also in the kidneys. NEC increased expression of several TJ proteins and caused disruption of claudin-2 in renal tubules. These observed changes can help explain some of the clinical findings observed in NEC.

M1 to M2 macrophage polarization in heparin-binding epidermal growth factor-like growth factor therapy for necrotizing enterocolitis

BACKGROUND

Macrophages can be polarized into proinflammatory (M1) and anti-inflammatory (M2) subtypes. However, whether macrophage polarization plays a role in necrotizing enterocolitis (NEC) remains unknown.

MATERIALS AND METHODS

Macrophages were derived from the THP-1 human monocyte cell line. Apoptosis of human fetal small intestinal epithelial FHs-74 cells was determined by Annexin V/propidium iodide flow cytometry and by Western blotting to detect cleaved caspase-3. The effect of heparin-binding epidermal growth factor-like growth factor (HB-EGF) on macrophage polarization was determined by flow cytometry with M1/M2 markers and real time polymerase chain reaction. In vivo, experimental NEC was induced in mouse pups by repeated exposure to hypoxia, hypothermia, and hypertonic feedings. Intestinal histologic sections were subjected to immunohistochemical staining for the detection of M1 and M2 macrophages.

RESULTS

In vitro, FHs-74 cell apoptosis was increased after coculture with macrophages and lipopolysaccharide (LPS). This apoptosis was increased by exposure to M1-conditioned medium and suppressed by exposure to M2-conditioned medium. HB-EGF significantly decreased LPS-induced M1 polarization and promoted M2 polarization via signal transducers and activators of transcription 3 activation. Addition of HB-EGF to LPS-stimulated macrophages suppressed the proapoptotic effects of the macrophages on FHs-74 cells. In vivo, we found enhanced intestinal macrophage infiltration in pups subjected to NEC, most of which were M1 macrophages. HB-EGF treatment of pups subjected to experimental NEC significantly reduced M1 and increased M2 polarization and protected the intestines from NEC.

CONCLUSIONS

M1 macrophages promote NEC by increasing intestinal epithelial apoptosis. HB-EGF protects the intestines from NEC by preventing M1 and promoting M2 polarization.

Early maternal separation induces alterations of colonic epithelial permeability and morphology

BACKGROUND

Early maternal separation could lead to significant intestinal barrier and epithelial dysfunction. However, the exact mechanism remains to be elucidated and need to be investigated.

METHODS

Neonatal C57BL/6 mice were subjected to maternal separation: Maternal separation (MS) daily 3 h between postnatal day (PND) 5-9, single separation (SS) 3 h on PND 9 and no separation (NS). Colon and ileum permeability was measured by Ussing chamber. Severity of morphological changes in the colon was evaluated by blinded grading of histological stained sections.

RESULTS

Trans-epithelial resistance of colon and ileum did not change indicating that the tissues remained intact during the course of the experiment. Permeability of trans-cellular tracer Horseradish peroxidase (HRP) was significantly increased in the colon of MS compared to SS and NS (p < 0.05 for SS and p < 0.001 for NS), but there was no difference in para-cellular permeability of fluorescein isothiocyanate-conjugated dextran (FD4). However, there was no change in permeability of both HRP and FD4 in the ileum. MS and SS groups had marked intestinal epithelium morphology changes in comparison to controls (p < 0.05).

CONCLUSION

These preliminary observations indicate that neonatal maternal separation increases colonic trans-cellular permeability. This increase may be caused by the change of the transmural colonic morphology. The underlying mechanism is unknown and further investigation is necessary as it is of relevance to the development of early intestinal diseases such as necrotizing enterocolitis.

The ErbB4 ligand neuregulin-4 protects against experimental necrotizing enterocolitis

Necrotizing enterocolitis (NEC) affects up to 10% of premature infants, has a mortality of 30%, and can leave surviving patients with significant morbidity. Neuregulin-4 (NRG4) is an ErbB4-specific ligand that promotes epithelial cell survival. Thus, this pathway could be protective in diseases such as NEC, in which epithelial cell death is a major pathologic feature. We sought to determine whether NRG4-ErbB4 signaling is protective in experimental NEC. NRG4 was used i) in the newborn rat formula feeding/hypoxia model; ii) in a recently developed model in which 14- to 16-day-old mice are injected with dithizone to induce Paneth cell loss, followed by Klebsiella pneumoniae infection to induce intestinal injury; and iii) in bacterially infected IEC-6 cells in vitro. NRG4 reduced NEC incidence and severity in the formula feed/hypoxia rat model. It also reduced Paneth cell ablation-induced NEC and prevented dithizone-induced Paneth cell loss in mice. In vitro, cultured ErbB4(-/-) ileal epithelial enteroids had reduced Paneth cell markers and were highly sensitive to inflammatory cytokines. Furthermore, NRG4 blocked, through a Src-dependent pathway, Cronobacter muytjensii-induced IEC-6 cell apoptosis. The potential clinical relevance of these findings was demonstrated by the observation that NRG4 and its receptor ErbB4 are present in human breast milk and developing human intestine, respectively. Thus, NRG4-ErbB4 signaling may be a novel pathway for therapeutic intervention or prevention in NEC.

Argininosuccinate lyase in enterocytes protects from development of necrotizing enterocolitis

Necrotizing enterocolitis (NEC), the most common neonatal gastrointestinal emergency, results in significant mortality and morbidity, yet its pathogenesis remains unclear. Argininosuccinate lyase (ASL) is the only enzyme in mammals that is capable of synthesizing arginine. Arginine has several homeostatic roles in the gut and its deficiency has been associated with NEC. Because enterocytes are the primary sites of arginine synthesis in neonatal mammals, we evaluated the consequences of disruption of arginine synthesis in the enterocytes on the pathogenesis of NEC. We devised a novel approach to study the role of enterocyte-derived ASL in NEC by generating and characterizing a mouse model with enterocyte-specific deletion of Asl (Asl(flox/flox); VillinCre(tg/+), or CKO). We hypothesized that the presence of ASL in a cell-specific manner in the enterocytes is protective in the pathogenesis of NEC. Loss of ASL in enterocytes resulted in an increased incidence of NEC that was associated with a proinflammatory state and increased enterocyte apoptosis. Knockdown of ASL in intestinal epithelial cell lines resulted in decreased migration in response to lipopolysaccharide. Our results show that enterocyte-derived ASL has a protective role in NEC.

Predicting disease severity of necrotizing enterocolitis: how to identify infants for future novel therapies

Necrotizing enterocolitis (NEC) remains a very devastating problem within the very low birth weight neonatal population. Several experimental therapies are being tested in animal models and soon may be ready for human trials. Despite this progress, we currently have no way to identify infants who would be optimal targets for therapy. Specifically, we are unable to predict which infants will progress to the more severe Bell's stage of disease that may necessitate surgery. Ideally, an algorithm could be constructed that would encompass multiple neonatal and maternal risk factors as well as potential biologic markers of disease so that these infants could be identified in a more timely fashion. This review summarizes the known risk factors and biomarkers of disease in hopes of stimulating clinical research to identify such an “early warning” NEC algorithm.

Heparin-binding EGF-like growth factor (HB-EGF) promotes cell migration and adhesion via focal adhesion kinase

BACKGROUND

Cell migration and adhesion are essential in intestinal epithelial wound healing and recovery from injury. Focal adhesion kinase (FAK) plays an important role in cell-extracellular matrix signal transduction. We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) promotes intestinal epithelial cell (IEC) migration and adhesion in vitro. The present study was designed to determine whether FAK is involved in HB-EGF-induced IEC migration and adhesion.

MATERIALS AND METHODS

A scrape wound healing model of rat IECs was used to examine the effect of HB-EGF on FAK-dependent cell migration in vitro. Immunofluorescence and Western blot analyses were performed to evaluate the effect of HB-EGF on the expression of phosphorylated FAK (p-FAK). Cell adhesion assays were performed to determine the role of FAK in HB-EGF-induced cell adhesion on fibronectin (FN).

RESULTS

HB-EGF significantly increased healing after scrape wounding, an effect that was reversed in the presence of an FAK inhibitor 14 (both with P < 0.05). HB-EGF increased p-FAK expression and induced p-FAK redistribution and actin reorganization in migrating rat IECs. Cell adhesion and spreading on FN were significantly increased by HB-EGF (P < 0.05). FAK inhibitor 14 significantly inhibited both intrinsic and HB-EGF-induced cell adhesion and spreading on FN (both with P < 0.05).

CONCLUSIONS

FAK phosphorylation and FAK-mediated signal transduction play essential roles in HB-EGF-mediated IEC migration and adhesion.

ErbB receptors and their growth factor ligands in pediatric intestinal inflammation

The ErbB tyrosine kinases (epidermal growth factor receptor (EGFR), ErbB2/HER2, ErbB3, and ErbB4) are cell surface growth factor receptors widely expressed in many developing mammalian tissues, including in the intestinal tract. Signaling elicited by these receptors promotes epithelial cell growth and survival, and ErbB ligands have been proposed as therapeutic agents for intestinal diseases of pediatric populations, including inflammatory bowel disease (IBD), necrotizing enterocolitis (NEC), and inflammation associated with total parenteral nutrition (TPN). Furthermore, emerging evidence points to reduced ErbB ligand expression and thus reduced ErbB activity in IBD, NEC, and TPN models. This review will discuss the current understanding of the role of ErbB receptors in the pathogenesis and potential treatment of pediatric intestinal inflammation, with focus on the altered signaling in disease and the molecular mechanisms by which exogenous ligands are protective.

Heparin-binding EGF-like growth factor (HB-EGF) therapy for intestinal injury: Application and future prospects

Throughout the past 20 years, we have been investigating the potential therapeutic roles of heparin-binding EGF-like growth factor (HB-EGF), a member of the epidermal growth factor family, in various models of intestinal injury including necrotizing enterocolitis (NEC), intestinal ischemia/reperfusion (I/R) injury, and hemorrhagic shock and resuscitation (HS/R). Our studies have demonstrated that HB-EGF acts as an effective mitogen, a restitution-inducing reagent, a cellular trophic factor, an anti-apoptotic protein and a vasodilator, via its effects on various cell types in the intestine. In the current paper, we have reviewed the application and therapeutic effects of HB-EGF in three classic animal models of intestinal injury, with particular emphasis on its protection of the intestines from NEC. Additionally, we have summarized the protective functions of HB-EGF on various target cells in the intestine. Lastly, we have provided a brief discussion focusing on the future development of HB-EGF clinical applications for the treatment of various forms of intestinal injury including NEC.

The role of growth factors in intestinal regeneration and repair in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease resulting in major neonatal morbidity and mortality. The pathology is poorly understood, and the means of preventing and treating NEC are limited. Several endogenous growth factors have been identified as having important roles in intestinal growth as well as aiding intestinal repair from injury or inflammation. In this review, we will discuss several growth factors as mediators of intestinal regeneration and repair as well as potential therapeutic agents for NEC.

HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix interactions and intercellular adhesions

Restitution is a critical form of intestinal epithelial cell (IEC) healing. We have previously shown that heparin-binding epidermal-like growth factor (HB-EGF) is necessary for IEC restitution; however, the mechanisms by which HB-EGF promotes restitution remain poorly understood. This study was designed to investigate whether HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix (ECM) interactions and intercellular adhesions. The effect of HB-EGF administration was examined in a murine necrotizing enterocolitis (NEC) model in vivo and an IEC line scrape-wound healing model in vitro. We evaluated the effect of HB-EGF on the expression of integrins, E-cadherin/β-catenin, and integrin α5β1-dependent cell-ECM interactions. We found that HB-EGF promoted intestinal restitution and the expression of integrin α5β1. HB-EGF promoted integrin α5β1-dependent cell adhesion and spreading. In addition, HB-EGF decreased the expression E-cadherin/β-catenin, via the activation of v-erb-b2 erythroblastic leukemia viral oncogene homolog (ErbB-1). We conclude that HB-EGF promotes intestinal restitution by affecting integrin-ECM interactions and intercellular adhesions.

Heparin-binding epidermal growth factor-like growth factor and mesenchymal stem cells act synergistically to prevent experimental necrotizing enterocolitis

BACKGROUND

We have shown that administration of heparin-binding EGF (epidermal growth factor)-like growth factor (HB-EGF) protects the intestines from experimental necrotizing enterocolitis (NEC). We have also demonstrated that systemically administered mesenchymal stem cells (MSC) can engraft into injured intestines. This study investigated the effects of HB-EGF on MSC in vitro, and whether MSC and HB-EGF can act synergistically to prevent NEC in vivo.

STUDY DESIGN

In vitro, the effect of HB-EGF on MSC proliferation, migration, and apoptosis was determined. In vivo, rat pups received MSC either intraperitoneally (IP) or intravenously (IV). Pups were assigned to 1 of 7 groups: Group 1, breast-fed; Group 2, experimental NEC; Group 3, NEC+HB-EGF; Group 4, NEC+MSC IP; Group 5, NEC+HB-EGF+MSC IP; Group 6, NEC+MSC IV; or Group 7, NEC+HB-EGF+MSC IV. Mesechymal stem cell engraftment, histologic injury, intestinal permeability, and mortality were determined.

RESULTS

Heparin-binding EGF-like growth factor promoted MSC proliferation and migration, and decreased MSC apoptosis in vitro. In vivo, MSC administered IV had increased engraftment into NEC-injured intestine compared with MSC administered IP (p < 0.05). Heparin binding EGF-like growth factor increased engraftment of IP-administered MSC (p < 0.01) and IV-administered MSC (p < 0.05). Pups in Groups 3 to 7 had a decreased incidence of NEC compared with nontreated pups (Group 2), with the lowest incidence in pups treated with HB-EGF+MSC IV (p < 0.01). Pups in Group 7 had a significantly decreased incidence of intestinal dilation and perforation, and had the lowest intestinal permeability, compared with other treatment groups (p < 0.01). Pups in all experimental groups had significantly improved survival compared with pups exposed to NEC, with the best survival in Group 7 (p < 0.05).

CONCLUSIONS

Heparin-binding EGF-like growth factor and MSC act synergistically to reduce injury and improve survival in experimental NEC.

Heparin-binding epidermal growth factor-like growth factor improves intestinal barrier function and reduces mortality in a murine model of peritonitis

BACKGROUND

The morbidity and mortality associated with bacterial peritonitis remain high. Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is a potent intestinal cytoprotective agent. The aim of this study was to evaluate the effect of HB-EGF in a model of murine peritonitis.

METHODS

HB-EGF(-/-) knockout (KO) mice and their HB-EGF(+/+) wild-type (WT) counterparts were subjected to sham operation, cecal ligation and puncture (CLP), or CLP with HB-EGF treatment (800 μg/kg IP daily). Villous length, intestinal permeability, intestinal epithelial cell (IEC) apoptosis, bacterial load in peritoneal fluid (PF) and mesenteric lymph nodes (MLN), inflammatory cytokine levels, and survival were determined.

RESULTS

After exposure to CLP, HB-EGF KO mice had significantly shorter villi (1.37 ± 0.13 vs 1.96 ± 0.4 relative units; P < .03), increased intestinal permeability (17.01 ± 5.18 vs 11.50 ± 4.67 nL/min/cm2; P < .03), increased IEC apoptotic indices (0.0093 ± 0.0033 vs 0.0016 ± 0.0014; P < .01), and increased bacterial counts in PF (25,313 ± 17,558 vs 11,955 ± 6,653 colony forming units [CFU]/mL; P < .05) and MLN (19,009 ± 11,200 vs 5,948 ± 2,988 CFU/mL/g; P < .01) compared with WT mice. Administration of HB-EGF to WT and HB-EGF KO mice exposed to CLP led to significantly increased villous length and decreased intestinal permeability, IEC apoptosis and bacterial counts in MLN (P < .05). Survival of HB-EGF KO mice subjected to CLP was significantly improved with administration of HB-EGF (P < .05).

CONCLUSION

HB-EGF gene KO increases susceptibility to peritonitis-induced intestinal injury, which can be reversed by administration of HB-EGF. These results support a protective role of HB-EGF in peritonitis-induced sepsis.

Necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common acquired gastrointestinal disease of premature neonates and is a serious cause of morbidity and mortality. NEC is one of the leading causes of death in neonatal intensive care units. Surgical treatment is necessary in patients whose disease progresses despite medical therapy. Surgical options include peritoneal drainage and laparotomy, with studies showing no difference in outcome related to approach. Survivors, particularly those requiring surgery, face serious sequelae.

Worms, flies and four-legged friends: the applicability of biological models to the understanding of intestinal inflammatory diseases

Diseases of intestinal inflammation, including Crohn's disease, ulcerative colitis and necrotizing enterocolitis, cause substantial acute and chronic disability in a large proportion of the population. Crohn's disease and ulcerative colitis, which are collectively referred to as inflammatory bowel disease (IBD), lead to recurrent episodes of intestinal dysfunction and systemic illness, whereas necrotizing enterocolitis is characterized by the development of dramatic and all too often fatal intestinal necrosis in infants. To determine the molecular underpinnings of these disorders, investigators have explored a variety of animal models that vary widely in their complexity. These experimental systems include the invertebrate nematode Caenorhabditis elegans, the more complex invertebrate Drosophila melanogaster, and vertebrate systems including mice, rats and other mammals. This review explores the experimental models that are used to mimic and evaluate the pathogenic mechanisms leading to these diseases of intestinal inflammation. We then highlight, as an example, how the use of different experimental models that focus on the role of Toll-like receptor 4 (TLR4) signaling in the gut has revealed important distinctions between the pathogenesis of IBD and necrotizing enterocolitis. Specifically, TLR4-mediated signaling plays a protective role in the development of Crohn's disease and ulcerative colitis, whereas this signaling pathway plays a causative role in the development of necrotizing enterocolitis in the newborn small intestine by adversely affecting intestinal injury and repair mechanisms.

Gram negative bacteria are associated with the early stages of necrotizing enterocolitis

Introduction

Necrotizing enterocolitis (NEC) affects 5–10% of infants born weighing less than 1500 g. Most models of NEC recapitulate late-stage disease with gut necrosis and elevated inflammatory mediators. Evaluation of NEC at earlier, less lethal stages of disease will allow investigation of initial disease triggers and may advance our understanding of temporal relationships between factors implicated in NEC pathogenesis. In this manuscript, we describe our investigation of early NEC and test the hypothesis that bacteria and inflammatory mediators differ between animals with early NEC and disease free animals.

Methods

On DOL7 C3HeB/FeJ pups were fed liquid formula with 1×10⁴Streptococcus thoraltensis, Serratia marcescens, and Pseudomonas aeruginosa every 3 h. To initiate NEC, pups underwent asphyxia (100% N₂ for 90 s) and hypothermia (4°C for 10 min) after feeding. Pups were euthanized at 72 h. Intestines were collected for histologic NEC scoring and DNA/RNA extraction. Bacterial populations were identified by 16S rRNA pyrosequencing and principal component analysis (PCA). RNA isolates underwent QRT-PCR for Toll-like Receptor 4 (TLR4) and inducible nitric oxide synthase (iNOS).

Results

Despite histologic, intestinal damage in mice with NEC, no gross necrosis was observed suggesting early disease. QRT-PCR yielded no difference between groups in TLR4 or iNOS mRNA levels. PCA demonstrated relative clustering of microbial communities based on presence or absence of NEC. 16S pyrosequencing demonstrated similar phyla between groups (Firmicutes and Proteobacteria predominated in all animals). However, the colonic microbiota of animals with NEC had more Citrobacter (p<0.01), Klebsiella (p<0.05), and Tatumella (p<0.05), while that of animals without NEC had more Streptococcus (p<0.01) and Enterococcus (p<0.01).

Conclusion

Citrobacter, Klebsiella, and Tatumella are associated with NEC. Differential colonic bacteria were identified despite the lack of inflammatory mediator elevation traditionally associated with NEC. This suggests a temporal relationship between bacteria and inflammatory mediators such that alterations in gut microbiota are associated with early NEC, while inflammatory mediator elevation is associated with advanced NEC.

Mice overexpressing the gene for heparin-binding epidermal growth factor-like growth factor (HB-EGF) have increased resistance to hemorrhagic shock and resuscitation

BACKGROUND

The aim of the current study was to determine whether overexpression of heparin-binding epidermal growth factor-like growth factor (HB-EGF) could protect the intestines from injury after hemorrhagic shock and resuscitation in mice.

METHODS

Hemorrhagic shock and resuscitation was induced in HB-EGF transgenic and wild type mice. Cross-reacting material 197 (5 mg/kg) was administered to a subset of HB-EGF transgenic mice to block the overexpressed HB-EGF. Intestinal histologic injury scores, intestinal epithelial cell apoptosis indices, and gut barrier function were determined. The Student t test and 1-way analysis of variance were employed to compare the differences between groups.

RESULTS

All mice subjected to hemorrhagic shock and resuscitation had significantly increased intestinal histologic injury scores, apoptosis indices, and intestinal permeability compared with sham-operated mice. Compared with wild type mice, HB-EGF transgenic mice had significantly decreased histologic injury (mean injury grade 2.79 ± 0.84 vs 3.88 ± 1.43, P = .02), apoptosis indices (mean apoptosis index 8.77 ± 5.23 vs 17.91 ± 13.23, P = .03), and mucosal permeability (FITC-dextran 4 clearance 13.06 ± 5.67 vs 20.03 ± 7.81 nL/min/ m(2), P = .02) at 3 hours of reperfusion. HB-EGF transgenic mice subjected to hemorrhagic shock and resuscitation and treated with cross-reacting material 197 had a significantly increased histologic injury (mean injury grade 3.63 ± 1.00 vs 2.79 ± 0.84, P = .04) and mucosal permeability (FITC-dextran 4 clearance 22.87 ± 9.69 vs 13.06 ± 5.67 nL/min/cm2, P = .01) at 3 hours of reperfusion compared with non-cross-reacting material 197 treated transgenic mice, with no significant changes in apoptosis indices. Cross-reacting material 197 did not reverse the decreased apoptosis observed in HB-EGF transgenic mice subjected to hemorrhagic shock and resuscitation, which suggests that mechanisms in addition to decreased apoptosis may be responsible for the intestinal cytoprotective effects of endogenous HB-EGF overexpression.

CONCLUSION

Overexpression of HB-EGF increases resistance to hemorrhagic shock and resuscitation in mice.