Turnover of radioactive mucin precursors in the colon of patients with Hirschsprung's disease correlates with the development of enterocolitis

Current understanding of Hirschsprung-associated enterocolitis: Pathogenesis, diagnosis and treatment

Hirschsprung-associated enterocolitis (HAEC) was described in 1886 by Harald Hirschsprung and is a potentially deadly complication of Hirschsprung Disease. HAEC is classically characterized by abdominal distension, fever, and diarrhea, although there can be a variety of other associated symptoms, including colicky abdominal pain, lethargy, and the passage of blood-stained stools. HAEC occurs both pre-operatively and post-operatively, is the presenting symptom of HSCR in up to 25% of infants and varies in overall incidence from 20 to 60%. This article reviews our current understanding of HAEC pathogenesis, diagnosis, and treatment with discussion of areas of ongoing research, controversy, and future investigation.

Cholinergic Signaling Attenuates Pro-Inflammatory Interleukin-8 Response in Colonic Epithelial Cells

Infants affected by Hirschsprung disease (HSCR), a neurodevelopmental congenital disorder, lack ganglia of the intrinsic enteric nervous system (aganglionosis) in a variable length of the colon, and are prone to developing severe Hirschsprung-associated enterocolitis (HAEC). HSCR patients typically show abnormal dense innervation of extrinsic cholinergic nerve fibers throughout the aganglionic rectosigmoid. Cholinergic signaling has been reported to reduce inflammatory response. Consequently, a sparse extrinsic cholinergic innervation in the mucosa of the rectosigmoid correlates with increased inflammatory immune cell frequencies and higher incidence of HAEC in HSCR patients. However, whether cholinergic signals influence the pro-inflammatory immune response of intestinal epithelial cells (IEC) is unknown. Here, we analyzed colonic IEC isolated from 43 HSCR patients with either a low or high mucosal cholinergic innervation density (fiber-low versus fiber-high) as well as from control tissue. Compared to fiber-high samples, IEC purified from fiber-low rectosigmoid expressed significantly higher levels of IL-8 but not TNF-α, IL-10, TGF-β1, Muc-2 or tight junction proteins. IEC from fiber-low rectosigmoid showed higher IL-8 protein concentrations in cell lysates as well as prominent IL-8 immunoreactivity compared to IEC from fiber-high tissue. Using the human colonic IEC cell line SW480 we demonstrated that cholinergic signals suppress lipopolysaccharide-induced IL-8 secretion via the alpha 7 nicotinic acetylcholine receptor (a7nAChR). In conclusion, we showed for the first time that the presence of a dense mucosal cholinergic innervation is associated with decreased secretion of IEC-derived pro-inflammatory IL-8 in the rectosigmoid of HSCR patients likely dependent on a7nAChR activation. Owing to the association between IL-8 and enterocolitis-prone, fiber-low HSCR patients, targeted therapies against IL-8 might be a promising immunotherapy candidate for HAEC treatment.

Engineering the Mucus Barrier

Mucus selectively controls the transport of molecules, particulate matter, and microorganisms to the underlying epithelial layer. It may be desirable to weaken the mucus barrier to enable effective delivery of drug carriers. Alternatively, the mucus barrier can be strengthened to prevent epithelial interaction with pathogenic microbes or other exogenous materials. The dynamic mucus layer can undergo changes in structure (e.g., pore size) and/or composition (e.g., protein concentrations, mucin glycosylation) in response to stimuli that occur naturally or are purposely administered, thus altering its barrier function. This review outlines mechanisms by which mucus provides a selective barrier and methods to engineer the mucus layer from the perspective of strengthening or weakening its barrier properties. In addition, we discuss strategic design of drug carriers and dosing formulation properties for efficient delivery across the mucus barrier.

Exploring the role and diversity of mucins in health and disease with special insight into non-communicable diseases

Mucins are major glycoprotein components of the mucus that coats the surfaces of cells lining the respiratory, digestive, gastrointestinal and urogenital tracts. They function to protect epithelial cells from infection, dehydration and physical or chemical injury, as well as to aid the passage of materials through a tract i.e., lubrication. They are also implicated in the pathogenesis of benign and malignant diseases of secretory epithelial cells. In Human there are two types of mucins, membrane-bound and secreted that are originated from mucous producing goblet cells localized in the epithelial cell layer or in mucous producing glands and encoded by MUC gene. Mucins belong to a heterogeneous family of high molecular weight proteins composed of a long peptidic chain with a large number of tandem repeats that form the so-called mucin domain. The molecular weight is generally high, ranging between 0.2 and 10 million Dalton and all mucins contain one or more domains which are highly glycosylated. The size and number of repeats vary between mucins and the genetic polymorphism represents number of repeats (VNTR polymorphisms), which means the size of individual mucins can differ substantially between individuals which can be used as markers. In human it is only MUC1 and MUC7 that have mucin domains with less than 40% serine and threonine which in turn could reduce number of PTS domains. Mucins can be considered as powerful two-edged sword, as its normal function protects from unwanted substances and organisms at an arm's length while, malfunction of mucus may be an important factor in human diseases. In this review we have unearthed the current status of different mucin proteins in understanding its role and function in various non-communicable diseases in human with special reference to its organ specific locations. The findings described in this review may be of direct relevance to the major research area in biomedicine with reference to mucin and mucin associated diseases.

Mucus Barriers to Microparticles and Microbes are Altered in Hirschsprung's Disease

Mucus forms a protective hydrogel layer over the intestinal epithelium, presenting a selective and robust barrier to the uptake of particulates and microbe invasion. Disease can alter mucus production and composition, thus potentially modifying mucosal barrier properties. Hirschsprung's disease (HD) is a developmental abnormality of the nervous system often complicated by intestinal infection. An investigation of colonic mucus barrier properties in an HD animal model, endothelin receptor B mutant mice, revealed significantly reduced microsphere (passive) and microbe (active) transport rates (7-fold and 3.6-fold, respectively, in proximal colonic mucus) relative to wild-type. Transport differences were evident in both the ganglionic and aganglionic colon segments, in agreement with the risk of HD-associated enterocolitis after surgery to remove aganglionic colon segments. The development of therapies aimed at altering colonic mucus barrier properties could be explored towards preventing the onset of enterocolitis in HD.

Altered goblet cell differentiation and surface mucus properties in Hirschsprung disease

Hirschsprung disease-associated enterocolitis (HAEC) leads to significant mortality and morbidity, but its pathogenesis remains unknown. Changes in the colonic epithelium related to goblet cells and the luminal mucus layer have been postulated to play a key role. Here we show that the colonic epithelium of both aganglionic and ganglionic segments are altered in patients and in mice with Hirschsprung disease (HSCR). Structurally, goblet cells were altered with increased goblet cell number and reduced intracellular mucins in the distal colon of biopsies from patients with HSCR. Endothelin receptor B (Ednrb) mutant mice showed increased goblet cell number and size and increased cell proliferation compared to wild-type mice in aganglionic segments, and reduced goblet cell size and number in ganglionic segments. Functionally, compared to littermates, Ednrb^−/− mice showed increased transepithelial resistance, reduced stool water content and similar chloride secretion in the distal colon. Transcript levels of goblet cell differentiation factors SPDEF and Math1 were increased in the distal colon of Ednrb^−/− mice. Both distal colon from Ednrb mice and biopsies from HSCR patients showed reduced Muc4 expression as compared to controls, but similar expression of Muc2. Particle tracking studies showed that mucus from Ednrb^−/− mice provided a more significant barrier to diffusion of 200 nm nanoparticles as compared to wild-type mice. These results suggest that aganglionosis is associated with increased goblet cell proliferation and differentiation and subsequent altered surface mucus properties, prior to the development of inflammation in the distal colon epithelium. Restoration of normal goblet cell function and mucus layer properties in the colonic epithelium may represent a therapeutic strategy for prevention of HAEC.

Hirschsprung-associated enterocolitis: pathogenesis, treatment and prevention

Hirschsprung-associated enterocolitis (HAEC) is a common and sometimes life-threatening complication of Hirschsprung disease (HD). Presenting either before or after definitive surgery for HD, HAEC may manifest clinically as abdominal distension and explosive diarrhea, along with emesis, fever, lethargy, and even shock. The pathogenesis of HAEC, the subject of ongoing research, likely involves a complex interplay between a dysfunctional enteric nervous system, abnormal mucin production, insufficient immunoglobulin secretion, and unbalanced intestinal microflora. Early recognition of HAEC and preventative practices, such as rectal washouts following a pull-through, can lead to improved outcomes. Treatment strategies for acute HAEC include timely resuscitation, colonic decompression, and antibiotics. Recurrent or persistent HAEC requires evaluation for mechanical obstruction or residual aganglionosis, and may require surgical treatment with posterior myotomy/myectomy or redo pull-through. This chapter describes the incidence, pathogenesis, treatment, and preventative strategies in management of HAEC.

Bacterial invasion of HT29-MTX-E12 monolayers: effects of human breast milk

AIM

The supramucosal gel, crucial for gut barrier function, might be compromised in necrotizing enterocolitis (NEC). Breast milk is associated with a reduced incidence of NEC. We compared the effects of human breast milk (BM) versus a neonatal formula, Nutriprem 1 (FF), on adherence, internalisation, and penetration of NEC-associated Escherichia coli through monolayers of mucus producing intestinal cells, HT29-MTX-E12 (E12).

METHODS

E12 cells were grown to confluence on membranes permeable to bacteria. E. coli, reference strain and isolated from a NEC-affected intestine, were cultured in LB broth, labelled with fluorescein and biotinylated. Bacteria were suspended in tissue culture medium (TC) or mixtures of TC with BM or FF and applied to the E12 cultures. Bacterial numbers were assessed by fluorescence. DyLight 650-labelled neutravidin, which cannot cross cell membrane, evaluated extracellular bacteria. Fluorescence of basolateral medium was measured to quantify translocation. Bacterial concentrations were compared using the Mann Whitney U test.

RESULTS

After 1h exposure, E12 cultures adhered or internalised more NEC-derived bacteria than standard strain E. coli and more suspended in FF than BM (P<0.001). A greater proportion of NEC-derived bacteria internalised when suspended in TC or BM. In FF, the NEC-derived strain internalised least. More translocation occurred in BM incubations compared to FF in the first 1-4h: NEC-E. coli less than the reference strain. After 24h translocated bacterial populations were equal.

CONCLUSION

In this pilot study, breast milk was associated with relatively less adhesion and internalisation of NEC-associated E. coli to mucus covered E12s compared to formula milk.

The pathogenesis of Hirschsprung's disease-associated enterocolitis

Hirschsprung's disease-associated enterocolitis (HAEC) remains the most life-threatening complication in Hirschsprung disease (HD) patients. The pathogenesis of HAEC has not been determined and many hypotheses regarding the etiology of HAEC have been proposed. These include a possible causal relationship between the abnormal enteric nervous system development in HD and the development of enterocolitis. Based on the complex genetic causes of HD that have been discovered and the resultant heterogeneous group of patients that exists, the causes of HAEC are likely multiple. New insights regarding the relationship of the role of the enteric nervous system and its interaction between intestinal barrier function, innate host immunity, and commensal microflora have been discovered, which may shed light on this perplexing problem. This review presents current known risk factors of HAEC and the proposed theories and supporting evidence for the potential etiologies of HAEC.

[Enterocolitis as a complication of late-diagnosed Hirschsprung disease]

Enterocolitis is the most serious complication of Hirschsprung disease. Early management of these patients can decrease the severity of this complication. Hirschsprung disease is more common in patients with trisomy 21 than in the general population. Furthermore, the risk of developing enterocolitis is higher in this population. We report on an infant with trisomy 21 who developed enterocolitis as a complication of Hirschsprung disease that was diagnosed late when the infant presented with septic shock leading to death of the patient.

New insights into the pathogenesis of Hirschsprung's associated enterocolitis

The management of Hirschsprung's disease (HD) has made dramatic strides over the last 20 years. Research into the embryological development and migration of ganglion cell has enabled a greater understanding of the pathogenesis of the disease. Coupled with new techniques in surgery, such as laparoscopy-assisted pull-through and the transanal pull-through, this knowledge has led to improved outcomes for children with HD. However, although our appreciation of Hirschsprung's associated enterocolitis and its aetiology has increased, there are continued references in the literature to a multitude of theories of pathogenesis. The purpose of this review is to delineate the theories and demonstrate the evidence supporting or otherwise contradicting each other.

Enterocolitis complicating Hirschsprung's disease

Enterocolitis remains a relatively common complication of Hirschsprung's disease with significant morbidity and mortality. The etiology of Hirschsprung's enterocolitis (HEC) is multifactorial and remains poorly understood. Preventative measures and better treatment modalities will evolve out of a better understanding of the underlying pathophysiology. Prompt recognition of HEC allows early intervention and a potential reduction in disease severity and mortality. This review of HEC describes the epidemiology, clinical and pathological features and current best practice in management. Some of the areas of research into etiology and treatment are discussed.

MUC-2 mucin production in Hirschsprung's disease: possible association with enterocolitis development

BACKGROUND/PURPOSE

The etiology of Hirschsprung's-associated enterocolitis (HAEC) is unknown. Previous investigations have suggested that abnormal production of mucins may have an etiologic role. Recently, a series of mucin genes have been identified. MUC-2 is the predominant mucin expressed in humans. The authors have shown previously in vitro that use of MUC-2 can prevent bacterial translocation. Based on this, it was hypothesized that those patients with Hirschsprung's disease (HD) would have an abnormal production of MUC-2 compared with normal patients.

METHODS

Fresh stool specimens were collected from children with a diagnosis of HD (with or without HAEC) and from age-matched control patients. Protein was extracted, and MUC-2 was detected with Western blot analysis. MUC-2 protein expression was quantified by densitometry measurements. Results are expressed as mean density +/- SD. Statistical comparison was done with unpaired t tests, with P less than.05 being considered significant.

RESULTS

MUC-2 expression was detected in all control patients (mean density, 121 +/- 47). MUC-2 level was lowest in one child with a viral-induced diarrhea (density = 71). In those patients with HD, levels of MUC-2 protein expression were significantly lower (P <.05) than controls (12 +/- 15 for all HD patients). Levels of MUC-2 were lowest (nondetectable) in 2 HD patients who had clinical evidence of HAEC.

CONCLUSIONS

MUC-2 production is markedly depressed in patients with Hirschsprung's disease and is absent with enterocolitis. This decline in protein expression may result in a decrease in epithelial barrier function and be a predisposing factor in the development of HAEC.

Preoperative enterocolitis is associated with poorer long-term bowel function after Soave-Boley endorectal pull-through for Hirschsprung's disease

BACKGROUND/PURPOSE

The purpose of the investigation was to apply a semiquantitative scoring system for bowel function to patients who had undergone endorectal pull-through (ERPT) for Hirschsprung's disease (HD) and to use this to analyse the clinical factors relating to functional outcome.

METHODS

The case note details of 63 patients undergoing ERPT for HD were reviewed. A questionnaire using a semiquantitative scoring system for 6 aspects of bowel function was sent to parents of 55 patients. The total functional score (TFS) for each patient was calculated, and a statistical analysis was performed to determine which clinical factors were significantly related to bowel functional outcome.

RESULTS

Fifty (91%) of the parents returned the questionnaire. TFS was "good" in 45%, "fair" in 33% and "poor" in 22%. There was a statistically significant difference in the scores of those who had preoperative Hirschsprung's associated enterocolitis (HAEC) TFS = 8.0 and those who did not, TFS 12.7 (P <.01) The sex of the patient, length of aganglionic segment, timing of ERPT (early/late), staging of ERPT (1 or 2), presence/absence of anastomotic stricture, and presence or absence of Down's syndrome did not statistically significantly affect TFS.

CONCLUSIONS

Preoperative HAEC was the most important factor in relation to functional outcome after ERPT for HD. The reason remains unclear.

Histochemical and genetic analysis of colonic mucin glycoproteins in Hirschsprung's disease

BACKGROUND/PURPOSE

Mucin glycoproteins (mucins) recently have been shown to be deficient in the colonic mucosa of patients with Hirschsprung's disease (HD). The authors performed a detailed histo- and immunohistochemical analysis of mucins in the colonic mucosa and studied the expression of mucin genes to characterize histologically mucin quality and gene expression in HD compared with controls.

METHODS

Paraffin-embedded 4-microm thick sections from patients with HD (n = 11 ganglionic, 10 aganglionic) and controls (n = 19) were taken. Slides were stained with mild periodic acid Schiff with and without saponification with KOH (reacts with O-actylated mucins), high iron diamine/alcian blue (differentiates sulphated v nonsulphated mucins), the monoclonal antimucin antibodies, PR3A5 (against di- and tri-O-acetylated sialic acids) and 91.9H (against sulphated mucins). O-acetylation and sulphation both confer an increased resistance of mucins to bacterial degradation and are thought to be important in the defensive function of the colonic mucus gel layer. In situ hybridization was used to study expression of the mucin genes MUC 1, 2, 3, 4, 5AC, 5B, 6, 7, and 8. [35S]-sulphate-labelled antisense oligonucleotide 48mer probes designed to the known tandem repeat domains of MUC genes were used. After hybridization and washing the slides were opposed to Hyperfilm MP for 7 days. The autoradiographs were scored by three independent observers for differences in expression and by image analysis. Those with positive findings were dipped in photographic emulsion, developed, and counterstained for photomicrographs.

RESULTS

There were different patterns of staining dependent on the region of the colon and especially the age of the patient with three reagents. No significant differences in the histological staining pattern was detected between HD patients and controls. The colonic mucins in HD were found to be primarily O-acetylated and sulphated. The MUC gene expression was similar in patients and controls. MUC2 and 4 were strongly expressed, MUC1, 3, and 5B had moderate to weak expression, and MUC 5AB, 6, 7, and 8 had baseline expression.

CONCLUSIONS

The mucin glycoproteins in children with HD, although quantitatively deficient, show no qualitative differences on histo- and immunohistochemical staining from normal controls. The expression of all the known mucin genes, the genetic control of mucin secretion, and the quality of mucins, is similar to normal controls.