Gastrointestinal expression and partial cDNA cloning of murine Muc2

To help us investigate the role of mucin in the protection of the colonic epithelium in the mouse, we aimed to identify the murine colonic mucin (MCM) and its encoding gene. We isolated MCM, raised an anti-MCM antiserum, and studied the biosynthesis of MCM in the gastrointestinal tract. Isolated MCM resembled other mucins in physicochemical properties. Anti-MCM recognized MCM as well as rat and human MUC2 on Western blots, interacting primarily with peptide epitopes, indicating that MCM was identical to murine Muc2. Using anti-MCM and previously characterized anti-human and anti-rat MUC2 antibodies, we identified a murine Muc2 precursor in the colon of approximately 600 kDa, which appeared similar in size to rat and human MUC2 precursors. Western blotting, immunoprecipitation of metabolically labeled mucins, and immunohistochemistry showed that murine Muc2 was expressed in the colon and the small intestine but was absent in the stomach. To independently identify murine Muc2, we cloned a cDNA fragment from murine colonic mRNA, encoding the 302 NH2-terminal amino acids of murine Muc2. The NH2 terminus of murine Muc2 showed 86 and 75% identity to the corresponding rat and human MUC2 peptide sequences, respectively. Northern blotting with a murine Muc2 cDNA probe showed hybridization to a very large mRNA, which was expressed highly in the colon and to some extend in the small intestine but was absent in the stomach. In situ hybridization showed that the murine Muc2 mRNA was confined to intestinal goblet cells. In conclusion, by two independent sets of experiments we identified murine Muc2, which appears homologous to rat and human MUC2. Because Muc2 is prominently expressed in the colon, it is most likely to be the predominant mucin in the colonic mucus layer.

Strategic biochemical analysis of mucins

MUC-type mucins comprise a family of structurally related molecules, which are expressed in epithelia of the body that are in close contact with the milieu. Because of their large sizes and very complex structures, containing very extensive O-glycosylation, MUC-type mucins are difficult to study by conventional techniques. Many see MUC-type mucins as protective molecules; however, functional studies on the individual MUC-type mucins are very scarce. At present, essential steps in MUC research are to characterize the specific expression patterns of each MUC-type mucin in the body and to find methods to reliably quantify these MUC-type mucins. These aims can only be met at the level of the primary sequences of the MUC-type mucins, as the O-glycosylation even within one species of MUC-type mucin is not only very complex, but may also vary among individuals, organs, and cell types. We will discuss some recent advances in mucin research, particularly the identification of MUC precursor molecules in metabolic labeling experiments. We will try to define some strategic considerations in the study of the expression patterns of MUC-type mucins, which circumvent the complications caused by the very complex and heterogeneous O-glycosylation of the molecules.

Regulation of lactase and sucrase-isomaltase gene expression in the duodenum during childhood

BACKGROUND

In children, lactase and sucrase-isomaltase are essential intestinal glycohydrolases, and insufficiency of either enzyme causes diarrhea and malnutrition. Little is known about the regulation of lactase and sucrase-isomaltase expression in the duodenum during childhood. In this study, the mechanisms of regulation of duodenal expression of both enzymes were examined in a study population with ages ranging from 1 to 18 years.

METHODS

Duodenal biopsy specimens from 60 white children were used to analyze tissue morphology and to quantify lactase and sucrase-isomaltase mRNA and protein.

RESULTS

Among healthy subjects, high interindividual variability was noted in both mRNA and protein levels for lactase and sucrase-isomaltase. Lactase mRNA level per subject did not correlate with sucrase-isomaltase mRNA level and thus appeared independent. Both lactase and sucrase-isomaltase protein levels correlated significantly with their respective mRNA levels. For each enzyme, a significant inverse correlation was observed between the degree of villus atrophy and mRNA levels. Aging from 1 to 18 years did not result in significant changes in mRNA or protein levels of either enzyme. Immunostaining patterns within the duodenal epithelium for lactase differed from sucrase-isomaltase in adjacent sections, illustrating independent regulation at the cellular level.

CONCLUSIONS

In the duodenum of white children, lactase and sucrase-isomaltase seem primarily regulated at the transcriptional level. The expression of each enzyme in the intestinal epithelium is regulated by an independent mechanism. Lactase and sucrase-isomaltase exhibit stable mRNA and protein levels in healthy children as they grow to adulthood. Mucosal damage affected levels of both enzymes negatively.

MUC5B is the prominent mucin in human gallbladder and is also expressed in a subset of colonic goblet cells

To elucidate the roles of human gallbladder mucin (HGBM), such as in gallstone formation and cytoprotection, it is essential to identify HGBM and study its expression. This was performed by metabolic labeling, Western blotting, immunohistochemistry, and RT-PCR. In a large number of individuals, antibodies against purified HGBM and against MUC5B detected a mucin precursor (approximately 470 kDa) in the gallbladder and colon, but not in the small intestine. In the gallbladder, Western blotting using specific anti-MUC5B antibodies showed that this mucin precursor represented an identical mucin, MUC5B. RT-PCR experiments demonstrated a similar tissue distribution pattern of MUC5B mRNA. Immunohistochemistry with anti-HGBM and anti-MUC5B showed staining in gallbladder epithelial cells and colonic goblet cells in the crypt base, but not in the small intestine; double labeling showed that HGBM was located in small granules within goblet cells, colocalizing to MUC2-containing goblet cells. Metabolic labeling demonstrated the secretion of mature MUC5B in the colon. Conclusively, MUC5B is identified as the prominent HGBM and is also expressed and secreted in the colon.

Molecular cloning of human gastric mucin MUC5AC reveals conserved cysteine-rich D-domains and a putative leucine zipper motif

To further clone the human gastric mucin MUC5AC cDNA, we screened a human gastric cDNA library with previously identified MUC5AC sequences. We obtained 32 independent clones encoding newly identified sequences comprising the entire N-terminal sequence of MUC5AC, up to 3024 bp upstream of the previously identified MUC5AC sequences. The N-terminus of MUC5AC shows high homology (43% identity) with the N-terminus of MUC2 and contains three domains homologous to the D-domains found in the pro-von Willebrand factor. Furthermore, the N-terminus of MUC5AC contains a putative leucine zipper motif not found in any other mucin identified so far. Moreover, a large central repetitive sequence was identified encoding approximately 2500 amino acids (7.5 kb). We were able to establish that the MUC5AC cDNA together with the previously identified 6.1 kb of MUC5AC cDNA sequence is about 16.6 kb, encoding 5525 amino acids. A model of the domain structure of MUC5AC is presented.

Pediatric duodenal biopsies: mucosal morphology and glycohydrolase expression do not change along the duodenum

BACKGROUND

Duodenal mucosal biopsies are routinely taken for diagnosis in children with complaints of the upper gastrointestinal tract. Surprisingly, little is known about the usefulness of proximal duodenal versus distal duodenal biopsies for routine diagnostic purposes. This study evaluated the comparability of proximal and distal duodenal biopsies with respect to mucosal morphology as well as glycohydrolase expression as an indicator of intestinal epithelial function.

METHODS

Specimens obtained in duodenal endoscopic biopsies from 64 children, ranging in age from 3 months to 18 years with normal or affected mucosa, were studied. Biopsies were performed in anatomically defined regions in the bulbus duodeni (the very proximal part of the duodenum) and distally of the papilla of Vater (distal of the pancreatic duct). Biopsy specimens were paraformaldehyde-fixed for histologic examination and immunohistochemical evaluation or were homogenized to isolate RNA. Crypt/villus morphology was assessed as is routinely determined by pathologists. In addition, several aspects of lactase and sucrase-isomaltase expression as paradigms of intestinal brush border enzymes were assessed: localization at the cellular level, semiquantitative immunohistochemistry, and quantitative measurement of the messenger RNA levels of the respective brush border glycohydrolases.

RESULTS

As anticipated, there was a wide interpatient variation in mucosal morphology and expression of lactase and sucrase-isomaltase. Nonetheless, the consistent finding was that in each patient, measurements of morphology and lactase and sucrase-isomaltase gene expression were very similar between samples obtained in the proximal and distal biopsies.

CONCLUSIONS

Biopsies performed in either location in the duodenum are equally suitable for diagnostic workup of patients suspected of mucosal abnormalities affecting morphology or small intestinal brush border glycohydrolase activities.

Intestinal carbamoyl phosphate synthase I in human and rat. Expression during development shows species differences and mosaic expression in duodenum of both species

The clinical importance of carbamoyl phosphate synthase I (CPSI) relates to its capacity to metabolize ammonia, because CPSI deficiencies cause lethal serum ammonia levels. Although some metabolic parameters concerning liver and intestinal CPSI have been reported, the extent to which enterocytes contribute to ammonia conversion remains unclear without a detailed description of its developmental and spatial expression patterns. Therefore, we determined the patterns of enterocytic CPSI mRNA and protein expression in human and rat intestine during embryonic and postnatal development, using in situ hybridization and immunohistochemistry. CPSI protein appeared during human embryogenesis in liver at 31-35 e. d. (embryonic days) before intestine (59 e.d.), whereas in rat CPSI detection in intestine (at 16 e.d.) preceded liver (20 e.d.). During all stages of development there was a good correlation between the expression of CPSI protein and mRNA in the intestinal epithelium. Strikingly, duodenal enterocytes in both species exhibited mosaic CPSI protein expression despite uniform CPSI mRNA expression in the epithelium and the presence of functional mitochondria in all epithelial cells. Unlike rat, CPSI in human embryos was expressed in liver before intestine. Although CPSI was primarily regulated at the transcriptional level, CPSI protein appeared mosaic in the duodenum of both species, possibly due to post-transcriptional regulation.

The oligomerization of a family of four genetically clustered human gastrointestinal mucins

Mucins are synthesized and secreted by many epithelia. They are complex glycoproteins that offer cytoprotection. In their functional configuration, mucins form oligomers by a biosynthetic process that is poorly understood. A family of four human gastrointestinal mucin genes (MUC2, MUC5AC, MUC5B, and MUC6) is clustered to chromosome 11p15.5. To study oligomerization of these related mucins, we performed metabolic labeling experiments with [35S]amino acids in LS174T cells, and isolated mucin precursors by specific immunoprecipitations that were analyzed on SDS-PAGE. Each of the precursors of MUC2, MUC5AC, MUC5B, and MUC6 formed a single species of disulfide-linked homo-oligomer within 1 h after pulse labeling. Based on apparent molecular masses, these oligomeric precursors were most likely dimers. Inhibition of vesicular RER-to-Golgi transport, with brefeldin A and CCCP, did not affect the dimerization of MUC2 precursors, localizing dimerization to the RER. O-Glycosylation of MUC2 followed dimerization. Inhibition of N-glycosylation by tunicamycin retarded, but did not inhibit, dimerization, indicating that N-glycans play a role in efficient dimerization of MUC2 precursors. Based on sequence homology, the ability of MUC2, MUC5AC, MUC5B and MUC6 to dimerize most likely resides in their C-terminal domains. Thus, the RER-localized dimerization of secretory mucins likely proceeds by similar mechanisms, which is an essential step in the formation of the human gastrointestinal mucus-gels.

Molecular cloning of human MUC3 cDNA reveals a novel 59 amino acid tandem repeat region

The human MUC3 gene is highly expressed in small intestine and gallbladder. Thus far only 646 basepairs of its cDNA encoding 17 amino acid repeats have been cloned. In order to further clone the human MUC3 cDNA, a human small intestinal cDNA library was constructed and screened with a cDNA probe encompassing the 17 amino acid tandem repeat region of human MUC3. In two subsequent screenings of the library resulting positive clones were used as probes. In total, 27 partial MUC3 cDNA clones were isolated and sequenced that define a semi-unique region and a novel 177 nucleotide tandem repeat region, located upstream of the region encoding the 17 amino acid tandem repeats. The 177 nucleotide repeat region is at least 5 kb in length and encodes 59 amino acid repetitive peptides with a consensus sequence of VSTTPVASSEASTLSTTPVDTSTPVTTSTQASSSPTTAEGTSMPTSTPSEGSTPLTSMP, that is notably different from the 17 amino acid repeat of MUC3 or any other known mucin repeat.

Treatment of defaecation problems in children: the role of education, demystification and toilet training

To evaluate the effect of education in children with chronic defaecation problems, a prospective 6-week intervention study was designed. A total of 54 children (5-14 years) underwent an education programme, with demystification of symptoms and advice about diet and toilet training. The present treatment was continued. After 6 weeks, children with persistent problems received biofeedback training with a follow up of 1 year. The intervention programme was successful in 8 children (15%). Biofeedback training was successful in 49% of the remaining group after 1 year.

CONCLUSION

A total of 15% of the children with chronic defaecation problems seen at a referral centre could surprisingly be helped by a simple education programme with, demystification and toilet training. Further studies evaluating treatment in children with defaecation problems should account for the primary effect of these measures.

Biosynthesis of mucins (MUC2-6) along the longitudinal axis of the human gastrointestinal tract

Little is known about the biosynthesis of mucin molecules in humans. Our aim was to examine the mucin biosynthesis (MUC2-6) along the longitudinal axis of the healthy human gastrointestinal tract. Biopsies of human stomach and small and large intestine were metabolically labeled with 35S-labeled amino acids, [35S]sulfate, or[3H]galactose, immunoprecipitated with antibodies against MUC2-6, and analyzed by reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), MUC5AC [apparent molecular weight (M(r)) 500,000] and MUC6 (apparent M(r) 400,000) were detected in the stomach but not in the small or large intestine, MUC3 (apparent M(r) 550,000) was detected in duodenum and jejunum, MUC2 (apparent M(r)600,000) was detected throughout the small and large intestine, and MUC4 (apparent M(r) > 900,000) was detected predominantly in the large intestine. Interestingly, some individuals displayed double bands of MUC2 and MUC3 precursors, suggesting allelic variation within the respective genes. Between small and large intestine mature secreted MUC2 showed differences in mobility on SDS-PAGE, suggesting differences in glycosylation. Each of the MUC2, MUC3, MUC4, MUC5AC, and MUC6 precursors could be distinguished electrophoretically, and each showed region-specific expression along the gastrointestinal tract.

An immunocompetent infant with cow's milk allergy and cytomegalovirus colitis

A 5-week-old, severely ill, infant is described with diarrhoea and rectal bleeding, followed by vomiting and dehydration after introduction of a cow's milk formula. A diagnosis of cow's milk allergy was made because of the clinical presentation of an allergic enterocolitis, the rapid improvement after introduction of a hypo-allergenic formula and development of colic directly after rechallenge with cow's milk. Furthermore a highly specific IgE for alpha-lactalbumin strongly supported the diagnosis. Because of recurrent rectal bleeding a limited colonoscopy was performed at the age of 10 weeks. Surprisingly a second diagnosis of histopathologically proven cytomegalovirus (CMV) colitis was made. Extensive immunological screening revealed no signs of immunodeficiency. The child thrived without any treatment for CMV and developed normally. This is the first description of an immunocompetent infant with CMV colitis.

CONCLUSION

It cannot be excluded that the allergic colitis facilitated the CMV colitis, or vice versa CMV colitis triggered cow's milk protein induced entero-colitis. Further attention should be given to children with bloody diarrhoea to establish a possible relationship between CMV infection and cow's milk protein allergy.

Increased C/EBP in fetal rat small intestine precedes initiation of differentiation marker mRNA synthesis

Morphogenesis, initiation of differentiation marker gene expression, and their correlation with CCAT/enhancer binding protein (C/EBP) expression were analyzed in the developing fetal rat small intestine. Expressions of mRNAs for lactase-phlorizin hydrolase (LPH), intestinal alkaline phosphatase (IALP), carbamoyl-phosphate synthetase (CPS), and three isoforms of C/EBP were simultaneously determined by Northern blot analysis from 15 to 19 days of gestation. At 17 days of gestation, prior to villus formation as demonstrated by light and electron microscopy, only CPS and C/EBPalpha, -beta, and -delta expression could clearly be detected. Both LPH and IALP mRNA were definitely detectable in proximal and middle intestine on day 18, as soon as the stratified epithelium of the early intestine had been transformed into a single layer of columnar epithelium lining villi. This distribution was confirmed by in situ hybridization for LPH mRNA. During the period of transformation when the columnar epithelium and villi were forming, no LPH or IALP mRNA was detectable in the immature distal one-third of the fetal intestine. Preceding villus morphogenesis, immunostaining demonstrated nuclear localization of C/EBPalpha protein in intestinal epithelial cells, with continued expression in all enterocytes through 19 days of gestation. Enhanced expression of C/EBPalpha mRNA and protein began 24 h prior to the initiation of the differentiation markers, suggesting that it may play a role in regulation of fetal intestinal differentiation.

How accurate is the recall of bowel habits in children with defaecation disorders?

The aim was to assess in children with defaecation disorders, the accuracy of recalled information as provided by the child and/or parents compared to diary information and to evaluate its effect on diagnostic grouping. In this prospective study, recalled information, obtained initially by a telephone interview, was compared with recorded information provided by a 4-week diary. Recalled and recorded data were compared using Kappa indices. Subsequently, children were assigned to three diagnostic groups: constipation, solitary encopresis and a rest group. Based on these diagnoses, the first two groups were allocated for laxative treatment. Analysis of recalled and recorded data was performed in 46 children (5-14 years). Most defaecation parameters showed fair agreement, only limited agreement occurred for frequency of soiling episodes. Identical clinical groups using the two methods were obtained in 63% of the children. Particularly, the assessment of large amounts of stool and the number of soiling episodes were responsible for the shift in the diagnostic groups. A total of 83% children were correctly allocated for treatment using recalled data.

Problems in diagnosis of IBD in children

Children and adolescents with inflammatory bowel disease (IBD) present unique challenges to physicians and all health-care providers. The most important aspect is that children are not small adults. They are characterized by a highly dynamic state of growth and physical change as well as a constant alteration in psychological status. It will not be difficult to recognize IBD, even in children, when it presents with classical symptoms such as bloody diarrhoea, abdominal pain and weight loss. However, some children will present with abdominal pain and depression. Not infrequently these children are diagnosed as being depressed and are seen and treated by psychologists and psychiatrists for different periods of time. In addition, several children will be initially diagnosed as having a bacterial gastroenteritis with a proven positive faecal culture. It seems to be the triggering event in these children, and if adequate therapy fails, colonoscopy is indicated. Recently, Beattie et al. showed that in children seen for chronic abdominal pain simple routine blood tests including full blood count and erythrocyte sedimentation rate are almost always abnormal in children with IBD. But most importantly, growth retardation is common in children with IBD and is more often found in Crohn's disease (CD) than in ulcerative colitis (UC). Faltering growth is a sign of a catabolic situation. Therefore, it is essential to follow the growth of children at the beginning and during treatment of IBD. Growth retardation can be the first symptom of IBD and is often already present before other symptoms of IBD become apparent. Rarely, extra-intestinal manifestations, particularly arthritis, can be the first and sometimes only initial symptom for months to years in children with IBD. About 2% of all patients with IBD present before the age of 10 years, but 30% present between the age of 10 and 19 years. A significant proportion of young patients with IBD will develop the disease just prior to or during puberty. Adolescent growth is characterized by rapid accumulation of lean body mass and any inflammatory disease occurring at this time is likely to have a major impact on nutritional status and growth. This rapid growth requires an appropriate increase in nutritional substrates and failure to achieve catch-up growth may ultimately lead to poor cumulative growth over time. Most of the growth retardation is seen in children with CD, approximately 30%. However, also in UC 15% will show a reduction in growth. The higher percentage in CD could be due to the disease itself or to the relative subtlety of the intestinal manifestations of CD, mainly abdominal pain and general malaise. Not only growth, but also delayed puberty, is a sign of an ongoing disease that most likely needs more intensive treatment. It has been shown that the severity of disease activity plays a more important role in the occurrence of growth retardation than steroid treatment. Therefore in paediatrics it is important to state that growth retardation during medical treatment equals undertreatment. In contrast to adults, the potential benefit of nutritional therapy should be seriously considered in addition to aggressive medical therapy including steroids and other immunosuppressive agents such as azathioprine. The most convincing evidence that malnutrition is primarily responsible for growth failure is based on depletion studies. The malnutrition itself is caused by ongoing inflammation and loss of appetite. Recommendations for nutritional therapy include an increase in energy and protein intake to 150% of recommended daily allowances for height and age. Some studies have shown the benefit of nocturnal nasogastric infusion as supplements of daily intake. Importantly, nutritional support has been shown to be as effective as steroids in achieving remission of disease in children. Furthermore, no significant differences have been shown in studies using elemental versus polymeric diets.

Prenatal ethanol exposure alters the expression of intestinal hydrolase mRNAs in newborn rats

To gain insight into the postnatal growth delay induced by ethanol in utero, we characterized functional impairments of the small intestine of neonatal rats prenatally exposed to ethanol using a well-described model of gestational alcoholism (25% ethanol w/v in the drinking water). Expression of the intestinal enzymes-lactase-phlorizin hydrolase (LPH) and intestinal alkaline phosphatase (IAP)-that are critical for enteral nutrition of neonates was studied. Characteristic patterns of LPH and IAP expression along the proximal-distal (horizontal) and crypt-villus (vertical) axes of the small intestine, as well as the intracellular localization of LPH and IAP mRNAs and immunoreactive proteins within absorptive enterocytes, were not altered by prenatal exposure to ethanol. However, a 10- to 15-fold increase in the number of LPH and IAP mRNA molecules per absorptive enterocyte was found throughout the intestine of ethanol-exposed neonates, compared with controls, whereas lactase and alkaline phosphatase activities per enterocyte remained unchanged. These findings suggest that ethanol in utero alters the mRNA abundance of epithelial enzymes in newborn rat small intestine. Changes in mRNA abundance could be an important aspect of enterocyte adaptation to high ethanol concentrations in gastrointestinal amniotic fluid of ethanol-exposed fetuses.

Randomised trial of biofeedback training for encopresis

AIMS

To evaluate biofeedback training in children with encopresis and the effect on psychosocial function.

DESIGN

Prospective controlled randomised study. PATIENT INTERVENTIONS: A multimodal treatment of six weeks. Children were randomised into two groups. Each group received dietary and toilet advice, enemas, oral laxatives, and anorectal manometry. One group also received five biofeedback training sessions.

MAIN OUTCOME MEASURES

Successful treatment was defined as less than two episodes of encopresis, regular bowel movements, and no laxatives. Psychosocial function after treatment was assessed using the Child Behaviour Checklist.

RESULTS

Children given laxatives and biofeedback training had higher success rates than those who received laxatives alone (39% v 19%) at the end of the intervention period. At 12 and 18 months, however, approximately 50% of children in each group were successfully treated. Abnormal behaviour scores were initially observed in 35% of children. Most children had improved behaviour scores six months after treatment. Children with an initial abnormal behaviour score who were successfully treated had a significant improvement in their behavioural profiles.

CONCLUSIONS

Biofeedback training had no additional effect on the success rate or behaviour scores. Psychosocial problems are present in a subgroup of children with encopresis. The relation between successful treatment and improvement in behavioural function supports the idea that encopresis has an aetiological role in the occurrence and maintenance of behavioural problems in children with encopresis.

[The relationship between intake of dietary fiber and chronic constipation in children]

OBJECTIVE

Evaluation of the feeding patterns of children with chronic constipation, in particular dietary fibres, energy and fluid intake and their influence on colonic transit time. In addition, the effect of dietary recommendations regarding fibres was assessed.

DESIGN

Prospective randomized study.

SETTING

Department of Paediatric Gastroenterology and Nutrition, Academic Medical Centre, Amsterdam, the Netherlands.

METHOD

Children with at least 2 months of complaints related to constipation were enrolled and both dietary intake and colonic transit time were evaluated. After dietary and laxative treatment, in some combined with biofeedback training, and a follow-up of 6 months, a randomized sample were again evaluated regarding their transit times and dietary patterns.

RESULTS

In 73 consecutive children mean fibre intake was the same as in healthy controls, although energy and fluid intake were lower. Colonic transit time was increased compared with healthy controls and no relationship was established between fibre intake and transit time. At 6 months no significant increase in mean fibre intake was observed and no relationship was found between either transit time and change in fibre intake or cure and change in fibre intake. In the cured patients no increase of their mean fibre intake could be observed.

CONCLUSION

The amount of dietary fibres played no pathogenic part in chronic constipation. Dietary advice did not change the mean fibre content of the diet. In addition, changes in fibre intake had no effect on colonic transit time or cure.

The human intestinal cell lines Caco-2 and LS174T as models to study cell-type specific mucin expression

Mucin expression was studied during proliferation and differentiation of the enterocyte-like Caco-2 and goblet cell-like LS174T cell lines. Caco-2 cells express mRNAs of MUC1, MUC3, MUC4 and MUC5A/C whereas MUC2 and MUC6 mRNAs are virtually absent. Furthermore, MUC3 mRNA is expressed in a differentiation dependent manner, as is the case for enterocytes. Concomitantly MUC3 protein precursor (approximately 550 kDa) was detected in Caco-2 cells. In LS174T cells mucin mRNAs of MUC1, MUC2 and MUC6 are constitutively expressed at high levels, whereas MUC3, MUC4 and MUC5A/C mRNAs are present at low levels. At the protein level LS174T cells express the goblet cell specific mucin protein precursors MUC2, MUC5A/C and MUC6 with apparent molecular masses of about 600 kDa, 470/500 kDa and 400 kDa respectively. MUC3 protein is not detectable. Furthermore, human gallbladder mucin protein (approximately 470 kDa precursor), of which the gene has not yet been identified, is expressed in LS174T cells. In addition, synthesis and secretion of the goblet cell specific mature MUC2, MUC5A/C and human gallbladder mucin was demonstrated in LS174T cells. It is concluded that Caco-2 and LS174T cell lines provide excellent in vitro models to elucidate the cell-type specific mechanisms responsible for mucin expression.

Colonic transit time in constipated children: does pediatric slow-transit constipation exist?

In adults, slow-transit constipation is a well-established form of constipation with abdominal pain and an empty rectum on examination. Marker studies in these patients, mainly women, show a markedly slowed transit time in all colonic segments. No studies in constipated children are available that assess the existence of slow-transit constipation. In a prospective study, a total of 94 referred constipated pediatric patients, 63 boys and 31 girls (median age, 8.0 years), underwent colonic-transit-time measurements using radioopaque markers to evaluate the pattern of transit. In addition, orocecal-transit-time measurements using the hydrogen breath (lactulose) test, anorectal manometry, and behavior studies using the Child Behavior Checklist were performed in all children. Based on the upper limit (mean + 2 SD) of total colonic transit time (CTT) in constipated children, we arbitrarily separated patients into two groups. Children with CTTs > 100 h were said to have pediatric slow-transit constipation (PSTC), while patients with CTTs < 100 h were said to have normal- or delayed-transit constipation (NDTC). In 94 constipated children, PSTC was found in 24 children; in 70 children, total CTT was < 100 h (NDTC). Total and segmental CTTs were significantly prolonged in PSTC (median, 189 h; range, 104.4-384) versus NDTC (median, 46.8 h; range, 3.6-99.4) hours. No significant differences were found in orocecal transit time. Significant clinical differences in children with PSTC versus those with NDTC existed regarding nighttime soiling (71 vs. 11%); daytime soiling episodes (14 vs. 7 each week, median), and nighttime soiling episodes (5 vs. 0 each week, median); absent urge to defecate (33 vs. 14%); and palpable abdominal (71 vs. 39%) and/or rectal (71 vs. 13%) masses. All manometric parameters were comparable in the two groups, except for a significantly lower maximal squeeze pressure with PSTC. Using the Child Behavior Checklist, both groups differed significantly from controls (26 and 43%, respectively), with no significant differences in behavior problems found between the NDTC and the PSTC groups. In conclusion, based on objective marker studies, our findings suggest the existence of pediatric slow-transit constipation. This entity can be recognized by clinical features, most importantly nighttime soiling and a palpable rectal mass. The probability of PSTC with both of these symptoms was 0.82; in the absence of these two symptoms, it was 0.07. It is of interest that CTTs in PSTC are comparable with CTTs in adults with slow-transit constipation, although the clinical presentation is clearly different. Further studies are needed to investigate whether the prolonged CTT characterizes a distinct form of constipation in children or is an epiphenomenon of the underlying constipation itself. The mechanisms responsible for the slow transit in these children and the appropriate therapeutic approach need to be studied.

Biofeedback training in treatment of childhood constipation: a randomised controlled study

BACKGROUND

Because abnormal defaecation dynamics, which can be modified by biofeedback, are considered to be the underlying problem in constipation, biofeedback training may be a useful treatment for constipation. This treatment has mainly been studied in uncontrolled trials. We evaluated defaecation dynamics and clinical outcome in chronically constipated children in a randomised study comparing conventional treatment and conventional treatment with biofeedback training.

METHODS

Patients, 5 to 16 years old, were referred to the Academic Medical Center in Amsterdam by general practitioners, school doctors, paediatricians, and psychiatrists. They had to fulfil at least two of four criteria for paediatric constipation and were included if they had been treated medically for at least one month before randomisation. Patients had a medical history, abdominal and rectal examination, and anorectal manometry at the start and end of the 6-week intervention period. The conventional group received laxative treatment with additional dietary advice, toilet training, and maintenance of a diary of bowel habits. The biofeedback group received the same conventional treatment and additionally five biofeedback training sessions. During the first 3 weeks, patients visited the outpatient clinic weekly; two subsequent visits were twice monthly.

FINDINGS

94 patients were randomised to conventional treatment (CT) and 98 to conventional treatment with additional biofeedback training (CT+BF). Normal defaecation dynamics increased in the CT group from 41% to 52% (not significant) and in the CT+BF group from 38% to 86% (p = 0.001). At 6 weeks, more patients in the CT+BF group showed normal defaecation dynamics, compared to the CT group (p < 0.001). This result was unaltered by controlling for baseline status in a logistic regression model. At 1 year, successful treatment (defaecation frequency > or = 3/week, soiling and/or encopresis < 2/month, and no laxatives) was accomplished in 59% of the CT and 50% of the CT+BF group (p = 0.24). The results were maintained after 1 1/2 years follow-up. No association was found between achievement of normal defaecation dynamics and clinical outcome.

INTERPRETATION

Additional biofeedback training compared to conventional therapy did not result in higher success rates in chronically constipated children. Furthermore, achievement of normal defaecation dynamics was not associated with success: abnormal defaecation dynamics seem not to play a crucial role in the pathogenesis of childhood constipation. Intensive conventional laxative treatment should remain the first choice in chronically constipated children.

Quantitative analysis of MUC2 synthesis in ulcerative colitis

MUC2 is the predominant mucin in the human colon responsible for the protective mucus layer. We developed methods to quantify MUC2 biosynthesis, which were used to study the regulation of MUC2 expression in the colon of normal individuals and of patients with ulcerative colitis. Colonic biopsies were metabolically labeled, and biosynthesis of MUC2 precursor was quantified using SDS-PAGE. Total MUC2 and MUC2 mRNA were quantified using blotting techniques. MUC2 precursor biosynthesis and total MUC2 levels were significantly decreased in ulcerative colitis patients with active inflammation compared to controls. In contrast, both these parameters returned to control values during remission of the inflammation, demonstrating that colonic biosynthesis and total amounts of MUC2 vary according to the activity of the disease. However, MUC2 mRNA levels were similar in all patients and independent of disease activity, indicating that these variations in MUC2 synthesis are post-transcriptionally regulated.

MUC2 is the prominent colonic mucin expressed in ulcerative colitis

BACKGROUND

It has been shown that MUC2 is the prominent mucin synthesised in healthy colon.

AIM

To identify the predominant mucins in ulcerative colitis (UC) and to study their biosynthesis.

METHODS AND RESULTS

Mucin was purified from UC resection specimens. This mucin on sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) presented as one, high molecular weight, periodic acid/Schiff's reagent (PAS) stainable band. Amino acid composition showed a close resemblance to that of MUC2. Immunoprecipitation with a specific anti-MUC2 antiserum confirmed that this mucin was MUC2. In addition, on the mRNA level MUC2 was also the most prominent mucin expressed in UC. Polyclonal antiserum was elicited, mainly recognising mucin peptide epitopes of UC and normal colonic mucin. Biosynthetic studies with [35S]amino acids showed that the MUC2-precursor in UC displayed a molecular mass on SDS-PAGE of approximately 600 kDa. This precursor was converted into a mature MUC2 with anomalous mobility on SDS-PAGE of 550 kDa and was secreted. Only this 550 kDa band could be labelled with [35S]sulphate and stained by PAS.

CONCLUSIONS

This study shows that in parallel with the mucin expression in healthy controls, MUC2 is the major mucin expressed in UC. Qualitatively, MUC2 biosynthesis seems unchanged in UC.

[Consensus inflammatory intestinal diseases in children: ulcerative colitis and Crohn disease. Work Group Academic Medical Center, Amsterdam]

Members of different societies, including Paediatrics, Gastroenterology, Clinical Chemistry, Radiology and Pathology, involved in the treatment of children with inflammatory bowel disease (IBD) reached consensus during 12 meetings about definition, clinical and diagnostic work-up as well as initial treatment options in paediatric IBD. On the basis of history and physical examination a distinction is made between colitis-like or Crohn-like appearance. Further laboratory investigations are required in the presence of malnutrition, extraintestinal manifestations or growth retardation. Pathology plays an important part in the final diagnosis. Special attention is given to pubertal staging and height measurements as routine aspects of the treatment of children with IBD.

Mucin gene structure and expression: protection vs. adhesion

The cloning of mucin cDNAs brought about by the application of molecular biology and molecular analyses constitutes a major step in understanding mucin structure and function. Here two classes of mucins are described: epithelium-associated and endothelium/leukocyte-associated mucins, which have thus far been described separately in the literature. The epithelial mucins are generally believed to play a role in cytoprotection. The endothelial and leukocyte class of mucins are adhesion molecules involved in lymphocyte homing and lymphocyte activation or are part of the adhesion cascade that plays a role in the initiation of inflammation. Mucins in general contain many threonine and serine residues, which are extensively O-glycosylated. Due to this profound glycosylation, mucins have a filamentous conformation. By virtue of their extended filamentous, and often negatively charged, structure, mucins can act as a barrier protecting the cell. However, when an opposing cell has specific receptors for mucins, adhesion can override the barrier function. Therefore, mucins may be powerful two-edged swords: they are both protective and adhesive.