Child Health Needs and the Pediatric Gastroenterology Workforce: 2020-2040

This article is part of an American Board of Pediatrics Foundation-sponsored effort to analyze and forecast the pediatric subspecialty workforce between 2020 and 2040. Herein, an overview of the current pediatric gastroenterology workforce is provided, including demographics, work characteristics, and geographic distribution of practitioners. Brief context is provided on the changing nature of current practice models and the increasing prevalence of some commonly seen disorders. On the basis of a rigorous microsimulation workforce projection model, projected changes from 2020 to 2040 in the number of pediatric gastroenterologists and clinical workforce equivalents in the United States are presented. The article closes with a brief discussion of training, clinical practice, policy, and future workforce research implications of the data presented. This data-driven analysis suggests that the field of pediatric gastroenterology will continue to grow in scope and complexity, propelled by scientific advances and the increasing prevalence of many disorders relevant to the discipline. The workforce is projected to double by 2040, a growth rate faster than most other pediatric subspecialties. Disparities in care related to geography, race, and ethnicity are among the most significant challenges for the years ahead. Changes to training and education, incentives to meet the needs of underserved populations, and new multidisciplinary models for health care delivery will be necessary to optimally meet the volume, diversity, and complexity of children with gastroenterological diseases in the years ahead.

Academic Careers in Advocacy: Aligning Institutional Values Through Use of an Advocacy Portfolio

Academic children's hospitals must embrace advocacy as a central component of their missions to discover new knowledge and improve the health of the communities and patients they serve. To do so, they must ensure faculty have both the tools and the opportunities to develop and articulate the work of advocacy as an academic endeavor. This can be accomplished by integrating the work of advocacy at the community and policy-change levels into the traditional value systems of academic medicine, especially the promotions process, to establish its legitimacy. Academic pediatric institutions can support this transformation through robust training and professional development programs and establishing opportunities, resources, and leadership positions in advocacy. The adoption of an advocacy portfolio can be used to align these activities and accomplishments to institutional values and promotion. This alignment is crucial to supporting the advocacy work of pediatricians at a time in which community engagement and systems and policy change must be added to professional activities to ensure optimal outcomes for all children.

An Initiative to Increase Residency Program Diversity

A physician workforce that reflects the patient population is associated with improved patient outcomes and promotes health equity. Notwithstanding, racial and ethnic disparities persist within US medical schools, making some individuals underrepresented in medicine (URM). We sought to increase the percentage of URM residents who matched into our pediatric residency programs from a baseline of 5% to 35% to achieve demographic parity with our patients. We developed a multifaceted approach using multiple iterative tests of change, with the primary strategy being increased visibility of URM trainees and faculty to residency applicants. Strategies included applicant interviews with URM faculty, interview dinners with URM residents, visibility at academic conferences for URM trainees, development of targeted marketing materials, and a visiting student program supported by networking with URM residents. The primary outcome measure was the percentage of matched residents in the categorical pediatrics, child neurology, and medical genetics training programs who identified as URM. The percentage of URM residents increased to 16% (6 of 37) in 2018, 26% (11 of 43) in 2019, 19% (8 of 43) in 2020, and 21% (9 of 43) in 2021 (a four-year average of 22% URM residents; P = .0002). This progress toward a more representative residency program was met by challenges, such as pipeline concerns, the minority tax, and recruitment during a pandemic. We were able to implement small, low-resource strategies that had a large cumulative impact and could be implemented in other residency programs. Specific tactics and challenges encountered are discussed in this special article.

Characterization of Electronic Health Record Use Outside Scheduled Clinic Hours among Primary Care Pediatricians: A Retrospective Descriptive Task Analysis of Electronic Health Record Access Log Data (Preprint)

Background

Many of the benefits of electronic health records (EHRs) have not been achieved at expected levels because of a variety of unintended negative consequences such as documentation burden. Previous studies have characterized EHR use during and outside work hours, with many reporting that physicians spend considerable time on documentation-related tasks. These studies characterized EHR use during and outside work hours using clock time versus actual physician clinic schedules to define the outside work time.

Objective

This study aimed to characterize EHR work outside scheduled clinic hours among primary care pediatricians using a retrospective descriptive task analysis of EHR access log data and actual physician clinic schedules to define work time.

Methods

We conducted a retrospective, exploratory, descriptive task analysis of EHR access log data from primary care pediatricians in September 2019 at a large Midwestern pediatric health center to quantify and identify actions completed outside scheduled clinic hours. Mixed-effects statistical modeling was used to investigate the effects of age, sex, clinical full-time equivalent status, and EHR work during scheduled clinic hours on the use of EHRs outside scheduled clinic hours.

Results

Primary care pediatricians (n=56) in this study generated 1,523,872 access log data points (across 1069 physician workdays) and spent an average of 4.4 (SD 2.0) hours and 0.8 (SD 0.8) hours per physician per workday engaged in EHRs during and outside scheduled clinic hours, respectively. Approximately three-quarters of the time working in EHR during or outside scheduled clinic hours was spent reviewing data and reports. Mixed-effects regression revealed no associations of age, sex, or clinical full-time equivalent status with EHR use during or outside scheduled clinic hours.

Conclusions

For every hour primary care pediatricians spent engaged with the EHR during scheduled clinic hours, they spent approximately 10 minutes interacting with the EHR outside scheduled clinic hours. Most of their time (during and outside scheduled clinic hours) was spent reviewing data, records, and other information in EHR.

Recent advances in pediatric gastroenterology, hepatology and nutrition

Pediatric gastroenterology, hepatology and nutrition are rapidly evolving, exciting and diverse disciplines. Because the field is so expansive, this commentary highlights important trends, rather than narrowly focusing on specific advances. Examples of advances in the highest impact and rapidly moving areas of pediatric gastroenterology are reviewed, including the intestinal microbiome, biomedical genomics, the biology of unique gastrointestinal cell types, and microRNAs (miRNAs).

Salt-induced pattern formation in evaporating droplets of lysozyme solutions

Solute self-organization during evaporation of colloidal sessile droplets has attracted the attention of researchers over the past few decades due to a variety of technological applications. Recently, pattern formation during evaporation of various biofluids has been studied due to potential applications in screening and diagnosis. The complex morphological patterns in the deposit are unique to various disorders and are influenced by various physical mechanisms occurring during evaporation. These complex patterns can be better understood by studying evaporation of model solutions of biological relevance. Here, we examine the general features of pattern formation during sessile droplet evaporation of aqueous lysozyme solutions with varying concentrations of NaCl. Lysozyme is a globular protein found in biological fluids such as tears and saliva. The morphological evolution of the droplet is studied by time-lapse video during evaporation via reflection optical microscopy. The final deposits exhibit an amorphous peripheral ring and interior regions containing crystallites and dendritic forms, dependent on NaCl concentration. Scanning electron microscopy (SEM) images demonstrate the multi-scale hierarchical nature of these structures.

Characteristic size for onset of coffee-ring effect in evaporating lysozyme-water solution droplets

Liquid droplets containing suspended particles deposited on a solid surface often form a ring-like structure due to the redistribution of solute during evaporation, a phenomenon known as the "coffee ring effect". The complex patterns left on the substrate after evaporation are characteristic of the nature of the solute and the particle transport mechanisms. In this study, the morphological evolution and conditions for coffee ring formation for simplified model biological solutions of DI water and lysozyme are examined by AFM and optical microscopy. Lysozyme is a globular protein found in high concentration, for example, in human tears and saliva. The drop diameters studied are very small, ranging from 1 to 50 μm. In this size range, protein motion and the resulting dried residue morphology are highly influenced by the decreased evaporation time of the drop. In this work, we consider the effect of droplet size and concentration on the morphology of the deposited drop as well as the minimal conditions for coffee ring formation in this system. Two distinct deposit types are observed: a simple cap-shaped deposit for drops with small diameters and a ring-like deposit at larger diameters. Ring formation occurs at a critical diameter, which depends systematically on initial lysozyme concentration.

Knockout of Mkp-1 exacerbates colitis in Il-10-deficient mice

Il-10-deficient mice develop colitis associated with exaggerated Th1/Th17 responses and are a valuable model of inflammatory bowel disease. Mkp-1 is a major negative regulator of MAPKs, and its expression is enhanced by IL-10. To understand the role of Mkp-1 in the regulation of intestinal mucosal immune responses, we studied the effect of Mkp-1 deletion on the pathogenesis of colitis in Il-10(-/-) mice. We found that knockout of Mkp-1 on an Il-10(-/-) background accelerated the development of colitis. Compared with Il-10(-/-) mice, colitis not only appeared earlier but also was more severe in Il-10(-/-)/Mkp-1(-/-) mice. Il-10(-/-) mice exhibited a mild intestinal inflammation in the specific pathogen-free environment, and rectal prolapse rarely appeared before 6 mo of age. In contrast, the majority of Il-10(-/-)/Mkp-1(-/-) mice developed severe colitis rapidly and presented with rectal prolapse after only 2-3 mo. The colon of Il-10(-/-)/Mkp-1(-/-) mice showed diffuse transmural chronic inflammation and mucosal hyperplasia, with significantly more proliferating crypt epithelial cells than those of Il-10(-/-) mice. In addition to the severe colitis, Il-10(-/-)/Mkp-1(-/-) mice also developed conjunctivitis and blepharitis. The colon of Il-10(-/-)/Mkp-1(-/-) mice contained significantly higher levels of proinflammatory cytokines and exhibited greater MAPK activities than did the colon of Il-10(-/-) mice. Splenocytes and lymphocytes from Il-10(-/-)/Mkp-1(-/-) mice produced higher levels of Th1 cytokines ex vivo upon activation than did cells from Il-10(-/-) mice. Our studies support a pivotal role of Mkp-1 as a negative regulator of mucosal immune responses and highlight its protective function against inflammatory bowel disease.

Lysozyme pattern formation in evaporating drops

Liquid droplets containing suspended particles deposited on a solid, flat surface generally form ringlike structures due to the redistribution of solute during evaporation (the "coffee ring effect"). The forms of the deposited patterns depend on interactions between solute(s), solvent, and substrate. In this study, deposition patterns from droplets of a simplified model biological fluid (DI water + lysozyme) are examined by scanning probe and optical microscopy. The overall lysozyme residue morphology is complex (with both a perimeter "rim" and undulating interior) but varies little with concentration. However, the final packing of lysozyme molecules is strongly dependent on initial concentration.

Quantitative V-L-S Growth Model and Experiments of Fe Catalyzed Si Nanowire Formation

We report the formation of Si nanowires (SiNWs) by vapor-liquid-solid (V-L-S) mechanism where Si atoms are pumped from Si wafer. This happens when a material has the large difference of activity in its pure (Si) and alloy state (Si-Fe). We developed a kinetic model to quantitatively describe the growth of the nanowires. The model predicts that the length of the nanowires increases linearly with the growth time.

Disruption of ZAS3 in mice alters NF-kappaB and AP-1 DNA binding and T-cell development

The large zinc finger proteins, ZAS, regulate the transcription of a variety of genes involved in cell growth, development, and metastasis. They also function in the signal transduction of the TGF-beta and TNF-alpha pathways. However, the endogenous protein of a representative member, ZAS3, is rapidly degraded in primary lymphocytes, which limits the determination of its physiological function in vitro. Therefore, we have generated mice with targeted disruption of ZAS3. Oligonucleotide-based microarray analyses revealed subtle but consistent differences in the expression of genes, many of which are associated with receptor or signal transduction activities between ZAS3+/+ and ZAS3-/- thymi. Gel mobility shift assays showed altered DNA binding activities of NF-kappaB and AP-1 proteins in ZAS3-deficient tissues, including the thymus. Lymphocyte analysis suggested a subtle but broad function of ZAS3 in regulating T-cell development and activation. In CD3+ ZAS3-/- thymocytes, the CD4/ CD8 ratio was decreased and CD69 expression was decreased. In peripheral CD4+ ZAS3-/- lymphocytes we observed an increased number of memory T cells.

Dendrimer Pattern Formation in Evaporating Drops

The redistribution of organic solutes during drop evaporation is a nanoscale self-assembly process with relevance to technologies ranging from inkjet printing of organic displays to synthesis of biosmart interfaces for sensing and screening. We have used solutions of dendrimer molecules with incrementally varying terminal site chemistry to explore whether the condensed dendrimer patterns resulting from microdroplet evaporation sensitively depend on, and are characteristic of, the surface chemistry of the solute molecules. This hypothesis has been experimentally confirmed by comparing the behavior of microdroplets of G4, G4-25%C12, and G4-50%C12 dendrimers dissolved in pentanol and deposited on mica substrates. For the dilute concentration studied here, the presence of periodically 'scalloped' dendrimer rings is ubiquitous. The instability wavelength of the scalloped rings is found to be proportional to the width of the ring, similar to observations of the rim instability in dewetting holes. The effect of dendrimer surface chemistry is obvious in the detailed structure of the self-assembled rings. G4 rings are diffuse and disordered with no evidence for layered growth. G4-25%C12 exhibits highly ordered ring structures and the onset of monomolecular terracing. G4-50%C12 exhibits highly periodic scallops and very distinct monomolecular height terraced growth of the rings with flat terraces and sharply defined steps. On the basis of these results, it is likely that the morphology of condensed molecule-based ring patterns formed by evaporation of microdroplets on surfaces can be used as a 'fingerprint' to identify, for example, solute molecule surface chemistry and concentration and function as a sensor for a variety of biochemical events.

Differential trafficking of transforming growth factor-beta receptors and ligand in polarized epithelial cells

Epithelial cells in vivo form tight cell-cell associations that spatially separate distinct apical and basolateral domains. These domains provide discrete cellular processes essential for proper tissue and organ development. Using confocal imaging and selective plasma membrane domain activation, the type I and type II transforming growth factor-beta (TGFbeta) receptors were found to be localized specifically at the basolateral surfaces of polarized Madin-Darby canine kidney (MDCK) cells. Receptors concentrated predominantly at the lateral sites of cell-cell contact, adjacent to the gap junctional complex. Cytoplasmic domain truncations for each receptor resulted in the loss of specific lateral domain targeting and dispersion to both the apical and basal domains. Whereas receptors concentrate basolaterally in regions of direct cell-cell contact in nonpolarized MDCK cell monolayers, receptor staining was absent from areas of noncell contact. In contrast to the defined basolateral polarity observed for the TGFbeta receptor complex, TGFbeta ligand secretion was found to be from the apical surfaces. Confocal imaging of MDCK cells with an antibody to TGFbeta1 confirmed a predominant apical localization, with a stark absence at the basal membrane. These findings indicate that cell adhesion regulates the localization of TGFbeta receptors in polarized epithelial cultures and that the response to TGFbeta is dependent upon the spatial distribution and secretion of TGFbeta receptors and ligand, respectively.

Gastrointestinal polyps and polyp syndromes in adolescents

Although gastrointestinal polyps are more common in the first decade of life than during adolescence, underlying genetic polyposis syndromes are more likely in adolescents. In the past decade, the discovery of gene defects associated with polyposis syndromes has improved classification of these disorders, assisted in the stratification of cancer risk, and permitted more precise diagnosis. Genetic testing is now clinically available for the gene defects that occur in familial adenomatous polyposis coli, Peutz-Jeghers syndrome, Cowden syndrome, and juvenile polyposis syndrome. This review outlines clinical features, genetics, and management strategies for the major polyposis syndromes that affect adolescents.

Gastrointestinal polyps and polyposis syndromes in children

Gastrointestinal polyps are common during childhood and most often present with painless rectal bleeding. Most polyps occur as isolated colonic lesions and are not harbingers of an underlying genetic disorder, nor do they bestow a risk of gastrointestinal cancer. The astute pediatrician must be aware, however, that occasionally polyps may occur in the context of a genetic polyposis disorder characterized by an increase in the life-time risk of cancer in the gastrointestinal tract and other organ systems. This review outlines the major polyposis syndromes affecting children and highlights associated findings that might clue the alert physician to an underlying diagnosis. Recent developments in the understanding of the genetics of each disorder are emphasized.

Relationship of high energy expenditure and variation in dietary intake with reporting accuracy on 7 day food records and diet histories in a group of healthy adult volunteers

OBJECTIVES

To assess the accuracy of reporting from both a diet history and food record and identify some of the characteristics of more accurate reporters in a group of healthy adult volunteers for an energy balance study.

DESIGN

Prospective measurements in free-living people.

SETTING

Wollongong, Australia.

SUBJECTS

Fifteen healthy volunteers (seven male, eight female; aged 22-59 y; body mass index (BMI) 19-33 kg/m(2)) from the local community in the city of Wollongong, Australia.

INTERVENTIONS

Measurement of energy intake via diet history interview and 7 day food records, total energy expenditure by the doubly labelled water technique over 14 days, physical activity by questionnaire, and body fat by dual-energy X-ray absorptiometry.

RESULTS

Increased misreporting of energy intake was associated with increased energy expenditure (r=0.90, P<0.0001, diet history; r(S)=0.79, P=0.0005, food records) but was not associated with age, sex, BMI or body fat. Range in number of recorded dinner foods correlated positively with energy expenditure (r(S)=0.63, P=0.01) and degree of misreporting (r(S)=0.71, P=0.003, diet history; r(S)=0.63, P=0.01, food records). Variation in energy intake at dinner and over the whole day identified by the food records correlated positively with energy expenditure (r=0.58, P=0.02) and misreporting on the diet history (r=0.62, P=0.01).

CONCLUSIONS

Subjects who are highly active or who have variable dietary and exercise behaviour may be less accurate in reporting dietary intake. Our findings indicate that it may be necessary to screen for these characteristics in studies where accuracy of reporting at an individual level is critical.

Removal of esophageal foreign bodies in the pediatric ED: is ketamine an option?

The objective of the study was to evaluate our experience with esophageal foreign body (EFB) removal comparing the use of ketamine-midazolam (K-M) and fentanyl-midazolam (F-M) in the emergency department (ED), to admission and general anesthesia (GA) in the operating room (OR). A retrospective review of all children undergoing EFB removal at our institution during a 2-year period was conducted. A total of 93 patients were identified: K-M 57/93 (61.2%), F-M 28/93 (30.1%), GA 5/93 (5.4%), and 3/93 (3.2%) by other means. Mean procedure durations were 4.8 min for K-M and 7.0 min for F-M. Mean lengths of stay (LOS) for ED procedures were 3.6 hrs for K-M and 5.7 hrs for F-M, versus 17.7 hrs if admitted. Transient hypoxemia occurred in 10.7% of K-M and 15.4% of F-M. Removal of EFBs in the ED may obviate the need for admission. In our experience, the use of K-M is associated with fewer airway complications, shorter removal times, and an overall shorter LOS.

Children's knowledge, anticipatory anxiety, procedural distress, and recall of esophagogastroduodenoscopy

BACKGROUND

This study evaluates the relations among children's knowledge of esophagogastroduodenoscopy (EGD) and anticipatory anxiety, procedural distress, and the nature of postprocedural recall and evaluations.

METHODS

One hundred patients, aged 8 to 17 years, completed self-report measures of knowledge and anxiety before EGD. Parents completed a self-report measure assessing how they prepared their children. Nurses and trained observers completed observational ratings of distress. Children's recall and evaluation of the procedure were assessed by self-report 1 hour after the procedure and by telephone that evening.

RESULTS

Most children knew about the major components of EGD. Children with greater knowledge experienced less distress and reported that they would be less anxious and upset when undergoing future EGDs. Children with greater anticipatory anxiety exhibited more procedural distress. Children's distress varied by the phase of the procedure. Children who were more distressed during intravenous line insertion experienced greater distress during esophageal intubation and the endoscopic examination. Approximately 20% of patients reported at least some memory of the procedure even at the end of the day. Children with greater recall reported greater aversion and a more negative attitude toward future EGDs.

CONCLUSIONS

This study provides information about children's distress during EGD and the effects of conscious sedation on patients' memories and attitudes toward future procedures. The study indicates that preparation before EGD may reduce patient distress.

Ras-mediated suppression of TGFbetaRII expression in intestinal epithelial cells involves Raf-independent signaling

Ras-transformed intestinal epithelial cells are resistant to the growth inhibitory actions of TGFbeta and have a marked decrease in expression of the TGFbeta type II receptor (TGFbetaRII). Rat intestinal epithelial cells (RIE) were stably transfected with activated Ras, Sos and Raf constructs and tested for expression of TGFbetaRII and sensitivity to growth inhibition by TGFbeta. The parental RIE line and the RIE-Raf cells were non-transformed in morphology and were sensitive to TGFbeta (70-90% inhibited). In contrast, the RIE-Ras and RIE-Sos lines were transformed, resistant to TGFbeta and expressed 5- to 10-fold decreased levels of the TGFbetaRII mRNA and protein. Cyclin D1 protein expression was repressed by TGFbeta treatment in parental RIE and RIE-Raf cells, whereas levels of cyclin D1 in RIE-Ras and RIE-Sos cells remained unchanged. Treatment of RIE-Ras cells with 25 microM farnesyl transferase inhibitor, FTI L739,749, for 48 hours restored expression of TGFbetaRII to levels equivalent to control cells. In addition, treatment of RIE-Ras cells for 48 hours with PD-98059, a specific MAPKK inhibitor, also increased expression of TGFbetaRII to control levels. Collectively these results suggest that downregulation of TGFbetaRII and loss of sensitivity to growth inhibition by TGFbeta in Ras-transformed intestinal epithelial cells is not mediated exclusively by the conventional Ras/Raf/MAPKK/MAPK pathway. However, activation of MAPK, perhaps by an alternate Ras effector pathway, appears to be necessary for Ras-mediated downregulation of TGFbetaRII.

Heparin binding epidermal growth factor-like growth factor is a transforming growth factor beta-regulated gene in intestinal epithelial cells

Heparin binding epidermal growth factor-like growth factor (HB-EGF) is an EGF-related peptide with prominent effects on cell growth and migration. We explored potentially unique characteristics of HB-EGF in the intestinal epithelial cell line RIE-1. HB-EGF stimulated [(3)H]thymidine incorporation to a level equivalent to transforming growth factor alpha (TGFalpha). HB-EGF also rapidly activated MAPK and induced cyclin D1 in mid-G1 with kinetics similar to TGFalpha. Unlike TGFalpha, HB-EGF mRNA was induced within 1 h by a variety of stimuli, including TGFbeta1. Maximal induction by TGFbeta (7-fold) occurred within 2 h of treatment. Actinomycin D decay curves showed that TGFbeta1 had no effect on HB-EGF mRNA half-life (T(1/2) 20 min). Induction of HB-EGF by TGFbeta1 was not affected by pretreatment with the MEK inhibitor PD-98059 while inhibition of protein kinase C either partially (calphostin C) or completely (staurosporin) blocked induction. Our results suggest that major differences exist in the regulation of the closely related EGF family members TGFalpha and HB-EGF. TGFbeta and HB-EGF, structurally unrelated peptides with potent effects on wound healing, may function coordinately to mediate responses to wounding or cell injury in the intestinal epithelium.

Pharmacological inhibition of Ras-transformed epithelial cell growth is linked to down-regulation of epidermal growth factor-related peptides

BACKGROUND & AIMS

Posttranslational farnesylation is required for Ras activation. Farnesyl transferase inhibitors (FTIs) selectively block protein farnesylation and reduce the growth of many Ras-transformed cells in vitro and in vivo. Activated Ras transforms rat intestinal epithelial (RIE-1) cells by a mechanism distinct from NIH 3T3 fibroblasts in that an epidermal growth factor receptor (EGFR) autocrine loop contributes significantly to the Ras-transformed RIE-1 phenotype.

METHODS

The ability of FTIs to block growth of Ras-transformed RIE-1 cells was evaluated, and these results were correlated with decreased EGFR ligand production.

RESULTS

FTI L744,832 caused a selective, dose-dependent, reversible blockade in proliferation of H-Ras-transformed RIE-1 cells, whereas control cell lines, K-Ras-transformed cells, and activated raf-transfected RIE cells were unaffected. The growth-inhibitory effects of L744,832 correlated with loss of farnesylated H-Ras protein and a marked reduction in transforming growth factor (TGF)-alpha and amphiregulin expression. Inhibition of proliferation of H-Ras RIE-1 cells by L744,832 was overcome by exogenous TGF-alpha, and enhanced growth inhibition was achieved by EGFR blockade in combination with L744,832. +

CONCLUSIONS

These data suggest that one mechanism by which FTIs inhibit growth of H-Ras-transformed epithelial cells is by reducing Ras-induced EGFR ligand production.

Increased intestinal epithelial proliferation in metallothioneine-transforming growth factor alpha transgenic mice

BACKGROUND AND AIM

The epidermal growth factor (EGF) peptide family includes six closely-related proteins, all of which bind to the EGF receptor. In the intestinal epithelium, transforming growth factor alpha (TGFalpha) appears to be the most physiological ligand for the EGF receptor. The present studies were designed to examine the effect of TGFalpha overexpression on duodenal epithelial proliferation using a metallothioneine-inducible promoter/enhancer transgenic mouse (MT-TGFalpha). The MT-TGFalpha mouse model was further studied to determine the in vivo effect of unregulated TGFalpha production on the physiological proliferative responses to fasting and refeeding.

METHODS

MT-TGFalpha mice were given 25 mM oral ZnSO4 to induce transgene expression and were studied 1 to 2 months later. Duodenal histology was analyzed morphometrically in well-oriented transverse sections. The vincristine metaphase-arrest technique was used to assess proliferation in duodenal crypts. Immunohistochemical staining and in situ hybridization were used to assess transgenic TGFalpha protein and mRNA expression, respectively.

RESULTS

Normally fed MT-TGFalpha mice had deeper crypts (0.12 vs. 0.08 mm), longer villi (0.66 vs. 0.54 mm), and greater luminal diameters (2.65 vs. 2.19 mm) compared to controls (P<0.05 for all three dimensions). The crypt cell mitotic index in normally fed transgenic mice was 1.5 fold greater than the index in normally fed controls (20+/-2 vs. 35+/-4 mitoses per crypt; P <0.05). Fasting and refeeding MT-TGFalpha mice resulted in no significant change in their high baseline rate of crypt proliferation, while proliferation in control mice rose from a lower baseline during fasting to a level with refeeding that approximated rates in MT-TGFalpha mice. Transgenic TGFalpha protein and mRNA were localized to the villus epithelial compartment with little or no evidence of mRNA or protein expression in the crypt epithelium.

CONCLUSION

Overproduction of TGFalpha in the mouse duodenal epithelium results in a pronounced increase in crypt epithelial cell proliferation and a resulting increase in the dimension of the crypt/villus unit. This appears to be mediated through a paracrine and/or juxtacrine effect on crypt cells by TGFalpha produced in the villus epithelium. Fasting and refeeding experiments suggest that TGFalpha may also play a role in the proliferative response to refeeding or that the full potential for proliferation is realized by TGFalpha overexpression alone. Collectively, these studies suggest that TGFalpha is a physiological autocrine and paracrine regulator of small intestinal epithelial proliferation.

Recurrent abdominal pain: a potential precursor of irritable bowel syndrome in adolescents and young adults

OBJECTIVES

To assess symptoms of irritable bowel syndrome (IBS) in patients with recurrent abdominal pain (RAP) 5 years after their initial evaluation, to identify the relation of IBS symptoms to functional disability and health service use, and to determine the extent to which IBS symptoms are associated with life stress and poor psychosocial adjustment.

METHODS

Patients with RAP (n = 76) and control subjects (n = 49) completed a telephone interview; measures included the Bowel Disease Questionnaire, the Functional Disability Inventory, the Life Events Questionnaire, the Family Inventory of Life Events, the Center for Epidemiological Studies Depression Scale, the Self-Perception Profile for Adolescents, and the Health Resources Inventory.

RESULTS

Five years after the initial evaluation, patients with RAP reported significantly more episodes of abdominal pain than did control subjects, as well as significantly higher levels of functional disability, school absence, and clinic visits for abdominal distress. Female patients with RAP were more likely than female control subjects to meet the Manning criteria for IBS. Among patients with RAP, higher levels of IBS symptoms were associated with significantly greater functional disability, more clinic visits, more life stress, higher levels of depression, and lower academic and social competence.

CONCLUSION

Female patients with a history of RAP may be at increased risk of IBS during adolescence and young adulthood. Among adolescents and young adults with a history of RAP, IBS symptoms are likely to be associated with high levels of disability and health service use.

Type II TGF(beta) receptor expression in intestinal cell lines and in the intestinal tract

The recent identification and cloning of mammalian transforming growth factor beta (TGFbeta) receptors permits further analysis of the importance of the TGFbeta family in intestinal biology. Expression of the type II TGFbeta receptor was examined in gastrointestinal cell lines and tissues. The 5.5 kb type II mRNA species was detected in poly-(A) mRNA isolated from the rat small bowel and colon. Northern blot analysis of RNA isolated from epithelial and non-epithelial small intestinal cell fractions showed the majority of receptor mRNA localized in the non-epithelial compartment. Immunohistochemical localization in the small intestine and colon supported the RNA findings; that is, expression was greatest in the lamina propria and muscularis. Staining was also detectable in the epithelium, where it was most prominent in the villus tip cells and absent in crypt cells. These findings mirror expression of TGFbeta in the epithelial compartment. The IEC-6, IPEC and RIE-1 cell lines, all of which are non-transformed, were growth inhibited by TGFbeta and expressed type II receptor mRNA and protein. By contrast, the ras-transfected RIE-1, HT-29, Caco-2 and SW-620 transformed lines were not growth inhibited by TGFbeta and all demonstrated a marked reduction in type II TGFbeta receptor mRNA expression and protein abundance by cross-linking. In conclusion, (i) colocalization of both ligand and receptor establishes the existence of potential autocrine and/or paracrine pathways for TGFbeta in the normal intestine and (ii) down-regulation of the type II TGFbeta receptor occurs in association with cellular transformation and may contribute to intestinal carcinogenesis.

Transforming growth factor-alpha

Major advances in understanding growth factor biology, especially in epithelial cells, have resulted from work with TGF-alpha over the past decade. It is clear that TGF-alpha is a potent epithelial oncoprotein, but equally important biological activities in normal epithelial homeostasis have been described. A number of major challenges lie ahead. Foremost is the formidable task of dissecting out the individual contributions of each EGF-related peptide in the biological response to stimulation of the EGFR. Appreciation of the complexity of heterodimerization of receptors within the EGFR family will be equally important in the final analysis. These considerations assure the continued vitality and productivity of investigation of the EGF-related peptide/EGFR axis.

Early proliferative events following intestinal resection in the rat

Partial resection of the small intestine results in compensatory proliferation and adaptation in the remaining small intestinal mucosa. The molecular mechanisms governing the proliferative response are not known, nor has the timing of events associated with proliferation been adequately defined, particularly during the period just after resection. We designed experiments to characterize early (within 24 h) proliferative events associated with proximal intestinal resection and sought to determine the cell type that first responds to proliferative stimuli. Twenty-one day old male Sprague-Dawley rats underwent a 70% proximal intestinal resection or transection (control). Poly(A) RNA was isolated from the distal (ileal) remnants. Northern blots showed a marked induction of the immediate early genes zif-268, nup-475, and c-myc 1-3 h following resection, but not following transection. Immunohistochemical analysis of c-myc expression in ileal crypt epithelial cells showed a biphasic induction that was most marked 6 h after resection and less prominent 24 h after resection. Immunostaining with 5-bromodeoxyuridine (5-BrdU) was restricted to ileal crypt nuclei and was maximal 24 h after resection. All these events were observed in the absence of nutrient intake. Taken together, these data show that a potent nutrient-independent stimulus for intestinal epithelial cell proliferation occurs within minutes of partial small intestinal resection and that the first targets of this stimulus are crypt epithelial cells in the residual intestine.

Expression of a novel sodium-hydrogen exchanger in the gastrointestinal tract and kidney

We have recently cloned a novel Na+/H+ exchanger (NHE-2) from rat small intestinal cDNA library. The present report characterizes the expression of (NHE-2) mRNA in the rat small intestine, stomach, and kidney using Northern blot analysis and in situ hybridization techniques. NHE-2 mRNA was detected in the surface epithelium of the stomach, villus but not crypt epithelial cells of the small intestine and in the distal convoluted, but not in the proximal tubules of the kidney. This distribution suggests a functional role in the transport of sodium across the apical membrane of the gastrointestinal tract and the kidney.

Auto- and cross-induction within the mammalian epidermal growth factor-related peptide family

Several polypeptide growth factors related to epidermal growth factor (EGF) have been identified recently, including transforming growth factor-alpha (TGF-alpha), amphiregulin (AR), heparin-binding EGF-like growth factor (HB-EGF), and betacellulin (BTC). These peptides all bind to the EGF receptor (EGFr). In an effort to understand redundancy within this peptide family and interactions among these related peptides, we compared the biological activities of EGF, TGF-alpha, AR, and HB-EGF in an EGF-responsive, nontransformed intestinal epithelial line (RIE-1) and also determined the effect of individual EGF-related peptides on the expression of related family members in these cells. TGF-alpha, AR, HB-EGF, and EGF were equipotent in stimulating [3H]thymidine incorporation by RIE-1 cells and bound the EGFr with equivalent affinity. Each EGF-related peptide induced the mRNA expression of the remaining family members, including BTC. HB-EGF and AR mRNAs were induced rapidly (within 30 min) and to a greater extent than TGF-alpha and BTC mRNAs, suggesting heterogeneity in the molecular mechanisms for induction. This same pattern was observed for all EGF-related peptides tested. A similar pattern of mRNA induction was observed in secondary cultures of human keratinocytes and in LIM1215 colon adenocarcinoma cells. Nuclear run-on analysis showed that induction of AR and HB-EGF is, at least in part, regulated at the level of gene transcription. Concurrent treatment with HB-EGF and cycloheximide resulted in superinduction of HB-EGF and AR, suggesting that these peptides are immediate early genes in RIE-1 cells. Our results demonstrate an equivalent biological response to EGF-related peptides in RIE-1 cells and further indicate that extensive auto-induction and cross-induction occur within the EGF-related peptide family in several EGF-responsive epithelial cell types.

Localization of transforming growth factor beta isoforms in the normal murine small intestine and colon

BACKGROUND

The transforming growth factor beta (TGF-beta) proteins are key regulators of cellular growth and differentiation. Previous studies have shown that TGF-beta 1 is a potent growth inhibitor of cultured jejunal epithelial cells. The reported distribution of TGF-beta 1 messenger RNA (mRNA) expression along the intestinal villus has been controversial. The purpose of the current study is to determine the loci of TGF-beta protein expression in the normal small intestine and colon.

METHODS

Intestinal localization of TGF-beta isoform mRNA and protein was examined by Northern blot analysis and immunohistochemistry using isoform specific reagents.

RESULTS

TGF-beta 1, TGF-beta 2, and TGF-beta 3 mRNA were found in homogenates from the intact mouse jejunum and colon. The three isoforms colocalized in these tissues. Expression in the small intestinal epithelium was most prominent in cells located on the villus tip, and no staining was detected in the crypt. Occasional lymphocytes in the lamina propria were immunopositive, and all layers of the muscularis were moderately stained. This pattern was seen in all regions of the small intestine. The surface epithelium of the colon was intensely immunopositive, whereas cells in the glands were only weakly stained.

CONCLUSIONS

TGF-beta molecules may serve overlapping functions in the intestinal tract, and expression in the epithelium may function to arrest growth of cells emerging from the crypt and induce or maintain the terminally differentiated state.

Butyrate rapidly induces growth inhibition and differentiation in HT-29 cells

Selected G1 events associated with butyrate-induced differentiation were examined in HT-29 colon adenocarcinoma cells. [3H]Thymidine incorporation by HT-29 cells was decreased to 40% of control levels by treatment with 5 mM butyrate for 24 h, and cell numbers decreased to 21% of control levels after 48 h of treatment. Cells released from butyrate arrest entered S phase approximately 24 h after release, and serum-deprived HT-29 cells escaped growth inhibition if butyrate was added 8 h or more after serum restimulation. Northern analysis of RNA isolated from rapidly growing HT-29 cells showed a marked induction of alkaline phosphatase mRNA expression within 12 h of treatment with 5 mM butyrate. The appearance of alkaline phosphatase mRNA was temporally associated with a 5-fold increase in expression of transforming growth factor beta 1 (TGF-beta 1) mRNA. Expression of the nuclear protooncogene c-myc began to decrease 30 min after treatment with butyrate and was decreased 4.5-fold 4 h after treatment; however, expression of other immediate-early genes (nup/475 and zif/268) was not significantly affected. Histochemical staining of HT-29 monolayers showed that no cells were positive for alkaline phosphatase protein prior to treatment, and 90% were positive 48 h after treatment. TGF-beta 1 and TGF-beta 2 had no effect on HT-29 cell growth. TGF-beta 1 did not induce alkaline phosphatase mRNA or histochemical positivity. These data indicate that butyrate arrests HT-29 cell growth early in G1.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal Na+/H+ exchanger activity is up-regulated by bowel resection in the weanling rat

Increased Na+/H+ exchanger activity is associated with cellular hyperplasia. Cellular hyperplasia is an adaptive response to small-intestinal resection. Therefore, we hypothesized that the small-intestinal Na+/H+ exchanger activity increases in response to small-intestinal resection. Twenty-one-d-old, male Sprague-Dawley rats were randomly divided to receive either a 70% small intestinal resection (n = 59), or a mid-small intestinal transection (n = 49). Seven d postoperatively, the animals were killed and the Na+/H+ exchanger activity of the intestinal remnants was studied by a well validated brush border membrane vesicle technique. The initial rate of Na+ uptake in the presence of an outwardly directed pH gradient and the Vmax of the amiloride-sensitive Na+ uptake were significantly increased (p < 0.01 and p < 0.001, respectively) in the resection as compared with the transection remnants and to a greater magnitude in the distal as compared with the proximal remnants. Km values were not significantly different. The amiloride-sensitive Na+ uptake in the setting of various intravesicular pH was significantly greater (p < 0.001) in the distal resection as compared with the distal transection remnants, with points of enhanced Na+/H+ exchanger activity of intravesicular pH 6.62 and 6.87, respectively. The presence and activation of the Na+/H+ exchanger's internal modifier site was confirmed by demonstrating the effect of intravesicular pH on Na+ efflux. The present study demonstrates an up-regulation of intestinal Na+/H+ exchange activity in a small-bowel resection model in the weanling rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased production of transforming growth factor alpha following acute gastric injury

Transforming growth factor alpha (TGF-alpha) production recently has been found in normal mammalian gastric mucosa. Inasmuch as TGF-alpha and epidermal growth factor (EGF) both stimulate epithelial cell migration and proliferation and suppress gastric acid secretion, the authors of the current study proposed that these growth factors may participate in tissue repair after acute gastric mucosal injury. Consequently, TGF-alpha and EGF production were examined after orogastric administration of either acidified taurocholate or 0.6 mol/L HCl to rats. TGF-alpha messenger RNA (mRNA) expression increased in a dose- and time-dependent manner after administration of taurocholate, whereas EGF mRNA expression was not detected. Radioimmunoassay of gastric mucosal scrapings obtained 6 hours after gastric injury induced by 0.6 mol/L HCl showed a 2.1-fold increase in immunoreactive TGF-alpha but no increase in immunoreactive EGF. In addition, there was a 68-fold increase in immunoreactive TGF-alpha in gastric juice within 30 minutes of gastric instillation of HCl and, again, no increase in immunoreactive EGF. There is a rapid appearance of TGF-alpha in the gastric juice within 30 minutes of injury, which is followed by increased expression of TGF-alpha mRNA and protein in the gastric mucosa. These studies suggest that locally produced TGF-alpha may participate in gastric mucosal repair following acute gastric injury to rats.

Production of transforming growth factor-alpha by normal rat small intestine

Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) are similar in structure and biological activity. In the present study, the distributions of TGF-alpha mRNA, TGF-alpha immunoreactivity, and TGF-alpha-EGF receptor mRNA were examined in epithelial and nonepithelial compartments of the jejunum, and the effect of TGF-alpha on growth of a jejunal crypt cell line (IEC-6) was determined. Epithelial cells eluted from the rat jejunal cryptvillus axis expressed TGF-alpha mRNA at twofold higher levels in the villus tip than in the crypt and EGF receptor mRNA at sevenfold higher levels in the villus tip. Expression of these two mRNA transcripts in the subepithelium was low. Immunohistochemical staining showed TGF-alpha immunoreactivity predominantly in the epithelium and muscularis. Immunostaining of villus cells was uniform, whereas crypt cells did not stain. IEC-6 cells bound 125I-EGF to a single class of high-affinity (dissociation constant = 833 pM) receptors. EGF and TGF-alpha (10 ng/ml) only modestly stimulated IEC-6 cell growth in the presence of 5% serum but increased expression of the protooncogenes c-jun and c-myc threefold over control cells. These findings suggest that, among the potential physiological roles for TGF-alpha produced by the jejunal epithelium, promotion of cell migration and modulation of fluid and electrolyte transport may be as relatively important as stimulation of cell proliferation.

Idiopathic neonatal iron-storage disease

A 21-day-old infant presented with anemia, conjugated hyperbilirubinemia, hypoproteinemia, and a severe coagulopathy. The hospital course was marked by progressive hepatic failure, encephalopathy, and renal insufficiency. The infant died on day 15 of hospitalization. Postmortem examination showed diffuse hepatic fibrosis and marked siderosis of the liver, pancreas, kidney, adrenal glands, and the duodenal epithelium, with sparing of the reticuloendothelial system. These findings were characteristic of idiopathic neonatal iron-storage disease. Previously reported cases are summarized and discussed. An increased awareness and understanding of this rapidly fatal disorder will be important for genetic counseling and possibly in defining an aberrant mechanism in the handling of iron.

The cell biology of transforming growth factor beta

The TGF beta family of polypeptide growth factors regulates a remarkable diversity of cellular functions, many of which are not directly associated with cell growth. The present review has summarized many of the recent studies that have just begun to conceptually integrate this expanding array of TGF beta functions into the context of a three-dimensional, multicellular organ or tissue, be it normal or diseased. This fascinating research strongly implicates TGF beta as a key modulator of a wide variety of important physiologic and pathophysiologic processes.

Effects of EGF and PMA on the growth and proliferation of IEC-6 cells

Proliferation of an epithelial line (IEC-6) derived from the crypts of rat jejunum was induced with epidermal growth factor (EGF). EGF enhanced synthesis of protein, RNA, and DNA in a dose-dependent manner. Protein synthesis increased within 6-12 hours of exposure to EGF and remained elevated for 72 hours. Maximal 3H-thymidine incorporation occurred 48 hours after addition of EGF. The stimulatory effect of EGF on 3H-thymidine incorporation was two-fold greater in serum-free media than in media containing fetal calf serum (FCS). In contrast to EGF, phorbol-12-myristate-13-acetate (PMA) decreased 3H-thymidine uptake by IEC-6 cells and had no effect on either protein synthesis or RNA synthesis. EGF did not alter protein kinase-C activity in IEC-6 cells whereas PMA induced enzyme activity: activity was translocated from cytosol to membrane. Moreover, the EGF-associated increase in 3H-thymidine uptake was not altered by amiloride. These data suggest protein kinase-C activation may not be involved in the proliferation of IEC-6 cells.

Localization of transforming growth factor alpha and its receptor in gastric mucosal cells. Implications for a regulatory role in acid secretion and mucosal renewal

Transforming growth factor alpha (TGF alpha) shares with epidermal growth factor (EGF) structural homology (35%), a common cell-surface membrane receptor (TGF alpha/EGF receptor), and a nearly identical spectrum of biological activity, including inhibition of gastric acid secretion. Herein, we report expression of TGF alpha mRNA in normal gastric mucosa of the adult guinea pig, rat, and dog. TGF alpha mRNA was also detected in matched surgically resected gastric mucosa and adjacent gastric carcinoma from 10 patients, and in gastric mucosa adjacent to a benign ulcer from an additional patient. TGF alpha protein was quantitated by radioimmunoassay and was present in tumor and adjacent mucosa. TGF alpha/EGF receptor mRNA was also detected in gastric mucosa from all species studied. Localization of TGF alpha and TGF alpha/EGF receptor mRNA expression was examined in samples of unfractionated guinea pig gastric mucosa and from chief cell-enriched and parietal cell-enriched fractions. All samples exhibited TGF alpha and TGF alpha/EGF receptor expression. The TGF alpha signal was greatest in the parietal cell fraction (5.8-fold increase), but was also enhanced in the chief cell fraction (1.9-fold increase) relative to the unfractionated gastric mucosa. Like TGF alpha expression, TGF alpha/EGF receptor mRNA expression was most intense in the parietal cell-enriched fraction (7.8-fold increase), but was also increased in the chief cell-enriched fraction (2.7-fold increase) relative to the unfractionated guinea pig gastric mucosa. We conclude that TGF alpha and TGF alpha/EGF receptor genes are expressed in normal adult mammalian gastric mucosa. These findings, when interpreted in light of described actions of TGF alpha and EGF, provide evidence that local production of TGF alpha could play an important role in the regulation of acid secretion and mucosal renewal in the stomach.

Regulation of intestinal epithelial cell growth by transforming growth factor type beta

A nontransformed rat jejunal crypt cell line (IEC-6) expresses transforming growth factor type beta 1 (TGF-beta 1) mRNA, secretes latent 125I-labeled TGF-beta 1 competing activity into culture medium, and binds 125I-labeled TGF-beta 1 to specific, high-affinity (Kd = 3.7 pM) cell surface receptors. IEC-6 cell growth is markedly inhibited by TGF-beta 1 and TGF-beta 2 with half-maximal inhibition occurring between 0.1 and 1.0 ng of TGF-beta 1 per ml. TGF-beta 1-mediated growth inhibition is not associated with the appearance of biochemical markers of enterocyte differentiation such as alkaline phosphatase expression and sucrase activity. TGF-beta 1 (10 ng/ml) increases steady-state levels of its own mRNA expression within 8 hr of treatment of rapidly growing IEC-6 cells. In freshly isolated rat jejunal enterocytes that are sequentially eluted from the crypt villus axis, TGF-beta 1 mRNA expression is most abundant in terminally differentiated villus tip cells and least abundant in the less differentiated, mitotically active crypt cells. We conclude that TGF-beta 1 is an autoregulated growth inhibitor in IEC-6 cells that potentially functions in an autocrine manner. In the rat jejunal epithelium, TGF-beta 1 expression is most prominently localized to the villus tip--i.e., the region of the crypt villus unit that is characterized by the terminally differentiated phenotype. These data suggest that TGF-beta 1 may function in coordination of the rapid cell turnover typical for the intestinal epithelium.