Standardizing Randomized Controlled Trials in Celiac Disease: An International Multidisciplinary Appropriateness Study

BACKGROUND & AIMS

There is a need to develop safe and effective pharmacologic options for the treatment of celiac disease (CeD); however, consensus on the appropriate design and configuration of randomized controlled trials (RCTs) in this population is lacking.

METHODS

A 2-round modified Research and Development/University of California Los Angeles Appropriateness Method study was conducted. Eighteen gastroenterologists (adult and pediatric) and gastrointestinal pathologists voted on statements pertaining to the configuration of CeD RCTs, inclusion and exclusion criteria, gluten challenge, and trial outcomes. Two RCT designs were considered, representing the following distinct clinical scenarios for which pharmacotherapy may be used: trials incorporating a gluten challenge to simulate exposure; and trials evaluating reversal of histologic changes, despite attempted adherence to a gluten-free diet. Each statement was rated as appropriate, uncertain, or inappropriate, using a 9-point Likert scale.

RESULTS

For trials evaluating prevention of relapse after gluten challenge, participants adherent to a gluten-free diet for 12 months or more with normal or near-normal-sized villi should be enrolled. Gluten challenge should be FODMAPS (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) free, and efficacy evaluated using histology with a secondary patient-reported outcome measure. For trials evaluating reversal of villus atrophy, the panel voted it appropriate to enroll participants with a baseline villus height to crypt depth ratio ≤2 and measure efficacy using a primary histologic end point. Guidance for measuring histologic, endoscopic, and patient-reported outcomes in adult and pediatric patients with CeD are provided, along with recommendations regarding the merits and limitations of different end points.

CONCLUSIONS

We developed standardized recommendations for clinical trial design, eligibility criteria, outcome measures, gluten challenge, and disease evaluations for RCTs in patients with CeD.

Superior outcomes with double-balloon enteroscopy for small bowel lesion marking followed by intracorporeal as opposed to extracorporeal resection and reconstruction

BACKGROUND

Double-balloon enteroscopy (DBE) is used for the diagnosis and therapy of small bowel disease. Endoscopic sampling and marking small bowel lesions destined for surgery permit intracorporeal resection and reconstruction (IRR), thereby facilitating a complete minimally invasive technique. There are limited data that compare outcomes of IRR to conventional extracorporeal resection and reconstruction (ERR). The purpose of this study was to evaluate the surgical outcomes of patients undergoing pre-operative DBE for lesion marking followed by laparoscopic IRR compared to those undergoing ERR.

METHODS

A retrospective chart review was performed on patients who underwent DBE followed by small bowel resection from 2006 to 2017 at a single tertiary care medical center. IRR was defined as laparoscopic inspection to identify the lesion (previously marked by DBE or by laparoscopic-assisted DBE) followed by intra-abdominal bowel resection and anastomosis with specimen extraction via minimal extension of a laparoscopic port site. ERR was defined as extracorporeal resection and/or reconstruction performed via a conventional or mini-laparotomy abdominal incision.

RESULTS

A total of 82 patients met inclusion criteria and were reviewed. Thirty-two patients (39%) had ERR and 50 patients (61%) had IRR. The most common indications for DBE were small bowel bleeding (76%) and small bowel mass or thickening on prior imaging studies (16%). Successful DBE was higher in the IRR group when compared to the ERR group, but not significantly different (90% vs 75%, p-value 0.07). Patients who underwent IRR had faster bowel function recovery (2 vs 4 days, p < 0.01), shorter time to discharge (3 vs 7 days, p < 0.01), and fewer post-operative complications (10 vs 18; p < 0.01), when compared to the ERR group.

CONCLUSION

DBE successfully facilitated laparoscopic small bowel IRR and this approach was associated with faster return of bowel function, shorter recovery time, and decreased morbidity when compared to ERR.

Gall Bladder Disease and the Risk of Small Bowel Cancer—Results from a Nationwide Swedish Cohort Study

Simple Summary

Gallbladder disease (GBD) has been linked to small bowel cancer, but earlier reports have been based on a few cancer cases and no previous studies have adjusted for potential confounders. We report a 1.4-fold increased risk of small bowel adenocarcinoma, 1.8-fold increased risk of adenomas, and a 2.1-fold increased risk of carcinoids in patients with GBD compared to matched comparators. Absolute risks were low, however (<1 per 1000 patients followed for 10 years) for all three outcomes. We lacked detailed data on body mass index, cigarette smoking, and GBD biomarkers. Further results from an observational study, like ours, cannot establish a causal relationship or rule out the presence of residual confounding. The increased risk of carcinoid, seen 11–16 years after GBD diagnosis, may represent an etiologically plausible causal link to carcinoid development and warrants further study. The reported low absolute risks argue against targeted surveillance for small bowel cancer after GBD diagnosis. In conclusion, this study reports a moderately increased relative risk of small bowel cancers and adenomas in patients with GBD; absolute risks were however low.

Abstract

Background and aims: Small bowel cancer is a rare but rising malignancy. The etiology is poorly understood and there is a need for large-scale studies. Gallbladder disease (GBD), inducing localized inflammation, has been suggested to increase small bowel cancer risk. Methods: We retrieved nationwide data from Sweden’s 28 pathology departments on all adults (age 20–79) with pathology-confirmed GBD diagnosed in 1965–2017. In total 156,390 GBD patients were matched with up to 5 matched comparators from the general population and follow-up started one year after GBD diagnosis. We used stratified Cox regression to calculate hazard ratios (HRs) for small bowel adenocarcinoma, adenomas, and carcinoids. Results: During a median follow-up of 12 years, we identified 92 small bowel adenocarcinomas, 132 adenomas, and 81 carcinoid tumors in the GBD cohort. Corresponding incidence rates were 4.8, 6.9, and 4.2 per 100,000 person-years (PY), compared to 3.2, 3.2, and 1.8 in matched comparators. The adjusted HR was 1.42 (95% CI = 1.08–1.87) for small bowel adenocarcinoma, 1.79 (95% CI = 1.41–2.27) for adenoma, and 2.07 (95% CI = 1.52–2.81) for carcinoid. The excess cancer risk was most pronounced during the first year of follow-up for adenocarcinomas and during the first six years for adenomas while for carcinoids the HR peaked 10–15 years after start of follow-up. Conclusions: In this nationwide cohort study, GBD was associated with an increased risk of small bowel cancer. The excess risk of small bowel adenocarcinoma was mainly seen during the first years of follow-up while small bowel carcinoid risk peaked 11–16 years after GBD diagnosis.

Celiac Disease and Its Role in the Development of Metabolic Bone Disease

Celiac disease (CD) is an immune-mediated enteropathy that occurs in genetically susceptible hosts with the ingestion of gluten-containing products. Ongoing gluten consumption leads to intestinal damage, characterized by villous blunting and increased intraepithelial lymphocytes, resulting in malabsorption. Pertinent to the development of bone disease, malabsorption of calcium and vitamin D leads to secondary hyperparathyroidism and metabolic bone disease among individuals with CD. In this article, we review the pathogenesis of CD and the effects of malabsorption on bone health. Imbalances in bone resorption and formation particularly in individuals with CD and persistent disease activity ultimately lead to a state of bone loss and impaired mineralization. Initiation of a gluten-free diet is critical in the management of CD-related metabolic bone disease, demonstrating improvements in bone mineral density within the first year of dietary adherence.

Capsule Endoscopy and Enteroscopy in Celiac Disease

Celiac disease predominantly involves the proximal small bowel, but villus atrophy can be patchy, spare the duodenum, and be present more distally. Video capsule endoscopy is more sensitive than standard endoscopy to detect villus atrophy, and can define extent of disease, though it cannot obtain biopsies. Duodenal biopsy is the gold standard for diagnosis. Video capsule endoscopy assists in special circumstances when biopsy is not possible, and in equivocal diagnosis. Video capsule endoscopy and enteroscopy are recommended for evaluating complicated celiac disease, especially refractory celiac disease type II. Future developments include computer-assisted capsule programs and advanced capsule and enteroscope design.

Reovirus infection triggers inflammatory responses to dietary antigens and development of celiac disease

Viral infections have been proposed to elicit pathological processes leading to the initiation of T helper 1 (T_H1) immunity against dietary gluten and celiac disease (CeD). To test this hypothesis and gain insights into mechanisms underlying virus-induced loss of tolerance to dietary antigens, we developed a viral infection model that makes use of two reovirus strains that infect the intestine but differ in their immunopathological outcomes. Reovirus is an avirulent pathogen that elicits protective immunity, but we discovered that it can nonetheless disrupt intestinal immune homeostasis at inductive and effector sites of oral tolerance by suppressing peripheral regulatory T cell (pT_reg) conversion and promoting T_H1 immunity to dietary antigen. Initiation of T_H1 immunity to dietary antigen was dependent on interferon regulatory factor 1 and dissociated from suppression of pT_reg conversion, which was mediated by type-1 interferon. Last, our study in humans supports a role for infection with reovirus, a seemingly innocuous virus, in triggering the development of CeD.

Celiac patients' attitudes regarding novel therapies

BACKGROUND

The only current treatment for celiac disease (CD) is a gluten-free diet (GFD). Novel therapies are in development to supplement or replace a GFD. Knowledge of patients' attitudes toward these therapies is limited. The aim of this study was to determine attitudes about novel therapies in securely diagnosed patients with CD on a GFD and to correlate factors associated with these attitudes.

METHODS

A survey was created with two scenarios: a novel therapy that protects against cross contamination while on a GFD and one that allows intentional gluten consumption. The survey also included the Celiac Dietary Adherence Test and the CD Quality of Life (QOL) surveys.

RESULTS

A total of 182/284 (64%) CD patients completed the survey. Significantly more respondents would take a novel therapy to protect against cross contamination compared with one that allows intentional gluten consumption (87% vs. 65%; P<0.001). This difference was significant among women but not men. In both scenarios, protection against bowel inflammation was significantly more important than symptom control, and side effects were more important than cost. For a novel therapy that would allow intentional gluten consumption, a one-time injection was preferred over a daily pill, and patients willing to take this therapy had significantly lower QOL scores.

CONCLUSIONS

CD patients on a GFD are interested in novel therapies. There were notable differences in attitudes by gender and QOL. Considering patient preferences, drugs with daily or less frequent dosing that protect against bowel inflammation from gluten cross contamination would be best accepted.

Gastrostomy tube placement is safe in advanced amyotrophic lateral sclerosis

OBJECTIVES

To evaluate the safety and effect on survival of insertion of a gastrostomy tube (G-tube) in patients with amyotrophic lateral sclerosis (ALS) who have upright forced vital capacity (uFVC) ≤ 50% predicted. Current guidelines, which are based on higher rates of post-procedure complications in ALS patients with advanced respiratory dysfunction, have led to a recommendation to perform G-tube insertion before the FVC drops to <50% predicted, even when the patient has no significant dysphagia.

METHODS

We assessed 41 ALS patients who received a G-tube, mostly by insertion of a percutaneous endoscopic gastrostomy (PEG) tube by a dedicated team that included a gastroenterologist and one of two anesthesiologists using Monitored Anesthesia Care with deep sedation, and 61 patients who did not receive a G-tube. uFVC was ≤50% predicted in 12 of 41 patients who received a G-tube and in 18 of 61 who did not.

RESULTS

The procedure was safe regardless of FVC status, with low rates of post-operative complications in both low and high FVC groups. There was no survival benefit for patients who received a G-tube when compared with those who did not.

DISCUSSION

PEG insertion is safe in ALS patients with significant respiratory muscle weakness when performed by a dedicated team, which suggests that the recommendation for G-tube placement should not be based on the patient's respiratory status.

Small Bowel Endoscopy

OPINION STATEMENT

The small bowel is a challenging area for endoscopic evaluation and therapy due to its length and angulated configuration. A small lumen diameter and segmental peristalsis made it a perfect fit for examination by a novel ingestible wireless camera in a capsule. The development of capsule endoscopy changed the diagnosis and management of bleeding lesions, ulcers, and tumors deep in the small bowel, allowing earlier diagnosis with excellent patient acceptance. Device-assisted enteroscopy revolutionized small bowel therapy, particularly management of bleeding, Peutz-Jeghers polyposis, and tumor marking for minimally invasive surgery. Small bowel stricture dilation in select patients is safe and effective. Tools for a spectrum of small bowel therapies are available but remain suboptimal to tackle lesions on angulated folds deep in the small bowel. Universal terminology to describe the endoscopic appearance of vascular lesions will facilitate studies of endoscopic and medical therapy. The future holds improvements in imaging, easier advancement through the small bowel, and therapeutic capacity. This review focuses on methods of small bowel endoscopy, therapy, and outcomes.

Clinical nutrition in the hepatogastroenterology curriculum

Gastroenterology (GE) used to be considered a subspecialty of internal medicine. Today, GE is generally recognized as a wide-ranging specialty incorporating capacities, such as hepatology, oncology and interventional endoscopy, necessitating GE-expert differentiation. Although the European Board of Gastroenterology and Hepatology has defined specific expertise areas in Advanced endoscopy, hepatology, digestive oncology and clinical nutrition, training for the latter topic is lacking in the current hepatogastroenterology (HGE) curriculum. Given its relevance for HGE practice, and being at the core of gastrointestinal functioning, there is an obvious need for training in nutrition and related issues including the treatment of disease-related malnutrition and obesity and its associated metabolic derangements. This document aims to be a starting point for the integration of nutritional expertise in the HGE curriculum, allowing a central role in the management of malnutrition and obesity. We suggest minimum endpoints for nutritional knowledge and expertise in the standard curriculum and recommend a focus period of training in nutrition issues in order to produce well-trained HGE specialists. This article provides a road map for the organization of such a training program. We would highly welcome the World Gastroenterology Organisation, the European Board of Gastroenterology and Hepatology, the American Gastroenterology Association and other (inter)national Gastroenterology societies support the necessary certifications for this item in the HGE-curriculum.

Gastro 2013 APDW/WCOG Shanghai working party report: chronic diarrhea: definition, classification, diagnosis

Diarrhea is best defined as passage of loose stools often with more frequent bowel movements. For clinical purposes, the Bristol Stool Form Scale works well to distinguish stool form and to identify loose stools. Laboratory testing of stool consistency has lagged behind. Acute diarrhea is likely to be due to infection and to be self-limited. As diarrhea becomes chronic, it is less likely to be due to infection; duration of 1 month seems to work well as a cut-off for chronic diarrhea, but detailed scientific knowledge is missing about the utility of this definition. In addition to duration of diarrhea, classifications by presenting scenario, by pathophysiology, and by stool characteristics (e.g. watery, fatty, or inflammatory) may help the canny clinician refine the differential diagnosis of chronic diarrhea. In this regard, a careful history remains the essential part of the evaluation of a patient with diarrhea. Imaging the intestine with endoscopy and radiographic techniques is useful, and biopsy of the small intestine and colon for histological assessment provides key diagnostic information. Endomicroscopy and molecular pathology are only now being explored for the diagnosis of chronic diarrhea. Interest in the microbiome of the gut is increasing; aside from a handful of well-described infections because of pathogens, little is known about alterations in the microbiome in chronic diarrhea. Serological tests have well-defined roles in the diagnosis of celiac disease but have less clearly defined application in autoimmune enteropathies and inflammatory bowel disease. Measurement of peptide hormones is of value in the diagnosis and management of endocrine tumors causing diarrhea, but these are so rare that these tests are of little value in screening because there will be many more false-positives than true-positive results. Chemical analysis of stools is of use in classifying chronic diarrhea and may limit the differential diagnosis that must be considered, but interpretation of the results is still evolving. Breath tests for assessment of carbohydrate malabsorption, small bowel bacterial overgrowth, and intestinal transit are fraught with technical limitations that decrease sensitivity and specificity. Likewise, tests of bile acid malabsorption have had limited utility beyond empirical trials of bile acid sequestrants.

Small bowel imaging in celiac disease

Celiac disease is a common inflammatory disease of the small intestine triggered by gluten in genetically susceptible individuals. Diagnosis is made by serologic testing and upper endoscopy with small bowel biopsy in most individuals. Celiac patients may present with abdominal pain or nonspecific gastrointestinal complaints that result in radiologic imaging before diagnosis of celiac disease. Wireless video capsule endoscopy, device-assisted enteroscopy, and enterography allow careful examination of the entire small bowel and targeted sampling of suspicious lesions. This review focuses on the role of device-assisted enteroscopy and radiologic imaging, in particular enterography, in celiac disease.

Small bowel tumors

Although rare, small bowel tumors may cause significant morbidity and mortality if left undetected. New endoscopic modalities allow full examination of the small bowel with improved diagnosis. However, isolated mass lesions may be missed by capsule endoscopy or incomplete balloon-assisted enteroscopy. Therefore the use of radiologic imaging and intraoperative enteroscopy for diagnosis should not be forgotten. Endoscopic resection of small bowel polyps and certain vascular tumors is possible but requires proper training. Advances in endoscopic tools are likely to broaden the endoscopic management of small bowel tumors. This article describes the general features of small bowel tumors, clinical presentation, and diagnostic tests followed by a description of the more common tumor types and their management.

Long-term outcomes after double-balloon enteroscopy for obscure gastrointestinal bleeding

BACKGROUND & AIMS

Long-term outcomes after doubleballoon enteroscopy (DBE), performed for the evaluation of obscure gastrointestinal bleeding, have not been determined.

METHODS

We invited 274 patients undergoing DBE at Stanford University or the University of Chicago between 2004 and 2006 to participate in the study; 135 (49%) agreed (mean age, 64 +/- 14.8; range, 23-90 years). Telephone interviews were conducted at a mean of 11 and 30 months after DBE.

RESULTS

Arteriovenous malformations (AVMs) were detected in 43% of the cohort. One hundred one patients (37%; 56 with overt, 45 with occult bleeding) were interviewed 12 +/- 5 (range, 6-26) months after DBE. At 12 months, 43% reported no further overt bleeding or iron/transfusion needs, 23% reported overt bleeding, and 35% reported ongoing iron and/or transfusions. Eighty-five patients (31%) participated in the second survey, conducted 30 +/- 5.7 (range, 19-51) months after DBE. Fifty (59%) reported no overt bleeding or iron/transfusion needs, 20 (24%) reported overt bleeding, and 15 (18%) reported ongoing iron and/or transfusions. In the 40 patients evaluated after endoscopic treatment for AVMs, 17 (43%) reported no bleeding or iron therapy at 12 months and 16 of 29 (55%) at 30 months. Of the 40 patients with normal DBE examinations to the depth of insertion, 19 of 40 (48%) reported no bleeding or iron/transfusion needs at 12 months and 25 of 43 (58%) at 30 months.

CONCLUSIONS

At 30 months after DBE, up to 60% of patients report no further bleeding. Patients with AVMs or normal examinations to the depth of insertion are most likely to report recurrent hemorrhage.

Screening for celiac disease in short bowel syndrome

BACKGROUND

Malabsorptive diarrhea due to short bowel syndrome (SBS) results in nutrition compromise, often requiring parenteral nutrition (PN). Activation of latent celiac disease can occur after gastrointestinal surgery. Our objective was to determine whether undiagnosed celiac disease contributes to malabsorption in patients with SBS.

METHODS

Adult subjects with SBS were tested for celiac disease using immunoglobulin A (IgA) tissue transglutaminase (TTG) antibody and total IgA level. Subjects with an elevated IgA tissue transglutaminase were offered upper endoscopy with biopsies of the duodenum.

RESULTS

Eighteen subjects were enrolled. The subjects were predominantly white, and the most common cause of SBS was Crohn's disease. The mean length of remaining small bowel was 93.1 +/- 54.6 cm. All subjects had undergone surgeries, resulting in loss of the ileocecal valve. Five subjects were found to have an elevated total IgA. A single patient was found to have an elevated IgA tissue transglutaminase antibody, and subsequent endoscopy demonstrated active gastroduodenal Crohn's disease, without features of celiac disease.

CONCLUSIONS

No subjects were IgA deficient, but 5 subjects were found to have elevated IgA levels. Undiagnosed celiac disease did not contribute to malabsorption in our small cohort of predominantly white SBS patients. Larger studies are warranted.

P2Z purinoceptors

In response to tetra-anionic ATP4-, P2Z receptors signal opening of a non-selective plasma membrane pore which permits passage across cell membranes of ions, nucleotides and other small molecules that are usually membrane impermeant. P2Z receptor-induced pores on murine macrophages, macrophage-like cell lines and human culture-matured macrophages are permeable to molecules of up to 831 Da. The function of P2Z receptors is unknown. Also unknown is whether the binding site for ATP4- and the transmembrane pore, the properties that characterize P2Z receptors, reside on a single protein or reflect the activities of two or more proteins. That ATP(4-) -unresponsive cell lines do not express connexin 43 has led Beyer and Steinberg to suggest that opening or surface expression of this gap junction protein is induced by P2Z receptors. Xenopus oocytes, injected with cRNA transcribed from a pool of 100 cDNA clones isolated from a murine macrophage-derived cDNA library, and treated with ATP4-, express a non-selective membrane conductance characteristic of P2Z receptors. The conductance induced with cRNA is smaller than that induced by mRNA from macrophages, suggesting the presence of a dominant subunit of a multicomponent receptor in this pool of 100 cDNA clones.

Hepatitis B virus reactivation after kidney transplantation and new onset lymphoma

A case of hepatitis B virus (HBV) reactivation after kidney transplantation is reported. The presence of antibodies against hepatitis B surface antigen (HBsAg) and hepatitis B core antigen (HBcAg) before transplantation indicated previous infection with HBV. Eight years after transplantation, a diffuse, large B-cell lymphoma occurred, and the patient was positive for HBsAg and hepatitis B e antigen, in association with normal activity of serum aminotransferases. Postmortem liver histology did not show any sign of portal tract or lobular inflammation despite the presence at immunostaining of extensive intranuclear and cytoplasmic positivity for HBcAg, indicating active viral replication. Natural immunity to HBV may not protect against reactivation in patients with a suppressed immune system. In this setting, periodic follow-up of HBV serology in patients at highest risk for HBV reactivation to allow for early diagnosis and prompt treatment with lamivudine is highly recommended.

Mitochondrial neurogastrointestinal encephalomyopathy: an autosomal recessive disorder due to thymidine phosphorylase mutations

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder defined clinically by severe gastrointestinal dysmotility; cachexia; ptosis, ophthalmoparesis, or both; peripheral neuropathy; leukoencephalopathy; and mitochondrial abnormalities. The disease is caused by mutations in the thymidine phosphorylase (TP) gene. TP protein catalyzes phosphorolysis of thymidine to thymine and deoxyribose 1-phosphate. We identified 21 probands (35 patients) who fulfilled our clinical criteria for MNGIE. MNGIE has clinically homogeneous features but varies in age at onset and rate of progression. Gastrointestinal dysmotility is the most prominent manifestation, with recurrent diarrhea, borborygmi, and intestinal pseudo-obstruction. Patients usually die in early adulthood (mean, 37.6 years; range, 26-58 years). Cerebral leukodystrophy is characteristic. Mitochondrial DNA (mtDNA) has depletion, multiple deletions, or both. We have identified 16 TP mutations. Homozygous or compound heterozygous mutations were present in all patients tested. Leukocyte TP activity was reduced drastically in all patients tested, 0.009 +/- 0.021 micromol/hr/mg (mean +/- SD; n = 16), compared with controls, 0.67 +/- 0.21 micromol/hr/mg (n = 19). MNGIE is a recognizable clinical syndrome caused by mutations in thymidine phosphorylase. Severe reduction of TP activity in leukocytes is diagnostic. Altered mitochondrial nucleoside and nucleotide pools may impair mtDNA replication, repair, or both.

Bone mass and gastrointestinal disease

Several gastrointestinal and liver diseases impair the absorption of calcium, phosphate, and/or vitamin D, and are associated with an increased incidence of bone disease. Changes in bone mineral density (BMD) using dual-energy X-ray absorptiomety (DXA) have been best studied in the malabsorptive disorder, celiac disease. Celiac disease is an inflammatory condition of the small intestine triggered by ingesting gluten present in wheat, rye, or barley. Chronic inflammation leads to intestinal atrophy and nutrient malabsorption. The disease affects the proximal small bowel; the site where calcium is best absorbed. About 70% of adults with celiac disease have abnormally low BMD values. Treatment with a gluten-free diet increases BMD, but not to normal values. As celiac disease may not be detected until adult life, the failure to reach normal BMD on a gluten-free diet can be explained, at least in part, by the failure to reach peak bone mass. All individuals with malabsorptive disorders should be screened for secondary bone disease. The development of easier and less expensive methods to assess BMD will facilitate screening those at risk for bone disease.

Zinc and intestinal function

Zinc is an abundant trace element in the human body that is essential for growth and development and immune function. It is important for the formation of biomembranes and zinc finger motifs found in DNA transcription factors and has catalytic function in metalloenzymes. The intestine is the site of zinc absorption and the major route of zinc excretion. Dietary inadequacy or conditions that decrease zinc absorption or increase its losses from the gastrointestinal tract, urine, or skin may quickly cause zinc deficiency due to the limited availability of rapidly exchangeable zinc pools in the body. Diarrhea is both a sign and a cause of zinc deficiency. The mechanism by which zinc deficiency causes diarrhea is not known. At this time, there is no readily available sensitive test for the detection of zinc deficiency, and therefore clinical suspicion remains the main mode of detection. In some individuals with diarrheal disease, zinc supplementation lessens diarrhea. Those receiving prolonged supplemental zinc therapy need to be monitored for copper deficiency.

Regulation of endocytic trafficking and acidification are independent of the cystic fibrosis transmembrane regulator

Cystic fibrosis is associated with mutations of the cystic fibrosis transmembrane regulator (CFTR), a cAMP-regulated plasma membrane Cl- channel. Mutations in the CFTR have been reported to not only impair Cl-transport at the plasma membrane but also inhibit organelle acidification and disrupt cAMP-regulated plasma membrane recycling. Comparisons of cultured pancreatic adenocarcinoma cells expressing the delta 508 mutant CFTR (CFPAC-1 cells) with genetically matched CFPAC-1 cells transfected with the wild-type CFTR demonstrate that expression of wild-type CFTR restores cAMP-mediated plasma membrane Cl- transport, but has no effect on pH regulation of endosomes labeled with either transferrin or wheat germ agglutinin. Endosome pH was, in all cases, similar in the two cell lines and unaffected by treatment with the cAMP agonist forskolin. Forskolin treatment had no effect on transferrin internalization, but increased recycling by 30-40% in both cell lines. The kinetics of wheat germ agglutinin recycling were negligibly affected by forskolin in either cell line. These results demonstrate that endocytic acidification and cAMP-mediated endocytic protein redistribution are similar in genetically matched CFPAC-1 cells which differ only in the expression of mutant or wild-type CFTR.

Inhibition of Na/H exchange in avian intestine by atrial natriuretic factor

Effects of 8-bromo-cGMP (8-Br-cGMP) and synthetic rat atriopeptin III (APIII) on sodium absorption by isolated chicken villus enterocytes and intact chicken ileal mucosa were determined. In isolated cells, both agents significantly decreased initial rates of influx of 22Na and caused a persistent decrease in intracellular pH (pHi); effects that are not additive to those caused by amiloride (10(-3) M). The ED50 for APIII was 0.3 nM. In intact mucosa, both 8-Br-cGMP (10(-4) M) and 5-(N-methyl-N-isobutyl)amiloride (MIBA) (10(-5) M) reduced JNams and JNa.net, their effects were not additive. APIII (10(-7) M) significantly increased cellular cGMP but not cAMP. Both 8-Br-cGMP (10(-4) M) and APIII (10(-7) M) stimulated a persistent increase in cytosolic calcium (Cai), which could be prevented by pretreating the cells with the cytosolic calcium buffering agent MAPTAM or with H-8, an inhibitor of cyclic nucleotide-dependent protein kinases. Furthermore, pretreatment of cells with H-8 or the calmodulin inhibitor, calmidazolium (CM), prevented the effects of 8-Br-cGMP and APIII on pHi. However, the pHi response to subsequent addition of the calcium-ionophore ionomycin was blocked only by CM and not by H-8. These data suggest that APIII and 8-Br-cGMP inhibit amiloride-sensitive Na/H exchange by increasing Cai, an event requiring activation of cGMP-dependent protein kinase.

Calcium-mediated cyclic AMP inhibition of Na-H exchange in small intestine

8-Bromo cyclic AMP (cAMP) (10(-4) M) inhibits Na absorption in isolated chicken enterocytes as has been reported previously. Direct measurements of intracellular pH (pHi) using 5,6-carboxyfluorescein diacetate showed that both 8-bromo cAMP and the diuretic amiloride (10(-3) M) stimulated a persistent decrease in pHi of approximately 0.1 pH units, effects that were Na dependent and were not additive when cells were stimulated with both agents. These results suggest inhibition of an amiloride-sensitive Na/H exchange by cAMP. Direct measurements of intracellular Ca [Ca]i were also made using quin 2. 8-Bromo cAMP (10(-4) M) stimulated an immediate and persistent (greater than 10 min) increase in [Ca]i of approximately 20 nM, an effect that was not dependent on extracellular Ca. Pretreatment of cells with the specific calmodulin inhibitor calmidazolium (10(-7) M) and the intracellular Ca-buffering agent MAPTAM blocked cAMP's effects on pH and Na uptake, but did not interfere with amiloride's effects. An increase in [Ca]i stimulated by the Ca ionophore A23187 (10(-6) M) was sufficient by itself to decrease pHi and inhibit amiloride-sensitive Na influx in isolated enterocytes. We conclude that cAMP stimulates the release of endogenous Ca in isolated enterocytes. This increase in [Ca]i appears to be essential for inhibition of amiloride-sensitive Na-H exchange by this cyclic nucleotide.