Characterization of esophageal submucosal glands in pig tissue and cultures

Oral viscous budesonide solution for enhanced localized treatment of eosinophilic esophagitis through improved mucoadhesion and permeation

Eosinophilic esophagitis (EoE) is a chronic inflammatory disease of the esophagus that is immune/antigen-mediated and often requires targeted treatment. In clinical practice, an oral viscous budesonide suspension prepared by adding sucralose to a budesonide suspension for inhalation (Pulmicort®) is used to treat adult EoE and enhance retention in the esophageal mucosa. Inspired by this off-label drug use, oral viscous budesonide solutions (OVBSs) were developed in this study, and their capacities for adhesion, permeation, and stability were explored. Given the insolubility of budesonide as a BCS II drug, we first evaluated its equilibrium solubility and found that Transcutol® HP was an excellent choice for creating an OVBS at a concentration of 0.2 mg/g. The rheological properties of the OVBSs were evaluated with a rheometer, and shear-thinning, which aids in swallowing, was observed. The addition of hydroxyethyl cellulose (HEC) increased the adhesion strength of the preparation, which was associated with the hydration and thickening mechanism. This result was confirmed in a dynamic gelation study and in vitro elution experiment conducted with porcine esophagus tissue. Furthermore, the permeabilities of the OVBSs in the porcine esophagus were evaluated with a Franz diffusion cell device. >80 % of the budesonide was released after 24 h, and the release profile was similar to that of the solution. To explore the storage conditions of OVBSs, critical factors such as pH, content, and impurities were determined. It was found that OVBSs exhibited different behaviors at different pH values and temperatures. Notably, the OVBSs containing 1.7 % HEC could be stored for >6 months at a temperature of 5 °C ± 3 °C and a pH of 4.5 without significant degradation. Overall, this study demonstrated that OVBSs have the potential to adhere to the esophageal mucosa, permeate the tissue, and remain stable during storage. Moreover, OVBSs exhibit a distinct advantage over traditional converted inhalation-to-oral budesonide therapies by enabling flexible dose adjustment in clinical applications, thereby potentially minimizing systemic side effects commonly associated with oral glucocorticoid administration.

Promises and Limitations of Current Models for Understanding Barrett's Esophagus and Esophageal Adenocarcinoma

BACKGROUND & AIMS

This review was developed to provide a thorough and effective update on models relevant to esophageal metaplasia, dysplasia, and carcinogenesis, focusing on the advantages and limitations of different models of Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC).

METHODS

This expert review was written on the basis of a thorough review of the literature combined with expert interpretation of the state of the field. We emphasized advances over the years 2012-2023 and provided detailed information related to the characterization of established human esophageal cell lines.

RESULTS

New insights have been gained into the pathogenesis of BE and EAC using patient-derived samples and single-cell approaches. Relevant animal models include genetic as well as surgical mouse models and emphasize the development of lesions at the squamocolumnar junction in the mouse stomach. Rat models are generated using surgical approaches that directly connect the small intestine and esophagus. Large animal models have the advantage of including features in human esophagus such as esophageal submucosal glands. Alternatively, cell culture approaches remain important in the field and allow for personalized approaches, and scientific rigor can be ensured by authentication of cell lines.

CONCLUSIONS

Research in BE and EAC remains highly relevant given the morbidity and mortality associated with cancers of the tubular esophagus and gastroesophageal junction. Careful selection of models and inclusion of human samples whenever possible will ensure relevance to human health and disease.

Comparative Histology and Histochemistry of the Parotid Gland and Mandibular Gland in the Lowland Tapir (Tapirus terrestris Perissodactyla) and Aardvark (Orycteropus afer Tubulidentata)

In terrestrial mammals, the parotid and mandibular glands secrete different types of saliva into the oral cavity. Both glands were obtained from two female lowland tapirs (Tapirus terrestris) and one female aardvark (Orycteropus afer) from the Wroclaw Zoological Garden (Poland) and examined by light microscopy (hematoxylin and eosin, mucicarmine, periodic acid-Schiff, Alcian blue pH 1.0, Alcian blue pH 2.5, Alcian blue pH 2.5/PAS, and Hale's dialysed iron). Both the parotid glands observed in the lowland tapir and aardvark were compound alveolar serous secretory units, and in both species, the secretion was composed of neutral and acidic mucopolysaccharides (sialo and sulfated mucins). However, in both the lowland tapir and aardvark, a histological examination found the stroma of the mandibular gland was divided into very large lobes by poorly marked connective tissue. While many interlobar and striated ducts were found in the aardvark, very few were found in the lowland tapir. The mandibular gland was a branched tubular (mucous secretion) type in the lowland tapir, but it was a branched tubuloalveolar (mucous-serous) type in the aardvark. In all tested glands, the secretion was composed of neutral mucopolysaccharides, acid-sulfated mucosubstances, and sialomucins.

An Endoscopic and Histologic Study on Healing of Radiofrequency Ablation Wounds in Patients With Barrett's Esophagus

INTRODUCTION

Radiofrequency ablation (RFA) of Barrett's esophagus (BE) inflicts a wound spanning 3 epithelial types (stratified squamous, Barrett's metaplasia, gastric epithelium), yet the esophageal injury heals almost completely with squamous epithelium. Knowledge of how this unique wound heals might elucidate mechanisms underlying esophageal metaplasia. We aimed to prospectively and systematically characterize the early endoscopic and histologic features of RFA wound healing.

METHODS

Patients with nondysplastic BE had endoscopy with systematic esophageal photographic mapping, biopsy, and volumetric laser endomicroscopy performed before and at 1, 2, and 4 weeks after RFA.

RESULTS

Seven patients (6 men; mean age 56.1 ± 10.9 years) completed this study. Squamous re-epithelialization of RFA wounds did not only progress exclusively through squamous cells extending from the proximal wound edge but also progressed through islands of squamous epithelium sprouting throughout the ablated segment. Volumetric laser endomicroscopy revealed significant post-RFA increases in subepithelial glandular structures associated with the squamous islands. In 2 patients, biopsies of such islands revealed newly forming squamous epithelium contiguous with immature-appearing squamous cells arising from esophageal submucosal gland ducts. Subsquamous intestinal metaplasia (SSIM) was found in biopsies at 2 and/or 4 weeks after RFA in 6 of 7 patients.

DISCUSSION

RFA wounds in BE are re-epithelialized, not just by squamous cells from the proximal wound margin but by scattered squamous islands in which esophageal submucosal gland duct cells seem to redifferentiate into the squamous progenitors that fuel squamous re-epithelialization. SSIM can be found in most patients during the healing process. We speculate that this SSIM might underlie Barrett's recurrences after apparently successful eradication.

Mechanisms and pathophysiology of Barrett oesophagus

Barrett oesophagus, in which a metaplastic columnar mucosa that can predispose individuals to cancer development lines a portion of the distal oesophagus, is the only known precursor of oesophageal adenocarcinoma, the incidence of which has increased profoundly over the past several decades. Most evidence suggests that Barrett oesophagus develops from progenitor cells at the oesophagogastric junction that proliferate and undergo epithelial-mesenchymal transition as part of a wound-healing process that replaces oesophageal squamous epithelium damaged by gastroesophageal reflux disease (GERD). GERD also seems to induce reprogramming of key transcription factors in the progenitor cells, resulting in the development of the specialized intestinal metaplasia that is characteristic of Barrett oesophagus, probably through an intermediate step of metaplasia to cardiac mucosa. Genome-wide association studies suggest that patients with GERD who develop Barrett oesophagus might have an inherited predisposition to oesophageal metaplasia and that there is a shared genetic susceptibility to Barrett oesophagus and to several of its risk factors (such as GERD, obesity and cigarette smoking). In this Review, we discuss the mechanisms, pathophysiology, genetic predisposition and cells of origin of Barrett oesophagus, and opine on the clinical implications and future research directions.

Esophagogastric junction adenocarcinoma shares characteristics with gastric adenocarcinoma: Literature review and retrospective multicenter cohort study

The incidence of esophagogastric junction (EGJ) adenocarcinoma has been gradually increasing in Asia, just like in Western countries a few decades ago. Despite recent advances in next-generation sequencing and multimodal treatments, EGJ adenocarcinoma is still an aggressive malignancy with poor outcomes. Clinically, EGJ adenocarcinoma can be separated into Barrett's adenocarcinoma and cardiac adenocarcinoma, with frequent similarities observed. Barrett's adenocarcinoma is likely to be of gastric origin in terms of its premalignant background, risk factors, and stem cell regulators. Recent comprehensive genomic analyses suggest that immunotherapy may be essential for high-level microsatellite instability (MSI-H)- and Epstein-Barr virus (EBV)-associated subtypes, and against the immunosuppressive phenotype in genomically stable (GS) subtypes, in the treatment of EGJ and gastric adenocarcinoma. Although the chromosomal instability (CIN) subtype dominates EGJ adenocarcinoma, there is still a need to investigate the other molecular subtypes and their targets. Because of the distinctive characteristics of tumor location of EGJ adenocarcinoma, we also described the results of a multicenter cohort study of EGJ adenocarcinoma, comparing Siewert type I (distal esophagus), II (cardia of the stomach), and III (subcardia) tumors. We show that type I tumors were frequently accompanied by Barrett's esophagus (78%, P < .0001), with a significantly unfavorable outcome (multivariate EGJ-cancer-specific mortality hazard ratio = 1.81, 95% CI, 1.06-2.97; P = .031). In addition, over half (56%) of these cases experienced disease recurrence in the lymph nodes. Our findings suggest that Barrett's adenocarcinoma may be an aggressive phenotype of EGJ adenocarcinoma due to the potential risk of tumor spread through the complex lympho-vascular network of the esophagus.

Ussing Chamber Methods to Study the Esophageal Epithelial Barrier

The Ussing chamber was developed in 1949 by Hans Ussing and quickly became a powerful tool to study ion and solute transport in epithelia. The chamber has two compartments strictly separating the apical and basolateral sides of the tissue under study. The two sides of the tissue are connected via electrodes to a modified electrometer/pulse generator that allows measurement of electrical parameters, namely, transepithelial voltage, current, and resistance. Simultaneously, permeability of the tissue to specific solutes or markers can be monitored by using tracers or isotopes to measure transport from one side of the tissue to the other. In this chapter, we will describe the use of the Ussing chamber to study the barrier properties of the mouse esophageal epithelium. We will also briefly describe the use of the modified Ussing chamber to simultaneously study transepithelial and cellular electrophysiology in the rabbit esophageal epithelium. Lastly, we will cover the use of the Ussing chamber to study bicarbonate secretion in the pig esophagus. These examples highlight the versatility of the Ussing chamber technique in investigating the physiology and pathophysiology of epithelia including human biopsies.

Pathogenesis and Cells of Origin of Barrett's Esophagus

In patients with Barrett's esophagus (BE), metaplastic columnar mucosa containing epithelial cells with gastric and intestinal features replaces esophageal squamous mucosa damaged by gastroesophageal reflux disease. This condition is estimated to affect 5.6% of adults in the United States, and is a major risk factor for esophageal adenocarcinoma. Despite the prevalence and importance of BE, its pathogenesis is incompletely understood and there are disagreements over the cells of origin. We review mechanisms of BE pathogenesis, including transdifferentiation and transcommitment, and discuss potential cells of origin, including basal cells of the squamous epithelium, cells of esophageal submucosal glands and their ducts, cells of the proximal stomach, and specialized populations of cells at the esophagogastric junction (residual embryonic cells and transitional basal cells). We discuss the concept of metaplasia as a wound-healing response, and how cardiac mucosa might be the precursor of the intestinal metaplasia of BE. Finally, we discuss shortcomings in current diagnostic criteria for BE that have important clinical implications.

A slippery slope: On the origin, role and physiology of mucus

The mucosa of the gastrointestinal tract, eyes, nose, lungs, cervix and vagina is lined by epithelium interspersed with mucus-secreting goblet cells, all of which contribute to their unique functions. This mucus provides an integral defence to the epithelium against noxious agents and pathogens. However, it can equally act as a barrier to drugs and delivery systems targeting epithelial passive and active transport mechanisms. This review highlights the various mucins expressed at different mucosal surfaces on the human body, and their role in creating a mucoid architecture to protect epithelia with specialized functions. Various factors compromising the barrier properties of mucus have been discussed, with an emphasis on how disease states and microbiota can alter the physical properties of mucus. For instance, Akkermansia muciniphila, a bacterium found in higher levels in the gut of lean individuals induces the production of a thickened gut mucus layer. The aims of this article are to elucidate the different physiological, biochemical and physical properties of bodily mucus, a keen appreciation of which will help circumvent the slippery slope of challenges faced in achieving effective mucosal drug and gene delivery.

Porcine Esophageal Submucosal Gland Culture Model Shows Capacity for Proliferation and Differentiation

BACKGROUND & AIMS

Although cells comprising esophageal submucosal glands (ESMGs) represent a potential progenitor cell niche, new models are needed to understand their capacity to proliferate and differentiate. By histologic appearance, ESMGs have been associated with both overlying normal squamous epithelium and columnar epithelium. Our aim was to assess ESMG proliferation and differentiation in a 3-dimensional culture model.

METHODS

We evaluated proliferation in human ESMGs from normal and diseased tissue by proliferating cell nuclear antigen immunohistochemistry. Next, we compared 5-ethynyl-2'-deoxyuridine labeling in porcine ESMGs in vivo before and after esophageal injury with a novel in vitro porcine organoid ESMG model. Microarray analysis of ESMGs in culture was compared with squamous epithelium and fresh ESMGs.

RESULTS

Marked proliferation was observed in human ESMGs of diseased tissue. This activated ESMG state was recapitulated after esophageal injury in an in vivo porcine model, ESMGs assumed a ductal appearance with increased proliferation compared with control. Isolated and cultured porcine ESMGs produced buds with actively cycling cells and passaged to form epidermal growth factor-dependent spheroids. These spheroids were highly proliferative and were passaged multiple times. Two phenotypes of spheroids were identified: solid squamous (P63+) and hollow/ductal (cytokeratin 7+). Microarray analysis showed spheroids to be distinct from parent ESMGs and enriched for columnar transcripts.

CONCLUSIONS

Our results suggest that the activated ESMG state, seen in both human disease and our porcine model, may provide a source of cells to repopulate damaged epithelium in a normal manner (squamous) or abnormally (columnar epithelium). This culture model will allow the evaluation of factors that drive ESMGs in the regeneration of injured epithelium. The raw microarray data have been uploaded to the National Center for Biotechnology Information Gene Expression Omnibus (accession number: GSE100543).

Large Animal Models: The Key to Translational Discovery in Digestive Disease Research

Gastrointestinal disease is a prevalent cause of morbidity and mortality and the use of animal models have been instrumental in studying mechanisms of digestive pathophysiology. As investigators attempt to translate the wealth of basic science information developed from rodent, models, large animal models provide a number of translational advantages. The pig, in particular, is arguably one of the most powerful models of human organ systems, including the gastrointestinal tract. The pig has provided important tools and insight into intestinal ischemia/reperfusion injury, intestinal mucosal repair, as well as new insights into esophageal injury and repair. Porcine model development has taken advantage of the size of the animal, allowing increased surgical and endoscopic access. In addition, cellular tools such as the intestinal porcine epithelial cell line and porcine enteroids are providing the methodology to translate basic science findings using in-depth mechanistic analyses. Further opportunities in porcine digestive disease modeling include developing additional transgenic pig strains. Collectively, porcine models hold great promise for the future of clinically relevant digestive disease research.

Characterization of oncocytes in deep esophageal glands

Deep esophageal glands play a vital role in the protection and regeneration of the esophageal mucosa. Conditions such as gastroesophageal reflux disease and Barrett's esophagus have been associated with a change in the usual glands by oncocytic metaplasia. However, little is known regarding the function of oncocytes or the relevance of this metaplastic change in the human esophagus. We hypothesized that oncocytes of deep esophageal glands also express markers characteristic of a ductal epithelial phenotype because similar oncocytes have been described as part of large ductal epithelial cells in salivary glands. We used immunohistochemical stains to define structural, functional, proliferative, and potential stem/progenitor characteristics of oncocytes. Oncocytes did not express mucins or lysozyme C, two molecules found in mucous cells and used for antimicrobial defense. Oncocytes did not express CK5, a cytokeratin found in myoepithelial cells and basal epithelial cells, but expressed CK7, a cytokeratin found in intralobular ductal epithelial cells and luminal epithelial cells of the main duct. Oncocytes expressed cystic fibrosis transmembrane conductance regulator and sodium/potassium ATPase, ion channels that play a role in bicarbonate secretion. Membrane-bound beta-catenin was detected in oncocytes, but these cells did not express the proliferative marker Ki67. Approximately, a third of oncocytes expressed SOX9 and p63, transcription factors expressed in epithelial progenitor cells in multiple organs. Moreover, oncocytes expressed CD44, a transmembrane Glycoprotein expressed in cancer stem cells. Taken together, our data show that oncocytes express markers of intralobular ductal epithelial cells and luminal epithelial cells of the main duct. Additionally, our observations suggest that oncocytes act as epithelial progenitor cells and play a role in bicarbonate secretion. Since oncocytic metaplasia is associated with conditions of chronic acid injury, it is possible that oncocytes replace the mucous cells in deep esophageal glands (dEG) as an adaptive change to counteract injury from acid reflux. The marker characterization suggests that oncocytes may originate from transdifferentiation of myoepithelial and mucous cells. This transdifferentiation might lead to an overall decrease of mucins production and secretion by the dEG and a subsequent reduction of the protection conferred by the viscoelastic mucous layer.

Oesophageal adenocarcinoma and gastric cancer: should we mind the gap?

Over recent decades we have witnessed a shift in the anatomical distribution of gastric cancer (GC), which increasingly originates from the proximal stomach near the junction with the oesophagus. In parallel, there has been a dramatic rise in the incidence of oesophageal adenocarcinoma (OAC) in the lower oesophagus, which is associated with antecedent Barrett oesophagus (BO). In this context, there has been uncertainty regarding the characterization of adenocarcinomas spanning the area from the lower oesophagus to the distal stomach. Most relevant to this discussion is the distinction, if any, between OAC and intestinal-type GC of the proximal stomach. It is therefore timely to review our current understanding of OAC and intestinal-type GC, integrating advances from cell-of-origin studies and comprehensive genomic alteration analyses, ultimately enabling better insight into the relationship between these two cancers.

Cytoskeletal changes induced by allosteric modulators of calcium-sensing receptor in esophageal epithelial cells

The calcium-sensing receptor (CaSR), a G-protein-coupled receptor, plays a role in glandular and fluid secretion in the gastrointestinal tract, and regulates differentiation and proliferation of epithelial cells. We examined the expression of CaSR in normal and pathological conditions of human esophagus and investigated the effect of a CaSR agonist, cinacalcet (CCT), and antagonist, calhex (CHX), on cell growth and cell-cell junctional proteins in primary cultures of porcine stratified squamous esophageal epithelium. We used immunohistochemistry and Western analysis to monitor expression of CaSR and cell-cell adhesion molecules, and MTT assay to monitor cell proliferation in cultured esophageal cells. CCT treatment significantly reduced proliferation, changed the cell shape from polygonal to spindle-like, and caused redistribution of E-cadherin and β-catenin from the cell membrane to the cytoplasm. Furthermore, it reduced expression of β-catenin by 35% (P < 0.02) and increased expression of a proteolysis cleavage fragment of E-cadherin, Ecad/CFT2, by 2.3 folds (P < 0.01). On the other hand, CHX treatment enhanced cell proliferation by 27% (P < 0.01), increased the expression of p120-catenin by 24% (P < 0.04), and of Rho, a GTPase involved in cytoskeleton remodeling, by 18% (P < 0.03). In conclusion, CaSR is expressed in normal esophagus as well as in Barrett's, esophageal adenocarcinoma, squamous cell carcinoma, and eosinophilic esophagitis. Long-term activation of CaSR with CCT disrupted the cadherin-catenin complex, induced cytoskeletal remodeling, actin fiber formation, and redistribution of CaSR to the nuclear area. These changes indicate a significant and complex role of CaSR in epithelial remodeling and barrier function of esophageal cells.

Animal Models of Barrett's Esophagus and Esophageal Adenocarcinoma-Past, Present, and Future

Esophageal adenocarcinoma is the fastest rising cancer in the United States. It develops from long-standing gastroesophageal reflux disease which affects >20% of the general population. It carries a very poor prognosis with 5-year survival <20%. The disease is known to sequentially progress from reflux esophagitis to a metaplastic precursor, Barrett's esophagus and then onto dysplasia and esophageal adenocarcinoma. However, only few patients with reflux develop Barrett's esophagus and only a minority of these turn malignant. The reason for this heterogeneity in clinical progression is unknown. To improve patient management, molecular changes which facilitate disease progression must be identified. Animal models can provide a comprehensive functional and anatomic platform for such a study. Rats and mice have been the most widely studied but disease homology with humans has been questioned. No animal model naturally simulates the inflammation to adenocarcinoma progression as in humans, with all models requiring surgical bypass or destruction of existing antireflux mechanisms. Valuable properties of individual models could be utilized to holistically evaluate disease progression. In this review paper, we critically examined the current animal models of Barrett's esophagus, their differences and homologies with human disease and how they have shaped our current understanding of Barrett's carcinogenesis.

The immunophenotypic relationship between the submucosal gland unit, columnar metaplasia and squamous islands in the columnar-lined oesophagus

AIMS

To characterize the immunophenotypic relationship between the squamous and the glandular compartments in the oesophagus of patients with columnar-lined oesophagus (CLO).

METHODS AND RESULTS

Eight tissue blocks from three oesophageal resection specimens from patients who underwent oesophagectomy for adenocarcinoma of the oesophagus were selected for immunohistochemical analysis. The markers of intestinal differentiation [CK20, CDX2 and MUC2] were all expressed in the expected pattern, solely in the glandular compartment of the resection specimens. CK4, CK17 and lysozyme were expressed in both the glandular and the squamous compartments. In addition, CK17 expression was found on both the squamous and glandular margins of the squamocolumnar transformation zones and in the submucosal gland (SMG) intraglandular and excretory ducts.

CONCLUSIONS

There is an immunophenotypic relationship between the squamous and the glandular compartments of the CLO, with expression of lysozyme, CK4 and CK17 in both squamous and columnar cells. These overlapping immunophenotypes indicate similar differentiation paths, and link the SMG unit with the columnar metaplasia and the neosquamous islands in CLO. Our findings support the theory of a cellular origin of CLO and neosquamous islands from the SMG unit.

Genetic and cellular mechanisms regulating anterior foregut and esophageal development

Separation of the single anterior foregut tube into the esophagus and trachea involves cell proliferation and differentiation, as well as dynamic changes in cell-cell adhesion and migration. These biological processes are regulated and coordinated at multiple levels through the interplay of the epithelium and mesenchyme. Genetic studies and in vitro modeling have shed light on relevant regulatory networks that include a number of transcription factors and signaling pathways. These signaling molecules exhibit unique expression patterns and play specific functions in their respective territories before the separation process occurs. Disruption of regulatory networks inevitably leads to defective separation and malformation of the trachea and esophagus and results in the formation of a relatively common birth defect, esophageal atresia with or without tracheoesophageal fistula (EA/TEF). Significantly, some of the signaling pathways and transcription factors involved in anterior foregut separation continue to play important roles in the morphogenesis of the individual organs. In this review, we will focus on new findings related to these different developmental processes and discuss them in the context of developmental disorders or birth defects commonly seen in clinics.

Review: Experimental models for Barrett's esophagus and esophageal adenocarcinoma

Several different cell culture systems and laboratory animal models have been used over the years to study Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC). Most of the existing models have key differences with the human esophagus and complex pathogenesis of disease. None of the models offers an ideal system for the complex study of environmental exposure, genetic risk, and prevention strategies. In fact, different model systems may be required to answer different specific research questions about the pathogenesis of BE and EAC. Given the high mortality associated with EAC and the fact that current screening strategies miss most cases of EAC, advances in basic and translational science related to esophageal injury, repair, and carcinogenesis are clearly needed. This review describes several of the existing and potential model systems for BE and EAC with their benefits and disadvantages.

Ion transport mechanisms linked to bicarbonate secretion in the esophageal submucosal glands

The esophageal submucosal glands (SMG) secrete HCO(3)(-) and mucus into the esophageal lumen, where they contribute to acid clearance and epithelial protection. This study characterized the ion transport mechanisms linked to HCO(3)(-) secretion in SMG. We localized ion transporters using immunofluorescence, and we examined their expression by RT-PCR and in situ hybridization. We measured HCO(3)(-) secretion by using pH stat and the isolated perfused esophagus. Using double labeling with Na(+)-K(+)-ATPase as a marker, we localized Na(+)-coupled bicarbonate transporter (NBCe1) and Cl(-)-HCO(3)(-) exchanger (SLC4A2/AE2) to the basolateral membrane of duct cells. Expression of cystic fibrosis transmembrane regulator channel (CFTR) was confirmed by immunofluorescence, RT-PCR, and in situ hybridization. We identified anion exchanger SLC26A6 at the ducts' luminal membrane and Na(+)-K(+)-2Cl(-) (NKCC1) at the basolateral membrane of mucous and duct cells. pH stat experiments showed that elevations in cAMP induced by forskolin or IBMX increased HCO(3)(-) secretion. Genistein, an activator of CFTR, which does not increase intracellular cAMP, also stimulated HCO(3)(-) secretion, whereas glibenclamide, a Cl(-) channel blocker, and bumetanide, a Na(+)-K(+)-2Cl(-) blocker, decreased it. CFTR(inh)-172, a specific CFTR channel blocker, inhibited basal HCO(3)(-) secretion as well as stimulation of HCO(3)(-) secretion by IBMX. This is the first report on the presence of CFTR channels in the esophagus. The role of CFTR in manifestations of esophageal disease in cystic fibrosis patients remains to be determined.

Cellular origin of Barrett's metaplasia and oesophageal stem cells

Barrett's oesophagus is a metaplastic pre-malignant disorder and the only established precursor lesion for oesophageal adenocarcinoma. Barrett's oesophagus develops when the normal stratified squamous epithelium of the lower oesophagus is replaced by a columnar lined mucosa with intestinal differentiation, usually in the context of chronic gastro-oesophageal reflux disease. The cellular and molecular mechanisms by which this metaplastic transformation occurs are poorly understood. Abnormal differentiation of multipotent stem cells in the squamous oesophagus, triggered by exposure to refluxate, is one potential mechanism. These stem cells could be located in the basal layer of the squamous oesophageal epithelium and/or in the neck region of the oesophageal submucosal gland ducts; however, their exact location and identification are still matter of discussion. Three-dimensional models combined with state-of-the-art imaging techniques are now applied to characterize the squamous epithelium in human oesophageal samples, and this could unveil essential information to identify these progenitor cells. Locating stem cells in human squamous oesophagus could have important implications for our understanding of Barrett's oesophagus and remarkably improve our future strategies for its prevention.

The effect of tegaserod on esophageal submucosal glands bicarbonate and mucin secretion

Tegaserod, a 5-HT4 partial agonist, was shown to reduce esophageal acid exposure in patients with gastroesophageal reflux disease; however, its mechanism of action is poorly understood. Therefore, we have examined the effect of tegaserod on luminal bicarbonate and mucin secretion in the isolated perfused pig esophagus. We also studied its role in esophageal protection using SMG-bearing pig esophagus in comparison to the rabbit esophagus, which is devoid of them. The tissues were mounted in Ussing chambers, and acid injury was replicated by exposing the lumen to acid (pH 1.6) or acid/pepsin (pH 2.5). In pig esophagus, tegaserod increased bicarbonate secretion, but had no effect on basal mucin secretion. In Ussing chambers, tegaserod reduced injury to pig, but not rabbit esophagus exposed to acid (pH 2.5) plus pepsin. These results indicate that tegaserod stimulates SMG bicarbonate secretion, an effect that likely accounts for the observed protection against acid-pepsin injury to pig, but not rabbit, esophagus.