Experimental Barrett's esophagus and the origin of intestinal metaplasia

Barrett's esophagus: "All diseases are divine and all are human"

Barrett's esophagus (BE) is a controversial condition. The significance of this condition lies in its premalignant potential, so it is important that clinically applicable biomarkers be identified for early detection and targeted prevention. Dysplasia is currently used as main biomarker, but others most recently surveyed in cancer also include microRNAs. Classically, BE was considered to be an acquired disease related to pathological gastroesophageal acid and bile reflux. However, some cases are associated with genetic predisposition, representing an inherited, familial form of BE. The actual gene, or genes, involved in this condition have not yet been identified. Main therapeutic options include medical treatment and antireflux surgery. Both types of treatment are equally efficient in controlling symptoms and neither is able to cause the metaplastic segment to disappear, which is why the risk of malignancy remains. However, we may use endoscopic radiofrequency to eradicate BE and replace it by the typical squamous epithelium of the esophagus. The currently accepted indications of radiofrequency in BE include low- and high-grade dysplasia, but not Barrett's esophagus without dysplasia. In conclusion, BE may have two different presentations: environmental ("human", reflux) or sporadic BE, which is the most common form, and genetic ("divine", inherited) or familiar BE, less common but with a greater risk for malignancy. As they might be two different diseases, surveillance programs and treatments should also be different.

Rebamipide Alters the Esophageal Microbiome and Reduces the Incidence of Barrett's Esophagus in a Rat Model

BACKGROUND

Barrett's esophagus (BE) is characterized by a distinct Th2-predominant cytokine profile. However, antigens that shift the immune response toward the Th2 profile are unknown.

AIM

We examined the effects of rebamipide on the esophageal microbiome and BE development in a rat model.

METHODS

BE was induced by esophagojejunostomy in 8-week-old male Wistar rats. Rats were divided into control and rebamipide-treated group receiving either a normal or a 0.225 % rebamipide-containing diet, respectively, and killed 8, 16, 24, and 32 weeks after the operation. PCR-amplified 16S rDNAs extracted from esophageal samples were examined by terminal-restriction fragment length polymorphism (T-RFLP) analysis to assess microbiome composition. The dynamics of four bacterial genera (Lactobacillus, Clostridium, Streptococcus, and Enterococcus) were analyzed by real-time PCR.

RESULTS

The incidences of BE in the control and rebamipide group at 24 and 32 weeks were 80 and 100, and 20 and 33 %, respectively. T-RFLP analysis of normal esophagus revealed that the proportion of Clostridium was 8.3 %, while that of Lactobacillales was 71.8 %. The proportions of Clostridium increased and that of Lactobacillales decreased at 8 weeks in both groups. Such changes were consistently observed in the control but not in the rebamipide group. Clostridium and Lactobacillus expression was lower and higher, respectively, in the rebamipide group than in the control group.

CONCLUSIONS

Rebamipide reduced BE development and altered the esophageal microbiome composition, which might play a role in BE development.

Increased risk of Barrett's esophagus among individuals born preterm or small for gestational age

BACKGROUND & AIMS

Gastroesophageal reflux is common in infants during their first year of life, especially in those born preterm or small for gestational age (SGA). We assessed whether being born preterm or SGA increased the risk of developing Barrett's esophagus (BE) in adulthood.

METHODS

We performed a population-based case-control study of patients with BE (cases) that were diagnosed at 2 Swedish hospitals from January 1, 1986, through December 31, 2005. We identified the birth hospital of the cases; data on perinatal characteristics such as gestational age at birth and birth weight were collected from original birth records. We also obtained and collected information on the 3 singleton live births, of the same sex, born after each case at the same maternity ward (controls). In total, we analyzed data from 331 cases and 852 matched controls. We used conditional logistic regression to determine odds ratios (ORs), determined 95% confidence intervals (CIs), and adjusted for potential confounding factors.

RESULTS

Compared with infants born with a normal birth weight (3000-3999 g), infants with low birth weight (<2500 g) were at increased risk of BE (adjusted OR, 8.22; 95% CI, 2.83-23.88). This was mainly due to an effect of SGA rather than preterm birth. Specifically, compared with infants with normal birth weight for gestational age (25th-75th percentiles), the odds of BE among very SGA infants (<3rd percentile) was nearly tripled (adjusted OR, 2.95; 95% CI, 1.35-6.44).

CONCLUSIONS

On the basis of a population-based study of patients with BE in Sweden, infants born SGA have a 3-fold increase in risk for developing BE as adults, compared with infants of normal birth weight for gestational age.

Risk of oesophageal adenocarcinoma among individuals born preterm or small for gestational age

BACKGROUND

Gastroesophageal reflux is a main risk factor for oesophageal adenocarcinoma (EAC). Infants born preterm or small for gestational age (SGA) regurgitate more than infants born at term, and some data support the hypothesis of an association with oesophagitis, Barrett's oesophagus and EAC. This study aimed to assess the association between risk of EAC and preterm or SGA birth.

METHODS

In this population-based case-control study, all incident cases of EAC in Sweden between 1st January 1998 and 31st December 2004 with retrievable birth records were eligible as cases. We sampled three matched controls per case from the birth ledger at the same delivery ward as the respective case. Data on gestational age, birth weight and other perinatal exposures were extracted from the original birth records. For comparison, we collected perinatal data for cases of cardia adenocarcinoma and oesophageal squamous cell carcinoma and controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated.

RESULTS

The risk of EAC increased by 13% per week of shorter duration of gestation (OR 1.1, 95%CI 1.0-1.3), while SGA did not influence the risk. No effect of preterm birth or SGA was found on the risk of cardia adenocarcinoma or oesophageal squamous cell carcinoma.

CONCLUSION

Preterm birth, but not SGA, might lead to an increased risk of EAC as an adult.

Barrett's Esophagus: Emerging Knowledge and Management Strategies

The incidence of esophageal adenocarcinoma (EAC) has increased exponentially in the last 3 decades. Barrett's esophagus (BE) is the only known precursor of EAC. Patients with BE have a greater than 40 folds higher risk of EAC compared with the general population. Recent years have witnessed a revolution in the clinical and molecular research related to BE. However, several aspects of this condition remain controversial. Data regarding the true prevalence of BE have varied widely. Recent studies have suggested a lower incidence of EAC in nondysplastic BE (NDBE) than previously reported. There is paucity of prospective data showing a survival benefit of screening or surveillance for BE. Furthermore, the ever-increasing emphasis on healthcare cost containment has called for reexamination of the screening and surveillance strategies for BE. There is a need for identification of reliable clinical predictors or molecular biomarkers to risk-stratify patients who might benefit the most from screening or surveillance for BE. Finally, new therapies have emerged for the management of dysplastic BE. In this paper, we highlight the key areas of controversy and uncertainty surrounding BE. The paper discusses, in detail, the current literature about the molecular pathogenesis, biomarkers, histopathological diagnosis, and management strategies for BE.

Role of Th-2 cytokines in the development of Barrett's esophagus in rats

BACKGROUND

Barrett's esophagus is characterized by a distinct Th-2-predominant cytokine profile, unlike the pro-inflammatory nature of reflux esophagitis. The aim of this study was to examine the role of Th-2 cytokines during the development of Barrett's esophagus, using a rat model.

METHODS

Barrett's esophagus was induced by Levrat's esophagojejunostomy technique in Brown-Norway (BN) rats. Rats were killed at 8, 15, 30, and 50 weeks after the operation. We studied the incidences of esophagitis and Barrett's esophagus, and the mRNA expression of cytokines and CDX2 by real-time reverse transcriptase-polymerase chain reaction and immunohistochemical staining. Finally, we compared the incidence of Barrett's esophagus in BN rats with that in Sprague-Dawley (SD) rats.

RESULTS

Esophagitis was found in all rats. Barrett's esophagus appeared 8 weeks after the operation, and its incidence and length increased over time. Levels of Th-2 cytokines such as interleukin (IL)-4, IL-10, and IL-13 were significantly increased in Barrett's esophagus as compared to those in non-Barrett's esophagus, while there were no differences in the levels of pro-inflammatory cytokines. The peak of elevated IL-4 mRNA was observed before that of CDX2 mRNA. IL-4 was co-localized in CD4-positive cells and CDX2-positive goblet cells. The incidence of Barrett's esophagus was more common in BN rats (8/10, 80%) than in SD rats (2/7, 28%) at 30 weeks.

CONCLUSION

Th-2 cytokines, especially IL-4, may play a crucial role in the development of Barrett's esophagus in an early phase. These results provide understanding of the pathogenesis of Barrett's esophagus from the aspect of the Th-2 immune response.

History, molecular mechanisms, and endoscopic treatment of Barrett's esophagus

This report is an adjunct to the American Gastroenterological Association Institute's medical position statement and technical review on the management of Barrett's esophagus, which will be published in the near future. Those documents will consider a number of broad questions on the diagnosis, clinical features, and management of patients with Barrett's esophagus, and the reader is referred to the technical review for an in-depth discussion of those topics. In this report, we review historical, molecular, and endoscopic therapeutic aspects of Barrett's esophagus that are of interest to clinicians and researchers.

Advances in research on Barrett's esophagus

Over the past 20 years, the incidence of esophageal adenocarcinoma has increased dramatically. Barrett's esophagus is an acquired premalignant condition in which an abnormal columnar epithelium replaces the stratified squamous epithelium that normally lines the distal esophagus. Barrett's esophagus is often associated with long-standing gastroesophageal reflux disease. Gastric and/or bile contents may contribute to the development and malignant progression of Barrett's esophagus. At present, the uniform histopathologic definitions and diagnostic criteria for Barrett's esophagus, intestinal metaplasia at the gastroesophageal junction and cardiac metaplasia have not been established, and the correlation between Helicobactor pylori infection and gastroesophageal reflux disease is still a matter of ongoing debate. Recent studies have suggested that esophageal injury in Barrett's esophagus heals through the proliferation and differentiation of muti-potential progenitor cells derived from the bone marrow rather than from the injured organ itself. MicroRNAs (miRNAs) are potentially useful for development of biomarkers for evaluation of the prognosis of Barrett's esophagus and for early detection, chemoprevention, and treatment of esophageal cancer.

Cdx genes, inflammation, and the pathogenesis of intestinal metaplasia

Intestinal metaplasia (IM) is a biologically interesting and clinically relevant condition in which one differentiated type of epithelium is replaced by another that is morphologically similar to normal intestinal epithelium. Two classic examples of this are gastric IM and Barrett's esophagus (BE). In both, a chronic inflammatory microenvironment, provoked either by Helicobacter pylori infection of the stomach or acid and bile reflux into the esophagus, precedes the metaplasia. The Caudal-related homeodomain transcription factors Cdx1 and Cdx2 are critical regulators of the normal intestinal epithelial cell phenotype. Ectopic expression of Cdx1 and Cdx2 occurs in both gastric IM as well as in BE. This expression precedes the onset of the metaplasia and implies a causal role for these factors in this process. We review the observations regarding the role of chronic inflammation and the Cdx transcription factors in the pathogenesis of gastric IM and BE.

Acid, bile, and CDX: the ABCs of making Barrett's metaplasia

Barrett's esophagus, a squamous-to-columnar cell metaplasia that develops as a result of chronic gastroesophageal reflux disease (GERD), is a risk factor for esophageal adenocarcinoma. The molecular events underlying the pathogenesis of Barrett's metaplasia are poorly understood, but recent studies suggest that interactions among developmental signaling pathways, morphogenetic factors, and Caudal homeobox (Cdx) genes play key roles. Strong expression of Cdx genes normally is found in the intestine but not in the esophagus and stomach. When mice are genetically engineered so that their gastric cells express Cdx, the stomach develops a metaplastic, intestinal-type epithelium similar to that of Barrett's esophagus. Exposure to acid and bile has been shown to activate the Cdx promoter in certain esophageal cell lines, and Cdx expression has been found in inflamed esophageal squamous epithelium and in the specialized intestinal metaplasia of Barrett's esophagus. Barrett's metaplasia must be sustained by stem cells, which might be identified by putative, intestinal stem cell markers like leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) and doublecortin and CaM kinase-like-1 (DCAMKL-1). Emerging concepts in tumor biology suggest that Barrett's cancers may develop from growth-promoting mutations in metaplastic stem cells or their progenitor cell progeny. This report reviews the roles of developmental signaling pathways and the Cdx genes in the development of normal gut epithelia and the potential mechanisms whereby GERD may induce the esophageal expression of Cdx genes and other morphogenetic factors that mediate the development of Barrett's metaplasia. The role of stem cells in the development of metaplasia and in carcinogenesis and the potential for therapies directed at those stem cells also is addressed.

Bone marrow progenitor cells contribute to esophageal regeneration and metaplasia in a rat model of Barrett's esophagus

Barrett's esophagus develops when refluxed gastric juice injures the esophageal squamous lining and the injury heals through a metaplastic process in which intestinal-type columnar cells replace squamous ones. The progenitor cell that gives rise to Barrett's metaplasia is not known, nor is it known why the condition is predisposed to malignancy. We studied the contribution of bone marrow stem cells to the development of Barrett's esophagus in an animal model. Twenty female rats were given a lethal dose of irradiation followed by tail vein injection of bone marrow cells from male rats. Ten days later, the female rats were randomly assigned to undergo either esophagojejunostomy, a procedure that causes reflux esophagitis with intestinal metaplasia, or a sham operation. The rats were killed at 8 weeks and serial sections of the snap-frozen esophagi were cut and mounted on slides. The first and last sections were used for histological evaluation and the intervening sections were immunostained for cytokeratin to identify epithelial cells and analyzed for Y chromosome by fluorescence in situ hybridization (FISH). Histological evaluation of the esophagi from rats that had esophagojejunostomy revealed ulcerative esophagitis and multiple areas of intestinal metaplasia. FISH analyses showed that some of the squamous epithelial cells and some of the columnar epithelial cells lining the glands of the intestinal metaplasia were positive for Y chromosome. These observations suggest that multi-potential progenitor cells of bone marrow origin contribute to esophageal regeneration and metaplasia in this rat model of Barrett's esophagus.

Reflux injury of esophageal mucosa: experimental studies in animal models of esophagitis, Barrett's esophagus and esophageal adenocarcinoma

Barrett's esophagus (BE), a gastroesophageal reflux associated complication, is defined as the replacement of normal esophageal squamous mucosa by specialized intestinal columnar mucosa with the appearance of goblet cells. The presence of BE is associated with an increased risk of developing esophageal adenocarcinoma (EAC). Although the exposure of gastroduodenal contents to the esophageal mucosa is considered to be an important risk factor for the development of esophagitis, BE and EAC, the mechanisms of reflux esophageal injury are not fully understood. Animal models are now being used extensively to identify the mechanisms of damage and to devise protective and mitigating strategies. Experimental studies on animal models by mimicking the processing of gastroesophageal reflux injury have bloomed during the past decades, however, there is controversy regarding which experimental model for reflux esophagitis, experimental BE and experimental EAC is best. In this review article we aim to clarify the basic understanding of gastroesophageal reflux injury and its complications of BE and EAC, as well as to present current understanding of the reflux experimental models. The animal models of experimental esophageal injury are summarized with focus on the surgical procedures to guide the investigator in choosing or developing a correct animal model in future studies. In addition, our own experimental studies of the animal models are also briefly discussed.

Duodenal-content reflux into the esophagus leads to expression of Cdx2 and Muc2 in areas of squamous epithelium in rats

The molecular events responsible for the transdifferentiation of epithelial cells of the esophagus to a columnar cell type are not well understood. Cdx2 has been detected in Barrett's esophagus, so we sought evidence of Cdx2 expression during the process of transdifferentiation of the esophageal squamous epithelium into a glandular phenotype. Thirty-two rats underwent an esophago-jejunostomy to produce esophagitis of 20, 25, 30, or 35 weeks of duration. The spectrum of esophageal lesions induced by chronic reflux was examined for expression of Cdx2 and Muc2 by immunohistochemistry. Five animals developed glandular metaplasia and adenosquamous carcinoma, two developed only glandular metaplasia, and two had adenosquamous carcinoma alone. Nuclear Cdx2 expression was detected in 57% (four of seven) and 43% (three of seven) of foci of glandular metaplasia and adenosquamous carcinomas, respectively. Cdx2 staining was detectable in some squamous and some mucus secreting cells. Perinuclear and perivacuolar staining of Muc2 was detected focally in 71% (five of seven) and 57% (four of seven) of areas with glandular metaplasia and adenosquamous carcinoma, respectively. We show that duodenal-content reflux into the esophagus switches on the expression of Cdx2 protein in esophageal keratinocytic cells, promoting a mucinous transdifferentiation process with secretion of intestinal mucin Muc2.

On the histogenesis of Barrett's oesophagus and its associated squamous islands: a three-dimensional study of their morphological relationship with native oesophageal gland ducts

Current hypotheses concerning the histogenesis and regression of Barrett's oesophagus are based predominantly on animal models. Our study was formulated to assess, in human tissue, the morphological relationship between oesophageal gland ducts and both Barrett's oesophagus and their associated squamous islands. Serial sections were cut through a total of 46 blocks of archived oesophageal resection tissue containing oesophageal gland ducts underlying Barrett's epithelium. Serial sections were also taken through 15 squamous islands, taken from the same archived tissue, to assess their underlying histology: 21 of the ducts opened onto overlying Barrett's epithelium; in 17 there was a relatively sharp distinction between the two cell types, at the junction, whereas in four there was continuity and a gradual morphological change between the cells of the oesophageal gland ducts and the Barrett's epithelium. All 15 squamous islands sectioned were found to be continuous with an underlying gland duct. This study suggests an interrelationship between Barrett's epithelium and oesophageal gland ducts. More definitively we confirm that squamous islands are universally associated with oesophageal gland duct epithelium. These findings are of fundamental importance for the development of more targeted management strategies for Barrett's oesophagus.