Changing role of in vivo models in columnar-lined lower esophagus

Barrett's esophagus

Barrett's esophagus is an acquired metaplastic abnormality in which the normal stratified squamous epithelium lining of the esophagus is replaced by an intestinal-like columnar epithelium. While in itself a benign and asymptomatic disorder, the clinical importance of this relatively common condition relates to its role as a precursor lesion to esophageal adenocarcinoma, the incidence of which has dramatically increased in Western populations in recent years. Although known to arise as a consequence of chronic gastroesophageal reflux, the cellular and molecular mechanisms underlying development Barrett's esophagus and its progression to cancer remain unclear.

New models of neoplastic progression in Barrett's oesophagus

Research in Barrett's oesophagus, and neoplastic progression to OAC (oesophageal adenocarcinoma), is hobbled by the lack of good pre-clinical models that capture the evolutionary dynamics of Barrett's cell populations. Current models trade off tractability for realism. Computational models are perhaps the most tractable and can be used both to interpret data and to develop intuitions and hypotheses for neoplastic progression. Tissue culture models include squamous cell lines, Barrett's oesophagus cell lines and OAC cell lines, although it was recognized recently that BIC-1, SEG-1 and TE-7 are not true OAC cell lines. Some of the unrealistic aspects of the micro-environment in two-dimensional tissue culture may be overcome with the development of three-dimensional organotypic cultures of Barrett's oesophagus. The most realistic, but least tractable, model is a canine surgical model that generates reflux and leads to an intestinal metaplasia. Alternatively, rat surgical models have gained popularity and should be tested for the common genetic features of Barrett's oesophagus neoplastic progression in humans including loss of CDKN2A (cyclin-dependent kinase inhibitor 2A) and TP53 (tumour protein 53), generation of aneuploidy and realistic levels of genetic diversity. This last feature will be important for studying the effects of cancer-prevention interventions. In order to study the dynamics of progression and the effects of an experimental intervention, there is a need to follow animals longitudinally, with periodic endoscopic biopsies. This is now possible and represents an exciting opportunity for the future.

New models of neoplastic progression in Barrett's oesophagus

Research in Barrett's oesophagus, and neoplastic progression to OAC (oesophageal adenocarcinoma), is hobbled by the lack of good pre-clinical models that capture the evolutionary dynamics of Barrett's cell populations. Current models trade off tractability for realism. Computational models are perhaps the most tractable and can be used both to interpret data and to develop intuitions and hypotheses for neoplastic progression. Tissue culture models include squamous cell lines, Barrett's oesophagus cell lines and OAC cell lines, although it was recognized recently that BIC-1, SEG-1 and TE-7 are not true OAC cell lines. Some of the unrealistic aspects of the micro-environment in two-dimensional tissue culture may be overcome with the development of three-dimensional organotypic cultures of Barrett's oesophagus. The most realistic, but least tractable, model is a canine surgical model that generates reflux and leads to an intestinal metaplasia. Alternatively, rat surgical models have gained popularity and should be tested for the common genetic features of Barrett's oesophagus neoplastic progression in humans including loss of CDKN2A (cyclin-dependent kinase inhibitor 2A) and TP53 (tumour protein 53), generation of aneuploidy and realistic levels of genetic diversity. This last feature will be important for studying the effects of cancer-prevention interventions. In order to study the dynamics of progression and the effects of an experimental intervention, there is a need to follow animals longitudinally, with periodic endoscopic biopsies. This is now possible and represents an exciting opportunity for the future.

Adenomatous polyp with intestinal metaplasia of the esophagus (Barrett esophagus) in a dog

Multiple endoscopic biopsy specimens of esophageal mucosa were received from a 13-year-old castrated male standard Poodle. The dog was presented for painful swallowing. Endoscopically, the distal aspect of the esophagus was inflamed with a polypoid mass that protruded into the esophageal lumen. Histologically, the stratified squamous epithelium overlying the mass and lining the adjacent esophageal mucosa was replaced by papillary projections covered by columnar epithelium with goblet cells supported by a fibrous stroma. This article reports a case of spontaneous esophageal adenomatous polyp with intestinal metaplasia (Barrett esophagus) and reviews the pathogenesis of esophageal metaplasia and adenocarcinoma.

Esophageal adenocarcinoma in "mice and men": back to basics!

Adenocarcinoma related to Barrett's esophagus (BE) is increasing in the West faster than any other cancer. There are many potential chemopreventive agents as well as predictive biomarkers of cancer progression, but what is required is a robust high-throughput model in which to test hypotheses preclinically. The pathophysiology of metaplasia and cancer has been studied in 10 animal species. Though they have considerable genetic divergence, anatomical dissimilarity, and experimental flaws, they have provided some data to test in the clinic, especially relating to activation of common genetic pathways, role of hypergastrinemia, and duodenogastric reflux in cancer progression. In this regard, the human postesophagectomy model, which has a 30% recurrence of BE within 3 yr and a 5% recurrence of adenocarcinoma over 10 yr, is now being utilized to understand how human metaplasia occurs. Furthermore, improved clinical trial designs mean that more sophisticated questions can be addressed in man.

Effect of Roux-en-Y surgery and medical intervention on Barrett's-type changes: an in vivo model

In animal models, mixed acid and bile reflux into lower esophagus induces histological changes comparable to Barrett's metaplasia (BM) and neoplasia. The aim of this study was to compare the effects of Roux-en-Y (REY) surgery and medical therapy on BM in animals before the development of neoplasia. Vagus preserving esophagojejunostomy operation was performed on Sprague-Dawley rats to achieve gastroduodenal reflux (GDR) into the esophagus in 30 animals. After 3 months, changes were reversed in 10 animals (Group REY) by REY operation, 10 animals (Group proton pump inhibitor [PPI]) were given PPI during the postoperative period, and 10 animals (Group GDR) did not have further intervention. At 4 months, histological examination of the lower esophagus was performed by an experienced pathologist. Physiological parameters were also analyzed in all animals preoperatively and at 4 months postoperatively. The length of columnar mucosa, degree of acute inflammation, degree of metaplasia, and composite BM score were significantly reduced by REY surgery compared with medical therapy and with control (columnar mucosa in cm [mean +/- standard error of the mean] Group REY 0.44 +/- 0.06, Group PPI 0.92 +/- 0.08, P < 0.001/Group GDR 1.17 +/- 0.31, P < 0.03). There was no neoplasia seen in any specimen. At 4 months, postoperatively controls Group REY surgery showed significantly more normalization of physiological parameters to preoperative levels than Group PPI (P < 0.05). REY surgery is potentially more beneficial than medical therapy in reversing the histological and biochemical changes of Barrett's esophagus due to GDR.

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.

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.

Reflux, Barrett's oesophagus and adenocarcinoma: burning questions

The incidence of oesophageal adenocarcinoma is increasing rapidly in Western populations. Gastro-oesophageal reflux disease is a strong risk factor for both this tumour and the pre-cancerous lesion Barrett's oesophagus, but the underlying disease mechanisms remain unclear. Developing a better understanding of the aetiology and pathogenesis of Barrett's oesophagus, including the induction of DNA damage and genetic alterations, might provide opportunities for improved management of individuals with this disease. This could include a better rationale for screening and surveillance programmes, as well as targeted intervention strategies.