Barrett's esophagus and associated adenocarcinoma in a mouse surgical model

Trefoil factor 1 inhibits the development of esophageal adenocarcinoma from Barrett's epithelium

Trefoil factor family 1 (TFF1) is one of three members of the trefoil factor family that are abundantly expressed in the gastrointestinal mucosal epithelium. Recent studies have shown that TFF1 acts as a tumor suppressor in gastric, pancreatic and hepatocellular carcinogenesis; however, little is known about its function in esophageal carcinogenesis, especially in esophageal adenocarcinoma (EAC). Barrett's epithelium is the metaplastic columnar epithelium of the esophagus and a known premalignant lesion of EAC. To investigate the role of TFF1 in EAC development, a mouse model of Barrett's epithelium was employed, and human specimens of EAC were assessed by immunohistochemistry (IHC) and methylation-specific PCR. Wild-type (WT) mice underwent gastrojejunostomy on the forestomach, resulting in the development of Barrett's epithelium-like (BE-like) epithelium adjacent to the anastomotic site. BE-like epithelium in these mice expressed TFF1, indicating the association of TFF1 with esophageal adenocarcinoma. TFF1-knockout (TFF1KO) mice underwent the same procedure as well, revealing that a deficiency in TFF1 resulted in the development of adenocarcinoma in the anastomotic site, presumably from BE-like epithelium. IHC of human samples revealed strong TFF1 expression in Barrett's epithelium, which was lost in some EACs, confirming the association between TFF1 and EAC development. Aberrant DNA hypermethylation in TFF1 promoter lesions was detected in TFF1-negative human EAC samples, further confirming not only the role of TFF1 in EAC but also the underlying mechanisms of TFF1 regulation. In addition, IHC revealed the nuclear translocation of β-catenin in human and mouse EAC, suggesting that activation of the Wnt/β-catenin pathway was induced by the loss of TFF1. In conclusion, these results indicate that TFF1 functions as a tumor suppressor to inhibit the development of esophageal carcinogenesis from Barrett's epithelium.

Serial Endoscopic Evaluation of Esophageal Disease in a Cancer Model: A Paradigm Shift for Esophageal Adenocarcinoma (EAC) Drug Discovery and Development

A rat model of surgically induced reflux recapitulates the development and progression of human esophageal adenocarcinoma (EAC). In this study, reflux was induced in rats followed by postoperative endoscopy with biopsy, to diagnose and monitor disease progression. Overall, percentage agreement between visual endoscopy and gold standard histology was 95%, with disease-specific classification accuracies of 100% and 75% for Barrett's with dysplasia and EAC, respectively. Additionally, the percentage agreement for biopsy in tumors >4 mm was 75%. Thereby, establishing endoscopic evaluation as a reliable tool to assess disease progression and provide biopsies for downstream correlates in a de novo EAC model.

Preclinical models for the study of Barrett's carcinogenesis

Barrett's esophagus (BE) is clinically significant, as it is the only known precursor lesion for esophageal adenocarcinoma. To develop improved therapies for the treatment of BE, a greater understanding of the disease process at the molecular genetic level is needed. However, achieving a greater understanding will require improved preclinical models so that the disease process can be more closely studied and novel therapies can be tested. Our concise review highlights progress in the development of preclinical models for the study of BE and identifies the most suitable model in which to test novel therapies.

Columnar Metaplasia in Three Types of Surgical Mouse Models of Esophageal Reflux

BACKGROUND AND AIMS

Esophageal adenocarcinoma develops in the setting of gastroesophageal reflux and columnar metaplasia in distal esophagus. Columnar metaplasia arising in gastroesophageal reflux models has developed in rat; however, gastroesophageal reflux models in mice have not been well-characterized.

METHODS

One hundred thirty-five C57Bl/6J mice aged 8 weeks old were divided into the following operations: esophagogastrojejunostomy (side-to-side) (EGJ), esophageal separation and esophagojejunostomy (end-to-side) (EJ), and EJ and gastrectomy (end-to-side) (EJ/TG). The animals were euthanized after 40 weeks and the histology of the junction was examined. Immunohistochemistry for p53, PDX-1, and CDX-2 was performed.

RESULTS

Metaplasia developed in 15/33 (45.5%) of EGJ, 0/38 (0%) of EJ, and 6/39 (15.4%) of EJ/TG (P < .05) and dysplasia developed 7/33 (21.2%) of EGJ, 0% of EJ, and 1/39 (2.6%) of EJ/TG. p53 was positive in all of the dysplastic regions, 12/15 (80%) metaplasias in the EGJ model, and 1/6 (16.7%) metaplasia in the EJ/TG model. CDX-2 was positive in all cases of metaplasias, but decreased in some cases of dysplasia. PDX-1 was positive in 7/8 (88%) cases of dysplasia and in 15/21 (71%) cases of metaplasia (P < .05).

CONCLUSIONS

The EGJ model, which causes reflux of gastric acid and duodenal content, developed metaplasia and dysplasia most frequently. No metaplasia developed in the EJ model in which gastric juice and duodenal content mixed before reflux. Thus, duodenal contents alone can induce columnar metaplasia and dysplasia; however, the combination of gastric acid with duodenal content reflux can cause metaplasia and dysplasia more efficiently.

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.

From reflux esophagitis to Barrett’s esophagus and esophageal adenocarcinoma

The occurrence of gastroesophageal reflux disease is common in the human population. Almost all cases of esophageal adenocarcinoma are derived from Barrett’s esophagus, which is a complication of esophageal adenocarcinoma precancerous lesions. Chronic exposure of the esophagus to gastroduodenal intestinal fluid is an important determinant factor in the development of Barrett’s esophagus. The replacement of normal squamous epithelium with specific columnar epithelium in the lower esophagus induced by the chronic exposure to gastroduodenal fluid could lead to intestinal metaplasia, which is closely associated with the development of esophageal adenocarcinoma. However, the exact mechanism of injury is not completely understood. Various animal models of the developmental mechanisms of disease, and theoretical and clinical effects of drug treatment have been widely used in research. Recently, animal models employed in studies on gastroesophageal reflux injury have allowed significant progress. The advantage of using animal models lies in the ability to accurately control the experimental conditions for better evaluation of results. In this article, various modeling methods are reviewed, with discussion of the major findings on the developmental mechanism of Barrett’s esophagus, which should help to develop better prevention and treatment strategies for Barrett’s esophagus.

Strategy for prevention of cancers of the esophagus

The following, from the 12th OESO World Conference: Cancers of the Esophagus, includes commentaries on the animal reflux-inflammation models for Barrett's esophagus and esophageal adenocarcinoma; genomic/epigenomic analyses; eflornithine-based combinations; the molecular derangements that promote neoplastic transformation; the role of COX-2 inhibitors, proton pump inhibitors, and phase II trials in Barrett's adenocarcinoma; statins in chemoprevention and treatment of esophageal cancer; and biomarkers as potential targets in Barrett's adenocarcinoma.

Establishing magnetic resonance imaging as an accurate and reliable tool to diagnose and monitor esophageal cancer in a rat model

OBJECTIVE

To assess the reliability of magnetic resonance imaging (MRI) for detection of esophageal cancer in the Levrat model of end-to-side esophagojejunostomy.

BACKGROUND

The Levrat model has proven utility in terms of its ability to replicate Barrett's carcinogenesis by inducing gastroduodenoesophageal reflux (GDER). Due to lack of data on the utility of non-invasive methods for detection of esophageal cancer, treatment efficacy studies have been limited, as adenocarcinoma histology has only been validated post-mortem. It would therefore be of great value if the validity and reliability of MRI could be established in this setting.

METHODS

Chronic GDER reflux was induced in 19 male Sprague-Dawley rats using the modified Levrat model. At 40 weeks post-surgery, all animals underwent endoscopy, MRI scanning, and post-mortem histological analysis of the esophagus and anastomosis. With post-mortem histology serving as the gold standard, assessment of presence of esophageal cancer was made by five esophageal specialists and five radiologists on endoscopy and MRI, respectively.

RESULTS

The accuracy of MRI and endoscopic analysis to correctly identify cancer vs. no cancer was 85.3% and 50.5%, respectively. ROC curves demonstrated that MRI rating had an AUC of 0.966 (p<0.001) and endoscopy rating had an AUC of 0.534 (p = 0.804). The sensitivity and specificity of MRI for identifying cancer vs. no-cancer was 89.1% and 80% respectively, as compared to 45.5% and 57.5% for endoscopy. False positive rates of MRI and endoscopy were 20% and 42.5%, respectively.

CONCLUSIONS

MRI is a more reliable diagnostic method than endoscopy in the Levrat model. The non-invasiveness of the tool and its potential to volumetrically quantify the size and number of tumors likely makes it even more useful in evaluating novel agents and their efficacy in treatment studies of esophageal cancer.

Development and characterization of a surgical mouse model of reflux esophagitis and Barrett's esophagus

Ideally, an animal model of Barrett's esophagus should recapitulate the human disease histologically and immunohistochemically, and be readily susceptible to genetic manipulation. We have developed such a model using a strain of mice commonly used for transgenic and knockout manipulations. We induced reflux by esophagojejunostomy (EJ) in 20 C57Bl/6 mice. At defined time points, sections of the esophagus were stained with H&E and Alcian blue, and immunohistochemical staining was performed for Sox9 (a transcription factor in Barrett's metaplasia), cytokeratin (CK) 8/18 (a columnar marker) and CK14 (a squamous marker). Procedural mortality was 40% for the first ten animals, 20% for the next 10. Reflux esophagitis developed by 13 weeks, and intestinal metaplasia with goblet cells developed by 34 weeks. The metaplasia expressed CK8/18, but not CK14, and exhibited nuclear immunostaining for Sox9. Nuclear Sox9 was also seen in scattered basal cells of squamous epithelium close to the EJ anastomosis. EJ can be performed successfully in C57Bl/6 mice, resulting in reflux esophagitis and intestinal metaplasia that exhibits phenotypic and molecular features of human Barrett's metaplasia. This surgical model in a mouse strain that is easy to manipulate genetically should be a valuable tool for studying the pathogenesis of Barrett's esophagus.

Columnar metaplasia in a surgical mouse model of gastro-esophageal reflux disease is not derived from bone marrow-derived cell

The incidence of esophageal adenocarcinoma has increased in the last 25 years. Columnar metaplasia in Barrett's mucosa is assumed to be a precancerous lesion for esophageal adenocarcinoma. However, the induction process of Barrett's mucosa is still unknown. To analyze the induction of esophageal columnar metaplasia, we established a mouse gastro-esophageal reflux disease (GERD) model with associated development of columnar metaplasia in the esophagus. C57BL/6 mice received side-to-side anastomosis of the esophagogastric junction with the jejunum, and mice were killed 10, 20, and 40 weeks after operation. To analyze the contribution of bone marrow-derived cells to columnar metaplasia in this surgical GERD model, some mice were transplanted with GFP-marked bone marrow after the operation. Seventy-three percent of the mice (16/22) showed thickened mucosa in esophagus and 41% of mice (9/22) developed columnar metaplasia 40 weeks after the operation with a mortality rate of 4%. Bone marrow-derived cells were not detected in columnar metaplastic epithelia. However, scattered epithelial cells in the thickened squamous epithelia in regions of esophagitis did show bone marrow derivation. The results demonstrate that reflux induced by esophago-jejunostomy in mice leads to the development of columnar metaplasia in the esophagus. However, bone marrow-derived cells do not contribute directly to columnar metaplasia in this mouse model.

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.

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.

Positive correlation of image analysis by mini-endoscopy with micro-PET scan and histology in rats after esophagoduodenal anastomosis

BACKGROUND

Visual inspection of induced carcinogenic transformation is of crucial interest when evaluating growth patterns and therapeutic effects. In previous studies we have used micro-PET scan to analyze the esophageal adenocarcinoma (EAC) transformation in an intact rat model of esophagoduodenal anastomosis (EDA), in which intestinal metaplasia and EAC were reproduced successfully. Our current study aimed to test the feasibility of evaluating the outcomes of our EDA model with a recently developed mini-endoscope.

METHODS

EDA was performed as described previously. Postoperative rats underwent evaluation with upper endoscopy with the mini-endoscope (±endoscopic biopsy) and a micro-PET scan with (18)F-FDG 3 months after the EDA procedure. Rats were euthanized and the esophagi were collected for histological observation, immunohistochemical staining, and TdT labeling assay. We compared the endoscopic images with the radiographic images of (18)F-FDG uptake by micro-PET scan and correlated the endoscopic images with the histological changes in the EDA rats.

RESULTS

The endoscope provided visualization of the entire esophageal tract and upper stomach, with the smallest detectable lesion being 0.5 mm in diameter. Mini-endoscopy was performed regularly and was tolerated without any significant procedure-related alterations in the esophageal tract. The visualized esophageal lesion correlated well with the micro-PET image and the histological changes in the EDA rats.

CONCLUSIONS

The new mini-endoscope constitutes a practical and reliable tool for diagnosis and regular follow-up of the esophagus in rats. Lesions identified by endoscopic observation were consistent with the changes found in the micro-PET scan, histopathology, and alteration of cellular and molecular events in esophageal mucosa. This instrument will allow for serial endoscopic evaluations, similar to endoscopic screening in humans, which will significantly enhance the preclinical development and evaluation of experimental intravesical antitumor therapies.

In vivo cancer biomarkers of esophageal neoplasia

The emergence of in vivo cancer biomarkers is promising tool for early detection, risk stratification, and therapeutic intervention in the esophagus, where adenocarcinoma is increasing at a rate that is faster than any other in industrialized nations. Exciting advances in target identification, probe development, and optical instrumentation are creating tremendous new opportunities for advancing techniques of molecular imaging. Progress in these areas is being made with small animal models of esophageal cancer using surgical approaches to induce reflux of acid and bile, and these findings are beginning to be evaluated in the clinic. Further identification of relevant targets, characterization of specific probes, and development of endoscopic imaging technologies are needed to further this direction in the field of molecular medicine. In the future, new methods that use in vivo cancer biomarkers for the early detection of neoplastic changes in the setting of Barrett's esophagus will become available.

Endoscopic evaluation of esophago-gastro-jejunostomy in rat model of Barrett's esophagus

Endoscopy can be used to monitor the onset of metaplastic transformation and to observe the progression of neoplasia in small animal models of Barrett's esophagus. By avoiding animal sacrifice, the natural history of this disease can be studied in a longitudinal fashion. We aim to characterize the endoscopic features of esophageal mucosa at various stages of the metaplasia-dysplasia-carcinoma sequence in a rat reflux model of Barrett's for comparison with histology. Acid and bile reflux was produced by introducing a side-to-side esophago-gastro-jejunostomy in Sprague-Dawley rats. Endoscopic examination of the distal esophagus was performed in 24 surgically altered and 4 control rats, between weeks 24 and 36 after the operation in 4-week intervals, and all rats were biopsied and sacrificed at 36 weeks. Endoscopic images were classified based on the surface mucosal patterns of the distal esophagus and then compared with histology. The endoscopic appearance was classified as: (i) normal, characterized by a smooth surface; (ii) intestinal metaplasia, defined as elevated plaques/ridges, deep grooves, and thin linear folds; (iii) dysplasia, indicated by coarse folds/grooves, meshlike villi, and foveolar appearance; and (iv) carcinoma, suggested by irregular-shaped mass lesions with ulcerations. The endoscopic criteria for intestinal metaplasia yielded a sensitivity of 100% in comparison with histology. Intestinal metaplasia with high-grade dysplasia was found in two rats and with low-grade dysplasia in three rats. Both focally invasive squamous cell carcinoma and invasive adenocarcinoma were found in one rat. Small animal endoscopy in a rat model of Barrett's esophagus can be used to perform surveillance, classify mucosal patterns, observe the onset of intestinal metaplasia, and monitor the progression of neoplastic transformation, representing a useful tool for studying the natural history of this disease.

Establishment and characterization of a bona fide Barrett esophagus-associated adenocarcinoma cell line

Esophageal adenocarcinoma currently has one of the most rapidly increasing tumor incidences in the United States, with the vast majority of cases occurring on the backdrop of metaplastic epithelium (Barrett esophagus). The availability of appropriate cell line models is essential for maintaining the pace of esophageal cancer research and for pre-clinical validation of new therapeutic modalities. The identity of several of the widely utilized esophageal adenocarcinoma cell lines (BIC-1, SEG-1 and TE-7) have recently been called into question. Here we describe the establishment and characterization of a bona fide esophageal cancer cell line, JH-EsoAd1, from a patient with Barrett-associated adenocarcinoma. The rapid dissemination of this cancer cell line to the esophageal cancer research community should help ameliorate the current scarcity of preclinical models in this disease.

Bile acid-stimulated expression of the farnesoid X receptor enhances the immune response in Barrett esophagus

OBJECTIVES

Barrett's esophagus (BE) is a premalignant condition of the esophagus. It is a consequence of mucosal injury from chronic gastroesophageal reflux in which bile acids are an important toxic component. The farnesoid X receptor (FXR) is a nuclear receptor involved in the regulation of bile acid synthesis, transport, and absorption. FXR activation is also involved in the induction of the innate immune response. This suggests that FXR is involved in the pathogenesis and the inflammation seen in BE.

METHODS

mRNA levels of FXR and the FXR-regulated genes, ileal bile acid-binding protein (IBABP), small heterodimer partner (SHP), and chemokines interleukin (IL)-8 and macrophage inflammatory protein 3 alpha (MIP3 alpha), were determined by real time-polymerase chain reaction (RT-PCR). Protein expression was determined by immunohistochemistry.

RESULTS

FXR was not expressed in squamous epithelium of healthy subjects (N = 7), but was present in both squamous and columnar epithelium of BE patients. Compared to the squamous epithelium of BE patients, their columnar epithelium displayed a 2.3-fold (P= 0.02) increase in FXR mRNA. Also, IBABP (2.2-fold; P= 0.0029), SHP (2.7-fold; P= 0.007), IL-8 (1.5-fold; P= 0.04), and MIP3 alpha (1.7-fold; P= 0.019) transcription levels were increased. Exposure of esophageal cell line TE7 to deoxycholic acid (DCA) resulted in a similar induction. The induction was abolished by the FXR antagonist guggulsterone.

CONCLUSIONS

Expression levels of the bile acid receptor FXR, the bile acid metabolism genes IBABP and SHP, and the chemokines IL-8 and MIP3 alpha are increased in Barrett's epithelium. The in vitro induction of FXR by DCA suggests that bile acids can actively induce the inflammatory response in BE by recruiting immune cells.

Carcinogenesis in reflux disease--in search for bile-specific effects

Bile reflux may play a key role for esophageal carcinogenesis in reflux disease. In search for bile-specific effects, the animal model of esophageal cancer was applied in a mutagenesis assay. Big Blue transgenic mice were operated with microsurgical techniques. Seven had total gastrectomy with esophagojejunostomy creating esophageal reflux of bile and five had a sham operation. After 24 weeks, the mutation frequency (MF) was measured through standard Big Blue mutagenesis assay in the esophageal mucosa and the duodenum as control. Esophageal reflux resulted in esophagitis in the distal esophagus. The MF in esophageal mucosa was 1.6 times higher in animals with reflux than in sham-operated animals; it was identical in the duodenum. In conclusion, the mutagenic potential of bile reflux has been confirmed. However, mechanisms of carcinogenesis in the esophageal cancer model other than chronic inflammation could not be identified because of the only moderately increased MF.

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.

Alterations in manganese superoxide dismutase expression in the progression from reflux esophagitis to esophageal adenocarcinoma

BACKGROUND

Comprehensive understanding of the basic mechanisms in the progression of esophagitis, Barrett esophagus (BE), and esophageal adenocarcinoma (EAC) is urgently needed to develop a management strategy for an effective screening of BE and management of EAC. The aim of this study is to provide a detailed insight of the histology and the cellular and molecular events associated with the genesis of BE and EAC under the esophagoduodenal reflux conditions.

METHODS

Esophagoduodenal anastomosis (EDA) was performed on rats. Animals were weighed weekly and killed after 1, 2, 3, 4, 5, and 6 months. The entire esophagi were examined for macroscopic and microscopic changes and for manganese superoxide dismutase (MnSOD) expression, and TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) assay was performed.

RESULTS

Morphological transformation from esophagitis (100% of animals) to BE (66% of animals) to EAC was observed after 3 months. There was marked loss of MnSOD expression in animals with esophagitis and BE at 1 and 2 months, with an increase in expression during the transformation to dysplasia and EAC. Increased proliferation and apoptosis was observed and reached a peak at months 1 and 2. Greatly increased levels of 8-hydroxy-deoxyguanosine was found during the progression to EAC.

CONCLUSIONS

The morphological transformation of the esophageal mucosa is an adaptive process, and it is an important foundation for the transdifferentiation of BE and cancer. The significant loss of MnSOD expression to achieve BE and then the adaptive increase in expression to achieve dysplasia and EAC during this transformation may represent a predictive marker in identifying patients who will progress from BE to EAC.

A novel external esophageal perfusion model for reflux esophageal injury

The current animal models of esophagitis and Barrett's esophagus consist of surgeries that divert the gastroduodenal contents to the esophagus. The limitations of these models are the inability to control the amount and concentration of the refluxate and the causing of significant postoperative stress and morbidity. Eighteen adult rats were cannulated at the upper esophagus and connected to a subcutaneous osmotic micropump to perfuse the esophageal lumen with bile and acid. Animals were sacrificed after 7 days of perfusion. Histological changes were determined. Cell proliferation, apoptosis, lipid peroxidation, and glutathione were measured. Histopathological changes in the bile- or acid-perfused esophagus were consistent with the findings associated with reflux esophagitis. Enhanced proliferation and apoptosis were seen, along with increased oxidative stress. The external esophageal perfusion model enabled precise control of the injurious agent. It induced the histologic and cellular injury of reflux esophagitis after 7 days.

Esophageal injury with external esophageal perfusion

BACKGROUND

External esophageal perfusion (EEP) with the idea that esophageal perfusion can be controlled with a single ingredient at a constant rate and concentration, might be used to dissect the injurious role of gastro-duodenal secretions for the progression from esophagitis to Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC). This study is to evaluate the EEP rat model for esophagitis induced by using a micro-osmotic pump with bile perfusion.

METHODS

Eighteen adult rats underwent the EEP procedure. Bile (0.5% bovine bile, pH 7.4) was used as perfusion agent and three types of perfusions were performed: 1 week perfusion, 2 weeks perfusion, and 4 weeks perfusion compared to saline perfusion and sham operation. Histological changes, cell proliferation, apoptosis, 8-hydroxy-deoxyguanosine (8-OH-dG) and Manganese superoxide dismutase (MnSOD) were observed after perfusion and compared.

RESULTS

The bile perfusion for 1 week, 2 weeks, and 4 weeks induced mucosa infiltration of inflammatory cells, basal cell hyperproliferation, and papillae hypertrophy in all animals. Histopathology and cellular changes consistent with the findings associated with reflux esophagitis. The apoptotic index, the proliferating index, and expression of 8-OH-dG were significantly increased in the esophageal mucosa compared to controls. MnSOD expression was decreased with bile perfusion compared to saline controls.

CONCLUSIONS

The external esophageal perfusion model enabled precise control of the injurious agent. It induced the typical histological injury and cellular changes seen in severe reflux esophagitis. The cellular changes in apoptosis, proliferation and anti-oxidant defense make this model unique for reflux esophagitis studies. Further studies are needed to induce Barrett's esophagus and esophageal adenocarcinoma.

Flavopiridol reduces malignant transformation of the esophageal mucosa in p27 knockout mice

The cyclin-dependent kinase (cdk) inhibitor p27 preferentially inactivates cdk complexes required for progression through the G1/S transition. Loss of p27 is associated with aggressive behavior in a variety of tumors, including Barrett's associated adenocarcinoma (BAA). We have previously shown that gastroduodenal-esophageal reflux (GDER) together with N-methyl-N-benzylnitrosamine (MBN) induces Barrett's esophagus (BE) and malignant transformation of the esophageal mucosa in mice. This process is enhanced in a p27 null background. Here, we show that chronic flavopiridol administration sharply reduced the prevalence of BE in GDER/MBN-treated p27 knockout mice when compared to animals treated with diluent only (7 vs 26%, P=0.0079). Similarly, flavopiridol reduced the prevalence of BAA (11 vs 32%, P=0.0098) and overall cancer prevalence (15 vs 60%, P<0.0001). In addition, appropriate molecular targeting by flavopiridol in tumor cells was confirmed by downregulation of cyclin D1, a known target of this pan-cdk inhibitor. The results of this study represent the experimental basis for chemoprevention with cdk inhibitors in human BE and BAA.

p27 and Barrett's esophagus: a review*

The rising prevalence of Barrett's esophagus and Barrett's associated adenocarcinoma in the Western world has stimulated increasing interest in this disease. This has resulted in a plethora of articles concerning its molecular biology, but the tumor suppressor gene, p27, has received little attention. In this article, we review the literature concerning the role of p27 in Barrett's esophagus and its malignant transformation, and we evaluate its possible role as an important clinical biomarker, as well as potential chemopreventive clinical agents aimed at substituting its antitumoral activity.

Effect of reflux and esophagitis on esophageal volume and acid clearance in piglets

BACKGROUND/AIMS

The study investigates esophageal motor function and esophageal clearance immediately after surgical induction of reflux in piglets and 8 weeks later after peptic esophagitis has developed.

METHODS

Twenty-four sedated, nonintubated piglets were divided into three groups: sham (laparotomy only), reflux (distal esophageal myotomy), and reflux + esophagitis (8 weeks after myotomy). All animals underwent stationary manometry of the esophagus with a four-lumen perfused assembly after injection of 1-, 2-, and 3-mL boluses of saline and acid into the proximal esophagus. Simultaneous pH monitoring allowed assessment of acid clearance. Wave features and clearance times after saline and acid were compared among groups.

RESULTS

There were minor changes in peristaltic activity of the esophagus after saline boluses in animals with reflux. Acid clearance time was prolonged, especially the time to re-establish resting esophageal pH, in animals with esophagitis. These changes, which were volume-dependent, were related to the loss of peristaltic organization of the esophageal waves. The esophageal wave frequency, amplitude, and duration were only slightly changed by the induction of reflux and by esophagitis.

CONCLUSIONS

The esophagus affected by acid reflux, with or without esophagitis, was capable of near-normal motor responses after boluses of saline. Reflux impaired the peristaltic response to acid, and the effect was more pronounced when reflux and esophagitis were both present. The acid clearance time was also strikingly prolonged in the presence of reflux and esophagitis. The results suggest that long episodes of reflux seen on pH tracings from individuals with esophagitis might be secondary both to acid-related motor dysfunction and large volumes of refluxate.

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

Columnar-lined lower esophagus (CLE) or Barrett's esophagus (BE) is caused by chronic reflux of the gastrointestinal tract and can progress to invasive adenocarcinoma. However, the pathophysiology, cell of origin, and management of this condition is incompletely understood. This review evaluates the role of in vivo models in resolving these debates. A search was performed on the Ovid and Pub Medline for 1964-2001 and Cochrane Collaboration. The keywords used were adenocarcinoma, animal model, Barrett's esophagus, columnar-lined esophagus, esophageal neoplasms, and esophageal carcinogenesis. All relevant papers were scrutinized and an attempt at tabulation was made. In vivo models have been used at several stages of debate on the pathophysiology of BE. They provide conclusive evidence for its acquired nature secondary to duodenogastroesophageal reflux. The cell of origin of experimental BE may arise from adjacent columnar epithelium, basal layer multipotent cells, or esophageal glands. Experimental work on BE is lacking in assessing therapeutic modalities.

Chronic acid exposure leads to activation of the cdx2 intestinal homeobox gene in a long-term culture of mouse esophageal keratinocytes

To explore mechanisms whereby Malpighian keratinocytes can transdifferentiate into an intestinal-like epithelium, as observed in the early steps of Barrett's esophagus (BE) development, long-standing cultures of esophageal keratinocytes derived from normal mouse esophageal explants were developed. These cells were able to form multilayers and to differentiate on filter support by the formation of differentiated layers of basal cells (cytokeratine 14 positive) on which secondary suprabasal cell layers (cytokeratine 4 positive) spontaneously developed. Thus, these cultured cells, referred to as P3E6, reproduced, at least in part, the proliferation and stratification pattern existing in the normal esophagus. Because chronic exposure to acid pH is known to be a critical factor for BE development, culture medium at pH 3.5 was added into the apical chamber of cell cultures. This led to a decrease in the overall number of cells but it did not affect cell proliferation. Furthermore, external acid environment triggered expression of the GFP reporter gene fused downstream of the cdx2 intestinal homeogene regulatory sequences in P3E6 transfected cells. Expression of the endogenous CDX2 protein, detected by western blot and immunocytochemical analysis, correlated with promoter activation. These findings demonstrate that chronic exposure of esophageal keratinocytes to acid pH induces transcription of cdx2, an intestinal specific homeobox gene known to play a critical role in the differentiation and maintenance of intestinal epithelial functions. The results suggest that chronic acid exposure can modify the fate of P3E6 esophageal keratinocytes towards an intestinal program. This can be a key step in the development of intestinal metaplasia often observed in esophagus-cardia junction.

Malignant transformation of the esophageal mucosa is enhanced in p27 knockout mice

OBJECTIVE

In a previous study, we showed that experimentally induced gastroduodenal-esophageal reflux in mice treated with a carcinogen can result in Barrett esophagus and Barrett-associated adenocarcinoma. Since we have shown that most Barrett-associated adenocarcinomas in human beings have lost the tumor suppressor gene p27, we sought to determine whether cancer would be more likely to develop in p27 knockout mice than in p27 heterozygous or p27 wild type mice.

METHODS

Three groups of mice were treated by esophagojejunostomy resulting in gastroduodenal-esophageal reflux and by a carcinogen (N -methyl-N -benzylnitrosamine): group I (50 wild type), group II (45 p27 heterozygous), and group III (50 p27 knockout). The mice were killed 18 to 20 weeks after operation and studied macroscopically and histopathologically.

RESULTS

Barrett esophagus developed in 7 (14%) mice in group I, 4 (8.9%) mice in group II, and 13 (26%) mice in group III. Cancers developed in 30 (60%) mice in group I, 31 (68%) mice in group II, and 43 (86%) mice in group III. Ten percent of the cancers in group I were adenocarcinomas, as were 16.1% in group II, and 23.3% in group III. The difference between rates of Barrett esophagus in groups I and II compared with group III was statistically significant (P =.035), as was true of the cancer rates (P =.006). The percentage of cancers that were adenocarcinomas was highest in group III, but not significantly different from groups I and II.

CONCLUSIONS

This experimental mouse model of Barrett esophagus and Barrett- associated adenocarcinoma is similar to what occurs in human beings and may be useful in developing methods to inhibit malignant transformation of Barrett esophagus.