Mechanisms of oxidant production in esophageal squamous cell and Barrett's cell lines

Gastro-Esophageal Junction Precancerosis: Histological Diagnostic Approach and Pathogenetic Insights

Barrett's esophagus (BE) was initially defined in the 1950s as the visualization of gastric-like mucosa in the esophagus. Over time, the definition has evolved to include the identification of goblet cells, which confirm the presence of intestinal metaplasia within the esophagus. Chronic gastro-esophageal reflux disease (GERD) is a significant risk factor for adenocarcinoma of the esophagus, as intestinal metaplasia can develop due to GERD. The development of adenocarcinomas related to BE progresses in sequence from inflammation to metaplasia, dysplasia, and ultimately carcinoma. In the presence of GERD, the squamous epithelium changes to columnar epithelium, which initially lacks goblet cells, but later develops goblet cell metaplasia and eventually dysplasia. The accumulation of multiple genetic and epigenetic alterations leads to the development and progression of dysplasia. The diagnosis of BE requires the identification of intestinal metaplasia on histologic examination, which has thus become an essential tool both in the diagnosis and in the assessment of dysplasia's presence and degree. The histologic diagnosis of BE dysplasia can be challenging due to sampling error, pathologists' experience, interobserver variation, and difficulty in histologic interpretation: all these problems complicate patient management. The development and progression of Barrett's esophagus (BE) depend on various molecular events that involve changes in cell-cycle regulatory genes, apoptosis, cell signaling, and adhesion pathways. In advanced stages, there are widespread genomic abnormalities with losses and gains in chromosome function, and DNA instability. This review aims to provide an updated and comprehensible diagnostic approach to BE based on the most recent guidelines available in the literature, and an overview of the pathogenetic and molecular mechanisms of its development.

Signaling Pathways in the Pathogenesis of Barrett's Esophagus and Esophageal Adenocarcinoma

Barrett's esophagus (BE) is a premalignant lesion that can develop into esophageal adenocarcinoma (EAC). The development of Barrett's esophagus is caused by biliary reflux, which causes extensive mutagenesis in the stem cells of the epithelium in the distal esophagus and gastro-esophageal junction. Other possible cellular origins of BE include the stem cells of the mucosal esophageal glands and their ducts, the stem cells of the stomach, residual embryonic cells and circulating bone marrow stem cells. The classical concept of healing a caustic lesion has been replaced by the concept of a cytokine storm, which forms an inflammatory microenvironment eliciting a phenotypic shift toward intestinal metaplasia of the distal esophagus. This review describes the roles of the NOTCH, hedgehog, NF-κB and IL6/STAT3 molecular pathways in the pathogenesis of BE and EAC.

Alginates for Protection Against Pepsin-Acid Induced Aerodigestive Epithelial Barrier Disruption

OBJECTIVE

Gastroesophageal reflux disease (GERD) and laryngopharyngeal reflux (LPR) are chronic conditions caused by backflow of gastric and duodenal contents into the esophagus and proximal aerodigestive tract, respectively. Mucosal barrier dysfunction resultant from the synergistic actions of chemical injury and the mucosal inflammatory response during reflux contributes to symptom perception. Alginates effectively treat symptoms of mild to moderate GERD and have recently shown benefit for LPR. In addition to forming a "raft" over gastric contents to reduce acidic reflux episodes, alginates have been found to bind the esophageal mucosa thereby preserving functional barrier integrity measured by transepithelial electrical resistance. The aim of this study was to further examine the topical protective capacity of alginate-based Gaviscon Advance (GA) and Double Action (GDA) against pepsin-acid mediated aerodigestive epithelial barrier dysfunction in vitro.

STUDY DESIGN

Translational.

METHODS

Immortalized human esophageal and vocal cord epithelial cells cultured in transwells were pretreated with liquid formula GA, GDA, matched viscous placebo solution, or saline (control), then treated for 1 h with saline, acid (pH 3-6) or pepsin (0.1-1 mg/ml) at pH 3-6. Endpoint measure was taken of horseradish peroxidase (HRP) allowed to diffuse across monolayers for 2 h.

RESULTS

Pepsin (0.1-1 mg/ml) at pH 3-6 increased HRP flux through cultures pretreated with saline or placebo (p < 0.05); acid alone did not. GA and GDA prevented barrier dysfunction.

CONCLUSIONS

GA and GDA preserved epithelial barrier function during pepsin-acid insult better than placebo suggesting that protection was due to alginate. These data support topical protection as a therapeutic approach to GERD and LPR. Laryngoscope, 132:2327-2334, 2022.

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.

Evolutionary dynamics in Barrett oesophagus: implications for surveillance, risk stratification and therapy

Cancer development is a dynamic evolutionary process characterized by marked intratumoural heterogeneity at the genetic, epigenetic and phenotypic levels. Barrett oesophagus, the pre-malignant condition to oesophageal adenocarcinoma (EAC), is an exemplary system to longitudinally study the evolution of malignancy. Evidence has emerged of Barrett oesophagus lesions pre-programmed for progression to EAC many years before clinical detection, indicating a considerable window for therapeutic intervention. In this Review, we explore the mechanisms underlying clonal expansion and contraction that establish the Barrett oesophagus clonal mosaicism over time and space and discuss intrinsic genotypic and extrinsic environmental drivers that direct the evolutionary trajectory of Barrett oesophagus towards a malignant phenotype. We propose that understanding and exploiting the evolutionary dynamics of Barrett oesophagus will identify novel therapeutic targets, improve prognostic tools and offer the opportunity for personalized surveillance programmes geared to prevent progression to EAC.

The role of hypoxia-inducible factors in the development of chronic pathology

This review highlights the current understanding of hypoxia-inducible factors (HIFs) role as regulators of oxygen-dependent reactions and inducers of genes expression in human organism. The focus is on the most significant relationships between the activation or inhibition of the HIFs intracellular system and development of the inflammatory process in various organs, chronic diseases of gastrointestinal tract, osteoarticular system, kidneys as well as hematological, endocrine and metabolic disorders.

Reflux esophagitis is associated with higher risks of acute stroke and transient ischemic attacks in patients hospitalized with atrial fibrillation: A nationwide inpatient sample analysis

Reflux esophagitis (RE) is a subset of gastroesophageal reflux disease (GERD) with endoscopic evidence of esophageal inflammation, which has been linked to an increased incidence of atrial fibrillation (AF). However, data on the effect of RE on patient outcomes is limited. We sought to examine the potential association of RE with outcomes of patients with AF in a nationwide study.The National Inpatient Sample (NIS) database was queried to identify hospitalized adult patients with AF and RE between 2010 and 2014. Primary outcomes included inpatient mortality, length of stay (LOS), and total hospital charges. AF related complications such as acute stroke, transient ischemic attack (TIA) and acute heart failure were assessed as secondary outcomes. Propensity score matching and multivariate regression analysis were used.Six lakh sixty seven thousands five hundred twenty patients were admitted for primary diagnosis of AF out of which 5396 had a secondary diagnosis of RE. In the AF with RE cohort, the average age was 73.6 years, 41.5% were male, and 79.9% were Caucasian. There was a greater prevalence of concomitant dyslipidemia, chronic liver disease and chronic pulmonary disease (P < .01) when compared to the AF without RE cohort. Patients with AF and RE also had higher incidence of acute strokes and TIAs (P < .05), longer LOS (P < .001), and higher hospital charges (P < .05) with no difference in acute heart failure (P = .08), hospital mortality (P = .12), or CHA2DS2-VASc score (P = .67).In hospitalized patients with AF, RE was associated with a higher rate of acute stroke and TIAs, longer LOS, and greater hospital charges.

Non-surgical animal model of gastroesophageal reflux disease by overeating induced in mice

Previous animal models of gastroesophageal reflux disease (GERD) were not physiological and required a variety of surgical procedures. Therefore, the animal model developed by conditions that are similar to the pathogenesis of GERD is necessary. The aim is to establish a non-surgical animal model with GERD caused by overeating induced in mice. To induce mice to overeat, we designed dietary control protocols including repetitive fasting and feeding. The esophageal tissues were evaluated with GERD markers to prove the establishment of a GERD animal model. Mice fasted every other day (group 2) showed more pronounced overeating feature and demonstrated evident changes similar to the macroscopic and microscopic findings of GERD, the expressions of inducible nitric oxide synthase and substance P were stronger. The higher frequency of fasting and overeating could cause GERD effectively. The dietary control can make mice overeat, which elicits the change of lower esophageal mucosa similar to GERD. Thus, the overeating-induced mouse may be used as a GERD mouse model.

Mucosal pathogenesis in gastro-esophageal reflux disease

BACKGROUND

Despite gastro-esophageal reflux disease affecting up to 20% of Western populations, relatively little is known about the molecular mechanisms underlying its most troublesome symptom: heartburn. Recent findings have unveiled the role of components of the esophageal mucosa in the pathogenesis of GERD including sensory nociceptive nerves and inflammatory mediators. Erosive esophagitis was long believed to develop as a result of acid injury at the esophageal lumen, but novel concepts suggest the generation of reflux-induced esophageal injury as a result of cytokine-mediated inflammation. Moreover, the localization and characterization of mucosal afferent nerves vary between GERD phenotypes and could explain the heterogeneity of symptom perception between patients who experience similar levels of acid reflux.

PURPOSE

The purpose of this review is to consider the crosstalk of different factors of the esophageal mucosa in the pathogenesis of GERD, with a particular focus on mucosal innervation and molecular basis of acid-induced cytokine response. We discuss the current understanding of the mucosal response to acid injury, the nociceptive role of acid-sensitive receptors expressed in the esophageal mucosa, and the role of esophageal epithelial cells in initiating the onset of erosive esophagitis.

In Barrett's epithelial cells, weakly acidic bile salt solutions cause oxidative DNA damage with response and repair mediated by p38

The frequency of esophageal adenocarcinoma is rising despite widespread use of proton pump inhibitors (PPIs), which heal reflux esophagitis but do not prevent reflux of weakly acidic gastric juice and bile in Barrett's esophagus patients. We aimed to determine if weakly acidic (pH 5.5) bile salt medium (WABM) causes DNA damage in Barrett's cells. Because p53 is inactivated frequently in Barrett's esophagus and p38 can assume p53 functions, we explored p38's role in DNA damage response and repair. We exposed Barrett's cells with or without p53 knockdown to WABM, and evaluated DNA damage, its response and repair, and whether these effects are p38 dependent. We also measured phospho-p38 in biopsies of Barrett's metaplasia exposed to deoxycholic acid (DCA). WABM caused phospho-H2AX increases that were blocked by a reactive oxygen species (ROS) scavenger. WABM increased phospho-p38 and reduced bromodeoxyuridine incorporation (an index of S phase entry). Repair of WABM-induced DNA damage proceeded through p38-mediated base excision repair (BER) associated with reduction-oxidation factor 1-apurinic/apyrimidinic endonuclease I (Ref-1/APE1). Cells treated with WABM supplemented with ursodeoxycholic acid (UDCA) exhibited enhanced p38-mediated responses to DNA damage. All of these effects were observed in p53-intact and p53-deficient Barrett's cells. In patients, esophageal DCA perfusion significantly increased phospho-p38 in Barrett's metaplasia. WABM exposure generates ROS, causing oxidative DNA damage in Barrett's cells, a mechanism possibly underlying the rising frequency of esophageal adenocarcinoma despite PPI usage. p38 plays a central role in oxidative DNA damage response and Ref-1/APE1-associated BER, suggesting potential chemopreventive roles for agents like UDCA that increase p38 activity in Barrett's esophagus.NEW & NOTEWORTHY We found that weakly acidic bile salt solutions, with compositions similar to the refluxed gastric juice of gastroesophageal reflux disease patients on proton pump inhibitors, cause oxidative DNA damage in Barrett's metaplasia that could contribute to the development of esophageal adenocarcinoma. We also have elucidated a critical role for p38 in Barrett's metaplasia in its response to and repair of oxidative DNA damage, suggesting a potential chemopreventive role for agents like ursodeoxycholic acid that increase p38 activity in Barrett's esophagus.

Biomarkers of Barrett's Esophagus: From the Laboratory to Clinical Practice

The currently recommended approach to managing cancer risk for patients with Barrett's esophagus is endoscopic surveillance including a biopsy protocol to sample the esophageal tissue randomly to detect dysplasia. However, there are numerous limitations in this practice that rely on the histopathological grading of dysplasia alone to make clinical decisions. The availability of in silico models demonstrating the potential cost-effectiveness of biomarker-based stratification has increased interest in finding a clinically relevant "Barrett's biomarker." The success of endoscopic eradication therapy in preventing neoplastic progression of dysplastic Barrett's esophagus has promoted the desire to stratify non-dysplastic Barrett's esophagus to those with "high risk" that may benefit from endotherapy. Furthermore, on the other end of the spectrum, there is interest in searching for a "low risk" marker that may identify those that would not likely benefit from endoscopy screening or surveillance. This review highlights recent data from the genomics (r)evolution revealing new genetic biomarkers of susceptibility to the development of Barrett's esophagus and novel pathways for its neoplastic progression, addresses the development of new modes of tissue sampling and imaging to detect early neoplasia in Barrett's esophagus, and discusses current progress in moving biomarkers from the laboratory into clinical practice in the era of precision medicine.

Aspirin prevents NF-κB activation and CDX2 expression stimulated by acid and bile salts in oesophageal squamous cells of patients with Barrett's oesophagus

OBJECTIVE

In previous studies using oesophageal squamous cells from patients with Barrett's oesophagus (normal oesophageal squamous (NES)-B cells) and from patients without Barrett's oesophagus (NES-G cells), we showed that acid and bile salts induced caudal-related homeobox transcription factor 2 (CDX2) expression only in NES-B cells. CDX2, a transcription factor required to form intestinal epithelium, is a target of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signalling, which can be inhibited by aspirin. We explored mechanisms underlying differences between NES-B and NES-G cells in CDX2 expression and effects of aspirin on that CDX2 expression.

DESIGN

We exposed NES-B and NES-G cells to acid and bile salts, with and without aspirin, and evaluated effects on IκB-NF-κB-PKAc complex activation, p65 NF-κB subunit function, and CDX2 expression.

RESULTS

In both NES-B and NES-G cells, acid and bile salts activated nicotinamide adenine dinucleotide phosphate oxidase to generate H₂O₂, which activated the IκB-NF-κB-PKAc complex. NES-B cells exhibited higher levels of phosphorylated IκB and p65 and greater NF-κB transcriptional activity than NES-G cells, indicating greater IκB-NF-κB-PKAc complex activation by acid and bile salts in NES-B cells, and p65 siRNA prevented their increased expression of CDX2. Aspirin blocked IκB phosphorylation, p65 nuclear translocation, CDX2 promoter activation and CDX2 expression induced by acid and bile salts in NES-B cells.

CONCLUSIONS

Differences between NES-B and NES-G cells in NF-κB activation by acid and bile salts can account for their differences in CDX2 expression, and their CDX2 expression can be blocked by aspirin. These findings might explain why some patients with GORD develop Barrett's oesophagus while others do not, and why aspirin might protect against development of Barrett's oesophagus.

A new paradigm for GERD pathogenesis. Not acid injury, but cytokine-mediated inflammation driven by HIF-2α: a potential role for targeting HIF-2α to prevent and treat reflux esophagitis

Traditionally, reflux esophagitis was assumed to develop as a caustic, chemical injury inflicted by refluxed acid. Recently, however, studies in rats and humans suggest that reflux esophagitis develops as a cytokine-mediated inflammatory injury, with hypoxia inducible factor (HIF)-2α playing a major role. In response to the reflux of acid and bile, HIF-2α in esophageal epithelial cells becomes stabilized, thereby increasing production of pro-inflammatory cytokines that attract T lymphocytes and other inflammatory cells to damage the esophagus. Recent studies have identified small molecule inhibitors of HIF-2α that demonstrate exquisite isoform selectivity, and clinical trials for treatment of HIF-2α-driven kidney cancers are ongoing. It is conceivable that a HIF-2α-directed therapy might be a novel approach to prevention and treatment of reflux esophagitis.

Metaplasia: tissue injury adaptation and a precursor to the dysplasia-cancer sequence

Metaplasia is the replacement of one differentiated somatic cell type with another differentiated somatic cell type in the same tissue. Typically, metaplasia is triggered by environmental stimuli, which may act in concert with the deleterious effects of microorganisms and inflammation. The cell of origin for intestinal metaplasia in the oesophagus and stomach and for pancreatic acinar-ductal metaplasia has been posited through genetic mouse models and lineage tracing but has not been identified in other types of metaplasia, such as squamous metaplasia. A hallmark of metaplasia is a change in cellular identity, and this process can be regulated by transcription factors that initiate and/or maintain cellular identity, perhaps in concert with epigenetic reprogramming. Universally, metaplasia is a precursor to low-grade dysplasia, which can culminate in high-grade dysplasia and carcinoma. Improved clinical screening for and surveillance of metaplasia might lead to better prevention or early detection of dysplasia and cancer.

Activation of NADPH oxidases leads to DNA damage in esophageal cells

Gastroesophageal reflux disease (GERD) is the strongest known risk factor for esophageal adenocarcinoma. In the center of tumorigenic events caused by GERD is repeated damage of esophageal tissues by the refluxate. In this study, we focused on a genotoxic aspect of exposure of esophageal cells to acidic bile reflux (BA/A). Analyzing cells generated from patients with Barrett's esophagus and human esophageal specimens, we found that BA/A cause significant DNA damage that is mediated by reactive-oxygen species. ROS originate from mitochondria and NADPH oxidases. We specifically identified NOX1 and NOX2 enzymes to be responsible for ROS generation. Inhibition of NOX2 and NOX1 with siRNA or chemical inhibitors significantly suppresses ROS production and DNA damage induced by BA/A. Mechanistically, our data showed that exposure of esophageal cells to acidic bile salts induces phosphorylation of the p47^phox subunit of NOX2 and its translocation to the cellular membrane. This process is mediated by protein kinase C, which is activated by BA/A. Taken together, our studies suggest that inhibition of ROS induced by reflux can be a useful strategy for preventing DNA damage and decreasing the risk of tumorigenic transformation caused by GERD.

Reflux esophagitis and its role in the pathogenesis of Barrett's metaplasia

Reflux esophagitis damages the squamous epithelium that normally lines the esophagus, and promotes replacement of the damaged squamous lining by the intestinal metaplasia of Barrett's esophagus, the precursor of esophageal adenocarcinoma. Therefore, to prevent the development of Barrett's metaplasia and esophageal adenocarcinoma, the pathogenesis of reflux esophagitis must be understood. We have reported that reflux esophagitis, both in a rat model and in humans, develops as a cytokine-mediated inflammatory injury (i.e., cytokine sizzle), not as a caustic chemical injury (i.e., acid burn), as traditionally has been assumed. Moreover, reflux induces activation of hypoxia inducible factor (HIF)-2α, which enhances the transcriptional activity of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) causing increases in pro-inflammatory cytokines and in migration of T lymphocytes, an underlying molecular mechanism for this cytokine-mediated injury. In some individuals, reflux esophagitis heals with Barrett's metaplasia. A number of possibilities exist for the origin of the progenitor cells that give rise to this intestinal metaplasia including those of the esophagus, the proximal stomach, or the bone marrow. However, intestinal cells are not normally found in the esophagus, the stomach, or the bone marrow. Thus, the development of Barrett's intestinal metaplasia must involve some molecular reprogramming of key developmental transcription factors within the progenitor cell, a process termed transcommitment, which may be initiated by the noxious components of the gastric refluxate. This review will highlight recent studies on the pathogenesis of reflux esophagitis and on reflux-related molecular reprogramming of esophageal squamous epithelial cells in the pathogenesis of Barrett's metaplasia.

Modeling Esophagitis Using Human Three-Dimensional Organotypic Culture System

Esophagitis, whether caused by acid reflux, allergic responses, graft-versus-host disease, drugs, or infections, is a common condition of the gastrointestinal tract affecting nearly 20% of the US population. The instigating agent typically triggers an inflammatory response. The resulting inflammation is a risk factor for the development of esophageal strictures, Barrett esophagus, and esophageal adenocarcinoma. Research into the pathophysiology of these conditions has been limited by the availability of animal and human model systems. Three-dimensional organotypic tissue culture (OTC) is an innovative three-dimensional multicellular in vitro platform that recapitulates normal esophageal epithelial stratification and differentiation. We hypothesized that this platform can be used to model esophagitis to better understand the interactions between immune cells and the esophageal epithelium. We found that human immune cells remain viable and respond to cytokines when cultured under OTC conditions. The acute inflammatory environment induced in the OTC significantly affected the overlying epithelium, inducing a regenerative response marked by increased cell proliferation and epithelial hyperplasia. Moreover, oxidative stress from the acute inflammation induced DNA damage and strand breaks in epithelial cells, which could be reversed by antioxidant treatment. These findings support the importance of immune cell-mediated esophageal injury in esophagitis and confirms the utility of the OTC platform to characterize the underlying molecular events in esophagitis.

Autophagy levels are elevated in barrett's esophagus and promote cell survival from acid and oxidative stress

Autophagy is a highly conserved mechanism that is activated during cellular stress. We hypothesized that autophagy may be induced by acid reflux, which causes injury, and inflammation, and therefore, contributes to the pathogenesis of Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC). Currently, the role of autophagy in BE and EAC is poorly studied. We quantitatively define autophagy levels in human BE cell lines, a transgenic mouse model of BE, and human BE, and EAC biopsies. Human non-dysplastic BE had the highest basal number of autophagic vesicles (AVs), while AVs were reduced in normal squamous cells and dysplastic BE cells, and nearly absent in EAC. To demonstrate a functional role for autophagy in BE pathogenesis, normal squamous (STR), non-dysplastic BE (CPA), dysplastic BE (CPD), and EAC (OE19) cell lines were exposed to an acid pulse (pH 3.5) followed by incubation in the presence or absence of chloroquine, an autophagy inhibitor. Acid exposure increased reactive oxygen species (ROS) levels in STR and CPA cells. Chloroquine alone had a small impact on intracellular ROS or cell survival. However, combination of chloroquine with the acid pulse resulted in a significant increase in ROS levels at 6 h in STR and CPA cells, and increased cell death in all cell lines. These findings establish increased numbers of AVs in human BE compared to normal squamous or EAC, and suggest that autophagy functions to improve cell survival after acid reflux injury. Autophagy may thus play a critical role in BE pathogenesis and progression. © 2015 Wiley Periodicals, Inc.

Role of nitric oxide in the pathogenesis of Barrett’s-associated carcinogenesis

Barrett’s esophagus (BE), a premalignant condition to Barrett’s adenocarcinoma (BAC), is closely associated with chronic inflammation due to gastro-esophageal reflux. Caudal type homeobox 2 (CDX2), a representative marker of BE, is increased during the metaplastic and neoplastic transformation of BE. Nitric oxide (NO) has been proposed to be a crucial mediator of Barrett’s carcinogenesis. We previously demonstrated that CDX2 might be induced directly under stimulation of large amounts of NO generated around the gastro-esophageal junction (GEJ) by activating epithelial growth factor receptor in a ligand-independent manner. Thus, we reviewed recent developments on the role of NO in Barrett’s carcinogenesis. Notably, recent studies have reported that microbial communities in the distal esophagus are significantly different among groups with a normal esophagus, reflux esophagitis, BE or BAC, despite there being no difference in the bacterial quantity. Considering that microorganism components can be one of the major sources of large amounts of NO, these studies suggest that the bacterial composition in the distal esophagus might play an important role in regulating NO production during the carcinogenic process. Controlling an inflammatory reaction due to gastro-esophageal reflux or bacterial composition around the GEJ might help prevent the progression of Barrett’s carcinogenesis by inhibiting NO production.

Chemoprevention in Barrett's Esophagus: Current Status

Chemoprevention in Barrett's esophagus is currently applied only in research settings. Identifying pathways that can be targeted by safe, pharmaceutical or natural compounds is key to expanding the scope of chemoprevention. Defining meaningful surrogate markers of cancer progression is critical to test the efficacy of chemopreventive approaches. Combinatorial chemoprevention that targets multiple components of the same pathway or parallel pathways could reduce the risk and improve the efficacy of chemoprevention. Here we discuss the role of chemoprevention as an independent or an adjuvant management option in BE-associated esophageal adenocarcinoma.

Mechanisms of Barrett's oesophagus: intestinal differentiation, stem cells, and tissue models

Barrett's oesophagus (BE) is defined as any metaplastic columnar epithelium in the distal oesophagus which replaces normal squamous epithelium and which predisposes to cancer development. It is this second requirement, the predisposition to cancer, which makes this condition both clinically highly relevant and an important area for ongoing research. While BE has been defined pathologically since the 1950's (Allison and Johnstone, Thorax 1955), and identified as a risk factor for esophageal adenocarcinoma since the 1970's (Naef A.P., et al J Thorac Cardiovasc Surg. 1975), our understanding of the molecular events giving rise to this condition remains limited. Herein we will examine what is known about the intestinal features of BE and how well it recapitulates the intestinal epithelium, including stem identity and function. Finally, we will explore laboratory models of this condition presently in use and under development, to identify new insights they may provide into this important clinical condition.

Chemoprevention in Barrett's oesophagus

Increasing incidence of oesophageal adenocarcinoma along with poor survival entails novel preventive strategies. Agents that target pro-oncogenic pathways in Barrett's mucosa could halt this neoplastic transformation. In this review, we will use epidemiological associations and molecular mechanisms to identify novel chemoprevention targets in Barrett's oesophagus. We will also discuss recent chemoprevention trials.

Reflux composition influences the level of NF-κB activation and upstream kinase preference in oesophageal adenocarcinoma cells

Oesophageal adenocarcinoma (OA) incidence is rising and prognosis is poor. Understanding the molecular basis of this malignancy is key to finding new prevention and treatment strategies. Gastroesophageal reflux disease is the primary cause of OA, usually managed with acid suppression therapy. However, this often does little to control carcinogenic bile acid reflux. The transcription factor nuclear factor kappa B (NF-κB) plays a key role in the pathogenesis of OA and its activity is associated with a poor response to chemotherapy, making it an attractive therapeutic target. We sought to decipher the role of different bile acids in NF-κB activation in oesophageal cell lines using short, physiologically relevant exposure times. The effect of an acidic or neutral extracellular pH was investigated concurrently, to mimic in vivo conditions associated with or without acid suppression. We found that some bile acids activated NF-κB to a greater extent when combined with acid, whereas others did so in its absence, at neutral pH. The precise composition of an individual's reflux, coupled with whether they are taking acid suppressants may therefore dictate the extent of NF-κB activation in the oesophagus, and hence the likelihood of histological progression and chemotherapy success. Regardless of pH, the kinase inhibitor of κB kinase was pivotal in mediating reflux induced NF-κB activation. Its importance was confirmed further as its increased activation was associated with histological progression in patient samples. We identified further kinases important in acid or bile induced NF-κB signalling in oesophageal cells, which may provide suitable targets for therapeutic intervention.

Modeling inflammation and oxidative stress in gastrointestinal disease development using novel organotypic culture systems

Gastroesophageal reflux disease (GERD), Barrett's esophagus (BE), graft-versus-host disease (GVHD), and inflammatory bowel diseases such as ulcerative colitis and Crohn's disease are common human gastrointestinal diseases that share inflammation as a key driver for their development. A general outcome resulting from these chronic inflammatory conditions is increased oxidative stress. Oxidative stress is caused by the generation of reactive oxygen and nitrogen species that are part of the normal inflammatory response, but are also capable of damaging cellular DNA, protein, and organelles. Damage to DNA can include DNA strand breaks, point mutations due to DNA adducts, as well as alterations in methylation patterns leading to activation of oncogenes or inactivation of tumor suppressors. There are a number of significant long-term consequences associated with chronic oxidative stress, most notably cancer. Infiltrating immune cells and stromal components of tissue including fibroblasts contribute to dynamic changes occurring in tissue related to disease development. Immune cells can potentiate oxidative stress, and fibroblasts have the capacity to contribute to advanced growth and proliferation of the epithelium and any resultant cancers. Disease models for GERD, BE, GVHD, and ulcerative colitis based on three-dimensional human cell and tissue culture systems that recapitulate in vivo growth and differentiation in inflammatory-associated microphysiological environments would enhance our understanding of disease progression and improve our ability to test for disease-prevention strategies. The development of physiologically relevant, human cell-based culture systems is therefore a major focus of our research. These novel models will be of enormous value, allowing us to test hypotheses and advance our understanding of these disorders, and will have a translational impact allowing us to more rapidly develop therapeutic and chemopreventive agents. In summary, this work to develop advanced human cell-based models of inflammatory conditions will greatly improve our ability to study, prevent, and treat GERD, BE, GVHD, and inflammatory bowel disease. The work will also foster the development of novel therapeutic and preventive strategies that will improve patient care for these important clinical conditions.

Bile acids increase levels of microRNAs 221 and 222, leading to degradation of CDX2 during esophageal carcinogenesis

BACKGROUND & AIMS

Bile reflux contributes to development of Barrett's esophagus (BE) and could be involved in its progression to esophageal adenocarcinoma (EAC). We investigated whether bile acids affect levels or functions of microRNAs (MIRs) 221 and 222, which bind to the 3'-UTR of p27Kip1 messenger RNA to inhibit its translation. Reduced p27Kip1 increases degradation of the transcription factor CDX2; levels of CDX2 have been reported to decrease during progression of BE to EAC.

METHODS

We used quantitative reverse transcriptase polymerase chain reaction to compare levels of MIRs 221 and 222 and immunohistochemistry to compare levels of p27Kip1 and CDX2 proteins in areas of BE and EAC from each of 11 patients. We examined the effects of bile acid exposure on levels of MIRs 221 and 222 and CDX2 in EAC cells. We investigated the effects of inhibitors of MIRs 221 and 222 on growth of human EAC xenograft tumors in NOD/SCID/IL-2Rγ(null) mice.

RESULTS

Levels of MIRs 221 and 222 increased and levels of p27Kip1 and CDX2 decreased in areas of EAC vs BE. Levels of MIRs 221 and 222 increased, along with activity of nuclear bile acid receptor/farnesoid X receptor (FXR), when cultured cells were exposed to bile acids. Incubation of cells with bile acids increased degradation of CDX2; this process was reduced when cells were also incubated with proteasome inhibitors. Overexpression of MIRs 221 and 222 reduced levels of p27Kip1 and CDX2, and knockdown of these MIRs increased levels of these proteins in cultured cells. Inhibitors of MIRs 221 and 222 increased levels of p27Kip1 and CDX2 in EAC cells and reduced growth of xenograft tumors in NOD/SCID/IL-2Rγ(null) mice.

CONCLUSIONS

We observed increased levels of MIRs 221 and 222 in human EAC tissues, compared with areas of BE from the same patient. We found that exposure of esophageal cells to bile acids activates FXR and increases levels of MIRs 221 and 222, reducing levels of p27Kip1 and promoting degradation of CDX2 by the proteasome. Our work opened the perspective of therapeutically targeting this pathway either via FXR antagonists or inhibitors of MIRs as a treatment option for BE and EAC.

Bile acid at low pH reduces squamous differentiation and activates EGFR signaling in esophageal squamous cells in 3-D culture

BACKGROUND

Barrett's esophagus is a preneoplastic metaplasia in which the normal squamous epithelium of the esophagus changes to an intestinal, columnar phenotype due to long-term gastro-esophageal reflux. The major components of this reflux are bile and stomach acid. Previous in vitro studies on the effect of bile and acid on esophageal cells have predominantly relied on transformed esophageal squamous cells or cancer cells grown in monolayer culture.

DISCUSSION

In this study, we expanded our previous work using an immortalized primary esophageal squamous cell line (EPC1). We demonstrate that EPC1 cells form a multi-layer, stratified epithelium when grown on polyester transwell filters in media supplemented with calcium. When exposed to short pulses of bile and pH 5, but not either condition alone, EPC1 cells demonstrate a reduction in stratification layers and reduced expression of squamous epithelium-specific genes. Bile at pH 5 also causes activation of epidermal growth factor receptor and down-stream pathways. Blocking epidermal growth factor receptor activation partially attenuates the effects of bile acid and pH 5. These results suggest that bile at low pH, but not bile or low pH alone, promotes loss of differentiation status of stratified squamous esophageal epithelium in vitro, possibly by initiating a mucosal repair response through epidermal growth factor activation.

Reflux induces DNA strand breaks and expression changes of MMP1+9+14 in a human miniorgan culture model

Gastroesophageal reflux disease has been implicated in the pathogenesis of adenocarcinoma of the oesophagus. The same applies to laryngopharyngeal reflux (LPR) and squamous cell cancer of the head and neck, but so far, this link has not been proven. The impact of low pH and bile acids has not been studied extensively in cells other than oesophageal cancer cell lines and tissue. The aims of this study were to investigate the pathogenic potential of reflux and its single components on the mucosa of the upper respiratory tract. We measured DNA stability in human miniorgan cultures (MOCs) and primary epithelial cell cultures (EpCs) in response to reflux by the alkaline comet assay. As matrix metalloproteinases (MMPs) are involved in extracellular matrix remodelling processes and may contribute to cancer progression, we studied the expression of MMP1, -9, and -14 in MOCs, EpC, UM-SCC-22B, and FADUDD. DNA strand breaks (DNA-SBs) increased significantly at low pH and after incubation with human or artificial gastric juice. Single incubation with glycochenodeoxycholic acid also showed a significant increase in DNA-SBs. In epithelial cell cultures, human gastric juice increased the number of DNA-SBs at pH 4.5 and 5.5. Artificial gastric juice significantly up regulated the gene expression of MMP9. Western blot analysis confirmed the results of gene expression analysis, but the up regulation of MMP1, -9, and -14 was donor-specific. Reflux has the ability to promote genomic instability and may contribute to micro environmental changes suitable for the initiation of malignancy. Further functional gene analysis may elucidate the role of laryngopharyngeal reflux in the development of head neck squamous cell carcinoma (HNSCC).

Investigation of the esophageal Rho-kinase expression in patients with Barrett's esophagus

The mechanisms responsible for the malignant transformation in Barrett's esophagus (BE) are still poorly understood. The authors have evaluated the role of Rho-kinase (ROCK1 and ROCK2) expressions in patients with BE. All patients underwent upper gastrointestinal system endoscopy, which was confirmed histologically. Real-time PCR revealed no marked change in gene expressions of ROCK1 and ROCK2 at mRNA levels in BE when compared to controls. Immunohistochemical and western blot analyses showed no change in ROCK1 and ROCK2 protein expressions in BE. This study demonstrates that Rho-kinase gene and protein expressions are not modified in BE.

The role of nitric oxide in the induction of caudal-type homeobox 2 through epidermal growth factor receptor in the development of Barrett's esophagus

OBJECTIVE

The high concentration of nitric oxide (NO) around the gastro-esophageal junction (GEJ) might play an important role in the development of Barrett's esophagus (BE), a precursor of Barrett's adenocarcimona. Although previous studies revealed that the expression of caudal-type homeobox 2 (CDX2), an important marker of BE, might be induced through Epidermal Growth Factor Receptor (EGFR), the roles of NO in this signal transduction remain unclear.

MATERIAL AND METHODS

First, we investigated the expressions of EGFR, CDX2 and nitrotyrosine by immunohistochemical study for BE and squamous epithelium of human specimens. Second, we studied the effect of peroxynitrite, peroxynitrite stimulator, SIN-1, or NO donor, NOC7, on the expression of phosphorylated EGFR and CDX2 in KYSE30, an EGFR-rich human esophageal squamous cell carcinoma cell-line. Specific inhibitors for EGFR, AG1478 and small interfering RNA for EGFR (EGFR-siRNA) were employed to elucidate the role of EGFR in the induction of CDX2.

RESULTS

The immunohistochemical study revealed that the expressions of EGFR, CDX2 and nitrotyrosine in BE were stronger than those in squamous epithelium with positive correlations. Exposure to peroxynitrite, SIN-1 or NOC7 induced EGFR phosphorylation and CDX2 expression in dose- and time-dependent manners. Both EGFR phosphorylation and CDX2 induction were significantly diminished by AG 1478 and EGFR-siRNA.

CONCLUSIONS

We revealed for the first time that extrinsic NO might directly induce CDX2 expression through EGFR phosphorylation. We suggested that NO had an important role in the development of BE from squamous epithelium around GEJ.

Inducible nitric oxide synthase (iNOS) and nitric oxide (NO) are important mediators of reflux-induced cell signalling in esophageal cells

Nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) has been implicated in both DNA damage induction and aberrant cell signalling in various tissue and cell backgrounds. We investigated here the role of iNOS and NO in DNA damage induction and nuclear factor-kappa B (NF-κB) signalling in esophageal cells in vitro. As esophageal adenocarcinoma develops in a background of Barrett's esophagus secondary to reflux disease, it is possible that inflammatory mediators like NO may be important in esophageal cancer development. We show that reflux components like stomach acid and bile acids [deoxycholic acid (DCA)] can induce iNOS gene and protein expression and produce NO generation in esophageal cells, using real-time PCR, western blotting and NO sensitive fluorescent probes, respectively. This up-regulation of iNOS expression was not dependent on NF-κB activity. DCA-induced DNA damage was independent of NF-κB and only partially dependent on iNOS and NO, as measured by the micronucleus assay. These same reflux constituents also activated the oncogenic transcription factor NF-κB, as measured by transcription factor enzyme-linked immunosorbent assay and gene expression studies with NF-κB linked genes (e.g. interleukin-8). Importantly, we show here for the first time that basal levels of NF-κB activity (and possibly acid and DCA-induced NF-κB) are dependent on iNOS/NO and this may lead to a positive feedback loop whereby induced iNOS is upstream of NF-κB, hence prolonging and potentially amplifying this signalling, presumably through NO activation of NF-κB. Furthermore, we confirm increased protein levels of iNOS in esophageal adenocarcinoma and, therefore, in neoplastic development in the esophagus.

Inflammation and Barrett's carcinogenesis

Barrett's esophagus (BE) is one of the most common premalignant lesions in which normal squamous epithelium of the esophagus is replaced by metaplastic columnar epithelium. Esophageal adenocarcinoma (EA) develops through progression from BE to low- and high-grade dysplasia (LGD/HGD) and to adenocarcinoma. It is widely accepted that inflammation can increase cancer risk, promoting tumor progression. Therefore, inflammation is regarded as the seventh hallmark of cancer. In recent years, the inflammation-cancer connection of Barrett's carcinogenesis has been intensively studied, unraveling genetic abnormalities. Besides genetic alterations, inflammation is also epigenetically linked to loss of protein expression through transcriptional silencing via promoter methylation. Key mediators linking inflammation and Barrett's carcinogenesis include reactive oxygen species (ROS), NFκB, inflammatory cytokines, prostaglandins, and specific microRNAs (miRNAs). Therefore, the decipherment of molecular pathways that contain these and novel inflammatory key mediators is of major importance for diagnosis, therapy, and prognosis. The detailed elucidation of the signaling molecules involved in Barrett's carcinogenesis will be important for the development of pharmaceutical inhibitors. We herein give an overview of the current knowledge of the inflammation-mediated genetic and epigenetic alterations involved in Barrett's carcinogenesis. We highlight the role of oxidative stress and deregulated DNA damage checkpoints besides the NFκB pathway.

Cell culture models for studying the development of Barrett's esophagus: a systematic review

Background

Barrett’s esophagus (BE) is a premalignant condition caused by chronic gastroesophageal reflux. BE patients have an increased risk of developing esophageal adenocarcinoma (EAC). As many aspects of this condition are still unknown, there is a need for in vitro models to study BE development.

Aim

To review the literature on cell lines and incubation conditions for studying BE development.

Methods

A literature search was performed using PubMed, EMBASE and the Cochrane library, combining the words esophagus, cell line, culture, Barrett’s, bile, acid, exposure, reflux and adenocarcinoma.

Results

A wide range of cell lines and incubation conditions to study BE development have been reported. The most commonly used cell lines are derived from epithelium from patients with BE or EAC. A 25-minute incubation with 200 μM bile salts induced cell proliferation and Akt phosphorylation. However, increased CDX2 and MUC2 expression was only observed with longer incubations or higher bile salt concentrations. Two-hundred μM bile at pH 6 showed a higher toxicity to EAC cells than the same concentration at pH 7. Multiple 5-minute exposures with 200 μM bile at pH 4 or pH 7 increased CK8/18 and COX2 in BE epithelial cells.

Conclusions

Two-hundred μM conjugated primary or secondary bile salts at pH 4 for multiple short exposures is able to induce BE specific factors in BE cell lines. In SQ and EAC cell lines; however, higher concentrations of secondary bile salts for 8 h are needed to induce BE specific molecules. Due to the high variability in reported methods, it is difficult to determine the most effective in vitro setup for studying the development of BE.

Oxidative stress-induced posttranslational modification of TRPV1 expressed in esophageal epithelial cells

Human esophageal epithelium is continuously exposed to physical stimuli or to gastric acid that sometimes causes inflammation of the mucosa. Transient receptor potential vanilloid 1 (TRPV1) is a nociceptive, Ca(2+)-selective ion channel activated by capsaicin, heat, and protons. It has been reported that activation of TRPV1 expressed in esophageal mucosa is involved in gastroesophageal reflux disease (GERD) or in nonerosive GERD symptoms. In this study, we examined the expression and function of TRPV1 in the human esophageal epithelial cell line Het1A, focusing in particular on the role of oxidative stress. Interleukin-8 (IL-8) secreted by Het1A cells upon stimulation by capsaicin or acid with/without 4-hydroxy-2-nonenal (HNE) was measured by ELISA. Following capsaicin stimulation, the intracellular production of reactive oxygen species (ROS) was determined using a redox-sensitive fluorogenic probe, and ROS- and HNE-modified proteins were determined by Western blotting using biotinylated cysteine and anti-HNE antibody, respectively. HNE modification of TRPV1 proteins was further investigated by immunoprecipitation after treatment with synthetic HNE. Capsaicin and acid induced IL-8 production in Het1A cells, and this production was diminished by antagonists of TRPV1. Capsaicin also significantly increased the production of intracellular ROS and ROS- or HNE-modified proteins in Het1A cells. Moreover, IL-8 production in capsaicin-stimulated Het1A cells was enhanced by synthetic HNE treatment. Immunoprecipitation studies revealed that TRPV1 was modified by HNE in synthetic HNE-stimulated Het1A cells. We concluded that TRPV1 functions in chemokine production in esophageal epithelial cells, and this function may be regulated by ROS via posttranslational modification of TRPV1.

In vitro and ex vivo models of extended reflux exposure demonstrate that weakly acidic mixed reflux heightens NF-kB-mediated gene expression

The development of Barrett's esophagus and its progression to adenocarcinoma are clearly linked to reflux of acid and bile. Our objective in this study was to develop an optimized ex vivo biopsy culture technique to study the molecular signaling events induced after insult with individual refluxate constituents. We illustrate the utility of this method by showing results for NF-kB centered cell signaling, and compare the results with those obtained from esophageal cell lines. We show that upregulation of the two NF-kB target genes show differences in pH preference, with IL-8 being preferentially upregulated by DCA at neutral pH, and IkB being upregulated by neutral DCA, acidic DCA, and acid alone. This was found to be true in both cell lines and biopsy cultures. The maximum responses were noted in both models when mixed reflux (DCA at pH 6) was utilized, perhaps reflecting the pH preference of DCA (pKa 6.2). Both the optimized ex vivo models, and the in vitro cell lines show that bile and acid are capable of inducing NF-kB dependent gene expression, with some interesting differences in preferred transcriptional target. In conclusion, in both cells and cultured biopsies, similar reflux driven gene expression changes were noted, with maximum effects noted with DCA exposures at pH 6.

Inhibitory effect of rosiglitazone on the acid-induced intracellular generation of hydrogen peroxide in cultured feline esophageal epithelial cells

Peroxisome proliferator-activated receptor-gamma (PPARγ) agonists have been reported to enhance antioxidant defenses by increasing levels of catalase and copper-zinc superoxide dismutase (Cu/Zn SOD) in oligodendrocyte progenitor cells. In this study, we investigated the effects of the PPARγ agonist, rosiglitazone, on hydrogen peroxide (H(2)O(2)) generation by acidified medium at pH 5.5 (AM5.5), which is in the pH range of duodenogastric refluxates, in primary cultured feline esophageal epithelial cells (EEC). Successful isolation of EEC was identified by immunocytochemistry. AM5.5- and rosiglitazone-induced cell viabilities were determined using 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyltetrazolium bromide assays. The NAD(P)H oxidase activity was measured, and expression of catalase or SOD protein by AM5.5 in the absence and presence of rosiglitazone was assessed using western blotting analysis. PPARγ protein and mRNA were constitutively expressed in EEC. In the incubation with rosiglitazone alone, cell viability was shown more than 90% at 0-10 μM for 72 h. After exposure to AM5.5 for 8 h, intracellular H(2)O(2) was significantly generated. Treatment with rosiglitazone prior to and during exposure to AM5.5 inhibited the H(2)O(2) generation whereas the specific PPARγ antagonist GW9662 offsets the inhibitory action of rosiglitazone. H(2)O(2) generation was also prevented by a nonspecific ROS scavenger N-acetylcysteine or an inhibitor of NADPH oxidase diphenyleneiodonium. The enhanced AM5.5-induced NAD(P)H oxidase activity was not suppressed by rosiglitazone. Instead, the pretreatment of rosiglitazone enhanced the protein expression of catalase, Cu/Zn SOD, and Mn SOD, which are endogenous antioxidative enzymes. These findings indicate that rosiglitazone inhibits AM5.5-induced intracellular H(2)O(2) production, which occurs via NAD(P)H oxidase activation, by using a PPARγ-dependent pathway, and that the underlying mechanism involves an increase in the expression of catalase and SOD proteins.

The role of secondary bile acids in neoplastic development in the oesophagus

Bile acids have been demonstrated, through the use of animal models and clinical association studies, to play a role in neoplastic development in Barrett's metaplasia. How specific bile acids promote neoplasia is as yet unknown, as are the exact identities of the important bile acid subtypes. The combination of bile subtype with appropriate pH is critical, as pH alters bile acid activity enormously. Hence glycine-conjugated bile acids are involved in neoplastic development at acidic pH (pH ~4), and unconjugated bile acids are involved in neoplastic development at more neutral pH (~6). Bile acids (at the appropriate pH) are potent DNA-damaging agents, due to the induction of ROS (reactive oxygen species), which are mainly induced by bile-induced damage to mitochondrial membranes, allowing leakage of ROS into the cytosol. These ROS also induce pro-survival signalling pathways [e.g. via PKC (protein kinase C)-dependent NF-kappaB (nuclear factor kappaB) activity]. Interestingly, NOS (nitric oxide synthase), through induction of NO may exacerbate this NF-kappaB activity and form a positive-feedback loop to amplify the activation of NF-kappaB by deoxycholic acid in particular. This combination of induced DNA damage and cell survival by bile acids is of major importance in neoplasia. Antioxidants and the tertiary bile acid UDCA (ursodeoxycholic acid) can block bile-induced DNA damage and bile-induced NF-kappaB activity, and should be considered in chemopreventative strategies.

The resistance of esophageal adenocarcinoma to bile salt insult is associated with manganese superoxide dismutase expression

BACKGROUND

Bile acids are implicated as etiologic agents in esophageal cancer. We sought to analyze the impact of bile acid exposure on esophageal epithelial cells, Barrett's metaplastic cells (BE), esophageal adenocarcinoma cells (EAC), and esophageal squamous carcinoma cell (ESC). We sought to determine if cellular resistance is related to manganese superoxide dismutase expression.

METHODS

Cells were exposed to sodium choleate (CA), sodium deoxycholate (DCA), sodium glycocholate (GCA), sodium taurocholate (TCA), or a 1:1 mixture (MIX) of reagents at concentrations in the range 0.2-0.8 mM. Cell viability was evaluated by MTT assay. Manganese superoxide dismutase (MnSOD) expression was analyzed by Western blot. Statistical analysis was performed using SPSS ver. 17.0, SPSS Inc., Chicago, IL.

RESULTS

Bile salt exposure inhibited cell viability in esophageal squamous cells in time- and growth-dependent manner. There was a 50% decrease in cell viability from 4 to 24 h. BE, EAC, and ESC cell lines were more resistant to bile insult. In untreated cell lines, MnSOD expression was significantly decreased in EAC and ESC cell lines compared with esophageal squamous epithelial cells and BE cells (P=0.002). Exposure of ESC cells to bile salt increased MnSOD expression.

CONCLUSION

The confirmation of the role of reactive oxygen species (ROS) and bile acids in esophageal carcinogenesis has interesting implications for chemoprevention in patients with reflux esophagitis and Barrett's esophagus. Further studies are necessary to assess the preventative role of antioxidant supplementation.

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.

In benign Barrett's epithelial cells, acid exposure generates reactive oxygen species that cause DNA double-strand breaks

Cells that sustain double-strand breaks (DSB) can develop genomic instability, which contributes to carcinogenesis, and agents that cause DSBs are considered potential carcinogens. We looked for evidence of acid-induced DNA damage, including DSBs, in benign Barrett's epithelial (BAR-T) cell lines in vitro and in patients with Barrett's esophagus in vivo. In BAR-T cells, we also explored the mechanisms underlying acid-induced DNA damage. We exposed BAR-T cells to acid in the presence of a fluorescent probe for reactive oxygen species (ROS) and in the presence or absence of disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (which prevents intracellular acidification) and N-acety-l-cysteine (a scavenger of ROS). DSBs were detected by Western blotting and immunofluorescence for histone H2AX phosphorylation and by CometAssay. During endoscopy in patients with Barrett's esophagus, we took biopsy specimens from the metaplastic mucosa before and after esophageal perfusion with 0.1 N HCl for 3 min and sought DSBs by Western blotting for histone H2AX phosphorylation. In BAR-T cells, acid exposure resulted in ROS production and caused a time-dependent increase in levels of phospho-H2AX that continued for at least 48 h. Pretreatment with disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate or N-acety-l-cysteine prevented the acid-induced increase in phospho-H2AX levels. DSBs also were detected in biopsy specimens of Barrett's metaplasia following esophageal acid perfusion in all of 6 patients with Barrett's esophagus. Acid exposure causes DSBs in Barrett's epithelial cells through ROS produced as a consequence of intracellular acidification. These findings suggest that acid can be considered a carcinogen in Barrett's esophagus.

Regulation of CDX2 expression in esophageal adenocarcinoma

Reflux of acidic gastric contents and bile acids into the lower esophagus has been identified to have a central role in esophageal malignancy and is reported to upregulate caudal-related homologue 2 (CDX2), a regulatory gene involved in embryonic development and axial patterning of the alimentary tract. The aim of this study was to characterize the expression of CDX2 in a well-defined series of human esophageal tissues, comprising reflux-induced esophagitis, premalignant Barrett esophagus (BE), and primary esophageal adenocarcinoma (EADC). To explore potential molecular regulatory mechanisms, we also studied the expression of beta-catenin, SOX9, and CDX2 promoter methylation in esophageal tissues, in addition to the effect of bile acids and nitric oxide (NO) on CDX2 expression in the normal human esophageal cell line Het1A. Relative to matched normal esophageal epithelia, CDX2 was overexpressed in esophagitis (37% for RNA; cytoplasmic immunoreactivity in 48% of tissues), a high proportion (91%) of BE tissues, and in EADC (57% for RNA; cell nuclear immunopositivity in 80%). An association with beta-catenin expression was seen, but not with SOX9 or CDX2 promoter methylation. In Het1A cells, CDX2 was upregulated following exposure to bile acids and NO, alone and in combination. These results further implicate CDX2 and beta-catenin in the molecular pathogenesis of human EADC. The observed synergistic effect of NO on the efficacy of bile acid-induction of CDX2 suggests a novel role for NO in modulating the development of the Barrett phenotype and esophageal adenocarcinogenesis.

Bile acids as endogenous etiologic agents in gastrointestinal cancer

Bile acids are implicated as etiologic agents in cancer of the gastrointestinal (GI) tract, including cancer of the esophagus, stomach, small intestine, liver, biliary tract, pancreas and colon/rectum. Deleterious effects of bile acid exposure, likely related to carcinogenesis, include: induction of reactive oxygen and reactive nitrogen species; induction of DNA damage; stimulation of mutation; induction of apoptosis in the short term, and selection for apoptosis resistance in the long term. These deleterious effects have, so far, been reported most consistently in relation to esophageal and colorectal cancer, but also to some extent in relation to cancer of other organs. In addition, evidence is reviewed for an association of increased bile acid exposure with cancer risk in human populations, in specific human genetic conditions, and in animal experiments. A model for the role of bile acids in GI carcinogenesis is presented from a Darwinian perspective that offers an explanation for how the observed effects of bile acids on cells contribute to cancer development.

Inflammation and esophageal carcinogenesis

The incidence of esophageal adenocarcinoma is increasing largely in Western populations, and patients diagnosed with this cancer continue to have a poor prognosis. The major risk factors are gastroesophageal reflux disease and Barrett's esophagus, both of which are associated with inflammation of the esophageal squamous epithelium, a condition called reflux esophagitis. The cellular mechanisms contributing to cancer development in the esophagus are poorly understood. The chronic inflammation that is present in Barrett's esophagus creates an environment suitable for DNA damage and altered expression of genes involved in cellular proliferation and inhibition of apoptosis. Key players in the inflammatory cascade include generation of free radicals, activation of kinases pathways and transcription factors, and production of cytokines and inflammatory enzymes. The current review highlights the link between reflux-induced inflammation and esophageal carcinogenesis. Understanding the molecular pathways involved in inflammation-associated esophageal tumorigenesis could enable the development of targeted therapies and offer a better therapeutic treatment in esophageal cancer.

Different redox states in malignant and nonmalignant esophageal epithelial cells and differential cytotoxic responses to bile acid and honokiol

Esophageal adenocarcinoma (EAC) is a highly lethal cancer in western countries. EAC cells are believed to develop from esophageal epithelial cells through complex transformation processes involving inflammation and oxidative stress. The purpose of this study was to compare the redox status of malignant and nonmalignant esophageal epithelial cells and to test their responses to bile acid-induced oxidative stress and to treatment with honokiol (HNK), a natural product with anticancer activity. We demonstrated that esophageal adenocarcinoma cells express significantly higher levels of antioxidant molecules and were resistant to reactive oxygen species (ROS) stress induced by bile acid, but were sensitive to the cytotoxic action of HNK. Mechanistic study showed that HNK caused cancer cell death by disruption of mitochondrial transmembrane potential and was correlated with cyclophilin D (CypD) expression. Inhibition of CypD by cyclosporin A or abrogation of its expression by siRNA significantly suppressed the cytotoxicity of HNK, suggesting that CypD may be a key molecule that mediates the cytotoxicity. Our study suggests that the high antioxidant capacity in EAC cells confers on them the ability to survive the oxidative microenvironment in the reflux esophagus, and that HNK is a promising compound to kill the transformed cells preferentially.

Differences in activity and phosphorylation of MAPK enzymes in esophageal squamous cells of GERD patients with and without Barrett's esophagus

We hypothesized that, in esophageal squamous epithelial cells, there are differences among individuals in the signal transduction pathways activated by acid reflux that might underlie the development of Barrett's esophagus. To explore that hypothesis, we immortalized nonneoplastic, esophageal squamous cells from patients with gastroesophageal reflux disease (GERD) with (NES-B3T) and without (NES-G2T) Barrett's esophagus and used those cells to study acid effects on MAPK proteins. During endoscopy in patients with GERD with and without Barrett's esophagus, we took biopsy specimens from the distal squamous esophagus to study MAPK proteins before and after esophageal perfusion with 0.1 N HCl. We used immunoblotting and Western blotting to study MEK1/2 phosphorylation at two activating sites (serines 217/221), MEK1 phosphorylation at an inhibitory site (threonine 286), and MEK1/2 activity. After acid exposure, both cell lines exhibited increased MEK1/2 phosphorylation at the activating sites; the NES-B3T cells had higher levels of MEK1 phosphorylation at the inhibitory site, however, and only the NES-G2T cells showed an acid-induced increase in MEK1/2 activity. Similarly, in the squamous epithelium of patients with GERD with and without Barrett's esophagus, acid perfusion increased MEK1/2 phosphorylation at the activating sites in both patient groups; the Barrett's patients had higher levels of MEK1 phosphorylation at the inhibitory site, however, and only the patients without Barrett's demonstrated an acid-induced increase in ERK1/2 phosphorylation. In esophageal squamous cell lines and biopsies from patients with GERD with and without Barrett's esophagus, we have found differences in MAPK pathways activated by acid exposure. We speculate that these differences might underlie the development of Barrett's metaplasia.