Bile acids in combination with low pH induce oxidative stress and oxidative DNA damage: relevance to the pathogenesis of Barrett's oesophagus

Systematic review: the role of bile acids in the pathogenesis of gastro-oesophageal reflux disease and related neoplasia

BACKGROUND

Factors other than acid may play a role in gastro-oesophageal reflux disease (GERD) and its complications.

AIM

To assessed the role of bile acids in the pathogenesis of GERD, Barrett's oesophagus and Barrett's-related neoplasia.

METHODS

We conducted a systematic review of computerised bibliographic databases for original articles involving humans or human oesophageal tissue or cells that assessed exposure to or manipulation of bile acids. Outcomes assessed included GERD symptoms; gross oesophageal injury; Barrett's oesophagus and related neoplasia; and intermediate markers of inflammation, proliferation or neoplasia.

RESULTS

Eighty-three original articles were included. In in vivo studies, bile acids concentrations were higher in the oesophageal aspirates of patients with GERD than controls, and bile acids infusions triggered GERD symptoms, especially in high concentrations or in combination with acid. In ex vivo/in vitro studies, bile acids stimulated squamous oesophageal cells and Barrett's epithelial cells to produce inflammatory mediators (e.g., IL-8 and COX-2) and caused oxidative stress, DNA damage and apoptosis. They also induced squamous cells to change their gene expression pattern to resemble intestinal-type cells and caused Barrett's cells to increase expression of intestinal-type genes.

CONCLUSIONS

In aggregate, these studies suggest that bile acids may contribute to the pathogenesis of symptoms, oesophagitis and Barrett's metaplasia with related carcinogenesis in patients with GERD. However, all study results are not uniform and substantial differences in study parameters may explain at least some of this variation.

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.

Characterization of squamous esophageal cells resistant to bile acids at acidic pH: implication for Barrett's esophagus pathogenesis

Barrett's esophagus (BE) is a premalignant condition, where normal squamous epithelium is replaced by intestinal epithelium. BE is associated with an increased risk of developing esophageal adenocarcinoma (EAC). However, the BE cell of origin is not clear. We hypothesize that BE tissue originates from esophageal squamous cells, which can differentiate to columnar cells as a result of repeated exposure to gastric acid and bile acids, two components of refluxate implicated in BE pathology. To test this hypothesis, we repeatedly exposed squamous esophageal HET1A cells to 0.2 mM bile acid (BA) cocktail at pH 5.5 and developed an HET1AR-resistant cell line. These cells are able to survive and proliferate after repeated 2-h treatments with BA at pH 5.5. HET1AR cells are resistant to acidification and express markers of columnar differentiation, villin, CDX2, and cytokeratin 8/18. HET1AR cells have increased amounts of reactive oxygen species, concomitant with a decreased level and activity of manganese superoxide dismutase compared with parental cells. Furthermore, HET1AR cells express proteins and activate signaling pathways associated with inflammation, cell survival, and tumorigenesis that are thought to contribute to BE and EAC development. These include STAT3, NF-κB, epidermal growth factor receptor (EGFR), cyclooxygenase-2, interleukin-6, phosphorylated mammalian target of rapamycin (p-mTOR), and Mcl-1. The expression of prosurvival and inflammatory proteins and resistance to cell death could be partially modified by inhibition of STAT3 signaling. In summary, our study shows that long-term exposure of squamous cells to BA at acidic pH causes the cells to display the same characteristics and markers as BE.

Transformation of benign Barrett's epithelium by repeated acid and bile exposure over 65 weeks: a novel in vitro model

The mechanism by which gastroesophageal reflux promotes metaplasia→dysplasia→carcinoma is unknown. The aim of the study is to determine if repeated exposure to acid and bile confers a tumorigenic phenotype in a telomerase (hTERT)-immortalized benign Barrett's cell line (BAR-T). BAR-T cells were exposed to acid (pH 4) (A) and bile salt (200 μM glycochenodeoxycholic acid) (B) daily for 5 min up to 65+ weeks. The control cells were grown in parallel without any A or B treatment. Cell morphology, proliferation, transformation, and molecular changes in the gene expression for COX-2, TC22, p53 and p53 target genes were analyzed at 8-12 weeks intervals. At 46 weeks BAR-T cells exposed to (A+B) showed distinct phenotypic changes: forming clusters and acini, and at 65 weeks displayed foci in monolayer, and formed distinct colonies in soft agar. Untreated cells did not show any such changes. In A+B-treated BAR-T cells, COX-2 mRNA increased 10- to 20-fold, TC22 mRNA increased by 2- to 3-fold at 22-65 weeks, p53, MDM2, PERP, and p21mRNA increased 2.5-, 6.4-, 4-, and 2.6-fold respectively when compared to untreated cells at 34 weeks. However, at 58 weeks onward, there was a sharp decline of p53 and its target genes to the baseline level. At 65 weeks A+B-treated BAR-T cells formed tumor in nude mice whereas untreated cells did not. We demonstrate a novel in vitro model of transformation of a benign Barrett's cell line following repeated exposure to A+B over the course of 65 weeks.

Hydrophobic bile acid-induced micronuclei formation, mitotic perturbations, and decreases in spindle checkpoint proteins: relevance to genomic instability in colon carcinogenesis

We show, for the first time, that hydrophobic bile acids cause aberrations of the mitotic machinery of colon cells that can give rise to aneuploidy, the chromosomal perturbations common in colon tumors. First, we show that DOC induces a statistically significant fourfold increase in the number of micronuclei in NCM-460 cells (a noncancerous colon cell line) and a threefold increase in the number of micronuclei in binucleated HT-29 colon cancer cells using the cytokinesis block micronucleus assay. Second, we observed mitotic aberrations after DOC treatment, including improper alignment of chromosomes at the metaphase plate, lagging chromosomes during anaphase, anaphase/telophase chromatin bridges, multipolar divisions, and formation of polynucleated cells. It was determined that there was a statistically significant threefold increase in the number of aberrant metaphases after short-term and long-term exposure of HT-29 and HCT-116 cells, respectively. Third, we showed with Western blots and immunohistochemistry that a likely basis for these mitosis-related perturbations included decreased expression of the spindle checkpoint proteins, Mad2, BubR1, and securin. Fourth, results of DOC treatment on nocodazole-challenged cells further indicated deficiencies in activation of the spindle assembly checkpoint. This study provides mechanisms by which hydrophobic bile acids can induce genomic instability in colon epithelial cells.

The biliary HCO(3)(-) umbrella: a unifying hypothesis on pathogenetic and therapeutic aspects of fibrosing cholangiopathies

This review focuses on the hypothesis that biliary HCO(3)(-) secretion in humans serves to maintain an alkaline pH near the apical surface of hepatocytes and cholangiocytes to prevent the uncontrolled membrane permeation of protonated glycine-conjugated bile acids. Functional impairment of this biliary HCO(3)(-) umbrella or its regulation may lead to enhanced vulnerability of cholangiocytes and periportal hepatocytes toward the attack of apolar hydrophobic bile acids. An intact interplay of hepatocellular and cholangiocellular adenosine triphosphate (ATP) secretion, ATP/P2Y- and bile salt/TGR5-mediated Cl(-)/ HCO(3)(-) exchange and HCO(3)(-) secretion, and alkaline phosphatase-mediated ATP breakdown may guarantee a stable biliary HCO(3)(-) umbrella under physiological conditions. Genetic and acquired functional defects leading to destabilization of the biliary HCO(3)(-) umbrella may contribute to development and progression of various forms of fibrosing/sclerosing cholangitis.

Chemoprotective effects of curcumin in esophageal epithelial cells exposed to bile acids

AIM: To investigate the ability of curcumin to counteract the impact of bile acids on gene expression of esophageal epithelial cells.

METHODS: An esophageal epithelial cell line (HET-1A) was treated with curcumin in the presence of deoxycholic acid. Cell proliferation and viability assays were used to establish an appropriate dose range for curcumin. The combined and individual effects of curcumin and bile acid on cyclooxygenase-2 (COX-2) and superoxide dismutase (SOD-1 and SOD-2) gene expression were also assessed.

RESULTS: Curcumin in a dose range of 10-100 μmol/L displayed minimal inhibition of HET-1A cell viability. Deoxycholic acid at a concentration of 200 μmol/L caused a 2.4-fold increase in COX-2 gene expression compared to vehicle control. The increased expression of COX-2 induced by deoxycholic acid was partially reversed by the addition of curcumin, and curcumin reduced COX-2 expression 3.3- to 1.3-fold. HET-1A cells exposed to bile acid yielded reduced expression of SOD-1 and SOD-2 genes with the exception that high dose deoxycholic acid at 200 μmol/L led to a 3-fold increase in SOD-2 expression. The addition of curcumin treatment partially reversed the bile acid-induced reduction in SOD-1 expression at all concentrations of curcumin tested.

CONCLUSION: Curcumin reverses bile acid suppression of gene expression of SOD-1. Curcumin is also able to inhibit bile acid induction of COX-2 gene expression.

Effects of Nissen fundoplication on endoscopic endoluminal radiofrequency ablation of Barrett's esophagus

BACKGROUND

Endoscopic endoluminal radiofrequency ablation is achieving increasing acceptance as a mode of eliminating Barrett's metaplasia and, thus, reducing the risk of developing esophageal adenocarcinoma. It is believed that reducing exposure of the esophageal epithelium to acid is essential to achieve long-term ablation of Barrett's esophagus. However, it is unclear whether use of proton pump inhibitors or antireflux operations are more effective to accomplish this goal.

METHODS

All patients who underwent endoscopic endoluminal radiofrequency ablation with the BARRx device (BARRx Medical, Sunnyvale, CA) were reviewed for date of initial ablation, length of Barrett's epithelium, presence or performance of Nissen fundoplication, all follow-up endoscopy and treatment, and posttreatment biopsy results. Patients were categorized by presence of Nissen fundoplication and presence of Barrett's metaplasia or dysplasia by biopsy at least 12 months following ablation and at last endoscopic follow-up. Data were analyzed by Fisher's exact test and Mann-Whitney U-test.

RESULTS

Of 77 patients ablated, 47 had documented endoscopic follow-up at 12 months or longer following the ablation. Of these, 19 patients had Nissen fundoplication before, at the same time, or after ablation. Median length of Barrett's epithelium, with interquartile range (IQR), was 3 (2-12) cm in patients with fundoplication compared with 3 (2-7) cm without fundoplication (P = NS). Median follow-up was 15 (12-24) months in fundoplication patients compared with 12.5 (12-17) months without (P = NS). One of 19 patients with fundoplication had persistent or recurrent Barrett's epithelium, compared with 7 of 28 without fundoplication (P = 0.03). Of patients without fundoplication, those who had persistent or recurrent Barrett's had median Barrett's length of 10 cm (6-12 cm) compared with 3 cm (2-5 cm) in patients who had ablated Barrett's (P = 0.03). Follow-up length was similar in those with ablated epithelium, 15 months (12-19 months), compared with those with persistent or recurrent Barrett's, 12 months (12-13 months) (P = NS).

CONCLUSIONS

Patients who had fundoplication in conjunction with endoluminal radiofrequency ablation were more likely to achieve durable ablation compared with patients who were treated with proton pump inhibitor therapy. It appears that patients with long-segment Barrett's esophagus are at higher risk for persistent or recurrent Barrett's metaplasia. Consideration should be given for an antireflux operation in patients with long-segment Barrett's esophagus and planned endoluminal radiofrequency ablation.

Barrett esophagus: an update

Many developments have been made in the field of Barrett esophagus that have tremendous clinical implications. There are new definitions of Barrett esophagus that have had an immediate clinical impact on cancer risk and screening. Of interest is the definition by the British Society of Gastroenterology, which does not require the presence of intestinal metaplasia for a diagnosis of Barrett esophagus. Imaging techniques that allow improved visualization of intestinal metaplasia at the cellular level are now being used in clinical practice. New hypotheses elucidating the progression from squamous epithelium to intestinal metaplasia have been proposed. Indeed, the crucial role that transcription factors have in the pathogenesis of Barrett esophagus has been clarified. Improved characterization of the molecular mechanisms underlying Barrett esophagus is an incentive to undertake more basic science research in this field. Such research could also help with the development of chemoprevention strategies for this precancerous condition. This Review discusses the advances in understanding of the pathogenesis, diagnosis and treatment of Barrett esophagus.

Genetic diversity during the development of Barrett's oesophagus-associated adenocarcinoma: how, when and why?

Recent investigations into Barrett's oesophagus at the level of individual crypts have found significant genetic heterogeneity within a single lesion. Furthermore, this genetic diversity has been shown to predict cancer development. In the present article, we review the genetic alterations implicated in disease progression in Barrett's oesophagus and discuss how genetic diversity could arise during tumorigenesis. Three arguments are discussed: a high mutation rate coupled with strong selection, clonal interaction driving progression, and a hitherto unidentified alteration that disrupts epithelial cell homoeostasis. Suggestions are made for future research to distinguish which of these theories is the predominant mechanism in Barrett's oesophagus-associated tumorigenesis.

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.

Inflammatory mediators in gastroesophageal reflux disease: impact on esophageal motility, fibrosis, and carcinogenesis

Gastroesophageal reflux disease (GERD) is one of the most common problems in clinical practice today. It is widely believed that functional and structural abnormalities of the gastroesophageal junction as well as an abnormal exposure to gastroduodenal contents are the main contributors to its pathogenesis. Novel findings of the inflammatory process in GERD suggest a far more complex process involving multifaceted inflammatory mechanisms. This review summarizes knowledge about the expression of inflammatory mediators in GERD and their potential cellular sources and provides an integrated concept of disease pathogenesis. In addition we evaluate the contribution of inflammatory mediators to well-known complications of GERD, namely motility abnormalities, fibrosis, and carcinogenesis. Novel findings regarding the pathophysiology of esophageal inflammation should enhance our understanding of GERD and its complications and provide new treatment insights.

An integrative genomic approach in oesophageal cells identifies TRB3 as a bile acid responsive gene, downregulated in Barrett's oesophagus, which regulates NF-kappaB activation and cytokine levels

Reflux of gastroduodenal contents and consequent inflammatory responses are associated with the development of Barrett's oesophagus (BO) and the promotion of oesophageal adenocarcinoma (OAC). Deregulation of inflammatory processes is a hallmark of oesophageal cancer. In this study, we aimed to investigate (i) the transcriptional responses to deoxycholic acid (DCA) in cell lines representative of either end of the oesophageal cancer sequence, (ii) the expression of DCA-regulated genes in data charting oesophageal carcinogenesis and (iii) the impact of these genes on oesophageal inflammatory signalling. Gene expression microarrays were utilized to demonstrate differential transcriptional responses between squamous (HET-1A) and adenomatous (SKGT4) cell lines exposed to DCA. Differential basal and DCA-inducible expression of cytokines such as interleukin (IL) 8 was observed between both cell types. A cohort of DCA-regulated genes specific to each cell type was identified in microarray experimentation and subsequently validated. Cell type-specific genes included TRB3, CXCL14, GDF15 and LIF in HET-1A cells, with COX2-, ESM1-, URHF1- and IL1alpha-and IL1beta-specific expression in SKGT4 cells. Over 30% of the genes altered in BO and OAC were shown to be regulated by DCA utilizing an integrative genomic approach. One such gene, tribbles-homology-3 (TRB3) was induced specifically in HET-1A cells, absent in SKGT4 cells and decreased in BO samples in silico and in vivo. Inhibition and re-introduction of TRB3 in HET-1A and SKGT4 cells, respectively, demonstrated the ability of TRB3 to regulate inflammatory signalling through nuclear factor-kappaB. This study identifies mechanisms through which bile acids such as DCA, in conjunction with the loss of key signalling molecules, could regulate oesophageal metaplasticity.

Inflammatory mediators in gastroesophageal reflux disease: impact on esophageal motility, fibrosis, and carcinogenesis

Gastroesophageal reflux disease (GERD) is one of the most common problems in clinical practice today. It is widely believed that functional and structural abnormalities of the gastroesophageal junction as well as an abnormal exposure to gastroduodenal contents are the main contributors to its pathogenesis. Novel findings of the inflammatory process in GERD suggest a far more complex process involving multifaceted inflammatory mechanisms. This review summarizes knowledge about the expression of inflammatory mediators in GERD and their potential cellular sources and provides an integrated concept of disease pathogenesis. In addition we evaluate the contribution of inflammatory mediators to well-known complications of GERD, namely motility abnormalities, fibrosis, and carcinogenesis. Novel findings regarding the pathophysiology of esophageal inflammation should enhance our understanding of GERD and its complications and provide new treatment insights.

Role of the micro-environment in Barrett's carcinogenesis

Most epithelial cancers occur on the background of chronic exposure to damaging agents which is reflected in the long lag phase from development of a pre-invasive lesion to the development of a carcinoma. Luminal refluxate has long been recognized to be associated with Barrett's oesophagus, although causal mechanisms have not been clearly defined. Recently, obesity and dietary nitric oxide have also been implicated in the disease pathogenesis. We have demonstrated that acid can alter cell kinetics and, together with nitric oxide, can induce double-stranded DNA breaks. Aside from exposure to luminal factors, the stromal micro-environment may also be important. There is increasing evidence to suggest that inflammatory pathways such as TGF (transforming growth factor) beta may play a role in Barrett's oesophagus carcinogenesis. Hence stromal-epithelial-luminal interactions may influence cell behaviour. As sequelae to this, it is possible that the niches created by the micro-environment may influence genetic epithelial diversity observed within the Barrett's oesophagus segment.

Protective effects of glycoursodeoxycholic acid in Barrett's esophagus cells

Barrett's esophagus (BE) is a premalignant condition associated with the development of esophageal adenocarcinoma (EAC). Previous studies have implicated hydrophobic bile acids and gastric acid in BE and EAC pathogenesis. In this study, we tested the hypothesis that DNA damage, cytotoxicity and oxidative stress induced by bile acids and gastric acid can be attenuated by the cytoprotective, hydrophilic bile acid glycoursodeoxycholic acid (GUDCA). Non-dysplastic BE cells were exposed for 10 min to pH 4 and/or bile acid cocktail or to pH 4 and a modified cocktail consisting of a mixture of bile acids and GUDCA. DNA damage was evaluated by the comet assay; cell viability and proliferation were measured by trypan blue staining and the MTS assay; reactive oxygen species (ROS) were measured using hydroethidium staining; oxidative DNA/RNA damage was detected by immunostaining with antibody against 8-OH-dG; thiol levels were measured by 5-chloromethylfluorescein diacetate (CMFDA) staining; and the expression of antioxidant proteins was evaluated by western blotting. DNA damage and oxidative stress were significantly increased, while thiol levels were decreased in BE cells treated with pH 4 and bile acid cocktail compared with cells treated with pH 4 alone or untreated cells. Bile acids and low pH also significantly decreased cell proliferation. Expression of the antioxidant enzymes, MnSOD and CuZnSOD, was elevated in the cells treated with bile acids and low pH. When GUDCA was included in the medium, all these effects of pH 4 and bile acids were markedly reduced. In conclusion, treatment of BE cells with acidified medium and a bile acid cocktail at physiologically relevant concentrations induces DNA damage, cytotoxicity, and ROS. The cytoprotective bile acid, GUDCA, inhibits these deleterious effects by inhibiting oxidative stress.

The role of oxidative DNA damage, DNA repair, GSTM1, SOD2 and OGG1 polymorphisms in individual susceptibility to Barrett’s esophagus

Determination of the genetic alterations, which play a role in the etiology of Barrett’s esophagus (BE), could help identify high-risk individuals for esophageal adenocarcinoma (EA). The aim of the present study was to investigate the role of oxidative DNA damage, glutathione (GSH) concentration as oxidative stress parameters and DNA repair capacity, GSTM1, SOD1 Ala16Val and OGG1 Ser326Cys genetic polymorphisms as individual susceptibility parameters in the etiology of BE. The study groups comprised BE patients who were clinically diagnosed (n = 40) and a healthy control group (n = 40). Basal DNA damage, pyrimidine and purine base damage after H2O2 induction, H 2O2 sensitivity, DNA repair capacity, oxidized pyrimidine and purine base damage repair were evaluated in peripheral blood lymphocytes with a modified comet assay using specific endonucleases (Endo III and Fpg). Polymerase chain reaction—restriction length polymorphism (PCR-RFLP)-based assays were used for genotyping. The patient group showed elevated levels of basal DNA damage, pyrimidine base damage and H2O2 sensitivity as compared to controls (p < .05). DNA repair capacity, oxidized pyrimidine and purine base damage repair capacity, were not statistically different between patients and controls. GSH concentration was found to be significantly lower in smoking patients than in the controls (p < .05). None of the genetic variations changed the risk of having BE disease. However, patients carrying the variant OGG1 Cys allele showed elevated levels of pyrimidine base damage as compared to patients carrying the wild-type OGG1 Ser (p < .05). The results of this study point to a role of oxidative DNA damage in BE. However, DNA repair capacity, GSTM1, SOD1 Ala16Val and OGG1 Ser326Cys genetic polymorphisms appeared to play no role in the individual susceptibility to this disease.

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.

The role of an alginate suspension on pepsin and bile acids - key aggressors in the gastric refluxate. Does this have implications for the treatment of gastro-oesophageal reflux disease?

OBJECTIVES

During a reflux event the oesophagus is exposed to a heterogeneous mixture of gastric juice components. The role of non-acid components of the refluxate in causing damage to the oesophagus is now well established but no therapeutic option exists to address this.

METHODS

The role of Gaviscon Advance (GA), a raft-forming alginate suspension, in protecting the oesophagus from damage by pepsin and bile acids (aggressors) was investigated using a series of in-vitro models.

KEY FINDINGS

GA was able to dose-dependently inhibit pepsin activity over and above the neutralisation effect of the formulation. This was evident against both protein and collagen substrates using two distinct colorimetric assays. GA was able to retard the diffusion of pepsin and multiple bile acids using a Franz cell model. Using the raft-forming mode of action GA was able to remove both pepsin and multiple bile acids from a simulated reflux event. There was capacity in the GA raft to accommodate aggressors from multiple reflux events.

CONCLUSIONS

GA can specifically remove both pepsin and bile acids from the refluxate, limit their diffusion and affect enzymatic activity of pepsin. There is a role for GA to reduce the damaging potential of the refluxate and thus protect the oesophagus.

Barrett's oesophagus: an ideal model to study cancer genetics

Chronic gastro-oesophageal reflux disease can induce a metaplastic change of the distal oesophagus called Barrett's oesophagus whereby the normal squamous epithelium is substituted by a columnar epithelium. Patients with Barrett's oesophagus are at increased risk of oesophageal adenocarcinoma which occurs through dysplastic stages with increasing degree of cellular and architectural disorganization. Barrett's oesophagus represents an ideal model to study the genetic events supporting the onset of an invasive tumour since patients with this condition are surveilled with endoscopic tissue sampling until high grade dysplasia or intramucosal carcinoma develop. However, due to the relatively low incidence of this disease compared to other cancers, i.e. colon and breast, it is only recently that researchers have concentrated on understanding the genetic events supporting the onset of Barrett's and its transformation to cancer. Here, we review the knowledge acquired so far on the genetic and molecular alterations along the oesophageal metaplasia-dysplasia-carcinoma sequence.

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.

Bile constituents in hibernating golden-mantled ground squirrels (Spermophilus lateralis)

Background

Golden-mantled ground squirrels (S. lateralis) are anorexic during the winter and survive by exploiting hibernation to reduce energetic demands. The liver normally plays a critical role in fueling and regulating metabolism and one might expect significant changes in hepatobiliary function with hibernation. We analyzed bile collected from animals in summer, animals in winter that were either torpid, active between bouts of torpor, or which failed to enter hibernation in order to characterize the effects of hibernation on hepatobiliary function per se.

Results

Surprisingly, hibernator bile did not differ from summer squirrel bile in key characteristics including [bile acids], [cholesterol], [free fatty acids], [lecithin], and osmolality. One major distinction between summer and winter squirrels was that winter squirrels experience >5 fold increases in [bilirubin]. Such an increase may have significant physiological consequences that could aid in survivorship of torpor. Animals that failed to hibernate, despite being anorexic, were very similar to summer squirrels in all measured parameters except they had lower bile acid and lecithin concentrations.

Conclusion

The data indicate that despite extended anorexia, differences in metabolic fuel privation, and bouts of reduced body temperatures, hibernators normally do not experience broad changes in hepatobiliary function.

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.

Barrett's oesophagus

Barrett's oesophagus is a metaplastic change of the lining of the oesophagus, such that the normal squamous epithelium is replaced by specialised or intestinalised columnar epithelium. The disorder seems to be a complication of chronic gastro-oesophageal reflux disease, although asymptomatic individuals might also be affected, and it is a risk factor for the development of oesophageal adenocarcinoma, a cancer with rapidly increasing incidence in developed societies. We review the presentation, epidemiology, and risk factors for this condition. We discuss the molecular changes necessary for the development of Barrett's oesophagus and its progression to cancer, and new strides in both the endoscopic detection of the lesion and the treatment of dysplastic disease. Also, we assess the effectiveness of efforts to screen patients at risk of Barrett's oesophagus, and whether such efforts avert cancer death. We conclude with a discussion of future directions for research, focusing on treatment of early neoplasia, and modifications of current practices to show our evolving understanding of this condition.

Sodium deoxycholate causes nitric oxide mediated DNA damage in oesophageal cells

Patients with chronic gastro-oesophageal reflux disease experience the reflux of acid and bile into the distal oesophagus. The secondary bile salt sodium deoxycholate (NDC) is implicated in the induction of mucosal injury during reflux episodes. This study hypothesized that NDC damages DNA in oesophageal cells by an oxidative mechanism. In the oesophageal cell line HET1-A, increased production of nitric oxide (NO) was measured in NDC-treated cells. Protection from DNA strand breaks induced by NDC (10 microm) was observed in cells coincubated with the nitric oxide scavenger C-PTIO (p<0.012) or pre-incubated with the NO synthase inhibitor L-NAME (p<0.009) or the NFkappaB inhibitor, TPCK (p<0.036). Collectively these data implicate the involvement of NFkappaB and nitric oxide synthase in the DNA damage induced by NDC in oesophageal cells. In conclusion, NDC-driven NO production may play an important role in inducing DNA damage during episodes of gastro-oesophageal reflux and thereby contribute to reflux-related carcinogenesis.

DNA hypermethylation regulates the expression of members of the Mu-class glutathione S-transferases and glutathione peroxidases in Barrett's adenocarcinoma

BACKGROUND

The accumulation of reactive oxygen species and subsequent oxidative DNA damage underlie the development of Barrett's oesophagus (BO) and its progression to Barrett's dysplasia (BD) and adenocarcinoma (BAC).

METHODS

The promoter regions of 23 genes of the glutathione S-transferase (GST) and glutathione peroxidase (GPX) families were systematically analysed. Quantitative bisulfite pyrosequencing, real-time RT-PCR, western blot and immunohistochemical (IHC) analysis methods were utilised in this study.

RESULTS

14 genes were identified that have CpG islands around their transcription start sites: GSTs (GSTM2-M5, GSTA4, GSTP1, GSTZ1, GSTT2, GSTO1 and GSTO2) and GPXs (GPX1, GPX3, GPX4 and GPX7). Analysis of an initial set of 20 primary samples demonstrated promoter DNA hypermethylation and mRNA downregulation of GPX3, GPX7, GSTM2, GSTM3 and GSTM5 in more than half of the BAC samples. Further analysis of 159 primary human samples (37 normal, 11 BO, 11 BD and 100 BACs) indicated frequent hypermethylation (>or=10% methylation) of GPX3 (62%), GPX7 (67%), GSTM2 (69.1%) and GSTM3 (15%) in BACs. A significant inverse correlation between DNA methylation and mRNA expression level was shown for GPX3 (p<0.001), GPX7 (p = 0.002), GSTM2 (p<0.001) and GSTM5 (p = 0.01). Treatment of oesophageal cancer cell lines with 5-aza-2'-deoxycytidine and trichostatin-A led to reversal of the methylation pattern and re-expression of these genes at the mRNA and protein levels. The IHC analysis of GPX3, GPX7 and GSTM2 on a tissue microarray that contained 75 BACs with normal squamous oesophageal samples demonstrated an absent to weak staining in tumours (52% for GPX3, 57% for GPX7 and 45% for GSTM2) and a moderate to strong immunostaining in normal samples.

CONCLUSION

Epigenetic inactivation of members of the glutathione pathway can be an important mechanism in Barrett's tumourigenesis.

Barrett's esophagus: pathogenesis, treatment, and prevention

Esophageal adenocarcinoma is the most common type of esophageal cancer seen in the United States and Western Europe. Barrett's esophagus (BE) is a well-known risk factor for esophageal adenocarcinoma and is believed to be found in 6% to 12% of patients undergoing endoscopy for gastroesophageal reflux disease and in more than 1% of all patients undergoing endoscopy. This article focuses on the pathogenesis, treatment, and prevention of BE.

The bile acid deoxycholic acid has a non-linear dose response for DNA damage and possibly NF-kappaB activation in oesophageal cells, with a mechanism of action involving ROS

Deoxycholic acid (DCA) is a secondary bile acid implicated in various cancers of the gastrointestinal (GI) tract. In oesophageal adenocarcinoma, DCA is believed to contribute to carcinogenesis during reflux where stomach contents enter the lower oesophagus. It is imperative that we understand the mechanisms whereby oesophageal carcinogens function in order that therapeutic options may be developed. We have previously shown that DCA can damage chromosomes and does so through its generation of reactive oxygen species (ROS). We show here, after detailed experiments, that DCA appears to have a non-linear dose response for DNA damage. DCA induces DNA damage (as measured by the micronucleus assay) at doses of 100 microM and higher in oesophageal OE33 cells, but fails to induce such DNA damage below this cut-off dose. We also show that in terms of NF-kappaB activation (as measured by up-regulation of two NF-kappaB target genes) by DCA, a similar dose response is observed. This dose-response data may be important clinically as DCA exposure to the oesophagus may be used as a way to identify the 10% of Barrett's oesophagus patients currently progressing to cancer from the 90% of patients who do not progress. Only quantitative studies measuring DCA concentrations in refluxates correlated with histological progression will answer this question. We further show here that ROS are behind DCAs ability to activate NF-kappaB as antioxidants (epigallocatechin gallate, resveratrol and vitamin C) abrogate DCAs ability to up-regulate NF-kappaB-controlled genes. In conclusion, low doses of DCA appear to be less biologically significant in vitro. If this were to be confirmed in vivo, it might suggest that reflux patients with low DCA concentrations may be at a lower risk of cancer progression compared to patients with high levels of DCA in their refluxate. Either way, antioxidant supplementation may possibly help prevent the deleterious effects of DCA in the whole GI tract.

Bile acid exposure up-regulates tuberous sclerosis complex 1/mammalian target of rapamycin pathway in Barrett's-associated esophageal adenocarcinoma

Barrett's esophagus, a columnar metaplasia of the lower esophagus epithelium related to gastroesophageal reflux disease, is the strongest known risk factor for the development of esophageal adenocarcinoma (EAC). Understanding the signal transduction events involved in esophageal epithelium carcinogenesis may provide insights into the origins of EAC and may suggest new therapies. To elucidate the molecular pathways of bile acid-induced tumorigenesis, the newly identified inflammation-associated signaling pathway involving I kappaB kinases beta (IKK beta), tuberous sclerosis complex 1 (TSC1), and mammalian target of rapamycin (mTOR) downstream effector S6 kinase (S6K1) was confirmed to be activated in immortalized Barrett's CPC-A and CPC-C cells and esophageal cancer SEG-1 and BE3 cells. Phosphorylation of TSC1 and S6K1 was induced in response to bile acid stimulation. Treatment of these cells with the mTOR inhibitor rapamycin or the IKK beta inhibitor Bay 11-7082 suppressed bile acid-induced cell proliferation and anchorage-independent growth. We next used an orthotopic rat model to evaluate the role of bile acid in the progression of Barrett's esophagus to EAC. Of interest, we found high expression of phosphorylated IKK beta (pIKK beta) and phosphorylated S6K1 (pS6K1) in tumor tissues and the Barrett's epithelium compared with normal epithelium. Furthermore, immunostaining of clinical EAC tissue specimens revealed that pIKK beta expression was strongly correlated with pS6K1 level. Together, these results show that bile acid can deregulate TSC1/mTOR through IKK beta signaling, which may play a critical role in EAC progression. In addition, Bay 11-7082 and rapamycin may potentially be chemopreventive drugs against Barrett's esophagus-associated EAC.

Field defects in progression to gastrointestinal tract cancers

A field of defective tissue may represent a pre-malignant stage in progression to many cancers. However, field defects are often overlooked in studies of cancer progression through assuming tissue at some distance from the cancer is normal. We indicate, however, the generality of field defects in gastrointestinal cancers, including cancers of the oropharynx, esophagus, stomach, bile duct, pancreas, small intestine and colon/rectum. Common features of these field defects are reduced apoptosis competence, aberrant proliferation and genomic instability. These features are often associated with high bile acid exposure and may explain the association of dietary-related factors with cancer progression.

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

We hypothesized that differences among individuals in reflux-induced oxidant production by esophageal squamous epithelial cells might contribute to the development of Barrett's esophagus. We studied the effects of acid and bile acids on the production of reactive oxygen species (ROS) in esophageal squamous cell lines derived from gastroesophageal reflux disease patients with (NES-B3T) and without (NES-G2T) Barrett's esophagus and in a Barrett's epithelial cell line (BAR-T). Cells were incubated with an ROS-sensitive probe and exposed to acidic medium, neutral bile acid medium, or acidic bile acid medium. ROS were quantified in the presence and absence of diphenyleneiodonium chloride (DPI, an NADPH oxidase inhibitor), N(G)-monomethyl-l-arginine (l-NMMA, a nitric oxide synthase inhibitor), and rotenone (a mitochondrial electron transport chain inhibitor). Acidic bile acid medium induced ROS production in both squamous cell lines; however, only DPI blocked ROS production by NES-B3T cells, whereas both DPI and l-NMMA blocked ROS production by NES-G2T cells. In BAR-T cells, acidic medium and acidic bile acid medium induced the production of ROS; l-NMMA prevented ROS production after exposure to acidic medium, whereas ROS production induced by acidic bile acid medium was blocked by DPI. These studies demonstrate that there are differences between esophageal squamous cells and Barrett's epithelial cells and between esophageal squamous cells from gastroesophageal reflux disease patients with and without Barrett's esophagus in the mechanisms of oxidant production induced by exposure to acid and bile acids.

Activation of the interleukin-6/STAT3 antiapoptotic pathway in esophageal cells by bile acids and low pH: relevance to barrett's esophagus

OBJECTIVES

The molecular factors contributing to the development of Barrett's esophagus (BE) are unclear. Our previous studies showed that BE tissues secrete interleukin-6 (IL-6) and express proteins associated with IL-6 signaling, including IL-6 receptor, activated signal transducer and activators of transcription 3 (STAT3), and antiapoptotic proteins Bcl-x(L) and Mcl-1. Here, we test the hypothesis that bile acids and gastric acids, two components of refluxate associated with gastresophageal reflux disease, activate the IL-6/STAT3 pathway.

MATERIALS AND METHODS

Immunohistochemistry was used to assess levels of phosphorylated STAT3 in esophageal tissue samples from BE patients with different grades of dysplasia. Seg-1 esophageal adenocarcinoma cells were evaluated for STAT3 activation and IL-6 and Bcl-x(L) expression by molecular biology techniques, including Western blot, reverse transcription-PCR, and ELISA after exposure to control media (pH 7.4), media supplemented with a 0.1 mmol/L bile acid cocktail with media at pH 4 or media at pH 4 with bile acid cocktail.

RESULTS

Immunohistochemical analysis showed that activated, phosphorylated STAT3 is expressed in nuclei of dysplastic BE and cancer tissues. Treatment of Seg-1 cells with media containing bile acid cocktail and acidified to pH 4 resulted in increased activation of STAT3, IL-6 secretion, and increased expression of Bcl-x(L). Inhibition of the STAT3 pathway using STAT3 small interfering RNA or Janus-activated kinase inhibitor resulted in increased apoptosis.

CONCLUSIONS

The IL-6/STAT3 antiapoptotic pathway is induced by short exposure to bile acid cocktail and low pH. This alteration, if persistent in vivo, may underlie the development of dysplastic BE and tumor progression.

Bile acids induce overexpression of homeobox gene CDX-2 and vascular endothelial growth factor (VEGF) in human Barrett's esophageal mucosa and adenocarcinoma cell line

OBJECTIVE

Barrett's esophagus (BE) is an acquired precancerous condition that develops from mucosal injury incurred after chronic gastroesophageal acid and bile reflux. The mechanism of progression of carcinogenesis in BE is still not fully understood. Recently, the role of bile acids and the homeobox gene transcription factor CDX-2 has been suggested in the pathogenesis of BE. The aims of the present study were 1) to compare the mRNA and protein expression of CDX-2 in biopsies obtained from patients with BE and normal squamous epithelium and 2) to study the effect of two different bile salts, ursodeoxycholic acid (UDCA) and deoxycholic acid (DCA), on the mRNA expression of CDX-2 and vascular endothelial growth factor (VEGF) in Barrett's the adenocarcinoma cell line (OE-33).

MATERIAL AND METHODS

CDX-2 expression was measured in Barrett's mucosa and normal esophageal mucosa obtained from 15 patients with BE histologically diagnosed by immunohistochemistry, Western blot, and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In in vitro experiments, OE-33 cells were incubated with DCA (100 microM) and UDCA (100 microM) in neutral and shortly acidified media (pulse acidification). The expression of CDX-2 and VEGF was assessed by quantitative RT-PCR.

RESULTS

Both mRNA and protein expression of CDX-2 were significantly up-regulated in Barrett's mucosa as compared to normal esophageal mucosa. In neutral medium, OE-33 cells showed an increase in CDX-2 expression after incubation with DCA or UDCA. After short acidification of the medium, expression of CDX-2 in OE-33 cells was significantly higher than that in cells incubated in neutral pH. The addition of DCA and UDCA did not cause any further alteration in CDX-2 expression. In neutral and acidified medium, VEGF mRNA expression was only significantly up-regulated by DCA, but not by UDCA.

CONCLUSIONS

Bile acids, especially in acidic medium, increase expression of CDX-2. DCA appears to be a stronger stimulant of the expression of VEGF than UDCA in the Barrett's carcinoma cell line, indicating a stronger carcinogenic potential of this bile salt.

In non-neoplastic Barrett's epithelial cells, acid exerts early antiproliferative effects through activation of the Chk2 pathway

Acid exerts pro-proliferative effects in Barrett's-associated esophageal adenocarcinoma cells. In non-neoplastic Barrett's epithelial (BAR-T) cells, in contrast, we have shown that acid exposure has antiproliferative effects. To explore our hypothesis that the acid-induced, antiproliferative effects are mediated by alterations in the proteins that regulate the G(1)-S cell cycle checkpoint, we exposed non-neoplastic Barrett's cells to acidic media (pH 4.0) and analyzed G(1)-S checkpoint proteins' expression, phosphorylation, and activity levels by Western blot. We studied acid effects on growth (by cell counts), proliferation (by flow cytometry and bromodeoxyuridine incorporation), cell viability (by trypan blue staining), and apoptosis (by annexin V staining), and we used caffeine and small interfering RNA to assess the effects of checkpoint kinase 2 (Chk2) inhibition on G(1)-S progression. Acid exposure significantly decreased cell numbers without affecting cell viability and with only a slight increase in apoptosis. Within 2 h of acid exposure, there was a delay in progression through the G(1)-S checkpoint that was associated with increased phosphorylation of Chk2, decreased levels of Cdc25A, and decreased activity of cyclin E-cyclin-dependent kinase 2; by 4 h, a continued delay at G(1)-S was associated with increased expression of p53 and p21. Caffeine and Chk2 siRNA abolished the acid-induced G(1)-S delay at 2 but not at 4 h. We conclude that acid exposure in non-neoplastic BAR-T cells causes early antiproliferative effects that are mediated by the activation of Chk2. Thus, we have elucidated a mechanism whereby acid can exert disparate effects on proliferation in neoplastic and non-neoplastic BAR-T cells.

Nitric oxide and acid induce double-strand DNA breaks in Barrett's esophagus carcinogenesis via distinct mechanisms

BACKGROUND & AIMS

The luminal microenvironment including acid and nitric oxide (NO) has been implicated in Barrett's esophagus carcinogenesis. We investigated the ability of acid and NO to induce DNA damage in esophageal cells.

METHODS

Transformed and primary Barrett's esophagus and adenocarcinoma cells were exposed to either acid, (pH 3.5), +/- antioxidant or NO from a donor or generated by acidification of nitrite in the presence of ascorbate +/- NO scavenger. Phosphorylation of histone H2AX and the neutral comet assay were used to detect DNA double-strand breaks (DSBs). Intracellular levels of reactive oxygen species and NO were detected with fluorescent dyes. Mitochondrial viability was measured with a rhodamine dye. Long-term survival was assessed by clonogenic assay.

RESULTS

Exposure to acid (pH 3.5) for > or =15 minutes induced DSBs in all cell lines (P < .05). There was a concomitant increase in intracellular reactive oxygen species in the absence of mitochondrial damage, and pretreatment with antioxidants inhibited DNA damage. Exposure to physiologic concentrations of NO produced from the NO donor or acidification of salivary nitrite induced DSBs in a dose- (>25 micromol/L) and cell-dependent manner (adenocarcinoma >Barrett's esophagus, P < .05). This occurred preferentially in S-phase cells consistent with stalled replication forks and was blocked with a NO scavenger. NO also induced DSBs in primary Barrett's esophagus cells treated ex vivo. Cells were able to survive when exposed to acid and NO.

CONCLUSIONS

Both acid and NO have the potential to generate DSBs in the esophagus and via distinct mechanisms.

Review article: the pathophysiology of gastro-oesophageal reflux disease

BACKGROUND

Gastro-oesophageal reflux disease (GERD) is a common condition that develops when the reflux of stomach contents causes troublesome symptoms and/or complications.

AIM

To review the current knowledge on the underlying factors contributing to GERD, with particular emphasis on the most recent research.

METHODS

Literature searches were conducted in Medline and EMBASE. The abstracts from recent large congresses were also reviewed to ensure coverage of the latest findings.

RESULTS

The pathophysiological factors causing GERD can be split into those inducing greater exposure of the oesophagus to stomach contents, and those that provide increased perception of reflux or increased mucosal damage. Transient lower oesophageal sphincter relaxations, which are likely to be triggered by gastric distension, appear to be a key physiological cause of GERD. Excessive reflux may also be provoked by impaired oesophageal or gastric clearance mechanisms. Pre-epithelial, epithelial and post-epithelial defences all normally protect the oesophagus from injury, and may be compromised in individuals with GERD. Heartburn could also be caused by oesophageal hypersensitivity as a result of visceral neural pathway dysfunction.

CONCLUSION

The pathophysiology of GERD is multifactorial, and abnormalities in the gastro-oesophageal junction, the stomach, the oesophagus and the nervous system may all contribute to this disease state.

Simultaneous detection of apoptosis and mitochondrial superoxide production in live cells by flow cytometry and confocal microscopy

Annexin V and Sytox Green are widely used markers to evaluate apoptosis in various cell types using flow cytometry and fluorescent microscopy. Recently, a novel fluoroprobe MitoSOX Red was introduced for selective detection of superoxide in the mitochondria of live cells and was validated for confocal microscopy and flow cytometry. This protocol describes simultaneous measurements of mitochondrial superoxide generation with apoptotic markers (Annexin V and Sytox Green) by both flow cytometry and confocal microscopy in endothelial cell lines. The advantages of the described flow cytometry method over other cell-based techniques are the tremendous speed (1-2 h), exquisite precision and the possibility of simultaneous quantitative measurements of mitochondrial superoxide generation and apoptotic (and other) markers, with maximal preservation of cellular functions. This method combined with fluorescent microscopy may be very useful to reveal important spatial-temporal changes in mitochondrial superoxide production and execution of programmed cell death in virtually any cell type.