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

Bile acids: from digestion to cancers

Bile acids (BAs) are cholesterol metabolites that have been extensively studied these last decades. BAs have been classified in two groups. Primary BAs are synthesized in liver, when secondary BAs are produced by intestinal bacteria. Recently, next to their ancestral roles in digestion and fat solubilization, BAs have been described as signaling molecules involved in many physiological functions, such as glucose and energy metabolisms. These signaling pathways involve the activation of the nuclear receptor FXRα or of the G-protein-coupled receptor TGR5. These two receptors have selective affinity to different types of BAs and show different expression patterns, leading to different described roles of BAs. It has been suggested for long that BAs could be molecules linked to tumor processes. Indeed, as many other molecules, regarding analyzed tissues, BAs could have either protective or pro-carcinogen activities. However, the molecular mechanisms responsible for these effects have not been characterized yet. It involves either chemical properties or their capacities to activate their specific receptors FXRα or TGR5. This review highlights and discusses the potential links between BAs and cancer diseases and the perspectives of using BAs as potential therapeutic targets in several pathologies.

Barrett's esophagus: proton pump inhibitors and chemoprevention II

The following on proton pump inhibitors (PPIs) and chemoprevention in relation to Barrett's esophagus includes commentaries on 48-h pH monitoring, pH-impedence, bile acid testing, dyspepsia, long/short segment Barrett's esophagus, nonerosive reflux disease (NERD), functional heartburn, dual-release delivery PPIs, immediate-release PPIs, long-term PPI use, prokinetic agents, obesity, baclofen, nocturnal acid breakthrough, nonsteroidal anti-inflammatory drugs (NSAIDs), and new PPIs.

The risk of oesophageal adenocarcinoma after gastrectomy for peptic ulcer disease

BACKGROUND

The influence of bile reflux in the development of oesophageal adenocarcinoma remains controversial. This was tested in a cohort of patients who had undergone gastrectomy, a procedure often entailed by substantial bile reflux.

METHODS

A population-based cohort study of patients who had undergone gastrectomy for peptic ulcer disease in 1964-2008 in Sweden. Follow-up for cancer and censoring for death were achieved through linkages to nationwide registries of Cancer and Population, respectively. The number of observed cancer cases in the gastrectomy cohort was divided by the expected number, calculated from the incidence of the entire Swedish population of corresponding age, sex and calendar year. Relative risks were thus presented as standardised incidence ratios with 95% confidence intervals.

RESULTS

After exclusion of all person-years the first year after surgery, the final gastrectomy cohort comprised of 19,767 patients. These patients were followed up for a median of 17 years, and contributed with a total of 348,231 person-years at risk. The observed number of patients with oesophageal adenocarcinoma (n=7) was not higher than the expected (n=11.6), providing a standardised incidence ratio of 0.6 (95%CI 0.2-1.2). There were no clear differences between sexes, age groups or latency intervals after gastrectomy.

CONCLUSIONS

Gastrectomy for peptic ulcer disease does not appear to increase the risk of oesophageal adenocarcinoma.

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.

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.

Hydrophobic bile acids, genomic instability, Darwinian selection, and colon carcinogenesis

Sporadic colon cancer is caused predominantly by dietary factors. We have selected bile acids as a focus of this review since high levels of hydrophobic bile acids accompany a Western-style diet, and play a key role in colon carcinogenesis. We describe how bile acid-induced stresses cause cell death in susceptible cells, contribute to genomic instability in surviving cells, impose Darwinian selection on survivors and enhance initiation and progression to colon cancer. The most likely major mechanisms by which hydrophobic bile acids induce stresses on cells (DNA damage, endoplasmic reticulum stress, mitochondrial damage) are described. Persistent exposure of colon epithelial cells to hydrophobic bile acids can result in the activation of pro-survival stress-response pathways, and the modulation of numerous genes/proteins associated with chromosome maintenance and mitosis. The multiple mechanisms by which hydrophobic bile acids contribute to genomic instability are discussed, and include oxidative DNA damage, p53 and other mutations, micronuclei formation and aneuploidy. Since bile acids and oxidative stress decrease DNA repair proteins, an increase in DNA damage and increased genomic instability through this mechanism is also described. This review provides a mechanistic explanation for the important link between a Western-style diet and associated increased levels of colon cancer.