Effect of endotoxin on opossum oesophageal motor function

The Role of Microbiota in the Pathogenesis of Esophageal Adenocarcinoma

Simple Summary

Esophageal adenocarcinoma has a poor 5-year survival rate and is among the highest mortality cancers. Changes in the esophageal microbiome have been associated with cancer pathogenesis; however, the molecular mechanism remains obscure. This review article critically analyzes the molecular mechanisms through which microbiota may mediate the development and progression of esophageal adenocarcinoma and its precursors-gastroesophageal reflux disease and Barrett’s esophagus. It summarizes changes in esophageal microbiome composition in normal and pathologic states and subsequently discusses the role of altered microbiota in disease progression. The potential role of esophageal microbiota in protecting against the development of esophageal adenocarcinoma is also discussed. By doing so, this article highlights specific directions for future research developing microbiome-mediated therapeutics for esophageal adenocarcinoma.

Abstract

Esophageal adenocarcinoma (EAC) is associated with poor overall five-year survival. The incidence of esophageal cancer is on the rise, especially in Western societies, and the pathophysiologic mechanisms by which EAC develops are of extreme interest. Several studies have proposed that the esophageal microbiome may play an important role in the pathophysiology of EAC, as well as its precursors—gastroesophageal reflux disease (GERD) and Barrett’s esophagus (BE). Gastrointestinal microbiomes altered by inflammatory states have been shown to mediate tumorigenesis directly and are now being considered as novel targets for both cancer treatment and prevention. Elucidating molecular mechanisms through which the esophageal microbiome potentiates the development of GERD, BE, and EAC will provide a foundation on which new therapeutic targets can be developed. This review summarizes current findings that elucidate the molecular mechanisms by which microbiota promote the pathogenesis of GERD, BE, and EAC, revealing potential directions for additional research on the microbiome-mediated pathophysiology of EAC.

Gastrointestinal dysmotility in critically ill patients

Gastrointestinal (GI) motility disorders are commonly present in critical illness. Up to 60% of critically ill patients have been reported to experience GI dysmotility of some form necessitating therapeutic intervention. It has been attributed to various factors, related to both the underlying disease and the therapeutic interventions undertaken. The assessment of motility disturbances can be challenging in critically ill patients, as the available tests used to detect abnormal motility have major limitations in the setting of an Intensive Care Unit. Critically ill patients with GI dysmotility require a multifaceted treatment approach that addresses multiple causes and utilizes multiple pharmacological pathways. In this review, we discuss the pathophysiology, assessment and management of GI dysmotility in critically ill patients.

Inhibition of pacemaker activity in interstitial cells of Cajal by LPS via NF-κB and MAP kinase

AIM: To investigate lipopolysaccharide (LPS) related signal transduction in interstitial cells of Cajal (ICCs) from mouse small intestine.

METHODS: For this study, primary culture of ICCs was prepared from the small intestine of the mouse. LPS was treated to the cells prior to measurement of the membrane currents by using whole-cell patch clamp technique. Immunocytochemistry was used to examine the expression of the proteins in ICCs.

RESULTS: LPS suppressed the pacemaker currents of ICCs and this could be blocked by AH6809, a prostaglandin E2-EP2 receptor antagonist or NG-Nitro-L-arginine Methyl Ester, an inhibitor of nitric oxide (NO) synthase. Toll-like receptor 4, inducible NO synthase or cyclooxygenase-2 immunoreactivity by specific antibodies was detected on ICCs. Catalase (antioxidant agent) had no action on LPS-induced action in ICCs. LPS actions were blocked by nuclear factor κB (NF-κB) inhibitor, actinomycin D (a gene transcription inhibitor), PD 98059 (a p42/44 mitogen-activated protein kinases inhibitor) or SB 203580 [a p38 mitogen-activated protein kinases (MAPK) inhibitor]. SB 203580 also blocked the prostaglandin E2-induced action on pacemaker currents in ICCs but not NO.

CONCLUSION: LPS inhibit the pacemaker currents in ICCs via prostaglandin E2- and NO-dependent mechanism through toll-like receptor 4 and suggest that MAPK and NF-κB are implicated in these actions.

Extracellular signal-regulated kinase (ERK) is involved in LPS-induced disturbances in intestinal motility

BACKGROUND

Lipopolysaccharide (LPS) is a causative agent of sepsis. A relationship has been described between LPS, free radicals, and cyclooxygenase-2 (COX-2). Here, we investigate the role of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases (MAPK) in the effect of LPS on intestinal motility, oxidative stress status, and COX-2 expression.

METHODS

Rabbits were injected with (i) saline, (ii) LPS, (iii) U0126, an ERK MAPK inhibitor, or (iv) U0126+LPS. Duodenal contractility was studied in an organ bath with acetylcholine, prostaglandin E(2), and KCl added. Neuromuscular function was assessed by electrical field stimulation (EFS). Neurotransmitter blockers were used to study the EFS-elicited contractile response. The formation of products of oxidative damage to proteins (carbonyls), lipids, [malondialdehyde (MDA), and 4-hydroxyalkenals (4-HDA)] was quantified in plasma and intestine. The protein expression of phospho-ERK (p-ERK), total ERK, and COX-2 in the intestine was measured by western blot, and p-ERK was localized by immunohistochemistry.

KEY RESULTS

Acetylcholine, prostaglandin E(2), and KCl-induced contractions decreased with LPS. Electrical field stimulation induced a neurogenic contraction that was reduced by LPS. Lipopolysaccharide increased p-ERK and COX-2 expression and the levels of carbonyls and MDA+4-HDA. U0126 blocked the effect of LPS on acetylcholine, prostaglandin E(2), KCl, and EFS-induced contractions, the levels of carbonyls and MDA+4-HDA and p-ERK and COX-2 expression. Phospho-ERK was detected mostly in the neurons of the myenteric and submucosal ganglia.

CONCLUSIONS & INFERENCES

We can suggest that ERK is involved in the mechanism of action of LPS in the intestine.

Generation of nitric oxide in the opossum lower esophageal sphincter during physiological experimentation

Lipopolysaccharide (LPS), given in vivo, modulates opossum esophageal motor functions by inducing the inducible nitric oxide synthase (iNOS), which increases nitric oxide (NO) production. Superoxide, a NO scavenger, is generated during this endotoxemia. Superoxide is cleared by superoxide dismutase (SOD) and catalase (CAT) to protect the physiological function of NO. This study examined whether lower esophageal sphincter (LES) motility, NO release, and iNOS and nitrotyrosine accumulation in the LES are affected by LPS in vitro. Muscle strips from the opossum LES were placed in tissue baths containing oxygenated Krebs buffer. NO release was measured with a chemiluminescence NOx analyzer, and Western blots were performed to analyze iNOS and nitrotyrosine production. The percent change in resting LES tone after a 6-hour exposure to LPS was significantly increased compared to pretreatment values. The percent LES relaxation upon electrical stimulation was significantly decreased in the control group at 6 hours, indicating that the LPS treatment had an effect. The NO concentration in the tissue bath of LPS- treated muscle without nerve stimulation was significantly less than that of LPS treatment combined with SOD/CAT or SOD/CAT alone. iNOS and nitrotyrosine were detectable and increased over time in the LES muscle of both the control and LPS-treated groups. Antioxidant enzymes may play a role in regulating NO-mediated neuromuscular functions in the LES.

Mechanisms of gastroesophageal reflux in critically ill mechanically ventilated patients

BACKGROUND & AIMS

Gastroesophageal reflux is a major problem in mechanically ventilated patients and may lead to pulmonary aspiration and erosive esophagitis. Transient lower esophageal sphincter relaxations are the most common mechanism underlying reflux in nonventilated patients. The mechanisms that underlie reflux in critically ill ventilated patients have not been studied. The aim of this study was to determine the mechanisms underlying gastroesophageal reflux in mechanically ventilated patients in the intensive care unit.

METHODS

In 15 mechanically ventilated intensive care unit patients, esophageal motility, pH, and intraluminal impedance (11/15 patients) were recorded for 1 hour before and 5 hours during continuous nasogastric feeding.

RESULTS

Basal lower esophageal sphincter pressure was uniformly low (2.2 +/- 0.4 mmHg). The median (interquartile range) acid exposure (pH <4) was 39.4% (0%-100%) fasting and 32% (7.5%-94.2%) fed. Acid reflux occurred in 10 patients, but slow drifts in esophageal pH were also an important contributor to acid exposure. If esophageal pH decreased to pH <4, it tended to remain so for prolonged periods. A total of 46 acid reflux events were identified. Most (55%) occurred because of absent lower esophageal sphincter pressure alone; 45% occurred during straining or coughing.

CONCLUSIONS

Gastroesophageal reflux in mechanically ventilated patients is predominantly due to very low or absent lower esophageal sphincter pressure, often with a superimposed cough or strain. These data suggest that measures that increase basal LES pressure may be useful to prevent reflux in ventilated patients.

Role of prostaglandins in lipopolysaccharide effects on K+-induced contractions in rabbit small intestine

AIM

The mediators of the pathophysiologcal symptoms of septic shock are not completely understood. The aim of this work was to investigate the effect of lipopolysaccharide (LPS) on the K+-induced response of longitudinal segments of rabbit small intestine in vitro and the possible role of prostaglandins.

METHODS AND RESULTS

Rabbits were treated with intravenously injected LPS. After 90 min animals were killed and intestinal segments were mounted in an organ bath. Lipopolysaccharide (0.2 microg kg-1) inhibited K+-induced contractions (60 mm) by 68% in duodenum, 58% in jejunum and 52% in ileum. Indomethacin antagonized LPS actions when injected 15 min before LPS. PGE2 reduced K+-induced contractions, imitating LPS effects. In contrast, contractions induced by K+ increased when intestinal segments were incubated in vitro with LPS for 90 min. The LPS (0.3 microg mL-1) increased K+-induced contractions (60 mm) by 46% in duodenum, 63% in jejunum and 85% in ileum. The LPS effect was antagonized by indomethacin at 10-6 m in duodenum and jejunum and at 10-8 m in ileum. PGE2 evoked dose-dependent contractions when added to the bath in duodenum, jejunum and ileum.

CONCLUSION

These results suggest that effect of LPS on K+-induced contractions in the rabbit small bowel may be mediated by prostaglandin E2.

Esophageal dysmotility and the change of synthesis of nitric oxide in a feline esophagitis model

The present study explores the changes of nitric oxide synthesis and esophageal dysmotility in a feline model of esophagitis. Perfusion of the esophagus with acid produced inflammatory changes of esophageal mucosa. The esophageal motility was measured before and after the perfusion. The nitric oxide synthase activity, the l-arginine uptake, and the content of cyclic guanine monophosphate of the muscle and the mucous membrane were determined and the NADPH-diaphorase was stained. Esophagitis impairs the motility of the esophagus. The nitric oxide synthase activity, the content of cyclic guanine monophosphate, the NADPH-diaphorase stain and the maximum velocity of l-arginine uptake of lower esophageal sphincter of the cats in the acid perfusion group were higher than those of the control group. The maximum velocity of l-arginine transport and the content of cyclic guanine monophosphate of the mucosa in the acid perfusion group were lower than those of the control group. The results suggested that during esophagitis there is an alteration of the l-arginine/nitric oxide synthase/nitric oxide pathway in the esophagus, which may be one of the important mechanisms of esophageal motility dysfunction.

Effect of lipopolysaccharide on rabbit small intestine muscle contractility in vitro: role of prostaglandins

The purpose of this study was to investigate the effect of lipopolysaccharide (LPS) on spontaneous contractions and acetylcholine (ACh) induced contractions of rabbit intestinal segments in vitro, with two different protocols: intestinal segments isolated from LPS-treated rabbits and intestinal segments incubated with LPS. The frequency of spontaneous movements decreased significantly in LPS-treated rabbits at 2 microg kg-1 in the duodenum and 20 microg kg-1 in the duodenum, jejunum and ileum. LPS (0.2 microg kg-1) reduced significantly the ACh contractions (10-6 mol L-1) in the duodenum (61%), jejunum (48%) and ileum (21%). Indomethacin (1, 5 and 10 mg kg-1) administered 15 min before LPS (0.2 microg kg-1) antagonized the LPS effects on the ACh-induced contractions. Prostaglandin (PG)E2 (8 microg kg-1) inhibited significantly the frequency of spontaneous contractions in the ileum and reduced the ACh-induced contractions in the three segments, mimicking the LPS effects. The amplitude and frequency of contractions in rabbit intestinal segments previously incubated with LPS (0.03, 0.3, 3 and 30 microg mL-1) were not modified with respect to the control. The ACh-induced contractions (10-4 mol L-1) were significantly reduced after 90 min of incubation with LPS. The inhibition of LPS (0.3 microg mL-1) was 43% in the duodenum, 35% in the jejunum and 17% in the ileum. Indomethacin added before LPS blocked the effect of LPS on the ACh-induced contractions in the duodenum, jejunum and ileum. These results show that LPS decreases intestinal contractility in rabbits and suggest that PGs are implicated in these actions.

Lipopolysaccharide temporarily impairs sphincter of Oddi motility

The aim of our study was to determine the effect of lipopolysaccharide (LPS) on sphincter of Oddi (SO) motility. Opossums received saline, Escherichia coli LPS (1.0 mg/kg), or E. coli LPS (1.0 mg/kg) and aminoguanidine (50 mg/kg), and the SO was removed 6-24 h later. At 12 h LPS decreased electrical field stimulation (EFS)-induced relaxation and increased baseline tone. These changes were reversed when the animals were pretreated with aminoguanidine. The dose-dependent decrease in EFS-induced relaxation by N(omega)-nitro-l-arginine was impaired after LPS, but not in animals that received LPS and aminoguanidine. The impaired EFS-induced relaxation after LPS was reversed when l-arginine was added to the tissue bath. Serum levels of NO(-)(2)/NO(-)(3) were increased with LPS as compared to saline or both LPS and aminoguanidine. Inducible nitric oxide synthase mRNA was readily seen in SO segments after LPS. LPS impairs EFS-induced relaxation and increases baseline tone of the SO. The effects of LPS on SO motility appear to be mediated by nitric oxide.