Antioxidant activity of commercial soft and hard wheat (Triticum aestivum L.) as affected by gastric pH conditions

Phenolic compounds from soft and hard wheat and their milling fractions were extracted into distilled deionized water, and their in vitro antioxidant activities were evaluated. Wheat samples were used as such (nontreated) or subjected to pH adjustment (treated) in order to simulate gastrointestinal pH conditions. The total phenolic content (TPC) was determined using Folin-Ciocalteu's procedure. The total antioxidant activity (TAA) was determined using Trolox equivalent antioxidant capacity assay and expressed as Trolox equivalents. The antioxidant activity of wheat extracts was also evaluated using the beta-carotene bleaching assay, scavenging of 2,2-diphenyl-1-picrylhydrazyl radical, and inhibition of oxidation of human low density lipoprotein cholesterol. The TPC, TAA, and antioxidant potential, evaluated using different methods of wheat samples, were significantly increased following gastrointestinal tract-simulated pH changes. Thus, digestion taking place in the gastrointestinal tract in vivo may also enhance the antioxidant properties of the extracts.

Baclofen decreases acid and non-acid post-prandial gastro-oesophageal reflux measured by combined multichannel intraluminal impedance and pH

BACKGROUND

Omeprazole controls acid but not non-acid reflux. The GABA B agonist baclofen decreases acid reflux through the inhibition of transient lower oesophageal sphincter relaxations (TLESRs) and should similarly decrease non-acid reflux. Using combined multichannel intraluminal impedance and pH (MII/pH), we compared acid and non-acid reflux after placebo and baclofen.

METHODS

Nine healthy volunteers and nine heartburn patients underwent two 2-h studies of combined MII/pH in right lateral decubitus after a refluxogenic meal in random order: on placebo and after baclofen 40 mg p.o. Tracings were analysed for acid and non-acid reflux episodes, re-reflux and symptoms in the heartburn patients.

RESULTS

In normal subjects baclofen significantly reduced the median number of episodes of acid (7 vs. 1, P = 0.02), non-acid (2 vs. 0, P = 0.005), and all reflux combined (10 vs. 2, P = 0.006); re-reflux was not reduced (0 vs. 0, P = N.S.). In heartburn patients, baclofen significantly decreased the median number of episodes of acid (15 vs. 6, P = 0.004), non-acid (4 vs. 2, P = 0.003), re-reflux (2 vs. 0, P = 0.02), and all reflux combined (23 vs. 8, P = 0.004); it also reduced the median number of acid-related (9 vs. 1, P = 0.008) and non-acid-related (1 vs. 0, P = 0.04) symptoms.

CONCLUSIONS

Baclofen reduces post-prandial acid and non-acid reflux and their associated symptoms. GABA B agonists may have a role in treating GERD.

Effect of gastric acid on the pathogenesis of subglottic stenosis

A case of subglottic stenosis, recalcitrant to conventional therapy, was associated with asymptomatic aspiration of gastric acid into the larynx. Once the reflux was controlled by use of an antacid regimen and an H2 blocker, the subglottic stenosis resolved and the patient could be decannulated. This case led to the use of an experimental canine model of subglottic stenosis to examine gastric acid as a pathogenic factor in the development of subglottic stenosis. In control animals, mucosal lesions healed without development of stenosis. In experimental animals with mucosal lesions painted with gastric acid, subglottic stenosis developed. When perichondrium and cartilage were violated and gastric acid applied, stenosis was even more severe and developed more rapidly.

The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome

Gastric acidity is likely a key factor shaping the diversity and composition of microbial communities found in the vertebrate gut. We conducted a systematic review to test the hypothesis that a key role of the vertebrate stomach is to maintain the gut microbial community by filtering out novel microbial taxa before they pass into the intestines. We propose that species feeding either on carrion or on organisms that are close phylogenetic relatives should require the most restrictive filter (measured as high stomach acidity) as protection from foreign microbes. Conversely, species feeding on a lower trophic level or on food that is distantly related to them (e.g. herbivores) should require the least restrictive filter, as the risk of pathogen exposure is lower. Comparisons of stomach acidity across trophic groups in mammal and bird taxa show that scavengers and carnivores have significantly higher stomach acidities compared to herbivores or carnivores feeding on phylogenetically distant prey such as insects or fish. In addition, we find when stomach acidity varies within species either naturally (with age) or in treatments such as bariatric surgery, the effects on gut bacterial pathogens and communities are in line with our hypothesis that the stomach acts as an ecological filter. Together these results highlight the importance of including measurements of gastric pH when investigating gut microbial dynamics within and across species.

Chronic cough due to gastroesophageal reflux. Clinical, diagnostic, and pathogenetic aspects

BACKGROUND

Gastroesophageal reflux (GER) is a common cause of chronic cough. Moreover, chronic cough can be the sole presenting manifestation of GER disease (GERD). It has been suggested recently that GER most often causes chronic cough by stimulating the distal esophagus. To gain further diagnostic and pathophysiologic knowledge, we prospectively evaluated a group of patients with chronic cough likely to be due to GER with extensive gastrointestinal and respiratory studies and then observed their response to antireflux therapy.

METHODS

We prospectively characterized 12 subjects whose chronic cough was likely to be due to GER by chest radiographs, barium esophagography, 24-h esophageal pH monitoring (EPM) with probes in the distal and proximal esophagus, esophagoscopy, and bronchoscopy. Then, prior to instituting antireflux therapy, we objectively counted coughs during the distal esophageal infusion of 0.1 N HCl or 0.9 percent saline solution administered in a randomized, double-blind, standardized fashion (ie, Bernstein acid-perfusion test).

RESULTS

Gastroesophageal reflux was determined to cause cough in all subjects based on disappearance of cough with antireflux therapy. It was clinically "silent" in 75 percent. The EPM was the test most frequently abnormal (sensitivity, 92 percent). Distal esophageal data revealed that 10 of 12 subjects had GER-induced coughs (12 +/- 12) while only 7 of 12 had an abnormal esophageal pH conventional parameter (eg, percent time pH < 4). Compared with the distal esophagus, GER to the proximal esophagus occurred (p = 0.017) and induced cough (p = 0.004) less often. Compared with baseline (9.3 +/- 17.6), there were no differences in coughs induced by the infusion of saline solution (9.2 +/- 15.9) or acid (15.1 +/- 26.7); the number of coughs induced by acid was negatively correlated with distal esophageal acid-GER events during EPM (r = -0.64, p = 0.01). Neither bronchoscopy nor chest radiographs were consistent with aspiration.

CONCLUSIONS

There is a clinical profile that prospectively predicts which patients have chronic cough due to GER. The cough was most likely due to stimulation of the distal esophagus, not aspiration. Intraesophageal acid is unlikely to be the sole mediator in gastric juice causing the cough. While EPM is the single most helpful diagnostic test, conventionally utilized diagnostic indices of GERD can be misleadingly normal; observing GER-induced coughs is more frequently helpful.

Activity/Stability of Human Pepsin: Implications for Reflux Attributed Laryngeal Disease

OBJECTIVES/HYPOTHESIS

Exposure of laryngeal epithelia to pepsin during extra-esophageal reflux causes depletion of laryngeal protective proteins, carbonic anhydrase isoenzyme III (CAIII), and squamous epithelial stress protein Sep70. The first objective of this study was to determine whether pepsin has to be enzymatically active to deplete these proteins. The second objective was to investigate the effect of pH on the activity and stability of human pepsin 3b under conditions that might be found in the human esophagus and larynx.

STUDY DESIGN

Prospective translational research study.

METHODS

An established porcine in vitro model was used to examine the effect of active/inactive pepsin on laryngeal CAIII and Sep70 protein levels. The activity and stability of pepsin was determined by kinetic assay, measuring the rate of hydrolysis of a synthetic pepsin-specific substrate after incubation at various pH values for increasing duration.

RESULTS

Active pepsin is required to deplete laryngeal CAIII and Sep70. Pepsin has maximum activity at pH 2.0 and is inactive at pH 6.5 or higher. Although pepsin is inactive at pH 6.5 and above, it remains stable until pH 8.0 and can be reactivated when the pH is reduced. Pepsin is stable for at least 24 hours at pH 7.0, 37 degrees C and retains 79% +/- 11% of its original activity after re-acidification at pH 3.0.

CONCLUSIONS

Detectable levels of pepsin remain in laryngeal epithelia after a reflux event. Pepsin bound there would be enzymatically inactive because the mean pH of the laryngopharynx is pH 6.8. Significantly, pepsin could remain in a form that would be reactivated by a subsequent decrease in pH, such as would occur during an acidic reflux event or possibly after uptake into intracellular compartments of lower pH.

Role of acid and duodenogastric reflux in esophageal mucosal injury: a review of animal and human studies

The role of acid and duodenogastric reflux (DGR) in the development of esophageal mucosal injury has been extensively investigated using both animal and human models. In this report, clinical and experimental data are reviewed. The mechanisms by which gastric and duodenal contents produce esophageal mucosal injury are also discussed. Acid and pepsin are unquestionably important in causing mucosal damage at low pH values in both animal and human models. Animal models suggest synergistic damaging potential for conjugated bile acids and HCI as well as that of unconjugated bile acids and trypsin in more neutral pH values. Human evidence for the involvement of bile and its constituents has been controversial; however, the advent of better technology to detect DGR is beginning to clarify the role of these constituents. The contribution of each methodology in clarifying the extent of involvement of DGR in esophageal mucosal injury is reviewed. Despite some conflicting results, preliminary human studies support the results from the animal data suggesting synergistic damaging effects for both bile and acid in esophageal mucosal injury. The implication of these studies in treating gastroesophageal reflux disease are discussed.

Review article: proton pump inhibitors and bacterial overgrowth

Proton pump inhibitors are potent drugs producing profound suppression of gastric acid secretion. Consequently, they are highly effective at treating acid-related disorders. There have been concerns that the suppression of gastric acid will alter the bacterial flora of the upper gastrointestinal tract and lead to complications such as cancer, enteric or other infections and malabsorption. Studies have confirmed that proton pump inhibitors do alter the bacterial population but present evidence indicates that this only rarely leads to clinical disease. As with all drugs, proton pump inhibitors should only be used for disorders shown clearly to benefit from the therapy and where the benefits will outweigh the small risks associated with them. Further research to more fully quantify the risk associated with PPI therapy is required.

The role of gastric acid in preventing foodborne disease and how bacteria overcome acid conditions

The secretion of hydrochloric acid by the stomach plays an important role in protecting the body against pathogens ingested with food or water. A gastric fluid pH of 1 to 2 is deleterious to many microbial pathogens; however, the neutralization of gastric acid by antacids or the inhibition of acid secretion by various drugs may increase the risk of food- or waterborne illnesses. Peptic ulcer disease is often treated by decreasing or eliminating gastric acid secretion, and such treatment blocks the protective antibacterial action of gastric fluid. The majority of peptic ulcer disease cases originate from Helicobacter pylori infections. Treatment of H. pylori-induced peptic ulcers with antibiotics reduces the need for drugs that inhibit gastric acid secretion and thereby diminishes the risk of food- and waterborne illness for peptic ulcer disease patients. Many bacterial pathogens, such as Escherichia coli, Salmonella Typhimurium, and H. pylori, can circumvent the acid conditions of the stomach by developing adaptive mechanisms that allow these bacteria to survive in acid environments. As a consequence, these bacteria can survive acidic stomach conditions and pass into the intestinal tract, where they can induce gastroenteritis.

Role of preoperative carbohydrate loading: a systematic review

INTRODUCTION

Surgical stress in the presence of fasting worsens the catabolic state, causes insulin resistance and may delay recovery. Carbohydrate rich drinks given preoperatively may ameliorate these deleterious effects. A systematic review was undertaken to analyse the effect of preoperative carbohydrate loading on insulin resistance, gastric emptying, gastric acidity, patient wellbeing, immunity and nutrition following surgery.

METHODS

All studies identified through PubMed until September 2011 were included. References were cross-checked to ensure capture of cited pertinent articles.

RESULTS

Overall, 17 randomised controlled trials with a total of 1,445 patients who met the inclusion criteria were identified. Preoperative carbohydrate drinks significantly improved insulin resistance and indices of patient comfort following surgery, especially hunger, thirst, malaise, anxiety and nausea. No definite conclusions could be made regarding preservation of muscle mass. Following ingestion of carbohydrate drinks, no adverse events such as apparent or proven aspiration during or after surgery were reported.

CONCLUSIONS

Administration of oral carbohydrate drinks before surgery is probably safe and may have a positive influence on a wide range of perioperative markers of clinical outcome. Further studies are required to determine its cost effectiveness.

Sensory neurons signal for an increase in rat gastric mucosal blood flow in the face of pending acid injury

Disruption of the gastric mucosal barrier is quickly followed by an increase in gastric mucosal blood flow, which is thought to be a defensive reaction to prevent further injury. This study examined how this increase in blood flow is brought about. When the stomach of urethane-anesthetized rats was perfused with 0.15N HCl, disruption of the gastric mucosal barrier with 15% ethanol increased the disappearance of acid from the gastric lumen and enhanced gastric mucosal blood flow. This increase in blood flow was blocked by local arterial infusion of tetrodotoxin (60 ng/min) to the stomach and by chemical ablation of capsaicin-sensitive sensory neurons. Inhibition of the blood flow increase was associated with exaggeration of gross and histological injury to the mucosa. IV injection of atropine (0.2 mg/kg) or pyrilamine (2 mg/kg) did not affect blood flow increase in response to barrier disruption, whereas morphine injection (2 mg/kg) inhibited it. The current findings show that the increase in gastric mucosal blood flow that follows disruption of the gastric mucosal barrier in the presence of acid is mediated by sensory neurons that seem to monitor acid back-diffusion and in turn signal for a protective increase in blood flow.

Acid tolerance of gastrointestinal pathogens

The ability of pathogenic bacteria to survive in the face of host defense systems is intimately linked to virulence. This is exemplified by gastrointestinal pathogens that must survive exposure to extreme acid conditions within the stomach and organic acid conditions within the small intestine. These organisms have evolved complex systems to respond to acid stress, and recent work has revealed new genetic components involved in survival and virulence. Here, we review recent work on four gastrointestinal pathogens, focusing on studies that reveal both acid-inducible resistance systems and inherent (basal state) acid-resistance systems.

Infection and AIDS in adult macaques after nontraumatic oral exposure to cell-free SIV

Unprotected receptive anal intercourse is a well-recognized risk factor for infection with human immunodeficiency virus-type 1 (HIV-1). Isolated human case reports have implicated HIV-1 transmission by oral-genital exposure. Adult macaques exposed nontraumatically to cell-free simian immunodeficiency virus (SIV) through the oral route became infected and developed acquired immunodeficiency syndrome (AIDS). The minimal virus dose needed to achieve systemic infection after oral exposure was 6000 times lower than the minimal dose required to achieve systemic infection after rectal exposure. Thus, unprotected receptive oral intercourse, even in the absence of mucosal lesions, should be added to the list of risk behaviors for HIV-1 transmission.

Synergism of acid and duodenogastroesophageal reflux in complicated Barrett's esophagus

BACKGROUND

The role of acid and duodenogastroesophageal reflux (DGER) in the development of complications in Barrett's esophagus is controversial. We characterized the esophageal reflux constituents in patients with and without complications of Barrett's esophagus.

METHODS

Using a new fiber-optic system we studied 12 normal subjects (six male; mean age, 46 years) and 20 patients with Barrett's esophagus (17 male; mean age, 58 years), nine with uncomplicated (seven male; mean age, 55 years) and 11 with complicated Barrett's esophagus (seven with stricture, two with ulcer, and two with dysplasia; 10 male; mean age, 61 years). Fasting gastric bile acid concentrations were measured. Twenty-four-hour ambulatory acid and bilirubin measurements were obtained with the fiber-optic system by using a glass electrode and fiber-optic sensor. The data were then analyzed for percent total time pH < 4 and > 7 and bilirubin absorbance > 0.14%.

RESULTS

Percent times pH < 4, bilirubin absorbance > 0.14%, and fasting gastric bile acid concentrations were significantly greater in patients with complicated Barrett's esophagus compared with patients with uncomplicated Barrett's esophagus with both being higher than the controls. Acid reflux paralleled bile reflux in the two Barrett's esophagus groups (r = 0.44, p < 0.05), but percent time pH > 7 did not differentiate between the two groups.

CONCLUSIONS

(1) Patients with complicated Barrett's esophagus reflux significantly greater amounts of both acid and duodenal contents than patients with uncomplicated Barrett's esophagus. (2) Complications in Barrett's esophagus may be due to synergism between acid and bile rather than either constituent alone.

Prevalence of acid reflux in functional dyspepsia and its association with symptom profile

AIM

A subset of functional dyspepsia patients respond to acid suppressive therapy, but the prevalence of non-erosive reflux disease in functional dyspepsia and its relevance to symptoms have never been established. The aim of the present study was to study 24 hour pH monitoring in consecutive functional dyspepsia patients.

METHODS

A total of 247 patients with dyspeptic symptoms (166 women, mean age 44 (SEM 1) year), with a negative upper gastrointestinal endoscopy and without dominant symptoms of heartburn participated in the study. In all patients, the severity of dyspeptic symptoms and the presence of heartburn was assessed by a questionnaire and a 24 hour oesophageal pH monitoring study was performed. All patients underwent a gastric emptying breath test and in 113 a gastric barostat study was performed.

RESULTS

Abnormal pH monitoring (acid exposure >5% of time) was found in 58 patients (23%). Of 21 patients with a positive heartburn questionnaire, 76% had pathological pH monitoring, while this was the case in only 18.5% of patients with a negative heartburn questionnaire. Demographic characteristics and the prevalence of other pathophysiological mechanisms did not differ between heartburn negative patients with normal or abnormal acid exposure. Pathological acid exposure in heartburn negative patients was associated with the presence of epigastric pain (65 v 84%, p<0.005) and of moderate or severe pain (48 v 69%, p = 0.005).

CONCLUSION

Pathological oesophageal acid exposure is only present in a subset of heartburn negative functional dyspepsia patients, which are characterised by a higher prevalence of epigastric pain.

Abnormal functional and morphological regulation of the gastric mucosa in histamine H2 receptor-deficient mice

To clarify the physiological roles of histamine H2 receptor (H2R), we have generated histamine H2R-deficient mice by gene targeting. Homozygous mutant mice were viable and fertile without apparent abnormalities and, unexpectedly, showed normal basal gastric pH. However, the H2R-deficient mice exhibited a marked hypertrophy with enlarged folds in gastric mucosa and an elevated serum gastrin level. Immunohistochemical analysis revealed increased numbers of parietal and enterochromaffin-like (ECL) cells. Despite this hypertrophy, parietal cells in mutant mice were significantly smaller than in wild-type mice and contained enlarged secretory canaliculi with a lower density of microvilli and few typical tubulovesicles in the narrow cytoplasm. Induction of gastric acid secretion by histamine or gastrin was completely abolished in the mutant mice, but carbachol still induced acid secretion. The present study clearly demonstrates that H2R-mediated signal(s) are required for cellular homeostasis of the gastric mucosa and normally formed secretory membranes in parietal cells. Moreover, impaired acid secretion due to the absence of H2R could be overcome by the signals from cholinergic receptors.

Adaptation of Escherichia coli O157:H7 to pH alters membrane lipid composition, verotoxin secretion, and resistance to simulated gastric fluid acid

The influence of adaptation to pH (from pH 5.0 to 9.0) on membrane lipid composition, verotoxin concentration, and resistance to acidic conditions in simulated gastric fluid (SGF) (pH 1.5, 37 degrees C) was determined for Escherichia coli O157:H7 (HEC, ATCC 43895), an rpoS-deficient mutant of ATCC 43895 (HEC-RM, FRIK 816-3), and nonpathogenic E. coli (NPEC, ATCC 25922). Regardless of the strain, D values (in SGF) of acid-adapted cells were higher than those of non-acid-adapted cells, with HEC adapted at pH 5.0 having the greatest D value, i.e., 25.6 min. Acid adaptation increased the amounts of palmitic acid (C16:0) and decreased cis-vaccenic acid (C18:1 omega 7c) in the membrane lipids of all strains. The ratio of cis-vaccenic acid to palmitic acid increased at acidic pH, causing a decrease in membrane fluidity. HEC adapted to pH 8.3 and HEC-RM adapted to pH 7.3 exhibited the greatest verotoxin concentrations (2,470 and 1,460 ng/ml, respectively) at approximately 10(8) CFU/ml. In addition, the ratio of extracellular to intracellular verotoxin concentration decreased at acidic pH, possibly due to the decrease of membrane fluidity. These results suggest that while the rpoS gene does not influence acid resistance in acid-adapted cells it does confer decreased membrane fluidity, which may increase acid resistance and decrease verotoxin secretion.

CYP2C19 genotype status and intragastric pH during dosing with lansoprazole or rabeprazole

BACKGROUND

CYP2C19 has an important role in the catabolism of several proton pump inhibitors. However, the relative contribution of CYP2C19-mediated metabolism varies among the different proton pump inhibitors.

AIM

To determine the effect of CYP2C19 genotype status on intragastric pH during dosing with lansoprazole or rabeprazole.

SUBJECTS AND METHODS

The subjects were 20 male volunteers without Helicobacter pylori infection. Their CYP2C19 genotype status was determined by a polymerase chain reaction-restriction fragment length polymorphism method. Twenty-four-hour monitoring of intragastric acidity was performed three times: once without medication, once on the last day of a 7-day course of rabeprazole, and once on the last day of a 7-day course of lansoprazole.

RESULTS

Subjects were divided into three groups on the basis of their CYP2C19 genotype status: homozygous extensive metabolizers (homo-EMs, n=7), heterozygous extensive metabolizers (hetero-EMs, n=9), and poor metabolizers (PMs, n=4). The median pH during rabeprazole administration was not influenced by CYP2C19 genotype. On the other hand, the median pH in PMs during lansoprazole dosing was higher than in homo-EMs and hetero-EMs. The percentage of time with pH < 4.0 had a similar tendency to that of median pH.

CONCLUSION

CYP2C19 genotype status influences gastric acid suppression by lansoprazole, but not by rabeprazole.

Role of refluxed acid in pathogenesis of laryngeal disorders

The neuroanatomic proximity of the larynx to the hypopharynx and proximal esophagus make it particularly vulnerable to diseases that occur in those 2 areas. This is particularly true of gastroesophageal reflux disease (GERD). There is increasing awareness of this relationship, and dysphonias from gastroesophageal reflux (GER) are far more common than previously realized. The symptoms and findings of reflux laryngitis, vocal nodules, Reinke's edema, contact ulcer and granuloma, laryngeal stenosis, and paroxysmal laryngospasm are presented, and diagnostic protocols for each disorder are suggested. The treatment varies with the severity of each problem. Conservative lifestyles and dietary control are helpful, but long-term medical therapy with H2, H1, and prokinetic drugs are usually needed. Surgical therapy may be indicated for such life-threatening problems as laryngeal stenosis and paroxysmal laryngospasm. The need for physician and patient awareness, research, and improved and less expensive therapy are discussed.

Hydrogen ion concentration in the mucus layer on top of acid-stimulated and -inhibited rat gastric mucosa

BACKGROUND/AIMS

The gastric mucosa is covered by a continuous layer of bicarbonate-containing mucus gel; the question arises how acid, formed in the gastric glands, moves into the lumen.

METHODS

The pH in the gastric mucus gel and gel thickness were measured in anesthetized rats with pH-sensitive microelectrodes (tip diameter, 1-5 microns).

RESULTS

During pentagastrin (40 micrograms.kg-1.h-1) stimulation of acid secretion, the pH was higher in the gel than in the lumen (pH 2) up to a distance of 115 +/- 18 microns from the epithelial surface and maximal (pH 7.2 +/- 0.1) at the surface. A similar pH gradient was recorded at luminal pH 3. After omeprazole (10 mumol/kg) inhibition of endogenous acid secretion and with exogenous acid in the lumen, the pH profile was broader: 204 +/- 26 microns at luminal pH 2 and 231 +/- 63 microns at luminal pH 3. In contrast, the pH at the epithelial surface was lower (pH 6.8-6.9). The gel thickness (200-300 microns) was similar in all groups.

CONCLUSIONS

The significantly higher surface pH in acid-secreting stomachs probably reflects better availability of interstitial mucosal bicarbonate. Bulk transport of secreted acid in channels created by the gland luminal hydrostatic pressure may additionally act to limit acidification of the mucus gel.

Lipoxin A(4) regulates bronchial epithelial cell responses to acid injury

Aspiration of gastric acid commonly injures airway epithelium and, if severe, can lead to respiratory failure from acute respiratory distress syndrome. Recently, we identified cyclooxygenase-2 (COX-2)-derived prostaglandin E(2) (PGE(2)) and lipoxin A(4) (LXA(4)) as pivotal mediators in vivo for resolution of acid-initiated acute lung injury. To examine protective mechanisms for these mediators in the airway, we developed an in vitro model of acid injury by transiently exposing well-differentiated normal human bronchial epithelial cells to hydrochloric acid. Transmission electron microscopy revealed selective injury to superficial epithelial cells with disruption of cell attachments and cell shedding. The morphological features of injury were substantially resolved within 6 hours. Acid triggered and early marked increases in COX-2 expression and PGE(2) production, and acid-induced PGE(2) significantly increased epithelial LXA(4) receptor (ALX) expression. LXA(4) is generated in vivo during acute lung injury, and we observed that nanomolar quantities increased basal epithelial cell proliferation and potently blocked acid-triggered interleukin-6 release and neutrophil transmigration across well-differentiated normal human bronchial epithelial cells. Expression of recombinant human ALX in A549 airway epithelial cells uncovered ALX-dependent inhibition of cytokine release by LXA(4). Together, these findings indicate that injured bronchial epithelial cells up-regulate ALX in a COX-2-dependent manner to promote LXA(4)-mediated resolution of airway inflammation.

The role of the hiatus hernia in gastro-oesophageal reflux disease

A sliding hiatus hernia disrupts both the anatomy and physiology of the normal antireflux mechanism. It reduces lower oesophageal sphincter length and pressure, and impairs the augmenting effects of the diaphragmatic crus. It is associated with decreased oesophageal peristalsis, increases the cross-sectional area of the oesophago-gastric junction, and acts as a reservoir allowing reflux from the hernia sac into the oesophagus during swallowing. The overall effect is that of increased oesophageal acid exposure. The presence of a hiatus hernia is associated with symptoms of gastro-oesophageal reflux, increased prevalence and severity of reflux oesophagitis, as well as Barrett's oesophagus and oesophageal adenocarcinoma. The efficacy of treatment with proton pump inhibitors is reduced. Our view on the significance of the sliding hiatus hernia in gastro-oesophageal reflux disease has changed enormously in recent decades. It was initially thought that a hiatus hernia had to be present for reflux oesophagitis to occur. Subsequently, the hiatus hernia was considered an incidental finding of little consequence. We now appreciate that the hiatus hernia has major patho-physiological effects favouring gastro-oesophageal reflux and hence contributing to oesophageal mucosal injury, particularly in patients with severe gastro-oesophageal reflux disease.

Mechanisms of gastroesophageal reflux in healthy premature infants

OBJECTIVES

The aim of this study was to characterize the motor events responsible for gastroesophageal reflux (GER) and esophageal acid clearance in a cohort of healthy preterm infants.

STUDY DESIGN

Esophageal motility was recorded for 2 to 3 hours after a feeding in 24 preterm infants, 31 to 38 weeks' postmenstrual age, by using a sleeveside hole micromanometric assembly incorporating a pH probe.

RESULTS

Sixty acid GER episodes were recorded by pH probe, and 133 non-acid GER episodes were recorded manometrically by the presence of esophageal common cavities. Of the 193 GER episodes, 159 (82%) were associated with transient lower esophageal sphincter relaxation (TLESR). TLESRs were significantly longer in duration than single swallows (15.1 seconds vs 5.6 seconds, P < .001) and had lower nadir pressures (0.8 mm Hg vs 2.3 mm Hg, P < .001). A total of 3216 esophageal body pressure waves were analyzed; 70% of swallow-induced pressure waves were peristaltic in sequence compared with 5% of swallow-unrelated pressure waves. During periods of esophageal acidification (pH below 4), peristaltic esophageal body pressure wave sequences cleared acid refluxate more effectively than nonperistaltic pressure wave sequences.

CONCLUSIONS

In healthy preterm infants, TLESRs are the predominant mechanism underlying GER, and esophageal clearance mechanisms are well developed by at least 31 weeks' postmenstrual age.

The role of intragastric acidity and stress ulcus prophylaxis on colonization and infection in mechanically ventilated ICU patients. A stratified, randomized, double-blind study of sucralfate versus antacids

This study evaluates the effects of sucralfate and antacids on intragastric acidity, colonization of stomach, oropharynx and trachea, and the incidence of ventilator-associated pneumonia (VAP) in mechanically ventilated patients in intensive care units. We conducted a prospective randomized double-blind trial in which patients were stratified on initial gastric pH. Intragastric acidity was measured with computerized, continuous intragastric monitoring. The diagnosis of VAP was established with protected specimen brush and/or bronchoalveolar lavage. The study included consecutive eligible patients with mechanical ventilation and nasogastric tube.

INTERVENTIONS

After stratification on initial intragastric pH into two groups, patients from both groups were randomly assigned to receive either antacids (a suspension of aluminum hydroxide and magnesium hydroxide), 30 mL every 4 h, or sucralfate, 1 g every 4 h. Continuous intragastric pH monitoring was performed in 112 patients (58 antacids, 54 sucralfate). Using predetermined criteria, colonization of stomach, oropharynx, and trachea, and the incidence of VAP were assessed. Altogether, 141 patients were included (74 receiving antacids, 67 sucralfate) and continuous intragastric pH monitoring was performed in 112 patients, with a mean of 75 h per patient. The median pH and the percentage of time with a pH < 4.0 were calculated from each measurement. No significant differences in median pH values (4.7 +/- 2.2 and 4.5 +/- 2.0 for antacids and sucralfate, respectively) were observed. Median pH values were higher in patients with gastric bacterial colonization than in noncolonized patients (5.5 +/- 2.1 and 3.3 +/- 2.0, p < 0.01), but colonization of oropharynx and trachea was not related to intragastric acidity. Thirty-one patients (22%) developed VAP, with a similar incidence in both treatment groups. In addition, antibiotic use, duration of hospitalization, and mortality rates were similar in both groups. Enteral feeding did not change intragastric acidity significantly but increased gastric colonization with Enterobacteriaceae, without influencing oropharyngeal and tracheal colonization. Antacids and sucralfate had a similar effect on intragastric acidity, colonization rates, and incidence of VAP. Intragastric acidity influenced gastric colonization but not colonization of the upper respiratory tract or the incidence of VAP. Therefore, it is unlikely that the gastropulmonary route is important for the development of VAP.