Carbonic anhydrase is present in human oesophageal epithelium and submucosal glands

New food approaches to reduce and/or eliminate increased gastric acidity related to gastroesophageal pathologies

OBJECTIVE

Gastroesophageal reflux disease is very common in industrialized countries and rapidly and significantly increasing even in developing countries. The approach in this study is one not commonly found to date in the scientific literature. To assess the ability of reduced-carbohydrate diets and foods that are enriched with acid potential of hydrogen (pH; lemon and tomato) to quickly and exponentially reduce symptoms that are related to conditions such as gastritis and gastroesophageal reflux and unrelated to Helicobacter pylori.

METHODS

After the administration of an anamnestic test, 130 patients were selected including 73 women and 57 men, 21 to 67 y, and with a gastritis diagnosis for 92 patients (56 women, 36 men) and reflux gastritis for 38 patients (17 women, 21 men). Study participants followed three dietary treatments in succession. Each treatment lasted 2 wk and treatments were separated by 2 wk of washout. The patients followed a diet that consisted primarily of proteins and fats and included the exponential reduction of glycides (simple and complex). In addition, the treatment provided for the daily intake of the juice of two lemons and approximately 100 g of fresh orange tomato without seeds eaten either raw or cooked and peeled.

RESULTS

During treatment and at the end of 2 wk of treatment, the patients reported significant improvements including an almost total disappearance of symptoms that were related to the disease in question.

CONCLUSIONS

This study shows that a carbohydrate-free diet and/or highly hypoglycidal diet that is enriched with acid pH foods appears to lead to a decrease in the pH of the gastric contents, thus inhibiting the further production of hydrochloric acid with a reduction or disappearance of heartburn symptoms that are typical of gastroesophageal diseases.

Bicarbonate availability for vocal fold epithelial defense to acidic challenge

OBJECTIVES

Bicarbonate is critical for acid-base tissue homeostasis. In this study we investigated the role of bicarbonate ion transport in vocal fold epithelial defense to acid challenges. Acidic insults to the larynx are common in gastric reflux, carcinogenesis and metastasis, and acute inflammation.

METHODS

Ion transport was measured in viable porcine vocal fold epithelium. First, 18 vocal folds were exposed to either the carbonic anhydrase antagonist acetazolamide or to vehicle. Second, 32 vocal folds were exposed to either a control buffer or a bicarbonate-free buffer on their luminal or basolateral surface or both. Third, 32 vocal folds were challenged with acid in the presence of bicarbonate-free or control buffer.

RESULTS

The vocal fold transepithelial resistance was greater than 300 Ω*cm(2), suggesting robust barrier integrity. Ion transport did not change after exposure to acetazolamide (p > 0.05). Exposure to bicarbonate-free buffer did not compromise vocal fold ion transport (p > 0.05). Ion transport increased after acid challenge. This increase approached statistical significance and was the greatest for the control buffer and for the bicarbonate-free buffer applied to the basolateral surface.

CONCLUSIONS

Bicarbonate secretion may contribute to vocal fold defense against acid challenge. Our data offer a potential novel role for bicarbonate as a therapeutic agent to reduce pH abnormalities in the larynx and prevent associated pathological changes.

Oesophageal sensation in response to high PCO(2) and acidic solutions in nonerosive reflux disease

BACKGROUND

Heartburn is commonly associated with the presence of acid in the oesophageal lumen. However, in patients with nonerosive reflux disease (NERD), the mechanism by which acid traverses the mucosa is not clear. We hypothesized that the luminal acid signal traverses the oesophageal epithelium in the form of the highly permeant gas CO(2) , which then is reconverted to H(+) in the submucosa.

MATERIALS AND METHODS

  Ten patients with heartburn, normal upper endoscopy and increased oesophageal acid exposure (NERD patients) and 10 healthy subjects were enrolled. Perceptual responses to intraoesophageal acid (0·1 N HCl solution) and a high PCO(2) solution were determined using a randomized cross over design. Stimulus-response functions to perfusions were quantified by three parameters: lag time to symptom perception, intensity rating and perfusion sensitivity score.

RESULTS

 In NERD patients, the difference in lag time to typical symptom perception, intensity rating and perfusion sensitivity score between high PCO(2) and acid perfusions was statistically significant (P = 0·02, 0·01 and 0·02, respectively). However, the difference in the same perfusion parameters between acid and high PCO(2) perfusions was nonsignificant in healthy controls. When NERD and controls were compared, the difference between the different perfusion variables was nonsignificant (adjusted to age).

CONCLUSIONS

In NERD subjects, acid perfusion reliably evoked heartburn symptoms of greater intensity than in healthy controls. Nevertheless, a high PCO(2) perfusion failed to produce symptoms in either group.

Electrical parameters and ion species for active transport in human esophageal stratified squamous epithelium and Barrett's specialized columnar epithelium

The human esophagus is lined by stratified squamous epithelium (ESSE), and in some subjects with reflux disease the distal esophagus becomes lined by Barrett's specialized columnar epithelium (BSCE). ESSE and BSCE differ both histologically and functionally, the latter evident by differences in their in vivo transmural electrical potential difference (PD), ESSE averaging -15 mV and BSCE being greater than -25 mV. In this report we examine the basis for this difference in PD. This is done by mounting endoscopic biopsies of ESSE from 25 subjects without esophageal disease and BSCE from 19 with Barrett's esophagus in mini-Ussing chambers for electrical recordings basally and after bathing solution ion replacement. The results show that the PD of human ESSE reflects a low level of active ion transport (5.1 +/- 0.8 muA/cm(2)) combined with a high level of tissue (electrical) resistance (344 +/- 34 Omega.cm(2)) and that of BSCE reflects a high level of active transport (43.6 +/- 11.6 muA/cm(2)) combined with a low level of resistance (69 +/- 8 Omega.cm(2)). Furthermore, active transport in ESSE was principally due to sodium absorption whereas in BSCE it was equally divided between sodium absorption and anion (chloride/bicarbonate) secretion, the latter through an apical membrane, 4-acetamido4'-isothiocyano-2,2'-stilbenedisulfonic acid-sensitive anion channel. As an anion-secreting tissue with bicarbonate secretory capacity more than fivefold greater than ESSE, BSCE is better suited than ESSE for defense of the esophagus against reflux disease.

HCO3- secretion in the esophageal submucosal glands

The mammalian esophagus has the capacity to secrete a HCO(3)(-) and mucin-rich fluid in the esophageal lumen. These secretions originate from the submucosal glands (SMG) and can contribute to esophageal protection against refluxed gastric acid. The cellular mechanisms by which glandular cells achieve these secretions are largely unknown. To study this phenomenon, we used the pH-stat technique to measure luminal alkali secretion in an isolated, perfused pig esophagus preparation. Immunohistochemistry was used to localize receptors and transporters involved in HCO(3)(-) transport. The SMG-bearing esophagus was found to have significant basal alkali secretion, predominantly HCO(3)(-), which averaged 0.21 +/- 0.04 microeq.h(-1).cm(-2). This basal secretion was doubled when stimulated by carbachol but abolished by HCO(3)(-) or Cl(-) removal. Basal- and carbachol-stimulated secretions were also blocked by serosal application of atropine, pirenzipine, DIDS, methazolamide, and ethoxzolamide. The membrane-impermeable carbonic anhydrase inhibitor benzolamide, applied to the serosal bath, partially inhibited basal HCO(3)(-) secretion and blocked the stimulation by carbachol. Immunohistochemistry using antibodies to M(1) cholinergic receptor or carbonic anhydrase-II enzyme showed intense labeling of duct cells and serous demilunes but no labeling of mucous cells. Labeling with an antibody to Na(+)-(HCO(3)(-))(n) (rat kidney NBC) was positive in ducts and serous cells, whereas labeling for Cl(-)/HCO(3)(-) exchanger (AE2) was positive in duct cells but less pronounced in serous cells. These data indicate that duct cells and serous demilunes of SMG play a role in HCO(3)(-) secretion, a process that involves M(1) cholinergic receptor stimulation. HCO(3)(-) transport in these cells is dependent on cytosolic and serosal membrane-bound carbonic anhydrase. HCO(3)(-) secretion is also dependent on serosal Cl(-) and is mediated by DIDS-sensitive transporters, possibly NBC and AE2.

Cell biology of laryngeal epithelial defenses in health and disease: preliminary studies

Esophageal epithelium has intrinsic antireflux defenses, including carbonic anhydrases (CAs I to IV) that appear to be protective against gastric reflux. This study aimed to investigate the expression and distribution of CA isoenzymes in laryngeal epithelium. Laryngeal biopsy specimens collected from the vocal fold and interarytenoid regions were analyzed by Western blotting and immunofluorescence. Carbonic anhydrases I and II were expressed by the majority of samples analyzed. In contrast, CA III was differentially expressed in the interarytenoid samples and was not detected in any vocal fold samples. The expression of CA III was increased in esophagitis as compared to normal esophageal tissue. Carbonic anhydrase I and III isoenzymes were distributed cytoplasmically in the basal and lower prickle cell layers. The laryngeal epithelium expresses some CA isoenzymes and has the potential to protect itself against laryngopharyngeal reflux. Laryngeal tissue may be more sensitive to injury due to reflux damage than the esophageal mucosa because of different responses of CA isoenzymes.

Esophageal submucosal glands: structure and function

A three-tiered defense system exists in the esophagus, which serves a dual purpose of both limiting the degree of gastroesophageal reflux and minimizing the risk of acid-induced mucosal injury. The antireflux barrier, composed of both the lower esophageal sphincter and the diaphragmatic pinchcock, is the first line of defense and serves to limit the frequency and volume of refluxed gastric contents. When the antireflux barrier fails, the second line of defense, esophageal clearance, comes into play and serves to limit the duration of contact between gastric contents and the esophageal epithelium. Mechanisms involved in esophageal clearance include gravity and esophageal peristalsis, which remove volume, and secretions from swallowed saliva and esophageal submucosal glands, which neutralize acid. The third line of defense, tissue resistance, is necessary when acid contact time is prolonged such as when esophageal clearance is either ineffective or not operative (e.g., during sleep). Most studies that have examined esophageal clearance mechanisms have focused on the roles of esophageal peristalsis and salivary secretion, but the role of submucosal gland secretions is less well understood. This article reviews the structure and function of esophageal submucosal glands and discusses the potential role of their secretory products in esophageal clearance and tissue resistance.

Carbonic anhydrase isoenzymes I, II, III, and IV are present in human esophageal epithelium

Carbonic anhydrase (CA) isoenzymes have been widely studied in the gastrointestinal tract, where they mediate membrane transport events and pH regulation. However, the esophagus has generally received scant attention. In an immunohistochemical study confirmed by Western blotting, we have detected for CA isoenzymes (CAI, II, III, and IV) in the epithelium of human esophagus. Isoenzymes I, III, and sometimes IV (< 10%) were present in the cytoplasm of basal cells and II and IV in the cytoplasm and cell surface membranes, respectively, of suprabasal cells (prickle cells). The localization of CAIV to the plasma membranes was confirmed by electron microscopic immunocytochemistry. CA was effectively divided at the basal-suprabasal interface between low-activity CAI and III (basal) and high-activity CAII and IV (suprabasal). Carbonic anhydrase in esophageal epithelial cells may have several functions: elimination of CO2 and metabolites, participation in membrane transport events during active cell growth, and pH regulation as a protective mechanism against acidic gastric reflux.