Transepithelial leak in Barrett's esophagus patients: The role of proton pump inhibitors

AIM： To determine if the observed paracellular sucrose leak in Barrett＇s esophagus patients is due to their pro- ton pump inhibitor （PPI） use. METHODS： The in vivo sucrose permeability test was administered to healthy controls, to Barrett＇s patients and to non-Barrett＇s patients on continuous PPI thera- py. Degree of leak was tested for correlation with pres- ence of Barrett＇s, use of PPIs, and length of Barrett＇s segment and duration of PPI use. RESULTS： Barrett＇s patients manifested a near 3-fold greater, upper gastrointestinal sucrose leak than healthy controls. A decrease of sucrose leak was ob- served in Barrett＇s patients who ceased PPI use for 7 d.Although initial introduction of PPI use （in a PPI-na＇ive population） results in dramatic increase in sucrose leak, long-term, continuous PPI use manifested a slow spon- taneous decline in leak. The sucrose leak observed in Barrett＇s patients showed no correlation to the amount of Barrett＇s tissue present in the esophagus. CONCLUSION： Although future research is needed to determine the degree of paracellular leak in actual Barrett＇s mucosa, the relatively high degree of leak ob- served with in vivo sucrose permeability measurement of Barrett＇s patients reflects their PPI use and not their Barrett＇s tissue perse.

Omeprazole induces gastric transmucosal permeability to the peptide bradykinin

AIM:To investigate omeprazole-induced transepithelial gastric leak and its effects on the permeability of the peptides bradykinin and oxytocin.METHODS:Rat gastric corpus tissue was isolated and mounted in an Ussing chamber apparatus to evaluate the permeability of 3H-bradykinin,3H-oxytocin,and 14CEDTA in the presence or absence of omeprazole.Thinlayer chromatography was performed to identify any metabolic breakdown products of the peptides resulting from permeation through the gastric tissue,and thereby calculate the true flux of the peptide.RESULTS:The flux rate ofintact 3H-bradykinin increased substantially after omeprazole addition (109.5%) compared to the DMSO vehicle control (14%).No corresponding change in flux ofintact 3H-oxytocin was observed under the same conditions (11.9% and 6.4% in the DMSO-and omeprazole-treated conditions,respectively).After exposure to omeprazole,the flux rate of 14C-EDTA also increased dramatically (122.3%) compared to the DMSO condition (36.3%).CONCLUSION:The omeprazole-induced gastric leak allows for transmucosal permeability to charged molecules as well as non-electrolytes.This induced leak will allow certain peptides to permeate.

Absence of Na^+/sugar cotransport activity in Barrett's metaplasia

AIM:To evaluate the presence of Na+-dependent, active, sugar transport in Barrett's epithelia as an intestinal biomarker, based on the well-documented, morphological intestinal phenotype of Barrett's esophagus (BE). METHODS: We examined uptake of the nonmeta- bolizable glucose analogue, alpha-methyl-D-glucoside (AMG), a substrate for the entire sodium glucose cotransporter (SGLT) family of transport proteins. During upper endoscopy, patients with BE or with uncomplicated gastroesophageal reflux disease (GERD) allowed for duodenal, gastric fundic, and esophageal mucosal biopsies to be taken. Biopsies were incubated in bicarbonate-buffered saline (KRB) containing 0.1 mmol/L 14C-AMG for 60 min at 20℃. Characterized by abundant SGLT, duodenum served as a positive control while gastric fundus and normal esophagus, known to lack SGLT, served as negative controls. RESULTS: Duodenal biopsies accumulated 249.84 ± 35.49 (SEM) picomoles AMG/μg DNA (n = 12), gastric fundus biopsies 36.20 ± 6.62 (n = 12), normal esophagus 12.10 ± 0.59 (n = 3) and Barrett's metaplasia 29.79 ± 5.77 (n = 8). There was a statistical difference (P < 0.01) between biopsies from duodenum and each other biopsy site but there was no statistically significant difference between normal esophagus and BE biopsies. 0.5 mmol/L phlorizin (PZ) inhibited AMG uptake into duodenal mucosa by over 89%, but had nosignificant effect on AMG uptake into gastric fundus, normal esophagus, or Barrett's tissue. In the absence of Na+ (all Na+ salts replaced by Li+ salts), AMG uptake in duodenum was decreased by over 90%, while uptake into gastric, esophageal or Barrett's tissue was statistically unaffected. CONCLUSION: Despite the intestinal enterocyte phenotype of BE, Na+-dependent, sugar transport activity is not present in these cells.

Sieving characteristics of cytokine-and peroxide-induced epithelial barrier leak:Inhibition by berberine

AIM: To study whether the inflammatory bowel disease (IBD) colon which exhibits varying severity and cytokine levels across its mucosa create varying types of transepithelial leak. METHODS: We examined the effects of tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-1-β (IL1β) and hydrogen peroxide (H2O2) - singly and in combinations - on barrier function of CACO-2 cell layers. Our focus was on the type (not simply the magnitude) of transepithelial leak generated by these agents as measured by transepithelial electrical resistance (TER) and transepithelial flux of 14C-D-mannitol, 3H-Lactulose and 14C-Polyethylene glycol as radiolabeled probe molecules. The isoquinoline alkaloid, berberine, was then examined for its ability to reduce specific types of transepithelial leak. RESULTS: Exposure to TNF-α alone (200 ng/mL; 48 h) induced a 50% decrease in TER, i.e., increased leak of Na+ and Cl- - with only a marginal but statistically significant increase in transepithelial leak of 14C-mannitol (Jm). Exposure to TNF-α + IFN-γ (200 ng/mL; 48 h) + IL1β (50 ng/mL; 48 h) did not increase the TER change (from TNF-α alone), but there was now a 100% increase in Jm. There however was no increase in transepithelial leak of two larger probe molecules, 3H-lactulose and 14C-polyethylene glycol (PEG). However, exposure to TNF-α + IFN-γ + IL1β followed by a 5 h exposure to 2 mmol/L H2O2 resulted in a 500% increase in 14C-PEG leak as well as leak to the luminal mitogen, epidermal growth factor. CONCLUSION: This model of graded transepithelial leak is useful in evaluating therapeutic agents reducing IBD morbidity by reducing barrier leak to various luminal substances.

Zinc and gastrointestinal disease

This review is a current summary of the role that both zinc deficiency and zinc supplementation can play in the etiology and therapy of a wide range of gastrointestinal diseases. The recent literature describing zinc action on gastrointestinal epithelial tight junctions and epithelial barrier function is described. Zinc enhancement of gastrointestinal epithelial barrier function may figure prominently in its potential therapeutic action in several gastrointestinal diseases.