Essential role of the electroneutral Na+-HCO3- cotransporter NBCn1 in murine duodenal acid-base balance and colonic mucus layer build-up in vivo.

Duodenal epithelial cells need efficient defence strategies during gastric acidification of the lumen, while colonic mucosa counteracts damage by pathogens by building up a bacteria-free adherent mucus layer. Transport of HCO3(-) is considered crucial for duodenal defence against acid as well as for mucus release and expansion, but the transport pathways involved are incompletely understood. This study investigated the significance of the electroneutral Na(+)-HCO3(-) cotransporter NBCn1 for duodenal defence against acid and colonic mucus release. NBCn1 was localized to the basolateral membrane of duodenal villous enterocytes and of colonic crypt cells, with predominant expression in goblet cells. Duodenal villous enterocyte intracellular pH was studied before and during a luminal acid load by two-photon microscopy in exteriorized, vascularly perfused, indicator (SNARF-1 AM)-loaded duodenum of isoflurane-anaesthetized, systemic acid-base-controlled mice. Acid-induced HCO3(-) secretion was measured in vivo by single-pass perfusion and pH-stat titration. After a luminal acid load, NBCn1-deficient duodenocytes were unable to recover rapidly from intracellular acidification and could not respond adequately with protective HCO3(-) secretion. In the colon, build-up of the mucus layer was delayed, and a decreased thickness of the adherent mucus layer was observed, suggesting that basolateral HCO3(-) uptake is essential for optimal release of mucus. The electroneutral Na(+)-HCO3(-) cotransporter NBCn1 displays a differential cellular distribution in the murine intestine and is essential for HCO3(-)-dependent mucosal protective functions, such as recovery of intracellular pH and HCO3(-) secretion in the duodenum and secretion of mucus in the colon.

[The outbreak of acute gastroenteritis caused by Norwalk like viruses in Zadar general hospital (2007)]. / Nozokomijalna epidemija akutnog gastroenteritisa uzrokovana norovirusima u opcoj bolnici Zadar 2007. Godine.

OBJECTIVE: Early detection of clinical signs and symptoms of acute gastroenteritis and appropriate preventive measures to stop the spread of infection. METHODS: Epidemiological inspection, clinical examination of hospitalized patients followed by standard bacteriologic and virologic analysis. Norovirus antigen was detected in stool specimen by enzyme immunoassay (EIA). RESULTS: An epidemic of acute gastroenteritis caused by Norwalk like viruses lasted for two weeks (January 26-February 9, 2007). A total of 39 cases were recorded, including 22 (56.4%) inpatients and 17 (43.6%) healthcare workers with disease symptoms. All patients (n = 22; 100%) were hospitalized at Department of Internal Medicine, Cardiology Ward; 11 (64.7%) healthcare workers were working at Cardiology Ward, 3 (17.6%) at Diagnostic Cardiology Laboratory where patients underwent their diagnostic procedures, and 1 (5.9%) healthcare worker at Department of Anesthesiology and Intensive Care was patient consultant at Cardiac Intensive Care Unit. Other healthcare workers, 1 (5.9%) from Department of Neurosurgery and Department of Pathology each, were in family contact with two health care workers employed at Cardiology Ward. DISCUSSION: The Hospital Infection Control Committee was informed about the outbreak of acute gastroenteritis on day 8 of the outbreak. Anti-epidemic measures (according to the source of infection detected and to the mechanisms of transmission) were implemented after epidemiological inspection on day 1 of event recording and continued for two more weeks after the occurrence of the disease clinical symptoms in the last patient involved. CONCLUSION: It is necessary to promptly inform the Hospital Infection Control Committee on the epidemic outbreak for effective and timely anti-epidemic measures to stop the spread of acute gastroenteritis caused by Norwalk like viruses.

Increased epithelial permeability is the primary cause for bicarbonate loss in inflamed murine colon.

BACKGROUND: Bicarbonate loss into the lumen occurs during intestinal inflammation in different species. However, candidate pathways like CFTR or DRA are inhibited in the inflamed gut. This study addressed the question whether and how inflammation-associated increased intestinal permeability may result in epithelial HCO(3)(-) loss. METHODS: Murine proximal colon was studied because it does not express functional DRA but is inflamed in the tumor necrosis factor α overexpressing mouse model (TNF(ΔARE)). Luminal alkalization, (3)H-mannitol fluxes, impedance spectroscopy, and dilution potentials were measured in Ussing chambers, whereas expression and localization of tight junction-associated proteins were analyzed by Western blots and immunohistochemistry. RESULTS: Luminal alkalization rates and (3)H-mannitol fluxes were increased in TNF(+/ΔARE) proximal colon, whereas forskolin-stimulated I(sc) was not altered. Epithelial resistance was reduced, but subepithelial resistance increased. The epithelial lining was intact, and enterocyte apoptosis rate was not increased despite massively increased Th1 cytokine levels and lymphoplasmacellular infiltration. Measurement of dilution potentials suggested a loss of cation selectivity with increased anion permeability. Western analysis revealed a downregulation of occludin expression and an upregulation of both claudin-2 and claudin-5, with no change in ZO-1, E-cadherin, claudin-4, and claudin-8. Immunohistochemistry suggested correct occludin localization but reduced tight junction density in TNF(+/ΔARE) surface epithelium. CONCLUSIONS: Inflammation during TNF-α overexpression leads to increased epithelial permeability in murine proximal colon, decreased tight junctional cation selectivity, and increased HCO(3)(-) loss into the lumen. Inflammation-associated colonic HCO(3)(-) loss may occur through leaky tight junctions rather than through HCO(3)(-) secreting ion transporters.

Loss of downregulated in adenoma (DRA) impairs mucosal HCO3(-) secretion in murine ileocolonic inflammation.

BACKGROUND: Ileocolonic luminal pH has been reported to be abnormally low in inflammatory bowel disease (IBD) patients, and one of the causative factors may be reduced epithelial HCO(3)(-) secretory rate (J(HCO3)(-)). Disturbances in J(HCO3)(-) may occur due to inflammation-induced changes in the crypt and villous architecture, or due to the effect of proinflammatory cytokines on epithelial ion transporters. METHODS: To discriminate between these possibilities, the tumor necrosis factor alpha (TNF-α) overexpressing (TNF(+/ΔARE)) mouse model was chosen, which displays high proinflammatory cytokine levels in both ileum and colon, but develops only mild colonic histopathology and diarrhea. HCO(3)(-) secretion, mRNA expression, immunohistochemistry, and fluid absorptive capacity were measured in ileal and mid-colonic mucosa of TNF(+/ΔARE) and wildtype (WT) (TNF(+/+)) mice in Ussing chambers, and in anesthetized mice in vivo. RESULTS: The high basal J(HCO3)(-) observed in WT ileal and mid-colonic mucosa were luminal Cl(-) -dependent and strongly decreased in TNF(+/ΔARE) mice. Downregulated in adenoma (DRA) mRNA and protein expression was strongly decreased in TNF(+/ΔARE) ileocolon, whereas cystic fibrosis transmembrane conductance regulator (CFTR), Na(+) /H(+) exchanger 3 (NHE3), Na(+) /HCO(3)(-) cotransporter (NBC), and epithelial sodium channel (ENaC) expression was not significantly altered. This indicates that the severe defect in ileocolonic J(HCO3)(-) was due to DRA downregulation. Fluid absorption was severely depressed in the ileum but only mildly affected in the mid-distal colon, preventing the development of overt diarrhea. CONCLUSIONS: Even mild ileocolonic inflammation may result in a decrease of epithelial HCO(3)(-) secretion, which may contribute to alterations in surface pH, intestinal flora, and mucus barrier properties.