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

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 epithe...

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Published in:Inflammatory bowel diseases 2013-04, Vol.19 (5), p.904-911
Main Authors: Juric, Marina, Xiao, Fang, Amasheh, Salah, May, Oliver, Wahl, Kristin, Bantel, Heike, Manns, Michael P, Seidler, Ursula, Bachmann, Oliver
Format: Article
Language:English
Subjects:
Animals
Bicarbonates - metabolism
Blotting, Western
Cadherins - metabolism
Cell Membrane Permeability - physiology
Claudins - metabolism
Colon - immunology
Colon - metabolism
Colon - pathology
Cytokines - metabolism
Female
Inflammation - physiopathology
Intestinal Mucosa - immunology
Intestinal Mucosa - metabolism
Male
Mice
Mice, Inbred C57BL
Mice, Knockout
Tight Junctions - physiology
Tumor Necrosis Factor-alpha - physiology
Zonula Occludens-1 Protein - metabolism
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Summary: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. 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. 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. 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.
ISSN:1078-0998
1536-4844
DOI:10.1097/mib.0b013e3182813322