Disruption of the Mucosal Barrier During Gut Ischemia Allows Entry of Digestive Enzymes Into the Intestinal Wall

Department of Bioengineering, Institute of Engineering in Medicine, University of California-San Diego, La Jolla, California 92093, USA.
Shock (Augusta, Ga.) (Impact Factor: 3.05). 11/2011; 37(3):297-305. DOI: 10.1097/SHK.0b013e318240b59b
Source: PubMed


Intestinal ischemia is associated with high morbidity and mortality, but the underlying mechanisms are uncertain. We hypothesize that during ischemia the intestinal mucosal barrier becomes disrupted, allowing digestive enzymes access into the intestinal wall initiating autodigestion. We used a rat model of splanchnic ischemia by occlusion of the superior mesenteric and celiac arteries up to 30 min with and without luminal injection of tranexamic acid as a trypsin inhibitor. We determined the location and activity of digestive proteases on intestinal sections with in situ zymography, and we examined the disruption of two components of the mucosal barrier: mucin isoforms and the extracellular and intracellular domains of E cadherin with immunohistochemistry and Western blot techniques. The results indicate that nonischemic intestine has low levels of protease activity in its wall. After 15-min ischemia, protease activity was visible at the tip of the villi, and after 30 min, enhanced activity was seen across the full thickness of the intestinal wall. This activity was accompanied by disruption of the mucin layer and loss of both intracellular and extracellular domains of E cadherin. Digestive protease inhibition in the intestinal lumen with tranexamic acid reduced morphological damage and entry of digestive enzymes into the intestinal wall. This study demonstrates that disruption of the mucosal epithelial barrier within minutes of intestinal ischemia allows entry of fully activated pancreatic digestive proteases across the intestinal barrier triggering autodigestion.

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    • "Tranexamic acid had additional protective effects that were not present with the other MMP inhibitors. It preserved mucin 13, which could improve epithelial survival in non-flushed intestines [6], [18], and the decrease in occludin levels, while not significantly better than saline animals, was also not significantly different from pre-ischemic levels. Histology from the combined treatment of tranexamic acid with glucose suggests that tranexamic acid may also help the preservation of epithelial attachments to the basement membrane in the ex vivo study (Figure 5C), which may reduce anoikis, helping to preserve the epithelial barrier component. "
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    ABSTRACT: In intestinal ischemia, inflammatory mediators in the small intestine's lumen such as food byproducts, bacteria, and digestive enzymes leak into the peritoneal space, lymph, and circulation, but the mechanisms by which the intestinal wall permeability initially increases are not well defined. We hypothesize that wall protease activity (independent of luminal proteases) and apoptosis contribute to the increased transmural permeability of the intestine's wall in an acutely ischemic small intestine. To model intestinal ischemia, the proximal jejunum to the distal ileum in the rat was excised, the lumen was rapidly flushed with saline to remove luminal contents, sectioned into equal length segments, and filled with a tracer (fluorescein) in saline, glucose, or protease inhibitors. The transmural fluorescein transport was determined over 2 hours. Villi structure and epithelial junctional proteins were analyzed. After ischemia, there was increased transmural permeability, loss of villi structure, and destruction of epithelial proteins. Supplementation with luminal glucose preserved the epithelium and significantly attenuated permeability and villi damage. Matrix metalloproteinase (MMP) inhibitors (doxycycline, GM 6001), and serine protease inhibitor (tranexamic acid) in the lumen, significantly reduced the fluorescein transport compared to saline for 90 min of ischemia. Based on these results, we tested in an in-vivo model of hemorrhagic shock (90 min 30 mmHg, 3 hours observation) for intestinal lesion formation. Single enteral interventions (saline, glucose, tranexamic acid) did not prevent intestinal lesions, while the combination of enteral glucose and tranexamic acid prevented lesion formation after hemorrhagic shock. The results suggest that apoptotic and protease mediated breakdown cause increased permeability and damage to the intestinal wall. Metabolic support in the lumen of an ischemic intestine with glucose reduces the transport from the lumen across the wall and enteral proteolytic inhibition attenuates tissue breakdown. These combined interventions ameliorate lesion formation in the small intestine after hemorrhagic shock.
    PLoS ONE 05/2014; 9(5):e96655. DOI:10.1371/journal.pone.0096655 · 3.23 Impact Factor
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    • "Together the mucin and epithelial tight junctions form the mucosal barrier that is responsible for keeping the intestinal contents, including pancreatic digestive enzymes and digested food particles, compartmentalized in the intestine's lumen. Failure of the barrier as a result of ischemia allows the contents of the intestine to penetrate into the wall of the intestine and contribute to further intestinal damage (Chang et al. 2012a,b). "
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    ABSTRACT: The small intestine plays a key role in the pathogenesis of multiple organ failure following circulatory shock. Current results show that reduced perfusion of the small intestine compromises the mucosal epithelial barrier, and the intestinal contents (including pancreatic digestive enzymes and partially digested food) can enter the intestinal wall and transport through the circulation or mesenteric lymph to other organs such as the lung. The extent to which the luminal contents of the small intestine mediate tissue damage in the intestine and lung is poorly understood in shock. Therefore, rats were assigned to three groups: No-hemorrhagic shock (HS) control and HS with or without a flushed intestine. HS was induced by reducing the mean arterial pressure (30 mmHg; 90 min) followed by return of shed blood and observation (3 h). The small intestine and lung were analyzed for hemorrhage, neutrophil accumulation, and cellular membrane protein degradation. After HS, animals with luminal contents had increased neutrophil accumulation, bleeding, and destruction of E-cadherin in the intestine. Serine protease activity was elevated in mesenteric lymph fluid collected from a separate group of animals subjected to intestinal ischemia/reperfusion. Serine protease activity was elevated in the plasma after HS but was detected in lungs only in animals with nonflushed lumens. Despite removal of the luminal contents, lung injury occurred in both groups as determined by elevated neutrophil accumulation, permeability, and lung protein destruction. In conclusion, luminal contents significantly increase intestinal damage during experimental HS, suggesting transport of luminal contents across the intestinal wall should be minimized.
    10/2013; 1(5):e00109. DOI:10.1002/phy2.109
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    • "Mesenteric ischemia causes a hypoxic cell degeneration process in intestinal epithelial cells (23). This process disrupts the mucosal barrier and allows the entry of digestive enzymes into the intestinal wall, leading to autodigestion of the intestinal structure (24). In the case of reperfusion after mesenteric ischemia, intestinal damage is known to be caused by more than the ischemia alone (25). "
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    ABSTRACT: Introduction There is no valid and reliable diagnostic test for early diagnosis of acute mesenteric ischemia (AMI). The aim of this study was to measure the plasma levels of diamine oxidase (DAO) and citrulline in AMI to gain insight into its early diagnosis. Material and methods A total of 21 Wistar albino rats were divided into three groups, that is, control group, short-term ischemia group, and prolonged ischemia group. The superior mesenteric artery was occluded for 15 min in the short-term ischemia group and for 12 h in the prolonged ischemia group. Twelve hours later, the experiment was terminated and plasma DAO and citrulline levels were measured. Intestinal tissue was evaluated for the histopathological changes. Results Compared to the control group, the short-term and prolonged ischemia groups showed significant increases in the plasma levels of DAO, whereas the plasma citrulline levels decreased significantly. Prolonged ischemia caused a larger increase in the plasma DAO levels and a larger decrease in the plasma citrulline levels compared to the short-term ischemia (p=0.011 and p=0.021, respectively). Intestinal damage was shown to develop more in the prolonged ischemia group (p=0.001). Conclusion In the early period of AMI, the plasma DAO levels increase while citrulline levels decrease, and the extent of these changes depends on the duration of ischemia.
    Libyan Journal of Medicine 03/2013; 8:1-6. DOI:10.3402/ljm.v8i0.20596 · 1.06 Impact Factor
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