Bio

Professional Education


  • Doctor of Philosophy, University of California San Diego (2012)
  • Master of Science, University of Texas Arlington (2006)
  • Bachelor of Science, University of Texas Arlington (2006)

Stanford Advisors


Publications

Journal Articles


  • Impaired small-bowel barrier integrity in the presence of lumenal pancreatic digestive enzymes leads to circulatory shock. Shock Kistler, E. B., Alsaigh, T., Chang, M., Schmid-Schönbein, G. W. 2012; 38 (3): 262-267

    Abstract

    In bowel ischemia, impaired mucosal integrity may allow intestinal pancreatic enzyme products to become systemic and precipitate irreversible shock and death. This can be attenuated by pancreatic enzyme inhibition in the small-bowel lumen. It is unresolved, however, whether ischemically mediated mucosal disruption is the key event allowing pancreatic enzyme products systemic access and whether intestinal digestive enzyme activity in concert with increased mucosal permeability leads to shock in the absence of ischemia. To test this possibility, the small intestinal lumen of nonischemic rats was perfused for 2 h with either digestive enzymes, a mucin disruption strategy (i.e., mucolytics) designed to increase mucosal permeability, or both, and animals were observed for shock. Digestive enzymes perfused included trypsin, chymotrypsin, elastase, amylase, and lipase. Control (n = 6) and experimental animals perfused with pancreatic enzymes only (n = 6) or single enzymes (n = 3 for each of the five enzyme groups) maintained stable hemodynamics. After mucin disruption using a combination of enteral N-acetylcysteine, atropine, and increased flow rates, rats (n = 6) developed mild hypotension (P < 0.001 compared with groups perfused with pancreatic enzymes only after 90 min) and increased intestinal permeability to intralumenally perfused fluorescein isothiocyanate-dextran 20 kd (P < 0.05) compared with control and enzyme-only groups, but there were no deaths. All animals perfused with both digestive enzymes and subjected to mucin disruption (n = 6) developed hypotension and increased intestinal permeability (P < 0.001 after 90 min). Pancreatic enzymes were measured in the intestinal wall of both groups subjected to mucin disruption, but not in the enzyme-only or control groups. Depletion of plasma protease inhibitors was found only in animals perfused with pancreatic enzymes plus mucin disruption, implicating increased permeability and intralumenal pancreatic enzyme egress in this group. These experiments demonstrate that increased bowel permeability via mucin disruption in the presence of pancreatic enzymes can induce shock and increase systemic protease activation in the absence of ischemia, implicating bowel mucin disruption as a key event in early ischemia. Digestive enzymes and their products, if allowed to penetrate the gut wall, may trigger multiorgan failure and death.

    View details for DOI 10.1097/SHK.0b013e31825b1717

    View details for PubMedID 22576000

  • Breakdown of Mucin as Barrier to Digestive Enzymes in the Ischemic Rat Small Intestine PLOS ONE Chang, M., Alsaigh, T., Kistler, E. B., Schmid-Schoenbein, G. W. 2012; 7 (6)

    Abstract

    Loss of integrity of the epithelial/mucosal barrier in the small intestine has been associated with different pathologies that originate and/or develop in the gastrointestinal tract. We showed recently that mucin, the main protein in the mucus layer, is disrupted during early periods of intestinal ischemia. This event is accompanied by entry of pancreatic digestive enzymes into the intestinal wall. We hypothesize that the mucin-containing mucus layer is the main barrier preventing digestive enzymes from contacting the epithelium. Mucin breakdown may render the epithelium accessible to pancreatic enzymes, causing its disruption and increased permeability. The objective of this study was to investigate the role of mucin as a protection for epithelial integrity and function. A rat model of 30 min splanchnic arterial occlusion (SAO) was used to study the degradation of two mucin isoforms (mucin 2 and 13) and two epithelial membrane proteins (E-cadherin and toll-like receptor 4, TLR4). In addition, the role of digestive enzymes in mucin breakdown was assessed in this model by luminal inhibition with acarbose, tranexamic acid, or nafamostat mesilate. Furthermore, the protective effect of the mucin layer against trypsin-mediated disruption of the intestinal epithelium was studied in vitro. Rats after SAO showed degradation of mucin 2 and fragmentation of mucin 13, which was not prevented by protease inhibition. Mucin breakdown was accompanied by increased intestinal permeability to FITC-dextran as well as degradation of E-cadherin and TLR4. Addition of mucin to intestinal epithelial cells in vitro protected against trypsin-mediated degradation of E-cadherin and TLR4 and reduced permeability of FITC-dextran across the monolayer. These results indicate that mucin plays an important role in the preservation of the mucosal barrier and that ischemia but not digestive enzymes disturbs mucin integrity, while digestive enzymes actively mediate epithelial cell disruption.

    View details for DOI 10.1371/journal.pone.0040087

    View details for Web of Science ID 000305892100199

    View details for PubMedID 22768227

  • DISRUPTION OF THE MUCOSAL BARRIER DURING GUT ISCHEMIA ALLOWS ENTRY OF DIGESTIVE ENZYMES INTO THE INTESTINAL WALL SHOCK Chang, M., Kistler, E. B., Schmid-Schoenbein, G. W. 2012; 37 (3): 297-305

    Abstract

    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.

    View details for DOI 10.1097/SHK.0b013e318240b59b

    View details for Web of Science ID 000300622300011

    View details for PubMedID 22089198

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