Mechanisms of postburn intestinal barrier dysfunction in the rat: roles of epithelial cell renewal, E-cadherin, and neutrophil extravasation.
OBJECTIVE
Our group has previously shown that the intestinal epithelium exhibits increased postburn barrier permeability and bacterial translocation associated with deranged neutrophil activity. The purpose of this investigation is to explore possible underlying intestinal structural mechanisms, leading to those functional changes with emphasis on (1) neutrophil influx and extravasation in the intestinal lamina propria 1-3 days after burn and (2) enterocyte proliferation, migration, apoptosis, and E-cadherin junctional epithelium levels 3 days after burn.


METHODS
Freshly isolated ileum specimens were quick frozen, then cut by a cryostat into 30-micron-thick sections. Sections from day 1 postburn rats were immunostained with (1) anti-granulocyte or anti-elastase antibodies to assess neutrophil influx or (2) combined anti-granulocyte and anti-von Willebrand factor double immunolabeling to compare levels of neutrophil extravasation. Sections from day 3 postburn rats were immunostained with (1) bromodeoxyuridine immunohistochemistry 1, 3, 6, or 18 hrs after bromodeoxyuridine injection to assess enterocyte proliferation and migration, (2) cytokeratin-18 M30-immunohistochemistry to compare levels of enterocyte apoptosis, and (3) E-cadherin immunohistochemistry to compare junctional E-cadherin integrity. Ileal myeloperoxidase activity and bacterial translocation of Enterococcus faecalis were assessed biochemically and by E. faecalis-specific bacterial cultures, respectively, in day 3 postburn rats.


METHODS
: Research laboratories in a medical center and an academic institution.


METHODS
Male Sprague-Dawley rats given sham treatment or treatment as a burn model with full-thickness skin scald over 30% total body surface area.


CONCLUSIONS
We report (1) increased levels of neutrophil influx and extravasation in villi lamina propriae, including elastase-positive cells (postburn day 1), (2) heightened levels of intestinal myeloperoxidase activity (postburn day 3), (3) decreased levels of epithelial cell proliferation, migration, and E-cadherin (postburn day 3), and (4) increased enterocyte apoptosis and E. faecalis bacterial translocation (postburn day 3). Based on these structural and functional abnormalities, we propose a mechanism for burn injury-related intestinal barrier dysfunction that includes increased trans- and para-cellular leakage caused by impaired enterocyte renewal and decreased junctional E-cadherin levels subsequent to increased neutrophil influx and extravasation within the villus lamina propria microenvironment.
Trauma/Critical Care Labs, Department of Surgery, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA. walghoul@csu.edu
Walid M
WM
Al-Ghoul
Mehdi
M
Khan
Nadeem
N
Fazal
Mohammed M
MM
Sayeed
D000818:Animals; D018988:Bacterial Translocation; D002056:Burns / Q000378:metabolism*; D015820:Cadherins / Q000378:metabolism*; D004195:Disease Models, Animal; D013293:Enterococcus faecalis / Q000502:physiology; D020895:Enterocytes / Q000378:metabolism; D007082:Ileum / Q000378:metabolism / Q000503:physiopathology; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000503:physiopathology*; D007633:Keratins / Q000378:metabolism; D008297:Male; D009504:Neutrophils / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D015820:Cadherins; D007633:Keratins