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Research I: Introduction
Septic shock is characterized by hemodynamic imbalance and the production
of proinflammatory and antiinflammatory molecules called cytokines.
These cytokines are released by various cells throughout the body,
where they gain access to the circulation and are delivered to target
cells in various tissues. Thus, a systemic inflammatory response
is mounted with collateral damage to tissues and organs, and this
is further aggravated by insufficient tissue perfusion due in part
to a dysfunctional blood clotting system.
The causes of septic shock are not well understood. In many cases,
a localized infection or blood borne infectious agent can be identified
in septic patients, but this is not always the case (1) . This, or
some other unknown stimulus, provokes a systemic inflammatory response
with widespread production of inflammatory mediators including cytokines.
We, and others in the field, believe that this "cytokine storm" is
the cause of the majority of the morbidity and mortality of septic
shock. A considerable portion of our research is directed towards
a better understanding of the molecular mechanisms underlying the
septic disease process.
In addition to septic shock, our laboratory also studies hemorrhagic
shock, which is caused by a significant and rapid loss of blood. This
elicits a systemic inflammatory response that is similar to, but distinct
from, septic shock. Our laboratory also uses ischemia and reperfusion
injury in experimental animals to study the effects of decreased local
perfusion and its deleterious effects on organ function.
An important component of sepsis is the progressive
loss of organ function often referred to as the multiple organ dysfunction
syndrome (MODS). Each year 750,000 cases of MODS are diagnosed in
critically ill patients the United States (2) . Organ failure, both
in terms of the number of organs failing (3, 4) and the degree of
organ dysfunction (3, 5) , is the strongest predictor of death in
the critically ill patient. Although the clinical manifestations of MODS can
be varied, the organs involved typically include the lungs, kidneys, liver,
and/or gut. There is widespread agreement that MODS results from the deleterious
effects of a dysregulated inflammatory response, but the cellular basis for
the development of organ system dysfunction in this syndrome is both poorly
understood and inadequately investigated.
Our research focuses on the function of epithelial cells, which
play a critical role in the function of all organs. Sheets of epithelial
cells, a single cell thick, typically form the boundaries of compartments
of distinct chemical environments within organs. Two properties of
epithelial cells are required for this compartmentalization function.
First, epithelial cells form tight intercellular junctions (see Figure
1) that prevent the passive diffusion of substances through the paracellular
space between adjacent cells (6, 7) . Second, the tight junctions
perform a gating function that partitions the plasma membrane into
apical and basal/lateral domains. The epithelial cells express protein
pumps and channels that transport ions and metabolites to either
the basal or apical exterior of the cell. This results in directed
movement of solutes such as the H + or Na + ions from one side of
the cell to the other. One example of this is the Na + , K + , ATPase,
which is located predominantly in the basolateral membrane of intestinal
epithelial cells. This protein pumps three Na + ions from the cell
interior to the basal (blood side) of the intestinal epithelium while
importing two K + ions into the cell at the expense of one ATP molecule.
This results in the establishment and maintenance of increased Na
+ concentration outside relative to inside the cell. The resulting
ion gradient can be used as an energy source to drive nutrients and
ions across the epithelium by other transporters. These ion gradients
across various compartments in organs are absolutely required for
many of the specialized functions of these cells and of the organs
they compose.
We use a combination of epithelial cell lines grown in culture and
animal models of sepsis to better understand the molecular and cellular
events associated with systemic inflammation and MODS. Our studies
using the human Caco-2 intestinal epithelial cells have focused on
the barrier function of these cells under both normal and immunostimulated
conditions. We have shown that proinflammatory cytokines decrease the
barrier function of this cell line (8-10) . We have further shown that
this NO · -dependent defect in epithelial paracellular barrier
function is most likely the consequence of decreased expression and
improper targeting of proteins that make up the tight junction complexes
between adjacent epithelial cells (11) . This loss of tight junction
protein expression is thought to increase the paracellular permeability
of the epithelium. We have also shown that this phenomenon ( i.e. ,
decreased expression of tight junction proteins with consequent increased
paracellular permeability) occurs in various organs obtained from mice
subjected to a systemic inflammatory insult. These organs include the
liver (12) , lung (13) , ileum (14) , and colon (14) . Figure 2 shows
the dramatic decrease in the expression of a key tight junction protein
called zonula occludens (ZO)-1 in lung of mice injected with Gram-negative
bacterial lipopolysaccharide (LPS). We believe that this aspect of
epithelial dysfunction with its associated decrease in epithelial barrier
function and organ compartmentalization may underlie a considerable
portion of the pathology of MODS.
We
have recently begun studying two novel compounds that modulate the inflammatory
process in immunostimulated epithelial cells in tissue culture and in animal
models of systemic inflammation. Ethyl pyruvate (15) and nicotinamide adenine
dinucleotide (NAD + ) (16) have been shown to protect epithelial cells from
the deleterious effects of proinflammatory cytokines. Both compounds were
shown to improve survival in animal model of systemic inflammation (17, 18)
(Delude, Han, Uchiyama, Yang, Fink, unpublished observations). We are hopeful
that these two compounds may lead to the development of effective therapies
for the treatment of critically ill patients.
Below are links to several pages
that expand on our group's research. As with most web based projects, this
website is a work in progress. If you are interested in this research you
may contact either Dr. Fink or Dr. Delude directly. Any errors or comments
concerning the science on these laboratory web pages should be directed
to Dr. Delude.
Literature Cited:
1. Schlag, G., H. Redl, and S. Hallstrom. 1991. The cell in shock: the origin
of multiple organ failure. Resuscitation 21:137 .
2. Angus, D. C., W. T. Linde-Zwirble, J. Lidicker, G. Clermont, J. Carcillo,
and M. R. Pinsky. 2001. Epidemiology of severe sepsis in the United States:
analysis of incidence, outcome, and associated costs of care. Crit Care
Med 29:1303 .
3. Vincent, J. L., R. Moreno, J. Takala, S. Willatts, A. De Mendonca, H. Bruining,
C. K. Reinhart, P. M. Suter, and L. G. Thijs. 1996. The SOFA (Sepsis-related
Organ Failure Assessment) score to describe organ dysfunction/failure. On behalf
of the Working Group on Sepsis-Related Problems of the European Society of
Intensive Care Medicine. Intensive Care Med 22:707 .
4. Hebert, P. C., A. J. Drummond, J. Singer, G. R. Bernard, and J. A. Russell.
1993. A simple multiple system organ failure scoring system predicts mortality
of patients who have sepsis syndrome. Chest 104:230 .
5. Bone, R. C., R. Maunder, G. Slotman, H. Silverman, T. M. Hyers, M. D. Kerstein,
and J. J. Ursprung. 1989. An early test of survival in patients with the adult
respiratory distress syndrome. The PaO2/FIo2 ratio and its differential response
to conventional therapy. Prostaglandin E1 Study Group. Chest 96:849 .
6. Schneeberger, E. E., and R. D. Lynch. 1992. Structure, function, and regulation
of cellular tight junctions. Am J Physiol 262:L647 .
7. Stevenson, B. R. 1999. Understanding tight junction clinical physiology
at the molecular level. J Clin Invest 104:3 .
8. Unno, N., M. J. Menconi, M. Smith, and M. P. Fink. 1995. Nitric oxide mediates
interferon-gamma-induced hyperpermeability in cultured human intestinal epithelial
monolayers. Crit Care Med 23:1170 .
9. Salzman, A. L., M. J. Menconi, N. Unno, R. M. Ezzell, D. M. Casey, P. K.
Gonzalez, and M. P. Fink. 1995. Nitric oxide dilates tight junctions and depletes
ATP in cultured Caco- 2 BBe intestinal epithelial monolayers. Am J Physiol
268:G361 .
10. Menconi, M. J., N. Unno, M. Smith, D. E. Aguirre, and M. P. Fink. 1998.
Nitric oxide donor-induced hyperpermeability of cultured intestinal epithelial
monolayers: role of superoxide radical, hydroxyl radical, and peroxynitrite. Biochim
Biophys Acta 1425:189 .
11. Han, X., M. P. Fink, and R. L. Delude. 2003. Proinflammatory cytokines
cause NO·-dependent and -independent changes in expression and localization
of tight junction proteins in intestinal epithelial cells. Shock 19:229 .
12. Han, X., M. P. Fink, T. Uchiyama, R. Yang, and R. L. Delude. 2003. Increased
iNOS activity is essential for hepatic epithelial tight junction dysfunction
in endotoxemic mice. Am J Physiol Gastrointest Liver Physiol In press
.
13. Han, X., M. P. Fink, T. Uchiyama, and R. L. Delude. 2003. Increased iNOS
activity is essential for pulmonary epithelial tight junction dysfunction in
endotoxemic mice. Am J Physiol Lung Cell Mol Physiol In press .
14. Han, X., M. P. Fink, R. Yang, and R. L. Delude. Increased iNOS activity
is essential for intestinal epithelial tight junction dysfunction in endotoxemic
mice. submitted .
15. Sappington, P. L., X. Han, R. Yang, R. L. Delude, and M. P. Fink. 2003.
Ethyl pyruvate ameliorates intestinal epithelial barrier dysfunction in endotoxemic
mice and immunostimulated caco-2 enterocytic monolayers. J Pharmacol Exp
Ther 304:464 .
16. Han, X., T. Uchiyama, P. L. Sappington, A. Yaguchi, M. P. Fink, and R.
L. Delude. 2003. NAD + ameliorates inflammation-induced epithelial barrier
dysfunction in cultured enterocytes and mouse ileal mucosa. J Pharmacol
Exp Ther In press .
17. Yang, R., D. J. Gallo, J. J. Baust, T. Uchiyama, S. K. Watkins, R. L.
Delude, and M. P. Fink. 2002. Ethyl pyruvate modulates inflammatory gene expression
in mice subjected to hemorrhagic shock. Am J Physiol Gastrointest Liver
Physiol 283:G212 .
18. Tawadrous, Z. S., R. L. Delude, and M. P. Fink. 2002. Resuscitation from
hemorrhagic shock with Ringer's ethyl pyruvate solution improves survival and
ameliorates intestinal mucosal hyperpermeability in rats. Shock 17:473 . |
