Norman W. Weisbrodt

Post-injury Multiple Organ Failure: The Role Of The Gut

ABSTRACT— Despite intensive investigation, the pathogenesis of post‐injury multiple organ failure (MOF) remains elusive. Laboratory and clinical research strongly suggests that the gastrointestinal tract (i.e., the gut) plays a pivotal pathogenic role. Since its inception in 1988, the Trauma Research Center (TRC) at the University of Texas‐Houston Medical School (UTHMS) has focused its efforts on elucidating the role of the gut in post‐injury MOF. On the basis of our observations and those of others, we believe that 1) shock with resulting gut hypoperfusion is an important inciting event, 2) the reperfused gut is a source of proinflammatory mediators that can amplify the early systemic inflammatory response syndrome (SIRS) and thus contribute to early MOF, 3) early gut hypoperfusion causes an ileus in both the stomach and small bowel that sets the stage for progressive gut dysfunction so that the proximal gut becomes a reservoir for pathogens and toxins that contribute to late sepsis‐associated MOF, and 4) late infections cause further worsening of this gut dysfunction. Thus, the gut can be both an instigator and a victim of MOF. The purpose of this article is to provide the rationale behind these beliefs and to provide a brief overview of the ongoing research projects in the TRC at UTHMS.

The nature of heme/iron-induced protein tyrosine nitration

Recently, substantial evidence has emerged that revealed a very close association between the formation of nitrotyrosine and the presence of activated granulocytes containing peroxidases, such as myeloperoxidase. Peroxidases share heme-containing homology and can use H2O2 to oxidize substrates. Heme is a complex of iron with protoporphyrin IX, and the iron-containing structure of heme has been shown to be an oxidant in several model systems where the prooxidant effects of free iron, heme, and hemoproteins may be attributed to the formation of hypervalent states of the heme iron. In the current study, we have tested the hypothesis that free heme and iron play a crucial role in NO2-Tyr formation. The data from our study indicate that: (i) heme/iron catalyzes nitration of tyrosine residues by using hydrogen peroxide and nitrite, a reaction that revealed the mechanism underlying the protein nitration by peroxidase, H2O2, and NO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document}; (ii) H2O2 plays a key role in the protein oxidation that forms the basis for the protein nitration, whereas nitrite is an essential element that facilitates nitration by the heme(Fe), H2O2, and the NO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document} system; (iii) the formation of a Fe(IV) hypervalent compound may be essential for heme(Fe)-catalyzed nitration, whereas O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{{\bullet}-}}}\end{equation*}\end{document} (ONOO− formation), •OH (Fenton reaction), and compound III are unlikely to contribute to the reaction; and (iv) hemoprotein-rich tissues such as cardiac muscle are vulnerable to protein nitration in pathological conditions characterized by the overproduction of H2O2 and NO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document}, or nitric oxide.

Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling

Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor-mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine-induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada -/- and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder.

GRADIENTS OF CONTRACTIONS IN THE OPOSSUM ESOPHAGUS

Contractions of longitudinal and circular smooth muscle strips from the opossum esophagus were monitored in vitro. Three types of experiments were performed. (1) KC1-induced contractions were recorded isometrically, and the time intervals between rhythmic contractions were measured by computer. In longitudinal muscle strips, the interval between contractions increased progressively from 1.95 sec for strips taken 6 cm from the gastroesophageal junction (GES) to 3.15 sec for strips taken 1 cm from the GES. There was no gradient in circular muscle strips. (2) Contractions were induced by transmural electrical stimulation. The ability of strips to follow stimuli at progressively shorter interstimulus intervals was determined. Circular muscle strips, but not longitudinal muscle strips, showed a gradient in the ability to follow high frequency stimulation. (3) The stimulus-response delay was determined with transmural electrical stimulation. For circular muscle strips, the delay increased from 0.8 sec for strips taken 12 cm from the GES to 2.2 sec for strips taken 1 cm from the GES. No gradient existed for longitudinal muscle strips. Thus, differences exist over very short segments of the esophagus, in the nerves, muscle, or both, which may partially account for peristaltic movements. A hypothesis is proposed about the nature of peristalsis in the smooth muscle of the esophagus.

Altered small bowel propulsion associated with parasitism.

Experiments were designed to test the hypothesis that alterations of intestinal motility accompany enteric helminth infections. Motility was measured in rats during the intestinal phase of infection with the nematode Trichinella spiralis by following the transit of radioactive chromium through the gut. Intraduodenal catheters were surgically implanted in rats. One week after the operation one group of animals was infected with 8 x 10(3) T. spiralis larvae and a second group was infected with 16 x10(3) larvae. A third group of uninfected rats served as controls. Three, four, or five days postinfection, Na2 51CrO4 was injected through the catheter into the duodenum or fasted animals and its propulsion through the small bowel was allowed to progress for 15 min. The distribution of radioactivity throughout the small intestine and cecum was then plotted as a function of gut length. Intestinal transit was increased significantly by infection. The leading edge of radioactivity transversed 100% of the gut length in infected rats and 70% in controls. The amount of injected radioactivity transversing the midpoint of the small intestine was estimated by regression equations to be 38% of the injected dose for control rats and 59 and 57% for infected groups. Increased propulsive activity in parasitized rats was associated with inflammatory changes and a significant reduction in disaccharidase levels in the gut mucosa. The latter conditions were most marked in the proximal small bowel where the majority of worms resided.

Roles of IL-1 and TNF in the decreased ileal muscle contractility induced by lipopolysaccharide

Gastrointestinal stasis during sepsis may be associated with gastrointestinal smooth muscle dysfunction. Endotoxin [lipopolysaccharide (LPS)] impairs smooth muscle contraction, in part through inducible nitric oxide synthase (NOS II) and enhanced nitric oxide production. We studied the roles of tumor necrosis factor-α (TNF) and interleukin-1 (IL-1) in this process by using TNF binding protein (TNFbp) and IL-1 receptor antagonist (IL-1ra). Rats were treated with TNFbp and IL-1ra, or their vehicles, 1 h before receiving LPS or saline. At 5 h after LPS, contractility was measured in strips of ileal longitudinal smooth muscle, and NOS II activity was measured in full-thickness segments of ileum. LPS decreased maximum stress (mean ± SE) from 508 ± 55 (control) to 355 ± 33 g/cm2( P < 0.05). Pretreatment with TNFbp plus IL-1ra prevented the LPS-induced decrease. Separate studies of TNFbp alone or IL-1ra alone indicated that, at the doses and timing used, TNFbp was more effective. LPS also increased NOS II activity by >10-fold ( P < 0.01) over control. This increase was prevented by TNFbp plus IL-1ra ( P = not significant vs. control). We conclude that the LPS-induced increase in NOS II activity and the decrease in ileal muscle contractility are mediated by TNF and IL-1.Gastrointestinal stasis during sepsis may be associated with gastrointestinal smooth muscle dysfunction. Endotoxin [lipopolysaccharide (LPS)] impairs smooth muscle contraction, in part through inducible nitric oxide synthase (NOS II) and enhanced nitric oxide production. We studied the roles of tumor necrosis factor-alpha (TNF) and interleukin-1 (IL-1) in this process by using TNF binding protein (TNFbp) and IL-1 receptor antagonist (IL-1ra). Rats were treated with TNFbp and IL-1ra, or their vehicles, 1 h before receiving LPS or saline. At 5 h after LPS, contractility was measured in strips of ileal longitudinal smooth muscle, and NOS II activity was measured in full-thickness segments of ileum. LPS decreased maximum stress (mean +/- SE) from 508 +/- 55 (control) to 355 +/- 33 g/cm2 (P < 0.05). Pretreatment with TNFbp plus IL-1ra prevented the LPS-induced decrease. Separate studies of TNFbp alone or IL-1ra alone indicated that, at the doses and timing used, TNFbp was more effective. LPS also increased NOS II activity by >10-fold (P < 0.01) over control. This increase was prevented by TNFbp plus IL-1ra (P = not significant vs. control). We conclude that the LPS-induced increase in NOS II activity and the decrease in ileal muscle contractility are mediated by TNF and IL-1.

Hypothermia protects against gut ischemia/reperfusion-induced impaired intestinal transit by inducing heme oxygenase-1

PURPOSE Gut ischemia/reperfusion (I/R) elicits an inflammatory response that impairs intestinal transit. We have previously shown that regional intraischemic hypothermia (IH) protects against moderate gut I/R-induced mucosal injury, is associated with decreased NF-kappaB activity and inducible nitric oxide synthase induction and preserves heme oxygenase-1 (HO-1) expression. HO-1 provides cytoprotection in various models of oxidant stress. We, therefore, tested the hypothesis that IH protects against gut I/R-induced impaired intestinal transit via HO-1 induction. MATERIALS AND METHODS At laparotomy (lap), Sprague-Dawley rats had duodenal catheters placed followed by sham or gut I/R (superior mesenteric artery occlusion for 75 min) with or without regional IH (15 degrees C). Each animal was placed on a heating blanket maintaining systemic normothermia (37 degrees C). At 12 or 24 h of reperfusion, small intestinal transit was determined by quantitating the distribution of a tracer (FITC dextran) in the intestine 30 min after instillation (expressed as geometric center of distribution). Ileal samples were obtained for histology and HO-1 expression, assessed by Western immunoblot at 12 and 24 h of reperfusion. In separate experiments, rats were pretreated with an HO-1 inhibitor Sn protoporphyrin IX (25 mumol/kg, ip), 1 h before superior mesenteric artery occlusion and transit measured as above. RESULTS Rats treated with I/R had increased histological injury and impaired intestinal transit at both 12 and 24 h compared with sham. Rats treated with I/R+IH exhibited histological injury and transit comparable with sham controls. I/R induced HO-1 expression at 12 and 24 h of reperfusion and IH augmented this I/R-induced HO-1 expression. Sn protoporphyrin IX abrogated IH protection against histological injury and impaired transit. CONCLUSION We conclude that intraischemic regional hypothermia protects against histological injury and impaired intestinal transit caused by severe gut I/R injury. Hypothermic protection under these conditions is in part due to HO-1 expression.

Resuscitation-induced gut edema and intestinal dysfunction

BACKGROUND Mesenteric venous hypertension and subsequent gut edema play a pivotal role in the development of intra-abdominal hypertension. Although gut edema is one cause of intra-abdominal hypertension, its impact on gut function is unknown. The purpose of this study was to create a model of acute hydrostatic gut edema and to evaluate its effect on gut motility and barrier function. METHODS The first study, group A, evaluated the effect of gut edema on transit over time using 20 mL/kg 0.9% saline. The second study, group B, focused on the 12-hour time period using 80 mL/kg 0.9% saline. Rats were randomized to superior mesenteric vein partial occlusion (venous hypertension) or sham surgery. At 6, 12, and 24 hours, group A underwent intestinal transit and tissue water weight measurements. At 12 hours, group B underwent tissue water, transit, ileal permeability and resistance, lactate and myeloperoxidase activity, and mucosal injury measurements. RESULTS Venous hypertension with fluid resuscitation caused acute hydrostatic gut edema, delayed intestinal transit, increased mucosal permeability to macromolecules, and decreased tissue resistance over time. Mucosal injury was minimal in mesenteric venous hypertension. CONCLUSION Acute mesenteric venous hypertension and resuscitation-induced gut edema, in the absence of ischemia/reperfusion injury, is associated with delayed intestinal transit and altered gut barrier function.

Neural organization of esophageal peristalsis: role of vagus nerve.

The purpose of this investigation was 2-fold: first, to determine the velocity of peristalsis in the smooth muscle area of opossum esophagus before and after administration of atropine; second, to evaluate the role of the vagus nerves in the control of the propagative nature of esophageal peristalsis. Intraluminal pressures were measured through a pressure transducer recorder system attached to continuously perfused catheters. The velocity of peristalsis in the lower third of the esophagus progressively decreased from 3.25 plus or minus 0.20 (SE) cm per sec at the 70 to 80% level to 2.17 plus or minus 0.14 (SE) at the 80 to 90%level to 1.83 plus or minus 0.10 (SE) at the 90 to 100% level. After administration of intraperitoneal atropine (100 mug per kg), the velocities were 3.1 plus or minus 0.26 (SE) cm per sec, 2.38 plus or minus 0.22 (SE), and 1.74 plus or minus 0.10 (SE), respectively, at the 70 to 80%, 80 to 90%, and 90 to 100% levels. The changes were not statistically significant. Electrical stimulation of the distal cut end of the vagus nerve induced peristaltic contractions. The velocities of peristalsis after electrical stimulation of the vagus nerve were 3.24 plus or minus 0.72 (SE) cm per sec, 2.81 plus or minus 0.64 (SE), and 1.84 plus or minus 0.34 (SE), respectively, at the 70 to 80%, 80 to 90%, and 90 to 100% levels. Results of this study indicate that the velocity of peristalsis in the smooth muscle area of the opossum esophagus has a caudally decreasing gradient. Bilateral cervical vagotomy and stimulation of the distal cut end initiates peristaltic contraction indicating that the propagative nature of peristalsis in the smooth musurrent, does not alter mucosal cyclic AMP. Dibutyryl cyclic AMP decreased net sodium absorption and increased short circuit current; findings which were qualitatively identical to those produced by taurochenodeoxycholic acid. These studies support the proposal that bile salts stimulate colonic electrolyte secretion by increasing mucosal cyclic AMP.

Resuscitation-induced intestinal edema decreases the stiffness and residual stress of the intestine

We have shown that acute edema impairs intestinal transit and we wanted to know whether this could be from changes in the physical characteristics of the intestine. Our hypothesis was that acute edema will change the physical characteristics of the intestine, which were measured by standardized engineering measures of elastic modulus, to determine stiffness and opening angle, and to determine residual stress. Rats were randomized to sham, mild edema (80 mL/ kg of normal saline resuscitation), and severe edema groups (80 mL/kg of normal saline resuscitation with intestinal venous hypertension). Segments of distal ileum were hung to a fixed point in a tissue bath and to a tensiometer and were stretched in increments of 1 mm, recording the new length and the corresponding force from the tensiometer to determine elastic modulus. Next, two transverse cuts were made yielding a 1- to 2-mm-thick ring-shaped segment of tissue and were then cut radially to open the ring. The opening angle was measured. Acute intestinal edema led to a decrease in transit, elastic modulus, and opening angle of the intestine in the absence of ischemic injury. Acute intestinal edema leads to a significant loss in stiffness and residual stress and is a plausible explanation for how acute edema impairs intestinal transit.