Intestinal mucosal permeability to 51Cr-ethylenediaminetetraacetic acid is increased after bilateral lower extremity ischemia-reperfusion in the rat

Is metabolic stress a common denominator in inflammatory bowel disease?

The enteric epithelium represents the major boundary between the outside world and the body, and in the colon it is the interface between the host and a vast and diverse microbiota. A common feature of inflammatory bowel disease (IBD) is decreased epithelial barrier function, and while a cause-and-effect relationship can be debated, prolonged loss of epithelial barrier function (whether this means the ability to sense bacteria or exclude them) would contribute to inflammation. While there are undoubtedly individual nuances in IBD, we review data in support of metabolic stress--that is, perturbed mitochondrial function--in the enterocyte as a contributing factor to the initiation of inflammation and relapses in IBD. The postulate is presented that metabolic stress, which can arise as a consequence of a variety of stimuli (e.g., infection, bacterial dysbiosis, and inflammation also), will reduce epithelial barrier function and perturb the enterocyte-commensal flora relationship and suggest that means to negate enterocytic metabolic stress should be considered as a prophylactic or adjuvant therapy in IBD.

Metabolic stress evokes decreases in epithelial barrier function

The epithelial lining of the gastrointestinal tract is the major interface between the external world (e.g., the gut lumen) and the body, and as such the proper maintenance and regulation of epithelial barrier function is a key determinant of digestive health and host well-being. Many enteropathies are associated with increased gut permeability, including inflammatory bowel disease (IBD). Maintaining the barrier function of the epithelium, independent of whether paracellular or transcellular permeation pathways are considered, is an energy-dependent process. Here we present an overview of the impact that metabolic stress (e.g., reductions in epithelial ATP synthesis) can have on permeability characteristics of epithelial monolayers and show that metabolic stress in the presence of a commensal flora results in a significant loss of epithelial integrity, and that this increase in epithelial permeability can be enhanced by the presence of tumor necrosis factor-alpha (TNFalpha). We speculate that the combination of these factors in vivo would result in significant perturbations in epithelial barrier function that could be of pathophysiological significance and contribute to the initiation of IBD or the induction of disease relapses.

Heme oxygenase modulates small intestine leukocyte adhesion following hindlimb ischemia/reperfusion by regulating the expression of intercellular adhesion molecule-1

OBJECTIVE

Heme oxygenase is the rate-limiting enzyme in the degradation of heme into carbon monoxide, iron, and bilirubin. Recent evidence suggests that the induction of heme oxygenase-1 is associated with potent anti-inflammatory properties. The objectives of this study were to determine the temporal, regional, and cellular distribution of heme oxygenase-1 within the small intestine and its role in modulating remote intestinal leukocyte recruitment following trauma induced by hindlimb ischemia/reperfusion.

DESIGN

Randomized, controlled, prospective animal study.

SETTING

Hospital surgical research laboratory.

SUBJECTS

Male C57BL/6 mice.

INTERVENTIONS

Mice underwent 1 hr of bilateral hindlimb ischemia, followed by 3, 6, 12, or 24 hrs of reperfusion.

MEASUREMENTS AND MAIN RESULTS

Heme oxygenase-1 messenger RNA, heme oxygenase-1 protein, and heme oxygenase activity were measured using reverse transcription polymerase chain reaction, Western blot, immunohistochemistry, and spectrophotometric assay, respectively. The jejunum was also exteriorized to quantify the flux of rolling and adherent leukocytes and R-Phycoerythrin conjugated intercellular adhesion molecule-1 monoclonal antibody fluorescence intensity in submucosal postcapillary venules with the use of intravital microscopy. Ischemia/reperfusion led to a significant increase in heme oxygenase-1 messenger RNA in the jejunum and ileum 3 hrs following limb reperfusion, with a subsequent increase in heme oxygenase-1 protein and heme oxygenase activity at 6 hrs. Ischemia/reperfusion also led to a significant 1.4-fold increase in leukocyte rolling, whereas inhibition of heme oxygenase via injection of tin protoporphyrin IX (20 micromol/kg intraperitoneally) resulted in a three-fold increase in leukocyte adhesion, compared with ischemia/reperfusion alone. This increase in adhesion was significantly reduced to baseline in mice treated with intercellular adhesion molecule-1 monoclonal antibody before heme oxygenase inhibition (40 microg/mouse), whereas inhibition of heme oxygenase activity following ischemia/reperfusion also led to a significant increase in R-Phycoerythrin intercellular adhesion molecule-1 monoclonal antibody fluorescence intensity.

CONCLUSIONS

Our data suggest that remote trauma induced by hindlimb ischemia/reperfusion leads to an increase in heme oxygenase activity within the small intestine, which modulates intercellular adhesion molecule-1 dependent intestinal leukocyte adhesion.

Use of an isolated intestinal circuit to evaluate the effect of ischemia and reperfusion on mucosal permeability of the equine jejunum

OBJECTIVES

To evaluate the efficacy of an isolated perfusion circuit and the effect of ischemia-reperfusion on mucosal permeability of the jejunum.

STUDY DESIGN

In vitro study of intestinal mucosal permeability.

ANIMALS

Twelve healthy adult horses.

METHODS

A control segment of jejunum was placed in an isolated perfusion circuit for 240 minutes and mucosal permeability was measured. After detecting no deleterious effects of the isolated system on the control intestine, low flow ischemia was created in experimental segments for 20, 40, 60 and 90 minutes followed by 60 minutes of reperfusion and mucosal permeability was evaluated. At the completion of the studies, histologic evaluation was used to determine mucosal grades, surface area, and volume.

RESULTS

Control tissue was maintained in the isolated circuit for 240 minutes without effect on mucosal grade, surface area, or volume relative to intact tissue. After ischemia-reperfusion, mucosal grade increased, and volume and surface area decreased progressively with longer periods of ischemia. Mucosal clearance of albumin remained constant during 240 minutes of perfusion in control tissue and was elevated after ischemia-reperfusion.

CONCLUSIONS

No deleterious changes were noted in jejunum perfused with this isolated circuit, whereas alterations in mucosal permeability were present after ischemia-reperfusion.

CLINICAL RELEVANCE

The isolated perfusion circuit successfully maintained an isolated segment of jejunum within physiologic limits, and can be used to evaluate the effects of injury and the efficacy of pharmaceuticals to attenuate these changes.

NF-kappaB activation has tissue-specific effects on immune cell apoptosis during polymicrobial sepsis

Studies indicate that critically ill patients who succumb to sequela of sepsis/multiorgan failure, as well as septic animals, exhibit an apparently pathological increase in apoptosis (Ao) in the immune system. However, the mechanisms regulating these changes are unclear. Studies also indicate that, dependent on the cell population and the nature and/or duration of the stimuli, activation of the nuclear factor (NF)-kappaB can either suppress or enhance Ao. Thus, the aim of this study was to determine the contribution of NF-kappaB activation to the onset of Ao seen in divergent immune cell populations during sepsis, as produced by cecal ligation and puncture (CLP). To assess this, C3H/HeN mice were pretreated (for 1 h) subcutaneously with either 100 mg/kg body weight of pyrrolidine dithiocarbamate (PDTC), an NF-kappaB inhibitor, or with saline vehicle, prior to subjecting them to CLP or Sham-CLP (Sham). Thymocytes, phagocytes, and Peyers Patch cells were harvested 24 h later, and the extent of Ao was determined by flow cytometry. The results indicate that PDTC pretreatment had no marked effect on the increase in thymocyte or phagocyte Ao seen following CLP, but there was a significant decline in the extent of Ao observed in septic mouse Peyer's patch B cells. To the extent that this was a result of NF-kappaB inhibition, we demonstrate by Western analysis, electrophoretic mobility shift assay (EMSA) and transfactor assay that the translocation of c-Rel to septic mouse Peyer's patch B cell nuclei is attenuated by PDTC. PDTC pretreatment also markedly reduced the number of Peyer's patch B cells that were producing IgA as well as attenuated the increase of proinflammatory cytokines in the blood. Interestingly, PDTC pretreatment did not restore peritoneal macrophage function or improve animal survival. Taken together, the inability of PDTC pretreatment to alter the Ao response of thymocytes or phagocytes, while inhibiting the increase in Peyer's patch B cell Ao in septic mice, implies not only that the activation of NF-kappaB has highly tissue/cell-specific effects that must be discerned when trying to clarify the pathophysiological role of NF-kappaB in sepsis, but that the activation of NF-kappaB may contribute to the early adaptive responses required by the host to fend off septic challenge.

Antithrombin III prevents deleterious effects of remote ischemia-reperfusion injury on healing of colonic anastomoses

BACKGROUND

Antithrombin III is known as the most important natural inhibitor of thrombin activity and has been shown to attenuate local harmful effects of ischemia-reperfusion injury in many organs. In recent animal studies, delaying effect of remote organ ischemia-reperfusion injury on healing of intestinal anastomoses has been demonstrated. In this study, we investigated whether antithrombin III reduces deleterious systemic effects of ischemia-reperfusion injury on healing of colonic anastomoses in rats.

METHODS

Anastomosis of the left colon was performed in 24 rats that were divided into three groups: sham operated control (group I, n = 8), 30 minutes of intestinal ischemia-reperfusion by superior mesenteric artery occlusion (group II, n = 8), antithrombin III treated group (250 U/kg before and after the ischemia-reperfusion, group III, n = 8). On postoperative day 6, all animals were sacrificed, and bursting pressure and tissue hydroxyproline content of the anastomoses were assessed and compared.

RESULTS

On postoperative day 6 the mean bursting pressures were 149.6 +/- 4.8, 69.8 +/- 13.5, and 121.8 +/- 8.7 mm Hg for groups I, II, and III, respectively (P = 0.000). Mean tissue hydroxyproline concentration values were 389.5 +/- 29.6, 263.1 +/- 10.0, and 376.0 +/- 33.8 microg/mg for groups I, II, III respectively (P = 0.005).

CONCLUSIONS

This study showed that, antithrombin III treatment significantly prevented the delaying effect of remote organ ischemia-reperfusion injury on anastomotic healing in the colon. Further clinical studies are needed to clarify whether antithrombin may be a useful therapeutic agent to increase the safety of the anastomosis during particular operations where remote organ ischemia-reperfusion injury takes place.

The role of endogenous heme oxygenase in the initiation of liver injury following limb ischemia/reperfusion

BACKGROUND/AIMS

Heme oxygenase (HO) derived liver protection was tested in mice following 1 h bilateral hindlimb ischemia and either 1.5 or 3 h reperfusion.

METHODS

Groups consisted of limb ischemia/reperfusion (I/R), sham (no I/R), I/R+chromium mesoporphyrin (I/R+CrMP;40 micromol/kg, i.p.), or I/R+hemin (10 mg/kg, i.p.). The vital dye propidium iodide (PI), was used to measure hepatocellular death (#/0.1 mm(3)), while the number of sinusoids perfused by red blood cells (SP(RBC)) were measured from the periportal (Pp) and pericentral (Pc) zones of liver acini using intravital microscopy. Whole organ injury was estimated from serum alanine aminotransferase (ALT).

RESULTS

SP(RBC) reduced within 1.5 h with no further decline following 3 h. CrMP resulted in a dramatic loss of SP(RBC) following 3 h only. Hemin restored perfusion in both zones. Hepatocellular death and organ injury increased at 1.5 and 3 h. At 1.5 h, CrMP further increased cell death in the Pc zone, as well as whole organ injury, while hemin restored cell viability. Increased HO mRNA, protein and activity suggested induction within 3 h.

CONCLUSIONS

HO does not protect perfusion during the early stage (1.5 h), but becomes increasingly important in preserving liver perfusion and cell viability during the later stage (3 h) of liver injury.

Intestinal mitochondrial dysfunction in surgical stress

BACKGROUND

Surgical stress is associated with altered intestinal function. Our earlier study using a rat model indicated that oxidative stress plays an important role in this process. Since mitochondria are crucial to cellular function and survival and are both a target as well as a source of reactive oxygen species, the present study looks at the changes in enterocyte mitochondria during surgical stress.

METHODS

Surgical stress was induced by opening the abdominal wall and handling the intestine as done during laparotomy. Mitochondria were prepared from the isolated enterocytes at different time periods after surgical stress. The effect of surgical stress on enterocyte mitochondrial ultrastructure, respiration, anti-oxidant enzyme activity, thiol redox status, calcium flux, permeability, and matrix enzymes was then studied.

RESULTS

Surgical stress resulted in alterations in mitochondrial respiration and thiol redox status. It was also associated with altered mitochondrial matrix enzyme activity, decreased superoxide dismutase activity, induction of mitochondrial permeability transition, and swelling, as well as impairment of mitochondrial calcium flux. These alterations were seen at a maximum of 60 min following surgical stress and were reversed by 24 h.

CONCLUSIONS

Laparotomy and mild intestinal handling itself results in enterocyte mitochondrial damage. Since mitochondria are important cellular organelles, this damage can probably lead to compromised intestinal function.

Nitric oxide protects the intestine from the damage induced by laparotomy and gut manipulation

BACKGROUND

The intestine is highly susceptible to free radical-induced damage, and our earlier work has shown that surgical stress induces the generation of oxygen free radicals in enterocytes, resulting in intestinal damage along with ultrastructural changes. Since nitric oxide (NO) is an important mediator of gastrointestinal function, this study looked at the effect of NO on surgical stress-induced intestinal alterations.

MATERIALS AND METHODS

Control rats and rats pretreated with the NO donor l-arginine were subjected to surgical stress by opening the abdominal wall and handling the intestine as done during laparotomy. Enterocytes were isolated and homogenate prepared, and the protection offered by l-arginine against damage due to surgical stress was determined and compared with normal controls. Protection to structural as well as functional aspects of the intestine was also examined.

RESULTS

Intestinal manipulation affected intestinal structure as assessed by electron microscopy. Functional impairment of the enterocyte was also evident, with increased xanthine oxidase activity resulting in production of superoxide anion. This impairment is more dramatic in the crypt cells. Increased protease activity was also seen following laparotomy and handling. Pretreatment with the NO synthase substrate l-arginine prevented these damaging effects. Arginine protection was abolished in the presence of the NO synthase inhibitor NG-nitro-l-arginine methyl ester, indicating the role of NO.

CONCLUSION

Stress in the small intestine due to any surgery can affect enterocyte structure and function. These damaging effects can be prevented by NO, an important modulator of cellular function.

Gut mucosal injury is attenuated by recombinant bactericidal/permeability-increasing protein in hind limb ischemia-reperfusion injury

Lower limb ischemia-reperfusion injury (IRI) is associated with increased gut permeability to endotoxin, which not only directly damages enterocytes but also stimulates a systemic inflammatory response syndrome (SIRS), compounding gut injury. Recombinant bactericidal/permeability-increasing protein (rBPI21) is a novel anti-endotoxin therapy with proven benefit in sepsis. Its potential role in modulating remote gut injury in hind limb IRI was studied. Male Wistar rats were chosen for a prospective randomized control trial (n = 10 per group). The control group and two groups undergoing 3 hr bilateral hind limb ischemia with 2 hr reperfusion (I/R) were randomized to receive intravenously either control protein thaumatin at 2 mg/kg or rBPI21 at 2 mg/kg, respectively. Quantitative morphometric assessment of the small bowel was used as a measure of gut injury and, using an ex vivo everted gut sac model, translocation of 14C-labeled polyethylene glycol (PEG) was used as a measure of gut permeability. Our results indicate that hind limb IRI is associated with remote gut mucosal injury and increased permeability to macromolecules. rBPI21 anti-endotoxin therapy modulates remote gut injury associated with lower limb IRI in this model.

Ileal mucosal response to bacterial toxin challenge

BACKGROUND

The cause of postinjury intestinal mucosal barrier disruption remains obscure. The present study examines the hypothesis that the bacterial toxin formyl-methionyl leucyl phenylalanine (FMLP) plays an initial role in this process.

METHODS

Mucosal permeability to fluorescein isothiocyanate-labeled dextran (4,400 molecular weight) was measured in perfused distal rat ileum with and without FMLP. Dextran and myeloperoxidase appearance in the lumenal perfusate was assessed in response to surrogates of traumatic stress: ischemia/reperfusion, total abdominal irradiation, and total parenteral nutrition. Recovery of FMLP in the effluent of static closed and perfused ileal loops was determined by mass spectrometry. Release of mast cell mediators in the presence of FMLP was determined in ileal everted sacs.

RESULTS

Seventy-five percent of FMLP was recovered in perfusion effluent in contrast to 5% in closed loops. There was a transient increase in ileal permeability in FMLP/perfused, untreated rats, and in ischemia/reperfusion and total parenteral nutrition treated rats that was recorded with a concomitant increment in myeloperoxidase (inflammatory marker) in all experimental models except irradiated rats, which were unresponsive to FMLP. FMLP responsiveness was associ. ated with a significant rise in release of serotonin (mast cell mediator).

CONCLUSION

These results suggest that mast cells and other resident inflammatory cells within the gut wall are involved in FMLP-induced changes in mucosal barrier permeability and raise the possibility that under conditions of traumatic stress, proinflammatory mediators within the gut wall might be activated by toxic factors in the gut lumen.

Role of xanthine oxidase in small bowel mucosal dysfunction after surgical stress

BACKGROUND

The small intestine is highly susceptible to surgical stress even at remote locations. An earlier study using a rat model indicated that oxidative stress plays an important role in this process. The enzyme xanthine oxidase is an important source of free radicals in the small intestine. The role of this enzyme in intestinal damage after surgical stress was examined.

METHODS

Rats pretreated with xanthine oxidase inhibitors were subjected to surgical stress by opening the abdomen and handling the intestine, as done during laparotomy. Enterocytes at various stages of differentiation were isolated and the protection offered by xanthine oxidase inhibitors against damage due to surgical stress was determined and compared with normal controls. Protection against ultrastructural changes to the mucosa, as well as mitochondrial function was examined.

RESULTS

Surgical stress affected both the villus as well as crypt cells, causing increased superoxide generation, accompanied by increased activity of xanthine oxidase. Xanthine oxidase inhibitors ameliorated the increased superoxide generation, and protected against mitochondrial damage and ultrastructural changes in the intestine.

CONCLUSION

Surgical stress affects both the villus and crypt cell populations in the small intestine. The enzyme xanthine oxidase maybe an important mediator of surgical stress in the intestine.

Effect of local and remote ischemia-reperfusion injury on healing of colonic anastomoses

BACKGROUND

Although the effect of locally applied ischemia-reperfusion (I-R) injury on gastrointestinal anastomoses has been studied, to our knowledge there is no previous study that investigates the effect of remote I-R injury on gastrointestinal anastomotic healing. The aim of this study was to investigate and compare the effects of local I-R injury and remote I-R injury on the healing of colonic anastomoses.

METHODS

Anastomosis of the right colon was performed in 30 rats that were divided into 5 groups. Group 1 was the control group. In Group 2, I-R was applied to the colonic segment containing the anastomosis. Unilateral lower extremity I-R, unilateral renal I-R, and segmental small intestinal I-R was applied to the rats in Groups 3, 4, and 5, respectively, at the same time as colonic anastomosis. On the fourth postoperative day, animals were killed and bursting pressure and tissue hydroxyproline concentration of the anastomoses were analyzed and compared.

RESULTS

The mean bursting pressure values were: 143 mm Hg in Group 1, 40.8 mm Hg in Group 2, 82.8 mm Hg in Group 3, 46.1 mm Hg in Group 4, and 52.3 mm Hg in Group 5 (P <.0001; 1-way analysis of variance). Mean tissue hydroxyproline concentration values were: 5.3 microg/mg in Group 1, 1.6 microg/mg in Group 2, 2.2 microg/mg in Group 3, 1.3 microg/mg in Group 4, and 1.5 microg/mg in Group 5 (P <. 0001, 1-way analysis of variance). Bursting pressure and tissue hydroxyproline concentration values had a good correlation r = 0.86, P <.001, Pearson correlation analysis).

CONCLUSIONS

This study showed that I-R injury is a systemic phenomenon, and remote organ I-R can significantly delay anastomotic healing. This has to be kept in mind when constructing an intestinal anastomosis in the presence of local or remote I-R injury.

Cytokines contribute to early hepatic parenchymal injury and microvascular dysfunction after bilateral hindlimb ischemia

PURPOSE

Hepatic dysfunction may contribute to death from multiple organ dysfunction after abdominal aortic surgery. Several factors are likely responsible, and the purpose of this study was to determine whether the cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin 1 (IL-1) are involved in initiating this remote hepatic injury.

METHODS

In a normotensive rat model of 4-hour bilateral hindlimb ischemia/reperfusion (I/R), we measured systemic TNF-alpha and IL-1 levels throughout the I/R period. Rats were randomly assigned to either the 3-hour control group, the 3-hour I/R group, or the I/R group with administration of a polyclonal antibody (PAb) to TNF-alpha (I/R + TNF-alpha PAb). Direct evidence of lethal hepatocyte injury through the labeling of nuclei by propidium iodide (per 10(-1)mm(3)) and altered microvascular perfusion were assessed by using intravital microscopy.

RESULTS

Systemic TNF-alpha peaked at 83.97 pg/mL (P <.05, n = 5) at 30 minutes of reperfusion and returned to baseline in 60 to 90 minutes. No significant change in systemic IL-1 was detected (P <.05, n = 4). Alanine aminotransferase increased 2.5-fold in the I/R group through 3 hours of reperfusion (P <.05, n = 4), and TNF-alpha PAb did not attenuate this alanine aminotransferase increase (P <.05, n = 6). Lethal hepatocyte injury increased by 8-fold in the I/R group compared with the control group (P <.05, n = 5), whereas TNF-alpha PAb significantly reduced this injury (P <.05, n = 4). No regional differences in injury were noted within the acinus. Total perfusion within the microvascular unit did not drop; however, significant flow heterogeneity was observed. The proportion of continuously perfused sinusoids declined in the I/R group after 3 hours of reperfusion in both periportal (62.0 +/- 2.2, P <.05) and, to a lesser, although significant, degree, in the pericentral regions (73. 2 +/- 1.73, P <.05).

CONCLUSION

By scavenging extracellular TNF-alpha with a PAb, we provide direct evidence that TNF-alpha contributes to, but is not solely responsible for, early remote hepatocellular injury and microvascular dysfunction. The administration of TNF-alpha PAb reduced lethal hepatocyte injury in both regions of the acinus and also improved perfusion in the periportal region (76.8 +/- 5.41, P <.05), but not in the pericentral region. This suggests that TNF-alpha released during reperfusion mediates early remote hepatocellular injury and microvascular dysfunction after a remote ischemic insult.

Microcirculatory perfusion deficits are not essential for remote parenchymal injury within the liver

A normotensive model of hindlimb ischemia-reperfusion in Wistar rats was used to test the hypothesis that microvascular perfusion deficits contribute to the initiation of remote hepatic injury during a systemic inflammatory response. Animals were randomly assigned to one of three groups: 4 h of ischemia with 6 h of reperfusion (I/R-6; n = 4), 4 h of ischemia with 3 h of reperfusion (I/R-3; n = 5), or no ischemia (naive; n = 5). With intravital fluorescence microscopy, propidium iodide (PI; 0.05 mg/100 g body wt) was injected for the in vivo labeling of lethally injured hepatocytes (number/10(-1) mm(3)). PI-positive hepatocytes increased progressively over the 6-h period (naive 32.9 +/- 7.8 vs. I/R-3 92.8 +/- 11.5 vs. I/R-6 232 +/- 39.2), with no difference between periportal and pericentral regions of the lobule. Additionally, a significant decrease in continuously perfused sinusoids (naive 70.0 +/- 1.5 vs. I/R-3 65.0 +/- 1.0 vs. I/R-6 48.8 +/- 0.9%) was measured. Regional sinusoidal perfusion differences were only observed after 3 h of limb reperfusion. Indirect measures of hepatocellular injury using alanine transaminase levels support the progressive nature of hepatic parenchymal injury (0 h 57.8 +/- 6.5 vs. 3 h 115.3 +/- 20.7 vs. 6 h 125.6 +/- 19.5 U/l). Evidence from this study suggests that remote hepatic parenchymal injury occurs early and progresses after the induction of a systemic inflammatory response and that microvascular perfusion deficits are not essential for the initiation of such injury.

Surgical stress and the small intestine: role of oxygen free radicals

BACKGROUND

Any surgical procedure can be associated with altered intestinal function. The mechanism involved in these changes at the cellular level during surgical stress has not been worked out. This study looked at the biochemical and functional alterations, along with ultrastructural changes, in the intestine during surgical stress in a simple rat model.

METHODS

Surgical stress was induced by opening the abdominal wall and handling the intestine as during laparotomy. The effect of oxidative stress on the enterocyte and altered intestinal permeability as well as the ultrastructural changes to the mucosa were studied.

RESULTS

Surgical stress results in oxidative stress on enterocytes, as evidenced by increased xanthine oxidase and decreased catalase activity along with altered thiol redox status. This was associated with increased intestinal permeability and widened intercellular spaces. These changes were prominent at 60 minutes after laparotomy and returned to normal by 24 hours.

CONCLUSIONS

Mild intestinal handling is capable of inducing oxidative stress in enterocytes; this could be one of the mechanisms by which intestinal mucosal alterations occur during surgical stress.

Femur fracture induces site-specific changes in T-cell immunity

BACKGROUND

Trauma is associated with altered host defense and susceptibility to infection, in part due to cytokine dysregulation and altered T-cell immunity. The gut-associated lymphoid tissue (GALT) provides a defense against infection and contributes to the process of mucosal healing by T-cell activation and cytokine production.

OBJECTIVE

To determine whether femur fracture induces alterations in Peyer's patch and splenic T-cell phenotype, proliferative response, and cytokine expression following traumatic injury.

METHODS

Mice underwent femur fracture or sham procedure and, 48 h later, lymphocytes were isolated from spleen and Peyer's patches. Lymphocytes were cultured, and lipopolysaccharide (10 microg/ml) was added in some cultures. Cells and supernatant were harvested at 48 h. Proliferation was analyzed by [3H]thymidine, and interleukin-10 (IL-10) protein was measured by ELISA in the culture supernatant. T-cell phenotype was determined by flow cytometry.

RESULTS

Femur fracture induced a significant increase in proliferative response in Peyer's patch immunocytes. In contrast, no significant differences were identified in splenocyte proliferative response 48 h after femur fracture injury. Femur fracture induced a significant decrease in IL-10 protein expression of both splenocytes and Peyer's patches. Femur fracture also induced a significant increase in the fraction of CD3(+), CD4(+), and T-cell receptor-alpha beta Peyer's patch immunocytes, whereas splenocytes demonstrated no significant phenotypic change.

CONCLUSION

Femur fracture is associated with significant alterations in Peyer's patch but not splenic T-cell phenotype and proliferative response early (48 h) after injury. Changes in the GALT immune response may contribute to intestinal mucosal dysfunction and increased susceptibility to gut-derived sepsis after traumatic injury.

Effects of tourniquet compression on neuromuscular function

Neuromuscular function in New Zealand White rabbits was evaluated after thigh tourniquet compression in the directly compressed quadriceps muscles and the distal tibialis anterior by measuring isometric contractile function after supramaximal stimulation of the motor nerve. Tourniquet compression resulted in markedly decreased force production beneath and distal to the tourniquet. Two days after compression, maximal quadriceps force production was decreased to 46% of control values with 125 mm Hg compression and 21% of control values after 350 mm Hg compression. Maximum tibialis anterior force production declined to 70% of control values after 125 mm Hg thigh compression and 24% of control values after 350 mm Hg thigh compression. Functional deficits were greater in the directly compressed quadriceps muscles, but the quadriceps and tibialis anterior had significantly increased impairment when the tourniquet inflation pressure was increased from 125 mm Hg to 350 mm Hg. Three weeks after compression, quadriceps function had returned to 94% of control value after 125 mm Hg compression and 83% after 350 mm Hg. Tibialis anterior function returned to 88% of control values after 125 mm Hg thigh compression and 83% after 350 mm Hg. Clinically, the use of lower inflation pressures may minimize the complications of tourniquet use and enhance postoperative recovery.

Increased Mucosal B-Lymphocyte Apoptosis During Polymicrobial Sepsis Is a Fas Ligand But Not an Endotoxin-Mediated Process

Sepsis is reported to induce an increase in the rate of apoptosis (Ao), in immature lymphoid cells residing in hematopoietic tissues such as the thymus and bone marrow. Alternatively, secondary lymphoid tissue, such as the spleen exhibit little innate (unstimulated) Ao. However, it is unknown whether or not polymicrobial sepsis has any effects on the frequency of Aoin mucosal lymphoid tissue and what, if any, are the functional consequences of such a change. To assess this, Peyer's patch cells were harvested from C3H/HeN (endotoxin-sensitive) mice killed 12 or 24 hours after the onset of polymicrobial sepsis (cecal ligation and puncture [CLP]). The results indicate that the percentage of cells that were Ao+ as determined by flow cytometry were markedly increased at 24 hours, but not at 12 hours post-CLP. This correlates well with evidence of increased DNA fragmentation as well as histological changes observed both at a light and transmission electron microscopic level of the Peyer's patch Ao. Phenotypically, these changes were restricted to the B220+ (B-cell) population that also exhibited a marked increase of Fas/Apo-1 antigen expression. The functional consequence of this increased apoptosis appears to be associated with the endogenous stimulation (activation) of IgA production by mucosal B lymphocytes and increased nuclear c-Rel expression. Furthermore, we found that Peyer's patch lymphocytes isolated from C3H/HeJ-Faslgld(endotoxin-tolerant/Fas ligand- [FasL] deficient) as opposed to C3H/HeJ (endotoxin-tolerant) inbred mice did not exhibit increased Ao after CLP. These findings indicate that increased B-cell Ao appears to be a FasL-Fas antigen-mediated process, but is not due to endotoxin sensitivity. In conclusion, we speculate that the increased Fas-associated apoptosis detected in mucosal B cells (as opposed to splenic or bone marrow B cells) may be due to increased luminal antigens other than endotoxin, released due to gut barrier integrity breakdown during sepsis.

Mechanism of intestinal mucosal immune dysfunction following trauma-hemorrhage: increased apoptosis associated with elevated Fas expression in Peyer's patches

Although intestinal mucosal immune dysfunction occurs after trauma and hemorrhage and appears to contribute to infectious complications, the mechanism is not known. In this regard, the inappropriate induction of immune cell apoptosis may contribute to the immune dysfunction following trauma and hemorrhage. To study this, we examined Peyer's patch cells for evidence of apoptosis and changes in Fas protein expression, as well as alterations in the relative lymphocyte subpopulations after trauma and hemorrhagic shock. Male C3H/HeN mice underwent sham operation, trauma (i.e., laparotomy), hemorrhagic shock (mean arterial blood pressure of 35 +/- 5 mmHg for 90 min, followed by adequate crystalloid resuscitation), or trauma plus hemorrhage. Peyer's patch cells were isolated at 24 and 72 hr after the procedure. The percentage of apoptotic cells, Fas protein expression, and cell percentage of phenotype were determined by flow cytometry. The results indicate that trauma alone induced no significant change in the measured parameters. However, (i) there were a significant decrease in total viable cell yield and an increased apoptosis in Peyer's patch cells at 24 and 72 hr following hemorrhage or trauma plus hemorrhage; (ii) the increased apoptosis in Peyer's patch was predominantly in cells of the B-cell lineage; (iii) the increased apoptosis was associated with an elevated Fas expression. In conclusion, hemorrhage alone or trauma plus hemorrhage can induce increased apoptosis in Peyer's patch cells, which is associated with the increased Fas expression. Thus, apoptotic involution may play an important role in the depression of intestinal mucosal immune function after trauma and hemorrhagic shock.