Differential changes in intestinal permeability following burn injury

Lung Protection After Severe Thermal Burns With Adenosine, Lidocaine, and Magnesium (ALM) Resuscitation and Importance of Shams in a Rat Model

The management of severe burns remains a complex challenge. Adenosine, lidocaine, and magnesium (ALM) resuscitation therapy has been shown to protect against hemorrhagic shock and traumatic injury. The aim of the present study was to investigate the early protective effects of small-volume ALM fluid resuscitation in a rat model of 30% total body surface area (TBSA) thermal injury. Male Sprague-Dawley rats (320-340 g; n = 25) were randomly assigned to: 1) Sham (surgical instrumentation and saline infusion, without burn, n = 5), 2) Saline resuscitation group (n = 10), or 3) ALM resuscitation group (n = 10). Treatments were initiated 15-min after burn trauma, including 0.7 mL/kg 3% NaCl ± ALM bolus and 0.25-0.5 mL/kg/h 0.9% NaCl ± ALM drip, with animals monitored to 8.25-hr post-burn. Hemodynamics, cardiac function, blood chemistry, hematology, endothelial injury markers and histopathology were assessed. Survival was 100% for Shams and 90% for both ALM and Saline groups. Shams underwent significant physiological, immune and hematological changes over time as a result of surgical traums. ALM significantly reduced malondialdehyde levels in the lungs compared to Saline (P = .023), and showed minimal alveolar destruction and inflammatory cell infiltration (P < .001). ALM also improved cardiac function and oxygen delivery (21%, P = .418 vs Saline), reduced gut injury (P < .001 vs Saline), and increased plasma adiponectin (P < .001 vs baseline). Circulating levels of the acute phase protein alpha 1-acid glycoprotein (AGP) increased 1.6-times (P < .001), which may have impacted ALM's therapeutic efficacy. We conclude that small-volume ALM therapy significantly reduced lung oxidative stress and preserved alveolar integrity following severe burn trauma. Further studies are required to assess higher ALM doses with longer monitoring periods.

WITHDRAWN: Early enteral nutrition versus late enteral nutrition for burns patients: A systematic review and meta-analysis

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Protection against early intestinal compromise by lipid-rich enteral nutrition through cholecystokinin receptors

OBJECTIVE

Early gut wall integrity loss and local intestinal inflammation are associated with the development of inflammatory complications in surgical and trauma patients. Prevention of these intestinal events is a potential target for therapies aimed to control systemic inflammation. Previously, we demonstrated in a rodent shock model that lipid-rich enteral nutrition attenuated systemic inflammation and prevented organ damage through a cholecystokinin receptor-dependent vagal pathway. The influence of lipid-rich nutrition on very early intestinal compromise as seen after shock is investigated. Next, the involvement of cholecystokinin receptors on the nutritional modulation of immediate gut integrity loss and intestinal inflammation is studied.

DESIGN

Randomized controlled in vivo study.

SETTING

University research unit.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Liquid lipid-rich nutrition or control low-lipid feeding was administered per gavage before hemorrhagic shock. Cholecystokinin receptor antagonists were used to investigate involvement of the vagal antiinflammatory pathway.

MEASUREMENTS AND MAIN RESULTS

Gut permeability to horseradish peroxidase increased as soon as 30 mins postshock and was prevented by lipid-rich nutrition compared with low-lipid (p<.01) and fasted controls (p<.001). Furthermore, lipid-rich nutrition reduced plasma levels of enterocyte damage marker ileal lipid binding protein at 60 mins (p<.05). Early gut barrier dysfunction correlated with rat mast cell protease plasma concentrations at 30 mins (rs=0.67; p<.001) and intestinal myeloperoxidase levels at 60 mins (rs=0.58; p<.05). Lipid-rich nutrition significantly reduced plasma rat mast cell protease (p<.01) and myeloperoxidase (p<.05) before systemic inflammation was detectable. Protective effects of lipid-rich nutrition were abrogated by cholecystokinin receptor antagonists (horseradish peroxidase; p<.05 and rat mast cell protease; p<.05).

CONCLUSIONS

Lipid-rich enteral nutrition prevents early gut barrier loss, enterocyte damage, and local intestinal inflammation before systemic inflammation develops in a cholecystokinin receptor-dependent manner. This study identifies activation of the vagal antiinflammatory pathway with lipid-rich nutrition as a potential therapy in patients prone to develop a compromised gut.

The effect of hepatocyte growth factor on gut mucosal apoptosis and proliferation, and cellular mediators after severe trauma

BACKGROUND

A severe burn injury is associated with an impairment of gut mucosal integrity and function, which is due to increases in small-bowel epithelial cell apoptosis and decreases in cell proliferation. Hepatocyte growth factor (HGF) was shown to improve regeneration in the liver, mesentery, and skin. The purpose of this study was to determine whether HGF can improve small-bowel homeostasis after injury and the cellular mechanisms by which these changes occur.

METHODS

Rats were pair-fed, underwent thermal trauma, and received saline (0.9% NaCl; n = 28) or HGF (200 microg/kg iv every 12 hours, n = 28). Small intestine and serum were taken at 1, 2, 5, and 7 days after injury. Measures were mucosal apoptosis, proliferation, villous morphology, and apoptotic and proliferative mediators, such as caspase-3 and caspase-7, Fas and Fas-ligand, Bcl-2, and Bax. In addition, serum cytokines were determined.

RESULTS

Gut epithelial cell apoptosis was increased in the saline and HGF groups after the thermal injury. Despite an increase in serum tumor necrosis factor-alpha and interleukin-1beta, HGF did not affect small-bowel cell apoptosis, but it improved proliferation at days 1 and 2 after injury, which was associated with increased villous height and cell per villous, compared with saline controls, P < .05. Increased mucosal cell proliferation was associated with increased Bcl-2 in the HGF group, P < .05. HGF had no effect on apoptotic mediators, such as Fas, Fas-L, or caspase-3 and caspase-7.

CONCLUSIONS

HGF improves small-bowel morphology after a severe burn by increasing mucosal Bcl-2 and, concomitantly, small-bowel epithelial cell proliferation.

Exacerbation of intestinal permeability in rats after a two-hit injury: burn and Enterococcus faecalis infection

OBJECTIVE

To determine alterations in intestinal epithelial permeability to solutes in burn injured rats with and without Enterococcus faecalis infection and the role of neutrophils in the intestinal permeability changes.

DESIGN

Prospective sham-controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats were subjected to 30% total body surface burn (B group), E. faecalis infection (EF group) induced via intra-abdominal implantation of bacterial pellet, or combination of burn injury and E. faecalis infection (B+EF group).

MEASUREMENTS AND MAIN RESULTS

In vivo measurements of intestinal permeability were carried out after intraluminal injection of H lactulose and C mannitol in the ileum of sham, B, EF, and B+EF groups of rats, 1 and 2 days after injury. Lactulose permeability was increased in the injured rat groups (B, EF, B+EF) on day 1 postinjury compared with sham. The combined injury group (B+EF) had the highest level of lactulose permeability. Although a significant change in lactulose permeability from day 1 to day 2 postinjury could not be demonstrated in the B and EF groups, lactulose permeability in the B+EF group on day 2 postinjury markedly decreased from day 1 but was still significantly higher than that in the sham group. Mannitol permeability was increased in all injured rat groups on day 1 postinjury; on day 2 it remained elevated post-B, decreased post-EF, and further increased after B+EF. Ex vivo measurements of lactulose movements across intestinal epithelial monolayers (IEC-18) were carried out in the presence of blood neutrophils from sham, B, EF, or B+EF rats. We also measured ex vivo transepithelial migration of neutrophils from sham, B, EF, or B+EF rat groups. Neither the transepithelial lactulose movement in the presence of neutrophils from, nor neutrophil migration in, the B or EF rats was significantly different from sham. However, a significant increase in transepithelial lactulose movement and neutrophil migration occurred in the B+EF group. Immunoblot analyses and in situ histochemical localizations of intestinal tight junction proteins, occludin and claudin-3, showed decreases in the distribution of occludin but not claudin-3 in the B, EF, and B+EF groups.

CONCLUSIONS

Alterations in intestinal solute permeability and disruption of tight junction integrity after a two-hit injury with burn and E. faecalis infection, but not after individual injuries of burn or E. faecalis infection, are likely associated with heightened neutrophil flux across the intestinal epithelium.

The effects of thermal injury on transcellular permeability and intestinal P-glycoprotein in rats

This study was designed to assess intestinal drug transport via transcellular absorption and intestinal P-glycoprotein content following thermal injury in rats using propranolol as a marker substrate. Male, Sprague Dawley rats (n=30) underwent either a 30% total body surface area full thickness burn or sham treatment. Twenty-four hours later, animals were anesthetized, underwent laparotomy and the proximal jejunum was cannulated. The jejunal segment was perfused with buffer containing [3H] propranolol. Following euthanasia, jejunal tissue was harvested for Western immunoblotting of P-glycoprotein and villin, and immunohistochemical analysis of P-glycoprotein. Dramatic structural changes in jejunal integrity were observed following thermal injury; however, no significant differences in the absorption characteristics of propranolol following thermal injury were observed. Mean effective permeability of propranolol was 5.67+/-1.79 and 5.85+/-1.67cm/sx10(-5) for burn and sham groups, respectively (P>0.05). P-glycoprotein and villin content in the jejunum were significantly decreased in burn animals. The transcellular transport of propranolol is unaffected 24h following thermal injury in rats, despite alterations in intestinal P-glycoprotein content. The decrease in P-glycoprotein and villin content in thermally injured animals may reflect loss of mature enterocytes at the villus tips.

Activation of poly(ADP-ribose) polymerase in severe hemorrhagic shock and resuscitation

This study examines activation of poly(ADP-ribose) polymerase (PARP) in the ileum during hemorrhage and resuscitation and determines if inhibition of PARP reduces organ dysfunction and metabolic acidosis. Awake, nonheparinized rats were hemorrhaged (40 mmHg, 60 min). Resuscitation used Ringer's solution (2 1/3 x shed volume) and packed red blood cells (2/3 shed volume). Ileal PARP activity was elevated at the end of hemorrhage (3.6-fold) and 10 min of resuscitation (5-fold). The subsequent decline in PARP activity observed after 60 min of resuscitation was not due to cleavage by caspase-3. Ileum permeability increased 10-fold and circulating liver enzymes increased 4- to 6-fold following 60 min of resuscitation in animals pretreated with 3-aminobenzoic acid, a structural analog that does not inhibit PARP. Pretreatment with 3-aminobenzamide (3-AB), a PARP inhibitor, reduced these changes, whereas posttreatment with a bolus of 3-AB was ineffective. Metabolic acidosis, accumulation of lactate, and base deficit was reduced by pretreatment with 3-AB. PARP is activated in the ileum by hemorrhage and by resuscitation. Activation of PARP contributes to organ dysfunction in the ileum and liver and appears to be central to the development of metabolic acidosis.

Dynamics of tissue neutrophil sequestration after cutaneous burns in rats

BACKGROUND

Neutrophil recruitment in organs after burns may cause local vascular damage, which can be reduced by agents blocking neutrophil adhesion to the vascular wall. Because these agents may increase susceptibility to infection, it is important to characterize the dynamics of neutrophil sequestration in order to optimize an eventual anti-adhesion therapy.

MATERIALS AND METHODS

Rats were scald burned over 20 or 40% of their total body surface area (TBSA) and saline resuscitated. Sham controls were used. Myeloperoxidase (MPO) activity was measured in lungs, liver, kidney, gut, and burned skin up to 1 week postburn. Extravascular accumulation of (125)I-labeled bovine serum albumin ((125)I-BSA) was measured at 12 h postburn.

RESULTS

MPO activity in lungs, liver, and kidney was increased within 3 h postburn and returned to normal within 24-48 h. Peak MPO levels occurred at 6-12 h postburn and were similar for both burn sizes. No MPO increase was observed in gut. MPO levels in burned skin did not increase before 6 h, peaked at 24 h, decreased at 48 h, but remained elevated for up to 7 days. Neutrophil recruitment in lungs and liver was confirmed histochemically. No neutrophils were found in kidneys. Extravascular (125)I-BSA was increased in lungs, liver, kidneys, and gut, in the 40% TBSA group only.

CONCLUSIONS

Neutrophil sequestration in remote organs is a transient phenomenon while neutrophil homing into the wound site is sustained. Neutrophil accumulation dynamics are independent of burn size, although a minimum size is required to trigger vascular damage. Temporary early anti-adhesion therapy to reduce lung and liver neutrophil sequestration with little impact on neutrophil homing into the burn wound may be possible.

Nitric oxide and intestinal barrier failure

The systemic inflammatory response syndrome (SIRS) is a leading cause of morbidity and mortality in adults and children. Various proinflammatory mediators have been implicated in the pathogenesis of SIRS; however, their mechanisms of action are poorly defined. Recent evidence suggests that nitric oxide (NO) plays a regulatory role in gut barrier function. Sustained upregulation of NO production in the intestine can lead to intestinal epithelial injury through the formation of peroxynitrite. Peroxynitrite can nitrate mitochondrial proteins and inhibit cellular respiration. The resultant changes in mitochondrial function lead to activation of the caspase cascade, subsequent DNA fragmentation, and enterocyte apoptosis. Enterocyte apoptosis results in a transient "bare area" in the intestinal epithelium where bacteria can attach and then penetrate the lamina propria. Bacteria that successfully escape the immune system may in turn incite a systemic inflammatory response.

Effect of alcohol on bacterial translocation in rats

Bacterial translocation has been proposed to be important in the pathophysiology of sepsis, as well as to be a consequence of sepsis. To study the effect of alcohol on bacterial translocation from the gut, normal Sprague-Dawley rats were administered alcohol by gavage by two regimens: Acute (3.7 g/kg, one dose) or Subacute (1 of 2 doses, 2.4 or 3.7 g/kg/day once daily for 14 days). Mesenteric lymph node cultures were performed, and portal venous blood was assayed for endotoxin. Ileal and cecal permeability studies were performed in the Acute and Subacute groups using fluorescein isothiocyanate-labeled dextrans of either 4,000 or 70,000 kDa size. As an index of the effect of systemic endotoxin, tissues from mesenteric lymph nodes, liver, and intestinal Peyer's patches were assayed for the presence of mRNA for tumor necrosis factor. Additionally, because extrapulmonary sepsis has been shown to suppress pulmonary antibacterial defenses, animals in the Subacute group were challenged by aerosol inoculation with Pseudomonas aeruginosa to determine bacterial clearance and alveolar cellular responses. The results show that neither of the alcohol regimens resulted in bacterial growth from mesenteric lymph nodes or portal blood. Animals in the Subacute group had more endotoxin present in portal blood than did the Control group (92.9 pg/ml vs. 40.2 pg/ml; p < 0.02). None of the animals had demonstrable mRNA for tumor necrosis factor in any of the tissues assayed. There were no demonstrable increases in ileal or cecal permeability for either the small or large molecular weight dextran in either alcohol group. Furthermore, there was no delay in the clearance of P. aeruginosa from the lung in the Subacute group, but these animals recruited fewer neutrophils into the airspaces in response to this challenge than did the Control animals. Thus, alcohol intoxication does not result in bacterial translocation from the gut in this model. Despite higher levels of portal venous endotoxin in the animals in the Subacute alcohol group, no adverse systemic consequences of this phenomenon could be demonstrated.