Combination therapy that targets secondary pulmonary changes after abdominal trauma

AICAR attenuates organ injury and inflammatory response after intestinal ischemia and reperfusion

Intestinal ischemia and reperfusion (I/R) is encountered in various clinical conditions and contributes to multiorgan failure and mortality as high as 60% to 80%. Intestinal I/R not only injures the intestine, but affects remote organs such as the lung leading to acute lung injury. The development of novel and effective therapies for intestinal I/R are critical for the improvement of patient outcome. AICAR (5-aminoimidazole-4-carboxyamide ribonucleoside) is a cell-permeable compound that has been shown to possess antiinflammatory effects. The objective is to determine that treatment with AICAR attenuates intestinal I/R injury and subsequent acute lung injury (ALI). Male Sprague Dawley rats (275 to 325 g) underwent intestinal I/R injury with blockage of the superior mesenteric artery for 90 min and subsequent reperfusion. At the initiation of reperfusion, vehicle or AICAR (30 mg/kg BW) was given intravenously (IV) for 30 min. At 4 h after reperfusion, blood and tissues were collected for further analyses. Treatment with AICAR significantly decreased the gut damage score and the water content, indicating improvement in histological integrity. The treatment also attenuated tissue injury and proinflammatory cytokines, and reduced bacterial translocation to the gut. AICAR administration after intestinal I/R maintained lung integrity, attenuated neutrophil chemotaxis and infiltration to the lungs and decreased lung levels of tumor necrosis factor (TNF)-α and interleukin (IL)-6. Inflammatory mediators, lung-inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) proteins, were decreased in the lungs and lung apoptosis was significantly reduced after AICAR treatment. These data indicate that AICAR could be developed as an effective and novel therapeutic for intestinal I/R and subsequent ALI.

Activation of AMPK attenuates neutrophil proinflammatory activity and decreases the severity of acute lung injury

AMP-activated protein kinase (AMPK) is activated by increases in the intracellular AMP-to-ATP ratio and plays a central role in cellular responses to metabolic stress. Although activation of AMPK has been shown to have anti-inflammatory effects, there is little information concerning the role that AMPK may play in modulating neutrophil function and neutrophil-dependent inflammatory events, such as acute lung injury. To examine these issues, we determined the effects of pharmacological activators of AMPK, 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) and barberine, on Toll-like receptor 4 (TLR4)-induced neutrophil activation. AICAR and barberine dose-dependently activated AMPK in murine bone marrow neutrophils. Exposure of LPS-stimulated neutrophils to AICAR or barberine inhibited release of TNF-alpha and IL-6, as well as degradation of IkappaBalpha and nuclear translocation of NF-kappaB, compared with findings in neutrophil cultures that contained LPS without AICAR or barberine. Administration of AICAR to mice resulted in activation of AMPK in the lungs and was associated with decreased severity of LPS-induced lung injury, as determined by diminished neutrophil accumulation in the lungs, reduced interstitial pulmonary edema, and diminished levels of TNF-alpha and IL-6 in bronchoalveolar lavage fluid. These results suggest that AMPK activation reduces TLR4-induced neutrophil activation and diminishes the severity of neutrophil-driven proinflammatory processes, including acute lung injury.

Hydroxyethyl starch inhibits neutrophil adhesion and transendothelial migration

A resuscitation strategy that significantly alters the state of neutrophil (PMN) activation may impact organ function and survivability after shock. Various resuscitative fluids have been shown to elicit a severe immune activation and an upregulation of cellular injury markers, whereas other fluids have been shown to be protective. Recent studies have demonstrated that hydroxyethyl starch (HES), an artificial colloid, may exert significant anti-inflammatory effects, whereas conflicting studies with the same substance have shown an increase in PMN activation. Successful manipulation of the early immune events associated with hemorrhage and resuscitation will require a better understanding of the possible pro- or anti-inflammatory effects of resuscitation fluids. Our study investigated the effect of HES directly on PMN and cultured vascular endothelial cells in vitro. The effect of HES on PMN surface expression of CD11b and L-selectin was measured by flow cytometry. PMN activation response to HES was measured using a shape-change assay in response to formyl-methionyl-leucyl-phenylalanine (f-MLP). The effect of HES on endothelial cell surface expression of E-selectin, P-selectin, vascular cell adhesion molecule-1(VCAM-1), and intracellular adhesion molecule-1 (ICAM-1) was evaluated by enzyme-linked immunoabsorbant assay. PMN rolling, adhesion, and migration events were measured using direct microscopy under conditions simulating microvascular flow. PMN surface expression of CD11b and L-selectin in whole blood samples and isolated PMNs were unaffected by exposure to HES. HES had no effect on the normal f-MLP dose-dependent increase in PMN activation. In the absence of IL-1 stimulation, there was a small but statistically significant (P < 0.05) increase in ICAM-1 after exposure to HES. After stimulation with IL-1 (10 U/mL), HES had no effect on the expression of P-selectin, E-selectin, ICAM-1, or VCAM-1. Under simulated microvascular flow conditions in vitro, HES significantly diminished the PMN tethering rate (P < 0.05) and the transendothelial migration rate (P < 0.05) in a dose-dependent manner. HES significantly alters the function of the PMN at the interface of the PMN responding to activated endothelium. The effect occurs, surprisingly, without a coincident effect on the state of PMN activation or a significant change in the surface expression of the adhesion molecules responsible for PMN-endothelial interaction.

Apoptosis and Necrosis in the Development of Acute Lung Injury after Hemorrhagic Shock

Acute lung injury can be a complication of hemorrhagic shock. Mechanisms of injury include neutrophil-derived inflammatory products that induce necrosis within the lung. Recent data has shown apoptosis, in addition to necrosis, as a pathway leading toward acute lung injury in shock models. This study quantitates apoptotic and necrotic cells in the lung after hemorrhagic shock. Mongrel pigs (20–30 kg) under general anesthesia (with pancuronium and pentobarbital) underwent instrumentation with placement of carotid and external jugular catheters. The animals were randomized to sham hemorrhage (n = 6) and to hemorrhagic shock (n = 7). The hemorrhagic shock group then underwent hemorrhage (40–45% blood volume) to a systolic blood pressure of 40–50 mm Hg for 1 hour. The animals were then resuscitated with shed blood plus crystalloid to normalization of heart rate and blood pressure. The animals were observed under general anesthesia for 6 hours after resuscitation, then sacrificed, and lungs were harvested. Lung injury parameters including histology (H&E stain), apoptosis [terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling (TUNEL)], and myeloperioxidase activity (spectrophotometric assay) were assessed. Hemorrhagic shock induced marked loss of lung architecture, neutrophil infiltration, alveolar septal thickening, hemorrhage, and edema in H&E staining. Furthermore, MPO activity, a marker for neutrophil infiltration and activation, was more than doubled as compared to controls (44.0 vs 20.0 Grisham units activity/g). Apoptosis (cell shrinkage, membrane blebbing, apoptotic bodies) and necrosis (cellular swelling, membrane lysis) in neutrophils, macrophages, as well as in alveolar cells was demonstrated and quantified by H&E staining use. Apoptosis was confirmed and further quantified by positive TUNEL signaling via digital semiquantitative analysis, which revealed a significant increase in apoptotic cells (16.0 vs 2.5 cells/hpf, shock vs control, respectively) and necrotic cells (16.0 vs 2.0 cells/hpf, shock vs control, respectively). Acute lung injury is a complex pathophysiologic process. Apoptosis in cells (neutrophils, macrophages, alveolar cells) is induced within the lung after hemorrhagic shock. The role of apoptosis in pulmonary dysfunction after hemorrhagic shock has yet to be determined.

Burn injury and pulmonary sepsis: development of a clinically relevant model

BACKGROUND

Despite improvements in the early resuscitation of the critically injured, mortality from multiple organ failure has remained stable, with the lung often the first organ to fail. Early intubation and mechanical ventilation predispose patients to the development of pneumonia and respiratory failure. Our objective was to establish a murine model of combined injury, consisting of burn/trauma and pulmonary sepsis with reproducible end-organ responses and mortality.

METHODS

Male B6D2F1 mice were divided into four groups: burn/infection (BI), burn (B), infection (I), and sham (S). Burned animals had a full-thickness 15% dorsal scald burn. BI and I groups were inoculated intratracheally with Pseudomonas aeruginosa (3-5 x 103 colony-forming units). S and B animals received saline intratracheally. All animals were resuscitated with 2 mL of intraperitoneal saline. Mortality was recorded at 24, 48, and 72 hours. Bacterial sepsis was confirmed by tissue Gram's stain of the lungs and positive organ and blood cultures for Pseudomonas aeruginosa. Femoral bone marrow cells were collected at 72 hours from surviving animals. Clonogenic potential was assessed by response to macrophage (M) colony-stimulating factor (CSF) and granulocyte-macrophage (GM) CSF in a soft agar assay and the data were represented as colonies per femur. Isolated alveolar macrophages and whole lung tissue were assayed for levels of the inflammatory cytokines tumor necrosis factor-alpha and interleukin-6.

RESULTS

Mortality at 72 hours was 30% in BI, 12% in I, and <10% in B and S groups. Pneumonia was documented in all infected animals at 24 hours by Gram's stain and positive tissue cultures for Pseudomonas aeruginosa. Systemic sepsis as confirmed by blood, and remote organ cultures was seen in BI animals only. Significantly increased responsiveness to M-CSF stimulations was noted in all groups (BI, 8,291 +/- 1,402 colonies/femur; B, 6,357 +/- 806 colonies/femur; and I, 8,054 +/- 1,112 colonies/femur; p < 0.05) relative to sham (3,369 +/- 883 colonies/femur, p < 0.05). Maximal responsiveness to GM-CSF stimulation was noted in the BI group (11,932 +/- 982 colonies/femur, p < 0.05), and similar GM responsiveness was noted in all other groups (B, 7,135 +/- 548 colonies/femur; I, 7,023 +/- 810 colonies/femur; and S, 6,829 +/- 1,439 colonies/femur). Alveolar macrophage release of the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-6 increased in all animals, but the magnitude of increase was not proportional to the strength of the inciting stimulus.

CONCLUSION

Although minimal perturbations were seen after burn or pulmonary infection alone, the combined insult of burn and pulmonary sepsis resulted in statistically significant hematopoietic changes with increased monocytopoiesis. Only the combined injury resulted in systemic sepsis and significantly increased mortality. We have developed a clinically relevant model of trauma and pulmonary sepsis that will allow further clarification of the inflammatory response after injury and infection.

Novel resuscitation strategy for pulmonary contusion after severe chest trauma

BACKGROUND

Adenosine A2a receptor stimulation can increase coronary perfusion and also reduce leukocyte-mediated inflammatory responses in some conditions. Hextend is a novel colloid solution that may have antioxidant properties. All these actions might be beneficial after severe chest trauma, but have never been investigated. To fill these gaps, this study evaluated the therapeutic potential of a novel adenosine A2a agonist during fluid resuscitation from severe chest trauma with either standard-of-care crystalloid or Hextend.

METHODS

Anesthetized, ventilated swine received unilateral, blunt trauma to the right chest via captive bolt gun, followed by a 10- to 12-mL/kg arterial hemorrhage. After 25 minutes of shock, ATL-146e was started (10 ng/kg/min intravenously for 180 minutes). After an additional 5 minutes, the minimum amount of either colloid (Hextend, 5% hetastarch in lactate-buffered, balanced electrolyte solution) or crystalloid (lactated Ringer's [LR] solution) was administered to maintain mean arterial pressure > 70 mm Hg and heart rate < 100 beats/min and to correct lactate for 180 minutes postinjury. Cardiopulmonary function was monitored and serial bronchoalveolar lavage samples were analyzed for protein, leukocyte infiltration, and expression of cyclooxygenase (COX)-1 and COX-2 isozymes as markers of the inflammatory cascade.

RESULTS

Fluid requirements were reduced by half with Hextend compared with LR (p < 0.05). ATL-146e in either Hextend or LR transiently increased cardiac output, cardiac contractility, and systemic oxygen delivery (all p < 0.05). Pao(2)/Fio(2) ratio was 50 to 100 higher and bronchoalveolar lavage leukocytes were reduced by half with Hextend versus LR (both p < 0.05), but there was no added effect of ATL-146e. COX-1 expression was induced in macrophages (Mphis), whereas COX-2 was induced in neutrophils. Neither Hextend nor ATL-146e reduced COX expression.

CONCLUSION

Hextend reduced the volume for initial resuscitation, which may offer logistical advantages in prehospital field conditions or whenever there is limited medical resources or prolonged transport times; ATL-146e improved early cardiac performance without causing hypotension or bradycardia; when administered 25 to 30 minutes after injury, neither Hextend nor ATL-146e altered inflammatory changes in pulmonary Mphis or infiltrating PMNs; and further studies are needed to determine whether these short-term benefits correlate with long-term outcome.

Hemodynamic actions of acute ethanol after resuscitation from traumatic brain injury

BACKGROUND

The purposes of this study were to determine how clinically relevant levels of acute ethanol (EtOH) influence cerebral perfusion pressure (CPP), cerebral venous O saturation (Scvo ), and systemic hemodynamics after fluid resuscitation from traumatic brain injury (TBI); and to test the hypothesis that the actions of EtOH on these variables are mediated by adenosine.

METHODS

Anesthetized swine were ventilated (Fio = 0.4) and instrumented. In protocol 1, EtOH (3.5 g/kg, n = 11) or its vehicle (n = 17) was administered orally before TBI + 40% hemorrhage. At 90 minutes post-TBI, resuscitation consisted of shed blood + saline. In protocol 2, either saline (n = 15) or an adenosine-regulating agent (5-amino-4-imidazolecarboxamide riboside) in saline (1 mg/kg bolus + 12 mg/kg/h intravenously [i.v.]) (n = 5), was administered i.v. before TBI + 45% hemorrhage. At 90 minutes post-TBI, resuscitation consisted of saline only (three times shed blood volume). In protocol 3, EtOH was administered i.v. (1 g/kg; 20% vol/vol in saline) followed by either an adenosine receptor antagonist (theophylline, 10 mg/kg) or an adenosine uptake inhibitor (dipyridamole, 0.25 mg/kg).

RESULTS

In protocol 1, with no EtOH, 11 of 17 (65%) survived post-TBI hypotension. Mean arterial blood pressure, cardiac index, and mixed venous oxygen saturation were stable for 1 hour at 40% to 60% below their respective baselines, whereas lactate increased three- to fourfold (all p < 0.05). After fluid resuscitation, most variables rapidly corrected, but intracranial pressure was increased 10 to 15 mm Hg (p < 0.05). With EtOH, 9 of 11 (82%) survived post-TBI hypotension (p = 0.42 vs. no EtOH). After resuscitation from TBI, there were significant effects of EtOH on systemic hemodynamics (mean arterial pressure, cardiac index, mixed venous oxygen saturation), on CPP, on lactate, and on Scvo at normo- and hypercapnia (all p < 0.05). The data from protocol 2 showed that essentially none of these changes were duplicated with an adenosine-regulating agent. In protocol 3, i.v EtOH produced small but significant changes in Scvo, intracranial pressure, and lactate, at normo-, hyper-, and hypocapnia. Dipyridamole and theophylline tended to have opposite, albeit small and not statistically significant, effects on these variables relative to EtOH alone.(2) (2)

CONCLUSION

Acute EtOH (200-300 mg/dL) did not increase mortality after TBI + secondary hypotension, as long as cardiopulmonary support was provided. With EtOH, CPP was maintained and cerebral blood flow appeared to be adequate, if not excessive, with respect to cerebral metabolic demand, as judged by changes in Scvo at normo-, hyper-, and hypocapnia. These changes were probably not mediated, but might have been modulated, by increases in endogenous adenosine.