A sensitive immunoassay to detect the alpha-chemokine GRO in rabbit blood and lung fluids

Depletion of phagocytes in the reticuloendothelial system causes increased inflammation and mortality in rabbits with Pseudomonas aeruginosa pneumonia

Phagocytes of the reticuloendothelial system are important in clearing systemic infection; however, the role of the reticuloendothelial system in the response to localized infection is not well-documented. The major goals of this study were to investigate the roles of phagocytes in the reticuloendothelial system in terms of bacterial clearance and inflammatory modulation in sepsis caused by Pseudomonas pneumonia. Macrophages in liver and spleen were depleted by administering liposome encapsulated dichloromethylene diphosphonate (clodronate) intravenously 36 h before the instillation of Pseudomonas aeruginosa into the lungs of anesthetized rabbits. Blood samples were analyzed for bacteria and cytokine concentrations. Lung injury was assessed by the bidirectional flux of albumin and by wet-to-dry weight ratios. Blood pressure and cardiac outputs decreased more rapidly and bacteremia occurred earlier in the clodronate-treated rabbits compared with the nondepleted rabbits. Plasma TNF-alpha (1.08 +/- 0.54 vs. 0.08 +/- 0.02 ng/ml) and IL-8 (6.8 +/- 1.5 vs. 0.0 +/- 0.0 ng/ml) were higher in the depleted rabbits. The concentration of IL-10 in liver of the macrophage-depleted rabbits was significantly lower than in normal rabbits at 5 h. Treatment of macrophage-depleted rabbits with intravenous IL-10 reduced plasma proinflammatory cytokine concentrations and reduced the decline in blood pressure and cardiac output. These results show that macrophages in the reticuloendothelial system have critical roles in controlling systemic bacteremia and reducing systemic inflammation, thereby limiting the systemic effects of a severe pulmonary bacterial infection.

Effect of Toll-like receptor 4 blockade on pulmonary inflammation caused by mechanical ventilation and bacterial endotoxin

Mechanical ventilation (MV) and lipopolysaccharide (LPS) synergistically increase inflammation and lung injury. The goal of this study was to determine whether blockade of CD14 or Toll-like receptor 4 (TLR4) would reduce inflammation caused by LPS and MV. Rabbits were pretreated with anti-TLR4 or anti-CD14 monoclonal antibodies, followed by endobronchial LPS and MV. Blockade of TLR4 reduced the number of neutrophils and the amount of CXCL8 in bronchoalveolar lavage fluid. In contrast, blockade of CD14 did not significantly decrease the number of neutrophils or the amount of CXCL8. These data show that TLR4 blockade reduces pulmonary inflammation caused by the combination of LPS and Mechanical ventilation.

Animal models of acute lung injury

Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury.

Spatial and temporal heterogeneity of ventilator-associated lung injury after surfactant depletion

Volutrauma and atelectrauma have been proposed as mechanisms of ventilator-associated lung injury, but few studies have compared their relative importance in mediating lung injury. The objective of our study was to compare the injury produced by stretch (volutrauma) vs. cyclical recruitment (atelectrauma) after surfactant depletion. In saline-lavaged rabbits, we used high tidal volume, low respiratory rate, and low positive end-expiratory pressure to produce stretch injury in nondependent lung regions and cyclical recruitment in dependent lung regions. Tidal changes in shunt fraction were assessed by measuring arterial Po(2) oscillations. After ventilating for times ranging from 0 to 6 h, lungs were excised, sectioned gravitationally, and assessed for regional injury by evaluation of edema formation, chemokine expression, upregulation of inflammatory enzyme activity, and alveolar neutrophil accumulation. Edema formation, lung tissue interleukin-8 expression, and alveolar neutrophil accumulation progressed more rapidly in dependent lung regions, whereas macrophage chemotactic protein-1 expression progressed more rapidly in nondependent lung regions. Temporal and regional heterogeneity of lung injury were substantial. In this surfactant depletion model of acute lung injury, cyclical recruitment produced more injury than stretch.

Mechanical ventilation with moderate tidal volumes synergistically increases lung cytokine response to systemic endotoxin

Previous animal studies have identified a role for activation of innate immunity in the pathogenesis of ventilator-associated lung injury. These studies have used large tidal volume ventilation to study the effect of alveolar overdistension on induction of inflammatory pathways. We hypothesized an alternative mechanism for the pathogenesis of lung injury in which moderate tidal volume ventilation does not independently cause clinical inflammation but rather interacts with innate immune activation by bacterial products, resulting in an enhanced inflammatory response. We measured cytokine expression and lung injury in normal and lipopolysaccharide (LPS)-treated anesthetized rabbits randomized to either spontaneous respiration or mechanical ventilation. Outcome parameters were analyzed by two-way factorial analysis of variance to identify synergism between ventilation and systemic LPS. Mechanical ventilation alone resulted in minimal cytokine expression in the lung but did enhance LPS-induced expression of tumor necrosis factor-α, the CXC chemokines interleukin-8 and growth-related protein-α, and the CC chemokine monocyte chemoattractant protein-1. Increased mRNA expression and activation of the transcription factors nuclear factor-κB and activator protein-1 accompanied the cytokine responses. We conclude that moderate volume ventilation strategies augment the innate immune response to bacterial products in the lung and may play a role in the development of acute lung injury in patients with sepsis.

Persistence of diaphragmatic contraction influences the pulmonary inflammatory response to mechanical ventilation

Because we already showed (Brégeon, F., Roch, A., Delpierre, S., Ghigo, E., Autillo-Touati, A., Kajikawa, O., Martin, T., Pugin, J., Portugal, H., Auffray, J., Jammes, Y., 2002. Conventional mechanical ventilation of healthy lungs induced pro-inflammatory cytokine gene transcription, Respir. Physiol. Neurobiol. 132, 191-203) that non-injurious mechanical ventilation (MV) elicited inflammatory signal in paralyzed rabbits having normal lungs, we examined the role of neuromuscular blockade in the pulmonary inflammatory response. In the bronchoalveolar lavage fluid (BALF), leukocyte count, MCP-1 and IL-8 cytokine concentrations (ELISA) and mRNAs (reverse transcription polymerase chain reaction, RT-PCR) were measured in paralyzed (P) or non-paralyzed (NP) rabbits ventilated for a 6-h period. Compared to the P group and despite the tidal volume was the same, we measured in the NP one a lower compliance of the respiratory system (Crs,stat), a longer inspiratory time (Ti), a negative inspiratory tracheal pressure (Ptr) wave preceding the pump-induced positive pressure wave, and a higher peak tracheal pressure. Moreover, in NP animals, gross autopsy showed negligible lung abnormalities, and marked reduction of leukocyte count and lung cytokines (P < 0.05). Thus, the absence of neuromuscular blockade decreased the pulmonary chemotactic response to MV suggesting that the total suppression of negative pressure waves elicited by the diaphragmatic (di) contractions could be involved in this lung response to positive pressure MV.

Differential regulation of membrane CD14 expression and endotoxin-tolerance in alveolar macrophages

CD14 is important in the clearance of bacterial pathogens from lungs. However, the mechanisms that regulate the expression of membrane CD14 (mCD14) on alveolar macrophages (AM) have not been studied in detail. This study examines the regulation of mCD14 on AM exposed to Escherichia coli in vivo and in vitro, and explores the consequences of changes in mCD14 expression. The expression of mCD14 was decreased on AM exposed to E. coli in vivo and AM incubated with lipopolysaccharide (LPS) or E. coli in vitro. Polymyxin B abolished LPS effects, but only partially blocked the effects of E. coli. Blockade of extracellular signal-regulated kinase pathways attenuated LPS and E. coli-induced decrease in mCD14 expression. Inhibition of proteases abrogated the LPS-induced decrease in mCD14 expression on AM and the release of sCD14 into the supernatants, but did not affect the response to E. coli. The production of tumor necrosis factor-alpha in response to a second challenge with Staphylococcus aureus or zymosan was decreased in AM after incubation with E. coli but not LPS. These studies show that distinct mechanisms regulate the expression of mCD14 and the induction of endotoxin tolerance in AM, and suggest that AM function is impaired at sites of bacterial infection.

Therapeutic hypercapnia is not protective in the in vivo surfactant-depleted rabbit lung

Permissive hypercapnia because of reduced tidal volume is associated with improved survival in lung injury, whereas therapeutic hypercapnia-deliberate elevation of arterial Pco2-protects against in vivo reperfusion injury and injury produced by severe lung stretch. No published studies to date have examined the effects of CO2 on in vivo models of neonatal lung injury. We used an established in vivo rabbit model of surfactant depletion to investigate whether therapeutic hypercapnia would improve oxygenation and protect against ventilator-induced lung injury. Animals were randomized to injurious (tidal volume, 12 mL/kg; positive end-expiratory pressure, 0 cm H2O) or protective ventilatory strategy (tidal volume, 5 mL/kg; positive end-expiratory pressure, 12.5 cm H2O), and to receive either control conditions or therapeutic hypercapnia (fraction of inspired CO2, 0.12). Oxygenation (alveolar-arterial O2 difference, arterial Po2), lung injury (alveolar-capillary protein leak, impairment of static compliance), and selected bronchoalveolar lavage and plasma cytokines (IL-8, growth-related oncogene, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha) were measured. Injurious ventilation resulted in a large alveolar-arterial O2 gradient, elevated peak airway pressure, increased protein leak, and impaired lung compliance. Therapeutic hypercapnia did not affect any of these outcomes. Tumor necrosis factor-alpha was not increased by mechanical stretch in any of the groups. Therapeutic hypercapnia abolished the stretch-induced increase in bronchoalveolar lavage monocyte chemoattractant protein-1, but did not affect any of the other mediators studied. Therapeutic hypercapnia may attenuate the impairment in oxygenation and inhibit certain cytokines. Because hypercapnia inhibits certain cytokines but does not alter lung injury, the pathogenic role of these cytokines in lung injury is questionable.

Conventional mechanical ventilation of healthy lungs induced pro-inflammatory cytokine gene transcription

We investigated the potential inflammatory reaction induced by mechanical ventilation (MV) using 10 ml/kg tidal volume and no positive end-expiratory pressure (PEEP) in control (C, n = 8), spontaneously breathing (SB, n = 12) and mechanically ventilated (MV, n = 12) rabbits with normal lungs. After 6 h (MV and SB groups) or immediately (C group), lungs were removed for measurement of wet-to-dry (W/D) weight ratio and for bronchoalveolar lavage (BAL). Pulmonary mechanics were also studied. MV animals developed a modest but significant (P < 0.01) impairment of arterial blood oxygenation and had higher W/D lung weight ratio than C ones. In MV group, BAL macrophage count was greater (P < 0.05) than in SB one. MV induced an upregulation of MCP-1, TNF-alpha, and IL-1beta gene transcription (mRNAs), without significant elevation of the corresponding protein cytokines in the BAL supernatant, except for MCP-1 (P < 0.05). These data suggest that MV, even using moderate tidal volume, elicits a pro-inflammatory stimulus to the lungs.

Association of IL-8 and MCP-1 with the development of reexpansion pulmonary edema in rabbits

BACKGROUND

The aim of this study is to determine the relationships between the cytokines and the inflammatory response in reexpansion pulmonary edema (RPE).

METHODS

We examined the cell population, epithelial permeability measured by Evans blue dye (EB), betaglucuronidase and cytokine concentrations in bronchoalveolar lavage fluid (BALF) and/or blood using a rabbit RPE model.

RESULTS

We confirmed that RPE is characterized by recruitment of polymorphonuclear leukocytes (PMNs), the release of PMN granular contents into the air spaces, and increased vascular permeability. These findings were highly correlated with increased interleukin-8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) concentrations in the BALF. Growth related oncogene (GRO) was detected in the BALF from only 2 of the 7 reexpanded lungs while TNFalpha was not detected in any rabbits. A similar but less severe inflammatory response to the reexpanded lung was found in the contralateral lung.

CONCLUSIONS

IL-8 and MCP-1 may play important roles in the development of RPE; the inflammatory response is independent of TNFalpha and unilateral reexpansion of the lung induces an inflammatory response not only in the reexpanded lung but also in the contralateral lung.

Septic shock and acute lung injury in rabbits with peritonitis: failure of the neutrophil response to localized infection

The major goal of this study was to investigate the mechanisms that link the host response to a local infection in the peritoneal cavity with the development of sepsis and lung injury. Rabbits were infected by intraperitoneal inoculation of fibrin clots containing Escherichia coli at 10(8), 10(9), or 10(10) cfu/clot. Physiologic, bacteriologic, and inflammatory responses were monitored, and the lungs were examined postmortem. At a dose of 10(8) cfu/clot the animals had resolving infection, and a dose of 10(9) cfu/clot resulted in persistent infection at 24 h, with minimal systemic manifestations. In contrast, inoculation of 10(10) cfu/clot resulted in rapidly lethal local infection, with septic shock and lung injury. The onset of septic shock was associated with a paradoxical lack of identifiable polymorphonuclear leukocytes (PMN; neutrophils) in the peritoneal cavity. The absence of PMN in the peritoneum was due in part to lysis of intraperitoneal PMN, because the peritoneal fluids contained free myeloperoxidase and induced rapid death of normal rabbit PMN in vitro. Although most animals became bacteremic, only those with a severe systemic inflammation response developed lung injury. These data show that control of an infection in the first compartment in which bacteria enter the host is a critical determinant of the systemic response. Above a threshold dose of bacteria, failure of the local neutrophil response is a key mechanism associated with deleterious systemic responses. Bacteremia alone is not sufficient to cause lung injury. Lung injury occurs only in the setting of a severe systemic inflammatory response and an inadequate leukocyte response at the primary site of infection.

Inhibition of the tissue factor-thrombin pathway limits infarct size after myocardial ischemia-reperfusion injury by reducing inflammation

Functional inhibition of tissue factor (TF) has been shown to improve coronary blood flow after myocardial ischemia/reperfusion (I/R) injury. TF initiates the coagulation protease cascade, resulting in the generation of the serine protease thrombin and fibrin deposition. Thrombin can also contribute to an inflammatory response by activating various cell types, including vascular endothelial cells. We used a rabbit coronary ligation model to investigate the role of TF in acute myocardial I/R injury. At-risk areas of myocardium showed increased TF expression in the sarcolemma of cardiomyocytes, which was associated with a low level of extravascular fibrin deposition. Functional inhibition of TF activity with an anti-rabbit TF monoclonal antibody administered either 15 minutes before or 30 minutes after coronary ligation reduced infarct size by 61% (P = 0.004) and 44% (P = 0.014), respectively. Similarly, we found that inhibition of thrombin with hirudin reduced infarct size by 59% (P = 0.014). In contrast, defibrinogenating the rabbits with ancrod had no effect on infarct size, suggesting that fibrin deposition does not significantly contribute to infarct size. Functional inhibition of thrombin reduced chemokine expression and inhibition of either TF or thrombin reduced leukocyte infiltration. We propose that cardiomyocyte TF initiates extravascular thrombin generation, which enhances inflammation and injury during myocardial I/R.

Effect of CD14 blockade in rabbits with Escherichia coli pneumonia and sepsis

CD14, a pattern recognition receptor found on myeloid cells, is a critical component of the innate immune system that mediates local and systemic host responses to Gram-negative and Gram-positive bacterial products. Previous studies in normal animals have tested the effect of CD14 blockade on the systemic response to i.v. LPS. The goals of the study were to determine whether CD14 blockade protected against the deleterious systemic response associated with Escherichia coli pneumonia and to determine whether this strategy affected the pulmonary response to tissue infection. Rabbits were pretreated with either anti-CD14 mAb or isotype control mAb at 2.5 mg/kg. E. coli (1 x 109 CFU) was inoculated into the lungs, and the animals were observed for either 4 or 24 h. The blockade of CD14 improved the mean arterial blood pressure (p = 0.001) and decreased the i.v. fluid requirements (p = 0.01). Although this therapy protected the vascular compartment, rabbits treated with anti-CD14 mAb had increased bacterial burdens in the bronchoalveolar lavage fluid recovered from the instilled lung (p = 0.005) and widened alveolar-arterial oxygen difference. Blockade of CD14 prevents the deleterious systemic responses that occur in sepsis; however, other measures are necessary to control bacterial proliferation at the primary site of infection.

Pathogenesis of septic shock in Pseudomonas aeruginosa pneumonia

The pathogenesis of septic shock occurring after Pseudomonas aeruginosa pneumonia was studied in a rabbit model. The airspace instillation of the cytotoxic P. aeruginosa strain PA103 into the rabbit caused a consistent alveolar epithelial injury, progressive bacteremia, and septic shock. The lung instillation of a noncytotoxic, isogenic mutant strain (PA103DeltaUT), which is defective for production of type III secreted toxins, did not cause either systemic inflammatory response or septic shock, despite a potent inflammatory response in the lung. The intravenous injection of PA103 did not cause shock or an increase in TNF-alpha, despite the fact that the animals were bacteremic. The systemic administration of either anti-TNF-alpha serum or recombinant human IL-10 improved both septic shock and bacteremia in the animals that were instilled with PA103. Radiolabeled TNF-alpha instilled in the lung significantly leaked into the circulation only in the presence of alveolar epithelial injury. We conclude that injury to the alveolar epithelium allows the release of proinflammatory mediators into the circulation that are primarily responsible for septic shock. Our results demonstrate the importance of compartmentalization of inflammatory mediators in the lung, and the crucial role of bacterial cytotoxins in causing alveolar epithelial damage in the pathogenesis of acute septic shock in P. aeruginosa pneumonia.