Chemotactic gradients predict neutrophilic alveolitis in endotoxin-treated rats

Liraglutide pretreatment attenuates sepsis-induced acute lung injury

There are no effective targeted therapies to treat acute respiratory distress syndrome (ARDS). Recently, the commonly used diabetes and obesity medications, glucagon-like peptide-1 (GLP-1) receptor agonists, have been found to have anti-inflammatory properties. We, therefore, hypothesized that liraglutide pretreatment would attenuate murine sepsis-induced acute lung injury (ALI). We used a two-hit model of ALI (sepsis+hyperoxia). Sepsis was induced by intraperitoneal injection of cecal slurry (CS; 2.4 mg/g) or 5% dextrose (control) followed by hyperoxia [HO; fraction of inspired oxygen ([Formula: see text]) = 0.95] or room air (control; [Formula: see text] = 0.21). Mice were pretreated twice daily with subcutaneous injections of liraglutide (0.1 mg/kg) or saline for 3 days before initiation of CS+HO. At 24-h post CS+HO, physiological dysfunction was measured by weight loss, severity of illness score, and survival. Animals were euthanized, and bronchoalveolar lavage (BAL) fluid, lung, and spleen tissues were collected. Bacterial burden was assessed in the lung and spleen. Lung inflammation was assessed by BAL inflammatory cell numbers, cytokine concentrations, lung tissue myeloperoxidase activity, and cytokine expression. Disruption of the alveolar-capillary barrier was measured by lung wet-to-dry weight ratios, BAL protein, and epithelial injury markers (receptor for advanced glycation end products and sulfated glycosaminoglycans). Histological evidence of lung injury was quantified using a five-point score with four parameters: inflammation, edema, septal thickening, and red blood cells (RBCs) in the alveolar space. Compared with saline treatment, liraglutide improved sepsis-induced physiological dysfunction and reduced lung inflammation, alveolar-capillary barrier disruption, and lung injury. GLP-1 receptor activation may hold promise as a novel treatment strategy for sepsis-induced ARDS. Additional studies are needed to better elucidate its mechanism of action.NEW & NOTEWORTHY In this study, pretreatment with liraglutide, a commonly used diabetes medication and glucagon-like peptide-1 (GLP-1) receptor agonist, attenuated sepsis-induced acute lung injury in a two-hit mouse model (sepsis + hyperoxia). Septic mice who received the drug were less sick, lived longer, and displayed reduced lung inflammation, edema, and injury. These therapeutic effects were not dependent on weight loss. GLP-1 receptor activation may hold promise as a new treatment strategy for sepsis-induced acute respiratory distress syndrome.

A two-hit model of sepsis plus hyperoxia causes lung permeability and inflammation

Mouse models of acute lung injury (ALI) have been instrumental for studies of the biological underpinnings of lung inflammation and permeability, but murine models of sepsis generate minimal lung injury. Our goal was to create a murine sepsis model of ALI that reflects the inflammation, lung edema, histological abnormalities, and physiological dysfunction that characterize ALI. Using a cecal slurry (CS) model of polymicrobial abdominal sepsis and exposure to hyperoxia (95%), we systematically varied the timing and dose of the CS injection, fluids and antibiotics, and dose of hyperoxia. We found that CS alone had a high mortality rate that was improved with the addition of antibiotics and fluids. Despite this, we did not see evidence of ALI as measured by bronchoalveolar lavage (BAL) cell count, total protein, C-X-C motif chemokine ligand 1 (CXCL-1) or by lung wet:dry weight ratio. Addition of hyperoxia [95% fraction of inspired oxygen ([Formula: see text])] to CS immediately after CS injection increased BAL cell counts, CXCL-1, and lung wet:dry weight ratio but was associated with 40% mortality. Splitting the hyperoxia treatment into two 12-h exposures (0-12 h and 24-36 h) after CS injection increased survival to 75% and caused significant lung injury compared with CS alone as measured by increased BAL total cell count (92,500 vs. 240,000, P = 0.0004), BAL protein (71 vs. 103 µg/mL, P = 0.0030), and lung wet:dry weight ratio (4.5 vs. 5.5, P = 0.0005), and compared with sham as measured by increased BAL CXCL-1 (20 vs. 2,372 pg/mL, P < 0.0001) and histological lung injury score (1.9 vs. 4.2, P = 0.0077). In addition, our final model showed evidence of lung epithelial [increased BAL and plasma receptor for advanced glycation end products (RAGE)] and endothelial (increased Syndecan-1 and sulfated glycosaminoglycans) injury. In conclusion, we have developed a clinically relevant mouse model of sepsis-induced ALI using intraperitoneal injection of CS, antibiotics and fluids, and hyperoxia. This clinically relevant model can be used for future studies of sepsis-induced ALI.

Haptoglobin-2 variant increases susceptibility to acute respiratory distress syndrome during sepsis

Acute respiratory distress syndrome (ARDS) is an inflammatory lung disorder that frequently complicates critical illness and commonly occurs in sepsis. Although numerous clinical and environmental risk factors exist, not all patients with risk factors develop ARDS, raising the possibility of genetic underpinnings for ARDS susceptibility. We have previously reported that circulating cell-free hemoglobin (CFH) is elevated during sepsis, and higher levels predict worse outcomes. Excess CFH is rapidly scavenged by haptoglobin (Hp). A common HP genetic variant, HP2, is unique to humans and is common in many populations worldwide. HP2 haptoglobin has reduced ability to inhibit CFH-mediated inflammation and oxidative stress compared with the alternative HP1. We hypothesized that HP2 increases ARDS susceptibility during sepsis when plasma CFH levels are elevated. In a murine model of sepsis with elevated CFH, transgenic mice homozygous for Hp2 had increased lung inflammation, pulmonary vascular permeability, lung apoptosis, and mortality compared with wild-type mice. We then tested the clinical relevance of our findings in 496 septic critically ill adults, finding that HP2 increased ARDS susceptibility after controlling for clinical risk factors and plasma CFH. These observations identify HP2 as a potentially novel genetic ARDS risk factor during sepsis and may have important implications in the study and treatment of ARDS.

Bronchipret® syrup containing thyme and ivy extracts suppresses bronchoalveolar inflammation and goblet cell hyperplasia in experimental bronchoalveolitis

BACKGROUND/PURPOSE

Acute bronchitis (AB) is a common lung condition characterized by inflammation of the large bronchi in response to infection. Bronchipret(®) syrup (BRO), a fixed combination of thyme and ivy extracts has been effectively used for the treatment of AB. Combining in vivo and mechanistic in vitro studies we aimed to provide a better understanding of the therapeutic potential of BRO on key aspects of AB and to identify potential mechanisms of action.

METHODS

Bronchoalveolitis in rats was induced by intratracheal LPS instillation. BRO was administered p.o. once daily at 1- to 10-fold equivalents of the human daily dose. Animals were sacrificed 24-72 h post LPS challenge to analyze leukocyte numbers in lung tissue, bronchoalveolar lavage fluid (BALF) and blood as well as goblet cells in bronchial epithelium. Inhibitory effects of BRO analogue on leukotriene (LT) production were determined in human neutrophils and monocytes as well as on isolated 5-lipoxygenase (5-LO).

RESULTS

BRO significantly reversed the LPS-induced increase in leukocyte numbers in lung tissue, BALF and blood as well as goblet cell numbers in bronchial epithelium. In vitro, BRO analogue suppressed cellular release of LTB4 (IC50 = 36 µg⋅ml(-1)) and cysLT (IC50 = 10 µg⋅ml(-1)) and inhibited the activity of isolated 5-LO (IC50 = 19 µg⋅ml(-1)).

CONCLUSION

BRO exerts significant anti-inflammatory effects and attenuates goblet cell metaplasia in LPS-induced bronchoalveolitis in vivo potentially via interference with 5-LO/LT signaling. These effects may contribute to its observed clinical efficacy in AB.

Modulation of chemokine gradients by apheresis redirects leukocyte trafficking to different compartments during sepsis, studies in a rat model

Introduction

Prior work suggests that leukocyte trafficking is determined by local chemokine gradients between the nidus of infection and the plasma. We recently demonstrated that therapeutic apheresis can alter immune mediator concentrations in the plasma, protect against organ injury, and improve survival. Here we aimed to determine whether the removal of chemokines from the plasma by apheresis in experimental peritonitis changes chemokine gradients and subsequently enhances leukocyte localization into the infected compartment, and away from healthy tissues.

Methods

In total, 76 male adult Sprague–Dawley rats weighing 400 g to 600 g were included in this study. Eighteen hours after inducing sepsis by cecal ligation and puncture, we randomized these rats to apheresis or sham treatment for 4 hours. Cytokines, chemokines, and leukocyte counts from blood, peritoneal cavity, and lung were measured. In a separate experiment, we labeled neutrophils from septic donor animals and injected them into either apheresis or sham-treated animals. All numeric data with normal distributions were compared with one-way analysis of variance, and numeric data not normally distributed were compared with the Mann–Whitney U test.

Results

Apheresis significantly removed plasma cytokines and chemokines, increased peritoneal fluid-to-blood chemokine (C-X-C motif ligand 1, ligand 2, and C-C motif ligand 2) ratios, and decreased bronchoalveolar lavage fluid-to-blood chemokine ratios, resulting in enhanced leukocyte recruitment into the peritoneal cavity and improved bacterial clearance, but decreased recruitment into the lung. Apheresis also reduced myeloperoxidase activity and histologic injury in the lung, liver, and kidney. These Labeled donor neutrophils exhibited decreased localization in the lung when infused into apheresis-treated animals.

Conclusions

Our results support the concept of chemokine gradient control of leukocyte trafficking and demonstrate the efficacy of apheresis to target this mechanism and reduce leukocyte infiltration into the lung.

The molecular link between C-C-chemokine ligand 2-induced leukocyte recruitment and hyperalgesia

The chemokine C-C-chemokine ligand 2 (CCL2) (formerly known as MCP, macrophage chemotactic protein) is one of the important genes upregulated in different types of pain both in animals and humans. CCL2 governs the recruitment of C-C chemokine receptor 2-expressing monocytes into inflamed tissue. In contrast to neutrophilic chemokines, intraplantar injection of CCL2 in Wistar rats recruited macrophages and neutrophils and simultaneously lowered nociceptive thresholds. CCL2-induced hyperalgesia was abolished by prior systemic leukocyte depletion by cyclophosphamide and was reconstituted by local adoptive transfer of donor macrophages but not of neutrophils. Antagonists against transient receptor potential vannilloid 1 inhibited thermal and against transient receptor potential ankyrin 1 blocked mechanical hyperalgesia. Peripheral but not central activation of cyclooxygenase-2 (Cox-2) were critical for CCL2-induced hyperalgesia. In vitro CCL2 did not directly stimulate Cox-2 expression or prostaglandin E2 formation but slightly enhanced the formation of reactive oxygen species in monocytes and macrophages. In vivo, increased immunoreactivity for 4-hydroxy-2-nonenal (4-HNE), a downstream product of reactive oxygen species and known inducer of Cox-2, was observed and colocalized with Cox-2 in ED1 (CD68) positive infiltrating cells. No hyperalgesia, 4-HNE, or Cox-2 immunoreactivity was seen in leukocyte-depleted rats that were reconstituted with macrophages in the absence of CCL2, supporting the important role of CCL2.

PERSPECTIVE

CCL2 plays a dual role: 1) promoting monocyte/macrophage recruitment into tissue; and 2) potentially stimulating macrophages in the tissue to produce 4-HNE and subsequently Cox-2, all resulting in the induction of hyperalgesia via transient receptor potential vannilloid 1 and transient receptor potential ankyrin 1. This encourages pharmacological efforts targeting CCL2/C-C chemokine receptor 2 and macrophages for treatment of inflammatory pain.

Ozone inhalation promotes CX3CR1-dependent maturation of resident lung macrophages that limit oxidative stress and inflammation

Inhalation of ambient ozone alters populations of lung macrophages. However, the impact of altered lung macrophage populations on the pathobiology of ozone is poorly understood. We hypothesized that subpopulations of macrophages modulate the response to ozone. We exposed C57BL/6 mice to ozone (2 ppm × 3 h) or filtered air. At 24 h after exposure, the lungs were harvested and digested and the cells underwent flow cytometry. Analysis revealed a novel macrophage subset present in ozone-exposed mice, which were distinct from resident alveolar macrophages and identified by enhanced Gr-1(+) expression [Gr-1 macrophages (Gr-1 Macs)]. Further analysis showed that Gr-1(+) Macs exhibited high expression of MARCO, CX3CR1, and NAD(P)H:quinone oxioreductase 1. Gr-1(+) Macs were present in the absence of CCR2, suggesting that they were not derived from a CCR2-dependent circulating intermediate. Using PKH26-PCL to label resident phagocytic cells, we demonstrated that Gr-1 Macs were derived from resident lung cells. This new subset was diminished in the absence of CX3CR1. Interestingly, CX3CR1-null mice exhibited enhanced responses to ozone, including increased airway hyperresponsiveness, exacerbated neutrophil influx, accumulation of 8-isoprostanes and protein carbonyls, and increased expression of cytokines (CXCL2, IL-1β, IL-6, CCL2, and TNF-α). Our results identify a novel subset of lung macrophages, which are derived from a resident intermediate, are dependent upon CX3CR1, and appear to protect the host from the biological response to ozone.

Lack of the receptor for advanced glycation end-products attenuates E. coli pneumonia in mice

Background

The receptor for advanced glycation end-products (RAGE) has been suggested to modulate lung injury in models of acute pulmonary inflammation. To study this further, model systems utilizing wild type and RAGE knockout (KO) mice were used to determine the role of RAGE signaling in lipopolysaccharide (LPS) and E. coli induced acute pulmonary inflammation. The effect of intraperitoneal (i.p.) and intratracheal (i.t.) administration of mouse soluble RAGE on E. coli injury was also investigated.

Methodology/Principal Findings

C57BL/6 wild type and RAGE KO mice received an i.t. instillation of LPS, E. coli, or vehicle control. Some groups also received i.p. or i.t. administration of mouse soluble RAGE. After 24 hours, the role of RAGE expression on inflammation was assessed by comparing responses in wild type and RAGE KO. RAGE protein levels decreased in wild type lung homogenates after treatment with either LPS or bacteria. In addition, soluble RAGE and HMGB1 increased in the BALF after E. coli instillation. RAGE KO mice challenged with LPS had the same degree of inflammation as wild type mice. However, when challenged with E. coli, RAGE KO mice had significantly less inflammation when compared to wild type mice. Most cytokine levels were lower in the BALF of RAGE KO mice compared to wild type mice after E. coli injury, while only monocyte chemotactic protein-1, MCP-1, was lower after LPS challenge. Neither i.p. nor i.t. administration of mouse soluble RAGE attenuated the severity of E. coli injury in wild type mice.

Conclusions/Significance

Lack of RAGE in the lung does not protect against LPS induced acute pulmonary inflammation, but attenuates injury following live E. coli challenge. These findings suggest that RAGE mediates responses to E. coli-associated pathogen-associated molecular pattern molecules other than LPS or other bacterial specific signaling responses. Soluble RAGE treatment had no effect on inflammation.

Early enhanced local neutrophil recruitment in peritonitis-induced sepsis improves bacterial clearance and survival

Neutrophils are critical for the rapid eradication of bacterial pathogens, but they also contribute to the development of multiple organ failure in sepsis. We hypothesized that increasing early recruitment of neutrophils to the focus of infection will increase bacterial clearance and improve survival. Sepsis was induced in mice, using cecal ligation and puncture (CLP); blood samples were collected at 6 and 24 h; and survival was followed for 28 d. In separate experiments, peritoneal bacteria and inflammatory cells were measured. Septic mice predicted to die based on IL-6 levels (Die-P) had higher concentrations of CXCL1 and CXCL2 in the peritoneum and plasma compared with those predicted to live (Live-P). At 6 h, Live-P and Die-P had equivalent numbers of peritoneal neutrophils and bacteria. In Die-P mice the number of peritoneal bacteria increased between 6 and 24 h post-CLP, whereas in Live-P it decreased. The i.p. injection of CXCL1 and CXCL2 in naive mice resulted in local neutrophil recruitment. When given immediately after CLP, CXC chemokines increased peritoneal neutrophil recruitment at 6 h after CLP. This early increase in neutrophils induced by exogenous chemokines resulted in significantly fewer peritoneal bacteria by 24 h [CFU (log) = 6.04 versus 4.99 for vehicle versus chemokine treatment; p < 0.05]. Chemokine treatment significantly improved survival at both 5 d (40 versus 72%) and 28 d (27 versus 52%; p < 0.02 vehicle versus chemokines). These data demonstrate that early, local treatment with CXC chemokines enhances neutrophil recruitment and clearance of bacteria as well as improves survival in the CLP model of sepsis.

CXCL5 regulates chemokine scavenging and pulmonary host defense to bacterial infection

The chemokine sink hypothesis pertaining to erythrocyte Duffy Antigen Receptor for Chemokines (DARC) during inflammation has received considerable attention, but lacks direct in vivo evidence. Here we demonstrate, using mice with a targeted deletion in CXCL5, that CXCL5 bound erythrocyte DARC and impaired its chemokine scavenging in blood. CXCL5 increased the plasma concentrations of CXCL1 and CXCL2 in part through inhibiting chemokine scavenging, impairing chemokine gradients and desensitizing CXCR2, which led to decreased neutrophil influx to the lung, increased lung bacterial burden and mortality in an Escherichia coli pneumonia model. In contrast, CXCL5 exerted a predominant role in mediating neutrophil influx to the lung during inflammation after LPS inhalation. Platelets and lung resident cells were the sources of homeostatic CXCL5 in blood and inflammatory CXCL5 in the lung respectively. This study presents a paradigm whereby platelets and red cells alter chemokine scavenging and neutrophil-chemokine interaction during inflammation.

Neutrophil-mediated lung permeability and host defense proteins

Neutrophil recruitment to the alveolar space is associated with increased epithelial permeability. The present study investigated in mice whether neutrophil recruitment to the lung leads to accumulation of plasma-derived host defense proteins in the alveolar space and whether respiratory burst contributes to this increase in permeability. Albumin, complement C1q, and IgM were increased in bronchoalveolar lavage (BAL) fluid 6 h after intratracheal LPS challenge. Neutrophil depletion before LPS treatment completely prevented this increase in BAL fluid protein concentration. Respiratory burst was not detected in neutrophils isolated from BAL fluid, and BAL proteins were increased in mice deficient in a key subunit of the respiratory burst apparatus, gp91(phox), similar to wild-type mice. Neutrophil recruitment elicited by intratracheal instillation of the chemokines macrophage inflammatory protein-2 and keratinocyte-derived chemokine was also accompanied by accumulation of albumin, C1q, and IgM. During neutrophil recruitment to the alveolar space, epithelial permeability facilitates delivery of host defense proteins. The observed increase in epithelial permeability requires recruitment of neutrophils, but not activation of the respiratory burst, and occurs with chemokine-induced neutrophil migration independent of LPS exposure.

Ultrastructural changes of the air-blood barrier in mice after intratracheal instillation of lipopolysaccharide and ultrafine carbon black particles

Epidemiological studies have indicated associations between exposure to increased concentrations of ambient ultrafine particles and adverse health effects especially in susceptible individuals. To ellucidate the mechanisms underlying the findings from epidemiological studies, mice pretreated with lipopolysaccharide (LPS) (acute lung injury model) were intratracheally instilled with ultrafine carbon black particles (UFCB), and the air-blood barrier was observed to examine the translocation pathway of UFCB from the lung into the systemic circulation. In addition, lung toxicity induced by the intratracheal instillation of LPS and UFCB was studied with the use of electron microscope. LPS treatment induced acute inflammatory changes with increased number of activated macrophages and neutrophils in the degenerated alveolar walls. UFCB were demonstrated on or in the denuded basement membrane in the air-blood barrier; these findings were associated with edematous changes and fragmentation of the cytoplasms of alveolar epithelial cell type 1, and the damages of alveolar epithelial cell type 1 were frequently observed in the close vicinity of the clumps of UFCB. These findings suggest that translocation of the exposed ultrafine particles may be enhanced in the lung tissues with acute inflammatory changes.

High-molecular-weight hyaluronan--a possible new treatment for sepsis-induced lung injury: a preclinical study in mechanically ventilated rats

Introduction

Mechanical ventilation with even moderate-sized tidal volumes synergistically increases lung injury in sepsis and has been associated with proinflammatory low-molecular-weight hyaluronan production. High-molecular-weight hyaluronan (HMW HA), in contrast, has been found to be anti-inflammatory. We hypothesized that HMW HA would inhibit lung injury associated with sepsis and mechanical ventilation.

Methods

Sprague–Dawley rats were randomly divided into four groups: nonventilated control rats; mechanical ventilation plus lipopolysaccharide (LPS) infusion as a model of sepsis; mechanical ventilation plus LPS with HMW HA (1,600 kDa) pretreatment; and mechanical ventilation plus LPS with low-molecular-weight hyaluronan (35 kDa) pretreatment. Rats were mechanically ventilated with low (7 ml/kg) tidal volumes. LPS (1 or 3 mg/kg) or normal saline was infused 1 hour prior to mechanical ventilation. Animals received HMW HA or low-molecular-weight hyaluronan via the intraperitoneal route 18 hours prior to the study or received HMW HA (0.025%, 0.05% or 0.1%) intravenously 1 hour after injection of LPS. After 4 hours of ventilation, animals were sacrificed and the lung neutrophil and monocyte infiltration, the cytokine production, and the lung pathology score were measured.

Results

LPS induced lung neutrophil infiltration, macrophage inflammatory protein-2 and TNFα mRNA and protein, which were decreased in the presence of both 1,600 kDa and 35 kDa hyaluronan pretreatment. Only 1,600 kDa hyaluronan completely blocked both monocyte and neutrophil infiltration and decreased the lung injury. When infused intravenously 1 hour after LPS, 1,600 kDa hyaluronan inhibited lung neutrophil infiltration, macrophage inflammatory protein-2 mRNA expression and lung injury in a dose-dependent manner. The beneficial effects of hyaluronan were partially dependent on the positive charge of the compound.

Conclusions

HMW HA may prove to be an effective treatment strategy for sepsis-induced lung injury with mechanical ventilation.

Disease-specific gene expression profiling in multiple models of lung disease

RATIONALE

Microarray technology is widely employed for studying the molecular mechanisms underlying complex diseases. However, analyses of individual diseases or models of diseases frequently yield extensive lists of differentially expressed genes with uncertain relationships to disease pathogenesis.

OBJECTIVES

To compare gene expression changes in a heterogeneous set of lung disease models in order to identify common gene expression changes seen in diverse forms of lung pathology, as well as relatively small subsets of genes likely to be involved in specific pathophysiological processes.

METHODS

We profiled lung gene expression in 12 mouse models of infection, allergy, and lung injury. A linear model was used to estimate transcript expression changes for each model, and hierarchical clustering was used to compare expression patterns between models. Selected expression changes were verified by quantitative polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

A total of 24 transcripts, including many involved in inflammation and immune activation, were differentially expressed in a substantial majority (9 or more) of the models. Expression patterns distinguished three groups of models: (1) bacterial infection (n = 5), with changes in 89 transcripts, including many related to nuclear factor-kappaB signaling, cytokines, chemokines, and their receptors; (2) bleomycin-induced diseases (n = 2), with changes in 53 transcripts, including many related to matrix remodeling and Wnt signaling; and (3) T helper cell type 2 (allergic) inflammation (n = 5), with changes in 26 transcripts, including many encoding epithelial secreted molecules, ion channels, and transporters.

CONCLUSIONS

This multimodel dataset highlights novel genes likely involved in various pathophysiological processes and will be a valuable resource for the investigation of molecular mechanisms underlying lung disease pathogenesis.

Divergent signaling pathways in phagocytic cells during sepsis

Neutrophil accumulation in the lung plays a pivotal role in the pathogenesis of acute lung injury during sepsis. Directed movement of neutrophils is mediated by a group of chemoattractants, especially CXC chemokines. Local lung production of CXC chemokines is intensified during experimental sepsis induced by cecal ligation and puncture (CLP), as reflected by rising levels of MIP-2 and cytokine-induced neutrophil chemoattractant-1 in bronchoalveolar lavage fluids. Alveolar macrophages are primed and blood neutrophils are down-regulated for production of MIP-2 and cytokine-induced neutrophil chemoattractant production in response to LPS and C5a. Under these conditions of stimulation, activation of MAPKs (p38, p42/p44) occurs in sham neutrophils but not in CLP neutrophils, while under the same conditions phosphorylation of p38 and p42/p44 occurs in both sham and CLP alveolar macrophages. These data indicate that, under septic conditions, there is impaired signaling in neutrophils and enhanced signaling in alveolar macrophages, resulting in CXC chemokine production, and C5a appears to play a pivotal role in this process. As a result, CXC chemokines increase in lung, setting the stage for neutrophil accumulation in lung during sepsis.

Relationship between macrophage inflammatory peptide-2 and acute pancreatitis-associated lung injury

AIM: To investigate the changes of macrophage inflammatory peptide-2 (MIP-2) in lung injury induced by acute pancreatitis (AP).

METHODS: SD rats were randomized into AP group (n = 12) and control group (n = 6). Rat model of AP was induced by retrograde injection of 50 g/L sodium deoxycholate (DCA) into the pancreatic and biliary duct. Half of the rats were killed in both groups at 3 h, and the rest were killed at 6 h. The lung injury was evaluated by myeloperoxidase (MPO) activity and histopathological scoring, and the content of MIP-2 was detected in serum, pancreas, and lung by enzyme-linked immunosorbent assay (ELISA).

RESULTS: Histopathological scores for the lung tissues were higher in AP group than those in control group (3 h: t = 2.14, P = 0.035; 6 h: t = 3.12, P = 0.009), and the activity of lung MPO was also significantly higher (6 h: t = 2.72, P = 0.015). The levels of serum MIP-2 were markedly increased in AP group than those in the controls (3 h: t = 3.76, P = 0.007; 6 h: t = 2.42, P = 0.023), and the levels of serum MIP-2 were positively correlated with the histopathological scores for the pancreatic and lung tissues, respectively (r = 0.42, P = 0.014; r = 0.35, P = 0.036). MIP-2 levels in the lung tissues were positively correlated with the histological scores for the pancreatic tissues and serum amylase level (r = 0.38, P = 0.023; r = 0.42, P = 0.016).

CONCLUSION: MIP-2 is highly correlated with lung injury induced by AP, and probably plays an important role in pathogenesis of lung injury.

Bactericidal function of alveolar macrophages in mechanically ventilated rabbits

Protective ventilation strategies have been universally embraced because of reduced mortality. We tested the hypothesis that tidal volume (VT) in an in vivo model of mechanical ventilation would modulate bactericidal function of alveolar macrophages (AMs). Adult New Zealand White rabbits were mechanically ventilated for 4 h with a VT of 6 ml/kg (low) or a VT of 12 ml/kg (traditional), with each group receiving 3 cm H2O positive end-expiratory pressure with and without intratracheal lipopolysaccharide (LPS) instillation (20 mg/kg). AMs were isolated from bronchoalveolar lavage fluid taken from the whole left lung and used for bacterial killing assays. There were no significant differences in steady-state levels of nitrite or AM phagocytosis and killing of Klebsiella pneumoniae, although these values trended to be slightly higher in the traditional VT group. However, bronchoalveolar lavage fluid protein concentrations were significantly increased in traditional VT groups receiving LPS compared with animals ventilated with a low VT (1,407.8 +/- 121.4 versus 934.7 +/- 118.2; P < 0.001). Lung wet:dry weight ratio in the traditional VT group was increased when compared with the low VT group without LPS (7.3 +/- 0.4 versus 6.1 +/- 0.3, respectively; P < 0.05). Additionally, IL-8 expression was significantly greater under conditions of LPS treatment and mechanical ventilation at VT of 12 ml/kg. These results suggest that the traditional ventilator approach (12 ml/kg VT) in a model of in vivo mechanical ventilation results in lung pathology without affecting AM antibacterial function.

Increased and prolonged pulmonary fibrosis in surfactant protein C-deficient mice following intratracheal bleomycin

Recent reports have linked mutations in the surfactant protein C gene (SFTPC) to familial forms of pulmonary fibrosis, but it is uncertain whether deficiency of mature SP-C contributes to disease pathogenesis. In this study, we evaluated bleomycin-induced lung fibrosis in mice with genetic deletion of SFTPC. Compared with wild-type (SFTPC+/+) controls, mice lacking surfactant protein C (SFTPC-/-) had greater lung neutrophil influx at 1 week after intratracheal bleomycin, greater weight loss during the first 2 weeks, and increased mortality. At 3 and 6 weeks after bleomycin, lungs from SFTPC-/- mice had increased fibroblast numbers, augmented collagen accumulation, and greater parenchymal distortion. Furthermore, resolution of fibrosis was delayed. Although remodeling was near complete in SFTPC+/+ mice by 6 weeks, SFTPC-/- mice did not return to baseline until 9 weeks after bleomycin. By terminal dUTP nick-end labeling staining, widespread cell injury was observed in SFTPC-/- and SFTPC+/+ mice 1 week after bleomycin; however, ongoing apoptosis of epithelial and interstitial cells occurred in lungs of SFTPC-/- mice, but not SFTPC+/+ mice, 6 weeks after bleomycin. Thus, SP-C functions to limit lung inflammation, inhibit collagen accumulation, and restore normal lung structure after bleomycin.

Effects of systemic and local CXC chemokine administration on the ethanol-induced suppression of pulmonary neutrophil recruitment

BACKGROUND

Acute alcohol intoxication impairs the neutrophil response to intrapulmonary infection, resulting in impaired host defense and increased patient morbidity and mortality. We recently showed that intratracheal (IT) chemokine administration promotes pulmonary neutrophil migration in rats and that this process is enhanced by systemic administration of the Glu-Leu-Arg (ELR+) and CXC chemokine cytokine-induced neutrophil chemoattractant (CINC). Here we hypothesized that exogenous chemokine administration would mitigate the suppressive effect of alcohol on neutrophil recruitment into the lung.

METHODS

Macrophage inflammatory protein-2 (MIP-2), a rat ELR+ CXC chemokine, or live Klebsiella pneumoniae (K. pneumoniae) was administered it to induce alveolar neutrophil migration in the absence or presence of acute ethanol intoxication. Depending on the experimental protocol, rats received either intravenous (IV) CINC or IT chemokines (CINC and MIP-2) 20 min after it MIP-2 or K. pneumoniae. Rats were euthanized 90 min or four hr after the first IT injection for sample collection.

RESULTS

Neutrophil counts were significantly elevated in bronchoalveolar lavage fluid (BALF) of rats receiving IT MIP-2 compared with vehicle-treated rats, and this response was significantly decreased in animals pretreated with ethanol. CINC IV enhanced the neutrophil response to IT MIP-2 in both the absence and presence of acute ethanol intoxication. In rats challenged with K. pneumoniae, ethanol pretreatment significantly reduced BALF levels of CINC and MIP-2, suppressed alveolar neutrophil recruitment, and decreased whole-lung myeloperoxidase activity. CINC IV did not alter BALF neutrophil counts in the absence or presence of ethanol administration 4 hr after IT K. pneumoniae. Alternatively, IT chemokine instillation partially restored BALF neutrophil recruitment but not whole-lung myeloperoxidase activity in ethanol-treated rats.

CONCLUSIONS

Ethanol significantly inhibits the pulmonary inflammatory responses to both MIP-2 and K. pneumoniae. Exogenous chemokine administration may be a useful means to enhance host defenses in the ethanol-intoxicated host, although the results of this study also indicate that ethanol intoxication can impair neutrophil recruitment, independent of its effects on local chemotactic gradients.

Ventilation-induced neutrophil infiltration and apoptosis depend on apoptosis signal-regulated kinase 1 pathway*

OBJECTIVE

Positive pressure ventilation with large tidal volumes has been shown to cause release of cytokines, including macrophage inflammatory protein (MIP)-2, a functional equivalent of human interleukin-8, neutrophil infiltration, and apoptosis. The mechanisms regulating ventilation-induced cytokine production and lung cell death are unclear. Based on our previous in vitro and in vivo models of lung cell stretch, we hypothesized that high tidal volume ventilation-induced MIP-2 production, neutrophil infiltration, and apoptosis are dependent on the activation of apoptosis signal-regulated kinase 1 (ASK1), the upstream activator of c-Jun N-terminal kinase (JNK).

DESIGN

: Prospective, controlled animal experiment.

SETTING

University research laboratory.

SUBJECTS

Male C57BL/6 mice, weighting 20-25 g.

INTERVENTIONS

C57BL/6 mice were exposed to high tidal volume (30 mL/kg) or low tidal volume (6 mL/kg) mechanical ventilation for 15 mins to 5 hrs.

MEASUREMENTS AND MAIN RESULTS

High tidal volume ventilation induced MIP-2 messenger RNA expression, MIP-2 protein production, neutrophil migration into the lung, airway epithelial cell apoptosis, and activation of ASK1, JNK, and activator protein (AP)-1 DNA binding in a dose-dependent and time-dependent manner. ASK1 inhibition with thioredoxin attenuated high tidal volume ventilation-induced MIP-2 messenger RNA expression, MIP-2 protein production, neutrophil migration into the lung, airway epithelial cell apoptosis, activation of JNK, and AP-1 DNA binding.

CONCLUSIONS

Our data showed that high tidal volume ventilation-induced MIP-2 production, neutrophil sequestration, and apoptotic cell death were dependent, in part, on activation of the ASK1/JNK/AP-1 pathway.

Lung-marginated monocytes modulate pulmonary microvascular injury during early endotoxemia

RATIONALE

The role of monocytes in acute endotoxemia has been ascribed to systemic release of mediators within the central circulation. Little is known about the potential role of "marginated" monocytes in regulating microvascular inflammatory signaling.

OBJECTIVES

To investigate whether lung-marginated monocytes can locally activate pulmonary endothelial cells through cell contact-dependent interactions in early endotoxemia.

METHODS

Mice were challenged with LPS to produce acute endotoxemia and pulmonary vascular injury. Adoptive transfer of ex vivo LPS-stimulated donor leukocytes to recipient mice was also performed to evaluate cell-associated inflammatory signaling between monocytes and endothelial cells within the lung. Cell suspensions from excised lungs were analyzed by flow cytometry for expression of tumor necrosis factor alpha (TNF-alpha) on monocytes and cell adhesion molecules on endothelial cells.

RESULTS

Substantial numbers of monocytes rapidly marginated to the lungs after endotoxin challenge in mice, and lung-marginated monocytes expressed significantly higher levels of membrane TNF than circulating monocytes, due to higher TNF production by the marginated cells. Injection of activated wild-type donor leukocytes to wild-type or TNF receptor double knockout recipients demonstrated that lung-marginated monocytes can induce TNF-dependent upregulation of adhesion molecules on pulmonary endothelial cells. Injection of activated donor leukocytes from TNF knock-in mice that express uncleavable mutant membrane TNF also induced adhesion molecule upregulation in wild-type recipients without a systemic soluble TNF release.

CONCLUSIONS

These results reveal a previously unacknowledged role for lung-marginated monocytes in early endotoxemia, exerting local, cell-associated TNF signaling within the pulmonary microcirculation, contributing to the evolution of pulmonary vascular injury.

Central nervous system injury triggers hepatic CC and CXC chemokine expression that is associated with leukocyte mobilization and recruitment to both the central nervous system and the liver

The administration of interleukin-1beta to the brain induces hepatic CXC chemokine synthesis, which increases neutrophil levels in the blood, liver, and brain. We now show that such hepatic response is not restricted to the CXC chemokines. CCL-2, a CC chemokine, was released by the liver in response to a tumor necrosis factor (TNF)-alpha challenge to the brain and boosted monocyte levels. Furthermore, a clinically relevant compression injury to the spinal cord triggered hepatic chemokine expression of both types. After a spinal cord injury, elevated CCL-2 and CXCL-1 mRNA and protein were observed in the liver by TaqMan reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay as early as 2 to 4 hours. Simultaneously, we observed elevated levels of these chemokines and circulating leukocyte populations in the blood. Leukocytes were recruited to the liver at this early stage, whereas at the site of challenge in the central nervous system, few were observed until 24 hours. Artificial elevation of blood CCL-2 triggered dose-dependent monocyte mobilization in the blood and enhanced monocyte recruitment to the brain after TNF-alpha challenge. Attenuation of hepatic CCL-2 production with corticosteroids resulted in reduced monocyte levels after the TNF-alpha challenge. Thus, combined production of CC and CXC hepatic chemokines appears to amplify the central nervous system response to injury.

Effects of inhaled carbon monoxide on acute lung injury in mice

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are major causes of morbidity and mortality in the intensive care unit, but despite continuing research few effective therapies have been identified. In recent years, inhaled carbon monoxide (CO) has been reported to have cytoprotective effects in several animal models of tissue injury. We therefore evaluated the effects of inhaled CO in three different in vivo mouse models of ALI. Anesthetized C57BL/6 mice were ventilated with oxygen in the presence or absence of CO (500 parts per million) for 1 h before lung injury was induced by lipopolysaccharide (LPS) or oleic acid (OA) administration. Ventilation was then continued with the same gases for a further 2–3 h, with hemodynamic and respiratory parameters monitored throughout. Intratracheal LPS administration induced lung injury with alveolar inflammation (increased lavage fluid neutrophils, total protein, and cytokines). In contrast, intravenous LPS induced a predominantly vascular lung injury, with increased plasma TNF and increased neutrophil activation (surface Mac-1 upregulation and L-selectin shedding) and sequestration within the pulmonary vasculature. Intravenous OA produced deteriorations in lung function, reflected by changes in respiratory mechanics and blood gases and lavage fluid neutrophil accumulation. However, addition of CO to the inspired gas did not produce significant changes in the measured physiological or immunological parameters in the mouse models used in this study. Thus the results do not support the hypothesis that use of inhaled CO is beneficial in the treatment of ALI and ARDS.

Erythromycin exerts in vivo anti-inflammatory activity downregulating cell adhesion molecule expression

1. Macrolides have long been used as anti-bacterial agents; however, there is some evidence that may exert anti-inflammatory activity. Therefore, erythromycin was used to characterize the mechanisms involved in their in vivo anti-inflammatory activity. 2. Erythromycin pretreatment (30 mg kg(-1) day(-1) for 1 week) reduced the lipopolysaccharide (LPS; intratracheal, 0.4 mg kg(-1))-induced increase in neutrophil count and elastase activity in the bronchoalveolar lavage fluid (BALF) and lung tissue myeloperoxidase activity, but failed to decrease tumor necrosis factor-alpha and macrophage-inflammatory protein-2 augmented levels in BALF. Erythromycin pretreatment also prevented lung P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) mRNA upregulation in response to airway challenge with LPS. 3. Mesentery superfusion with LPS (1 mug ml(-1)) induced a significant increase in leukocyte-endothelial cell interactions at 60 min. Erythromycin pretreatment abolished the increases in these parameters. 4. LPS exposure of the mesentery for 4 h caused a significant increase in leukocyte rolling flux, adhesion and emigration, which were inhibited by erythromycin by 100, 93 and 95%, respectively. 5. Immunohistochemical analysis showed that LPS exposure of the mesentery for 4 h caused a significant enhancement in P-selectin, E-selectin, ICAM-1 and VCAM-1 expression that was downregulated by erythromycin pretreatment. 6. Flow cytometry analysis indicated that erythromycin pretreatment inhibited LPS-induced CD11b augmented expression in rat neutrophils. 7. In conclusion, erythromycin inhibits leukocyte recruitment in the lung and this effect appears mediated through downregulation of CAM expression. Therefore, macrolides may be useful in the control of neutrophilic pulmonary diseases.

Protective role of urinary trypsin inhibitor in acute lung injury induced by lipopolysaccharide

Urinary trypsin inhibitor (UTI), a serine protease inhibitor, has been widely used as a drug for patients with acute inflammatory disorders such as disseminated intravascular coagulation, shock, and pancreatitis. However, direct contribution of UTI to inflammatory diseases has not been established. The present study analyzed acute inflammatory lung injury induced by lipopolysaccharide (LPS) in UTI-deficient (-/-) mice and corresponding wild-type (WT) mice. UTI (-/-) and WT mice were treated intratracheally with vehicle or LPS (125 mug/kg). The cellular profile of bronchoalveolar lavage fluid, lung water content, histology, and expression of proinflammatory molecules in the lung were evaluated. After LPS challenge, both genotypes of mice revealed neutrophilic lung inflammation and pulmonary edema. UTI (-/-) mice, however, showed more prominent infiltration of inflammatory cells and edema than WT mice. After LPS challenge in both genotypes of mice, the lung levels of mRNA and/or protein expression of interleukin-1beta, macrophage inflammatory protein-1alpha, macrophage chemoattractant protein-1, keratinocyte chemoattractant, and intercellular adhesion molecule-1 (ICAM-1) were elevated in both groups, but to a greater extent in UTI (-/-) mice than in WT mice. These results suggest that UTI protects against acute lung injury induced by bacterial endotoxin, at least partly, through the inhibition of the enhanced local expression of proinflammatory cytokines, chemokines, and ICAM-1.

Prospective study of neutrophil chemokine responses in trauma patients at risk for pneumonia

Neutrophil hyperactivity contributes to organ failure, whereas hypofunction permits sepsis. The chemokine receptors CXCR1 and CXCR2 are central to polymorphonuclear neutrophil (PMN) function. We prospectively assessed CXCR function and expression in PMNs from trauma patients at high risk for pneumonia and their matched volunteer controls. CXCR2-specific calcium flux and chemotaxis were desensitized by injury, returning toward normal after 1 week. CXCR1 responses were relatively maintained. These defects appeared to be caused by preferential suppression of CXCR2 surface expression. To evaluate potential mechanisms of in vivo chemokine receptor regulation further we studied cross-desensitization of chemokine receptors in normal PMNs. Susceptibility to desensitization was in the order CXCR2 > CXCR1 > formyl peptide or C5a receptors. Trauma desensitizes CXC receptors, with CXCR2 being especially vulnerable. Desensitization is most marked immediately postinjury, generally resolving by Day 7. High-affinity chemoattractant receptors responsible for PMN chemotaxis from bloodstream to tissue appear to be regulated by injury. Receptors for end-target chemoattractants regulate CXCR1 and CXCR2 but resist suppression themselves and respond normally after injury. CXCR2 desensitization occurs before pneumonia, which developed in 44% of these patients. Suppression of high-affinity PMN receptors, like CXCR2, may predispose to pneumonia after trauma or other inflammatory conditions that lead to systemic inflammatory response syndrome.

Faster activation of polymorphonuclear neutrophils in resistant mice during early innate response to Pseudomonas aeruginosa lung infection

Polymorphonuclear neutrophils (PMNs) are crucial for the outcome of Pseudomonas aeruginosa lung infection in patients with cystic fibrosis. We compared PMNs and inflammatory cytokines in the lungs and blood from susceptible BALB/c and resistant C3H/HeN mice 1 and 2 days after intratracheal challenge with alginate embedded P. aeruginosa. These parameters were correlated with the quantitative bacteriology and histopathology of the lungs. After challenge, the content of granulocyte colony-stimulating factor (G-CSF) and macrophage inflammatory protein-2 (MIP-2) was increased in the lungs and the sera and the percentage of PMNs was increased in the blood. However, 2 days after challenge the concentration of G-CSF and MIP-2 was higher in the lungs and sera of BALB/c mice. CD11b expression was higher on the PMNs of the C3H/HeN mice. The expression of CD62L on PMNs of both strains of mice was decreased 1 day after bacterial challenge, whereas the expression was increased after 2 days of challenge on PMNs of C3H/HeN mice only. These changes were accompanied by a more severe lung inflammation in BALB/c mice and faster clearance of the bacteria in C3H/HeN mice. In conclusion, the rapid early bacterial clearance in the lungs of C3H/HeN mice could be explained by faster activation of the PMNs, as indicated by the higher up-regulation of CD11b. The severe lung inflammation in BALB/c mice may be caused by the early higher content of G-CSF in the sera mobilizing PMNs from the bone marrow and the persistent chemotactic gradient provided by MIP-2 in the lungs.

NF-kappaB p50 facilitates neutrophil accumulation during LPS-induced pulmonary inflammation

Background

Transcription factors have distinct functions in regulating immune responses. During Escherichia coli pneumonia, deficiency of NF-κB p50 increases gene expression and neutrophil recruitment, suggesting that p50 normally limits these innate immune responses. p50-deficient mice were used to determine how p50 regulates responses to a simpler, non-viable bacterial stimulus in the lungs, E. coli lipopolysaccharide (LPS).

Results

In contrast to previous results with living E. coli, neutrophil accumulation elicited by E. coli LPS in the lungs was decreased by p50 deficiency, to approximately 30% of wild type levels. Heat-killed E. coli induced neutrophil accumulation which was not decreased by p50 deficiency, demonstrating that bacterial growth and metabolism were not responsible for the different responses to bacteria and LPS. p50 deficiency increased the LPS-induced expression of κB-regulated genes essential to neutrophil recruitment, including KC, MIP-2, ICAM-1, and TNF-α suggesting that p50 normally limited this gene expression and that decreased neutrophil recruitment did not result from insufficient expression of these genes. Neutrophils were responsive to the chemokine KC in the peripheral blood of p50-deficient mice with or without LPS-induced pulmonary inflammation. Interleukin-6 (IL-6), previously demonstrated to decrease LPS-induced neutrophil recruitment in the lungs, was increased by p50 deficiency, but LPS-induced neutrophil recruitment was decreased by p50 deficiency even in IL-6 deficient mice.

Conclusion

p50 makes essential contributions to neutrophil accumulation elicited by LPS in the lungs. This p50-dependent pathway for neutrophil accumulation can be overcome by bacterial products other than LPS and does not require IL-6.

Endogenous peripheral antinociception in early inflammation is not limited by the number of opioid-containing leukocytes but by opioid receptor expression

Endogenous inhibition of inflammatory pain is mediated by leukocytes that secrete opioid peptides upon exposure to stress (cold water swim stress, CWS) or after local injection of corticotropin releasing factor (CRF). Since in early inflammation few opioid-containing leukocytes are detected and since peripheral opioid-mediated antinociception is low we examined whether antinociception could be augmented by increased recruitment of opioid-containing polymorphonuclear cells (PMN). Rats were intraplantarly (i.pl.) injected with Freund's complete adjuvant (FCA) and with the PMN-recruiting chemokine macrophage inflammatory protein-2 (MIP-2, 1-10 microg; control: saline) for 2 h. Intraplantar leukocytes were quantified by flow cytometry. Paw pressure threshold (PPT) was determined before and after exposure to CWS, i.pl. injection of CRF and opioid peptides. Opioid receptors (OR) were measured by binding studies in dorsal root ganglia (DRG) and by immunohistochemistry in the paw. Our studies showed that (i) MIP-2 injection dose-dependently augmented recruitment of PMN and opioid-containing leukocytes (5-fold increase in cells/paw, P < 0.05), (ii) PPT was not different between groups at baseline and after CWS or CRF (maximum MPE: 20+/-2.3-29+/-7.2%, P < 0.05), (iii) injection of opioid peptides dose-dependently increased the PPT (P < 0.05, maximum MPE: and 18+/-2.6-21+/-3.6%), (iv) MOR (micro OR, MOP) binding sites in the ipsilateral DRG were unchanged (24+/-2-22+/-1.2 fmol/mg protein, P < 0.05, ANOVA) and (v) the number of MOR and DOR (delta OR, DOP) stained nerve fibers in peripheral tissue were unaltered (both P > 0.05, t-test). In summary, antinociception during early inflammation is apparently not limited by the number of opioid-containing leukocytes but by OR availability.

Selective transport of cytokine-induced neutrophil chemoattractant from the lung to the blood facilitates pulmonary neutrophil recruitment

The CXC chemokines cytokine-induced neutrophil chemoattractant (CINC) and macrophage inflammatory protein-2 (MIP-2) are potent neutrophil chemoattractants in rats. We have previously shown that CINC, unlike MIP-2 and most other proinflammatory cytokines, is elevated in the systemic circulation in response to an intratracheal (IT) challenge. Therefore, we hypothesized that CINC generated within the lung selectively enters the vascular compartment to facilitate pulmonary neutrophil recruitment. Rats were administered IT LPS, and plasma CINC and MIP-2 levels were measured 90 min and 4 h after injection, along with mRNA expression in lung, spleen, liver, and kidney. Ninety minutes and 4 h after IT LPS, CINC and MIP-2 mRNA expression were largely confined to lung homogenate, but of the two chemokines, only CINC was present in plasma. In separate experiments, rats received IT injections of recombinant CINC and/or MIP-2. Here, plasma levels of CINC, but not MIP-2, were significantly increased throughout the 4-h observation period. This finding was verified by individually administering125I-labeled forms of each chemokine. Instillation of recombinant MIP-2 or CINC into the lung increased the number of neutrophils recovered in bronchoalveolar lavage fluid at 4 h, and this effect was enhanced when both chemokines were administered together. In addition, intravenous (IV) CINC, but not IV MIP-2, increased pulmonary neutrophil recruitment in response to IT MIP-2. Our results show that CINC, in contrast to MIP-2, is selectively transported from the lung to the systemic circulation, where it promotes neutrophil migration into the lung in response to a chemotactic stimulus.

Neutrophil depletion attenuates interleukin-8 production in mild-overstretch ventilated normal rabbit lung

OBJECTIVE

Acute lung injury induced by lung overstretch is associated with neutrophil influx, but the pathogenic role of neutrophils in overstretch-induced lung injury remains unclear.

DESIGN

To assess the contribution of neutrophils, we compared the effects of noninjurious large tidal volume (Vt) ventilation on lungs in normal and neutrophil-depleted animals.

SETTING

Research animal laboratory.

SUBJECTS

Twenty-six male Japanese white rabbits.

INTERVENTIONS

Animals were mechanically ventilated for 4 hrs with one of the three following protocols: large Vt (20 mL/kg), small Vt (8 mL/kg), and large Vt (20 mL/kg) with neutrophil depletion achieved by a single dose of vinblastine injection (0.75 mg/kg) intravenously 4 days before the experiment.

MEASUREMENTS AND MAIN RESULTS

Large Vt ventilation produced alveolar neutrophil influx compared with low Vt (p =.002) without evidence of edema or increased epithelial permeability. The neutrophil influx was accompanied by increases in interleukin-8 in bronchoalveolar lavage fluid (p =.04). Immunohistochemistry of large Vt lungs showed increased interleukin-8 staining in bronchial epithelial cells, alveolar epithelium, alveolar macrophages, and smooth muscles of pulmonary vessels. Neutrophil depletion attenuated the interleukin-8 increase in the lung. Large Vt did not increase plasma interleukin-8 or tumor necrosis factor-alpha in plasma and bronchoalveolar lavage fluid. No expression of p-selectin or intercellular adhesion molecule-1 was observed.

CONCLUSIONS

Cyclic overstretching of normal rabbit lungs with noninjurious large Vt produced neutrophil influx and interleukin-8 increase in bronchoalveolar lavage fluid. Production of pulmonary interleukin-8 by lung overstretch might require the interaction between resident lung cells and migrated neutrophils. This study suggests that large Vt ventilation potentiates the predisposed, subclinical lung injury, such as nosocomial pneumonia or aspiration of gastric contents.

Inflammatory chemoreceptor cross-talk suppresses leukotriene B4 receptor 1-mediated neutrophil calcium mobilization and chemotaxis after trauma

G protein-coupled chemoattractants recruit neutrophils (PMN) to sites of injury and infection. The leukotrienes (LT) and CXC chemokines (CXC) and their receptors (BLT1/BLT2 and CXCR1/CXCR2) are all known to play roles in these responses. Each system has been studied separately in vitro, but in vivo they act concurrently, and the clinical interactions between the two systems are unstudied. We prospectively studied calcium mobilization and chemotactic responses to LTB(4) in PMN from major trauma patients. The responses of the high affinity BLT1 receptor were suppressed at the 3-day postinjury time point, but recovered by 1 wk. Trauma patients had transient elevations of plasma LT and CXC levels. Functional deficits identical with those in trauma PMN were reproduced in vitro by exposing healthy PMN to CXCs at the elevated plasma concentrations found. Functional responses to LTB(4) were suppressed by cross-talk with CXC and BLT2 receptors that desensitize BLT1. Since the suppression of intracellular calcium mobilization was prominent, we also studied the role of suppressed cell calcium mobilization in the defective chemotactic responses to LTB(4). We noted that PMN chemotaxis to LTB(4) showed far more dependence on store-operated calcium entry than on the release of cellular calcium stores, and that store-operated calcium responses to BLT1 activation were markedly inhibited during the same time period as was chemotaxis. The intermittent release of inflammatory mediators after injury can blunt PMN responses to LTs by suppressing BLT1 as well as downstream calcium entry. Diminished LT receptor activity due to cross-talk with CXC receptors can inhibit PMN recruitment to infective sites. This may predispose injured patients to septic complications.

Regulation of pulmonary and systemic bacterial lipopolysaccharide responses in transgenic mice expressing human elafin

The control of lung inflammation is of paramount importance in a variety of acute pathologies, such as pneumonia, the acute respiratory distress syndrome, and sepsis. It is becoming increasingly apparent that local innate immune responses in the lung are negatively influenced by systemic inflammation. This is thought to be due to a local deficit in cytokine responses by alveolar macrophages and neutrophils following systemic bacterial infection and the development of a septic response. Recently, using an adenovirus-based strategy which overexpresses the human elastase inhibitor elafin locally in the lung, we showed that elafin is able to prime lung innate immune responses. In this study, we generated a novel transgenic mouse strain expressing human elafin and studied its response to bacterial lipopolysaccharide (LPS) when the LPS was administered locally in the lungs and systemically. When LPS was delivered to the lungs, we found that mice expressing elafin had lower serum-to-bronchoalveolar lavage ratios of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), macrophage inflammatory protein 2, and monocyte chemoattractant protein 1, than wild-type mice. There was a concomitant increase in inflammatory cell influx, showing that there was potential priming of innate responses in the lungs. When LPS was given systemically, the mice expressing elafin had reduced levels of serum TNF-alpha compared to the levels in wild-type mice. These results indicate that elafin may have a dual function, promoting up-regulation of local lung innate immunity while simultaneously down-regulating potentially unwanted systemic inflammatory responses in the circulation.

A potent inhibitor of cytosolic phospholipase A2, arachidonyl trifluoromethyl ketone, attenuates LPS-induced lung injury in mice

Acute respiratory distress syndrome (ARDS) is an acute lung injury of high mortality rate, and sepsis syndrome is one of the most frequent causes of ARDS. Metabolites of arachidonic acid, including thromboxanes and leukotrienes, are proinflammatory mediators and potentially involved in the development of ARDS. A key enzyme for the production of these inflammatory mediators is cytosolic phospholipase A(2) (cPLA(2)). Recently, it has been reported that arachidonyl trifluoromethyl ketone (ATK) is a potent inhibitor of cPLA(2). In the present study, we hypothesized that pharmacological intervention of cPLA(2) could affect acute lung injury. To test this hypothesis, we examined the effects of ATK in a murine model of acute lung injury induced by septic syndrome. The treatment with ATK significantly attenuated lung injury, polymorphonuclear neutrophil sequestration, and deterioration of gas exchange caused by lipopolysaccharide and zymosan administration. The current observations suggest that pharmacological intervention of cPLA(2) could be a novel therapeutic approach to acute lung injury caused by sepsis syndrome.

Keratinocyte growth factor pretreatment is associated with decreased macrophage inflammatory protein-2alpha concentrations and reduced neutrophil recruitment in acid aspiration lung injury

A two-hit model of acid aspiration was used to examine the effect of keratinocyte growth factor (KGF) on chemokine levels and neutrophil recruitment into the lung. Mice were subjected to cecal ligation and puncture and then either KGF or saline, intratracheally (i.t.). Forty-eight hours later, the mice were given i.t. acid. After 8 h, neutrophil counts in bronchoalveolar lavage (BAL) fluid were significantly decreased in animals pretreated with KGF (23 +/- 4 x 10(3)/mouse) compared with saline (74 +/- 2 x 10(3)/mouse). In addition, the BAL fluid IL-6 levels were decreased in the KGF-treated group (88+/- 44 pg/mL) compared with the saline group (166 +/- 34 pg/mL). To examine the mechanism behind the KGF-induced reduction in neutrophil influx, the murine chemokines KC and macrophage inflammatory protein (MIP)-2alpha were measured. KC levels in plasma and BAL fluid were not significantly different between the treatment groups. Likewise, levels of MIP-2alpha in plasma were not affected by KGF treatment. However, 8 h after acid aspiration, MIP-2alpha concentrations were significantly lower in the KGF-treated group. The ratio of MIP-2alpha in BAL fluid versus plasma was lower in the KGF group (0.72 +/- 0.28) than in the saline group at 3 h (2.23 +/- 0.93) and also significantly lower in the KGF group (3.02 +/- 0.78) compared with the saline group (6.23 +/- 1.19) at 8 h. In this study, KGF pretreatment after acid aspiration was associated with reduced neutrophil recruitment into the lung and a decrease in MIP-2alpha gradients between BAL fluid and plasma.

Modulation of endotoxin-induced NF-kappa B activation in lung and liver through TNF type 1 and IL-1 receptors

We investigated the requirement for tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1 receptors in the pathogenesis of the pulmonary and hepatic responses to Escherichia coli lipopolysaccharide (LPS) by studying wild-type mice and mice deficient in TNF type 1 receptor [TNFR1 knockout (KO)] or both TNF type 1 and IL-1 receptors (TNFR1/IL-1R KO). In lung tissue, NF-kappaB activation was similar among the groups after exposure to aerosolized LPS. After intraperitoneal injection of LPS, NF-kappaB activation in liver was attenuated in TNFR1 KO mice and further diminished in TNFR1/IL-1R KO mice; however, in lung tissue, no impairment in NF-kappaB activation was found in TNFR1 KO mice and only a modest decrease was found in TNFR1/IL-1R KO mice. Lung concentrations of KC and macrophage-inflammatory peptide 2 were lower in TNFR1 KO and TNFR1/IL-1R KO mice after aerosolized and intraperitoneal LPS. We conclude that LPS-induced NF-kappaB activation in liver is mediated through TNF-alpha- and IL-1 receptor-dependent pathways, but, in the lung, LPS-induced NF-kappaB activation is largely independent of these receptors.

Neutrophil modulation of the pulmonary chemokine response to lipopolysaccharide

When cells within the intrapulmonary compartment are exposed to pathogens or their products such as lipopolysaccharide, they produce CXC chemokines in order to attract circulating neutrophils into the lower respiratory tract. Previous studies have shown that as neutrophils (PMNs) enter the lung, bronchoalveolar lavage (BAL) chemokine levels are decreased. In this study, we determined the intrapulmonary and systemic responses to two important rat chemokines, cytokine-induced neutrophil chemoattractant (CINC) and macrophage inflammatory protein-2 (MIP-2), to intratracheal (i.t.) LPS (100 microg in 0.5 mL of phosphate-buffered saline) under neutropenic (cyclophosphamide [CPA]) and neutrophilic (G-CSF) conditions. By 4 h after i.t. LPS, CPA pretreatment decreased PMN recruitment 83% and G-CSF increased PMN recruitment 91% compared with recruitment into the lung in vehicle-pretreated rats (42.7 +/- 19.3 million PMNs). Neutropenic rats had increased CINC and MIP-2 concentrations in BAL fluid 4 h after i.t. LPS when compared with levels seen in vehicle controls (P < 0.05). In vitro LPS-stimulated chemokine production by alveolar macrophages obtained from CPA- and vehicle-pretreated animals did not differ. The increase in BAL fluid chemokine levels in neutropenic rats corresponded to increased chemotaxis of neutrophils to BAL fluid from CPA-pretreated rats as compared with the chemotaxis response of PMN to BAL fluid from vehicle-pretreated rats. In contrast, G-CSF enhancement of neutrophil recruitment decreased chemotactic activity of BAL fluid collected 4 h after i.t. LPS. These data show that as neutrophils are recruited into the lung, they alter chemokine levels, which most likely serves to down-regulate the inflammatory response.

Trauma-hemorrhage-induced neutrophil priming is prevented by mesenteric lymph duct ligation

Our objective in this study was to test the hypothesis that priming of neutrophils (PMN) in vivo by trauma-hemorrhagic shock (T/HS) is mediated by factors carried in intestinal lymph that prime PMNs by enhancing their responses to inflammatory mediators. Previous studies have shown that T/HS-induced lung injury is mediated by factors contained in mesenteric lymph and that ligation of the main mesenteric lymph duct (LDL) can prevent T/HS-induced lung injury. Since T/HS-induced lung injury is associated with PMN infiltration, one mechanism underlying this protective effect may be the prevention of PMN priming and activation. Therefore, we assessed the ability of T/HS to prime PMN responses to inflammatory agonists, and the ability of mesenteric lymph duct division to protect against such T/HS-induced PMN priming in an all-rat system. PMN were collected from male rats 6 h after laparotomy (trauma) plus hemorrhagic shock (30 mmHg for 90 min; T/HS) or trauma plus sham shock (T/SS). Uninstrumented rats were used as controls (UC). In a second set of experiments, rats were subjected to T/HS with or without mesenteric lymph duct division. PMN were then stimulated with chemokine (GRO, MIP-2) and lipid (PAF) chemoattractants, and cell calcium flux was used to quantify responses to those agonists. T/SS primed PMN responses to GRO, MIP-2. and PAF in comparison to UC rats, but the addition of shock (T/HS) amplified PMN priming in a significant manner, especially in response to GRO. Mesenteric lymph duct division prior to T/HS diminished PMN priming to the levels seen in T/SS. This reversal of priming was significant for GRO and GRO/MIP-2 given sequentially, with the other agonist regimens showing similar trends. The results support the concept that trauma and hemorrhagic shock play important additive roles in inflammatory PMN priming. Entry of gut-derived inflammatory products into the circulation via mesenteric lymph seems to play a dominant role in mediating the conversion of physiologic shock insults into immunoinflammatory PMN priming. Shock-induced gut lymph priming enhances PMN responses to many important chemoattractants, most notably the chemokines, and mesenteric lymph duct division effectively reverses such priming to priming levels seen in trauma without shock.

In vivo lipid-derived free radical formation by NADPH oxidase in acute lung injury induced by lipopolysaccharide: a model for ARDS

Intratracheal instillation of lipopolysaccharide (LPS) activates alveolar macrophages and infiltration of neutrophils, causing lung injury/acute respiratory distress syndrome. Free radicals are a special focus as the final causative molecules in the pathogenesis of lung injury caused by LPS. Although in vitro investigation has demonstrated radical generation after exposure of cells to LPS, in vivo evidence is lacking. Using electron spin resonance (ESR) and the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN), we investigated in vivo free radical production by rats treated with intratracheal instillation of LPS. ESR spectroscopy of lipid extract from lungs exposed to LPS for 6 h gave a spectrum consistent with that of a POBN/carbon-centered radical adduct (aN=14.94+/-0.07 G and abetaH=2.42+/-0.06 G) tentatively assigned as a product of lipid peroxidation. To further investigate the mechanism of LPS-initiated free radical generation, rats were pretreated with the phagocytic toxicant GdCl3, which significantly decreased the production of radical adducts with a corresponding decrease in neutrophil infiltration. NADPH oxidase knockout mice completely blocked phagocyte-mediated, ESR-detectable radical production in this model of acute lung injury. Rats treated intratracheally with LPS generate lipid-derived free radicals via activation of NADPH oxidase.

Interactions of lung stretch, hyperoxia, and MIP-2 production in ventilator-induced lung injury

The use of positive pressure mechanical ventilation can cause ventilator-induced lung injury (VILI). We hypothesized that hyperoxia in combination with large tidal volumes (VT) would accentuate noncardiogenic edema and neutrophil infiltration in VILI and be dependent on stretch-induced macrophage inflammatory protein-2 (MIP-2) production. In rats ventilated with VT 20 ml/kg, there was pulmonary edema formation that was significantly increased by hyperoxia. Total lung neutrophil infiltration and MIP-2 in bronchoalveolar lavage (BAL) fluid were significantly elevated, in animals exposed to high VT both on room air (RA) and with hyperoxia. Hyperoxia markedly augmented the migration of neutrophils into the alveoli. Anti-MIP-2 antibody blocked migration of neutrophils into the alveoli in RA by 51% and with hyperoxia by 65%. We concluded that neutrophil migration into the alveoli was dependent on stretch-induced MIP-2 production. Hyperoxia significantly increased edema formation and neutrophil migration into the alveoli with VT 20 ml/kg, although BAL MIP-2 levels were nearly identical to VT 20 ml/kg with RA, suggesting that other mechanisms may be involved in hyperoxia-augmented neutrophil alveolar content in VILI.

Evidence that glutamine is involved in neutrophil function

Phosphate-dependent glutaminase (PDG) activity, a key enzyme of glutamine metabolism, was determined in neutrophils obtained from the intra-peritoneal cavity (PC) or bronchoalveolar space (BAS) after administration of 1 ml or 100 microl, respectively of saline, glycogen solution (1%) or lipopolysaccharide (LPS 0.1 mg (100 microl)(-1)). Neutrophils were obtained by lavage of both sites with 20 ml saline 24 h after the administration of the stimuli. Glycogen and LPS, depending on the site the cells were obtained from, differently modulated PDG activity. Cells from BAS stimulated by glycogen or LPS had raised PDG activity to 30.5 +/- 5.2 and 42.7 +/- 12.1 nmol min(-1) mg(-1) protein, respectively, when compared with saline (9.1 +/- 0.9 nmol min(-1) mg(-1) protein); mean +/- SEM. On the other hand, cells from PC showed different PDG activity: 52.0 +/- 12.6 nmol min(-1) mg(-1) for saline, 36.5 +/- 9.5 nmol min(-1) mg(-1) for glycogen, and 76.6 +/- 11.2 nmol min(-1) mg(-1) for LPS; mean +/- SEM. Therefore, PDG activity varies with the site from which neutrophils are obtained and the stimulus imposed. The effect of glutamine on nitric oxide (NO) and tumour necrosis factor (TNF) production by peritoneal neutrophils, obtained after glycogen administration, cultured in the presence of LPS (0.5 microg ml(-1)) was also examined. The addition of glutamine at concentrations varying from 2 to 20 mM did not markedly affect NO production. Glutamine alone at 2 mM did not modify the production of TNF but in the presence of LPS caused a significant decrease. So, glutamine may preserve the function of neutrophils during infections and injuries.

Compartmentalization of macrophage inflammatory protein-2, but not cytokine-induced neutrophil chemoattractant, in rats challenged with intratracheal endotoxin

An important feature of the pulmonary inflammatory response is that the production of certain cytokines and chemokines is largely confined to the lung. This study investigated the local and systemic responses of macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (CINC) in rats administered with either intratracheal or intravenous lipopolysaccharide (LPS). Intratracheal LPS induced a significant increase in MIP-2 in bronchoalveolar lavage (BAL) fluid with no detectable MIP-2 in the plasma. In contrast, CINC was significantly increased in both BAL fluid and the plasma after intratracheal LPS challenge. Cell-associated MIP-2 was increased in the pulmonary-recruited neutrophils (PMNs) but not in the circulating PMNs in rats given intratracheal LPS. Cell-associated CINC was increased in both the recruited and circulating PMNs in these animals. Intravenous LPS caused a marked increase in plasma MIP-2 and CINC, whereas only a small elevation of both MIP-2 and CINC concentrations in BAL fluid was observed. The lack of CINC compartmentalization compared to MIP-2 implies that these C-X-C chemokines are regulated differentially and may have different effects upon polymorphonuclear leukocyte (PMN) recruitment into the alveolar space in response to intrapulmonary LPS or bacterial challenge.

Disruption of neutrophil migration in a conditional transgenic model: evidence for CXCR2 desensitization in vivo

We developed transgenic mice conditionally expressing the neutrophil chemoattracting chemokine KC and the beta-galactosidase gene in multiple tissues. In these transgenic mice, doxycycline treatment induced a strong up-regulation in the expression of KC in several tissues, including heart, liver, kidney, skin, and skeletal muscle. Expression of KC within these tissues led to a rapid and substantial increase in the serum levels of KC (serum KC levels were higher than 200 ng/ml 24 h after treatment). Accordingly, beta-galactosidase expression was also detected after injection of doxycycline and was highest in skeletal muscle, pancreas, and liver. Surprisingly, despite expression of KC in multiple tissues, no neutrophil infiltration was observed in any of the tissues examined, including skin. Doxycycline treatment of nontransgenic mice grafted with transgenic skin caused dense neutrophilic infiltration of the grafts, but not the surrounding host skin, indicating that the KC produced in transgenic tissues was biologically active. In separate experiments, neutrophil migration toward a localized source of recombinant KC was impaired in animals overexpressing KC but was normal in response to other neutrophil chemoattractants. Analysis of transgenic neutrophils revealed that high concentrations of KC in transgenic blood had no influence on L-selectin cell surface expression but caused desensitization of the receptor for KC, CXCR2. These results confirm the neutrophil chemoattractant properties of KC and provide a mechanistic explanation for the paradoxical lack of leukocyte infiltration observed in the presence of elevated concentrations of this chemokine.