Contribution of neutrophils to acute lung injury

Role of chemokines in the pathogenesis of acute lung injury

Acute lung injury (ALI) is due to an uncontrolled systemic inflammatory response resulting from direct injury to the lung or indirect injury in the setting of a systemic process. Such insults lead to the systemic inflammatory response syndrome (SIRS), which includes activation of leukocytes-alveolar macrophages and sequestered neutrophils-in the lung. Although systemic inflammatory response syndrome is a physiologic response to an insult, systemic leukocyte activation, if excessive, can lead to end organ injury, such as ALI. Excessive recruitment of leukocytes is critical to the pathogenesis of ALI, and the magnitude and duration of the inflammatory process may ultimately determine the outcome in patients with ALI. Leukocyte recruitment is a well orchestrated process that depends on the function of chemokines and their receptors. Understanding the mechanisms that contribute to leukocyte recruitment in ALI may ultimately lead to the development of effective therapeutic strategies.

Role of thioredoxin in lung disease

Thioredoxin system is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. It includes thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH. Trx plays an essential role in cell function by limiting oxidative stress directly via antioxidant effects and indirectly by proteins interaction with key signal transduction molecules. A variety of signaling molecules have been implicated in the cytoprotection conferred by Trx, such as autophagic proteins, p38 mitogen-activated protein kinase, nuclear factor-κB, phosphatidylinositol 3-kinase. Recent studies indicated that Trx may contribute to the pathogenesis of COPD, asthma and lung injury. Enhanced Trx expression or application of recombinant Trx afforded protection in preclinical models of pulmonary tissue injury, which suggested Trx may be used in future therapeutic applications. The focus of this review is on the significance of Trx in various pulmonary diseases, which as a potential therapeutic strategy to protect against oxidative stress and inflammation.

Disruption of platelet-derived chemokine heteromers prevents neutrophil extravasation in acute lung injury

RATIONALE

Acute lung injury (ALI) causes high mortality, but its molecular mechanisms and therapeutic options remain ill-defined. Gram-negative bacterial infections are the main cause of ALI, leading to lung neutrophil infiltration, permeability increases, deterioration of gas exchange, and lung damage. Platelets are activated during ALI, but insights into their mechanistic contribution to neutrophil accumulation in the lung are elusive.

OBJECTIVES

To determine mechanisms of platelet-mediated neutrophil recruitment in ALI.

METHODS

Interference with platelet-neutrophil interactions using antagonists to P-selectin and glycoprotein IIb/IIIa or a small peptide antagonist disrupting platelet chemokine heteromer formation in mouse models of ALI.

MEASUREMENTS AND MAIN RESULTS

In a murine model of LPS-induced ALI, we uncover important roles for neutrophils and platelets in permeability changes and subsequent lung damage. Furthermore, platelet depletion abrogated lung neutrophil infiltration, suggesting a sequential participation of platelets and neutrophils. Whereas antagonists to P-selectin and glycoprotein IIb/IIIa had no effects on LPS-mediated ALI, antibodies to the platelet-derived chemokines CCL5 and CXCL4 strongly diminished neutrophil eflux and permeability changes. The two chemokines were found to form heteromers in human and murine ALI samples, positively correlating with leukocyte influx into the lung. Disruption of CCL5-CXCL4 heteromers in LPS-, acid-, and sepsis-induced ALI abolished lung edema, neutrophil infiltration, and tissue damage, thereby revealing a causal contribution.

CONCLUSIONS

Taken together, our data identify a novel function of platelet-derived chemokine heteromers during ALI and demonstrate means for therapeutic interference.

Cannabidiol, a non-psychotropic plant-derived cannabinoid, decreases inflammation in a murine model of acute lung injury: role for the adenosine A(2A) receptor

Acute lung injury is an inflammatory condition for which treatment is mainly supportive because effective therapies have not been developed. Cannabidiol, a non-psychotropic cannabinoid component of marijuana (Cannabis sativa), has potent immunosuppressive and anti-inflammatory properties. Therefore, we investigated the possible anti-inflammatory effect of cannabidiol in a murine model of acute lung injury. Analysis of total inflammatory cells and differential in bronchoalveolar lavage fluid was used to characterize leukocyte migration into the lungs; myeloperoxidase activity of lung tissue and albumin concentration in the bronchoalveolar lavage fluid were analyzed by colorimetric assays; cytokine/chemokine production in the bronchoalveolar lavage fluid was also analyzed by Cytometric Bead Arrays and Enzyme-Linked Immunosorbent Assay (ELISA). A single dose of cannabidiol (20mg/kg) administered prior to the induction of LPS (lipopolysaccharide)-induced acute lung injury decreases leukocyte (specifically neutrophil) migration into the lungs, albumin concentration in the bronchoalveolar lavage fluid, myeloperoxidase activity in the lung tissue, and production of pro-inflammatory cytokines (TNF and IL-6) and chemokines (MCP-1 and MIP-2) 1, 2, and 4days after the induction of LPS-induced acute lung injury. Additionally, adenosine A(2A) receptor is involved in the anti-inflammatory effects of cannabidiol on LPS-induced acute lung injury because ZM241385 (4-(2-[7-Amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol) (a highly selective antagonist of adenosine A(2A) receptor) abrogated all of the anti-inflammatory effects of cannabidiol previously described. Thus, we show that cannabidiol has anti-inflammatory effects in a murine model of acute lung injury and that this effect is most likely associated with an increase in the extracellular adenosine offer and signaling through adenosine A(2A) receptor.

Chest computed tomography findings in severe influenza pneumonia occurring in neutropenic cancer patients

OBJECTIVE

To describe the chest computed tomography findings for severe influenza H1N1 infection in a series of hospitalized neutropenic cancer patients.

METHODS

We performed a retrospective systematic analysis of chest computed tomography scans for eight hospitalized patients with fever, neutropenia, and confirmed diagnoses of influenza H1N1. The clinical data had been prospectively collected.

RESULTS

Six of eight patients (75%) developed respiratory failure and required intensive care. Prolonged H1N1 shedding was observed in the three mechanically ventilated patients, and overall hospital mortality in our series was 25%. The most frequent computed tomography findings were ground-glass opacity (all patients), consolidation (7/8 cases), and airspace nodules (6/8 cases) that were frequently moderate or severe. Other parenchymal findings were not common. Five patients had features of pneumonia, two had computed tomography findings compatible with bronchitis and/or bronchiolitis, and one had tomographic signs of chronicity.

CONCLUSION

In this series of neutropenic patients with severe influenza H1N1 infection, chest computed tomography demonstrated mainly moderate or severe parenchymatous disease, but bronchiolitis was not a common feature. These findings associated with febrile neutropenia should elicit a diagnosis of severe viral infection.

The monomer-dimer equilibrium and glycosaminoglycan interactions of chemokine CXCL8 regulate tissue-specific neutrophil recruitment

Chemokines exert their function by binding the GPCR class of receptors on leukocytes and cell surface GAGs in target tissues. Most chemokines reversibly exist as monomers and dimers, but very little is known regarding the molecular mechanisms by which the monomer-dimer equilibrium modulates in vivo function. For the chemokine CXCL8, we recently showed in a mouse lung model that monomers and dimers are active and that the monomer-dimer equilibrium of the WT plays a crucial role in regulating neutrophil recruitment. In this study, we show that monomers and dimers are also active in the mouse peritoneum but that the role of monomer-dimer equilibrium is distinctly different between these tissues and that mutations in GAG-binding residues render CXCL8 less active in the peritoneum but more active in the lung. We propose that tissue-specific differences in chemokine gradient formation, resulting from tissue-specific differences in GAG interactions, are responsible for the observed differences in neutrophil recruitment. Our observation of differential roles played by the CXCL8 monomer-dimer equilibrium and GAG interactions in different tissues is novel and reveals an additional level of complexity of how chemokine dimerization regulates in vivo recruitment.

Phenotypic and functional plasticity of cells of innate immunity: macrophages, mast cells and neutrophils

Hematopoietic cells, including lymphoid and myeloid cells, can develop into phenotypically distinct 'subpopulations' with different functions. However, evidence indicates that some of these subpopulations can manifest substantial plasticity (that is, undergo changes in their phenotype and function). Here we focus on the occurrence of phenotypically distinct subpopulations in three lineages of myeloid cells with important roles in innate and acquired immunity: macrophages, mast cells and neutrophils. Cytokine signals, epigenetic modifications and other microenvironmental factors can substantially and, in some cases, rapidly and reversibly alter the phenotype of these cells and influence their function. This suggests that regulation of the phenotype and function of differentiated hematopoietic cells by microenvironmental factors, including those generated during immune responses, represents a common mechanism for modulating innate or adaptive immunity.

Regulation of alveolar epithelial Na+ channels by ERK1/2 in chlorine-breathing mice

The mechanisms by which the exposure of mice to Cl(2) decreases vectorial Na(+) transport and fluid clearance across their distal lung spaces have not been elucidated. We examined the biophysical, biochemical, and physiological changes of rodent lung epithelial Na(+) channels (ENaCs) after exposure to Cl(2), and identified the mechanisms involved. We measured amiloride-sensitive short-circuit currents (I(amil)) across isolated alveolar Type II (ATII) cell monolayers and ENaC single-channel properties by patching ATII and ATI cells in situ. α-ENaC, γ-ENaC, total and phosphorylated extracellular signal-related kinase (ERK)1/2, and advanced products of lipid peroxidation in ATII cells were measured by Western blot analysis. Concentrations of reactive intermediates were assessed by electron spin resonance (ESR). Amiloride-sensitive Na(+) channels with conductances of 4.5 and 18 pS were evident in ATI and ATII cells in situ of air-breathing mice. At 1 hour and 24 hours after exposure to Cl(2), the open probabilities of these two channels decreased. This effect was prevented by incubating lung slices with inhibitors of ERK1/2 or of proteasomes and lysosomes. The exposure of ATII cell monolayers to Cl(2) increased concentrations of reactive intermediates, leading to ERK1/2 phosphorylation and decreased I(amil) and α-ENaC concentrations at 1 hour and 24 hours after exposure. The administration of antioxidants to ATII cells before and after exposure to Cl(2) decreased concentrations of reactive intermediates and ERK1/2 activation, which mitigated the decrease in I(amil) and ENaC concentrations. The reactive intermediates formed during and after exposure to Cl(2) activated ERK1/2 in ATII cells in vitro and in vivo, leading to decreased ENaC concentrations and activity.

Adverse biophysical effects of hydroxyapatite nanoparticles on natural pulmonary surfactant

Inhaled nanoparticles (NPs) must first interact with the pulmonary surfactant (PS) lining layer that covers the entire internal surface of the respiratory tract and plays an important role in surface tension reduction and host defense. Interactions with the PS film determine the subsequent clearance, retention, and translocation of the inhaled NPs and hence their potential toxicity. To date, little is known how NPs interact with PS, and whether or not NPs have adverse effects on the biophysical function of PS. We found a time-dependent toxicological effect of hydroxyapatite NPs (HA-NPs) on a natural PS, Infasurf, and the time scale of surfactant inhibition after particle exposure was comparable to the turnover period of surfactant metabolism. Using a variety of in vitro biophysicochemical characterization techniques, we have determined the inhibition mechanism to be due to protein adsorption onto the HA-NPs. Consequently, depletion of surfactant proteins from phospholipid vesicles caused conversion of original large vesicles into much smaller vesicles with poor surface activity. These small vesicles, in turn, inhibited biophysical function of surfactant films after adsorption at the air-water interface. Cytotoxicity study found that the HA-NPs at the studied concentration were benign to human bronchial epithelial cells, thereby highlighting the importance of evaluating biophysical effect of NPs on PS. The NP-PS interaction mechanism revealed by this study may not only provide new insight into the toxicological study of nanoparticles but also shed light on the feasibility of NP-based pulmonary drug delivery.

2-(2-Fluorobenzamido)benzoate ethyl ester (EFB-1) inhibits superoxide production by human neutrophils and attenuates hemorrhagic shock-induced organ dysfunction in rats

Neutrophil activation after trauma-hemorrhagic shock (T/H) has been implicated in the development of multiple organ dysfunction (MOD). In this study, we report that a small chemical compound, 2-(2-fluorobenzamido)benzoic acid ethyl ester (EFB-1), exhibited a potent inhibitory effect on the formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-induced superoxide anion (O2•-) release and CD11b expression by human neutrophils. Additionally, administration of EFB-1 in rats subjected to T/H caused a significant improvement in MOD. EFB-1 treatment induced an increase in cAMP formation and protein kinase (PK) A activity in FMLP-activated neutrophils, which occurred through the selective inhibition of cAMP-specific phosphodiesterase (PDE) activity but not an increase in adenylate cyclase function or cGMP-specific PDE activity. FMLP-induced phosphorylation of protein kinase B (AKT), but not calcium mobilization, was reduced by EFB-1. The inhibitory effects of EFB-1 on O(2•-) production, CD11b expression, and AKT phosphorylation were reversed by PKA inhibitors (H89 and KT5720). Significantly, administration of EFB-1 (1 mg/kg body wt) attenuated the myeloperoxidase activity of the intestines, lungs, and liver and reduced the wet/dry weight ratio of the intestines and lungs and plasma alanine aminotransferase and aspartate aminotransferase levels in Sprague-Dawley rats after T/H. Therefore, EFB-1 is a new inhibitor of cAMP-specific PDE that potently suppresses O(2•-) release and CD11b expression by human neutrophils and attenuates T/H-induced MOD in rats.