Elastase activity in bronchoalveolar lavage fluid from oxygen-exposed, Pseudomonas-infected baboons

Animals devoid of pulmonary system as infection models in the study of lung bacterial pathogens

Biological disease models can be difficult and costly to develop and use on a routine basis. Particularly, in vivo lung infection models performed to study lung pathologies use to be laborious, demand a great time and commonly are associated with ethical issues. When infections in experimental animals are used, they need to be refined, defined, and validated for their intended purpose. Therefore, alternative and easy to handle models of experimental infections are still needed to test the virulence of bacterial lung pathogens. Because non-mammalian models have less ethical and cost constraints as a subjects for experimentation, in some cases would be appropriated to include these models as valuable tools to explore host-pathogen interactions. Numerous scientific data have been argued to the more extensive use of several kinds of alternative models, such as, the vertebrate zebrafish (Danio rerio), and non-vertebrate insects and nematodes (e.g., Caenorhabditis elegans) in the study of diverse infectious agents that affect humans. Here, we review the use of these vertebrate and non-vertebrate models in the study of bacterial agents, which are considered the principal causes of lung injury. Curiously none of these animals have a respiratory system as in air-breathing vertebrates, where respiration takes place in lungs. Despite this fact, with the present review we sought to provide elements in favor of the use of these alternative animal models of infection to reveal the molecular signatures of host-pathogen interactions.

Proteinase-activated receptor-1 mediates elastase-induced apoptosis of human lung epithelial cells

Apoptosis of distal lung epithelial cells plays a pivotal role in the pathogenesis of acute lung injury. In this context, proteinases, either circulating or leukocyte-derived, may contribute to epithelial apoptosis and lung injury. We hypothesized that apoptosis of lung epithelial cells induced by leukocyte elastase is mediated via the proteinase activated receptor (PAR)-1. Leukocyte elastase, thrombin, and PAR-1-activating peptide, but not the control peptide, induced apoptosis in human airway and alveolar epithelial cells as assessed by increases in cytoplasmic histone-associated DNA fragments and TUNEL staining. These effects were largely prevented by a specific PAR-1 antagonist and by short interfering RNA directed against PAR-1. To ascertain the mechanism of epithelial apoptosis, we determined that PAR-1AP, thrombin, and leukocyte elastase dissipated mitochondrial membrane potential, induced translocation of cytochrome c to the cytosol, enhanced cleavage of caspase-9 and caspase-3, and led to JNK activation and Akt inhibition. In concert, these observations provide strong evidence that leukocyte elastase mediates apoptosis of human lung epithelial cells through PAR-1-dependent modulation of the intrinsic apoptotic pathway via alterations in mitochondrial permeability and by modulation of JNK and Akt.

Proteomic analysis of pulmonary edema fluid and plasma in patients with acute lung injury

Proteomics is the large-scale analysis of protein profiles. This approach has not yet been reported in the study of acute lung injury (ALI). This study details protein profiles in plasma and pulmonary edema fluid (EF) from 16 ALI patients and plasma and bronchoalveolar lavage fluid (BALF) from 12 normal subjects. More than 300 distinct protein spots were evident in the EF and BALF of both normal subjects and ALI patients. Of these, 158 were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In the plasma and EF protein profile of ALI patients, there were multiple qualitative changes. For instance, in all normal subjects, but in only one of the ALI patients, seven distinct surfactant protein A isoforms were evident. Nearly all ALI patients also had protein spots that indicate truncation or other posttranslational modifications. Several of these novel changes could serve as new biomarkers of lung injury.

Degradation of pulmonary surfactant protein D by Pseudomonas aeruginosa elastase abrogates innate immune function

The alveolar epithelium is lined by surfactant, a lipoprotein complex that both reduces surface tension and mediates several innate immune functions including bacterial aggregation, alteration of alveolar macrophage function, and regulation of bacterial clearance. Surfactant protein-D (SP-D) participates in several of these immune functions, and specifically it enhances the clearance of the pulmonary pathogen Pseudomonas aeruginosa, a common cause of morbidity and mortality in cystic fibrosis (CF) patients. P. aeruginosa secretes a variety of virulence factors including elastase, a zinc-metalloprotease, which degrades both SP-A and SP-D. Here we show that SP-D is cleaved by elastase to produce a stable 35-kDa fragment in a time-, temperature-, and dose-dependent manner. Degradation is inhibited by divalent metal cations, a metal chelator, and the elastase inhibitor, phosphoramidon. Sequencing the SP-D degradation products localized the major cleavage sites to the C-terminal lectin domain. The SP-D fragment fails to bind or aggregate bacteria that are aggregated by intact SP-D. SP-D fragment is observed when normal rat bronchoalveolar lavage (BAL) is treated with Pseudomonas aeruginosa elastase, and SP-D fragments are present in the BAL of CF lung allograft patients. These data show that degradation of SP-D occurs in the BAL environment and that degradation eliminates many normal immune functions of SP-D.

Proteases and lung injury

OBJECTIVE

Acute respiratory distress syndrome (ARDS) represents an inflammatory process that is initiated by diverse systemic and/or pulmonary insults, resulting in a clinical syndrome of severe respiratory distress and refractory hypoxemia. Neutrophils and their cytotoxic products, including oxidants and proteases, such as elastase, have been implicated as playing a key role in the pathophysiology of ARDS. This article reviews some of the physiologic actions of proteases, specifically elastase, the evidence for neutrophil elastase involvement in ARDS, and the potential therapeutic use of neutrophil elastase inhibitors in lung injury.

DATA SOURCE

A review of published literature (original articles and reviews) in English from 1965 to 2002.

CONCLUSION

Although the data support a key role for neutrophil elastase in the pathogenesis of ARDS, further study is needed to fully define the actions of neutrophil elastase, and how these actions affect host functions, before we can exploit this knowledge for therapeutic benefit.