Effects of Pseudomonas aeruginosa elastase on alveolar epithelial permeability in guinea pigs

The Role of Pseudomonas aeruginosa Virulence Factors in Cytoskeletal Dysregulation and Lung Barrier Dysfunction

Pseudomonas (P.) aeruginosa is an opportunistic pathogen that causes serious infections and hospital-acquired pneumonia in immunocompromised patients. P. aeruginosa accounts for up to 20% of all cases of hospital-acquired pneumonia, with an attributable mortality rate of ~30-40%. The poor clinical outcome of P. aeruginosa-induced pneumonia is ascribed to its ability to disrupt lung barrier integrity, leading to the development of lung edema and bacteremia. Airway epithelial and endothelial cells are important architecture blocks that protect the lung from invading pathogens. P. aeruginosa produces a number of virulence factors that can modulate barrier function, directly or indirectly, through exploiting cytoskeleton networks and intercellular junctional complexes in eukaryotic cells. This review summarizes the current knowledge on P. aeruginosa virulence factors, their effects on the regulation of the cytoskeletal network and associated components, and molecular mechanisms regulating barrier function in airway epithelial and endothelial cells. A better understanding of these processes will help to lay the foundation for new therapeutic approaches against P. aeruginosa-induced pneumonia.

Elastase as a potential biomarker for radiation-induced gut wall injury of the distal bowel in an experimental mouse model

BACKGROUND AND PURPOSE

Traditionally, elastase has been used to study exocrine activity of the pancreas in patients with chronic pancreatitis and cystic fibrosis, and calprotectin as a marker for gut-wall inflammation in patients with inflammatory bowel disease. The aim of the study was to find out whether elastase and calprotectin could be used as inflammatory markers for radiation-induced gut wall injury of the distal bowel.

MATERIAL AND METHODS

Adult male mice were exposed to two, three, or four fractions of 6 Gy or 8 Gy irradiation to the sigmoid and rectum of the large bowel, using a linear accelerator. Fecal samples were collected from mice at 1, 3, and 6 weeks post-irradiation. The fecal levels of elastase and calprotectin were analyzed using ELISA.

RESULTS

Three and 6 weeks after irradiation, we found a dose-effect relationship between dose of ionizing radiation and the fecal level of elastase; that is significantly higher levels of elastase were observed in mice that had received a high irradiation dose. We also found that irradiated mice hosted in the same cage had a comparable level (either high or low) of elastase. No significant differences were observed from the calprotectin data.

CONCLUSIONS

We found a clear association between the dose of ionizing radiation to the distal colon and the level of elastase in the fecal samples.

Mechanism of fibroblast inflammatory responses to Pseudomonas aeruginosa elastase

Receptor tyrosine kinases, including the epidermal growth factor receptors (EGFR), are able to activate the mitogen-activated protein kinases (MAPK) via several adaptor proteins and protein kinases such as Raf. EGFR can be activated by a variety of extracellular stimuli including neutrophil elastase, but we are aware of no report as to whether Pseudomonas aeruginosa produced elastase (PE) could elicit such signalling through EGFR activation. We sought to test the inference that PE modulates inflammatory responses in human lung fibroblasts and that the process occurs by activation of the EGFR/MAPK pathways. We utilized IL-8 cytokine expression as a pathway-specific end point measure of the fibroblast inflammatory response to PE. Western blot analysis was performed to detect phosphorylation of EGFR and signal transduction intermediates. Northern blot, real-time PCR, and ELISA methods were utilized to determine cytokine gene expression levels. We found that PE induces phosphorylation of the EGFR and the extracellular signal-regulated proteins (ERK1/2) of the MAPK pathway, and nuclear translocation of NF-κB. Furthermore, enzymically active PE enhances IL-8 mRNA and protein secretion. Pretreatment of the cells with specific inhibitors of EGFR, MAPK kinase and NF-κB markedly attenuated the PE-induced signal proteins phosphorylation and IL-8 gene expression and protein secretion. Collectively, the data show that PE produced by Pseudomonas aeruginosa can modulate lung inflammation by exploiting the EGFR/ERK signalling cascades and enhancing IL-8 production in the lungs via NF-κB activation.

Inhibition of protein kinase C attenuates Pseudomonas aeruginosa elastase-induced epithelial barrier disruption

Pseudomonas aeruginosa pulmonary infection compromises the human airway epithelium, and can be especially devastating to immunocompromised or debilitated individuals. We have reported earlier that P. aeruginosa elastase (PE) increases paracellular permeability in epithelial cell monolayers by mechanisms involving tight junction (TJ) disruption and cytoskeletal reorganization, leading to destruction of epithelial barrier function. The aim of this study was to investigate putative TJ targets and potential mechanisms by which PE induces barrier disruption. We found that PE decreased localization of TJ proteins, occludin and zonula occludens (ZO)-1, in membrane fractions, and induced reorganization of F-actin within 1 hour. Although inhibition of protein kinase (PK) C α/β signaling modestly altered the extent of cytoskeletal disruption and ZO-1 translocation, we found PKC signaling to play a significant role in decreased occludin functionality during PE exposure. Furthermore, elevated PKC levels correlated with decreased levels of TJ proteins in membrane fractions, and increased paracellular permeability in a time-dependent manner. Therefore, we conclude that PKC signaling is involved during PE-induced epithelial barrier disruption via TJ translocation and cytoskeletal reorganization. Specifically, occludin, as well as associated ZO-1 and F-actin, may be early targets of PE pathogenesis occurring via a PKC-dependent pathway.

Efficacy of calcium-EDTA as an inhibitor for metallo-β-lactamase in a mouse model of Pseudomonas aeruginosa pneumonia

In this study, we have evaluated the efficacy of calcium-EDTA (Ca-EDTA) as an inhibitor of bacterial metalloenzymes, such as metallo-β-lactamase (MBL) and other proteases, in a mouse model of Pseudomonas aeruginosa pneumonia. The simultaneous presence of Ca-EDTA (32 μg/ml) reduced the MICs of imipenem (IPM) in all MBL-producing P. aeruginosa isolates (IMP-1, -2, -7, and -10 and VIM-2) but not non-MBL-producing strains. In the pneumonia model, mice were intranasally infected with MBL-producing P. aeruginosa and then kept under conditions of hyperoxia to mimic ventilator-associated pneumonia. With both intranasal and subcutaneous administrations, Ca-EDTA significantly potentiated survival benefits of IPM compared to those of IPM alone. Ca-EDTA combination therapy induced a significant reduction of the bacterial burden in the lungs (P < 0.05). Furthermore, the inhibition activity of Ca-EDTA against MBL activity was confirmed by using the purified IMP-1 enzyme, which was characterized by a 50% inhibitory concentration (IC(50)) of 55 ± 8.2 μM. Finally, the protective effects of Ca-EDTA were demonstrated by culture supernatant-induced epithelial cell damage and acute lung injury in mice. These data suggest the therapeutic potential of Ca-EDTA not only by the blocking of MBLs but also by neutralizing tissue-damaging metalloproteases in P. aeruginosa infections.

Role of the corneal epithelial basement membrane in ocular defense against Pseudomonas aeruginosa

Pseudomonas aeruginosa can invade corneal epithelial cells and translocates multilayered corneal epithelia in vitro, but it does not penetrate the intact corneal epithelium in vivo. In healthy corneas, the epithelium is separated from the underlying stroma by a basement membrane containing extracellular matrix proteins and pores smaller than bacteria. Here we used in vivo and in vitro models to investigate the potential of the basement membrane to defend against P. aeruginosa. Transmission electron microscopy of infected mouse corneas in vivo showed penetration of the stroma by P. aeruginosa only where the basement membrane was visibly disrupted by scratch injury, suggesting that the intact basement membrane prevented penetration. This hypothesis was explored using an in vitro Matrigel Transwell model to mimic the corneal basement membrane. P. aeruginosa translocation of multilayered corneal epithelia grown on Matrigel was approximately 100-fold lower than that of cells grown without Matrigel (P < 0.005, t test). Matrigel did not increase transepithelial resistance. Matrigel-grown cells blocked translocation by a P. aeruginosa protease mutant. Without cells, Matrigel also reduced traversal of P. aeruginosa and the protease mutant. Fluorescence microscopy revealed a relative accumulation of bacteria at the superficial epithelium of cells grown on Matrigel at 3 h compared to cells grown on uncoated filters. By 5 h, bacteria accumulated beneath the cells, suggesting direct trapping by the Matrigel. These findings suggest that the basement membrane helps defend the cornea against infection via physical barrier effects and influences on the epithelium and that these roles could be compromised by P. aeruginosa proteases.

Hyperoxia exaggerates bacterial dissemination and lethality in Pseudomonas aeruginosa pneumonia

Effects of hyperoxia on lethality in mice with Pseudomonas aeruginosa pneumonia were defined, and protective roles of macrolides were examined both in vitro and in vivo. Sub-lethal hyperoxia accelerated lethality of mice with P. aeruginosa pneumonia. Bacterial number was not different in the lungs, but higher in the liver of mice in hyperoxic conditions. Filter-sterilized culture supernatants of bacteria induced loss of viability of alveolar epithelial cells, which was exaggerated in hyperoxia. Metalloprotease blocking by inhibitor or gene-disruption in bacteria resulted in partial reduction of cytotoxic activity in culture supernatants. Co-culture of bacteria with sub-inhibitory concentrations of macrolides, such as azithromycin, reduced cytotoxic activity in the culture supernatants. Azithromycin provided significant survival benefit in hyperoxia-pneumonia model, which was associated with suppression of bacterial dissemination to extra-pulmonary organs. These results suggest that hyperoxia serves as an important cofactor for bacterial dissemination and lethality of P. aeruginosa pneumonia. Our data identify the potential of macrolides to protect individuals with P. aeruginosa pneumonia in the setting of hyperoxia.

Evaluation of two-way protein fluxes across the alveolo-capillary membrane by scintigraphy in rats: effect of lung inflation

Pulmonary microvascular and alveolar epithelial permeability were evaluated in vivo by scintigraphic imaging during lung distension. A zone of alveolar flooding was made by instilling a solution containing99mTc-albumin in a bronchus. Alveolar epithelial permeability was estimated from the rate at which this tracer left the lungs. Microvascular permeability was simultaneously estimated measuring the accumulation of111In-transferrin in lungs. Four levels of lung distension (corresponding to 15, 20, 25, and 30 cmH2O end-inspiratory airway pressure) were studied during mechanical ventilation. Computed tomography scans showed that the zone of alveolar flooding underwent the same distension as the contralateral lung during inflation with gas. Increasing lung tissue stretch by ventilation at high airway pressure immediately increased microvascular, but also alveolar epithelial, permeability to proteins. The same end-inspiratory pressure threshold (between 20 and 25 cmH2O) was observed for epithelial and endothelial permeability changes, which corresponded to a tidal volume between 13.7 ± 4.69 and 22.2 ± 2.12 ml/kg body wt. Whereas protein flux from plasma to alveolar space (111In-transferrin lung-to-heart ratio slope) was constant over 120 min, the rate at which99mTc-albumin left air spaces decreased with time. This pattern can be explained by changes in alveolar permeability with time or by a compartment model including an intermediate interstitial space.

Quorum sensing : une nouvelle cible thérapeutique pour Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacteria causing a wide variety of infections. The bacterial virulence depends on a large panel of cell-associated and extracellular factors. Quorum sensing (QS) allows cell-to-cell communication: sensing the environment, this system coordinates the expression of various genes within the bacterial population. QS is based on an interaction between a small diffusible molecule, an acylhomoserine lactone (AHL), and a transcriptionnal activator. Two QS systems, the las and rhl systems, have been identified in P. aeruginosa. The las system associates the transcriptionnal activator protein LasR and LasI responsible for the synthesis of a specific AHL: C12-HSL. This system was shown to activate the expression of a large number of virulence factors. Similarly, the rhl system associates the transcriptionnal activator protein RhlR with RhlI, which is responsible for the synthesis of another AHL: C4-HSL. Synthesis and secretion of a number of virulence factors are controlled by QS. Utilization of different animals models showed the crucial role of QS in the pathogenesis of P. aeruginosa infections. The discovery of QS has given a new opportunity to treat bacterial infection by another means than growth inhibition. New drugs inhibiting QS were recently discovered: furanone compounds can repress a large number of QS-regulated genes, including numerous P. aeruginosa virulence factor genes. Furanone administration to mice infected with P. aeruginosa significantly reduced lung bacterial load compared with the control group.

Rhamnolipids are virulence factors that promote early infiltration of primary human airway epithelia by Pseudomonas aeruginosa

The opportunistic bacterium Pseudomonas aeruginosa causes chronic respiratory infections in cystic fibrosis and immunocompromised individuals. Bacterial adherence to the basolateral domain of the host cells and internalization are thought to participate in P. aeruginosa pathogenicity. However, the mechanism by which the pathogen initially modulates the paracellular permeability of polarized respiratory epithelia remains to be understood. To investigate this mechanism, we have searched for virulence factors secreted by P. aeruginosa that affect the structure of human airway epithelium in the early stages of infection. We have found that only bacterial strains secreting rhamnolipids were efficient in modulating the barrier function of an in vitro-reconstituted human respiratory epithelium, irrespective of their release of elastase and lipopolysaccharide. In contrast to previous reports, we document that P. aeruginosa was not internalized by epithelial cells. We further report that purified rhamnolipids, applied on the surfaces of the epithelia, were sufficient to functionally disrupt the epithelia and to promote the paracellular invasion of rhamnolipid-deficient P. aeruginosa. The mechanism involves the incorporation of rhamnolipids within the host cell membrane, leading to tight-junction alterations. The study provides direct evidence for a hitherto unknown mechanism whereby the junction-dependent barrier of the respiratory epithelium is selectively altered by rhamnolipids.

Airway epithelial integrity is protected by a long-acting beta2-adrenergic receptor agonist

Airway epithelial integrity may be impaired by bacterial exoproducts, which are able to degrade tight junction-associated proteins such as zonula occludens 1 (ZO-1). We have investigated the protective effect of salmeterol, a long-acting beta(2)-adrenergic agonist, on Pseudomonas aeruginosa-induced alteration of the epithelial junctional barrier. We demonstrate in human airway epithelial cells (HAEC) that salmeterol induces a time-dependent increase in ZO-1 protein, although no significant change in ZO-1 transcripts was observed. When HAEC cultures were exposed to P. aeruginosa (PAO1) supernatants, apical expression of ZO-1 protein was maintained in salmeterol-pretreated HAEC cultures, whereas it disappeared after PAO1 exposure in cultures not pretreated with salmeterol. Western blot experiments showed that the 220-kD ZO-1 protein was decreased after PAO1 incubation but was still present in salmeterol-pretreated HAEC extracts. The functional activity of ZO-1 protein was monitored by measuring transepithelial resistance and analyzing the diffusion of a low molecular weight tracer through the intercellular spaces. After PAO1 incubation, the epithelial integrity of HAEC was impaired, as shown by a decrease in transepithelial resistance and increased paracellular permeability, but was not significantly altered after salmeterol preincubation. These results demonstrate that salmeterol may contribute to the protection of the airway epithelium barrier against bacterial virulence factors.

Pseudomonas aeruginosa infections in the neonatal intensive care unit

Pseudomonas aeruginosa is a highly adaptable gram-negative bacillus with the ability to cause serious disease in vulnerable populations. This article reviews the relevant epidemiology of this pathogen in the hospital setting with particular attention to the neonatal unit. Issues related to reservoirs of the organism with special consideration of the hands of staff are also addressed. Virulence factors and pathogenic mechanisms are highlighted as well as the important role of antimicrobial resistance patterns. Finally, there is a discussion of the clinical syndromes found in neonates and the appropriate antibiotic usage strategies for effective treatment of this pathogen of continuing importance.

Effect of crystalloid resuscitation and inhalation injury on extravascular lung water: clinical implications

STUDY OBJECTIVE

Arterial thermal dilution with an integrated fiberoptic monitoring system (COLD Z-021; Pulsion Medical Systems; Munich, Germany) allows measurement of extravascular lung water (EVLW) and pulmonary permeability index (PPI). The aim of this study was to evaluate the widespread clinical assumption that early respiratory failure following burn and inhalation injury is due to interstitial fluid accumulation in the lung.

DESIGN

Clinical, prospective study.

SETTING

ICU of a university referral center of burn care.

PATIENTS

Thirty-five severely burned adults (> 20% of body surface area).

INTERVENTIONS

Resuscitation therapy was guided by the results of hemodynamic monitoring using the intrathoracic blood volume (ITBV) as a cardiac preload indicator. The resuscitation goals included a normalization of preload (ITBV > 850 mL/m(2)) and cardiac index (> 3.5 L/min/m(2)) within 24 h after ICU admission. Fluid loading was implemented to reach these goals.

MEASUREMENTS AND RESULTS

One hundred forty lung water measurements were performed at 0 h, 12 h, 24 h, and 48 h after admission to the ICU. Significant elevation of EVLW and PPI was found in three measurements (2%) at 48 h after ICU admission, and was in one patient associated with inhalation injury. EVLW and PPI were not significantly different between patients with and without inhalation injury. No correlation was found between resuscitation volume and EVLW (r(2) = 0.02) or between the alveolar-arterial oxygen pressure difference and EVLW (r(2) = 0.017). Chest radiograph abnormalities were found in 2 of 22 patients with inhalation injury; these were not associated with increased values of EVLW.

CONCLUSION

Early fluid accumulation in the lung in burned patients is very uncommon, even in the presence of inhalation injury. There is no evidence that thermal injury causes an increase in pulmonary capillary membrane permeability.

Pseudomonas aeruginosa virulence factors delay airway epithelial wound repair by altering the actin cytoskeleton and inducing overactivation of epithelial matrix metalloproteinase-2

To investigate the role of P. aeruginosa virulence factors in the repair of human airway epithelial cells (HAEC) in culture, we evaluated the effect of stationary-phase supernatants from the wild-type strain PAO1 on cell migration, actin cytoskeleton distribution, epithelial integrity during and after repair of induced wounds, and the balance between matrix metalloproteinases (MMP) and their tissue inhibitors (TIMP). PAO1 supernatant altered wound repair by slowing the migration velocity in association with altered actin cytoskeleton polymerization in the lamellipodia of migrating airway epithelial cells and delaying or inhibiting the restoration of epithelial integrity after wound closure. PAO1 virulence factors overactivated two of the gelatinolytic enzymes, MMP-2 and MMP-9, produced by HAEC during repair. During HAEC repair in the presence of PAO1 virulence factors, enhanced MMP-2 activation was associated with decreased rates of its specific inhibitor TIMP-2, whereas enhanced MMP-9 activation was independent of changes of its specific inhibitor TIMP-1. These inhibitory effects were specific to P. aeruginosa elastase-producing strains (PAO1 and lipopolysaccharide-deficient AK43 strain); supernatants from P. aeruginosa strain elastase-deficient PDO240 and Escherichia coli strain DH5alpha had no inhibitory effect. To mimic the effects of P. aeruginosa, we further analyzed HAEC wound closure in the presence of increasing concentrations of activated MMP-9 or MMP-2. Whereas increasing concentrations of active MMP-9 accelerated repair, excess activated MMP-2 generated a lower migration velocity. All these data demonstrate that P. aeruginosa virulence factors, especially elastase, may impede airway epithelial wound closure by altering cell motility and causing an imbalance between pro- and activated forms of MMP-2.

Microbial metalloproteases and pathogenesis

Zinc metalloproteases produced by human pathogenic microorganisms show a wide variety of pathological actions. In local infections, the proteases cause necrotic or hemorrhagic tissue damage through digestion of structural components of the ground substance, and also form edematous lesions through generation of inflammatory mediators, while in systemic infections, the proteases act as a synergistic virulence factor through disordered proteolysis of many plasma proteins. Clostridial neurotoxins, Bacteroides fragilis enterotoxin and Bacillus anthracis lethal factor are also zinc metalloproteases.

The role of Pseudomonas aeruginosa elastase as a potent inflammatory factor in a rat air pouch inflammation model

Pseudomonas aeruginosa, an opportunistic pathogen, can cause life threatening infections in patients compromised by underlying respiratory disease like bronchiectasis, cystic fibrosis and diffuse panbronchiolitis. Most strains of P. aeruginosa produce some kind of protease with broad substrate specificities during the infectious state in the host. P. aeruginosa elastase, one of the strongest exotoxins, has a tissue-damaging proteolytic activity and is capable of degrading such plasma proteins as immunoglobulins, complement factor and cytokines. The present study focused on the effect of P. aeruginosa elastase and was designed to evaluate the neutrophil accumulation at the inflammation site mediated by P. aeruginosa elastase in the inflammatory response in the host. An air pouch model in rats, considered as a useful model of inflammation, was used to analyze the number of leukocytes, the volume of exudate and the concentration of interleukin-8 after the injection of P. aeruginosa elastase into the pouch cavity. The number of neutrophils and the volume of exudate in the pouch cavity increased significantly at 4 h, peaked at 8 h in a dose-dependent manner and then decreased at 24 h. The concentration of interleukin-8 in pouch fluid peaked 4 h earlier than the peak of the neutrophil number. The enzymatic activity of P. aeruginosa elastase seemed to reinforce the inflammation process. The influence of lipopolysaccharide contamination was negligible. Although these observations were made in the subcutaneous cavity, they indicate that P. aeruginosa elastase plays a role as an immunoprovocative factor in the inflammatory response in cases of infection with P. aeruginosa.

Neutralizing monoclonal antibodies to an extracellular Pseudomonas cepacia protease

Pseudomonas cepacia produces at least two extracellular proteases with apparent molecular masses of 36,000 and 40,000 Da. The 36-kDa protease has high proteolytic activity and the 40-kDa protease has low proteolytic activity with hide powder azure as a substrate. Monoclonal antibodies (MAbs) were raised against the purified 36- and 40-kDa proteases. Several MAbs directed against the 36-kDa protease were found to recognize the 40-kDa protease by Western immunoblot analysis. Similarly, a MAb directed against the 40-kDa protease recognized the 36-kDa protease, suggesting that these two proteases may be immunologically related. A MAb directed against the 36-kDa protease, designated 36-6-8, and a MAb directed against the 40-kDa protease (MAb G-11) cross-reacted with other extracellular proteases, such as Pseudomonas aeruginosa elastase and alkaline protease, Pseudomonas pseudomallei protease, and the Vibrio cholerae hemagglutinin/protease. MAb 36-6-8 neutralized the P. cepacia 36-kDa protease, P. aeruginosa elastase, P. pseudomallei protease, and V. cholerae hemagglutinin/protease but did not affect P. aeruginosa alkaline protease activity. In contrast, MAb G-11 to the 40-kDa protease neutralized only the P. cepacia 36-kDa protease. This evidence suggests that the neutralizing MAb, 36-6-8, recognizes an epitope conserved among some metalloproteases. This epitope may lie at or near the active site of the P. cepacia 36-kDa protease and P. aeruginosa elastase.

Comparative in vitro exoenzyme-suppressing activities of azithromycin and other macrolide antibiotics against Pseudomonas aeruginosa

The inhibitory effects of azithromycin (AZM), a new 15-membered macrolide antibiotic, on the production of exotoxin A, total protease, elastase, and phospholipase C by Pseudomonas aeruginosa were determined, and the virulence-suppressing effects of AZM were compared with those of erythromycin (EM), roxithromycin (RXM), and rokitamycin (RKM). The effect of exposure of P. aeruginosa PA103 or B16 in cultures to sub-MICs of these macrolide antibiotics on the production of exoenzymes was determined. AZM suppressed the in vitro production of extracellular and intracellular exotoxin A by P. aeruginosa PA103 more than did EM, even at a concentration of only 2 micrograms/ml. At concentrations of between 4 and 32 micrograms/ml, AZM also inhibited total protease, elastase, and phospholipase C production by P. aeruginosa B16 more than did EM, RXM, and RKM. AZM was effective in suppressing exotoxin A and total protease production through 24 h of incubation in the presence of drug at sub-MICs, but it had no significant effect on either the growth of P. aeruginosa or its total protein production. Moreover, at a concentration of 4 micrograms/ml, AZM suppressed exoenzyme production by other strains of P. aeruginosa more than did EM. These findings indicate that AZM, EM, RXM, and RKM each has an inhibitory effect on exoenzyme production separate from the antimicrobial effect and that, of these macrolides, AZM has the strongest virulence-suppressing effect.

A bacterial protease perturbs the paracellular barrier function of transporting epithelial monolayers in culture

Tight junctions between cells and adhesion to the substratum maintain the barrier function of epithelia throughout the body. Damage to the epithelial barrier by microbial products allows penetration of bacteria and promotion of infection. We studied the effects of Pseudomonas elastase (PE) on the barrier function of epithelia by using Madin-Darby canine kidney (MDCK) epithelial cells; these cells form tight junctions (zonula occludens [ZO]) in vitro. PE decreased electrical resistance across the monolayers in a concentration- and time-dependent manner. Immunostaining of selected proteins of the ZO and zonula adherens was used to explore the effects of PE on junctional proteins. PE-treated monolayers of MDCK cells had markedly decreased immunostaining of ZO-1, a protein of the ZO, but light microscopy of PE-treated cells revealed no obvious morphologic changes. A chromium release assay indicated that, even with marked changes in transmonolayer electrical resistance, the permeability defect was not due to membrane disruption. Fluorescence staining of F-actin indicated diminution of cellular microfilaments in PE-treated cells, but E cadherin (uvomorulin), a protein of the zonula adherens, was unaffected by the enzyme. Elastases from porcine pancreas and human leukocytes with similar enzymatic activity (6 U/ml) did not decrease transmonolayer electrical resistance or degrade ZO-1. These results suggest that PE disturbs the barrier function of epithelial monolayers, in part, by changing the cell architecture and altering at least one protein of the ZO.

Clearance of 99mTc-labeled albumin from lungs in anesthetized guinea pigs

Gamma imaging was used to measure the rate of clearance of aerosolized 99mTc-human serum albumin (HSA) from the lungs of control guinea pigs and guinea pigs that received increased lung inflation or lung injury. Anesthetized guinea pigs were ventilated for 6 min with an aerosol of HSA and the radioactivity in the chest was monitored for 2 h with a gamma camera to determine whether the clearance rate would be a reliable assessment of lung epithelial permeability. Increased lung volumes were effected by application of 5 or 7 cm H2O positive end-expired pressure (5-PEEP and 7-PEEP, respectively). Lung injury was induced either by intravenous oleic acid (OA, 27-73 microliters/kg) or inhalation of nitrogen dioxide (NO2, 80-100 ppm) for 2 h. Postmortem extravascular lung water volume (EVLW) provided an assessment of the degree of lung injury. Tracer clearance rates in animals receiving 5 or 7 cm H2O PEEP were not significantly different from controls (K = 0.15 +/- 0.05 and 0.24 +/- 0.10 vs 0.12 +/- 0.03%/min, respectively, p > .05). Animals exposed to NO2 had faster tracer clearance rates (K = 0.33 +/- 0.21%/min, p < .05) and higher EVLW (5.8 +/- 3.0 vs 3.7 +/- 0.2 mL/g dry lung, p < .05) than controls. Clearance rates of HSA from the lungs of NO2-exposed guinea pigs correlated well with injury as assessed by EVLW (r = .93, p < .01). Clearance rates of HSA and EVLW in animals receiving oleic acid were significantly higher than controls and the group receiving 5 cm H2O PEEP (K = 0.58 +/- 0.41%/min, EVLW = 8.1 +/- 0.8 mL/g dry lung tissue, p < .05), but there was no correlation between these parameters in this injury model. It is concluded that imaging of the disappearance of radiolabeled HSA in the guinea pig can be a useful index of lung epithelial permeability, but this technique is limited to certain models of lung injury.

Interaction of Pseudomonas aeruginosa with human lung fibroblasts: role of bacterial elastase

Colonization of cell surfaces by Pseudomonas aeruginosa is mediated by bacterial adherence, which, in turn, is influenced by both host and microbial factors. Previous studies with this organism suggest that elastase contributes to tissue invasion and necrosis. We studied the effects of Pseudomonas elastase (PE) on the adherence of P. aeruginosa to human lung fibroblast monolayers. Treatment of fibroblasts with PE (1 microgram/ml or 0.06 U/ml) increased adherence of 35S-labeled P. aeruginosa to cells, but heat-inactivated PE did not affect bacterial adhesion. Immunocytochemistry of cultured cells showed that PE (0.06 to 0.63 U/ml) decreased fibronectin (Fn) on the cell surface and extracellular matrix of cultured human lung fibroblasts. Data obtained by cytofluorography indicated that elastase also decreased Fn receptors on fibroblasts. Additional evidence for Fn degradation was provided by SDS-PAGE analysis of soluble Fn and proteins from surface iodinated cell monolayers treated with PE. We conclude that the increased bacterial adherence to fibroblasts may be due, in part, to elastase-induced proteolysis of Fn and its receptors on cell surfaces. Degradation of Fn could thus influence the extent and course of Pseudomonas infection in the lungs.

Inhibition of Aspergillus fumigatus elastase with monoclonal antibodies produced by using denatured elastase as an immunogen

In preparing monoclonal antibodies to the elastase from Aspergillus fumigatus, we found that the enzyme was weakly immunogenic in BALB/c mice. Antiserum titers were only 1:1,000 to 1:5,000, and hybridomas secreted nonspecific immunoglobulin M (IgM). Denaturing the elastase in 0.5% sodium dodecyl sulfate at 80 degrees C for 10 min prior to injection increased titers of antiserum against the nondenatured (native) enzyme 10-fold. Of eight hybridomas selected following immunization with the denatured enzyme, seven produced IgG reactive with the native enzyme and one produced nonspecific IgM. The nondenatured immunogen tested again yielded mainly IgM producers. Immunoblots and enzyme-linked immunosorbent assay showed that the IgG monoclonal antibodies were reactive with both the denatured and nondenatured fungal elastases; none cross-reacted with human neutrophil elastase, porcine pancreatic elastase, or Pseudomonas elastase. Elastase-specific polyclonal antibody produced in mice inhibited elastase activity beginning at a molar ratio (antibody to elastase) of 4:1, and activity was completely inhibited at 14.5:1. Some individual monoclonal antibodies partially inhibited elastase, but certain pairs, at a molar ratio of each antibody to elastase of 5.4:1, acted synergistically to inhibit the activity completely.

Zinc and iron regulate translation of the gene encoding Pseudomonas aeruginosa elastase

A lasB-lacZ translational fusion (pTS400) was used to examine expression of the elastase gene (lasB) in Pseudomonas aeruginosa strain PAO1. Expression from the lasB-lacZ fusion was enhanced when PAO1(pTS400) was grown in a defined medium containing elevated levels of zinc (6.0 micrograms ml-1). Transcript accumulation studies on PAO1(pTS400) and PAO1 showed that the addition of zinc had a slight negative effect on lasB transcription. These results indicated that zinc regulates the expression of elastase at the translational level. A comparison between zinc regulation and iron regulation was also made. Iron has a negative effect on lasB-lacZ expression. When PAO1(pTS400) was grown in a defined medium with a low iron content (0.1 microgram ml-1) the bacteria still responded to zinc. The independent effects of low iron and high zinc concentrations suggest separate control mechanisms for the two factors. Transcript accumulation studies on PAO1 and PAO1 (pTS400) indicated that early in the growth curve iron did not influence transcription of lasB or lasB-lacZ. Later in the growth curve a slight increase in lasB-lacZ transcription was observed only in PAO1(pTS400) grown in low iron. These results suggest that the iron regulation of lasB occurs predominantly at the translational level. Finally, when PAO1(pTS400) was grown in a complex peptone-based medium, a high level of transcript accumulation accounted for elastase expression. Alterations of iron and zinc concentrations of this medium did not affect the expression of elastase. These results suggest that there may be additional environmental cues regulating lasB transcription.

Pseudomonas aeruginosa elastase and elastolysis revisited: recent developments

With the determination of the three-dimensional structure of elastase and the probable identification of the active site and key residues involved in proteolytic activity, our knowledge of the molecular details of this interesting protease is rapidly increasing. Pseudomonas elastase appears to be remarkably similar to the Bacillus metalloproteinase thermolysin. A further significant development has been the discovery of the lasA gene and the fact that Pseudomonas elastase and alkaline proteinase appear to act in concert with the LasA protein to display the notable elastolytic activity exhibited by isolates of this organism. Biochemical and genetic studies indicate that LasA is a second elastase which may be an important virulence factor that has been overlooked in previous studies.