Function and composition of pulmonary surfactant and surfactant-derived fatty acid profiles are altered in young adults with cystic fibrosis

Albumin Proteins as Delivery Vehicles for PFAS Contaminants into Respiratory Membranes

Poly- and perfluoroalkyl substances (PFAS) are a family of chemicals that have been used in a wide range of commercial products. While their use is declining, the prevalence of PFAS, combined with their chemical longevity, ensures that detectable levels will remain in the environment for years to come. As such, there is a pressing need to understand how PFAS contaminants interact with other elements of the human exposome and the consequences of these interactions for human health. Using serum albumin as a model system, we show that proteins can bind PFAS contaminants and facilitate their incorporation into model pulmonary surfactant systems and lipid bilayers. Protein-mediated PFAS delivery significantly altered the structure and function of both model membrane systems, potentially contributing to respiratory dysfunction and airway diseases in vivo. These results provide valuable insights into the synergistic interaction between PFAS contaminants and other elements of the human exposome and their potential consequences for human health.

Exposure to the Pseudomonas aeruginosa secretome alters the proteome and secondary metabolite production of Aspergillus fumigatus

The fungal pathogen Aspergillus fumigatus is frequently cultured from the sputum of cystic fibrosis (CF) patients along with the bacterium Pseudomonas aeruginosa. A. fumigatus secretes a range of secondary metabolites, and one of these, gliotoxin, has inhibitory effects on the host immune response. The effect of P. aeruginosa culture filtrate (CuF) on fungal growth and gliotoxin production was investigated. Exposure of A. fumigatus hyphae to P. aeruginosa cells induced increased production of gliotoxin and a decrease in fungal growth. In contrast, exposure of A. fumigatus hyphae to P. aeruginosa CuF led to increased growth and decreased gliotoxin production. Quantitative proteomic analysis was used to characterize the proteomic response of A. fumigatus upon exposure to P. aeruginosa CuF. Changes in the profile of proteins involved in secondary metabolite biosynthesis (e.g. gliotoxin, fumagillin, pseurotin A), and changes to the abundance of proteins involved in oxidative stress (e.g. formate dehydrogenase) and detoxification (e.g. thioredoxin reductase) were observed, indicating that the bacterial secretome had a profound effect on the fungal proteome. Alterations in the abundance of proteins involved in detoxification and oxidative stress highlight the ability of A. fumigatus to differentially regulate protein synthesis in response to environmental stresses imposed by competitors such as P. aeruginosa. Such responses may ultimately have serious detrimental effects on the host.

The Challenges of Eating Well for People Living with Cystic Fibrosis: an Interview Study Exploring the Use of Mindful Eating Approaches and Behaviours to Support Optimal Nutritional Status

BACKGROUND

Nutritional status and weight are closely linked to lung function and health status in cystic fibrosis (CF). The investigation of eating behaviours has shown mindfulness practices to be useful in modifying eating behaviours, particularly with obesity; to date, no research specifically explores how these concepts may be utilised within a CF population who face specific challenges in eating behaviours.

METHOD

Adult patients (n = 20, M = 8, age range 21-62 years) were recruited from a UK CF regional centre to take part in qualitative semi-structured interviews. Experiences of eating behaviours focusing on the use of mindful (or mindless) eating as barriers and enablers to achieving and maintaining optimal nutritional status were explored. Data were analysed using thematic analysis with a contextualist approach to understand how participants experienced eating behaviours within the context of health and weight status.

RESULTS

Participants engaged readily in discussions of eating behaviour describing active self-regulation of food eaten and calorie intake. Participants who struggled to maintain weight employed strategies to increase calorie intake such as distraction and multitasking while eating. Most participants reported no pleasure in food, describing eating as another treatment to endure. Confusion existed around how to eat healthily for CF alongside co-morbid health conditions including diabetes, cholesterol and heart disease.

CONCLUSION

Participants were highly aware of their eating behaviours, engaging in intentional and deliberate preparations, which could be described as mindful, for making eating a more automatic or mindless activity. Modifications to usual mindful eating interventions are needed to support people with CF.

Genome-wide association study of signature genetic alterations among pseudomonas aeruginosa cystic fibrosis isolates

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes diverse human infections including chronic airway infection in patients with cystic fibrosis (CF). Comparing the genomes of CF and non-CF PA isolates has great potential to identify the genetic basis of pathogenicity. To gain a deeper understanding of PA adaptation in CF airways, we performed a genome-wide association study (GWAS) on 1,001 PA genomes. Genetic variations identified among CF isolates were categorized into (i) alterations in protein-coding regions, either large- or small-scale, and (ii) polymorphic variation in intergenic regions. We introduced each CF-associated genetic alteration into the genome of PAO1, a prototype PA strain, and validated the outcomes experimentally. Loci readily mutated among CF isolates included genes encoding a probable sulfatase, a probable TonB-dependent receptor (PA2332~PA2336), L-cystine transporter (YecS, PA0313), and a probable transcriptional regulator (PA5438). A promoter region of a heme/hemoglobin uptake outer membrane receptor (PhuR, PA4710) was also different between the CF and non-CF isolate groups. Our analysis highlights ways in which the PA genome evolves to survive and persist within the context of chronic CF infection.

Abnormal n-6 fatty acid metabolism in cystic fibrosis contributes to pulmonary symptoms

Cystic fibrosis (CF) is a recessively inherited fatal disease that is the subject of extensive research and ongoing development of therapeutics targeting the defective protein, cystic fibrosis transmembrane conductance regulator (CFTR). Despite progress, the link between CFTR and clinical symptoms is incomplete. The severe CF phenotypes are associated with a deficiency of linoleic acid, which is the precursor of arachidonic acid. The release of arachidonic acid from membranes via phospholipase A₂ is the rate-limiting step for eicosanoid synthesis and is increased in CF, which contributes to the observed inflammation. A potential deficiency of docosahexaenoic acid may lead to decreased levels of specialized pro-resolving mediators. This pathophysiology may contribute to an early and sterile inflammation, mucus production, and to bacterial colonization, which further increases inflammation and potentiates the clinical symptoms. Advances in lipid technology will assist in elucidating the role of lipid metabolism in CF, and stimulate therapeutic modulations of inflammation.

Comparative Analysis of the Core Proteomes among the Pseudomonas Major Evolutionary Groups Reveals Species-Specific Adaptations for Pseudomonas aeruginosa and Pseudomonas chlororaphis

The Pseudomonas genus includes many species living in diverse environments and hosts. It is important to understand which are the major evolutionary groups and what are the genomic/proteomic components they have in common or are unique. Towards this goal, we analyzed 494 complete Pseudomonas proteomes and identified 297 core-orthologues. The subsequent phylogenomic analysis revealed two well-defined species (Pseudomonas aeruginosa and Pseudomonas chlororaphis) and four wider phylogenetic groups (Pseudomonas fluorescens, Pseudomonas stutzeri, Pseudomonas syringae, Pseudomonas putida) with a sufficient number of proteomes. As expected, the genus-level core proteome was highly enriched for proteins involved in metabolism, translation, and transcription. In addition, between 39–70% of the core proteins in each group had a significant presence in each of all the other groups. Group-specific core proteins were also identified, with P. aeruginosa having the highest number of these and P. fluorescens having none. We identified several P. aeruginosa-specific core proteins (such as CntL, CntM, PlcB, Acp1, MucE, SrfA, Tse1, Tsi2, Tse3, and EsrC) that are known to play an important role in its pathogenicity. Finally, a holin family bacteriocin and a mitomycin-like biosynthetic protein were found to be core-specific for P. cholororaphis and we hypothesize that these proteins may confer a competitive advantage against other root-colonizers.

Adapting to the Airways: Metabolic Requirements of Pseudomonas aeruginosa during the Infection of Cystic Fibrosis Patients

Pseudomonas aeruginosa is one of the major causes of morbidity and mortality of cystic fibrosis patients. During the infection, the bacteria colonize the nutritional rich lung mucus, which is present in the airway secretions in the patients, and they adapt their phenotype accordingly to the lung environment. In the airways, P. aeruginosa undergoes a broad metabolic rewiring as a consequence of the nutritional and stressful complexity of the lungs. However, the role of such metabolic rewiring on the infection outcome is poorly understood. Here, we review the metabolic evolution of clinical strains of P. aeruginosa during a cystic fibrosis lung infection and the metabolic functions operating in vivo under patho-physiological conditions. Finally, we discuss the perspective of modeling the cystic fibrosis environment using genome scale metabolic models of P. aeruginosa. Understanding the physiological changes occurring during the infection may pave the way to a more effective treatment for P. aeruginosa lung infections.

Biological Obstacles for Identifying In Vitro-In Vivo Correlations of Orally Inhaled Formulations

Oral inhalation of drugs is the classic therapy of obstructive lung diseases. In contrast to the oral route, the link between in vitro and in vivo findings is less well defined and predictive models and parameters for in vitro-in vivo correlations are missing. Frequently used in vitro models and problems in obtaining in vivo values to establish such models and to identify the action of formulations in vivo are discussed. It may be concluded that major obstacles to link in vitro parameters on in vivo action include lack of treatment adherence and incorrect use of inhalers by patients, variation in inhaler performance, changes by humidity, uncertainties about lung deposition, and difficulties to measure drug levels in epithelial lining fluid and tissue. Physiologically more relevant in vitro models, improvement in inhaler performance, and better techniques for in vivo measurements may help to better understand importance and interactions between individual in vitro parameters in pulmonary delivery.

Use of PBPK Modeling To Evaluate the Performance of Dissolv It, a Biorelevant Dissolution Assay for Orally Inhaled Drug Products

The dissolution of inhaled drug particles in the lungs is a challenge to model using biorelevant methods in terms of (i) collecting a respirable emitted aerosol fraction and dose, (ii) presenting this to a small volume of medium that is representative of lung lining fluid, and (iii) measuring the low concentrations of drug released. We report developments in methodology for each of these steps and utilize mechanistic in silico modeling to evaluate the in vitro dissolution profiles in the context of plasma concentration–time profiles. The PreciseInhale aerosol delivery system was used to deliver Flixotide aerosol particles to DissolvIt apparatus for measurement of dissolution. Different media were used in the DissolvIt chamber to investigate their effect on dissolution profiles, these were (i) 1.5% poly(ethylene oxide) with 0.4% l-alphaphosphatidyl choline, (ii) Survanta, and (iii) a synthetic simulated lung lining fluid (SLF) based on human lung fluid composition. For fluticasone proprionate (FP) quantification, solid phase extraction was used for sample preparation with LC–MS/MS analysis to provide an assay that was fit for purpose with a limit of quantification for FP of 312 pg/mL. FP concentration–time profiles in the flow-past perfusate were similar irrespective of the medium used in the DissolvIt chamber (∼0.04–0.07%/min), but these were significantly lower than transfer of drug from air-to-perfusate in isolated perfused lungs (0.12%/min). This difference was attributed to the DissolvIt system representing slower dissolution in the central region of the lungs (which feature nonsink conditions) compared to the peripheral regions that are represented in the isolated lung preparation. Pharmacokinetic parameters (C_max, T_max, and AUC_0-∞) were estimated from the profiles for dissolution in the different lung fluid simulants and were predicted by the simulation within 2-fold of the values reported for inhaled FP (1000 μg dose) administered via Flixotide Evohaler 250 μg strength inhaler in man. In conclusion, we report methods for performing biorelevant dissolution studies for orally inhaled products and illustrate how they can provide inputs parameters for physiologically based pharmacokinetic (PBPK) modeling of inhaled medicines.

Genetic Association of Pulmonary Surfactant Protein Genes, SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD With Cystic Fibrosis

Surfactant proteins (SP) are involved in surfactant function and innate immunity in the human lung. Both lung function and innate immunity are altered in CF, and altered SP levels and genetic association are observed in Cystic Fibrosis (CF). We hypothesized that single nucleotide polymorphisms (SNPs) within the SP genes associate with CF or severity subgroups, either through single SNP or via SNP-SNP interactions between two SNPs of a given gene (intragenic) and/or between two genes (intergenic). We genotyped a total of 17 SP SNPs from 72 case-trio pedigree (SFTPA1 (5), SFTPA2 (4), SFTPB (4), SFTPC (2), and SFTPD (2)), and identified SP SNP associations by applying quantitative genetic principles. The results showed (a) Two SNPs, SFTPB rs7316 (p = 0.0083) and SFTPC rs1124 (p = 0.0154), each associated with CF. (b) Three intragenic SNP-SNP interactions, SFTPB (rs2077079, rs3024798), and SFTPA1 (rs1136451, rs1059057 and rs4253527), associated with CF. (c) A total of 34 intergenic SNP-SNP interactions among the 4 SP genes to be associated with CF. (d) No SNP-SNP interaction was observed between SFTPA1 or SFTPA2 and SFTPD. (e) Equal number of SNP-SNP interactions were observed between SFTPB and SFTPA1/SFTPA2 (n = 7) and SP-B and SFTPD (n = 7). (f) SFTPC exhibited significant SNP-SNP interactions with SFTPA1/SFTPA2 (n = 11), SFTPB (n = 4) and SFTPD (n = 3). (g) A single SFTPB SNP was associated with mild CF after Bonferroni correction, and several intergenic interactions that are associated (p < 0.01) with either mild or moderate/severe CF were observed. These collectively indicate that complex SNP-SNP interactions of the SP genes may contribute to the pulmonary disease in CF patients. We speculate that SPs may serve as modifiers for the varied progression of pulmonary disease in CF and/or its severity.

Unique Lipid Signatures of Extracellular Vesicles from the Airways of Asthmatics

Asthma is a chronic inflammatory disease process involving the conductive airways of the human lung. The dysregulated inflammatory response in this disease process may involve multiple cell-cell interactions mediated by signaling molecules, including lipid mediators. Extracellular vesicles (EVs) are lipid membrane particles that are now recognized as critical mediators of cell-cell communication. Here, we compared the lipid composition and presence of specific lipid mediators in airway EVs purified from the bronchoalveolar lavage (BAL) fluid of healthy controls and asthmatic subjects with and without second-hand smoke (SHS) exposure. Airway exosome concentrations were increased in asthmatics, and correlated with blood eosinophilia and serum IgE levels. Frequencies of HLA-DR⁺ and CD54⁺ exosomes were also significantly higher in asthmatics. Lipidomics analysis revealed that phosphatidylglycerol, ceramide-phosphates, and ceramides were significantly reduced in exosomes from asthmatics compared to the non-exposed control groups. Sphingomyelin 34:1 was more abundant in exosomes of SHS-exposed asthmatics compared to healthy controls. Our results suggest that chronic airway inflammation may be driven by alterations in the composition of lipid mediators within airway EVs of human subjects with asthma.

Lack of glyoxylate shunt dysregulates iron homeostasis in Pseudomonas aeruginosa

The aceA and glcB genes, encoding isocitrate lyase (ICL) and malate synthase, respectively, are not in an operon in many bacteria, including Pseudomonas aeruginosa, unlike in Escherichia coli. Here, we show that expression of aceA in P. aeruginosa is specifically upregulated under H2O2-induced oxidative stress and under iron-limiting conditions. In contrast, the addition of exogenous redox active compounds or antibiotics increases the expression of glcB. The transcriptional start sites of aceA under iron-limiting conditions and in the presence of iron were found to be identical by 5' RACE. Interestingly, the enzymatic activities of ICL and isocitrate dehydrogenase had opposite responses under different iron conditions, suggesting that the glyoxylate shunt (GS) might be important under iron-limiting conditions. Remarkably, the intracellular iron concentration was lower while the iron demand was higher in the GS-activated cells growing on acetate compared to cells growing on glucose. Absence of GS dysregulated iron homeostasis led to changes in the cellular iron pool, with higher intracellular chelatable iron levels. In addition, GS mutants were found to have higher cytochrome c oxidase activity on iron-supplemented agar plates of minimal media, which promoted the growth of the GS mutants. However, deletion of the GS genes resulted in higher sensitivity to a high concentration of H2O2, presumably due to iron-mediated killing. In conclusion, the GS system appears to be tightly linked to iron homeostasis in the promotion of P. aeruginosa survival under oxidative stress.

Metabolism and Pathogenicity of Pseudomonas aeruginosa Infections in the Lungs of Individuals with Cystic Fibrosis

Individuals with the genetic disease cystic fibrosis (CF) accumulate mucus or sputum in their lungs. This sputum is a potent growth substrate for a range of potential pathogens, and the opportunistic bacterium Pseudomonas aeruginosa is generally most difficult of these to eradicate. As a result, P. aeruginosa infections are frequently maintained in the CF lung throughout life, and are the leading cause of death for these individuals. While great effort has been expended to better understand and treat these devastating infections, only recently have researchers begun to rigorously examine the roles played by specific nutrients in CF sputum to cue P. aeruginosa pathogenicity. This chapter summarizes the current state of knowledge regarding how P. aeruginosa metabolism in CF sputum affects initiation and maintenance of these infections. It contains an overview of CF lung disease and the mechanisms of P. aeruginosa pathogenicity. Several model systems used to study these infections are described with emphasis on the challenge of replicating the chronic infections observed in humans with CF. Nutrients present in CF sputum are surveyed, and the impacts of these nutrients on the infection are discussed. The chapter concludes by addressing the future of this line of research including the use of next-generation technologies and the potential for metabolism-based therapeutics.

Modeling In Vivo Interactions of Engineered Nanoparticles in the Pulmonary Alveolar Lining Fluid

Increasing use of engineered nanomaterials (ENMs) in consumer products may result in widespread human inhalation exposures. Due to their high surface area per unit mass, inhaled ENMs interact with multiple components of the pulmonary system, and these interactions affect their ultimate fate in the body. Modeling of ENM transport and clearance in vivo has traditionally treated tissues as well-mixed compartments, without consideration of nanoscale interaction and transformation mechanisms. ENM agglomeration, dissolution and transport, along with adsorption of biomolecules, such as surfactant lipids and proteins, cause irreversible changes to ENM morphology and surface properties. The model presented in this article quantifies ENM transformation and transport in the alveolar air to liquid interface and estimates eventual alveolar cell dosimetry. This formulation brings together established concepts from colloidal and surface science, physics, and biochemistry to provide a stochastic framework capable of capturing essential in vivo processes in the pulmonary alveolar lining layer. The model has been implemented for in vitro solutions with parameters estimated from relevant published in vitro measurements and has been extended here to in vivo systems simulating human inhalation exposures. Applications are presented for four different ENMs, and relevant kinetic rates are estimated, demonstrating an approach for improving human in vivo pulmonary dosimetry.

Cholesteryl esters are elevated in the lipid fraction of bronchoalveolar lavage fluid collected from pediatric cystic fibrosis patients

Background

Host-derived lipids including cholesteryl esters (CEs) such as cholesteryl linoleate have emerged as important antibacterial effectors of innate immunity in the airways and cholesteryl linoleate has been found elevated in the context of inflammation. Cystic fibrosis (CF) patients suffer from chronic infection and severe inflammation in the airways. Here, we identified and quantified CEs in bronchoalveolar lavage fluid (BALF) from CF patients and non-CF disease controls, and tested whether CE concentrations are linked to the disease.

Materials and Methods

CEs in BALF from 6 pediatric subjects with CF and 7 pediatric subjects with non-CF chronic lung disease were quantified by mass spectral analysis using liquid chromatography coupled with tandem mass spectrometry and multiple reaction monitoring. BALFs were also examined for total lipid, total protein, albumin, and, as a marker for inflammation, human neutrophil peptide (HNP) 1–3 concentrations. Statistical analysis was conducted after log 10 transformation of the data.

Results

Total lipid/protein ratio was reduced in CF BALF (p = 0.018) but the concentrations of CEs, including cholesteryl linoleate, were elevated in the total lipid fraction in CF BALF compared to non-CF disease controls (p < 0.050). In addition, the concentrations of CEs and HNP1-3 correlated with one another (p < 0.050).

Conclusions

The data suggests that the lipid composition of BALF is altered in CF with less total lipid relative to protein but with increased CE concentrations in the lipid fraction, likely contributed by inflammation. Future longitudinal studies may reveal the suitability of CEs as a novel biomarker for CF disease activity which may provide new information on the lipid mediated pathophysiology of the disease.

[Significance of surfactant proteins in the diagnosis of therapeutic diseases]

The lung provides not only respiration, but also the functioning of innate immunity mechanisms. The hydrophilic proteins SP-A and SP-D are responsible for the regulation of the latter. In the literature, there is evidence for elevated serum SP-A and SP-D levels in respiratory diseases accompanied by enhanced mucosal inflammation of the lung or its parenchymal injury and their association with age and cardiovascular diseases has been recently found. Studies of the efficiency of using SP-A and SP-D as specific markers for inflammatory lung diseases are presently worthwhile.

Essential genome of Pseudomonas aeruginosa in cystic fibrosis sputum

Defining the essential genome of bacterial pathogens is central to developing an understanding of the biological processes controlling disease. This has proven elusive for Pseudomonas aeruginosa during chronic infection of the cystic fibrosis (CF) lung. In this paper, using a Monte Carlo simulation-based method to analyze high-throughput transposon sequencing data, we establish the P. aeruginosa essential genome with statistical precision in laboratory media and CF sputum. Reconstruction of the global requirements for growth in CF sputum compared with defined growth conditions shows that the latter requires several cofactors including biotin, riboflavin, and pantothenate. Comparison of P. aeruginosa strains PAO1 and PA14 demonstrates that essential genes are primarily restricted to the core genome; however, some orthologous genes in these strains exhibit differential essentiality. These results indicate that genes with similar molecular functions may have distinct genetic roles in different P. aeruginosa strains during growth in CF sputum. We also show that growth in a defined growth medium developed to mimic CF sputum yielded virtually identical fitness requirements to CF sputum, providing support for this medium as a relevant in vitro model for CF microbiology studies.

Computational multiscale toxicodynamic modeling of silver and carbon nanoparticle effects on mouse lung function

A computational, multiscale toxicodynamic model has been developed to quantify and predict pulmonary effects due to uptake of engineered nanomaterials (ENMs) in mice. The model consists of a collection of coupled toxicodynamic modules, that were independently developed and tested using information obtained from the literature. The modules were developed to describe the dynamics of tissue with explicit focus on the cells and the surfactant chemicals that regulate the process of breathing, as well as the response of the pulmonary system to xenobiotics. Alveolar type I and type II cells, and alveolar macrophages were included in the model, along with surfactant phospholipids and surfactant proteins, to account for processes occurring at multiple biological scales, coupling cellular and surfactant dynamics affected by nanoparticle exposure, and linking the effects to tissue-level lung function changes. Nanoparticle properties such as size, surface chemistry, and zeta potential were explicitly considered in modeling the interactions of these particles with biological media. The model predictions were compared with in vivo lung function response measurements in mice and analysis of mice lung lavage fluid following exposures to silver and carbon nanoparticles. The predictions were found to follow the trends of observed changes in mouse surfactant composition over 7 days post dosing, and are in good agreement with the observed changes in mouse lung function over the same period of time.

Exon B of human surfactant protein A2 mRNA, alone or within its surrounding sequences, interacts with 14-3-3; role of cis-elements and secondary structure

Human surfactant protein A, an innate immunity molecule, is encoded by two genes: SFTPA1 (SP-A1) and SFTPA2 (SP-A2). The 5' untranslated (5'UTR) splice variant of SP-A2 (ABD), but not of SP-A1 (AD), contains exon B (eB), which is an enhancer for transcription and translation. We investigated whether eB contains cis-regulatory elements that bind trans-acting factors in a sequence-specific manner as well as the role of the eB mRNA secondary structure. Binding of cytoplasmic NCI-H441 proteins to wild-type eB, eB mutant, AD, and ABD 5'UTR mRNAs were studied by RNA electromobility shift assays (REMSAs). The bound proteins were identified by mass spectroscopy and specific antibodies (Abs). We found that 1) proteins bind eB mRNA in a sequence-specific manner, with two cis-elements identified within eB to be important; 2) eB secondary structure is necessary for binding; 3) mass spectroscopy and specific Abs in REMSAs identified 14-3-3 proteins to bind (directly or indirectly) eB and the natural SP-A2 (ABD) splice variant but not the SP-A1 (AD) splice variant; 4) other ribosomal and cytoskeletal proteins, and translation factors, are also present in the eB mRNA-protein complex; 5) knockdown of 14-3-3 β/α isoform resulted in a downregulation of SP-A2 expression. In conclusion, proteins including the 14-3-3 family bind two cis-elements within eB of hSP-A2 mRNA in a sequence- and secondary structure-specific manner. Differential regulation of SP-A1 and SP-A2 is mediated by the 14-3-3 protein family as well as by a number of other proteins that bind UTRs with or without eB mRNA.

Surfactant protein a in cystic fibrosis: supratrimeric structure and pulmonary outcome

Background

The state of oligomerization of surfactant associated protein-A (SP-A) monomers differs between individuals. This likely affects SP-A’s functional properties and could thereby influence clinical status in patients with lung diseases. In this study we focus on SP-A structure in cystic fibrosis (CF) compared to both healthy subjects and disease controls.

Methods

SP-A composition and function were assessed in both bronchoalveolar lavage (BAL) fluid and serum of 46 CF patients with mild disease, 25 patients with chronic bronchitis and 22 healthy subjects by gel chromatography and a functional agglutination assay. Relation of SP-A agglutination ability to disease severity of the subjects was explored.

Results

SP-A was present in seven major oligomeric forms with the majority of SP-A being structurally organized as complex oligomeric forms. More complex oligomeric forms were associated with better SP-A function with regard to its agglutination ability. These forms were more frequently observed in BAL than in serum, but there were no differences between disease groups. In CF patients, more complex forms of SP-A were associated with better lung function.

Conclusions

Organizational structure of SP-A affects its functional activity and is linked to disease severity in CF.

Hemolytic phospholipase C inhibition protects lung function during Pseudomonas aeruginosa infection

RATIONALE

The opportunistic pathogen Pseudomonas aeruginosa causes both acute and chronic lung infections and is particularly problematic in patients with cystic fibrosis and those undergoing mechanical ventilation. Decreased lung function contributes significantly to morbidity and mortality during P. aeruginosa infection, and damage inflicted by P. aeruginosa virulence factors contributes to lung function decline.

OBJECTIVES

We sought to describe direct contribution of a bacterial phospholipase C/sphingomyelinase, PlcHR, to alteration of host lung physiology and characterize a potential therapeutic for protection of lung function.

METHODS

We infected C57Bl/6 mice with P. aeruginosa wild-type or isogenic plcHR deletion strains and measured lung function using computer-controlled ventilators. For in vivo testing, miltefosine was delivered intraperitoneally 1 hour after infection. Infection and respiratory endpoints were at 24 hours after infection.

MEASUREMENTS AND MAIN RESULTS

P. aeruginosa wild-type infection caused significant lung function impairment, whereas the effects of a ΔplcHR strain infection were much less severe. Surfactometry analysis of bronchoalveolar lavage fluid indicated that PlcHR decreased pulmonary surfactant function. Miltefosine has structural similarity to the PC and sphingomyelin substrates of PlcHR, and we found that it inhibits the cleavage of these choline-containing lipids in vitro. Miltefosine administration after P. aeruginosa infection limited the negative effects of PlcHR activity on lung function.

CONCLUSIONS

We have directly linked production of a single virulence factor in P. aeruginosa with effects on lung function, and demonstrated that the inhibitor miltefosine protects lung function from PlcHR-dependent surfactant dysfunction.

Dynamics of liquid plugs of buffer and surfactant solutions in a micro-engineered pulmonary airway model

We describe a bioinspired microfluidic system that resembles pulmonary airways and enables on-chip generation of airway occluding liquid plugs from a stratified air-liquid two-phase flow. User-defined changes in the air stream pressure facilitated by mechanical components and tuning the wettability of the microchannels enable generation of well-defined liquid plugs. Significant differences are observed in liquid plug generation and propagation when surfactant is added to the buffer. The plug flow patterns suggest a protective role of surfactant for airway epithelial cells against pathological flow-induced mechanical stresses. We discuss the implications of the findings for clinical settings. This approach and the described platform will enable systematic investigation of the effect of different degrees of fluid mechanical stresses on lung injury at the cellular level and administration of exogenous therapeutic surfactants.

Cystic fibrosis lung disease starts in the small airways: can we treat it more effectively?

The aims of this article are to summarize existing knowledge regarding the pathophysiology of small airways disease in cystic fibrosis (CF), to speculate about additional mechanisms that might play a role, and to consider the available or potential options to treat it. In the first section, we review the evidence provided by pathologic, physiologic, and imaging studies suggesting that obstruction of small airways begins early in life and is progressive. In the second section we discuss how the relationships between CF transmembrane conductance regulator (CFTR), ion transport, the volume of the periciliary liquid layer and airway mucus might lead to defective mucociliary clearance in small airways. In addition, we discuss how chronic endobronchial bacterial infection and a chronic neutrophilic inflammatory response increase the viscosity of CF secretions and exacerbate the clearance problem. Next, we discuss how the mechanical properties of small airways could be altered early in the disease process and how remodeling can contribute to small airways disease. In the final section, we discuss how established therapies impact small airways disease and new directions that may lead to improvement in the treatment of small airways disease. We conclude that there are many reasons to believe that small airways play an important role in the pathophysiology of (early) CF lung disease. Therapy should be aimed to target the small airways more efficiently, especially with drugs that can correct the basic defect at an early stage of disease.

Modulation of gene expression in Actinobacillus pleuropneumoniae exposed to bronchoalveolar fluid

BACKGROUND

Actinobacillus pleuropneumoniae, the causative agent of porcine contagious pleuropneumonia, is an important pathogen of swine throughout the world. It must rapidly overcome the innate pulmonary immune defenses of the pig to cause disease. To better understand this process, the objective of this study was to identify genes that are differentially expressed in a medium that mimics the lung environment early in the infection process.

METHODS AND PRINCIPAL FINDINGS

Since bronchoalveolar lavage fluid (BALF) contains innate immune and other components found in the lungs, we examined gene expression of a virulent serovar 1 strain of A. pleuropneumoniae after a 30 min exposure to BALF, using DNA microarrays and real-time PCR. The functional classes of genes found to be up-regulated most often in BALF were those encoding proteins involved in energy metabolism, especially anaerobic metabolism, and in cell envelope, DNA, and protein biosynthesis. Transcription of a number of known virulence genes including apxIVA and the gene for SapF, a protein which is involved in resistance to antimicrobial peptides, was also up-regulated in BALF. Seventy-nine percent of the genes that were up-regulated in BALF encoded a known protein product, and of these, 44% had been reported to be either expressed in vivo and/or involved in virulence.

CONCLUSIONS

The results of this study suggest that in early stages of infection, A. pleuropneumoniae may modulate expression of genes involved in anaerobic energy generation and in the synthesis of proteins involved in cell wall biogenesis, as well as established virulence factors. Given that many of these genes are thought to be expressed in vivo or involved in virulence, incubation in BALF appears, at least partially, to simulate in vivo conditions and may provide a useful medium for the discovery of novel vaccine or therapeutic targets.

CYTOKINE STIMULATION BYPSEUDOMONAS AERUGINOSA—STRAIN VARIATION AND MODULATION BY PULMONARY SURFACTANT

Pulmonary surfactant and its components are part of the first-line immune defense within the lung. Here the authors show that the surfactant protein (SP) SP-D, but not SP-A, agglutinates some clinical isolates of Pseudomonas aeruginosa and Stenotrophomonas maltophilia. No agglutination of Staphylococcus aureus or Burkholderia cepacia was observed. The SP-D-induced agglutination of P. aeruginosa was not dependent on a specific lipopolysaccharide (LPS) serotype. The authors also show that SP-D, but not SP-A, increased the tumor necrosis factor (TNF alpha) release from human monocytic cells in response to a subset of P. aeruginosa and P. aeruginosa LPS. A clinical preparation of surfactant (Alveofact) blocked the TNF alpha release from monocytic cells induced by P. aeruginosa or its LPS. SP-A reversed the inhibitory effect of Alveofact in 6/8 strains of P. aeruginosa and 2/9 preparations of P. aeruginosa LPS. SP-D did not significantly alter the TNF alpha production induced by vital P. aeruginosa in the presence of Alveofact but markedly increased the TNF alpha release induced by a preparation of rough and smooth P. aeruginosa LPS. In summary, this study shows that the immunomodulatory properties of SP-A and SP-D specifically depend on the colonizing strain of P. aeruginosa. In addition, the authors show that the function of SP-A and SP-D is modulated in the presence of surfactant lipids.

Preliminary evidence for cell membrane amelioration in children with cystic fibrosis by 5-MTHF and vitamin B12 supplementation: a single arm trial

Background

Cystic fibrosis (CF) is one of the most common fatal autosomal recessive disorders in the Caucasian population caused by mutations of gene for the cystic fibrosis transmembrane conductance regulator (CFTR). New experimental therapeutic strategies for CF propose a diet supplementation to affect the plasma membrane fluidity and to modulate amplified inflammatory response. The objective of this study was to evaluate the efficacy of 5-methyltetrahydrofolate (5-MTHF) and vitamin B12 supplementation for ameliorating cell plasma membrane features in pediatric patients with cystic fibrosis.

Methodology and Principal Findings

A single arm trial was conducted from April 2004 to March 2006 in an Italian CF care centre. 31 children with CF aged from 3 to 8 years old were enrolled. Exclusion criteria were diabetes, chronic infections of the airways and regular antibiotics intake. Children with CF were supplemented for 24 weeks with 5-methyltetrahydrofolate (5-MTHF, 7.5 mg /day) and vitamin B12 (0.5 mg/day). Red blood cells (RBCs) were used to investigate plasma membrane, since RBCs share lipid, protein composition and organization with other cell types. We evaluated RBCs membrane lipid composition, membrane protein oxidative damage, cation content, cation transport pathways, plasma and RBCs folate levels and plasma homocysteine levels at baseline and after 24 weeks of 5-MTHF and vitamin B12 supplementation. In CF children, 5-MTHF and vitamin B12 supplementation (i) increased plasma and RBC folate levels; (ii) decreased plasma homocysteine levels; (iii) modified RBC membrane phospholipid fatty acid composition; (iv) increased RBC K⁺ content; (v) reduced RBC membrane oxidative damage and HSP70 membrane association.

Conclusion and Significance

5-MTHF and vitamin B12 supplementation might ameliorate RBC membrane features of children with CF.

Trial Registration

ClinicalTrials.gov NCT00730509

Airway monitoring by collection and mass spectrometric analysis of exhaled particles

We describe a new method for simultaneously collecting particles in exhaled air for subsequent chemical analysis and measuring their size distribution. After forced exhalation, particles were counted and collected in spots on silicon wafers with a cascade impactor. Several phospholipids were identified by time-of-flight secondary ion mass spectrometric analysis of the collected spots, suggesting that the particles originated from the lower airways. The amount of particles collected in ten exhalations was sufficient for characterizing the phospholipid composition. The feasibility of the technique in respiratory research is demonstrated by analysis of the phospholipid composition of exhaled particles from healthy controls, patients with asthma, and patients with cystic fibrosis. We believe this technology will be useful for monitoring patients with respiratory disease and has a high potential to detect new biomarkers in exhaled air.

Innate immune activation and cystic fibrosis

Since inflammation and infection occur so early in infancy in cystic fibrosis, the function of innate immune defence in cystic fibrosis has been questioned by many investigators. This review aims to summarize the findings relating to the physical, humoral and cellular components of innate immune defence in cystic fibrosis, and highlights the roles of neutrophils, macrophages and epithelial cells in these activities. In addition, recently identified links between antioxidant defences and cystic fibrosis transmembrane conductance regulator (CFTR) function, and how these may impact on innate lung defence, are summarized.

Long-term exposure to LPS enhances the rate of stimulated exocytosis and surfactant secretion in alveolar type II cells and upregulates P2Y2 receptor expression

Bacterial LPS is a potent proinflammatory molecule. In the lungs, LPS induces alterations in surfactant pool sizes and phospholipid (PL) contents, although direct actions of LPS on the alveolar type II cells (AT II) are not yet clear. For this reason, we studied short- and long-term effects of LPS on basal and agonist-stimulated secretory responses of rat AT II by using Ca(2+) microfluorimetry, a microtiter plate-based exocytosis assay, by quantitating PL and (3)H-labeled choline released into cell supernatants and by using quantitative PCR and Western blot analysis. Long term, but not short term, exposures to LPS led to prolonged ATP-induced Ca(2+) signals and an increased rate in vesicle fusions with an augmented release of surfactant PL. Most notably, the stimulatory effect of LPS was ATP-dependent and may be mediated by the upregulation of the purinergic receptor subtype P2Y(2). Western blot analysis confirmed higher levels of P2Y(2), and suramin, a P2Y receptor antagonist, was more effective in LPS-treated cells. From these observations, we conclude that LPS, probably via Toll-like receptor-4, induces a time-dependent increase in P2Y(2) receptors, which, by yet unknown mechanisms, leads to prolonged agonist-induced Ca(2+) responses that trigger a higher activity in vesicle fusion and secretion. We further conclude that chronic exposure to endotoxin sensitizes AT II to increase the extracellular surfactant pool, which aids in the pulmonary host defense mechanisms.

Surfactant protein A and surfactant protein D variation in pulmonary disease

Surfactant proteins A (SP-A) and D (SP-D) have been implicated in pulmonary innate immunity. The proteins are host defense lectins, belonging to the collectin family which also includes mannan-binding lectin (MBL). SP-A and SP-D are pattern-recognition molecules with the lectin domains binding preferentially to sugars on a broad spectrum of pathogen surfaces and thereby facilitating immune functions including viral neutralization, clearance of bacteria, fungi and apoptotic and necrotic cells, modulation of allergic reactions, and resolution of inflammation. SP-A and SP-D can interact with receptor molecules present on immune cells leading to enhanced microbial clearance and modulation of inflammation. SP-A and SP-D also modulate the functions of cells of the adaptive immune system including dendritic cells and T cells. Studies on SP-A and SP-D polymorphisms and protein levels in bronchoalveolar lavage and blood have indicated associations with a multitude of pulmonary inflammatory diseases. In addition, accumulating evidence in mouse models of infection and inflammation indicates that recombinant forms of the surfactant proteins are biologically active in vivo and may have therapeutic potential in controlling pulmonary inflammatory disease. The presence of the surfactant collectins, especially SP-D, in non-pulmonary tissues, such as the gastrointestinal tract and genital organs, suggest additional actions located to other mucosal surfaces. The aim of this review is to summarize studies on genetic polymorphisms, structural variants, and serum levels of human SP-A and SP-D and their associations with human pulmonary disease.

Chronic Pseudomonas aeruginosa infection reduces surfactant levels by inhibiting its biosynthesis

Chronic Pseudomonas aeruginosa infection, as occurs in cystic fibrosis, is associated with decreased surfactant phospholipid levels. To investigate mechanisms, we measured synthesis of dipalmitoylphosphatidylcholine (DPPC), the major surfactant phospholipid. Mice received an agarose bead slurry alone, or were infected with beads containing a clinical mucoid isolate of P. aeruginosa. Bacterial infection after 3 days resulted in a approximately 50% reduction in surfactant DPPC content versus control. These changes in surfactant were associated with co-ordinate reductions in mRNAs and immunoreactive levels for CTP: phosphocholine cytidylyltransferase (CCTalpha), the rate-regulatory enzyme required for DPPC synthesis. P. aeruginosa infection of murine lung epithelia decreased CCTalpha gene transcription without altering mRNA stability and by a mechanism other than release of a soluble extracellular inhibitor. Promoter deletional analysis revealed that P. aeruginosa activates a negative response element from -1019 to -799 bp of the CCTalpha proximal 5'-flanking region. Exposure of cells to a P. aeruginosa mutant strain producing alginate reduced CCTalpha promoter activity, whereas these effects were not observed in strains defective in alginate synthesis. Murine type II cells isolated from P. aeruginosa-infected CCTalpha promoter-beta-galactosidase transgenic mice exhibited significantly reduced CCT and beta-galactosidase enzyme activities versus control. Thus, a mucoid P. aeruginosa strain reduces mRNA synthesis of a key biosynthetic enzyme thereby decreasing levels of surfactant.

Phospholipid directed motility of surface-motile bacteria

Myxococcus xanthus is a surface-motile bacterium that has adapted at least one chemosensory system to allow directed movement towards the slowly diffusible lipid phosphatidylethanolamine (PE). The Dif chemosensory pathway is remarkable because it has at least three inputs coupled to outputs that control extracellular matrix (ECM) production and lipid chemotaxis. The methyl-accepting chemotaxis protein, DifA, has two different sensor inputs that have been localized by mutagenesis. The Dif chemosensory pathway employs a novel protein that slows adaptation. Lipid chemotaxis may play important roles in the M. xanthus life cycle where prey-specific and development-specific attractants have been identified. Lipid chemotaxis may also be an important mechanism for locating nutrients by lung pathogens such as Pseudomonas aeruginosa.

Association of common haplotypes of surfactant protein A1 and A2 (SFTPA1 and SFTPA2) genes with severity of lung disease in cystic fibrosis

Most individual cystic fibrosis transmembrane conductance regulator (CFTR) mutations appear not to correlate directly with severity of lung damage in cystic fibrosis (CF). Components of innate immunity, namely, mannose-binding lectin (MBL2), and surfactant protein A1 and A2 genes (SFTPA1 and SFTPA2), were shown to be critical in pulmonary host defenses. A pilot association study was conducted to identify genetic modifiers of lung disease in adult patients with CF. The structural and promoter (-221x/y) variants of MBL2, variants at codons 19, 50, 62, and 219 of SFTPA1, and at codons 9, 91, and 223 for SFTPA2, were studied in 135 adults with CF and compared to their forced expired volume in 1 sec (FEV1), diffusion of CO (DLCO), and other pulmonary scores. Predicted FEV1 was significantly lower in adults with the SFTPA1 6A3 allele and SFTPA2 1A1) allele (P = 0.01 and 0.009, respectively). The extended haplotype 6A3/1A1, which includes SFTPA1 and SFTPA2, was associated with lower pulmonary function, using FEV1 (P = 0.005) and poor pulmonary scores which were determined by American Medical Association, American Thoracic Society, and modified Shwachman-Kulczycki scores. Lower FEV1 and DLCO values were associated with MBL2 coding variants in those who had the DeltaF508 CFTR mutation (P = 0.03 and 0.004, respectively). These results support the current hypothesis that variants in pulmonary host defense molecules are potentially genetic modifiers of pulmonary disease in CF. Further work in larger populations is required to provide important new insights into the pathogenesis of CF.

Pseudomonas aeruginosa et surfactant rôle de SP-A et SP-D

Surfactant-associated proteins A and D (SP-A and SP-D) are two pulmonary collectins that bind to bacterial, fungal and viral pathogens and have multiples classes of receptors on pneumocyte and macrophage membrane. They are chemoattractant for phagocytes, enhance uptake and killing of bacteria by macrophages and neutrophils. These molecules also act as activation ligand on macrophages and neutrophils to enhance phagocytosis, resulting in an increased bacterial clearance. Depending on activation of cells by stimuli, SP-A and SP-D modulate production of antimicrobial free radicals by phagocytes and secretion of cytokines. In vivo, SP-A deficient mice infected with Pseudomonas aeruginosa (P. aeruginosa) have decreased bacterial clearance and exacerbated inflammatory response in the lungs. Serious alterations in macrophages and increased production of reactive oxygen species were found in non-infected SP-D deficient mice. Patients with cystic fibrosis are frequently colonized by P. aeruginosa. Decreased levels of SP-A and SP-D have been measured in bronchoalveolar lavage fluid of these patients, as well as patients with acute pneumonia but no chronic lung disease. P. aeruginosa secretes various proteases, among them, elastase and protease IV have been found to degrade SP-A and SP-D and abrogate their immune function. However, further investigations are necessary to examine whether these deficiencies facilitate P. aeruginosa infections or stand as consequences.

Pathogen-host interactions in Pseudomonas aeruginosa pneumonia

Pseudomonas aeruginosa is an important pathogen causing a wide range of acute and chronic infections. P. aeruginosa rarely causes infection in the normal host, but is an efficient opportunistic pathogen causing serious infections in patients who are mechanically ventilated, individuals who are immunocompromised, and patients with malignancies or HIV infection. Among these risk groups, the most vulnerable hosts are neutropenic and patients who are mechanically ventilated. In addition, P. aeruginosa is the most prevalent chronic infection contributing to the pathogenesis of cystic fibrosis. Because of the ubiquitous nature of P. aeruginosa and its ability to develop resistance to antibiotics, it continues to be problematic from a treatment perspective. The pathogenicity of P. aeruginosa is largely caused by multiple bacterial virulence factors and genetic flexibility enabling it to survive in varied environments. Lung injury associated with P. aeruginosa infection results from both the direct destructive effects of the organism on the lung parenchyma and exuberant host immune responses. This article focuses on the major bacterial virulence factors and important aspects of the host immunity that are involved in the pathogenesis of serious P. aeruginosa infection. In addition to antibiotic therapy, strategies directed toward enhancing host defense and/or limiting excessive inflammation could be important to improve outcome in P. aeruginosa lung infections.

Host defense functions of pulmonary surfactant

Surfactant is a complex of lipids and proteins that reduces surface tension at the air/liquid interface of the lung and regulates immune cell function. Surfactant immune function is primarily attributed to two proteins: SP-A and SP-D. SP-A and SP-D are members of a protein family known as 'collectins', which are distinguished by their N-terminal collagen-like region and their C-terminal lectin domain. The lectin domain binds preferentially to sugars on the surface of pathogens and thereby opsonizes them for uptake by phagocytes. The collectins also modulate the functions of cells of the adaptive immune network including dendritic cells and T lymphocytes. In addition, recent studies show that bacterial products degrade surfactant. In summary, surfactant plays an important role in lung host defense. Surfactant degradation or inactivation may contribute to enhanced susceptibility to lung inflammation and infection.

Intrapleural Tissue Plasminogen Activator for Complicated Pleural Effusions

BACKGROUND

This study is aimed at evaluating the safety and efficacy of intrapleural tissue plasminogen activator (TPA) for complicated pleural effusions, including posttraumatic hemothorax.

METHODS

Data were retrospectively collected from hospitalized patients over a 4-year period (1999-2003) who were treated with intrapleural TPA after failing drainage by tube thoracostomy. Pre- and post-TPA imaging studies were reviewed and scored by a blinded radiologist.

RESULTS

Forty-one consecutive patients with 42 effusions were identified with the following indications: 6 traumatic hemothoraces (14%), 22 loculated pleural effusions (52%), 2 line-associated hemothoraces (5%), and 12 empyemas (29%). Nine patients (22%) required operative drainage including two with posttraumatic hemothoraces. All patients managed nonoperatively demonstrated radiographic improvement after TPA administration. One patient (2.4%) developed hematuria, requiring transfusion. No trauma patient required TPA-related blood transfusion and no deaths were attributable to TPA therapy.

CONCLUSION

Intrapleural TPA administration appears safe for use in complicated pleural effusions and may decrease the need for operative intervention.

Pseudomonas aeruginosa degrades pulmonary surfactant and increases conversion in vitro

Although it is known that surfactant lipids and proteins are altered in patients with Pseudomonas aeruginosa infections, the mechanisms and implications of these alterations are not clear. In this study, the effects of P. aeruginosa on the surfactant large aggregate fraction were examined using an in vitro surface area cycling model. Large aggregates were isolated from porcine bronchoalveolar lavage fluid and incubated with supernatants from P. aeruginosa cultures (PAO1, parent strain; PAO1-A1, lasA-negative mutant; PAO1-B1, elastase-negative mutant) or purified elastase. Amounts of surfactant protein (SP)-A and SP-B, phospholipid content, and large aggregate conversion were assessed. In addition, lipid degradation was assessed by incubating a mixture of radiolabeled phospholipids with P. aeruginosa supernatants. The results demonstrated that SP-A was degraded by PAO1 and PAO1-A1 supernatants, and by purified elastase. SP-B was degraded by PAO1 and PAO1-B1 supernatants, but not by elastase. P. aeruginosa supernatants degraded phospholipids, a process inhibited by ZnCl(2). P. aeruginosa supernatants and elastase increased conversion. The data suggest that protein degradation facilitates increased conversion, and that phospholipid degradation and conversion enhance degradation of surfactant proteins. In conclusion, P. aeruginosa secretes multiple virulence factors that cooperate to result in degradation of surfactant components and alteration of large aggregate conversion.

Pulmonary Surfactant, Lung Function, and Endobronchial Inflammation in Cystic Fibrosis

Cystic fibrosis (CF) lung disease is primarily a disease of the small airways. We hypothesized that even in patients with normal lung function, a reduced surfactant function would be present and favor small airway obstruction. Bronchoalveolar lavages from 76 patients with CF (5-31 years, median 11) with well-conserved lung function (FEV1 94% predicted, range 78-121) and from 10 healthy control subjects were investigated. The deviation of the biophysical surfactant performance from normal, assessed in a bubble surfactometer, was small; however, the ability of the surfactant to maintain the patency of a narrow airway (% open) was significantly reduced. Surfactant protein (SP)-C level was increased, SP-B and SP-D were unchanged, whereas SP-A was decreased. Among the patients with CF, neutrophilic inflammation was modestly related to a poorer surfactant activity, but not to lung function. SP-D was reduced in proportion to the degree of inflammation and in the presence of bacteria. These findings in a large cohort of patients with CF with normal lung function show that the endobronchial airway inflammation is linked to early perturbations of the biophysical properties and immunologic components of pulmonary surfactant and opens fields for novel therapeutic interventions.

Pseudomonas aeruginosa protease IV degrades surfactant proteins and inhibits surfactant host defense and biophysical functions

Pulmonary surfactant has two distinct functions within the lung: reduction of surface tension at the air-liquid interface and participation in innate host defense. Both functions are dependent on surfactant-associated proteins. Pseudomonas aeruginosa is primarily responsible for respiratory dysfunction and death in cystic fibrosis patients and is also a leading pathogen in nosocomial pneumonia. P. aeruginosa secretes a number of proteases that contribute to its virulence. We hypothesized that P. aeruginosa protease IV degrades surfactant proteins and results in a reduction in pulmonary surfactant host defense and biophysical functions. Protease IV was isolated from cultured supernatant of P. aeruginosa by gel chromatography. Incubation of cell-free bronchoalveolar lavage fluid with protease IV resulted in degradation of surfactant proteins (SP)-A, -D, and -B. SPs were degraded in a time- and dose-dependent fashion by protease IV, and degradation was inhibited by the trypsin-like serine protease inhibitor Nalpha-p-tosyl-L-lysine-chloromethyl ketone (TLCK). Degradation by protease IV inhibited SP-A- and SP-D-mediated bacterial aggregation and uptake by macrophages. Surfactant treated with protease IV was unable to reduce surface tension as effectively as untreated surfactant, and this effect was inhibited by TLCK. We speculate that protease IV may be an important contributing factor to the development and propagation of acute lung injury associated with P. aeruginosa via loss of surfactant function within the lung.

A novel extracellular phospholipase C of Pseudomonas aeruginosa is required for phospholipid chemotaxis

Pseudomonas aeruginosa and other bacterial pathogens express one or more homologous extracellular phospholipases C (PLC) that are secreted through the inner membrane via the twin arginine translocase (TAT) pathway. Analysis of TAT mutants of P. aeruginosa uncovered a previously unidentified extracellular PLC that is secreted via the Sec pathway (PlcB). Whereas all presently known PLCs of P. aeruginosa (PlcH, PlcN and PlcB) hydrolyse phosphatidylcholine (PC), only PlcB is active on phosphatidylethanolamine (PE). plcB candidates were identified based on deductions made from bioinformatics data and extant DNA microarray data. Among these candidates, a gene (PA0026) required for the expression of an extracellular PE-PLC was identified. The protein encoded by PA0026 has limited, but significant similarity, over a short region (approximately 60aa of 328), to a class of zinc-dependent prokaryotic PLCs. A conserved His residue of PlcB (His216) that is required for coordinate binding of zinc in this class of PLCs was mutated. Analysis of this mutant established that the protein encoded by PA0026 is PlcB. Three in-dependent recently published reports indicate that homoserine lactone-mediated quorum sensing regulates the expression of PA0026 (i.e. plcB). PlcB, but not PlcH or PlcN, is required for directed twitching motility up a gradient of certain kinds of phospholipids. This response shows specificity for the fatty acid moiety of the phospholipid.

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.