Surfactant in airway disease

Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

A novel non-invasive method allowing for discovery of pathologically relevant proteins from small airways

Background

There is a lack of early and precise biomarkers for personalized respiratory medicine. Breath contains an aerosol of droplet particles, which are formed from the epithelial lining fluid when the small airways close and re-open during inhalation succeeding a full expiration. These particles can be collected by impaction using the PExA method (Particles in Exhaled Air), and are derived from an area of high clinical interest previously difficult to access, making them a potential source of biomarkers reflecting pathological processes in the small airways.

Research question

Our aim was to investigate if PExA method is useful for discovery of biomarkers that reflect pathology of small airways.

Methods and analysis

Ten healthy controls and 20 subjects with asthma, of whom 10 with small airway involvement as indicated by a high lung clearance index (LCI ≥ 2.9 z-score), were examined in a cross-sectional design, using the PExA instrument. The samples were analysed with the SOMAscan proteomics platform (SomaLogic Inc.).

Results

Two hundred-seven proteins were detected in up to 80% of the samples. Nine proteins showed differential abundance in subjects with asthma and high LCI as compared to healthy controls. Two of these were less abundant (ALDOA4, C4), and seven more abundant (FIGF, SERPINA1, CD93, CCL18, F10, IgM, IL1RAP). sRAGE levels were lower in ex-smokers (n = 14) than in never smokers (n = 16). Gene Ontology (GO) annotation database analyses revealed that the PEx proteome is enriched in extracellular proteins associated with extracellular exosome-vesicles and innate immunity.

Conclusion

The applied analytical method was reproducible and allowed identification of pathologically interesting proteins in PEx samples from asthmatic subjects with high LCI. The results suggest that PEx based proteomics is a novel and promising approach to study respiratory diseases with small airway involvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-022-09348-y.

Key question

Can the PExA method identify individual protein profiles that reflect pathology of small airways, using the SOMAscan platform?

What is the bottom line?

Two hundred-seven proteins were detected in up to 80% of the PEx samples, with a strong overrepresentation of proteins related to innate immune responses, including nine proteins that that discriminated subjects with asthma and high LCI as compared to healthy controls.

Why read on

The results support that PEx based proteomics is a novel and promising approach to study respiratory diseases with small airway involvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-022-09348-y.

Aerosol Delivery of Paclitaxel-Containing Self-Assembled Nanocochleates for Treating Pulmonary Metastasis: An Approach Supporting Pulmonary Mechanics

Paclitaxel (PTX) is a potent anticancer agent, which is clinically administered by infusion for treating pulmonary metastasis of different cancers. Systemic injection of PTX is promising in treating pulmonary metastasis of various cancers but simultaneously leads to many severe complications in the body. In this study, we have demonstrated a noninvasive approach for delivering PTX to deep pulmonary tissues via an inhalable phospholipid-based nanocochleate platform and showed its potential in treating pulmonary metastasis of melanoma cancer. Nanocochleates have been previously explored for oral delivery of anticancer drugs; their application for aerosol-based administration has not been accomplished in the literature thus far. Our results showed that the PTX-carrying aerosol nanocochleates (PTX-CPTs) possessed excellent pulmonary surfactant action characterized by high surface activity and encouraging in vitro terminal airway patency when compared to the marketed Taxol formulation, which is known to contain a high amount of Cremophore EL. We observed under in vitro twin-impinger analysis that the PTX-CPT had a high tendency to get deposited in stage II (alveolar region of lungs), indicating the capability of CPT to reach the deep alveolar region. Further, while exposed to the human lung adenocarcinoma cell line (A549), the PTX-CPT showed excellent cytotoxicity mediated by enhanced cellular uptake via energy-dependent endocytosis. Aerosol-based administration of PTX-CPT in a pulmonary metastatic murine melanoma model (B16F10) resulted in significant (p < 0.05) tumor growth inhibition when compared to an intravenous dose of Taxol. Inhibition of tumor growth in aerosol-based PTX-CPT-treated animals was evident by the significant (p < 0.05) reduction in numbers of tumor nodules and percent metastasis area covered by melanoma cells in the lung when compared to other treatment groups. Overall, our finding suggests that PTX can be safely administered in the form of an aerosol using a newly developed CPT system, which serves a dual purpose as both a drug delivery carrier and a pulmonary surfactant in treating pulmonary metastasis.

The effect of pulmonary surfactant on the airway smooth muscle after lipopolysaccharide exposure and its mechanisms

Pulmonary surfactant has a relaxing effect on the airway smooth muscle (ASM), which suggests its role in the pathogenesis of respiratory diseases associated with hyperreactivity of the ASM, such as asthma and chronic obstructive pulmonary disease (COPD). The ASM tone may be directly or indirectly modified by bacterial wall component lipopolysaccharide (LPS). This study elucidated the effect of LPS on the ASM reactivity and the role of surfactant in this interaction. The experiments were performed using ASM of adult guinea pigs by in vitro method of tissue organ bath (ASM unexposed-healthy or exposed to LPS under in vitro conditions) and ASM of animals intraperitoneally injected with LPS at a dose 1 mg/kg of b.w. once a day during 4-day period. Variable response of LPS was controlled by cyclooxygenase inhibitor indomethacin and relaxing effect of exogenous surfactant was studied using leukotriene and histamine receptor antagonists. The exogenous surfactant has relaxing effect on the ASM, but does not reverse LPS-induced smooth muscle contraction. The results further indicate participation of prostanoids and potential involvement of leukotriene and histamine H1 receptors in the airway smooth muscle contraction during LPS exposure.

Mitigation of Hydrochloric Acid (HCl)-Induced Lung Injury in Mice by Aerosol Therapy of Surface-Active Nanovesicles Containing Antioxidant and Anti-inflammatory Drugs

Acute lung injury leading to alveolar inflammation and surfactant dysfunction remains a medical challenge. Surface-active lipid nanovesicles of 200-250 nm size with antioxidant D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) and anti-inflammatory drug dexamethasone disodium phosphate (DXP) dual combination (Dual-NV) were developed for delivery as aerosols by nebulization in acid lung injury models. Drug deposition studies showed Dual-NV deposited ∼2.5 times more DXP compared to equivalent DXP solution. Nanovesicles are actively internalized by A549 cells through ATP- and clathrin-dependent pathways. The nanovesicles could be phagocytosed by RAW 264.7 macrophages and were nonimmunogenic and did not elicit overproduction of TNF-α, IL-1β, and IL-6. Dual-NV aerosol therapy at 200 mg/kg body weight, in HCl acid-induced lung injury in mice, markedly reduced pulmonary hemorrhage and protein leakage and improved capillary (airway) patency to ∼96%. Dual-NV aerosol therapy also significantly lowered production of inflammatory cytokine IL-1β, IL-6, and TNF-α and reduced oxidative stress by ∼95% in the injured group. Surface-active Dual-NV aerosol therapy is promising for replenishing the dysfunctional surfactant pool and mitigating inflammation and oxidative stress in lung injuries.

The Effect of Dexamethasone, Adrenergic and Cholinergic Receptor Agonists on Phospholipid Metabolism in Human Osteoarthritic Synoviocytes

Phospholipids (PLs) possess the unique ability to contribute to synovial joint lubrication. The aim of our study was to determine for the first time the effect of dexamethasone and some adrenergic and cholinergic agonists on the biosynthesis and release of PLs from human fibroblast-like synoviocytes (FLS). Osteoarthritic human knee FLS were treated with dexamethasone, terbutaline, epinephrine, carbachol, and pilocarpine, or the glucocorticoid receptor antagonist RU 486. Simultaneously PL biosynthesis was determined through the incorporation of stable isotope-labeled precursors into PLs. Radioactive isotope-labeled precursors were used to radiolabel PLs for the subsequent quantification of their release into nutrient media. Lipids were extracted and quantified using electrospray ionization tandem mass spectrometry or liquid scintillation counting. Dexamethasone significantly decreased the biosynthesis of phosphatidylcholine, phosphatidylethanolamine (PE), PE-based plasmalogen, and sphingomyelin. The addition of RU 486 abolished these effects. A release of PLs from FLS into nutrient media was not recognized by any of the tested agents. None of the adrenergic or cholinergic receptor agonists modulated the PL biosynthesis. We demonstrate for the first time an inhibitory effect of dexamethasone on the PL biosynthesis of FLS from human knees. Moreover, our study indicates that the PL metabolism of synovial joints and lungs are differently regulated.

Exhaled particles and small airways

BACKGROUND

Originally, studies on exhaled droplets explored properties of airborne transmission of infectious diseases. More recently, the interest focuses on properties of exhaled droplets as biomarkers, enabled by the development of technical equipment and methods for chemical analysis. Because exhaled droplets contain nonvolatile substances, particles is the physical designation. This review aims to outline the development in the area of exhaled particles, particularly regarding biomarkers and the connection with small airways, i e airways with an internal diameter < 2 mm.

MAIN BODY

Generation mechanisms, sites of origin, number concentrations of exhaled particles and the content of nonvolatile substances are studied. Exhaled particles range in diameter from 0.01 and 1000 μm depending on generation mechanism and site of origin. Airway reopening is one scientifically substantiated particle generation mechanism. During deep expirations, small airways close and the reopening process produces minute particles. When exhaled, these particles have a diameter of < 4 μm. A size discriminating sampling of particles < 4 μm and determination of the size distribution, allows exhaled particle mass to be estimated. The median mass is represented by particles in the size range of 0.7 to 1.0 μm. Half an hour of repeated deep expirations result in samples in the order of nanogram to microgram. The source of these samples is the respiratory tract ling fluid of small airways and consists of lipids and proteins, similarly to surfactant. Early clinical studies of e g chronic obstructive pulmonary disease and asthma, reported altered particle formation and particle composition.

CONCLUSION

The physical properties and content of exhaled particles generated by the airway reopening mechanism offers an exciting noninvasive way to obtain samples from the respiratory tract lining fluid of small airways. The biomarker potential is only at the beginning to be explored.

The influence of lung surfactant liquid crystalline nanostructures on respiratory drug delivery

The respiratory route increasingly has been used for both local and systemic drug delivery. Although drug is absorbed rapidly after respiratory delivery, the role of lung surfactant in drug delivery is not well understood. The human lung contains only around 15mL of surface lining fluid spread over ∼100m² surface. The fluid contains lung surfactant at a concentration of 8-24mg/kg/body weight; the lung surfactant which is lipo-protein in nature can form different liquid crystalline nanostructures. After a brief overview of the anatomy of respiratory system, the review has focused on the current understanding of lung surface lining fluid, lung surfactants and their composition and possible self-assembled nanostructures. The role of lung surfactant in drug delivery and drug dissolution has been briefly considered. Lung surfactant may form different liquid crystalline phases which can have an active role in drug delivery. The hypotheses developed in this review focuses on the potential roles of surface epithelial fluid containing liquid crystalline nanostructures in defining the dissolution mechanism and rate. The hypotheses also focus an understanding how liquid crystalline nanostructures can be used to control dissolution rate and how the nanostructures might be changed to influence delivery and induce toxicity.

Pulmonary surfactant in the airway physiology: a direct relaxing effect on the smooth muscle

Beside alveoli, surface active material plays an important role in the airway physiology. In the upper airways it primarily serves in local defense. Lower airway surfactant stabilizes peripheral airways, provides the transport and defense, has barrier and anti-edematous functions, and possesses direct relaxant effect on the smooth muscle. We tested in vitro the effect of two surfactant preparations Curosurf® and Alveofact® on the precontracted smooth muscle of intra- and extra-pulmonary airways. Relaxation was more pronounced for lung tissue strip containing bronchial smooth muscle as the primary site of surfactant effect. The study does not confirm the participation of ATP-dependent potassium channels and cAMP-regulated epithelial chloride channels known as CFTR chloride channels, or nitric oxide involvement in contractile response of smooth muscle to surfactant.By controlling wall thickness and airway diameter, pulmonary surfactant is an important component of airway physiology. Thus, surfactant dysfunction may be included in pathophysiology of asthma, COPD, or other diseases with bronchial obstruction.

Surface-active drug loaded lipopolymeric nanohybrid aerosol therapy: potential non-invasive way to mitigate lipopolysaccharide mediated inflammation in murine lungs

Non-invasive aerosol therapy of surface-active lipopolymeric nanohybrids co-delivers two drugs in inflamed lungs and also replenishes the depleted lung surfactant pool in inflamed alveoli following cellular uptake by the cells.

The potential role of nano- and micro-technology in the management of critical illnesses

In recent years nanomedicine has become an attractive concept for the targeted delivery of therapeutic and diagnostic compounds to injured or inflamed organs. Nanoscale drug delivery systems have the ability to improve the pharmacokinetics and increase the biodistribution of therapeutic agents to target organs, thereby resulting in improved efficacy and reduced drug toxicity. These systems are exploited for therapeutic purposes to carry the drug in the body in a controlled manner from the site of administration to the therapeutic target. The mortality in many of the critical illnesses such as sepsis and acute respiratory distress syndrome continues to remain high despite of an increased understanding of the molecular pathogenesis of these diseases. Several promising targets that have been identified as potential therapies for these devastating diseases have been limited because of difficulty with delivery systems. In particular, delivery of peptides, proteins, and miRNAs to the lung is an ongoing challenge. Hence, it is an attractive strategy to test potential targets by employing nanotechnology. Here some of the novel nanomedicine approaches that have been proposed and studied in recent years to facilitate the delivery of therapeutic agents in the setting of critical illnesses such as acute respiratory distress syndrome, sepsis and ventilator associated pneumonia are reviewed.

Effect of inhaled dry powder mannitol on mucus and its clearance

Insufficient hydration at the airway surface can make mucus adherent and poorly cleared. Cough, the major mechanism of mucus clearance in disease, is ineffective when mucus is adhesive. Inhaled mannitol creates an osmotic drive for water to move into the airway lumen. The consequent increased hydration of the airway surface decreases the adherence of mucus to the epithelium, facilitates the coupling of mucus and cilia thereby increasing mucus clearance. Inhaled mannitol also promotes effective coughing and stimulates mucociliary clearance. The beneficial effect of mannitol on mucus and its clearance has been demonstrated in patients with asthma, bronchiectasis and cystic fibrosis. Inhaled dry powder mannitol (Bronchitol™) is promising to be an effective treatment for the clearance of retained airway secretions.

The involvement of phospholipases A2 in asthma and chronic obstructive pulmonary disease

The increased morbidity, mortality, and ineffective treatment associated with the pathogenesis of chronic inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD) have generated much research interest. The key role is played by phospholipases from the A2 superfamily: enzymes which are involved in inflammation through participation in pro- and anti-inflammatory mediators production and have an impact on many immunocompetent cells. The 30 members of the A2 superfamily are divided into 7 groups. Their role in asthma and COPD has been studied in vitro and in vivo (animal models, cell cultures, and patients). This paper contains complete and updated information about the involvement of particular enzymes in the etiology and course of asthma and COPD.

A microfluidic-based bubble generation platform enables analysis of physical property change in phospholipid surfactant layers by interfacial ozone reaction

The air-liquid interface filled with pulmonary surfactant is a unique feature of our lung alveoli. The mechanical properties of this interface play an important role in breathing and its malfunction induced by an environmental hazard, such as ozone, relates to various lung diseases. In order to understand the interfacial physics of the pulmonary surfactant system, we employed a microfluidic bubble generation platform with a model pulmonary surfactant composed of two major phospholipids: DPPC (1,2-dipalmitoyl-sn-phosphatidylcholine) and POPG (1-palmitoyl-2-oleoyl-sn-phosphatidylglycerol). With fluorescence imaging, we observed the ozone-induced chemical modification of the unsaturated lipid component of the lipid mixture, POPG. This chemical change due to the oxidative stress was further utilized to study the physical characteristics of the interface through the bubble formation process. The physical property change was evaluated through the oscillatory behaviour of the monolayer, as well as the bubble size and formation time. The results presented demonstrate the potential of this platform to study interfacial physics of lung surfactant system under various environmental challenges, both qualitatively and quantitatively.

Epithelium damage and protection during reopening of occluded airways in a physiologic microfluidic pulmonary airway model

Airways of the peripheral lung are prone to closure at low lung volumes. Deficiency or dysfunction of pulmonary surfactant during various lung diseases compounds this event by destabilizing the liquid lining of small airways and giving rise to occluding liquid plugs in airways. Propagation of liquid plugs in airways during inflation of the lung exerts large mechanical forces on airway cells. We describe a microfluidic model of small airways of the lung that mimics airway architecture, recreates physiologic levels of pulmonary pressures, and allows studying cellular response to repeated liquid plug propagation events. Substantial cellular injury happens due to the propagation of liquid plugs devoid of surfactant. We show that addition of a physiologic concentration of a clinical surfactant, Survanta, to propagating liquid plugs protects the epithelium and significantly reduces cell death. Although the protective role of surfactants has been demonstrated in models of a propagating air finger in liquid-filled airways, this is the first time to study the protective role of surfactants in liquid plugs where fluid mechanical stresses are expected to be higher than in air fingers. Our parallel computational simulations revealed a significant decrease in mechanical forces in the presence of surfactant, confirming the experimental observations. The results support the practice of providing exogenous surfactant to patients in certain clinical settings as a protective mechanism against pathologic flows. More importantly, this platform provides a useful model to investigate various surface tension-mediated lung diseases at the cellular level.

In situ enhancement of pulmonary surfactant function using temporary flow reversal

Acute respiratory distress syndrome is a pulmonary disease with a mortality rate of ∼40% and 75,000 deaths annually in the United States. Mechanical ventilation restores airway patency and gas transport but leads to ventilator-induced lung injury. Furthermore, surfactant replacement therapy is ineffective due to surfactant delivery difficulties and deactivation by vascular proteins leaking into the airspace. Here, we demonstrated that surfactant function can be substantially improved (up to 50%) in situ in an in vitro pulmonary airway model using unconventional flows that incorporate a short-term retraction of the air-liquid interface, leading to a net decrease in cellular damage. Computational fluid dynamic simulations provided insights into this method and demonstrated the physicochemical hydrodynamic foundation for the improved surfactant microscale transport and mobility. This study may provide a starting point for developing novel ventilation waveforms to improve surfactant function in edematous airways.

Therapeutic role of terbutaline in a rat whole-lung lavage model

Whole-lung lavage (WLL) is the preferred therapy for patients with pulmonary alveolar proteinosis (PAP). However, WLL can cause fluid retention, surfactant lost, and hypoxia. Terbutaline has been shown to accelerate the rate of alveolar fluid clearance and augment surfactant secretion. The present study aimed at investigating effects of terbutaline and oxygen ventilation in rats with WLL. Forty rats were randomly divided into control, ventilation, NS (normal saline) + ventilation, LT (terbutaline in low concentration, 10(-4) M) + ventilation, and HT (terbutaline in high concentration, 10(-3) M) + ventilation groups. The left thoracic cavity was opened and a cannula was inserted into the left bronchus. The left lung was ventilated, while the right lung was lavaged. Arterial blood gas, electrocardiogram, histological changes, and wet/dry ratio of lung tissues were examined. The concentrations of total protein (TP), total phospholipids (TPL), and disaturated phosphatidylcholine (DSPC) in recovery fluid were measured. For the in vitro study, alveolar type II (ATII) cells were isolated from healthy male rats, incubated for 24 hours, and divided into control, LT, and HT groups and exposed to different concentration of terbutaline (10(-4) and 10(-3) M) for 2 hours, followed by measuring sodium-potassium adenosine triphosphatase (Na(+),K(+)-ATPase) activity. Oxygen ventilation significantly increased Pao(2)/Fio(2) after lavage in the ventilation group, as compared to control group (249.4 ± 7.9 vs 210.6 ± 9.4; P = .001). Compared with NS + venlitation group, a higher concentration of terbutaline decreased the wet/dry ratio of lung tissues (5.0 ± 0.1 vs 5.6 ± 0.1; P = .007), increased the concentrations of TPL (175.9 ± 14.0 vs 162.0 ± 6.8 mg/L; P = .031) and DSPC (93.2 ± 6.9 vs 70.9 ± 6.2 mg/L, P = .0001) in the recovery fluid, and alleviated hypoxia significantly. Terbutaline in both low and high doses increased Na(+),K(+)-ATPase activity in ATII cells (62.5 ± 2.4 and 62.6 ± 2.8 vs 32.2 ± 2.1 mmol/h/mg protein; P < .01). Theses results show that the administration of terbutaline facilitates alveolar fluid absorption and increases surfactant secretion during lung lavage, the former is partly driven by increasing Na(+),K(+)-ATPase activity. The modified lavage method, with the use of terbutaline and oxygen ventilation, is one of potential therapies for patients with PAP.

Nanovesicle aerosols as surfactant therapy in lung injury

Acute lung injury causes inactivation of pulmonary surfactant due to leakage of albumin and other markers. Current surfactants are ineffective in this condition and are instilled intratracheally. Nanovesicles of 300 ± 50 nm composed of nonlamellar phospholipids were developed as pulmonary surfactant aerosols for therapy in acid-induced lung injury. A combination of dipalmitoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine was used. The size and composition of the nanovesicles were optimized for an improved airway patency in the presence of albumin and serum. In an acid-induced lung injury model in mice, on treatment with nanovesicle aerosols at a dose of 200 mg/kg, the alveolar protein leakage decreased from 8.62 ± 0.97 μg/mL to 1.94 ± 0.74 μg/mL, whereas the airway patency of the bronchoalveolar lavage fluid increased from 0.6 ± 0.0% to 91.7 ± 1.05%. Nanovesicle aerosols of nonlamellar lipids improved the resistance of pulmonary surfactants to inhibition and were promising as a noninvasive aerosol therapy in acute lung injury.

FROM THE CLINICAL EDITOR

In acute lung injury, intrinsic surfactants are inactivated via albumin leakage and other mechanisms. Currently existing intratracheal surfactants are ineffective in this condition. The authors demonstrate that novel nanovesicle aerosols of nonlamellar lipids improved the resistance of pulmonary surfactants to inhibition and are promising as a noninvasive aerosol therapy in acute lung injury.

Pulmonary surfactant in respiratory syncytial virus bronchiolitis: the role in pathogenesis and clinical implications

Respiratory syncytial virus (RSV) bronchiolitis is the leading cause of lower respiratory tract infection, and the most frequent reason for hospitalization among infants throughout the world. In addition to the acute consequences of the disease, RSV bronchiolitis in early childhood is related to further development of recurrent wheezing and asthma. Despite the medical and economic burden of the disease, therapeutic options are limited to supportive measures, and mechanical ventilation in severe cases. Growing evidence suggests an important role of changes in pulmonary surfactant content and composition in the pathogenesis of severe RSV bronchiolitis. Besides the well-known importance of pulmonary surfactant in maintenance of pulmonary homeostasis and lung mechanics, the surfactant proteins SP-A and SP-D are essential components of the pulmonary innate immune system. Deficiencies of such proteins, which develop in severe RSV bronchiolitis, may be related to impairment in viral clearance, and exacerbated inflammatory response. A comprehensive understanding of the role of the pulmonary surfactant in the pathogenesis of the disease may help the development of new treatment strategies. We conducted a review of the literature to analyze the evidences of pulmonary surfactant changes in the pathogenesis of severe RSV bronchiolitis, its relation to the inflammatory and immune response, and the possible role of pulmonary surfactant replacement in the treatment of the disease.

Comparative study of clinical pulmonary surfactants using atomic force microscopy

Clinical pulmonary surfactant is routinely used to treat premature newborns with respiratory distress syndrome, and has shown great potential in alleviating a number of neonatal and adult respiratory diseases. Despite extensive study of chemical composition, surface activity, and clinical performance of various surfactant preparations, a direct comparison of surfactant films is still lacking. In this study, we use atomic force microscopy to characterize and compare four animal-derived clinical surfactants currently used throughout the world, i.e., Survanta, Curosurf, Infasurf and BLES. These modified-natural surfactants are further compared to dipalmitoyl phosphatidylcholine (DPPC), a synthetic model surfactant of DPPC:palmitoyl-oleoyl phosphatidylglycerol (POPG) (7:3), and endogenous bovine natural surfactant. Atomic force microscopy reveals significant differences in the lateral structure and molecular organization of these surfactant preparations. These differences are discussed in terms of DPPC and cholesterol contents. We conclude that all animal-derived clinical surfactants assume a similar structure of multilayers of fluid phospholipids closely attached to an interfacial monolayer enriched in DPPC, at physiologically relevant surface pressures. This study provides the first comprehensive survey of the lateral structure of clinical surfactants at various surface pressures. It may have clinical implications on future application and development of surfactant preparations.

Reduced airway inflammation in CD26/DPP4-deficient F344 rats is associated with altered recruitment patterns of regulatory T cells and expression of pulmonary surfactant proteins

INTRODUCTION

CD26 is highly expressed on lung epithelial cells as well as on immune cells. Ovalbumin (OVA)-induced airway inflammation induces a further increase of CD26 expression. CD26-deficient rat strains exhibit blunted clinical courses in models of experimental asthma.

OBJECTIVE

(1) To investigate the involvement of regulatory T cells (Tregs) and the surfactant system in a rat model of genetic CD26 deficiency. (2) To investigate regulatory mechanisms dependent on the endogenous CD26 expression. (3) To investigate the impact of CD26 on surfactant protein (SP)-levels under inflammatory conditions.

METHODS

Wild-type and CD26-deficient F344 rats were sensitized to and challenged with OVA. Subsequently, airway inflammation, SP levels as well as surface tension of the bronchoalveolar lavage (BAL) fluid were evaluated.

RESULTS

CD26 deficiency led to decreased airway inflammation, e.g. reduced numbers of eosinophils and activated T cells in the BAL. Remarkably, the CD26-deficient rats exhibited a significantly increased influx of FoxP3(+) Tregs into the lungs and increased IL-10-secretion/production by draining lymph node cells in culture experiments. Furthermore, in OVA-challenged CD26-deficient rats, the increase of the expression of the collectins SP-A and SP-D as well as of the surface tension-active SP-B was significantly less pronounced than in the CD26-positive strain. Only in the wild-type rats, functional alterations of the surfactant system, e.g. the increased surface tension were obvious after OVA challenge.

CONCLUSION

Reduced airway inflammation in CD26-deficient F344 rats appear to be mediated by differences in the recruitment and activity of Tregs. This altered inflammation is associated with differences in the SP expression as well as function.

Effect of D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) on surfactant monolayers

In the present study, the effects of an amphiphilic polymer, d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) on model surfactant monolayers dipalmitoylphosphatidylcholine (DPPC), a binary mixture of DPPC with palmitoyloleoyl phosphatidylglycerol (DPPC-POPG) 9:1 (w/w) and binary mixture of DPPC and oleic acid (DPPC-OA) were evaluated. The ability of TPGS to act as an antioxidant adjuvant for pulmonary surfactants was also evaluated. Compression isotherms of surfactant monolayers at 37 °C in a Langmuir-Blodgett trough showed that DPPC and DPPC:TPGS mixed monolayers (1:0.25-1:1, w/w) exhibited low minimum surface tensions (MST) of 1-2 mN/m. Similarly [DPPC:POPG (9:1, w/w)]:TPGS mixed films of 1:0.25-1:1 weight ratios reached 1-2 mN/m MST. DPPC:POPG:TPGS liposomes adsorbed to surface tensions of 29-31 mN/m within 1s. While monolayers of DPPC:OA (1:1, w/w) reached high MST of ∼11 mN/m, DPPC:OA:TPGS (1:1:0.25, w/w) film reached near zero MST suggesting that low concentrations of TPGS reverses the effect of OA on DPPC monolayer. Capillary surfactometer studies showed DPPC:TPGS and [DPPC:POPG (9:1, w/w)]:TPGS liposomes maintained 84-95% airway patency. Fluorescence spectroscopy of Laurdan loaded DPPC:TPGS and DPPC:POPG:TPGS liposomes revealed no segregation of lipid domains in the lipid bilayer. Addition of TPGS to soybean liposome significantly reduced thiobarbituric acid reactive substance (TBARS) by 29-39% confirming its antioxidant nature. The results suggest a potential use of TPGS as an adjuvant to improve the surfactant activity as well as act as an antioxidant by scavenging free radicals.

Up-regulation of the extrinsic coagulation pathway in acute asthma--a case study

INTRODUCTION

In the normal airway, the hemostatic balance is antithrombotic and favors fibrinolysis. Acute asthma is associated with inflammatory cell infiltrate and plasma exudation in the airways. Postmortem specimens following status asthmaticus suggest a role for the activation of the extrinsic coagulation cascade and intraluminal fibrin formation. The authors report a chance observation of fibrin formation in the airways of a patient with moderate asthma 5 days before a severe exacerbation requiring hospital admission.

METHODS

Alpha-2 macroglobulin, an index of plasma leakage, coagulation factors, and D-dimers were measured by enzyme-linked immunosorbent assay (ELISA) in hypertonic saline-induced sputum, as part of a study into airway repair in stable asthma. All subjects were required to have stable symptoms and measures of asthma prior to sampling.

RESULTS

The subject's baseline forced expiratory volume in one second (FEV(1)) was 94% predicted and fraction of exhaled nitric oxide (FeNO) level was 30 ppb prior to sputum induction. Differential sputum cell count revealed an airways neutrophilia (neutrophils 81.1%, eosinophils 0.19%). D-dimers were 70-fold and 22-fold higher than the median value for patients with stable moderate and severe asthma, respectively. Plasma exudation was 42-fold higher than in stable moderate asthma, but on a par with levels found in severe stable asthma, and locally produced coagulation factors may therefore be involved. Levels of fibrinogen, plasminogen, plasminogen activator inhibitor (PAI)-1 and thrombin-activatable fibrinolysis inhibitor (TAFI) were all at least an order of magnitude higher than those seen in stable moderate or severe asthma.

CONCLUSIONS

Acute exacerbation of moderate asthma appears to be associated with a shift to a profibrinogenic, possibly antifibrinolytic, environment in the airways.

Overcoming rapid inactivation of lung surfactant: analogies between competitive adsorption and colloid stability

Lung surfactant (LS) is a mixture of lipids and proteins that line the alveolar air-liquid interface, lowering the interfacial tension to levels that make breathing possible. In acute respiratory distress syndrome (ARDS), inactivation of LS is believed to play an important role in the development and severity of the disease. This review examines the competitive adsorption of LS and surface-active contaminants, such as serum proteins, present in the alveolar fluids of ARDS patients, and how this competitive adsorption can cause normal amounts of otherwise normal LS to be ineffective in lowering the interfacial tension. LS and serum proteins compete for the air-water interface when both are present in solution either in the alveolar fluids or in a Langmuir trough. Equilibrium favors LS as it has the lower equilibrium surface pressure, but the smaller proteins are kinetically favored over multi-micron LS bilayer aggregates by faster diffusion. If albumin reaches the interface, it creates an energy barrier to subsequent LS adsorption that slows or prevents the adsorption of the necessary amounts of LS required to lower surface tension. This process can be understood in terms of classic colloid stability theory in which an energy barrier to diffusion stabilizes colloidal suspensions against aggregation. This analogy provides qualitative and quantitative predictions regarding the origin of surfactant inactivation. An important corollary is that any additive that promotes colloid coagulation, such as increased electrolyte concentration, multivalent ions, hydrophilic non-adsorbing polymers such as PEG, dextran, etc. added to LS, or polyelectrolytes such as chitosan, also promotes LS adsorption in the presence of serum proteins and helps reverse surfactant inactivation. The theory provides quantitative tools to determine the optimal concentration of these additives and suggests that multiple additives may have a synergistic effect. A variety of physical and chemical techniques including isotherms, fluorescence microscopy, electron microscopy and X-ray diffraction show that LS adsorption is enhanced by this mechanism without substantially altering the structure or properties of the LS monolayer.

Maternal exposure to particulate matter increases postnatal ozone-induced airway hyperreactivity in juvenile mice

RATIONALE

Epidemiologic studies implicate air pollutant exposure during pregnancy as a risk factor for wheezing in offspring. Ozone exposure is linked to exacerbations of wheezing in children.

OBJECTIVES

To determine if maternal pulmonary exposure to traffic-related particles during pregnancy augments ozone-induced airway hyperresponsiveness in offspring.

METHODS

C57BL6 time-mated mice were given NIST SRM#1648 (particulate matter [PM]) 0.48 mg, saline vehicle, or no treatment by tracheal insufflation twice weekly for 3 weeks. PM exposure augmented maternal lung inflammation and placental TNF-alpha, Keratinocyte-derived cytokine (KC), and IL-6 (measured at gestation Day 18). After parturition, dams and litters were exposed to air or ozone 1 ppm 3 h/d, every other day, thrice weekly for 4 weeks. Respiratory system resistance in pups was measured at baseline and after administration of nebulized methacholine.

MEASUREMENTS AND MAIN RESULTS

Ozone increased airway hyperresponsiveness, but the increase was greatest in pups born to PM-treated dams. Whole-lung TNF-alpha, IL-1beta, KC, IL-6, and MCP-1 were increased in ozone-treated pups, with the greatest increase in pups born to dams given PM. Airway epithelial mucous metaplasia estimated by periodic acid-Schiff Alcian blue staining was increased in ozone-exposed pups born to PM-treated dams. Alveolar development, determined by morphometry, and airway smooth muscle bulk, estimated using alpha-actin histochemistry, were unaffected by prenatal or postnatal treatment.

CONCLUSIONS

Maternal pulmonary exposure to PM during pregnancy augments placental cytokine expression and postnatal ozone-induced pulmonary inflammatory cytokine responses and ozone-induced airway hyperresponsiveness without altering airway structure.

Noninflammatory mechanisms of airway hyper-responsiveness in bronchial asthma: an overview

Airway hyper-responsiveness (AHR) is a cardinal feature of asthma. Its absence has been considered useful in excluding asthma, whereas it may be present in other diseases such as atopic rhinitis and chronic obstructive pulmonary disease. AHR is often considered an epiphenomenon of airway inflammation. Actually, the response of airways to constrictor stimuli is modulated by a complex array of factors, some facilitating and others opposing airway narrowing. Thus, it has been suggested that AHR, and perhaps asthma, might be present even without or before the development of airway inflammation. We begin this review by highlighting some terminological and methodological issues concerning the measurement of AHR. Then we describe the neurohumoral mechanisms controlling airway tone. Finally, the pivotal role of airway smooth muscle and internal and external modulation of airway caliber in vivo are discussed in detail.

Physiologic dysfunction of the asthmatic lung: what's going on down there, anyway?

Asthma is a syndrome of lung dysfunction characterized by airflow obstruction, reversibility to bronchodilators, and airways hyperresponsiveness (AHR). There is a growing body of evidence that suggests that the principle defect in asthma is the occlusion of the airway lumen by liquid, fibrin, and mucus. The fall in FEV(1) observed in asthma is best explained by a loss of communicating airspaces and the rise in residual lung volume. Imaging studies in both human patients and experimental animals support this hypothesis. An increased propensity for the airways to close can be a cause of AHR. We conclude that loss of lung volume plays a central role in determining the dysfunction of the asthmatic lung as measured by FEV(1). Together, these recent findings provide a better understanding of the causes of airflow obstruction and AHR, suggesting new avenues for the development of more effective asthma therapies.

Advances with surfactant

In this article, the physiology of surfactant is reviewed along with the research that lead to its current clinical uses. Acute lung injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) will also be reviewed because they represent pulmonary disease processes in which secondary deficiency and surfactant inactivation occur, for which surfactant may prove to be an effective treatment. Finally, research using surfactant as a treatment for other pulmonary diseases, such as bronchiolitis and asthma, will be briefly highlighted. These studies may one day lead to new treatment opportunities in the realm of emergency medicine.